Frequency accurate coherent electro-optic dual-comb spectroscopy in real-time.

Electro-optic dual-comb spectrometers have proved to be a promising technology for sensitive, high-resolution and rapid spectral measurements. Electro-optic combs possess very attractive features like simplicity, reliability, bright optical teeth, and typically moderate but quickly tunable optical spans. Furthermore, in a dual-comb arrangement, narrowband electro-optic combs are generated with a level of mutual coherence that is sufficiently high to enable optical multiheterodyning without inter-comb stabilization or signal processing systems. However, this valuable tool still presents several limitations; for instance, on most systems, absolute frequency accuracy and long-term stability cannot be guaranteed; likewise, interferometer-induced phase noise restricts coherence time and limits the attainable signal-to-noise ratio. In this paper, we address these drawbacks and demonstrate a cost-efficient absolute electro-optic dual-comb instrument based on a frequency stabilization mechanism and a novel adaptive interferogram acquisition approach devised for electro-optic dual-combs capable of operating in real-time. The spectrometer, completely built from commercial components, provides sub-ppm frequency uncertainties and enables a signal-to-noise ratio of 10000 (intensity noise) in 30 seconds of integration time.

Frequency-tunable photonic frequency synthesis from an optical frequency comb reference.

We present an architecture for photonic-assisted RF signal synthesization that uses as a reference the optical repetition frequency of an optical frequency comb. The setup, which is based on a multiharmonic photonic phase frequency detector, enables a perfect phase-locking of a voltage-controlled oscillator to multiples and submultiples of the repetition frequency of the reference comb, operating hence as an optically referenced phase-locked frequency-tunable synthesizer. The design of the system, which is also capable of operating with RF reference inputs, is very well suited for highly stable signal generation and optical clock distribution networks, as signal synthesization is performed directly from the provided optical reference.