Study On Silicon Photonics Integrated Solid-state Lidar Optical Phased Array

Since the Lidar was proposed,due to its advantages of high resolution,good directivity,and strong anti-interference ability,it has been widely applied in the fields of intelligent vehicles,intelligent transportation,unmanned aerial vehicles,smart cities,atmospheric,and environmental monitoring.The Lidar can be categorized into the solid-state Lidar and the mechanical Lidar according to whether mechanical parts are required to control the beam pointing.Compared to the traditional mechanical Lidar,the solid-state Lidar features high integration,small volume,good stability,and low cost.The solid-state Lidar has gradually become the mainstream development direction of Lidar.With the development of optoelectronic integration technology,optical phased array(OPA)solid-state Lidar has gradually attracted the attention of researchers all over the world.It combines traditional phased array radar with optoelectronic integration technology,and integrates multiple unit devices on a silicon photonic chip.It can provide,not only more flexible beam pointing,faster speed and higher precision,but also be compatible with complementary metal oxide semiconductor process technology for scale manufacture.Therefore,optical phased array has gradually become a key research topic of solid-state Lidar.In this thesis,we focus on the optical phased array technology and develop new methods to improve the far-field distribution,scanning range,main lobe power,detection distance,and other performance of optical phased array.We have deeply explored the optical phased array from theory to experiment and then to application.The main research contents are as follows:1.The theory of uniform distribution of optical phased array Lidar far-field.The far-field intensity of the laser emitted by the Flash Lidar shows the Gaussian distribution whose intensity of the edge is weaker than that of the center.It leads to the reduction or even loss of the imaging range of the detected object.To solve the issue,we propose to use the amplitude modulation method of optical phased array for realizing the uniform distribution in far-field of light for the first time.We modulate the amplitude of the OPA by the finite impulse response digital filter designed by window function theory.Consequently,the near rectangular far-field distribution of one-dimensional and two-dimensional OPA is achieved successfully.2.Research and fabrication of longitudinal large scanning range OPA.The way to improve the longitudinal scanning capability has always been a difficult problem in the OPA Lidar design.The highest modulation efficiency is only0.3 °/nm,when achieving longitudinal beam control by tuning wavelength.It is attributed to the relatively weak angular dispersion of the waveguide grating.This results in a very limited longitudinal scanning range of the OPA within the fixed wavelength range.Therefore,we propose a multi-line integrated optical phased array scheme,which integrates four OPAs on one chip.The OPAs can be selected by thermo-optic switches.This method overcomes the limitation of scanning area in limited wavelength range.We design and implement two chip structures to improve the wavelength angle tuning efficiency to 0.57 °/nm and 0.95 °/nm respectively and realized large-scale scanning with a small wavelength tuning range.3.Research and fabrication of high laser damage threshold and high power OPA.Firstly,we explore key factors that determine the main lobe power of silicon photonics OPA chips.The transmission capacity and damage threshold of Si waveguide and SiN waveguide deposited by plasma enhanced chemical vapor deposition under the condition of high input laser power were investigated and analyzed in detail.Secondly,we design and fabricate a 64-channel one-dimensional high-power optical phased array chip by utilizing the SiN with high damage threshold and the Si with high thermos-optic coefficient.We achieve wide steering of 110° by sub-wavelength spacing and avoid power crosstalk by varying the width of the waveguides.The resultant device can emit main lobe power as high as 720 m W,which is the highest value reported so far.4.Research and fabrication of wide scanning and long-distance ranging OPA.We further developed a 64-channel large-range two-dimensional optical phased array chip utilizing the SiN with high damage threshold and the Si with high thermo-optic coefficient.The beam scanning range reaches 96°×14.4° and the main lobe power is up to 690 m W.The chip embedded in the time of flight and frequency modulated continuous wave Lidar systems can be used to detect distances of 20 m and109 m,respectively.At the same time,the ranging ability of the field of view edge beam of the chip is also explored.The edge beam can also detect the distance of 14 m and 82 m in the above two systems,which proves the long-distance ranging in the full field of view of the optical phased array.In summary,this thesis mainly summarizes our studies on the design theory and key technology of the core chip of silicon-based optoelectronic integrated optical phased array Lidar.According to the different parameters of the optical phased array,we propose specific schemes to improve the far-field distribution,scanning range and main lobe power of one-dimensional and two-dimensional chips.In the end,we successfully build the Lidar ranging system using optical phased array,paving the way to practical application.