Experimental demonstration of a microdisk resonator filter/buffer utilizing two-mode interference.

We have experimentally demonstrated a microdisk-resonator (MDR)-based filter for filtering and buffering applications utilizing two-mode interference. Optical filtering or buffering behavior can be generated by the coherent interference between two orthogonal whispering-gallery modes (WGMs) in a MDR symmetrically coupled to two bus waveguides. MDRs were fabricated using nanofabrication processes on a silicon-on-insulator platform. Multiple resonances of WGMs are excited in a MDR and unique filter characteristics have been observed for two spectrally nearby resonances. The measured results agree well with the theoretical simulation. Bandpass filtering is achieved with a 3 dB bandwidth of 0.66 nm and an in-band ripple of less than 1 dB when the two resonances are detuned, while the filter can function as an optical buffer with an insertion loss of 5.85 dB and a predicted time delay of 15 ps when the two resonances are approximately aligned. Furthermore, the influence of resonance spacing is analyzed on the performance of this filter.