Patent Publication Number: US-2023139244-A1

Title: Photonic crystal surface-emitting laser device and optical system

Description:
FIELD 
     The subj ect matter herein generally relates to a field of laser detection technology, and more particularly, to a photonic crystal surface-emitting laser device and an optical system having the photonic crystal surface-emitting laser device. 
     BACKGROUND 
     Photonic Crystal Surface-Emitting Laser (shorted as PCSEL) devices have the advantages of good beam quality, small size, low energy consumption, easy integration, and high reliability, and are widely used in scanning lidar systems (shorted as LiDAR). The photonic crystal surface emitting laser device in the traditional LiDAR includes a diffraction grating to control the emission angle of the laser light. However, the traditional diffraction grating has a single control over the emission angle of the laser beam, and it is easy to generate multiple laser spots with symmetrical distribution at the same time, which is not conducive to beam scanning. 
     Therefore, there is room for improvement within the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present disclosure will now be described, by way of embodiments, with reference to the attached figures. 
         FIG.  1    is a schematic diagram of an embodiment of an optical system according to the present disclosure. 
         FIG.  2    is a diagram of an embodiment of a photonic crystal surface-emitting laser device according to the present disclosure. 
         FIG.  3    is a cross-sectional view of the photonic crystal surface-emitting laser device taken along III-III line of  FIG.  2   . 
         FIG.  4    is a diagram of an embodiment of a photonic crystal layer according to the present disclosure. 
         FIG.  5    is a diagram of an embodiment of a photonic crystal layer according to the present disclosure . 
         FIG.  6    is a diagram of an embodiment of a metasurface according to the present disclosure. 
         FIG.  7 A  is a diagram of an embodiment of a diffraction unit according to the present disclosure. 
         FIG.  7 B  is a diagram of an embodiment of a diffraction unit according to the present disclosure. 
         FIG.  7 C  is a diagram of an embodiment of a diffraction unit according to the present disclosure. 
         FIG.  8    is a diagram of an embodiment of emission angles of the laser light diffracted by the diffraction unit of  FIGS.  7 A,  7 B, and  7 C . 
         FIG.  9 A  is a diagram of an embodiment of a pillar according to the present disclosure. 
         FIG.  9 B  is a diagram of an embodiment of a pillar according to the present disclosure. 
         FIG.  9 C  is a diagram of an embodiment of a pillar according to the present disclosure. 
         FIG.  9 D  is a diagram of an embodiment of a pillar according to the present disclosure. 
         FIG.  9 E  is a diagram of an embodiment of a pillar according to the present disclosure. 
         FIG.  9 F  is a diagram of an embodiment of a pillar according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     The disclosure is illustrated by way of example and not by way of limitation in thefigures of the accompanying drawings, in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.” 
     The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. 
       FIG.  1    illustrates an embodiment of an optical system  100 . The optical system  100  includes a plurality of photonic crystal surface-emitting laser devices  1 . The optical system  100  may be a face recognition sensing device or a lidar, which may be applied to various consumer electronic devices such as smart phones, augmented reality (AR) glasses, or virtual reality (VR) glasses, and may be applied to automobiles, household equipment, or medical equipment, and may also be applied to unmanned carrier in smart chemical factories or automated warehousing. When the photonic crystal surface-emitting laser devices  1  are applied to the above-mentioned various optical systems  100 , the photonic crystal surface-emitting laser devices  1  are configured to emit laser light according to a driving signal, so that the optical systems  100  can realize functions such as three-dimensional image sensing and flight ranging. 
     The optical system  100  further includes a control device  2  electrically connected to each of the plurality of photonic crystal surface-emitting laser devices  1 . The control device  2  is configured to output a driving signal to each of the plurality of photonic crystal surface-emitting laser devices  1 . In at least one embodiment, the control device  2  may include, but not limited to, a chip, a chip set or a control motherboard. The plurality of photonic crystal surface-emitting laser devices  1  are arranged into a laser emitting array, and each of the plurality of photonic crystal surface-emitting laser devices  1  is independently controlled by the control device  2  to be in an on state or in an off state. Each of the plurality of photonic crystal surface-emitting laser devices  1  emits laser light when it is in the on state, and does not emit laser light when it is in the off state. In the laser emitting array, at least two of the plurality of photonic crystal surface-emitting laser devices  1  emit laser light in different directions. 
     During a working period, the control device  2  controls one or more photonic crystal surface-emitting laser devices  1  to turn on according to a direction, a distance or a size of the objected to be detected. By changing a working state (on or off) of each of the plurality of photonic crystal surface-emitting laser devices  1  in different working periods, a direction and a shape of the laser light emitted by the laser emitting array in different working periods can be changed. 
     Referring to  FIGS.  2  and  3   , each of the plurality of photonic crystal surface-emitting laser devices  1  includes a substrate  10 , a buffer layer  11 , a first cladding layer  12 , a light emitting layer  13 , and a photonic crystal layer  14  that are stacked in sequence. In at least one embodiment, the buffer layer  11  may be omitted. In at least one embodiment, the first cladding layer  12  may be omitted. 
     The substrate  10  is an insulating substrate for carrying and growing the buffer layer  11 , the first cladding layer  12 , the light emitting layer  13 , and the photonic crystal layer  14 . The substrate  10  may made of n-type gallium arsenide. In at least one embodiment, the buffer layer  11  may be made of n-type gallium arsenide. 
     The light emitting layer  13  includes a plurality of quantum well light-emitting layers  131  and a plurality of energy barrier layers  132 . The plurality of quantum well light-emitting layers  131  and the plurality of energy barrier layers  132  are stacked alternately. That is, one of the plurality of quantum well light-emitting layers  131  and one of the plurality of energy barrier layers  132  are stacked alternately. In at least one embodiment, the light emitting layer  13  includes three to five quantum well light-emitting layers  131  and four to six energy barrier layers  132  that are alternately stacked. Each of the quantum well light-emitting layers  131  may be made of indium gallium arsenide, and each of the energy barrier layers  132  may be made of gallium arsenide. In at least one embodiment, the quantum well light-emitting layer  131  may be made of AlGaAs or InGaAsP, and the energy barrier layer  132  may be made of AlGaAs or AlGaInAs. 
     The light emitting layer  13  is configured to generate photons driven by the driving signal. The photons generated by the light emitting layer  13  propagate in all directions. The photons are incident into the photonic crystal layer  14  and generate a vibration on Bragg diffraction in the photonic crystal layer  14 , and until the photonic crystal surface-emitting laser device  1  reaches a balance state of gain and loss, the photons incident into the photonic crystal layer  14  generates laser light. In at least one embodiment, a wavelength of the laser light emitted by the photonic crystal surface-emitting laser device  1  is in a range of 905 nm to 1550 nm (including the end value). 
     The photonic crystal layer  14  includes an ohmic contact layer  141  and a second cladding layer  142  stacked on the ohmic contact layer  141 . The second cladding layer  142  is located between the ohmic contact layer  141  and the light emitting layer  13 . In at least one embodiment, the ohmic contact layer  141  may be made of p-type gallium arsenide. In at least one embodiment, the ohmic contact layer  141  may be made of indium phosphide or indium gallium arsenide phosphide. 
     In at least one embodiment, the first cladding layer  12  may be made of n-type AlGaAs, the second cladding layer  142  may be p-type AlGaAs. The first cladding layer  12  cooperates with the second cladding layer  142  to lock the photons generated by the light emitting layer  13 , thereby reducing the propagation of the photons toward the photonic crystal layer  14 . In at least one embodiment, the first cladding layer  12  and the second cladding layer  142  may be respectively made of AlInAs, InP or gallium arsenide phosphide. 
     Referring to  FIG.  4   , the photonic crystal layer  14  includes a first photonic crystal region  143  and a second photonic crystal region  144  surrounding a periphery of the first photonic crystal region  143 . Photons incident into the first photonic crystal region  143  to generate laser light through a vibration on Bragg diffraction. The second photonic crystal region  144  is configured to reflect the received photons to the first photonic crystal region  143 , so as to reduce photon loss and improve the luminous efficiency of the photonic crystal surface-emitting laser device  1 . 
     A plurality of first through holes  145  arranged at intervals are defined in the first photonic crystal region  143 , and a plurality of second through holes  146  arranged at intervals are defined in the second photonic crystal region  144 . Each of the plurality of first through holes  145  penetrates the ohmic contact layer  141  and the second cladding layer  142 , and each of the plurality of second through holes  146  penetrates the ohmic contact layer  141  and the second cladding layer  142 . The plurality of first through holes  145  and the plurality of second through holes  146  may be both circular through holes. Diameters of the plurality of first through holes  145  may be the same, and diameters of the plurality of second through holes  146  may be the same. The diameter of each of the plurality of first through holes  145  is greater than the diameter of each of the plurality of second through holes  146 , an energy position of a selected mode in a reciprocal space of the first photonic crystal region  143  is not aligned with an energy position of the same mode in a reciprocal space of the second photonic crystal region  144 . So that the resonant wavelength of the first photonic crystal region  143  can fall within the energy gap of the second photonic crystal region  144 . As a result, the second photonic crystal region  144  can be used as a reflecting mirror in the horizontal direction to reflect photons to the first photonic crystal region  143  to generate laser light through the vibration on Bragg diffraction. In at least one embodiment, each of the plurality of first through holes  145  and each of the plurality of second through holes  146  may be, but not limited to, oval, triangular, quadrangular, L-shaped, V-shaped. In the present disclosure, a shape of the first through hole  145  refers to a shape of an opening of the first through hole  145  on the photonic crystal layer  14 , and a shape of the second through hole  146  refers to a shape of an opening of the second through hole  146  on the photonic crystal layer  14 . 
     An area where the photonic crystal surface-emitting laser device  1  can emit laser light is defined as a light-emitting area S. In at least one embodiment, an area where the first photonic crystal region  143  is located is the light-emitting area S. 
     One the one hand, the smaller the area occupied by the first photonic crystal region  143  is, the smaller the driving signal threshold is, that is, the smaller the current threshold required to drive the photonic crystal surface-emitting laser device  1  to emit laser light is. The smaller the current threshold is, the shorter the time required to reach the current threshold is, which is beneficial to improve the operation speed of the photonic crystal surface-emitting laser device  1 . 
     On the other hand, the smaller the area occupied by the first photonic crystal region  143  is, the smaller the light-emitting area of the photonic crystal surface-emitting laser device  1  is. The smaller the light-emitting area of a single photonic crystal surface-emitting laser device  1  is, the more the number of the photonic crystal surface-emitting laser devices  1  that can be accommodated by the laser emitting array of the same area is. The more the number of the photonic crystal surface-emitting laser devices  1  in the laser emitting array is, the more diverse the directions and shapes of the laser light emitted by the laser emitting array. 
     In the present disclosure, the photonic crystal layer  14  includes the first photonic crystal region  143  and the second photonic crystal region  144 , and the first photonic crystal region  143  emits laser light, which is beneficial to reduce the light-emitting area S of the photonic crystal surface-emitting laser devices  1 , thereby facilitating the improvement of the operating speed of the photonic crystal surface-emitting laser devices  1 , and facilitating the diversification of the directions and shapes of the laser light emitted by the laser emitting array applying the photonic crystal surface-emitting laser device  1 . 
     Referring to  FIG.  4   , in at least one embodiment, the first photonic crystal region  143  may be a rectangle, and the second photonic crystal region  144  may be a rectangular frame surrounding the first photonic crystal region  143 . Referring to  FIG.  5   , in at least one embodiment, the first photonic crystal region  143  may be a hexagon, and the second photonic crystal region  144  may be a hexagonal frame surrounding the first photonic crystal region  143 . In at least one embodiment, the first photonic crystal region  143  may be a circle, and the second photonic crystal region  144  may be a circular frame. In the present disclosure, a shape of the first photonic crystal region  143  refers to a shape of an orthographic projection of the first photonic crystal region  143  on the substrate  10 , a shape of the second photonic crystal region  144  refers to a shape of an orthographic projection of the second photonic crystal region  144  on the substrate  10 . 
     The shape of the first photonic crystal region  143  depends on a lattice type of a photonic crystal material in the photonic crystal layer  14 . For example, when the lattice type of the photonic crystal material is triangular lattice or honeycomb lattice, the first photonic crystal region  143  is hexagonal; when the lattice type of the photonic crystal material is square lattice, the first photonic crystal region  143  is quadrilateral (or rectangle). 
     Referring to  FIG.  3   , in at least one embodiment, the photonic crystal surface-emitting laser device  1  further includes a metasurface  15 . The metasurface  15  is located on a surface of the substrate  10  facing away from the photonic crystal layer  14 . The laser light generated by the photonic crystal layer  14  is diffracted by the metasurface  15  and then exits from a side of the metasurface  15  facing away from the photonic crystal layer  14 . 
     The photonic crystal layer  14  is arranged opposite to the metasurface  15 , that is, at least a portion of an orthographic projection of the photonic crystal layer  14  on the light emitting layer  13  overlaps an orthographic projection of the metasurface  15  on the light emitting layer  13 . In at least one embodiment, the orthographic projection of the photonic crystal layer  14  on the light emitting layer  13  completely overlaps the orthographic projection of the metasurface  15  on the light emitting layer  13 . In at least one embodiment, the orthographic projection of the metasurface  15  on the light emitting layer  13  may completely cover the orthographic projection of the photonic crystal layer  14  on the light emitting layer  13 . In this way, the laser light generated by the photonic crystal layer  14  may be incident into the metasurface  15  as much as possible, and the utilization rate of the laser light may be improved. 
     Referring to  FIG.  6   , the metasurface  15  includes a base  151  and a plurality of pillars  152  protruding from one surface of the base  151 . The plurality of pillars  152  are arranged at intervals. Another surface of the base  151  facing away from the surface having the pillars  152  is in direct contact with the surface of the substrate  10 . The base  151  and the plurality of pillars  152  are made of the same material, and the base  151  and the plurality of pillars  152  are integrally formed. The plurality of pillars  152  are formed by etching a plate including the base  151 . In at least one embodiment, the metasurface  15  and the substrate  10  are made of the same material. 
     Each of the plurality of pillars  152  may be a cylinder. In at least one embodiment, distances between any two adjacent pillars  152  may be the same. In at least one embodiment, the distances between any two adjacent pillars  152  may be not all the same, that is, the distances between some adjacent pillars  152  may be different, and the distances between some adjacent pillars  152  may be the same. In at least one embodiment, diameters and/or heights of any two pillars  152  are different. The plurality of pillars  152  on the base  151  are divided into a plurality of diffraction units  150 , and each of the plurality of diffraction units  150  includes a plurality of adjacently arranged pillars  152  to diffract the received laser light. 
       FIGS.  7 A,  7 B, and  7 C  are illustrated several embodiments of structures of the diffraction units  150 .  FIG.  8    is illustrated an embodiment of emission directions of the laser light diffracted by the diffraction units  150  of  FIGS.  7 A,  7 B, and  7 C . The emission direction may also be called an emission angle, and a direction perpendicular to the metasurface  15  is taken as the 0° direction. Therefore, the emission direction of the laser light diffracted and emitted by the metasurface  15  can be changed by changing the size (including diameter, height, etc.), the shape, and the quantity of each of the pillars of each of the diffraction units  150 . 
     Further, since the emission direction of the laser light can be changed by the metasurface  15 , when the metasurface  15  controls the laser light to concentrate in a certain direction, it is equivalent to converging the laser light. In at least one embodiment, the laser light finally emitted by the metasurface  15  can form a single light spot or a plurality of light spots through the convergence of the laser light by the metasurface  15 . According to the degree of the convergence of the laser light, a size of the light spot can be controlled. Therefore, the number and the size of the spots formed by the laser light can be changed by changing the size (including diameter, height, etc.), the shape, and the quantity of each of the pillars of each of the diffraction units  150 . 
     In at least one embodiment, each of the pillars  152  may be a column of other shapes. For example, the pillar  152  may be an elliptical cylinder shown in  FIG.  9 A , a quadrangular prism shown in  FIG.  9 B , a triangular prism shown in  FIG.  9 C  or  FIG.  9 D , a L-shaped cylinder shown in  FIG.  9 E , a V-shaped cylinder shown in  FIG.  9 F , a +-shaped cylinder, or a C-shaped cylinder. In the present disclosure, a shape of the pillar  152  refers to a shape of an orthographic projection of the pillar  152  on the base  151 . 
     In at least one embodiment, the photonic crystal surface-emitting laser device  1  may be a flip-chip structure. After the buffer layer  11 , the first cladding layer  12 , the light emitting layer  13 , and the photonic crystal layer  14  are grown on the surface of the substrate  10 , the photonic crystal surface-emitting laser device  1  is inverted and carried by a flip chip substrate  200 , and the metasurface  15  is formed on the surface of the substrate  10  facing away from the photonic crystal layer  14 . In at least one embodiment, the substrate  10  may be thinned first, and then the metasurface  15  is formed. In at least one embodiment, a thickness of the substrate  10  after being thinned is 10% to 90% of a thickness of the substrate  10  before being thinned, preferably, the thickness of the substrate  10  after being thinned is 20% to 70% of the thickness of the substrate  10  before being thinned. Thinning the substrate  10  is beneficial to heat dissipation. Further, since the laser light needs to pass through the substrate  10  before being emitted, thinning the substrate  10  is also beneficial to reduce an absorption of the laser light by the substrate  10  and reduce the loss of the laser light. 
     Referring to  FIG.  3   , in at least one embodiment, the photonic crystal surface-emitting laser device  1  may further include a first transparent conductive layer  161  and a second transparent conductive layer  162 . The first transparent conductive layer  161  is located on a surface of the metasurface  15  facing away from the photonic crystal layer  14 , the second transparent conductive layer  162  is located on a surface of the photonic crystal layer  14  facing away from the substrate  10 . Both the first transparent conductive layer  161  and the second transparent conductive layer  162  are made of indium tin oxide (ITO). The first transparent conductive layer  161  and the second transparent conductive layer  162  are configured to diffuse current, so that the current distribution is more uniform. 
     In at least one embodiment, the first transparent conductive layer  161  covers the first surface of the base  151  with the pillars  152 , and fills spaces between any two pillars  152 . A thickness of the first transparent conductive layer  161  is less than a height of each of the pillars  152 , so that the pillars  152  protrude from the first transparent conductive layer  161 . That is, each of the spaces between any two pillars  152  is not completely filled by the first transparent conductive layer  161 . 
     Therefore, when the laser light is incident from the photonic crystal layer  14  into the metasurface  15 , the laser light needs to pass through two dielectric layers with different refractive indices successively. In at least one embodiment, the two dielectric layers with different refractive indices are defined as a first dielectric layer  153  and a second dielectric layer  154 . The first dielectric layer  153  is a dielectric layer composed of a portion of the pillars  152  combined with the first transparent conductive layer  161  and the first transparent conductive layer  161 . The laser light has a first deflection angle α1 after passing through the first dielectric layer  153 . The second dielectric layer  154  is a dielectric layer composed of a portion of pillars  152  not combined with the first transparent conductive layer  161  and air. The laser light has a second deflection angle α2 after passing through the second dielectric layer  154 . The laser light passes through the two dielectric layers with different refractive indices and undergoes two angular deflections, so that a deflection angle of the laser light finally emitted by the photonic crystal surface-emitting laser device  1  is the sum of the angular deflections, that is, α1 + α2. 
     The first transparent conductive layer  161  fills the spaces between the pillars  152  which is beneficial to increase the deflection angle of the laser light finally emitted by the photonic crystal surface-emitting laser device  1 , so that the laser light finally emitted has a larger deflection angle range. As a result, when the photonic crystal surface-emitting laser device  1  is applied in the optical system  100 , the optical system  100  has a larger detection range. 
     In at least one embodiment, the photonic crystal surface-emitting laser device  1  may further include a first electrode  171  and a second electrode  172 . The first electrode  171  is located on a side of the substrate  10  facing away from the photonic crystal layer  14 , and is in electrical contact with the first transparent conductive layer  161 . The second electrode  172  is located on a surface of the second transparent conductive layer  162  facing away from the photonic crystal layer  14 , and is in electrical contact with the second transparent conductive layer  162 . The first electrode  171  and the second electrode  172  are configured to be electrically connected to the control device  2  to receive the driving signal. The first electrode  171  and the second electrode  172  are metals, such as titanium (Ti), germanium (Ge), nickel (Ni), gold (Au), platinum (Pt) or alloys thereof. In at least one embodiment, the first electrode  171  is n-type electrode, the second electrode  172  is p-type electrode. 
     When driving signals are applied to the first electrode  171  and the second electrode  172  respectively (the driving signal applied to the first electrode  171  and the driving signal applied to the second electrode  172  are different), the driving current is injected from the side of the photonic crystal layer  14  facing the transparent substrate  10 . The light emitting layer  13  is driven by the driving current to generate photons. The photons generated by the light emitting layer  13  are incident into the photonic crystal layer  14  and generate a vibration on Bragg diffraction in the photonic crystal layer  14 , and when the photonic crystal surface-emitting laser device  1  reaches a balance state of gain and loss, laser light is generated. The laser light incident into the metasurface  15  is diffracted by the metasurface  15  with a specific structure, and then emitted by the metasurface  15  in a specific shape and a specific angle. 
     In at least one embodiment, the photonic crystal surface-emitting laser device  1  may further include insulating layers  18 . Each of the insulating layers  18  may be made of silicon nitride (SiN x ), silicon dioxide (SiO 2 ), or polymethyl methacrylate (PMMA). One of the insulating layers  18  is located between the substrate  10  and the first electrode  171 , the other is located between the second electrode  172  and the photonic crystal layer  14 . The insulating layers  18  are mainly arranged on peripheries of the first electrode  171 , the second electrode  172 , the substrate  10 , and the photonic crystal layer  14  to protect each layer in the photonic crystal surface-emitting laser device  1 . 
     The above photonic crystal surface-emitting laser device  1  and the optical system  100  include the metasurface  15 , and the metasurface  15  includes the base  151  and the plurality of pillars  152  arranged on the base  151  at intervals. At least two of the plurality of pillars  152  have different shapes and/or different sizes. The metasurface  15  is used for receiving laser light, diffracting the laser light and then emitting it. By setting the shapes, the sizes, and the quantity of the plurality of pillars  152 , the expected emission angle of the laser light may be obtained, and the number of the light spots formed by the laser light and the sizes of the light spots formed by the laser light may be controlled. That is, the above photonic crystal surface-emitting laser device  1  and the optical system  100  may realize not only the deflection of the laser light but also shaping the laser light through the metasurface  15 , which is beneficial to realize the diversified control of the laser light. 
     It is to be understood, even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.