阅读说明：本技术 带激光控制的固态lidar发送器 (Solid-state LIDAR transmitter with laser control ) 是由 R·海瑞尔 N·茨欧尼 M·卡斯皮 M·弗盖尔 M·J·道诺万 于 2020-04-06 设计创作，主要内容包括：一种具有矩阵可寻址激光器驱动电路的固态LIDAR发送器,包括向矩阵可寻址激光器驱动电路的列提供第一电压电位的第一电总线和向矩阵可寻址激光器驱动电路的行提供第二电压电位的第二电总线。多个列开关将多个列连接到第一电总线。多个行开关将多个行连接到第二电总线。发送器包括多个串联连接的二极管,所述二极管包括与另一个二极管串联连接的激光二极管,其中所述多个串联连接的二极管中的相应一个电连接在矩阵可寻址激光器驱动电路的相应列和相应行之间以形成LIDAR发送器。第二二极管中的至少一些增加串联连接的二极管的整体反向击穿电压。(A solid-state LIDAR transmitter with a matrix-addressable laser driver circuit includes a first electrical bus providing a first voltage potential to columns of the matrix-addressable laser driver circuit and a second electrical bus providing a second voltage potential to rows of the matrix-addressable laser driver circuit. A plurality of column switches connect the plurality of columns to the first electrical bus. A plurality of row switches connect the plurality of rows to the second electrical bus. The transmitter comprises a plurality of series-connected diodes comprising a laser diode connected in series with another diode, wherein a respective one of the plurality of series-connected diodes is electrically connected between a respective column and a respective row of the matrix-addressable laser driver circuit to form a LIDAR transmitter. At least some of the second diodes increase the overall reverse breakdown voltage of the series-connected diodes.)

1. A solid state light detection and ranging LIDAR transmitter having a matrix-addressable laser drive circuit, the LIDAR transmitter comprising:

a) a first electrical bus providing a first voltage potential to the columns of the matrix-addressable laser drive circuit;

b) a second electrical bus providing a second voltage potential to the rows of the matrix-addressable laser drive circuit;

c) a plurality of column switches, each of the plurality of column switches connecting one of the plurality of columns to a first electrical bus;

d) a plurality of row switches, each of the plurality of row switches connecting one of the plurality of rows to a second electrical bus; and

e) a plurality of series-connected diodes including laser diodes electrically connected in series with second diodes, a respective one of the plurality of series-connected diodes electrically connected between a respective column and a respective row of the matrix-addressable laser driver circuit to form the LIDAR transmitter, wherein at least some of the second diodes increase an overall reverse breakdown voltage of the series-connected diodes to reduce optical crosstalk when the LIDAR transmitter is energized.

2. The solid-state LIDAR transmitter of claim 1, wherein at least some of the second diodes comprise active P-N junctions that generate optical gain that increases brightness of the associated laser diodes.

3. The solid-state LIDAR transmitter of claim 1, wherein at least some of the second diodes do not generate optical gain.

4. The solid-state LIDAR transmitter of claim 1, wherein at least some of the second diodes are photodiodes.

5. The solid-state LIDAR transmitter of claim 1, wherein at least some of the second diodes are monolithically integrated with the laser diode.

6. The solid-state LIDAR transmitter of claim 1, wherein at least some of the second diodes are positioned on a substrate separate from a substrate of the laser diode.

7. The solid-state LIDAR transmitter of claim 1, wherein at least some of the plurality of series-connected diodes are configured to have a total reverse breakdown voltage that exceeds an absolute value of a maximum drive voltage provided by the first and second electrical buses.

8. The solid-state LIDAR transmitter of claim 1, wherein at least some of the laser diodes comprise at least two serially connected apertures.

9. The solid state LIDAR transmitter of claim 1, wherein at least some of the laser diodes comprise at least two active regions separated by a tunnel junction.

10. The solid state LIDAR transmitter of claim 1, wherein at least some of the laser diodes comprise surface emitting laser diodes.

11. The solid state LIDAR transmitter of claim 1, wherein at least some of the laser diodes comprise vertical cavity surface emitting laser diodes.

12. The solid-state LIDAR transmitter of claim 1, wherein the first electrical bus is configured to provide a positive voltage to an anode of the laser diode.

13. The solid-state LIDAR transmitter of claim 1, wherein the second electrical bus is configured to provide a ground potential to a cathode of the laser diode.

14. The solid-state LIDAR transmitter of claim 1, wherein at least some of the plurality of column switches and the plurality of row switches comprise transistors.

15. The solid state LIDAR transmitter of claim 1, wherein at least some of the plurality of column switches and the plurality of row switches comprise asymmetric switch driver circuits.

16. The solid state LIDAR transmitter of claim 15, wherein the asymmetric switch driver circuit comprises a GaN FET driver circuit.

17. The solid state LIDAR transmitter of claim 1, wherein at least some of the plurality of column switches and at least some of the plurality of row switches comprise enhancement-mode MOSFET power transistors.

18. The solid-state LIDAR transmitter of claim 1, wherein at least some of the plurality of column switches and at least some of the plurality of row switches comprise GaN power transistors.

19. The solid-state LIDAR transmitter of claim 1, wherein at least some of the laser diodes are configured to emit optical radiation between 830nm and 1000 nm.

20. The solid-state LIDAR transmitter of claim 1, wherein a number of the plurality of rows is the same as a number of the plurality of columns.

21. The solid-state LIDAR transmitter of claim 1, wherein a number of the plurality of rows is not equal to a number of the plurality of columns.

22. The solid-state LIDAR transmitter of claim 1, further comprising a power supply that generates the first voltage potential and the second voltage potential, wherein the power supply is configured to enter a reduced-power mode when the first voltage potential and the second voltage potential are not generated.

23. A method of generating a light detection and ranging LIDAR light beam, the method comprising:

a) providing a two-dimensional array of laser devices comprising a plurality of series-connected diodes, including a laser diode electrically connected in series with a second diode, and wherein a respective one of the plurality of series-connected diodes is electrically connected between a column and a row of a respective matrix-addressable laser driver circuit;

b) configuring at least some of the second diodes to increase an overall reverse breakdown voltage of the series-connected diodes to reduce optical crosstalk in the LIDAR beam;

c) switching the first voltage potential to a selected column of the matrix-addressable laser drive circuit; and

d) the second voltage potential is switched to a selected row of the matrix-addressable laser driving circuit to forward bias the selected laser diode in the two-dimensional array of laser devices to cause emission of a LIDAR beam having a desired pattern while reducing optical crosstalk by the serially-connected second diodes.

24. The method of generating a LIDAR beam of claim 23, wherein switching the first voltage potential to the selected column of the matrix-addressable laser drive circuit comprises applying a voltage greater than 10V.

25. The method of generating a LIDAR beam of claim 23, wherein switching the first voltage potential to the selected column of the matrix-addressable laser drive circuit comprises switching for a predetermined time to generate the LIDAR beam comprising a train of light pulses.

26. The method of generating a LIDAR beam of claim 23, further comprising selecting at least one of the first voltage and the second voltage such that the two-dimensional array of laser devices causes emission of the LIDAR beam having a peak power in excess of 20 watts.

27. The method of generating a LIDAR beam of claim 23, wherein switching the first voltage potential to the selected column of the matrix-addressable laser drive circuit and switching the second voltage potential to the selected row of the matrix-addressable laser drive circuit are performed at a rate that generates pulses in the train of light pulses having a pulse duration of less than 10 nanoseconds.

28. The method of generating a LIDAR beam of claim 25, wherein switching the first voltage potential to a selected column of the matrix-addressable laser drive circuit and switching the second voltage potential to a selected row of the matrix-addressable laser drive circuit are performed to reduce power consumption when no pulse is generated.

29. The method of generating a LIDAR beam of claim 28, further comprising turning off a power supply that supplies the first voltage potential and the second voltage potential when no pulse is generated.

30. The method of generating a LIDAR beam of claim 23, wherein switching the first voltage potential to the selected column of the matrix-addressable laser drive circuit comprises switching for a predetermined time to maintain a transient temperature rise in a junction of the laser diode below 20 ℃.

31. The method of generating a LIDAR beam of claim 23, wherein at least some of the laser diodes emit a beam having a wavelength between 830nm and 1000 nm.

32. The method of generating a LIDAR beam of claim 23, wherein the first voltage potential is greater than a breakdown voltage of at least some of the laser diodes.

Background

Autonomous, self-driving, and semi-autonomous automobiles use a combination of different sensors and technologies, such as radar, image recognition cameras, and ultrasonic transducers, for detecting and locating surrounding objects. These sensors enable many improvements in driver safety, including collision warning, automatic emergency braking, lane departure warning, lane keeping assist, adaptive cruise control, and automatic (piloted) driving. Among these sensor technologies, light detection and ranging (LIDAR) systems play a crucial role, enabling real-time, high-resolution three-dimensional mapping of the surrounding environment.

Drawings

In accordance with preferred and exemplary embodiments and further advantages thereof, the present teachings are more particularly described in the following detailed description taken in conjunction with the accompanying drawings. Those skilled in the art will appreciate that the drawings described below are for illustration purposes only. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the present teachings. These drawings are not intended to limit the scope of the applicants' teachings in any way.

Fig. 1A illustrates a schematic diagram of a solid-state LIDAR system.

Fig. 1B illustrates a two-dimensional projection of a system field of view (FOV) of the LIDAR system of fig. 1A.

Fig. 2 illustrates a perspective view of a structure of a known bottom-emitting Vertical Cavity Surface Emitting Laser (VCSEL) that may be used in a LIDAR system according to the present teachings.

Fig. 3 illustrates a schematic diagram of an embodiment of a two-dimensional (2D) monolithic VCSEL array with 256 individual laser emitters for use in a solid-state LIDAR system according to the present teachings.

Figure 4 illustrates an exemplary cascaded two-port circuit model of an embodiment of individual semiconductor lasers for a VCSEL array in accordance with the present teachings.

Figure 5A illustrates an electrical schematic diagram of an embodiment of a matrix-addressable laser driving circuit for controlling a two-dimensional laser array having row/column matrix addressability according to one embodiment of the present teachings.

Figure 5B illustrates an embodiment of a matrix-addressable laser drive circuit configured as a voltage driver in accordance with the present teachings in which row/column matrix addressability is used to fire individual lasers within a 2D laser array.

Figure 5C illustrates an electrical schematic diagram of a single matrix-addressable laser driver configured as a high-side current driver that may be used with a 2D laser array having row/column matrix addressability according to one embodiment of the present teachings.

Figure 5D illustrates an electrical schematic diagram of a single matrix-addressable laser driver configured as a low-side current driver that may be used with a 2D laser array having row/column matrix addressability according to one embodiment of the present teachings.

Figure 5E illustrates an electrical schematic diagram of a matrix-addressable laser drive circuit configured with a high-side voltage driver for the columns, a low-side voltage driver for the rows, and switches that can be used to apply additional voltages to the rows, which can be used with a 2D laser array with row/column matrix addressing capability, according to one embodiment of the present teachings.

FIG. 5F illustrates a voltage potential timing diagram showing one method of operating a matrix-addressable laser driving circuit, according to one embodiment of the present teachings.

Figure 5G illustrates an electrical schematic diagram of a matrix-addressable laser driving circuit configured with a high-side capacitive discharge circuit in a capacitor charging mode, according to one embodiment of the present teachings.

Fig. 5H illustrates an electrical schematic of the matrix-addressable laser drive circuit described in connection with fig. 5G, but configured with a high-side capacitive discharge circuit in capacitor discharge mode for the laser diodes 2,2 (second row and second column), according to one embodiment of the present teachings.

FIG. 5I illustrates a voltage potential timing diagram showing across capacitor C according to one embodiment of the present teachings₂And a voltage potential across the laser diodes 2,2 in the second row and the second column.

Figure 5J illustrates an electrical schematic diagram of a matrix-addressable laser driver circuit configured with a low-side capacitive discharge circuit in a capacitor charging mode, according to one embodiment of the present teachings.

Fig. 5K illustrates an electrical schematic of the matrix-addressable laser driver circuit described in connection with fig. 5J, but configured with a low-side capacitive discharge circuit in capacitor discharge mode for the laser diodes 2,2 (second row and second column), according to one embodiment of the present teachings.

FIG. 5L illustrates a voltage potential timing diagram showing a voltage potential across capacitor C according to one embodiment of the present teachings₂And a voltage potential across the laser diodes 2,2 in the second row and the second column.

Fig. 6 illustrates an embodiment of a combined high-side and low-side GaN FET driver circuit for electrically driving laser diodes in a matrix address laser driver circuit in a LIDAR system laser array according to the present teachings.

Figure 7 illustrates a typical current-voltage curve for an embodiment of a semiconductor diode in a matrix address laser driver circuit according to the present teachings.

FIG. 8 illustrates voltages induced at nodes in a matrix while energizing a single laser within a two-dimensional array having row/column matrix addressability according to an embodiment of a matrix address laser drive circuit controller according to the present teachings.

Fig. 9 illustrates an embodiment of a LIDAR system array in accordance with the present teachings in which physical connections to the array enable a denser layout for associated electronic circuitry on a Printed Circuit Board (PCB).

FIG. 10 illustrates a schematic diagram of an embodiment of a 2x2 laser array with matrix address laser drive circuit control circuitry showing possible current paths when one laser is energized in accordance with the present teachings.

FIG. 11 illustrates a schematic diagram of an embodiment of a 2x2 laser array including lasers with a second diode in series with each laser diode in a matrix address laser drive circuit according to the present teachings.

Figure 12 illustrates an embodiment of a plurality of series diodes including a VCSEL array with an additional diode connected in series with each laser diode as part of a separate carrier in accordance with the present teachings.

Detailed Description

The present teachings will now be described in more detail with reference to exemplary embodiments thereof as illustrated in the accompanying drawings. While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein.

Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present teachings. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

It should be understood that the various steps of the methods of the present teachings may be performed in any order and/or simultaneously as long as the teachings remain operational. Further, it should be understood that the apparatus and methods of the present teachings can include any number or all of the described embodiments, so long as the teachings remain operable.

Most commercial LIDAR systems for autonomous vehicles today use a small number of lasers, in combination with some method of mechanically scanning the environment. Current automotive applications and future autonomous automotive applications make the use of solid state semiconductor based LIDAR systems highly desirable. Solid state LIDAR systems, particularly those without moving parts, exhibit better reliability and can operate over a wider range of environmental operating ranges than current LIDAR systems. Such solid state systems used in LIDAR systems may also be physically compact and relatively low cost.

One approach to solid-state LIDAR is to use a large number of lasers to project each laser at a unique angle to the desired FOV, thereby avoiding the need for mechanical scanning. However, it is a challenge to electrically connect the driver circuitry to a large number of lasers while maintaining the ability to operate them individually. One solution is to arrange the multiple lasers in a two-dimensional matrix and then employ a matrix-addressable laser driver circuit that can simultaneously meet the needs to control the individual lasers and/or groups of lasers in the array and provide optimal electrical characteristics (e.g., current, voltage, and timing) to energize the lasers. Methods and apparatus of the present teachings relate to laser control methods and system architectures that enable individual control of 2D laser matrices while ensuring low cost systems.

Fig. 1A illustrates a schematic diagram of a solid-state LIDAR system 100 in which individual lasers in a (fire) transmitter array 102 may be independently excited. The system shown in fig. 1A does not employ a flash transmitter to illuminate the field of view of the entire system simultaneously. Alternatively, each laser in the transmitter array 102 may be excited independently, with the beam emitted by each laser corresponding to a 3D projection angle that subtends only a portion of the entire system field of view. One example of such a transmitter is described in detail in U.S. patent publication No.2017/0307736a1, assigned to the present assignee. U.S. patent publication No.2017/0307736a1 is incorporated by reference herein in its entirety.

The beams from the lasers in the laser array 102 share transmitter optics 104 that project the beams 106 to a target 108 at a target plane 110. A portion of the light from the incident light beam 106 is reflected by the target 108. Portions of the reflected beam 112 share receiver optics 114. The detector array 116 receives the reflected light projected by the receiver optics 114. In various embodiments, the detector array 116 is solid state, with no moving parts. The detector array 116 may have a smaller number of individual detector elements than the transmitter array 102 has individual lasers.

The measurement resolution of the LIDAR system 100 is not determined by the size of the detector elements in the detector array 116, but rather by the number of lasers in the transmitter array 102 and the collimation of the individual beams. A processor (not shown) in the LIDAR system 100 performs a time-of-flight (TOF) measurement that determines a distance to a target 108, which target 108 reflects a beam 106 from a laser in the laser array 102, as detected at a detector array 116.

One feature of the system of the present teachings is that individual lasers and/or groups of lasers in transmitter array 102 can be individually controlled. Another feature of the system of the present teachings is that individual detectors and/or groups of detectors in the detector array 116 can be individually controlled. Such control provides various desired performance characteristics, including control of field of view, optical power level, scanning, and/or other characteristics.

Fig. 1B illustrates a two-dimensional projection of the system field of view 150 of the LIDAR system of fig. 1A. The field of view of the individual detectors in the detector array is represented by a small square 152. The illuminated measurement points associated with the individual lasers in the transmitter are illustrated by circle 154. As an example of a case with one energized laser element in the array, light from the laser hits individual detector fields of view in the entire field of view of the LIDAR system of fig. 1A. This received light detector field of view is highlighted by the hash marks in the particular square 156 and the field of view of the measurement points from the individual lasers is shown as a particular black circle 158, which corresponds to a particular individual laser in the laser array.

As can be seen in FIG. 1B, the measurement points shown by circle 158 fall within an individual detector whose field of view has been shown in square 156 with a cross-hatched pattern for identification. This figure illustrates that the 3D resolution of some embodiments of the LIDAR system is determined by the number of lasers, as each laser corresponds to a particular projection angle that results in the size of the circle 154 at the target range, and the relative sizes of the circle 154 and the square 152 representing the fields of view of the individual detector elements. Thus, the various fields of view may be established by controlling specific individual lasers or groups of lasers in the transmitter array to selectively energize and transmit laser pulses and/or specific individual detectors or groups of detectors in the receiving array to convert received optical signals in the field of view of the detector(s) into electrical signals. One feature of the present teachings is an array drive control system that is capable of providing such selective device control for an array of laser devices capable of illuminating a target.

In some embodiments, the field of view of the individual detectors in the detector array is the active area of the detectors. The size of the individual detectors within the array is largely determined by the electrical characteristics of the device. For example, as the size of the active area of an Avalanche Photodiode (APD) detector increases, the capacitance of the detector increases, thereby reducing the opto-electrical bandwidth of the device. The bandwidth of the APD must be maintained high enough to avoid attenuating or distorting the received signal. Typical values for optical-to-electrical (O/E) bandwidth and APD capacitance are 350MHz and less than 2pF, respectively, in a LIDAR system with a laser pulse width <10 nanoseconds and a rise/fall time of 1 nanosecond. In general, in order to cover the entire field of view of a LIDAR system while maintaining acceptable electrical detector performance, an array of detectors must be used. The overall physical size and dimensions of the array are determined by the required field of view and the specifications of the receiver optical lens system.

Fig. 2 illustrates a perspective view of a structure of a known bottom emitting VCSEL 200 that may be used in a LIDAR system according to the present teachings. The area of the emission aperture 202 of the VCSEL 200 is typically from a few microns in diameter (for mW power operation) to 100 microns or more in diameter (for CW power operation of 100mW and more). The VCSEL 200 is fabricated on a substrate 204, which may be, for example, GaAs or many other semiconductor materials. An N-type Distributed Bragg Reflector (DBR) layer 206 is positioned on the substrate. An active region 208 is constructed on the n-type DBR layer 206, followed by a hole that may be formed in an oxide material. A p-type DBR layer 212 is then grown over the active region. Typically, the p-type DBR layer 212 is highly reflective and the n-type DBR layer 206 is partially reflective, resulting in a light output 214 from the bottom, substrate side of the layer structure. The active region 208, oxide aperture 210 and p-type DBR layer 212 are formed in a mesa (mesa) structure in the illustrated device. Top contact 216 and bottom contact 218 are used to provide current to the active region to generate output light. The oxide hole 210 confines current to the active region 208. Top contact 216 is p-type and bottom contact 218 is n-type.

An emission aperture 202 is formed in the bottom contact 218 to allow the output light 214 to exit from the bottom substrate side of the bottom emitting VCSEL 200. Note that only one emission aperture 202 is shown in fig. 2, as fig. 2 illustrates only one element of the multi-element VCSEL array. This type of VCSEL may be a separate single element or may be part of a multi-element VCSEL that may be fabricated as a one-or two-dimensional array on substrate 204. The VCSEL contacts 216, 218 can be individually addressed and/or they can be electrically connected together in various configurations to address groups of VCSELs using a common electrical input signal. One feature of the present teachings is a system and method for controlling the excitation of one or more VCSEL 200 devices in an array with appropriate drive signals for LIDAR system applications.

In some embodiments, the VCSEL array used in the solid state LIDAR system of the present teachings is monolithic and the lasers all share a common substrate on which the lasers are integrated. A variety of common substrate types may be used. For example, the common substrate may be a semiconductor material. The common substrate may also comprise a ceramic material. In other embodiments, the 2D VCSEL array is assembled from a set of 1D bars or even individual dies.

In some embodiments, the VCSEL is a top emitting VCSEL device. In other embodiments, the VCSEL device is a bottom emitting VCSEL. Individual VCSEL devices may have either a single large emitting aperture or individual VCSELs may be formed from two or more sub-apertures within a larger effective emitting diameter. The set of sub-apertures that form the larger effective emitting area is sometimes referred to as a cluster.

Fig. 3 illustrates a schematic diagram of an embodiment of a 2D monolithic VCSEL array 300 with 256 individual laser emitters 302 for use in a solid state LIDAR system according to the present teachings. Each laser transmitter 302 has a transmitting aperture 304 with a diameter "a". The emission from each individual laser emitter 302 substantially fills the entire emission aperture. Thus, each laser emitter 302 generates a laser beam having an initial diameter "a" equal to the diameter 304 of the emitting aperture. Laser emitters 302 are evenly spaced apart at a spacing dx 306 in the horizontal direction and at a spacing dy 308 in the vertical direction. The overall dimension of the array measured from the center of the outermost laser is distance Dx310 in the horizontal direction and distance Dy 312 in the vertical direction. The actual chip size will be slightly larger in dimension than the distance Dx310 and the distance Dy 312. In various embodiments, the emitter 302 may produce a beam having various shapes other than a circular emitter shape. For example, ovals, squares, rectangles, and various odd shapes may be implemented in various embodiments. In embodiments where the lasers are arranged in a 2D array, the rows and columns of lasers may be electrically driven in a matrix-addressable manner.

Some embodiments of the present teachings utilize a bottom emitting high power array of VCSEL devices with a single large aperture per laser, such as the configuration shown in figure 3. Other embodiments of the present teachings utilize a high power array of top or bottom emission of VCSELs, where the total emission area includes sub-apertures. However, those skilled in the art will recognize that the present teachings are not limited to any particular configuration of top and bottom emitting VCSEL devices and associated emission apertures.

A two-dimensional VCSEL array may be used as a building block for a LIDAR system according to the present teachings to create a platform that allows the transmitter to have small physical dimensions. For example, a 2DVCSEL array with 256 high power individual lasers may be built on a monolithic chip of approximately 4mmx4 mm. Such a monolithic chip may be used with selected optical elements to keep the physical dimensions as small as possible, for example, by using a microlens array, a shared lens of dimensions less than 20mm, or a diffractive optic of maximum dimension about 20 mm.

However, LIDAR systems according to the present teachings place certain requirements on 2D VCSEL arrays. In particular, it is desirable that the 2D VCSEL array allows for independent simultaneous control of all VCSEL devices. In certain modes of operation of the LIDAR system of the present teachings, each VCSEL within the matrix is fired at a different time. For such operation, the VCSEL array needs to be operated in a matrix-addressable manner, where the lasers can be excited individually, but not always simultaneously.

Figure 4 illustrates an exemplary cascaded two-port circuit model 400 of an embodiment of individual semiconductor lasers for a VCSEL array in accordance with the present teachings. The intrinsic laser junction is represented by the well-known symbol of diode 402. The active region of the lasing laser is sandwiched between the p-n junctions of the diodes. The circuit model 400 comprises a driver connection 404, which supplies a voltage V_dAs well as the electrical characteristics of the metal contacts 406. In addition, circuit model 400 includes parasitic element 408, which includes parasitic pad current 408i_pAnd parasitic chip current 410i_pPad resistance losses in the form of.

In one embodiment, the solid state LIDAR system of the present teachings uses VCSEL devices that are assembled using heterogeneous integration techniques. For example, these devices may be flip-chip bonded to silicon electronics to provide a highly compact method of connecting and electrically driving VCSELs. See, for example, Plant et al, "256-Channel Bidirectional Optical Interconnect Using VCSELs and Photodiodes on CMOS", IEEE Journal of Lightwave Technology, Vol.19, No.8, month 8 of 2001. See also U.S. Pat. No.7,702,191 entitled "Electro-Optical Chip Assembly" and U.S. Pat. No.8,675,706 entitled "Optical Illuminator at Fire Devices in Parallel". However, these known heterogeneous integration techniques are mainly directed to applications in the optical communication market where simultaneous parallel operation of multiple channels is desired as a solution to increase data transmission throughput.

Figure 5A illustrates an electrical schematic diagram of an embodiment of a matrix-addressable laser driving circuit configured as a 2D laser array 500 with row/column matrix addressability according to one embodiment of the present teachings. For simplicity, in this and the following figures, the diode symbol 502 is used to represent the laser, but it should be understood that the model 400 described in connection with fig. 4 represents the laser more accurately, and that such a model will be used for practical design. Also, for simplicity, only the 4x4 matrix of diodes is shown in diagram 500, and the voltage and/or current drivers that drive the matrix-addressable laser drive circuits are not shown. However, it will be appreciated that in practice the matrix of laser diodes is MxN, where M and N are any integers greater than or equal to two, and in some embodiments, M and N are large numbers.

The matrix-addressable laser driving circuit for the 2D laser array 500 is configured such that the VCSEL device 502 is connected to the anodes 504, 504 ', 504 "'. The rows of VCSEL devices 502 are connected by cathodes 506, 506 ', 506 ", 506'". This anode-column and cathode-row connection configuration shown in diagram 500 allows individual lasers 502 to be turned on/off through row and column operations without requiring separate access to the cathodes and anodes of the individual lasers 502.

Figure 5B illustrates an embodiment of a matrix-addressable laser drive circuit configured as a voltage driver in accordance with the present teachings in which row/column matrix addressability is used to fire a single laser 502 within a 2D laser array 500. The power source 548 applies a voltage potential 550 relative to ground 552 via an anode contact electrical bus 554 and a ground bus 552, the anode contact electrical bus 554 being connected to the anode columns 504, 504 ', 504 "' by a series of switches 556, 556 ', 556"' and the ground bus 552 being connected to the cathode rows 506, 506 ', 506 "' by a series of switches 558, 558 ', 558"'. The power supply 548 is generated withVoltage potentials 550, V of desired voltage potential waveform₊. The anode column of the VCSEL that is energized on is connected via switch 556' to a voltage potential 550, which voltage potential 550 is high enough to forward bias the VCSEL, diode 550. The cathode row 506 'containing that VCSEL is connected to a ground bus 552 via a switch 558' to complete the circuit, allowing current to flow through the VCSEL, exciting the laser to emit light. The other cathodes and anodes are set to an "on" state in which the power source 548 does not provide any particular voltage level to them by opening the switches 556, 556 "'and opening the switches 558, 558"'.

In an alternative embodiment of the circuit shown in fig. 5B, the cathodes 506, 506 "and 506" "are not" on "but are connected to a power supply 548 (or another power supply) that provides a voltage potential waveform having a voltage that is set at some predetermined voltage level during operation, which is less than V +. In other words, the potential on ground bus 552 indicated in fig. 5B may not be a ground potential, but instead may be a voltage level set by power supply 548 that is less than V + during operation, such that voltage potential 550 is applied relative to a predetermined voltage. In these embodiments, the switches 556, 556 "', 558"' will switch between the anode or cathode voltage potential 550 and a voltage source (not shown) set to this defined voltage level. This alternative embodiment may have performance advantages, such as reduced crosstalk. A more detailed circuit implementing this embodiment is described in conjunction with fig. 5E.

One feature of the laser array controller of the present teachings is that it can use a variety of laser drive circuits to provide the desired laser drive characteristics. In some embodiments, the power supply 548 driving the laser generates a high current, short duration pulse. In these embodiments, the power supply 548 is designed to provide the necessary high current and short duration pulses. Also, the matrix can be operated by causing the power supply 548 to apply a potential waveform having a defined voltage (so-called voltage driver) or a current waveform having a defined current level (so-called current driver).

In some embodiments, the power supply 548 is configured to produce a waveform that reduces power dissipation when no pulses are generated. This can be accomplished, for example, by using a circuit configuration that provides a near or complete shut down of the output of the power supply 548 during the down time between application of short duration pulses. In one such embodiment, the power supply energizes the laser driver during a wake-up period prior to generating the short duration pulse, and then generates the pulse. The power supply 548 produces a waveform off at the time between pulses, which is initiated after the pulses have been fired. This waveform off period is preceded by a wake-up period before the short duration pulse is generated again. Some power supplies also have a "low power" state for further reducing power consumption. For example, in a practical implementation, a controller in the power supply or a separate controller may execute a series of commands, such as the following: (1) placing the laser driver power supply in a "low power state"; (2) placing the laser driver power supply in a "wake-up" mode; (3) turning "on" the laser driver power output; (4) turning "off" the laser driver power output; and (5) returning the laser driver to a "low power state".

Figure 5C illustrates an electrical schematic diagram of a single matrix-addressable laser driver 570 configured as a high-side current driver that may be used with a 2D laser array having row/column matrix addressability according to one embodiment of the present teachings. The high-side configured laser driver 570 includes a Field Effect Transistor (FET)572 with the FET source coupled to the supply potential V + and the FET drain coupled to the anode of the laser diode 574. The drive current for the laser diode 574 is provided by a voltage controlled current source 576 such that the laser current is proportional to the drive voltage.

Figure 5D illustrates an electrical schematic diagram of a single matrix-addressable laser driver 580 configured as a low-side current driver that may be used with a 2D laser array having row/column matrix addressability according to one embodiment of the present teachings. The laser driver 580 includes a voltage controlled current source 582 having an input coupled to a power supply. The output of the voltage controlled current source 582 is connected to the anode of the laser diode 584. A Field Effect Transistor (FET)586 has a source coupled to the anode of the laser diode 584 and a drain coupled to ground.

Fig. 5E illustrates an electrical schematic of a matrix-addressable laser drive circuit 590 configured with a high-side voltage driver 591 for the columns, a low-side voltage driver 592 for the rows, and switches that may be used to apply additional voltages to the rows, which may be used with a 2D laser array with row/column matrix addressing capability, according to one embodiment of the present teachings. A voltage divider circuit 593 is used to set the voltage between the rows of the 2D laser array. The voltage divider circuit 593 is controlled by applying a charging signal to its FET gate. The laser diode 594 is shown with its associated parasitic capacitor.

The configuration of the matrix-addressable laser driver circuit 590 is similar to the alternative embodiment of the circuit shown in fig. 5B, where the cathode of the laser diode is not at ground potential but at another potential during normal operation. However, in this circuit, the addition of switch 593 allows for more complex control of the voltage applied to the cathode. In the matrix-addressable laser drive circuit 590 configuration shown in fig. 5E, the cathode of the laser diode is at a potential determined by a voltage divider 593, the voltage divider 593 being controlled by a charging signal applied to its FET gate. Operating the matrix-addressable laser drive circuit 590 so that the laser diodes are reverse biased so that the cathodes are at a potential other than ground can have a number of performance advantages. One such performance advantage is that cross talk between laser diodes can be significantly reduced.

Fig. 5F illustrates a voltage timing diagram 599 showing one method of operating the matrix-addressable laser driver circuit 590 described in connection with fig. 5E. Waveforms of a column drive signal C2595 applied to the high side voltage driver 591, a row drive signal R2596 applied to the low side voltage driver 592, and a charging signal 597 applied to the voltage divider 593 are shown.

The light pulses are generated only when both the column drive signal 595 and the row drive signal 596 are high. The pulse duration of the row drive signal determines the width of the light pulse. The duty cycle depends on various operating parameters. For example, in one method of operation, the duty cycle of the light pulses is 1%. The column drive signal 595 pulses are longer than the row drive signal 596 pulses. This prevents contention between row and column pulses.

An important feature of the methods and apparatus of the present teachings is that various laser driver circuit configurations and methods of operation reduce crosstalk and, thus, improve performance. With reference to the matrix-addressable laser driver circuit 590 described in connection with fig. 5E, crosstalk can occur when a laser diode is excited indirectly via an electrical path through its associated parasitic capacitor and low-side driver. In the configuration shown in fig. 5E, this undesirable result may be prevented by charging the parasitic capacitor to a voltage + V, which sets the laser diode 594 to reverse bias. Thus, when a desired laser diode is activated, no other laser diode should emit light. However, the method of biasing the laser diode 594 under continuous reverse bias conditions would result in an increased device failure rate and reduced overall device reliability. One solution according to the present teachings is to energize the low side driver to discharge the parasitic capacitor of the laser diode during the remaining duty cycle when the laser diode is not intentionally energized. For example, energization is typically completed at a 1% duty cycle for about 99% off duration.

Fig. 5G illustrates an electrical schematic of a matrix-addressable laser drive circuit 620 configured with a high-side capacitance discharge circuit 622 in a capacitor charging mode. The driver circuit 620 is similar to the driver circuit 500 described in conjunction with fig. 5A, but includes a high-side capacitance discharge circuit 622. In the capacitor charging mode, all high-side switches 624 and all low-side switches 626 are open, allowing capacitors C1-C3630 to charge with a time constant to the full potential applied to driver circuit 620, which is indicated as-V.

Fig. 5H illustrates an electrical schematic of the matrix-addressable laser driver circuit 620 described in connection with fig. 5G, but configured with a high-side capacitive discharge circuit 622 in a capacitor discharge mode for the laser diodes 2,2 (second row and second column). In the capacitor discharge mode for laser diodes 2, both the high-side switch 624 and the low-side switch 626 are closed, causing the current in path 632 to discharge.

FIG. 5I illustrates a voltage potential timing diagram 635 showing across capacitor C₂And a voltage potential across the laser diodes 2,2 in the second row and the second column. Switches LS2 and HS2 close until initial time t₀. At time t₀Previously, the potential C2+ was at ground potential and the potential C2-was at-V potential. At time t₀The switches LS 2626 and HS 2624 are closed, so that the potential C2 "is transferred to ground and the potential C2+ is charged to + V, at time t₁These potentials are reached. After the anode of the laser diode 2,2 is charged to the + V potential, the capacitor C2 is discharged from the potential C2+ via the laser diode 2, thereby generating an optical pulse. At time t₂Switches LS2 and HS2 close to initiate the condition for the next pulse. The result of this switching sequence is that the discharge control method generates analog drive pulses, where the power consumption is independent of the pulse width.

Fig. 5J illustrates an electrical schematic of a matrix-addressable laser driver circuit 640 configured with a low-side capacitive discharge circuit 642 in a capacitor charging mode. The driver circuit 640 is similar to the driver circuit 500 described in connection with fig. 5A, but includes a low side capacitance discharge circuit 642. In the capacitor charging mode, all of the low-side switches 644 and all of the high-side switches 646 are open, allowing the capacitors C1-C3626 to charge to the full potential applied to the driver circuit 640 with a time constant, which is indicated as the + V potential.

Fig. 5K illustrates an electrical schematic of the matrix-addressable laser driver circuit 640 described in connection with fig. 5J, but configured with the low-side capacitive discharge circuit 642 in a capacitor discharge mode for the laser diodes 2,2 (second row and second column). In the capacitor discharge mode for laser diodes 2, both the high-side switch and the low-side switch are closed, causing the current in path 648 to discharge.

FIG. 5L illustrates a voltage potential timing diagram 650 showing a cross-capacitor C₂And a voltage potential across the laser diodes 2,2 in the second row and the second column. Switches LS2 and HS2 are initially open. At time t₀Previously, when switches LS2 and HS2 were open, the C2+ potential on capacitor C2 was + V potential and the C2-potential was ground potential. At time t₀Switches LS2 andHS2 closes, driving C2+ to ground, and causing C2-to begin charging from ground to-V. At time t₁The capacitor C2 starts to discharge with a time constant via the laser diode 2, thereby causing the laser diode 2,2 to generate an optical pulse. At time t₂Switches LS2 and HS2 close, initiating the condition for the next pulse. The result of this switching sequence is also that the discharge control method generates analog drive pulses, where the power consumption is independent of the pulse width.

Fig. 6 illustrates an embodiment of a combined high-side and low-side GaN FET driver circuit 600 for electrically driving laser diodes in a matrix address laser driver circuit in a LIDAR system laser array according to the present teachings. Such driver circuits are also referred to in the art as asymmetric switch driver circuits. In various embodiments of the LIDAR system of the present teachings, a driver circuit 600 is connected to each of the column/row anode/cathode connections shown in fig. 5A-B, where the driver circuit 600 is configured as an on-off driver that includes a high-side drive electrical input 602 and a low-side drive electrical input 604.

More specifically, referring to fig. 5B and 6, the unit cell 560 in the electrical schematic 500 is configured with the drive circuit 600 in the following manner. The transistors 602, Q1 correspond to a switch 556 that connects the voltage potential 550 to the laser anode 504. Transistors 604, Q2 correspond to switch 558 which connects ground 552 to laser cathode 506. The high side driver input 606 is electrically connected to the gate of the transistor 602. The low side driver input 608 is electrically connected to the gate of the transistor 604.

The asymmetric, on-off driver circuit 600 is adapted to inject well-controlled, short-duration, high-bias current pulses into the laser junction 610 to excite the laser and cause it to emit light. For a pulsed TOF LIDAR system, the ideal optical power output pulse should be in the range of a few nanoseconds duration and should provide a high peak output power in that duration. In some embodiments, the asymmetric, on-off driver circuit 600 is configured and operated such that the peak output power from the laser is at or minimally below the eye-safe limit.

One feature of the present teachings is array drive controlThe circuit may be configured to optimize the driving based on characteristics of a current-voltage (IV) curve of the laser transmitter. FIG. 7 illustrates a typical current-voltage curve 700 for an embodiment of a semiconductor diode 702 in a matrix address laser driver circuit according to the present teachings. The current-voltage curve graphically represents the relationship between the current flowing through the VCSEL device and the voltage applied across the VCSEL device. As shown in fig. 7, when the laser diode 702 is forward biased, the voltage at the anode 704 will be positive with respect to the cathode 706, and a forward or positive current 708 will flow through the diode 702. The current-voltage characteristic of the diode is non-linear and exceeds a threshold voltage V_thAfter 710, the positive current 708 increases exponentially from nominal zero.

When the laser diode is reverse biased with the voltage at the cathode positive with respect to the anode, the laser diode blocks current flow except for a very small leakage current. The laser diode continues to block current flow until the reverse voltage across the diode becomes greater than its breakdown voltage (V)_br712). Once breakdown is reached, the current increases exponentially in the negative direction and the power drain is relatively high due to the relatively high voltage and current, resulting in overheating and burning out of the laser diode. The laser generates light under forward bias conditions.

The current-voltage behavior of each laser, in combination with the method of controlling the laser drive to energize the individual lasers, significantly affects the operational performance and reliability of the laser array. One feature of the matrix-addressable laser drive circuits of the present teachings is that they can be configured to minimize adverse effects, such as optical crosstalk. Optical crosstalk occurs when other lasers in the array (other than the single laser that is intentionally forward biased to power) are simultaneously forward biased because current and/or voltage leaks from the electrical driver that supplies the excitation laser. Thus, other lasers emit light, even if such emission is undesirable. This optical crosstalk situation adversely affects the performance of the LIDAR system by illuminating measurement points that are not intended to be illuminated and/or illuminating a wider target area than is intended to be illuminated.

FIG. 8 illustrates voltages induced at nodes in a matrix when energizing individual lasers within a two-dimensional array having row/column matrix addressability according to an embodiment of a matrix-address laser drive circuit controller 800 of the present teachings. The matrix-addressable laser drive circuit controller 800 provides a voltage at each node in the matrix, similar to the operation of the embodiment described in connection with fig. 5B. For example, switch 802 connects the second column to a supply voltage 804 and switch 806 connects the second row laser to ground 808. This switch configuration causes a voltage V' 810 to be induced at the anode of each row except for the rows intentionally grounded through the connection of switch 806 to ground 808. The voltage V' 810 results in a voltage V "812 at the corresponding cathode of each laser in the array. The exact values of the voltages V' 810 and V "812 are a function of V +804 and the actual current-voltage curve for the particular laser diode.

In the case where the value of the supply voltage 804 is less than the reverse breakdown voltage of the laser pulse, the forward voltage drop of the laser (i.e., the absolute value of V +) is less than V_brAnd V_thIn sum, almost no reverse current flows through the laser diode. This condition improves the reliability of the device. Also, if the voltage at the cathode is less than the threshold voltage (i.e., V)<V_th) Then little forward current flows through the diodes on the same row as the active laser 814.

Fig. 9 illustrates an embodiment of a VCSEL array chip 900 of a LIDAR system mounted on a carrier 902 in accordance with the present teachings. Physical connections to the array make the layout of the associated electronic circuitry on the Printed Circuit Board (PCB) substrate more dense. A 16x16 array 904 of transmitter clusters 906 including nine apertures 908 of addressable VCSEL devices is shown. The carrier 902 has a plurality of electrical edge connectors 910, 910 ', each connected to a row edge 914 or a column edge 914 ' of the array 904 by wire bonds 912, 912 '. The connections of the anode and cathode alternate on both sides of the circuit on which the PCB is connected to the VCSEL. This alternating connection pattern results in a wider PCB spacing between the row and column circuitry, which enables the GaN FETs to be placed closer to the VCSEL array, making the circuit layout more compact, thereby reducing the physical footprint.

As previously mentioned, one aspect of the LIDAR system of the present teachings is the ability to individually energize each VCSEL located within a 2D matrix-addressable configuration in a laser array with a minimum number of required electrical drivers. When the array is driven in a matrix-addressable manner, the minimum number of drivers required is equal to M + N, row/column, where M is the number of columns and N is the number of rows, respectively. In contrast, if each VCSEL device in the array has its own dedicated driver, the number of drivers would be much higher, equal to MxN. For example, a 16x16 element VCSEL array using matrix addressing as described herein requires only 32 drivers, whereas 256 drivers are required if each VCSEL has its own dedicated driver.

It will be appreciated that for matrix addressing, it is not possible to operate all lasers completely independently at the same time. In other words, only certain lasers can be fired at a given time. However, this limitation is not important for the LIDAR system described herein, as in typical operation only one laser within a particular monolithic array is energized at a time, so as to make no ambiguity as to which measurement point in space is illuminated. Energizing one laser in a particular monolithic array at a time also helps to maintain level 1 human eye safety.

It should also be understood that matrix addressing is well known in the electronic arts. However, the aspect of using matrix addressing in LIDAR systems requiring short duration, extremely high optical power pulses and low duty cycles has not been known before. As described above, a LIDAR system with 256 lasers has a working distance of 100m (the shortest time between pulses is 1 microsecond), a duty cycle of only 0.002%, and a pulse duration of 5 nanoseconds. Matrix addressing has been used to excite optical communication laser devices, which typically operate with relatively low peak power (mW compared to W) and relatively long pulse duration and a-50% duty cycle. Under these conditions, the power drive requirements are very different from the operation of high power lasers in the most advanced LIDAR applications.

For example, pulsed TOF LIDAR systems for greater than 100-m range operation using 905-nm wavelength lasers typically require optical pulses with peak powers in excess of 20 watts and pulse durations of less than 10 nanoseconds. Assuming that the laser device has a 1W/a efficiency under pulsed conditions, the corresponding drive voltages and currents on the individual lasers are in the 10 volt range and are in the 10 amp range. Of course, if voltages greater than 10V are applied to a matrix-addressable array, unwanted electrical and optical crosstalk is likely to occur. When reverse bias conditions exist for such voltages, the VCSEL devices in the matrix are also likely to be damaged or destroyed.

One of the main factors affecting the reliability of the laser is the average temperature and the transient temperature of the device. If the pulse energy is controlled to keep the transient temperature rise of the device sufficiently low, the peak current and voltage values can be relatively high as long as the duration of the pulse is sufficiently short. Even under reverse bias conditions where thermal runaway is an important issue, transient reverse current is acceptable for reliability as long as the temperature rise near the junction is low enough. For example, assuming the material properties of GaAs have specific heat and density, a1 uJ pulse into a 2 micron thick 100 micron diameter junction will cause the temperature of the junction to rise to-9 ℃. A20V/10A square wave pulse of 5 ns duration corresponds to 1 uJ energy. The resulting transient temperature rise will be of the order of a few degrees and may therefore not be sufficient to degrade the reliability of the device.

Fig. 10 illustrates a schematic diagram of an embodiment of a 2x2 laser array with a matrix drive control circuit 1000 showing possible current paths when one laser 1002 is energized in accordance with the present teachings. For simplicity, only the 2x2 matrix is shown in this figure. It should be understood that the electrical behavior of the 2x2 matrix can be extended to larger MxN matrices.

Fig. 10 is presented to illustrate the potential problems caused by the high voltages necessary for most advanced LIDAR applications. In fig. 10, VCSEL device L221002 is intentionally forward biased and emits light because column 2 1004 is connected to drive voltage bus 1006, V +, and row 2 1008 is connected to ground bus 1010. The current flowing through the VCSEL device L22 is indicated by the solid line 1012 with an arrow in the figure. Ideally, all other VCSEL devices 1014, 1016, 1018 in the matrix are turned off because row 1 1020 and column 1 1022 are open and not connected to the ground bus 1010 or the V + bus 1006.

However, in addition to the main path of solid line 1012, there is the possibility of a second current path. This second current path is indicated by dashed line 1024 with directional arrows. When V + on bus 1006 is applied to column 2 1004 by closing switches 1026, 1028, VCSEL device 1016L12 will apply V + on bus 1006 at the anode and will induce a voltage at the cathode, denoted V' 1030, to satisfy the condition that this path is nominally open, where no current can flow. Note that when the voltage V + on bus 1006 is initially applied to column 2 1004, voltage V' 1030 may initially be zero. When this happens, a transient current may occur with sufficient forward voltage of VCSEL devices L121016 and L221018 to cause it to emit undesired light, which results in optical crosstalk. In this case, crosstalk is additional undesired light generated within the field of view, not the light generated by VCSEL device L221002.

Since the cathodes are connected in a given row, voltage V' 1030 will also be applied to the cathode of VCSEL device L111014 and this will immediately place VCSEL device L111014 in a reverse bias condition. The voltage V "1032 will be induced at the anode of the VCSEL device L111014 to satisfy the current/voltage relationship. If voltage V' 1030 is less than the reverse breakdown voltage of L111014, then the current is typically less than 1 μ A. A small current through L111014 will also flow through L211018, putting it in a forward biased state. The voltage V "will correspond to the forward IV curve of L211018. To avoid emitting light from L21, the current through L211018 should be below the laser threshold current, which is expected to be in the range of 10 to 100mA for LIDAR applications.

However, if the voltage V' 1030 is greater than the breakdown voltage of the VCSEL device L111014, then a higher current will flow through the circuit. If this current is higher than the threshold current of L211018, light will be generated in both VCSEL device L121016 and VCSEL device L211018, which results in the generation of undesired optical crosstalk. It will therefore be appreciated that the voltage V' 1030 cannot be arbitrarily large but must be constrained so that it is always less than the reverse breakdown voltage of the VCSEL device, or at least that the current flowing through the corresponding path is not sufficient to cause light to be emitted from both VCSEL devices L121016 and L211018.

Accordingly, one aspect of the present teachings is to recognize that for certain VCSEL devices used for LIDAR applications, it is desirable to constrain the voltage V' 1030 to be less than the reverse breakdown voltage to avoid undesirable optical crosstalk. Furthermore, the continuous current flow under reverse bias conditions is undesirable because it can be a potential reliability issue for the laser diode, depending on factors such as time, energy associated with the current, and the resulting thermal rise in the laser diode.

Under operating conditions where the voltage V' 1030 causes significant transient current to flow through the devices 1014, 1016, and 1018, the pulse energy should be low enough not to significantly affect reliability, and the transient temperature rise in these devices should be below 20 ℃.

The use of many known VCSEL device structures for LIDAR applications will result in the generation of unwanted optical crosstalk, since voltages of 10V-80V are typically required to generate the high power optical pulses required for most advanced LIDAR applications, while the reverse breakdown voltage of a typical VCSEL device with a single active region is in the range of 5V to 15V.

Accordingly, another aspect of a LIDAR system that uses matrix-addressable control circuits according to the present teachings to drive laser arrays for LIDAR applications is the design of the VCSEL devices themselves to have a desired operating specification that reduces or illuminates optical crosstalk and at the same time has high reliability. That is, VCSEL devices according to the present teachings are specifically designed such that operating conditions prevent unwanted optical crosstalk from affecting system performance. One way to prevent unwanted optical crosstalk is to fabricate VCSEL devices with laser structures that can achieve relatively high reverse bias operating conditions without entering breakdown conditions.

Can increase V_thOr V_brOne possible laser structure, or both, includes multiple junctions in series within a VCSEL device. Laser structures with multiple tandem junctions have been demonstrated in devices using tunnel junctions, which separate the active junctions. It should be understood that the use ofMany other similar laser structures with multiple junctions. Although the use of multiple junctions will increase V_thHowever, because of the high pulse voltages and currents, the impact on efficiency and device performance is generally acceptable for this application.

Figure 11 illustrates a schematic diagram of an embodiment of a 2x2 laser array including lasers with a second diode in series with each laser diode in a matrix address laser drive circuit 1100 according to the present teachings. Similar to the schematic diagram of the 2x2 laser array 1000 described in connection with fig. 10, the laser array 1100 includes VCSEL devices 1102, 1104, 1106, 1108 in a matrix. Further, second diode devices 1110, 1112, 1114, 1116 are electrically connected in series with the laser diodes 1102, 1104, 1106, 1108. In some embodiments, VCSEL devices 1102, 1104, 1106, 1108 are GaAs laser diodes and second diode devices 1110, 1112, 1114, 1116 are silicon diodes. Similar to the schematic diagram of the 2x2 laser array 1000 described in connection with fig. 10, there is a drive voltage bus 1118, a ground bus 1120, two columns 1122, 1124 and two rows 1126, 1128.

In operation, when the two switches 1132, 1134 are closed, laser drive current flows through path 1130, shown in bold lines, in the direction indicated by the arrows. The second diodes 1110, 1112, 1114, 1116 will increase the forward voltage drop between the column and row anode and cathode connections. However, since the typical forward voltage drop for GaAs laser diodes is about 2V to 3V, and for silicon diodes about 1V to 2V, the additional forward voltage drop is not significant, since the matrix-addressed laser driver circuit 1100 is designed to generate high optical power from each laser, and therefore it typically operates at a drive voltage in excess of 10V. As such, this additional forward pressure drop does not have a significant impact on performance. In some embodiments, more than one additional diode is added in series with the laser diode.

Different embodiments use different diode types to implement the second diode 1110, 1112, 1114, 1116 connected in series, or a plurality of additional diodes connected in series. For example, some embodiments stack the second diodes 1110, 1112, 1114, 1116 monolithically with the respective lasers 1102, 1104, 1106, 1108 within a chip. The chip may be a GaAs chip, similar to that shown in fig. 2, but with an additional layer structure forming one or more diodes in series. In some embodiments, the stacked second diode is another active P-N junction that generates an optical gain that beneficially increases the brightness of the VCSEL. In other embodiments, the stacked second diode is not optically active, so it does not contribute to the generated light. In some embodiments, the stacked second diode is a photodiode. In some embodiments, the implementation of a stacked structure utilizes a tunnel junction to separate the two stacked diodes to keep the resistance of the overall structure relatively low.

VCSEL devices with stacked or cascaded multi-diode regions are known in the art. See, e.g., "Bipolar Cascade VCSELs with 130% Differential Quantum Efficiency", annular Report 2000, Optoelectronics Department, University of ULM. Also, multiple diode cascaded VCSEL structures have been used to increase overall brightness. See, e.g., U.S. patent publication No. US2015/0311673A 1. Furthermore, VCSELs have been fabricated with integrated photodiodes. See, for example, U.S. patent No.6,717,972. However, the prior art does not teach the use of a matrix address laser driver circuit 1100 configured for LIDAR applications using such a structure.

Another VCSEL device structure in accordance with the present teachings that achieves relatively high reverse bias operating conditions without entering a breakdown condition connects two or more VCSEL devices in series in a single laser transmitter configuration. This can be achieved by appropriately arranging the anode and cathode connections during the chip manufacturing process.

In high power VCSEL lasers, it is common to connect more than one emitter aperture in parallel within a single emitter. For example, the VCSEL array described in connection with fig. 9 is a 16x16 array 904, which includes nine apertures 908 of addressable top-emitting VCSEL devices, where the individual apertures within each individual emitter are connected in parallel. Series connected VCSEL devices have recently been developed for high power applications, but without taking into account optical cross talk and forward voltage drop issues. See, for example, U.S. patent publication No.2019/0036308a1, which describes series connected single chip VCSEL devices. Such devices may be configured to reduce optical crosstalk in accordance with the present teachings.

Another VCSEL device structure according to the present teachings that achieves relatively high reverse bias operating conditions without entering a breakdown condition incorporates an additional diode into a counter substrate or IC bonded to the VCSEL device. Fig. 12 illustrates an embodiment of a plurality of diodes 1200 configured in series, including a VCSEL array 1202 with an additional diode 1204 connected in series with each laser diode 1206 as part of a separate carrier 1208 according to the present teachings. In some embodiments, the carrier 1208 is an integrated circuit. For example, the integrated circuit may be an inexpensive silicon-based integrated circuit.

The carrier 1208 can be electrically connected to the array 1202 in various ways. For example, the carrier 1208 may be electrically bonded to the array 1202 using bump bond connectors 1210. In the configuration shown in fig. 12, the bottom emitting VCSEL laser array 1202 is bonded to a carrier. For simplicity, the figure shows only a single row of VCSEL emitters sharing a common cathode connection 1212. The anode connections 1214 extend perpendicular to the plane shown in the figure. Each VCSEL diode 1206 is paired with a diode 1204 on a carrier 1208. It should be understood that additional diodes may be added in series in this and other configurations described herein to further reduce the likelihood of optical crosstalk. For some configurations, more than two diodes are connected in series to achieve the desired reverse voltage induced in the matrix to reduce or eliminate optical crosstalk.

Equivalents of

While applicants 'teachings are described in conjunction with various embodiments, there is no intent to limit applicants' teachings to such embodiments. On the contrary, the applicants' teachings encompass various alternatives, modifications, and equivalents, as will be recognized by those skilled in the art, which may be made without departing from the spirit and scope of the present teachings.