Extraordinary wavelength dependence of self-collimation effect in photonic crystal with low structural symmetry

• Low symmetric 2D photonic crystals with star shape are explored to achieve wavelength selectivity by means of self-collimation phenomena.
• Flat equi-frequency contour is responsible for self-collimation and tilted version of same contour provides wavelength selection.
• The structure operates in a wavelength interval from 1484.5 nm to 1621.5 nm with a broad bandwidth of Δω = 8.82%.
• 19 dB inter-channel crosstalk and coupling efficiency above 97% are achieved.
• Diffraction-limited beam propagation along different channels is shown by finite-difference time-domain method.

We present the optical properties of a new type of photonic crystal (PC) named star-shaped PC (STAR-PC) with anomalous equi-frequency contours. Intentionally introducing low-symmetry in the primitive unit cell gives rise to progressively tilting flat contours, which are observed in the fifth band of the transverse magnetic mode. Due to the intrinsic dispersive feature of the proposed PCs, i.e. tilted self-collimation, the incident signal with different wavelengths can be successfully separated in a spatial domain without introducing any corrugations or complexities inside the structure. We show numerical investigations of wavelength selective characteristic of the proposed PC structure in both time and frequency domains. The STAR-PC approach can be considered a good candidate for the wavelength division applications in the design of compact photonic integrated circuits. For the purpose of wavelength separation implementations, the proposed structure may operate within the wavelength interval of 1484.5–1621.5 nm with a broad bandwidth of 8.82%. The corresponding inter-channel crosstalk value is as low as −19 dB and the calculated transmission efficiency is above 97%.