Wei Wu, Qibing Sun, Yi Wang, Yu Yang, Xianshun Ming, Lei Shi, Keyi Wang, Wei Zhao, Leiran Wang, "Mid-infrared broadband optical frequency comb generated in MgF2 resonators," Photonics Res. 10, 1931 (2022)

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- Photonics Research
- Vol. 10, Issue 8, 1931 (2022)

Fig. 1. (a) Image of the MgF 2 crystalline microresonator. (b) Calculated fundamental mode intensity profiles in resonators with 30° wedge angle at 4.78 μm. (c) Measured transmission spectrum (blue line) of the resonator and Lorentzian fit (red line) in the communication band. (d) Optical microscopic image of the As 2 S 3 tapered fiber waist with a subwavelength diameter of ∼ 1.5 μm .

Fig. 2. (a) Integrated dispersion curve around the pump versus mode number μ . (b) Intracavity power as the pumping laser is tuned across a cavity resonance from the blue to red detuning. The inset shows the zoom-in for the dashed box. (c) Spectral envelope evolution corresponding to panel (b). (d) Temporal waveforms (orange) and optical spectra (blue) corresponding to the (i) MI, (ii) multi-soliton, and (iii) single-soliton states.

Fig. 3. (a) Temporal and (b) spectral evolution of the single soliton formation. (c) Evolution of intracavity average power plotted versus time. The inset shows the zoom-in for the dashed square.

Fig. 4. Experimental setup for the generation of MIR OFCs in the MgF 2 resonator. QCL, quantum cascade laser (inset, photograph of QCL module); AL, aspheric lens; ChG TF, As 2 S 3 tapered fiber; BS, beam splitter; PD, photodetector; OSC, oscilloscope; GM, gold mirror; FTIS, Fourier transform infrared spectrometer.

Fig. 5. MIR frequency comb spectrum with different pump-resonance detuning in the MgF 2 resonators of (a) ∼ 2 mm diameter and (b) ∼ 9 mm diameter, and the pump QCL operated at 4.78 μm (black line). (c) MIR frequency comb spectrum with evenly spaced modes in MgF 2 resonators with diameters of ∼ 2 mm (blue line) and ∼ 9 mm (red line).

Fig. 6. MIR frequency comb spanning from 3380 nm to 7760 nm. Spectrum generated by a ∼ 2 mm diameter MgF 2 resonator under pump power of about (a) 200 mW, (b) 240 mW, and (c) 280 mW.

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