Transmission Characteristics of T-ray Multilayer Interference Filters

An optical multilayer interference filter is made from two or more different dielectric materials layered in such a way that it promotes constructive or destructive wave interference for a selected frequency in the direction normal to the layers. Usually, each layer has the thickness of a quarter of wavelength at which the stop-band is required. In this paper, a quarter-wavelength multilayer interference filter is realised for T-ray applications. The dielectric materials used are high-resistivity silicon and free space, both of which have high transparency to T-rays and flat all-pass responses over the frequencies of interest. The designed thickness of both materials is in the order of a hundred microns, and thus allows the novelty of a retrofittable assembled structure. An analysis of the affect of the number of layers on the spectral response is given for the first time. The THz-TDS measurement of the fabricated structure is demonstrated to be in agreement with theory.