Analysis of an optical energy interrupter for MEMS based safety and arming systems

This paper describes an investigation into the development of a LIGA optical energy interrupter for use in a MEMS-based Safety and Arming (S&A) system. The energy interrupter acts as a switch to selectively couple optical power between input and output fiber optic waveguides using either a reflectance or direct coupling technique. This device is a critical component of the S&A system, which must perform its task in a zero-tolerance manner to ensure reliable and safe operation of naval ordnance. The union of fiber optic components with LIGA-based MEMS structures allows development of an energy interruption junction that will isolate the low and high voltage sections of an optical charging circuit. A movable LIGA barrier interacts with optical fibers in order to align or misalign the optical propagation path between the source and receiver in the circuit. The implementation of such a design allows for the "Safe" operational mode of an S&A system with the optic path broken, and an "Arm" mode during energy transfer. Effects such as fiber misalignment, light scattering, and multiple reflections are sources of potential failure modes for this micromachined optical system. This paper is concerned with the effects of fiber misalignment of system reliability. Three primary fiber/barrier topologies are discussed. Computer simulations used to establish the positioning and geometric tolerances in the MEMS structure to ensure maximum functional reliability are described, and experimental results are presented.