Study Of Large-Scale In-Phased Vertical Cavity Surface Emitting Laser Array And Integrated Phase-Controlled Beam Steering Chip

Beam steering devices are widely used in both military and civil fields.With the development of modern photoelectric system towards integration,portability and low power consumption,the ultimate goal of the beam steering devices is to reduce their size,weight and power consumption.Nonmechanical beam steering devices have the advantages of fast response and high reliability due to the use of electrically controlled optical phased array to realize beam steering,so they have been developed rapidly and become the mainstream beam steering technology.However,in these nonmechanical beam steering devices,the coherent light generated by the laser source has to pass through optical system,optical fiber or waveguide,and then incident into the spatial optical phased array.The separation of the three parts results in complex packaging,difficulty in miniaturization,and low coupling efficiency between the laser source and the optical phased array.Therefore,the integration of optical phased array and laser source is an important development direction to solve these problems,which puts forward special requirements on the structure and performance of the laser source.Vertical cavity surface emitting laser(VCSEL)has the characteristics of plane structure and vertical emission,so it is very suitable to integrate optical phased array on its surface.Although a single VCSEL with small aperture can obtain coherent light,its output power is low,and it is difficult to integrate optical phased array on its surface due to its small area.By increasing the aperture of the single VCSEL,high power can be obtained,but its near-field is very uneven,and the optical intensity incident into each element of the optical phased array is nonuniform,resulting in ineffective operation of optical phased array.The advanced fabrication technology of VCSELs makes them easy to form a large-scale two-dimensional VCSEL array with uniform near-field.But for the conventional VCSEL array,the laser beams emitted from each array element are incoherent,integrating optical phased array with these arrays can not achieve beam steering.In this dissertation,a miniaturized laser beam steering chip is proposed.Protonimplant-defined in-phase coherently coupled VCSEL array is used as a coherent laser source with large area and uniform near-field,and then is integrated with transmitted optical phased array by conventional technology.The in-phased VCSEL array provides a coherent laser source with stable power and wavelength,and the optical phased array controls the beam propagation direction.Each element of the two parts corresponds to each other one by one,without optical system,optical fiber or waveguide,so as to form a micro,high coupling-efficiency,and simple-structure integrated phased control beam steering chip.In this dissertation,the working mechanism,structure design,fabrication and characterization of large-scale two-dimensional proton-implant-defined in-phased VCSEL array and integrated beam steering chip are systematically studied under the support of the Nation Natural Foundation of China.The problems of small scale,low output power and low beam quality of the proton-implant-defined in-phased VCSEL array are solved.Large-scale high-beam-quality in-phase coupled VCSEL arrays with uniform near-field are realized.The key technical bottlenecks of the integration technology and preparation process of the liquid crystal optical phased array and VCSEL array are broken through,and micro phased controlled beam steering chip is realized.The main research works are as follows:1.Coupling mechanism,structure design,fabrication and uniform near-field realization of large-scale and high beam quality implant-defined in-phased VCSEL arraysTraditional coherent VCSEL arrays often use ring electrode,which face current spreading problem.The high lateral resistance introduced by the implant damage near the array surface can prevent the injected current spreading to the array centre,which leads to more severe current spreading problem,restricting the array scale below 3×3.Metal grid electrode can be used to solve the current spreading problem,but the out-ofphase mode tends to be dominant in the array,and the optical energy is dispersed on four lobes in the far-field field.Through reasonable design of the array structure and proton implant parameters,even if metal grid electrode is used,in-phase mode can still be obtained.By engineering the array structure and implant depth,large-scale square10×10 in-phased VCSEL array with divergence lower than 1.89 degrees and output power higher than 10 m W.And 127-element in-phased VCSEL array with divergence angle less than 1.76 degrees and output power for the in-phase mode of 13 m W are realized,of which the in-phase mode can be maintained from threshold to maximum output pouwer.This lays a foundation for the development of micro integrated phase controlled beam steering chip based on in-phase coupled VCSEL array and liquid crystal optical phased array.2.Study on the optical coupling phenomenon and the influence of nonuniform near-field on far-field characteristics of in-phase coupled VCSEL arrayOptical coupling phenomenon in two-dimensional implant-defined coherently coupled VCSEL arrays are studied via both experiments and theoretical calculations.The effects of optical coupling on the output power,lasing mode,threshold and lasing spectrum of the array are studied.The optical coupling phenomenon is analyzed by using effective refractive index model.Besides,a two-dimensional in-phased VCSEL array model is established by finitedifference time-domain method,and the influence of nonuniformity on the far-field characteristics of the array is simulated and analyzed.On the other hand,an addressable in-phased VCSEL array is designed and fabricated.The influence of nonuniform nearfield on the far-field characteristics of the array is studied and discussed experimentally,and the measures to solve the nonuniformity are proposed,which provides an alternative method for the preparation of large-scale high beam quality in-phased VCSEL array.3.Establishment and analysis of theoretical model of the beam steering chipThe beam steering model and theory of optical phased array are analyzed,and the influence of phase difference,incident wavelength,element size,inter-element spacing and other parameters on the beam steering range is studied in theory.The phase shiftvoltage characteristic of liquid crystal optical phased array is calculated according to the elastic deformation theory of liquid crystal,which provides the theory guidance and basis for the design and preparation of integrated phase-controlled beam steering chip.4.Structure design,integration technology and characterization of the beam steering chipThe designed and fabricated in-phased VCSEL arrays are used as large-area coherent light source with uniform near-field.Taking the advantages of plane structure and vertical emission,the transmitted liquid crystal optical phased array is directly integrated on the VCSEL array's surface,so that forming the micro integrated beam steering chip.The structure design,integration technology and characterization technology of the integrated chip are studied.The key process problems such as phased array wiring and uneven box thickness are solved.The influence of different VCSEL array structures on the steering angle of the integrated chip is analyzed and discussed.One-dimensional integrated beam steering chip with a steering range of 6.06 degrees is achieved,and the power stability and wavelength stability are excellent during steering.