Techniques to measure and manipulate the carrier-envelope phase within femtosecond optical parametric oscillators allow their outputs to be stabilized in a way that produces a frequency-comb structure, potentially tunable throughout the transparency band of the gain material. In this review we describe the fundamental principles of phase control, on which the development of singly- and doubly-resonant optical parametric oscillator frequency combs is based. We give examples of practical embodiments of such combs, and discuss in detail several applications, including spectroscopy, metrology, quantum computation and astrophotonics.
Kobayashi, Y., Torizuka, K., Marandi, A., Byer, R. L., McCracken, R. A., Zhang, Z., & Reid, D. T. (2015). Femtosecond optical parametric oscillator frequency combs. Journal of Optics, 17(9), . https://doi.org/10.1088/2040-8978/17/9/094010