Tuning the Effective PT Phase of Plasmonic Eigenmodes

Abstract

We experimentally observe an effective PT -phase transition through the exceptional point in a hybrid plasmonic-dielectric waveguide system. Transmission experiments reveal fundamental changes in the underlying Eigenmode interactions as the environmental refractive index is tuned, which can be unambiguously attributed to a crossing through the plasmonic exceptional point. These results extend the design opportunities for tuneable non-Hermitian physics to plasmonic systems.Hermitian systems and their operators are used to describe a wide range of physical phenomena to predict the evolution of Eigenstates via unitary operations containing purely real Eigenvalues [1,2]. Recently, increasing attention has been dedicated to non-Hermitian systems, which are non-conservative and generally yield complex Eigenvalue spectra [3]. Non-Hermitian systems are typically created by opening a Hermitian system to the environment by including dissipation and/or gain. Interestingly, coupled non-Hermitian systems can yield purely real Eigenvalues which respect parity-time (PT ) symmetry via an appropriate balance of gain and loss [4,5]. In an unbalanced scenario, a PT -broken system shows complex conjugate Eigenvalue pairs. The PT -symmetric (PTS) and PT -broken (PTB) regimes are separated by the exceptional point (EP), where the Eigenvalues coalesce, which is associated with several interesting physical phenomena, such as level repulsion [6], reflectionless propagation [7], and topological phase transitions [8].

Crossing the exceptional point in a fiber-plasmonic waveguide -INVITED

“…Finally, an intermediate refractive index nID=1.438 shows no oscillations and the highest loss -a confirmation that the EP was locked via the additional degree of freedom of tuning nID. Since this device operates near the plasmonic cutoff, this sensor has a sensitivity >50μm/RIU for nID>1.43 [7], which, to the best of our knowledge, is one of the highest values measured for a plasmonic device to date.…”

“…A recent report presented nanostructures with localized plasmon resonances that show discrete frequency spectra [6], but experimental observations of EPs in plasmonic waveguides have so far been limited. Here, we present measurements of the transition across the plasmonic EP in a waveguide system, namely a tuneable hybrid plasmonic fiber [7].…”

Nanoscale nonlinear plasmonics in photonic waveguides and circuits

“…Complementary to approaching improvements from a material perspective, it may be that other waveguide geometries may provide enhanced nonlinear interactions as a pathway for investigating new physics-for example, non-Hermitian systems [285], accessible via plasmonic waveguides [286], exhibit slow light effects at their exceptional point [287], where they are also extremely sensitive to their environment [288]. Related concepts [289] might prove a worthwhile avenue for chip-based nonlinear sensing of nanoscale events.…”

Sensitivity Enhanced Refractive Index Fiber Sensor Based on Long-Range Surface Plasmon Resonance in SiO2-Au-TiO2 Heterostructure

“…Thus, the n eff of LRSPP mode will be close to the material RI of analyte according to effective-medium theory [38,39]. It changes more slowly than that of the MOF's core mode, which is simultaneously determined by the material dispersion of silica and the MOF's waveguide dispersion [39]. Moreover, there is a break around the wavelength of 1925 nm in their dispersion curves, in which the avoided-crossing phenomenon occurs.…”

“…We find that most of electric field of the LRSPP mode distributes in the analyte region. Thus, the n eff of LRSPP mode will be close to the material RI of analyte according to effective-medium theory [38,39]. It changes more slowly than that of the MOF's core mode, which is simultaneously determined by the material dispersion of silica and the MOF's waveguide dispersion [39].…”