Laser chip and method for manufacturing a laser chip

Abstract

The application relates to the technical field of optical communication, and provides a laser chip, which comprises an electro-absorption modulator and a semiconductor optical amplifier, further comprises a reflection grating for reflecting spontaneous emission light of the reflection semiconductor optical amplifier, the semiconductor optical amplifier is arranged on the light-emitting side of the electro-absorption modulator, the reflection grating is arranged in the area where the semiconductor optical amplifier is located, and the reflection grating is arranged close to the area where the electro-absorption modulator is located. A laser chip preparation method is also provided. Through the arrangement of the reflection grating, the spontaneous emission light of the semiconductor optical amplifier can be reflected, optical crosstalk is reduced, and signal quality is improved.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, specifically to a laser chip and its fabrication method. Background Technology

[0002] In recent years, with the rapid development of Internet technology, the ever-increasing bandwidth demands of users have driven the fiber optic access PON market to gradually upgrade to 50G-PON solutions. This has also placed demands on the performance of semiconductor lasers, as light source devices, requiring high power and high bandwidth. By integrating the semiconductor optical amplifier (SOA) into the electro-absorption modulated laser (EML), higher output optical power can be achieved at the same power consumption level compared to existing EMLs. It also leverages the advantages of EMLs, such as large modulation bandwidth and low chirp, and can even generate negative chirp in the input optical signal. EML-SOA integrated devices have become an ideal choice for light source chips in 50G PON high-speed optical networks. However, integrating the SOA at the back end of the EML can cause optical crosstalk between different operating zones, especially the spontaneous emission light generated by the SOA when operating under high current conditions (as shown in the figure below, taking a 1342nm EML-SOA laser as an example) which interferes with the EAM. The presence of this optical crosstalk will degrade the laser's linewidth, side-mode rejection ratio, and relative intensity noise. Especially during high-speed modulation, optical crosstalk can easily cause the laser to fall into a self-pulsing or chaotic operating state, ultimately leading to modulation signal distortion. To address this problem, researchers have attempted to reduce end-face light reflection, such as tilting the output end-face, using passive windows on the output end-face, and applying high-reflection coatings. However, these methods have failed to solve the optical crosstalk problem from SOA to EAM in practical applications. Summary of the Invention

[0003] The purpose of this invention is to provide a laser chip and its fabrication method, which can at least solve some of the defects in the prior art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a laser chip, including an electroabsorption modulator and a semiconductor optical amplifier, and further including a reflective grating for reflecting the spontaneous emission light of the reflective semiconductor optical amplifier, the semiconductor optical amplifier being disposed on the light-emitting side of the electroabsorption modulator, the reflective grating being disposed in the region where the semiconductor optical amplifier is located, and the reflective grating being disposed close to the region where the electroabsorption modulator is located.

[0005] Furthermore, the reflective grating is located on the front or back of the semiconductor optical amplifier.

[0006] Furthermore, the front side of the quantum well of the semiconductor optical amplifier is covered with a cladding, and the reflective grating is located in the cladding.

[0007] Furthermore, it also includes a laser source, with the electroabsorption modulator located on the light-emitting side of the laser source.

[0008] Furthermore, a mode selection grating is provided in the area where the laser source is located.

[0009] Furthermore, the mode selection grating is located on the front or back of the laser light source.

[0010] Furthermore, the grating periods of the mode selection grating and the reflection grating are different.

[0011] Furthermore, the grating period of the reflective grating is greater than the grating period of the mode-selective grating.

[0012] Furthermore, the quantum well of the laser light source and the quantum well of the semiconductor optical amplifier may have the same or different structures.

[0013] This invention provides another technical solution: a method for fabricating a laser chip, comprising the following steps:

[0014] S1, an electro-absorption modulator quantum well and a semiconductor optical amplifier quantum well are epitaxially grown on a substrate.

[0015] S2, a reflective grating is set in the semiconductor optical amplifier quantum well region at the junction of the electro-absorption modulator quantum well and the semiconductor optical amplifier quantum well.

[0016] S3, continue to complete the fabrication of the electroabsorption modulator and the semiconductor optical amplifier.

[0017] S4, when the electro-absorption modulator and the semiconductor optical amplifier are working, the reflective grating reflects the spontaneous emission light of the semiconductor optical amplifier, preventing the spontaneous emission light from entering the electro-absorption modulator.

[0018] Compared with the prior art, the beneficial effects of the present invention are: by setting a reflective grating, the spontaneous emission light of the semiconductor optical amplifier can be reflected, reducing optical crosstalk and improving signal quality. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the spontaneous emission optical noise of a semiconductor optical amplifier.

[0020] Figure 2 A reflection spectrum of a reflection grating for a laser chip provided in an embodiment of the present invention;

[0021] Figure 3 This is a schematic diagram of the structure of a laser chip provided in an embodiment of the present invention;

[0022] In the attached figures, the following labels are used: 1-N-side electrode; 2-substrate; 3-first quantum well; 4-second quantum well; 5-mode selection grating; 6-reflection grating; 7-cladding; 8-P-side electrode; 9-electrically isolated region; 10-high reflectivity film; 11-antireflection film. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1:

[0025] Please see Figure 3 This invention provides a laser chip including an electro-absorption modulator (EMA), a semiconductor optical amplifier (SOA), and a reflective grating 6 for reflecting the spontaneous emission light of the reflective SOA. The SOA is disposed on the light-emitting side of the EMA, and the reflective grating 6 is disposed in the region where the SOA is located, close to the region where the EMA is located. In this embodiment, by setting the reflective grating 6, the spontaneous emission light of the SOA can be reflected, reducing optical crosstalk and improving signal quality. Specifically, as... Figure 1 As shown, the electroabsorption modulated laser (EML) suffers from signal distortion caused by spontaneous emission crosstalk of the SOA after integrating a semiconductor optical amplifier (SOA). To solve this problem, the reflective grating 6 is directly fabricated within the chip, allowing it to be fabricated during the growth process without significantly altering existing chip fabrication techniques or requiring additional external structures to address crosstalk. The final structure is identical to existing laser chip structures, preserving existing applications while effectively resolving crosstalk and significantly improving performance. Figure 2 As shown.

[0026] Please see Figure 3 The reflective grating 6 is located on either the front or back of the semiconductor optical amplifier. In this embodiment, the reflective grating 6 can be positioned in the area where the semiconductor optical amplifier is located at the junction of the electroabsorption modulator and the semiconductor optical amplifier; specifically, it can be located on either the front or back of the semiconductor amplifier. Figure 3 The image shows the front, or top, of the semiconductor amplifier.

[0027] Please see Figure 3The front side of the quantum well of the semiconductor optical amplifier is covered by a cladding layer 7, and the reflective grating 6 is located within the cladding layer 7. In this embodiment, the reflective grating 6 is specifically located within the cladding layer 7, which is significantly different from the existing approach of taking measures outside the chip to solve optical crosstalk. Designing the reflective grating 6 within the cladding layer 7 does not change the overall structure of the chip, nor does it change the overall growth steps. It only requires adding a step to grow the reflective grating 6 after the quantum well is grown. It can also be performed together with the step of growing the mode selection grating 5, thus improving manufacturing efficiency.

[0028] Please see Figure 3 The chip also includes a laser light source (DFB), and the electroabsorption modulator is located on the light-emitting side of the laser light source. In this embodiment, the laser light source is to the left of the electroabsorption modulator, and the semiconductor optical amplifier is to the right of the electroabsorption modulator. Preferably, a mode selection grating 5 is provided in the area where the laser light source is located. The mode selection grating 5 is designed to be used for the working mode selection of the laser light source. The mode selection grating 5 can be located above or below the quantum well of the laser light source, such as... Figure 3 The image shows a quantum well positioned above a laser source.

[0029] Please see Figure 2 and Figure 3 The mode-selection grating 5 and the reflection grating 6 have different grating periods, with the grating period of the reflection grating 6 being greater than that of the mode-selection grating 5. Specifically, the mode-selection grating 5 and the reflection grating 6 have different grating periods, with the reflection grating 6 having a greater grating period than the mode-selection grating 5, and the reflection grating 6 has extremely low reflectivity at the laser lasing wavelength, which can be less than 0.1%. Preferably, the overall length of the reflection grating 6 region is 10–30 μm, and the reflection spectrum of the reflection grating 6 is as follows: Figure 2 As shown (using a 1342nm EML-SOA laser as an example).

[0030] Please see Figure 3 The quantum well structures of the laser light source and the quantum well structures of the semiconductor optical amplifier may be the same or different. In this embodiment, as... Figure 3 The DFB quantum well and the SOA quantum well have the same structure. For easy identification, it is defined as the first quantum well 3. The EAM quantum well can have a different structure. For easy identification, it is defined as the second quantum well 4.

[0031] Please see Figure 3The subsequent chip fabrication follows the conventional semiconductor laser manufacturing process, and can be designed as a buried heterojunction structure or a ridge waveguide structure. The laser chip is topped with a cladding layer 7. After the waveguide structure is fabricated, the following steps are performed sequentially: fabrication of the electrical isolation region 9, BCB fabrication, P-side electrode 8 fabrication (including DFB electrode, EAM electrode, and SOA electrode), thinning and polishing, and N-side electrode 1 fabrication. After stripping, a high-reflectance film 10 is deposited on the end face of the chip near the DFB region, and an anti-reflection film 11 is deposited on the end face near the SOA region.

[0032] Example 2:

[0033] Please see Figure 3 This invention provides a method for fabricating a laser chip, comprising the following steps: S1, epitaxially growing an electro-absorption modulator quantum well and a semiconductor optical amplifier quantum well on a substrate 2; S2, setting a reflective grating 6 in the semiconductor optical amplifier quantum well region at the junction of the electro-absorption modulator quantum well and the semiconductor optical amplifier quantum well; S3, continuing the fabrication of the electro-absorption modulator and the semiconductor optical amplifier; S4, when the electro-absorption modulator and the semiconductor optical amplifier are working, the reflective grating 6 reflects the spontaneous emission light of the semiconductor optical amplifier, preventing the spontaneous emission light from entering the electro-absorption modulator. In this embodiment, by setting the reflective grating 6, the spontaneous emission light of the semiconductor optical amplifier can be reflected, reducing optical crosstalk and improving signal quality. Specifically, as shown... Figure 1 As shown, the electroabsorption modulated laser (EML) suffers from signal distortion caused by spontaneous emission crosstalk of the SOA after integrating a semiconductor optical amplifier (SOA). To solve this problem, the reflective grating 6 is directly fabricated within the chip, allowing it to be fabricated during the growth process without significantly altering existing chip fabrication techniques or requiring additional external structures to address crosstalk. The final structure is identical to existing laser chip structures, preserving existing applications while effectively resolving crosstalk and significantly improving performance. Figure 2 As shown.

[0034] As an optimized solution for an embodiment of the present invention, please refer to Figure 3 The subsequent chip fabrication follows the conventional semiconductor laser manufacturing process, and can be designed as a buried heterojunction structure or a ridge waveguide structure. The laser chip is topped with a cladding layer 7. After the waveguide structure is fabricated, the following steps are performed sequentially: fabrication of the electrical isolation region 9, BCB (Benzocyclobutene is an active resin), fabrication of the P-side electrodes 8 (including DFB, EAM, and SOA electrodes), thinning and polishing, and fabrication of the N-side electrodes 1. After stripping, a high-reflectivity film 10 is deposited on the end face of the chip near the DFB region, and an anti-reflection film 11 is deposited on the end face near the SOA region.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A laser chip, comprising an electroabsorption modulator and a semiconductor optical amplifier, characterized in that: It also includes a laser source and a reflective grating for reflecting the spontaneously emitted light of the reflective semiconductor optical amplifier. The semiconductor optical amplifier is located on the light-emitting side of the electroabsorption modulator. The reflective grating is located in the region where the semiconductor optical amplifier is located. The reflective grating is located close to the region where the electroabsorption modulator is located. A mode-selective grating is located in the region where the laser source is located. The grating period of the reflective grating is greater than the grating period of the mode-selective grating. The reflectivity of the reflective grating at the laser lasing wavelength is less than 0.1%.

2. The laser chip as described in claim 1, characterized in that: The reflective grating is located on the front or back of the semiconductor optical amplifier.

3. The laser chip as described in claim 1, characterized in that: The front side of the quantum well of the semiconductor optical amplifier is covered with a cladding, and the reflective grating is located in the cladding.

4. The laser chip as described in claim 1, characterized in that: The electroabsorption modulator is located on the light-emitting side of the laser light source.

5. The laser chip as described in claim 1, characterized in that: The mode selection grating is located on the front or back of the laser light source.

6. The laser chip as described in claim 1, characterized in that: The quantum well of the laser light source and the quantum well of the semiconductor optical amplifier may have the same or different structures.

7. A method for fabricating a laser chip, characterized in that, The method for fabricating a laser chip as described in any one of claims 1-6 includes the following steps: S1, an electro-absorption modulator quantum well and a semiconductor optical amplifier quantum well are epitaxially grown on a substrate. S2, a reflective grating is set in the semiconductor optical amplifier quantum well region at the junction of the electro-absorption modulator quantum well and the semiconductor optical amplifier quantum well. S3, continue to complete the fabrication of the electroabsorption modulator and the semiconductor optical amplifier. S4, when the electro-absorption modulator and the semiconductor optical amplifier are working, the reflective grating reflects the spontaneous emission light of the semiconductor optical amplifier, preventing the spontaneous emission light from entering the electro-absorption modulator.

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