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Universal transient radiation dynamics by abrupt and soft temporal transitions in optical waveguides
Amir Shlivinski1, Yakir Hadad2
1School of Electrical and Computer Engineering, Ben-Gurion University, Beer Sheva, Israel.
Nanophotonics (Berlin, Germany)
|April 4, 2025
Summary
An optical waveguide with changing material properties radiates energy. Researchers found a formula for the radiation frequency, showing a time-dependent chirp, and a decay rate for the field amplitude.
Area of Science:
- Optics and Photonics
- Electromagnetism
- Materials Science
Background:
- Open optical waveguides can radiate energy when their material properties change over time.
- Understanding this radiation is crucial for designing advanced optical and terahertz (THz) devices.
Purpose of the Study:
- To theoretically investigate and characterize the radiation emitted by an optical waveguide undergoing temporal material transitions.
- To derive an exact formula for the instantaneous radiation frequency and its temporal decay rate.
Main Methods:
- Asymptotic evaluation of path integrals in the complex frequency (Laplace) plane.
- Derivation of an asymptotically exact formula for instantaneous radiation frequency.
- Full-wave simulations to verify analytical results.
Main Results:
- A simple formula for instantaneous radiation frequency was derived, showing a time-dependent chirp.
- The formula depends on ambient properties and guided mode wavenumber, not specific waveguide structure.
- A time decay rate of t^-3/2 for the radiative field amplitude was established.
- Analytical results were validated using simulations of indium tin oxide waveguides.
Conclusions:
- Theoretical findings provide insights into radiation from general optical waveguides with temporal transitions.
- The derived formula offers a tool for analyzing and designing THz and optical setups.
- Potential applications include sensing and imaging technologies.
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