Fig. 1. Fig.‍ ‍1　Change of the band gap range with the radius of the dielectric cylinder

Fig. 2. Fig.‍ ‍2　Band structure of the complete two-dimensional photonic crystal

Fig. 3. Principle of the resonant coupling unit

Fig. 4. Transmittance distribution at the output

Fig. 5. Influence of the radius of the dielectric cylinder in the microcavity on the transmittance

Fig. 6. Influence of the radius of the medium cylinder outside the microcavity on the transmittance

Fig. 7. Influence of the radius of the dielectric cylinder at the output end on the transmittance

Fig. 8. Schematic diagram of the six-channel wavelength division multiplexer

Fig. 9. Transmittance distribution diagram of the six-channel wavelength division multiplexer

Fig. 10. Field distribution diagram of the wavelength division multiplexer under the corresponding wavelength excitation source. （a） 1.3298 μm; （b） 1.4316 μm; （c） 1.4419 μm; （d） 1.5564 μm; （e） 1.5966 μm; （f） 1.6191 μm