Solid-state LIDAR transmitter with laser control

Abstract

A solid-state LIDAR transmitter having a matrix-addressable laser driver circuit includes a first electrical bus that provides a first voltage potential to columns of the matrix-addressable laser driver circuit and a second electrical bus that provides a second voltage potential to rows of the matrix-addressable laser driver circuit. A plurality of column switches connect a plurality of columns to the first electrical bus. A plurality of row switches connect a plurality of rows to the second electrical bus. The transmitter includes a plurality of diodes connected in series, the diodes including 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 the LIDAR transmitter. At least some of the second diodes increase the overall reverse breakdown voltage of the series-connected diodes.

Description

[0001] The section headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described in this application in any way.

[0002] Cross - Reference to Related Applications

[0003] This application is a non - provisional application of U.S. Provisional Patent Application No. 62 / 831,668, titled "Solid - State LIDAR Transmitter with Laser Control", filed on April 9, 2019. The entire content of U.S. Provisional Patent Application No. 62 / 831,668 is incorporated herein by reference. Background of the Invention

[0004] Autonomous, self - driving, and semi - autonomous vehicles 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 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. Brief Description of the Drawings

[0005] The present teachings are described more specifically in the following detailed description in conjunction with the accompanying drawings, according to preferred and exemplary embodiments and their further advantages. Those skilled in the art will understand that the drawings described below are for illustrative purposes only. The drawings are not necessarily drawn to scale, but generally focus on illustrating the principles of the present teachings. These drawings are not intended to limit the scope of the applicant's teachings in any way.

[0006] Figure 1A A schematic diagram of a solid - state LIDAR system is illustrated.

[0007] Figure 1B Is illustrated Figure 1A A two - dimensional projection of the system field of view (FOV) of the LIDAR system.

[0008] Figure 2 A perspective view of the structure of a known bottom - emitting vertical - cavity surface - emitting laser (VCSEL) that can be used in a LIDAR system according to the present teachings is illustrated.

[0009] Figure 3 A schematic diagram of an embodiment of a two - dimensional (2D) monolithic VCSEL array with 256 individual laser emitters used in a solid - state LIDAR system according to the present teachings is illustrated.

[0010] Figure 4 Illustrates an exemplary cascaded two-port circuit model of an individual semiconductor laser for a VCSEL array according to the present teachings.

[0011] Figure 5A Illustrates an electrical schematic of an embodiment of a matrix-addressable laser driver circuit for controlling a two-dimensional laser array having row / column matrix addressability according to one embodiment of the present teachings.

[0012] Figure 5B Illustrates an embodiment of a matrix-addressable laser driver circuit configured as a voltage driver according to the present teachings, wherein row / column matrix addressability is used to excite individual lasers within a 2D laser array.

[0013] Figure 5C Illustrates an electrical schematic of an individual matrix-addressable laser driver configured as a high-side current driver according to one embodiment of the present teachings, which can be used with a 2D laser array having row / column matrix addressability.

[0014] Figure 5D Illustrates an electrical schematic of an individual matrix-addressable laser driver configured as a low-side current driver according to one embodiment of the present teachings, which can be used with a 2D laser array having row / column matrix addressability.

[0015] Figure 5E Illustrates an electrical schematic of a matrix-addressable laser driver circuit configured according to one embodiment of the present teachings with a high-side voltage driver for columns, a low-side voltage driver for rows, and a switch that can be used to apply an additional voltage to the rows, which can be used with a 2D laser array having row / column matrix addressing capabilities.

[0016] Figure 5F Illustrates a voltage potential timing diagram according to one embodiment of the present teachings, which shows a method of operating a matrix-addressable laser driver circuit.

[0017] Figure 5G Illustrates an electrical schematic of a matrix-addressable laser driver circuit configured according to one embodiment of the present teachings with a high-side capacitor discharge circuit in capacitor charging mode.

[0018] Figure 5H Illustrates an embodiment according to the present teachings in combination with Figure 5G the electrical schematic of the matrix-addressable laser driver circuit described, but configured with a high-side capacitor discharge circuit in capacitor discharge mode for laser diode 2,2 (second row and second column).

[0019] Figure 5IIllustrates a voltage potential timing diagram according to an embodiment of the present teachings, which shows the voltage potential across capacitor C2 and across the laser diode 2,2 in the second row and second column.

[0020] Figure 5J Illustrates an electrical schematic of a matrix-addressable laser driver circuit configured with a low-side capacitive discharge circuit in capacitor charging mode according to an embodiment of the present teachings.

[0021] Figure 5K Illustrates an embodiment according to the present teachings in combination with Figure 5J the electrical schematic of the matrix-addressable laser driver circuit described, but configured with a low-side capacitive discharge circuit in capacitor discharge mode for the laser diode 2,2 (second row and second column).

[0022] Figure 5L Illustrates a voltage potential timing diagram according to an embodiment of the present teachings, which shows the voltage potential across capacitor C2 and across the laser diode 2,2 in the second row and second column.

[0023] Figure 6 Illustrates an embodiment of a high-side and low-side GaN FET driver circuit for driving a combination of laser diodes in a matrix-addressable laser driver circuit in an LIDAR system laser array according to the present teachings.

[0024] Figure 7 Illustrates a typical current-voltage curve of an embodiment of a semiconductor diode in a matrix-addressable laser driver circuit according to the present teachings.

[0025] Figure 8 Illustrates the voltage induced at nodes in a matrix while exciting a single laser within a two-dimensional array having row / column matrix addressability in an embodiment of a matrix-addressable laser driver circuit controller according to the present teachings.

[0026] Figure 9 Illustrates an embodiment of a LIDAR system array according to the present teachings, wherein the physical connection to the array enables a more dense layout for the associated electronic circuitry on a printed circuit board (PCB).

[0027] Figure 10 Illustrates a schematic diagram of an embodiment of a 2x2 laser array having a matrix-addressable laser driver circuit control circuit according to the present teachings, which shows possible current paths when one laser is excited.

[0028] Figure 11 Illustrates a schematic diagram of an embodiment of a 2x2 laser array according to the present teachings including lasers having a second diode in series with each laser diode in a matrix-addressable laser driver circuit.

[0029] Figure 12 Illustrated is an embodiment of multiple series diodes in accordance with the present teachings, which includes a VCSEL array, with additional diodes connected in series with each laser diode that is part of a separate carrier. Detailed Description

[0030] The present teachings will now be described in more detail with reference to the exemplary embodiments of the present teachings as illustrated in the accompanying drawings. Although the present teachings are described in conjunction with various embodiments and examples, it is not intended to limit the present teachings to such embodiments. On the contrary, as will be understood by those skilled in the art, the present teachings include various alternatives, modifications, and equivalent forms. Those of ordinary skill in the art who can obtain the teachings herein will recognize additional embodiments, modifications, and examples, as well as other fields of use, all of which are within the scope of the present disclosure as described herein.

[0031] References in the specification to "an embodiment" or "embodiments" mean 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 phrase "in an embodiment" appearing in various places in the specification does not necessarily all refer to the same embodiment.

[0032] It should be understood that the various steps of the methods of the present teachings can be performed in any order and / or simultaneously, so long as the teachings remain operable. Additionally, 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.

[0033] Most commercial LIDAR systems currently used in autonomous vehicles use a small number of lasers, in combination with some method of mechanically scanning the environment. Current automotive applications and future autonomous vehicle applications highly desire the use of solid-state semiconductor-based LIDAR systems. Compared to current LIDAR systems, solid-state LIDAR systems, especially those without moving parts, exhibit better reliability and can operate over a wider range of environmental working conditions. Such solid-state systems used in LIDAR systems can also be physically compact and relatively low in cost.

[0034] One approach to solid-state LIDAR is to use a large number of lasers, each projected at a unique angle onto a desired FOV, thus obviating the need for mechanical scanning. However, electrically connecting a drive circuit to a large number of lasers while maintaining the ability to operate them individually is a challenge. One solution is to arrange the multiple lasers in a two-dimensional matrix and then employ a matrix-addressable laser drive circuit that can simultaneously meet the needs of controlling 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. The methods and apparatus of this teaching relate to a laser control method and system architecture that enables individual control of a 2D laser matrix while ensuring a low-cost system.

[0035] Figure 1A FIG. illustrates a schematic diagram of a solid-state LIDAR system 100 in which individual lasers in a transmitter array 102 can be fired independently. Figure 1A The system shown does not employ a flash transmitter to simultaneously illuminate the entire field of view of the system. Instead, each individual laser in the transmitter array 102 can be fired independently, and the light beam emitted by each laser corresponds to a 3D projection angle that only faces a portion of the entire field of view of the system. An example of such a transmitter is described in detail in U.S. Patent Publication No. 2017 / 0307736A1 assigned to the present assignee. The entire content of U.S. Patent Publication No. 2017 / 0307736A1 is incorporated herein by reference.

[0036] The light beams from the lasers in the laser array 102 share the transmitter optics 104 that project the light beam 106 onto 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. A portion of the reflected light beam 112 shares the 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 and has no moving parts. The detector array 116 can have a smaller number of individual detector elements than the transmitter array 102 has individual lasers.

[0037] 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 light beams. A processor (not shown) in the LIDAR system 100 performs time-of-flight (TOF) measurements that determine the distance to the target 108 that reflects the light beam 106 from the lasers in the laser array 102, as detected at the detector array 116.

[0038] One feature of the system of the present teachings is that individual lasers and / or groups of lasers in the transmitter array 102 can be controlled individually. 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 controlled individually. This control provides various desired performance characteristics, including control of the field of view, optical power levels, scanning, and / or other characteristics.

[0039] Figure 1B illustrates Figure 1A a two-dimensional projection of the system field of view 150 of the LIDAR system of. The field of view of individual detectors in the detector array is represented by small squares 152. The illuminated measurement points associated with individual lasers in the transmitter are illustrated by circles 154. As an example of the case of having one excited laser element in the array, the light from the laser hits Figure 1A the field of view of individual detectors in the entire field of view of the LIDAR system of. This detector field of view that receives light is highlighted by hash marks in a 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.

[0040] In Figure 1B it can be seen that the measurement points shown by the circles 158 fall within the individual detectors, where the field of view of that individual detector has been shown in the square 156 with a cross-hatch pattern for identification. This figure illustrates that the 3D resolution of some embodiments of the LIDAR system is determined by the number of lasers, since each laser corresponds to a particular projection angle, which results in the size of the circles 154 at the target range, and the relative sizes of the circles 154 representing the field of view of the individual detector elements and the squares 152. Thus, various fields of view can be established by selectively exciting and transmitting laser pulses with a particular individual laser or group of lasers in the transmitter array and / or converting the optical signals in the received (one or more) detector fields of view into electrical signals with a particular individual detector or group of detectors in the receiver array. 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.

[0041] In some embodiments, the field of view of an individual detector in a detector array is the active area of the detector. 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 so as not to attenuate or distort the received signal. In a LIDAR system with a laser pulse width < 10 nanoseconds and a rise / fall time of ~1 nanosecond, typical values for the opto-electrical (O / E) bandwidth and the APD capacitance are 350 MHz and less than 2 pF, respectively. Generally, in order to cover the entire field of view of the 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.

[0042] Figure 2 A perspective view of the structure of a known bottom-emitting VCSEL 200 that can be used in a LIDAR system according to the present teachings is illustrated. The area of the emission aperture 202 of the VCSEL 200 typically ranges from a few microns in diameter (for mW power operation) to 100 microns or more in diameter (for 100 mW and greater CW power operation). The VCSEL 200 is fabricated on a substrate 204, which can 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 holes that can be formed in an oxide material. Then a p-type DBR layer 212 is grown on the active region. Generally, the p-type DBR layer 212 is highly reflective and the n-type DBR layer 206 is partially reflective, resulting in light output 214 from the bottom, substrate side of the layer structure. The active region 208, oxide holes 210, and p-type DBR layer 212 form in a mesa structure in the device shown. Top contact 216 and bottom contact 218 are used to provide current to the active region to generate output light. The oxide holes 210 confine the current to the active region 208. The top contact 216 is p-type and the bottom contact 218 is n-type.

[0043] The 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 Figure 2 only one emission aperture 202 is shown because Figure 2Only one element of the multi-element VCSEL array is illustrated. A VCSEL of this type can be a stand-alone single element, or it can be part of a multi-element VCSEL that can be fabricated as a one-dimensional or two-dimensional array on a 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, having appropriate drive signals for LIDAR system applications.

[0044] 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 can be used. For example, the common substrate can be a semiconductor material. The common substrate can also include ceramic materials. In other embodiments, the 2D VCSEL array is assembled from a set of 1D bars or even individual die.

[0045] In some embodiments, the VCSEL is a top-emitting VCSEL device. In other embodiments, the VCSEL device is a bottom-emitting VCSEL. An individual VCSEL device can have either a single large emission aperture, or an individual VCSEL can be formed from two or more sub-apertures within a larger effective emission diameter. A set of sub-apertures that form a larger effective emission area is sometimes referred to as a cluster.

[0046] Figure 3 A schematic illustration of an embodiment of a 2D monolithic VCSEL array 300 having 256 individual laser emitters 302 used in a solid-state LIDAR system in accordance with the present teachings is shown. Each laser emitter 302 has an emission aperture 304 with a diameter of "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" that is equal to the diameter of the emission aperture 304. The laser emitters 302 are evenly spaced in the horizontal direction by a pitch dx 306 and in the vertical direction by a pitch dy 308. The total size of the array measured from the center of the outermost lasers is a distance Dx 310 in the horizontal direction and a distance Dy 312 in the vertical direction. The actual chip size will be slightly larger in dimension than the distance Dx 310 and the distance Dy 312. In various embodiments, the emitter 302 can generate beams having various shapes other than a circular emitter shape. For example, ellipses, squares, rectangles, and various odd shapes can be implemented in various embodiments. In embodiments where the lasers are arranged in a 2D array, the rows and columns of the lasers can be electrically driven in a matrix-addressable manner.

[0047] Some embodiments of the present teachings utilize a bottom-emitting high-power array of VCSEL devices having a single large aperture per laser, such as Figure 3 the configuration shown in. Other embodiments of the present teachings utilize a high-power array of top-emitting or bottom-emitting 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.

[0048] A two-dimensional VCSEL array can be used as a building block for a LIDAR system according to the present teachings to establish a platform that allows the transmitter to have a small physical size. For example, a 2D VCSEL array with 256 high-power individual lasers can be constructed on a monolithic chip approximately 4 mm x 4 mm. Such a monolithic chip can be used with selected optical elements to keep the physical dimensions as small as possible, e.g., by using a microlens array, a shared lens with dimensions less than 20 mm, or a diffractive optical device with a maximum dimension of approximately 20 mm.

[0049] However, a LIDAR system according to the present teachings places certain requirements on the 2D VCSEL array. In particular, it is desirable for the 2D VCSEL array to allow independent and simultaneous control of all VCSEL devices. In a certain operating mode of the LIDAR system of the present teachings, each VCSEL within the matrix is excited at different times. For such an operation, the VCSEL array needs to be operated in a matrix-addressable manner, where the lasers can be individually excited, but not always simultaneously.

[0050] Figure 4 Illustrated is an exemplary cascaded two-port circuit model 400 for an individual semiconductor laser of a VCSEL array according to the present teachings. The intrinsic laser junction is represented by the symbol of a well-known diode 402. The active region of the laser-emitting laser is sandwiched between the p-n junctions of the diode. The circuit model 400 includes a driver connection 404 that supplies a voltage V d as well as the electrical characteristics of the metal contact 406. In addition, the circuit model 400 includes parasitic elements 408, which include pad resistance losses in the form of a parasitic pad current 408i p and a parasitic chip current 410i p in the form of.

[0051] 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 can be flip chips bonded to silicon electronics to provide a highly compact way to connect to and electrically drive the 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, August 2001. See also U.S. Patent No. 7,702,191 titled "Electro-Optical Chip Assembly" and U.S. Patent No. 8,675,706 titled "Optical Illuminator that Fire Devices in Parallel." However, these known heterogeneous integration techniques are mainly targeted at applications in the optical communication market, where multi-channel simultaneous parallel operation is desired as a solution to increase data transmission throughput.

[0052] Figure 5A FIG. illustrates an electrical schematic of an embodiment of a matrix-addressable laser driver circuit for a 2D laser array 500 configured to have 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 lasers, but it should be understood that the model 400 described in conjunction with Figure 4 more accurately represents the lasers, and such models will be used in the actual design. Also, for simplicity, only a 4x4 diode matrix is shown in the schematic 500, and the voltage and / or current drivers for driving the matrix-addressable laser driver circuit are not shown. However, it can be understood 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.

[0053] The matrix-addressable laser driver circuit for the 2D laser array 500 is configured such that the VCSEL devices 502 are connected to anodes 504, 504', 504", 504'". The rows of the VCSEL devices 502 are connected through cathodes 506, 506', 506", 506'". This anode-column and cathode-row connection configuration shown in the schematic 500 allows individual lasers 502 to be turned on / off by operation of the rows and columns without the need to separately access the cathodes and anodes of individual lasers 502.

[0054] Figure 5BFIG. illustrates an embodiment of a matrix-addressable laser driver circuit configured as a voltage driver in accordance with the present teachings, where row / column matrix addressability is used to energize individual lasers 502 within a 2D laser array 500. A power supply 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 is connected to anode columns 504, 504', 504", 504'" through a series of switches 556, 556', 556", 556''', and the ground bus 552 is connected to cathode rows 506, 506', 506", 506''' through a series of switches 558, 558', 558", 558'''. The power supply 548 generates a voltage potential 550, V with a desired voltage potential waveform. + . The anode column of the VCSEL to be energized ON is connected to the voltage potential 550 via the switch 556', and the voltage potential 550 is high enough to forward bias the VCSEL, diode 550. The cathode row 506' containing that VCSEL is connected to the ground bus 552 via the switch 558' to complete the circuit, allowing current to flow through the VCSEL and energizing the laser to emit light. The other cathodes and anodes are set to the "open" state, where the power supply 548 does not provide any specific voltage level to them by opening the switches 556, 556", 556''' and opening the switches 558, 558", 558'''.

[0055] In Figure 5B an alternative embodiment of the circuit shown, the cathodes 506, 506" and 506""" are not "open" but are connected to a power supply 548 (or another power supply) that provides a voltage potential waveform having a voltage set at a certain predetermined voltage level during operation, and this voltage is less than V+. In other words, Figure 5B the potential on the ground bus 552 indicated in Figure 5E may not be the ground potential, but instead can be a voltage level less than V+ set by the power supply 548 during operation, such that the voltage potential 550 is applied relative to the predetermined voltage. In these embodiments, the switches 556, 556", 556''', 558, 558", 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 for implementing this embodiment is described in conjunction with

[0056] One feature of the laser array controller of the present teachings is that it can use a variety of laser driver circuits to provide the desired laser driving characteristics. In some embodiments, the power supply 548 that drives the lasers generates high current, short duration pulses. 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 having the power supply 548 apply a potential waveform with a defined voltage (a so-called voltage driver) or a current waveform with a defined current level (a so-called current driver).

[0057] In some embodiments, the power supply 548 is configured to produce a waveform that reduces power dissipation when no pulses are being generated. This can be achieved, for example, by using a circuit configuration that provides a near or complete turn-off of the output of the power supply 548 during the downtime between the application of short duration pulses. In one such embodiment, the power supply energizes the laser driver during a wake-up period before generating a short duration pulse and then generates the pulse. The power supply 548 produces a waveform turn-off during the time between pulses, which is initiated after the pulse has been fired. This waveform turn-off period is preceded by a wake-up period before another short duration pulse is generated. 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 can execute a series of commands such as the following: (1) place the laser driver power supply in the "low power state"; (2) place the laser driver power supply in the "wake-up" mode; (3) "turn on" the laser driver power supply output; (4) "turn off" the laser driver power supply output; and (5) return the laser driver to the "low power state".

[0058] Figure 5C An electrical schematic of a single matrix addressable laser driver 570 configured as a high-side current driver in accordance with an embodiment of the present teachings is illustrated, which can be used with a 2D laser array having row / column matrix addressability. The high-side configured laser driver 570 includes a field effect transistor (FET) 572, where the FET source is coupled to the power supply potential V+ and the FET drain is 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.

[0059] Figure 5DFIG. illustrates an electrical schematic of a single matrix-addressable laser driver 580 configured as a low-side current driver according to an embodiment of the present teachings, which can be used with a 2D laser array having row / column matrix addressability. 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 a 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.

[0060] Figure 5E FIG. illustrates an electrical schematic of a matrix-addressable laser drive circuit 590 configured with a high-side voltage driver 591 for columns, a low-side voltage driver 592 for rows, and switches that can be used to apply an additional voltage to the rows, which can be used with a 2D laser array having row / column matrix addressing capabilities. 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. A laser diode 594 is shown together with its associated parasitic capacitor.

[0061] The configuration of the matrix-addressable laser drive circuit 590 is similar to an alternative embodiment of the circuit shown in Figure 5B wherein 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 the switch 593 allows for more complex control of the voltage applied to the cathode. In the Figure 5E configuration of the matrix-addressable laser drive circuit 590 shown in, the cathode of the laser diode is at a potential determined by the voltage divider 593, which is controlled by a charging signal applied to its FET gate. Operating the matrix-addressable laser drive circuit 590 such that the laser diode is reverse-biased so that the cathode is at a potential other than ground potential can have many performance advantages. One such performance advantage is that crosstalk between laser diodes can be significantly reduced.

[0062] Figure 5F FIG. illustrates a voltage timing diagram 599, which shows one method of operating the matrix-addressable laser drive circuit 590 described in conjunction with Figure 5E The waveforms of the column drive signal C2 595 applied to the high-side voltage driver 591, the row drive signal R2 596 applied to the low-side voltage driver 592, and the charging signal 597 applied to the voltage divider 593 are shown.

[0063] An optical pulse is 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 optical pulse width. The duty cycle depends on various operating parameters. For example, in one operating method, the duty cycle of the optical pulse is 1%. The column drive signal 595 has a longer pulse than the row drive signal 596. This prevents competition between the row and column pulses.

[0064] An important feature of the methods and apparatus of this teaching is that the various laser driver circuit configurations and operating methods reduce crosstalk and thus improve performance. Referring to the matrix-addressable laser driver circuit 590 described in connection with Figure 5E crosstalk occurs when a laser diode is indirectly excited via a circuit path through its associated parasitic capacitor and low-side driver. In the Figure 5E configuration shown, this undesirable result can be prevented by charging the parasitic capacitor to the voltage +V, which sets the laser diode 594 to reverse bias. Thus, when the desired laser diode is excited, no other laser diodes should emit light. However, biasing the laser diode 594 under continuous reverse bias conditions will result in an increased device failure rate and reduced overall device reliability. One solution according to this teaching is to drive the low-side driver during the remaining duty cycle to discharge the parasitic capacitor of the laser diode when the laser diode is not intentionally excited. For example, the driving is typically done at a 1% duty cycle for approximately 99% of the off duration.

[0065] Figure 5G An electrical schematic of a matrix-addressable laser driver circuit 620 configured with a high-side capacitive discharge circuit 622 in capacitor charge mode is illustrated. The driver circuit 620 is similar to the driver circuit 500 described in connection with Figure 5A but includes a high-side capacitive discharge circuit 622. In capacitor charge mode, all high-side switches 624 and all low-side switches 626 are open, allowing the capacitors C1-C3 630 to charge to the full potential applied to the driver circuit 620, which is indicated as -V, with a time constant.

[0066] Figure 5H An electrical schematic of the matrix-addressable laser driver circuit 620 described in connection with Figure 5G is illustrated, but configured with the high-side capacitive discharge circuit 622 in capacitor discharge mode for laser diode 2,2 (second row, second column). In capacitor discharge mode for laser diode 2,2, the high-side switch 624 and the low-side switch 626 are both closed, causing current to discharge in path 632.

[0067] Figure 5IThe voltage potential timing diagram 635 is illustrated, which shows the voltage potentials across the capacitor C2 and across the laser diodes 2,2 in the second row and second column. The switches LS2 and HS2 are closed until the initial time t0. Before time t0, the potential C2+ is at ground potential and the potential C2- is at -V potential. At time t0, the switches LS2 626 and HS2 624 are closed, causing the potential C2- to transition to ground potential and charging the potential C2+ to +V potential, reaching these potentials at time t1. After the anode of the laser diodes 2,2 is charged to +V potential, the capacitor C2 discharges from the potential C2+ through the laser diodes 2,2, thereby generating a light pulse. At time t2, the switches LS2 and HS2 are closed to initiate the conditions 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.

[0068] Figure 5J The electrical schematic of a matrix-addressable laser driver circuit 640 configured with a low-side capacitive discharge circuit 642 in a capacitor charging mode is illustrated. The driver circuit 640 is similar to the driver circuit 500 described in conjunction with Figure 5A but includes the low-side capacitive discharge circuit 642. In the capacitor charging mode, all the low-side switches 644 and all the high-side switches 646 are open, thereby allowing the capacitors C1-C3 626 to charge to the full potential applied to the driver circuit 640, which is indicated as the +V potential, with a time constant.

[0069] Figure 5K The electrical schematic of a matrix-addressable laser driver circuit 640 described in conjunction with Figure 5J is illustrated, but configured with a 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 the laser diodes 2,2, both the high-side switch and the low-side switch are closed, thereby causing current to discharge in the path 648.

[0070] Figure 5LIllustrated is a voltage potential timing diagram 650, which shows the voltage potential across capacitor C2 and across the laser diodes 2,2 in the second row and second column. Switches LS2 and HS2 are initially open. Before time t0, when switches LS2 and HS2 are open, the C2+ potential on capacitor C2 is the +V potential and the C2- potential is the ground potential. At time t0, switches LS2 and HS2 close, driving C2+ to ground and causing C2- to start charging from ground to -V. At time t1, capacitor C2 starts discharging via laser diodes 2,2 with a time constant, causing laser diodes 2,2 to generate light pulses. At time t2, switches LS2 and HS2 close, thus initiating the conditions 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.

[0071] Figure 6 Illustrated is an embodiment of a high-side and low-side GaN FET driver circuit 600 for driving a combination of laser diodes in a matrix address laser driver circuit in an electrically driven LIDAR system laser array according to the present teachings. Such a driver circuit is also known in the art as an asymmetric switch driver circuit. In various embodiments of the LIDAR system of the present teachings, the driver circuit 600 is connected to Figure 5A each of the column / row anode / cathode connections shown in -B, where the driver circuit 600 is configured as an on-off driver and includes a high-side drive electrical input 602 and a low-side drive electrical input 604.

[0072] More specifically, referring to Figure 5B and Figure 6 , the cell 560 in the electrical schematic 500 is configured with the driver circuit 600 in the following manner. Transistor 602, Q1, corresponds to switch 556 that connects voltage potential 550 to laser anode 504. Transistor 604, Q2, corresponds to switch 558 that connects ground 552 to laser cathode 506. High-side driver input 606 is electrically connected to the gate of transistor 602. Low-side driver input 608 is electrically connected to the gate of transistor 604.

[0073] The asymmetric, on-off driver circuit 600 is suitable for injecting 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 in duration and should provide a high peak output power within 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 safety limit.

[0074] One feature of the present teachings is that the array drive control circuit can be configured to optimize driving based on characteristics of the current-voltage (IV) curve of the laser transmitter. Figure 7 Illustrated is a typical current-voltage curve 700 of an embodiment of a semiconductor diode 702 in a matrix address laser drive 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 Figure 7 shown, when the laser diode 702 is forward biased, the voltage at the anode 704 will be positive relative 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 after exceeding the threshold voltage V th 710, the positive current 708 starts to increase exponentially from nominally zero.

[0075] When the laser diode is reverse biased with the voltage at the cathode positive relative 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 br 712). Once breakdown is reached, the current increases exponentially in the negative direction, and since the voltage and current are relatively high, the self-consumption power is also relatively high, resulting in overheating and burnout of the laser diode. Laser light is generated under forward bias conditions.

[0076] The current-voltage behavior of each individual laser, combined with the method of controlling the laser drive to energize the individual laser, significantly affects the operating 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 intentionally forward biased for energization) are forward biased simultaneously because current and / or voltage leaks from the electrical driver supplying the energizing laser. As a result, other lasers emit light even though such emission is not desired. This optical crosstalk situation has an adverse effect on the performance of the LIDAR system by illuminating measurement points not intended to be illuminated and / or illuminating a wider target area than intended to be illuminated.

[0077] Figure 8 Illustrated is the voltage induced at a node in the matrix when energizing a single laser within a two-dimensional array having row / column matrix addressability by a matrix-address laser drive circuit controller 800 according to the present teachings. The matrix addressable laser drive circuit controller 800 provides a voltage at each node in the matrix, similar to in combination with Figure 5BOperation of the described embodiment. For example, switch 802 connects the second column to the power supply voltage 804 and switch 806 connects the second row of lasers to ground 808. This switch configuration causes a voltage V'810 to be induced at the anode of each row except the row intentionally grounded through the connection of switch 806 to ground 808. The voltage V'810 creates 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.

[0078] In the case where the value of the power 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 br and V th sum, and little 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.

[0079] Figure 9 An embodiment of a VCSEL array chip 900 of a LIDAR system mounted on a carrier 902 in accordance with the present teachings is illustrated. The physical connections to the array make the layout of the associated electronic circuitry on a printed circuit board (PCB) substrate more dense. A 16x16 array 904 of transmitter clusters 906 including nine small apertures 908 for addressable VCSEL devices is shown. The carrier 902 has a plurality of electrical edge connectors 910, 910', each electrical edge connector being connected to a row edge 914 or a column edge 914' of the array 904 by wire bonding 912, 912'. The connections of the anodes and cathodes alternate on either side of the circuit on the PCB to which the VCSELs are connected. This alternating connection pattern results in a wider PCB spacing between the row and column circuits, which enables the GaN FETs to be placed closer to the VCSEL array, thus making the circuit layout more compact and reducing the physical footprint.

[0080] 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, row / column-wise, the minimum number of drivers required is equal to M+N, where M is the number of columns and N is the number of rows, respectively. In contrast, if each VCSEL device in the array had 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 if each VCSEL had its own dedicated driver, 256 drivers would be required.

[0081] It should be understood that for matrix addressing, it is not possible to achieve fully independent operation of all lasers simultaneously. In other words, only certain lasers can be excited at a given time. However, this limitation is not important for the LIDAR systems described herein because in typical operation, only one laser within a particular monolithic array is energized at a time so that there is no ambiguity as to which measurement point in space is being illuminated. Energizing one laser within a particular monolithic array at a time also helps to maintain Class 1 eye safety.

[0082] It should also be understood that matrix addressing is well known in the electronics art. However, the aspect of using matrix addressing in LIDAR systems that require short-duration, extremely high optical power pulses, and low duty cycles was previously unknown. As described above, a LIDAR system with 256 lasers operating at a 100-m range (with a minimum time between pulses of 1 microsecond) has a duty cycle of only 0.002% and a pulse duration of 5 nanoseconds. Matrix addressing has been used to energize optical communication laser devices, which typically operate at relatively low peak powers (mW compared to W), relatively long pulse durations, and a duty cycle of ~50%. Under these conditions, the electrical drive requirements are very different from the operation of high-power lasers in state-of-the-art LIDAR applications.

[0083] For example, a pulsed TOF LIDAR system for operation at ranges greater than 100 m using 905-nm wavelength lasers typically requires optical pulses with a peak power of more than 20 watts and a pulse duration of less than 10 nanoseconds. Assuming a 1W / A efficiency of the laser device under pulsed conditions, the corresponding drive voltage and current on an individual laser are in the range of 10 volts and 10 amperes, respectively. Of course, if a voltage greater than 10 V is applied to a matrix-addressable array, unwanted electrical and optical crosstalk is likely to occur. When such a voltage is present under reverse-biased conditions, the VCSEL devices in the matrix are also very likely to be damaged or destroyed.

[0084] One of the main factors affecting the reliability of a laser is the average and transient temperature of the device. If the pulse energy is controlled to keep the transient temperature rise of the device low enough, then the peak current and voltage values can be relatively high as long as the pulse duration is short enough. Even under reverse bias conditions where thermal runaway is an important issue, the 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 a specific heat and density, a 1 μJ pulse entering a 2-μm thick, 100-μm diameter junction will cause the temperature of that junction to rise by ~9 °C. A 20 V / 10 A square wave pulse with a duration of 5 ns is equivalent to 1 μJ of energy. The resulting transient temperature rise will only be on the order of a few degrees and may therefore not be sufficient to degrade the reliability of the device.

[0085] Figure 10 FIG. illustrates a schematic diagram of an embodiment of a 2x2 laser array with a matrix drive control circuit 1000 according to the present teachings, showing the possible current paths when one laser 1002 is excited. 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 a larger MxN matrix.

[0086] Given Figure 10 is to illustrate the potential problems caused by the high voltages necessary for state-of-the-art LIDAR applications. In Figure 10 , since the second column 1004 is connected to the drive voltage bus 1006, V+, and the second row 1008 is connected to the ground bus 1010, the VCSEL device L22 1002 is intentionally forward-biased and emits light. The current flowing through the VCSEL device L22 is indicated by the solid arrowed line 1012 in the figure. Ideally, all other VCSEL devices 1014, 1016, 1018 in the matrix are turned off because the first row 1020 and the first column 1022 are open and not connected to the ground bus 1010 or the V+ bus 1006.

[0087] However, in addition to the main path of the solid line 1012, there is also the possibility of a second current path. This second current path is indicated by the dashed line 1024 with a direction arrow. When V+ on the bus 1006 is applied to the second column 1004 by closing the switches 1026, 1028, the VCSEL device 1016L12 will apply V+ on the bus 1006 at the anode and will induce a voltage represented as V’1030 at the cathode to meet the condition that this path is nominally open where no current can flow. It should be noted that when the voltage V+ on the bus 1006 is initially applied to the second column 1004, the voltage V’1030 can initially be zero. When this occurs, there may be a transient current with sufficient forward voltage of the VCSEL devices L12 1016 and L22 1018 to cause them to emit unwanted light, which results in optical crosstalk. In this case, the crosstalk is the extra unwanted light generated within the field of view rather than the light generated by the VCSEL device L22 1002.

[0088] Since the cathodes are connected in a given row, the voltage V’1030 will also be applied to the cathodes of the VCSEL devices L111014 and this will immediately place the VCSEL device L11 1014 in a reverse-biased condition. The voltage V”1032 will be induced at the anode of the VCSEL device L11 1014 to satisfy the current / voltage relationship. If the voltage V’1030 is less than the reverse breakdown voltage of L11 1014, then the current is typically less than 1 μA. The small current flowing through L11 1014 will also flow through L21 1018, placing it in a forward-biased state. The voltage V” will correspond to the forward IV curve of L21 1018. To avoid light emission from L21, the current flowing through L211018 should be below the laser threshold current, which is expected to be in the range of 10 to 100 mA for LIDAR applications.

[0089] However, if the voltage V’1030 is greater than the breakdown voltage of the VCSEL device L11 1014, then a higher current will flow through the circuit. If this current is higher than the threshold current of L21 1018, then light will be generated in both the VCSEL device L12 1016 and the VCSEL device L21 1018, which results in the generation of unwanted optical crosstalk. Therefore, it can be understood 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 the current flowing through the corresponding path is not sufficient to cause light emission from these two VCSEL devices L12 1016 and L21 1018.

[0090] Accordingly, one aspect of the present teachings is to recognize that for a particular VCSEL device used in LIDAR applications, it is desirable to constrain the voltage V'1030 to be less than the reverse breakdown voltage to avoid unwanted optical crosstalk. Additionally, continuous current flow under reverse bias conditions is undesirable as it can be a potential reliability issue for the laser diode, depending on factors such as time, the energy associated with the current, and the resulting thermal rise in the laser diode.

[0091] Under operating conditions where the voltage V'1030 causes significant transient current to flow through devices 1014, 1016, and 1018, the pulse energy should be low enough so as not to significantly affect reliability, and the transient temperature rise in these devices should be below 20°C.

[0092] Using many known VCSEL device structures for LIDAR applications will result in the generation of unwanted optical crosstalk because typically voltages of 10V - 80V are required to generate the high-power optical pulses needed for state-of-the-art 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.

[0093] Accordingly, another aspect of a LIDAR system that uses a matrix-addressable control circuit according to the present teachings to drive a laser array for LIDAR applications is the design of the VCSEL device itself to have desired operating specifications that reduce or eliminate optical crosstalk and simultaneously have high reliability. That is, a VCSEL device according to the present teachings is specifically designed such that the operating conditions prevent unwanted optical crosstalk from affecting system performance. One way to prevent unwanted optical crosstalk is to fabricate a VCSEL device having a laser structure that can achieve relatively high reverse bias operating conditions without entering the breakdown condition.

[0094] V can be increased th or V br One possible laser structure that includes either or both is multiple junctions in series within the VCSEL device. A laser structure with multiple series junctions has been demonstrated in devices using tunnel junctions that separate the active junctions. It should be understood that many other similar laser structures with multiple junctions can be used. Although using multiple junctions increases V th , due to the high pulse voltages and currents, the impact on efficiency and device performance is generally acceptable for this application.

[0095] Figure 11 A schematic diagram illustrates an embodiment of a 2x2 laser array of lasers according to the present teachings that includes a second diode in series with each laser diode in the matrix-address laser drive circuit 1100. Similar to that combined with Figure 10Schematic diagram of the described 2x2 laser array 1000, where the laser array 1100 includes VCSEL devices 1102, 1104, 1106, 1108 in a matrix. In addition, second diode devices 1110, 1112, 1114, 1116 are electrically connected in series with laser diodes 1102, 1104, 1106, 1108. In some embodiments, the VCSEL devices 1102, 1104, 1106, 1108 are GaAs laser diodes and the second diode devices 1110, 1112, 1114, 1116 are silicon diodes. Similar to the 2x2 laser array 1000 described in conjunction with Figure 10 Schematic diagram of the described 2x2 laser array 1000, there are drive voltage buses 1118, ground buses 1120, two columns 1122, 1124 and two rows 1126, 1128.

[0096] In operation, when two switches 1132, 1134 are closed, the laser drive current flows through the path 1130 shown in thick lines in the direction indicated by the arrow. 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 of a GaAs laser diode is about 2V to 3V, while for a silicon diode it is about 1V to 2V, the additional forward voltage drop is not significant because the matrix addressed laser drive circuit 1100 is designed to generate high optical power from each laser, so it typically operates at a drive voltage of more than 10V. Accordingly, this additional forward voltage 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.

[0097] Different embodiments use different diode types to implement the second diodes 1110, 1112, 1114, 1116 connected in series, or multiple additional diodes connected in series. For example, some embodiments monolithically stack the second diodes 1110, 1112, 1114, 1116 with the corresponding lasers 1102, 1104, 1106, 1108 within the chip. The chip can be a GaAs chip, similar to Figure 2 the chip shown in, but with an additional layer structure forming one or more series diodes. In some embodiments, the stacked second diode is another active P-N junction that generates optical gain that beneficially increases the VCSEL brightness. 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 the stacked structure utilizes a tunnel junction to separate the two stacked diodes to keep the overall resistance relatively low.

[0098] VCSEL devices with stacked or cascaded multi - diode regions are known in the art. See, for example, "Bipolar Cascade VCSEL with 130% Differential Quantum Efficiency", Annual Report 2000, Optoelectronics Department, University of ULM. Also, multi - diode cascade VCSEL structures have been used to increase overall brightness. See, for example, U.S. Patent Publication No. US2015 / 0311673A1. Also, VCSELs have been fabricated with integrated photodiodes. See, for example, U.S. Patent No. 6,717,972. However, the prior art does not teach a matrix - addressed laser driver circuit 1100 configured for LIDAR applications using such a structure.

[0099] Another VCSEL device structure according to this teaching that achieves relatively high reverse - bias operating conditions without entering breakdown conditions 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.

[0100] 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 Figure 9 is a 16x16 array 904 that includes nine small apertures 908 of addressable top - emitting VCSEL devices, where the individual apertures within each single emitter are connected in parallel. Recently, series - connected VCSEL devices have been developed for high - power applications, but the issues of optical crosstalk and forward voltage drop have not been considered. See, for example, U.S. Patent Publication No. 2019 / 0036308A1, which discloses a series - connected single - chip VCSEL device. According to this teaching, such devices can be configured to reduce optical crosstalk.

[0101] Another VCSEL device structure according to this teaching that achieves relatively high reverse - bias operating conditions without entering breakdown conditions incorporates additional diodes into a mating substrate or IC bonded to the VCSEL device. Figure 12 An embodiment of a plurality of diodes 1200 in series configuration is illustrated, which includes a VCSEL array 1202, with additional diodes 1204 connected in series with each laser diode 1206 as part of a separate carrier 1208 according to this teaching. In some embodiments, the carrier 1208 is an integrated circuit. For example, the integrated circuit can be an inexpensive silicon - based integrated circuit.

[0102] The carrier 1208 can be electrically connected to the array 1202 in various ways. For example, the carrier 1208 can be electrically bonded to the array 1202 using a bump bonding connector 1210. In Figure 12 the configuration shown, the bottom-emitting VCSEL laser array 1202 is bonded to the carrier. For simplicity, the figure only shows 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 the carrier 1208. It should be understood that additional diodes can be added in series to this and other configurations described 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.

[0103] Equivalent

[0104] Although the applicant's teachings are described in conjunction with various embodiments, it is not intended to limit the applicant's teachings to such embodiments. On the contrary, as will be recognized by those skilled in the art, the applicant's teachings cover various alternatives, modifications, and equivalent forms that can be made without departing from the spirit and scope of this teaching.

Claims

1. A solid-state light detection and ranging LIDAR transmitter having a matrix-addressable laser driver circuit, the LIDAR transmitter comprising: a) A first electrical bus that provides a first voltage potential to a plurality of columns of a matrix-addressable laser driver circuit; b) A plurality of column switches, each of the plurality of column switches connecting one of the plurality of columns to the first electrical bus; c) Multiple sets of serially-connected diodes, each set of serially-connected diodes including a laser diode serially electrically connected to a second diode, and a corresponding set of the multiple sets of serially-connected diodes being electrically connected between a corresponding column and a corresponding row of the matrix-addressable laser driver circuit to form a LIDAR transmitter; and d) A voltage divider that determines the potential of the cathode of the laser diode, wherein at least some of the second diodes increase the overall reverse breakdown voltage of the sets of serially-connected diodes, the voltage divider being configured such that the cathode of the laser diode is at a potential other than ground potential, thereby reducing optical crosstalk when the LIDAR transmitter is energized, and wherein the voltage of the corresponding row connected to a set of the multiple sets of serially-connected diodes connected to the first voltage potential through a column switch remains below the overall reverse breakdown voltage, thereby reducing crosstalk between the set of the multiple sets of serially-connected diodes connected to the first voltage potential through a column switch and at least two adjacent sets of the multiple sets of serially-connected diodes when the LIDAR transmitter is energized.

2. The LIDAR transmitter according to claim 1, wherein at least some of the second diodes include an active P-N junction that generates an optical gain that increases the brightness of the associated laser diode.

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

4. The LIDAR transmitter according to claim 1, wherein at least some of the second diodes are photodiodes.

5. The LIDAR transmitter according to claim 1, wherein at least some of the second diodes are monolithically integrated with the laser diodes.

6. The LIDAR transmitter according to claim 1, wherein at least some of the second diodes are located on a substrate separate from the substrate of the laser diodes.

7. The LIDAR transmitter according to claim 1, wherein at least some of the groups of serially connected diodes are configured to have an overall reverse breakdown voltage that exceeds the absolute value of the maximum drive voltage provided by the first electrical bus.

8. The LIDAR transmitter according to claim 1, wherein at least some of the laser diodes include at least two holes connected in series.

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

10. The LIDAR transmitter according to claim 1, wherein at least some of the laser diodes include surface-emitting laser diodes.

11. The LIDAR transmitter according to claim 1, wherein at least some of the laser diodes include vertical-cavity surface-emitting laser diodes.

12. The LIDAR transmitter according to claim 1, wherein the first electrical bus is configured to provide a positive voltage to the anodes of the laser diodes.

13. The LIDAR transmitter according to claim 1, wherein at least some of the plurality of column switches include transistors.

14. The LIDAR transmitter according to claim 1, wherein at least some of the plurality of column switches include an asymmetric switch driver circuit.

15. The LIDAR transmitter according to claim 14, wherein the asymmetric switch driver circuit includes a GaN FET driver circuit.

16. The LIDAR transmitter according to claim 1, wherein at least some of the plurality of column switches include enhancement-mode MOSFET power transistors.

17. The LIDAR transmitter according to claim 1, wherein at least some of the plurality of column switches include GaN power transistors.

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

19. The LIDAR transmitter according to claim 1, wherein the number of rows of the matrix-addressable laser driver circuit is the same as the number of columns of the plurality of columns.

20. The LIDAR transmitter according to claim 1, wherein the number of rows of the matrix-addressable laser driver circuit is not equal to the number of columns of the plurality of columns.

21. The LIDAR transmitter according to claim 1, further comprising a power supply that generates a first voltage potential, wherein the power supply is configured to enter a reduced power mode when the first voltage potential is not generated.

22. A method of generating a light detection and ranging LIDAR beam, the method comprising: a) Providing a two-dimensional array of laser devices including multiple sets of serially-connected diodes, each set of serially-connected diodes including a laser diode serially electrically connected to a second diode, and a corresponding set of the multiple sets of serially-connected diodes being electrically connected between a column and a row of a corresponding matrix-addressable laser driver circuit; b) Setting the potential of the cathode of the laser diode to a potential other than ground potential, thereby reducing optical crosstalk in the LIDAR beam; c) Switching the first voltage potential to a selected column of the matrix-addressable laser driver circuit; And d) Switching a second voltage potential to a selected row of the matrix-addressable laser driver circuit, thereby forward biasing the selected laser diode in the two-dimensional array of laser devices, thereby causing the emission of a LIDAR beam having a desired pattern, while reducing optical crosstalk through the serially-connected second diodes, wherein the voltage of the corresponding row connected to a set of the multiple sets of serially-connected diodes connected to the first voltage potential through a column switch remains below the overall reverse breakdown voltage of the serially-connected diodes, thereby reducing crosstalk between the set of the multiple sets of serially-connected diodes connected to the first voltage potential through a column switch and at least two adjacent sets of the multiple sets of serially-connected diodes when the LIDAR is energized.

23. The method according to claim 22, wherein switching the first voltage potential to a selected column of the matrix-addressable laser driver circuit includes applying a voltage greater than 10 V.

24. The method according to claim 22, wherein switching the first voltage potential to a selected column of the matrix-addressable laser driver circuit includes switching for a predetermined time to generate a LIDAR beam including a train of optical pulses.

25. The method according to claim 22, further comprising selecting at least one of a first voltage potential and a second voltage potential such that a two-dimensional array of laser devices causes the emission of a LIDAR beam having a peak power of more than 20 watts.

26. The method according to claim 22, wherein switching the first voltage potential to a selected column of the matrix-addressable laser driver circuit and switching the second voltage potential to a selected row of the matrix-addressable laser driver circuit are performed at a rate to generate pulses having a pulse duration of less than 10 nanoseconds in a train of optical pulses.

27. The method according to claim 24, wherein switching the first voltage potential to the selected columns of the matrix-addressable laser driver circuit and switching the second voltage potential to the selected rows of the matrix-addressable laser driver circuit are performed to reduce power consumption when no pulses are generated.

28. The method according to claim 27, further comprising turning off the power supplies that generate the first voltage potential and the second voltage potential when no pulses are generated.

29. The method according to claim 22, wherein switching the first voltage potential to the selected columns of the matrix-addressable laser driver circuit comprises switching for a predetermined time to keep the transient temperature rise in the junction of the laser diode below 20 °C.

30. The method according to claim 22, wherein at least some of the laser diodes emit light beams having wavelengths between 830 nm and 1000 nm.

31. The method according to claim 22, wherein the first voltage potential is greater than the breakdown voltage of at least some of the laser diodes.

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