Research On Vertical Cavity Surface Emitting Lasers For Atomic Clocks

Vertical Cavity Surface Emitting Lasers(VCSELs)have experienced rapid development since their first appearance in 1978.It has many advantages that traditional edge-emitting lasers are difficult to match,such as: small sizes,low threshold current,high conversion efficiency,good longitudinal mode uniformity,round output spot,on-chip testing of the chip,and easy integration into large area arrays and so on.Based on these advantages,VCSELs have rapidly occupied the semiconductor laser market in recent years,and have played an important role in the fields of optical communication,sensing,and storage.The atomic clock is an advanced timing device with an accuracy of 1 second per20 million years.It is widely used in global navigation systems.Atomic clock sensors rely on spectroscopic analysis of alkali atoms(rubidium or cesium),which are present in small steam chambers.The corresponding spectral wavelengths of cesium are894.6 nm(D1)and 852.3 nm(D2),and the spectral wavelengths of rubidium are795.0 nm(D1)and 780.2 nm(D2).VCSELs have the characteristics of low power consumption and circular output beam,making them the first choice of the light source of the atomic clock.In order to improve the accuracy and stability of the atomic clock sensor,the VCSEL light source must have the characteristics of a single longitudinal mode corresponding to the spectral wavelengths of alkali atoms,a narrow spectral linewidth,a fundamental transverse mode,and stable linear polarization.However,the traditional structure of VCSEL is affected by its structure and the manufacturing process,it is difficult to fully meet the above characteristics,which has an adverse effect on the application of atomic clocks.Taking the 795 nm VCSEL as an example,a research of the VCSEL is carried out for the above problems in this thesis.The content of this thesis is summarized as follows: The development history,basic knowledge of VCSEL,and the current research status of VCSEL for atomic clocks at home and abroad are briefly introduced in Chapter 1.The related theories of VCSEL’s photoelectric characteristics,mode characteristics,thermal characteristics,and polarization characteristics are analyzed in detail in Chapter 2.In Chapter 3,the material system and structural parameters of the795 nm VCSEL are determined using PICS3 D simulation software.In order toimprove the output mode characteristics of VCSEL and obtain narrow spectral linewidth,we innovatively designed a concentric ring grating structure for 795 nm VCSEL,and obtained the optimized parameters through software simulation.At the same time,a surface polarization control strip grating for 795 nm VCSEL was designed and simulated to achieve stable linear polarization output.In Chapter 4,the manufacturing process of VCSEL is introduced,and the device is tested and analyzed using related testing equipment.The results show that the concentric ring grating structure can make the VCSEL realize the fundamental transverse mode output,and the spectral linewidth is reduced from 0.5 nm to 0.2 nm.The surface polarization control strip grating makes the orthogonal polarization suppression ratio(OPSR)of the laser reach 25.8 d B,and realizes a stable linear polarization output.In the last chapter,the research content and results are summarized and the future research direction is clear.