12.5 GHz spectral linewidth optical DWDM photonic crystal demultiplexer in L Band communication window

We propose a Dense Wavelength Division Multiplexing (DWDM) Demultiplexer for L band (1565–1635 nm) applications. The design comprises a Y-shaped branch, a circular ring cavity (CRC), a bus waveguide, and a drop waveguide. To simplify the fabrication process, a CRC cavity is used instead of a regular large ring resonator in the design. The diameter of the CRC cavity is 820 nm. Coupled mode theory is used to examine the behaviour of the proposed demultiplexer. Proposed design achieves a narrow resonant wavelength of 12.5 GHz with a 0.1 nm spectral linewidth, a high-quality factor of 15,789, and minimal cross-talk of − 85 dB between adjacent channels. The results confirm that there is a transmission peak at one of the output port, with simultaneous drop of transmission power i.e. zero, at other output port. Additionally, the results convey that the reflection is zero at the peak resonant wavelength for all channels. Further, the proposed design offers a fabrication tolerance of ± 1 nm for air hole and CRC radii at which the resonant wavelength and transmission would not be effected.