Methodology of filter-type multi-dithering phase control for quasi parallel light interference

Abstract

The quasi parallel light interference is one kind of basic ways to use the energy of interference light to interact with matter. Because the phase of each parallel light beam needs to meet the coherent condition, it is required that the phase of each light beam be controlled timely. There are some kinds of phase control methods, such as the heterodyne phase-locking method, the stochastic parallel gradient descent algorithm, the self-referred and self-synchronous phase-locking method the multi-dithering phase-locking method, etc. Among them, the multi-dithering method needs not the referenc light, it is to load multi-frequency sinusoid signals to the phase modulator, and realize the recognition of phase difference and the output of feedback voltage by multiplying circuit and integrating circuit. In view of the shortcomings of the existing methods, a scheme of filter-type multi-dithering phase control for quasi parallel light interference is proposed, in which the phase differences are identified and corrected by the modulation signals and filtering signals of different frequencies. Theoretical analysis of coherent light intensity for the scheme is made. The principle of filter-type multi-dithering phase control method is put forward, and the numerical analysis and simulation experiment for filter-type multi-dithering phase control method are carried out. In the simulation experiment, the fiber interference light path is used to simulate the light intensity of quasi parallel light interference at one point in space, and the change of photoelectric signal indicates the change of interference light intensity. The phase control feedback loop is composed of photoelectric signal amplifying circuit, bandpass filtering circuit, amplitude measuring circuit, direct current amplifying circuit and adder circuit. The results have shown that the phase difference among light beams can be recognized by the method, and the direct current voltage signal that is proportional to the phase difference of signal can be fed to control the phase modulator. The phase difference can be corrected. The control bandwidth is 2.5 kHz, and the output voltage range of phase control is 0.034.45 V. Compared with the classical multi-dithering method, the method of filter-type multi-dithering phase control has some advantages. Each multiplying circuit in the classical method needs a very small amplitude reference signal, which causes the reference signal to have a very small range of values, and the relationship between integral time and modulation period needs considering. The integral time is usually ten times longer than the modulation period, which causes the control bandwidth of the system to decrease. However, the feedback loop of the filter-type multi-dithering phase control method does not require any reference signal, so each signal does not affect each other, and the increase in the number of beams does not have a significant influence on the control bandwidth either. Therefore the filter-type multi-dithering phase control method is a useful phase-control method.