Optical coherent perfect absorption and amplification in a time-varying medium
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
Time-invariant photonic structures amplify or absorb light on the basis of their intrinsic material gain or loss. The coherent interference of multiple beams in space, for example, in a resonator, can be exploited to tailor the wave interaction with material gain or loss, respectively maximizing lasing or coherent perfect absorption. By contrast, a time-varying system is not bound to conserve energy, even in the absence of material gain or loss, and can support amplification or absorption of a probe wave through parametric phenomena. Here we demonstrate theoretically and experimentally how a subwavelength film of indium tin oxide, whose bulk permittivity is homogeneously and periodically modulated via optical pumping, can be dynamically tuned to act both as a non-resonant amplifier and as a perfect absorber, by manipulating the relative phase of two counterpropagating probe beams. This extends the concept of coherent perfect absorption to the temporal domain. We interpret this result as selective switching between the gain and loss modes present in the momentum bandgap of a periodically modulated medium. By tailoring the relative intensity of the two probes, high-contrast modulation can be achieved with up to 80% absorption and 400% amplification. Our results demonstrate control of gain and loss in time-varying media at optical frequencies and pave the way towards coherent manipulation of light in Floquet-engineered complex photonic systems.
Date Issued
2026-02-01
Date Acceptance
2025-12-11
Citation
Nature Photonics, 2026, 20 (2), pp.163-169
ISSN
1749-4885
Publisher
Springer Science and Business Media LLC
Start Page
163
End Page
169
Journal / Book Title
Nature Photonics
Volume
20
Issue
2
Copyright Statement
Copyright © The Author(s), under exclusive licence to Springer Nature Limited 2026. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Publication Status
Published
Date Publish Online
2026-01-26