Study on Continuous Wavelength Tuning of Arbitrarily Selected Transmission Spectrum in Optical Fiber Multiwavelength Filter Using Heterogeneous Wave Retarder Combination

In this paper, we investigated the continuous wavelength tuning capability of an arbitrarily selected transmission spectrum(ASTS) in optical fiber multiwavelength filter using heterogeneous wave retarder combination. The multiwavelength filter consists of a polarization beam splitter(PBS), two polarization-maintaining fiber(PMF) segments of the same length(∼7.12m), a wave retarder combination of a half-wave retarder(HWR) and a quarter-wave retarder(QWR), and another wave retarder combination of two QWRs, forming a polarization-diversity loop. The theoretical transmittance function of the filter was derived using the Jones matrix formulation. For an ASTS obtained at a specific set of orientation angles of the four wave retarders, we identified the wave retarder orientation angles that allowed the ASTS to be continuously shifted. Wavelength tuning was implemented by shifting all polarization states on the output polarization trace of the second PMF in the direction of wavelength decrease. From the identified sets of the wave retarder orientation angles, we calculated eight transmission spectra whose wavelengths were tuned by 0.1nm. Finally, these calculation results were experimentally verified.