The role of fiber sensing technologies in MEMS/MOEMS

Micromachining technology has potential for fabrication of precision-defined integrated optic (IO) circuits and offers easy alignment procedures for optical fibers, reducing packaging costs. The main difficulties in fiber sensing technologies are optical fiber alignment requirements, high temperature and vibration effects sensitivity, and phase noise. An alternative is the use of MEMS/MOEMS to approach these problems, combining fiber-optic technology and silicon micromachining. Integrated sensors, when linked by optical fibers, can provide EMI immunity and isolation from high voltage circuits. Detection of displacements of cantilever beams, microbridges, or membranes is used to sense the physical parameter, converting mechanical displacement to a change in optical intensity, and serves as the basis for sensors, since many physical parameters (temperature, pressure, force, acceleration) can be converted to a displacement or strain. The interest in silicon micromachining is also demonstrated in coupling of optical fibers to optoelectronic devices by passive alignment of fiber on a V-groove shaped silicon microbench. Finally, highly reproducible processes such as focused ion beam (FIB) may fabricate near-field optical sensors with nanometer apertures at the apex of tapered fibers. In this paper, a number of sensors are discussed in order to analyse how silicon micromachining contributes to fiber optic sensor technology.