Highly efficient self-collimation based waveguide for Mid-IR applications

• The channel-less, light position-invariant, broadband, and broad angle waveguide is introduced in hole-type 2D square array PC.
• SC is achieved in the first band of the structure which guaranties the suppression of out-of-plane scatterings resulting in high transmission in practice.
• A realizable waveguide for Mid-IR applications using PbTe is presented for spectral width of 30 nm around central wavelength of 4.1175 μm.
• Optimized coupling efficiency of about 70% has been obtained for both polarizations around the central frequency using a row of holes.

An efficient backbone is introduced for optical integrated circuits at Mid-IR region using PbTe (nPbTe ∼ 6) as the background material in a hole-type 2D square lattice photonic crystal in this article. The proposed waveguide benefits insensitivity to the polarization and is also virtually all-angle. Furthermore, it is applicable to a broad spectral width of 30 nm considering only a small compromise of 3° on the degree of self-collimation which will not cause a significant challenge in practical integrated applications. Here, based on finite difference time domain analysis, a complete study on coupling efficiency of the introduced structure is presented. It is shown that for optimized anti-reflection, the structure benefits a coupling efficiency of ∼70% for TE and TM polarizations around the central wavelength of λ = 4.1175 μm. In this study, a single row of hole-type anti-reflection is used which does not affect the all-angle SC property of the proposed waveguide.