Investigation on Strong Coupling Behaviors of THz Subwavelength Directional Couplers

To achieve strong coupling, conventional fiber-based directional couplers often require complicated fabrication. Here, by placing two identical THz subwavelength fibers parallel to each other and by simply tuning the separation in between, we investigate the strong coupling characteristics of the directional fiber coupler, which has not been experimentally explored before in the THz region. This strong coupling directional coupler is able to provide superior performance with an extremely short coupling length (30 times of wavelength) and a record low insertion loss (<; 0.3 dB). These performances are much improved when compared with the previously reported THz fiber/waveguide-based directional couplers.