Research On Liquid Crystal Optical Phased Array Technology And Application

The phase-only liquid crystal optical phased array(LCOPA)fabricated by nematic liquid crystal material has the advantages of fast response speed,high resolution,small volume,light weight and flexible programmability,thus,it has become a frontier hot spot in the research of optical phased array in recent years.As an excellent optical device,this thesis focuses on the investigation of the technology and application of LCOPA.The main contributions of this thesis are as the following:1.To realize high precision and diffraction efficiency non-mechanical beam steering based on LCOPA,the grating lobes of the LCOPA are researched in detail,and the analytical expressions of the far-field intensity distribution for all the models are derived.Subsequently we can obtain both the locations and the intensities of the grating lobes,from which we can find that the the locations and intensities of the grating lobes are codetermined by the single slit diffraction and the multi-slit interference.The experimental results show that the binary grating models can more accurately illustrate the grating lobe formation mechanism of the LCOPA.2.To overcome the low output power of the system,the principles of coherent beam combination based on phased array of two dimensional LCOPA are investigated.The influence of the additional phase of each subarray on the coherent beam combination is analyzed in detail,and the method to achieve continuously steering of coherently combined beam is proposed.Meanwhile,based on the self-made LCOPA in the lab,we carry out experiments to demonstrate the one dimensional steering of the coherently combined beam.3.To create arbitrary vectorial optical fields,a versatile vectorial optical field generator(VOF-Gen)based on LCOPA is designed and built.The coordinate relationships among the four LCOPA sections in the VOF-Gen are derived,and the calculation formulae of the phase patterns applied to each LCOPA section are also presented.The method to realize the non-mechanical transverse precise alignment of the 4 f systems in the VOF-Gen is proposed,which effectively reduces the complexity of the optical path alignment in the VOF-Gen and increases the flexibility of the system.4.To overcome the adverse factors in the VOF-Gen that will affect the precision in creating vectorial optical field,the adaptive close loop structure of the VOF-Gen is constructed.The close loop setup can significantly improve the performance of the VOF-Gen system and broaden its applicability in a wider range of applications.The polarization modulation of the VOF-Gen is calibrated,which improve the precision of the polarization ratio and retardation modulation;meanwhile,the calibration could also reduce the mutual coupling effect between these two degrees of freedom.An iterative method to calibrate the amplitude modulation is also presented,which could converge rapidly in several steps and is effective to optimize the amplitude distribution on a pixel-by-pixel basis.5.A universal mathematical model for controlling the spin axis orientation of the diffraction limited vector field is established.Through coherently superposition of the fields radiated from the electric dipoles located at the focal point of the high numerical aperture lens,we can obtain the analytical expression of the required incident optical field in the pupil plane of the lens.Then,we employ the optimized VOF-Gen to generate several pupil fileds corresponding to focused beams with spin axis oriented at different directions,and the electric field distributions of the tightly focused fields are detailedly simulated by Richard-Wolf vector diffraction theory in the ideal and experimental cases.Meanwhile,the spin densities of the focused beams are calculated to quantitatively analyze their spin axis orientations.