Research Of Optical Phased Arrays Amplifier Stage Based On Volume Holographic Grating

Optical phased array is a new non-mechanical beam direction control technology, which has advantage of high resolution, high scanning speed, small size, strong anti-interference ability and confidentiality, etc...So it has broad application prospects in the precise control of beam and scanning field. However, the limited capacity of the beam deflection is an important factor in limiting the further development of optical phased array, which need amplification stage device to further extended scan range. In the study of the amplification stage device, amplifier based on the transmission-type volume holographic Bragg grating is one of the most viable technology, and play an important role in the development of optical phased array applications. This paper aimed at applying transmission volume holographic grating amplifier on optical phased array amplifier stage, studied some of the key issues by theoretical analysis, numerical simulation and experimental study. The main contents are as follows:The application background of transmission volume holographic grating for optical phased array amplifier stages is outlined, and research status of volume holographic grating devices are reviewed from two aspects of theoretical and experimental study, the limitations and needs of further study is pointed out.According to the number of volume holographic grating in it, angle amplifier can be divided into amplifier based on single-channel volume grating and amplifiers based on multiplexing volume grating. In this paper, in accordance with the principle of gradual and orderly progress, amplifier based on single-channel volume holographic gratings is analyzed theoretically and experimentally firstly. Kogelnik coupled-wave theory is introduced and compared with other theories. In numerical simulation, the influence regularity of structure parameters on the performance of grating is summarized systematically, the design value of the grating parameters are optimized, and error analysis and tolerance optimization were discussed. In experiments, the laws summarized from numerical simulation were verified, and recommendations of processing monomer grating are given. The results showed that:(1)parameters which affect the diffraction efficiency of grating are mainly medium thickness and refractive index modulation; parameters which have significant impacts on the angular selectivity are grating period and medium thickness;(2)grating period error and grating vector slant angle error will cause serious diffraction angle error, which can be ameliorated by reading with long wavelength, or by increasing refractive index of the space back of the gratings; to reduce the affect of grating thickness error to diffraction efficiency, we need to increase medium thickness, on the contrary, to reduce the affect of refractive index modulation error to diffraction efficiency, we need to reduce medium thickness, so it is necessary to estimate severity and control-difficulty of these two types of errors in practice, meanwhile combine with the optical phased array system’s requirements to select a compromise design scheme to determine the thickness of the media.(3)quake, beam quality and polarization will all affect the quality of making gratings, so we should take quakeproof measures, optimize beam quality and adjust polarization of two writing beams to make gratings of higher quality.Multiplexed volume holographic gratings were studied. Coupled wave theory for multiplexing volume holographic grating is derived, and compared with Kogelnik coupled-wave theory. The scope of the two theories is pointed out. The main issues existing in multiplexed grating are discussed, and three crosstalk-optimization methods are proposed, which validated and analyzed experimentally. The results showed that:(1) When the Bragg angle interval between two adjacent VHG is less than the sum of angular selectivity, multiple coupled-wave theory should be used to describe the interaction between different VHG; When the Bragg angle interval between two adjacent VHG is larger than the sum of angular selectivity, single coupled wave theory can be used to approximately simulation the diffraction conditions in multiplexer gratings.(2)Sub-peak suppression effect in multiplexer gratings is caused by the coupling-competition;(3)Increasing vector slant angle interval, reducing the grating period and increasing the thickness of the media will all reduce the crosstalk in multiplexed gratings. Increasing vector slant angle interval can reduce crosstalk directly, but will seriously reduce the angular magnification. It needs to increase several millimeters of medium to weaken crosstalk, but this will not affect the angular magnification. Reducing the grating period of adjacent VHG will make the Bragg angle position stagger and reduce crosstalk, and has little effect on the magnification, so it is the best solution to reduce crosstalk. In fact, we can combine with these crosstalk optimizing methods to get a better amplifier.