AU2021104550A4

AU2021104550A4 - VCSEL Linear Array for Multi-line Lidar

Info

Publication number: AU2021104550A4
Application number: AU2021104550A
Authority: AU
Inventors: Yuanyuan Guo; Zhiwei Jia; Li Li; Pu Li; Anbang Wang; Longsheng WANG; Tong Zhao
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2021-07-26
Filing date: 2021-07-26
Publication date: 2021-09-23
Anticipated expiration: 2029-07-26

Abstract

The invention discloses a VCSEL linear array for multi-line lidar, which specifically comprises a semiconductor substrate (1), an m-element VCSEL linear array (2) and an optical microlens array (3). Each element of the linear array (2) is completely independent, and can output completely irrelevant m laser signals. Each independent VCSEL element corresponds to one microlens element of the optical microlens array (3) at the substrate surface. The laser is emitted from the direction of the substrate, collimated by the microlens array (3) at the substrate surface, and the emission angle of the laser beam emitted by each VCSEL element is adjusted, and finally the m-line laser beam (4) is output. The m-line laser beam includes m laser beams, each of which has a different emitting angle, covering an angle range. The application of the VCSEL linear array can simplify the optical scanning structure of the lidar and reduce the cost of the lidar. FIGURES 3 2 4 M Channel Figure 1 108 109 101 107 106 104 103 105 Figure 2 -- -- -- - - - -- - --- --- -- - ---- ---- ----- 9 II- ~------------------IF ------------- ---- ---- --- ---- 9 7r s-. ---- --- 201 --2 Figure 3

Description

FIGURES

3

2

4

M Channel Figure 1

108 109

101

107 106 104 103 105

Figure 2

------- - - -- - ------ -- - ---- ---- ----- 9

IF II- ~------------------ ------------- ---- ---- --- ---- 9 7r s-. ---- ---

201 2 --

Figure 3

VCSEL Linear Array for Multi-line Lidar

TECHNICAL FIELD

The invention relates to the technical field of laser detection and semiconductor

optoelectronic devices, in particular to a vertical cavity surface emitting laser

(VCSEL) linear array for multi-line lidar.

BACKGROUND

Unmanned driving technology is a cutting-edge technology that will soon change

human life. Lidar plays an irreplaceable role in the development of unmanned driving

technology. In recent years, many enterprises and scientific research institutions have

done a lot of work in multi-line operation, beam scanning and weight reduction of

lidar, which continuously meet the requirements of unmanned driving for lidar.

Especially in multi-line operation, commercial lidar with 64 lines or more has come

out, and the number of lines of unmanned lidar has become an important index to

measure its performance.

Nowadays, the widely used method to realize multi-line operation of lidar is to

use multiple lasers to work at the same time, emit laser signals at different vertical

angles, and combine with horizontal rotation to realize multi-line operation. The

method of multiple lasers will greatly increase the size and weight of lidar, and

increase the cost of devices, which is very unfavorable for the practical application of

lidar. Using integrated laser linear array chip can reduce the volume increase and cost

increase caused by laser itself. However, the beam control of the linear array of

ordinary edge-emitting semiconductor lasers is a big problem, which is difficult, costly and unstable. Therefore, the application of laser array in lidar is still in the research stage. VCSEL has the advantage of high power beam quality, which can be used to make not only linear array but also two-dimensional area array, so it has great application potential in lidar, but VCSEL array also has the difficulty of beam regulation.

Different from the edge-emitting laser, VCSEL's light emitting direction is

perpendicular to the epitaxial plane, which is convenient for integrating optical

elements, thus realizing the control of the output laser beam. The most common

optical element is lens, which has been used to collimate and focus VCSEL beams by

integrating microlenses [Patent No.CN 107453201 A], and the microlens processing

technology has also developed.

SUMMARY

Aiming at the difficulty of adjusting and controlling VCSEL array beams, the

invention proposes to fabricate microlens on the substrate surface of VCSEL with

light-emitting from substrate side, so as to realize the collimation of VCSEL output

laser beams and the adjustment of beam direction. Furthermore, for the application of

multi-line lidar, the VCSEL linear array without external beam control is realized,

which is of great significance for reducing the volume, weight and cost of multi-line

lidar.

The invention provides a VCSEL linear array for multi-line lidar, which

comprises:

A semiconductor substrate (1), which is the substrate for fabrication of VCSEL;

It can be made of GaAs, InP, and GaSb, which depends on the material system of

VCSEL;

An m-element VCSEL linear array (2) and m is the lines number of the

corresponding lidar. Each VCSEL element in the array is independent of each other,

and there is no interaction, such as mode coupling, phase synchronization, power

superposition, etc., so that the array can output m completely irrelevant laser signals;

An optical microlens array (3), which is directly fabricated on the back of the

semiconductor substrate (1), can be either a refractive lens or a diffractive lens. Each

independent VCSEL element has a corresponding microlens. The laser emitted by

VCSEL diverges in the substrate and propagates to the microlens, and then the lens

collimate the divergent laser and control the light-emitting direction.

After being collimated and regulated by the micro lens array, the m completely

incoherent lasers have different beam directions and are distributed in an angle range,

thus forming a multi-line laser beam (4) which meets the requirements of lidar

application. The realization of the invention can simplify the optical scanning

structure of the lidar, thereby reducing the volume and weight, and combining the

integration characteristics, thereby reducing the cost of the lidar.

This patent does not limit the types and structures of VCSELs. Considering the

application of lidar, each VCSEL element should have the characteristics of high

power, and the laser wavelength is in the atmospheric window band, thus ensuring the

long-distance operation of lidar. The microlens array is directly fabricated on the back of the substrate, which can be refractive lens or diffractive lens. The specific fabricating technology and design optimization of the microlens array are not described in this patent.

The method is technically characterized in that: based on the existing integrated

microlens VCSEL, microlenses are used for collimating laser beams and adjusting the

direction of laser beams, so as to construct a VCSEL linear array and realize

multi-line laser beam output for multi-line lidar;

The VCSEL linear array for multi-line lidar has the following advantages:

1. According to the VCSEL linear array, the number of output laser lines can be

increased by integrating more VCSELs, and the angle coverage and distribution of

output multi-line laser beams can be regulated and controlled through the design

adjustment of substrate microlenses, so that the number of lines, the vertical scanning

range change and the vertical resolution control of lidar can be realized;

2. The VCSEL linear array is applied to lidar, and the adjustment of lidar line

number can be realized only by replacing the VCSEL linear array chip, without

redesigning and adjusting the whole lidar;

3. The fabrication required by the VCSEL linear array is the existing mature

process technology and does not involve complex process, so the realization of the

practical application of the invention will reduce the device cost of the multi-line

lidar.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic diagram of the overall structure of a VCSEL linear array

for multi-line lidar described in this patent, in which: 1 is a semiconductor substrate, 2

is a VCSEL linear array, 3 is an optical microlens array, and 4 represents output of

multi-line laser beams.

Figure 2 is a cross-sectional schematic diagram of the specific device structure of

the VCSEL linear array with 16-line laser output, in which: 101 is GaAs

semiconductor substrate; 102 is distributed Bragg reflector (DBR) composed of

variable component AlGaAs with reflectivity of 84%; 103 is laser active area, and 104

is distributed Bragg reflector composed of variable component AlGaAs superlattice

with reflectivity greater than 99.5%; 105 is GaAs secondary epitaxial layer; 106 is

SiO2 insulating layer; 107 and 108 are epitaxial surface and substrate surface

electrode layers respectively; 109 is microlens array.

Figure 3 is a 16-line laser output effect diagram of the VCSEL linear array, in

which: 201 is the VCSEL linear array and 202 is the output 16-line laser beam.

DESCRIPTION OF THE INVENTION

In order to make the technical scheme and advantagess of the present invention

clearer, the present invention will be further described in detail with reference to

specific embodiments and figures. It should be understood that the specific examples

described here are only used to explain the present invention, and are not used to limit

the present invention.

The lidar for unmanned driving technology,

The lidar for unmanned technology aims to further improve the integration of

lidar and reduce the cost of it.The invention provides a VCSEL linear array for

multi-line lidar.

Fig. 1 is a schematic diagram of the overall structure of a VCSEL linear array for

multi-line lidar described in this patent. As shown in fig. 1, the VCSEL linear array

for multi-line lidar includes a semiconductor substrate (1), an m-element VCSEL

linear array (2), and an optical microlens array (3). Semiconductor substrate (1) is the

base for fabricating VCSEL; Each laser in the M-element VCSEL linear array (2) is

independent of each other and has no interaction such as mode coupling, phase

synchronization and power superposition, so that the array can output M completely

irrelevant laser signals. An optical microlens array (3) directly mounted on the back of

the semiconductor substrate (1); Each independent VCSEL has a microlens

corresponding to it, and the laser emitted by VCSEL diverges in the substrate and

propagates to the back microlens; The function of the lens is to collimate the

divergent laser light and control the light emitting direction. After being collimated

and regulated by the micro lens array, each laser beam has a different beam direction

and is distributed in a certain angle range, thus forming a multi-line laser beam (4) for

the application of lidar.

This embodiment is a 16-element VCSEL linear array for 16-line unmanned

vehicle lidar. The VCSEL adopts buried structure based on GaAs substrate, with

working wavelength of 808 nm, and the pulse output power of a single VCSEL is

greater than 2 W with the specific device structure shown in fig. 2. Only three

VCSELs in the linear array of VCSELs are shown in fig. 2, and the actual linear array

includes 16 VCSELs.

As shown in fig. 2, the 16-line VCSEL linear array in the specific embodiment

specifically includes nine parts 101-109, and the descriptions of each part are shown

in the attached drawings. The GaAs semiconductor substrate (101) corresponds to 1 in

fig. 1. Two DBR parts (102 and 104) sandwich the active region (103) to form a

vertical cavity resonant structure of VCSEL. The light reflectivity of 102 is about

84%, and the light reflectivity of 104 is greater than 99.5%, so VCSEL generates laser

light and emits it from the substrate direction. After etching the VCSEL circular mesa

structure array, the semi-insulating GaAs material (105) is secondarily epitaxially

used as the photoelectric isolation of each VCSEL element, and the transverse optical

confinement waveguide structure of VCSEL device is formed at the same time, and

102-105 together form a VCSEL linear array, corresponding to 2 in fig. 1. The SiO2

insulating layer (106) plays a role in consolidating electrical isolation and transverse

waveguide. The materials and planar structures of the two electrode layers (107 and

108) are different depending on the process platform and the specific use, which is not

described in detail in this patent. 106-108 belong to further implementation details

and can be attributed to the VCSEL array part. The microlens array (109) corresponds

to 3 infig. 1. In this embodiment, the embossed microlens processed by laser direct

writing is adopted. The microlens array is directly fabricated on the back of the

substrate (101). Each VCSEL cell has a corresponding microlens, and 16 VCSELs

emit 16 independent laser beams. Each microlens collimates and adjusts the direction of one laser beam. In this embodiment, the effect diagram of the output 16-line laser beam is shown in fig. 3 and the laser beams output by VCSEL elements at both ends form an included angle of 12.4° with the normal of the array plane, and the included angle of the laser beams output to the middle VCSEL element decreases in turn, thus forming a scanning beam of a 16-line lidar with a vertical scanning range of 24.8°.

Based on the principle that the size of lidar is as small as possible, in order to reduce

the size of light exit, in this embodiment, 16-line laser beams first converge to the

middle and then diverge in their respective directions, and the position where the

beams converge is the light exit of lidar.

The above specific embodiment further illustrates the purpose, technical scheme

and beneficial effects of the present invention. It should be understood that the

embodiments are only specific embodiments of the present invention and are not used

to limit the present invention. Any modifications, equivalent substitutions and

improvements made within the spirit and principle of the present invention should be

included in the protection scope of the present invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A VCSEL linear array for multi-line lidar comprises a semiconductor substrate

(1), an m-element VCSEL linear array (2) and an optical microlens array (3);

Each element of the linear array (1) is completely independent, and can output

completely irrelevant m laser signals; The laser is emitted from the direction of the

substrate, collimated by the microlens array (3) at the substrate surface, and the

emission angle of the laser beam is adjusted, and finally the m-line laser beam (4) is

output.

2. The VCSEL linear array for multi-line lidar according to claim 1, which is

characterized in that each VCSEL element is completely independent and can output

m laser beams which are completely irrelevant to each other.

3. The VCSEL linear array for multi-line lidar according to claim 1, which is

characterized in that the microlens array (3) is directly fabricated on the back of the

semiconductor substrate (1) to process the laser beams.

4. The microlens array according to claim 3, which is characterized in that each

microlens in the array corresponds to a VCSEL element in the linear array, and the

microlens not only plays the role of beam collimation, but also plays the role of

adjusting and controlling the beam direction.

5. The microlens array according to claim 3, which is characterized in that the

adjustment and control of the beam direction is not only applicable to linear arrays,

but also to two-dimensional area arrays, further improving the chip integration.

6. The VCSEL linear array for multi-line lidar according to claim 1, which is

characterized in that it can output multiple independent, collimated multi-line laser

beams with different directions, and meet the application requirements of multi-line

lidar.