Laser stabilization systems can be used to counteract or correct optical path changes caused by external vibrations or other factors, which plays a vital role in imaging, optical communication and other applications. The most common approach is to use electrical feedback loops, such as the PI or PID type. Electro-optical modulator can be used to control power, and the servo system bandwidth is very high. Reasonable design of feedback circuit is very important to achieve effective noise suppression in a large bandwidth range.
In order to stabilize the laser in the process of transmission, CoreMorrow uses the piezo tilt stage to build a first-order and second-order laser stabilization system. The laser stabilization system is a piezo laser deflection stabilization system which uses an external PSD position detector to close the loop. The target position coordinates of the beam receiving are set in advance. The light source reaches the PSD position detector after interfering with the piezo tilt stage and compensating the reflection. The interference piezo tilt stage is to simulate the external interference.
The suitable system can be selected according to the different light source. The first-order laser stabilization system is suitable for positioning, and the second-order laser stabilization system is suitable for orientation. For example, parallel light can be stabilized by a first-order laser system. However, due to the deviation of the spot position of the point light source, additional position correction is required, which requires a second-order laser stabilization system to adjust. The two system structures are shown as follows.
In the schematic diagram above, how does the piezo controller realize the closed-loop control to compensate the optical path deviation?
Closed-loop Control Process
In the laser stabilization system, the closed-loop control is accomplished by CoreMorrow piezo controller coupled with an external PSD position detector module.
For the external PSD position detector and 0~10V target control signal, the remaining parts are CoreMorrow piezo tilt stage and piezo controller system.
In the system, the piezo tilt stage is the actuator, which controls the deflection direction of the reflector lens, namely the direction of the optical path. The piezo controller is a closed-loop control and voltage output source. The function of the piezo controller is shown in the light green box on the left.
The laser stabilization system has two important signals, the control signal and the sensing feedback signal, which are processed in the servo module (including comparison and adaptive adjustment). The processed signals are output through the drive module for power amplification (including voltage and current amplification) and applied to the piezo tilt stage, so that the piezo tilt stage can be driven for deflection. At the same time, the deflection of the piezo tilt stage changes the optical path, so that the feedback signal of the PSD sensor also changes accordingly. The feedback signal is collected, processed, and entered into the servo module, and is compared with the target signal. According to the difference value, the control signal is adjusted. The control signal then adjusts the output voltage, so that the voltage applied to the piezo tilt stage changes, thus changing the steering of the piezo tilt stage and the optical path... Proceed to the next cycle, and so on, stabilizing the final position of the laser at the target position.
Function of Piezo Controller
The closed-loop principle of the laser-stabilized system can be explained in detail by the function of the piezo controller, as outlined below:
1)Power Amplification
The driving voltage of the piezo tilt stage is generally 0~120V or 150V, while the control input voltage is usually small, such as 0~10V or 0~5V, so it is necessary to amplify the control input voltage to meet the requirements of the piezo stage driving. Through the power amplification of piezo controller, the input target control analog signal is amplified and output.
Note: The target control signal is generally 0~10V, and can also be set to other ranges, please confirm with your sales when purchasing.
2)Collection, Processing and Comparison of Sensing Signals
The optical power signal received by the PSD detector changes with the steering adjustment of the piezo tilt stage. The piezo controller will collect, process and compare the voltage signal returned by the PSD position detector, and servo adjust the corresponding deviation signal, and amplify the output to the piezo tilt stage, so as to change the deflection direction of the piezo tilt stage.
All the above is the general process of CoreMorrow laser stabilization system. The PSD position detector can detect the spot of the beam in real time and feed back to the compensating piezo controller. The compensating piezo controller can collect, process and amplify the sensor signal fed back by the PSD position detector, and output the corresponding compensating control voltage signal to the compensating piezo tilt stage. The compensating piezo tilt stage then adjust the angle quickly according to the compensated control voltage signal, so that the optical signal can be received accurately and completely, so as to achieve the purpose of imaging or optical communication.
The Difference Between Piezo Tilt Stage Built-in Sensor and External PSD Closed-loop
faster response speed and higher resolution, so the external PSD position detector can improve the speed of beam adjustment. In addition, PSD can directly measure the position of light spot, which is a direct reaction to the direction of beam deflection. The closed-loop version of the piezo tilt stage with built-in sensor is characterized by a linear relationship between the control voltage and the deflection angle, which can ensure that the actual deflection angle of the piezo tilt stage is consistent with the expected control adjustment of the deflection angle. The beam tracking and stabilization can be observed through the computer display.
In this system, when the compensating piezo tilt stage is turned on, the position detector displays the effect as shown in the figure on the left below. There is a deviation between the spot and the target position; After starting the compensating piezo tilt stage, it can be intuitively seen from the software that the light spot is stable at the preset target position, as shown in the figure below.
Conclusion
The compensation control of piezo deflection system makes the transmission of light more accurate and stable. One of the most important factors is that the piezo tilt stage has ultra-high deflection accuracy and ultra-fast deflection speed. CoreMorrow P33.T2K piezo tilt stage and E70.D3S piezo controller provide the nanoradian level deflection accuracy and the deflection response speed up to millisecond or even sub-millisecond, which play a decisive role in the whole laser stabilization process.