Zhen Chai

Tunable ultracompact chip-integrated multichannel filter based on plasmon-induced transparencies

Nanoscale multichannel filter is realized in plasmonic circuits directly, which consists of four plasmonic nanocavities coupled via a plasmonic waveguide etched in a gold film. The feature device size is only 1.35 μm, which is reduced by five orders of magnitude compared with previous reports. The optical channels are formed by transparency windows of plasmon-induced transparencies. A shift of 45 nm in the central wavelengths of optical channels is obtained when the plasmonic coupled-nanocavities are covered with a 100-nm-thick poly(methyl methacrylate) layer. This work opens up the possibility for the realization of solid quantum chips based on plasmonic circuits.

Low-power and ultrafast all-optical tunable plasmon-induced transparency in plasmonic nanostructures

We report an ultrafast and low-power all-optical tunable plasmon-induced transparency in a plasmonic nanostructure consisting of a gold nanowire grating embedded in a polycrystalline lithium niobate layer, realized based on strong quantum confinement enhancing nonlinearity. The all-optical tunability is realized based on the third-order nonlinear Kerr effect. A shift of 30 nm in the central wavelength of the transparency window is achieved under excitation of a pump light with an intensity as low as 7 MW/cm2. An ultrafast response time of 69 ps is reached because of ultrafast relaxation dynamics of bound electrons in polycrystalline lithium niobate.

Active control of chirality in nonlinear metamaterials

An all-optical tunabe chirality is realized in a photonic metamaterial, the metamolecule of which consists of a nonlinear nano-Au:polycrystalline indium-tin oxide layer sandwiched between two L-shaped gold nano-antennas twisted 90° with each other. The maximum circular dichroism reached 30%. Under excitation of a 40 kW/cm2 weak pump light, the peak in the circular dichroism shifts 45 nm in the short-wavelength direction. An ultrafast response time of 35 ps is maintained. This work not only opens up the possibility for the realization of ultralow-power and ultrafast all-optical tunable chirality but also offers a way to construct ultrahigh-speed on-chip biochemical sensors.

All-optical tunable on-chip plasmon-induced transparency based on two surface-plasmon-polaritons absorption

All-optical tunable on-chip plasmon-induced transparency is realized in integrated plasmonic circuits based on two surface-plasmon-polaritons absorption induced polymerization of SU-8 photoresist. Owing to the enhanced interaction between surface plasmon polaritons and SU-8 guaranteed by the slow light effect around the transparency window and the strong light confinement effect of the plasmonic nanocavity modes, a continuous shift range of 24 nm in the central wavelength of the transparency window was obtained. The threshold power of the two surface-plasmon-polaritons absorption induced polymerization of SU-8 was as low as 100 μW, which is three orders of magnitude less than previous reports.

Ultracompact all-optical full-adder and half-adder based on nonlinear plasmonic nanocavities

Abstract Ultracompact chip-integrated all-optical half- and full-adders are realized based on signal-light induced plasmonic-nanocavity-modes shift in a planar plasmonic microstructure covered with a nonlinear nanocomposite layer, which can be directly integrated into plasmonic circuits. Tremendous nonlinear enhancement is obtained for the nanocomposite cover layer, attributed to resonant excitation, slow light effect, as well as field enhancement effect provided by the plasmonic nanocavity. The feature size of the device is <15 μm, which is reduced by three orders of magnitude compared with previous reports. The operating threshold power is determined to be 300 μW (corresponding to a threshold intensity of 7.8 MW/cm2), which is reduced by two orders of magnitude compared with previous reports. The intensity contrast ratio between two output logic states, “1” and “0,” is larger than 27 dB, which is among the highest values reported to date. Our work is the first to experimentally realize on-chip half- and full-adders based on nonlinear plasmonic nanocavities having an ultrasmall feature size, ultralow threshold power, and high intensity contrast ratio simultaneously. This work not only provides a platform for the study of nonlinear optics, but also paves a way to realize ultrahigh-speed signal computing chips.

Chip-integrated all-optical diode based on nonlinear plasmonic nanocavities covered with multicomponent nanocomposite

Abstract Ultracompact chip-integrated all-optical diode is realized experimentally in a plasmonic microstructure, consisting of a plasmonic waveguide side-coupled two asymmetric plasmonic composite nanocavities covered with a multicomponent nanocomposite layer, formed directly in a plasmonic circuit. Extremely large optical nonlinearity enhancement is obtained for the multicomponent nanocomposite cover layer, originating from resonant excitation, slow-light effect, and field enhancement effect. Nonreciprocal transmission was achieved based on the difference in the shift magnitude of the transparency window centers of two asymmetric plasmonic nanocavities induced by the signal light, itself, for the forward and backward propagation cases. An ultralow threshold incident light power of 145 μW (corresponding to a threshold intensity of 570 kW/cm2) is realized, which is reduced by seven orders of magnitude compared with previous reports. An ultrasmall feature size of 2 μm and a transmission contrast ratio of 15 dB are obtained simultaneously.

Structural surface wave properties of amorphous Bi2Te3 by pulsed laser deposition in the visible and near-infrared regions

Owing to the unique properties of evanescent fields, surface waves show great applications in near field enhancement and in breaking the resolution limit. In this work, we found the amorphous-state Bi2Te3 film deposited by pulsed laser deposition exhibits surface wave properties in an ultrawide waveband ranging from the visible to near-infrared regions. We analyze the surface wave in three ways: the propagation form, localized form, and coupling with a gold nanobar. This work not only breaks the strict limit of a Bi2Te3 topological crystalline insulator but also widens the wavelength region of surface waves compared with a previous report.Owing to the unique properties of evanescent fields, surface waves show great applications in near field enhancement and in breaking the resolution limit. In this work, we found the amorphous-state Bi2Te3 film deposited by pulsed laser deposition exhibits surface wave properties in an ultrawide waveband ranging from the visible to near-infrared regions. We analyze the surface wave in three ways: the propagation form, localized form, and coupling with a gold nanobar. This work not only breaks the strict limit of a Bi2Te3 topological crystalline insulator but also widens the wavelength region of surface waves compared with a previous report.

Ultrafast chip-integrated all-optical switch in photonic circuits

We report a picosecond and low-power all-optical switch with multiple operating wavelengths in integrated photonic circuits, on-chip-triggered by a control light. The sample configuration combines the advantages of plasmonics and photonics, i.e. plasmonic nanostructures used as core units interconnected by ultralow-loss dielectric slot waveguides. A large nonlinearity enhancement is obtained based on resonant excitation, local field effect, and field enhancement effect, while fast response is maintained by intermolecular energy transfer. A fast response of 63 ps and ultralow control light intensity of 450 kW/cm2 are achieved.