Design Optimization And Experimental Investigation Of Silicon-based Optical Phased Array

In the age of intelligent technology,some optical sensors represented by Lidar(Light detection and ranging)have attracted much attentions due to the rise of intelligent applications,such as driverless cars,intelligent robots,etc.For Lidar systems,rapid,precise as well as large-angle beam steering is essential during their operating process.Among beam scanning systems,the mechanical scanning systems have been gradually abandoned for some disadvantages such as slow response,high power consumption and large size.And silicon-based optical phased arrays(OPAs)has great superiorities in terms of the power consumption,integration and scanning range,making them dominant in beam scanning devices.In our work,we optimize the design of superlattice phased array based on previous research,and fabricate optical phased array devices on silicon-on-insulator(SOI)that can be used for large-angle scanning.With thermo-optic phase modulation and wavelength tuning,two-dimensional beam steering is realized in an one-demensional(1D)OPA.The main contents of our work are as follows:(1)The basic theory of optical phased array is introduced and derived in detail.In the 1D structure,the far-field pattern from the OPAs is carefully analyzed from the calculation of a radiating element.Based on these theories,the scanning characteristics of the OPAs are investigated.(2)On the basis of the coupling theory in superlattice waveguides and previous research in our group,the ultra-density superlattice antenna array is further optimized to achieve a large range of beam scanning.The simulation results show that the antenna array with a narrower pitch of 0.85 ?m can achieve a maximum beam scanning of 122°,the FWHM is 4.6° with 20 elements,and the sidelobe suppression level is above 7.7 d B.As for another dimension,the beam width of the far-field beam is reduced to 3.2° by optimizing the etching depth of the grating.Additionly,the wavelength tuning from 1.4 ?m to 1.6 ?m can make the scanning range of the beam reach 34° in another direction.(3)The phase error is estimated before designing the whole device,and it is corrected by calculating them in each waveguide.The electrodes for thermo-optic tuning of the device are designed.By simulating and testing electrodes of different materials and sizes,more reliable electrode parameters are obtained.In addition,optical phased array devices were successfully fabricated on the Optoelectronic Micro and nano Fabrication Facility.The influence of the process error is analyzed,and the corresponding solutions are given based on the experimental experience.(4)The far-field patterns of OPA were characterized by constructing the feedback optimization measured systems.Taking a 1 × 10 OPA with an antenna pitch of 0.9 ?m as an example,the beam is steered in the range of 22° × 4°(limited by measured systems)in the far field by controlling phase in waveguides and wavelength,respectively.Moreover,there is not any grating-lobes in the far-field of view during scanning process.The test results are basically consistent with the simulation results,which verifies the feasibility of the superlattice optical phased array to achieve a wide range scanning.Finally,the measurement solutions for this large-angle scanning devices are given in this paper.