MONOLITHIC WAVELENGTH-FLATTENED 1 X 7 SINGLE-MODE FUSED FIBER COUPLERS - THEORY, FABRICATION, AND ANALYSIS

The basic theory of monolithic 1 x 7 couplers is presented. The results of fabricating eighty-two devices are described, and the steady improvement in achieved device performance is shown leading to the fabrication of a controlled batch of eleven devices. These devices have excess losses of < 0.1 dB together with good coupling uniformity to the seven output fibers. Maximum insertion losses are all around 10 dB or less, which is seen to compare favorably with devices obtained by concatenating 2 x 2 couplers. It is shown that to obtain an equal power split between the center and outer fibers it is necessary to control carefully the degree of fusion of the structure. An analysis of this coupling behavior is presented.