Edge emitting laser based on cavity facet etching and integrated microlens with lamination and preparation method and application thereof

Abstract

The application provides a side emitting laser based on cavity etching and integrated microlens and a preparation method and application thereof. The application relates to the technical field of semiconductor laser fiber coupling, and the side emitting laser comprises a substrate, the upper end of the substrate is sequentially epitaxially grown with 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, the side emitting laser is provided with an n-type metal electrode and a p-type metal electrode, and the p-type metal electrode is arranged at the upper end of the passivation layer; a converging convex lens is formed at the light emitting cavity surface of the side emitting laser formed by the n-type waveguide layer, the active region and the p-type waveguide layer; meanwhile, the application also provides a method for preparing the side emitting laser and application thereof. The side emitting laser has high alignment precision, can significantly improve fiber coupling efficiency, is simple to operate, is suitable for industrial mass production and preparation, and has popularization value.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser fiber coupling technology, and in particular to an edge-emitting laser based on cavity surface etching and bonding integrated microlenses, its fabrication method and application. Background Technology

[0002] Semiconductor lasers possess outstanding advantages such as small size, long lifespan, light weight, high electro-optical conversion efficiency, and high reliability. They can be directly modulated, have high integration capabilities, and are widely used in industries such as industry, medicine, aerospace, and direct materials processing. Their unique advantages of miniaturization and high efficiency make them the most common light source in fiber optic communication, fiber laser pumping, laser medicine, high-speed laser printing, and fiber optic sensing. However, semiconductor lasers have a small emitting area and asymmetrical waveguide structures, resulting in significant differences in divergence angles in directions parallel and perpendicular to the junction plane, which greatly limits their practical application range. High-efficiency coupling of semiconductor lasers with single-mode fibers can effectively solve this problem. Single-mode fibers (SMFs) have a small core diameter (typically 5–10 μm), large bandwidth, and a special structural design that allows them to transmit only one mode of light, making them widely used for long-distance transmission. They also exhibit low inter-mode dispersion and can homogenize the beam spot, improving beam quality. Their coupling with semiconductor lasers can serve as a seed source for fiber lasers, further expanding the application range of semiconductor lasers, while simultaneously placing high demands on the coupling efficiency between the two.

[0003] Coupling between single-mode fiber and semiconductor laser can be categorized into indirect coupling and direct coupling, depending on the presence or absence of optical elements between them. Indirect coupling involves placing optical elements between the single-mode fiber and the semiconductor laser. These elements compress the fast-axis divergence angle of the laser, allowing more laser beam to couple into the fiber. Such coupling systems are complex, have low integration, and are not easily portable. Direct coupling, on the other hand, does not place optical elements between the single-mode fiber and the semiconductor laser. Instead, it involves processing the end faces of either the single-mode fiber or the semiconductor laser to create a specific shape, thus shaping the laser beam. The coupling efficiency between a semiconductor laser and a single-mode fiber depends on the degree of mode field matching. Because the divergence angles of a semiconductor laser differ significantly between directions parallel and perpendicular to the junction plane, resulting in an elliptical far-field beam, while the fiber mode field is circular, direct coupling leads to significant light loss due to mode field mismatch, reducing coupling efficiency. To address this challenge, several solutions have been proposed: The first is to introduce a tapered structure to alter the waveguide distribution of the semiconductor laser in directions parallel and perpendicular to the junction plane, thereby changing the overall waveguide characteristics. However, this approach complicates the manufacturing process of the semiconductor laser, resulting in lower device stability and yield, making it unsuitable for mass production. The second solution involves finely machining the fiber end face to create microlenses of different shapes, which shape the beam. This second solution is frequently used in actual production. By modifying the fiber end face, a direct coupling method is employed to couple the single-mode fiber to the semiconductor laser. However, this approach requires high coupling precision, and there is still room for improvement in coupling efficiency.

[0004] Therefore, the coupling of semiconductor lasers with optical fibers in existing technologies still faces problems such as difficult fabrication processes, low device stability and yield, and low device coupling efficiency. Thus, it is necessary to propose a side-emitting laser structure and its fabrication method that can improve optical fiber coupling efficiency, addressing these challenges. Summary of the Invention

[0005] The main objective of this invention is to provide a side-emitting laser structure with improved fiber coupling efficiency, its fabrication method, and its application, aiming to solve the technical problems of existing technologies such as difficult fabrication processes, low device stability and yield, and low device coupling efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a side-emitting laser, comprising a substrate, wherein 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 sequentially on the upper end of the substrate. The side-emitting laser is provided with an n-type metal electrode and a p-type metal electrode, the p-type metal electrode being 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 opposite sides, the n-type metal electrode is disposed on the substrate. A converging convex lens is formed at the emission cavity surface of the side-emitting laser formed by the n-type waveguide layer, the active region, and the p-type waveguide layer.

[0008] Furthermore, the converging convex lens on the output cavity surface of the side-emitting laser can be elliptical, circular, square, or rectangular in shape.

[0009] Furthermore, the converging convex lens has an anti-reflection film on one side of its cavity surface and a high-reflection film on the other side of its cavity surface.

[0010] Preferably, the high-reflectivity film is an oxide dielectric film, such as aluminum oxide (Al2O3) or silicon dioxide (SiO2) as a low refractive index material.

[0011] Preferably, the antireflective film can be a single layer, a double layer, or a multilayer.

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

[0013] Furthermore, the substrate is one of GaAs, GaN, or InP; the n-type confinement layer is Al. x Ga 1-x As、Al x Ga 1-x One of N or InP; the n-type waveguide layer is Al. y Ga 1-y As、Al y Ga 1-y 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 them has a barrier layer of GaAs. y P 1-y Or one of GaN; the p-type waveguide layer is 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 The passivation layer is one of N or InP; 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 values ​​of x and y are 0≤x≤1 and 0≤y≤1, respectively.

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

[0015] This invention provides a method for fabricating the aforementioned side-emitting laser, comprising 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 sequentially on the substrate, 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 the substrate; form a p-type metal electrode at the top of the passivation layer;

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

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

[0020] Furthermore, the step of forming a microlens with photoresist is as follows: a microlens mold is prepared using photoresist; a microconvex lens is transferred to the light-emitting cavity surface to form a converging convex lens.

[0021] Furthermore, the dry etching step is as follows: using 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 ion acceleration voltage is between 2V and 30kV.

[0023] This invention provides an application of the aforementioned side-emitting laser in improving fiber coupling efficiency, wherein the fiber end face is aligned with the output cavity face of the side-emitting laser.

[0024] Furthermore, the optical fiber is a flat-ended 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 multimode optical fiber.

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

[0027] This invention provides a converging convex lens formed at the output cavity surface of the side-emitting laser, which is composed of an n-type waveguide layer, an active region, and a p-type waveguide layer. This lens can adjust the divergence angle of the laser chip, improve the fiber coupling efficiency of the semiconductor laser, reduce complex subsequent coupling processes, improve device alignment accuracy, and significantly enhance fiber coupling efficiency. This invention also provides a method for forming the converging convex lens at the output cavity surface of the side-emitting laser. Through various methods such as wet etching, dry etching, femtosecond laser etching, or photoresist microlens formation, the converging convex lens is successfully formed at the output cavity surface of the emitting laser. This method offers high alignment accuracy, is simple to operate, is suitable for large-scale industrial production, and has significant potential for widespread application. Attached Figure Description

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

[0029] Figure 2 This is a schematic diagram of a side-emitting laser chip containing a converging convex lens.

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

[0031] Figure 4 This is a physical image of a side-emitting laser and fiber optic coupling device.

[0032] Figure 5 This is a schematic diagram of a side-emitting laser and an optical fiber coupling device.

[0033] Figure 6 Schematic diagram of a microscope at the position of the side-emitting laser coupled with the optical fiber.

[0034] Figure 7 This is a schematic diagram showing the relationship between the output power of a side-emitting laser and the input current and voltage.

[0035] Figure 8This is a schematic diagram of the fiber coupling efficiency curves before and after the fabrication of the converging convex lens.

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

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

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

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

[0040] The labels in the figure have the following meanings: 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. Detailed Implementation

[0041] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection 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 terms such as "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0043] Example 1

[0044] This embodiment provides a side-emitting laser, such as Figure 1 and Figure 2As shown, the system 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 epitaxially grown sequentially 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 side-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 opposite 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 side-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 method for fabricating the above-mentioned side-emitting laser, including the following steps:

[0046] 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 sequentially on the 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 at the top 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, forming 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: Epitaxial growth of laser chip. An n-type GaAs substrate is provided, and n-type Al2O3 chips are epitaxially grown sequentially on the GaAs substrate. 0.4 Ga 0.6 As confinement layer, n-type Al 0.2 Ga 0.8 As waveguide layer, In 0.18 Ga 0.82 As active region, p-type Al 0.2 Ga 0.8 As waveguide layer, p-type Al 0.4 Ga 0.6 As a confinement layer. After growth is complete, a passivation layer is deposited on the p-type confinement layer. Following pre-baking, spin-coating of a tackifier, spin-coating of photoresist, soft baking, exposure with a photomask, development, hardening, and dry etching, an etched mesa is formed.

[0051] Step 2: Fabrication of device metal electrodes. After the laser chip structure is etched, the electrodes are fabricated on n-type Al... 0.4 Ga 0.6 As confinement layer and p-type Al 0.4Ga 0.6 The metal electrodes were fabricated using an As confinement layer and magnetron sputtering was employed. The pressure inside the chamber was reduced to 0.1 Pa, and the operating voltage was 450 V. The n-type and p-type metal electrodes were Ti / Al / Ti / Au and Ti / Au, respectively.

[0052] Step 3: Etching of the Converging Lens at the Emission Cavity Surface. After the chip metal electrodes are fabricated, the next step is to fabricate the converging convex lens at the emission cavity surface. A SiO2 layer is deposited on the surface and sides of the laser chip using wet etching as a mask. A layer of photoresist is spin-coated onto the emission cavity surface. After development and hardening, the SiO2 layer inside the photoresist is etched away 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 emission cavity surface. The emission cavity surface is then etched using an etching solution composed of HBr, H2O2, and H2O (2:1:60), ultimately forming the converging convex lens, i.e., a micro-convex lens, such as... Figure 1 and Figure 2 This diagram illustrates the mesa formed by etching the laser chip of a laser emitter and a diagram containing a converging lens. Preferably, the lens has a diameter of 20 μm, a radius of curvature R of 20 μm, a material refractive index n of 3.5, and a focal length of 50 μm. The converging convex lens focuses light as follows: Figure 3 As shown, it can be seen that after the incident light n1 is refracted by the converging convex lens, the outgoing light n2 converges inward.

[0053] Step 4: Coating the front and rear cavity surfaces of the laser. Vacuum evaporation coating can be used to coat the front and rear cavity surfaces of the laser. An antireflection film is deposited on the side where the microlens is etched, and a high-reflection film is deposited on the other cavity surface. The antireflection film is made of Al2O3, and the high-reflection film is made of four pairs of SiO2 / TiO2 multilayer films, resulting in an edge-emitting laser.

[0054] Example 2

[0055] This embodiment provides a side-emitting laser. A method for fabricating the aforementioned side-emitting laser is also provided, comprising the following steps:

[0056] Step 1: Epitaxial growth of laser chip. An n-type GaAs substrate is provided, and n-type Al2O3 chips are epitaxially grown sequentially on the GaAs substrate. 0.6 Ga 0.4 As confinement layer, n-type Al 0.3 Ga 0.7 As waveguide layer, In 0.18 Ga 0.82 As active region, p-type Al 0.3 Ga 0.7 As waveguide layer, p-type Al 0.6 Ga 0.4As a confinement layer. After growth is complete, a passivation layer is deposited on the p-type confinement layer. Following pre-baking, spin-coating of a tackifier, spin-coating of photoresist, soft baking, exposure with a photomask, development, hardening, and dry etching, an etched mesa is formed.

[0057] Step 2: Fabrication of device metal electrodes. After the laser chip structure is etched, the electrodes are fabricated on n-type Al... 0.6 Ga 0.4 As confinement layer and p-type Al 0.6 Ga 0.4 The metal electrodes were fabricated using an As confinement layer and magnetron sputtering was employed. The pressure inside the chamber was reduced to 0.1 Pa, and the operating voltage was 450 V. Both the n-type and p-type metal electrodes were made of Ti / Al / Ti / Au.

[0058] Step 3: Etching of the convex lens on the light-emitting cavity surface. After the chip metal electrodes are fabricated, the next step is to fabricate the convex lens on the light-emitting cavity surface. A dry etching method is used, employing a focused ion beam (FIB) system to etch the light-emitting end face, forming a micro-convex lens on the light-emitting end face. The ion source in the FIB system is gallium (Ga) ions, and the ion acceleration voltage is 10kV.

[0059] Step 4: Coating the front and rear cavity surfaces of the laser. Vacuum evaporation coating can be used to coat the front and rear cavity surfaces of the laser. An antireflection film is deposited on the side where the microlens is etched, and a high-reflection film is deposited on the other cavity surface. The antireflection film is a TiO2 / Al2O3 bilayer, and the high-reflection film is a four-pair SiO2 / TiO2 multilayer film system, resulting in a side-emitting laser.

[0060] Example 3

[0061] This embodiment provides a side-emitting laser. A method for fabricating the aforementioned side-emitting laser is also provided, comprising the following steps:

[0062] Step 1: Epitaxial growth of laser chip. An n-type GaAs substrate is provided, and n-type Al2O3 chips are epitaxially grown sequentially on the GaAs substrate. 0.6 Ga 0.4 As confinement layer, n-type Al 0.3 Ga 0.7 As waveguide layer, In 0.18 Ga 0.82 As active region, p-type Al 0.3 Ga 0.7 As waveguide layer, p-type Al 0.6 Ga 0.4 As a confinement layer. After growth is complete, a passivation layer is deposited on the p-type confinement layer. Following pre-baking, spin-coating of a tackifier, spin-coating of photoresist, soft baking, exposure with a photomask, development, hardening, and dry etching, an etched mesa is formed.

[0063] Step 2: Fabrication of device metal electrodes. After the laser chip structure is etched, the electrodes are fabricated on n-type Al... 0.6 Ga 0.4 As confinement layer and p-type Al 0.6 Ga 0.4 The metal electrodes were fabricated using an As confinement layer and magnetron sputtering was employed. The pressure inside the chamber was reduced to 0.1 Pa, and the operating voltage was 450 V. Both the n-type and p-type metal electrodes were made of Ti / Al / Ti / Au.

[0064] Step 3: Etching of the Emerging Cavity Surface Convex Lens. After the chip metal electrodes are fabricated, the emerging cavity surface convex lens is fabricated. The convex lens is fabricated using photoresist. The specific process is as follows: the original convex lens template is prepared by photolithography combined with thermal reflow. First, in the photolithography part, a circular silicon wafer is selected as the substrate, immersed in acetone solution, and then placed in an ultrasonic cleaner for ultrasonic cleaning for 10 minutes. After ultrasonic cleaning, the silicon wafer is cleaned with anhydrous ethanol for 2 minutes. Finally, the cleaned silicon wafer is cleaned with deionized water and the surface residual moisture is dried with nitrogen. Photoresist AZ4620 is dropped onto the silicon wafer and spin-coated at 2000 rpm for 15 seconds to obtain a uniform photoresist film with a thickness of 4 μm. Then, the silicon substrate is pre-baked in an oven at 100°C for 10 minutes to remove excess solvent and moisture from the photoresist. Next, the designed photomask is placed on the silicon wafer, and the photoresist template is exposed to ultraviolet high-pressure mercury lamp for 180 seconds. Then, the photoresist is developed using a developer to remove solvent residue between the photoresist pillars. Finally, the entire sample is placed on a hot plate and heated to 140°C for 15 minutes for reflow. The photoresist at the top of the cured pillars melts under high temperature, and due to surface tension, forms a hemispherical structure with a certain curvature, ultimately yielding a microlens mold. The resulting micro-convex lens is then transferred to the light-emitting cavity surface of the laser chip to form a focusing convex lens.

[0065] Step 4: Coating the front and rear cavity surfaces of the laser. Vacuum evaporation coating can be used to coat the front and rear cavity surfaces of the laser. An antireflection film is deposited on the side where the microlens is etched, and a high-reflection film is deposited on the other cavity surface. The antireflection film is a TiO2 / Al2O3 bilayer, and the high-reflection film is a four-pair SiO2 / TiO2 multilayer film system, resulting in a side-emitting laser.

[0066] Example 4

[0067] This embodiment provides a side-emitting laser. A method for fabricating the aforementioned side-emitting laser is also provided, comprising the following steps:

[0068] Step 1: Epitaxial growth of laser chip. An n-type GaAs substrate is provided, and n-type Al2O3 chips are epitaxially grown sequentially on the GaAs substrate. 0.6 Ga 0.4 As confinement layer, n-type Al 0.3 Ga 0.7 As waveguide layer, In 0.18 Ga 0.82 As active region, p-type Al 0.3 Ga 0.7 As waveguide layer, p-type Al 0.6 Ga 0.4 As a confinement layer. After growth is complete, a passivation layer is deposited on the p-type confinement layer. Following pre-baking, spin-coating of a tackifier, spin-coating of photoresist, soft baking, exposure with a photomask, development, hardening, and dry etching, an etched mesa is formed.

[0069] Step 2: Fabrication of device metal electrodes. After the laser chip structure is etched, the electrodes are fabricated on n-type Al... 0.6 Ga 0.4 As confinement layer and p-type Al 0.6 Ga 0.4 The metal electrodes were fabricated using an As confinement layer and magnetron sputtering was employed. The pressure inside the chamber was reduced to 0.1 Pa, and the operating voltage was 450 V. Both the n-type and p-type metal electrodes were made of Ti / Al / Ti / Au.

[0070] Step 3: Etching of the Emerging Cavity Surface Convex Lens. After the chip metal electrodes are fabricated, the emerging cavity surface convex lens is fabricated. The convex lens is fabricated using photoresist. The specific process is as follows: the original convex lens template is prepared by photolithography combined with thermal reflow. First, in the photolithography part, a circular silicon wafer is selected as the substrate, immersed in acetone solution, and then placed in an ultrasonic cleaner for ultrasonic cleaning for 10 minutes. After ultrasonic cleaning, the silicon wafer is cleaned with anhydrous ethanol for 2 minutes. Finally, the cleaned silicon wafer is cleaned with deionized water and the surface residual moisture is dried with nitrogen. Photoresist AZ4620 is dropped onto the silicon wafer and spin-coated at 2000 rpm for 15 seconds to obtain a uniform photoresist film with a thickness of 4 μm. Then, the silicon substrate is pre-baked in an oven at 100°C for 10 minutes to remove excess solvent and moisture from the photoresist. Next, the designed photomask is placed on the silicon wafer, and the photoresist template is exposed to ultraviolet high-pressure mercury lamp for 180 seconds. Then, the photoresist is developed using a developer to remove solvent residue between the photoresist pillars. Finally, the entire sample is placed on a hot plate and heated to 140°C for 15 minutes for reflow. The photoresist at the top of the cured pillars melts under high temperature, and due to surface tension, forms a hemispherical structure with a certain curvature, ultimately yielding a microlens mold. The resulting micro-convex lens is then transferred to the light-emitting cavity surface of the laser chip to form a focusing convex lens.

[0071] Step 4: Coating the front and rear cavity surfaces of the laser. Vacuum evaporation coating can be used to coat the front and rear cavity surfaces of the laser. An antireflection film is deposited on the side where the microlens is etched, and a high-reflection film is deposited on the other cavity surface. The antireflection film is a TiO2 / Al2O3 bilayer, and the high-reflection film is a four-pair SiO2 / TiO2 multilayer film system, resulting in a side-emitting laser.

[0072] Example 5

[0073] 1. Testing Method

[0074] Semiconductor laser fiber coupling testing, the device used for semiconductor laser fiber coupling, such as... Figure 4 As shown, its specific structure is as follows: Figure 5As shown, the laser chip of Example 1 is attached to the substrate with silver paste, the substrate is soldered to the semiconductor cooler (TEC), and the TEC is soldered inside the housing. The n-type and p-type metal electrodes of the chip are led out to the corresponding pins of the housing using a gold wire ball soldering machine, and the tunable constant current source is turned on. The flat-end optical fiber is fixed to a six-dimensional adjustment frame using an optical fiber clamp. Under a microscope, the fiber's front, back, left, right, top, and bottom are adjusted using the three-dimensional adjustment frame to align the fiber end face with the laser chip's light-emitting end face. Examples 1-3 involve alignment with the flat-end optical fiber; Example 4 involves alignment with the tapered optical fiber. Under a microscope, the aligned object appears as shown... Figure 6 As shown, the relationship between power and voltage / current is tested. The coupling efficiency of the flat-end and tapered optical fibers of the conventional laser chip and the laser chip with a converging lens etched in Example 3 is compared using a photodetector and an optical power meter. This method is also used to verify the edge-emitting lasers in other examples.

[0075] 2. Test Results

[0076] Example 3: The relationship between the output power of the side-emitting laser and the input current and voltage is shown in the curve. Figure 7 As shown, it is working normally; the fiber coupling efficiency before and after fabrication of the converging convex lens is as follows: Figure 8 As shown, it can be seen that the coupling efficiency of the edge-emitting laser with a converging lens is above 85% under various currents, which is much greater than that of the same laser without a converging lens; the horizontal slow-axis divergence angle and the vertical fast-axis divergence angle distribution are as follows. Figure 9-12 As shown, it can be seen that the horizontal slow-axis divergence angle and vertical fast-axis divergence angle distribution of the edge-emitting laser with a converging convex lens are more concentrated, and the coupling performance is significantly improved.

[0077] Furthermore, based on the above research, this invention also tested the coupling efficiency of single-mode fiber, multimode fiber, and tapered fiber using the same converging convex lens as in Example 2. The coupling efficiencies were 85%, 92%, and 95%, respectively. This invention also investigated the effect of lens fabrication process on coupling efficiency using the same converging convex lens as in Example 4. Using a GaAs-based directly etched spherical microlens (R = 20 μm), the coupling efficiency of the 1550 nm laser increased from 18% to 65%. Using a SiO2 hot-melt reflow lens (R = 50 μm), the divergence angle of the 850 nm laser decreased from 40° to 15°, and the multimode fiber (MMF) coupling efficiency reached 85%. The effect of the fabrication process on performance is shown in Table 1.

[0078] Table 1. Effect of fabrication process on coupling performance

[0079]

[0080] The above preferred embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A side-emitting laser, characterized in that, The system includes a substrate, on which 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 sequentially. An n-type metal electrode and a p-type metal electrode are disposed on the upper end of the passivation layer. When the n-type and p-type metal electrodes are on the same side, the n-type metal electrode is disposed on the n-type confinement layer; when the n-type and p-type metal electrodes are on opposite sides, the n-type metal electrode is disposed on the substrate. A converging convex lens is formed at the output cavity surface of the side-emitting laser formed by the n-type waveguide layer, the active region, and the p-type waveguide layer. The converging convex lens is integrally formed from the semiconductor material of the output cavity surface through etching. The converging convex lens and the semiconductor material of the output cavity surface are of the same continuous material, and there is no heterogeneous material interface between them. The edge-emitting laser is fabricated through the following steps: 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 sequentially on the substrate, and deposit a passivation layer on the p-type confinement layer; Step 2: Form an n-type metal electrode on the n-type confinement layer or the substrate; form a p-type metal electrode at the top of the passivation layer; Step 3: Form a converging convex lens at the output cavity surface of the side-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 converging convex lens on the output cavity surface of the side-emitting laser can be elliptical, circular, square, or rectangular.

3. The edge-emitting laser according to claim 1, characterized in that, The converging convex lens has an anti-reflection film on one side of its cavity surface and a high-reflection film on the other side of its 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 them has a barrier layer of GaAs. y P 1-y Or one of GaN; the p-type waveguide layer and p-type confinement layer are Al y Ga 1-y As、Al y Ga 1-y The passivation layer is 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 values ​​of x and y are 0≤x≤1 and 0≤y≤1, respectively.

5. The edge-emitting laser according to claim 1, characterized in that, In step 3, the converging convex lens is formed by wet etching. The wet etching steps are as follows: a SiO2 layer is deposited on the surface of the side-emitting laser as a mask, a layer of photoresist is spin-coated on the output cavity surface, and after development and hardening, the SiO2 layer inside the photoresist is etched away using an etching solution composed of NH4F, HF and H2O with a ratio of 1-2:1-2:6-10, exposing the n-type waveguide layer, active region and p-type waveguide layer at the output cavity surface; the output cavity surface is etched using an etching solution composed of HBr, H2O2 and H2O with a ratio of 1-2:1-2:50-70 to form the converging convex lens.

6. The edge-emitting laser according to claim 1, characterized in that, In step 3, the converging convex lens is formed by photoresist, and the steps are as follows: a microlens mold is prepared using photoresist; the microlens is transferred to the light-emitting cavity surface to form a converging convex lens.

7. The side-emitting laser according to claim 1, characterized in that, In step 3, the converging convex lens is formed by dry etching. The dry etching step is as follows: using 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.

8. The application of the side-emitting laser according to any one of claims 1-7 in improving fiber coupling efficiency, characterized in that, The fiber end face is aligned with the output cavity face of the side-emitting laser.

9. The application according to claim 8, characterized in that, The optical fiber is a flat-ended optical fiber, a tapered optical fiber, or a wedge-shaped optical fiber.

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