Input polarization-independent multi-channel switching using cascaded long-period fiber grating and polarization-maintaining fiber

Novel multi-wavelength switching filters based on cascaded long-period fiber grating (LPG) and polarization-maintaining fiber (PMF) in a Sagnac loop configuration are proposed and experimentally demonstrated. While the multi-channel spectrum of PMF Sagnac loop filter is controlled by the polarization state in the loop, the polarization-independence of the LPG filter is used to drop one channel. The polarization-independence of the cascaded LPG filter is also used for the fixed periodic loss spectrum to drop multiple channels in the loop. Although the polarization state of the optical wave filter is switched by the electro-optic modulator in the loop, the device is independent of the polarization state of the input light due to the bi-directional polarization compensation of the Sagnac loop interferometer. This device can be used to achieve all-channel gating and odd/even-channel switching with fine channel selectivity and high speed response.