CN114122910A

CN114122910A - Laser chip, light source module and laser radar

Info

Publication number: CN114122910A
Application number: CN202010884996.2A
Authority: CN
Inventors: 费嘉瑞; 向少卿
Original assignee: Hesai Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2020-08-28
Filing date: 2020-08-28
Publication date: 2022-03-01

Abstract

The invention provides a laser chip comprising a plurality of VCSEL units, wherein each VCSEL unit comprises: the light emitting mesas of the VCSEL units are densely distributed on the laser chip; the electrode is arranged on the light-emitting table top, is annular and defines a light-emitting window in a track shape or a round-corner polygon shape; the dense arrangement is that the number of VCSEL units which can be arranged in a certain area is the largest. The preferred embodiment of the invention adopts the runway-shaped light-emitting table surface or the round polygonal light-emitting table surface, increases the area of the light-emitting table surface of a single VCSEL, reduces the gap, increases the area ratio of the total light-emitting surface on the chip, and further increases the light-emitting power density of the laser chip.

Description

Laser chip, light source module and laser radar

Technical Field

The invention generally relates to the technical field of laser radars, in particular to a laser chip, a light source module comprising the laser chip and a laser radar.

Background

The Vertical Cavity Surface Emitting Laser (VCSEL) has stable optical path and small wavelength temperature drift; the VCSEL area array has the characteristics of easy integration and relatively simple process, and is the first choice of a light source of a low-cost high-performance sensor. However, in the application of VCSEL as the light source of lidar, the light emitting power of a single VCSEL is low, and the requirement of the detection distance of the lidar target on the power of the light source is not met, so that when VCSEL is used as the light source of lidar, it is usually composed of several tens to several thousands of independent light emitting mesas and channels between the mesas with proper size to form an area array.

As shown in fig. 1, the existing VCSEL planar array design adopts a circular light emitting mesa, a circular contact electrode is formed outside the light emitting mesa, and a through hole of an inner ring of the electrode is used as a light emitting window. Although the chip area is utilized to the maximum extent by using the honeycomb-shaped close-packed mode in fig. 1, it can be seen that, in the VCSEL chip using the circular light-emitting mesa, a large amount of chip area still exists between the adjacent light-emitting mesas except the light-emitting region, which cannot participate in the light-emitting process, and the power density of light emission is limited. The statements in this background section merely represent techniques known to the public and are not, of course, representative of the prior art.

Disclosure of Invention

In order to solve the problem of light emitting area loss caused by process limitation of a VCSEL area array chip with a circular light emitting table surface and improve the duty ratio of the light emitting area in the whole chip area, so that the light emitting power density of the VCSEL area array chip is improved, the invention provides a laser chip which comprises a plurality of VCSEL units, wherein each VCSEL unit comprises:

the light emitting mesas of the VCSEL units are densely distributed on the laser chip; and

the electrode is arranged on the luminous table top, is annular and defines a light-emitting window in a track shape or a round-corner polygon shape;

the dense arrangement is that the number of VCSEL units which can be arranged in a certain area is the largest.

According to an aspect of the invention, wherein the plurality of racetrack shaped light emitting mesas are arranged in an array on the laser chip.

According to an aspect of the invention, the rounded polygonal light emitting mesas comprise rounded rectangular light emitting mesas arranged in an array on the laser chip.

According to an aspect of the invention, wherein the plurality of rounded polygonal light emitting mesas comprise rounded regular hexagonal light emitting mesas arranged in a honeycomb pattern on the laser chip.

According to an aspect of the invention, the rounded polygonal light emitting mesas comprise rounded rhombus light emitting mesas arranged in a honeycomb fashion on the laser chip.

According to an aspect of the present invention, the shape of the light emitting mesa is set such that the minimum distance between any one point of the light emitting region and the electrode is not greater than a preset value, and the preset value is set according to the current density of the active region such that the current of any one point of the active region is not less than the threshold current required for stimulated luminescence.

The present invention also provides a light source module, including:

the laser chip as described above; and

a driving chip configured to be electrically connected with an electrode of the laser chip.

According to an aspect of the present invention, the light source module further includes a beam shaping unit configured to shape the laser light emitted from the light source module into a beam having a circular or approximately circular cross section.

According to an aspect of the invention, wherein the beam shaping unit comprises one or more of a converging lens, an optical fiber.

The invention also provides a laser radar which comprises the light source module.

The invention also provides a method for laser pulse emission by using the laser chip.

The preferred embodiment of the invention provides a laser chip, which comprises a runway-shaped light-emitting mesa or a rounded polygonal light-emitting mesa, the total area of the light-emitting mesas which can be distributed in the same area is increased, the gaps among VCSEL units are reduced, the area occupation ratio of the total light-emitting surface on the chip is increased, and the light-emitting power density of the laser chip is increased. And when a runway-shaped light emitting table surface is preferably adopted, the area of the light emitting table surface of the single VCSEL unit is increased, and the area of a light emitting window of the single VCSEL unit is increased under the condition that the ring-shaped electrodes with the same width are adopted on the light emitting table surface. .

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 schematically illustrates a prior art VCSEL area array of circular light emitting mesas;

fig. 2A schematically shows the structure of a surface emitting VCSEL;

figure 2B schematically illustrates the structure of a bottom emitting VCSEL;

fig. 3 schematically shows the active region current of a VCSEL unit as a function of the distance of the active region light emission location from the electrode;

FIG. 4A schematically illustrates a VCSEL area array of racetrack shaped light emitting mesas according to a preferred embodiment of the invention;

FIG. 4B shows a partial enlarged view of FIG. 4A;

FIG. 5 schematically illustrates a VCSEL area array of rounded rectangular light emitting mesas according to a preferred embodiment of the present invention;

FIG. 6 schematically illustrates a VCSEL area array of rounded regular hexagonal light emitting mesas according to a preferred embodiment of the present invention;

FIG. 7 schematically illustrates a VCSEL area array of rounded diamond light emitting mesas according to a preferred embodiment of the present invention;

fig. 8 schematically illustrates a light source module according to a preferred embodiment of the present invention;

fig. 9A schematically illustrates a beam shaping unit of a light source module according to a preferred embodiment of the present invention;

fig. 9B schematically illustrates a beam shaping unit of a light source module according to a preferred embodiment of the present invention.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection, either mechanically, electrically, or in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.

The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.

The embodiments of the present invention will be described in conjunction with the accompanying drawings, and it should be understood that the embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

The light Emitting direction of a Vertical Cavity Surface Emitting Laser (VCSEL) is perpendicular to the Surface of a chip, no Cavity Surface damage exists, and integration of a two-dimensional high-density array is easy to realize, so that the output power can be improved.

As shown in fig. 2, a VCSEL commonly used at present includes a top emission structure and a bottom emission structure. The top emission structure adopts Metal-organic Chemical Vapor Deposition (MOCVD) technology to sequentially grow n-DBR → active region → oxide layer → p-DBR on the n-type GaAs substrate, wherein the DBR is a Distributed Bragg Reflector (DBR) which is a periodic structure layer with up to nearly one hundred layers, and light emitted in the resonant cavity forms laser output after reciprocating and oscillating for multiple times through the DBR structure. The distributed Bragg reflector is used as a laser cavity mirror, and the quantum well active region is clamped between the n-DBR and the p-DBR. And then manufacturing metal contact layers (namely electrodes) on the outer surfaces of the substrate and the p-DBR, manufacturing a light-emitting window on the p-DBR or the n-DBR to obtain light beams, and finally bonding the light beams with a heat sink with good heat conductivity to improve the heat dissipation performance of the chip. The bottom emission structure is generally used for generating 976-1064 nm-band laser, the manufacturing process of the MOCVD technology and the process of manufacturing a metal contact layer (namely an electrode) on the outer surface are the same as those of the top emission structure, then the substrate is generally thinned to be below 150 mu m so as to reduce the absorption loss of the substrate, a layer of antireflection film is grown so as to improve the quality of a laser beam, and finally the gain chip is installed on a heat sink.

The VCSEL array of the top emission structure usually shares an N-type substrate with a plurality of VCSEL lasers, each VCSEL anode can be connected with a supply voltage, and the area array VCSEL lasers are driven by a common cathode. A VCSEL array with a bottom emission structure, as shown in fig. 2B, may be driven with a common anode. The light emitting power of a single VCSEL is low, and in the laser radar, an array containing tens of VCSEL units to thousands of VCSEL units is usually used as a light emitting channel, and the VCSELs of one light emitting channel are simultaneously driven to emit light to form a probe beam. Preferably, one or more light emitting channels may be provided on one laser chip.

The light emitting principle of the VCSEL is that metal contact layers (namely electrodes) are respectively prepared at the top end and the bottom end of a light emitting table top, wet oxidation is carried out on the side wall of the table top to obtain a current limiting hole, and light is generated and amplified when current passes through a quantum well active region from the top end of the table top through the current limiting hole so as to generate laser. When the injection current I of the VCSEL is smaller than the threshold current Ith, the output power P of the laser is small and is the fluorescence of spontaneous emission, and the output power of the fluorescence is slowly increased along with the increase of the injection current. When the injection current I is greater than the threshold current Ith, the output power P increases sharply with an increase in the injection current I, when the P-I curve is substantially linear. When I increases again, the P-I curve begins to curve non-linearly due to the junction temperature rising with increasing injection current I, resulting in a slower rate of increase of power P.

As shown in fig. 3, since the current needs to flow from the metal electrode to the center of the active region laterally, the current density of the region farther away from the metal electrode (closer to the center of the active region) is smaller due to the resistance of the epitaxial structure, so that the light emitting mesa is over-sized, which results in weak or no light emission in the center region of the active region. As shown in fig. 3, the current density decreases from the surrounding electrodes to the center of the active region, and the inner diameter of the ring-shaped metal electrode is limited to ensure that the threshold current is still reached at the center. Thus, an oversized current-limiting aperture results in a waste of light-emitting area within the aperture, which would result if the diameter of the VCSEL emitting mesa of the circular optical window exceeded 30 μm at an exemplary drive current level, such as 15A.

According to a preferred embodiment of the present invention, as shown in fig. 4A and 4B (fig. 4B is a partially enlarged view of fig. 4A), the present invention provides a laser chip 10 including a plurality of VCSEL units 11, wherein each VCSEL unit 11 includes: a light emitting mesa in a racetrack shape or a rounded polygon, and an electrode 112. The electrode 112 extends inward from the edge to a certain width on the upper surface of the light emitting mesa to form a ring shape similar to the cross-sectional shape of the light emitting mesa, and the light emitting region of the VCSEL unit is defined on the light emitting mesa to form the light emitting window 111, where the cross-section is a plane parallel to the surface of the VCSEL array chip. The light emitting mesas of the plurality of VCSEL units 11 are densely arranged on the laser chip 10.

According to a preferred embodiment of the present invention, as shown in fig. 4A, the light emitting mesa and the light exit window 111 are racetrack shaped, and a plurality of racetrack shaped light emitting mesas are arranged in an array on the laser chip 10. The straight edges of two adjacent VCSEL units are parallel to each other. In fig. 4A, in a plane parallel to the light emitting mesa, a first direction is defined parallel to the straight edge, a second direction is defined perpendicular to the straight edge, and the centers of the light emitting mesas of the plurality of VCSEL units arranged in the first direction are on a straight line to form a row of VCSELs; the centers of the light emitting mesas of the plurality of VCSEL units arranged in the second direction are in a straight line to form a row of VCSELs. The VCSEL units are arranged on the chip in a rectangular area array with multiple rows and multiple columns.

The laser chip 10 comprises a plurality of VCSEL units 11, each VCSEL unit 11 comprising a racetrack shaped light emitting mesa. Compared with the circular light-emitting table top in the prior art, the current of any point on the active region can reach the minimum current value required by the stimulated light only by the requirement that the distance between the two long sides is smaller than a certain preset value (the change of the current of the active region is discussed in detail in fig. 3), so that the area of the racetrack-shaped light-emitting table top is greatly increased. The runway-shaped light-emitting mesas are densely arranged on the laser chip 10, so that for the chips with the same area (compared with the VCSEL array chip with the circular light-emitting mesas shown in FIG. 1), the proportion of the total light-emitting area of the VCSEL to the whole chip area is increased, the power density is increased, and the power of the emergent light beam of the laser radar is increased.

Through proper design, the VCSEL area array chip 10 composed of the racetrack-shaped light-emitting mesa can increase the proportion of the light-emitting area on the chip by 100% or even higher (compared with a circular optical window VCSEL array on the chip with the same area) under the condition of ensuring proper current density distribution. Therefore, the utilization rate of the chip can be increased, and the luminous power density can be improved.

According to a preferred embodiment of the present invention, as shown in fig. 4B, the shape of the light emitting mesa is set such that: the minimum distance (shown by a dotted line in the figure) between any point of the active region and the electrode 112 is not greater than a preset value, and the preset value is set according to the current density of the excited active region, so that the current of any point of the active region is not less than the threshold current required by excited light.

As shown in fig. 4B, the edge of the racetrack-shaped light-emitting mesa is a metal electrode 112, and the metal electrode may extend in the longitudinal direction while maintaining a dimension limited by current density distribution in the short-side direction (for example, a diameter in the short-side direction does not exceed 30 μm), and the long-side edge is semicircular. The central region in the long axis direction can obtain the current passing from the two long sides to the center, so that the dimension in the long axis direction can be set to an arbitrary value in theory.

Because the size of a single device is increased, the resistance of the device is reduced, and therefore, under the condition of adopting the same driving current, the driving voltage can be reduced; or under the condition of the same driving voltage, the light emitting power higher than that of the VCSEL array with the circular light emitting table surface can be obtained.

According to a preferred embodiment of the present invention, as shown in fig. 5, the rounded polygonal light emitting mesas include rounded rectangular light emitting mesas arranged in an array on the laser chip 10.

According to a preferred embodiment of the present invention, as shown in fig. 6, the rounded polygonal light-emitting mesas include rounded regular hexagonal light-emitting mesas, and the rounded regular hexagonal light-emitting mesas are arranged in a honeycomb shape on the laser chip 10. Specifically, the straight edge of the light emitting mesa of each VCSEL unit is parallel to the straight edge of the light emitting mesa of another adjacent VCSEL unit, and two adjacent rows/rows of VCSEL units are staggered to form a honeycomb shape, so that the number of VCSEL units arranged in a certain area is the largest.

According to a preferred embodiment of the present invention, as shown in fig. 7, the rounded polygonal light-emitting mesas include rounded rhombus-shaped light-emitting mesas, and the rounded rhombus-shaped light-emitting mesas are arranged in a honeycomb shape on the laser chip 10.

According to a preferred embodiment of the present invention, the shape of the light emitting mesa is set such that the minimum distance from any one point of the light emitting region to the electrode is not more than a preset value, which is set according to the current density of the active region such that the current at any one point of the active region is not less than the threshold current required for stimulated light. The preferred embodiments of the rounded rectangle, rounded regular hexagon and rounded rhombus light-emitting mesa are also designed according to the distance from each point of the active area to the surrounding electrodes. In some embodiments, it is within the scope of the present invention to maintain the dimension limited by the current density distribution in the short side direction, but extend in the long side direction.

According to a preferred embodiment of the present invention, as shown in fig. 8, the present invention further provides a light source module 20, which includes the laser chip 11 and the driving chip 21. Wherein the driving chip 21 is electrically connected to the electrode 112 of the laser chip 11. The bonding points of the laser chip 11 and the bonding points of the driver chip 21 are electrically connected, and may be implemented in various ways: (1) the laser and the driver chip are tiled, and are not directly electrically connected with each other, but are connected to a bonding point (bonding pad) of the PCB through a laser, the driver chip is connected to the other bonding point of the PCB, and the two bonding points are electrically connected through a lead of the PCB; (2) the laser chip 11 is stacked on the driver chip 21, and the laser chip 11 is bonded to the driver chip 21 by a bonding wire.

According to a preferred embodiment of the present invention, as shown in fig. 9A and 9B, the light source module 20 further includes a beam shaping unit 22, and the beam shaping unit 22 is configured to shape the laser light emitted from the light source module 20 into a beam with a circular or approximately circular cross section. The cross-section is here taken in a plane perpendicular to the direction of propagation of the light beam.

The light-emitting table top of the traditional VCSEL is circular, the emitted laser spot is approximately circular, and the circular spot has wide application in the fields of laser illumination, laser ranging, laser radar and 3D sensing.

The light beams emitted by the runway-shaped light-emitting table surface and the round-corner rectangular light-emitting table surface in the preferred embodiment of the invention have larger divergence angles in the long edge direction, and under the condition that circularly symmetrical light spots are needed, a light beam shaping unit can be arranged on a laser emergent light path to compress the divergence angles in the long axis direction.

Laser spots emitted by the runway-shaped light-emitting table top and the rounded rectangular light-emitting table top in the preferred embodiment of the invention are approximate to an ellipse, and specific application can be performed in the laser radar according to the shapes of the spots, for example, in some application scenes, the field angle in a certain direction needs to be increased, and the light beams do not need to be diverged through other optical devices such as lenses.

As shown in fig. 9A, according to a preferred embodiment of the present invention, the laser spot emitted from the racetrack-shaped light emitting mesa or the rounded rectangular light emitting mesa is approximately elliptical, and the beam shaping unit package 22 in the light source module 20 includes a converging lens, which is compressed in the direction of the long axis by the divergence angle, so that the emergent spot is approximately circular. As shown in fig. 9B, according to a preferred embodiment of the present invention, the beam shaping unit 22 in the light source module 20 includes an optical fiber, and the shape of the end face of the optical fiber is shown in fig. 9B. The laser emitted by the runway-shaped luminous table surface or the round-corner regular polygon luminous table surface is transmitted and shaped through the optical fiber. The beam shaping unit 22 in the above two embodiments is configured to adjust the laser emitted from the light emitting mesa 111 in a racetrack shape or a rounded regular polygon shape.

According to a preferred embodiment of the present invention, the present invention further provides a lidar including the light source module 20 as described above.

The present invention also provides a method of laser pulse emission using the laser chip 10 as described above, according to a preferred embodiment of the present invention.

The preferred embodiment of the invention provides a laser chip which comprises a runway-shaped light-emitting mesa or a rounded polygonal light-emitting mesa, the area of the light-emitting mesa of a single VCSEL is increased, the gap is reduced, the area ratio of the total light-emitting surface on the chip is increased, and the light-emitting power density of the laser chip is increased.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A laser chip comprising a plurality of VCSEL units, wherein each VCSEL unit comprises:

2. The laser chip of claim 1, wherein the plurality of racetrack light emitting mesas are arranged in an array on the laser chip.

3. The laser chip of claim 1, wherein the plurality of rounded polygonal light emitting mesas comprise rounded rectangular light emitting mesas arranged in an array on the laser chip.

4. The laser chip of claim 1, wherein the plurality of rounded polygonal light emitting mesas comprise rounded regular hexagonal light emitting mesas arranged in a honeycomb pattern on the laser chip.

5. The laser chip of claim 1, wherein the plurality of rounded polygonal light emitting mesas comprise rounded diamond light emitting mesas arranged in a honeycomb pattern on the laser chip.

6. The laser chip of any one of claims 1-5, wherein the shape of the light emitting mesa is set such that the minimum distance from the electrode to any one point of the light emitting region is not greater than a preset value, the preset value being set according to the current density of the active region such that the current at any one point of the active region is not less than a threshold current required for stimulated light.

7. A light source module, comprising:

the laser chip of any one of claims 1-6; and

8. The light source module of claim 7, further comprising a beam shaping unit configured to shape the laser light emitted from the laser chip into a beam having a circular or approximately circular cross-section.

9. The light source module of claim 8, wherein the beam shaping unit comprises one or more of a converging lens, an optical fiber.

10. The light source module of any one of claims 7-9, wherein the laser chip comprises a plurality of VCSEL units, the VCSEL units comprise racetrack-shaped light emitting mesas, and the laser emitted from the laser chip is shaped by an optical fiber and then emitted.

11. A lidar comprising a light source module according to any of claims 7-10.

12. A method of laser pulse emission using the laser chip of any one of claims 1-6.