[0023] The present invention will be further described below with reference to the accompanying drawings and specific methods.
[0024] The present invention proposes a new set of laser steady power systems based on the NI CompactRIO system. The COMPACTRIO system runs a 1.33 GHz dual-core processor with a Linux RT system, and is equipped with programmable FPGA chips. Therefore, each input / output module of the system is directly connected to the FPGA chip, rather than through a bus connection, so CompactRIO system responds almost no delay compared to other controller architecture.
[0025] In addition, the LabVIEWFPGA software mounted in CompactRIO has a better graphical interaction interface, which can process and display graphics in real time, while the system also has 2GB DRAM and 4GB storage space. It is very suitable for processing and storage of real-time data.
[0026] In order to improve the response speed of the liquid crystal, the present invention employs the TNE (Transient Nematic Effect, transient "driving technology, which can effectively improve the liquid crystal response speed. When the liquid crystal phase delay needs to increase, the liquid crystal voltage is temporarily revoked, and the liquid crystal molecules experience natural relaxation of a period of time and begins to return to the initial position, and then apply an appropriate size drive voltage to maintain the desired phase delay.
[0027] Such as figure 1 As shown, a laser power stabilizing system based on FPGA and liquid crystal TNE effects, including the following modules: laser, isolator, two two-half waves (λ / 2), three polarization beam splitter PBS, Liquid crystal phase retarder (liquid crystal), two photodetector PD, CompactRIO system. The CompactRIO system includes analog output module Ni-9269, FPGA computing module CRIO-9055 and analog input module Ni-9239.
[0028] The optical path is completed, and the 795 nmdbr laser exit light passes through the isolator, and the isolator prevents light feedback. Thereafter, the combination of the λ / 2 wave plate and the polarization beam splitter PBS can then be subjected to the intensity of the transmitted light. Transmitted light sequentially passes through the liquid crystal phase delay and PBS, and the two constitute an actuator, which can realize the controllable attenuation of optical power. After the actuator and the CompactRIO system, the combination of the λ / 2 wave plate and the polarization beam splitter PBS is sequentially subjected to the combination of the λ / 2 wave plate and the polarization beam splitter; the two beams are collected by the photodetector PD1 and PD2. The photoelectric signal corresponding to the inner light of the PD1 is used for closed loop computing and control; the PD2 is only used to monitor the photobilization of the loop, not for calculation.
[0029] The photoelectric detector PD1 outputs a voltage signal corresponding to the inner light, converted into a digital signal by analog input module Ni-9239, and inputs the FPGA calculation module CRIO-9055, and the FPGA calculation module CRIO-9055 corresponds to the voltage signal and setting corresponding to the ring light. The voltage value corresponding to the laser power, outputs the drive square. Finally, the drive square wave is converted into an analog signal by analog output module Ni-9269, loaded into the liquid crystal phase delay of the actuator.
[0030] In the FPGA calculation module CRIO-9055, when the voltage signal of the ring light is smaller than the voltage value corresponding to the set power, the closed-loop control operation is performed by the PID algorithm, and the amplitude Vout of the drive square wave is calculated to reduce the liquid crystal phase delay. The phase delay of the unit, thereby increasing the laser power of the actuator, increasing the voltage signal corresponding to the ring light. The digital signal is converted to a set frequency + Vout / -Vout square wave as a drive square wave using the hardware timing in the FPGA computing module CRIO-9055. The frequency of the drive square is determined by the liquid crystal phase retarder.
[0031] When the voltage signal of the ring light is greater than the voltage value corresponding to the set power, in order to increase the phase delay of the liquid crystal phase retarder, the voltage signal corresponding to the laser power passed through the actuator is reduced. The magnitude VOUT of the drive square wave is calculated by the PID algorithm; the digital signal is converted to the set frequency + VOUT / -VOUT wave. In order to further enhance the reaction speed at which the liquid crystal phase retarder is increasing the phase delay, the driving square based on TNE effect is generated. In front of this + Vout / -vout square wave before the current PID cycle, add a section of the US-level zero signal, and finally get a driver wave. Among them, the duration of each driver wave depends on the cycle speed of the PID controller, which is a variant, usually about 125us.
[0032] Specifically, the right hand coordinate system is established, the angle between the PBS light transmitting shaft and the X direction is 0 °, the angle between the liquid crystal fast shaft and the X direction is 45 ° (the angle of the liquid crystal slow axis and the X direction is 135 °); Liquid Crystal Phase delay is δ ( V ), Related to the bipolar square wavelength value V, the empirical formula is:
[0033]
[0034] in, V c It is the threshold voltage that the liquid crystal molecules begin to deflect, and can be obtained by experiments; m is an empirical value, V 0 Is a constant, m and V 0 Unlike the wavelength. After the liquid crystal phase delay is determined, the laser light source scaling data can be utilized to fit the M and V 0; δ 0 The maximum phase delay amount of the liquid crystal.
[0035] The Jones matrix in the liquid crystal phase delay, the PBS transmission direction, the λ / 2 wave plate, and the PBS reflection direction are: , , ,. in, θ The angle of the λ / 2 wave plate and the angle of the X direction. i Indicate.
[0036] Transmitted light / loop outside Jones vector E 1 for:
[0037]
[0038] Among them, the Jones vector defined in the liquid crystal front incident light is , A is the electric field vector amplitude.
[0039] Light / ring light of light intensity I 1 for:
[0040]
[0041] Among them, e 1 * E 1 Conjugate matrix.
[0042] Reflective light / ring inner light Jones Vector e 2 for:
[0043]
[0044] Reflected light / ring inner light intensity I 2 for:
[0045]
[0046] Among them, e 2 * E 2 Conjugate matrix.
[0047] LCD laser Jones vector.
[0048] Laser after the actuator, the Jones vector.
[0049] Such as figure 2 As shown, as the voltage applied to the liquid crystal is increased, the liquid crystal phase delay amount δ ( V ) Gradually decrease, the optical function after the actuator is first reduced, and the increase in voltage divisions of the laser transmittance change amplitude and the speed of the response speed are used as the control section. Among them, e s Λ / 2 wave chips slow axis, E f It is a λ / 2 wave plate quick axis.
[0050] The liquid crystal response time is related to the direction of the voltage variation. When the voltage is reduced, the liquid crystal response time depends on the relaxation time of the liquid crystal molecules returns to the initial position, so the liquid crystal response speed is slow. The present invention utilizes TNE (TransientNematic Effect, transient angular effect) driving technology to improve liquid crystal response speed. When the liquid crystal phase delay needs to increase, the liquid crystal voltage is temporarily revoked, and the liquid crystal molecules experience the natural relaxation of a period of time and begins to return to the initial position, and then apply the driving voltage of the appropriate size (VOUT) to maintain the desired phase delay. When the voltage is increased, the response speed of the liquid crystal is faster, so the drive signal is not optimized.
[0051] image 3 and Figure 4 The horizontal coordinate is 80ms, and the left value coordinate system is the value returned by the photodetector, and the square wave coordinate system is not in the figure. Such as image 3 As shown, the driving square wavelength value is changed to 8Vpp → 6Vpp → 8VPP, and when the drive furnitier is reduced, the liquid crystal response reaches the steady state time to X2-x1 = 11.8 ms. Such as Figure 4 As shown, when the TNE effect of the liquid crystal is used based on the present invention, the driving square wave unit value is changed to 8Vpp → 6Vpp → 8VPP, the drive furniture range is reduced, and the time required for the liquid crystal response to the steady state shortened to X2-x1 = 1.3 MS.
[0052] The present invention utilizes the COMPACTRIO system to perform algorithm designs, using the FPGA chip to generate a TNE-based square wave, ie, a section of the US-level zero signal is added to each square wave, and no external waveform occurs. Such as Figure 5 As shown, the system of the present invention is superior to the power stabilization system based on STM 32, and thus the present invention improves the control rate and high frequency response capability.
[0053] The present invention is not limited to the above-described embodiment, and the same manner as in the above-described embodiments of the present invention is employed, and all other embodiments obtained in the preparation of creative labor without creative labor premises. Within the range.
