Study on Continuous Wavelength Tuning of General Comb Spectrum in First-Order Optical Fiber Comb Filter Using Dual 1/4 Waveplates

Abstract

In this study, we scrutinized the continuous wavelength tuning capability of a general comb spectrum(GCS) in an optical fiber comb filter using dual 1/4 waveplates. The comb filter is based on a polarization-diversity loop structure composed of a polarizing beam splitter, two equal-length segement of polarization-maintaining fiber(PMF), dual 1/4 waveplates located before one PMF segment, and a set of 1/2 waveplate and 1/4 waveplate positioned before the other PMF segment. Using the Jones calculus, we formulated the transfer matrix of the filter and draw out the filter transmittance function through this formulation. For a GCS obtained at a specific set of azimuth angles of the four waveplates, we found the waveplate azimuth angles that allowed the GCS to be continuously wavelength-tuned. These waveplate angle sets for the continuous wavelength tuning were identified using the relationship between the filter transmittance and the spectral evolution of the output polarization of the second PMF. From the identified sets of the waveplate angles, we calculated eight comb spectra whose wavelengths were tuned by 0.1nm, and then these theoretical results were experimentally demonstrated.