Optical MEMS: designing for reliability

Abstract

The inter-disciplinary nature of MEMS makes its design a highly involved process. In Optical MEMS the addition of optical parameters only increases the complexity. It is almost impossible for a designer to know where to start given the number of variables involved. In order to design a device that will meet the required specifications over its entire lifetime, reliability issues must be included in the design process. This paper develops a method that can be used to create a step-by-step design process involving reliability issues at every stage. The process begins by listing out the constants and constraints of the design. The constraints could be due to physical parameters, MEMS fabrication processes, optical reasons, reliability issues, etc. They affect the design in different ways; for example, two fibres cannot be brought closer than 250μm. This constraint will affect the optical design and the overall dimensions of the device. Taking all such constraints into account, an optical design process is outlined. The effect of individual errors is studied on a key parameter like insertion loss. This gives the designer information about which parameters the design is more sensitive to and will help in deciding the manufacturing tolerances required in the different stages. Using all of this data, an "ideal design" is developed. A Monte Carlo analysis is carried out on that design to show the effect of errors occurring simultaneously. The paper concludes with a flow chart of a suggested design process to be used when designing optical MEMS devices.