Abstract

Experiments in our laboratory^1-3 and elsewhere^4,5 show that the refractive index of germanosilicate fiber can be modified by a few parts in 10⁵ to upwards of 5 × 10^-4 by photobleaching the oxygen vacancy band of germania. Typically, the fiber core is exposed through the side of the cladding to UV radiation at a wavelength from 230 to 266 nm. Permanent phase gratings are "written," with a specified period, by using a pair of intersecting coherent beams. The periodic index modulation forms a Bragg grating that can be used for very narrow stop and pass-band filters, or as a means to stabilize laser diodes, and as reflectors in rare earth-doped fiber lasers. Other applications include taps and launchers, which are made by blazing the grating and selecting a suitable period to couple a bound mode into a radiating mode,⁶. and mode coupler and filters. This paper will review the design and performance of both active and passive Fiber Bragg Grating (FBG) components, and discuss the thermal stability and aging characteristics of the photo-induced index changes.

© 1991 Optical Society of America