Abstract

Optical fibers have been observed to change refractive index with UV exposure. We describe a novel approach to grating writing in optical fiber. This method involves writing the grating point-by-point through the side of the fiber by means of a UV laser source. The point-by-point writing is particularly flexible because the choices of pitch, length, and blaze of the grating are determined independently and thus offer a means of controlling the spectral response of the grating rather precisely. We demonstrate efficient mode conversion between forward-propagating modes, which gives as much as 96% conversion for near-optimal conditions over a FWHM bandwidth / = 1/300. The wavelength at which mode conversion occurs, from the fundamental LP01 to the higher order LP11 modes, is determined by the periodicity of the grating, which can be chosen to couple light at any wavelength of interest within the spectral range 6001700 nm and perhaps beyond. The technique is potentially useful for making devices such as optical fiber wavelength filters and mode converters for optical communications, as well as in interferometric and sensor applications.

© 1990 Optical Society of America