CN-122026217-A - Intelligent control method and system for PPLN frequency doubling system

CN122026217ACN 122026217 ACN122026217 ACN 122026217ACN-122026217-A

Abstract

The invention belongs to the technical field of laser technology and nonlinear optical frequency conversion, and discloses an intelligent control method for a PPLN frequency doubling system. The invention adopts a three-stage progressive optimal working point searching flow, effectively solves the problem of optimal matching temperature drift caused by crystal heat absorption and photorefractive effect under high power operation by a low-power rough scanning calibration reference temperature, gradient power approaching real-time tracking temperature drift and high-power dynamic locking closed-loop control mode, ensures that a system can work in an optimal state of quasi-phase matching under any input power, and simultaneously maintains a high-efficiency conversion interval all the time in the system output power adjustment process by a feedforward and feedback control strategy of power-temperature synchronous coordination, thereby avoiding efficiency dip caused by mismatch.

Inventors

ZHOU FANGZHOU
LI HAO
TONG YULONG
WANG YUBO
JIN CAOFAN

Assignees

上海聿凡领光通信有限公司

Dates

Publication Date: 20260512
Application Date: 20260413

Claims (9)

1. An intelligent control method for a PPLN frequency doubling system is characterized by comprising the following specific steps: Step one, system initialization and self-checking After the system is powered on, the initialization of hardware peripherals and control programs is completed, calibration parameters in a storage medium and a preset power-temperature matching curve are read, full-link hardware self-checking is executed, the on-line state and signal rationality of each detector, each sensor and each driving module are checked, and if the self-checking fails, error reporting is triggered and system starting is forbidden; step two, intelligent searching of the optimal working point When the system is started or the working state is required to be locked again, executing a three-stage progressive optimal working point searching process, controlling the optical fiber amplifier to enable the fundamental frequency optical power of the input PPLN crystal to be gradually increased from low to high, fine-adjusting the TEC working temperature of the PPLN crystal according to each power point, collecting the output frequency doubling optical power of the PPLN crystal in real time, comparing the fundamental frequency optical input power corresponding to the maximum value of the output power with the TEC temperature, locking the fundamental frequency optical input power to be the optimal working point of the system, and recording the reference frequency doubling efficiency; step three, power-temperature self-adaptive matching adjustment When receiving an output power adjustment instruction, the system enters a power-temperature synchronous matching mode, the required fundamental frequency light input power is reversely pushed according to the target frequency multiplication output power, the matched target TEC temperature is obtained based on a preset power-optimal temperature corresponding relation curve, and the output light power of the optical fiber amplifier and the TEC working temperature are synchronously adjusted by adopting a feedforward and feedback cooperative control strategy, so that the system is always maintained in a high-efficiency conversion interval in the adjustment process and in a target steady state; fourth, multi-layer intelligent protection control In the running process of the system, intelligent protection tasks of high-frequency polling are executed in parallel with the highest priority, full-dimension monitoring data of the PPLN crystal temperature, the fundamental frequency light input power, the seed light power and the laser output state are collected in real time, and the emergency shutdown protection actions are executed immediately after corresponding judgment logic is triggered aiming at abnormal working conditions of over-temperature, abnormal fluctuation of the input light power, power overshoot, seed light loss and laser failure, so that the fault state of the system is synchronously locked; running log record and state monitoring The method comprises the steps of starting a full-flow recording system, adjusting parameters, protecting and triggering, adding a time stamp and an event code for each record, storing a log in a circulating coverage nonvolatile storage mode, and simultaneously transmitting system running state data to a host computer in real time to realize remote monitoring and fault tracing.
2. The intelligent control method for the PPLN frequency doubling system according to claim 1, wherein the three-stage progressive optimal working point searching process in the second step is specifically divided into three stages, the first stage is low-power coarse scanning, basic frequency optical pumping power smaller than 10% of rated low power is set, a preset temperature interval is scanned in a preset temperature stepping mode, a frequency doubling power curve is recorded and an optimal matching temperature T_low in low power is locked and used as an initial reference point of high-power scanning, the second stage is gradient power approximation, pumping optical power is increased by 5% -10% each time from T_low, after TEC temperature is stabilized to be higher than 0.02 ℃, the current power is scanned in a small step of 0.05-0.1 ℃, the actual optimal matching temperature in the power is searched, the optimal matching temperature in the power is recorded and used as a scanning starting point of next higher power, the temperature drift curve in the step-by step power lifting process is tracked, the third stage is dynamic locking and reference recording, when the TEC temperature is stabilized to be higher than the target power, the corresponding working point is set and the optimal working point is used as a target point of the closed-loop, and the PID system is stabilized.
3. The intelligent control method for the PPLN frequency doubling system according to claim 1, wherein the preset power-optimal temperature corresponding relation curve in the third step is determined through experiments before delivery or in a self-learning stage of the system, corresponding optimal matching temperatures under different fundamental frequency light powers are fitted to generate or stored as a lookup table capable of being interpolated and inquired, the feedforward and feedback cooperative control strategy adopts a step synchronous adjustment mode to decompose target variable quantities of power and temperature into a plurality of steps, each step synchronously adjusts the power and the temperature to an intermediate set value, the next step is carried out after the system is stable, the frequency doubling light power is monitored in real time in the adjustment process, and if the actual output and the expected deviation exceed a threshold value, the temperature set value is finely adjusted to carry out closed loop correction.
4. The intelligent control method for the PPLN frequency doubling system according to claim 1, wherein in the fourth step, the intelligent protection task operates in a fixed high-frequency period of 1kHz, wherein the overtemperature protection judging logic is used for collecting the temperature of the PPLN crystal at the frequency of 10 Hz-100 Hz, if three continuous sampling values exceed an absolute temperature upper limit, the overtemperature protection is triggered, pumping source current of the optical fiber amplifier is immediately cut off, a TEC rapid cooling mode is started, the system enters a fault locking state and needs to be reset manually, and the absolute temperature upper limit is the optimal working point temperature plus 0.5 ℃ or the maximum allowable working temperature of the crystal is 65 ℃.
5. The intelligent control method for the PPLN frequency doubling system according to claim 1, wherein in the fourth step, the decision logic of the abnormal fluctuation of the input optical power is to perform statistical analysis on fundamental frequency optical power sampling data in a 1 second time window, when the power fluctuation amplitude exceeds 5% and the fluctuation frequency exceeds 10Hz, the decision logic of the abnormal fluctuation of the input optical power is to determine that the input optical stability is abnormal, immediately turn off an optical fiber amplifier pumping source, wait for the system to be stable, and manually check the light source if frequently triggered, the decision logic of the power overshoot is to detect the instantaneous change rate and the absolute amplitude of the fundamental frequency optical power in real time, and adopts an edge detection algorithm, when the slope of the power rising edge exceeds 50% of full range/millisecond, or the instantaneous value of the power exceeds 110% of a set maximum value, the FPGA hardware logic is directly triggered and protected, the operation priority of the FPGA hardware protection logic is higher than that of the software protection logic, the optical fiber amplifier pumping driving output is locked in microsecond level, after the triggering, the system enters a fault lock dead state, all the optical power output operation is disabled, and only manual reset unlocking is supported.
6. The intelligent control method for a PPLN frequency doubling system according to claim 1, wherein the decision logic for seed light loss in the fourth step is that after the pumping of the optical fiber amplifier is started, if the seed light power is lower than a preset threshold value and the duration exceeds 10ms, the decision logic for seed light loss is implemented, the pumping source of the optical fiber amplifier is immediately turned off, the system enters a standby-fault state and can be recovered only through manual reset, and the decision logic for laser failure is implemented, after a controller sends a laser driving current starting instruction, the decision logic for laser failure determines that the laser fails when no effective laser output light is detected within a specified time delay, cuts off the laser driving current and inhibits the optical fiber amplifier from being started.
7. The intelligent control method for the PPLN frequency doubling system of claim 1, wherein the multi-level intelligent protection control in the fourth step further comprises software authority protection, input numerical range limitation is set on a user operation interface, the controller performs back-end secondary verification on the received setting instruction, the instruction exceeding the safety range refuses to be executed and triggers a warning, and meanwhile hierarchical operation authority is set, modification of key parameters requires manager authority verification, and the key parameters comprise temperature limit and power limit.
8. An intelligent control system for a PPLN frequency doubling system for implementing the intelligent control method for a PPLN frequency doubling system according to any one of claims 1 to 7, comprising the following units: The optical link unit is used for constructing a frequency multiplication optical transmission path, and is sequentially connected with a narrow linewidth laser, an optical fiber amplifier, a PPLN frequency multiplication crystal integrated with a TEC and an optical splitting device for optical splitting monitoring along an optical path; The signal acquisition unit comprises a first photoelectric detector arranged at the input end of the PPLN crystal, a second photoelectric detector arranged at the output end of the PPLN crystal and a temperature sensor for monitoring the temperature of the PPLN crystal, and the real-time acquisition of fundamental frequency light input power, frequency doubling light output power and crystal working temperature is completed respectively; The core control unit takes a programmable logic device and a processor as control cores, the signal input end of the core control unit is connected with all detectors and sensors of the signal acquisition unit, the control output end of the core control unit is respectively connected with a current driving module of a narrow linewidth laser, a pumping driving module of an optical fiber amplifier and a TEC driving module of a PPLN crystal, an intelligent adjusting module and an intelligent protection module are arranged in the core control unit, and the whole flow of a corresponding intelligent control method is executed; And the log and communication module is used for completing the nonvolatile storage of the total events of the system, and simultaneously transmitting the running state data of the system to the upper computer in real time through the Ethernet or the serial port so as to realize remote monitoring and data interaction.
9. The intelligent control system for the PPLN frequency doubling system of claim 8, wherein the intelligent regulation module built in the core control unit comprises an optimal working point searching unit and a power-temperature synchronous matching unit, the optimal working point searching unit is used for executing a three-level progressive working point optimizing flow to complete automatic searching and locking of an optimal working point of the system, the power-temperature synchronous matching unit is used for synchronously coordinating parameter regulation of the optical fiber amplifier and the TEC according to an output regulation command to maintain a high-efficiency conversion state of the system, and the intelligent protection module built in the core control unit is provided with a highest operation priority and is used for monitoring full-dimensional working condition data in real time to complete judgment of abnormal working conditions and execution of emergency protection actions.

Description

Intelligent control method and system for PPLN frequency doubling system Technical Field The invention belongs to the technical field of laser technology and nonlinear optical frequency conversion, and particularly relates to an intelligent control method and system for a PPLN frequency doubling system. Background The laser technology is a core basic technology in a plurality of fields such as modern precise spectrum measurement, quantum information processing, laser radar, biomedical imaging, industrial precise processing and the like, and a laser frequency conversion technology based on a nonlinear optical effect is a core technology path for expanding a laser output wavelength range, obtaining high power, high beam quality and narrow linewidth specific wavelength laser, wherein a Periodically Polarized Lithium Niobate (PPLN) crystal has become a core nonlinear optical device which is most widely applied in a laser frequency doubling system by virtue of the remarkable advantages of high nonlinear optical coefficient, wide light transmission band, low transmission loss, designable quasi-phase matching period and the like. The technical proposal that the narrow linewidth laser is amplified by the optical fiber amplifier and then injected into the PPLN crystal to finish frequency multiplication conversion is an important implementation way for obtaining high-power and high-quality specific wavelength laser in the current industry, for example, 1560nm infrared laser can be efficiently multiplied to 780nm visible laser by the proposal, along with the continuous improvement of the requirements of each application field on the output power stability, conversion efficiency, long-term operation reliability and automatic operation capability of the frequency multiplication laser, the problems of performance shortboards and management and control of the PPLN frequency multiplication system in practical engineering application are gradually highlighted, the existing regulation and control and protection technology for the PPLN frequency multiplication system still has a plurality of technical defects which are difficult to solve in practical application, in the practical operation process of the PPLN frequency multiplication system, the frequency multiplication conversion efficiency of the PPLN crystal is seriously dependent on the precise matching of the working temperature and the input fundamental frequency optical power, the maximization of frequency multiplication efficiency can only be realized when the accurate matching of the two meets the quasi-phase matching condition, the existing regulation and control scheme for the operating point of the PPLN frequency multiplication system depends on manual regulation and experience judgment of operators, the optimal operating point of the system is difficult to quickly and accurately lock, the drifting problem of the optimal matching condition caused by the crystal thermal effect in the input power change process cannot be solved, the system is easy to operate in a non-optimal phase mismatch state for a long time, the problems of large fluctuation of the frequency multiplication light output power, low overall conversion efficiency and insufficient long-term operation stability occur, the full-automatic and high-precision optimizing and dynamic locking of the optimal operating point of the system cannot be realized, meanwhile, the PPLN crystal is used as a high-precision precise optical device and is extremely sensitive to abnormal working conditions such as over-temperature, input light power overshoot or severe fluctuation, and the like, and the abnormal working conditions are extremely easy to cause the damage of the optical end face of the crystal, the prior PPLN frequency doubling system is generally lack of comprehensive, rapid and automatic protection mechanisms, the condition monitoring and abnormal handling in the system operation process mainly depend on real-time monitoring and manual intervention of operators, serious response delay exists, timely handling of microsecond-level instantaneous power abnormal conditions cannot be achieved, the problems of incomplete protection dimension and incomplete protection logic exist, all-around monitoring and protection of various abnormal conditions in the system operation whole process cannot be achieved, permanent damage of a core optical device is easily caused by untimely and out-of-place handling of the abnormal conditions, serious equipment safety hidden danger exists, meanwhile, equipment damage risk caused by misoperation of manual parameters exists, the system operation reliability is low, the service life of the core device is short, and the use requirement of full-automatic unattended stable operation of the system cannot be met. Disclosure of Invention The invention aims to provide an intelligent control method and system for a PPLN frequency doubling system, so as to solve the problems in the background t