Model Building Of Acousto-Optic Modulator And Design Of Laser Power Control System For Laser Direct Writing

Laser direct writing technology is the main method of production of the binary optical mask and BOE. The control of the laser output power for binary optical device processing is very important, it is required that the laser output power is very stable, however, for many external factors, the laser output power will have the drift. This will affect the fine graphic quality on the photoresist directly, thereby, it will affect the diffraction efficiency of the binary optical device ultimately. on the one hand, while at the same speed at different radius of the ring brought to exposal, along with the increase of the diameter of the exposure clitellum, the exposure received on unit area of the photoresist in unit time will decrease, on the other hand, the output power of the laser used in the system have great fluctuations, the baseline also will drift. Therefore, for processing the lineation with the same width and depth on the substrate, we must control the laser output power so that the power is constant and continuously adjustable.In this thesis, we use the acousto-optic cell to control the He-Cd laser output power, design the appropriate controlling parameter by the simulate environment, in order to get the beam intensity control circuit with high stability. The main tasks in details are following:1. Analyze the operating principle of the acousto-optic cell, for getting the anticipated effect of the control system, the mathematical model of the acousto-optic cell is identified in MATLAB in order to get the transfer function of the acousto-optic cell.2. With the transfer function of acousto-optic modulator model which has been identified, we design the control system simulation model by using SIMULINK toolbox, in order to get the appropriate control system, use the PID controller which is widely used and tuning the parameters of the controller.3. The DSP core detection and control circuit is designed and used, which can realize accept the signal which is from photoelectric conversion circuit, sampling, filter, A/D conversion, disposal, operation (the PID arithmetic), D/A conversion through the output from the photoelectric detecting circuit.4. Analyze the performance of each unit in the control system, measure and contrast the laser intensity before and after being controlled, analyze the factors which affect the stability of the laser output power by the time, and adjust the controller parameters to improve precision.