Abstract:
In this paper, the design of a high signal-to-noise ratio (SNR) tunable filter using a single crystal photorefractive (PR) fiber is given. Because of the long physical structure, Bragg gratings of a large number of periods can be synthesized within the fiber. The wavelength selectivity of 105 order can be realized, which is suitable to develop a narrow-band filter in the order of 0.01 nm. By using a multiple grating structure in the fiber, a high SNR of about 40 db is achievable in practice. Since the PR fiber has a high electro-optic constant, the refractive index of the fiber can be varied by an applied electric field, for which the tuning speed can be in the ns range