Generation and Stabilization of a Terahertz Spanning Electro-Optic Modulated Oscillator Comb

We demonstrate a terahertz spanning electro-optic modulated comb simultaneously generated and filtered by an optoelectronic oscillator using an ultrahigh finesse etalon (free spectral range: 1.5 GHz & FWHM: 15 kHz) as a photonic filter. The Fabry Perot etalon is used as a stable reference filter for the oscillation of the RF signal. Photodetection of the optically filtered light provides oscillation signals that are commensurate with integer multiples of the free spectral range. By generating additional comblines prior to the etalon, we fully utilize the etalon's stability and filtering capabilities to lock & filter the optical carrier and the repetition rate. This combination of a photonically filtered optoelectronic oscillator and electro-optic modulated comb results in a spectrally flat comb of at least 110 optically filtered comblines, with < 10 Hz optical linewidth, spaced 10.5 GHz apart, and pulses compressible to under 1 ps. The fractional frequency stability was measured to be 2.5x10(-11) at 4 s averaging, demonstrating an order of magnitude improvement in stability over our previous work (5x10(-10)).