a, Schematic of a typical OPO and the proposed OEPO. b, Energy transitions in a typical OPO and in the proposed OEPO. Oscillation in the OPO is based on optical parametric amplification. The energy flows from the pump to the signal and idler through an optical nonlinear medium. There is no phase jump for the oscillating signals in the optical nonlinear medium. In the proposed OEPO, oscillation is based on electrical parametric frequency conversion. A pair of oscillations is converted into each other in the electrical nonlinear medium by the local oscillator (LO). There is a phase jump for the oscillating signals in the nonlinear medium, which leads to the unique mode properties of the proposed OEPO. c, Cavity modes of OPO and the proposed OEPO. The cavity modes of OPO are discrete, and the minimum mode spacing is the cavity free spectral range (FSR), which is 2π?τ where τ is the cavity delay. Due to the phase jump in the parametric frequency conversion process, the cavity modes of OEPO can be continuously tuned by tuning the LO. The minimum mode spacing is π?τ. PD: photodetector; LNA: low noise amplifier; BPF: bandpass filter.
by Tengfei Hao, Qizhuang Cen, Shanhong Guan, Wei Li, Yitang Dai, Ninghua Zhu, and Ming Li