Study on Pass-Band-Flattened Multiwavelength Filter with Wavelength Tunability Implemented by Using Quarter-Wave Polarization Transformation

By harnessing quarter-wave polarization transformation, we propose a multiwavelength filter based on polarization-diversity loop configuration, which can continuously adjust the wavelength of the pass-band-flattened transmission spectrum. The proposed filter consists of a polarization beam splitter, two polarization-maintaining fiber segments of the same length, one half-wave retarder, and three quarter-wave retarders. We found a combination of the orientation angles of the four wave retarders, which could induce an extra phase difference φ from 0° to 360° in the pass-band-flattened transmittance function derived using Jones formulation. Then, we implemented the wavelength adjustment of the pass-band-flattened transmission spectrum at a wavelength interval of 0.1nm through the theoretical calculation of transmission spectra. As a result, we experimentally demonstrated the theoretically predicted results by controlling the azimuth angles of the wavelength retarders within the filter.