Vertical-cavity surface-emitting laser, lidar, and vehicle

Abstract

The present disclosure relates to a vertical-cavity surface-emitting laser, a LiDAR, and a vehicle. The vertical-cavity surface-emitting laser comprises: a substrate; a first reflector, which is stacked on the substrate; an active layer, which is stacked on the first reflector; and a second reflector, which is stacked on the active layer, wherein light in a first polarization direction and a second polarization direction is formed inside the vertical-cavity surface-emitting laser. The vertical-cavity surface-emitting laser further comprises: a grating, which is arranged on the outer side of the second reflector, wherein a structure parameter of the grating is set, such that within an operating wave band of the vertical-cavity surface-emitting laser, the ratio of a longitudinal mode resonance quality factor of the light in the first polarization direction to a longitudinal mode resonance quality factor of the light in the second polarization direction is greater than or equal to a threshold value, and the vertical-cavity surface-emitting laser lasing the light in the first polarization direction.

Description

Vertical cavity surface emitting lasers, lidar and vehicles Technical Field

[0001] The present disclosure relates to the field of laser light sources, and more particularly to a vertical cavity surface emitting laser, a laser radar including the vertical cavity surface emitting laser, and a vehicle including the laser radar. Background Art

[0002] A vertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser with outstanding advantages in manufacturing process, threshold current, service life, and large array integration. It has been widely used in many fields, such as optical communication systems, integrated atomic clocks, laser frequency doubling, and gas detection. VCSELs form an optical resonant cavity perpendicular to the epitaxial structure layer and emit a laser beam perpendicular to the substrate surface.

[0003] Some LiDARs use vertical-cavity surface-emitting lasers (VCSELs) as their optical transmitters. LiDAR is a commonly used ranging device, boasting long detection range, high resolution, and minimal environmental interference. It is widely used in intelligent robots, drones, and autonomous vehicles. In recent years, with the rise of autonomous driving technology, LiDAR has gained increasing attention as a key detection component. LiDAR is a radar system that uses laser beams to detect target characteristics such as position and velocity. Its operating principle is to transmit a signal toward a target (for example, using a VCSEL to emit a laser beam). The received echo reflected from the target is then compared with the transmitted signal. After appropriate processing, relevant target information such as range, direction, altitude, speed, attitude, and even shape can be obtained, enabling detection, tracking, and identification of targets such as cars and pedestrians. In some LiDAR systems, using polarized VCSELs as optical transmitters can improve the overall transmission and reception efficiency of the LiDAR.

[0004] VCSELs without polarization design typically lack distinct polarization characteristics, resulting in approximately 50% energy loss in the polarization-splitting optical path of the LiDAR. Even standard VCSELs, due to factors such as the crystal phase and stress of their substrates, exhibit relatively stronger energy distribution in certain polarization directions. However, this polarization characteristic is not stable and can shift under significant operating conditions such as high and low voltages or high and low temperatures, causing noticeable changes in LiDAR performance.

[0005] Therefore, in order to improve the transceiver efficiency and stability of lidar, it is desirable for the VCSEL to have a stable polarization direction, and the higher the degree of polarization, the better. SUMMARY OF THE INVENTION

[0006] The present disclosure provides a vertical-cavity surface-emitting laser, comprising: a substrate; a first mirror stacked on the substrate; an active layer stacked on the first mirror; a second mirror stacked on the active layer, wherein the vertical-cavity surface-emitting laser forms light including a first polarization direction and a second polarization direction inside, and the vertical-cavity surface-emitting laser further comprises a grating disposed outside the second mirror, wherein the structural parameters of the grating are configured such that in the operating band of the vertical-cavity surface-emitting laser, the ratio of the longitudinal mode resonance quality factor of the light in the first polarization direction to the longitudinal mode resonance quality factor of the light in the second polarization direction is greater than or equal to a threshold, and the vertical-cavity surface-emitting laser emits light in the first polarization direction.

[0007] Optionally, the first polarization direction is parallel to the extending direction of the grating, and the second polarization direction is perpendicular to the extending direction of the grating; or the first polarization direction is perpendicular to the extending direction of the grating, and the second polarization direction is parallel to the extending direction of the grating.

[0008] Optionally, the threshold is greater than or equal to 1.1 and less than or equal to 1.3.

[0009] Optionally, before forming the grating, the longitudinal mode resonance quality factor of the vertical-cavity surface-emitting laser is Q_ref, after forming the grating, the longitudinal mode resonance quality factor of the light in the first polarization direction is Q1, and the longitudinal mode resonance quality factor of the light in the second polarization direction is Q2, where: the structural parameters of the grating are further configured such that Q1 is close to Q_ref and Q2 is much smaller than Q_ref; or the structural parameters of the grating are further configured such that Q2 is close to Q_ref and Q1 is much smaller than Q_ref.

[0010] Optionally, the structural parameters of the grating are further configured such that Q1 > Q_ref - 1000; or the structural parameters of the grating are further configured such that Q2 > Q_ref - 1000.

[0011] Optionally, the structural parameters of the grating are further configured such that Q1 < Q_ref + 1000; or the structural parameters of the grating are further configured such that Q2 < Q_ref + 1000.

[0012] Optionally, the structural parameters of the grating are further configured such that Q2 < Q_ref - 2000; or the structural parameters of the grating are further configured such that Q1 < Q_ref - 2000.

[0013] Optionally, the structural parameters of the grating include at least one of the period of the grating, the groove depth, the duty cycle, and the sidewall inclination angle.

[0014] Optionally, the period of the grating does not exceed the operating wavelength of the vertical cavity surface emitting laser.

[0015] Optionally, the period of the grating is set to be within the range of 300 nm - 400 nm, or within the range of 500 nm - 550 nm.

[0016] Optionally, the groove depth of the grating is set to be greater than or equal to 40 nm.

[0017] Optionally, the grating is formed by etching one or more layers of the second mirror.

[0018] Optionally, the vertical cavity surface emitting laser includes a passivation layer disposed outside the grating.

[0019] Optionally, the passivation layer includes silicon nitride.

[0020] Optionally, the first mirror and the second mirror include distributed Bragg reflectors.

[0021] The present disclosure also provides a lidar, which includes: a transmitter, the transmitter includes a laser, the laser includes any vertical cavity surface emitting laser as in the present disclosure, the laser is configured to emit outgoing light of the first polarization direction or the second polarization direction along a first optical path; and a receiver, the receiver includes a detector, the detector is configured to receive the reflected light of the outgoing light after being reflected by a target along a second optical path.

[0022] Optionally, at least part of the first optical path and the second optical path coincide, and the lidar includes a quarter-wave plate, wherein the quarter-wave plate is disposed on the first optical path and the second optical path.

[0023] Optionally, the lidar includes a polarization beam splitter, wherein the polarization beam splitter is configured to transmit the light of the first polarization direction and reflect the light whose polarization direction is perpendicular to the first polarization direction, or the polarization beam splitter is configured to reflect the light of the first polarization direction and transmit the light whose polarization direction is perpendicular to the first polarization direction.

[0024] The present disclosure also provides a vehicle, which includes any lidar in the present disclosure.

[0025] The VCSEL using the technology disclosed in the present invention can achieve more stable polarized light emission and further improve light extraction efficiency.

[0026] When the ratio of the longitudinal mode resonance quality factors of polarized light in different directions meets a threshold condition (for example, greater than or equal to a threshold), the VCSEL can achieve linearly polarized emission within a specific grating period range. When etching the grating, the grating period needs to be controlled to meet the requirements, and the requirements for parameters such as the grating duty cycle and sidewall tilt angle are relatively relaxed, thereby reducing the accuracy requirements for the grating etching process and the sensitivity to process deviations.

[0027] The laser radar disclosed in the present invention may include the VCSEL disclosed in the present invention to emit polarized light. In the laser radar, a larger reflection surface can be set when a polarization beam splitter is used to split the light, thereby improving the light output efficiency and reducing the restriction on the divergence angle; the loss of the reflected or transmitted echo light will also be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to further illustrate the various embodiments of the present disclosure, the embodiments of the present disclosure will be specifically presented with reference to the accompanying drawings. It should be understood that these drawings may only depict some embodiments of the present disclosure and therefore will not be considered as limiting the scope of protection claimed by the present disclosure.

[0029] In addition, the drawings show the main connection relationships or relative positional relationships of the various components, rather than all of these relationships, and the various components and connections in the drawings are not necessarily drawn to scale in reality.

[0030] FIG1 is a schematic structural diagram of a vertical cavity surface emitting laser (VCSEL) according to some embodiments of the present disclosure.

[0031] 2a-2b illustrate an exemplary process of forming a grating using selective etching according to some embodiments of the present disclosure.

[0032] 3a-3b illustrate an exemplary process of forming a grating using non-selective etching according to some embodiments of the present disclosure.

[0033] FIG4 is a schematic diagram illustrating exemplary structural parameters of a grating according to some embodiments of the present disclosure.

[0034] Figures 5a-5c show different epitaxial structures based on VCSEL according to some embodiments of the present disclosure, and the relationship between the ratio of the longitudinal mode resonance quality factor of TE polarized light to the longitudinal mode resonance quality factor of TM polarized light and different grating periods and duty cycles when the groove depth and sidewall tilt angle of the grating are constant.

[0035] FIG6 illustrates the effects of different etching depths on the longitudinal mode resonance quality factor of TM polarized light in an epitaxial structure according to some embodiments of the present disclosure.

[0036] FIG. 7 illustrates the total reflectivity of TE polarized light and TM polarized light within a VCSEL within a certain wavelength range according to some embodiments of the present disclosure.

[0037] FIG8 shows a schematic diagram of a lidar according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0038] The following detailed description refers to the accompanying drawings, which illustrate, by way of example, some embodiments in which the claimed subject matter may be practiced. It should be understood that the following embodiments are intended to describe some examples for illustrative purposes and should not be construed as limiting the present disclosure. Those skilled in the art, provided they fully understand the subject matter of the present disclosure, may make appropriate modifications and adjustments to the disclosed embodiments without departing from the scope of the claimed subject matter.

[0039] Unless otherwise defined, the terms used herein shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0040] The terms "first," "second," and the like in the description and claims of this application do not imply any order, quantity, or importance, but are merely used to distinguish different components or features.

[0041] The embodiments of the present application are exemplary implementations or examples. References in the specification to "an embodiment," "one embodiment," "some embodiments," "alternative embodiments," or "other embodiments" mean that the specific features and configurations described in conjunction with the embodiments are included in at least some embodiments of the present technology, but not necessarily all embodiments. The various appearances of "an embodiment," "one embodiment," or "some embodiments" do not necessarily refer to the same embodiment. Elements or aspects from one embodiment may be combined with elements or aspects of another embodiment.

[0042] In the description of this disclosure, the terms "upper," "lower," "top," "bottom," "left," "right," "vertical," "horizontal," and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. These terms are intended solely to facilitate the description of this disclosure and are not intended to indicate or imply that the devices or components referred to must have a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on this disclosure. In other embodiments where the orientation of devices or components is opposite or different from that shown, these positional descriptions may vary accordingly.

[0043] In the description of this disclosure, the term "and / or" is simply a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0044] To achieve polarized output of VCSEL, some possible approaches include:

[0045] Polarization selection is achieved by utilizing the internal stress of the VCSEL epitaxial structure or the stress introduced through the VCSEL epitaxial structure process. However, there is a high risk of fluctuations in the polarization selectivity ratio in high and low temperature environments and between different batches.

[0046] Polarization selection is achieved by utilizing crystal orientation and photoelectric effect inside the VCSEL, but the polarization selection ratio still varies greatly under high and low temperature environments.

[0047] Polarization selection is achieved using a high-contrast-grating (HCG), which at least partially replaces the top reflector of a VCSEL. Polarization selection is achieved through the high reflectivity difference between the top HCG and the two polarization directions. In this solution, the HCG completely or substantially replaces the top reflector, with the HCG providing the reflection. The HCG used in VCSELs can be made of Si or SiO2, which can achieve high reflectivity while also achieving a wide bandwidth. However, because it differs from the material systems of widely used GaAs- or InP-based VCSELs, it requires additional methods such as plasma-enhanced chemical vapor deposition (PECVD) to fabricate thin films such as Si / SiO2. Furthermore, the significant difference in thermal expansion coefficients between the different material systems can lead to stress between the materials and film robustness issues, which can affect device stability.

[0048] Polarization selection is achieved by etching a grating on the surface of a conventional VCSEL. Based on the conventional VCSEL epitaxial structure, a grating structure is etched on the light-emitting surface. This creates a relatively small reflectivity difference between the two polarization directions of light, and a threshold is used to select a specific polarization direction of the emitted laser light. The advantage of this solution is that, based on the conventional VCSEL design, the overall device performance is highly predictable while ensuring top reflectivity. The performance impact of the polarization grating is also easy to evaluate, and the performance requirements of the grating are lower than those of the HCG.

[0049] According to some embodiments of the present disclosure, a vertical cavity surface emitting laser may include: a substrate; a first reflector stacked on the substrate; an active layer stacked on the first reflector; and a second reflector stacked on the active layer, wherein the vertical cavity surface emitting laser internally forms light including a first polarization direction and a second polarization direction, and the vertical cavity surface emitting laser also includes a grating, which is arranged on the outside of the second reflector, wherein the structural parameters of the grating are configured so that in the operating band of the vertical cavity surface emitting laser, the ratio of the longitudinal mode resonance quality factor of the light in the first polarization direction to the longitudinal mode resonance quality factor of the light in the second polarization direction is greater than or equal to a threshold value, and the vertical cavity surface emitting laser emits light in the first polarization direction.

[0050] FIG1 illustrates a schematic structural diagram of a vertical cavity surface emitting laser (VCSEL) 10 according to some embodiments of the present disclosure. The VCSEL 10 may include a substrate 101, a bottom reflector (e.g., a first reflector) 102, an active layer 103, and a top reflector (e.g., a second reflector) 104. The bottom reflector 102 may be stacked onto the substrate 101, the active layer 103 may be stacked onto the bottom reflector 102, and the top reflector 104 may be stacked onto the active layer 103.

[0051] In some embodiments of the present disclosure, the substrate 101 may include gallium arsenide (GaAs) or indium phosphide (InP) material.

[0052] In some embodiments of the present disclosure, the bottom reflector 102 and the top reflector 104 of the VCSEL 10 may include any one of a semiconductor reflector, a Fabry-Perot (FP) reflector, a metal reflector, and a composite reflector. In some embodiments, the reflectors of the VCSEL 10 may be semiconductor reflectors, such as distributed Bragg reflectors (DBRs).

[0053] In some embodiments of the present disclosure, the bottom reflector 102 and the top reflector 104 of the VCSEL 10 may be DBRs. When the operating wavelength of the VCSEL 10 is between about 900 nm and 1000 nm, the DBRs may include aluminum gallium arsenide (e.g., AlGaAs). x Ga 1-x As, where x can take a value between 0 and 1). For Al operating in the band of about 900nm-1000nm x Ga 1-xFor an As-structured VCSEL 10, the DBR can be composed of a periodically alternating arrangement of high-aluminum (e.g., x can be 0.9 or greater) and low-aluminum materials (e.g., x can be 0.1 or less). When the VCSEL 10 operates in the 1500-1600 nm wavelength range, the DBR can include a combination of indium gallium arsenide phosphide / indium phosphide (InGaAsP / InP), aluminum gallium indium arsenide / aluminum indium arsenide (InGaAlAs / InAlAs), or gallium arsenide / aluminum gallium arsenide (GaAs / AlGaAs) materials.

[0054] In some embodiments of the present disclosure, the active layer 103 is disposed between the bottom reflector 102 and the top reflector 104 , forming at least a portion of the resonant cavity of the VCSEL 10 .

[0055] In some embodiments of the present disclosure, the VCSEL 10 may further include an oxide layer 107 , which may limit internal current and beam aperture to achieve low-threshold single-mode laser output.

[0056] In VCSEL 10, current can be injected into active layer 103, for example, via electrodes (not shown). The material in active layer 103 is stimulated to emit light, which resonates in the resonant cavity between top reflector 104 and bottom reflector 102, forming a beam with a consistent propagation direction, frequency, and phase. Depending on the polarization direction of the beam, the light generated within VCSEL 10 may include light with a first polarization direction and light with a second polarization direction.

[0057] According to some embodiments of the present disclosure, the VCSEL 10 further includes a grating 105 to achieve polarization selection. The grating 105 can be disposed on the outside of the top reflector 104, such as the top side as shown in FIG1 . In some embodiments of the present disclosure, the grating 105 can be formed by etching one or more layers of the top reflector 104. The present disclosure can achieve polarization selection by etching the grating 105 on the surface of the VCSEL. Therefore, in these embodiments, the grating 105 can be made of the same material as the top reflector 104.

[0058] In some embodiments of the present disclosure, the first polarization direction may be parallel to the extension direction of the grating 105, and the second polarization direction may be perpendicular to the extension direction of the grating 105. Alternatively, in some embodiments, the first polarization direction may be perpendicular to the extension direction of the grating 105, and the second polarization direction may be parallel to the extension direction of the grating 105. The extension direction of the grating 105 may be the m direction as shown in FIG1 .

[0059] In some embodiments of the present disclosure, light with a polarization direction parallel to the extension direction of the grating 105 may include TE polarized light, and light with a polarization direction perpendicular to the extension direction of the grating 105 may include TM polarized light. In the following description, for clarity, TE polarized light and TM polarized light are used as examples to introduce the technology of the present disclosure.

[0060] The grating 105 can be formed by exposure and etching directly on the upper interface of the top reflector 104. For example, the grating 105 can be formed by either selective etching or non-selective etching.

[0061] 2a-2b illustrate an exemplary process of forming a grating 105 using selective etching according to some embodiments of the present disclosure. In some embodiments of the present disclosure, an etch stop layer 201 may be formed at a specific depth (e.g., a predetermined depth) of the top reflector 104 during the process of forming the top reflector 104. After the top reflector 104 is formed, the top reflector 104 may be at least partially etched from one side (e.g., the upper side shown in FIG. 1 ) until the etch stop layer 201 is etched, thereby forming a grating 105 structure having a specific depth. Therefore, in the formed VCSEL 10 having the grating 105, the etching depth of the grating 105 may be easier to control and more accurate. In some embodiments, the etch stop layer 201 may include indium gallium phosphide (InGaP).

[0062] Figures 3a-3b illustrate an exemplary process for forming the grating 105 using non-selective etching, according to some embodiments of the present disclosure. During the non-selective etching process, one or more layers of the top reflector 104 may be etched to form the grating 105. The etch depth of the grating 105 may be determined by the etching rate and etching time. The sidewalls of the grating 105 formed using non-selective etching are steeper.

[0063] Returning to Figure 1 , in some embodiments of the present disclosure, the VCSEL 10 may include a passivation layer 105 disposed outside the grating 105, thereby providing better protection for the grating 105. In some embodiments of the present disclosure, the passivation layer 105 may comprise an insulating material, such as silicon nitride (SiN), to protect the surface of the grating 105 and to provide insulation and isolation for the grating 105. In other embodiments of the present disclosure, the passivation layer 105 may comprise silicon nitride (SiN) and aluminum oxide (Al2O3).

[0064] As an example, FIG1 shows an exemplary structural diagram of a VCSEL. It is understood that the VCSEL 10 may have more or fewer components than those shown in FIG1 without departing from the content of the present disclosure.

[0065] In some embodiments of the present disclosure, the structural parameters of the grating 105 can be configured such that, within the operating band of the VCSEL 10, the ratio of the longitudinal mode resonance quality factor (i.e., Q value) of TE polarized light to the longitudinal mode resonance quality factor of TM polarized light is greater than or equal to a threshold, and the VCSEL 10 can lase TE polarized light. In other embodiments of the present disclosure, the structural parameters of the grating 105 can be configured such that, within the operating band of the VCSEL 10, the ratio of the longitudinal mode resonance Q value of TM polarized light to the longitudinal mode resonance Q value of TE polarized light is greater than or equal to a threshold, and the VCSEL 10 can lase TM polarized light.

[0066] Q value refers to the quality factor, which is an indicator used to evaluate the quality of the optical resonant cavity in the laser. The Q value can be defined as = 2π × energy stored in the resonant cavity / energy lost per oscillation cycle. The resonant cavity formed by the epitaxial structure of different VCSELs has different quality factors. The scheme disclosed in the present invention changes the properties of the VCSEL resonant cavity by configuring the structural parameters of the grating 105, which can change the reflectivity and oscillation loss of TE polarized light and TM polarized light, thereby changing the longitudinal mode resonance Q value of TM polarized light (abbreviated as Q_TM) and the longitudinal mode resonance Q value of TE polarized light (abbreviated as Q_TE), and the ratio of the two meets the threshold condition, thereby realizing TE polarized light or TM polarized light lasing.

[0067] TE polarized light and TM polarized light have different reflectivities when incident vertically from the active region 103 onto the grating 105, resulting in different losses for TE polarized light and TM polarized light when resonating in the resonant cavity of the VCSEL 10. The threshold gain for achieving lasing is proportional to 1-√R, where R is the reflectivity. For polarization components with higher reflectivity, the loss of resonance is lower, and the threshold for achieving lasing is lower. For polarization components with lower reflectivity, the loss of resonance is greater, and the threshold for achieving lasing is higher. The polarization component with a lower threshold will be selectively excited, while the polarization component with a higher threshold will be suppressed, thereby achieving lasing of TE polarized light or TM polarized light.

[0068] In some embodiments of the present disclosure, the lasing thresholds of TE polarized light and TM polarized light can be adjusted by adjusting one or more of the structural parameters of the grating 105. In some embodiments of the present disclosure, based on certain epitaxial structures, the present disclosure proposes configuring the structural parameters of the grating 105 such that the ratio of the lasing threshold of TM polarized light to the lasing threshold of TE polarized light is 2.07.

[0069] Q_TE or Q_TM is directly related to the lasing threshold of the polarization mode. The technology disclosed in this disclosure proposes setting the ratio of Q_TE to Q_TM within a certain range to achieve the final lasing of TE polarized light or TM polarized light.

[0070] For VCSELs 10 with different epitaxial structures, the structural parameters of the grating 105 can be configured so that the ratio of the longitudinal mode resonant Q value of TE polarized light to the longitudinal mode resonant Q value of TM polarized light (Q_TE / Q_TM) is greater than or equal to 1.1, so that the VCSEL 10 ultimately emits TE polarized light. Alternatively, the structural parameters of the grating 105 can be configured so that the ratio of the longitudinal mode resonant Q value of TM polarized light to the longitudinal mode resonant Q value of TE polarized light (Q_TM / Q_TE) is greater than or equal to 1.1, so that the VCSEL 10 ultimately emits TM polarized light.

[0071] In some embodiments of the present disclosure, Q_TM / Q_TE can be greater than or equal to any value in the threshold range of 1.1-1.3, or Q_TE / Q_TM can be greater than or equal to any value in the threshold range of 1.1-1.3. In embodiments where the threshold is 1.3, the VCSEL 10 can emit TE polarized light or TM polarized light more stably, and the degree of polarization is substantially unaffected by the ratio.

[0072] In addition, the technology disclosed in the present invention also proposes setting the values ​​of Q_TE and Q_TM within a certain range, so as to achieve a certain light extraction efficiency of the final TE polarized light or TM polarized light.

[0073] Taking the TE polarized light lasing based on the grating 105 as an example, in some embodiments, the structural parameters of the grating 105 can be adjusted so that the lasing threshold of the TE polarized light after the grating 105 is formed is basically the same as the lasing threshold of the VCSEL 10 before the grating 105 is formed. If the grating 105 increases the reflectivity of the TE polarized light, its lasing threshold will be lowered, but too high a reflectivity may cause the TE polarized light to be confined in the cavity of the VCSEL 10 and unable to be emitted, ultimately affecting the light extraction efficiency. If the grating 105 reduces the reflectivity of the TE polarized light, its lasing threshold will be increased, and the loss of the TE polarized light will be increased, which will also affect the light extraction efficiency and may also affect the final polarization selection. For TM polarized light, its reflectivity needs to be reduced to increase the lasing threshold, thereby suppressing the lasing of TM polarized light.

[0074] Taking the TM polarized light lasing based on the grating 105 as an example, in some embodiments, the structural parameters of the grating 105 can be adjusted so that the lasing threshold of the TM polarized light after the grating 105 is formed is substantially the same as the lasing threshold of the VCSEL 10 before the grating 105 is formed. For TE polarized light, its reflectivity needs to be reduced as much as possible to increase the lasing threshold, thereby suppressing the lasing of TE polarized light.

[0075] The technology proposed in the present disclosure enables the lasing threshold of one polarization light to be substantially the same as the lasing threshold of the VCSEL 10 before the grating 15 is formed, and the lasing threshold of the other polarization light to be relatively high and the reflectivity to be relatively low, so that lasing cannot be formed, thereby achieving a certain light output efficiency of the polarization light of the VCSEL 10.

[0076] In some embodiments of the present disclosure, before the grating 105 is formed on the VCSEL 10, the longitudinal mode resonance quality factor of the VCSEL 10 can be expressed as Q_ref. When the grating 105 is formed on the VCSEL 10, one or more structural parameters of the grating 105 can be configured such that Q_TE is close to Q_ref and Q_TM is much smaller than Q_ref to lase TE polarized light, or such that Q_TM is close to Q_ref and Q_TE is much smaller than Q_ref to lase TM polarized light.

[0077] In some embodiments of the present disclosure, Q_TE being close to Q_ref can mean that the lasing threshold of the TE polarized light after the grating 105 is formed is substantially the same as the lasing threshold of the VCSEL 10 before the grating 105 is formed, and Q_TM being much smaller than Q_ref can mean that the lasing threshold of the TM polarized light has a relatively large increase compared to the lasing threshold of the VCSEL 10 before the grating 105 is formed, thereby achieving lasing of the TE polarized light and achieving a certain light output efficiency. Similarly, Q_TM being close to Q_ref can mean that the lasing threshold of the TM polarized light after the grating 105 is formed is substantially the same as the lasing threshold of the VCSEL 10 before the grating 105 is formed, and Q_TE being much smaller than Q_ref can mean that the lasing threshold of the TE polarized light has a relatively large increase compared to the lasing threshold of the VCSEL 10 before the grating 105 is formed, thereby achieving lasing of the TM polarized light and achieving a certain light output efficiency.

[0078] In some embodiments of the present disclosure, Q_TE or Q_TM being close to Q_ref can include setting Q_TE or Q_TM to, for example, Q_TE or Q_TM < Q_ref + 2500, for example, Q_TE or Q_TM < Q_ref + 2000, or for example, Q_TE or Q_TM < Q_ref + 1500. Additionally or alternatively, Q_TE or Q_TM being close to Q_ref can include setting Q_TE or Q_TM to, for example, Q_TE or Q_TM > Q_ref - 1500, or for example, Q_TE or Q_TM > Q_ref - 1200.

[0079] In some embodiments of the present disclosure, Q_TE or Q_TM being much smaller than Q_ref can include setting Q_TE or Q_TM to, for example, Q_TE or Q_TM < Q_ref - 1500, or for example, Q_TE or Q_TM < Q_ref - 1800.

[0080] In some embodiments of the present disclosure, for some epitaxial structures of the VCSEL 10, the structural parameters of the grating 105 can be configured such that Q_TE or Q_TM > Q_ref - 1000, so that Q_TE or Q_TM is close to Q_ref. The structural parameters of the grating 105 can be further configured such that Q_TE or Q_TM < Q_ref + 1000, so that Q_TE or Q_TM is further close to Q_ref, to achieve a certain light extraction efficiency for TE polarized light or TM polarized light. In some other embodiments of the present disclosure, the structural parameters of the grating 105 can be configured such that Q_TM or Q_TE < Q_ref - 2000, so that Q_TM or Q_TE is much smaller than Q_ref.

[0081] FIG. 4 shows a schematic diagram of exemplary structural parameters of the grating 105 according to some embodiments of the present disclosure. In some embodiments of the present disclosure, the structural parameters of the grating 105 can include at least one of the period (p) of the grating 105, the groove depth (d), the duty cycle (dc), and the sidewall inclination angle (θ). As shown in FIG. 4, the period p of the grating 105 = a + b. The groove depth (or can be called the etching depth) of the grating 105 is d. The duty cycle dc of the grating 105 = a / b. The sidewall inclination angle of the grating 105 is θ.

[0082] In some embodiments of the present disclosure, the period of the grating 105 is configured not to exceed the operating wavelength of the VCSEL 10. From the perspective of grating diffraction, if the period of the grating 105 is greater than the wavelength, the emitted laser will be affected by grating diffraction, thereby changing the far-field energy distribution and affecting the light extraction quality.

[0083] In some embodiments of the present disclosure, the process deviations of the structural parameters of the grating 105 during the manufacturing process are also considered. The technology of the present disclosure can reduce the sensitivity of the VCSEL 10 and the finally lasered polarized light to the process deviations of the grating 105. FIGS. 5a - 5c show the corresponding relationships between Q_TE / Q_TM and different periods (abscissa, p) and duty cycles (ordinate, dc) of the grating 105 based on different epitaxial structures of the VCSEL 10 according to the embodiments of the present disclosure, when the groove depth and sidewall inclination angle of the grating 105 are certain. FIGS. 5a - 5c show the part where Q_TE / Q_TM ≥ 1.1. It can be seen from FIGS. 5a - 5c that when the period of the grating 105 is in the range of 300 nm - 400 nm, or in the range of 500 nm - 550 nm (including the end values), linearly polarized emission can be achieved within a wide range of duty cycles (for example, 0.2 - 0.8).

[0084] When Q_TE / Q_TM≥1.1, within a specific grating period range (e.g., within the range of 300nm-400nm, or within the range of 500nm-550nm), the VCSEL 10 can achieve TE linear polarization emission. Therefore, in some embodiments of the present disclosure, when etching the grating 105, if the grating period is controlled to fall within the above period range, the requirements for other parameters of the grating 105, such as the duty cycle and sidewall tilt angle, are relatively relaxed, thereby reducing the accuracy requirements for the grating etching process and the sensitivity to process deviations.

[0085] Figure 6 shows the effect of different etching depths on Q_TM under an epitaxial structure according to some embodiments of the present disclosure. As shown in Figure 5, in an embodiment in which the VCSEL 10 is configured to laser TE polarized light, when the etching depth (i.e., groove depth d) of the grating 105 is reduced to 40nm, for a wider duty cycle range (0.2-0.8), the corresponding Q_TM is significantly improved compared to the Q_TM when the etching depth is 80nm or 120nm. When the etching depth of the grating 105 is less than 40nm, the lasing threshold of TM polarized light will be significantly reduced, which is not conducive to the suppression of TM polarized light and the selective lasing of TE polarized light. Therefore, in some embodiments of the present disclosure, the etching depth of the grating 105 can be set to be greater than or equal to 40nm.

[0086] The above, combined with FIG6 , describes the selection of the etching depth of the grating 105 in some embodiments, using the example of VCSEL 10 lasing TE polarized light. In some embodiments of the present disclosure, regardless of whether the VCSEL 10 lases TE polarized light or TM polarized light, the etching depth can be greater than or equal to 40 nm. This is because, for VCSELs with any epitaxial structure, a grating 105 with an excessively small etching depth has a limited effect on the reflectivity of light of different polarizations. Therefore, in some embodiments of the present disclosure, the etching depth can be greater than or equal to 40 nm to achieve the desired polarization selection.

[0087] Figure 7 shows the total reflectivity of TE-polarized light and TM-polarized light within a VCSEL 10 within a certain wavelength range, according to some embodiments of the present disclosure. The total reflectivity curves for TE-polarized light and TM-polarized light in Figure 7 show that the reflectivity of TE-polarized light is higher than that of TM-polarized light over a fairly wide spectral range (e.g., 880 nm-930 nm shown in Figure 7 ). Therefore, TM-polarized light is more difficult to excite than TE-polarized light, making it easier for the VCSEL 10 to achieve TE-polarized light lasing.

[0088] In some embodiments of the present disclosure, a laser radar 20 is provided. FIG8 shows a schematic diagram of a laser radar 20 according to some embodiments of the present disclosure. The laser radar 20 may include a transmitter 11, which may include a laser. The laser may include any of the VCSELs 10 described herein. The laser may be configured to emit TE-polarized or TM-polarized output light 16 along a first optical path.

[0089] The laser radar 20 may further include a receiver 15, which may include a detector. The detector may be configured to receive the return light 17 after the outgoing light 16 is reflected by a target (not shown) along the second optical path. In some embodiments, the detector may include a light detection circuit, a single photon avalanche diode (SPAD), an avalanche photodiode (APD), a silicon photomultiplier (SiPM), or a similar device.

[0090] As shown in Figure 8, in some embodiments of the present disclosure, the first optical path and the second optical path may at least partially overlap. The laser radar 20 may further include a quarter wave plate 13. The quarter wave plate 13 may be disposed in the first optical path and the second optical path.

[0091] In some embodiments of the present disclosure, as shown in FIG8 , the laser radar 20 may further include a polarization beam splitter 12. The polarization beam splitter 12 may be configured to transmit TE polarized light and reflect TM polarized light having a polarization direction perpendicular to the TE polarized light. In some embodiments, the polarization beam splitter 13 may also be configured to reflect TE polarized light and transmit TM polarized light having a polarization direction perpendicular to the TE polarized light.

[0092] As shown in Figure 8, linearly polarized outgoing light 16 (e.g., TE polarized light or TM polarized light) is reflected by the reflective surface 121 of the polarization beam splitter 12, passes through the quarter-wave plate 13, and then is reflected by the scanning mirror 14 before being emitted. The echo light 17 reflected from the target is reflected by the scanning mirror 14 and then passes through the quarter-wave plate 13 again, where it is converted to another polarization state (e.g., TE polarized light is converted to TM polarized light, or vice versa). It can then transmit through the polarization beam splitter 12 and be received by the receiver 15 at the receiving end.

[0093] The VCSEL 10 using the technology disclosed in the present invention can achieve more stable polarized light emission and further improve the light extraction efficiency. The laser radar 20 can include the VCSEL 10 disclosed in the present invention as a transmitter to emit linearly polarized light. In the laser radar 20, the use of a polarization beam splitter 12 for splitting light can set a larger reflection surface, thereby improving the light extraction efficiency and reducing the limitation on the divergence angle. The loss of the reflected or transmitted echo light 17 is also reduced. Therefore, compared with the traditional coaxial optical path for transmitting and receiving, the reception efficiency of the echo light 17 in the laser radar 20 with polarization beam splitting is also higher.

[0094] In some embodiments of the present disclosure, a vehicle is also provided. A vehicle according to the present disclosure may include any of the laser radars 20 described herein. In some embodiments, the vehicle may include an automobile, a truck, a motorcycle, a golf cart, an off-road vehicle, an agricultural vehicle, or any other vehicle described elsewhere herein (e.g., a bus, a boat, an airplane, a helicopter, a drone, a lawn mower, a bulldozer, a submarine, an all-terrain vehicle, a snowmobile, an aircraft, a recreational vehicle, an amusement park vehicle, agricultural equipment, construction equipment or vehicles, warehouse equipment or vehicles, factory equipment or vehicles, a tram, a train, a cart, a sidewalk delivery vehicle, a robotic device, etc.).

[0095] Therefore, without departing from the spirit of the present disclosure, those skilled in the art may make appropriate modifications and adjustments to the embodiments specifically described above. Therefore, it is intended that the subject matter claimed for protection is not limited to the specific examples disclosed, and that the subject matter claimed for protection also includes all implementations falling within the scope of the appended claims and their equivalents.

Claims

1. A vertical cavity surface emitting laser, comprising: A substrate; A first mirror, stacked on the substrate; An active layer, stacked on the first mirror; A second mirror, stacked on the active layer, wherein, the vertical cavity surface emitting laser forms light including a first polarization direction and a second polarization direction inside, and the vertical cavity surface emitting laser further includes a grating, the grating is arranged outside the second mirror, wherein the structural parameters of the grating are configured such that in the operating wavelength band of the vertical cavity surface emitting laser, the ratio of the longitudinal mode resonance quality factor of the light in the first polarization direction to the longitudinal mode resonance quality factor of the light in the second polarization direction is greater than or equal to a threshold value, and the vertical cavity surface emitting laser emits the light in the first polarization direction.

2. The vertical cavity surface emitting laser according to claim 1, wherein, the first polarization direction is parallel to the extending direction of the grating, and the second polarization direction is perpendicular to the extending direction of the grating; or the first polarization direction is perpendicular to the extending direction of the grating, and the second polarization direction is parallel to the extending direction of the grating.

3. The vertical cavity surface emitting laser according to claim 2, characterized in that, The threshold value is greater than or equal to 1.1 and less than or equal to 1.

3.

4. The vertical cavity surface emitting laser according to any one of claims 1-3, wherein, before forming the grating, the longitudinal mode resonance quality factor of the vertical cavity surface emitting laser is Q_ref, after forming the grating, the longitudinal mode resonance quality factor of the light in the first polarization direction is Q1, and the longitudinal mode resonance quality factor of the light in the second polarization direction is Q2, wherein: (a) The structural parameters of the grating are further configured such that Q1 is close to Q_ref, and Q2 is much smaller than Q_ref; or (b) The structural parameters of the grating are further configured such that Q2 is close to Q_ref, and Q1 is much smaller than Q_ref.

5. The vertical cavity surface emitting laser according to claim 4, wherein, (a) The structural parameters of the grating are further configured such that Q1 > Q_ref - 1000; or (b) The structural parameters of the grating are further configured such that Q2 > Q_ref - 1000.

6. The vertical cavity surface emitting laser according to claim 5, wherein, (a) The structural parameters of the grating are further configured such that Q1 < Q_ref + 1000; or (b) The structural parameters of the grating are further configured such that Q2 < Q_ref + 1000.

7. The vertical cavity surface emitting laser according to claim 4, wherein, (a) The structural parameters of the grating are further configured such that Q2 < Q_ref - 2000; or (b) The structural parameters of the grating are further configured such that Q1 < Q_ref - 2000.

8. The vertical cavity surface emitting laser according to claim 1, characterized in that, The structural parameters of the grating include at least one of the period of the grating, the groove depth, the duty cycle, or the sidewall inclination angle.

9. The vertical cavity surface emitting laser according to claim 8, characterized in that, The period of the grating does not exceed the operating wavelength of the vertical cavity surface emitting laser.

10. The vertical cavity surface emitting laser according to claim 9, characterized in that, The period of the grating is set to be in the range of 300 nm - 400 nm or in the range of 500 nm - 550 nm.

11. The vertical cavity surface emitting laser according to claim 8, characterized in that, The groove depth of the grating is set to be greater than or equal to 40 nm.

12. The vertical cavity surface emitting laser according to claim 1, characterized in that, The grating is formed by etching one or more layers of the second mirror.

13. The vertical cavity surface emitting laser according to claim 1, characterized in that, The vertical cavity surface emitting laser includes a passivation layer disposed outside the grating.

14. The vertical cavity surface emitting laser according to claim 13, characterized in that, The passivation layer includes silicon nitride.

15. The vertical cavity surface emitting laser according to claim 1, wherein The first mirror includes a distributed Bragg reflector, and the second mirror includes a distributed Bragg reflector.

16. A lidar, the lidar comprising: A transmitter, the transmitter including a laser, the laser including a vertical cavity surface emitting laser according to any one of claims 1 - 15, the laser being configured to emit outgoing light in the first polarization direction or the second polarization direction along a first optical path; And A receiver, the receiver including a detector, the detector being configured to receive the reflected light of the outgoing light reflected by a target along a second optical path.

17. The lidar according to claim 16, wherein, At least a part of the first optical path and the second optical path coincide, and the lidar includes a quarter - wave plate, wherein the quarter - wave plate is disposed on the first optical path and the second optical path.

18. The lidar according to claim 17, wherein, The lidar includes a polarization beam splitter, wherein, The polarization beam splitter is configured to transmit the light in the first polarization direction and reflect the light whose polarization direction is perpendicular to the first polarization direction, or The polarization beam splitter is configured to reflect the light in the first polarization direction and transmit the light whose polarization direction is perpendicular to the first polarization direction.

19. A vehicle, the vehicle including a lidar according to any one of claims 16 - 18.

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