DIELECTRIC MIRROR EMBEDDED OPTICAL-FIBER COUPLERS

Dielectric mirrors in multimode and single-mode silica fibers have been produced by a fusion-splicing technique. Mirrors oriented normally and at a 45-degrees angle to the axis have been studied. Fibers with angled internal mirrors serve as compact directional couplers with low excess optical loss (almost-equal-to 0.2 dB for multimode and 0.5 dB for single mode at 1.3 mum) and excellent mechanical properties. The reflectance is found to be wavelength dependent and strongly polarization dependent. Far-field scans of the reflected output power measured with a white-light source show a pattern that is almost circularly symmetric. The splitting ratio in a multimode coupler measured with a laser source is much less dependent on input coupling conditions than in conventional fused biconical-taper couplers. Spectral properties of multilayer mirrors oriented normally to the fiber axis have been investigated experimentally, and a matrix analysis has been used to explain the results.