Fig. 1. Schematic configuration of the experimental setup: pump light from a DFB laser is coupled into a WGMR via a rutile prism after being amplified by a Yb3+-doped fiber amplifier. The output light is collimated by an aspherical lens L. M is high reflection coated for the signal and anti-reflection coated for the pump and idler. A beam splitter (BS) is used to separate the signal into two beams; hence, the signal can be detected by the OSA and oscilloscope simultaneously. PD1, 2 are used for pump and signal detection, respectively. Inset: the glowing resonator and its outcoupled light recorded by a camera. The pink spot is the residual pump, the red one is the sum frequency of the pump and signal light, and the green is the frequency doubling of the pump.

Fig. 2. Transmitted pump and signal from our PPCLT WGMR. Free spectrum range of the WGMR is approximately 13.9 GHZ (R≈1.60  mm). The fundamental mode is over-coupled for a high-power signal output. The thermal-pulling effect is significant in our experiment because of the high pump power. Inset: the measured quality factor of a PPCLT WGMR under a weak coupling condition.

Fig. 3. Spectrum recorded by the OSA. The temperature of the resonator is around 23.3°C. The generated signal is at 1905 nm and the idler at 2410 nm when the pump wavelength is 1063.9 nm. The inset shows obtained the signal and idler power as a function of the coupled pump power. Both the generated light and pump light are corrected for absorption and the Fresnel reflection. The pump is also corrected for coupling efficiency.

Fig. 4. Tunability of a PPCLT WGMR with a period around 28.5 μm and R=1.75  mm. The poling period is chosen far away from the degeneracy point to offer a wide tuning range.