Beam Optimization Method For Optical Waveguide Phased Array Coupling With Fiber

Waveguide optical phased arrays has the characteristics of low driving voltage, low power consumption and fast response(ns), etc. It is one of the important development directions of optical phased array in the future. Due to the limitation of the fabrication process of the optical waveguide array device, there are some defects in the array device(such as the inconsistent thickness and inhomogeneous refractive index of each array element waveguide core). Transmitting through the optical waveguide array, the main lobe is deviated from the theoretical position, the side lobe intensity is high, which have great influence on scanning detection. The existing optical components and information processing systems are becoming more and more integrated and miniaturized, realizing optical waveguide array and fiber integrated package, which not only improve the efficiency of laser power utilization, but also reduce the size of system and improve the stability of the system. However, there are few reports on the study of optical waveguide phased array coupling with fiber. In the thesis, the coupling characteristics between fiber and optical waveguide arrays have been investigated systematically, the quality improvement method on output beam by optical waveguide phased array have been explored, realizing high accuracy and low side lobe beam scanning, which provides theoretical and experimental guidance for the performance improvement of optical waveguide phased array.Considering the actual system of laser beams through a single-mode fiber coupled to the optical waveguide array end, the fundamental mode of the single mode optical fiber is zero-order Bessel function, the incident field can be expressed by Gauss distribution. Based on the theoretical research of conventional plane beam incident optical phased array, according to slab waveguide theory and waveguide coupling theory. We studied the relationship between the optical power and the far-field distribution with the length of the waveguide of the optical waveguide array in the light of parallel beam and Gauss beam. Simulation and analysis are made on the different distance between fiber and Optical waveguide array under the Gauss beam. Experimental study of the effects of different distance on the far field distribution. When the distance reaches a certain value, the far field distribution is identical with that of the parallel beam.We found that there are some problems, such as large deflection angle error and small scanning range, which produced by uniform waveguide array power scheme directly, since there are some defects in the device due to the waveguide array processing technology. To solve this problem, the pattern search method is optimized for the beam, and the load voltage with high diffractive efficiency and low normalized accuracy error is obtained. The simulation results show that the diffraction efficiency is obviously improved and the normalized accuracy error is improved after loading optimization voltage. The experimental results show that the loading optimization voltage to the waveguide array, beam scanning range is 20 degrees, scanning angle error is less than 5.2mrad, and the half main width of the far field(FWHM) is 2.02 degrees, main side-lobe ratio is up to 15 d B for 1064 nm pulsed laser. While for 980 nm CW laser, its scanning range is 20 degrees, but the far field FWHM is 4 degrees, this is related to the performance parameters of the semiconductor laser used in the experiment.