Fabrication-robust, high-FSR, low-crosstalk mode-selective microring resonators

Mode-division multiplexing (MDM) has emerged as a promising approach for increasing optical interconnect bandwidth density by enabling multiple spatial channels within a single waveguide. In this work, we demonstrate fabrication-robust, high-free spectral range (FSR), and low-crosstalk mode-selective silicon microring resonators (MRRs) for the TE 0 , TE 1 , TE 2 , and TE 3 spatial modes. By engineering the phase matching conditions between a single-mode ring resonator and multimode bus waveguides, we realize mode- and wavelength-selective filtering while maintaining a compact 5 μm ring radius. The fabricated TE 1 , TE 2 , and TE 3 devices exhibit nominal crosstalk suppression values of 30.3 dB, 39.1 dB, and 28.8 dB, respectively. All fabricated devices demonstrate extinction ratios greater than 23.1 dB, full width at half maximum (FWHM) greater than 71.7 GHz, and FSRs up to 14.9 nm. Eye diagram and bit error rate (BER) measurements further demonstrate 25 Gb/s transmission using NRZ PRBS31 signals with BERs below 10 −12 for received optical powers of −7.5 dBm and above for all fabricated MRRs, with all eye diagrams remaining clearly open. Fabrication variation analysis further demonstrates robust operation under representative dimensional variations in waveguide geometry, with all fabricated device variations maintaining crosstalk suppression between 23 dB and 40 dB between the desired mode and all lower-order modes.