Micro-opto-mechanical systems

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Micro-opto-mechanical systems (MOMS)

Miniaturized optome-chanical devices or assemblies that are typically formed using micromachining techniques that borrow heavily from the microelectronics industry. The term may be used to distinguish devices and microsystems that combine optical and mechanical functions without the use of internal electronic devices or signals. Systems that use electronic devices as part of the microsystem may be referred to as MOEMS (micro-opto-electro-mechanical systems). In some cases, these terms may be used synonymously. A related area is MEMS (micro-electro-mechanical systems), in which electronic and mechanical functions are combined in a miniature device or system, but not necessarily implementing optical functions. The progress of MOMS technology has been greatly enabled by the simultaneous development of microelectronics and optical fiber-based telecommunications technology. See Integrated circuits, Micro-electro-mechanical systems (MEMS), Micro-opto-electro-mechanical systems (MOEMS), Optical communications


Although similar in concept to MOEMS technologies, MOMS has unique advantages for some applications. The use of only optical energy and signals gives MOMS an inherent immunity to electromagnetic interference (EMI) that is important for applications in electrically noisy or high-voltage environments. The absence of semiconductor electronic devices greatly increases the high-temperature tolerance of the system. MOMS devices can be designed to work immersed in liquids, which is of great importance for chemical sensing and biomedical applications. The fact that the power and signal sources can be remotely provided via an optical fiber, allowing the sensor to be passive, is of great utility and reduces the impact of a MOMS sensor on its local environment. MOMS can be used safely in flammable and explosive environments, making them uniquely valuable in the petrochemical industry.


Some examples of MOMS technology include optical pressure transducers—microphones or hydrophones that have a thin mechanical membrane that is one surface in a Fabry-Perot interferometer formed by the reflection from the membrane surface and the reflection from the end of the fiber. (A similar arrangement for sensing vibration is shown in the illustration.) Other versions have a planar optical waveguide on the surface of a sensitive membrane that is one arm of a two-beam Mach-Zehnder interferometer. Another example is an accelerometer in which a small mass is suspended from flexure attachments to the substrate. Optical fibers are positioned with a small gap in which the moving mass can interrupt the transfer of light from one fiber to another to modulate the light intensity transmitted through the fibers. One of the most well developed MOMS applications is optical sensing of the position of small cantilevers used in scanning tip microscopy processes such as atomic force microscopy. See Accelerometer, Pressure transducer