| Summary: | Signal processing at terahertz regime is essential towards the next-generation wireless communication system. Here, we propose polarization-maintaining sampled gratings based on subwavelength dielectric rectangular-core waveguides. In each sampling period, the Bragg grating section is achieved with periodic large and small photonic cells, while either large or small unmodulated straight waveguide is applied for the waveguide section. From numerical simulations, we observe two transmission dips for two orthogonally polarized waves. The averaged extinction ratio and the maximum full-width at half-maximum of the sampled gratings are 4 dB and 1.7 GHz, respectively. Using lower-loss polymer, the transmission losses of passband decrease significantly (from 7 dB to 2.8 dB) and the averaged extinction ratio of stopband increases (from 5 dB to 7.8 dB). Additionally, the filters offer large negative group-velocity dispersions (around −400 ps/mm/THz) for each stopband, and the values can be further reduced to −1800 ps/mm/THz of the lower-loss polymer-based grating. The simulations further suggest that, the spacing between two adjacent stopbands and the filtering properties of stopbands can be tuned by the duty cycle, sampling period and total length of the proposed sampled grating structures. Our work demonstrates that the proposed sampled gratings have great potential of polarization-maintaining dual-frequency filtering and dispersion compensation, which may find exciting applications for frequency- and polarization-multiplexing techniques in terahertz communication systems, as well as the quantum cascade lasers with single-mode operation.
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