Axis 3 – Active and Agile Compact Systems:
Where are we with frequency-comb generation?
Whispering-gallery mode optical resonators are devices made from transparent glass- or crystalline disks, spheres or rings of typically mm- to 50-µm-diameters. Though conceptually simple, they have the remarkable capability to internally trap light around their circumference during exceptionally long times (as qualified by their highest possible quality factor). They can thereby maximize light-matter interactions at low optical power for, e.g., nonlinear generation of novel sideband frequencies from a single laser spectral line, the so-called optical frequency combs. Such combs consist of a precise and extended sequence of discrete and equally spaced spectral lines, which makes them ideal optical rulers for a breadth of applications. Primarily they constitute absolute references for spectroscopy and ultra-high-precision optical clocks used in time-metrology. But, they are also expected to be disruptive as ultra-stable microwave optoelectronic oscillators for aerospace engineering, extremely high-repetition-rate pulsed sources for Tb/s optical fibre communications, and hopefully ultimate photon generators for quantum information and sensing.
Though fabrication of whispering gallery mode optical resonators is still a challenge, especially in their integrated on-chip version, frequency-comb generation has thus become a major thriving research area in photonics this last decade. EIPHI researchers are recognized among the world leaders of this competitively hot topic, which gave them the opportunity to write or contribute to two recent review papers, published in prestigious journals, which feature the up-to-date global advances, both from the physical, technological and application-driven point of views.
G.P. Lin, A. Coillet, Y.K. Chembo, “Nonlinear photonics with high-Q whispering-gallery-mode resonators”, Advances in Optics and Photonics 9, 4, 828-890 (Dec. 2017). DOI: 10.1364/AOP.9.000828
A. Pasquazzi et al., “Micro-combs: A novel generation of optical sources”, Physics Reports 729, 1-81 (Jan. 2018). DOI: 10.1016/j.physrep.2017.08.004