A method for fabricating a highly coupled modulated single mode laser

Abstract

The application relates to the technical field of lasers, in particular to a preparation method of a highly coupled modulation single-mode laser, which comprises a coupling module and two light-emitting modules, the light-emitting surfaces of the two light-emitting modules are located on the same side, the coupling module is located on the side of the light-emitting surface of the light-emitting module, two parallel light channels are arranged in the coupling module, the ends of the two light channels are respectively opposite to the light-emitting surfaces of the two light-emitting modules, a light outlet is arranged on the side of the coupling module away from the light-emitting module, the ends of the two light channels away from the light-emitting module are combined and are in communication with the light outlet, and a wave-lock ring is arranged between the two light channels. The lasers emitted by the two light-emitting modules enter the two light channels respectively, are coupled when passing through the wave-lock ring, and are finally discharged from the light outlet. The two light-emitting modules and the wave-lock ring are integrated on one chip, the design cost can be simplified and the module volume can be compressed in subsequent packaging, there is no redundant spatial light path, and the reliability and service life of the module are greatly improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lasers, in particular to a preparation method of a highly coupled modulation single-mode laser. BACKGROUND

[0002] The high-power single-mode 980 nm semiconductor laser chip and the pumping module can be widely applied to the fields of optical communication, submarine communication, satellite laser and space communication, laser radar and the like. At present, the lens coupling of the single-mode 980 module adopts a ball lens or C-lens scheme, and the advantages are low cost and coupling efficiency of 70%-85%; the wave selection usually adopts a VBG volume Bragg grating, and the coupling into the optical fiber after the wave selection is used.

[0003] The traditional scheme coupling needs multiple optical elements to collimate, couple and lock the wave; if two or more chips are coupled, the optical path design will be more complex, and the required space optical path elements are doubled. Moreover, the point fixing process of fixing the optical elements is prone to failure under high temperature and high humidity, and there are problems of poor mechanical vibration reliability and the like. SUMMARY

[0004] In order to solve the above problems, the application provides a preparation method of a highly coupled modulation single-mode laser.

[0005] One of the purposes of the application is to provide a highly coupled modulation single-mode laser, which adopts the following technical scheme:

[0006] The highly coupled modulation single-mode laser comprises a coupling module and two light-emitting modules, the two light-emitting modules are arranged side by side, the light-emitting surfaces of the two light-emitting modules are located on the same side, the coupling module is located on one side of the light-emitting surface of the light-emitting module, two parallel light paths are arranged in the coupling module, the ends of the two light paths are respectively opposite to the light-emitting surfaces of the two light-emitting modules, an optical output port is arranged on the side of the coupling module away from the light-emitting module, the ends of the two light paths away from the light-emitting module are merged and connected with the optical output port, and a wave locking ring is arranged between the two light paths.

[0007] By adopting the above technical scheme, the lasers emitted by the two light-emitting modules enter the two light paths respectively, are coupled when passing through the wave locking ring, and are finally discharged from the optical output port. The two light-emitting modules and the wave locking ring are integrated on one chip in the application, the design cost can be simplified and the module volume can be compressed in subsequent packaging, there is no redundant space optical path, and the reliability and service life of the module are greatly improved.

[0008] As a preferred, the light-emitting module comprises a light-emitting region and a buffer region, the buffer region is located between the light-emitting region and the coupling module, and the quantum wells in the buffer region are in a disordered structure.

[0009] By adopting the technical scheme, the quantum well band at the buffer region is widened, so that the laser of the light emitting region will not be absorbed when passing through the buffer region, and heat will not be accumulated at the end face, thereby improving the reliability life of the chip.

[0010] Preferably, the diameter R of the locking ring satisfies the optical path difference formula mlambda=2pirR, wherein m is a positive integer, lambda is the wavelength of light, and n is the refractive index of light in the coupling module.

[0011] Preferably, the light emitting module is provided with a high reflection film on the side away from the coupling module.

[0012] By adopting the technical scheme, the high reflection film reflects the light in the light emitting region, and ensures that the light is emitted from the buffer region.

[0013] Preferably, the coupling module comprises a substrate integrated with the light emitting module and an N-face cladding layer, the N-face cladding layer is provided with a passive waveguide layer, and the pattern of the optical path and the locking ring is formed on the passive waveguide layer.

[0014] Preferably, each of the light emitting modules is provided with a protruding ridge structure, and the two ridge structures are respectively opposite to the two optical paths.

[0015] Another object of the present application is to provide a preparation method of a highly coupled modulation single-mode laser, which adopts the following technical scheme:

[0016] A preparation method of a highly coupled modulation single-mode laser, for preparing the highly coupled modulation single-mode laser, comprises the following steps:

[0017] S1, growing an epitaxial layer on a substrate, the epitaxial layer comprising an N-face cladding layer, an N-face waveguide layer, an active region and a P-face waveguide layer arranged from bottom to top;

[0018] S2, etching one side of the epitaxial layer to the N-face cladding layer by one-side photolithography and dry etching to form a coupling groove, and the other side of the epitaxial layer being a light emitting module;

[0019] S3, growing a layer of SiN on the epitaxial layer, the SiN in the coupling groove forming a passive waveguide layer, and the height of the passive waveguide layer being not less than the height of the P-face waveguide layer in the light emitting module;

[0020] S4, etching and removing the SiN above the light emitting module, and sequentially growing a P-face cladding layer and a P-face cover layer;

[0021] S6, etching the pattern of the optical path and the locking ring on the upper surface of the passive waveguide layer by photolithography and electron beam exposure to form a coupling module.

[0022] By adopting the technical scheme, the quantum well vacancy-induced disorder, the passive waveguide selection and the coupling technology are introduced in the chip manufacturing process. The laser emitter, the coupling into the passive waveguide, the micro-ring selection and the coupling and output are integrated on the chip end, and an implementable process route is provided.

[0023] Preferably, the step of removing the SiN above the light-emitting module in S4 comprises,

[0024] S41, removing the SiN above the buffer zone by dry etching;

[0025] S42, growing a layer of SiO2 on the epitaxial layer, and performing rapid thermal annealing treatment in N2 at 930 DEG C;

[0026] S43, removing the SiO2 on the surface by dry etching;

[0027] S44, etching to remove the SiN above the light-emitting zone.

[0028] By adopting the technical scheme, the SiO2 layer on the buffer zone enhances the ability of Ga to diffuse outward from the semiconductor surface and produce vacancies, resulting in quantum well vacancy-induced disorder in the rapid thermal annealing process, and the band gap becomes larger. The SiN on the light-emitting zone and the coupling module prevents As from desorbing from the surface, and protects the region from the influence of rapid thermal annealing. The focus is on the active zone quantum well under the light-emitting zone.

[0029] Preferably, the step of removing the SiN above the light-emitting module in S4 comprises,

[0030] S51, etching to remove the P-face cover layer and the P-face cladding layer on the surface of the light-emitting zone and the buffer zone, exposing the P-face waveguide layer, and forming a convex ridge structure, the ridge structure penetrating the light-emitting zone and the buffer zone and being opposite to the optical path,

[0031] S52, etching to form two parallel ridge structures on the epitaxial layer, the two ridge structures being opposite to the two optical paths, respectively;

[0032] S53, growing SiN on the epitaxial layer;

[0033] S54, removing the SiN above the two ridge structures by photolithography.

[0034] Preferably, the step of removing the SiN above the light-emitting module in S4 comprises,

[0035] S7, evaporating seed metal Ti / Pt / Au on the light-emitting zone and the buffer zone by a metal stripping process;

[0036] S8, electroplating to form an electroplated layer on the seed metal.

[0037] In summary, the present application has the following beneficial technical effects:

[0038] The application integrates two light emitting modules and a wave-lock ring on one chip, which can simplify the design cost and compress the module volume on subsequent packaging, has no redundant spatial light path, and greatly improves the reliability and service life of the module. The convenience and simplicity of the application are more prominent when two or more chips are coupled. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a schematic diagram of the overall structure of Example 1;

[0040] Figure 2 is a schematic diagram of the structure for showing the light emitting module and the coupling module in Example 1;

[0041] Figure 3 is a schematic diagram of the top view structure of Example 1;

[0042] Figure 4 is a schematic diagram of the epitaxial structure in steps S1-S2 in Example 2;

[0043] Figure 5 is a schematic diagram of the epitaxial structure in step S3 in Example 2;

[0044] Figure 6 is a schematic diagram of the epitaxial structure in steps S41-S42 in Example 2;

[0045] Figure 7 is a schematic diagram of the epitaxial structure in step S43 in Example 2;

[0046] Figure 8 is a schematic diagram of the epitaxial structure in step S44 in Example 2;

[0047] Figure 9 is a schematic diagram of the epitaxial structure in steps S51-S52 in Example 2;

[0048] Figure 10 is a schematic diagram of the top view of the epitaxial structure in steps S51-S52 in Example 2;

[0049] Figure 11 is a schematic diagram of the epitaxial structure in steps S53-S6 in Example 2;

[0050] Figure 12 is a schematic diagram of the top view of the epitaxial structure in steps S53-S6 in Example 2;

[0051] Figure 13 is a schematic diagram of the top view of the epitaxial structure in step S9 in Example 2.

[0052] BRIEF DESCRIPTION OF DRAWINGS

[0053] 1, substrate; 2, N-cladding layer; 3, N-waveguide layer; 4, active region; 5, P-waveguide layer; 6, P-cladding layer; 7, P-cladding layer; 8, ridge structure; 9, light emitting module; 10, coupling module; 11, light emitting region; 12, buffer region; 13, light path; 14, circular arc path; 15, wave locking ring; 16, light outlet; 17, high reflection film; 18, passive waveguide layer; 19, seed gold; 20, electroplated layer; 21, N-gold. DETAILED DESCRIPTION

[0054] The application will be further described in detail below with reference to all the drawings.

[0055] Embodiment one

[0056] The embodiment of the application discloses a highly coupled modulation single-mode laser, referring to Figures 1 to 3 , comprising a substrate 1, an epitaxial layer is grown on the substrate 1, and the epitaxial layer comprises, from bottom to top, an N-cladding layer 2, an N-waveguide layer 3, an active region 4 and a P-waveguide layer 5.

[0057] Referring to Figures 1 to 3 , the epitaxial layer is divided into two regions, one is a light emitting region, and the other is a coupling region. Two light emitting modules 9 are formed in the light emitting region by processing, and a coupling module 10 is formed in the coupling region by processing. The laser emitted by the two light emitting modules 9 is coupled through the coupling module 10, and finally forms a laser beam. Thus, the purpose of integrating two laser modules and a coupling module 10 is achieved, thereby compressing the module volume, and the scheme of the application has no redundant spatial light path, and greatly improves the reliability and service life of the module.

[0058] Referring to Figures 1 to 3 , the two light emitting modules 9 are arranged side by side, the light emitting surfaces of the two light emitting modules 9 are located on the same side, and the back surfaces of the two light emitting modules 9 are provided with high reflection films 17 to ensure that the laser is emitted from the light emitting surfaces. The coupling module 10 is located on the side of the light emitting surface of the light emitting module 9.

[0059] Referring to Figures 1 to 3 , the light emitting module 9 comprises a light emitting region 11 and a buffer region 12, the buffer region 12 is located between the light emitting region 11 and the coupling module 10, and the quantum wells in the buffer region 12 are in a disordered structure. The energy band of the quantum well at the buffer region 12 is widened, so that the laser of the light emitting region 11 is not absorbed when passing through the buffer region 12, and heat is not accumulated at the end surface, which can improve the reliability and service life of the chip. A protruding ridge structure 8 is arranged on each light emitting module 9, and the ridge structure 8 penetrates the light emitting region 11 and the buffer region 12.

[0060] Referring to Figures 1 to 3The substrate 1 and the N-cladding layer 2 in the coupling module 10 are integrally arranged with the substrate 1 and the N-cladding layer 2 in the light-emitting module 9. The N-cladding layer 2 of the coupling module 10 is provided with a passive waveguide layer 18, and the material of the passive waveguide layer 18 is SiN. The passive waveguide layer 18 is provided with a pattern of the light channel 13 and the waveguide ring 15 through etching.

[0061] Referring to Figures 1 to 3 The light channel 13 is provided with two parallel light channels 13, and the ends of the two light channels 13 are opposite to the two ridge structures 8, respectively. The side of the coupling module 10 away from the light-emitting module 9 is provided with a circular arc channel 14 communicating the two light channels 13. The two laser beams emitted by the two light-emitting modules 9 enter the two light channels 13 and converge through the circular arc channel 14.

[0062] Referring to Figures 1 to 3 The side of the coupling module 10 away from the light-emitting module 9 is provided with a light outlet 16, and the light outlet 16 is located at the middle position of the circular arc channel 14 and communicates with the circular arc channel 14. The converged laser beams are finally emitted from the light outlet 16.

[0063] Referring to Figures 1 to 3 The waveguide ring 15 is in the form of a circular ring between the two light channels 13, and the diameter R of the waveguide ring 15 satisfies the formula mλ=2πnR, wherein m is a positive integer, λ is the wavelength of light, and n is the refractive index of the passive waveguide layer 18 in the coupling module 10. For example, to output a single-mode laser beam with a wavelength of 974 nm, n is 2, and m is 20, so that the radius R of the waveguide ring 15 is 3.1 um.

[0064] Embodiment two

[0065] The embodiment discloses a preparation method of a highly coupled modulation single-mode laser, which is used for preparing the highly coupled modulation single-mode laser in the above embodiment, and comprises the following steps. The embodiment takes 980 nm wavelength as an example.

[0066] Referring to Figure 4 S1, first, the epitaxial structure is grown, and the substrate 1, the N-cladding layer 2, the N-waveguide layer 3, the active region 4 and the P-waveguide layer 5 are sequentially arranged from bottom to top.

[0067] Referring to Figure 4 S2, the epitaxial structure in the coupling region is etched to the partial N-cladding layer through one-time photolithography and dry etching, so as to form a coupling groove, and the other side of the epitaxial layer is a light-emitting region.

[0068] Referring to Figure 5 S3, the photoresist is removed and cleaned, and a layer of SiN is grown by PECVD, the height of the SiN grown in the coupling groove is flat with or slightly higher than the P-waveguide layer 5 in the light-emitting region, and the SiN in the coupling groove forms the passive waveguide layer 18.

[0069] Reference Figure 6 S41. Remove the SiN in buffer 12 by dry etching through a single photolithography process; remove the resist and clean.

[0070] Reference Figure 6 In step S42, a SiO2 layer is grown using PECVD and then subjected to rapid thermal annealing in N2 at 930°C. The SiO2 layer on buffer zone 12 enhances Ga diffusion from the semiconductor surface and generates vacancies, leading to quantum well vacancy-induced disorder and a wider bandgap during rapid thermal annealing. Meanwhile, the SiN layer under the light-emitting region 11 and the coupling region prevents As desorption from the surface, protecting this region from the effects of rapid thermal annealing. The key focus is protecting the active region 4 quantum well beneath the light-emitting region 11; the quantum well beneath the coupling region has already been etched away.

[0071] Reference Figure 7 S43. The entire surface is etched using dry self-aligned etching, without photolithography, to remove SiO2 from the surface. The light-emitting area 11 and the coupling area are stopped at the SiN below or partially etched. The buffer zone 12 is stopped above the P waveguide, and the P waveguide layer is etched as little as possible.

[0072] Reference Figure 8 S44. The SiN above the light-emitting region 11 is removed using photolithography and wet etching. The photoresist above the light-emitting region 11 is removed and cleaned. Then, a secondary epitaxial growth of the P-bread layer 7 and the P-surface capping layer 6 continues. At this point, the traditional 980 epitaxial structure's light-emitting region, the quantum well vacancy-induced disorder buffer zone 12, and the coupling region of the unwired waveguide have been grown. Chip fabrication then commences.

[0073] First, the ridge portion is fabricated. This structure is crucial for generating a single mode in the light-emitting region, primarily providing longitudinal current injection constraint as well as transverse refractive index and optical field mode constraint.

[0074] Reference Figure 9 and Figure 10 S51. Through photolithography and etching, the P-side capping layer 6, P-side breading layer 7, and part of the P-side waveguide layer 5 are etched away above the light-emitting region 11 and the buffer zone 12, forming a raised ridge structure 8. The ridge structure 8 penetrates the light-emitting region 11 and the buffer zone 12; due to the presence of SiN, the coupling region will stop on the SiN after the P-side capping layer 6 and P-side breading layer 7 are etched away, because the etching rate of the etching gas to SiN is very slow, and the loss is acceptable. In terms of size: the ridge structure 8 is 4 μm wide and 2400 μm long.

[0075] Reference Figure 9 and Figure 10 S52, repeat S51, etching to form two parallel ridge structures 8.

[0076] ReferenceFigure 11 and Figure 12 After the ridge etching, a 130nm-thick insulating layer SiN is grown on the whole surface. Then, photoresist is spin-coated and the height of the photoresist is controlled to be slightly higher than the surface SiN.

[0077] Referring to Figure 11 and Figure 12 In S54, the SiN on the ridge structure 8 is removed by using self-aligned etching to etch part of the photoresist by dry etching, so as to open the ridge structure 8, and the photoresist is etched at other places. After the etching, the residual photoresist is removed and cleaned.

[0078] Referring to Figure 11 and Figure 12 In S6, the light-emitting region 11 and the buffer region 12 are covered by photoetching and electron beam exposure, the coupling region is etched with SiN passive waveguide, the light path 13 and the waveguide ring 15 pattern are etched, and the coupling module 10 is formed. The etching depth is 300nm; the total length of the coupling module 10 is 100um, the width of the light path 13 is 5um, the radius of the middle waveguide ring 15 is 3um, the width of the waveguide ring 15 is 500nm, the distance between the edge of the waveguide ring 15 and the light path 13 is 150nm; and the radius of the circular path 14 is 3.65um. Finally, the photoresist is removed and cleaned.

[0079] Referring to Figure 13 In S7, seed gold Ti / Pt / Au is evaporated on the light-emitting region 11 and the buffer region 12 by a metal stripping process, and the seed gold of the coupling module 10 and the photoresist are stripped off.

[0080] Referring to Figure 13 In S8, an electroplating layer with a thickness of about 3um is formed on the basis of the seed gold, and thus the P-face process is completed.

[0081] Referring to Figure 13 In S9, after the N-face is thinned and polished, N gold is grown, and then rapid thermal annealing is performed. Finally, a high-reflection film 17 with a reflectivity of 96% is plated on the left end surface of the light-emitting region 11.

[0082] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, so that: any equivalent changes made on the basis of the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method of fabricating a highly-coupled modulated single mode laser, comprising: The method comprises the following steps of: ​ S1, growing an epitaxial layer on a substrate (1), the epitaxial layer comprising, from bottom to top, an N-face cladding layer (2), an N-face waveguide layer (3), an active region (4), and a P-face waveguide layer (5); S2, etching one side of the epitaxial layer to the N-face cladding layer (2) by one-side photolithography and dry etching to form a coupling groove, and the other side of the epitaxial layer being a light-emitting module (9); S3, growing a layer of SiN on the epitaxial layer, the SiN in the coupling groove forming a passive waveguide layer (18), the height of the passive waveguide layer (18) not being lower than the height of the P-face waveguide layer (5) in the light-emitting module (9); S4, etching to remove the SiN above the light-emitting module (9) and growing a P-face cladding layer (7) and a P-face cover layer (6) in sequence; S6, etching the pattern of a light channel (13) and a waveguide ring (15) on the upper surface of the passive waveguide layer (18) by photolithography and electron beam exposure to form a coupling module (10); The height-coupled modulated single-mode laser comprises the coupling module (10) and two light-emitting modules (9), the two light-emitting modules (9) being arranged side by side and the light-emitting surfaces of the two light-emitting modules (9) being located on the same side, the coupling module (10) being located on the side of the light-emitting surface of the light-emitting module (9), the coupling module (10) being provided with two parallel light channels (13), the ends of the two light channels (13) being opposite to the light-emitting surfaces of the two light-emitting modules (9), the side of the coupling module (10) away from the light-emitting module (9) being provided with a light outlet (16), the ends of the two light channels (13) away from the light-emitting module (9) being merged and being in communication with the light outlet (16), and the two light channels (13) being provided with a waveguide ring (15) therebetween.

2. The method for fabricating a highly coupled modulated single-mode laser according to claim 1, characterized in that: The light-emitting module (9) comprises a light-emitting region (11) and a buffer region (12), the buffer region (12) being located between the light-emitting region (11) and the coupling module (10), and the quantum wells in the buffer region (12) being in a disordered structure.

3. The method for fabricating a highly coupled modulated single-mode laser according to claim 1, characterized in that: The diameter R of the waveguide ring (15) satisfies the optical path difference formula mλ=2πnR, wherein m is a positive integer, λ is the wavelength of light, and n is the refractive index of light in the coupling module (10).

4. The method for fabricating a highly coupled modulated single-mode laser according to claim 1, characterized in that: The side of the light-emitting module (9) away from the coupling module (10) is provided with a high-reflection film (17).

5. The method for fabricating a highly coupled modulated single-mode laser according to claim 1, characterized in that: The coupling module (10) comprises the substrate (1) and the N-face cladding layer (2) which are integrated with the light-emitting module (9), the N-face cladding layer (2) being provided with the passive waveguide layer (18), and the passive waveguide layer (18) being provided with the pattern of the light channel (13) and the waveguide ring (15).

6. The method for fabricating a highly coupled modulated single-mode laser according to claim 1, characterized in that: Each of the light-emitting modules (9) is provided with a raised ridge structure (8), and the two ridge structures (8) are opposite to the two light channels (13), respectively.

7. The method for fabricating a highly coupled modulated single-mode laser according to claim 1, characterized in that: The step of removing the SiN above the light-emitting module (9) in S4 comprises the following steps of: S41, removing the SiN above the buffer region (12) by dry etching; S42, growing a layer of SiO2 on the epitaxial layer and performing rapid thermal annealing treatment in N2 at 930℃; S43, removing the SiO2 on the surface by dry etching; S44, etching to remove the SiN above the light-emitting region (11).

8. The method of claim 1, wherein the highly-coupled modulated single mode laser is prepared by the steps of: The method further comprises the following steps between S4 and S6: ​ S51, etching and removing P-face cap layer (6) and P-face cladding layer (7) on the upper surface part of light emitting area (11) and buffer area (12) to expose P-face waveguide layer (5) and form convex ridge structure (8) which penetrates light emitting area (11) and buffer area (12) and is opposite to optical path (13), S52, etching on the epitaxial layer to form two parallel ridge structures (8) which are opposite to two optical paths (13) respectively; S53, growing SiN on the whole epitaxial layer; S54, removing SiN above the two ridge structures (8) by photolithography.

9. The method for fabricating a highly coupled modulated single-mode laser according to claim 1, characterized in that: Further comprising the following steps, S7, evaporating seed metal Ti / Pt / Au on light emitting area (11) and buffer area (12) by metal stripping process; S8, electroplating to form electroplating layer on the seed metal.

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