Research On Acousto-optic Deflector In Optical Signal Processing

Because acousto-optic deflector has low power, concentrated energy, wide bandwidth, good real-time and so on, it is widely used in many fields, such as laser scanning, radar and laser detection, and achieves unprecedented result. In the military field acousto-optic deflection technique plays a major role. It can effectively realize radar warning through changes of frequency and become a significant technique in the electronic counter. In the optical signal processing applications, acousto-optic deflector can complete fast and accurate beam deflection, and inhibit noise and spot diffusion. So it is conducive to signal processing in back-end and improvement of SNR. Therefore, in paper, according to the demand for detecting weak signal in the modern radar field, the mechanism of suppressing noise is discussed. And coherent detection acousto-optic receiver is built to solve the improvement of SNR and frequency resolution and achieve the optical signal processing in communications.The core component of the system——acousto-optic deflector is the focus of this article. In paper, the features of acousto-optic deflector are analyzed and researched. In the theoretical analysis, it is composed of three parts as follows: (i) The basic theory: From the viewpoint of parametric interaction, coupling equation, acousto-optic diffraction efficiency and Bragg diffraction bandwidth are derived; (ii) Frequency measurement principle of acousto-optic deflector: Single-frequency acousto-optic diffraction and multi-frequency acousto-optic diffraction are studied. In the meanwhile, the method of undermining intermodulation interference is proposed by study and simulation of intermodulation phenomenon in multi-frequency acousto-optic diffraction; (iii) Filtering characteristic of acousto-optic deflector: On the basis of the mechanism of acousto-optic deflector——the establishment of volume grating, filtering characteristic is analyzed and studied.In the experimental demonstration of multi-frequency detection and filtering characteristic of acousto-optic deflector, test platform of coherent detection acousto-optic system is constructed. Through observing changes of spectrum and spot, measure of weakening intermodulation is demonstrated. Furthermore, filtering characteristic is also proved by experiment from two aspects. (i) Filtering characteristic is testified by observation of diffraction intensity when signal and noise are added to the deflector; (ii) By observing system instantaneous bandwidth, frequency resolution and SNR, filtering characteristic is proved.