Laura C. Sinclair, Jean-Daniel Deschenes, Lindsay I. Sonderhouse, William C. Swann, Isaac H. Khader, Esther Baumann, Nathan R. Newbury, Ian R. Coddington
We describe design and operation of a robust self-referenced, optically coherent frequency comb. The system robustness is derived from a combination of an optics package based on polarization-maintaining fiber, high signal-to-noise ratio (SNR) detection of the control signals, and digitally-based feedback control for stabilization. The output is phase-coherent over the entire or nearly entire 1-to-2-m octave-spanning spectrum with a pulse repetition rate of ~ 200 MHz and a pulse-to-pulse timing jitter of a few femtoseconds, well within the requirements of almost all frequency-comb applications. The digital control enables the comb output to retain phase coherence with the input optical reference (i.e. avoid phase-slips) for over 90 hours, which is critical for phase-sensitive applications such as timekeeping. We show that this phase-slip free operation follows the fundamental limit set by the SNR of the detected control signals. Here we present a detailed discussion of the critical aspects of the comb design and fabrication, as well as the expected performance based on data acquired with three nearly identical combs. This frequency comb design should enable a wide-range of applications beyond the laboratory.