Fig. 3: Experimental setup and characterizations of the spectra, output power, pump threshold and parametric gain of the χ⁽²⁾ micro-waveguide with birefringence PM based on a ZGP crystal.

a The schematic of the experimental setup for optical parametric generation (OPG) from the χ⁽²⁾ waveguide. b The pump spectrum centered at 2.4 μm. c The measured OPG spectra from the χ⁽²⁾ waveguide with different pump peak powers. The generated LWIR idler wave has an octave-spanning spectrum covering 5.4 to 10.3 μm at −20 dB, which is in good agreement with the simulated result in Fig. 1a. The noise floor is marked by a gray dotted line. d The measured OPG output power shown in a linear scale as a function of pump pulse energy and average power. The measured pump threshold energy is ~616 pJ, corresponding to a peak power of 1.9 kW. In addition, When the pump energy is 6.5 nJ corresponding to an average power of 3.25 mW, a LWIR power of 0.72 mW is detected from the χ⁽²⁾ waveguide, corresponding to a power efficiency of 22% and a quantum efficiency of 74%. Meanwhile, further increasing the pump energy, the output power tends to saturate. Particularly, when the pump pulse energy is larger than 9 nJ, the LWIR output power decreases, due to parametric back conversion. e The OPG output intensity in a logarithm scale at different pump energy. A saturated parametric gain of >58.6 dB/cm calculated from the measured maximum idler power (0.83 mW) and minimum idler power (1.1 nW) is observed at a pump energy of 7.9 nJ, which indicates that a decent parametric gain could be provided by the χ⁽²⁾ waveguide device. The inset shows the measured beam profile of LWIR OPG from the χ⁽²⁾ waveguide, which agrees well with the simulated field profile shown in Fig. 1b.