Research About Liquid Crystal Phased Array Wavefront Phase Correction Algorithm

Liquid crystal optical phased array(LCOPA), which is made of the photoelectric material with characteristics in terms of big phase control depth, low driving voltage, is a new kind of programmable phase modulator device. LCOPA enjoys several advantages in terms of low power consuming, light mass, and easily combined with microelectronic control circuit, and thus has been widely used in application fields of the free space optical communication, laser radar and target tracking. Since the accuracy and efficiency of the beam deflection in LCOPA are limited by the viscous resistance and the manufacturing process of liquid crystal molecules, it is valuable of theory and proactivity to improve the performance of LCOPA by designing signal processing algorithms. Therefore, focus on the problems of establishing model for controlling beam, analyzing errors, correcting wavefront phase and wave-control voltage adaptively in LCOPA, the following contributions are provided:1) To understand the characters of electronic control in LCOPA, the birefringence properties of liquid crystal are studied. Specifically, we introduced a method of measuring the birefringence of liquid crystal. The method is based on the characters of double-refraction of liquid crystal molecule and the electronic-control double-refraction of liquid crystal, and outputs the corresponding relationship between voltage code and phase delay. This method provides a useful technology of understanding the properties of voltage and phase of LCOPA.2) To analyze the birefringence properties of LCOPA, the beam-control model for LCOPA is needed. The model is used to analyze the distribution of the wavefront phase of outputting side. Based on the working mechanisms of binary blazed grating and the microwave phased array, the periodic non-continuous scanning model and the aperiodic continuous scanning model are established, respectively. The two models provide a theoretical reference to observe the phase distribution of the outputting side, and also theoretically support the design of wavefront phase correction algorithm and wave-control voltage correction algorithm.3) To improve the accuracy and efficiency of beam directing in LCOPA, the impact model of the various factors should be first established. Here, we mainly consider thevoltage measurement, the extension area; the electrode duty ratio and liquid crystal surface, and construct the corresponding model. The model clearly characters the impact of the viscous resistance and the manufacturing process of liquid crystal molecules, and also provides a theatrical foundation to further understand the limitations of LCOPA in term of hardware.4) Limited by the hardware, the accuracy and efficiency of LCOPA is now also limited. We proposed an adaptive wavefront phase correction algorithm, which is a kind of method that improves the performance of beam control in LCOPA by signal processing algorithm. The algorithm can improve the efficiency and pointing accuracy of beam at the same time, and is the key technology of enhancing the performance of LCOPA beam.5) To conquer the problem that the available phase correction algorithms have drawbacks in terms of large amount of calculation and light path complex,we proposed an adaptive wave control voltage calibration algorithm. This algorithm does not need wavefront sensing and can easily achieve the closed-loop optimization of the wave-control voltage to improve the efficiency of laser beam deflection. In addition, the amount of calculation is low, and the construction of the hardware platform is simpler.