Abstract

Fiber Bragg gratings formed in germanosilicate optical fibers by ultraviolet (uv) irradiation [1] have developed rapidly in recent years. Numerous applications have been demonstrated that utilize fiber gratings as mirrors, in which a forward-propagating bound mode couples to a backward-propagating bound mode of the same type, and as mode converters, in which one type of bound mode couples to a different type. Fiber gratings can also function as effective loss filters by enabling the coupling of a bound mode to the radiation modes of the fiber [2]. Such filters have been demonstrated as spectrally selective loss elements for flattening the gain spectrum of an erbium-doped fiber amplifier [3]. Other potential applications of these filters for optical communications include filtering of amplified spontaneous emission (ASE) in optically amplified systems, and spectral clean-up filtering in wavelength-division multiplexed (WDM) systems. Furthermore, grating filters are desirable components for numerous other fiber-optic systems, such as fiber lasers and distributed sensor systems. The main advantages provided by fiber-grating filters for these applications include: low insertion loss, high spectral bandwidth, low back reflection, and potentially low cost.

© 1995 Optical Society of America