Fiber-optic strain-displacement sensor employing nonlinear buckling.

A new class of intrinsic fiber-optic strain-displacement sensors based on the precisely controlled nonlinear buckling of optical fibers and the resulting optical bend loss is introduced. A multimode fiber version of the sensor is described that exhibits a sensing range convenient for many structural monitoring applications (<100 nm to several millimeters), linear response over a wide range of displacements, and excellent repeatability. It is extremely simple to fabricate and employs inexpensive optoelectronics.

Reflective fiber ring resonator with polarization-independent operation.

A polarization-insensitive fiber-optic ring-resonator configuration based on a reflective mode of operation with a Faraday rotator mirror for birefringence compensation is reported. An output resonant-dip transfer function that is independent of the input polarization to the system is obtained, which is shown to produce a stable scale factor of the system.

Aberration-limited coupling efficiency from a plano-convex lens into an optical fiber.

Ray-tracing calculations of the coupling efficiency from a plano-convex lens of relatively low f/number ( approximately 2.35) into highly multimode step-index optical fibers have been performed for both orientations of the lens. The results of the calculations yield surprising discontinuities and asymmetries in the slope of the coupling efficiency versus longitudinal displacement.

Single-mode fiber diameter measurements using Lloyd's mirror.

An interferometric method for measurement of the fiber outside diameter with an uncertainty of <1 microm is proposed and experimentally demonstrated. The fringe pattern produced by placing the fiber in contact with a reflecting surface is utilized.

Remote polarization control for fiber-optic interferometers.

A simple method has been developed for control and prevention of polarization fade on a single output lead from a remotely located fiber-optic interferometer. The method has been demonstrated using a fiber-optic Michelson interferometer. In contrast to a previously suggested method, only a single detector is required.