Optical-to-microwave frequency chain utilizing a two-laser-based optical parametric oscillator network

A method for building an optical-to-microwave frequency chain and for measuring optical frequencies relative to the cesium primary frequency standard is described. Based on optical frequency division via parametric oscillators, the concept is to generate two known ratios (1/2 and 4/9) of an optical calibration frequencyf₁ whose frequency difference is measured relative to the cesium clock. The (1/2) ratio is obtained by either a 2:1 frequency division off₁ or second-harmonic generation of (l/2)f₁. The (4/9) ratio off₁ can be generated with a 3:1 frequency divider driven by a second laser atf₂ that is chosen to be near (2/3)f₁, which in turn is obtained with af₁-pumped 3:1 frequency divider. A set of auxiliary Optical Parametric Oscillators (OPOs) with outputs centered at (1/2)f₁ is used to facilitate the difference-frequency measurement between the two ratios. A practical configuration utilizing a YAG and a Ti: Al₂O₃ laser and its application to a number of precision measurements of interest are presented.