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In this paper, a compact all-optical five-channel demultiplexer (DEMUX) using 2D photonic crystal hexagonal cavities is proposed. The proposed DEMUX comprises bus/drop waveguides, photonic crystal waveguides containing four consecutive 120° bends, two power splitters, and hexagonal resonant cavities. By adjusting the radius and refractive index of the inner/coupling rods, position, and radius of the scattering rods, the operating wavelength and the output power of each port are managed. Normalized transmission spectra and calculations of band structure are calculated by the finite-difference time-domain (FDTD) and plane-wave expansion (PWE) methods, respectively. The resonant wavelengths of the proposed structure are 1328.7 nm, 1331.9 nm, 1335.4 nm, 1340.5 nm, and 1344.4 nm, respectively. Calculation results show that the average quality factor, optical transmission efficiency, passbands of channels, minimum and maximum crosstalk of nearly 6236, 95.98%, 0.22 nm, − 18.04 dB, and − 50.2 dB, respectively. The operating wavelength range of DEMUX is 1328 nm to 1345 nm and the average channel spacing between the channels nearly about 3.93 nm. The footprint of the device is 240 μm2. The advantageous features of the proposed structure are valuable for integration based on popular planar technology and optical communications systems.

In this paper, we first present the design of a nano-ring resonator-based filter, in which scattering rods are used at the corners of the structure. By choosing a suitable radius for the dielectric rods in the nano-ring resonator, low channel spacing and high-quality factor parameters have been achieved at 1586.8 nm wavelength. Then, using this filter, a 2-channel demultiplexer is developed. In the proposed demultiplexer, two lattice constants are used: a1 for the main structure and a2 for the structure in the nano-ring resonator. The difference in the lattice constants results in an increase in the quality factor. Some of the advantages of this 2-channel demultiplexer include an average quality factor of 5443, average channel spacing of 0.35 nm, and central wavelengths of 1554.5 nm and 1557.1 nm, respectively, for the first and second channels. Moreover, the minimum and maximum inter-channel cross talks are − 17.63 dB and − 12.1 dB, respectively. Due to the 2.6 nm inter-channels spacing, this structure can be exploited in optical integrated circuits, WDM and DWDM systems.