Signal extraction in a power-recycled Michelson interferometer with Fabry–Perot arm cavities by use of a multiple-carrier frontal modulation scheme

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Abstract
We present a signal extraction scheme for longitudinal sensing and control of an interferometric gravitational-wave detector based on a multiple-frequency heterodyne detection technique. Gravitational-wave detectors use multiple-mirror resonant optical systems where resonance conditions must be satisfied for multiple degrees of freedom that are optically coupled. The multiple-carrier longitudinal-sensing technique provides sensitive signals for all interferometric lengths to be controlled and successfully decouples them. The feasibility of the technique is demonstrated on a tabletop-scale power-recycled Michelson interferometer with Fabry–Perot arm cavities, and the experimentally measured values of the length-sensing signals are in good agreement with theoretical calculations.