Fig. 1. Characterization of waveguide surface profile and roughness. (a) Electron scanning image of χ⁽²⁾ ZGP waveguide; (b) Profile measurement of a ZGP waveguide with a 30º tilt for the side wall of the groove, measured by laser microscope (Olympus, OSL5000); (c) Measured cross-section of χ⁽²⁾ZGP waveguide; (d) Three-dimensional surface profile of χ⁽²⁾ ZGP waveguide

Fig. 2. F-P cavity loss measurement experimental device and test results. (a) Transmission loss experimental device diagram; (b)-(c) Transmission F-P interferogram for 8.5 mm and 6.6 mm ZGP samples measured at TE and TM polarization

Fig. 3. Experimental device for measuring transmission loss by truncation method. (a) 8 mm ZGP waveguide transmission loss experimental device; (b) 10 mm ZGP waveguide transmission loss experimental device

Fig. 4. Optical difference frequency experiment device based on ZGP and long-wave mid-infrared produce results. (a) Optical difference frequency experiment device based on ZnGeP₂ waveguide; (b) 2.4-2.5 μm tunable pump spectra; (c) 3.37-3.6 μm tunable signal spectra; (d) Idle frequency spectra covering a range of 7-10 μm, labeled as idle light corresponding to the pump

Fig. 5. The phase matching curve of a type I ZGP waveguide is plotted for three different pump wavelengths. (a) 2.4 µm; (b) 2.45 µm; (c) 2.5 µm