Abstract

Since the discovery of photo-induced gratings in germania-doped, single-mode fibers by Hill and coworkers in 1978, several extensions and applications of this phenomenon have been presented.^1-3 Permanent index gratings in two-mode, elliptical-core (e-core) optical fibers have been demonstrated, and their use in intermodal switching and chirped filters for dispersion compensation have been proposed.^4-6 We present here the effects of writing two-mode gratings in fibers and discuss their sensing implications. The effect of permanent-index gratings on the differential-phase modulation between the LP₀₁ and LP₁₁^even modes in two-mode fibers is analyzed in detail and the use of these grating-based sensors for weighted-sensing applications is proposed. Our results show that strained fibers exposed to high-power writing beams from an argon-ion laser could be used as sensing elements with varying beat-lengths and hence, varying sensitivities.

© 1992 Optical Society of America