JPH0451026A - wavelength conversion element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a wavelength conversion element that converts signal light of a certain wavelength into signal light of a specific wavelength.

[Prior art] Regarding the virtual charge polarization of quantum well structures and the optical Stark effect, see Applied Physics, Vol. 58, No. 12, pp. 1696-1.
On page 707 (1989), what has been discovered theoretically or experimentally so far is summarized and described in detail, and in the above description, from the perspective of utilizing the above new physical phenomenon.

It is argued that ultrafast optical modulation on the order of 100 femtoseconds is possible. In addition, since conventional elements are electrically driven and are subject to limitations on the CR time constant, in order to avoid this, Japanese Patent Application Laid-Open No. 177109/1986 uses optical rectification effect that causes direct current polarization inside the crystal due to light. We have obtained an optical device that modulates and switches light waves at high speed by causing a rate change.

[Problem to be solved by the invention]

However, although the above-mentioned prior art discusses the possibility of ultra-high-speed optical modulation, the above-mentioned literature does not mention the wavelength conversion element itself using a new physical phenomenon. In this method, a control light that blinks at a repetition frequency is made to enter the element surface from the outside of the element, and the incident light modulated by the control light is emitted from the opposite surface as output light, and the light intensity of the control light is is not directly modulated.

An object of the present invention is to obtain a wavelength conversion element using virtual charge polarization and the optical Stark effect.

[Means to solve the problem]

The above object is achieved by having a quantum well structure, and comprising means for inputting intensity-modulated laser light into the quantum well structure, and means for allowing a predetermined input signal light to pass through the quantum well structure. Ru.

That is, while the second conventional example is based on a change in refractive index due to the electro-optic effect, the present invention uses a quantum well structure that can realize virtual charge polarization and the optical Stark effect.
The configuration is such that light whose light intensity is directly modulated is input as control light to change the wavelength of the input signal light. The above-described typical configuration is shown in FIG. 1. Input signal light 4 is incident on a quantum well structure 2, and control light 5 is incident on the quantum well structure 2. FIGS. 4 and 5 show the relationship between the wavelength, that is, the photon energy.

Here, FIG. 4 shows a case of so-called virtual charge polarization in which an electric field is applied to a quantum well. The optical Stark effect occurs when the above electric field becomes O.

The most important point in the present invention is that the control light 5 is directly intensity modulated, that is, the electric field Ec of the control light 5 is
is expressed as shown in the following equation.

Yes, that is, the electric field amplitude is directly modulated at the frequency Δω. Moreover, the above ωC is an optical frequency.

[Effect]

With the above configuration, the wavelength of input signal light can be converted as shown below. Now, the photon energy of the control light is hωC, and the transition energy between the lowest quantum levels of the quantum well structure is.

Consider the case where Eg. hωC and Eg at this time
Let ΔC be the energy difference between the two. Here, when light with photon energy smaller than Ex enters the quantum well structure,
As described in the prior art described above, virtual charges as shown in FIG. 4 (indicated by - and + in the figure) are generated. The generation of the virtual charge causes a blue shift in the absorption spectrum to the higher energy side (transition from the solid line to the broken line in FIG. 5). It is proportional to the blue shift intensity at this time.

At this time, in the present invention, since the light intensity of the control light is modulated at the frequency Δω, the blue shift amount Δ is also modulated at the frequency Δω. When input signal light with an optical frequency of ω1° enters the quantum well structure as described above, it is affected by the frequency of Δω in the well structure, and
The optical frequency of the output light is ωln±Δω. therefore,
The optical frequency, or wavelength, can be converted by Δω.

The above phenomenon occurs particularly when hωc < Ex, that is, in the virtual charge polarization state and the optical Stark state. Further, when the quantum well structure is a quantum wire or a quantum box, the effect becomes even greater because the nonlinearity thereof is large.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing a first embodiment of a wavelength conversion element according to the invention, FIG. 2 is an explanatory diagram showing a second embodiment of the invention, and FIG. 3 is an explanatory diagram showing a third embodiment of the invention. 6 are explanatory diagrams showing a fourth embodiment of the present invention, and FIG. 7 is an explanatory diagram showing a fifth embodiment of the present invention.

In FIG. 1 showing a first embodiment of the present invention, an InP substrate 1 is provided with a multiple quantum well structure 2 consisting of an InGaAs quantum well layer with a film thickness of about 6n-, an InGaAsP barrier layer with a film thickness of about long, and an InP substrate 1. The optical confinement layer 3 is formed by MOCVD.
They were formed sequentially by the method. At this time, the transition wavelength between the lowest quantum levels of the multi-quantum well structure was set to 1.54μ theory. For the above semiconductor wavelength conversion element, the wavelength is 1.56
A control light beam 5 whose light intensity was modulated with a micrometer was inputted, and an input signal light 4 whose wavelength was changed to 650μ and was FSX modulated (frequency modulated) was input into the element. At this time, when the direct modulation frequency of the control light 5 is set to 40 GHz, the wavelength of the input signal light 4 is converted to a wavelength of 1.551.
An output signal 6 of a μm FSX signal was emitted.

In the second embodiment of the present invention shown in FIG. 2, the control light 5 is incident on the element of the first embodiment shown in FIG. 1 from within the plane of the multiple quantum well structure. That is, the input signal light 4 and the control light 7 were input from within the same plane. At this time, the polarization of the input signal light 4 was set to TE mode, and the control light 7 was set to 1M mode, and the control light 7 could be removed by providing a polarization filter at the output end to avoid the mixing effect of these two.

A third embodiment of the present invention shown in FIG. 3 has a multiple quantum well structure of the first and second embodiments.

A pair of electric field applying electrodes 10 and 11 were provided so that an electric field could be applied, and a variable voltage source 12 was also provided. Here, a first control light 5 (wavelength λc) similar to the first embodiment and a second control light 7 (wavelength λc8) similar to the second embodiment are incident on the input signal light 4 as control lights. It is configured so that it can be done. In this third embodiment, the lowest quantum level energy of the multiple quantum well structure 2 can be controlled by adjusting the electric field applied to the multiple quantum well structure. Therefore, it is possible to respond by adjusting the electric field according to the wavelength of the input signal light 4, so that the wavelength range of the input signal light that can be wavelength converted can be widened. A fourth embodiment of the present invention, shown in FIG. 6, replaces the multiple quantum well structure shown in the third embodiment with a quantum wire 13 or a quantum box structure. Here, the quantum wire or quantum box has a film thickness of about 1O in the quantization direction.
It is made of n@-bound InGaAs.

In this example, the nonlinear effect of the quantum wire or the quantum box is large, and the conversion efficiency of the wavelength of the input signal light 4, that is, the magnitude of the wavelength change and the conversion intensity can be increased.

A fifth embodiment of the present invention shown in FIG. 7 is an example in which a semiconductor laser that generates control light and a wavelength conversion element are integrated on the same substrate. First, after providing the diffraction grating 14 in the semiconductor laser section on the n-InP substrate 8,
The optical guide layer 15 and the InGaAsP active layer 16 were grown in sequence, and then a multiple quantum well structure was grown in the wavelength conversion element section. Then, a p-InP layer 9 was grown to form an n-side electrode 19, and a laser injection electrode 17 and an electric field application electrode 11 were formed.

The laser element in the prototype device oscillated by the current injected from the current source 20. At this time, the diffraction grating 1
A single longitudinal mode oscillation was caused by the Bragg reflection of 4. In the semiconductor laser section, the intensity of the laser light generated from the active layer 16 is directly modulated by the signal source 18, and the light is transmitted into the multi-quantum well structure 2. Further, the input signal light 4 passes through the laser section and is transmitted into the multiple quantum well structure 2. therefore,
Wavelength conversion occurs in the wavelength conversion element section having a multi-quantum well structure, and output signal light 6 is emitted. At this time, by adjusting the voltage of the variable voltage source 12, it was possible to effectively convert the wavelength according to the wavelength of the input signal light.

In the above embodiment, the case of InGaAsP system was shown, but other material systems such as GaARAs system and InG
Needless to say, it is applicable to aAQP system and InGaAQP system. In addition, in the above embodiment, if a structure adopted in a semiconductor laser such as a ridge type or a buried hetero type is used as the stripe structure, , the present invention is even more effective.

[Effects of the Invention] As described above, the wavelength conversion element according to the present invention has a quantum well structure, and includes means for inputting a laser beam whose intensity is modulated into the quantum well structure, and a means for inputting a predetermined input signal light into the quantum well structure. By providing a means for passing through the well structure, a wavelength conversion element can be realized with a simple configuration basically using a quantum well structure and directly modulated laser light.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a first embodiment of a wavelength conversion element according to the invention, FIG. 2 is an explanatory diagram showing a second embodiment of the invention, and FIG. 3 is an explanatory diagram showing a third embodiment of the invention. 4 is a diagram showing virtual charge polarization when an electric field is applied to a quantum well, FIG. 5 is a diagram showing a blue shift of the absorption spectrum, and FIG. 6 is an explanatory diagram showing a fourth embodiment of the present invention. FIG. 7 shows the fifth embodiment of the present invention.
It is an explanatory view showing an example. 2...Multi-quantum well structure 4...Input signal light 5.7
...Modulated laser light (control light)

Claims (1)

[Claims] 1. A configuration comprising a quantum well structure and means for inputting a laser beam whose intensity is modulated into the quantum well structure, and a predetermined input signal light passes through the quantum well structure. A wavelength conversion element equipped with. 2. The wavelength conversion according to claim 1, wherein the intensity-modulated laser beam has a photon energy smaller than the transition energy between the lowest quantum levels of the quantum well structure. element. 3. The intensity-modulated laser beam is characterized in that the intensity of the excitation laser beam that realizes the optical Stark effect and the virtual charge polarization state is modulated at a certain frequency. The wavelength conversion element described in item 1 or 2. 4. The wavelength conversion element according to claim 1 or 2, wherein the quantum well structure has an electric field applying means for applying an electric field. 5. The input signal light is incident from a direction parallel to the stacked surface of the quantum well structure, and the intensity-modulated laser light is incident from a direction not parallel to the stacked surface of the quantum well structure. A wavelength conversion element according to any one of claims 1 to 4. 6. Any one of claims 1 to 4, wherein the input signal light is incident along with the intensity-modulated laser light from a direction parallel to the laminated surface of the quantum well structure. The wavelength conversion element described in . 7. The wavelength conversion element according to item 6, wherein the input signal light has an irradiation direction perpendicular to a polarization direction of the intensity-modulated laser light. 8. The wavelength conversion element according to any one of claims 1 to 6, wherein the quantum well structure is a quantum wire or a quantum box. 9. The input signal light has a photon energy of ±10 near the transition energy between the lowest quantum levels of the quantum well structure.
The wavelength conversion element according to any one of claims 1 or 3 to 8, characterized in that the voltage is 0 meV. 10. Any one of claims 1 to 9, wherein the intensity-modulated laser light is emitted from a semiconductor laser integrated on the same substrate as the quantum well structure. The wavelength conversion element described in . 11. The above element is composed of InGaAsP,
Claims 1 to 10, characterized in that they are InGaAlAs, GaAlAs, and InGaAlP.
The wavelength conversion element described in any of the above.