20 years of developments in optical frequency comb technology and applications (1909.05384v1)

Abstract: Optical frequency combs were developed nearly two decades ago to support the world's most precise atomic clocks. Acting as precision optical synthesizers, frequency combs enable the precise transfer of phase and frequency information from a high-stability reference to hundreds of thousands of tones in the optical domain. This versatility, coupled with near-continuous spectroscopic coverage from the terahertz to the extreme ultra-violet, has enabled precision measurement capabilities in both fundamental and applied contexts. This review takes a tutorial approach to illustrate how 20 years of source development and technology has facilitated the journey of optical frequency combs from the lab into the field.

• The paper demonstrates that optical frequency combs revolutionized metrology by replacing complex frequency chains with mode-locked lasers, achieving over a hundredfold resolution improvement.
• The paper details the evolution from solid-state and fiber-based systems to compact chip-scale platforms, addressing challenges in nonlinear efficiency and mode regularity.
• The paper highlights diverse applications, including atomic clock comparisons, dual-comb spectroscopy, and ultra-low noise microwave generation for advanced scientific measurements.

Overview of Two Decades of Optical Frequency Comb Technology and Applications

The paper by Fortier and Baumann provides a comprehensive review of advancements in optical frequency comb (OFC) technology over the past two decades, tracing its journey from laboratory experimentation to widespread application. These devices, which originated to enhance atomic clock precision, now hold a versatile role in various scientific and industrial contexts, operating between terahertz and extreme ultra-violet frequencies.

Initially conceived to simplify the frequency measurement processes reliant on atomic clocks, OFCs replace complex frequency multiplication chains with straightforward, reliable mode-locked lasers. This innovation allowed for the precise transfer of frequency and phase information across broad optical spectra. The paper underscores how this breakthrough facilitated tremendous strides in optical metrology, permitting optical-to-microwave frequency conversions with resolutions improved by over a hundredfold compared to prior methods. The remarkable capability of OFCs to provide well-calibrated frequency spectrums enables their use in diverse fields, including molecular spectroscopy, precision ranging, and even atmospheric gas sensing.

Technological and Methodological Advancements

Fortier and Baumann detail the thematic progression of OFC development, starting from mode-locked laser systems, which harnessed optical nonlinearities for extreme spectral broadening. The transition from solid-state and fiber-based systems to compact semiconductor and micro-resonator platforms reflects ongoing efforts to reduce size, weight, and power requirements while expanding spectral reach. These latter platforms, despite facing challenges in nonlinear efficiency and mode regularity, present promising avenues for photonic integration and mass production.

Special attention is given to the mechanisms underlying OFC stabilization and performance, with discussion around noise management strategies and referencing schemes involving both microwave and optical domains. The intricacies of carrier-envelope offset frequency ($f_0$) detection and its stabilization are pivotal to the OFC's precise operation, with implications for synchronous application across various measuring contexts.

Impact on Optical Metrology and Beyond

The paper highlights OFCs as transformative tools in atomic clock comparisons, where their application has led to benchmarks previously unobtainable, such as exceeding $10^{-18}$ fractional stability in frequency standards. This precision is not only foundational for redefining the SI second but also excels in testing fundamental physics concepts like time dilation and gravitational shifts at new scales of sensitivity.

Further delineated are OFC applications in telecommunications and ultra-low noise microwave generation, wherein the precision of OFC phase coherence facilitates highly stable microwave signal derivation, impacting domains like radar and synchronization in high-energy physics experiments.

Moreover, the document explores emerging fields for OFCs, such as dual-comb spectroscopy, which significantly enhances temporal resolution and measurement speeds over traditional techniques. This sets the stage for robust implementations in atmospheric research, molecular spectroscopy, and potentially, space-based applications.

Implications and Future Perspectives

The authors address the OFC's move beyond the precise but costly metrology laboratory environments towards potential applications in broader commercial and scientific domains. Future discourse in the paper considers the momentum towards even more integrated, chip-scale OFC systems, which could make advanced frequency comb technologies more accessible across industries by offering lower cost and complexity without sacrificing performance.

The research paper by Fortier and Baumann asserts that ongoing developments in OFC technology, coupled with progress in related fields such as atomic clock transportability and photonic integration, promise to extend OFCs' applicability. As these technologies become increasingly compact and less resource-intensive, OFCs might find growing applications in global network synchronization, environmental analysis, and sophisticated communication systems.

In summary, this thorough review emphasizes the dual role of OFCs as both a revolutionary tool in precision frequency metrology and a facilitator of new scientific endeavors, underlining the prospect of their integration into a wider array of applications as advancements continue.