Study On Ultra-Low Grating Lobe Optical Phased Array Based On Array Optimization

Laser scanning technology has wide applications in laser radar,free-space optical communication,holographic imaging and biomedical imaging,etc.Optical phased array(OPA)is a new promising beam steering method,which can implement agile beam steering without moving or rotating the facilities.However,limited by the state-of-the-art fabrication levels,the realizable element interval of current OPA is much larger than half of the optical wavelength,which results in the formation of many grating lobes in the far-field.The existence of large grating lobes would not only degrade the quality of beam forming but also limit the beam scanning range.Thus,to achieve a wide-range optical beam steering applying an OPA,it is highly required to eliminate or reduce the effect of the grating lobes.In this paper,the research of grating lobe suppression of OPA is based on unequally-spaced technique by using a modified genetic algorithm.The theory of OPA is introduced in detail.In order to achieve ideal grating lobe suppression,the modified genetic algorithm is applied to optimize the element distribution of the unequally-spaced OPAs.And the multi-order interference imaging suppression of OPAs is further investigated.The main research contents include the following three aspects:1.The element distributions of one-dimensional and rectangular unequally-spaced OPAs are optimized by using a modified genetic algorithm to achieve a minimum peak side-lobe level(PSLL).Numerical simulations of one-dimensional and rectangular OPAs are carried out.The results show that compared with the conventional unequally-spaced OPAs,by optimizing the element distribution in an unequally-spaced OPA using the modified genetic algorithm,the grating lobes and side lobes can be better suppressed.2.A multi-circular OPA is proposed and investigated through simulation to realize fast and wide-range optical beam steering with ultra-low side lobes.By optimizing the element distribution of the multi-circular OPA by a modified genetic algorithm,the grating lobes can be well suppressed.The prominent feature of the proposed OPA is that,once the OPA is optimized towards a specific elevation direction by the modified genetic algorithm,a wide-angle optical beam steering with nearly the same side lobe suppression can be achieved without updating the OPA distribution,which makes it possible for fast optical beam steering over a wide scanning range.3.The suppression of multi-order interference imaging of unequally-spaced OPAs with random element distribution is studied.The phase distribution of the OPA is recovered based on the modified GS(Gerchberg-Saxton)algorithm.Furthermore,the feasibility of multi-order imaging suppression based on unequally-spaced OPAs with random element distribution is verified.