低纹波超辐射发光二极管的增透膜研制

Abstract

Objective The ripple index is one of the most crucial parameters of superluminescent diodes (SLDs). A low ripple index is necessary for the application of SLDs in sensing areas such as fiberoptic gyroscopes. Therefore, reduced reflectivity of the facet is required, and the main strategy involves coating with antireflective (AR) films. The reflectivity of the AR films is generally less than 0.1%, which is a strict requirement. Although the AR film designed using the plane wave method (PWM) is widely used, its performance in SLDs is not ideal, and the actual reflectivity deviates from the design value. Therefore, the purpose of this study is to design and fabricate AR films for SLDs that can effectively reduce the ripple index.Methods The first part is the simulation method. The finite difference time domain (FDTD) method is used to analyze the optical properties of the films, and a perfect matching layer (PML) is used as the boundary condition. In addition, to reduce the resource requirements of the FDTD method, a simplified simulation model is used, which highlights the main influencing factors. To optimize the films, parameters such as film thickness and refractive index are scanned by FDTD method to determine the parameter range of low reflectivity, and the particle swarm algorithm is used to obtain the optimal parameters within this range. For the coating process, the optical film is manufactured by reactive magnetron sputtering, and an AR ion beam assists the coating process. In addition, the film thickness is monitored and controlled online using a crystal oscillator control system . Reflectivity measurement of thin films is important, including direct measurement of the accompanying films and indirect measurement of the facet of the SLD . The SLD is indirectly measured by spectral ripple, which is also the mainstream reflectivity measurement method for other semiconductor optoelectronic devices. Results and DiscussionsThe simulation results show that the design of the PWM film faces many problems. For the singlelayer and doublelayer AR films, the reflection curve becomes blueshifted, and the shift exceeds 150 nm. In addition, the reflectivity is more than one order of magnitude higher than the designed value, and the deviation is further enlarged at a large angle. Therefore, the AR film designed by PWM does not meet the requirements and cannot be used for SLD. To solve these issues, the optical film is optimized. For singlelayer AR films, the average reflectivity is less than 0.11% and the lowest reflectivity is 0.04%. The optimized design of the doublelayer film provides better results: the average reflectivity is less than 0.05% and the lowest reflectivity is only 0.01%. The optimized design effectively reduces the reflectivity, particularly for the optimized doublelayer AR film, which has evident advantages over the film designed by PWM .The doublelayer AR films are prepared by reactive magnetron sputtering. After optimization, the reflectivity of the AR film on the companion substrate is 0.12%, and the ...