High refractive index composite materials for THz waveguides: trade-off between index contrast and absorption loss

TL;DR

This paper investigates the trade-off between high refractive index contrast and absorption loss in polymer composites for THz waveguides, demonstrating the importance of balancing these factors for effective Bragg reflector design.

Contribution

It introduces a method to optimize composite materials for THz waveguides by analyzing the impact of dopant concentration on index contrast and absorption loss.

Findings

High dopant concentration increases refractive index but also absorption.

Optimal design requires balancing index contrast and absorption loss.

Experimental validation confirms simulation predictions.

Abstract

Polymer compounds from titania-doped polyethylene are fabricated and their linear optical properties characterized by THz-TDS. We show that high concentration of dopants not only enhances the refractive index of the composite material, but also can dramatically raise its absorption coefficient. We demonstrate that the design of Bragg reflectors based on lossy composite polymers depends on finding a compromise between index contrast and corresponding losses. A small absorption value is also shown to be favorable, compared to an ideal lossless reflector, as it enables to smooth the transmission passbands. Transmission measurements of a fabricated hollowcore Bragg fiber confirm simulation results.