This paper presents an open and flexible digital phase lock loop optimized for laser stabilization systems. It is implemented on a cheap and easily accessible FPGA-based digital electronics platform (Red Pitaya) running a customizable open-source firmware. A PCbased software interface allows controlling the platform and optimizing the loop parameters remotely. Several tools are included to allow measurement of quantities of interest smoothly and rapidly. To demonstrate the platform's capabilities, we built a fiber noise canceler over a 400 m fiber link. Noise cancellation was achieved over a 30 kHz bandwidth, a value limited mainly by the delays introduced by the actuator and by the round-trip propagation over the fiber link. We measured a total latency of 565 ns for the platform itself, limiting the theoretically achievable control bandwidth to approximately 225 kHz.

The phase information provided by the beat note between frequency combs and two continuous-wave lasers is used to extrapolate the phase evolution of comb modes found in a spectral region obtained via nonlinear broadening. This thereafter enables using interferogram self-correction to fully retrieve the coherence of a dual-comb beat note between two independent fiber lasers. This approach allows the f − 2 f self-referencing of both combs, which is a significant simplification. Broadband near-infrared methane spectroscopy has been conducted to demonstrate the simplified system’s preserved performance.

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The impact of photodetector nonlinearity on dual-comb spectrometers is described and compared to that of Michelson-based Fourier transform spectrometers (FTS). The optical sampling occurring in the dual-comb approach, being the key difference with FTS, causes optical aliasing of the nonlinear spectral artifacts. Measured linear and nonlinear interferograms are presented to validate the model. Absorption lines of H13CN are provided to understand the impact of nonlinearity on spectroscopic measurements.

We add optical referencing to a technique interrogating gas samples with two frequency combs by varying their repetition rate difference periodically. The reduce interferogram measurement time yields an improved SNR and an optimized resolution.