Focused acoustic wave fiber optic reflection modulator

Abstract

An improved optical fiber modulator producing a focused acoustic wave propagating from an acoustic transducer surrounding an optical fiber having an in-fiber reflection grating changes the core refractive index in proportion to the induced strain at the core when the focused acoustic wave arrives at the optical fiber core, and focused acoustic waves can also modulate optical carrier phase in a length of optical fiber which may lie in an arm of an interferometer. In a preferred embodiment, the index change shifts the reflection spectrum of an in-fiber grating located in the portion of optical fiber core on which the focused acoustic wave is centered with the reflection spectrum shift producing a change in the grating reflectivity for a narrow bandwidth optical signal on a skirt of the grating spectrum. Electronic multiplexing means may be used to both transmit and receive signal information on a single optical carrier signal, and a plurality of acoustic wave modulators may be placed along a single optical fiber, simultaneously modulating a plurality of optical signals each having an optical frequency matched to one of the modulator gratings. Acoustic wave modulators may be tuned to a range of optical carrier frequencies using thermal or mechanical strain control, and a series of tuned modulators lined up along an optical fiber accessed through an optical circulator will reflect and modulate selected signals which are then forwarded back through the circulator onto a transmission line optical fiber.