JPH02226233A - Semiconductor optical amplifier - Google Patents

Abstract

PURPOSE:To improve the S/N and to increase the output level by removing unnecessary naturally emitted light which is generated by an optical amplification part and selecting and amplifying only input signal light with a desired wavelength. CONSTITUTION:External input light 8 is inputted to an amplification channel waveguide 4 and amplified optically, and only the light signal component with the desired wavelength is diffracted selectively by the slanting grating coupler 5a of the amplification channel waveguide 4 and guided out as slab waveguide light 9 to the slab waveguide between the amplification channel waveguide 4 and an output channel waveguide 6. Further, a slanting grating coupler 5b which is constituted on an opposite output channel waveguide 6 couples the light with the output channel waveguide 6 and the light is guided as output signal light out of the output end which is processed into a nonreflective end. Consequently, the naturally emitted light other than signal wavelength light which is generated in the semiconductor amplifier can be removed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a laser optical amplifier.

[Prior Art] In addition to the signal light component, a spontaneous emission light component is present in a laser amplifier, which causes an increase in noise.

Therefore, when using a conventional semiconductor laser amplifier, an optical frequency filter 101 for removing spontaneous emission light is placed at the rear of the semiconductor laser amplifier 100, as shown in FIG. In this case, the center wavelength λ is used as the input optical signal as shown in FIG. 17(a). Even if an optical signal 102 having a sharp spectrum centered around is input, the output light 103 of the semiconductor laser amplifier 100 will be as shown in FIG. 17(b).
Center wavelength λ. In addition to the signal amplification light component that exists in the signal amplification light component, a spontaneous emission light component over a wide wavelength range is superimposed.

Since the presence of such spontaneous emission light leads to the deterioration of the signal-to-noise ratio of the signal light as well as the multistage laser amplifier, it is removed as much as possible by passing it through the filter 101. the result,
The center wavelength λ from which spontaneous emission light is removed, as shown in FIG. 17(c). Output light 104 containing only nearby signal light components can be obtained.

Additionally, as shown in Figure 18, several proposals have been made to couple the laser amplification channel waveguide and the input/output channel waveguide with a directional coupler (
For example, USP 4,680,769 (S, E, Mil
ler: 1987), USP 4,747,65
0 (K, 5akuda: 1988)). In this case, the laser amplifier is composed of input/output waveguides 110 and 111 and a laser amplification waveguide 112 having an amplification section, as shown in FIG. Only a selection is made. Input signal light 1
13 is efficiently coupled to the laser amplification waveguide, and after amplification,
It is extracted as output signal light 116. The spontaneously emitted light (broken line in FIG. 18) generated at this time is scattered at the end of the waveguide and absorbed by the substrate.

[Problems to be Solved by the Invention] In the conventional technology described above, when an optical frequency filter is used, adjustment is complicated because the optical frequency filter is attached to the outside of the laser amplifier. Furthermore, a typical interference filter used as an optical frequency filter has a wavelength selection width of around 100 A, which makes it difficult to narrow the band, and even when the band is narrowed, the insertion loss increases. Furthermore, when using a traveling wave laser amplifier with anti-reflection treatment (AR) applied to both end faces as a semiconductor laser amplifier, performance degradation due to reflection is significant, and an optical frequency filter must be used to prevent reflection from the inserted optical device. It was necessary to devise measures such as arranging 101 diagonally.

In addition, when using a directional coupler, there is an essential problem that the desired wavelength selection and coupling efficiency cannot be obtained unless the spacing between the two waveguides is set accurately and the coupling length is set accurately. However, production was extremely difficult.

The present invention has been made in view of the drawbacks of the above-mentioned conventional techniques, and it is an object of the present invention to provide a semiconductor optical amplifier having a good S/N ratio and an amplification function compatible with wavelength multiplexing.

[Means for Solving the Problems] A semiconductor optical amplifier of the present invention includes a first channel waveguide provided with a grating coupler, a grating coupler optically coupled to the grating coupler of the first channel waveguide, and a second channel waveguide provided with an optical amplifier, and the optical coupling between the grating couplers is provided with the first channel waveguide. The light wave input/output end of each channel waveguide is provided with an antireflection coating, and the second channel waveguide is provided with an anti-reflection coating. The terminal end of the grating coupler provided in the channel waveguide is tapered, and the grating coupler is formed by a plurality of gratings with different periods.

[Effect]

The present invention has a channel waveguide equipped with an optical amplifier and a channel waveguide optically coupled to the channel waveguide,
By arranging both waveguides spatially separated and coupling them using a grating coupler, only the optical component of the signal wavelength is introduced into the output waveguide.
This removes unnecessary spontaneous emission light components and reduces noise.

Further, when the grating coupler is configured with a plurality of gratings having different periods, it is possible to simultaneously select and amplify optical signal components having a plurality of desired wavelengths from a wavelength-multiplexed optical signal.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a first embodiment of the present invention.

As shown in FIG. 1, the semiconductor optical amplifier of this embodiment has an amplification section partially provided with electrodes 7 for current injection, and a second amplifier section equipped with a tilted grating coupler 5a at one end.
It has an amplification channel waveguide 4, which is a channel waveguide, and an output channel waveguide 6, which is a passive waveguide and is a first channel waveguide for outputting light waves, which is equipped with a tilted grating coupler 5b. A slab-shaped waveguide is formed between both waveguides 4.6. In FIG. 1, 1 is an n-type GaAs substrate, 2 is a GaAs substrate including an active layer.
As/AlGaAs shrimp films 3a and 3b are dielectric films SiOx for antireflection.

In this case, external input light 8 is input to the amplification channel waveguide 4 and undergoes optical amplification, and the amplification channel waveguide 4
By the inclined grating coupler 5a, only the optical signal component of the desired wavelength is selectively diffracted and taken out as slab waveguide light 9 to the slab waveguide between the amplification channel waveguide 4 and the output channel waveguide 6, Furthermore, the output signal light 1 is coupled to the output channel waveguide 6 by the inclined grating coupler 5b configured in the facing output channel waveguide 6 from the output end which is subjected to anti-reflection treatment.
Extracted as 0.

In this way, the facing inclined grating couplers 5a,
By providing 5b, it becomes possible to remove spontaneously emitted light other than signal wavelengths generated inside the semiconductor optical amplifier. The end face of the amplification channel waveguide 4 on the side of the inclined grating coupler 5a is tapered so that the performance of the optical amplifier is not deteriorated by unnecessary reflection, and the unnecessary spontaneous emission light 11 is absorbed by the substrate 1. is necessary. Other methods for processing the non-reflective end of the channel waveguide include providing an oblique reflective surface to eliminate reflective coupling.

FIG. 2 is a cross-sectional view taken along the line AA' shown in FIG. 1, and shows the cross-sectional structure of the ridge channel waveguide section which is the amplification section of the amplification channel waveguide 4. As shown in FIG. 1 is an n-type GaAs substrate, 13 is a GaAs active layer, and 14 is an SC forming a waveguide.
(separate confinement) layer, 1
5.16 are n-type and p-type AlGaAs cladding layers, 17 is a GaAs cap layer, and 7.18 is an electrode.

12 is a 5iJ4 film for insulation. By current injection from the electrode 7, an optical amplification section having a gain is formed in the GaAs active layer 13 under the ridge.

FIG. 3 is a cross-sectional view taken along the line BB' shown in FIG. 1, showing the cross-sectional structure of the grating couplers 5a and 5b. A grating coupler 5 is installed in the two channel waveguides.
a, 5b are formed, and both channel waveguides 4.a and 5b are formed.
The space between 6 and 6 becomes a slab-shaped waveguide. The light wave incident on the grating coupler 5a undergoes Bragg diffraction, is emitted as slab waveguide light 9, and is coupled to the output channel waveguide 6 by the grating coupler 5b.

FIG. 4 is a plan view of the grating 5 coupling portion. In FIG. 4, the inclination angle of the grating coupler 5a is set so that the channel incident light 19 and the slab guided light 9 satisfy the Bragg condition.

FIG. 5 is a vector diagram showing the Bragg condition. In FIG. 5, βC and βS are the propagation constants of incident light and emitted light within the grating, respectively, K is the grating vector, and if the grating period is Δ, then IK
It is expressed as I=2π/Δ.

Regarding such a grating coupler that couples a channel waveguide and a slab waveguide, a proposed patent (Proposal No.
, CJYO No. 85629.85630) has a detailed description.

Next, a second embodiment of the present invention will be described.

As shown in FIG. 6, this embodiment is provided with three channel waveguides 30, 31, and 32 in order to enable bidirectional amplification as a semiconductor optical amplifier. Wavelength selection gratings 33a and 34b are formed on each of 30.32, and an optical amplification channel waveguide 31 having wavelength selection gratings 33b and 34a and an optical amplification section 35 is connected to channel waveguide 30.32.
Unnecessary spontaneous emission light is removed by separating the

In this embodiment, a light wave 36 incident from the input/output channel waveguide 30 side is wavelength-selected and optically amplified by the input/output channel waveguide 30 and the optical amplification channel waveguide 31, and the optical wave 36 is output from the input/output channel waveguide 32 side. A light wave 38 that is emitted as 37 and entered from the input/output channel waveguide 32 side is wavelength-selected and optically amplified by the input/output channel waveguide 32 and the optical amplification channel waveguide 31, and becomes a light wave 39 from the input/output channel waveguide 30 side. This enables optical amplification compatible with bidirectional optical transmission. However, in this case, the wavelengths of the light waves propagating in both directions are the same, or the wavelength selection gratings 33a and 33b
, 34a.

It is necessary to fall within the wavelength selection width of 34b.

In this way, by performing wavelength selection at both the input and output sections, wavelength selection becomes sharper, and since the optical amplification channel waveguide is completely separated from the input and output channel waveguides, spontaneous emission can be removed. This makes it more reliable. In addition, by separating the input/output channel waveguide and the optical amplification channel waveguide, it becomes possible to optimize the optical distribution at the input/output end and the waveguide structure of the optical amplification section independently. High efficiency can be achieved in connection etc.

Next, a third embodiment of the present invention will be described.

In this embodiment, as shown in FIG. 7, the optical coupling at the grating coupling portion is coupled in the opposite direction. That is, the light wave 36 propagates in the right direction through the input channel waveguide 70;
After being diffracted by the grating coupler 40a, it is converted into a light wave propagating leftward in the optical amplification channel waveguide 31. Furthermore, an optical amplification channel waveguide 31
Similarly, the coupling from the output channel waveguide 71 to the output channel waveguide 71 is reversely coupled.

As shown in FIG. 8, in the grating coupling portion of this embodiment, in two adjacent channel waveguides, a light wave 83 incident in the right direction from one channel waveguide 8I is directed to the left in the other channel waveguide 82. Light wave 8 emitted to
Converted to 4.

The above-mentioned 1. In the second embodiment, the direction of the grating vector was kept almost constant, but in this embodiment, a combination of gratings with different directions of the grating vector is used.

Grating couplers 40a, 40b shown in FIG.
FIG. 9 shows a vector diagram of a light wave that satisfies the Bragg condition. In FIG. 9, β1. β2 is the propagation constant of the channel waveguide 8182 shown in FIG.
βS is the propagation constant of the slab waveguide between both waveguides 81 and 82, Kl, and 2 are grating couplers 40a and 40b.
, and each grating period Δ1. If Δ2, its size is lK
+1=2π/Δ1, K, l=2π/Δ2.

As shown in FIG. 10, the intensity distribution of the light wave emitted from the above-mentioned grating coupling portion to the slab waveguide has a spatial distribution that is attenuated in the propagation direction.

First, in the reverse coupling of light waves by a grating as shown in FIG. 10(c), the intensity of the light wave 43 emitted to the slab portion by the first grating coupler 40a is as shown in FIG. 10(d). Since it is possible to bring the distribution close to the optimal intensity distribution of the light waves combined by the second grating coupler 40b (the distribution that provides the highest coupling efficiency), it is possible to increase the coupling between both channel waveguides 81 and 82. can. On the other hand, in the same direction coupling as shown in FIG. 10(a), the light intensity distribution of the output slab light 85 and the optimum light intensity distribution are antisymmetrical to each other, as shown in FIG. 10(b). Basically, it is difficult to match the intensity distribution, and there is no other way than to control the efficiency by tapering the end face of the grating, etc. to approximate a flat intensity distribution.

As described above, it is possible to increase the coupling efficiency by using reverse grating coupling.

Next, a fourth embodiment of the present invention will be described with reference to FIG. 11.

In this embodiment, an optical amplification channel waveguide 31 is connected to an input channel waveguide 70 and an output channel waveguide 71.
It is characterized by optical coupling forming a relatively large angle. In this way, by optically coupling channel waveguides at a large angle to each other, effects such as reducing crosstalk can be obtained.

Next, regarding the fifth embodiment of the present invention, FIGS.
This will be explained with reference to the figures.

This embodiment shows an example in which the present invention is applied to a wavelength multiplexing optical device.

First, explanation will be given with reference to FIG. 12. In this case, the wavelength λ
The input optical signal 46 of , and the input optical signal 47 of wavelength λ2 are wavelength-multiplexed and coupled into the input channel waveguide 70 . The input channel waveguide 70 is provided with grating couplers 42a and 43a having different periods, and the periods Δ1... Δ2 is the setting. The wavelength multiplexed optical signal is transmitted through the corresponding grating coupler 4.
After being diffracted by 2a and 43a and coupled to the slab waveguide, the light is diffracted again by grating couplers 42b and 43b provided in opposing portions of the optical amplification channel waveguide 31, and introduced into the optical amplification section where it is amplified. Ru. After amplification, only the desired optical signal wavelength is transmitted to the grating coupler 44a,
45a and introduced into the output channel waveguide 71, where it is output as an output optical signal.

Therefore, among the spontaneous emission light components generated in the optical amplification section of the optical amplification channel waveguide 31, the wavelength λ1 of the optical signal. λ
Light other than 2 is removed.

Next, referring to FIG. 13, the optical amplification channel waveguides 48 and 49 are arranged at respective wavelengths λl and λ2.
An example is shown in which each is individually configured to correspond to the following. By optically amplifying each wavelength multiplexed signal individually in this way, it becomes possible to increase the degree of freedom in design. Generally, when two or more wavelengths are incident, the gains in the optical amplification section are not equal, making it difficult to equalize the output levels.However, by providing an optical amplification channel waveguide for each wavelength, Gain equalization is facilitated by current control. Further, in the optical amplification section, as the output increases, carrier density modulation occurs and crosstalk between optical signals occurs, but by performing wavelength separation amplification, it is also possible to increase the optical output level.

In this embodiment, two-wavelength optical amplification has been described for the sake of simplicity, but it goes without saying that optical wavelength multiplexing of three or more wavelengths is also possible, and bidirectional optical amplification is also possible.

Next, a sixth embodiment of the present invention will be described with reference to FIG. 14.

In each of the embodiments described above, the input and output channel waveguides are separated from each other and coupled via the optical amplification channel waveguide, but if a "failure" occurs that prevents current injection into the optical amplification section. In such a case, the optical signal suffers a large loss, and there is an essential problem that information cannot be transmitted. In this embodiment, as a countermeasure against such a failure, the 14th
As shown in the figure, it is configured to output part of the input light as is, selectively amplify part of it, and combine it on the output side, so that transmitted light 51 and amplified light 52 are combined. is output. As a result, even if a failure occurs in which current cannot be injected into the optical amplification section and the amplified light 52 disappears, the transmitted light 51 can be output. In this embodiment, a grating coupler 53 provided in the input/output optical waveguide 50
a and 53b operate as wavelength selective branches,
During normal operation, the amplified light 52 is thick, so combining the transmitted light 51 is not a problem, but the configuration of the optical path forms an interference system,
Ripples may occur in the output light due to a change in the optical path difference between the two light waves. This ripple variation can be suppressed by adjusting the amount of current injection, and in order to ensure gain, the current injection region is divided into two parts, which correspond to the amplification section and the phase control region.

Next, a seventh embodiment of the present invention will be described with reference to FIG. 15.

In this embodiment, as shown in FIG. 15, a part of the optical signal whose wavelength has been selected in input/output channel waveguides 55 and 56 is coupled to an optical amplification channel waveguide 57, and the other part is coupled to a photodetector. Detection channel waveguide 58,59 including
to detect optical signals. The photodetector section is structurally the same as the optical amplification section, but performs photodetection by applying a reverse bias. By inserting the optical amplifier of this embodiment onto, for example, an optical path line, it becomes possible to tap an optical signal. Further, the branching loss caused by this tap can be compensated for by optical amplification.

In this embodiment, an example in which a photodetector is integrated is shown, but the present invention can also be applied to an optical device in which a light emitting element or the like as a light transmitter is integrated, or in which these are combined.

It goes without saying that it is also possible to integrate wavelength-multiplexed transmitting and receiving sections.

[Effects of the Invention] As explained above, the present invention has the following effects.

- According to the first aspect of the present invention, it is possible to remove unnecessary spontaneous emission light generated in the optical amplification section and selectively amplify only the input signal light of a desired wavelength, thereby improving the S/N ratio and increasing the output level. In addition to increasing the number of channel waveguides, it also facilitates spatial separation to suppress crosstalk between channel waveguides.
A high-performance optical amplifier can be provided.

(2) According to the second and third aspects of the present invention, it is possible to prevent performance deterioration of the optical amplifier due to reflection of unnecessary light, and also to remove spontaneously emitted light generated by the optical amplifier by absorbing it into the substrate.

(2) According to the fourth aspect, it becomes possible to perform wavelength separation amplification and secure gain for each separated optical signal, and it is possible to operate as an integrated optical node having an amplification function compatible with wavelength multiplexing. It becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the first embodiment of the present invention, FIG. 2 is a sectional view taken along line AA' in FIG. 1, FIG. 3 is a sectional view taken along line B-8' in FIG. 5 is a grating vector diagram, FIG. 6 is a perspective view showing the second embodiment of the present invention, FIG. 7 is a perspective view showing the third embodiment of the present invention, and FIG. 9 is an enlarged view of the grating coupling part, FIG. 9 is a grating vector diagram, FIG. 10 is an explanatory diagram showing the light intensity distribution of same direction coupling and opposite direction coupling, and FIG. 11 is a perspective view showing the fourth embodiment of the present invention. 12 and 13 are perspective views showing the fifth embodiment, FIG. 14 is a perspective view showing the sixth embodiment, FIG. 15 is a perspective view showing the seventh embodiment, and FIGS.
FIG. 18 is a diagram illustrating a conventional example. 1- n-type GaAs substrate, 2- GaAs/AlGaAs shrimp layer, 3a, 3b・
...Dielectric film, 2. 5a, 5b... inclined grating coupler, 6...
・Output channel waveguide, 7.18... Electrode, 8, 46.47... Input light, 9.85... Slab waveguide light, 10... Output signal light, 11... Spontaneous emission light , 12...Si3N4 insulating film, 13.GaAs active layer, 14...SC layer, 15.n-type AlGaAs cladding layer, 16.p-type AlGaAs cladding layer, 17...GaAs cap layer, 19... Channel incident light, 30, 32.55.56... Input/output channel waveguide, 31, 48.49.57... Optical amplification channel waveguide, 33a, 33b, 34a, 34b-... Wavelength selection grating, 35... Optical amplification section, 3637.38, 39, 83.84... Light wave, 40a
~45a 40b~45b 53a 53b 5
4a 54b - grating coupler, 50... input/output optical waveguide, 51... transmitted light, 52... amplified light, 58, 59... channel waveguide for detection, 70...
Input channel waveguide, 71... Output channel waveguide, 81, 82... Channel waveguide.

Claims (1)

[Claims] 1. A first channel waveguide equipped with a grating coupler, and a second channel equipped with a grating coupler and an optical amplifier optically coupled to the grating coupler of the first channel waveguide. A semiconductor optical amplifier comprising a waveguide, wherein optical coupling between the grating couplers is performed via a slab waveguide formed between the first and second channel waveguides. 2. The semiconductor optical amplifier according to claim 1, wherein each optical wave input/output end of each channel waveguide is provided with an antireflection film. 3. The semiconductor optical amplifier according to claim 1 or 2, wherein the end of the grating coupler provided in the second channel waveguide having the optical amplifier is tapered. 4. The semiconductor optical amplifier according to claim 1, 2 or 3, wherein the grating coupler is formed by a plurality of gratings with different periods.