Low-temperature multi-channel bandstop filters with ultra-wide stopbands in Fibonacci superconducting photonic crystals

Multi-channel bandstop filters are theoretically investigated in superconducting photonic crystals. The photonic system is composed of semiconductor and superconductor layers, stacked according to the Fibonacci sequence. As the incident light impinges perpendicularly, several wide transmission bandgaps appear in the frequency range between 0.5 and 7.5 PHz. Each bandgap can be used as a channel of the bandstop filter, exhibiting an ultra-wide stopband of about 0.3–0.6 PHz. The cutoff frequency of the bandstop filter has an obvious red shift by increasing permittivity and thickness of the semiconductor. The stopband width decreases by increasing semiconductor permittivity and superconductor thickness, while it increases by increasing semiconductor thickness. Both the cutoff frequency and stopband width are almost independent of low temperatures. Moreover, increasing incident angles brings about wider stopband width and blue shift of the critical frequency. Our study may be helpful in potential applications of wavelength-division-multiplexed optical communication systems.