Photorefractive Materials and Devices for Passive Components in WDM Systems

Abstract

The photorefractive effect is a phenomenon in which the local index of refraction is changed by the spatial variation of the light intensity. Although the phrase “photorefractive effect” has been traditionally used for such effects in electro-optic materials, new materials, including photopolymers and photosensitive glasses, have been developed in recent years and are playing increasingly important roles in optical fiber communication systems. Photopolymers in combination with liquid crystals are ideal materials for wavelength selective tunable devices. The improved optical quality and large dynamic range of photopolymers make them promising materials for holographic recording. Holographic gratings recorded in photopolymers can be employed as distributed Bragg reflectors (DBR). The large birefringence of liquid crystals can be used to tune the index of refraction to cover a large wavelength range (e.g., 40 nm). In addition, the combination of photopolymer and liquid crystal also leads to a new material known as holographic polymer dispersed liquid crystal (H-PDLC) which provides a medium for switchable holograms. Photonic devices made of these materials can be easily incorporated into an optical fiber system because of the low index of refraction of polymers and liquid crystals. Besides photopolymers, photosensitive glasses are also promising for applications in fiber optic systems. Fiber Bragg gratings (FBG) have been used as bandpass filters and dispersion compensators. In this chapter, we describe the applications of photopolymers, H-PDLCs, and FBGs in fiber optic devices. Specifically, some of the recent works on photonic devices such as filters, switches, and high performance dispersion compensators for wavelength division multiplexing (WDM) systems will be described.