Integrated optical and MEMS based design process for a variable optical attenuator

摘要

This paper presents the design, fabrication and characterization of a Variable Optical Attenuator (VOA). The VOA is based on a device known as the Mechanical Anti-reflection Switch (MARS) that has been well studied for modulation applications. Therefore, the requirements of the MEMS device need to be freshly ascertained and are done so in this paper taking the optical and MEMS parameters into account. In addition, the effect of the MEMS parameters on the optical ones and vise versa were also exploited in the design process. A good VOA should have a linear variation of attenuation with voltage and a large change in attenuation with a small change in voltage. In addition, the device should have as small an insertion loss as possible. Keeping this in mind, the dimensions of the device were chosen to achieve maximum performance. Four design variables were used to design MARS for the VOA application. This paper will discuss how they are related. A surface micro-machining fabrication method was developed using thermal evaporation and Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques. It includes a fluoroform (CHF3) based reactive ion etching for silicon nitride. The devices were released using low surface tension liquids and Rapid Thermal Annealing (RTA). The achieved process yield was over 90%. Several devices were tested and attenuation up to 5.6 dB was observed experimentally.