Optical frequency counter/synthesizer apparatus

One or more optical parametric oscillators are arrayed selectively singly, serially, and/or in parallel, and each oscillator is responsive to an input pump beam having a fractional stability to produce output signal and idler beams having fractional stabilities that correspond to or are better than the fractional stability of the pump beam and in such a way that the sum of the frequencies of the output signal and idler beams of each optical parametric oscillator is constrained to be equal to the frequency of the input beam thereof. One or more beat detectors are responsive to selected one or more signal and idler beams and reference beams of already known frequency and fractional stability to provide one or more beat detection signals having linewidths corresponding to or better than the linewidths of the selected one or more signal and idler beams and reference frequency beams and in such a way that the frequency of the one or more beat detection signals is constrained to be equal to the difference in frequency between the selected one or more signal and idler beams and reference frequency beams. The sum and difference frequency constraints completely determine the absolute frequencies of the several beams thereby enabling in selected different configurations ultrahigh resolution optical frequency calibration and recalibration, broadband ultrahigh resolution frequency synthesis and, among others, wideband frequency combs of phase-locked reference frequency outputs. In one parallel embodiment, optical frequencies may either be counted or synthesized relative to a microwave reference frequency, and vice versa.