Tunable Fabry-Perot interferometer operated in the terahertz range based on an effective refractive index control using pitch-variable subwavelength gratings.

We constructed a tunable Fabry-Perot interferometer (FPI) by controlling the effective refractive index of pitch-variable subwavelength gratings (PV-SWGs) that were incorporated into an FP cavity. The period of the PV-SWG can be varied to change the effective refractive index and shift the optical resonant frequency of the FPI. Compared with conventional methods that tune the optical resonance by adding fillers or deforming the cavity, the proposed FPI obtained a higher transmission and quality factor (Q-factor) for the transmittance peak, and its resonant frequency can be shifted by simply stretching the PV-SWG.