Antireflective vertical-cavity surface-emitting laser and chip

Abstract

An antireflective vertical-cavity surface-emitting laser and a chip are provided. The laser comprises an active region (30), and a lower Bragg reflection layer (10) and an upper Bragg reflection layer (20) which are located on two opposite sides of the active region (30), the active region (30) comprising at least five active layers (310) and a tunnel junction (330) located between the active layers (310), wherein a light anti-reflection storage cavity (40) is at least provided between the lower Bragg reflection layer (10) and the active region (30), or between the upper Bragg reflection layer (20) and the active region (30); the light anti-reflection storage cavity (40) is configured to increase the peak value of the intensity of a light field to be higher than that of the active region (30) and to store the light field energy; and the antireflective vertical-cavity surface-emitting laser operates under the conditions that the injection current density is greater than 10 kA / cm2, the slope efficiency is greater than 4 W / A, and the far-field divergence angle is less than or equal to 19°.

Description

Anti-reflection vertical cavity surface emitting laser and chip

[0001] This application claims priority to U.S. provisional patent application serial number 63 / 607,776, filed on December 8, 2023, entitled "Antireflective vertical-cavity surface-emitting laser," and to Chinese patent application number 202410506933.1, filed on April 25, 2024, with the Patent Office of China, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The embodiments of the present application relate to the technical field of semiconductor laser devices, for example, to an anti-reflection vertical cavity surface emitting laser and a chip. Background Art

[0003] Multi-junction vertical cavity surface emitting lasers (VCSELs) are becoming increasingly popular in automotive lidars, but traditional VCSELs generally have a divergence angle of 20° to 30°, which is quite large for most medium- and long-range scanning lidars (LiDARs).

[0004] The traditional method for reducing the divergence angle of a VCSEL beam is to extend the cavity length by using a cavity extension layer, thereby reducing the effective refractive index contrast between the inside and outside of the VCSEL's optical aperture and suppressing the generation of high-order transverse modes. However, increasing the VCSEL cavity length also reduces the spacing of the laser longitudinal modes, resulting in the emergence of multiple longitudinal modes in the VCSEL's emission spectrum, i.e., multiple spectral peaks. In addition to the designed lasing wavelength, these multiple spectral peaks may also include other undesirable spectral peaks that appear on one or both sides of the designed lasing wavelength. These undesirable spectral peaks are generally referred to as side modes. The emergence of side modes can lead to potential problems, such as the inability of the LiDAR receiver to recognize these side modes, resulting in reduced efficiency and crosstalk. Other methods for reducing the divergence angle include the use of high-contrast gratings (HCGs), slow-light optical amplifiers, microlens integration, or various types of current confinement, such as ion implantation and buried tunnel junctions. However, each of these methods has its own challenges, such as manufacturing complexity, high cost, low power density, and difficulty in achieving a uniform emission pattern.

[0005] Summary of the Invention

[0006] The embodiments of the present application provide an anti-reflection vertical cavity surface emitting laser and chip, which can greatly reduce the divergence angle, increase the brightness and spectral brightness, while maintaining single longitudinal mode lasing and avoiding the problems of complex manufacturing, high cost and low power density.

[0007] The embodiment of the present application provides an anti-reflection type vertical cavity surface emitting laser, comprising: a lower Bragg reflector; an active region located on one side of the lower Bragg reflector, the active region comprising at least five active layers and a tunnel junction located between the active layers; a current confinement layer provided in the active region or near the outside of the active region; an upper Bragg reflector located on a side of the active region away from the lower Bragg reflector; an optical anti-reflection storage cavity located at at least one location between the lower Bragg reflector and the active region and between the upper Bragg reflector and the active region; the optical anti-reflection storage cavity is configured to increase the peak value of the light field intensity to a value higher than the peak value of the light field intensity of the active region and to store light field energy; wherein the anti-reflection type vertical cavity surface emitting laser is provided with an injection current density greater than 10 kA / cm 2 , slope efficiency greater than 4W / A, and far-field divergence angle less than or equal to 19°.

[0008] An embodiment of the present application provides an anti-reflection vertical cavity surface emitting laser chip, comprising at least one laser array; the laser array comprises a plurality of anti-reflection vertical cavity surface emitting lasers as described in any embodiment of the present application; the laser array is a regularly arranged array, or a randomly arranged array, or an array with multiple addressable sub-arrays. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG1 is a schematic structural diagram of an anti-reflection type vertical cavity surface emitting laser provided in an embodiment of the present application;

[0010] FIG2 is a schematic structural diagram of a vertical cavity surface emitting laser with an extended cavity layer provided in the related art;

[0011] FIG3 is a far-field diagram of the laser array composed of the structure shown in FIG2 at a distance of 50 mm;

[0012] FIG4 is a light field intensity distribution diagram and a refractive index distribution diagram of the structure shown in FIG2 ;

[0013] FIG5 is a comparison diagram of the array laser spectrum and the FP longitudinal mode reflection spectrum of the laser array composed of the structure shown in FIG2 at different temperatures;

[0014] FIG6 is a schematic structural diagram of another anti-reflection type vertical cavity surface emitting laser provided in an embodiment of the present application;

[0015] FIG7 is a far-field diagram of the laser array composed of the structure shown in FIG6 at a distance of 50 mm;

[0016] FIG8 is a light field intensity distribution diagram and a refractive index distribution diagram of the structure shown in FIG6;

[0017] FIG9 is a comparison diagram of the array laser spectrum and the FP longitudinal mode reflection spectrum of the laser array composed of the structure shown in FIG6 at different temperatures;

[0018] FIG10 is a comparison diagram of light intensity changes of a vertical cavity surface emitting laser in the related art and an anti-reflection type vertical cavity surface emitting laser in an embodiment of the present application;

[0019] 11 to 15 are schematic diagrams illustrating the construction principle of an electric field distribution in an anti-reflection vertical cavity surface emitting laser according to an embodiment of the present application;

[0020] FIG. 16 is a graph showing the average M of a laser array composed of the structure shown in FIG. 6 and a laser array composed of the structure shown in FIG. 2 provided in an embodiment of the present application. 2 The relationship curve between the factor and the injected current, and the comparison diagram of the array near-field image and the array far-field image;

[0021] FIG17 is a comparison diagram of various photoelectric characteristics of the laser array having the structure shown in FIG6 and various laser arrays in related arts;

[0022] FIG18 is a diagram showing the light field intensity distribution and refractive index distribution in another anti-reflection vertical cavity surface emitting laser provided in an embodiment of the present application;

[0023] FIG19 is a diagram showing the relationship between a divergence angle and a light confinement factor of an oxide layer provided in an embodiment of the present application;

[0024] FIG20 is a diagram showing the relationship between the divergence angle and the effective cavity length provided in an embodiment of the present application;

[0025] FIG21 is a diagram showing the relationship between the brightness, spectral width, and spectral brightness of a laser array and the light confinement factor of an oxide layer, respectively, provided in an embodiment of the present application;

[0026] FIG22 is an average M of an AR-VCSEL array with different optical apertures provided in an embodiment of the present application. 2 The relationship between the factor and the current density;

[0027] FIG23 is a laser spectrum diagram of an AR-VCSEL with a 7-micron optical aperture at different output powers provided in an embodiment of the present application;

[0028] FIG24 is a comparison of near-field and far-field measured images of an AR-VCSEL with a 7-micron optical aperture at different output powers provided by an embodiment of the present application;

[0029] FIG25 is a comparison chart of brightness and power per unit effective area of ​​an AR-VCSEL provided in an embodiment of the present application and other types of semiconductor lasers used in lidar applications;

[0030] FIG26 is a comparison chart of spectral brightness and power per unit effective area of ​​an AR-VCSEL provided in an embodiment of the present application and other types of semiconductor lasers used in lidar applications;

[0031] FIG27 is a schematic structural diagram of a square laser array composed of four square AR-VCSELs provided in an embodiment of the present application;

[0032] FIG28 is a schematic diagram of a far-field image of the structure shown in FIG27 measured at an injection current of 5.5 A;

[0033] FIG29 is a graph of laser spectra measured when the structure shown in FIG27 is injected with an injection current of 5.5 A at different temperatures;

[0034] FIG30 is a graph showing various photoelectric characteristics of the structure shown in FIG27;

[0035] FIG31 is a schematic structural diagram of a hexagonal laser array composed of 37 hexagonal AR-VCSELs provided in an embodiment of the present application;

[0036] FIG32 is a schematic diagram of a far-field image of the structure shown in FIG31 measured at an injection current of 10 A;

[0037] FIG33 is a laser spectrum diagram of the structure shown in FIG31 measured at different temperatures when an injection current of 10 A is injected;

[0038] FIG34 is a graph showing various photocurrent characteristics of the structure shown in FIG31;

[0039] FIG35 is a diagram comparing the optoelectronic characteristics of various AR-VCSEL arrays provided in embodiments of the present application and various high-power laser arrays provided in related arts;

[0040] FIG36 is a schematic diagram of a free-space lens arrangement for single-emission laser spectrum measurement according to an embodiment of the present application;

[0041] FIG37 is a schematic structural diagram of a driving circuit of a light source provided in an embodiment of the present application. DETAILED DESCRIPTION

[0042] The following will describe the technical solutions in the embodiments of this application in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0043] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units listed, but may include other steps or units that are not listed or inherent to these processes, methods, products or devices.

[0044] As mentioned in the background art, the compactness, fast response and high energy conversion efficiency of VCSEL arrays make them the main light source for high-speed data communication and sensing. LiDAR systems equipped with VCSEL array solid-state light sources have been commercialized on self-driving cars. There are many performance indicators for high-resolution LiDAR light sources, such as power, power density, divergence angle, beam quality, beam parameter product, spectral width, brightness, spectral brightness, wavelength, temperature stability, pulse width, energy conversion efficiency, switching speed, module size and power per effective area. The brightness defined in formula (1), that is, the power density per unit solid angle ΔΩ (in steradian, sr), combines the first five indicators. In equation (1), Brighteness is brightness, Power density is power density, ΔΩ is solid angle, and A is the luminous area.

[0045] The spectral brightness is defined as

[0046] In formula (2), Spectral Brightness is the spectral brightness, Δλ is the spectral width, and the first six indicators are integrated.

[0047] Brightness is particularly important for LiDAR systems that utilize a scanning collimated laser beam. Higher brightness allows scanning LiDAR systems to detect longer distances and achieve higher angular resolution. On the receiving end, a narrow bandpass filter is often placed in front of the detector to achieve a high signal-to-noise ratio (SNR), thereby enabling longer detection range. System SNR is inversely proportional to the filter bandwidth; smaller filter bandwidths result in higher SNR. Traditionally, filter bandwidths cover the entire laser source wavelength offset range of -40°C to 125°C, as required by the Automotive Electronics Council standard. However, if the filter's wavelength offset temperature coefficient can be closely matched to the laser source, the filter bandwidth can be significantly narrowed. Furthermore, if the filter's angular wavelength offset can be minimized to negligible levels, the filter bandwidth can even approach the laser spectral width itself. In this scenario, spectral brightness becomes even more crucial in evaluating the laser source's ultimate ability to achieve a high SNR.

[0048] For array laser sources, the emitting area A is defined as the area of ​​the smallest circle or rectangle that surrounds all emitters. The solid angle can be expressed as Where θ is the divergence half-angle, which can be approximated as sinθ≈θ when θ is very small. The denominator AΔΩ (optical etendue, also known as the etendue) in equation (1) is conserved when the beam passes through any ideal collimating lens system. It will only increase if any optical device is not ideal during the propagation process. Similarly, the power can only be maintained or reduced due to any optical loss during the propagation process. As a result, the brightness and spectral brightness can only remain unchanged in a lossless ideal lens system, otherwise they will decrease. Therefore, in addition to improving the optical devices and increasing the laser emission power, reducing the etendue of the original laser beam from the bare chip is crucial to achieving high brightness and high spectral brightness of distant objects.

[0049] There has long been a debate between edge-emitting lasers (EELs) and VCSELs regarding the choice of light source for LiDAR. EELs were introduced to LiDAR applications earlier than VCSELs because a single EEL typically produces much higher power than a single-emitter VCSEL. However, preference has recently shifted toward VCSELs. Compared to high-power Fabry–Perot (FP) EELs, VCSELs offer a narrower spectral bandwidth (<2 nm) and better wavelength stability over temperature (0.06–0.07 nm / °C). Over a wide temperature range of -40–125°C, VCSEL wavelength drifts only 12 nm, allowing for very narrow filter bandwidths even without filters designed to match their wavelength drift. Some LiDAR filters can be specifically designed to match the VCSEL's wavelength temperature drift coefficient of 0.06–0.07 nm / °C. However, achieving a filter temperature drift coefficient as large as the 0.2–0.3 nm / °C of FP EELs is practically difficult, if not impossible. On the other hand, EELs with improved wavelength stability (such as distributed feedback (DFB) lasers and distributed Bragg reflector (DBR) lasers) require carefully designed Bragg gratings and additional manufacturing processes, such as electron beam lithography. Furthermore, VCSELs can produce excellent circularly symmetric beams, while EEL beam profiles are asymmetric. Finally, the inherent two-dimensional array manufacturability gives VCSELs unparalleled advantages in two-dimensional (2D) point cloud generation and chip-level optical integration, without the need for complex optics or complex packaging. Due to these advantages, many LiDAR manufacturers are adopting VCSEL arrays as their light sources. However, compared to EELs, traditional VCSEL array designs still require higher power density, smaller divergence angles, and higher spectral brightness to compete in LiDAR light sources.

[0050] There are several ways to increase VCSEL power density to 1000W / mm 2This is comparable to the power density of high-power EEL arrays. First, medium- and long-range LiDAR uses short nanosecond pulses and operates at a low duty cycle, resulting in relatively low average power. This prevents overheating of the laser chip, allowing for increased peak power. Furthermore, VCSELs can utilize tandem or multi-junction structures. By vertically connecting several PN junctions with a tunnel junction without increasing the emitting area, a slope efficiency (SE, measured in W / A) proportional to the number of PN junctions can be achieved, significantly increasing power density. From an energy-saving perspective, for a fixed required optical power output, the tandem structure effectively reduces input current by increasing the input voltage (not a problem for automotive applications, although more limited for consumer electronics). Lower current generates less waste heat from parasitic series resistance in the driver circuit, thereby improving system energy conversion efficiency. Leading VCSEL companies are now mass-producing 5- to 7-junction VCSELs and are developing additional junctions. In addition to multi-junction structures, VCSEL power density can be further improved by increasing the effective emitting area (fill factor) of the entire VCSEL array area and, if device lifetime permits, increasing the operating current.

[0051] EELs can also use multi-junction structures. However, their power density is limited by the necessary separation of the optical modes of each junction, because the tunnel junction must be placed at the optical field minimum between the optical modes to avoid losses due to absorption of the optical field energy. In addition, there are potential reliability issues such as catastrophic optical damage (COD), for example, if the spacing of the PN junctions is too close. Typically, the junctions in EELs are separated by up to several microns, appearing as separate emitters in near-field imaging. Therefore, applying multiple junctions in EELs will not increase their power density.

[0052] Since the power density of VCSELs is already sufficient to meet the needs of LiDAR, there is an urgent need to reduce their beam divergence to achieve higher brightness. Because lower beam divergence is usually accompanied by fewer high-order modes and a narrower spectral width, its impact on spectral brightness is doubled. The full divergence angle in D86 is defined as the angle through which the D86 beam width extends in the far field, where the D86 beam width is defined as the diameter of a circle centered at the center of mass of the beam profile and containing 86% of the light field energy. The D86 full divergence angle of oxide-layer (current confinement layer)-based VCSELs is generally 20° to 30°, which is quite large for most medium- and long-range (>100 meters) scanning LiDARs. Due to stronger lateral optical confinement, multi-junction VCSELs with multiple oxide layers for current confinement may have a larger divergence angle than single-junction VCSELs.

[0053] Reducing the number of oxide layers in a multi-junction VCSEL can result in a loss of power conversion efficiency (PCE); otherwise, additional current limiting, such as ion implantation, is required. The traditional approach to reducing the VCSEL beam divergence while maintaining efficiency is to extend the length of the cavity using cavity extension layers, thereby reducing the effective refractive index contrast (Δn) between the inside and outside of the VCSEL's optical aperture. This reduced refractive index contrast suppresses the generation of high-order transverse modes. Therefore, the cavity extension layer effectively acts as a high-order mode suppressor or "low-pass" mode filter. In filtering out low-quality beams (larger M 2 After the high-order mode beam (with a large divergence factor and a large divergence angle), the low-order mode beam with a smaller divergence angle will dominate the laser mode. Other methods to reduce the divergence angle include using high-contrast gratings (HCGs), using slow-light optical amplifiers, microlens integration, or using different types of current confinement, such as ion implantation and buried tunnel junctions. However, most of these methods have their own challenges, such as complex manufacturing, high cost, low power density, and difficulty in achieving a uniform emission pattern.

[0054] However, increasing the cavity length will cause new problems. After the cavity length is increased, the spacing of the longitudinal modes of the laser will also decrease, and the emission spectrum of the VCSEL will show multiple longitudinal modes, that is, multiple spectral peaks. Among these multiple spectral peaks, in addition to the designed lasing wavelength, there are other undesirable spectral peaks that appear on one or both sides of the designed lasing wavelength. These undesirable spectral peaks are usually called side modes. The appearance of side modes will lead to some potential problems, such as increasing the temperature drift coefficient of the light source and reducing the temperature stability; for example, the receiving end of the three-dimensional sensor and the lidar cannot recognize these side modes, resulting in reduced efficiency and crosstalk, etc.

[0055] The embodiment of the present application provides an anti-reflection type vertical cavity surface emitting laser (AR-VCSEL). FIG1 is a schematic structural diagram of an anti-reflection type vertical cavity surface emitting laser provided in the embodiment of the present application. Referring to FIG1 , the anti-reflection type vertical cavity surface emitting laser includes: a lower Bragg reflector 10; an active region 30 located on one side of the lower Bragg reflector 10, the active region 30 including at least five active layers 310 and tunnel junctions 330 located between the active layers 310; a current confinement layer 320 is provided in the active region 30 or near the outside of the active region 30; an upper Bragg reflector 2 0, located on the side of the active area 30 away from the lower Bragg reflector 10; the light anti-reflection storage cavity 40, located at at least one of between the lower Bragg reflector 10 and the active area 30 and between the upper Bragg reflector 20 and the active area 30; the light anti-reflection storage cavity 40 is configured to increase the peak value of the light field intensity to be higher than the peak value of the light field intensity of the active area 30, and to store light field energy; wherein, the anti-reflection vertical cavity surface emitting laser operates under the conditions of an injected current density greater than 10kA / cm2, a slope efficiency greater than 4W / A, and a far-field divergence angle (D86 full angle) less than or equal to 19°.

[0056] The anti-reflection vertical cavity surface emitting laser provided in the embodiments of the present application operates under conditions of an injected current density greater than 10 kA / cm2, a slope efficiency greater than 4 W / A, and a far-field divergence angle D86 full angle less than or equal to 19°. An anti-reflection storage cavity is provided at least one location between the multi-junction active region and the lower Bragg reflector layer and between the multi-junction active region and the upper Bragg reflector layer. The anti-reflection storage cavity can increase the peak light field intensity to a value higher than the peak light field intensity of the multi-junction active region and store light field energy, so that the light field intensity of the light-transmitting storage cavity is higher than the light field intensity of the multi-junction active region, thereby reducing the effective refractive index difference inside and outside the VCSEL light-emitting aperture, suppressing the generation of high-order modes, and reducing the divergence angle. At the same time, by increasing the light field intensity inside the anti-reflection storage cavity, the increase in cavity length can be reduced compared to the method of increasing cavity length in the related art, thereby improving the problem of multiple longitudinal modes in the emission spectrum of the VCSEL, thereby greatly reducing the divergence angle while maintaining single longitudinal mode lasing. In addition, there is no need to use high contrast grating (HCG), slow light optical amplifier, micro lens integration or different types of current limitation, thus avoiding problems such as complex manufacturing, high cost and low power density. The active region includes at least 5 active layers, and the laser is injected with a current density greater than 10kA / cm 2 , working under the working state of slope efficiency greater than 4W / A, the brightness and spectral brightness can be increased.

[0057] For a fair comparison, the embodiments of this application respectively tested the far-field divergence angle, light field distribution within the laser, and spectrum at different temperatures of a VCSEL array in the related art, as well as the far-field divergence angle, light field distribution within the laser, and spectrum at different temperatures of an AR-VCSEL array provided in the embodiments of this method. Each array consists of 37 lasers, with the distance between adjacent lasers being approximately 40 μm, and the optical aperture (aperture of the light-emitting hole) of each laser being 22 μm, forming a hexagonal light-emitting area of ​​approximately 250 μm in size (the array arrangement diagram can be referred to Figure 31).

[0058] Figure 2 is a schematic diagram of the structure of a vertical cavity surface emitting laser with an extended cavity layer, as provided in the related art. Each VCSEL in the VCSEL array is an extended cavity type VCSEL as shown in Figure 2. Referring to Figure 2, the extended cavity type VCSEL comprises an upper Bragg reflector layer 2, an active region 3 comprising a 6-junction active layer, an extended cavity layer 4, and a lower Bragg reflector layer 1. The active layer includes a quantum well 01, with tunnel junctions 02 disposed between adjacent active layers; and a current confinement layer 03 is disposed within each active layer. Figure 3 is a far-field image of the laser array comprising the structure shown in Figure 2 at a distance of 50 mm. Referring to Figure 3, the far-field divergence angle of the VCSEL array in the related art was measured to be 18.5°. Figure 4 is a light field intensity distribution diagram and a refractive index distribution diagram of the structure shown in Figure 2. Referring to Figure 4, the refractive index distribution and electric field intensity distribution along the vertical axis after the output level is normalized (the epitaxial direction is from left to right) are shown. The electric field intensity distributed in the entire active area 3 and the electric field intensity of the extension cavity layer 4 are relatively uniform, and the difference between the peak value of the electric field intensity distributed in the entire active area 3 and the peak value of the electric field intensity of the extension cavity layer 4 is small. The laser wavelength is designed to be 905mm. The extension cavity layer 4 acts as a high-order mode filter because it suppresses the generation of high-order transverse modes, reducing the divergence angle from the range of 20° to 30° to 18.5°. The reasons are analyzed as follows:

[0059] In a VCSEL, a current confining layer 03 is provided within or near the outside of the active region 3. The current confining layer 03 comprises an oxide layer; the oxide layer is epitaxially grown AlGaAs with a high Al content, with the oxidized region outside forming an insulating aluminum oxide film layer; wherein, the unoxidized region forms the light-emitting region for effective current injection, i.e., the light-emitting hole of the laser. The refractive index of the AlGaAs in the middle of the current confining layer 03 is different from that of the aluminum oxide on the outside. This results in a difference in the effective refractive index inside and outside the VCSEL light-emitting hole. The effective refractive index is determined based on the following formula:

[0060] Among them, n eff is the effective refractive index, n(z) is the refractive index in the z-axis direction, E 2(z) is the intensity of the light field in the z-axis direction (i.e., the direction of light emission). The integration range is the range of the light field in the laser.

[0061] The effective refractive index difference between the inside and outside of the VCSEL light-emitting hole is determined based on the following formula:

[0062] Among them, Δn eff is the effective refractive index difference between the inside and outside of the light-emitting hole, n 1_eff is the effective refractive index of the area where the light hole is located, n 2_eff is the effective refractive index outside the light-emitting hole, n1 is the material with high aluminum content (such as Al 0.98 Ga 0.02 As) refractive index, n2 is the refractive index of aluminum oxide. Γ ox is the light confinement factor of the oxide layer, determined based on the following formula:

[0063] Wherein, l is the thickness of the current confinement layer 320 in the z-axis direction, and p is the thickness of the entire optical field in the z-axis direction.

[0064] According to the step-index waveguide theory, linearly polarized (LP) lateral modes exist in the radially symmetric refractive index profile of weak refractive index guidance, which is applicable to the case of oxide-confined VCSELs. The beam quality of each LP mode depends on the mode order. The lowest-order mode, the so-called fundamental mode, has the highest beam quality, or the lowest M 2 Factor (M 2 =1), so once the mode is coupled from the waveguide to free space, the divergence angle is minimum. The higher the mode order, the 2 The higher the factor (M 2 >1), the larger the divergence angle. The number and order of allowed LP modes depends largely on the effective refractive index contrast between the core and cladding regions of the refractive index profile, which correspond to the inside and outside of the VCSEL light-emitting aperture. By minimizing Γ ox and Δn eff , reducing the number of allowed LP modes, resulting in a smaller divergence angle. Increasing the cavity length (setting the cavity extension layer 4), placing oxide layers at the nodes of the standing wave electron field, and reducing the number and thickness of oxide layers can help minimize Γ. ox and Δn eff .

[0065] However, longer cavity lengths also introduce new risks. The main issue is that the longitudinal mode spacing or free spectral range (FSR) decreases with the effective cavity length L. effThe FSR decreases with increasing latitudinal power, hindering the operation of a single longitudinal mode. In addition to the desired lasing mode, the VCSEL's emission spectrum also displays multiple lasing wavelengths, appearing on one or both sides of the designed lasing wavelength. Figure 5 compares the array laser spectrum and the reflection spectrum of the FP longitudinal mode at different temperatures for a laser array composed of the structure shown in Figure 2. The left panel of Figure 5 shows the reflection spectrum of the entire VCSEL structure in Figure 2 (black solid line), showing the FP longitudinal mode, and the photoluminescence spectrum (grey dashed line) measured from the active region to align with the central FP tilt angle for illustrative purposes. The FSR is narrow to ~7.5nm. The full width at half maximum (FWHM) of the photoluminescence (PL) spectrum measured from the active region 3 is approximately 20nm, which is greater than the mode spacing. If the two longitudinal modes are overlapped by the emission spectrum of the active region 3 and are within the stopband of the top DBR (upper Bragg reflector) and the bottom DBR (lower Bragg reflector), they emit lasers simultaneously. Referring to the right figure in FIG5 , the array laser spectra at different temperatures (from 25° C. to 125° C.) were detected, and both showed two longitudinal laser modes.

[0066] As shown in Figure 3, although Γ ox The divergence angle of this laser array is only 0.131%, but it is 18.5° (D86 full angle). However, for most applications, multi-longitudinal mode lasing (as shown in the right figure in Figure 5) is unacceptable because it may cause potential problems such as temperature instability and efficiency loss of the receiving filter. Although this multi-wavelength lasing can be corrected to a certain extent by reducing the stopband width of the top DBR (upper Bragg reflector layer 2) and reducing the refractive index contrast, it is limited by stress caused by epitaxial thickness, wafer bending, and subsequent manufacturing difficulties. For single-longitudinal mode oxide VCSELs with more than 5-junction active layers, it is difficult to achieve a D86 full angle of less than 16°. Better low-divergence designs are needed to more efficiently utilize the cavity length.

[0067] FIG6 is a schematic structural diagram of another anti-reflection vertical cavity surface emitting laser provided in an embodiment of the present application. Referring to FIG6 , each AR-VCSEL in the AR-VCSEL array is an anti-reflection vertical cavity surface emitting laser as shown in FIG6 . Referring to FIG6 , the anti-reflection vertical cavity surface emitting laser comprises an upper Bragg reflector 20, an active region 30 including a 6-junction active layer 310, an optical anti-reflection storage cavity 40, and a lower Bragg reflector 10. Tunnel junctions 330 are provided between adjacent active layers. A current confining layer 320 is provided within each active layer 310. The anti-reflection storage cavity 40 comprises an anti-reflection layer 41 and a light storage layer 42. The anti-reflection layer 41 is located between the light storage layer 42 and the active region 30. The anti-reflection layer 41 is configured to increase the peak optical field intensity of the light storage layer 42 to a value higher than that of the active region 30. The light storage layer 42 is configured to store optical field energy. FIG7 is a far-field diagram of the laser array composed of the structure shown in FIG6 at a distance of 50 mm. Referring to FIG7 , the far-field divergence angle of the AR-VCSEL array is measured to be 9.7°.

[0068] Along the direction from the active region 30 toward the optical anti-reflection storage cavity 40, the anti-reflection layer 41 includes a first anti-reflection interface located at the interface from low refractive index to high refractive index between the light storage layer 42 and the active region 30, and / or a second anti-reflection interface located at the interface from high refractive index to low refractive index between the light storage layer 42 and the active region 30. The optical path distance between the first anti-reflection interface and the nearest antinode of the standing wave light field is less than one-tenth of the lasing wavelength; and the optical path distance between the second anti-reflection interface and the nearest node of the standing wave light field is less than one-tenth of the lasing wavelength. FIG8 is a light field intensity distribution diagram and a refractive index distribution diagram of the structure shown in FIG6. Referring to FIG8, the anti-reflection layer 41 is formed by multiple layers of film with a thickness of one-quarter wavelength, which can be made of n-doped AlGaAs (can be called anti-reflection sublayers), with high and low aluminum content alternatingly arranged. The light storage layer 42 can be a 2-micron thick film made of AlGaAs. The thickness of the light storage layer is an odd multiple of half the lasing wavelength. Figure 8 exemplarily illustrates that the anti-reflection layer 41 includes a first anti-reflection interface and a second anti-reflection interface, which are arranged in a sequentially intersecting manner. Multiple anti-reflection interfaces are provided between the active region 30 and the light storage layer 42, gradually increasing the electric field strength from the active region 30 to the light storage layer 42.

[0069] In the embodiment of the present application, the cavity is not simply expanded on one side of the active region 30, but an anti-reflection layer 41 is added to extract light from the active region 30 and store it in the light storage layer 42, which acts like an optical dam and can accommodate photons to increase the intensity of the light field. This makes the total electric field energy in the light storage layer 42 several times that of an ordinary extended cavity layer with the same spatial volume. Optionally, the peak electric field intensities of different active layers are the same or different; the maximum peak electric field intensity in the active region is less than the maximum peak electric field intensity in the light anti-reflection storage cavity. As shown in Figure 8, when the two output levels are normalized to unity, the peak electric field intensity inside the light storage layer 42 is approximately three times the peak electric field intensity of the active region 30, and approximately four to five times the peak electric field intensity of the extended cavity layer 4 in Figure 4. FIG9 is a comparison of the array laser spectrum and the FP longitudinal mode reflection spectrum of the laser array composed of the structure shown in FIG6 at different temperatures. Referring to FIG9, the strong electric field strength inside the optical reservoir layer reduces the dependence of the divergence angle on the length of the extended cavity layer. Therefore, while maintaining a large FSR of about 16nm (left figure in FIG9), only a medium length optical reservoir layer 42 is required to achieve a smaller divergence angle, Γ ox A decrease of 0.027% was achieved while maintaining a single longitudinal mode (right graph in FIG9 ).

[0070] FIG10 is a graph comparing the intensity changes of a VCSEL in the related art and an anti-reflection VCSEL in an embodiment of the present invention. Referring to FIG10 , the electric field intensity at the interface between the active region and lower Bragg reflector in a conventional VCSEL structure (left figure in FIG10 ) is compared with the electric field intensity at the interface between the active region and anti-reflection layer in an AR-VCSEL structure (right figure in FIG10 ). In the anti-reflection layer, a quarter-wavelength spacer is provided on the side of the active region 30, causing the electric field antinode to shift from the initial refractive index decreasing interface in the left figure in FIG10 to the refractive index increasing interface in the right figure in FIG10 , along the direction from the active region 30 to the lower Bragg reflector 10. In other words, the anti-reflection layer 41 is composed of several pairs of layers similar to the lower Bragg reflector 10, but with a special π / 2 (quarter-wavelength) phase shift. Photons generated from the active region 30 and propagating toward the lower Bragg reflector 10 constructively interfere at each anti-reflection sub-layer and reach increasingly higher intensities until stabilizing at the light storage layer 42. It should be noted that in the AR-VCSEL structure of FIG10 , the anti-reflection layer 41 is located between the lower Bragg reflector 10 and the active region 30.

[0071] Figures 11 to 15 are schematic diagrams of the construction principle of the electric field distribution in an anti-reflection vertical cavity surface emitting laser provided in an embodiment of the present application. Referring to Figures 11 to 15, it is explained how the electric field is established in the AR-VCSEL. Referring to Figure 11, a simple 0.5λ cavity VCSEL with N-DBR and P-DBR is first represented by a standing wave electric field intensity and refractive index distribution diagram. The N-DBR includes a plurality of reflectors with an optical thickness of one-quarter the laser wavelength, and the plurality of reflectors are arranged alternately according to high and low refractive indices; the P-DBR includes a plurality of reflectors with an optical thickness of one-quarter the laser wavelength, and the plurality of reflectors are arranged alternately according to high and low refractive indices. Compared with the electric field at both ends of the structure (the electric field intensity at both ends of the structure is set to 1), the relative electric field intensity (>50) inside the 0.5λ cavity is very high. Referring to Figure 12, the cavity length is then extended from 0.5λ to 10.5λ. It should be noted that any cavity length of (1 / 2+m / 2)λ (m is a positive integer) will not interfere with the electric field distribution in the DBR. Referring to Figure 13, the thickness of one of the reflectors in the P-DBR is extended from 1 / 4λ to 3 / 4λ. It should be noted that the thickness of the DBR can be (1 / 4+m / 2)λ, where m is a positive integer, without affecting the electric field intensity anywhere else. Adding an additional spacing of (m / 2)λ within the DBR will not create another resonant cavity. Referring to Figure 14, the thickness of the 3 / 4λ layer in the P-DBR is extended to 11 3 / 4λ, the electric field intensity distribution in other places remains unchanged. 3 The / 4λ layer is replaced by the active region, which has 11 3 The optical thickness is 1 / 4λ. By placing multiple quantum wells at the antinodes of the standing electric field wave and the tunnel junction and oxide layer at the nodes, the electric field distribution is maximized. No additional cavities are added in this process. The initial 10.5λ cavity serves as the light storage layer.

[0072] The unique design provided by the embodiment of the present application converts a long cavity extension into a shorter extension, but with a stronger electric field. Such an antireflection storage cavity 40 can more effectively store photons within a unit cavity length, thereby more effectively reducing Γ ox The photons stored in the light storage layer have almost no sense of lateral confinement and are essentially "free" in the lateral direction, which significantly reduces the overall divergence angle. In some embodiments of the present application, the light confinement factor Γ of the oxide layer is ox Less than 0.16%.

[0073] FIG. 16 is a graph showing the average M of a laser array composed of the structure shown in FIG. 6 and a laser array composed of the structure shown in FIG. 2 provided in an embodiment of the present application. 2The relationship curve between the factor and the injection current, the comparison diagram of the array near-field image and the array far-field image, refer to Figure 16, which shows the average M of the laser in the AR-VCSEL array. 2 The curve of the factor changing with the injection current and the average M of the laser in the extended cavity VCSEL array 2 The curve of the factor changing with the injection current, as well as the comparison of the near-field images (images e and b, and images f and c in Figure 16, respectively) and far-field images (images g and d in Figure 16, respectively) of the AR-VCSEL array and the extended cavity VCSEL array are shown. 2 The factor is proportional to the far-field divergence angle (FF), M 2 =πrθ / λ=πrΘ / (2λ), where Θ is the full angle in D86 and θ is the divergence half angle (Θ=2θ). The average M of AR-VCSEL and extended cavity VCSEL at different current injection levels is 2 In the AR-VCSEL near-field image (e.g., image f in Figure 16), the sparse spots indicate that there are fewer transverse modes, which is consistent with the reduced Γ ox The near-field image and far-field image are measured at a current of 10A. Assuming that the beam waist radius (r) is equal to the optical aperture radius, the average M of the array is calculated. 2 factor.

[0074] Figure 17 is a comparison of various optoelectronic characteristics of the laser array composed of the structure shown in Figure 6 and various laser arrays in related technologies. Referring to Figure 17, the performance of AR-VCSEL, extended cavity VCSEL, the most advanced commercial multi-junction VCSEL and the most advanced commercial multi-junction EEL laser radar in terms of brightness, spectral brightness and optical output power within a 10° field of view. In contrast, the AR-VCSEL provided in the embodiment of the present application has significantly improved performance in all three indicators. Under the same array size and layout, the power of AR-VCSEL within a 10° field of view (FOV) is more than twice that of the extended cavity VCSEL. Brightness increases from 12.5kW*mm -2 sr -l Increased to 38.5kW*mm -2 sr -l , increased threefold; spectral brightness from 12.2kW*nm -1 mm -2 sr -1 Increased to 75.6kW*nm -1 mm -2 sr -1, increased by more than six times. Although the external quantum efficiency is slightly reduced due to the increase in high-order mode losses (see Figure 35). Compared with the most advanced commercial multi-junction EEL lidar, the power of the AR-VCSEL provided in this application is more than doubled within a 10° FOV range. Although the brightness of the AR-VCSEL in this application is still lower than that of the most advanced EEL, the spectral brightness is more than doubled, which can improve the performance of medium and long-range lidars equipped with narrow bandwidth filters. Although the EEL can achieve similar spectral brightness at a higher current, its value is lower due to the lack of a narrow bandwidth filter that matches its large temperature coefficient of wavelength shift. It should be noted that the anti-reflection layer 41 and the light storage layer 42 are not necessarily separable.

[0075] In one embodiment of the present application, Figure 18 shows the optical field intensity distribution and refractive index distribution in another anti-reflection vertical cavity surface emitting laser (VCSEL) provided in this embodiment. Referring to Figure 18, the anti-reflection layer can be embedded within the light storage layer, integrating the anti-reflection layer and the light storage layer. The optical anti-reflection storage cavity 40 comprises: a plurality of first semiconductor material layers 401 and a plurality of second semiconductor material layers 402; the first semiconductor material layers 401 and the second semiconductor material layers 402 are arranged alternately; the first semiconductor material layers 401 and the second semiconductor material layers 402 are identical in number and optical thickness; the first semiconductor material layers 401 and the second semiconductor material layers 402 have different refractive indices; and the thickness of the optical anti-reflection storage cavity 40 is an integer multiple of half the lasing wavelength. Compared to the active region 30, the structure and phase can be flexible as long as the electric field intensity is enhanced. The key to this electric field profile engineering is to ensure the cumulative phase shift of the entire optical reservoir, that is, the optical distance between the active region 30 and the lower Bragg reflector 10 is an integer of half a wave. The light anti-reflection storage cavity 40 provided in the embodiment of the present application provides great potential for engineering and tailoring of the light intensity distribution in AR-VCSEL.

[0076] Note that the AR-VCSEL design differs from the dual-cavity design (active-passive cavity), which is primarily used for narrow-bandwidth applications. If used for low-divergence purposes, the significant drop in the electric field between the passive and active cavities is not only inefficient in reducing Γox, but also leads to an increase in the total cavity length and a reduction in the FSR. It also differs from a passive cavity surface-emitting laser, in which a thinner active layer 310 is inserted into the quarter-wavelength high-refractive-index layer of its top DBR (upper Bragg reflector 20), allowing the dielectric material to form a passive cavity for better temperature stability or mode control. The anti-reflection cavity in this paper is a monolithic cavity that combines the active region 30 and the passive region. The thickness of its multi-junction active region 30 is typically much greater than the total thickness of its top DBR. Furthermore, considering the loss mechanism of the anti-reflection cavity, the anti-reflection mirror or layer inside the light storage layer does not contribute to the loss of the external mirror and therefore cannot be considered as part of the top DBR.

[0077] Based on the above embodiments, placing an oxide layer (current limiting layer 320) at the node of the standing wave electron field and / or reducing the thickness of the oxide layer can help minimize Γ ox and Δn eff In one embodiment of the present application, the optical path distance between the current limiting layer 320 and the nearest zero-value position of the standing wave optical field is less than one-tenth of the lasing wavelength. The current limiting layer 320 is located at the zero-value position of the standing wave optical field. In order to ensure the current limiting effect of the current limiting layer 320, when the current limiting layer 320 is outside the active region 30, the current limiting layer 320 is arranged within a range of two wavelengths along a side perpendicular to the active layer 310. The number of current limiting layers 320 is less than or equal to the number of active layers 310 and less than or equal to the number of tunnel junctions 330 plus one.

[0078] And / or, the light-emitting hole of the AR-VCSEL is located in the unoxidized area of ​​the oxide layer, and the thickness of the oxidized portion of the oxide layer near the outer edge of the optical hole is set to be less than 30nm to reduce the oxidation temperature. ox and Δn eff The thickness of the oxidized portion of the oxide layer near the outer edge of the optical hole is less than 20 nm; the thickness of the oxidized portion of the oxide layer near the outer edge of the optical hole is less than 15 nm.

[0079] Based on the aforementioned embodiments, an anti-reflection vertical cavity surface emitting laser (VCSEL) includes, in order, a dielectric layer, an electrical contact layer, a lateral current diffusion layer, a p-type upper Bragg reflector layer, an active region with an oxide layer, an optical anti-reflection storage cavity, an n-type lower Bragg reflector layer, and a substrate. Referring to Figure 1 , the active layer 310 comprises a PIN structure, comprising at least one quantum well 302. The active layers 310 are connected in series via tunnel junctions 330. It can be understood that each active layer 310 may include a quantum well 302 flanked by an N-type semiconductor layer 303 and a P-type semiconductor layer 301. Each active layer 310 has at most one current confinement layer 320, with the optical path distance between the tunnel junction 330 and the nearest node of the standing wave field being less than one-tenth of the lasing wavelength. Optionally, the tunnel junction 330 is located at a node of the standing wave field. Because the tunnel junction 330 is highly doped, this doping can cause optical absorption losses, reducing luminous efficiency. Therefore, placing it where the optical field is minimized can minimize optical losses. In the structure of the multi-layer active layer 310 , only one current confining layer 320 may be provided. The current confining layer 320 is located in the active layer 310 closest to the upper Bragg reflective layer 20 .

[0080] When the active layer 310 includes a single quantum well 302, the optical path distance between the quantum well 302 and the nearest peak position of the standing wave light field is less than one-fifth of the lasing wavelength. When the active layer 310 includes multiple quantum wells 302, the optical path distance between the center position of each quantum well and the nearest peak position of the standing wave light field is less than one-tenth of the lasing wavelength. Optionally, the center position of each quantum well is aligned with the peak of the electric field. Because quantum wells are where laser gain amplification occurs, aligning the center position of each quantum well with the position of the strongest light field can achieve a greater amplification effect.

[0081] The anti-reflection vertical cavity surface emitting laser further includes: an ion implantation layer; the ion implantation layer is located on a surface of the substrate on a side close to the n-type lower Bragg reflector layer, the ion implantation layer being configured to enhance electrical insulation between the substrate and the n-type lower Bragg reflector layer, or the ion implantation layer is located at the bottom of the oxidation trench, the ion implantation layer being configured to enhance electrical insulation between the bottom of the oxidation trench and the substrate; and a current confinement layer formed based on the sidewalls of the oxidation trench. The implanted ions include at least one of H ions, He ions, B ions, and O ions.

[0082] Based on the above embodiments, AR-VCSEL can achieve a low divergence angle while increasing the output optical power by increasing the number of junctions in the active layer 310. In order to expand the divergence angle range to meet different application purposes, this transmission embodiment designed and tested more than 50 different Γ oxThe AR-VCSEL and extended-cavity VCSEL structures were fabricated using the same 250μm array pattern. These designs included AR-VCSELs with 5, 6, 8, 10, and 14 junctions, as well as an extended-cavity VCSEL with 6 junctions. They were tested at room temperature, at a 20kHz repetition rate, under the same 3ns pulse drive conditions and with an injection current of 10A. The test results are shown in Figures 19 to 21 below.

[0083] FIG19 is a graph showing the relationship between the divergence angle and the light confinement factor of the oxide layer provided in an embodiment of the present application; As shown in FIG19 , the divergence angle and Γ ox There is a clear correlation between them. Almost all AR-VCSELs and extended cavity VCSELs, regardless of the number of junctions, follow the same trend line. The dotted trend line reveals an approximately linear relationship between the divergence angle and the oxidation confinement factor, and the divergence angle of the laser is positively correlated with the light confinement factor of the oxide layer. Through careful design, the AR-VCSEL provided in the embodiment of the present application achieves precise control of the divergence angle (D86) from 8° to 25°. According to the inventors' research, this is the first time that an ultra-small divergence angle (D86) of less than 10° has been achieved for a multi-junction VCSEL array under single longitudinal mode operation, simply by optimizing its epitaxial structure without using any type of lens, lateral grating or two-dimensional photonic crystal structure. The circular dots represent 46 measured data points of AR-VCSEL epitaxial designs, of which the solid dots represent the AR-VCSEL in Figure 6. The triangular dots represent 8 measured data points of extended cavity VCSEL designs, of which the solid represents the extended cavity VCSEL in Figure 2. The green, red, purple, brown, and blue circles represent 5J (7 designs), 6J (32 designs), 8J (3 designs), 10J (3 designs), and 14J (1 design) AR-VCSEL arrays, respectively.

[0084] FIG20 is a graph showing the relationship between the divergence angle and the effective cavity length provided by an embodiment of the present application. As shown in FIG20 , under the same cavity length, the AR-VCSEL array always exhibits a lower divergence angle. It is also worth noting that the divergence angle does not form a linear relationship with the effective cavity length, because for the same effective cavity length, Γ ox Can change.

[0085] FIG21 is a graph showing the relationship between the brightness, spectral width, and spectral brightness of a laser array provided in an embodiment of the present application and the light confinement factor of the oxide layer. The left graph in FIG21 shows the relationship between the brightness of the AR-VCSEL array and the extended cavity VCSEL array at 10A and the number of junctions of both arrays being 6 and Γ. ox The relationship curve between the spectrum width and Γ oxThe right figure in Figure 21 shows the relationship between the spectral brightness of the AR-VCSEL array and the extended cavity VCSEL array at 10A and the number of junctions of both arrays being 6 and Γ ox The relationship curve is shown. The same number of junctions was used between the AR-VCSEL array and the extended cavity VCSEL array to make a fair comparison. As shown in Figure 21, the brightness of the laser is negatively correlated with the light confinement factor of the oxide layer; the spectral brightness of the laser is negatively correlated with the light confinement factor of the oxide layer. Due to the full utilization of the emission area, the maximum brightness achieved by the embodiment of the present application with 6 junctions in an AR-VCSEL array with a size of 250 microns is about 40kw*mm -2 sr -1 The maximum brightness of a single laser is about 140kW*mm -2 sr -1 At 10A, the AR-VCSEL array achieves a spectral brightness of ~75.6kW*nm -1 mm -2 sr -l , a single laser is ~260kW*nm -1 mm -2 sr -l , similar to the EEL level of the most advanced LiDAR, which is typically 120kW*nm at high current -1 mm -2 sr -l , but it cannot be used without filter wavelength shift matching. For reference, the most advanced VCSEL array for lidar in the related art has a power of only ~12kW*nm -1 mm -2 sr -l Because the number of AR-VCSEL junctions can be increased, the light-emitting layer capacity can be greatly expanded, and the array emission size can be reduced, thereby increasing the spectral brightness and power of the AR-VCSEL by several times or even an order of magnitude. For example, in one embodiment of the present application, a power output of more than 100kW.mm has been achieved on a 6-junction AR-VCSEL array with a wavelength of 100μm. -2 sr -l In general, AR-VCSELs have the characteristics of high spectral brightness, high beam quality, and excellent temperature stability while maintaining the most cost-effective power per unit area.

[0086] In addition to changing the number of active layer junctions and the optical confinement factor Γ of the oxide layer oxIn one embodiment of the present application, another key parameter is also studied: the aperture value of the optical aperture (OA), that is, the aperture size of the light-emitting hole. Optionally, the aperture value ranges from 3μm to 22μm. Figure 22 shows the average M values ​​of an AR-VCSEL array with different optical apertures provided in an embodiment of the present application. 2 The relationship between the factor and the current density is shown in FIG22. Referring to FIG22, the embodiment of the present application provides a series of AR-VCSEL arrays with a size of 250 μm, each of which is densely populated with the same AR-VCSEL. The aperture values ​​of the optical aperture OA include 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm and 21 μm. All epitaxial structures are the same, such as the epitaxial structure shown in FIG6. Subsequently, their divergence angles are measured, and the average M in these arrays is calculated. 2 The results show that the aperture value of the optical aperture OA is related to the M 2 There is an obvious correlation between the values, as shown in Figure 22, with the decrease of the optical aperture OA, M 2 It is worth noting that when the aperture size is reduced to 7 μm, M 2 is close to 1, which indicates that the emitters in the AR-VCSEL array can operate in an almost single transverse mode lasing state.

[0087] In order to further study the 7um OA array sample and confirm the possibility of single-mode laser, the embodiment of the present application used a 100ns pulse driver for testing. The ability to better control the AR-VCSEL array at a lower current helps to determine the transition point between single-mode and multi-mode laser emission. Referring to Figure 36, the emission light of a specific emitter (AR-VCSEL) is coupled into the optical fiber (MM-Fibre) through the numerical aperture (NA) of the free-space lens (all other emitters in the laser array are completely optically blocked by silver paste). Figure 23 is a laser spectrum diagram of an AR-VCSEL with a 7-micron optical aperture at different output powers provided by an embodiment of the present application. Referring to Figure 23, the optical output powers include 35.4mW, 30.6mW, 28.4mW, 26.1mW, 18.3mW and 9.4mW. When the optical power is 28.4mW, the current is about 7.8mA (calculated by dividing the total array current by the number of emitters), and the current density is about 200A / mm 2The spectrum shows a side mode suppression ratio (SMSR) of nearly 40 dB for single-mode lasers. This confirms the achievement of high-power single-transverse-mode lasing in an AR-VCSEL array under 100 ns pulse conditions. The emitter's peak power reached 28.4 mW, exceeding the highest power of 14 mW reported for single-mode multi-junction VCSELs. Notably, the 7-micron optical aperture of an AR-VCSEL is much larger than that of conventional single-mode VCSELs without additional surface relief or complex structures, which typically have apertures of 3 to 4 microns.

[0088] In addition, Figure 24 is a comparison of the near-field and far-field measured images of an AR-VCSEL with a 7-micron optical aperture at different output powers provided by an embodiment of the present application. The embodiment of the present application also detects the near-field image (first row) and far-field image (second row) of the light emitted by the light-emitting hole. The light field is slightly elliptical, which may be caused by the imperfect circular shape of the light-emitting hole. When analyzing the side view of the far-field intensity, their shapes are very similar to Gaussian curves. For an AR-VCSEL with an optical aperture of 7μm for the light-emitting hole, its far-field divergence angle is 9.4°, which almost reaches the diffraction limit, which is a key feature of single-mode operation.

[0089] It must be acknowledged that at this stage, this application cannot conclusively confirm the coherence of the optical modes between continuous wave (as in most previous single-mode VCSEL work) and pulsed conditions (as in this work). This aspect requires further research in the future. In addition, it is important to note that in AR-VCSEL arrays, as well as in conventional VCSEL arrays, the light emitted by the individual emitters lacks coherence with each other. Therefore, even if each emitter operates in a single mode, the light field of the entire array cannot be considered a single mode. Instead, it represents the superposition of multiple single-mode light fields.

[0090] In one embodiment of the present application, the performance of the AR-VCSEL array is also compared with other semiconductor lasers used in lidar applications, for example, compared with a photonic crystal surface emitting laser (PCSEL) array. Due to its extremely high brightness, PCSEL arrays have recently been considered as a potential lidar light source. However, their low power density may limit such applications. Figure 25 is a comparison diagram of brightness and power per unit effective area of ​​an AR-VCSEL provided in an embodiment of the present application and other types of semiconductor lasers used in lidar applications. Figure 25 plots the relationship between brightness and power per unit area of ​​various semiconductor lasers. Figure 26 is a comparison diagram of spectral brightness and power per unit effective area of ​​an AR-VCSEL provided in an embodiment of the present application and other types of semiconductor lasers used in lidar applications. Figure 26 plots the relationship between spectral brightness and power per unit area of ​​various semiconductor lasers. In the competition for long-range lidar, the laser arrays in the lower right corner of Figures 25 and 26 (100um 18-junction AR-VCSEL array, 100um 6-junction AR-VCSEL array, 250um 14-junction AR-VCSEL array, 250um 6-junction AR-VCSEL array) will be favored. Figure 35 is a comparison of the optoelectronic characteristics of various AR-VCSEL arrays provided in the embodiments of the present application and various high-power laser arrays provided in the related art. Referring to Figure 35, the various AR-VCSEL arrays include a 250um 6-junction AR-VCSEL array, a 100um 6-junction AR-VCSEL array, and a 250um 14-junction AR-VCSEL array. The various high-power laser arrays provided in the related art include EEL arrays and PCSEL arrays. We examined and compared the optical power density versus current density, optical power versus input electrical power within a 10° field of view, total output power versus current, and external quantum efficiency versus current for AR-VCSEL arrays and other types of LiDAR semiconductor laser arrays. The power (current) density of the EEL was calculated by dividing the power (current) by the ridge area. The power density of all surface-emitting lasers was calculated by dividing the power by the total emitting area.

[0091] About divergence angle and brightness: For a 200m long-range scanning lidar, a collimated beam with a divergence angle of <0.03° is required to produce a spot size of 10cm. PCSEL provides a divergence angle of ~0.1°, which can significantly reduce the size of the collimating lens and can even eliminate the collimating lens at shorter distances or lower resolutions. In this sense, PCSEL has the advantage of smaller optical extension, allowing for a smaller spot size after collimation. However, when the laser spot size is smaller than the spatial resolution of the sensor, there is no additional benefit. For today's scanning lidars, 10~20kW*mm -2 sr -l The brightness is sufficient to match a sensor array with a pitch of 10 μm. The brightness range provided by the embodiment of the present application is 30 to 60 kW*mm -2 sr -l It may take several years to develop AR-VCSEL light sources that are sharp enough to match the next generation of sensor arrays with a pitch of ~6 μm, or 3 times the current pixel resolution.

[0092] In addition, Figure 27 is a schematic diagram of the structure of a square laser array composed of four square AR-VCSELs provided in an embodiment of the present application, Figure 28 is a schematic diagram of the far-field image of the structure shown in Figure 27 measured at an injection current of 5.5A, Figure 29 is a laser spectrum of the structure shown in Figure 27 measured at different temperatures (25°C, 50°C, 75°C, 100°C, 125°C) with an injection current of 5.5A, and Figure 30 is a graph of various photoelectric characteristic curves of the structure shown in Figure 27, including a curve of the relationship between the optical power and the current within the full angle of divergence, a curve of the relationship between the optical power and the current within a 10° divergence angle in the laser, a curve of the relationship between the power conversion efficiency and the current, a curve of the relationship between the optical power density and the current, a curve of the relationship between the brightness and the current, and a curve of the relationship between the spectral brightness and the current. Referring to Figures 27 to 30, the 100kW*mm of the 100μm-sized AR-VCSEL array provided in an embodiment of the present application -2 sr -l The brightness can meet the requirements of detector pixels below 5um. With the increase of the number of junctions, the reduction of the area, the reduction of the oxide layer and the enhancement of the light storage layer, the brightness of 200~1000kW*mm can be achieved. -2 sr -l AR-VCSEL arrays to match higher resolution sensor arrays.

[0093] Regarding power density or kilowatts per chip area: The biggest advantage of AR-VCSELs over PCSELs is power density. Chip area determines the number of chips that can be produced on a fixed-size semiconductor substrate, such as the 6-inch GaAs substrates widely used in VCSEL production. If the type of substrate, epitaxial thickness and number of regenerations, number and complexity of manufacturing layers, and on-wafer test time are all similar, then the production cost of the entire wafer will be similar. The unit cost of the chip produced is then proportional to the chip area. Therefore, in order to reduce costs, a smaller chip size is preferred to produce the same power. Although PCSELs can increase power density by sacrificing beam quality, the peak power density of PCSELs has been reported experimentally to be only ~60W / mm 2 AR-VCSEL and VCSEL can easily exceed 1000W / mm 2 (Figure 25) As shown in Figure 25, the 100um square 6-junction AR-VCSEL array provided in the embodiment of the present application can provide an optical power range of ~45W peak power and an optical power density range of ~4500W / mm 2 .

[0094] In addition, FIG31 is a schematic diagram of the structure of a hexagonal laser array composed of 37 hexagonal AR-VCSELs provided in an embodiment of the present application, FIG32 is a schematic diagram of the far-field image of the structure shown in FIG31 measured at an injection current of 10A, FIG33 is a laser spectrum of the structure shown in FIG31 measured at different temperatures (25°C, 65°C, 105°C, 125°C, etc.) with an injection current of 10A; FIG34 is a diagram of various photocurrent characteristic curves of the structure shown in FIG31, including the relationship curve between the optical power and the current within the full divergence angle, the relationship curve between the optical power and the current within the 10° divergence angle of the laser, the relationship curve between the power conversion efficiency and the current, the relationship curve between the optical power density and the current, the relationship curve between the brightness and the current, and the relationship curve between the spectral brightness and the current. Referring to FIG31 to FIG33, a 14-junction AR-VCSEL array with a size of 250um can generate a peak power of ~240W and a wavelength of ~5000W / mm 2 optical power density.

[0095] Based on these figures, it can be predicted that a 100μm square 18-junction AR-VCSEL array can reach 15,000W / mm 2Ignoring the expensive photolithography and regeneration processes of PCSELs, and considering only the semiconductor area used, AR-VCSELs produce the same optical power at a cost 10 to 100 times lower than PCSELs. The laser and sensor chip each account for 20 to 40% of the total cost of a lidar. With PCSEL technology, even if the cost of the transmitting lens (20% of the total lidar cost) is completely eliminated, the cost savings are far less than the (conservatively estimated) tenfold increase in total cost (2 to 4 times the total lidar cost) resulting from the larger chip area. In the market, to achieve the $100 bill of materials cost target for long-range primary lidars, the cost of the light source needs to be reduced by half. In such lidars, the total power of all light source chips is typically ~5 kilowatts. Therefore, $10 per kilowatt is a rough cost requirement for the laser chip. The AR-VCSEL, VCSEL, and even EEL markets can more or less meet this cost requirement, while PCSEL requires some revolutionary technology to increase its power density by 10 to 100 times to be competitive. Similar to PCSELs, wavelength- and temperature-stabilized DBR lasers can also achieve good brightness and spectral brightness. However, their power per unit chip area is on the far left of Figure 25, making them more expensive and less competitive for LiDAR. PCSELs and DBR lasers require complex manufacturing processes such as electron beam lithography, nanoimprinting, and epitaxial regrowth.

[0096] In addition to LiDAR, AR-VCSELs can also be used for structured light 3D sensing due to their small divergence angle, high beam quality, and minimized crosstalk between emitters. For data communication applications, AR-VCSELs can potentially achieve a single transverse mode to reduce chromaticity and modal dispersion, and have a larger oxide aperture than traditional single-mode VCSELs.

[0097] Furthermore, the AR-storage cavity 40 technology can facilitate other cutting-edge surface-emitting laser technologies. For example, the z-direction optical reservoir in AR-VCSELs can be combined with xy-plane photonic crystals, topological cavities, or metasurface structures, potentially achieving higher output power and efficiency for these surface-emitting lasers.

[0098] In summary, the AR-VCSEL, which combines the optical anti-reflection storage cavity 40 and the multi-junction active region, has the advantages of significantly reducing the divergence angle, high brightness, and high spectral brightness while maintaining single longitudinal mode lasing. By separately reconstructing the epitaxial layer, this unique design does not require a complex device structure or additional manufacturing steps. Using a standard low-cost VCSEL process, an ultra-small full divergence angle of 8.0° (D86) or 4.1° (FWHM) is achieved on a 250μm 6-junction AR-VCSEL array, with a brightness exceeding 40kW*mm -2 sr -l, spectral brightness is 75.6kW*nm -1 mm -2 sr -l By adopting a more compact array size of 100μm, the brightness of the AR-VCSEL array can be increased to 100kW*mm -2 sr -l Above, the spectral brightness is increased to 180kW*nm -1 mm -2 sr -l By increasing the number of junctions, a 14-junction AR-VCSEL array with a size of 250 μm was used to achieve 5000 W / mm 2 power density. By varying the oxide aperture size, a high-power single-transverse-mode laser of 28.4 mW was achieved in a single 6-junction AR-VCSEL emitter with an optical aperture of 7 μm. To the best of the applicant's knowledge, these are the best performing multi-junction VCSELs that have been published. AR-VCSELs complement the scalable high output power, near-circularly symmetric beam, and wavelength drift that can be matched to filters with temperature, showing more advantages over competing EELs. This application also compares AR-VCSELs with PCSELs in multiple aspects, demonstrating that power density is the most difficult challenge for PCSELs to overcome, and power density is key to low-cost lidar. Overall, AR-VCSELs exhibit well-balanced performance under the various requirements of lidar. In particular, for high-power, low-cost scanning lidars that require a divergence of 16° (D86) or less, the use of AR-VCSELs is the best solution.

[0099] The photoelectric characteristics of all VCSEL / ARVCSEL arrays were tested under short pulse conditions with a pulse width of 3ns and a frequency of 20kHz. The test environment temperature was room temperature. The driving circuit is shown in Figure 37 and includes a capacitor charging and discharging circuit 1011 and a capacitor charging and discharging driving circuit 1013. The capacitor charging and discharging circuit 1011 includes: a charging resistor R1, a charging and discharging capacitor C1 and a power supply 1012. The negative pole of the power supply 1012 is grounded, and the positive pole of the power supply 1012 is electrically connected to one end of the charging resistor R1. The other end of the charging resistor R1 is electrically connected to one end of the charging and discharging capacitor C1. The other end of the charging resistor R1 is electrically connected to one end of the charging and discharging capacitor C1. The other end of the charging resistor R1 is also electrically connected to one end of the light source 102. The capacitor charging and discharging driving circuit 1013 includes: a switch tube Q1 and a switch tube driving circuit 1014. One end of the switch tube driving circuit 1014 is grounded, the other end is electrically connected to the first end of the switch tube Q1 , the second end of the switch tube Q1 is grounded, and the third end of the switch tube Q1 is electrically connected to the other end of the light source 102 .

[0100] Photoluminescence spectra were measured at room temperature using a Nanometrics RPMBlue system using an OBIS LS 532nm continuous laser with an optical power of 20mW and a spot size of 20μm. Far-field patterns were acquired using an Ophir L11059 beam profiler camera operating at a current of 10A. Optical output power was measured using a Newport 819D-SL-3.3 integrating sphere. Laser spectra were acquired using an Ocean Insight HR4Pro spectrometer operating at a current of 10A with a resolution of 0.2nm. Single-mode laser spectra were acquired using an MS9740A spectrometer with a resolution of 0.07nm. Two-dimensional electric field intensity simulations were performed using the Ansys Lumerical FDTD solution. Full vector simulations were performed using perfectly matched layer (PML) boundary conditions, resulting in final simulation results with a minimum auto-shutdown value of 1E-5 and a maximum auto-shutdown value of 1E5. Simulations were performed with and without gain in the active layer. Comparing the simulated normalized E(z) field strength distribution maps with and without gain, the difference is less than 0.1%, confirming the stable static distribution.

[0101] An embodiment of the present application also provides an anti-reflection type vertical cavity surface emitting laser chip, comprising at least one laser array; the laser array comprises a plurality of anti-reflection type vertical cavity surface emitting lasers according to any embodiment of the present application; the laser array is a regularly arranged array, or a randomly arranged array, or an array having multiple addressable sub-arrays.

[0102] Optionally, the size of the laser array is less than or equal to 250 μm; the brightness of the laser array is greater than or equal to 40 kW*mm -2 sr -l , spectral brightness greater than or equal to 75.6kW*nm -1 mm -2 sr -l .

[0103] Optionally, when the number of junctions in the active layer of the anti-reflection type vertical cavity surface emitting laser is greater than or equal to 14 junctions, the optical power density of the anti-reflection type vertical cavity surface emitting laser chip is greater than or equal to 5000W / mm 2 .

[0104] It should be noted that the laser array in the embodiments of the present application can be in the shape of a rectangle, a circle, a regular hexagon, or the like. For a rectangular laser array, its dimension is the length or width. For a circular laser array, its dimension is the diameter. For a regular hexagonal laser array, its dimension is the diameter of the inscribed circle.

[0105] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the multiple steps described in this application can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of this application can be achieved. This is not limited herein.

Claims

1. An anti-reflection type vertical cavity surface emitting laser, comprising: Lower Bragg reflector layer; An active region, located on one side of the lower Bragg reflector layer, the active region comprising at least five active layers and tunnel junctions between the active layers; a current limiting layer is disposed in the active region or near the outer side of the active region; an upper Bragg reflection layer, located on a side of the active region away from the lower Bragg reflection layer; A light-enhancing-reflection storage cavity, located at least one of between the lower Bragg reflection layer and the active area and between the upper Bragg reflection layer and the active area; The light anti-reflection storage cavity is configured to increase the peak value of the light field intensity to be higher than the peak value of the light field intensity of the active region, and to store light field energy; The anti-reflection type vertical cavity surface emitting laser operates under the conditions that the injection current density is greater than 10kA / cm2, the slope efficiency is greater than 4W / A, and the far-field divergence angle is less than or equal to 19°.

2. The anti-reflection type vertical cavity surface emitting laser according to claim 1, wherein: The current limiting layer includes an oxide layer; the oxide layer is epitaxially grown AlGaAs with a high Al content, and the outer oxidized area forms an insulating aluminum oxide film layer; wherein the unoxidized area forms a light-emitting area for effective current injection; The optical path distance between the current limiting layer and the 0-value position of the nearest standing wave light field is less than one tenth of the lasing wavelength; when the current limiting layer is outside the active area, it is located within the range of two wavelengths along a side perpendicular to the active layer; the number of layers of the current limiting layer is less than or equal to the number of layers of the active layer and less than or equal to the number of tunnel junctions plus 1.

3. The anti-reflection type vertical cavity surface emitting laser according to claim 2, further comprising: Light-emitting hole; The light-emitting hole is located in a non-oxidized area of ​​the oxide layer, and the thickness of the oxidized portion of the oxide layer near the outer edge of the light-emitting hole is less than 30 nm.

4. The anti-reflection type vertical cavity surface emitting laser according to claim 3, wherein: The light confinement factor of the oxide layer is less than 0.16%.

5. The anti-reflection type vertical cavity surface emitting laser according to claim 1, wherein: The active layer comprises a PIN structure, and the PIN structure comprises at least one quantum well; the active layer is connected in series through the tunnel junction.

6. The anti-reflection type vertical cavity surface emitting laser according to claim 5, wherein: When the active layer includes one quantum well, the optical path distance between the quantum well and the nearest peak position of the standing wave light field is less than one-fifth of the lasing wavelength; when the active layer includes multiple quantum wells, the overall center position of each quantum well in the multiple quantum wells is less than the nearest peak position of the standing wave light field. The optical path distance at the position is less than one tenth of the lasing wavelength.

7. The anti-reflection type vertical cavity surface emitting laser according to claim 1, wherein: Along the direction opposite to the laser light emitting direction, the anti-reflection type vertical cavity surface emitting laser includes a dielectric layer, an electric contact layer, a lateral current diffusion layer, a p-type upper Bragg reflection layer, an active area with an oxide layer, the light anti-reflection storage cavity, an n-type lower Bragg reflection layer and a substrate in sequence.

8. The anti-reflection type vertical cavity surface emitting laser according to claim 7, further comprising: Ion implantation layer; The ion implantation layer is located on the surface of the substrate close to the n-type lower Bragg reflector layer, and the ion implantation layer is configured to enhance the electrical insulation between the substrate and the n-type lower Bragg reflector layer. Alternatively, the ion implantation layer is located at the bottom of the oxidation trench, and the ion implantation layer is configured to enhance the electrical insulation between the bottom of the oxidation trench and the substrate; the current limiting layer is formed based on oxidizing the sidewall of the oxidation trench; Wherein, the ions implanted into the ion implantation layer include at least one of H ions, He ions, B ions and O ions.

9. The anti-reflection type vertical cavity surface emitting laser according to claim 1, wherein: The peak values ​​of the electric field strengths of different active layers are the same or different; the maximum peak value of the electric field strength in the active region is smaller than the maximum peak value of the electric field strength in the optical anti-reflection storage cavity.

10. The anti-reflection type vertical cavity surface emitting laser according to any one of claims 1 to 9, wherein: The light anti-reflection storage cavity comprises: an anti-reflection layer and a light storage layer; the anti-reflection layer is located between the light storage layer and the active area; the anti-reflection layer is configured to increase the peak value of the light field intensity of the light storage layer to be higher than the peak value of the light field intensity of the active area; the light storage layer is configured to store light field energy; Wherein, the thickness of the light storage layer is an odd multiple of half the lasing wavelength; along the direction of the active area pointing to the light-enhancing transmittance storage cavity, the transmittance-enhancing layer includes at least one of the following: a first transmittance-enhancing interface between the light storage layer and the active area located at the interface from low refractive index to high refractive index, and a second transmittance-enhancing interface between the light storage layer and the active area located at the interface from high refractive index to low refractive index; the optical path distance between the first transmittance-enhancing interface and the nearest antinode of the standing wave light field is less than one tenth of the lasing wavelength; the optical path distance between the second transmittance-enhancing interface and the nearest node of the standing wave light field is less than one tenth of the lasing wavelength.

11. The anti-reflection type vertical cavity surface emitting laser according to any one of claims 1 to 9, wherein: The light anti-reflection storage cavity comprises: A plurality of first semiconductor material layers and a plurality of second semiconductor material layers; the first semiconductor material layers and the second semiconductor material layers are alternately arranged in sequence; The number and optical thickness of the first semiconductor material layer and the second semiconductor material layer are the same; the refractive index of the first semiconductor material layer and the second semiconductor material layer is different; the distance between the active area and the Bragg reflection layer adjacent to the optical anti-reflection storage cavity is an integer multiple of half the lasing wavelength.

12. The anti-reflection type vertical cavity surface emitting laser according to claim 10, wherein: A plurality of anti-reflection interfaces are arranged between the active region and the light storage layer, so that the electric field intensity from the active region to the light storage layer gradually increases.

13. An anti-reflection type vertical cavity surface emitting laser chip, comprising at least one laser array; the laser array comprises a plurality of anti-reflection type vertical cavity surface emitting lasers as described in any one of claims 1 to 12; the laser array is a regularly arranged array, or a randomly arranged array, or an array with multiple addressable sub-arrays.

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