Filters and electro-optic modulators on fiber end-faces

Passive and tunable optical filters as well as optical modulators, directly fabricated on the end-faces of optical fibers can provide a fast and low cost production. A hybrid layer system can be built up to a passive Fabry-Perot microcavity, where alternating dielectric high and low refractive materials are used as mirrors and a highly transparent polymer as the spacer material. The mirror design and the spacer thickness define the center operation wavelength and the filter bandwidth. Bandwidths of less than 1 nm (FWHM) at a wavelength of 1560 nm could be achieved for such microcavities on the end-faces of optical fibers. Enhancing the hybrid layer system by transparent conductive electrodes and by adding electro-optically active chromophores to the polymeric spacer material, the filters become tunable. The material used for the electrodes is indium tin oxide (ITO). The oxidic electrodes have to be merged with the dielectric mirrors and the polymeric spacer. Applying a voltage to the electro-optically active polymeric spacer utilizing such electrodes, the refractive index of the spacer can be changed and therefore the resonance criteria of the microcavity.