Reduced pulse energy for frequency stabilization with a dual-pitch periodically poled lithium niobate ridge waveguide

Techniques for stabilizing the carrier-envelope offset (CEO) frequency of an optical frequency comb are prerequisites for precision spectroscopy. A 2f-to-3f self-referencing interferometer (SRI) requires only a 2/3-octave bandwidth of supercontinuum (SC) light; however, it has not been regarded as a practical method because the conversion efficiency of third-harmonic generation is much lower than that of the second-harmonic generation. To solve this problem, we utilized a dual-pitch periodically poled lithium niobate (PPLN) ridge waveguide that has two different quasi-phase matching pitch sizes [Fig. 1(a)] [1]. Here, we report the advantage of using the dual-pitch PPLN ridge waveguide over using a single-pitch one, i.e., reduction of the pulse energy for stabilizing the CEO frequency.