Tunable terahertz guided-mode resonance filter with a variable grating period.

A variable grating period made of quartz has been applied to fabricate a tunable guided mode resonance (TGMR) filter with transverse-electric (TE) and -magnetic (TM) modes in the terahertz (THz) region. We prepared three TGMR filters with grating periods of 5.0, 3.3, and 1.7 μm/mm over the length of the filter. For the 5.0 μm/mm, the resolution of resonance frequency shift of the TE, TE, and TM was 3.6, 4.0, and 3.4 GHz/mm, respectively. With a metal slit spacing of 2 mm located in front of the TGMR filter, the movable range of the TGMR was 24 mm, and the resonance frequency could be shifted up to 87, 96, and 82 GHz, where the center frequencies of each resonance were 0.402, 0.579, and 0.460 THz, for the TE, TE, and TM, respectively. Furthermore, because the TGMR and guided mode resonance (GMR) filters are placed independently in the THz beam path, both tunable and fixed resonances can be obtained at the same time in the spectrum.