Low-Threshold Fully-Stabilized Mid-Infrared Frequency Comb Generation

Abstract

Optical Parametric Generation (OPG) has established itself as an alternative approach to difference frequency generation and optical parametrical oscillation for converting femtosecond pulses to the mid-infrared (MIR) spectral region [1] . Although it is a simple and robust technique, OPG on its own does not lead to pulse-to-pulse coherence – which is a prerequisite for fully-stabilized Optical Frequency Comb (OFC) generation - since the process is based on quantum noise amplification. Recently we have demonstrated a solution to this problem using single-pass femtosecond Continuous-Wave (CW) seeded OPG in MgO doped periodically poled lithium niobate (MgO: PPLN) [2] . This method allows one to generate fully-stabilized MIR OFC with high conversion efficiency (more than 40%) and high MIR output power [2] . In addition, it opens up opportunities for precise and independent control of carrier-envelope offset frequency and repetition rate of the MIR comb, which is valuable for metrological and spectroscopic applications. Despite the fact that in OPG the conversion efficiency is high, the pump pulse energies required to start up the process usually lie at the nJ level [1] , [2] . This is because the process takes place in a bulk nonlinear crystal. A natural step towards OPG threshold reduction is the use of nonlinear waveguides [3] , since it helps to enhance the light-matter interactions, which we are going to discuss in this work.