A high-speed wide-range laser frequency switching control system and a control method thereof

Abstract

The application discloses a high-speed wide-range laser frequency switching control system and a control method thereof. The application comprises a laser beat frequency detection unit, a reference source switching unit, a phase-sensitive detection unit, a loop filter unit, a frequency switching unit and a microcontroller. Two combined laser beams obtain a beat frequency signal through the laser beat frequency detection unit, and an error signal is obtained through the phase-sensitive detection unit together with a reference frequency selected by the reference source switching unit. After passing through the loop filter unit, a fast loop control signal and a slow loop control signal are output. The fast loop control signal is directly used for modulating the laser current, and the slow loop control signal is used for modulating the length of the laser external cavity after being processed by the frequency switching unit. The microcontroller unit provides a convenient external trigger interface, and corresponding units are controlled through digital logic signals. The application adopts a lock loss-relocking design, realizes high-speed wide-range switching of the laser frequency, and meets the demand of high-speed high-precision laser frequency time division multiplexing.

Description

Technical Field

[0001] This invention relates to laser control technology, specifically to a high-speed, wide-range laser frequency switching control system and its control method. Background Technology

[0002] Laser frequency switching control is a feedback control technology. Two lasers beat their frequencies to obtain a beat frequency signal, which is then phase-sensitively detected with a reference frequency. The resulting error signal is fed back to the controlled laser through a loop filter, thus forming a locking loop that locks the laser frequency difference to the reference frequency. Laser frequency switching control can be achieved by changing the reference frequency.

[0003] Existing frequency switching control technology changes the reference frequency while the loop is locked, and the laser frequency follows the change. However, it is limited by the loop locking bandwidth and the phase-sensitive detection bandwidth, and cannot achieve high-speed and wide-range frequency switching. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, this invention proposes a high-speed, wide-range laser frequency switching control system and its control method.

[0005] One objective of this invention is to provide a high-speed, wide-range laser frequency switching control system.

[0006] The high-speed, wide-range laser frequency switching control system of the present invention includes: a laser beat frequency detection unit, a reference source switching unit, a phase-sensitive detection unit, a loop filtering unit, a frequency switching unit, and a microcontroller; wherein, a laser beam is output from two lasers with different frequencies, the two laser beams with different frequencies are combined into a combined laser beam, the combined laser beam is input to the high-speed, wide-range laser frequency switching control system, and then returned to a laser after passing through the high-speed, wide-range laser frequency switching control system, forming a feedback loop;

[0007] The laser beat frequency detection unit includes a photodetector and an RF amplifier connected in series. The combined laser beam is input to the photodetector of the laser beat frequency detection unit. The photodetector beats the two laser beams with different frequencies to obtain a beat frequency signal. The beat frequency signal is an electrical signal. The beat frequency signal is amplified by the RF amplifier and input to the phase-sensitive detection unit.

[0008] The first and second reference frequencies are respectively input to the reference source switching unit. The signal selection input port of the reference source switching unit is connected to the first digital output port of the microcontroller. The first or second reference frequency is selected according to the input digital logic level and input to the phase-sensitive detection unit.

[0009] The phase-sensitive detection unit includes a high-frequency mixer and a digital frequency and phase detector connected in series. The amplified beat frequency signal is input to the RF input port of the high-frequency mixer. The first or second reference frequency selected by the reference source switching unit is input to the local oscillation input port of the high-frequency mixer. The high-frequency mixer reduces the frequency of the beat frequency signal to an intermediate frequency signal that the digital frequency and phase detector can recognize. This intermediate frequency signal is then input to the RF input port of the digital frequency and phase detector. An auxiliary reference frequency is input to the reference input port of the digital frequency and phase detector. The digital frequency and phase detector compares the intermediate frequency signal with the auxiliary reference frequency to obtain an error signal, which is then input to the loop filtering unit.

[0010] The loop filtering unit includes a high-speed proportional-integral-derivative (PID) loop controller and a low-speed integral loop controller connected in parallel. The output of the high-speed PID loop controller is connected to the fast modulation port of a laser via a first analog switch, and the output of the low-speed integral loop controller is connected to the frequency switching unit via a second analog switch. The control inputs of the first and second analog switches are connected to the second and third digital output ports of the microcontroller, respectively. When the control input of the first analog switch is high, the first analog switch is open; when it is low, the first analog switch is closed. When the control input of the second analog switch is low, the second analog switch is open; when it is high, the second analog switch is closed. Error signals are input to the high-speed PID loop controller and the low-speed integral loop controller, respectively. The error signals are returned to the fast modulation port of the laser via the high-speed PID loop controller. By adjusting the parameters of the high-speed PID loop controller, phase locking between the beat frequency signal and the reference frequency is achieved. The error signals are processed by the low-speed integral loop controller to obtain a slow loop control signal, which suppresses long-term drift of the laser. The slow loop control signal is input to the frequency switching unit. When both the first and second analog switches are closed, the feedback loop is closed; when both the first and second analog switches are open, the feedback loop is open.

[0011] The frequency switching unit includes a first adder, a second adder, an output signal latch, and a bias voltage analog switch. The output of the low-speed integral loop controller of the loop filter unit is connected to the first input of the first adder; the output of the output signal latch is connected to the second input of the first adder; the output of the first adder is connected to the first input of the second adder; the output of the bias voltage analog switch is connected to the second input of the second adder; and the output of the second adder is connected to the slow modulation port of the laser. The two inputs of the bias voltage analog switch are respectively connected to the first and second bias voltages. The fifth digital output port of the microcontroller is connected to the control input of the bias voltage analog switch. The output of the first adder is connected to the signal input of the output signal latch. The microcontroller's fourth digital output port is connected to the latch trigger input of the output signal latch; the slow loop control signal output by the loop filter unit is transmitted to the first input of the first adder, and the output of the output signal latch is sent to the second input of the first adder. The output signal obtained after addition is divided into two paths, one path is sent to the input of the output signal latch, and the other path is sent to the first input of the second adder. The first and second bias voltages are respectively input to the bias voltage analog switch, and the output of the bias voltage analog switch is sent to the second input of the second adder. The second adder adds the signal output by the output signal latch and the signal output by the bias voltage analog switch to obtain the processed slow loop control signal, which is transmitted to the slow modulation port of the laser.

[0012] The microcontroller includes a latch trigger port, a reset trigger port, a latch trigger port, a frequency selection port, and first to fifth digital output ports. The latch trigger port, reset trigger port, latch trigger port, and frequency selection port are collectively referred to as digital logic signal input interfaces. The host computer is connected to the digital logic signal input interfaces of the microcontroller. The first digital output port is connected to the signal selection input port of the reference source switching unit. The second and third digital output ports are connected to the control input ports of the first and second analog switches of the loop filter unit. The fourth digital output port is connected to the latch trigger input port of the output signal latch. The fifth digital output port is connected to the control input port of the bias voltage analog switch. The host computer sends latch trigger signals, reset trigger signals, latch trigger signals, and frequency selection signals to the latch trigger ports, reset trigger ports, latch trigger ports, and frequency selection ports of the microcontroller, respectively. All of these are digital logic signals. The latch trigger signals, reset trigger signals, and latch trigger signals are active on the rising edge, and the frequency selection signal is either high or low.

[0013] The high-speed, wide-range laser frequency switching control system performs locking, resetting, or latching functions.

[0014] To perform the locking function: the host computer simultaneously sends a lock trigger signal and a frequency selection signal to the microcontroller's lock trigger port and frequency selection port, respectively; the microcontroller sets its second digital output to high and its third digital output to low, transmitting this information to the first and second analog switches respectively. Both the first and second analog switches are then disconnected, breaking the feedback loop; simultaneously, the logic levels of the microcontroller's first and fifth digital outputs are consistent with the logic level of the frequency selection signal. When the first digital output is low, the reference source switching unit selects the first reference frequency; when the first digital output is high, the reference source switching unit selects the second reference frequency; the fifth digital output... When the fifth digital output is low, the bias voltage analog switch of the frequency switching unit selects the first bias voltage to the second adder; when the fifth digital output is high, the bias voltage analog switch of the frequency switching unit selects the second bias voltage to the second adder. After the slow port response time, the second digital output becomes low and closes the first analog switch. After the fast port response time, the third digital output becomes high and closes the second analog switch. The laser's output frequency is the sum of the first or second reference frequency and the auxiliary reference frequency, completing the locking function. Switching between the first and second reference frequencies allows for a wide range of adjustment of the laser's output frequency.

[0015] Executing the reset function: The host computer simultaneously sends a reset trigger signal and a frequency selection signal to the microcontroller's reset trigger port and frequency selection port, respectively; the microcontroller sets the second digital output to high level and the third digital output to low level and transmits this to the first and second analog switches, respectively. Both the first and second analog switches are disconnected, breaking the feedback loop; simultaneously, the logic levels of the microcontroller's first and fifth digital outputs are consistent with the logic level of the frequency selection signal. When the first digital output is low level, the signal of the reference source switching unit selects the first reference frequency; when the first digital output is high level, the signal of the reference source switching unit selects the second reference frequency. When the fifth digital output is low level, the bias voltage analog switch of the frequency switching unit selects the first bias voltage to the second adder; when the fifth digital output is high level, the bias voltage analog switch of the frequency switching unit selects the second bias voltage to the second adder, completing the reset function.

[0016] Executing the latching function: The host computer simultaneously sends a latch trigger signal and a frequency selection signal to the microcontroller's latch trigger port and frequency selection port, respectively; the microcontroller outputs a high level from the fourth digital output terminal to the output signal latch of the frequency switching unit, causing the output signal latch of the frequency switching unit to perform a latching operation, replacing the original latched value. Since the feedback loop is closed, the slow loop control signal returns to zero voltage to ensure that the laser frequency remains at the required frequency when the second analog switch of the loop filter unit is disconnected. After the latch response time, the fourth digital output terminal becomes low, completing the latching function.

[0017] The slow port response time is 300–2000 μs; the fast port response time is 50–200 μs; and the latch response time is 1–2 ms.

[0018] The output frequency difference between the two lasers with different frequencies is 1–12 GHz. The first reference frequency and the second reference frequency are both 1–12 GHz.

[0019] The photodetector of the laser beat frequency detection unit adopts a photodetector with a bandwidth of not less than 12 GHz.

[0020] The reference source switching unit uses a single-pole double-throw RF switch.

[0021] The auxiliary reference frequency ranges from 10 to 400 MHz. The sum of the first or second reference frequency and the auxiliary reference frequency determines the output frequency difference between the two lasers. When the first reference frequency is selected, the feedback loop is closed, a first bias voltage is applied, and the laser's output frequency is the sum of the first reference frequency and the auxiliary reference frequency. When the second reference frequency is selected, the feedback loop is closed, a second bias voltage is applied, and the laser's output frequency is the sum of the second reference frequency and the auxiliary reference frequency.

[0022] The first and second adders are analog adders built using standard operational amplifiers.

[0023] Another objective of this invention is to propose a high-speed, wide-range laser frequency switching control method.

[0024] The high-speed, wide-range laser frequency switching control method of the present invention includes the following steps:

[0025] 1) Two lasers with different frequencies output a laser beam, which is then combined into a single laser beam. The combined laser beam is input to a high-speed, wide-range laser frequency switching control system, and then returned to a single laser beam, forming a feedback loop.

[0026] 2) The combined laser beam is input to the photodetector of the laser beat frequency detection unit. The photodetector beats the two laser beams with different frequencies to obtain a beat frequency signal. The beat frequency signal is an electrical signal. The beat frequency signal is amplified by the radio frequency amplifier and input to the phase-sensitive detection unit.

[0027] 3) The first reference frequency and the second reference frequency are respectively input to the reference source switching unit. The reference source switching unit selects the first or second reference frequency to input to the phase-sensitive detection unit according to the input digital logic level.

[0028] 4) The amplified beat frequency signal is input to the RF input port of the high-frequency mixer of the phase-sensitive detection unit. The first or second reference frequency selected by the reference source switching unit is input to the local oscillation input port of the high-frequency mixer. The high-frequency mixer reduces the frequency of the beat frequency signal to an intermediate frequency signal that can be recognized by the digital frequency and phase detector. The intermediate frequency signal is then input to the RF input port of the digital frequency and phase detector. The auxiliary reference frequency is input to the reference input port of the digital frequency and phase detector. The digital frequency and phase detector compares the intermediate frequency signal with the auxiliary reference frequency to obtain an error signal, which is then input to the loop filter unit.

[0029] 5) The error signal is input to the high-speed PID loop controller and the low-speed integral loop controller respectively; the error signal returns to the fast modulation port of the laser after passing through the high-speed PID loop controller. By adjusting the parameters of the high-speed PID loop controller, the phase lock between the beat frequency signal and the reference frequency is achieved; the error signal passes through the low-speed integral loop controller to obtain the slow loop control signal, which suppresses the long-term drift of the laser. The slow loop control signal is input to the frequency switching unit.

[0030] 6) The slow loop control signal output by the loop filter unit is transmitted to the first input terminal of the first adder, and the output of the output signal latch is sent to the second input terminal of the first adder. The output signal obtained after addition is divided into two paths, one path is sent to the input terminal of the output signal latch, and the other path is sent to the first input terminal of the second adder. The first and second bias voltages are respectively input to the bias voltage analog switch. The output of the bias voltage analog switch is sent to the second input terminal of the second adder. The second adder adds the signal output by the output signal latch and the signal output by the bias voltage analog switch to obtain the processed slow loop control signal, which is transmitted to the slow modulation port of the laser.

[0031] 7) The high-speed, wide-range laser frequency switching control system performs locking, reset, or latching functions:

[0032] To perform the locking function: the host computer simultaneously sends a lock trigger signal and a frequency selection signal to the microcontroller's lock trigger port and frequency selection port, respectively; the microcontroller sets its second digital output to high and its third digital output to low, transmitting this information to the first and second analog switches respectively. Both the first and second analog switches are then disconnected, breaking the feedback loop; simultaneously, the logic levels of the microcontroller's first and fifth digital outputs are consistent with the logic level of the frequency selection signal. When the first digital output is low, the reference source switching unit selects the first reference frequency; when the first digital output is high, the reference source switching unit selects the second reference frequency; the fifth digital... When the output is low, the bias voltage analog switch of the frequency switching unit selects the first bias voltage to the second adder; when the fifth digital output is high, the bias voltage analog switch of the frequency switching unit selects the second bias voltage to the second adder. After the slow port response time, the second digital output becomes low and closes the first analog switch. After the fast port response time, the third digital output becomes high and closes the second analog switch. The laser's output frequency is the sum of the first or second reference frequency and the auxiliary reference frequency, completing the locking function. Switching between the first and second reference frequencies allows for a wide range of adjustment of the laser's output frequency.

[0033] Executing the reset function: The host computer simultaneously sends a reset trigger signal and a frequency selection signal to the microcontroller's reset trigger port and frequency selection port, respectively. The microcontroller sets its second digital output to high and its third digital output to low, transmitting these signals to the first and second analog switches, respectively. Both analog switches are then disconnected, breaking the feedback loop. Simultaneously, the logic levels of the microcontroller's first and fifth digital outputs are consistent with the logic level of the frequency selection signal. When the first digital output is low, the reference source switching unit selects the first reference frequency; when the first digital output is high, the reference source switching unit selects the second reference frequency. When the fifth digital output is low, the frequency switching unit's bias voltage analog switch selects the first bias voltage for the second adder; when the fifth digital output is high, the frequency switching unit's bias voltage analog switch selects the second bias voltage for the second adder.

[0034] Complete the reset function;

[0035] Executing the latching function: The host computer simultaneously sends a latch trigger signal and a frequency selection signal to the microcontroller's latch trigger port and frequency selection port, respectively; the microcontroller outputs a high level from the fourth digital output terminal to the output signal latch of the frequency switching unit, causing the output signal latch of the frequency switching unit to perform a latching operation, replacing the original latched value. Since the feedback loop is closed, the slow loop control signal returns to zero voltage to ensure that the laser frequency remains at the required frequency when the second analog switch of the loop filter unit is disconnected. After the latch response time, the fourth digital output terminal becomes low, completing the latching function.

[0036] Advantages of this invention:

[0037] This invention employs a clever unlock-relock design to circumvent the limitations of loop bandwidth and phase-sensitive detection bandwidth on laser frequency switching in the locked state, thus achieving high-speed, wide-range laser frequency switching. By introducing a latch into the frequency switching unit, long-term laser frequency drift is suppressed, ensuring the success rate of frequency switching. The microcontroller provides a convenient external trigger interface, allowing the corresponding functions to be implemented through simple digital logic signals. Attached Figure Description

[0038] Figure 1 This is a structural block diagram of an embodiment of the high-speed, wide-range laser frequency switching control system of the present invention;

[0039] Figure 2 This is a structural block diagram of a frequency switching unit in an embodiment of the high-speed, wide-range laser frequency switching control system of the present invention.

[0040] Figure 3 This is a block diagram showing the connection between the microcontroller and other units in one embodiment of the high-speed, wide-range laser frequency switching control system of the present invention.

[0041] Figure 4 This is a timing diagram of the execution locking function of an embodiment of the high-speed, wide-range laser frequency switching control system of the present invention;

[0042] Figure 5 This is a timing diagram of the execution unit reset function of an embodiment of the high-speed, wide-range laser frequency switching control system of the present invention;

[0043] Figure 6 This is a timing diagram of the execution latch function of an embodiment of the high-speed, wide-range laser frequency switching control system of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1As shown, the high-speed, wide-range laser frequency switching control system of this embodiment includes: a laser beat frequency detection unit, a reference source switching unit, a phase-sensitive detection unit, a loop filtering unit, a frequency switching unit, and a microcontroller; wherein, a laser beam is output from two lasers with different frequencies, the two laser beams with different frequencies are combined into a combined laser beam, the combined laser beam is input to the high-speed, wide-range laser frequency switching control system, and then returned to a laser after passing through the high-speed, wide-range laser frequency switching control system, forming a feedback loop;

[0046] The laser beat frequency detection unit includes a photodetector and an RF amplifier connected in series. The combined laser beam is input to the photodetector of the laser beat frequency detection unit. The photodetector beats the two laser beams with different frequencies to obtain a beat frequency signal. The beat frequency signal is an electrical signal. The beat frequency signal is amplified by the RF amplifier and input to the phase-sensitive detection unit.

[0047] The first and second reference frequencies are respectively input to the reference source switching unit. The signal selection input port of the reference source switching unit is connected to the first digital output port of the microcontroller. The first or second reference frequency is selected according to the input digital logic level and input to the phase-sensitive detection unit.

[0048] The phase-sensitive detection unit includes a high-frequency mixer and a digital frequency and phase detector connected in series. The amplified beat frequency signal is input to the RF input port of the high-frequency mixer. The first or second reference frequency selected by the reference source switching unit is input to the local oscillation input port of the high-frequency mixer. The high-frequency mixer reduces the frequency of the beat frequency signal to an intermediate frequency signal that the digital frequency and phase detector can recognize. The frequency is reduced to about 100MHz and input to the RF input port of the digital frequency and phase detector. A 100MHz auxiliary reference frequency is input to the reference input port of the digital frequency and phase detector. The digital frequency and phase detector compares the intermediate frequency signal with the auxiliary reference frequency to obtain an error signal, which is input to the loop filtering unit.

[0049] The loop filtering unit includes a high-speed proportional-integral-derivative (PID) loop controller and a low-speed integral loop controller connected in parallel. The output of the high-speed PID loop controller is connected to the fast modulation port of a laser via a first analog switch, and the output of the low-speed integral loop controller is connected to the frequency switching unit via a second analog switch. The control inputs of the first and second analog switches are connected to the second and third digital output ports of the microcontroller, respectively. When the control input of the first analog switch is high, the first analog switch is open; when it is low, the first analog switch is closed. When the control input of the second analog switch is low, the second analog switch is open; when it is high, the second analog switch is closed. Error signals are input to the high-speed PID loop controller and the low-speed integral loop controller, respectively. The error signals are returned to the fast modulation port of the laser via the high-speed PID loop controller. By adjusting the parameters of the high-speed PID loop controller, phase locking between the beat frequency signal and the reference frequency is achieved. The error signals are processed by the low-speed integral loop controller to obtain a slow loop control signal, which suppresses long-term drift of the laser. The slow loop control signal is input to the frequency switching unit. When both the first and second analog switches are closed, the feedback loop is closed; when both the first and second analog switches are open, the feedback loop is open.

[0050] like Figure 2 As shown, the frequency switching unit includes a first adder, a second adder, an output signal latch, and a bias voltage analog switch. The output of the low-speed integral loop controller of the loop filter unit is connected to the first input of the first adder, the output of the output signal latch is connected to the second input of the first adder, the output of the first adder is connected to the first input of the second adder, the output of the bias voltage analog switch is connected to the second input of the second adder, and the output of the second adder is connected to the slow modulation port of the laser. The two inputs of the bias voltage analog switch are respectively connected to the first and second bias voltages, and the fifth digital output port of the microcontroller is connected to the control input of the bias voltage analog switch. The output of the first adder is connected to the output signal latch. The signal input terminal of the microcontroller is connected to the latch trigger input terminal of the output signal latch. The slow loop control signal output by the loop filter unit is transmitted to the first input terminal of the first adder. The output of the output signal latch is sent to the second input terminal of the first adder. The output signal obtained after addition is divided into two paths. One path is sent to the input terminal of the output signal latch, and the other path is sent to the first input terminal of the second adder. The first and second bias voltages are respectively input to the bias voltage analog switch. The output of the bias voltage analog switch is sent to the second input terminal of the second adder. The second adder adds the signal output by the output signal latch and the signal output by the bias voltage analog switch to obtain the processed slow loop control signal, which is transmitted to the slow modulation port of the laser.

[0051] like Figure 3 As shown, the microcontroller includes a latch trigger port, a reset trigger port, a latch trigger port, a frequency selection port, and first to fifth digital output terminals. The latch trigger port, reset trigger port, latch trigger port, and frequency selection port are collectively referred to as digital logic signal input interfaces. The host computer is connected to the digital logic signal input interfaces of the microcontroller. The first digital output terminal is connected to the signal selection input port of the reference source switching unit. The second and third digital output terminals are connected to the control input terminals of the first and second analog switches of the loop filter unit. The fourth digital output port is connected to the latch trigger input terminal of the output signal latch. The fifth digital output port is connected to the control input terminal of the bias voltage analog switch. The host computer sends latch trigger signals, reset trigger signals, latch trigger signals, and frequency selection signals to the latch trigger ports, reset trigger ports, latch trigger ports, and frequency selection ports of the microcontroller, respectively. All of these are digital logic signals. The latch trigger signals, reset trigger signals, and latch trigger signals are active on the rising edge, and the frequency selection signal is either high or low.

[0052] In this embodiment, the controlled laser is a 780nm external cavity semiconductor laser with a piezoelectric ceramic voltage modulation port and a laser diode current modulation port. The reference laser is a 780nm external cavity semiconductor laser with its frequency locked to the Rb87 atomic spectral line. 0.5mW power laser beams are taken from both lasers and combined into a laser beat frequency detection unit. This unit uses a photodetector with a bandwidth of 12GHz and a load of 50Ω. The output signal is amplified by a 40dB gain RF amplifier before entering the phase-sensitive detection unit. Reference frequency 1 is 6.734GHz, and reference frequency 2 is 6.234GHz, both with a power of 10dBm. The single-pole double-throw RF switch used has a bandwidth of 10GHz. The phase-sensitive detection unit includes a high-frequency mixer with a bandwidth of 4-12GHz, a digital frequency and phase detector with a bandwidth of 200MHz, and a reference frequency of 100MHz. The loop filtering unit includes a high-speed PID loop controller with a maximum open-loop bandwidth of 40MHz. The low-speed integral loop controller has an integral speed adjustable from 0.01V / μs to 10000V / μs. The output signal latch in the frequency switching unit can latch voltages from -10V to +10V, and the bias voltage is adjustable from -5V to +5V. When the analog switch input logic is high, the bias voltage is turned on. The adder adds the slow loop control signal, the latch signal, and the bias voltage signal to obtain the processed slow loop control signal. The microcontroller's lock trigger, reset trigger, and latch trigger input signals are rising edge valid. When triggered, the frequency selection input signal logic state is read. The high-speed loop control signal is connected to the laser current modulation port, and the processed slow loop control signal is connected to the piezoelectric ceramic voltage modulation port.

[0053] The high-speed, wide-range laser frequency switching control system performs locking, resetting, or latching functions, with the timing of each function determined by... Figure 4 , Figure 5 and Figure 6 This indicates that the timing of the input frequency selection signal and the first and fifth digital outputs has been omitted.

[0054] like Figure 4 As shown, the locking function is executed as follows: the host computer simultaneously sends a lock trigger signal and a frequency selection signal to the lock trigger port and frequency selection port of the microcontroller, respectively; the microcontroller changes the second digital output terminal to a high level and the third digital output terminal to a low level, respectively, and transmits this to the first and second analog switches. Both the first and second analog switches are opened, breaking the feedback loop; simultaneously, the logic levels of the first and fifth digital output terminals of the microcontroller are consistent with the logic level of the frequency selection signal. When the first digital output terminal is low, the signal of the reference source switching unit selects the first reference frequency; when the first digital output terminal is high, the signal of the reference source switching unit selects the second reference frequency; when the fifth digital output terminal is low, the bias voltage analog switch of the frequency switching unit selects the first bias voltage. When the voltage is applied to the second adder and the fifth digital output is high, the bias voltage analog switch of the frequency switching unit selects the second bias voltage to the second adder. After 400μs, the second digital output goes low and closes the first analog switch. After another 100μs, the third digital output goes high and closes the second analog switch. The laser's output frequency is the sum of the first or second reference frequency and the auxiliary reference frequency, completing the locking function. The output of the reference source switching unit switches between the first reference frequency and the second reference frequency. When the output is the first reference frequency, the locking function will lock it at 6.834GHz, and when the output is the second reference frequency, the locking function will lock it at 6.334GHz, achieving a wide range of adjustment of the laser's output frequency.

[0055] like Figure 5As shown, the reset function is executed as follows: The host computer simultaneously sends a reset trigger signal and a frequency selection signal to the reset trigger port and frequency selection port of the microcontroller, respectively; the microcontroller sets the second digital output terminal to a high level and the third digital output terminal to a low level, respectively, and transmits this to the first and second analog switches. Both the first and second analog switches are disconnected, breaking the feedback loop; simultaneously, the logic levels of the first and fifth digital output terminals of the microcontroller are consistent with the logic level of the frequency selection signal. When the first digital output terminal is low, the signal of the reference source switching unit selects the first reference frequency; when the first digital output terminal is high, the signal of the reference source switching unit selects the second reference frequency; when the fifth digital output terminal is low, the bias voltage analog switch of the frequency switching unit selects the first bias voltage to the second adder; when the fifth digital output terminal is high, the bias voltage analog switch of the frequency switching unit selects the second bias voltage to the second adder, thus completing the reset function;

[0056] like Figure 6 As shown, the latching function is executed as follows: The host computer simultaneously sends a latch trigger signal and a frequency selection signal to the latch trigger port and frequency selection port of the microcontroller, respectively; the microcontroller outputs a high level from the fourth digital output terminal to the output signal latch of the frequency switching unit, causing the output signal latch of the frequency switching unit to perform a latching operation, replacing the original latched value, the feedback loop is closed, and the slow loop control signal returns to zero voltage to ensure that the laser frequency is maintained at the required frequency when the second analog switch of the loop filter unit is disconnected. After 1ms, the fourth digital output terminal becomes low, completing the latching function.

[0057] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A high-speed, wide-range laser frequency switching control system, characterized in that, The high-speed, wide-range laser frequency switching control system includes: a laser beat frequency detection unit, a reference source switching unit, a phase-sensitive detection unit, a loop filtering unit, a frequency switching unit, and a microcontroller; wherein, a laser beam is output from two lasers with different frequencies, the two laser beams with different frequencies are combined into a combined laser beam, the combined laser beam is input to the high-speed, wide-range laser frequency switching control system, and then returned to a laser after passing through the high-speed, wide-range laser frequency switching control system, forming a feedback loop; The laser beat frequency detection unit includes a photodetector and an RF amplifier connected in series. The combined laser beam is input to the photodetector of the laser beat frequency detection unit. The photodetector beats the two laser beams with different frequencies to obtain a beat frequency signal. The beat frequency signal is an electrical signal. The beat frequency signal is amplified by the RF amplifier and input to the phase-sensitive detection unit. The first and second reference frequencies are respectively input to the reference source switching unit. The signal selection input port of the reference source switching unit is connected to the first digital output port of the microcontroller. The first or second reference frequency is selected according to the input digital logic level and input to the phase-sensitive detection unit. The phase-sensitive detection unit includes a high-frequency mixer and a digital frequency and phase detector connected in series. The amplified beat frequency signal is input to the RF input port of the high-frequency mixer. The first or second reference frequency selected by the reference source switching unit is input to the local oscillation input port of the high-frequency mixer. The high-frequency mixer reduces the frequency of the beat frequency signal to an intermediate frequency signal that the digital frequency and phase detector can recognize. This intermediate frequency signal is then input to the RF input port of the digital frequency and phase detector. An auxiliary reference frequency is input to the reference input port of the digital frequency and phase detector. The digital frequency and phase detector compares the intermediate frequency signal with the auxiliary reference frequency to obtain an error signal, which is then input to the loop filtering unit. The loop filtering unit includes a high-speed proportional-integral-derivative (PID) loop controller and a low-speed integral loop controller connected in parallel. The output of the high-speed PID loop controller is connected to the fast modulation port of a laser via a first analog switch, and the output of the low-speed integral loop controller is connected to the frequency switching unit via a second analog switch. The control inputs of the first and second analog switches are connected to the second and third digital output ports of the microcontroller, respectively. When the control input of the first analog switch is high, the first analog switch is open; when it is low, the first analog switch is closed. When the control input of the second analog switch is low, the second analog switch is open; when it is high, the second analog switch is closed. Error signals are input to the high-speed PID loop controller and the low-speed integral loop controller, respectively. The error signals are returned to the fast modulation port of the laser via the high-speed PID loop controller. By adjusting the parameters of the high-speed PID loop controller, phase locking between the beat frequency signal and the reference frequency is achieved. The error signals are processed by the low-speed integral loop controller to obtain a slow loop control signal, which suppresses long-term drift of the laser. The slow loop control signal is input to the frequency switching unit. When both the first and second analog switches are closed, the feedback loop is closed; when both the first and second analog switches are open, the feedback loop is open. The frequency switching unit includes a first adder, a second adder, an output signal latch, and a bias voltage analog switch. The output of the low-speed integral loop controller of the loop filter unit is connected to the first input of the first adder; the output of the output signal latch is connected to the second input of the first adder; the output of the first adder is connected to the first input of the second adder; the output of the bias voltage analog switch is connected to the second input of the second adder; and the output of the second adder is connected to the slow modulation port of the laser. The two inputs of the bias voltage analog switch are respectively connected to the first and second bias voltages. The fifth digital output port of the microcontroller is connected to the control input of the bias voltage analog switch. The output of the first adder is connected to the signal input of the output signal latch. The microcontroller's fourth digital output port is connected to the latch trigger input of the output signal latch; the slow loop control signal output by the loop filter unit is transmitted to the first input of the first adder, and the output of the output signal latch is sent to the second input of the first adder. The output signal obtained after addition is divided into two paths, one path is sent to the input of the output signal latch, and the other path is sent to the first input of the second adder. The first and second bias voltages are respectively input to the bias voltage analog switch, and the output of the bias voltage analog switch is sent to the second input of the second adder. The second adder adds the signal output by the output signal latch and the signal output by the bias voltage analog switch to obtain the processed slow loop control signal, which is transmitted to the slow modulation port of the laser. The microcontroller includes a latch trigger port, a reset trigger port, a latch trigger port, a frequency selection port, and first to fifth digital output ports. The latch trigger port, reset trigger port, latch trigger port, and frequency selection port are collectively referred to as digital logic signal input interfaces. The host computer is connected to the digital logic signal input interfaces of the microcontroller. The first digital output port is connected to the signal selection input port of the reference source switching unit. The second and third digital output ports are connected to the control input ports of the first and second analog switches of the loop filter unit. The fourth digital output port is connected to the latch trigger input port of the output signal latch. The fifth digital output port is connected to the control input port of the bias voltage analog switch. The host computer sends latch trigger signals, reset trigger signals, latch trigger signals, and frequency selection signals to the latch trigger ports, reset trigger ports, latch trigger ports, and frequency selection ports of the microcontroller, respectively. All of these are digital logic signals. The latch trigger signals, reset trigger signals, and latch trigger signals are active on the rising edge, and the frequency selection signal is either high or low. The high-speed, wide-range laser frequency switching control system performs locking, resetting, or latching functions.

2. The high-speed, wide-range laser frequency switching control system as described in claim 1, characterized in that, The output frequency difference between the two lasers with different frequencies is 1 to 12 GHz.

3. The high-speed, wide-range laser frequency switching control system as described in claim 1, characterized in that, The first reference frequency and the second reference frequency are 1 to 12 GHz, respectively.

4. The high-speed, wide-range laser frequency switching control system as described in claim 1, characterized in that, The photodetector of the laser beat frequency detection unit is a photodetector with a bandwidth of not less than 12 GHz.

5. The high-speed, wide-range laser frequency switching control system as described in claim 1, characterized in that, The reference source switching unit uses a single-pole double-throw radio frequency switch.

6. The high-speed, wide-range laser frequency switching control system as described in claim 1, characterized in that, The frequency range of the auxiliary reference frequency is 10 to 400 MHz.

7. The high-speed, wide-range laser frequency switching control system as described in claim 1, characterized in that, The first and second adders are analog adders built using standard operational amplifiers.

8. A control method for a high-speed, wide-range laser frequency switching control system as described in claim 1, characterized in that, The control method includes the following steps: 1) Two lasers with different frequencies output a laser beam, which is then combined into a single laser beam. The combined laser beam is input to a high-speed, wide-range laser frequency switching control system, and then returned to a single laser beam, forming a feedback loop. 2) The combined laser beam is input to the photodetector of the laser beat frequency detection unit. The photodetector beats the two laser beams with different frequencies to obtain a beat frequency signal. The beat frequency signal is an electrical signal. The beat frequency signal is amplified by the radio frequency amplifier and input to the phase-sensitive detection unit. 3) The first reference frequency and the second reference frequency are respectively input to the reference source switching unit. The reference source switching unit selects the first or second reference frequency to input to the phase-sensitive detection unit according to the input digital logic level. 4) The amplified beat frequency signal is input to the RF input port of the high-frequency mixer of the phase-sensitive detection unit. The first or second reference frequency selected by the reference source switching unit is input to the local oscillation input port of the high-frequency mixer. The high-frequency mixer reduces the frequency of the beat frequency signal to an intermediate frequency signal that can be recognized by the digital frequency and phase detector. The intermediate frequency signal is then input to the RF input port of the digital frequency and phase detector. The auxiliary reference frequency is input to the reference input port of the digital frequency and phase detector. The digital frequency and phase detector compares the intermediate frequency signal with the auxiliary reference frequency to obtain an error signal, which is then input to the loop filter unit. 5) The error signal is input to the high-speed PID loop controller and the low-speed integral loop controller respectively; the error signal returns to the fast modulation port of the laser after passing through the high-speed PID loop controller. By adjusting the parameters of the high-speed PID loop controller, the phase lock between the beat frequency signal and the reference frequency is achieved; the error signal passes through the low-speed integral loop controller to obtain the slow loop control signal, which suppresses the long-term drift of the laser. The slow loop control signal is input to the frequency switching unit. 6) The slow loop control signal output by the loop filter unit is transmitted to the first input terminal of the first adder, and the output of the output signal latch is sent to the second input terminal of the first adder. The output signal obtained after addition is divided into two paths, one path is sent to the input terminal of the output signal latch, and the other path is sent to the first input terminal of the second adder. The first and second bias voltages are respectively input to the bias voltage analog switch. The output of the bias voltage analog switch is sent to the second input terminal of the second adder. The second adder adds the signal output by the output signal latch and the signal output by the bias voltage analog switch to obtain the processed slow loop control signal, which is transmitted to the slow modulation port of the laser. 7) The high-speed, wide-range laser frequency switching control system performs locking, reset, or latching functions: To perform the locking function: the host computer simultaneously sends a lock trigger signal and a frequency selection signal to the microcontroller's lock trigger port and frequency selection port, respectively; the microcontroller sets its second digital output to high and its third digital output to low, transmitting this information to the first and second analog switches respectively. Both the first and second analog switches are then disconnected, breaking the feedback loop; simultaneously, the logic levels of the microcontroller's first and fifth digital outputs are consistent with the logic level of the frequency selection signal. When the first digital output is low, the reference source switching unit selects the first reference frequency; when the first digital output is high, the reference source switching unit selects the second reference frequency; the fifth digital... When the output is low, the bias voltage analog switch of the frequency switching unit selects the first bias voltage to the second adder; when the fifth digital output is high, the bias voltage analog switch of the frequency switching unit selects the second bias voltage to the second adder. After the slow port response time, the second digital output becomes low and closes the first analog switch. After the fast port response time, the third digital output becomes high and closes the second analog switch. The laser's output frequency is the sum of the first or second reference frequency and the auxiliary reference frequency, completing the locking function. Switching between the first and second reference frequencies allows for a wide range of adjustment of the laser's output frequency. Executing the reset function: The host computer simultaneously sends a reset trigger signal and a frequency selection signal to the microcontroller's reset trigger port and frequency selection port, respectively; the microcontroller sets the second digital output to high level and the third digital output to low level and transmits this to the first and second analog switches, respectively. Both the first and second analog switches are disconnected, breaking the feedback loop; simultaneously, the logic levels of the microcontroller's first and fifth digital outputs are consistent with the logic level of the frequency selection signal. When the first digital output is low level, the signal of the reference source switching unit selects the first reference frequency; when the first digital output is high level, the signal of the reference source switching unit selects the second reference frequency. When the fifth digital output is low level, the bias voltage analog switch of the frequency switching unit selects the first bias voltage to the second adder; when the fifth digital output is high level, the bias voltage analog switch of the frequency switching unit selects the second bias voltage to the second adder, completing the reset function. Executing the latching function: The host computer simultaneously sends a latch trigger signal and a frequency selection signal to the microcontroller's latch trigger port and frequency selection port, respectively; the microcontroller outputs a high level from the fourth digital output terminal to the output signal latch of the frequency switching unit, causing the output signal latch of the frequency switching unit to perform a latching operation, replacing the original latched value. Since the feedback loop is closed, the slow loop control signal returns to zero voltage to ensure that the laser frequency remains at the required frequency when the second analog switch of the loop filter unit is disconnected. After the latch response time, the fourth digital output terminal becomes low, completing the latching function.

9. The control method as described in claim 8, characterized in that, The slow port response time is 300–2000 μs; the fast port response time is 50–200 μs.

10. The control method as described in claim 8, characterized in that, The latch response time is 1 to 2 ms.

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