Operation of an optically coherent frequency comb outside the metrology lab (1312.6072v1)

Abstract: We demonstrate a self-referenced fiber frequency comb that can operate outside the well-controlled optical laboratory. The frequency comb has residual optical linewidths of < 1 Hz, sub-radian residual optical phase noise, and residual pulse-to-pulse timing jitter of 2.4 - 5 fs, when locked to an optical reference. This fully phase-locked frequency comb has been successfully operated in a moving vehicle with 0.5 g peak accelerations and on a shaker table with a sustained 0.5 g rms integrated acceleration, while retaining its optical coherence and 5-fs-level timing jitter. This frequency comb should enable metrological measurements outside the laboratory with the precision and accuracy that are the haLLMarks of comb-based systems. Work of the U.S. government, not subject to copyright

Overview of the Self-Referenced Fiber Frequency Comb

The paper by Sinclair et al. presents the development and experimental evaluation of a self-referenced fiber frequency comb designed for operation outside the well-controlled optical laboratory environment. The significance of this paper lies in its focus on a coherent frequency comb system capable of maintaining high performance across challenging terrestrial conditions, potentially transforming applications in precision metrological measurements and spectroscopy outside traditional settings.

Technical Achievements

The fiber frequency comb demonstrated in this research achieves residual optical linewidths of less than 1 Hz, sub-radian residual optical phase noise, and pulse-to-pulse timing jitter between 2.4 and 5 femtoseconds when locked to an optical reference. Remarkably, the comb maintains its optical coherence even under the dynamic conditions of a moving vehicle or on a shaker table, with accelerations reaching up to 0.5 g rms integrated acceleration.

Design and Performance

The design primarily utilizes polarization-maintaining fiber and telecom-grade fiber-optic components, ensuring robustness against environmental perturbations like vibrations and alignment drifts. The incorporation of a semiconductor saturable absorber mirror (SESAM) facilitates self-mode-locking, enhancing the laser's compatibility with high-performance applications. The paper reports successful operation of an optically stabilized frequency comb with a 200 MHz repetition rate, providing comprehensive coverage from 1.05 µm to over 2.3 µm. This performance parallels that achieved within laboratory conditions, matching the stringent requirements for optical metrology applications such as optical clocks, precision LADAR, and spectroscopy.

Experimental Validation

Experimental validation conducted in high-vibration environments—such as in a moving vehicle or on shaker tables—substantiated the comb's resilience and optical coherence. Even in strong vibrational environments typical of terrestrial applications, the comb's Hz-level residual linewidths and femtosecond-level timing jitter indicate its readiness for deployment in diverse mobile platforms, including trucks, ships, and aircraft.

Implications and Future Directions

The findings of Sinclair et al. hold significant implications for the deployment of frequency comb technology in non-laboratory settings, particularly in trace gas sensing, clock-based geodesy, and free-space frequency transfer applications. The adaptation of fiber-based comb technology to robust field operation could expand the scope of precision metrology, facilitating measurements with high accuracy and reliability outside traditional laboratory environments.

Future directions may explore further improvements in mechanical packaging and vibration isolation techniques, potentially reducing sensitivity to vibrational interference and broadening the range of viable applications. Additionally, increasing the feedback bandwidth and conducting more comprehensive evaluations of different mobile platforms could refine the comb's operational stability and resilience.

In summary, this paper offers critical insights into the advancement of fieldable coherent frequency comb technology, laying the groundwork for future innovations in precision metrology and spectroscopy outside controlled laboratory settings.