Low-noise microwave signals from a frequency-stabilized Yb:Tungstate optical frequency comb

In this paper, an approach employing a 180-MHz repetition rate, diode-pumped Yb-doped tungstate (Yb:KYW) frequency comb is demonstrated. This approach to low noise microwave generation requires the Yb:KYW laser be self-referenced and phase-locked to a stable continuous wave (CW) laser. The Yb:KYW laser functions as an optical-to-microwave frequency divider. An octave spanning spectrum (650-1400 nm) is achieved from the Yb:KYW output after amplification in Yb: fiber, followed by compression and nonlinear broadening in microstructured optical fibre. The carrier envelope offset frequency is detected and stabilized with integrated phase noise of 0.3 rad (1 Hz to 1 MHz). The repetition rates of Yb:KYW laser are detected with high-speed P-I-N detectors and the 2^nd and 11^th harmonics of the respective microwave signals (near 2 GHz) are mixed to an audio frequency and counted with a high resolution counter.