Tunable Terahertz Generation in Dispersion‐Engineered ZnTe Waveguides

ABSTRACT The generation of coherent terahertz (THz) radiation with high efficiency, spectral tunability, and on‐chip compatibility remains a long‐standing challenge in the field of THz photonics. Here we present a dispersion‐engineered platform based on free‐standing zinc telluride (ZnTe) slab waveguides that enables tunable THz emission through modal phase matching. Frequency‐domain coupled‐mode analysis together with numerically computed optical and THz modal dispersion reveals that the fundamental optical and THz guided modes can satisfy the phase‐matching condition over a broad 0.1–3 THz frequency range, within the low‐loss spectral window of ZnTe. The engineered modal dispersion dictates the phase‐matched THz frequency, while THz absorption determines the effective nonlinear interaction length. Experimentally, we observe continuous shifts of the emitted THz spectrum with varying optical pump wavelength and slab geometry, in agreement with theoretical predictions. These results establish nonlinear crystal slab waveguides as a compact and spectrally reconfigurable platform for guided‐wave THz generation, enabling both narrowband and broadband operation within a single scalable architecture.