Patent Publication Number: US-2022239063-A1

Title: Laser emitting circuit and lidar

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of International Application No. PCT/CN2020/079374, filed Mar. 13, 2020, which claims the benefit of International Application No. PCT/CN2019/127055, filed Dec. 20, 2019, and International Application No. PCT/CN2019/111738, filed Oct. 17, 2019, the contents of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of laser circuit, in particular to a laser emitting circuit and a LiDAR. 
     BACKGROUND 
     For a LiDAR, a laser emitting circuit is used to emit laser. The working process of the laser emitting circuit is generally divided into three stages: an energy charging stage, an energy transfer stage, and an energy releasing stage. The energy charging stage includes charging one energy storage element and storing electrical energy in the energy storage element. The energy transfer stage includes transferring the electrical energy stored on the energy storage element to an energy transfer element after the energy charging stage is completed. The energy releasing stage includes releasing the electrical energy stored on the energy transfer element to drive a laser diode to emit laser after the transfer of the electrical energy is completed. Currently, with the development of the LiDAR, it is necessary for the LiDAR to complete the energy charging stage in a shorter time. However, the inventor found that in the process of reducing charging time, an original laser emitting circuit emitted laser in advance during the energy transfer stage, causing the phenomenon of “laser leakage,” that is, the laser emitting circuit emits light at an unanticipated time, which will affect the measurement performance of the LiDAR. 
     SUMMARY 
     A laser emitting circuit and a LiDAR provided in an embodiment of this application can solve the problem of laser leakage in the related art caused by the laser emitting circuit when the laser emitting circuit emits laser in the energy transfer stage. Technical solutions are as follows: 
     In a first aspect, an embodiment of this application provides a laser emitting circuit, including: 
     an energy charging circuit, connected to an energy releasing circuit, where the energy charging circuit includes a first energy storage element and is configured to charge the first energy storage element using an energy charging current from a power supply in an energy charging stage; 
     an energy transfer circuit, connected to the energy charging circuit and the energy releasing circuit, where the energy transfer circuit includes a second energy storage element and is configured to charge the second energy storage element using the energy transfer current from the first energy storage element in an energy transfer stage; where the energy transfer current maintains a reverse-biased state for the laser diode in an energy transfer stage; and 
     the energy releasing circuit, connected to the energy transfer circuit, where the energy releasing circuit includes a laser diode, and is configured to use the energy releasing current from the second energy storage element to drive the laser diode to emit light in an energy releasing stage. 
     In a second aspect, an embodiment of this application provides a laser emitting circuit, including: 
     an energy charging circuit, connected to an energy transfer circuit, and configured to store electrical energy; 
     the energy transfer circuit, connected to the energy charging circuit and an energy releasing circuit, and configured to transfer electrical energy stored in the energy charging circuit to the energy transfer circuit; the energy transfer circuit including an energy storage capacitor and a floating-ground diode, a first terminal of the energy storage capacitor being connected to the energy charging circuit, the first terminal of the energy storage capacitor being connected to a first terminal of an energy releasing switch element, a second terminal of the energy storage capacitor being connected to an anode of the floating-ground diode, the second terminal of the energy storage capacitor being connected to the energy releasing circuit, and a cathode of the floating-ground diode being grounded; and 
     the energy releasing circuit, connected to the energy transfer circuit and configured to use electrical energy stored in the energy transfer circuit to drive a laser diode to emit light; the energy releasing circuit including the energy releasing switch element and the laser diode, the first terminal of the energy releasing switch element being connected to the first terminal of the energy storage capacitor, a second terminal of the energy releasing switch element being grounded, the second terminal of the energy releasing switch element being connected to an anode of the laser diode, and a cathode of the laser diode being connected to the second terminal of the energy storage capacitor; 
     where the energy releasing circuit further includes a dynamic compensation capacitor, and the dynamic compensation capacitor is connected across two terminals of the energy releasing switch element. 
     In a third aspect, an embodiment of this application provides a LiDAR, including a forgoing laser emitting circuit. The beneficial effects brought by the technical solutions provided by some embodiments of this application include at least the following: 
     The structure of the laser emitting circuit is changed so that for the laser emitting circuit in the energy transfer stage, the energy transfer current from the energy storage element does not pass through the laser diode, and the laser diode is in a reverse-biased state relative to the energy transfer current. Therefore, the parasitic capacitance of an energy releasing switch element does not cause the laser diode to emit light in advance during an energy transfer charging process, which prevents the laser diode from emitting light at an unanticipated time, thereby solving the problem of laser leakage. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To explain embodiments of this application or the technical solutions in the prior art more clearly, the following briefly introduces the drawings that need to be used in the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of this application. The person skilled in the art can obtain other drawings based on these drawings without inventive work. 
         FIG. 1  is a schematic structural diagram of a laser emitting circuit in the prior art provided by an embodiment of this application; 
         FIG. 2  is a block diagram of a laser emitting circuit provided by an embodiment of this application; 
         FIG. 3  is a schematic structural diagram of a laser emitting circuit provided by an embodiment of this application; 
         FIG. 4 a    is another schematic structural diagram of an energy transfer circuit and an energy releasing circuit provided by an embodiment of the present application. 
         FIG. 4 b    is another schematic structural diagram of a laser emitting circuit provided by an embodiment of this application; 
         FIG. 5  is another schematic structural diagram of a laser emitting circuit provided by an embodiment of this application; 
         FIG. 6  is another schematic structural diagram of a laser emitting circuit provided by an embodiment of this application; and 
         FIG. 7  is another schematic structural diagram of a laser emitting circuit provided by an embodiment of this application. 
     
    
    
     DETAILED DESCRIPTION 
     To make the objectives, technical solutions and advantages of this application clearer, the embodiments of this application are described in further detail below with reference to the drawings. 
       FIG. 1  shows a schematic diagram of a laser emitting circuit in prior art. The working process of the laser emitting circuit is divided into three stages: an energy charging stage, an energy transfer stage, and an energy releasing stage. The three stages are described in detail below. 
     The energy charging stage: a gate of a switch tube Q 1  is connected to a pulse generator TX_CHG. The pulse generator TX_CHG sends rectangular pulses to control the on and off of the switch tube Q 1 . The pulse generator TX_EN sends rectangular pulses to control the on and off of a switch tube Q 2 . When the switch tube Q 1  is in an on-state and the switch tube Q 2  is in an off-state, the laser emitting circuit is in the energy charging stage. The current generated by the power supply VCC flows through an inductor L 1  and the switch tube Q 1  to form a loop and charge the inductor L 1 . It is assumed that the on-time of the switch tube Q 1  is Δt (Δt is also called energy charging time), and then the current increment in the inductor L 1  follows the formula: ΔI=(V CC ×Δt)/L 1  (Formula 1). 
     V CC  in Formula 1 represents a voltage of the power supply VCC, and L 1  represents an inductance of the inductor L 1 . Charged energy follows the formula: W L =½×L 1 ×ΔI 2  (Formula 2). 
     Formula 1 is substituted into Formula 2 to obtain 
     
       
         
           
             
               
                 
                   
                     
                       W 
                       L 
                     
                     = 
                     
                       
                         1 
                         2 
                       
                       × 
                       
                         
                           
                             ( 
                             
                               Vcc 
                               × 
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               t 
                             
                             ) 
                           
                           2 
                         
                         
                           L 
                           1 
                         
                       
                     
                   
                   . 
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     According to Formula 3, it can be seen that the charged energy W L  is inversely proportional to the inductance L 1 , and is proportional to the square of the on-time Δt of the switch tube Q 1 . When keeping the charged energy W L  unchanged, to reduce the on-time of the switch tube Q 1 , the inductance of the inductor L 1  needs to be reduced. 
     It can be seen from Formula 1 and Formula 2 that the pulse generator TX_CHG can control the width of the rectangular pulses to control the on-time of the switch tube Q 1 , that is, the energy charging time of the inductor L 1  is controlled, thereby changing the size of the charged energy and adjusting the emission power of the laser. 
     The energy transfer stage: when the switch tube Q 1  is in an off-state and the switch tube Q 2  is also in the off-state, the laser emitting circuit is in the energy transfer stage. Because the current of the inductor L 1  cannot change suddenly, the charged electrical energy is stored in the inductor L 1 . The inductor L 1  charges an energy storage element C 2  via a boost rectifier diode D 1  so that the charged electrical energy stored in the inductor L 1  can be transferred to the energy storage element C 2 . 
     Although the switch tube Q 1  and the switch tube Q 2  are in the off-state, parasitic capacitance is provided between drains and sources of the two switch tubes. The parasitic capacitance between the drain and the source of the switch tube Q 1  is denoted as C Q1-DS . The parasitic capacitance between the drain and the source of the switch Q 2  is denoted as C Q2-DS . 
     Then the current increment ΔI of the inductor L 1  is diverted via the following three branches: 
     Loop 1: current flows from the inductor L 1  through the parasitic capacitance C Q1-DS  to the ground GND to form a loop. The current in this loop is defined as I CQ1 . 
     Loop 2: current flows from the inductor L 1  through the boost rectifier diode D 1  and the energy storage element C 2  to the ground GND to form a loop. The current in this loop is defined as I C2 . 
     Loop 3: current flows from L 1  through the boost rectifier diode D 1 , a laser diode LD, and C Q2-DS  to the ground GND to form a loop. The current is defined as Tow. 
     Only Loop 2 of the above three loops is the main energy charging loop, which realizes the energy storage function of the energy storage element C 2 . Loop 1 and Loop 3 are both caused by the parasitic capacitance. 
     Given that the forward voltage drops of the boost rectifier diode D 1  and the laser diode LD are relatively small, which has relatively small influence on each loop, the influence of the boost rectifier diode D 1  and the laser diode LD on the voltage drop of the loop is ignored to simplify calculation, ΔI=I C2 +I CQ1 +I CQ2  (Formula 4) is obtained. 
     It is assumed that C Q1-DS =C Q2-DS =C 2 /N is provided, where N is a number greater than 0; C Q1-DS  represents the value of the parasitic capacitance of the switch tube Q 1 ; C Q2-DS  represents the value of the parasitic capacitance of the switch tube Q 2 ; and C 2  represents the value of the energy storage element C 2 . The values of current flowing through each loop are as follows: 
     
       
         
           
             
               
                 
                   
                     
                       I 
                       
                         
                           C 
                           ⁢ 
                           2 
                         
                         = 
                       
                     
                     ⁢ 
                     
                       N 
                       
                         N 
                         + 
                         2 
                       
                     
                     × 
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     I 
                   
                   ; 
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     
                       I 
                       
                         
                           C 
                           ⁢ 
                           Q 
                           ⁢ 
                           1 
                         
                         = 
                       
                     
                     ⁢ 
                     
                       1 
                       
                         N 
                         + 
                         2 
                       
                     
                     × 
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     I 
                   
                   ; 
                   and 
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     I 
                     
                       
                         C 
                         ⁢ 
                         Q 
                         ⁢ 
                         2 
                       
                       = 
                     
                   
                   ⁢ 
                   
                     1 
                     
                       N 
                       + 
                       2 
                     
                   
                   × 
                   Δ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     I 
                     . 
                   
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ) 
                 
               
             
           
         
       
     
     According to Loop 3, it can be seen that I CQ2  is equal to the current ILD of the laser diode LD, that is, I CQ2 =I LD  (Formula 8). A current threshold of the laser diode LD to emit light is set as I LD-TH . If I CQ2  is greater than the current threshold I LD-TH , the laser diode LD emits laser in the energy transfer stage, causing light leakage, that is, the laser emitting circuit emits light at an unanticipated time, thereby affecting the measurement performance of LiDAR. 
     For example, to achieve comprehensive performance of the LiDAR, such as, improving a frequency point of a system, realizing dual emission or multiple emission, and other functions, it is required to reduce the energy charging time Δt. 
     Under the premise of keeping the energy W L  of the inductor L 1  and the voltage of the power supply VCC unchanged, according to Formula 3, it can be seen that the inductance of the inductor L 1  in an energy charging circuit needs to be reduced accordingly. Then, according to Formula 1, it can be seen that if the inductance of the inductor L 1  decreases, the charging current ΔI generated by the inductor L 1  increases accordingly. Finally, according to Formula 7 and Formula 8, it can be seen that when the charging current ΔI increases, the current flowing through the laser diode LD during an energy transfer process also increases, so that the current flowing through the laser diode LD may meet the conditions of I CQ2 =I LD ≥I LD-TH . At this time, the laser diode LD emits light at an unanticipated time, causing the phenomenon of “laser leakage.” 
     The energy releasing stage: when the switch tube Q 1  is in an off-state and the switch tube Q 2  is in an on-state, the laser emitting circuit is in the energy releasing stage. The energy stored on the energy storage element C 2  passes through the laser diode LD and the switch tube Q 2  to the ground GND to form a loop and drive the laser diode LD to emit laser, thereby making the laser diode LD emit laser at an anticipated time. 
     To solve the above technical problems, an embodiment of this application provides a laser emitting circuit. As shown in  FIG. 2 , the laser emitting circuit of the embodiment of this application includes an energy charging circuit  201 , an energy transfer circuit  202 , and an energy releasing circuit  203 . 
     The energy charging circuit  201  is connected to the energy transfer circuit  202 . The energy charging circuit  201  includes a first energy storage element for storing electrical energy. The first energy storage element may be a capacitor or an inductor, or may include both the capacitor and the inductor. The energy charging circuit  201  charges the first energy storage element using the energy charging current from the power supply in the energy charging stage. 
     The energy transfer circuit  202  is connected to the energy charging circuit  201  and the energy releasing circuit  203 . The energy transfer circuit  202  includes a second energy storage element. The energy transfer circuit  202  charges the second energy storage element using the energy transfer current from the first energy storage element in the energy transfer stage. In the energy transfer stage, the energy transfer current maintains a reverse-biased state for the laser diode, so that a laser diode does not emit light in the entire energy transfer stage. The second energy storage element is configured to store electrical energy. The second energy storage element can be a capacitor or an inductor, or can include both the capacitor and the inductor. The energy releasing circuit  203  includes the forgoing laser diode and is configured to use the energy releasing current from the second energy storage element to drive the laser diode to emit light in the energy releasing stage. The energy releasing stage is the normal light-emitting time of the laser diode. 
     In an embodiment of this application, the structure of the laser emitting circuit is changed so that for the laser emitting circuit in the energy transfer stage, the energy transfer current from the energy storage element does not pass through the laser diode, and the laser diode is in a reverse-biased state relative to the energy transfer current. Therefore, the parasitic capacitance of an energy releasing switch element does not cause the laser diode to emit light in advance during an energy transfer charging process, which prevents the laser diode from emitting light at an unanticipated time, thereby solving the problem of laser leakage. 
     In some embodiments of this application, one or a plurality of energy transfer circuits  202  may be provided, and one or a plurality of energy releasing circuits  203  may also be provided. When a plurality of energy transfer circuits  202  is provided, a plurality of the energy releasing circuits  203  may be provided correspondingly, that is, the energy transfer circuit  202  and the energy releasing circuit  203  have a one-to-one mapping relationship. When one energy transfer circuit  202  is provided, a plurality of the energy releasing circuits  203  can be provided, that is, the energy transfer circuit  202  and the energy releasing circuit  203  have a one-to-multiple relationship. 
     Referring to  FIG. 3 , an embodiment of this application provides a schematic diagram of a laser emitting circuit. In some embodiments of this application, the energy charging circuit  201  includes a power supply VCC, an inductor L 1 , an energy charging switch element Q 1 , and a decoupling capacitor C 1 , where a first energy storage element is the inductor L 1 . The power supply VCC can be a DC power supply. A positive terminal of the power supply VCC is grounded via the decoupling capacitor C 1 , and the negative terminal of the power supply VCC is grounded. A first terminal of the inductor L 1  is connected to the positive terminal of the power supply VCC. A second terminal of the inductor L 1  is connected to a first terminal of the energy charging switch element Q 1 . The second terminal of the inductor L 1  is connected to the energy transfer circuit  202 . A second terminal of the energy charging switch element Q 1  is grounded. The energy charging switch element Q 1  can be a transistor or a metal-oxide-semiconductor (MOS) tube. For example, the transistor can be a PNP transistor or an NPN transistor, and the MOS tube can be an NMOS tube, a PMOS tube, or a GaN (Gallium Nitride) switch tube. 
     In some embodiments of this application, an energy releasing circuit  203  includes an energy releasing switch element Q 2  and a laser diode LD. An anode of the laser diode LD is connected to the energy transfer circuit  202 , and a cathode of the laser diode LD is connected to the first terminal of energy releasing switch element Q 2 . A second terminal of the energy releasing switch element Q 2  is grounded. The energy releasing switch element Q 2  can be the transistor or the MOS tube. For example, the transistor can be the PNP transistor or the NPN transistor, and the MOS tube can be the NMOS tube, the PMOS tube, or the GaN switch tube. 
     Optionally, the energy releasing circuit  203  further includes a dynamic compensation capacitor C 3 . The dynamic compensation capacitor C 3  is connected across the first terminal and the second terminal of the energy releasing switch element Q 2 . 
     In some embodiments of this application, the energy transfer circuit  202  includes a capacitor C 2  and a bypass diode D 2 . A second energy storage element is the capacitor C 2 . A first terminal of the capacitor C 2  is connected to the first terminal of the inductor L 1 . A second terminal of the capacitor C 2  is grounded. An anode of the bypass diode D 2  is connected to the second terminal of the inductor L 1 , and a cathode of the bypass diode D 2  is connected to the first terminal of the energy releasing switch element Q 2 . 
     Optionally, the energy transfer circuit  202  further includes a boost rectifier diode D 1 . An anode of the boost rectifier diode D 1  is connected to the second terminal of the inductor L 1 , and a cathode of the boost rectifier diode D 1  is connected to the first terminal of the capacitor C 2 . The boost rectifier diode D 1  has a one-way conduction function, which prevents the capacitor C 2  from reversely discharging electricity in the energy transfer stage and the energy releasing stage, causing the electrical energy in the capacitor C 2  to flow back and causing the electrical energy in the capacitor C 2  to leak. It can be understood that the boost rectifier diode D 1  may be a Schottky diode. 
     Taking both the energy charging switch element Q 1  and the energy releasing switch element Q 2  as the MOS tubes as an example, a working process of the laser emitting circuit is explained. 
     1. The Energy Charging Stage 
     A pulse generator TX_CHG sends rectangular pulses to a gate of the MOS tube Q 1  to control the MOS tube. 
     Q 1  is in an on-state, and the MOS tube Q 2  is in an off-state at this time. The power supply VCC charges the inductor L 1 . The decoupling capacitor C 1  is connected in parallel between the positive terminal and the negative terminal of the power supply VCC to be able to prevent the circuit from causing parasitic oscillation via a positive feedback path formed by the power supply VCC. 
     2. The Energy Transfer Stage 
     After energy charging is completed, the pulse generator TX_CHG stops sending the rectangular pulses to the MOS tube Q 1 . The MOS tube Q 1  is in an off-state, and the MOS tube Q 2  is still in the off-state. Because the current of the inductor L 1  cannot change suddenly, the inductor L 1  continues the energy transfer current generated by ΔI, and the energy transfer current is divided into two paths. One path of the energy transfer current flows through the boost rectifier diode D 1  and the capacitor C 2  to the ground to form a loop in which the energy charging current charges the energy storage element C 2 . The laser diode LD is in a reverse-biased state due to the bypass diode D 2 . Therefore, the laser diode LD does not emit light. The other path of the energy charging current flows through the bypass diode D 2  and the parasitic capacitance C Q2-DS  (not shown in the figure) of the MOS tube Q 2  to the ground to form another loop in which the energy charging current does not flow through the laser diode LD. Therefore, the laser diode LD does not emit light. 
     Obviously, neither of the forgoing two paths of energy transfer currents flows through the laser diode LD, and hence the laser diode LD does not emit light at an unanticipated time, thereby solving the problem of laser leakage. 
     3. The Energy Releasing Stage 
     The pulse generator TX_EN sends the rectangular pulses to the gate of the MOS tube Q 2  to control the MOS tube Q 2  to be in an on-state. The MOS tube Q 1  is in the off-state at this time. The electrical energy stored in the capacitor C 2  flows through the laser diode LD and a drain and a source of the MOS tube Q 2  to form an energy releasing (electric discharge) loop, and drive the laser diode LD to complete the laser emission. In addition, the dynamic compensation capacitor C 3  also forms its electric discharge loop via the drain and the source of the MOS tube Q 2 , and releases the electrical energy stored during the energy transfer to prepare for the next cycle of laser emission. 
       FIG. 4 a    is another schematic structural diagram of an energy transfer circuit and an energy releasing circuit provided by an embodiment of the present application. An energy transfer circuit  202  includes an energy storage capacitor C 2  and a floating-ground diode D 2 . An energy releasing circuit  203  includes the energy storage capacitor C 2 , an energy releasing switch element, and a laser diode LD. The energy releasing switch element includes two switch terminals and a control terminal (not shown in  FIG. 4 a   ). The control terminal is input with a control signal (such as a pulse signal) to control the on or off of the two switch terminals, thereby realizing the on-state or off-state of the energy releasing switch element. The energy releasing switch element can be a GaN switch tube, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), or an IGBT (Insulated Gate Bipolar Transistor). 
     A connection relationship between various elements in the energy transfer circuit  202  and the energy releasing circuit  203  is as follows: a first terminal of the energy storage capacitor C 2  is connected to the energy charging circuit  201 . The first terminal of the energy storage capacitor C 2  is connected to a first terminal of an energy releasing switch element. A second terminal of the energy storage capacitor C 2  is connected to an anode of a floating-ground diode D 2 . The second terminal of the energy storage capacitor C 2  is connected to a cathode (K) of the laser diode LD. A cathode of the floating-ground diode D 2  is grounded. An anode (A) of the laser diode LD is grounded, and the anode of the laser diode LD is connected to a second terminal of the energy releasing switch element. The first terminal and the second terminal of the energy releasing switch element in this embodiment refer to two switch terminals of the energy releasing switch element. 
     The working process of the laser emitting circuit in  FIG. 4 a    includes: 
     In an energy charging stage, an energy storage element in the energy charging circuit  201  stores the electrical energy supplied by a power supply. After energy charging is completed, an energy transfer stage is performed. 
     In the energy transfer stage, the energy releasing switch element is in an off-state, that is, both terminals of the energy releasing switch element are off. The energy charging circuit  201  uses stored electrical energy to charge the energy transfer circuit  202 . Specifically, the electrical energy is transferred to and stored in the energy storage capacitor C 2  of the energy transfer circuit  202 . Although the energy releasing switch element is in the off-state, the energy releasing switch element has certain parasitic capacitance. In fact, the current from the energy charging circuit  201  forms two loops. For one loop, the current flows through the energy storage capacitor C 2  and a floating-ground diode D 2  to the ground GND to form the loop. During the charging process of the energy storage capacitor C 2 , the laser emitting tube LD is in a reverse bias cut-off state, and energy transfer is completed. For the other loop, the current flows through the parasitic capacitance of the energy releasing switch element to the ground GND to form the loop. It can be seen that the two loops no longer pass through the laser diode LD. Therefore, the laser diode does not have “laser light leakage” during the energy transfer stage, that is, the laser diode does not emit light at an unanticipated time, thereby solving the problem of “the laser light leakage.” After the energy transfer of the energy storage capacitor C 2  is completed, the energy releasing stage is performed. 
     In the energy releasing stage, the energy releasing switch element is in an on-state. The electrical energy stored in the energy storage capacitor passes through the two terminals of the energy releasing switch element and the laser diode LD and goes back to the second terminal of the energy storage capacitor to form an energy releasing loop to drive the laser diode LD to emit light. 
     In one embodiment, the energy transfer circuit further includes a boost rectifier diode. An anode of the boost rectifier diode is connected to the energy charging circuit  201 , and a cathode of the boost rectifier diode is connected to the first terminal of the energy storage capacitor C 2 . The boost rectifier diode has a one-way conduction function. Only the energy charging circuit  201  is allowed to charge the energy storage capacitor C 2  during the energy transfer stage, thereby avoiding the backflow of the electrical energy in the energy storage capacitor C 2  caused when the potential of the energy storage capacitor C 2  is higher than that of the energy charging circuit  201 . It can be understood that the boost rectifier diode may be a Schottky diode. 
     In one or more embodiments, the energy releasing switch element is a transistor. A collector of the transistor is connected to a first terminal of the energy storage capacitor C 2 . An emitter of the transistor is grounded and connected to an anode of the laser diode LD. A base of the transistor is connected to an output terminal of a first pulse generator. The first pulse generator can send out pulses, such as rectangular pulses. When the rectangular pulses are at a high level, the collector and the emitter of the transistor are controlled to be on therebetween. When the rectangular pulses are at a low level, the collector and the emitter of the transistor are controlled to be off therebetween. The duration of the high level of the rectangular pulses is the on-time of the transistor. 
     In one or more embodiments, the energy releasing switch element is a transistor. An emitter of the transistor is connected to a terminal of the energy storage capacitor C 2 . A collector of the transistor is grounded. The collector of the transistor is connected to an anode of the laser diode LD. A base of the transistor is connected to an output terminal of a first pulse generator. The first pulse generator can send out the pulses, such as the rectangular pulses. When the rectangular pulses are at a high level, the collector and the emitter of the transistor are controlled to be off therebetween. When the rectangular pulses are at a low level, the collector and the emitter of the transistor are controlled to be on therebetween. The duration of the low level of the rectangular pulses is the on-time of the transistor. 
     In one or more embodiments, the energy releasing switch element is a GaN switch tube. The GaN switch tube is a MOS (Metal Oxide Semiconductor) tube. A drain of the GaN switch tube is connected to the first terminal of the energy storage capacitor C 2 . A source of the GaN switch tube is grounded, and the source of the GaN switch tube is connected to an anode of the laser diode. A gate of the GaN switch tube is connected to the output terminal of the first pulse generator. The first pulse generator can send the pulses, such as the rectangular pulses, to control the on or off between the collector and the emitter of the GaN switch tube. The duration of the rectangular pulses is the on-time of the GaN switch tube. 
     In one or more embodiments, the energy charging circuit includes a power supply, a decoupling capacitor, an inductor, and an energy charging switch element. The power supply is a DC power supply. A positive terminal of the power supply is connected to a first terminal of the inductor. A second terminal of the inductor is grounded via an energy charging switch element, and a second terminal of the inductor is connected to the first terminal of the energy storage capacitor C 2 . The decoupling capacitor is configured to eliminate parasitic coupling between the circuits. When the energy charging switch element is in an on-state, the power supply charges the inductor. After the charging is completed, electrical energy is stored in the inductor. The energy charging switch element can be the GaN switch tube, the MOSFET, or the IGBT. 
     Further, the energy charging switch element is a transistor. A collector of the transistor is connected to the first terminal of the energy storage capacitor C 2 . An emitter of the transistor is grounded. A base of the transistor is connected to an output terminal of a second pulse generator. The second pulse generator controls the transistor to be in the on-state by outputting a high level, and controls the transistor to be in the off-state by outputting a low level. 
     The energy charging switch element is a transistor. An emitter of the transistor is connected to the first terminal of the energy storage capacitor C 2 . A collector of the transistor is grounded. A base of the transistor is connected to an output terminal of a second pulse generator. The second pulse generator controls the transistor to be in the off-state by outputting a high level, and controls the transistor to be in the on-state by outputting a low level. 
     The energy charging switch element is a GaN switch tube. A drain of the GaN switch tube is connected to the first terminal of the energy storage capacitor C 2 . A source of the GaN switch tube is grounded. A gate of the GaN switch tube is connected to an output terminal of a second pulse generator. The second pulse generator is configured to control the on-time of the energy charging switch element. 
     In one or more embodiments, the energy releasing circuit  203  further includes a dynamic compensation capacitor. The dynamic compensation capacitor is connected across the two terminals of the energy releasing switch element, and the dynamic compensation capacitor is connected across the two switch terminals of the energy releasing switch element. The dynamic compensation capacitor can suppress current resonance caused by parasitic parameters of an electric discharge loop of the energy storage capacitor C 2 , and supplement dynamic impedance when the energy releasing switch element is turned on. 
     In one or more embodiments, capacitance of the dynamic compensation capacitor is smaller than that of the energy storage capacitor. 
     In one or more embodiments, the energy storage capacitor C 2  can be formed by connecting a plurality of capacitors in parallel to reduce the ESR (Equivalent Series Resistance) of the energy storage capacitor C 2 . It is understandable that capacitance of the plurality of capacitors may be equal or unequal. Preferably, the capacitance of the plurality of capacitors connected in parallel is equal. The respective capacitors with the same capacitance connected in parallel have better ESR consistency, and the electric discharge of the respective capacitors connected in parallel is more equal, which can better improve the efficiency of the energy storage capacitor. 
     It is understandable that a ground connection of various elements in  FIG. 4 a    (for example, the floating-ground diode D 2 , the laser diode LD, and the energy releasing switch element) can be changed and the various elements are connected to a negative terminal of a power supply, which can also achieve the same function as the laser emitting circuit in  FIG. 4 a   . It can be understood that the negative terminal of the power supply can be grounded. 
       FIG. 4 b    is another schematic diagram of a laser emitting circuit provided by an embodiment of this application. 
     In some embodiments of this application, an energy charging circuit  201  includes a power source VCC, an inductor L 1 , a decoupling capacitor C 1 , and an energy charging switch element Q 1 . The inductor L 1  is a first energy storage element. The connection relationship between various elements in the energy charging circuit  201  can refer to  FIG. 3 , which is not repeated herein. 
     In some embodiments of this application, the energy releasing circuit  203  includes an energy releasing switch element Q 2  and a laser diode LD. The energy charging switch element Q 1  can be a transistor or a MOS tube. For example, the transistor can be a PNP transistor or an NPN transistor, and the MOS tube can be an NMOS tube, a PMOS tube, or a GaN switch tube. 
     A cathode of the laser diode LD is connected to the energy transfer circuit  202 , and an anode of the laser diode LD is grounded. A first terminal of the energy releasing switch element Q 2  is connected to the energy transfer circuit  202 , and a second terminal of the energy releasing switch element Q 2  is connected to the anode of the laser diode LD. 
     Optionally, the energy releasing circuit  203  further includes a dynamic compensation capacitor C 3 . The dynamic compensation capacitor C 3  is connected across the first terminal and the second terminal of the energy releasing switch element. 
     In some embodiments of this application, the energy transfer circuit  202  includes a capacitor C 2  and a bypass diode D 2 . The capacitor C 2  is a second energy storage element. A first terminal of the capacitor C 2  is connected to a second terminal of the inductor L 1 . A second terminal of the capacitor C 2  is connected to the cathode of the laser diode LD. An anode of the bypass diode D 2  is connected to the cathode of the laser diode LD, and a cathode of the bypass diode D 2  is grounded. 
     Further, the energy transfer circuit  202  further includes a boost rectifier diode D 1 . An anode of the boost rectifier diode D 1  is connected to the second terminal of the inductor L 1 , and a cathode of the boost rectifier diode D 1  is connected to the first terminal of the capacitor C 2 . The boost rectifier diode D 1  has a one-way conduction function, which prevents the capacitor C 2  from reversely discharging electricity in the energy transfer stage and the energy releasing stage, causing the electrical energy in the capacitor C 2  to flow back and causing the electrical energy in the capacitor C 2  to leak. The boost rectifier diode D 1  may be a Schottky diode. 
     The connection relationship of each element in  FIG. 4 b    is as follows: a negative terminal of a power supply VCC is grounded. A positive terminal of the power supply VCC is grounded via the decoupling capacitor C 1 . A positive terminal of the power supply VCC is also connected to the inductor L 1  and a drain (D) of the MOS tube Q 1 . The drain of the MOS tube Q 1  is connected to an anode of the boost rectifier diode D 1 . A source (S) of the MOS tube Q 1  is grounded. A gate (G) of the MOS tube Q 1  is connected to an output terminal of a pulse generator TX_CHG. 
     A cathode of the boost rectifier diode D 1  is connected to a first terminal of the energy storage capacitor C 2 , and the cathode of the boost rectifier diode D 2  is also connected to the drain (D) of the MOS tube Q 2 . A second terminal of the energy storage capacitor C 2  is connected to an anode of the floating-ground diode D 2 , and a cathode of the floating-ground diode D 2  is grounded. A second terminal of the energy storage capacitor C 2  is connected to a cathode (K) of the laser diode LD. An anode (A) of the laser diode LD is grounded. The anode of the laser diode LD is connected to a source (S) of the MOS tube Q 2 . A gate (G) of the MOS tube Q 2  is connected to the output terminal of the pulse generator TX_EN. The dynamic compensation capacitor C 3  is connected across the source and the drain of the MOS tube Q 2 . 
     It is understandable that a ground connection of various elements in  FIG. 4 b    (for example, the decoupling capacitor C 1 , the MOS tube Q 1 , the floating-ground diode D 2 , the laser diode LD, and the MOS tube Q 2 ) can be changed and the various elements are connected to a negative terminal of a power supply, which can also achieve the same function as the laser emitting circuit in  FIG. 4 b   . It can be understood that a negative terminal of the power supply may be grounded. 
     Capacitance of the dynamic compensation capacitor C 3  is less than that of the energy storage capacitor C 2 , and the capacitance of the dynamic compensation capacitor C 3  can range from 2 pF to 10 nF. For example, the capacitance of the dynamic compensation capacitor C 3  is 100 pF. Capacitance of the energy storage capacitor C 2  can range from 2 pF to 20 nF. For example, the capacitance of the energy storage capacitor C 2  is 2 nF. An inductance of the inductor L 1  can range from 10 nH to 100 pH. For example, the inductance of the inductor L 1  is 330 nH. A value range of the parameter value of the forgoing elements is only for reference, and an embodiment of the present application is not limited thereto. 
     The energy charging switch element Q 1  and the energy releasing switch element Q 2  in  FIG. 4 b    can be MOS tubes. The working process of the laser emitting circuit is described below: 
     1. The Energy Charging Stage 
     The energy charging stage process can be referred to the description of the energy charging stage associated with  FIG. 3 . 
     The pulse generator TX_CHG sends rectangular pulses to the gate of the MOS tube Q 1  to control the MOS tube Q 1  to be in an on-state. The MOS tube Q 2  is in an off-state at this time. The power supply VCC charges the inductor. The decoupling capacitor C 1  is connected in parallel between positive and negative terminals of the power supply VCC to prevent the circuit from causing parasitic oscillation via a positive feedback path formed by the power supply VCC. The so-called decoupling is to prevent current fluctuations formed in a power supply circuit from affecting the normal operation of the circuit when the currents of front and rear circuits change. In other words, the decoupling circuit can effectively eliminate parasitic coupling between circuits. 
     2. The Energy Transfer Stage 
     After energy charging is completed, a pulse generator TX_CHG stops sending rectangular pulses to the MOS tube Q 1 . The MOS tube Q 1  is in an off-state, and the MOS tube Q 2  is still in an off-state at this time. Because the current of the inductor L 1  cannot change suddenly, at this time, the inductor L 1  continues the energy transfer current generated by ΔI, and the energy transfer current is divided into two paths after flowing through the boost rectifier diode D 1 . One path of the energy transfer current flows through the capacitor C 2  and the bypass diode D 2  to the ground to form a loop. In this loop, the energy charging current charges the capacitor C 2 . The laser diode LD is in a reverse-biased state due to the bypass diode D 2 . Therefore, the laser diode LD does not emit light. The other path of the energy charging current flows through the parasitic capacitance C Q2-DS  (not shown in the figure) of the MOS tube Q 2  to the ground to form another loop in which the energy charging current does not flow through the laser diode LD. Therefore, the laser diode LD does not emit light. Obviously, neither of the forgoing two paths of energy transfer currents flows through the laser diode LD, and hence the laser diode LD does not emit light at an unanticipated time, thereby solving the problem of laser leakage. 
     The improved laser emitting circuit has the following characteristics: the laser diode LD is changed from being originally connected to the drain of the MOS tube Q 2  to being connected to the second terminal of the energy storage capacitor C 2 . The second terminal of the energy storage capacitor C 2  is hovered by the laser diode LD being grounded, that is, the second terminal of the energy storage capacitor C 2  is no longer directly grounded. Therefore, the laser emitting circuit can also be called a “floating-ground circuit for eliminating laser light leakage.” 
     3. The Energy Releasing Stage 
     The pulse generator TX_EN sends the rectangular pulses to a gate of the MOS tube Q 2  to control the MOS tube Q 2  to be in the on-state. The MOS tube Q 1  is in the off-state at this time. The electrical energy stored in the capacitor C 2  passes through the MOS tube Q 2 , the laser diode LD, and the ground to form an energy releasing (electric discharge) circuit, and drives the laser diode LD to complete laser emission. In addition, the dynamic compensation capacitor C 3  also forms its electric discharge loop via a drain and a source of the MOS tube Q 2 , and releases the electrical energy stored during the energy transfer to prepare for the next cycle of the laser emission. 
       FIG. 5  is another schematic diagram of a laser emitting circuit provided by an embodiment of this application. 
     In some embodiments of this application, an energy charging circuit  201  includes a power source VCC, an inductor L 1 , a decoupling capacitor C 1 , and an energy charging switch element Q 1 . The inductor L 1  is a first energy storage element. The connection relationship of various elements in the energy charging circuit  201  can be referred to the description of  FIG. 3 , which is not repeated here. 
     In some embodiments of this application, an energy releasing circuit  203  includes a laser diode LD and an energy releasing switch element Q 2 . An anode of the laser diode LD is connected to an energy transfer circuit  202 , and a cathode of the laser diode LD is connected to a first terminal of the energy releasing switch element Q 2 . A second terminal of the energy releasing switch element Q 2  is grounded. The energy charging switch element Q 1  can be a transistor or a MOS tube. For example, the transistor can be a PNP transistor or an NPN transistor, and the MOS tube can be an NMOS tube, a PMOS tube, or a GaN switch tube. 
     Optionally, the energy releasing circuit  203  further includes a dynamic compensation capacitor C 3 . The dynamic compensation capacitor C 3  is connected across the first terminal and the second terminal of the energy releasing switch element. 
     In some embodiments of this application, the energy transfer circuit  202  includes a capacitor C 2  and a bypass diode D 2 . The capacitor C 2  is a second energy storage element. A first terminal of the capacitor C 2  is connected to an anode of the laser diode LD, and a cathode of the capacitor C 2  is grounded. A cathode of the bypass diode D 2  is connected to the anode of the laser diode LD, and an anode of the bypass diode D 2  is connected to a cathode of the laser diode LD. 
     Optionally, the energy transfer circuit  202  further includes a boost rectifier diode D 1 . An anode of the boost rectifier diode D 1  is connected to a second terminal of the inductor L 1 , and a cathode of the boost rectifier diode D 1  is connected to the cathode of the laser diode LD. The boost rectifier diode D 1  has a one-way conduction function, which prevents the capacitor C 2  from reversely discharging electricity in an energy transfer stage and an energy releasing stage, causing the electrical energy in the capacitor C 2  to flow back and causing the electrical energy in the capacitor C 2  to leak. The boost rectifier diode D 1  may be a Schottky diode. 
     The energy charging switch element Q 1  and the energy releasing switch element Q 2  in  FIG. 5  can be MOS tubes. The working process of the laser emitting circuit includes: 
     1. The Energy Charging Stage 
     The energy charging stage process can be referred to the description of the energy charging stage associated with  FIG. 3 , which is not repeated here. 
     2. The Energy Transfer Stage 
     After energy charging is completed, a pulse generator TX_CHG stops sending rectangular pulses to a MOS tube Q 1 . The MOS tube Q 1  is in an off-state, and the MOS tube Q 2  is still in an off-state at this time. Because the current of the inductor L 1  cannot change suddenly, the inductor L 1  continues the energy transfer current generated by ΔI, and the energy transfer current is divided into two paths after flowing through the boost rectifier diode D 1 . One path of the energy transfer current flows through a bypass diode D 2  and the capacitor C 2  to the ground to form a loop in which the energy charging current charges the capacitor C 2 . The laser diode LD is in a reverse-biased state due to the bypass diode D 2 . Therefore, the laser diode LD does not emit light. The other path of the energy charging current flows through the parasitic capacitance C Q2-DS  (not shown in the figure) of the MOS tube Q 2  to the ground to form another loop in which the energy charging current does not flow through the laser diode LD. Therefore, the laser diode LD does not emit light. Obviously, neither of the forgoing two paths of energy transfer currents flows through the laser diode LD, and hence the laser diode LD does not emit light at an unanticipated time, thereby solving the problem of laser leakage. 
     3. The Energy Releasing Stage 
     The pulse generator TX_EN sends the rectangular pulses to a gate of the MOS tube Q 2  to control the MOS tube Q 2  to be in an on-state. The MOS tube Q 1  is in the off-state at this time. The electrical energy stored in the capacitor C 2  flows through the laser diode LD and the MOS tube Q 2  to form an energy releasing (electric discharge) loop, and drive the laser diode LD to complete the laser emission. In addition, the dynamic compensation capacitor C 3  also forms its electric discharge loop via a drain and a source of the MOS tube Q 2 , and releases the electrical energy stored during the energy transfer to prepare for the next cycle of the laser emission. 
       FIG. 6  is another schematic diagram of a laser emitting circuit provided by an embodiment of this application. 
     In some embodiments of this application, one energy transfer circuit  202  is provided, and a plurality of energy releasing circuits  203  are provided, that is, the energy transfer circuit  202  and the energy releasing circuit  203  have a one-to-multiple relationship. The plurality of energy releasing circuits  203  are connected in parallel. A plurality of bypass diodes D 2  in the energy transfer circuit  202  are provided. The number of bypass diodes D 2  is equal to that of the energy releasing circuits  203 , that is, each energy releasing circuit  203  is provided with one bypass diode D 2 . In some embodiments, the plurality of energy releasing circuits  203  can also share one bypass diode D 2 . In  FIG. 6 , one energy transfer circuit  202  corresponds to three energy releasing circuits  203 , for illustration purpose. 
     The connection relationship and working principle of various elements in the energy charging circuit  201 , the energy transfer circuit  202  and the energy releasing circuit  203  in  FIG. 6  can be referred to in  FIG. 3 , which are not repeated here. 
       FIG. 7  is another schematic diagram of a laser emitting circuit provided by an embodiment of this application. 
     In some embodiments of this application, a plurality of energy transfer circuits  202  and a plurality of energy releasing circuits  203  are provided. The number of the energy transfer circuits  202  is equal to that of the energy releasing circuits  203 , that is, the energy transfer circuits  202  and the energy releasing circuits  203  have a one-to-one relationship. One energy transfer circuit  202  and one energy releasing circuit  203  form one circuit unit. Circuit units are connected in parallel. The laser emitting circuit in  FIG. 7  includes three circuit units, and each circuit unit includes one energy transfer circuit  202  and one energy releasing circuit  203 . 
     The connection relationship and working principle of various elements in the energy charging circuit  201 , the energy transfer circuit  202 , and the energy releasing circuit  203  in  FIG. 7  can be referred to in  FIG. 3 , which are not repeated here. 
     It should be noted that in embodiments of  FIGS. 3 to 7 , a decoupling capacitor C 1  is connected in parallel between positive and negative terminals of a power supply VCC to be able to prevent the circuit from causing parasitic oscillation via a positive feedback path formed by the power supply VCC. The so-called decoupling is to prevent current fluctuations formed in a power supply circuit from affecting the normal operation of the circuit when the currents of front and rear circuits change. In other words, a decoupling circuit can effectively eliminate parasitic coupling between the circuits. 
     It should be noted that in the embodiments of  FIGS. 3 to 7 , an energy charging switch element Q 1  or an energy releasing switch element Q 2  can be a transistor. A collector of the transistor is a first terminal of the energy charging switch element Q 1  or the energy releasing switch element Q 2 . An emitter of the transistor is a second terminal. A base of the transistor is an enable terminal. The base of the transistor is connected to an output terminal of a first pulse generator. The first pulse generator controls the transistor to be in an on-state by outputting a high electrical level, and controls the transistor to be in an off-state by outputting a low electrical level. 
     It should be noted that in the embodiments of  FIGS. 3-7 , an energy charging switch element Q 1  or an energy releasing switch element Q 2  can be a transistor. The emitter of the transistor is the first terminal of the energy charging switch element Q 1  or the energy releasing switch element Q 2 . The collector of the transistor is a second terminal of the energy charging switch element Q 1  or the energy releasing switch element Q 2 . The base of the transistor is the enable terminal and connected to the output terminal of the first pulse generator. The first pulse generator controls the transistor to be in the off-state by outputting the high electrical level, and controls the transistor to be in the on-state by outputting the low electrical level. 
     It should be noted that in the embodiments of  FIGS. 3-7 , the energy charging switch element Q 1  or the energy releasing switch element Q 2  can be a MOS tube. A drain of the MOS tube is a first terminal, and a GaN switch tube is a second terminal. A gate of the GaN switch tube is the enable terminal, which is connected to the output terminal of the first pulse generator. The first pulse generator is configured to control the on-time of the MOS tube. 
     It should be noted that the energy charging switch element Q 1  or the energy releasing switch element Q 2  can be a MOS tube. A source of the MOS tube is a first terminal, and a drain of the MOS tube is a second terminal. A gate of the MOS tube is the enable terminal, which is connected to the output terminal of the first pulse generator. The first pulse generator is configured to control the on-time of the MOS tube. 
     It should be noted that in the embodiments of  FIGS. 3-7 , a dynamic compensation capacitor C 3  can suppress current resonance caused by parasitic parameters of an electric discharge loop of a capacitor C 2 , and supplement dynamic impedance when the energy releasing switch element Q 2  is turned on. Optionally, capacitance of the dynamic compensation capacitor C 3  is smaller than that of the capacitor C 2 . Optionally, the capacitor C 2  can be formed by connecting the plurality of capacitors in parallel to reduce the ESR (Equivalent Series Resistance) of the capacitor C 2 . It is understandable that the capacitance values of the plurality of capacitors may be equal or unequal. Preferably, the capacitance values of the plurality of capacitors connected in parallel are equal. The respective capacitors with the same capacitance connected in parallel have better ESR consistency, and the electric discharge of the respective capacitors connected in parallel is more consistent, which can better improve the efficiency of the energy storage element. 
     It is understandable that in the embodiments of  FIG. 3-7 , a ground connection of various elements in the laser emitting circuit (for example, a bypass diode D 2 , a laser diode LD, and the energy releasing switch element) can be changed so that the various elements are connected to a negative terminal of a power supply, which can also achieve the same function as the laser emitting circuit in  FIGS. 3-7 . 
     An embodiment of this application further provides a LiDAR, including a laser emitting circuit described above. 
     Specifically, the forgoing laser emitting circuit can be applied to the LiDAR. In addition to the laser emitting circuit, the LiDAR can also include specific structures such as a power supply, a processing device, an optical receiving apparatus, a rotating body, a base, a housing, and a human-computer interaction apparatus. It is understandable that the LiDAR can be a single-channel LiDAR, and includes one channel of the forgoing laser emitting circuit. The LiDAR can also be a multi-channel LiDAR, and includes a plurality of channels of the forgoing laser emitting circuits and a corresponding control system. The quantity of the laser emitting circuits can be determined according to actual needs. 
     For the forgoing LiDAR, the structure of the laser emitting circuit is changed so that for the laser emitting circuit in an energy transfer stage, the energy transfer current from an energy storage element does not pass through a laser diode, and the laser diode is in a reverse-biased state relative to the energy transfer current. Therefore, the parasitic capacitance of an energy releasing switch element does not cause the laser diode to emit light in advance during an energy transfer charging process, which prevents the laser diode from emitting light at an unanticipated time, thereby solving the problem of laser leakage. 
     For the forgoing LiDAR, a laser diode is changed from being originally connected to a drain of MOS tube Q 2  to being connected to a second terminal of an energy storage capacitor C 2 . The second terminal of the energy storage capacitor C 2  is grounded via a cathode of the laser diode LD. The second terminal of the energy storage capacitor C 2  is hovered via the laser diode LD, that is, the second terminal of the energy storage capacitor C 2  is no longer directly grounded. In an energy transfer stage, parasitic capacitance of an energy releasing switch element does not cause the laser diode to emit light in advance during an energy transfer charging process, thereby avoiding the laser diode from emitting light at an unanticipated time, and solving the problem of laser light leakage. 
     The person skilled in the art can understand that all or part of the procedures in methods of the forgoing embodiments can be implemented by instructing relevant hardware via a computer program. The program can be stored in a computer readable storage medium. During execution, the computer program can include the procedures of the embodiments of the forgoing methods. A storage medium can be a magnetic disk, an optical disc, a read-only storage memory, a random storage memory, etc. 
     The forgoing descriptions are only preferred embodiments of this application, which of course cannot be used to limit the scope of this application. Therefore, equivalent changes made in accordance with the claims of this application still fall within the scope of the application.