Mid-infrared frequency combs at 10 GHz
Abijith S. Kowligy, David R. Carlson, Daniel D. Hickstein, Henry Timmers, Alexander J. Lind, Peter G. Schunemann, Scott B. Papp, Scott A. Diddams
Abstract
We demonstrate mid-infrared (MIR) frequency combs at 10 GHz repetition rate via intra-pulse difference-frequency generation (DFG) in quasi-phase-matched nonlinear media. Few-cycle pump pulses ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>≲</mml:mo> </mml:mrow> <mml:mn>15</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">f</mml:mi> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:math> , 100 pJ) from a near-infrared electro-optic frequency comb are provided via nonlinear soliton-like compression in photonic-chip silicon-nitride waveguides. Subsequent intra-pulse DFG in periodically poled lithium niobate waveguides yields MIR frequency combs in the 3.1–4.8 µm region, while orientation-patterned gallium phosphide provides coverage across 7–11 µm. Cascaded second-order nonlinearities simultaneously provide access to the carrier–envelope-offset frequency of the pump source via in-line <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>f</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>-</mml:mtext> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>2</mml:mn> <mml:mspace width="negativethinmathspace"/> <mml:mi>f</mml:mi> </mml:mrow> </mml:math> nonlinear interferometry. The high-repetition rate MIR frequency combs introduced here can be used for condensed phase spectroscopy and applications such as laser heterodyne radiometry.