Integrated Fabry–Perot Cavities: A Quantum Leap in Technology: Comparison
Please note this is a comparison between Version 3 by Vicky Zhou and Version 2 by Vicky Zhou.

Integrated Fabry–Perot cavities (IFPCs), often referred to as nanobeams due to their form factor and size, have profoundly modified the landscape of integrated photonics as a new building block for classical and quantum engineering. In this entry, the main properties of IFPCs will be summarized from the classical and quantum point of view. The classical will provide some of the main results obtained in the last decade, whereas the quantum point of view will exp

  • photonics
  • electromagnetism
  • Fabry–Perot
  • integrated optics
  • quantum optics

In the quest for faster optical communication, researchers have been motivated to explore innovative optoelectronic devices. In the meantime, electronics circuits are approaching their limits in terms of bandwidth and power efficiency. For these reasons, keeping signals in the optical domain is seen as a possible strategy to overcome these limitations and continue to improve the high-performance computing (HPC) throughput and power efficiency. To achieve this, optical micro-cavities, which confine light in small volumes at optical wavelength scales, have emerged as important components for signal processing functions. Fabry–Perot cavities, from their inception [1] to the present day, have found many applications in telecoms, spectroscopy and sensing technologies [2,3][2][3]. The development of integrated optics in the last few decades has brought renewed interest in integrated Fabry–Perot cavities (IFPCs). High-Q optical microcavities, in particular, characterized by their high quality factor (Q) and their ability to confine light in small modal volumes (VM), have been at the heart of recent advancements in optical telecommunication. They play a pivotal role in various signal processing functions [4], including channel-drop filtering, on–off switching and light modulation. Moreover, the exaltation of optical non-linearity and spontaneous emission inhibition or exaltation is primarily governed by the Q/VM ratio. Thus, the quest for ultra-small high-Q cavities [5] has been critical in optical telecommunications [6] and in quantum optics [7]. Several strategies have been proposed to obtain high-Q cavities, like photonic crystals [8], micro-rings, micro-disks [9[9][10],10], micro-toroids [11], micro-spheres [12], meta-materials [13], plasmonics [14] and other interesting schemes [15]. However, each of these strategies either produces very large Q factors in excess of 106, but with rather large volumes, or, for the case of plasmonic resonators, a non-CMOS-compatible fabrication process. This entry will focus on arguably the most promising approach, Fabry–Perot cavities. It is believed that a Q factor as large as 108 can be achieved with cavities offering mode volumes close to the theoretical limit of VM =(𝜆/2𝑛)3, where 𝜆 is the resonant wavelength and n is the waveguide’s refractive index.


  1. Perot, A.; Fabry, C. On the Application of Interference Phenomena to the Solution of Various Problems of Spectroscopy and Metrology. Astrophys. J. 1899, 9, 87.
  2. Protsenko, I.E.; Uskov, A.V. Quantum Fluctuations in the Small Fabry-Perot Interferometer. Symmetry 2023, 15, 346.
  3. Iwaguchi, S.; Ishikawa, T.; Ando, M.; Michimura, Y.; Komori, K.; Nagano, K.; Akutsu, T.; Musha, M.; Yamada, R.; Watanabe, I.; et al. Quantum Noise in a Fabry-Perot Interferometer Including the Influence of Diffraction Loss of Light. Galaxies 2021, 9, 9.
  4. Liu, Q.; Zeng, D.; Mei, C.; Li, H.; Huang, Q.; Zhang, X. Integrated photonic devices enabled by silicon traveling wave-like Fabry–Perot resonators. Opt. Express 2022, 30, 9450–9462.
  5. Vahala, K.J. Optical microcavities. Nature 2003, 424, 839–846.
  6. Velha, P.; Picard, E.; Charvolin, T.; Hadji, E.; Rodier, J.C.; Lalanne, P.; Peyrade, D. Ultra-High Q/V Fabry-Perot microcavity on SOI substrate. Opt. Express 2007, 15, 16090–16096.
  7. Azzini, S.; Grassani, D.; Galli, M.; Gerace, D.; Patrini, M.; Liscidini, M.; Velha, P.; Bajoni, D. Stimulated and spontaneous four-wave mixing in silicon-on-insulator coupled photonic wire nano-cavities. Appl. Phys. Lett. 2013, 103, 031117.
  8. Akahane, Y.; Asano, T.; Song, B.S.; Noda, S. High-Q photonic nanocavity in a two-dimensional photonic crystal. Nature 2003, 425, 944–947.
  9. Soltani, M.; Yegnanarayanan, S.; Adibi, A. Ultra-high Q planar silicon microdisk resonators for chip-scale silicon photonics. Opt. Express 2007, 15, 4694–4704.
  10. Michael, C.P.; Borselli, M.; Johnson, T.J.; Chrystal, C.; Painter, O. An optical fiber-taper probe for wafer-scale microphotonic device characterization. Opt. Express 2007, 15, 4745–4752.
  11. Armani, D.K.; Kippenberg, T.J.; Spillane, S.M.; Vahala, K.J. Ultra-high-Q toroid microcavity on a chip. Nature 2003, 421, 925–928.
  12. Cai, M.; Painter, O.; Vahala, K.J. Observation of Critical Coupling in a Fiber Taper to a Silica-Microsphere Whispering-Gallery Mode System. Phys. Rev. Lett. 2000, 85, 74–77.
  13. Huang, L.; Jin, R.; Zhou, C.; Li, G.; Xu, L.; Overvig, A.; Deng, F.; Chen, X.; Lu, W.; Alù, A.; et al. Ultrahigh-Q guided mode resonances in an All-dielectric metasurface. Nat. Commun. 2023, 14, 3433.
  14. Bin-Alam, M.S.; Reshef, O.; Mamchur, Y.; Alam, M.Z.; Carlow, G.; Upham, J.; Sullivan, B.T.; Ménard, J.M.; Huttunen, M.J.; Boyd, R.W.; et al. Ultra-high-Q resonances in plasmonic metasurfaces. Nat. Commun. 2021, 12, 974.
  15. Ginis, V.; Benea-Chelmus, I.C.; Lu, J.; Piccardo, M.; Capasso, F. Resonators with tailored optical path by cascaded-mode conversions. Nat. Commun. 2023, 14, 495.