Sensing Techniques and Interrogation Methods in Optical MEMS Accelerometers: A Review

In this article, we review optical MEMS accelerometers with a particular focus on sensing techniques and interrogation methods. Optical accelerometers find use in various application domains ranging from microgravity to inertial navigation to vibration sensing. The performance of an accelerometer is quantified in terms of its range, bandwidth, sensitivity, and resolution. The combination of sensing technique and interrogation method determines the optical accelerometer's performance. This article presents a classification in terms of guided-wave and free-space based optical sensing techniques used in acceleration measurement and their review. In free-space based sensing techniques, light propagating in free-space interacts with the mechanical structure resulting in modification of light properties at the receiver. In guided-wave based sensing techniques, light interaction with the mechanical structure is confined to the waveguide. Also, the different interrogation methods used in optical MEMS accelerometers are reviewed. The interrogation methods are classified as based on intensity modulation or frequency modulation of the optical signal received from sensor. In intensity-modulation based interrogation, light intensity at output is the measurand and, the cost and complexity of this class of methods is lower. In frequency-modulation based interrogation, the frequency or phase of the optical signal at the output is the measurand. Further, a high-resolution optical MEMS accelerometer based on waveguide Bragg gratings is described. A combination of free-space based sensing and intensity-modulation based interrogation methods will be suitable for consumer-grade accelerometer applications. For high-resolution applications like tactical and navigation grades, a combination of guided-wave sensing and frequency-modulation based interrogation methods would be appropriate.