Contactless Terahertz “Fiber Squeezer” for Tunable Dispersion Engineering in Unclad Silicon Dielectric Waveguides

The advancement of terahertz technology is impeded by a lack of viable options for dynamic reconfigurability in compact systems with fixed low‐loss interconnect. To address this absence, we bring conductive walls into proximity with an unclad microscale silicon waveguide core and thereby supply additional boundary conditions to manipulate guided waves through evanescent interaction. This is analogous to a fiber squeezer, in which a dielectric waveguide's dispersion is manipulated via enclosing walls, but in this case, a crucial distinction is that there is no physical contact whatsoever. Analytical and numerical investigations of this phenomenon show that the presence of the conductive walls increases the cutoff frequency and alters the dispersion profile of the waveguide. We implement proof‐of‐concept demonstrations that exploit this effect to realize mechanically tunable terahertz filters of two types: a high‐pass filter and a resonant notch, operating at ∼300 GHz. This experimental demonstration utilizes a featureless straight dielectric waveguide, and the desired frequency‐selective behavior is implemented contactlessly, and hence reversibly, having made no modification to the waveguide core. The capability for on‐demand dispersion tuning of low‐loss terahertz waveguides holds the potential to realize a broad range of practical reconfigurable systems to support diverse applications of terahertz waves.