Negative refraction and self-collimation in the far infrared with aligned carbon nanotube films

• Demonstrated far-infrared hyperbolic metamaterials based on aligned CNTs.
• Demonstrated negative energy refraction angle and loss-enhanced transmission.
• Demonstrated self-collimation in CNT thin films through energy streamlines.
• Predicted reflectance and penetration depth for tilted CNT films.
• Investigated the angle-dependent transmittance of tilted CNT films.

This study demonstrates the far-infrared self-collimation and low-loss transmission of aligned carbon nanotube (CNT) films or arrays. The anisotropic dielectric functions of the CNT array is modeled using the effective medium theory considering the degree of alignment. The spectral regions where hyperbolic dispersion is satisfied are in the far-infrared. In the hyperbolic regime, energy propagates inside the CNT film along the optical axis for nearly all incidence angles. The self-collimation effect is also examined for tilted CNT thin films by tracing the Poynting vector trajectories. Low-loss transmission is explored to understand the impact of alignment on the penetration depth and transmission through the film. In conjunction with the surface radiative properties, the self-collimation and transmission characteristics are distinguished between the two hyperbolic bands of the CNT film. The insight obtained from this work may lead to the utilization of CNT arrays in polarization filtering and infrared imaging.