Abstract: An optical filter is formed by writing at least one long-period Bragg array into an optical fiber which is tapered to define two substantially adiabatic transition areas delimiting an intermediate area in which the long-period Bragg grating is written to produce codirectional coupling between two guided modes in the intermediate area at a wavelength that is a function of the period of the grating.

Abstract: A multiport optical waveguide interferometer is provided which comprises at least two N.times.N couplers arranged in series on an array of fibers and separated by a short region such that the phase shift between the couplers is approximately equal to .pi.. A method for making such an interferometer comprises forming such couplers, for instance by a fused taper method with appropriate twist, where the fused, tapered and twisted zone is longer than usual and wherein the couplers are formed in series within such zone, separated by short regions of between 1-2 mm, and adjusted to achieve the flattest possible wavelength response.

Abstract: A compact, tunable, wavelength independent, all-fiber attenuator is produced by heating a single-mode fiber to create at least one taper therein through capillarity rather than through pulling, pushing or twisting the fiber. The attenuator may be tuned to achieve the desired value of attenuation and wavelength independence by imparting a small bend to the taper. The attenuator may be a fixed value attenuator or a variable attenuator. When a fixed value attenuator is desired, the tapered and bent structure is encapsulated in an adhesive and glued onto a substrate.