Research On The Characteristics Of Novel Subwavelength Gratings And Its Application In Photodetectors

Under the general trend of today’s information age,the rapid development of optical communication systems has put forward higher requirements for the performance of optoelectronic devices,which promotes the development of optoelectronic devices toward the goal of high performance,small size,and easy to integrate.High contrast subwavelength grating（HCSG）has the advantages of small size,strong function and high diffraction efficiency,which is of great significance to promote the development of multi-functional integrated devices.This paper innovatively proposes to use wet oxidation process to realize the HCSG with Al_0.9Ga_0.1As and Al₂O₃alternately arranged.Based on the rigorous coupled wave analysis theory method and the finite element theory method,the design and optimization are carried out.Through the simulation and selection of main structural parameters,a new type of HCSG with polarization beam splitting,power beam splitting and reflection functions is realized,and the new HCSG mirror is integrated with a photodetector.A high-performance resonant cavity-enhanced photodetector（Resonant Cavity-enhanced Photodetector,RCE PD）is realized.The main research content and research results of this paper are as follows:1.A novel Al_0.9Ga_0.1As/Al₂O₃HCSG is proposed,which is composed of Al_0.9Ga_0.1As and Al₂O₃alternately arranged.The grating structure is analyzed and designed based on the theoretical method of strict coupled wave analysis and finite element theory,and the functions of polarization beam splitting and power beam splitting are realized respectively.The polarizing beam splitter has a reflectivity of more than 95%for TE mode polarized light in the wide spectral range of 800-880nm,and a transmittance of more than 96%for TM mode polarized light.At 850nm wavelength,the polarization extinction ratio can reach41.37d B.In addition,has an 8°angle tolerance to incident light,and has a 20nm process tolerance.Under the condition of 850nm wavelength TM mode polarized light incident on the power beam splitter,the power efficiency of the 4-channel splitting from left to right and the incident light are 21.05%,19.36%,19.32%,21.01%,and the overall transmittance can reach 81%,has a good 1×4 beam splitting effect.2.A RCE PD based on Al_0.9Ga_0.1As/Al₂O₃HCSG is proposed.The Al_0.9Ga_0.1As/Al₂O₃HCSG is designed as a reflector.The structure is polarization-insensitive,with a reflectivity of 99.8%for TE mode polarized light and 99.1%for TM mode polarized light.The reflector is integrated with a PIN photodetector to realize RCE PD,and the overall device is simulated based on the transfer matrix theory method and numerical calculation method.The simulation results show that the quantum efficiency of the RCE PD reaches 90.6%,the full width at half maximum is close to 0.2nm,and the bandwidth of the structure can reach34.54GHz when the reverse bias voltage is 3V and the optical power of the light source is1m W,the bandwidth efficiency product is 31.3GHz.