Research On Gratings For Polarization Control Of Vertical Cavity Surface Emitting Lasers

Vertical cavity surface emitting lasers（VCSEL）were introduced in the late 1970s.Compared with edge-emitting lasers（EELs）,they have the advantages of small size,low power consumption,good beam quality,and ease of use.Integration and other advantages,are widely used in semiconductor lasers,optical communications,and sensing and other fields.However,due to the large lateral size and circular symmetry of the VCSEL,the polarization state of the output laser is unstable.Therefore,the stable control of its polarization state has become a research hotspot in the field of semiconductor lasers.At present,the main methods to solve the polarization instability of VCSELs are preparation of external cavity feedback structures,semiconductor dielectric gratings,surface relief structures,etc.Among them,the most popular one is to fabricate periodic grating structures on the light exit port of the VCSEL surface.The preparation of the structure usually adopts electron beam exposure technology,nano-imprint technology,micro-contact lithography technology and holographic lithography technology.However,these preparation methods are not only costly,but also time-consuming,making it difficult to achieve mass production.Therefore,economical,time-saving and reliable fabrication of VCSEL surface dielectric grating technology has become a key technology that needs to be broken through in this field.This thesis focuses on the polarization control of VCSEL.First,the gratings are fabricated by using the Telbert shift lithography exposure technique,and then the surface dielectric grating VCSEL are fabricated.Spectral and polarization tests are performed on the surface grating VCSELs to obtain the polarization suppression ratio of the VCSELs.The main innovations of the paper are as follows:1.A method of fabricating periodic gratings on Ga As substrates using Talbert shift lithography exposure technology is proposed,and the effects of process parameters and anti-reflection layers on the quality of the gratings are studied.First,a circular hole array periodic grating is fabricated on a Ga As substrate by a secondary photolithography process and a reactive ion etching process.Then,uniform gratings are fabricated by inductively coupled plasma etching equipment.The experimental results show that the dynamic tunable circular hole array periodic grating with a depth of 20-150 nm can be prepared by this process.When the exposure dose is 30 m J cm^-2,the exposure light intensity is 2 m W cm^-2,and the development time is 1 min.The exposed periodic grating meets the experimental requirements.2.A surface grating VCSEL with a center wavelength of 894 nm,a period of 300 nm,a duty ratio of 0.5,and an etching depth of 60 nm was successfully fabricated by the process of preparing a circular hole array periodic grating on a Ga As substrate.At the same time,the prepared surface grating VCSEL was subjected to spectral test,and the measured polarization suppression ratio was 14 d B.3.Ga As/Al_xO_y HCG with polarization selective properties is designed and applied to VCSEL.A three-dimensional HCG-VCSEL simulation model is created,and the mode,loss,tolerance and other characteristics of HCG-VCSEL are analyzed.On this basis,the selective wet etching of Al_xGa_1-xAs materials is experimentally studied,the experimental results are analyzed,and an improved experimental scheme is proposed.The main research achievements of this paper are the fabrication of periodic gratings on Ga As substrates and surface grating VCSELs on the prepared gratings,as well as research on tunable HCG-VCSEL.The successful preparation of periodic grating and the test of surface grating VCSEL show that the Telbert shift lithography exposure technology has unique advantages in the processing of micro-nano devices,and plays an important role in the application and development of VCSEL.The initial research on tunable HCG-VCSEL provides an important basis for the next preparation of the device.