Strong Higher-Order Fiber Bragg Gratings Written with an Amplitude Mask

Abstract

Reflective Bragg gratings have been written in optical fibers using UV induced index changes. Initial work used a standing wave interference pattern set up by light launched down the fiber core.1 The more versatile techniques of side-writing using bulk interferometric fringes2 and phase-masks3 followed. The field of phase-mask-written Bragg gratings in germano-silicate fibers has matured with the use of specially designed high-photosensitivity fiber and hydrogen loading.4 While gratings written with these methods can be precisely tailored in spectral shape, bandwidth and strength, a precise mask, a coherent laser, and very stable alignment during the exposure are needed. Multiple grating applications, including weak pump-diode stabilizers, fiber laser mirrors, and grating sensors may not require the high precision gratings produced with the phase mask method, but would benefit from an inexpensive mass production technique. In this paper we demonstrate an amplitude mask exposure technique to create strong higher order Bragg reflectors with minimal optics.