Direct Laser Writing of Birefringent Photonic Crystals for the Infrared Spectral Range

TL;DR

This paper demonstrates the fabrication of birefringent infrared photonic crystals using direct laser writing of polymer microwires, showing strong polarization-dependent reflectance in the mid-infrared range, which could enable new optical devices.

Contribution

It introduces a novel method to create all-dielectric birefringent photonic crystals in the infrared using single-step direct laser writing of subwavelength polymer structures.

Findings

Strong cross-polarized reflectance contrast at 6.5 μm wavelength.

Photonic crystals exhibit anisotropic optical behavior.

Finite element simulations agree with experimental results.

Abstract

Infrared optical photonic crystals fabricated using direct laser writing, which is based on the two-photon polymerization of suitable monomers, have received substantial interest since the emergence of this process. Two-photon polymerization could be a disruptive technology for the fabrication of all-dielectric photonic crystals in the infrared spectral range, as it allows the synthesis of large scale arrays of uniform structures with arbitrary geometries and arrangements. However, all-dielectric photonic crystals that provide birefringent optical responses in the infrared spectral range have not yet been demonstrated using direct laser writing techniques. Here we explore the form birefringence observed in photonic crystals composed of arrays of subwavelength-sized slanted polymer microwires. The photonic crystals investigated here were fabricated in a single fabrication step using direct laser writing of an infrared transparent photoresist (IP-Dip). A strong contrast of the cross-polarized reflectance of photonic crystals as a function of the in-plane orientation is observed in the mid-infrared spectral range at $\lambda$ $\approx$ 6.5~$\mu$m. This observation is indicative of an anisotropic optical behavior. Finite element based techniques corroborate the experimentally observed responses qualitatively.