Polarization-selective microring resonators.

Polarization-selective microring resonators (MRRs) are designed and demonstrated to work with resonances for only one of TE and TM polarizations for the first time, which can be used for realizing the crossing-free, compact and scalable multi-wavelength coherent receiver with dual polarizations. The present polarization-selective MRRs are realized by manipulating the polarization-dependence of the bending loss of the micro-resonators and the coupling ratio of the bent directional couplers introduced here. The demonstrated TM-type MRR and the TE-type MRR work well as a wavelength-selective optical filter for TM polarization and TE polarization, respectively, as designed. On the other hand, the resonance of the undesired orthogonal polarization mode is depressed significantly with very high extinction ratio. For the realized TM-type MRR, the peak-transmission at the drop port is depressed to be lower than -50dB and the loss of the transmission at the through port is very low (<0.5dB) when TE polarization mode is input. For the realized TE-type MRR, the peak-transmission at the drop port is depressed to be ~-40dB and the loss of the transmission at the through port is very low (<0.5dB) when TM-polarization mode is input. The present polarization-selective TM- and TE-type MRRs are useful for the applications with multiple wavelengths and dual polarizations.