Patent Publication Number: US-2022224074-A1

Title: Square pulse laser driver for vertical cavity surface emitting laser arrays

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This Patent Application claims priority to U.S. Provisional Patent Application No. 63/199,602, filed on Jan. 11, 2021, and entitled “LOW RIPPLE LASER DRIVE.” The disclosure of the prior Application is considered part of and is incorporated by reference into this Patent Application. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to lasers and laser drivers and to electrical drive circuits for driving a laser load of a vertical cavity surface emitting laser (VCSEL) to emit a square shaped optical pulse using multiple switches. 
     BACKGROUND 
     Time-of-flight-based (TOF-based) measurement systems, such as three-dimensional (3D) sensing systems, light detection and ranging (LIDAR) systems, and/or the like, emit optical pulses into a field of view, detect reflected optical pulses, and determine distances to objects in the field of view by measuring delays and/or differences between the emitted optical pulses and the reflected optical pulses. For some applications, a rectangular shaped pulse may be emitted into a field of view. TOF-based measurement systems are but one application of rectangular shaped optical pulses. A rectangular shaped pulse (also referred to as a “square shaped pulse”, a “square wave”, or a “pulse wave”, among other examples) is a non-sinusoidal periodic waveform in which an amplitude alternates at a steady frequency between fixed minimum and maximum values. In an ideal rectangular shaped pulse, transitions between the minimum and maximum values are instantaneous or near-instantaneous. 
     An electronic driver, which may also be referred to as an “electrical drive circuit”, provides current and voltage to an optical load to cause the optical load to generate optical pulses. An electronic driver for rectangular pulses provides current and voltage to an optical load to cause optical pulses from the optical load to approximate a rectangular shape. Rise-time, fall-time, overshoot, and ripple are examples, among others, of imperfections in the current, voltage, and/or optical pulse that prevent an electronic driver from causing an optical load to provide an ideal rectangular shaped optical pulse. 
     VCSELs may be used individually and/or in VCSEL arrays as the optical load for the aforementioned 3D sensing applications or other applications. VCSELs may be used for generating structured light (e.g., in flood illuminators), time-of-flight (TOF) measurement beams, and/or the like to enable 3D sensing applications or other applications. The VCSELs generate optical pulses, such as rectangular shaped pulses, to provide beams that may be used for facial recognition, gesture recognition, and/or the like. VCSELs may be included in smart phone devices, gaming devices, sensing devices, and/or the like. 
     A VCSEL array may include multiple VCSELs arranged in a particular configuration. For example, a VCSEL array may be arranged with a square grid of VCSELs, a radial grid of VCSELs, a hexagonal grid of VCSELs, a variable spacing grid of VCSELs, a random grid of VCSELs, and/or the like. A particular beam profile may be obtained for a collective output of the VCSEL array (e.g., multiple beams that, at a distance greater than a Rayleigh distance, collectively form a beam) via selection of a corresponding VCSEL array configuration. Parameters of a VCSEL may affect an emission pattern (e.g., a near field emission pattern or a far field emission pattern) of the VCSEL, which may affect operations of a system that includes the VCSEL and/or operations of a VCSEL array that includes the VCSEL. A single die may include one or more VCSEL arrays. A single die including multiple VCSEL arrays may physically separate the arrays or may intermix emitters of different VCSEL arrays. In some cases, all emitters in a VCSEL array operate at a common wavelength (e.g., all emitters in an example VCSEL array may operate at 940 nanometers (nm) or another wavelength that is the same for all the emitters). 
     SUMMARY 
     According to some implementations, an electrical drive circuit may include a first optical load terminal to receive an anode of a first optical load; a junction section that includes a first electrical junction and a second optical load terminal to receive a cathode of the first optical load and an anode of a second optical load; a third optical load terminal to receive a cathode of the second optical load; a first switch connected between the third optical load terminal and a common ground; a coupling capacitor connected between the first electrical junction and a second electrical junction; a second switch connected between the second electrical junction and the common ground; and an inductor connected from a second branch of the second electrical junction and between the second electrical junction and the common ground. 
     According to some implementations, an electrical drive circuit may include a first optical load terminal for receiving an anode of a first optical load; a first electrical junction point that comprises second optical load terminal for receiving a cathode of the first optical load and for receiving an anode of a second optical load; a third optical load terminal for receiving a cathode of the second optical load; a first electrical path from a common ground, through a first auxiliary capacitor, the first optical load terminal, the first electrical junction point, a coupling capacitor, a second electrical junction point, an inductor, a second auxiliary capacitor and back to the common ground; a second electrical path from the common ground through the second auxiliary capacitor, the inductor, the second electrical junction point, the coupling capacitor, the first electrical junction point, the second optical load, the third optical load terminal, and a first switch, and back to the common ground; and a second switch connected between the second electrical junction point and the common ground. 
     According to some implementations, a method may include setting, by a controller, a first switch of an electrical drive circuit to an off state and a second switch of the electrical drive circuit to an on state to charge an inductor of the electrical drive circuit; and setting, by the controller, the first switch of the electrical drive circuit to an on state and the second switch of the electrical drive circuit to an off state to discharge electrical current from the inductor into a second optical load, wherein the inductor is connected between an electrical junction and a voltage source, such that: a first alternating current flows through a first auxiliary capacitor, a first optical load, a coupling capacitor, the inductor and a second auxiliary capacitor, and a second alternating current flows through the second auxiliary capacitor, the inductor, the coupling capacitor, the second optical load, and the first switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1D  are diagrams of example electrical drive circuits described herein with connected optical loads. 
         FIGS. 2-4  are diagrams of example current flows through electrical drive circuits described herein with connected optical loads. 
         FIG. 5  is a diagram of example plots related to the performance and/or operation of an electrical drive circuit described herein with connected optical loads. 
         FIG. 6  is a flowchart of an example processes relating to driving optical loads to emit rectangular shaped optical pulses. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of example implementations refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. 
     Time-of-flight-based (TOF-based) measurement systems, such as 3D sensing (3DS) systems, LIDAR systems, and/or the like, emit optical pulses into a field of view, detect reflected optical pulses, and determine distances to objects in the field of view by measuring delays and/or differences between the emitted optical pulses and the reflected optical pulses. Some systems may have a relatively high pulse repetition rate or modulation frequency (e.g., up to 200 megahertz (MHz)). TOF-based measurement systems may include an electrical drive circuit (e.g., a laser driver) to control the provision of current and voltage to an optical load (e.g., a laser diode, a semi-conductor laser, a VCSEL, a VCSEL array, and/or the like) to emit optical pulses into a field of view. The optical load may also be termed a “laser load.” The optical pulse may be a rectangular shaped pulse (also referred to as a “square pulse,” a “square wave,” “a square wave shape,” or a “pulse wave,” among other examples) that is a non-sinusoidal periodic waveform in which an amplitude alternates at a steady frequency between fixed minimum and maximum values, ideally with instantaneous or near-instantaneous transitions between the minimum and maximum values. Some use cases may allow a non-steady frequency and/or non-periodic (e.g., irregular or random) triggering of electrical pulses, such as to achieve differing rise times, differing pulse amplitudes, or differing pulse timings, among other examples. 
     In general, emitting an optical pulse that has a well-defined origin in time and a rectangular shape may improve measurement precision and accuracy (e.g., as compared to optical pulses having a non-rectangular shape, a long rise time, a poorly-defined origin in time, and/or the like). To achieve such a rectangular shape, an emitted optical pulse should generally have a short rise time (e.g., a time during which power of the optical pulse is rising) and a short fall time (e.g., a time during which power of the optical pulse is falling). For example, the rise time of an optical pulse may be a time during which power of the optical pulse rises from 10% of peak power to 90% of peak power and may be referred to as a “10%-90% rise time”. Similarly, the fall time of an optical pulse may be a time during which power of the optical pulse falls from 90% of peak power to 10% of peak power and may be referred to as a “90%-10% fall time”. Thus, it may be advantageous to design an electrical drive circuit that minimizes rise time. Additionally, to ensure a rectangular shaped pulse, it may be advantageous to design an electrical drive circuit that minimizes ripple. In some configurations, multiple electrical drivers may be deployed to achieve a minimized rise time with a rectangular shaped pulse. However, such configurations that minimize rise time and/or achieve a rectangular shaped pulse may cause an undesirable level of electrical power usage and/or loss. 
     Some implementations described herein provide a method and/or an electrical drive circuit for driving a laser or optical load to emit a rectangular shaped optical pulse using multiple switches. When using multiple switches, some implementations described herein may include, among other components, a first and second laser load, a first switch and second switch, and a coupling capacitor and an inductor to store and charge current. When the first switch is opened and the second switch is closed, the inductor may be charged. When the first switch is closed and the second switch is opened, the inductor may discharge a direct current into the second laser load with a short rise time and a slow fall time and another direct current is received at the first laser load, from a main voltage source, with a slow rise time. Subsequently, when the first switch is opened and the second switch is closed, the first optical load may cease emitting with a short fall time and the inductor may be charged again. In this way, an optical pulse output, collectively, from the first laser load and the second laser load has a short rise time, a low ripple (resulting in a rectangular shape), and a short fall time. For example, as described herein, the first and second laser load may be driven to emit an optical pulse that has a short rise time (e.g., less than 1 nanosecond (ns), less than 100 picoseconds (ps)), a short fall time (e.g., less than 1 ns, less than 500 ps, less than 300 ps, and/or the like), and/or a flat top of the pulse. 
     A total electrical power loss may be less than prior art. For example, some implementations described herein may use an electrical drive circuit that includes a driver, a first connection point, a first laser load, a second connection point, a second laser load, and a third connection point (where the first laser load is between the first and second connection points, and the second laser load is between the second and third connection points). In this case, the first connection point may serve as an anode for the first laser load, the second connection point may serve as a cathode for the first laser load and an anode for the second laser load, and the third connection point may serve as a cathode for the second laser load. As a result, a single driver may drive two laser loads (the first laser load&#39;s rise time may be delayed relative to the second laser load&#39;s rise time by a half of a resonance frequency period) to achieve, in combination, for example, a square pulse with the rise time of less than 100 ps, for example. Moreover, based at least in part on achieving an optical pulse with a relatively short rise time, a rectangular shape, and a low level of electrical losses, an electrical drive circuit described herein may be used, for example, for 3DS applications with a relatively high pulse repetition rate or modulation frequency (e.g., a modulation frequency of up to 200 MHz). 
       FIGS. 1A-1D  are circuit diagrams of an example electrical drive circuit  100 / 100 ′/ 100 ″/ 100 ″′ described herein with connected optical loads. As shown in  FIG. 1A , the electrical drive circuit  100  may include a first voltage source  102  (connected to a common ground  140 ), a capacitor  104  (an auxiliary capacitor connected to the common ground  140  and in parallel with the first voltage source  102 ), a first laser load  106 , a second laser load  108 , a capacitor  110  (a coupling capacitor), an inductor  112 , a capacitor  114  (an auxiliary capacitor connected to the common ground  140  and in parallel with a second voltage source  116 ), the second voltage source  116  (connected to the common ground  140 ), a first switch  118  (connected to the common ground  140 ), and a second switch  120  (connected to the common ground  140 ). In some implementations, first switch  118  may be a high-speed switch, such as a high-speed field electrical transistor (FET) switch (with a switching speed of less than 1 nanosecond (ns)). In some implementations, second switch  120  may be a high-speed switch, such as a high-speed FET, or a low-speed switch, such as a low-speed FET (with a switching speed of less than 5 ns). Other types of switches may be possible. 
     In some implementations, the electrical drive circuit  100  may include a first electrical junction  122  (in a junction section between first laser load  106  and second laser load  108 ) and a second electrical junction  124 . Although some implementations are described herein in terms of a particular set of components, additional components, fewer components, or a different combination of components may be possible. 
     In some implementations, voltage sources  102 / 116  may include a direct current (DC) voltage source, a regulator, a DC-DC converter, an alternating current (AC)-DC converter, or another type of source to supply a DC voltage. In some implementations, voltage sources  102 / 116  may include capacitors  104 / 114 , respectively. In some implementations, first laser load  106  and/or second laser load  108  may include a component to emit an optical pulse. For example, first laser load  106  and/or second laser load  108  may include a laser diode, a VCSEL, an edge emitter, a multi junction laser, a semi-conductor laser, a semi-conductor laser load, a semi-conductor laser diode, or an array thereof, among other examples. First laser load  106  may include a first quantity of emitters, and second laser load  108  may include a second quantity of emitters that is approximately equal to the first quantity of emitters in quantity or output optical power (e.g., to achieve approximately equal optical power outputs, as described herein). In some cases, first laser load  106  and second laser load  108  may have approximately equal optical power outputs, which may include achieving approximately the same peak output power at respective peaks during an optical pulse and/or achieving approximately the same total output power during an entirety of an optical pulse (e.g., with different optical power/time responses). 
     In some implementations, the first laser load  106  and the second laser load  108  are provided separately or independently from the electrical drive circuit  100 . This is common where the electrical drive circuit is manufactured and/or sold independently of the lasers. In some implementations, the first laser load  106  and/or the second laser load  108  may be integrated into the electrical drive circuit  100 . In some implementations, an integrated circuit may be created that includes some components of the electrical drive circuit  100  and either or both of the laser loads  106 / 108 . In some implementations, a multi-VCSEL array may include a first VCSEL array that includes the first laser load  106 , and a second VCSEL array that includes the second laser load  108 . In some implementations, the emitters of different lasers of a multi-VCSEL array are interspaced. 
     In some implementations, electrical drive circuit  100  may be provided in a particular form factor. For example, discrete components of electrical drive circuit  100  may be assembled together on a printed circuit board and/or substrate. Additionally, or alternatively, one or more of the components of electrical drive circuit  100  may be integrated as a monolithic driver integrated circuit (e.g., semi-conductor) chip. In some implementations, one or more components of electrical drive circuit  100  may be partially integrated with a laser load  106 / 108 . In some implementations, the electrical drive circuit  100  may be assembled on a single substrate and integrated into a single device. Accordingly, the electrical drive circuit  100  may include an interface for a laser load  106 / 108  that may include one or more connection points, electrodes, traces, and/or other elements to connect a laser load  106 / 108  to the electrical drive circuit  100 , depending on the particular form of electrical drive circuit  100 . In some implementations, electrical drive circuit  100  and/or a laser load  106 / 108  may include or interface with one or more passive optical elements (not shown), such as a lens, a diffuser, or a transparent cover, among other examples. For example, first laser load  106  may be disposed within a threshold proximity of second laser load  108 , such that the laser loads  106 / 108  share the same passive optical element (e.g., the same lens or diffuser). Locating the first laser load  106  and the second laser load  108  proximate to one another is advantageous to minimize differences in the field of view between each laser load. If there was a large spacing between the two laser loads  106 / 108 , the arrival time of light from the two lasers in the coplanar plane could differ at extreme angles of the field of view causing the shape of the optical pulse to distort (e.g., a sloped or tilted top of the optical pulse). Thus, collocating first laser load  106  and second laser load  108  may improve an angular spread of the field of view. 
     As further shown in  FIG. 1A , first electrical junction  122  forms two branches of electrical drive circuit  100 . A first branch off first electrical junction  122  includes second laser load  108  and switch  118 . A second branch off first electrical junction  122  includes capacitor  110  and second electrical junction  124 . In the second branch off first electrical junction  122 , one end of second electrical junction  124  is connected to capacitor  110  and the other end of second electrical junction  124  defines two branches off electrical junction  124 . For example, a first branch off second electrical junction  124  includes second switch  120 . A second branch off second electrical junction  124  includes inductor  112 , capacitor  114 , and the second voltage source  116 . In the second branch  172  off second electrical junction  124 , one end of the inductor  112  is connected to the second electrical junction  124  and the other end of the inductor  112  is connected to the capacitor  114  and the second voltage source  116  while the capacitor  114  and the second voltage source  116  are also connected in parallel with a common ground. This configuration enables driving of first laser load  106  and second laser load  108  with a single charged inductor driver that provides a current to both laser loads  106 / 108  (time-shifted based on discharge of inductor  112  and operation of coupling capacitor  110 ) to cause a rectangular shaped (e.g., square shaped) pulse to be emitted. 
     In some implementations, first laser load  106  may be associated with a first operating wavelength (e.g., 940 nanometers (nm) or 1.5 millimeters (mm), among other examples) and second laser load  108  may be associated with a second operating wavelength that is approximately equal to the first operating wavelength, such as within +1-10% of the first operating wavelength. In this case, based on the first operating wavelength being approximately equal to the second operating wavelength, a collective output of the first laser load  106  and the second laser load  108  may be combined to form a rectangular shaped pulse. 
       FIG. 1B  shows an example electrical drive circuit  100 ′ configured for receiving two laser loads, such as two optical diode sources. As shown in  FIG. 1B , electrical drive circuit  100 ′ includes a set of laser load receivers (LLRs)  150 - 156 . For example, a first laser load receiver (LLR 1 )  150  and a second laser load receiver (LLR 2 )  152  may receive a first laser load (e.g., first laser load  106 ). Similarly, a third laser load receiver (LLR 3 )  154  and a fourth laser load receiver (LLR 4 )  156  may receive a second laser load (e.g., second laser load  108 ). Laser load receivers  150 / 152  and  154 / 156  may be pads or other electrical connection points that may receive a laser load (e.g., during assembly of an optical device, manufactured laser loads may be attached to a separately manufactured electrical drive circuit). In some implementations, LLR 2  and LLR 3  may be a common pad or other electrical connection point that may receive a first laser load and a second laser load. 
       FIG. 1C , shows an example electrical drive circuit  100 ″ configured with a set of optical load terminals. As shown in  FIG. 1C , electrical drive circuit  100 ″ includes a first optical load terminal  160  to receive an anode of a first laser load (e.g., first laser load  106 ), a second optical load terminal  162  to receive a cathode of the first laser load and an anode of a second laser load (e.g., second laser load  108 ), and a third optical load terminal  164  to receive a cathode of the second laser load. Second optical load terminal may be disposed in a junction section that includes a first electrical junction (e.g., first electrical junction  122 ). 
       FIG. 1D , shows an example electrical drive circuit  100 ″′ configured with a set of branches off of a second electrical junction (e.g., second electrical junction  124  defines a first branch and a second branch). For example, a first branch  170  off the second electrical junction includes a second switch (e.g., second switch  120 ) and a second branch  172  off the second electrical junction includes an inductor (e.g., inductor  112 ), a capacitor (e.g., capacitor  114 ), and a voltage source (e.g., the second voltage source  116 ). In the second branch  172  of  FIG. 1D , one end of the inductor  112  is connected to the second electrical junction  124  and the other end of the inductor  112  is connected to the capacitor  114  and the second voltage source  116  while the capacitor  114  and the second voltage source  116  are also connected in parallel with a common ground. 
     As indicated above,  FIGS. 1A-1D  are provided as examples. Other examples may differ from what is described with regard to  FIGS. 1A-1D . 
       FIG. 2  is a diagram of an example  200  of a current flow through the electrical drive circuit  100  described herein with connected optical loads. 
     As shown in  FIG. 2 , electrical drive circuit  100  may have a first AC current flow path  210  and a second AC current flow path  220 . First AC current flow path  210  may convey first AC electrical current and extend from the common ground  140  to capacitor  104 , to first laser load  106 , to first electrical junction  122 , to capacitor  110 , to second electrical junction  124 , to inductor  112 , to capacitor  114 , and to the common ground  140 . Second AC current flow path  220  may convey second AC electrical current and extend from the common ground, to capacitor  114 , to inductor  112 , to second electrical junction  124 , to capacitor  110 , to first electrical junction  122 , to second laser load  108 , to first switch  118 , and to the common ground  140 . 
     In some implementations, the respective AC current flow paths may correspond to complementary sloped currents in two laser loads, as depicted and described in more detail with regard to  FIG. 5 . For example, first AC current flow path  210  may have a positively sloped current into laser load  106 , and second AC current flow path  220  may have a negatively sloped current into laser load  108 . A resulting waveform output from laser load  106  and laser load  108  may be a rectangular waveform as a result of the complementary sloped currents received at laser load  106  and laser load  108 . A configuration of the complementary sloped currents and the resulting rectangular waveform is controllable by tuning a value of a V2 voltage at second voltage source  116 , which may cause an adjustment to an L1 inductor current at inductor  112 . 
     In some implementations, the first AC current flow path  210  and second AC current flow path  220  may have high frequency ripple currents that are 180 degrees phase shifted from each other and opposite in amplitude (e.g., as a result of parasitic resonances). The 180-degree phase shift between the ripple currents results in the ripple currents cancelling each other when parasitic inductances in the respective AC current flow paths are equal. A result of the cancelling of the ripple currents is that a combined optical pulse may have a relatively flat top without ripples (e.g., a portion of the combined optical pulse at approximately 2 nanoseconds (ns) to approximately 6 ns and at approximately 12 ns to approximately 16 ns, as shown in  FIG. 5 ). 
     As indicated above,  FIG. 2  is provided as an example. Other examples may differ from what is described with regard to  FIG. 2 . 
       FIG. 3  is a diagram of an example  300  of a current flow through the electrical drive circuit  100  described herein with connected optical loads. 
     As shown in  FIG. 3 , electrical drive circuit  100  may have a DC current flow path  310 . The DC current flow path  310  may extend from the common ground  140 , to the first voltage source  102 , to first laser load  106 , to first electrical junction  122 , to second laser load  108 , to first switch  118 , and to the common ground  140 . In some implementations, the DC current flow path  310  may represent a DC current after discharge of inductor  112 . For example, when first switch  118  is in an on state (e.g., closed) and second switch  120  is in an off state (e.g., opened), the first voltage source  102  may provide current through first laser load  106  and second laser load  108 . 
     As indicated above,  FIG. 3  is provided as an example. Other examples may differ from what is described with regard to  FIG. 3 . 
       FIG. 4  is a diagram of an example  400  of a current flow through the electrical drive circuit  100  described herein with connected optical loads. 
     As shown in  FIG. 4 , electrical drive circuit  100  may have an inductor ripple current flow path  410 . The inductor ripple current flow path  410  may extend from the common ground  140 , to capacitor  114 , to inductor  112 , to second electrical junction  124 , to second switch  120 , to the common ground  140 . In some implementations, inductor ripple current flow path  410  may represent an inductor charging current (an inductor charge current path). For example, when first switch  118  is in an off state (e.g., opened) and second switch  120  is in an on state (e.g., closed), inductor  112  stores energy. Second switch  120  may be associated with a first control voltage  420  (Vcharge) and first switch  118  may be associated with a second control voltage  430  (Vfire). 
     In some implementations, multiple cycles of changing states of switches  118 / 120  may be used to charge/discharge inductor  112 . For example, when a cycle is defined as a first time when first switch  118  is in an off state (second control voltage  430  is not provided) and second switch  120  is in an on state (first control voltage  420  is provided) and a second time when first switch  118  is in an on state (second control voltage  430  is provided) and second switch  120  is in an off state (first control voltage  420  is not provided), electrical drive circuit  100  may experience two cycles to fully charge and discharge inductor  112 . In some implementations, a magnitude of the supply voltages, V 1 ( 102 ) and V 2 ( 116 ), maybe based on a desired peak current in the laser loads  106 / 108 . 
     Based on having a faster rise time, electrical drive circuit  100  may allow connected optical loads to reach an optical pulse peak in a shorter period of time, thereby enabling a faster optical pulse repetition rate to get the same spatial resolution relative to other electrical drive circuits. By reducing an amount of time to achieve a configured level of spatial resolution, electrical drive circuits described herein may have lower total power consumption than other electrical drive circuits that can be used in sensing systems. Moreover, by using inductor  112  as a current source and splitting inductor ripple current into two laser loads, an amount of pulse ripple is reduced relative to a resonant ripple that uses a compensating current as a current source. Based on reducing a level of ripple, electrical drive circuits described herein may be used without dumping circuitry, thereby reducing power consumption relative to other electrical drive circuits for which dumping is required. 
     As indicated above,  FIG. 4  is provided as an example. Other examples may differ from what is described with regard to  FIG. 4 . 
       FIG. 5  is a diagram of example plots  500 / 510 / 520  of operation of an electrical drive circuit described herein with connected optical loads. 
     Example plot  500  shows a charging voltage and a discharging voltage in an electrical drive circuit described herein. For example, plot  500  shows a first control voltage  420  (Vcharge) and a second control voltage  430  (Vfire), which are provided by enabling/disabling switches  120  and  118 , respectively. Vcharge corresponds to an inductor ripple current flow path  410 . Vfire corresponds to DC current flow path  310 . Example plot  510  shows an example of a current, I(C 1 ), at capacitor  110  (a coupling capacitor disposed between first junction point  122  and second junction point  124 ). Example plot  520  shows an example of a first current, I(D 1 ), at first laser load  106 , a second current, I(D 2 ), at second laser load  108 , and a third current, I(D 3 ), that is a net current of an electrical drive circuit described herein (e.g., at first laser load  106  and second laser load  108 ). 
     An optical power output can correspond to a current, thus, I(D 1 ), I(D 2 ), and I(D 3 ), represent optical power outputs of a pulse from first laser load  106 , second laser load  108 , and a collective output of first laser load  106  and second laser load  108 , respectively. For example, configurations of electrical drive circuits described herein (e.g., the presence of particular components, such as inductors or capacitors, among other examples) result in currents providing a net current that creates a square shaped pulse. In other words, a shape of an optical pulse provided as a net optical pulse by a first laser load and a second laser load, as described herein, corresponds to a shape of a net current provided to the first laser load and the second laser load. 
     As shown in  FIG. 5 , at a first time, t 0 , the first control voltage  420  (Vcharge) may be at a configured value (e.g., 5.0 volts (V)) and the second control voltage  430  (Vfire) may be zeroed out (e.g., 0 V). In this state, inductor  112  may charge in connection with inductor ripple current flow path  410 . For example, at t 0 , first switch  118  may be in an off state, and second switch  120  may be in an on state. In some implementations, voltage sources  102  and  116  may provide a voltage of 1 V, 4 V, up to 10 V, or up to 30 V, among other examples. In some implementations, first voltage source  102  may have a voltage of 4 V, and second voltage source  116  may have a voltage of 9 V (in this case, capacitor  110  may have a capacitance in the range of 100 to 1500 picofarads (pF) and inductor  112  may have an inductance value in the range of 0.5 to 5 nanohenries (nH)). The voltage level may be configured based, at least in part, on a desired peak laser current, and a ratio of a magnitude of a first voltage from the first voltage source  102  to a magnitude of a second voltage from the second voltage source  116  may be configured to achieve a square shaped pulse in connection with a design of an electrical drive circuit described herein. 
     At a second time, t 1 , the first switch  118  may be in an on state, and the second switch  120  may be in an off state. The first control voltage  420  (Vcharge) may be zeroed out and the second control voltage  430  (Vfire) may be at the configured value. In this state, inductor  112  may discharge and current may flow to first laser load  106  and second laser load  108  in connection with currents of first AC current flow path  210 , second AC current flow path  220 . As shown in example plot  510 , inductor current I(C 1 ) at capacitor  110  is positive, resulting in inductor discharge current being forward biased (e.g., a ramp down) to second laser load  108  (e.g., which receives a majority of inductor discharge current). As shown in example plot  520 , at t 1 , I(D 2 ) current in second laser load  108  may rise to a maximum value with a fast rise time (e.g. 300 ps), while I(D 1 ) current in first laser load  106  is at a minimum value. 
     Between t 1  and a time t 2  (when the switches  118 / 120  are reversed and the control voltages  420 / 430  are reversed), I(D 2 ) current in second laser load  108  falls with a relatively slow fall time, and I(D 1 ) current in first laser load  106  rises with a relatively slow rise time. As shown in example plot  510 , the inductor current I(C 1 ) at capacitor  110  changes from positive to negative, resulting in the first laser load  106  becoming forward biased and beginning to receive more current (e.g., a ramp up). This, in connection with selecting a ratio of the first and second voltage sources, results in a relatively flat I(D 3 ) current, thereby resulting in a flat optical pulse. 
     At t 2 , I(D 1 ) falls with a fast fall time resulting in an end to the flat optical pulse. Based on the fast rise time of I(D 2 ) at t 1  and the fast fall time of I(D 1 ) at t 2  (and the ratio of the first and second voltage sources), the flat optical pulse may have a rectangular shape. 
     In this case, as shown, electrical drive circuits described herein achieve a similar square shaped optical pulse to other types of laser drivers, with reduced electrical power losses relative to the other types of laser drivers. By achieving relatively short rise times at laser loads  106  and  108  (faster rise times than is achieved using other techniques), electrical drive circuits described herein enable a pulse peak to be achieved with a reduced pulse width relative to other techniques, which reduces power consumption and enables faster pulse repetition rate to achieve a particular level of resolution. Moreover, in addition to achieving relatively short rise times (e.g., of less than 100 ps), electrical drive circuits described herein may also achieve a relatively high modulation frequency (e.g., a modulation frequency of up to 200 MHz). 
     As indicated above,  FIG. 5  is provided as an example. Other examples may differ from what is described with regard to  FIG. 5 . 
       FIG. 6  is a flowchart of an example process  600  associated with driving optical loads to emit rectangular shaped optical pulses. In some implementations, one or more process blocks of  FIG. 6  may be performed by a controller (e.g., one or more controllers connected to first switch  118  or second switch  120 ). For example, first switch  118  and second switch  120  may be connected to a single controller (e.g., with an inverter such that the single controller sets first switch  118  and second switch  120  to opposite states). Alternatively, first switch  118  may be connected to a first controller and second switch  120  may be connected to a second controller. In this case, the first controller and second controller may be synchronized to operate switches  118 / 120  and/or may be offset to account for signal delays to achieve a configured rise time and fall time. 
     As shown in  FIG. 6 , process  600  may include setting a first switch of an electrical drive circuit to an off state and a second switch of the electrical drive circuit to an on state to charge an inductor of the electrical drive circuit (block  610 ). For example, the controller may set a first switch of an electrical drive circuit to an off state and a second switch of the electrical drive circuit to an on state to charge an inductor of the electrical drive circuit, as described above. In some implementations, a single controller may control both the first switch and the second switch. In this case, the single controller may cause the first switch and the second switch to change respective states at approximately the same time, such as within approximately hundreds of picoseconds (less than 1000 picoseconds, less than 500 picoseconds, or less than 300 picoseconds, among other examples). Additionally, or alternatively, a plurality of controllers may cause the first switch and the second switch to change state. For example, a first controller may be synchronized with a second controller to cause the respective switches to change state at approximately the same time. 
     As further shown in  FIG. 6 , process  600  may include setting the first switch of the electrical drive circuit to an on state and the second switch of the electrical drive circuit to an off state to discharge electrical current from the inductor into a second optical load (block  620 ). For example, the controller may set the first switch of the electrical drive circuit to an on state and the second switch of the electrical drive circuit to an off state to discharge electrical current from the inductor into a second optical load, as described above. In some implementations, the inductor is connected between a second electrical junction and a second voltage source, such that: a first alternating current flows through a first auxiliary capacitor, a first optical load, a coupling capacitor, the inductor and a second auxiliary capacitor, and a second alternating current flows through the second auxiliary capacitor, the inductor, the coupling capacitor, the second optical load, and the first switch. 
     Process  600  may include additional implementations, such as any single implementation or any combination of implementations described below and/or in connection with one or more other processes described elsewhere herein. 
     In a first implementation, the second optical load is associated with a negatively sloped current during a rise time of an optical pulse and the first optical load is associated with a positively sloped current during the rise time of the optical pulse, such that an output of the first optical load and the second optical load is a square waveform. 
     In a second implementation, alone or in combination with the first implementation, setting the first switch of the electrical drive circuit to the off state and the second switch of the electrical drive circuit to the on state includes causing an inductor charge current to flow through the voltage source, the inductor, and the second switch, wherein the voltage source and the second switch are connected to a common ground, and wherein the second auxiliary capacitor is connected to the common ground and in parallel with the voltage source. 
     In a third implementation, alone or in combination with one or more of the first and second implementations, setting the first switch of the electrical drive circuit to the on state and the second switch of the electrical drive circuit to the off state includes causing a direct current to flow through another electrical source, the first optical load, the second optical load, and the first switch, wherein the other electrical source and the first switch are connected to a common ground, and wherein the first auxiliary capacitor is connected to the common ground and in parallel with the other electrical source. 
     Although  FIG. 6  shows example blocks of process  600 , in some implementations, process  600  may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted in  FIG. 6 . Additionally, or alternatively, two or more of the blocks of process  600  may be performed in parallel. 
     The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the implementations. Furthermore, any of the implementations described herein may be combined unless the foregoing disclosure expressly provides a reason that one or more implementations may not be combined. 
     It will be apparent that systems and/or methods described herein may be implemented in different forms of hardware, firmware, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods is not limiting of the implementations. Thus, the operation and behavior of the systems and/or methods are described herein without reference to specific software code—it being understood that software and hardware can be designed to implement the systems and/or methods based on the description herein. 
     As used herein, satisfying a threshold may, depending on the context, refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, or the like. 
     Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes each dependent claim in combination with every other claim in the claim set. As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiple of the same item. 
     No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Further, as used herein, the article “the” is intended to include one or more items referenced in connection with the article “the” and may be used interchangeably with “the one or more.” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items), and may be used interchangeably with “one or more.” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Also, as used herein, the term “or” is intended to be inclusive when used in a series and may be used interchangeably with “and/or,” unless explicitly stated otherwise (e.g., if used in combination with “either” or “only one of”).