Abstract: A waveguide interferometer includes a multicore fiber used a multicore waveguide, where the multicore waveguide includes a coupler section formed by tapering a portion of the multicore waveguide so that one core though which a light source is fed is optically coupled to another core that is terminated differently that the core into which the source signal is provided. The terminations respond differently upon being exposed to an environmental condition or substance, and the difference in response to the environmental condition or substance results in a shift in interference of the light reflected back through the multicore waveguide, which is detected with a detector on the same side of the multicore waveguide as the light source.

Abstract: A waveguide interferometer includes a multicore fiber used a multicore waveguide, where the multicore waveguide includes a coupler section formed by tapering a portion of the multicore waveguide so that one core though which a light source is fed is optically coupled to another core that is terminated differently that the core into which the source signal is provided. The terminations respond differently upon being exposed to an environmental condition or substance, and the difference in response to the environmental condition or substance results in a shift in interference of the light reflected back through the multicore waveguide, which is detected with a detector on the same side of the multicore waveguide as the light source.

Abstract: A device for selectively increasing higher-order mode losses comprises an optical fiber taper executed on a multi-mode fiber of a selected wavelength, and the fiber taper has separated regions, i.e. non-tapered fiber regions which have a first diameter equal to that of the main fiber. The tapered regions can also include transition regions in which the fiber diameter is reduced/increased, respectively, and a taper waist region which has a reduced diameter, where the taper level ratio between the regular diameter and the narrowed diameter is at least 20%, and the length of the transition regions are at least 0.5 mm on one side and may be zero on the other side, and the length of the taper waist with the narrower diameter is at least 0.5 mm. Furthermore, the taper area is coated with a filtering substance with attenuating properties between the tapered section and the cladding.