The exceptional points of non-Hermitian optical systems: Scattering matrix definition, coherent perfect absorption, and lasing

We explored exceptional points (EPs) in one dimensional non-Hermitian photonic crystals incorporated with a defect. The defect was asymmetric with respect to the center. Two EPs could be derived by modulating the normalized frequency and the gain-loss coefficient of defect. The reflection coefficient complex phase changed dramatically around EPs, and the change in complex phase was π at EPs. The electric field of EPs was mainly restricted to the defect, which can induce a giant Goos–Hänchen (GH) shift. Moreover, we found a coherent perfect absorption-laser point (CPA-LP) in the structure. A giant GH shift also existed around the CPA-LP. The study may have found applications in highly sensitive sensors.

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Dynamical Control of Broadband Coherent Absorption in ENZ Films

Micromachines ◽

10.3390/mi11010110 ◽

2020 ◽

Vol 11 (1) ◽

pp. 110 ◽

Cited By ~ 2

Author(s):

Vincenzo Bruno ◽

Stefano Vezzoli ◽

Clayton DeVault ◽

Thomas Roger ◽

Marcello Ferrera ◽

...

Keyword(s):

Scattering Matrix ◽

Subwavelength Structures ◽

Optical Nonlinearities ◽

Light Modulation ◽

Peak Wavelength ◽

Perfect Absorption ◽

Maximum Value ◽

Coherent Perfect Absorption ◽

On Chip ◽

Dynamical Control

Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of the scattering matrix and often requires engineered optical properties. For instance, thin film CPA benefits from complex nanostructures with suitable resonance, albeit at a loss of operational bandwidth. In this work, we theoretically and experimentally demonstrate a broadband CPA based on light-with-light modulation in epsilon-near-zero (ENZ) subwavelength films. We show that unpatterned ENZ films with different thicknesses exhibit broadband CPA with a near-unity maximum value located at the ENZ wavelength. By using Kerr optical nonlinearities, we dynamically tune the visibility and peak wavelength of the total energy modulation. Our results based on homogeneous thick ENZ media open a route towards on-chip devices that require efficient light absorption and dynamical tunability.

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Non-linear coherent perfect absorption in the proximity of exceptional points

Communications Physics ◽

10.1038/s42005-021-00782-2 ◽

2022 ◽

Vol 5 (1) ◽

Author(s):

Suwun Suwunnarat ◽

Yaqian Tang ◽

Mattis Reisner ◽

Fabrice Mortessagne ◽

Ulrich Kuhl ◽

...

Keyword(s):

Broad Band ◽

Exceptional Point ◽

Frequency Range ◽

Perfect Absorption ◽

Band Frequency ◽

Exceptional Points ◽

Coherent Perfect Absorption ◽

Non Linear ◽

Nonlinear Resonator ◽

High Absorption

AbstractCoherent perfect absorption is one of the possibilities to get high absorption but typically suffers from being a resonant phenomena, i.e., efficient absorption only in a local frequency range. Additionally, if applied in high power applications, the understanding of the interplay of non-linearities and coherent perfect absorption is crucial. Here we show experimentally and theoretically the formation of non-linear coherent perfect absorption in the proximity of exceptional point degeneracies of the zeros of the scattering function. Using a microwave platform, consisting of a lossy nonlinear resonator coupled to two interrogating antennas, we show that a coherent incident excitation can trigger a self-induced perfect absorption once its intensity exceeds a critical value. Note, that a (near) perfect absorption persists for a broad-band frequency range around the nonlinear coherent perfect absorption condition. Its origin is traced to a quartic behavior that the absorbance spectrum acquires in the proximity of the exceptional points of the nonlinear scattering operator.

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Parity-time symmetry and coherent perfect absorption in a cooperative atom response

Nanophotonics ◽

10.1515/nanoph-2020-0635 ◽

2021 ◽

Vol 10 (2) ◽

pp. 1357-1366

Author(s):

Kyle E. Ballantine ◽

Janne Ruostekoski

Keyword(s):

Collective Excitation ◽

Single Layer ◽

Many Body ◽

Dark Mode ◽

Perfect Absorption ◽

Exceptional Points ◽

Nonexponential Decay ◽

Time Symmetry ◽

Coherent Perfect Absorption ◽

Many Body Interactions

Abstract Parity-Time ( P T $\mathcal{P}\mathcal{T}$ ) symmetry has become an important concept in the design of synthetic optical materials, with exotic functionalities such as unidirectional transport and nonreciprocal reflection. At exceptional points, this symmetry is spontaneously broken, and solutions transition from those with conserved intensity to exponential growth or decay. Here, we analyze a quantum-photonic surface formed by a single layer of atoms in an array with light mediating strong cooperative many-body interactions. We show how delocalized collective excitation eigenmodes can exhibit an effective P T $\mathcal{P}\mathcal{T}$ symmetry and nonexponential decay. This effective symmetry is achieved in a passive system without gain by balancing the scattering of a bright mode with the loss from a subradiant dark mode. These modes coalesce at exceptional points, evidenced by the emergence of coherent perfect absorption where coherent incoming light is perfectly absorbed and scattered only incoherently. We also show how P T $\mathcal{P}\mathcal{T}$ symmetry can be generated in total reflection and by balancing scattering and loss between different polarizations of collective modes.

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Organic Sub-Bandgap Schottky Barrier Photodetectors with Near-Infrared Coherent Perfect Absorption

ACS Photonics ◽

10.1021/acsphotonics.1c00478 ◽

2021 ◽

Author(s):

Yeonghoon Jin ◽

Hyung Suk Kim ◽

Junghoon Park ◽

Seunghyup Yoo ◽

Kyoungsik Yu

Keyword(s):

Schottky Barrier ◽

Near Infrared ◽

Perfect Absorption ◽

Coherent Perfect Absorption

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Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption

Nanophotonics ◽

10.1515/nanoph-2021-0048 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Philipp Grimm ◽

Gary Razinskas ◽

Jer-Shing Huang ◽

Bert Hecht

Keyword(s):

Impedance Matching ◽

Plasmonic Waveguide ◽

Perfect Absorption ◽

Single Nanowire ◽

Coherent Perfect Absorption ◽

Potential Applications ◽

Plasmonic Nanoantennas ◽

Radiative Losses ◽

Additional Loss

Abstract Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g., plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in background-free sensing.

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