Periodically poled lithium niobate ridge waveguides with high conversion efficiency for 2f-to-3f self-referencing interferometer

The generation of second- and third-harmonic light with single- and dual-pitch periodically poled lithium niobate ridge waveguides for achieving a carrier-envelope-offset-locked frequency comb with low pulse energy is investigated. The wavelengths of both the second- and third-harmonic light converted by short- and long-wavelength components of supercontinuum spectra are precisely adjusted by selecting appropriate pitch size and controlling the temperature of the devices. The output powers of the second- and third-harmonic light are 9.1 and 4.8 μW, respectively, when using a 2/3-octave-wide supercontinuum light generated by a 1.2 nJ laser pulse at a repetition rate of 250 MHz.