WO2018192220A1 - 一种超结构光栅和可调谐激光器 - Google Patents

一种超结构光栅和可调谐激光器 Download PDF

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Publication number
WO2018192220A1
WO2018192220A1 PCT/CN2017/112142 CN2017112142W WO2018192220A1 WO 2018192220 A1 WO2018192220 A1 WO 2018192220A1 CN 2017112142 W CN2017112142 W CN 2017112142W WO 2018192220 A1 WO2018192220 A1 WO 2018192220A1
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mirror
layer
grating
region
tunable laser
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French (fr)
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武林
陈宏民
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Huawei Technologies Co Ltd
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Huawei Technologies Co Ltd
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Priority to JP2020505957A priority Critical patent/JP2020517122A/ja
Priority to EP17905992.8A priority patent/EP3605159B1/en
Publication of WO2018192220A1 publication Critical patent/WO2018192220A1/zh
Priority to US16/656,219 priority patent/US10931085B2/en
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1866—Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
    • G02B5/1871—Transmissive phase gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
    • H01S5/5063—Amplifier structures not provided for in groups H01S5/02 - H01S5/30 operating above threshold
    • H01S5/5072—Gain clamping, i.e. stabilisation by saturation using a further mode or frequency
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • H01S5/124—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers incorporating phase shifts
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2589—Bidirectional transmission
    • H04B10/25891—Transmission components
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0012—Optical design, e.g. procedures, algorithms, optimisation routines
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1814—Diffraction gratings structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings

Definitions

  • the present application relates to the field of optical fiber communications, and in particular to a superstructure grating and a tunable laser.
  • a tunable laser refers to a laser that can adjust the wavelength of an output optical signal within a certain range, and is mainly used in a large-capacity wavelength division multiplexing transmission system.
  • coherent modulation technology is used and becomes the mainstream solution for long-distance optical transmission of 100G and above.
  • Coherent modulation techniques have stringent requirements on the laser's excitation raywidth and other performance requirements.
  • Various new requirements also place higher demands on the size, cost, reliability and performance of tunable lasers.
  • the monolithic integrated tunable laser has the advantages of small size and high integration, and thus has become the mainstream technology in the field of optical communication.
  • a monolithically integrated tunable laser can be fabricated substantially through the docking of the gain region with an inactive region on an Indium Phosphide (InP) substrate.
  • the gain region is generally a multiple quantum well (MQW), while the passive region mainly includes a mirror and a phase segment. Wavelength tuning is achieved by adjusting the refractive index of the mirror or phase segment.
  • the reflection spectrum of the mirror is selective to the wavelength, and the commonly used mirror includes a distributed Bragg Reflection (DBR) or a microring resonator, and the reflection spectrum generated by the mirror is usually a dressing reflection spectrum.
  • DBR distributed Bragg Reflection
  • microring resonator the reflection spectrum generated by the mirror is usually a dressing reflection spectrum.
  • the Super Structure Grating has a dressing reflection spectrum.
  • the mirror area of the tunable laser can use SSG to reflect light.
  • the following formula (1) is the refractive index distribution of the SSG:
  • n(z) is The following formula (2) is satisfied between ⁇ F and ⁇ k and ⁇ k+1 .
  • n 0 is the average effective refractive index of the SSG
  • ⁇ k determines the period of the cosine function
  • ⁇ n is the difference between the maximum and minimum values of the effective refractive index of the grating
  • N indicates that the modulation function consists of N cosine functions
  • z represents The position of the grating along the propagation direction
  • ⁇ k is the phase of the kth cosine function
  • ⁇ F is determined by equation (2).
  • the reflection spectrum of a uniform grating has only one main peak, and the superstructure grating can modulate a uniform grating by a modulation function to form a dressing reflection spectrum.
  • the effective refractive index of the uniform grating is only two values of high refractive index n h and low refractive index n l .
  • the dotted line is represented as a modulation function of an SSG.
  • the modulation function of the SSG is a continuous periodic function of the simulation. After multiplying the uniform grating, the spatial distribution of the refractive index is also continuously changed, no longer only n h and n l two values, very difficult to make in the process.
  • a threshold value is usually selected to perform a two-stage digital discretization process on the continuous function represented by the equation (3).
  • the solid line in Figure 1 shows the effect of the super-structured grating modulation function using a threshold V 1 for two-level digital dispersion.
  • the discrete envelope function is also periodic for the continuous grating, but the refractive index is still only n.
  • the two values h and n l introduce a phase shift only when switching between the envelope functions "1" and "-1", so it is easy to process the SSG.
  • the total length of the SSG determines the reflectivity of the reflection peak and the FWHM.
  • the total length of the SSG corresponds to a specific reflectivity and FWHM, that is, the reflectance of the reflected peak corresponds to the FWHM. Therefore, for the second-order discrete SSG, the reflectivity and FWHM cannot be independently optimized to achieve performance. Good FWHM and reflectivity.
  • the reflectivity and FWHM of the SSG reflection peak are determined by the total length of the SSG, and the SSG reflectance and the FWHM cannot be optimized separately, so that the performance cannot be simultaneously satisfied. Reflectivity and FWHM.
  • Embodiments of the present application provide a superstructure grating and a tunable laser for separately optimizing the reflectance of the reflection peak of the superstructure grating and the FWHM, and satisfying the better reflectivity and FWHM.
  • the embodiment of the present application provides the following technical solutions:
  • an embodiment of the present application provides a superstructure grating that spatially and phase modulates a uniform grating by a modulation function to form a grooming reflection spectrum, and the modulation function is discrete by N thresholds.
  • (N+1) modulation function discrete values are obtained, and the N is a positive integer greater than or equal to 2; each of the (N+1) modulation function discrete values corresponds to a segment of refraction
  • (N+1) modulation function discrete values are obtained by discretizing the modulation function, and the reflectance of the reflection peak of the super-structure grating is passed through (N+1) modulation function discrete values
  • the length of the optical waveguide corresponding to the discrete value of the at least one modulation function is proportional to the total length of the grating of the superstructure grating, and the total length of the grating of the superstructure grating is adjusted.
  • the FWHM of the reflection peak of the superstructure grating passes the aforementioned proportional relationship and superstructure.
  • the total grating length of the grating is adjusted, that is, the reflectivity of the reflection peak of the superstructure grating and the FWHM can be adjusted by two dimensions.
  • the reflectivity of the reflection peak determines the threshold and output power of the tunable laser, and the FWHM of the reflection peak is determined.
  • the model selection of the laser the smaller the FWHM, the larger the side mode suppression ratio.
  • the tunable laser provided based on the embodiment of the present application can optimize the reflectance and the FWHM separately, so that the better reflectivity and FWHM can be simultaneously satisfied.
  • the modulation function performs discretization processing to obtain three discrete values of the modulation function, and the 3
  • the discrete values of the modulation functions have a discrete value of the modulation function corresponding to an optical waveguide having a uniform refractive index, and the discrete values of the remaining two modulation functions of the three modulation functions respectively correspond to a uniform grating.
  • the discrete values of the three modulation functions corresponding to the optical waveguide and the uniform grating with uniform refractive index can be obtained.
  • the reflectivity of the reflection peak of the super-structure grating is discretized by three modulation functions.
  • the (N+1) modulation function discrete values have two modulation function discretes
  • the values correspond to the same uniform grating.
  • a phase shift is added between the optical waveguides corresponding to the discrete values of the adjacent modulation functions.
  • a phase shift is cut between the optical waveguides, so that the reflection spectrum of the super-structure grating is flatter, and the reflection performance of the super-structure grating is improved.
  • the embodiment of the present application further provides a tunable laser, the tunable laser comprising: a reflective region, wherein the reflective region is configured to pass the superstructure according to any of the foregoing first aspects
  • the grating tunes the optical signal.
  • Embodiments of the present application also provide a tunable laser based on the aforementioned superstructure grating.
  • (N+1) modulation function discrete values are obtained by discretizing the modulation function, and the reflectance of the reflection peak of the super-structure grating is discretized by (N+1) modulation functions.
  • the ratio of the length of the optical waveguide corresponding to the discrete value of at least one of the modulation functions to the total length of the grating of the superstructure grating, and the total length of the grating of the superstructure grating are adjusted, and the FWHM of the reflection peak of the superstructure grating passes the aforementioned proportional relationship
  • the total length of the grating of the superstructure grating is adjusted, that is, the reflectivity of the reflection peak of the superstructure grating and the FWHM can be adjusted by two dimensions.
  • the reflectivity of the reflection peak determines the threshold and output power of the tunable laser, and the reflection peak
  • the FWHM determines the model selectivity of the laser. The smaller the FWHM, the larger the side mode suppression ratio.
  • the tunable laser provided based on the embodiment of the present application can optimize the reflectance and the FWHM separately, so that the better reflectivity and FWHM can be simultaneously satisfied.
  • the tunable laser further includes: a gain region and a phase region, wherein the reflective region includes: a first mirror and a second reflection a mirror; the gain region is respectively cascaded with the first mirror and the phase region through an optical waveguide; the phase region is cascaded with the gain region and the second mirror; the gain region For generating an optical signal; the phase region is for phase adjustment of the optical signal to enable the tunable laser to fine tune a lasing wavelength of the optical signal.
  • the generation and phase adjustment of the optical signal can be achieved by the gain and phase regions in the tunable laser, respectively, and the optical signal is transmitted through the reflective region after the lasing wavelength of the optical signal is fine tuned.
  • the tunable laser further includes: a semiconductor optical amplifier SOA and a photodetector PD; the first reflection a mirror is cascaded by the optical waveguide and the SOA, the second mirror being cascaded by the optical waveguide and the PD; the SOA for power amplification of the optical signal; the PD, for Power monitoring or power attenuation is performed on the optical signal. Power amplification of the optical signal as well as power monitoring or power attenuation can be achieved by SOA and PD in the tunable laser.
  • the tunable laser further includes: a first SOA and a second SOA; the first mirror Cascading through the optical waveguide and the first SOA, the second mirror being cascaded by the optical waveguide and the second SOA; the first SOA, for emitting light to the first mirror The signal is subjected to power amplification; and the second SOA is configured to perform power amplification on the optical signal emitted by the second mirror.
  • both the first mirror and the second mirror can be connected to one SOA, and the optical signal emitted by each mirror is power amplified, so that a more powerful optical signal can be emitted.
  • the tunable laser further includes: a multimode interference MMI coupler, a gain region, and a phase region;
  • the reflective region includes: a first reflection a mirror and a second mirror; one side of the MMI coupler has a port connected to the phase region, and the other side of the MMI coupler has two ports respectively associated with the first mirror and The second mirrors are connected; the two sides of the phase zone are respectively cascaded with the gain zone and one port of the MMI; the gain zone is for generating an optical signal; and the phase zone is for the light The signal is phase adjusted such that the tunable laser is capable of fine tuning the lasing wavelength of the optical signal.
  • the MMI coupler is used to couple the light reflected back by the first mirror and the second mirror together into the phase region.
  • the active gain region has a lower band gap, corresponding to the target output wavelength of the tunable laser, typically a multiple quantum well, which, when electrically injected, converts electrical energy into light energy to provide gain.
  • the tunable laser further includes: a phase adjustment module, wherein the phase adjustment module respectively The MMI coupler, the first mirror connection, or the phase adjustment module is respectively connected to the MMI coupler and the second mirror; the phase adjustment module is configured to match the first mirror The phase between the reflection spectrum and the reflection spectrum of the second mirror. Adding a phase adjustment module on the Y branch arm of the first mirror or the second mirror to match the phase of the reflection spectrum of the two mirrors, so that the first mirror or the second mirror can better pass through the MMI coupler wave.
  • the tunable laser further includes: an SOA and a PD; the first mirror has a first port The second mirror has a second port, the gain region has a third port; the first port is connected to the SOA or the PD, and/or the second port is connected to the SOA or The PD, and/or the third port is connected to the SOA or the PD; the SOA is configured to perform power amplification on the optical signal; and the PD is configured to perform power on the optical signal Monitoring or Power attenuation.
  • At least one of the first mirror, the second mirror and the gain region may be connected to the SOA through the optical waveguide, and the first mirror, the second mirror and the gain region may be connected to the PD through the optical waveguide, and the tunable laser is integrated SOA and PD can respectively achieve power amplification of optical signals as well as power monitoring or power attenuation.
  • the reflective region includes: a heating unit, a transport layer, a mirror, an upper barrier layer, a sacrificial layer, a lower barrier layer, and a substrate layer, wherein the heating unit is located above the transport layer
  • the transmission layer is located above the sacrificial layer, and includes, in order from top to bottom, an upper cladding layer, a waveguide layer and a lower cladding layer; the mirror is located in the transmission layer, and the mirror is used to pass The superstructure grating of any of the preceding aspects, wherein the optical signal is tuned; the upper barrier layer is between the transmission layer and the sacrificial layer; and the sacrificial layer is located at the upper barrier layer Between the lower barrier layer, a protective structure is formed in the sacrificial layer, the protective structure and the interlayer region form a hollow structure
  • the hollow structure is completely hollow; the transmission layer of the region where the mirror is located and the material of the transmission layer on both sides Between the gaps, a hollow structure is formed over the hollow structure; the voids are periodically arranged along the waveguide direction, the voids penetrating the upper cladding layer, the waveguide layer, the Defining the cladding layer and the upper barrier layer to reach a region where the hollow structure is located, and a support structure between the adjacent gaps for providing lateral mechanical support to the suspended structure, the support structure along the waveguide
  • the length period of the direction is not equal to the period of the modulation function of the superstructure grating.
  • the area between the corrosion windows is the support area of the suspended structure, and the area between the corrosion windows is not aligned with the peak or valley of the superstructure grating modulation function, ie as long as the peaks are not aligned Or the valleys are not aligned, and the two left and rightmost corrosion windows are used to prevent the temperature from being too low on both sides.
  • the transmission layer of the region where the mirror is located is completely isolated from the material of the two sides of the transmission layer to form a gap.
  • the void extends through the upper cladding layer, the waveguide layer, the lower cladding layer and the upper barrier layer to reach a region where the hollow structure is located, and a suspended structure is formed above the hollow structure and between the voids
  • the bottom of the sacrificial layer is not completely etched, and the sacrificial layer retains a bottom support structure for forming support for the suspended structure.
  • the reflective region in the tunable laser can be thermally tuned using a suspended structure to improve the thermal tuning efficiency of the superstructure grating.
  • the length of the bottom support structure along the waveguide direction is not equal to the period of the modulation function of the super-structure grating .
  • the super-structure grating is located under the upper cladding layer in the transmission layer of the region where the mirror is located a half portion; or, the superstructure grating is located in an upper half of an under cladding layer in a transmission layer of a region where the mirror is located; or, the superstructure grating is located at a waveguide layer in a region where the mirror is located; or The superstructure grating is located in each of the upper cladding layer and the waveguide layer in the transmission layer of the region where the mirror is located; or the superstructure grating is located in the lower cladding layer in the transmission layer of the region where the mirror is located There is a part in each of the waveguide layers.
  • the mirror is located in the upper cladding layer for tuning the wavelength of the optical signal.
  • the mirror may also be located in the lower cladding layer, or in the waveguide layer, or in the upper cladding layer and the waveguide layer.
  • the layers, or in the two layers of the lower cladding layer and the waveguide layer there are various implementations, which are only described herein.
  • the optical signal propagates in the upper cladding layer, the lower cladding layer, and the waveguide layer, and the superstructure grating is placed at these positions to reflect the optical signal.
  • the refractive index of the waveguide layer is higher than a refractive index of the upper cladding layer and a refractive index of the lower cladding layer . Therefore, when the optical signal propagates in the waveguide layer, total reflection is formed, so that the optical energy can be limited as much as possible in the waveguide layer, so that the waveguide layer can provide a low-loss propagation path of the optical signal and reduce the loss of optical signal propagation.
  • the reflective region further includes: an indium phosphide InP buffer layer, wherein The lower barrier layer is located between the sacrificial layer and the InP buffer layer; the InP buffer layer is located between the lower barrier layer and the substrate layer.
  • the main function of the InP buffer layer is to provide a better quality crystalline InP material, providing a better material basis for other layer materials.
  • 1 is an effect diagram of a modulation function of a superstructure grating in the prior art after two levels of dispersion
  • FIG. 2 is a schematic diagram showing the relationship between the reflectance of the reflection peak and the FWHM and the total length of the SSG of the super-structure grating after the second-stage discretization processing in the prior art;
  • FIG. 3 is an effect diagram of a modulation function of a super-structure grating in a three-stage discretization process according to an embodiment of the present application
  • FIG. 4 is a structural diagram of a super-structure grating after level 3 discretization processing in an embodiment of the present application
  • FIG. 5 is a schematic diagram showing the relationship between the reflectance of the super-structured grating after the three-stage discretization processing and the total length of the grating and the portion of the modulation function occupying the total length of the grating in one embodiment of the present application;
  • FIG. 6 is a schematic diagram showing the relationship between the FWHM of the super-structured grating after the 3-level discretization processing and the total length of the grating and the portion of the modulation function occupying the total length of the grating in one embodiment of the present application;
  • FIG. 7 is a schematic structural diagram of a tunable laser provided by an embodiment of the present application.
  • FIG. 8 is a schematic structural diagram of a tunable laser according to another embodiment of the present application.
  • FIG. 9 is a schematic structural diagram of a tunable laser according to another embodiment of the present application.
  • FIG. 10 is a schematic structural diagram of a tunable laser according to another embodiment of the present application.
  • FIG. 11 is a top plan view of a suspended structure mirror of a tunable laser provided by an embodiment of the present application.
  • Figure 12 is a cross-sectional view of the tunable laser along the 3'-3' position of Figure 11 provided by an embodiment of the present application;
  • Figure 13 is a cross-sectional view of the tunable laser along the 4'-4' position of Figure 11 provided by an embodiment of the present application;
  • FIG. 14 is a top plan view of a bottom support structure included in a tunable laser provided by an embodiment of the present application;
  • Figure 15 is a cross-sectional view of the tunable laser along the 3-3 position of Figure 14 provided by an embodiment of the present application;
  • FIG. 16 is a cross-sectional view of the tunable laser along the 1-1 position of FIG. 14 provided by an embodiment of the present application;
  • Figure 17 is a cross-sectional view of the tunable laser taken along line 2-2 of Figure 14 provided by an embodiment of the present application.
  • the embodiment of the present application provides an independent optimization of the reflectance and FWHM of the reflection peak of the super-structure grating, and at the same time satisfies the better reflectivity and FWHM.
  • the three conditions for generating a laser are: achieving particle number inversion, satisfying threshold conditions, and resonance conditions.
  • the first condition for generating laser light is the inversion of the number of particles.
  • the electrons in the valence band are pumped to the conduction band.
  • the heavily doped P-type and N-type materials are usually used to form the PN junction.
  • particle number inversion occurs near the junction region, electrons are stored in the high Fermi level, and holes are stored in the low Fermi level, and of course there are many others.
  • a method of generating a population inversion Realizing the inversion of the number of particles is a necessary condition for generating laser light, but it is not a sufficient condition.
  • the resonance condition refers to the fact that after the length L and the refractive index N of the cavity are determined, only light of a specific frequency can form a light oscillation, and a stable laser is output, which indicates that the cavity has a certain frequency selection effect on the output laser.
  • a monolithically integrated semiconductor tunable laser is usually formed by abutting a gain region and an inactive region on an Indium Phosphide (InP) substrate, and its planar schematic is shown in FIG. 7, including a reflection region, a gain region, and a phase adjustment.
  • the reflective area may include a first mirror and a second mirror.
  • the forbidden band width of the gain region is low, and when the electric injection is performed, the electric energy is converted into light energy to provide a gain;
  • the passive region mainly includes a mirror, and the forbidden band width of the passive region is greater than the laser wavelength. The photon energy is higher and the absorption of the laser is small, so it can provide very low absorption loss.
  • the passive region may also include a phase adjustment region for fine tuning the effective optical path within the cavity to change the laser output wavelength.
  • the two mirrors of the tunable laser have a comb-like reflection spectrum with multiple reflection peaks, and the reflection peaks can be adjusted.
  • the output wavelength of the laser can be adjusted by adjusting the reflection peaks.
  • the reflectance of the reflection peak and the FWHM are only related to the total length of the grating of the superstructure grating. As shown in FIG.
  • the total length of the grating of the superstructure grating in the prior art determines the reflectivity of the reflection peak and FWHM
  • the total grating length of the superstructure grating corresponds to a specific reflectivity and FWHM, that is, the reflectance of the reflection peak corresponds to the FWHM one by one, so the reflectivity and FWHM cannot be independently optimized separately to obtain better FWHM and reflection. rate.
  • the reflectance of the reflection peak and the FWHM can be adjusted by two dimensions, so that the reflectivity and the FWHM can be independently optimized, so that the reflectivity with better performance can be simultaneously satisfied. And FWHM.
  • An embodiment of the present application first provides a superstructure grating which spatially and amplitudeally modulates a uniform grating by a modulation function to form a dressing reflection spectrum, and the modulation function is discretized by N threshold values. Obtaining (N+1) discrete values of the modulation function, N being a positive integer greater than or equal to 2;
  • each discrete value of the modulation function corresponds to a section of optical waveguide with uniform refractive index Or corresponding to a uniform grating, the uniform grating is an optical waveguide with alternating high refractive index and low refractive index;
  • the reflectance of the reflection peak of the superstructure grating passes through at least one of the discrete values of the (N+1) modulation function discrete values, the length of the optical waveguide corresponding to the total length of the grating of the superstructure grating, and the superstructure grating Adjust the total length of the grating;
  • the FWHM of the reflection peak of the superstructure grating is adjusted by the aforementioned proportional relationship and the total length of the grating of the superstructure grating.
  • the modulation function of the super-structure grating is discretized by N thresholds to obtain (N+1) discrete values of the modulation function, that is, after the N-level discretization processing of the modulation function of the super-structure grating, (N+ 1) discrete values of the modulation function.
  • N discrete values of the modulation function
  • two threshold values may be selected to perform three levels of discretization processing on the modulation function of the super-structured grating, and three discrete values of the modulation function may be obtained, which is different from the prior art in which only one threshold is selected for the modulation function.
  • the two discrete values of the modulation function are completely different.
  • the super-structure grating provided by the embodiment of the present application is exemplified by taking the value of N as 2.
  • the super-structure grating provided by the embodiment of the present application can realize the reflectivity and FWHM of the reflection peak respectively, and the discrete values of the three modulation functions can be obtained after the third-order dispersion, and the following formula is an expression of the discrete value of the modulation function Profile_D(z). :
  • Threshold1 and Threshold2 are two thresholds.
  • the three threshold values of the modulation function Profile(z) are used to obtain three discrete values of the modulation function, as shown in FIG.
  • the modulation function of the super-structure grating is subjected to three-stage discretization processing.
  • the discrete modulation function has three values of 1,0,-1, so that after the modulation function acts on the uniform grating, the super-structure grating portion corresponding to 1 and -1 still only has high refractive index n h and low refractive index n l For each value, the superstructure grating portion corresponding to 0 has only a high refractive index n h .
  • FIG. 4 it is a structural diagram of a super-structure grating after three-stage discretization processing in one embodiment of the present application.
  • the modulation function is 1 or -1
  • ultra high refractive index gratings low refractive index n h and n l alternating with as uniform grating.
  • the superstructure gratings are all high refractive index n h , so that the effective reflection surface is reduced.
  • the reflectance of the reflection peak of the superstructure grating can be optimized.
  • the morphology of the superstructure grating is magnified and visible, and the shaded portion is a low refractive index portion.
  • the superstructure grating has only a high refractive index n h .
  • the reflectivity and FWHM of the grating can be adjusted by adjusting the ratio of the 0 portion of the discrete post-modulation function to the total length of the grating of the super-structure grating, and then combining the total length of the grating of the super-structure grating.
  • FIG. 5 is a relationship between the reflectance of the super-structured grating after the three-stage discretization processing and the total length of the grating and the proportion of the zero portion of the modulation function to the total length of the grating in one embodiment of the present application.
  • FIG. 5 is a relationship between the reflectance of the super-structured grating after the three-stage discretization processing and the total length of the grating and the proportion of the zero portion of the modulation function to the total length of the grating in one embodiment of the present application.
  • FIG. 6 is a schematic diagram showing the relationship between the FWHM of the super-structured grating after the three-stage discretization processing and the total length of the grating and the proportion of the zero portion of the modulation function in the total length of the grating in one embodiment of the present application, FIG. 5 and FIG. There are five lines, each corresponding to a super-structured grating of different grating lengths.
  • the ratio of the total length of the grating of the optical waveguide corresponding to the modulation function 0 is simply referred to as the ratio of 0 in the modulation function.
  • the superstructure grating When the modulation function is 0, the superstructure grating is all n h , so that the effective reflection surface will be By reducing the ratio of the total length of the grating of the optical waveguide corresponding to the modulation function 0, the reflectivity of the superstructure grating can be optimized. If the total length of the grating is longer, the reflectivity is larger. For FWHM, the longer the total length of the grating, the smaller the FWHM, the larger the proportion of the discrete value of the modulation function, and the smaller the FWHM.
  • the reflectivity and FWHM of such a superstructure grating are respectively related to the ratio of the total length of the grating and the discrete value of the modulation function of zero.
  • the reflectivity and FWHM of the superstructure grating are both related to the total length of the grating and the ratio of 0 in the modulation function, that is, the reflectivity is related to the total length of the grating and the ratio of 0 in the modulation function, FWHM and The total length of the grating and the ratio of 0 in the modulation function are related.
  • the reflectivity and FWHM of the superstructure grating can be optimized separately, for example, the total length of the grating is 294 um, and the modulation function is “0”.
  • the modulation function is discretized to obtain three discrete values of the modulation function, and the discrete values of the three modulation functions have a modulation function, and the discrete values correspond to a uniform refractive index.
  • the discrete values of the three modulation functions of the waveguide and the uniform grating, and the reflectance of the reflection peak of the superstructure grating through one of the discrete values of the three modulation functions, the discrete value of the modulation function corresponding to the refractive index uniformity of the optical waveguide length of the superstructure The proportional relationship of the total length of the grating of the grating, the total length of the grating of the superstructure grating, the reflectivity of the reflected peak, and the FWHM are adjusted to achieve simultaneous optimization of the reflectivity and the FWHM.
  • the three discrete values of the modulation function include: a first value, a second value, and a third value, wherein the first value corresponds to a uniform grating, and the second value corresponds to an optical waveguide having a uniform refractive index, The three values correspond to a uniform grating.
  • the first value and the third value may be discrete values 1 and -1 of the modulation function shown in FIG. 3, respectively, and the second value may be a discrete value 0 of the modulation function shown in FIG.
  • the discrete values of the (N+1) modulation functions have two discrete values of the modulation function corresponding to the same type of uniform grating, and the optical waveguides corresponding to the discrete values of the respective modulation functions in the modulation function are controlled.
  • the ratio of the total length of the grating can optimize the reflectivity of the superstructure grating.
  • the optical waveguide portion corresponding to the discrete value 0 of the modulation function has only a high refractive index or a low refractive index, so that the super-structure grating does not form a reflective interface when the value of the modulation function is a discrete value of the modulation function 0. .
  • the discrete values of the adjacent modulation functions when the sign of the discrete values of the adjacent modulation functions is different or one of the discrete values of the adjacent modulation functions has a discrete value of zero, the discrete values of the adjacent modulation functions respectively correspond to the light
  • a phase shift is added between the waveguides, and a phase shift is cut between the optical waveguides when the sign of the modulation function changes, thereby making the reflection spectrum of the superstructure grating flatter and improving the reflection performance of the superstructure grating.
  • the three-level discretization processing of the modulation function of the super-structure grating is described by taking the value of N as 2, and the present invention is not limited to the implementation of the present application.
  • the modulation function of the superstructure grating provided by the example can also be subjected to 4-level discretization processing, or more advanced discretization processing.
  • the super-structure grating can adopt more thresholds, and the modulation function can be higher than or equal to level 4 and the like. Processing.
  • the modulation function is 1, -1 or 0 substantially corresponding to different modulation forms of the uniform grating in the super-structure grating, with 4 levels of dispersion
  • the discrete value of the modulation function can take 1, 0.5, -0.5, -1, wherein the specific values of the discrete values of the respective modulation functions can be configured according to the application scenario, and only the corresponding modulation forms of the optical waveguides or uniform gratings in which the discrete values of the respective modulation functions are uniform and the values are uniform.
  • phase shift is introduced when the sign of the discrete value of the modulation function changes.
  • the discrete value of the modulation function can take 1, 0.5, 0, -0.5, -1, etc., for example, "1" "-1" still corresponds to the first uniform grating, 0.5 or -0.5
  • 0 corresponds to the optical waveguide with uniform refractive index, when the sign of the discrete values of the adjacent modulation functions is different or one of the discrete values of the adjacent modulation functions has a discrete value of zero. Introduce phase shift.
  • the description of the present application shows that the super-structure grating spatially and phase-modulates the uniform grating by a modulation function to form a dressing reflection spectrum, and the modulation function is discretized by N thresholds (N+ 1) discrete values of modulation functions, N is a positive integer greater than or equal to 2, wherein each of the discrete values of (N+1) modulation functions corresponds to an optical waveguide with a uniform refractive index or corresponding
  • the uniform grating is an optical waveguide with alternating high refractive index and low refractive index.
  • the length of the optical waveguide occupies the ratio of the total length of the grating of the superstructure grating, and the total length of the grating of the superstructure grating is adjusted.
  • the FWHM of the reflection peak of the superstructure grating is adjusted by the aforementioned proportional relationship and the total length of the grating of the superstructure grating, that is, The reflectivity and FWHM of the reflection peak of the superstructure grating can be adjusted by two dimensions.
  • the reflectivity of the reflection peak determines the threshold and output power of the tunable laser.
  • the FWHM of the reflection peak determines the model selectivity of the laser. The more FWHM Small, the side mode suppression ratio is larger.
  • the tunable laser provided based on the embodiment of the present application can optimize the reflectance and the FWHM separately, so that the better reflectivity and FWHM can be simultaneously satisfied.
  • the foregoing embodiment describes the superstructure grating provided by the present application.
  • a tunable laser provided by the present application is described.
  • the tunable laser includes: a reflective region, wherein the reflective region is used to pass the superstructure grating in the foregoing embodiment.
  • the optical signal is tuned, that is, the embodiment of the present application also provides a tunable laser based on the aforementioned superstructure grating.
  • (N+1) modulation function discrete values are obtained by discretizing the modulation function, and the reflectance of the reflection peak of the super-structure grating is discretized by (N+1) modulation functions.
  • the ratio of the length of the optical waveguide corresponding to the discrete value of at least one of the modulation functions to the total length of the grating of the superstructure grating, and the total length of the grating of the superstructure grating are adjusted, and the FWHM of the reflection peak of the superstructure grating passes the aforementioned proportional relationship
  • the total length of the grating of the superstructure grating is adjusted, that is, the reflectivity of the reflection peak of the superstructure grating and the FWHM can be adjusted by two dimensions.
  • the reflectivity of the reflection peak determines the threshold and output power of the tunable laser, and the reflection peak
  • the FWHM determines the model selectivity of the laser. The smaller the FWHM, the larger the side mode suppression ratio.
  • the tunable laser provided based on the embodiment of the present application can optimize the reflectance and the FWHM separately, so that the better reflectivity and FWHM can be simultaneously satisfied.
  • the tunable laser includes a gain region and a phase region, in addition to including a reflective region, wherein
  • the reflective area includes: a first mirror and a second mirror
  • the gain region is respectively cascaded with the first mirror and the phase region through the optical waveguide;
  • the phase region is cascaded with the gain region and the second mirror;
  • a phase region for phase adjustment of the optical signal enables the tunable laser to fine tune the lasing wavelength of the optical signal.
  • the super-structure grating provided by the foregoing embodiment of the present application may be disposed in the first mirror or may be disposed in the first mirror.
  • the positions of the first mirror and the second mirror may be interchanged, for example, the first mirror is a back mirror, and the second mirror is a front mirror.
  • the generation and phase adjustment of the optical signal can be achieved by the gain and phase regions in the tunable laser, respectively, and the optical signal is transmitted through the reflective region after the lasing wavelength of the optical signal is fine tuned.
  • a schematic diagram of a monolithically integrated tunable laser is composed of a gain section, a first mirror, a second mirror, and a phase section.
  • the gain region is located in the active region, and the gain region has a lower band gap, generally a multi-quantum well.
  • the electrical energy is converted into light energy to provide a gain.
  • the first mirror and the second mirror are equivalent and interchangeable, and the reflection spectra of the first mirror and the second mirror are wavelength selective for wavelength tuning, the first mirror and the second reflection
  • the mirror comprises the aforementioned superstructure grating, the reflection spectrum produced by the mirror is a dressing reflection spectrum, and the free spectral range of the first reflection mirror and the second mirror has a certain difference in the free spectral range, and then the two mirrors amplify the tuning range by the cursor effect .
  • the phase region provides phase adjustment, so that the laser can finely adjust the lasing wavelength, the light is generated in the gain region, and the first mirror and the second mirror reflect to form a resonance to generate a laser, and then transmit and exit from the first mirror and the second mirror. laser.
  • the first mirror, the second mirror and the phase region are all located in the passive region.
  • the forbidden band width of the passive region is higher than the photon energy of the laser wavelength, and the absorption of photons is very small, and the passive region can be regenerated by etching.
  • the technology etches off the MQW of the active region and then fabricates the compound with a larger band gap by secondary epitaxy.
  • both the first mirror and the second mirror can adopt the reflection spectrum of the first mirror and the second mirror of the superstructure grating described in the foregoing embodiments to be wavelength selective for wavelength tuning.
  • the phase region, the first mirror, and the second mirror can all be wavelength tuned by electrical injection, or by changing thermal injection, or other equivalent method to change the refractive index of the waveguide.
  • the tunable laser further includes: a semiconductor optical amplifier (SOA) and a photo Detector (PD);
  • SOA semiconductor optical amplifier
  • PD photo Detector
  • the first mirror is cascaded by the optical waveguide and the SOA, and the second mirror is cascaded by the optical waveguide and the PD;
  • the positions of the first mirror and the second mirror are interchangeable, and the power amplification and power monitoring or power attenuation of the optical signal can be realized by SOA and PD in the tunable laser, and it should be noted that
  • the left or right end of the tuned laser can be integrated with SOA for power amplification, or the left or right end of the tunable laser can be integrated with PD for power monitoring or power attenuation.
  • the tunable laser further includes: a first SOA and a second SOA;
  • the first mirror is cascaded by the optical waveguide and the first SOA
  • the second mirror is cascaded by the optical waveguide and the second SOA
  • a first SOA configured to perform power amplification on the optical signal emitted by the first mirror
  • the second SOA is configured to perform power amplification on the optical signal emitted by the second mirror.
  • the first mirror and the second mirror in the tunable laser can be connected to one SOA, and the optical signal emitted by each mirror is power amplified, so that a more powerful optical signal can be emitted.
  • the tunable laser further includes: a multi-mode interference (MMI) coupler, a gain region, and a phase region;
  • MMI multi-mode interference
  • the reflective area includes: a first mirror and a second mirror
  • the MMI coupler has one port on one side and is connected to the phase zone. There are two ports on the other side of the MMI coupler. Do not connect to the first mirror and the second mirror.
  • phase zone The two sides of the phase zone are respectively cascaded with the gain zone and one port of the MMI;
  • a phase region for phase adjustment of the optical signal enables the tunable laser to fine tune the lasing wavelength of the optical signal.
  • the tunable laser provided by one embodiment of the present application includes: a gain region, a phase region, an MMI coupler, a first mirror and a second mirror, the MMI coupler is a 1x2 coupler, and has a port on one side, and a phase The zones are coupled, and the other side has two ports, which are first coupled to the mirror and the second mirror, respectively.
  • the phase zone is cascaded with the gain zone and the MMI.
  • the MMI coupler is used to couple the light reflected back by the first mirror and the second mirror together into the phase region.
  • the active gain region has a lower band gap, corresponding to the target output wavelength of the tunable laser, typically a multiple quantum well, which, when electrically injected, converts electrical energy into light energy to provide gain.
  • the first mirror and the second mirror can be considered equivalent, the names can be interchanged, and the reflection spectra of the first mirror and the second mirror are wavelength selective for wavelength tuning, for example, first
  • the mirror and the second mirror comprise the aforementioned super-structure grating as a dressing reflection spectrum, and the free spectral range of the mirror reflection spectrum of the two mirrors is somewhat different, and the first laser mirror reflected back to the laser cavity of the mirror and the second mirror
  • the tuning range is amplified by the MMI combining and then by the additive cursor effect.
  • the phase region provides phase adjustment so that the laser can fine tune the lasing wavelength, and the first mirror, the second mirror, and the phase region are all located in the inactive region.
  • the phase region, the first mirror, and the second mirror can all be wavelength tuned by electrical injection, or by changing thermal injection, or other equivalent method to change the refractive index of the waveguide.
  • the tunable laser further includes: a phase adjustment module, wherein
  • the phase adjustment module is respectively connected to the MMI coupler, the first mirror, or the phase adjustment module to the MMI coupler and the second mirror respectively;
  • phase adjustment module for matching a phase between a reflection spectrum of the first mirror and a reflection spectrum of the second mirror.
  • a phase adjustment module is added on the Y branch arm of the first mirror or the second mirror to match the phase of the reflection spectrum of the two mirrors, so that the first mirror or the second mirror can be better coupled by MMI
  • the multiplexed wave is schematically illustrated in FIG. 10 by taking the phase adjustment module on the first mirror as an example.
  • the tunable laser further includes: SOA and PD;
  • the first mirror has a first port
  • the second mirror has a second port
  • the gain region has a third port
  • the first port is connected to the SOA or PD, and/or the second port is connected to the SOA or PD, and/or the third port is connected to the SOA or PD.
  • the integrated SOA and PD can achieve power amplification and power monitoring or power attenuation of the optical signal, respectively.
  • the left end of the gain zone is port 1
  • the right end of the first mirror is port 2
  • the right end of the second mirror is port 3.
  • Any one of the three ports can be integrated with SOA to amplify the output optical power, or integrated with PD. Power monitoring or power attenuation.
  • FIG. 11 is a top view of a suspended structure mirror of a tunable laser provided by an embodiment of the present application.
  • Figure 11 illustrates the principle of the mirror structure of the suspended structure of the tunable laser.
  • P1 to P7 are respectively a grating modulation function period, and there are 1 to 6 etching windows above and below the optical waveguide, respectively.
  • a support area is provided between two adjacent corrosion windows.
  • FIG. 12 a cross-sectional view of a tunable laser along the 3'-3' position in FIG. 11 provided for an embodiment of the present application, as shown in FIG. 13, is an illustration of an embodiment of the present application.
  • a cross-sectional view of a tunable laser at 4'-4' position in 11. a reflective region of the tunable laser, comprising: a heating unit, a transport layer, a mirror, an upper barrier layer, a sacrificial layer, a lower barrier layer, and a substrate layer, wherein
  • a heating unit located above the transport layer
  • the transport layer is located above the sacrificial layer and includes, in order from top to bottom, an upper cladding layer, a waveguide layer and a lower cladding layer;
  • a mirror located in the transport layer, for tuning the optical signal by the superstructure grating of any of the preceding claims 1 to 4;
  • a sacrificial layer between the upper barrier layer and the lower barrier layer, a protective structure formed in the sacrificial layer, the protective structure and the interlayer region forming a hollow structure, and the interlayer region comprising: a region between the transmission layer and the substrate layer;
  • the substrate layer is located below the lower barrier layer.
  • the reflective region further includes: an InP buffer layer, wherein the lower barrier layer is between the sacrificial layer and the InP buffer layer; and the InP buffer layer is between the lower barrier layer and the substrate layer.
  • the reflective region in the tunable laser can be thermally tuned by a suspended structure to improve the thermal tuning efficiency of the superstructure grating.
  • Figure 11 is a schematic view of a reflective region having a suspended structure
  • Figures 12 and 13 are schematic views of the 3'-3', 4'-4' cross-sections of Figure 12, respectively.
  • the reflective region includes, in order from the bottom to the top, a substrate layer, a lower barrier layer, a sacrificial layer, an upper barrier layer, an under cladding layer, a waveguide layer, an upper cladding layer, and a dielectric layer. Heating layer.
  • the advanced discrete superstructure grating is distributed at the interface of the waveguide layer and the upper cladding layer, and the black and white phase portion in Fig. 12 shows a mirror including the superstructure grating.
  • the substrate layer is a layer in which the semiconductor crystal needs to be grown on the basis of the crystal substrate, and the substrate layer is located under the lower barrier layer. If an InP buffer layer is also disposed in the reflective region, the InP buffer layer is located between the lower cladding layer and the substrate layer for providing a better crystal quality InP material, providing a better material basis for other layer materials.
  • the upper cladding layer, the waveguide layer, and the lower cladding layer are located between the dielectric layer and the InP buffer layer for providing a low loss transmission channel for the optical signal.
  • the dielectric layer is used to prevent the heater current from leaking into the upper cladding, the heater can generate heat by the current, the heating layer is used to change the temperature of the mirror region, the heating unit is used to supply heat to the mirror, and the heating resistor can be used.
  • the current flows through the heating resistor, which changes the temperature of the heating resistor.
  • the arrows below the heater indicate the direction of the heat flow.
  • the waveguide layer is made of Indium Gallium Arsenide Phosphide (InGaAsP) material.
  • the left and right sides of the sacrificial layer are protective structures, and the protective structures are located on both sides of the upper surface of the lower barrier layer along the propagation direction of the optical signal in the waveguide layer.
  • the hollow structure is completely hollow; a gap between the transport layer in the region where the mirror is located and the material on both sides of the transport layer, and a suspended structure between the gaps and the hollow structure;
  • the direction is periodically arranged, and the gap extends through the upper cladding layer, the waveguide layer, the lower cladding layer and the upper barrier layer to reach a region where the hollow structure is located, and a support structure is provided between the adjacent gaps for providing lateral mechanical support to the suspended structure.
  • the length period of the support structure along the waveguide direction is not equal to the period of the modulation function of the superstructure grating.
  • the optical waveguide includes a waveguide layer, which is composed of a waveguide layer and upper and lower cladding layers, and the area in the dotted frame is a preparation process.
  • the window for etching the sacrificial layer material, the etchant passes through the windows on both sides of the mirror, respectively etching the sacrificial layer material under the mirror to reach the hollow structure region.
  • a region above the hollow structure and between the windows on both sides of the optical waveguide forms a suspended structure as shown in FIGS. 12 and 13.
  • a region between the left and right protective structures in the sacrificial layer is a hollow structure, and the gap is from the dielectric layer.
  • the waveguide layer After passing through the upper cladding layer, the waveguide layer, the lower cladding layer and the upper barrier layer, it reaches the region where the hollow structure is located. At the same time, in order to avoid the performance of the grating reflection spectrum during thermal tuning, the area between the corrosion windows is the support area of the suspended structure.
  • the length of the support structure providing the lateral mechanical support in the waveguide direction is not equal to the period of the modulation function of the superstructure grating, thereby facilitating the deterioration of the flatness of the reflection spectrum of the superstructure grating during thermal tuning, thereby facilitating the adjustment Deterioration of laser performance.
  • the period of the length of the support structure along the waveguide direction is not equal to the period of the modulation function of the superstructure grating, and may include the case where the lateral support structure and any one of the specific peaks or troughs in the spatial period of the modulation function of the superstructure grating are misaligned, Improve the reflection flatness of superstructure gratings.
  • the peak in the spatial period of the modulation function refers to the maximum value in the spatial period of the modulation function
  • the valley in the spatial period of the modulation function refers to the minimum value in the spatial period of the modulation function.
  • the reflective region may not be provided with an InP buffer layer, and the lower barrier layer is directly on the substrate layer.
  • FIG. 11 the openings shown in FIG. 11 are intended to help those skilled in the art to better understand the embodiments of the present invention, and do not limit the scope of the embodiments of the present invention. It will be obvious to those skilled in the art that various modifications and changes can be made in the shape of the opening in accordance with the example of FIG. 11 which is within the scope of the embodiments of the present invention.
  • a tunable laser provided by an embodiment of the present application includes a top view of a bottom support structure.
  • the etchant enters the sacrificial layer by the voids to form a hollow structure.
  • the transmission layer in the region where the mirror is located is completely isolated from the material of the two sides of the transmission layer to form a gap, and the gap penetrates the upper cladding layer, the waveguide layer, the lower cladding layer and the upper barrier layer to reach the region where the hollow structure is located, above the hollow structure, the gap A suspended structure is formed between them.
  • FIG. 14 is a schematic diagram of a reflective region having a suspended structure
  • Figure 15 is a cross-sectional view of the tunable laser along the 3-3 position of Figure 14 provided by an embodiment of the present application, from position 3-3 of Figure 14.
  • the uncorroded region provides a bottom support structure
  • FIG. 16 is a cross-sectional view of the tunable laser along the 1-1 position of FIG.
  • FIG. Figure 17 is a cross-sectional view of the tunable laser of position 2-2 of Figure 14 provided with an embodiment of the present application, the sacrificial layer of the tunable laser is not completely etched, leaving a bottom support structure to provide the hollow structure Bottom support.
  • Figure 14 there are some periodic dashed boxes on both sides of the optical waveguide.
  • the area inside the dotted frame is the window used to etch the sacrificial layer material during the preparation process.
  • the etchant passes through the windows on both sides of the mirror and is respectively engraved.
  • the sacrificial layer material under the mirror is etched to form a suspended structure.
  • Figure 11 utilizes a lateral support structure for lateral mechanical support of the suspended structure.
  • the sacrificial layer under the suspended structure is not completely etched, and some pillars are formed.
  • the bottom of the suspended structure is supported by the bottom of the suspended structure.
  • the length of the bottom support structure along the waveguide direction is not equal to the period of the modulation function of the superstructure grating, thereby being thermally tuned It is advantageous to avoid deterioration of the flatness of the reflection spectrum of the super-structure grating, thereby facilitating the deterioration of the performance of the tunable laser.
  • the length of the bottom support structure along the waveguide direction is not equal to the period of the modulation function of the super-structure grating, and may specifically include the case where the bottom support structure and any one of the specific peaks or troughs of the modulation function space period of the super-structure grating are misaligned, The reflection flatness of the superstructure grating can be improved.
  • the peak in the spatial period of the modulation function refers to the maximum value in the spatial period of the modulation function
  • the valley in the spatial period of the modulation function refers to the minimum value in the spatial period of the modulation function.
  • the superstructure grating is located in the lower half of the upper cladding layer in the transmission layer of the region where the mirror is located;
  • the superstructure grating is located in the upper half of the lower cladding layer in the transport layer of the region where the mirror is located;
  • the superstructure grating is located in the waveguide layer in the transport layer of the region where the mirror is located;
  • the superstructure grating is located in each of the upper cladding layer and the waveguide layer in the transmission layer of the region where the mirror is located; or
  • the superstructure grating is located in a portion of the lower cladding layer and the waveguide layer in the transmission layer of the region where the mirror is located.
  • the mirror is located in the upper cladding layer for tuning the wavelength of the optical signal.
  • the mirror may also be located in the lower cladding layer, or in the waveguide layer, or on the upper layer.
  • the two layers of the cladding layer and the waveguide layer, or in the two layers of the lower cladding layer and the waveguide layer there are various implementations, which are only described herein.
  • the optical signal propagates in the upper cladding layer, the lower cladding layer, and the waveguide layer, and the superstructure grating is placed at these positions to reflect the optical signal.
  • the refractive index of the waveguide layer is higher than the refractive index of the upper cladding layer and the refractive index of the lower cladding layer. Therefore, when the optical signal propagates in the waveguide layer, total reflection is formed, so that the optical energy can be limited as much as possible in the waveguide layer, so that the waveguide layer can provide a low-loss propagation path of the optical signal and reduce the loss of optical signal propagation.
  • the reflectivity of the grating reflection peak determines the threshold value of the tunable laser, the output power and the like, and the FWHM of the grating reflection peak determines the model selectivity of the laser (FWHM defines the reflection peak). Sharpness), the smaller the theoretical FWHM is, the larger the side mode suppression ratio is. The ideal way is to optimize the two separately.
  • the embodiment of the present application proposes a three-level discrete or even higher-level discrete super-structure grating, and optimizes the reflection of the reflected peak by adjusting the length of the grating and the ratio of the optical waveguide corresponding to the discrete value of the modulation function to the total length of the grating of the super-structure grating.
  • Embodiments of the present application simultaneously propose a plurality of tunable lasers based on advanced discrete gratings, and a mirror structure for improving the thermal tuning efficiency of advanced discrete gratings, and improving the tuning efficiency by etching a sacrificial layer to form a suspended structure, and the bottom support structure is used for Mechanical support is provided to the suspended structure to ensure a fixed position of the suspended structure in the tunable laser.

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Abstract

一种超结构光栅和可调谐激光器，可同时满足性能较好的反射率和FWHM。超结构光栅通过调制函数对均匀光栅在空间上进行幅度和相位调制从而形成梳状反射谱，调制函数通过N个阈值进行离散化处理后得到(N+1)个调制函数离散值，N为大于或等于2的正整数；(N+1)个调制函数离散值中每个调制函数离散值对应于一段折射率均匀不变的光波导或对应于一段均匀光栅；超结构光栅的反射峰的反射率通过(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节；超结构光栅的反射峰的FWHM通过该比例关系、超结构光栅的光栅总长度进行调节。

Description

一种超结构光栅和可调谐激光器
本申请要求于2017年4月17日提交中国专利局、申请号为201710247396.3、发明名称为“一种超结构光栅和可调谐激光器”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及光纤通信领域，尤其涉及一种超结构光栅和可调谐激光器。
背景技术
在光通信领域中，可调谐激光器(Tunable Laser，TL)是指输出的光信号波长可在一定范围内进行调节的激光器，主要应用于大容量波分复用传输系统中。随着信息量爆炸式增长，通信市场规模持续快速膨胀，为了进一步提高带宽，相干调制技术被使用并成为100G及以上速率长距离光传输的业界主流方案。而相干调制技术对于激光器的激射线宽等性能有着苛刻的要求，各种新的需求对可调谐激光器的尺寸、成本、可靠性和性能等指标也提出了更高的要求。其中，单片集成可调谐激光器具有体积小、集成度高等优点，因此成为当前光通信领域的主流技术。
单片集成可调谐激光器可以大体上通过增益区与磷化铟(Indium Phosphide，InP)衬底上的无源区的对接制造得到。增益区一般为多量子阱(Multiple Quantum Well，MQW)，而无源区主要包括反射镜和相位区段。波长调谐是通过调节反射镜或者相位区段的折射率来实现。其中，反射镜的反射谱对波长具有选择性，常用的反射镜包括分布布拉格反射器(Distributed Bragg Reflection，DBR)或者微环谐振器，反射镜产生的反射谱通常为梳妆反射谱。
超结构光栅(Super Structure Grating，SSG)具有梳妆反射谱，可调谐激光器的反射镜区域可以使用SSG来反射光，如下公式(1)为SSG的折射率分布：
Figure PCTCN2017112142-appb-000001
在上述公式(1)中，当SSG具有偶数个反射峰时，n(z)的取值为
Figure PCTCN2017112142-appb-000002
当SSG具有奇数个反射峰时，n(z)的取值为
Figure PCTCN2017112142-appb-000003
ΔF与Λk、Λk+1之间满足如下公式(2)。
Figure PCTCN2017112142-appb-000004
其中，n0为SSG的平均有效折射率，Λk决定了余弦函数的周期，δn为光栅有效折射率最大值与最小值的差值，N表示调制函数由N个余弦函数组成，z表示光栅沿传播方向的位 置，φk为第k个余弦函数的相位，ΔF由式(2)决定。
由式(1)可以得到超结构光栅的调制函数为如下公式(3)：
Figure PCTCN2017112142-appb-000005
一段均匀光栅的反射谱只有一个主峰，超结构光栅可通过调制函数对一段均匀光栅进行调制形成梳妆反射谱。而均匀光栅的有效折射率只有高折射率nh与低折射率nl两个值。如图1所示，虚线表示为一个SSG的调制函数，SSG的调制函数为模拟的连续周期性函数，其与均匀光栅相乘后折射率的空间分布也为连续变化，不再只有nh与nl两个值，工艺上非常难制作。为了实现SSG容易制作，如式所示(4)，通常会选取一个阈值对式(3)所示的连续函数进行2级数字离散化处理。
Figure PCTCN2017112142-appb-000006
图1中的实线所示为超结构光栅调制函数使用一个阈值V1进行2级数字化离散的效果，离散后的包络函数对连续光栅的调制同样为周期性的，但折射率依然只有nh与nl两个值，仅在包络函数“1”和“-1”之间切换时会引入相移，因此容易加工制作出SSG。
如图2所示，为2级离散SSG反射峰的反射率、半高全宽(Full Width Half Maximum，FWHM)分别与SSG总长度的关系示意图，SSG总长度决定了反射峰的反射率与FWHM，一种SSG总长度对应一种特定的反射率与FWHM，即反射峰的反射率与FWHM一一对应，因此对于2级离散的SSG而言，无法分别对反射率和FWHM进行独立优化，以取得性能较好的FWHM和反射率。
综上可知，对于现有技术中的SSG，SSG反射峰的反射率和FWHM都是由SSG总长度决定的，无法对SSG的反射率和FWHM两者分别进行优化，因此无法同时满足性能较好的反射率和FWHM。
发明内容
本申请实施例提供了一种超结构光栅和可调谐激光器，用于对超结构光栅的反射峰的反射率和FWHM分别独立进行优化，同时满足性能较好的反射率和FWHM。
为解决上述技术问题，本申请实施例提供以下技术方案：
第一方面，本申请实施例提供一种超结构光栅，所述超结构光栅通过调制函数对均匀光栅在空间上进行幅度和相位调制从而形成梳妆反射谱，所述调制函数通过N个阈值进行离散化处理后得到(N+1)个调制函数离散值，所述N为大于或等于2的正整数；所述(N+1)个调制函数离散值中每个调制函数离散值对应于一段折射率均匀不变的光波导或对应于一段均匀光栅，所述均匀光栅为高折射率和低折射率交替变化的光波导；所述超结构光栅的反射峰的反射率通过所述(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占所述超结构光栅的光栅总长度的比例关系、所述超结构光栅的光栅总长度进 行调节；所述超结构光栅的反射峰的半高全宽FWHM通过所述比例关系、所述超结构光栅的光栅总长度进行调节。
在本申请的上述实施例中，通过将调制函数进行离散化得到(N+1)个调制函数离散值，超结构光栅的反射峰的反射率通过(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节，超结构光栅的反射峰的FWHM通过前述的比例关系、超结构光栅的光栅总长度进行调节，即超结构光栅的反射峰的反射率和FWHM都可以通过两个维度进行调节，反射峰的反射率决定了可调谐激光器的阈值和输出功率，反射峰的FWHM决定了激光器的选模特性，FWHM越小，边模抑制比越大。基于本申请实施例提供的可调谐激光器可以对反射率和FWHM分别进行优化，从而可以同时满足性能较好的反射率和FWHM。
结合第一方面，在第一方面的第一种可能的实现方式中，当所述N的取值为2时，所述调制函数进行离散化处理后得到3个调制函数离散值，所述3个调制函数离散值有一个调制函数离散值对应一段折射率均匀不变的光波导，所述3个调制函数离散值中其余两个调制函数离散值分别对应于一段均匀光栅。通过对超结构光栅的3级离散化处理可以得到分别对应于折射率均匀不变的光波导和均匀光栅的3个调制函数离散值，超结构光栅的反射峰的反射率通过3个调制函数离散值中有一个调制函数离散值所对应的折射率均匀不变的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节反射峰的反射率、FWHM，从而实现对反射率和FWHM的同时优化。
结合第一方面或第一方面的第一种可能的实现方式，在第一方面的第二种可能的实现方式中，所述(N+1)个调制函数离散值中存在两个调制函数离散值对应于同一种的均匀光栅。通过控制调制函数中各个调制函数离散值对应的光波导所占光栅总长度的比例，就可以优化超结构光栅的反射率了。
结合第一方面或第一方面的第一种可能的实现方式，在第一方面的第三种可能的实现方式中，当相邻的调制函数离散值的正负号不同或者所述相邻的调制函数离散值中有一个离散值为零时，所述相邻的调制函数离散值分别对应的光波导之间加入有相移。当调制函数的符号发生变化时在光波导之间切入相移，从而使得超结构光栅的反射谱更平坦，提高超结构光栅的反射性能。
第二方面，本申请实施例还提供一种可调谐激光器，所述可调谐激光器包括：反射区，其中，所述反射区，用于通过如前述第一方面中任一项所述的超结构光栅对光信号进行调谐。本申请实施例还提供基于前述的超结构光栅的可调谐激光器。在本申请实施例提供的可调谐激光器中，通过将调制函数进行离散化得到(N+1)个调制函数离散值，超结构光栅的反射峰的反射率通过(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节，超结构光栅的反射峰的FWHM通过前述的比例关系、超结构光栅的光栅总长度进行调节，即超结构光栅的反射峰的反射率和FWHM都可以通过两个维度进行调节，反射峰的反射率决定了可调谐激光器的阈值和输出功率，反射峰的FWHM决定了激光器的选模特性，FWHM越小，边模抑制比越大。基于本申请实施例提供的可调谐激光器可以对反射率和FWHM分别进行优化，从而可以同时满足性能较好的反射率和FWHM。
结合第二方面，在第二方面的第一种可能的实现方式中，所述可调谐激光器，还包括：增益区和相位区，其中；所述反射区包括：第一反射镜和第二反射镜；所述增益区通过光波导分别和所述第一反射镜、所述相位区进行级联；所述相位区与所述增益区、所述第二反射镜相级联；所述增益区，用于产生光信号；所述相位区，用于对所述光信号进行相位调节，使所述可调谐激光器能够微调所述光信号的激射波长。通过可调谐激光器中的增益区和相位区可以分别实现光信号的产生以及相位调节，在微调光信号的激射波长之后通过反射区将光信号发射出去。
结合第二方面的第一种可能的实现方式，在第二方面的第二种可能的实现方式中，所述可调谐激光器，还包括：半导体光放大器SOA和光探测器PD；所述第一反射镜通过光波导和所述SOA进行级联，所述第二反射镜通过光波导和所述PD进行级联；所述SOA，用于对所述光信号进行功率放大；所述PD，用于对所述光信号进行功率监测或功率衰减。通过可调谐激光器中的SOA和PD可以实现光信号的功率放大以及功率监测或功率衰减。
结合第二方面的第一种可能的实现方式，在第二方面的第三种可能的实现方式中，所述可调谐激光器，还包括：第一SOA和第二SOA；所述第一反射镜通过光波导和所述第一SOA进行级联，所述第二反射镜通过光波导和所述第二SOA进行级联；所述第一SOA，用于对所述第一反射镜射出的光信号进行功率放大；所述第二SOA，用于对所述第二反射镜射出的光信号进行功率放大。可调谐激光器中第一反射镜和第二反射镜都可以连接一个SOA，对每个反射镜射出的光信号进行功率放大，从而可以发射出功率更强的光信号。
结合第二方面，在第二方面的第四种可能的实现方式中，所述可调谐激光器，还包括：多模干涉MMI耦合器、增益区和相位区；所述反射区包括：第一反射镜和第二反射镜；所述MMI耦合器的一侧有一个端口，与所述相位区相连接，所述MMI耦合器的另一侧有两个端口，分别与所述第一反射镜和所述第二反射镜相连接；所述相位区两侧分别与增益区和MMI的一个端口相级联；所述增益区，用于产生光信号；所述相位区，用于对所述光信号进行相位调节，使所述可调谐激光器能够微调所述光信号的激射波长。MMI耦合器用于将第一反射镜和第二反射镜反射回来的光一起耦合进相位区。有源增益区的禁带宽度较低，对应于可调谐激光器的目标输出波长，一般为多量子阱，当受到电注入时，将电能转化为光能，从而提供增益。
结合第二方面的第四种可能的实现方式，在第二方面的第五种可能的实现方式中，所述可调谐激光器，还包括：相位调整模块，其中，所述相位调整模块分别和所述MMI耦合器、所述第一反射镜连接，或所述相位调整模块分别和所述MMI耦合器、所述第二反射镜连接；所述相位调整模块，用于匹配所述第一反射镜的反射谱和所述第二反射镜的反射谱之间的相位。在第一反射镜或第二反射镜的Y分支臂上添加相位调整模块，用以匹配两反射镜反射谱的相位，这样第一反射镜或第二反射镜可以更好的通过MMI耦合器合波。
结合第二方面的第四种可能的实现方式，在第二方面的第六种可能的实现方式中，所述可调谐激光器，还包括：SOA和PD；所述第一反射镜具有第一端口，所述第二反射镜具有第二端口，所述增益区具有第三端口；所述第一端口连接有所述SOA或所述PD，和/或所述第二端口连接有所述SOA或所述PD，和/或所述第三端口连接有所述SOA或所述PD；所述SOA，用于对所述光信号进行功率放大；所述PD，用于对所述光信号进行功率监测或 功率衰减。第一反射镜、第二反射镜和增益区中至少有一个端口可以通过光波导连接SOA，第一反射镜、第二反射镜和增益区中可以通过光波导连接PD，可调谐激光器通过集成的SOA和PD可以分别实现光信号的功率放大以及功率监测或功率衰减。
结合第二方面或第二方面的第一种可能、第二种可能或第三种可能或第四种可能或第五种可能或第六种可能的实现方式，在第二方面的第七种可能的实现方式中，所述反射区，包括：加热单元、传输层、反射镜、上阻挡层、牺牲层、下阻挡层和衬底层，其中，所述加热单元，位于所述传输层的上方；所述传输层，位于所述牺牲层上方，从上到下依次包括：上包层、波导层和下包层；所述反射镜，位于所述传输层中，所述反射镜用于通过前述第一方面中任一项所述的超结构光栅对光信号进行调谐；所述上阻挡层，位于所述传输层和所述牺牲层之间；所述牺牲层，位于所述上阻挡层和下阻挡层之间，所述牺牲层内形成有保护结构，所述保护结构与层间区域形成中空结构，所述层间区域包括：所述传输层与所述衬底层之间的区域；所述下阻挡层，位于所述牺牲层和所述衬底层之间；所述衬底层，位于所述牺牲层的下方。可调谐激光器中的反射区可以采用中空结构进行热调谐，提高超结构光栅的热调谐效率。
结合第二方面的第七种可能的实现方式，在第二方面的第八种可能的实现方式中，所述中空结构为完全空心；所述反射镜所在区域的传输层与两侧传输层材料之间具有空隙，在所述空隙之间、所述中空结构之上形成悬空结构；所述空隙沿着波导方向周期性排布，所述空隙贯穿所述上包层、所述波导层、所述下包层和所述上阻挡层之后到达所述中空结构所在区域，相邻的所述空隙之间有支撑结构，用于对所述悬空结构提供侧向机械支撑，所述支撑结构沿波导方向的长度周期不等于所述超结构光栅的调制函数的周期。为了在热调谐时不牺牲光栅反射谱的性能，腐蚀窗口之间的区域是悬空结构的支撑区域，腐蚀窗口之间的区域与超结构光栅调制函数的峰或者谷不对齐，即只要峰不对齐，或者谷不对齐即可，最左端与最右端的两个腐蚀窗口用来避免温度在两侧过低。
结合第二方面的第七种可能的实现方式，在第二方面的第九种可能的实现方式中，所述反射镜所在区域的传输层与两侧传输层材料之间完全隔离开形成空隙，所述空隙贯穿所述上包层、所述波导层、所述下包层和所述上阻挡层之后到达所述中空结构所在区域，在所述中空结构上方、所述空隙之间形成悬空结构；所述牺牲层中底部没有被完全腐蚀，所述牺牲层保留有底部支撑结构，所述底部支撑结构用于对所述悬空结构形成支撑。可调谐激光器中的反射区可以采用悬空结构进行热调谐，提高超结构光栅的热调谐效率。
结合第二方面的第九种可能的实现方式，在第二方面的第十种可能的实现方式中，所述底部支撑结构沿波导方向的长度周期不等于所述超结构光栅的调制函数的周期。
结合第二方面的第七种可能的实现方式，在第二方面的第十一种可能的实现方式中，所述超结构光栅位于所述反射镜所在区域的传输层中的上包层的下半部分；或，所述超结构光栅位于所述反射镜所在区域的传输层中的下包层的上半部分；或，所述超结构光栅位于所述反射镜所在区域的波导层；或，所述超结构光栅位于所述反射镜所在区域的传输层中的上包层和波导层中各存在一部分；或，所述超结构光栅位于所述反射镜所在区域的传输层中的下包层和波导层中各存在一部分。反射镜位于上包层中，用于调谐光信号的波长，不限的是，反射镜还可以位于下包层中，或者位于波导层中，或者位于上包层和波导层两 个层中，或者位于下包层和波导层两个层中，具体实现方式有多种，此处仅作说明。光信号在上包层、下包层、波导层中传播，超结构光栅放在这些位置才能对光信号进行反射。
结合第二方面的第七种可能的实现方式，在第二方面的第十二种可能的实现方式中，所述波导层的折射率高于上包层的折射率和下包层的折射率。因此光信号在波导层中传播时会形成全反射，这样可以将光能量尽可能限制在波导层中，从而波导层可以提供光信号的低损耗传播通道，减少光信号传播的损耗。
结合第二方面的第七种可能至第十二种可能的实现方式，在第二方面的第十三种可能的实现方式中，所述反射区，还包括：磷化铟InP缓冲层，其中，所述下阻挡层，位于所述牺牲层和所述InP缓冲层之间；所述InP缓冲层，位于所述下阻挡层和所述衬底层之间。InP缓冲层主要作用是提供晶体质量更好的InP材料，为其它层材料提供更好的材料基础。
附图说明
图1为现有技术中超结构光栅的调制函数进行2级离散后的效果图；
图2为现有技术中2级离散化处理后的超结构光栅的反射峰的反射率、FWHM分别与SSG总长度的关系示意图；
图3为本申请一个实施例中超结构光栅的调制函数进行3级离散化处理后的效果图；
图4为本申请一个实施例中3级离散化处理后的超结构光栅的结构图；
图5为本申请的一个实施例中3级离散化处理后的超结构光栅的反射率与光栅总长度、调制函数中0的部分占光栅总长度比例的关系示意图；
图6为本申请的一个实施例中3级离散化处理后的超结构光栅的FWHM与光栅总长度、调制函数中0的部分占光栅总长度比例的关系示意图；
图7为本申请一个实施例提供的可调谐激光器的组成结构示意图；
图8为本申请另一个实施例提供的可调谐激光器的组成结构示意图；
图9为本申请另一个实施例提供的可调谐激光器的组成结构示意图；
图10为本申请另一个实施例提供的可调谐激光器的组成结构示意图；
图11为本申请的一个实施例提供的可调谐激光器的悬空结构反射镜俯视图；
图12为本申请的一个实施例提供的沿图11中3′-3′位置的可调谐激光器的截面图；
图13为本申请的一个实施例提供的沿图11中4′-4′位置的可调谐激光器的截面图；
图14为本申请的一个实施例提供的可调谐激光器包括的底部支撑结构俯视图；
图15为本申请的一个实施例提供的沿图14中3-3位置的可调谐激光器的截面图；
图16为本申请的一个实施例提供的沿图14中1-1位置的可调谐激光器的截面图；
图17为本申请的一个实施例提供的沿图14中2-2位置的可调谐激光器的截面图。
具体实施方式
本申请实施例提供了一种对超结构光栅的反射峰的反射率和FWHM分别独立进行优化，同时满足性能较好的反射率和FWHM。
下面结合附图，对本申请的实施例进行描述。
本申请的说明书和权利要求书及上述附图中的术语“第一”、“第二”等是用于区别类似的对象，而不必用于描述特定的顺序或先后次序。应该理解这样使用的术语在适当情况下可以互换，这仅仅是描述本申请的实施例中对相同属性的对象在描述时所采用的区分方式。此外，术语“包括”和“具有”以及他们的任何变形，意图在于覆盖不排他的包含，以便包含一系列单元的过程、方法、系统、产品或设备不必限于那些单元，而是可包括没有清楚地列出的或对于这些过程、方法、产品或设备固有的其它单元。
产生激光的三个条件是：实现粒子数反转、满足阈值条件和谐振条件。产生激光的首要条件是粒子数反转，在半导体中就是要把价带内的电子抽运到导带，为了获得粒子数反转，通常采用重掺杂的P型和N型材料构成PN结，这样，在外加电压作用下，在结区附近就出现了粒子数反转，在高费米能级中贮存着电子，而在低费米能级中贮存着空穴，当然还有很多其它产生粒子数反转的方法。实现粒子数反转是产生激光的必要条件，但不是充分条件，要产生激光，还要有损耗极小的谐振腔，传统谐振腔的主要部分是两个互相平行的反射镜，受激辐射光在两个反射镜之间来回反射，不断引起新的受激辐射，使受激辐射光不断被放大。只有受激辐射放大的增益大于激光器内的各种损耗，即满足一定的阈值条件才能在输出端产生加强干涉，输出稳定激光。谐振条件指的是谐振腔的长度L和折射率N确定以后，只有特定频率的光才能形成光振荡，输出稳定的激光，这说明谐振腔对输出的激光有一定的选频作用。
单片集成半导体可调谐激光器通常由磷化铟(Indium Phosphide，InP)衬底上的增益区和无源区对接而成，其平面示意图如图7所示，包括反射区、增益区和相位调节区，该反射区可包括：第一反射镜和第二反射镜。其中，增益区的禁带宽度较低，当受到电注入时，将电能转化为光能，从而提供增益；无源区在结构上主要包括反射镜，无源区的禁带宽度比激光波长的光子能量更高，对激光的吸收小，因此能提供很低的吸收损耗。为了覆盖整个C波段(约40nm范围)，通常会利用两个反射镜的“游标效应”来扩大调谐范围，由于两个反射镜通常位于增益区的前面和后面，所以通常被分别称为前反射镜和后反射镜，可以认为两个反射镜是等价的，名称可以互换。此外，无源区还可以包含一个相位调节区，用于对谐振腔内的有效光程进行细调从而改变激光器输出波长。
可调谐激光器的两个反射镜都有梳状反射光谱，具有多个反射峰，反射峰是可以调节的，通过调节反射峰可以调节激光器的输出波长。现有技术中反射峰的反射率和FWHM只与超结构光栅的光栅总长度有关，如图2所示，现有技术中超结构光栅的光栅总长度决定了反射峰的反射率与FWHM，一种超结构光栅的光栅总长度对应一种特定的反射率与FWHM，即反射峰的反射率与FWHM一一对应，因此无法分别对反射率和FWHM进行独立优化，以取得性能较好的FWHM和反射率。本发明实施例中通过对调制函数的高级离散，使得反射峰的反射率和FWHM可以通过两个维度进行调节，使得反射率和FWHM可以分别独立进行优化，从而可以同时满足性能较好的反射率和FWHM。
本申请的一个实施例首先提供一种超结构光栅，这种超结构光栅通过调制函数对均匀光栅在空间上进行幅度和相位调制从而形成梳妆反射谱，调制函数通过N个阈值进行离散化处理后得到(N+1)个调制函数离散值，N为大于或等于2的正整数；
(N+1)个调制函数离散值中每个调制函数离散值对应于一段折射率均匀不变的光波导 或对应于一段均匀光栅，均匀光栅为高折射率和低折射率交替变化的光波导；
超结构光栅的反射峰的反射率通过(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节；
超结构光栅的反射峰的FWHM通过前述的比例关系、超结构光栅的光栅总长度进行调节。
其中，超结构光栅的调制函数通过N个阈值进行离散化处理后得到(N+1)个调制函数离散值，即对超结构光栅的调制函数进行N级离散化处理后，可以得到(N+1)个调制函数离散值。例如，本申请实施例中可以选取2个阈值对超结构光栅的调制函数进行3级离散化处理后可以得到3个调制函数离散值，这与现有技术中只选取1个阈值对调制函数进行2级离散后得到2个调制函数离散值完全不同，接下来以N的取值为2对本申请实施例提供的超结构光栅进行举例说明。
本申请实施例提供的超结构光栅可以实现分别对反射峰的反射率和FWHM进行优化，3级离散后可以得到3个调制函数离散值，如下公式为调制函数离散值Profile_D(z)的表达式：
Figure PCTCN2017112142-appb-000007
其中，Threshold1和Threshold2为两个阈值，本申请实施例中使用这两个阈值对调制函数Profile(z)进行3级离散化处理后可以得到3个调制函数离散值，如图3所示，为本申请一个实施例中超结构光栅的调制函数进行3级离散化处理后的效果图。离散后的调制函数有1，0，-1三个数值，这样调制函数作用在均匀光栅上之后，1与-1对应的超结构光栅部分依旧只有高折射率nh与低折射率nl两个值，0对应的超结构光栅部分只有高折射率nh。均匀光栅是高折射率nh与低折射率nl交替出现，高折射率nh与低折射率nl的界面处有反射。如图4所示，为本申请一个实施例中3级离散化处理后的超结构光栅的结构图。当调制函数为1或者-1时，超结构光栅为高折射率nh与低折射率nl交替出现，与均匀光栅一样。当调制函数为0时，超结构光栅全部为高折射率nh，这样有效反射面就会减少。因此通过控制调制函数0所占的比例，就可以优化超结构光栅的反射峰的反射率了。如图4所示，超结构光栅的形貌被放大后可见，阴影部分为低折射率部分，当调制函数等于0时，超结构光栅只有高折射率nh。
对于3级离散的超结构光栅可以通过调节离散后调制函数中0的部分占超结构光栅的光栅总长度的比例，再结合超结构光栅的光栅总长度一起来调节光栅的反射率与FWHM。如图5和图6所示，图5为本申请的一个实施例中3级离散化处理后的超结构光栅的反射率与光栅总长度、调制函数中0的部分占光栅总长度比例的关系示意图，图6为本申请的一个实施例中3级离散化处理后的超结构光栅的FWHM与光栅总长度、调制函数中0的部分占光栅总长度比例的关系示意图，图5和图6中分别有五条线，每条线对应不同光栅总长度的超结构光栅。将“调制函数0对应的光波导所占光栅总长度的比例”简称为“调制函数中0所占的比例”，调制函数为0时，超结构光栅全部为nh，这样有效反射面就会减少，通 过控制调制函数0对应的光波导所占光栅总长度的比例，就可以优化超结构光栅的反射率了，若光栅总长度越长，反射率也越大。对于FWHM，光栅总长度越长，FWHM越小，调制函数离散值0所占的比例越大，FWHM越小。这样超结构光栅的反射率和FWHM都分别和光栅总长度、调制函数离散值0所占的比例相关。这样便有两个应变量(光栅总长度、调制函数离散值0所占的比例)可以分别优化超结构光栅的反射峰的反射率和FWHM。如图5和图6所示，超结构光栅的反射率和FWHM都与光栅总长度以及调制函数中0的比例同时相关，即反射率与光栅总长度、调制函数中0的比例相关，FWHM与光栅总长度、调制函数中0的比例相关。由于引入了调制函数离散值对应的光波导长度占光栅总长度的比例关系作为设计自由度，超结构光栅的反射率与FWHM可以被分别进行优化，比如光栅总长度为294um，调制函数中“0”占光栅总长度的比例为0.3时，可以取得反射峰的反射率R＝0.2，FWHM＝1.08nm的超结构光栅。当超结构光栅的光栅总长度为412um，调制函数中“0”占光栅总长度的比例为0.6时，可以取得R＝0.2，FWHM＝0.77nm的超结构光栅。
在本申请的一个实施例中，当N的取值为2时，调制函数进行离散化处理后得到3个调制函数离散值，3个调制函数离散值有一个调制函数离散值对应一段折射率均匀不变的光波导，3个调制函数离散值中其余两个调制函数离散值分别对应于一段均匀光栅，通过对超结构光栅的3级离散化处理可以得到分别对应于折射率均匀不变的光波导和均匀光栅的3个调制函数离散值，超结构光栅的反射峰的反射率通过3个调制函数离散值中有一个调制函数离散值所对应的折射率均匀不变的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节反射峰的反射率、FWHM，从而实现对反射率和FWHM的同时优化。举例说明如下，3个调制函数离散值包括：第一数值、第二数值和第三数值，其中，第一数值对应于一段均匀光栅，第二数值对应一段折射率均匀不变的光波导，第三数值对应于一段均匀光栅。该第一数值、第三数值可以分别为图3所示的调制函数离散值1和-1，第二数值可以为图3所示的调制函数离散值0。
在本申请的一个实施例中，(N+1)个调制函数离散值中存在两个调制函数离散值对应于同一种的均匀光栅，通过控制调制函数中各个调制函数离散值对应的光波导所占光栅总长度的比例，就可以优化超结构光栅的反射率了。举例说明，如图3所示，调制函数离散值0对应的光波导部分只有高折射率或低折射率，从而在调制函数的取值为调制函数离散值0时超结构光栅不会形成反射界面。
在本申请的一个实施例中，当相邻的调制函数离散值的正负号不同或者相邻的调制函数离散值中有一个离散值为零时，相邻的调制函数离散值分别对应的光波导之间加入有相移，当调制函数的符号发生变化时在光波导之间切入相移，从而使得超结构光栅的反射谱更平坦，提高超结构光栅的反射性能。
需要说明的是，在本申请的前述实施例以及附图中以N的取值为2对超结构光栅的调制函数进行3级离散化处理为例进行了说明，不限的是，本申请实施例提供的超结构光栅的调制函数也可以进行4级离散化处理，或者更高级的离散化处理，超结构光栅可以采用更多的阈值，对调制函数进行大于等于4级等更高级别的离散化处理。举例说明如下，在对超结构光栅进行3级离散化处理的示例说明中，调制函数为1，-1或者0实质上对应了超结构光栅中对均匀光栅的不同调制形式，以4级离散为例，调制函数离散值可以取1、 0.5、-0.5、-1，其中各个调制函数离散值的具体取值可以根据应用场景来配置，只需要将各个调制函数离散值与各个取值均匀不变的光波导或均匀光栅的对应调制形式配置好即可，比如“1”“-1”对应于第1种均匀光栅，0.5或者-0.5对应于第2种均匀光栅，当调制函数离散值的正负号变化时引入相移。对于5级离散或者更高级别离散，调制函数离散值可以取1、0.5、0、-0.5、-1等等，比如“1”“-1”依旧对应第1种均匀光栅，0.5或者-0.5时对应于第2种均匀光栅，0对应于折射率均匀不变的光波导，当相邻的调制函数离散值的正负号不同或者相邻的调制函数离散值中有一个离散值为零时引入相移。
通过前述实施例对本申请的举例说明可知，超结构光栅通过调制函数对均匀光栅在空间上进行幅度和相位调制从而形成梳妆反射谱，该调制函数通过N个阈值进行离散化处理后得到(N+1)个调制函数离散值，N为大于或等于2的正整数，其中，(N+1)个调制函数离散值中每个调制函数离散值对应于一段折射率均匀不变的光波导或对应于一段均匀光栅，均匀光栅为高折射率和低折射率交替变化的光波导。通过将调制函数进行离散化得到(N+1)个调制函数离散值，超结构光栅的反射峰的反射率通过(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节，超结构光栅的反射峰的FWHM通过前述的比例关系、超结构光栅的光栅总长度进行调节，即超结构光栅的反射峰的反射率和FWHM都可以通过两个维度进行调节，反射峰的反射率决定了可调谐激光器的阈值和输出功率，反射峰的FWHM决定了激光器的选模特性，FWHM越小，边模抑制比越大。基于本申请实施例提供的可调谐激光器可以对反射率和FWHM分别进行优化，从而可以同时满足性能较好的反射率和FWHM。
前述实施例介绍本申请提供的超结构光栅，接下来说明本申请提供的一种可调谐激光器，该可调谐激光器包括：反射区，其中，反射区，用于通过前述实施例中的超结构光栅对光信号进行调谐，即本申请实施例还提供基于前述的超结构光栅的可调谐激光器。在本申请实施例提供的可调谐激光器中，通过将调制函数进行离散化得到(N+1)个调制函数离散值，超结构光栅的反射峰的反射率通过(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占超结构光栅的光栅总长度的比例关系、超结构光栅的光栅总长度进行调节，超结构光栅的反射峰的FWHM通过前述的比例关系、超结构光栅的光栅总长度进行调节，即超结构光栅的反射峰的反射率和FWHM都可以通过两个维度进行调节，反射峰的反射率决定了可调谐激光器的阈值和输出功率，反射峰的FWHM决定了激光器的选模特性，FWHM越小，边模抑制比越大。基于本申请实施例提供的可调谐激光器可以对反射率和FWHM分别进行优化，从而可以同时满足性能较好的反射率和FWHM。
在本申请的一个实施例中，请参阅图7所示，可调谐激光器，除了包括反射区，该可调谐激光器还包括：增益区和相位区，其中；
反射区包括：第一反射镜和第二反射镜；
增益区通过光波导分别和第一反射镜、相位区进行级联；
相位区与增益区、第二反射镜相级联；
增益区，用于产生光信号；
相位区，用于对光信号进行相位调节，使可调谐激光器能够微调光信号的激射波长。
其中，本申请前述实施例提供的超结构光栅可以设置在第一反射镜中，也可以设置在 第二反射镜中，如图7所示，第一反射镜和第二反射镜的位置可以互换，例如第一反射镜为后反射镜，第二反射镜为前反射镜。通过可调谐激光器中的增益区和相位区可以分别实现光信号的产生以及相位调节，在微调光信号的激射波长之后通过反射区将光信号发射出去。
如图7所示，为单片集成可调谐激光器的原理图，由增益区、第一反射镜、第二反射镜和相位区四段组成。其中，增益区位于有源区，增益区的禁带宽度较低，一般为多量子阱，当受到电注入时，将电能转化为光能，从而提供增益。第一反射镜和第二反射镜是等价的，可以互换，第一反射镜和第二反射镜的反射谱对波长具有选择性，用来进行波长调谐，第一反射镜和第二反射镜包括前述超结构光栅，反射镜产生的反射谱为梳妆反射谱，第一反射镜和第二反射镜的梳妆反射谱的自由光谱范围有一定差，然后两反射镜通过游标效应来放大调谐范围。相位区提供相位调节，使激光器可以微调激射波长，光在增益区产生，由第一反射镜和第二反射镜反射形成谐振产生激光，再从第一反射镜和第二反射镜透射，出射激光。第一反射镜、第二反射镜和相位区都位于无源区，无源区的禁带宽度比激光波长的光子能量更高，对光子的吸收非常小，无源区可以通过刻蚀再生长技术将有源区的MQW刻蚀掉，再通过二次外延将禁带宽度更大的化合物制造而来。其中，第一反射镜和第二反射镜都可以采用前述实施例中所描述的超结构光栅第一反射镜和第二反射镜的反射谱对波长具有选择性，用来进行波长调谐。相位区、第一反射镜和第二反射镜都可以通过电注入，或者改变热注入，或其他等效方法来改变波导的折射率进行波长调谐。
在本申请的另一个实施例中，请参阅图8所示，可调谐激光器，还包括：半导体光放大器(Semiconductor Optical Amplifier，SOA)和光探测器(Photo Detector，PD)；
第一反射镜通过光波导和SOA进行级联，第二反射镜通过光波导和PD进行级联；
SOA，用于对光信号进行功率放大；
PD，用于对光信号进行功率监测或功率衰减。
如图8所示，第一反射镜和第二反射镜的位置可以互换，通过可调谐激光器中的SOA和PD可以实现光信号的功率放大以及功率监测或功率衰减，需要说明的是，可调谐激光器左端或者右端可以分别集成SOA来进行功率放大，或者可调谐激光器左端或者右端可以分别集成PD进行功率监测或功率衰减。
在本申请的另一个实施例中，可调谐激光器，还包括：第一SOA和第二SOA；
第一反射镜通过光波导和第一SOA进行级联，第二反射镜通过光波导和第二SOA进行级联；
第一SOA，用于对第一反射镜射出的光信号进行功率放大；
第二SOA，用于对第二反射镜射出的光信号进行功率放大。
其中，可调谐激光器中第一反射镜和第二反射镜都可以连接一个SOA，对每个反射镜射出的光信号进行功率放大，从而可以发射出功率更强的光信号。
在本申请的一个实施例中，请参阅图9所示，可调谐激光器，还包括：多模干涉(Multi-mode Interference，MMI)耦合器、增益区和相位区；
反射区包括：第一反射镜和第二反射镜；
MMI耦合器的一侧有一个端口，与相位区相连接，MMI耦合器的另一侧有两个端口，分 别与第一反射镜和所述第二反射镜相连接。
相位区两侧分别与增益区和MMI的一个端口相级联；
增益区，用于产生光信号；
相位区，用于对光信号进行相位调节，使可调谐激光器能够微调所述光信号的激射波长。
其中，本申请一个实施例提供的可调谐激光器包括：增益区、相位区、MMI耦合器、第一反射镜和第二反射镜，MMI耦合器为1x2耦合器，一侧有一个端口，与相位区相联接，另一侧有两个端口，分别第一于反射镜和第二反射镜相联接。相位区与增益区和MMI相级联。MMI耦合器用于将第一反射镜和第二反射镜反射回来的光一起耦合进相位区。有源增益区的禁带宽度较低，对应于可调谐激光器的目标输出波长，一般为多量子阱，当受到电注入时，将电能转化为光能，从而提供增益。第一于反射镜和第二反射镜可以认为是等价的，名称可以互换，第一反射镜和第二反射镜的反射谱对波长具有选择性，用来进行波长调谐，例如第一于反射镜和第二反射镜包括前述超结构光栅为梳妆反射谱，两个反射镜的梳妆反射谱的自由光谱范围有一定差，第一于反射镜和第二反射镜反射回激光器谐振腔的激光通过MMI合波，再通过相加式游标效应来放大调谐范围。相位区提供相位调节，使激光器可以微调激射波长，第一反射镜、第二反射镜和相位区都位于无源区。相位区、第一反射镜和第二反射镜都可以通过电注入，或者改变热注入，或其他等效方法来改变波导的折射率进行波长调谐。
在本申请的一个实施例中，请参阅图10所示，相对于图9所示的可调谐激光器，该可调谐激光器还包括：相位调整模块，其中，
相位调整模块分别和MMI耦合器、第一反射镜连接，或相位调整模块分别和MMI耦合器、第二反射镜连接；
相位调整模块，用于匹配第一反射镜的反射谱和第二反射镜的反射谱之间的相位。
其中，在第一反射镜或第二反射镜的Y分支臂上添加相位调整模块，用以匹配两反射镜反射谱的相位，这样第一反射镜或第二反射镜可以更好的通过MMI耦合器合波，图10中以相位调整模块设置在第一反射镜上为例进行示意说明。
在本申请的一个实施例中，可调谐激光器，还包括：SOA和PD；
第一反射镜具有第一端口，第二反射镜具有第二端口，增益区具有第三端口；
第一端口连接有SOA或PD，和/或第二端口连接有SOA或PD，和/或第三端口连接有SOA或PD。
其中，第一反射镜、第二反射镜和增益区中至少有一个端口可以通过光波导连接SOA，第一反射镜、第二反射镜和增益区中可以通过光波导连接PD，可调谐激光器通过集成的SOA和PD可以分别实现光信号的功率放大以及功率监测或功率衰减。举例说明如下，增益区左端为端口1，第一反射镜右端为端口2，第二反射镜右端为端口3，三个端口任何其一可以集成SOA来对输出光功率进行放大，或集成PD进行功率监测或功率衰减。
在本申请的一个实施例中，请参阅图11所示，为本申请的一个实施例提供的可调谐激光器的悬空结构反射镜俯视图。图11中说明了可调谐激光器的悬空结构反射镜区域原理，P1至P7分别为1个光栅调制函数周期，在光波导的上方和下方分别有1至6的腐蚀窗口， 相邻两个腐蚀窗口之间为支撑区域。1号窗口左侧和6号窗口右侧分别有一个辅助窗口，用来避免反射区在P1的最左端或者P7的最右端温度过于小。
如图12所示，为本申请的一个实施例提供的沿图11中3′-3′位置的可调谐激光器的截面图，如图13所示，为本申请的一个实施例提供的沿图11中4′-4′位置的可调谐激光器的截面图。可调谐激光器的反射区，包括：加热单元、传输层、反射镜、上阻挡层、牺牲层、下阻挡层和衬底层，其中，
加热单元，位于传输层的上方；
传输层，位于牺牲层上方，从上到下依次包括：上包层、波导层和下包层；
反射镜，位于传输层中，反射镜用于通过前述权利要求1至4中任一项的超结构光栅对光信号进行调谐；
上阻挡层，位于传输层和牺牲层之间；
牺牲层，位于上阻挡层和下阻挡层之间，牺牲层内形成有保护结构，保护结构与层间区域形成中空结构，层间区域包括：传输层与衬底层之间的区域；
下阻挡层，位于牺牲层和衬底层之间；
衬底层，位于下阻挡层的下方。
在本申请的一些实施例中，反射区，还包括：InP缓冲层，其中，下阻挡层，位于牺牲层和InP缓冲层之间；InP缓冲层，位于下阻挡层和衬底层之间。
其中，可调谐激光器中的反射区可以采用悬空结构进行热调谐，提高超结构光栅的热调谐效率。图11所示为具有悬空结构的反射区域原理图，图12和图13分别是图12中3′-3′、4′-4′截面的示意图。如图12图13所示，反射区从材料结构上，从下到上依次包括：衬底层、下阻挡层、牺牲层、上阻挡层、下包层、波导层、上包层、介质层、加热层。高级离散的超结构光栅分布在波导层与上包层的界面处，图12中黑白相间部分所示为包含超结构光栅的反射镜。其中，衬底层是半导体晶体需要在晶体衬底基础上生长的层，衬底层位于下阻挡层之下。若反射区中还设置有InP缓冲层，则该InP缓冲层位于下包层和衬底层之间，用于提供晶体质量更好的InP材料，为其它层材料提供更好的材料基础。上包层、波导层、和下包层位于介质层和InP缓冲层之间，用于为光信号提供低损耗的传输通道。介质层用来防止加热器的电流泄漏到上包层中，加热器可以通过电流产生热量，加热层用来改变反射镜区的温度，加热单元用于给反射镜提供热量，可以采用加热电阻，电流流经加热电阻，就可以改变加热电阻的温度，加热器往下的几个箭头，表示热流的方向。波导层采用铟镓砷磷(Indium Gallium Arsenide Phosphide，InGaAsP)材料。在图12中牺牲层的左右两边为保护结构，保护结构沿着光信号在波导层中的传播方向位于下阻挡层的上表面的两侧。
在本申请的一个实施例中，中空结构为完全空心；反射镜所在区域的传输层与两侧传输层材料之间具有空隙，在空隙之间、中空结构之上形成悬空结构；空隙沿着波导方向周期性排布，空隙贯穿上包层、波导层、下包层和上阻挡层之后到达中空结构所在区域，相邻的空隙之间有支撑结构，用于对悬空结构提供侧向机械支撑，支撑结构沿波导方向的长度周期不等于超结构光栅的调制函数的周期。图11中所示的光波导两侧有一些周期性虚线框，光波导包含波导层，由波导层和上下包层一起组成，虚线框内的区域是制备工艺过程 中用来刻蚀牺牲层材料的窗口，刻蚀剂通过反射镜两侧的窗口，分别刻蚀反射镜下方的牺牲层材料，一直到达中空结构区域。中空结构上方、光波导两侧窗口之间的区域形成如图12和图13所示的悬空结构，图12中牺牲层中左右两个保护结构之间的区域为中空结构，空隙从介质层一直向下贯穿上包层、波导层、下包层和上阻挡层之后到达中空结构所在区域。同时为了在热调谐时不牺牲光栅反射谱的性能，腐蚀窗口之间的区域是悬空结构的支撑区域。提供侧向机械支撑的支撑结构沿波导方向的长度周期不等于超结构光栅的调制函数的周期，从而在热调谐时有利于避免超结构光栅的反射谱的平坦性恶化，从而有利于避免可调激光器性能的恶化。
支撑结构沿波导方向的长度周期不等于超结构光栅的调制函数的周期，可以包括如下情形：侧向支撑结构与超结构光栅的调制函数空间周期内的任意一个特定的波峰或波谷相错位，可以提高超结构光栅的反射平坦性。调制函数空间周期内的波峰是指调制函数空间周期内的极大值，调制函数空间周期内的波谷是指调制函数空间周期内的极小值。
需要说明的是，图11中1号窗口左侧和6号窗口右侧分别有一个辅助窗口，用来避免反射区在P1的最左端或者P7的最右端温度过于小。
需要说明的是，本申请的实施例中反射区也可以不设置InP缓冲层，此时下阻挡层直接位于衬底层上。
需要说明的是，图11所示的开口是为了帮助本领域技术人员更好地理解本发明实施例，而非要限制本发明实施例的范围。本领域技术人员根据所给出的图11的例子，显然可以对开口的形状进行各种等价的修改或变化，这样的修改或变化也落入本发明实施例的范围内。
在本申请的另一个实施例中，如图14所示，为本申请的一个实施例提供的可调谐激光器包括的底部支撑结构俯视图。刻蚀剂由空隙进入对牺牲层进行腐蚀，形成中空结构。反射镜所在区域的传输层与两侧传输层材料之间完全隔离开形成空隙，空隙贯穿上包层、波导层、下包层和上阻挡层之后到达中空结构所在区域，在中空结构上方、空隙之间形成悬空结构。悬空结构下方的牺牲层没有被完全腐蚀，牺牲层保留有底部支撑结构，底部支撑结构用于对悬空结构形成支撑。可调谐激光器中的反射区可以采用悬空结构进行热调谐，提高超结构光栅的热调谐效率。图14所示为具有悬空结构的反射区域原理图，图15为本申请的一个实施例提供的沿图14中3-3位置的可调谐激光器的截面图，从图14中3-3位置做截面可以看出，未被腐蚀的区域提供底部支撑结构，图16为本申请的一个实施例提供的沿图14中1-1位置的可调谐激光器的截面图，该图16类似于图13，图17为本申请的一个实施例提供的沿图14中2-2位置的可调谐激光器的截面图，该可调谐激光器的牺牲层未被完全蚀刻，保留有底部支撑结构，从而对中空结构提供底部支撑。
如图14所示光波导两侧有一些周期性虚线框，虚线框内的区域，是制备工艺过程中用来刻蚀牺牲层材料的窗口，刻蚀剂通过反射镜两侧的窗口，分别刻蚀反射镜下方的牺牲层材料，以形成悬空结构。与前述图11实施例的不同在于，图11利用侧向支撑结构对悬空结构进行侧向机械支撑。如图17所示，本实施例中悬空结构下方的牺牲层没有完全腐蚀完，形成一些柱子，本实施例正是利用悬空结构底部的柱子对悬空结构进行底部支撑。
底部支撑结构沿波导方向的长度周期不等于超结构光栅的调制函数的周期，从而在热调谐 时有利于避免超结构光栅的反射谱的平坦性恶化，从而有利于避免可调激光器性能的恶化。
底部支撑结构沿波导方向的长度周期不等于超结构光栅的调制函数的周期，具体可以包括如下情形：底部支撑结构与超结构光栅的调制函数空间周期内的任意一个特定的波峰或波谷相错位，可以提高超结构光栅的反射平坦性。调制函数空间周期内的波峰是指调制函数空间周期内的极大值，调制函数空间周期内的波谷是指调制函数空间周期内的极小值。
在本申请的一个实施例中，超结构光栅位于反射镜所在区域的传输层中的上包层的下半部分；或，
超结构光栅位于反射镜所在区域的传输层中的下包层的上半部分；或，
超结构光栅位于反射镜所在区域的传输层中的波导层；或，
超结构光栅位于反射镜所在区域的传输层中的上包层和波导层中各存在一部分；或，
超结构光栅位于反射镜所在区域的传输层中的下包层和波导层中各存在一部分。
其中，在图12和图13中，反射镜位于上包层中，用于调谐光信号的波长，不限的是，反射镜还可以位于下包层中，或者位于波导层中，或者位于上包层和波导层两个层中，或者位于下包层和波导层两个层中，具体实现方式有多种，此处仅作说明。光信号在上包层、下包层、波导层中传播，超结构光栅放在这些位置才能对光信号进行反射。
在本申请的一个实施例中，波导层的折射率高于上包层的折射率和下包层的折射率。因此光信号在波导层中传播时会形成全反射，这样可以将光能量尽可能限制在波导层中，从而波导层可以提供光信号的低损耗传播通道，减少光信号传播的损耗。
对于本申请实施例提供的可调谐激光器而言，光栅反射峰的反射率决定了可调谐激光器的阈值，输出功率等特性，光栅反射峰的FWHM决定了激光器的选模特性(FWHM定义反射峰的锐度)，理论上FWHM越小，边模抑制比越大，较为理想的方式是对两者分别进行优化。本申请实施例提出了3级离散甚至更高级别离散的超结构光栅，通过调节光栅的长度以及调制函数离散值对应的光波导占超结构光栅的光栅总长度的比例来分别优化反射峰的反射率以及FWHM。这样可以同时让激光器的阈值、输出功率与激光器的边模抑制比达到最优。本申请的实施例同时提出了基于高级离散光栅的多种可调谐激光器，以及提高高级离散光栅热调谐效率的反射镜结构，通过刻蚀牺牲层形成悬空结构来提高调谐效率，底部支撑结构用来对悬空结构提供机械支撑，从而保证悬空结构在可调谐激光器中的位置固定。

Claims (18)

  1. 一种超结构光栅，其特征在于，所述超结构光栅通过调制函数对均匀光栅在空间上进行幅度和相位调制从而形成梳妆反射谱，所述调制函数通过N个阈值进行离散化处理后得到(N+1)个调制函数离散值，所述N为大于或等于2的正整数；
    所述(N+1)个调制函数离散值中每个调制函数离散值对应于一段折射率均匀不变的光波导或对应于一段均匀光栅，所述均匀光栅为高折射率和低折射率交替变化的光波导；
    所述超结构光栅的反射峰的反射率通过所述(N+1)个调制函数离散值中的至少一个调制函数离散值所对应的光波导长度占所述超结构光栅的光栅总长度的比例关系、所述超结构光栅的光栅总长度进行调节；
    所述超结构光栅的反射峰的半高全宽FWHM通过所述比例关系、所述超结构光栅的光栅总长度进行调节。
  2. 根据权利要求1所述的超结构光栅，其特征在于，当所述N的取值为2时，所述调制函数进行离散化处理后得到3个调制函数离散值，所述3个调制函数离散值有一个调制函数离散值对应一段折射率均匀不变的光波导，所述3个调制函数离散值中其余两个调制函数离散值分别对应于一段均匀光栅。
  3. 根据权利要求1或2所述的超结构光栅，其特征在于，所述(N+1)个调制函数离散值中存在两个调制函数离散值对应于同一种的均匀光栅。
  4. 根据权利要求1或2所述的超结构光栅，其特征在于，当相邻的调制函数离散值的正负号不同或者所述相邻的调制函数离散值中有一个离散值为零时，所述相邻的调制函数离散值分别对应的光波导之间加入有相移。
  5. 一种可调谐激光器，其特征在于，所述可调谐激光器包括：反射区，其中，
    所述反射区，用于通过如权利要求1至4中任一项所述的超结构光栅对光信号进行调谐。
  6. 根据权利要求5所述的可调谐激光器，其特征在于，所述可调谐激光器，还包括：增益区和相位区，其中；
    所述反射区包括：第一反射镜和第二反射镜；
    所述增益区通过光波导分别和所述第一反射镜、所述相位区进行级联；
    所述相位区与所述增益区、所述第二反射镜相级联；
    所述增益区，用于产生光信号；
    所述相位区，用于对所述光信号进行相位调节，使所述可调谐激光器能够微调所述光信号的激射波长。
  7. 根据权利要求6的可调谐激光器，其特征在于，所述可调谐激光器，还包括：半导体光放大器SOA和光探测器PD；
    所述第一反射镜通过光波导和所述SOA进行级联，所述第二反射镜通过光波导和所述PD进行级联；
    所述SOA，用于对所述光信号进行功率放大；
    所述PD，用于对所述光信号进行功率监测或功率衰减。
  8. 根据权利要求6所述的可调谐激光器，其特征在于，所述可调谐激光器，还包括： 第一SOA和第二SOA；
    所述第一反射镜通过光波导和所述第一SOA进行级联，所述第二反射镜通过光波导和所述第二SOA进行级联；
    所述第一SOA，用于对所述第一反射镜射出的光信号进行功率放大；
    所述第二SOA，用于对所述第二反射镜射出的光信号进行功率放大。
  9. 根据权利要求5所述的可调谐激光器，其特征在于，所述可调谐激光器，还包括：多模干涉MMI耦合器、增益区和相位区；
    所述反射区包括：第一反射镜和第二反射镜；
    所述MMI耦合器的一侧有一个端口，与所述相位区相连接，所述MMI耦合器的另一侧有两个端口，分别与所述第一反射镜和所述第二反射镜相连接；
    所述相位区两侧分别与增益区和MMI的一个端口相级联；
    所述增益区，用于产生光信号；
    所述相位区，用于对所述光信号进行相位调节，使所述可调谐激光器能够微调所述光信号的激射波长。
  10. 根据权利要求9的可调谐激光器，其特征在于，所述可调谐激光器，还包括：相位调整模块，其中，
    所述相位调整模块分别和所述MMI耦合器、所述第一反射镜连接，或所述相位调整模块分别和所述MMI耦合器、所述第二反射镜连接；
    所述相位调整模块，用于匹配所述第一反射镜的反射谱和所述第二反射镜的反射谱之间的相位。
  11. 根据权利要求9的可调谐激光器，其特征在于，所述可调谐激光器，还包括：SOA和PD；
    所述第一反射镜具有第一端口，所述第二反射镜具有第二端口，所述增益区具有第三端口；
    所述第一端口连接有所述SOA或所述PD，和/或所述第二端口连接有所述SOA或所述PD，和/或所述第三端口连接有所述SOA或所述PD；
    所述SOA，用于对所述光信号进行功率放大；
    所述PD，用于对所述光信号进行功率监测或功率衰减。
  12. 根据权利要求5至11的可调谐激光器，其特征在于，所述反射区，包括：加热单元、传输层、反射镜、上阻挡层、牺牲层、下阻挡层和衬底层，其中，
    所述加热单元，位于所述传输层的上方；
    所述传输层，位于所述牺牲层上方，从上到下依次包括：上包层、波导层和下包层；
    所述反射镜，位于所述传输层中，所述反射镜用于通过前述权利要求1至4中任一项所述的超结构光栅对光信号进行调谐；
    所述上阻挡层，位于所述传输层和所述牺牲层之间；
    所述牺牲层，位于所述上阻挡层和下阻挡层之间，所述牺牲层内形成有保护结构，所述保护结构与层间区域形成中空结构，所述层间区域包括：所述传输层与所述下阻挡层之间的区域；
    所述下阻挡层，位于所述牺牲层和所述衬底层之间；
    所述衬底层，位于所述牺牲层的下方。
  13. 根据权利要求12所述的可调谐激光器，其特征在于，所述中空结构为完全空心；所述反射镜所在区域的传输层与两侧传输层材料之间具有空隙，在所述空隙之间、所述中空结构之上形成悬空结构；
    所述空隙沿着波导方向周期性排布，所述空隙贯穿所述上包层、所述波导层、所述下包层和所述上阻挡层之后到达所述中空结构所在区域，相邻的所述空隙之间有支撑结构，用于对所述悬空结构提供侧向机械支撑，所述支撑结构沿波导方向的长度周期不等于所述超结构光栅的调制函数的周期。
  14. 根据权利要求12所述的可调谐激光器，其特征在于，所述反射镜所在区域的传输层与两侧传输层材料之间完全隔离开形成空隙，所述空隙贯穿所述上包层、所述波导层、所述下包层和所述上阻挡层之后到达所述中空结构所在区域，
    在所述中空结构上方、所述空隙之间形成悬空结构；
    所述牺牲层中底部没有被完全腐蚀，所述牺牲层保留有底部支撑结构，所述底部支撑结构用于对所述悬空结构形成支撑。
  15. 根据权利要求14所述的可调谐激光器，其特征在于，所述底部支撑结构沿波导方向的长度周期不等于所述超结构光栅的调制函数的周期。
  16. 根据权利要求12所述的可调谐激光器，其特征在于，所述超结构光栅位于所述反射镜所在区域的传输层中的上包层的下半部分；或，
    所述超结构光栅位于所述反射镜所在区域的传输层中的下包层的上半部分；或，
    所述超结构光栅位于所述反射镜所在区域的波导层；或，
    所述超结构光栅位于所述反射镜所在区域的传输层中的上包层和波导层中各存在一部分；或，
    所述超结构光栅位于所述反射镜所在区域的传输层中的下包层和波导层中各存在一部分。
  17. 根据权利要求12所述的可调谐激光器，其特征在于，所述波导层的折射率高于上包层的折射率和下包层的折射率。
  18. 根据权利要求12至17中任一项所述的可调谐激光器，其特征在于，所述反射区，还包括：磷化铟InP缓冲层，其中，
    所述下阻挡层，位于所述牺牲层和所述InP缓冲层之间；
    所述InP缓冲层，位于所述下阻挡层和所述衬底层之间。
PCT/CN2017/112142 2017-04-17 2017-11-21 一种超结构光栅和可调谐激光器 Ceased WO2018192220A1 (zh)

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