Fig. 1. Small-signal gain of the degenerate OPA. (a) Short-pulse OPA measurement setup (The insets show a SEM image of the chip facets after polishing and a second-harmonic microscope image of the periodic poling before waveguide fabrication); (b) Top, triangular voltage driving the PZT in the delay line; bottom, measured detector output with and without the pump; (c) Measured signal spectrum with and without the pump; (d) Measured gain versus pump pulse energy (Input signal pulse energy in the waveguide is fixed at 0.2 fJ); (e) Measured gain versus input signal pulse energy for 1 pJ pump pulse energy, showing evidence of gain saturation over the entire range of signal energies measured^[11]

Fig. 2. Measurements in the large-gain regime through OPG. (a) OPG spectra for different pump energies; (b) OPG pulse energy versus pump pulse energy in the waveguide for a 6-mm-long device; (c) Extracted gain versus pump pulse energy, showing values exceeding 100 dB/cm^[11]

Fig. 3. (a) PPLN waveguide design; (b) Simplified schematic of the experimental setup (The blue lines stand for the 1 µm fs pump and the red for the 2 µm OPO signal); (c) Measured OPO optical spectra as a function of the pump laser repetition frequency for a pump power of 170 mW; (d) Coarsely sampled waterfall plot of the same data^[12]

Fig. 4. (a) Dimensions and composition of the OP-GaAs/AlGaAs rib waveguides; （b） Experimental setup for OPG in OP-GaAs waveguides (Inset: typical full-field spectrum at the waveguide output); （c） Idler and signal spectra for the 10, 11, and 12 μm waveguides. The corresponding pump wavelengths are 3.076, 3.004, and 2.92 μm, respectively; (d) Close-up of the modulations on the signal spectra, attributed to atmospheric CO₂ absorption between 4270 and 4375 nm^[13]

Fig. 5. (a) OP GaAs/AlGaAs waveguide; (b) The effect of pump pulse duration on the OPG process; (c) Experimental setup diagram for generating mid infrared supercontinuum spectra; (d) The supercontinuum spectrum generated in the OP GaAs waveguide; (e) The spectral distribution evolution calculated along the waveguide length; (f) When the pump wavelength is in the group velocity matching state, the optical parameters obtained generate spectra; (g) Computational evolution of spectral distribution along waveguide length^[14]

Fig. 6. Production process of ZGP waveguide. (a)-(b) Use ultraviolet curing optical adhesive to bond block ZGP crystal to fused silica substrate; (c) Grind and polish the crystal to a thickness of approximately 40 μm; (e)-(f) Ultra fast laser direct writing of ZGP crystal circular ridge waveguide structure; (g) For the ground ZGP on SiO₂ chip; (h) Waveguide scanning electron microscope images ^[15]

Fig. 7. (a) Experimental setup diagram of waveguide OPG; (b) Pump spectrum; (c) OPG spectra generated by different pump peak powers; (d) OPG output power as a function of pump pulse energy and average power; (e) OPG output intensity under different pump energies^[15]

Fig. 8. (a) Schematic diagram of a two-step conical method for SCF optimization; (b) Schematic diagram of conical SCF for Raman scattering; (c) Experimental setup for spontaneous Raman scattering and stimulated Raman amplification measurement; (d) Spontaneous Raman emission spectra at different average pump powers, with a pump wavelength of 1.99 μm; (e) The relationship between spontaneous Stokes power and coupled average pump power; (f) Spectral evolution of cascaded Raman scattering simulated by 2 μm pulse laser pumping; (g) The peak output power of Stokes waves varies with the length of the fiber; (h) Simulated spectral evolution using a 2.2 μm pulse laser pump; (i) The relationship between output Stokes peak power and fiber length^[18]

Fig. 9. Raman laser based on diamond micro resonator

Fig. 10. (a) The schematic diagram of the suspended rib As₂Se₃ waveguide; (b) The structure of the cascaded waveguide; (c) The schematic diagram of the cascading strategy for extending the SSFS range; (d)-(e) Spectral and temporal evolution of the Raman soliton as the pump pulse energy increases from 2.4 to 300 pJ; (f) Raman SSFS induced wavelength shift in the waveguide W1 and the cascaded waveguide^[21]

Fig. 11. (a) Schematic diagram of four wave mixing device; (b) When the pulses are temporally overlapped, the phase-matched idler is generated in the 3 μm band (red), and the signal undergoes spectral broadening due to FWM-induced phase modulation (inset). Without temporal overlap, the idler is not present (blue); (c) Tunable MIR light is generated from 2.6 to 3.6 μm for different waveguide widths in the experiment (solid lines) and from theoretical predictions (dashed lines)^[30]

Fig. 12. (a) Experimental setup for the generation of MIR OFCs in the MgF₂ resonator. MIR frequency comb spectrum with different pump-resonance detuning in the MgF₂ resonators of (b) ~2 mm diameter and (c) ~9 mm diameter, and the pump QCL operated at 4.78 μm (black line); (d) MIR frequency comb spectrum with evenly spaced modes in MgF₂ resonators with diameters of ~2 mm (blue line) and ~9 mm (red line). Spectrum generated by a ~2 mm diameter MgF₂ resonator under pump power of about (e) 200 mW, (f) 240 mW, and (g) 280 mW^[42]

Fig. 13. (a) Schematic diagram of an all sulfur glass integrated microresonator for MIR comb. The illustration shows the waveguide structure and mode field of the microresonator, as well as the transmission spectrum of chalcogenide glass; (b) The integrated dispersion curves of microresonators with different widths; (c) The generated Kerr frequency comb^[43]

Fig. 14. (a) SEM image of sulfur based glass waveguide; (b) SC generated by pumping at different peak powers^[48]