Edge-emitting laser based on cavity surface etching and fitting integrated micro lens and preparation method and application of edge-emitting laser

Abstract

The invention provides an edge-emitting laser based on a cavity surface etching and fitting integrated micro lens, and a preparation method and application of the edge-emitting laser. An edge-emitting laser relates to the technical field of semiconductor laser optical fiber coupling and comprises a substrate, an n-type limiting layer, an n-type waveguide layer, an active area, a p-type waveguide layer, a p-type limiting layer and a passivation layer are sequentially grown at the upper end of the substrate in an epitaxial mode, and an n-type metal electrode and a p-type metal electrode are arranged on the edge-emitting laser. The p-type metal electrode is arranged at the upper end of the passivation layer; a convergent convex lens is formed on the light-emitting cavity surface of the edge-emitting laser formed by the n-type waveguide layer, the active region and the p-type waveguide layer, and meanwhile, the invention also provides a method for preparing the edge-emitting laser and application of the edge-emitting laser. The edge-emitting laser is high in alignment precision, capable of remarkably improving the optical fiber coupling efficiency, easy and convenient to operate and suitable for industrial mass production and preparation, and has popularization value.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor laser fiber coupling, and particularly to an edge-emitting laser based on cavity surface etching and integrated micro-lens bonding, and a preparation method and application thereof. Background Art

[0002] Semiconductor lasers have outstanding advantages such as small volume, long life, light weight, high electro-optic conversion efficiency, and high reliability. They can be directly modulated and have high integration capabilities, and are widely used in industries, medical fields, aerospace, direct material processing, etc. Their unique advantages of miniaturization and high efficiency make them the most common light sources in fiber optic communication, fiber laser pumping, laser medicine, high-speed laser printing, and fiber optic sensing. However, the semiconductor laser has a small light-emitting area and an asymmetric waveguide structure, and there is a large difference in the divergence angles in the directions parallel and perpendicular to the junction plane, which greatly limits the actual application range of the semiconductor laser. The high-efficiency coupling of the semiconductor laser and the single-mode fiber can well solve this problem. The single-mode fiber (SMF) has a small core diameter (generally 5-10 μm), a large bandwidth, and a special structure design that allows it to transmit only one mode of light. It is widely used for long-distance transmission, has small inter-mode dispersion, and can homogenize the light spot and improve the beam quality. Its coupling with the semiconductor laser can be used as the seed source of the fiber laser, which makes the application range of the semiconductor laser wider, and at the same time puts forward high requirements for the coupling efficiency of the two.

[0003] When a single-mode fiber is coupled with a semiconductor laser, it can be divided into indirect coupling and direct coupling according to whether there is an optical element between the two. Indirect coupling means placing an optical element between the single-mode fiber and the semiconductor laser. Through the action of the optical element, the fast-axis divergence angle of the laser is compressed, so that more laser beams can be coupled into the fiber. Such a coupling system has complex components and low integration, making it inconvenient to carry. Direct coupling means not placing an optical element between the single-mode fiber and the semiconductor laser, but by processing the end face of the single-mode fiber or the semiconductor laser to make a special shape to achieve the purpose of shaping the laser beam. The coupling efficiency between the semiconductor laser and the single-mode fiber depends on the matching degree of their mode fields. Since the divergence angles of the semiconductor laser in the directions parallel and perpendicular to the junction plane are very different, the far-field light spot is elliptically distributed, while the fiber mode field is circularly distributed. When the two are directly coupled, large optical losses will be caused due to the mismatch of the mode fields, reducing the coupling efficiency. To solve this problem, different solutions have been proposed currently: The first solution is to introduce a tapered structure to change the waveguide distribution of the semiconductor laser in the directions parallel and perpendicular to the junction plane, so as to achieve the change of the overall waveguide characteristics. However, adopting this solution will make the manufacturing process of the semiconductor laser more complex, and the device stability and yield are relatively low, which is not suitable for mass production; The second solution is to finely process the fiber end face to make end face microlenses of different shapes to play a role in shaping the light beam. In actual production, the second solution is often adopted. By improving the fiber end face, the direct coupling method is used to complete the coupling between the single-mode fiber and the semiconductor laser. However, this solution requires high coupling accuracy and there is still room for improvement in the coupling efficiency.

[0004] Therefore, in the prior art, the coupling between the semiconductor laser and the fiber still has problems such as difficult manufacturing process, low device stability and yield, and low device coupling efficiency. Therefore, it is necessary to propose an edge-emitting laser structure and its preparation method that can improve the fiber coupling efficiency according to the above difficulties. Summary of the Invention

[0005] The main object of the present invention is to provide an edge-emitting laser structure and its preparation method and application for improving the fiber coupling efficiency, aiming to solve the technical problems existing in the prior art such as difficult manufacturing process, low device stability and yield, and low device coupling efficiency.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides an edge-emitting laser, which includes a substrate. An n-type confinement layer, an n-type waveguide layer, an active region, a p-type waveguide layer, a p-type confinement layer, and a passivation layer are sequentially epitaxially grown on the upper end of the substrate. The edge-emitting laser is provided with an n-type metal electrode and a p-type metal electrode. The p-type metal electrode is disposed on the upper end of the passivation layer. When the n-type metal electrode and the p-type metal electrode are on the same side, the n-type metal electrode is disposed on the n-type confinement layer; when the n-type metal electrode and the p-type metal electrode are on different sides, the n-type metal electrode is disposed on the substrate; a converging convex lens is formed at the light-emitting cavity surface of the edge-emitting laser formed by the n-type waveguide layer, the active region, and the p-type waveguide layer.

[0008] Further, the structure of the converging convex lens on the light-emitting cavity surface of the edge-emitting laser can be one of an ellipse, a circle, a square, or a rectangle.

[0009] Further, an antireflection film is provided on one cavity surface of the converging convex lens, and a high-reflection film is provided on the other cavity surface.

[0010] Preferably, the high-reflection film is an oxide dielectric film, such as alumina (Al2O3), silica (SiO2), etc. as low refractive index materials.

[0011] Preferably, the antireflection film can be single-layer, double-layer, or multi-layer.

[0012] Preferably, the antireflection film is a high refractive index material, such as zirconium oxide (ZrO2), titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), zinc selenide (ZnSe), etc.

[0013] Further, the substrate is one of GaAs, GaN, or InP; the n-type confinement layer is one of Al x Ga 1-x As, Al x Ga 1-x N, or InP; the n-type waveguide layer is one of Al y Ga 1-y As, Al y Ga 1-y N, or InP; the active region includes a quantum well and a barrier layer, where the quantum well is one of In x Ga 1-x N, or In x Ga 1-x As y P 1-y one of them, and the barrier layer is one of GaAs y P 1-y or GaN; the p-type waveguide layer is one of Al y Ga 1-y As, Al yGa 1-y One of N or InP; the p-type confinement layer is Al x Ga 1-x As, Al x Ga 1-x One of N or InP; the passivation layer is one of SiO2 or Si3N4; the n-type metal electrode and the p-type metal electrode are one of titanium (Ti) / aluminum (Al) / titanium (Ti) / gold (Au), gold (Au) / germanium (Ge) / nickel (Ni) / gold (Au), or titanium (Ti) / platinum (Pt) / gold (Au); wherein, the value ranges of x and y are 0≤x≤1 and 0≤y≤1 respectively.

[0014] Preferably, the active region includes a quantum well and two barrier layers, or includes multiple quantum wells and multiple barrier layers.

[0015] The present invention provides a method for manufacturing the above-mentioned edge-emitting laser, including the following steps:

[0016] Step 1: Epitaxially grow an n-type confinement layer, an n-type waveguide layer, an active region, a p-type waveguide layer, and a p-type confinement layer on a substrate in sequence, and deposit a passivation layer on the p-type confinement layer;

[0017] Step 2: Form an n-type metal electrode on the n-type confinement layer or on the substrate; form a p-type metal electrode on the upper end of the passivation layer;

[0018] Step 3: Perform dry etching, wet etching, femtosecond laser direct etching, or form a microlens with photoresist on the light-emitting end face to form a converging convex lens on the light-emitting cavity surface.

[0019] Further, the wet etching step is as follows: Deposit a SiO2 layer on the surface of the edge-emitting laser as a mask, spin-coat a layer of photoresist on the light-emitting cavity surface, after development and hardening, use an etching solution composed of NH4F, HF, and H2O (1-2:1-2:6-10) to etch away the SiO2 layer inside the photoresist, exposing the n-type waveguide layer, the active region, and the p-type waveguide layer at the light-emitting cavity surface; use an etching solution composed of HBr, H2O2, and H2O (1-2:1-2:50-70) to etch the light-emitting cavity surface to form a converging convex lens.

[0020] Further, the step of forming a microlens with photoresist is as follows: Prepare a microlens mold with photoresist; transfer the micro-convex lens to the light-emitting cavity surface to form a converging convex lens.

[0021] Further, the dry etching step is as follows: Use a focused ion beam system to perform ion beam etching on the light-emitting end face to form a converging convex lens on the light-emitting end face.

[0022] Preferably, the ion beam source in the focused ion beam system is gallium (Ga) ions, xenon (Xe) ions, etc., and the acceleration voltage of the ions is between 2V and 30kV;

[0023] The present invention provides the application of the above edge-emitting laser in improving the fiber coupling efficiency, and the end face of the optical fiber is aligned with the light-emitting cavity surface of the edge-emitting laser.

[0024] Furthermore, the optical fiber is a flat-end optical fiber, a tapered optical fiber or a wedge-shaped optical fiber.

[0025] Furthermore, the optical fiber is a single-mode optical fiber or a multi-mode optical fiber.

[0026] The beneficial effects of the present invention are as follows:

[0027] A converging convex lens is formed at the light-emitting cavity surface of the edge-emitting laser formed by the n-type waveguide layer, the active region, and the p-type waveguide layer in the present invention. The divergence angle of the laser chip can be adjusted, the fiber coupling efficiency of the semiconductor laser is improved, the complicated coupling process operation in the later stage is reduced, the alignment accuracy of the device is improved, and the fiber coupling efficiency is greatly improved. The present invention also provides a method for forming a converging convex lens at the light-emitting cavity surface of the edge-emitting laser. By means of wet etching, dry etching, femtosecond laser etching or forming a microlens with photoresist and other methods, a converging convex lens is successfully formed at the light-emitting cavity surface of the emitting laser. This method has high alignment accuracy, is easy to operate, is suitable for industrial mass production and preparation, and has popularization value. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the mesa formed after etching the laser chip of the edge-emitting laser.

[0029] Figure 2 It is a schematic diagram of the laser chip of the edge-emitting laser containing a converging convex lens.

[0030] Figure 3 It is a schematic diagram of the light-gathering principle of the converging convex lens.

[0031] Figure 4 It is a physical diagram of the edge-emitting laser and the fiber coupling device.

[0032] Figure 5 It is a schematic diagram of the edge-emitting laser and the fiber coupling device.

[0033] Figure 6 Schematic diagram of the microscope at the fiber coupling position of the edge-emitting laser.

[0034] Figure 7 It is a schematic diagram of the relationship curve between the output power of the edge-emitting laser and the input current and voltage.

[0035] Figure 8It is a schematic diagram of the optical fiber coupling efficiency curve before and after preparing a converging convex lens.

[0036] Figure 9 It is a schematic diagram of the horizontal slow-axis divergence angle distribution of a laser chip without a converging convex lens.

[0037] Figure 10 It is a schematic diagram of the horizontal slow-axis divergence angle distribution of a laser chip after preparing a converging convex lens.

[0038] Figure 11 It is a schematic diagram of the vertical fast-axis divergence angle distribution of a laser chip without a converging convex lens.

[0039] Figure 12 It is a schematic diagram of the vertical fast-axis divergence angle distribution of a laser chip after preparing a converging convex lens.

[0040] The meanings of the markings in the figure are as follows: 1 is the substrate; 2 is the n-type confinement layer; 3 is the n-type metal electrode; 4 is the n-type waveguide layer; 5 is the active region; 6 is the p-type waveguide layer; 7 is the p-type confinement layer; 8 is the passivation layer; 9 is the p-type metal electrode; 10 is the light-emitting cavity surface; 11 is the converging convex lens. Specific Embodiments

[0041] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the accompanying drawings are only for illustrative purposes and cannot be understood as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0043] Embodiment 1

[0044] This embodiment provides an edge-emitting laser, such as Figure 1 and Figure 2As shown in the figure, it includes a substrate 1. An n-type confinement layer 2, an n-type waveguide layer 4, an active region 5, a p-type waveguide layer 6, a p-type confinement layer 7, and a passivation layer 8 are sequentially epitaxially grown on the upper end of the substrate 1. An n-type metal electrode 3 and a p-type metal electrode 9 are provided on the edge-emitting laser. The p-type metal electrode 9 is disposed on the upper end of the passivation layer 8. When the n-type metal electrode 3 and the p-type metal electrode 9 are on the same side, the n-type metal electrode 3 is disposed on the n-type confinement layer 2; when the n-type metal electrode 3 and the p-type metal electrode 9 are on different sides, the n-type metal electrode 3 is disposed on the substrate 1; a converging convex lens 11 is formed at the light-emitting cavity surface 10 of the edge-emitting laser formed by the n-type waveguide layer 4, the active region 5, and the p-type waveguide layer 6.

[0045] This embodiment provides a preparation method for the above-mentioned edge-emitting laser, including the following steps:

[0046] Step 1: Sequentially epitaxially grow an n-type confinement layer, an n-type waveguide layer, an active region, a p-type waveguide layer, and a p-type confinement layer on a substrate, and deposit a passivation layer on the p-type confinement layer;

[0047] Step 2: Form an n-type metal electrode on the n-type confinement layer or the substrate; form a p-type metal electrode on the upper end of the passivation layer;

[0048] Step 3: Perform dry etching, wet etching, femtosecond laser direct etching, or photoresist to form a microlens on the light-emitting end face, and form a converging convex lens on the light-emitting cavity surface.

[0049] This embodiment preferably uses the wet etching method, and the specific steps are as follows:

[0050] Step 1: Laser chip epitaxial growth. Provide an n-type GaAs substrate, and sequentially epitaxially grow an n-type Al 0.4 Ga 0.6 As confinement layer, an n-type Al 0.2 Ga 0.8 As waveguide layer, an In 0.18 Ga 0.82 As active region, a p-type Al 0.2 Ga 0.8 As waveguide layer, a p-type Al 0.4 Ga 0.6 As confinement layer. After growth, deposit a passivation layer on the p-type confinement layer. After pre-baking, spin-coating a tackifier, spin-coating a photoresist, soft baking, exposing with a photomask, developing, hard baking, and dry etching, form an etching mesa;

[0051] Step 2: Device metal electrode preparation. After the laser chip structure etching is completed, respectively on the n-type Al 0.4 Ga 0.6 As confinement layer and the p-type Al 0.4Ga 0.6 The As confinement layer is used for the preparation of metal electrodes. The magnetron sputtering method is adopted, the pressure in the chamber is reduced to 0.1 Pa, the working voltage is 450 V, and the n-type and p-type metal electrodes are Ti / Al / Ti / Au and Ti / Au respectively;

[0052] Step 3: Etching the convex lens on the light-emitting cavity surface. After the metal electrodes of the chip are prepared, the preparation of the converging convex lens on the light-emitting cavity surface is carried out next. By means of wet etching, a SiO2 layer is deposited on the surface and side of the laser chip as a mask, and a layer of photoresist is spin-coated at the light-emitting cavity surface. After development and hardening. The SiO2 layer inside the photoresist is etched away by using an etching solution composed of NH4F, HF and H2O (1:1:8), exposing the n-type waveguide layer, active region and p-type waveguide layer at the light-emitting cavity surface. The light-emitting cavity surface is etched by using an etching solution composed of HBr, H2O2 and H2O (2:1:60), and finally a converging convex lens, that is, a micro convex lens, is formed, as Figure 1 and Figure 2 are the schematic diagram of the mesa formed after etching the laser chip emitting the laser and the schematic diagram containing the converging lens. Preferably, the lens diameter is 20 μm, the radius of curvature R is 20 μm, the refractive index n of the material is 3.5, and the focal length is 50 μm; The light-converging principle of the converging convex lens is as Figure 3 shown, and it can be seen that the incident light n1 converges inward after being refracted by the converging convex lens to become the outgoing light n2.

[0053] Step 4: Coating the front and rear end faces of the laser. The front and rear cavity surfaces of the laser can be coated by vacuum evaporation coating method. An antireflection film is evaporated on the side etched with the micro convex lens, and a high-reflection film is coated on the other cavity surface. The material used for the antireflection film is Al2O3, and the material used for the high-reflection film is a 4-pair SiO2 / TiO2 multilayer film system, obtaining a ridge-emitting laser.

[0054] Embodiment 2

[0055] This embodiment provides a ridge-emitting laser. And a preparation method of the above ridge-emitting laser is provided, including the following steps:

[0056] Step 1: Epitaxial growth of the laser chip. Provide an n-type GaAs substrate, and sequentially epitaxially grow an n-type Al 0.6 Ga 0.4 As confinement layer, an n-type Al 0.3 Ga 0.7 As waveguide layer, an In 0.18 Ga 0.82 As active region, a p-type Al 0.3 Ga 0.7 As waveguide layer, a p-type Al 0.6 Ga 0.4As confinement layer. After growth, a passivation layer is deposited on the p-type confinement layer. After pre-baking, spin-coating a tackifier, spin-coating a photoresist, soft-baking, exposing with a photomask, developing, hard-baking, and dry etching, an etched mesa is formed;

[0057] Step 2: Preparation of device metal electrodes. After the laser chip structure is etched, on the n-type Al 0.6 Ga 0.4 As confinement layer and the p-type Al 0.6 Ga 0.4 As confinement layer, the preparation of metal electrodes is carried out. Using the magnetron sputtering method, the pressure in the chamber is reduced to 0.1 Pa, the working voltage is 450 V, and both the n-type and p-type metal electrodes are Ti / Al / Ti / Au;

[0058] Step 3: Etching of the convex lens on the light-emitting cavity surface. After the chip metal electrodes are prepared, the preparation of the convex lens on the light-emitting cavity surface is carried out next. Using the dry etching method, the ion beam etching of the light-emitting end face is carried out by a focused ion beam (FIB) system to form a micro-convex lens on the light-emitting end face. The ion beam source in the focused ion beam system is gallium (Ga) ions, and the acceleration voltage of the ions is 10 kV;

[0059] Step 4: Coating of the front and rear end faces of the laser. The front and rear cavity surfaces of the laser can be coated by vacuum evaporation coating. Among them, an antireflection coating is evaporated on the side where the micro-convex lens is etched, and a high-reflection coating is coated on the other cavity surface. The material used for the antireflection coating is a TiO2 / Al2O3 double layer, and the material used for the high-reflection coating is a 4-pair SiO2 / TiO2 multilayer film system to obtain an edge-emitting laser.

[0060] Example 3

[0061] This example provides an edge-emitting laser. And a preparation method of the above-mentioned edge-emitting laser is provided, including the following steps:

[0062] Step 1: Epitaxial growth of the laser chip. Provide an n-type GaAs substrate, and sequentially epitaxially grow an n-type Al 0.6 Ga 0.4 As confinement layer, an n-type Al 0.3 Ga 0.7 As waveguide layer, an In 0.18 Ga 0.82 As active region, a p-type Al 0.3 Ga 0.7 As waveguide layer, a p-type Al 0.6 Ga 0.4 As confinement layer on the GaAs substrate. After growth, a passivation layer is deposited on the p-type confinement layer. After pre-baking, spin-coating a tackifier, spin-coating a photoresist, soft-baking, exposing with a photomask, developing, hard-baking, and dry etching, an etched mesa is formed;

[0063] Step 2: Preparation of device metal electrodes. After the laser chip structure is etched, on the n-type Al 0.6 Ga 0.4 As confinement layer and p-type Al 0.6 Ga 0.4 As confinement layer, the metal electrodes are prepared. The magnetron sputtering method is adopted. The pressure in the chamber is reduced to 0.1 Pa, and the working voltage is 450 V. The n-type and p-type metal electrodes are both Ti / Al / Ti / Au;

[0064] Step 3: Etching of the convex lens on the light-emitting cavity surface. After the chip metal electrodes are prepared, the preparation of the convex lens on the light-emitting cavity surface is carried out next. The micro-convex lens on the light cavity surface is prepared by photoresist. The specific process flow is as follows: The original micro-convex lens template is prepared by photolithography combined with thermal reflow process. First is the photolithography part. A circular silicon wafer is selected as the substrate, soaked in acetone solution, and then put into an ultrasonic cleaner for ultrasonic cleaning for 10 min. After the ultrasonic cleaning is completed, the above silicon wafer is cleaned with anhydrous ethanol for 2 min. Finally, the cleaned silicon wafer is cleaned with deionized water and dried with nitrogen to remove the residual moisture on the surface. The photoresist AZ4620 is dropped on the silicon wafer, and the spin coating process is used to rotate at a speed of 2000 rpm for 15 s to obtain a uniform photoresist film with a thickness of 4 μm. Then the silicon substrate is pre-baked and baked in an oven at 100 °C for 10 min to remove the excess solvent and moisture in the photoresist. Then the designed mask is placed on the silicon wafer, and under the irradiation of an ultraviolet high-pressure mercury lamp, the photoresist template is exposed, and the ultraviolet exposure time is 180 s. Then the developer supporting the photoresist is used for development to remove the solvent residue between the photoresist columns prepared by photolithography. Finally, the whole sample is placed on a hot plate and heated at 140 °C for 15 min for the thermal reflow process. The photoresist at the top of the solidified photoresist column will melt under the action of high temperature, and due to the action of its surface tension, a hemispherical structure with a certain curvature will be formed at its top, and finally a microlens mold is obtained. The above-obtained micro-convex lens is transferred to the light-emitting cavity surface of the laser chip to form a convex lens with a light-gathering effect;

[0065] Step 4: Coating the front and rear end faces of the laser. The front and rear cavity faces of the laser can be coated by vacuum evaporation coating method. Among them, an anti-reflection film is evaporated on the side etched with the micro-convex lens, and a high-reflection film is coated on the other cavity face. The material used for the anti-reflection film is a double layer of TiO2 / Al2O3, and the material used for the high-reflection film is a 4-pair SiO2 / TiO2 multi-layer film system to obtain an edge-emitting laser.

[0066] Example 4

[0067] This example provides an edge-emitting laser. And a preparation method of the above-mentioned edge-emitting laser is provided, including the following steps:

[0068] Step 1: Laser chip epitaxial growth. Provide an n-type GaAs substrate, and sequentially epitaxially grow an n-type Al 0.6 Ga 0.4 As confinement layer, an n-type Al 0.3 Ga 0.7 As waveguide layer, an In 0.18 Ga 0.82 As active region, a p-type Al 0.3 Ga 0.7 As waveguide layer, a p-type Al 0.6 Ga 0.4 As confinement layer. After growth, deposit a passivation layer on the p-type confinement layer. After pre-baking, spin-coating a tackifier, spin-coating a photoresist, soft baking, exposure with a photomask, development, hard baking, and dry etching, form an etched mesa;

[0069] Step 2: Device metal electrode preparation. After the laser chip structure is etched, respectively prepare metal electrodes on the n-type Al 0.6 Ga 0.4 As confinement layer and the p-type Al 0.6 Ga 0.4 As confinement layer. Adopt magnetron sputtering. Reduce the pressure in the chamber to 0.1 Pa, the working voltage is 450 V, and both the n-type and p-type metal electrodes are Ti / Al / Ti / Au;

[0070] Step 3: Etching of the convex lens on the light-emitting cavity surface. After the chip metal electrodes are prepared, the preparation of the convex lens on the light-emitting cavity surface is carried out next. The micro-convex lens on the light cavity surface is prepared using photoresist. The specific process flow is as follows: The original micro-convex lens template is prepared through photolithography combined with the thermal reflow process. First is the photolithography part. Select a circular silicon wafer as the substrate, soak it in acetone solution, and then put it into an ultrasonic cleaner for ultrasonic cleaning for 10 minutes. After the ultrasonic cleaning is completed, the above silicon wafer is cleaned with absolute ethanol for 2 minutes. Finally, the cleaned silicon wafer is cleaned with deionized water and the residual moisture on the surface is blown dry with nitrogen. Drop the photoresist AZ4620 on the silicon wafer and use the spin coating process to rotate at a speed of 2000 rpm for 15 seconds to obtain a uniform photoresist film with a thickness of 4 μm. Then the silicon substrate is pre-baked and baked in an oven at 100 °C for 10 minutes to remove the excess solvent and moisture in the photoresist. Next, place the designed mask on the silicon wafer and expose the photoresist template under the irradiation of an ultraviolet high-pressure mercury lamp. The ultraviolet exposure time is 180 seconds. Then use the developer supporting the photoresist for development to remove the solvent residue between the photoresist columns prepared by photolithography. Finally, place the entire sample on a hot plate and heat it at 140 °C for 15 minutes for the thermal reflow process. The photoresist at the top of the solidified photoresist column will melt under the action of high temperature and form a hemispherical structure with a certain curvature at its top due to the action of its surface tension, and finally a microlens mold is obtained. Transfer the above-obtained micro-convex lens to the light-emitting cavity surface of the laser chip to form a convex lens with a light-gathering effect;

[0071] Step 4: Coating the front and rear end faces of the laser. The front and rear cavity surfaces of the laser can be coated using the vacuum evaporation coating method. Among them, an antireflection coating is evaporated on the side etched with the micro-convex lens, and a high-reflection coating is deposited on the other cavity surface. The material used for the antireflection coating is a TiO2 / Al2O3 bilayer, and the material used for the high-reflection coating is a 4-pair SiO2 / TiO2 multilayer film system to obtain an edge-emitting laser.

[0072] Example 5

[0073] 1. Test method

[0074] Fiber coupling test of semiconductor lasers. The device used for the fiber coupling of semiconductor lasers is as Figure 4 shown, and its specific structure is as Figure 5As shown in the figure, the laser chip of the above-mentioned Embodiment 1 is pasted on the substrate through silver paste. The substrate is welded to the thermoelectric cooler (TEC), and the TEC is welded inside the package. The n-type and p-type metal electrodes of the chip are led out to the corresponding pins of the package by using a gold wire ball bonder, and the adjustable constant current source is turned on. The flat-end optical fiber is fixed on the six-axis adjustment frame through an optical fiber fixture. Under the microscope, the front, back, left, right, up, and down of the optical fiber are adjusted through the three-axis adjustment frame to complete the alignment of the optical fiber end face and the light-emitting end face of the laser chip. Among them, Embodiments 1-3 are aligned with the flat-end optical fiber; Embodiment 4 is aligned with the tapered optical fiber. Under the microscope, the actual object after alignment is as Figure 6 shown. The relationships between the test power, voltage, and current are measured. The flat-end and tapered optical fiber coupling efficiencies of the traditional laser chip and the laser chip with a converging convex lens etched in Embodiment 3 are compared through a photodetector and an optical power meter, and the edge-emitting lasers in other embodiments are verified by this method.

[0075] 2. Test Results

[0076] The relationship curve between the output power of the edge-emitting laser in Embodiment 3 and the input current and voltage is as Figure 7 shown, indicating that it works normally; the optical fiber coupling efficiencies before and after preparing the converging convex lens are as Figure 8 shown. It can be seen that the coupling efficiency of the edge-emitting laser with a converging convex lens is above 85% at each current, which is much greater than that of the same laser without a prepared converging convex lens; the distributions of the horizontal slow-axis divergence angle and the vertical fast-axis divergence angle are as Figures 9 - 12 shown. It can be known that the distributions of the horizontal slow-axis divergence angle and the vertical fast-axis divergence angle of the edge-emitting laser with a converging convex lens are more concentrated, and the coupling performance is significantly improved.

[0077] In addition, on the basis of the above research, the present invention also tested the coupling efficiencies of single-mode optical fiber, multi-mode optical fiber, and tapered optical fiber on the basis of the edge-emitting laser with the same converging convex lens in Embodiment 2, and the coupling efficiencies are 85%, 92%, and 95% respectively. The present invention also studied the influence of the lens preparation process on the coupling efficiency on the basis of the edge-emitting laser with the same converging convex lens in Embodiment 4. Using a spherical microlens (R = 20 μm) directly etched on a GaAs substrate, the coupling efficiency of a 1550 nm laser is increased from 18% to 65%. By using a SiO2 hot melt reflow lens (R = 50 μm), the divergence angle of an 850 nm laser is reduced from 40° to 15°, and the coupling efficiency of a multi-mode optical fiber (MMF) reaches 85%. The influence of the preparation process on the performance is shown in Table 1.

[0078] Table 1 Influence of Preparation Process on Coupling Performance

[0079]

[0080] In the above preferred embodiment, the object, technical solution and advantages of the present invention are further described in detail. It should be understood that the above description is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An edge emitting laser, characterized in that: The invention comprises a substrate, an n-type confinement layer, an n-type waveguide layer, an active region, a p-type waveguide layer, a p-type confinement layer and a passivation layer are epitaxially grown on the upper end of the substrate in sequence, an n-type metal electrode and a p-type metal electrode are arranged on the edge emitting laser, the p-type metal electrode is arranged on the upper end of the passivation layer, when the n-type metal electrode and the p-type metal electrode are on the same side, the n-type metal electrode is arranged on the n-type confinement layer; when the n-type metal electrode and the p-type metal electrode are on different sides, the n-type metal electrode is arranged on the substrate; a converging convex lens is formed at the light-emitting cavity surface of the edge emitting laser formed by the n-type waveguide layer, the active region and the p-type waveguide layer.

2. The edge emitting laser according to claim 1, characterized in that The structure of the converging convex lens on the light-emitting cavity surface of the edge-emitting laser can be one of elliptical, circular, square or rectangular.

3. The edge emitting laser according to claim 1, characterized in that An anti-reflection film is arranged on one cavity surface of the converging convex lens, and a high-reflection film is arranged on the other cavity surface.

4. The edge emitting laser according to claim 1, characterized in that The substrate is one of GaAs, GaN or InP; the n-type confinement layer and the n-type waveguide layer are Al x Ga 1-x As、Al x Ga 1-x One of N or InP; the active region comprises a quantum well and a barrier layer, wherein the quantum well is In x Ga 1-x N or In x Ga 1-x As y P 1-y One of the two, the barrier layer is GaAs y P 1-y or GaN; the p-type waveguide layer and the p-type confinement layer are Al y Ga 1-y As、Al y Ga 1-y One of N or InP; the passivation layer is one of SiO2 or Si3N4; the n-type metal electrode and the p-type metal electrode are one of titanium / aluminum / titanium / gold, gold / germanium / nickel / gold or titanium / platinum / gold; wherein the value ranges of x and y are 0≤x≤1, 0≤y≤1 respectively.

5. The method for preparing the edge emitting laser according to claim 1, characterized in that: The steps include: Step 1: epitaxially growing an n-type confinement layer, an n-type waveguide layer, an active region, a p-type waveguide layer and a p-type confinement layer on a substrate in sequence, and depositing a passivation layer on the p-type confinement layer; Step 2: forming an n-type metal electrode on the n-type confinement layer or on the substrate; forming a p-type metal electrode on the upper end of the passivation layer; Step 3: Perform dry etching, wet etching, femtosecond laser direct etching or photoresist etching on the light output end face to form a microlens, and form a converging convex lens on the light output cavity surface.

6. The method for preparing an edge emitting laser according to claim 5, characterized in that: The wet etching step is as follows: depositing a SiO2 layer as a mask on the surface of the edge-emitting laser, spin-coating a photoresist at the light-emitting cavity surface, and after development and hardening, etching away the SiO2 layer inside the photoresist using an etching solution composed of NH4F, HF and H2O in a ratio of 1-2:1-2:6-10 to expose the n-type waveguide layer, active area and p-type waveguide layer at the light-emitting cavity surface; etching the light-emitting cavity surface using an etching solution composed of HBr, H2O2 and H2O in a ratio of 1-2:1-2:50-70 to form a converging convex lens.

7. The method for preparing an edge emitting laser according to claim 5, characterized in that: The steps of forming a micro lens with photoresist are: preparing a micro lens mold with photoresist; and transferring the micro convex lens to the light emitting cavity surface to form a converging convex lens.

8. The method for preparing an edge emitting laser according to claim 5, characterized in that: The dry etching step is: using a focused ion beam system to perform ion beam etching on the light-emitting end face, so as to form a converging convex lens on the light-emitting end face.

9. Application of the edge emitting laser according to any one of claims 1 to 4 in improving the optical fiber coupling efficiency, characterized in that: The optical fiber end face is aligned with the light output cavity face of the edge emitting laser.

10. The use according to claim 9, characterized in that: The optical fiber is a flat-end optical fiber, a tapered optical fiber or a wedge-shaped optical fiber.

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