Yongkang Gong

Ultrafast all-optical switching in nanoplasmonic waveguide with Kerr nonlinear resonator

A novel ultrafast all-optical switching based on metal-insulator-metal nanoplasmonic waveguide with a Kerr nonlinear resonator is proposed and investigated numerically. With the finite-difference time-domain simulations, it is demonstrated that an obvious optical bistability of the signal light appears by varying the control-light intensity, and an excellent switching effect is achieved. This bistability originates from the intensity-dependent change induced in the dielectric constant of Kerr nonlinear material filled in the nanodisk resonator. It is found that the proposed all-optical switching exhibits femtosecond-scale feedback time.

Tunable band-pass plasmonic waveguide filters with nanodisk resonators

A novel and simple plasmonic filter based on metal-insulator-metal plasmonic waveguides with a nanodisk resonator is proposed and investigated numerically. By the resonant theory of disk-shaped nanocavity, we find that the resonance wavelengths can be easily manipulated by adjusting the radius and refractive index of the nanocavity, which is in good agreement with the results obtained by finite-difference time-domain (FDTD) simulations. In addition, the bandwidths of resonance spectra are tunable by changing the coupling distance between the nanocavity and waveguides. This result achieved by FDTD simulations can be accurately analyzed by temporal coupled mode theory. Our filters have important potential applications in high-density plasmonic integration circuits.

Induced transparency in nanoscale plasmonic resonator systems

An optical effect analogous to electromagnetically induced transparency (EIT) is observed in nanoscale plasmonic resonator systems. The system consists of a slot cavity as well as plasmonic bus and resonant waveguides, where the phase-matching condition of the resonant waveguide is tunable for the generation of an obvious EIT-like coupled resonator-induced transparency effect. A dynamic theory is utilized to exactly analyze the influence of physical parameters on transmission characteristics. The transparency effect induced by coupled resonance may have potential applications for nanoscale optical switching, nanolaser, and slow-light devices in highly integrated optical circuits.

Broad-bandgap and low-sidelobe surface plasmon polariton reflector with Bragg-grating-based MIM waveguide

Surface plasmon polariton reflector (SPPR) based on metal-insulator-metal (MIM) Bragg grating waveguide is numerically studied. A quasi-chirped technique is applied to the engraved grooves in the surface of the MIM waveguide, and a new kind of broad-bandgap SPPR is achieved. Meanwhile, by optimizing the profile of gap width between the metal and dielectric, the spectral sidelobe of SPPR is effectively suppressed and thus the performance o f the SPPR is further improved.

Enhancement of transmission efficiency of nanoplasmonic wavelength demultiplexer based on channel drop filters and reflection nanocavities.

We propose and numerically investigate a novel kind of nanoscale plasmonic wavelength demultiplexing (WDM) structure based on channel drop filters in metal-insulator-metal waveguide with reflection nanocavities. By using finite-difference time-domain simulations, it is found that the transmission efficiency of the channel drop filter can be significantly enhanced by selecting the proper distance between the drop and reflection cavities. The result can be exactly analyzed by the temporal coupled-mode theory. According to this principle, a nanoscale triple-wavelength demultiplexer with high drop efficiencies is designed. The proposed structure can find more applications for the ultra-compact WDM systems in highly integrated optical circuits.

Observations of four types of pulses in a fiber laser with large net-normal dispersion

Four different types of pulses are experimentally obtained in one erbium-doped all-fiber laser with large net-normal dispersion. The proposed laser can deliver the rectangular-spectrum (RS), Gaussian-spectrum (GS), broadband-spectrum (BS), and noise-like pulses by appropriately adjusting the polarization states. These kinds of pulses have distinctly different characteristics. The RS pulses can easily be compressed to femtosecond level whereas the pulse energy is restricted by the trend of multi-pulse shaping with excessive pump. The GS and BS pulses always maintain the single-pulse operation with much higher pulse-energy and accumulate much more chirp. After launching the pulses into the photonic-crystal fiber, the supercontinuum can be generated with the bandwidth of >700 nm by the BS pulses and of ~400 nm by the GS pulses, whereas it can hardly be generated by the RS pulses. The physical mechanisms behind the continuum generation are qualitatively investigated relating to different operating regimes. This work could help to a deeper insight of the normal-dispersion pulses.

High-channel-count plasmonic filter with the metal-insulator-metal Fibonacci-sequence gratings

Fibonacci-sequence gratings based on metal-insulator-metal waveguides are proposed. The spectrum properties of this structure are numerically investigated by using the transfer matrix method. Numerical results demonstrate that the proposed structure can generate high-channel-count plasmonic stop bands and can find significant applications in highly integrated dense wavelength division multiplexing networks.

Highly flexible all-optical metamaterial absorption switching assisted by Kerr-nonlinear effect

A three-dimensional metamaterial nanostructure for realizing all-optical absorption switching is proposed and investigated. The structure consists of dual metallic layers for allowing near-perfect absorption due to electric and magnetic resonances, and a nonlinear Kerr-dielectric layer for actively manipulating the nanostructure absorption. The finite-difference time-domain simulation results demonstrate that, by adjusting the incident optical intensity, the metamaterial absorption can be flexibly tuned from near unity to zero. The all-optical absorption switching structure can find potential applications in actively integrated photonic circuits for thermal sensing, photo detecting, and optical imaging.

Perfect absorber supported by optical Tamm states in plasmonic waveguide

Based on a two-dimensional plasmonic metal-dielectric-metal (MDM) waveguide with a thin metallic layer and a dielectric photonic crystal in the core, a novel absorber at visual and near-infrared frequencies is presented. The absorber spectra and filed distributions are investigated by the transfer-matrix-method and the finite-difference time-domain method. Numerical results show that attributing to excitation of the optical Tamm states in the MDM waveguide core, the optical wave is trapped in the proposed structure without reflection and transmission, leading to perfect absorption as high as 0.991. The proposed absorber can find useful application in all-optical integrated photonic circuits.

Optical bistability in metal-insulator-metal plasmonic waveguide with nanodisk resonator containing Kerr nonlinear medium

We numerically investigate the optical bistability effect in the metal-insulator-metal waveguide with a nanodisk resonator containing a Kerr nonlinear medium. It is found that the increase of the refractive index, which is induced by enhancing the incident intensity, can cause a redshift for the resonance wavelength. The local resonant field excited in the nanodisk cavity can significantly increase the Kerr nonlinear effect. In addition, an obvious bistability loop is observed in the proposed structure. This nonlinear structure can find important applications for all-optical switching in highly integrated optical circuits.