Abstract

Owing to their excellent properties and increasing availability, photorefractive Bragg gratings¹ have become ideal building blocks for creating new types of wavelength-selective optical components.^2,3 In this paper we introduce one such component: the grating-frustrated coupler, a novel all-fiber and very- low-loss channel-dropping filter (see Fig. 1). It consists of two single-mode fibers, fiber 1 and fiber 2, forming a 2 × 2 directional coupler. The two fibers are identical, except that the core of fiber 2 contains an index grating with Bragg wavelength| λ_B. At wavelengths far from λ_B, the device operates as a conventional coupler. Near λ_B, however, within a narrow spectral region known as the stop band, the strong grating operates in two ways to frustrate the transfer of optical power from fiber 1 to fiber 2: first, it introduces a strong dispersion, making the coupler asynchronous; second, it creates a barrier (photonic band gap) that rejects photons attempting to tunnel through. The grating-frustrated coupler can therefore be designed to transmit wavelengths within the grating stop band through fiber 1 while other wavelengths are coupled to fiber 2.

© 1994 Optical Society of America