Abstract: A small module for converting an electrical signal to a modulated light signal on an optical fiber comprises a housing, a laser mounted on a laser substrate within the housing, a GRIN lens and an optical isolator downstream from the laser, and a precision capillary for holding an optical fiber downstream from the optical isolator. The relative positions of the laser, lens, optical isolator and fiber are adjusted to maximize light output through the fiber. The optical fiber is sealed to the housing at one point and is free to move axially in the capillary for minimizing mechanical stress on the fiber.

Abstract: A single-mode optical fiber delay line for filtering at high frequencies utilizes an nth order cascaded recirculating configuration comprised of n+1 couplers. Each coupler has two input fibers and two output fibers. One of the output fibers of each coupler except the last is connected to one of the input fibers of the next coupler in cascade to form a feed-forward path. The other output fiber of each coupler except the first is connected to the other input fiber of the preceding coupler, thus forming a feed-backward path. The feed-forward path and the feed-backward path of adjacent couplers form a delay loop. The delay time in each succeeding delay loop is increased by an incremental delay .tau. equal to the reciprocal of the center frequency of the filter. The delay in the first delay loop is selected to be some multiple m of .tau., where m is an integer selected for a total delay T which permits the use of optical fiber of a length sufficient to avoid bending losses in the optical fiber.