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.

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

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.

Tunable band-pass plasmonic waveguide filters with nanodisk resonators

The tunable multi-channel wavelength demultiplexer (WDM) based on metal-insulator-metal plasmonic nanodisk resonators is designed and numerically investigated by utilizing Finite-Difference Time-Domain (FDTD) simulations. It is found that the channel wavelength of WDM is easily tuned by changing the geometrical parameters of the structure and the material filled in the nanodisk resonator. The multi-channel WDM structure consisting of a plasmonic waveguide and several nanodisk resonators increases the transmission up to 70% at telecommunication regime, which is two times higher than the results reported in a recent literature [Opt. Express 18, 11111 (2010)]. Our WDM can find important potential applications in highly integrated optical circuits.

Tunable multi-channel wavelength demultiplexer based on MIM plasmonic nanodisk resonators at telecommunication regime

Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.

https://hal.archives-ouvertes.fr/hal-00968839/document

Review of Terahertz Tomography Techniques

We present an improved analytical model describing transmittance of a metal-dielectric-metal (MDM) waveguide coupled to an arbitrary number of stubs. The model is built on the well-known analogy between MDM waveguides and microwave transmission lines. This analogy allows one to establish equivalent networks for different MDM-waveguide geometries and to calculate their optical transmission spectra using standard analytical tools of transmission-line theory. A substantial advantage of our model compared to earlier works is that it precisely incorporates the dissipation of surface plasmon polaritons resulting from ohmic losses inside any metal at optical frequencies. We derive analytical expressions for transmittance of MDM waveguides coupled to single and double stubs as well as to N identical stubs with a periodic arrangement. We show that certain phase-matching conditions must be satisfied to provide optimal filtering characteristics for such waveguides. To check the accuracy of our model, its results are compared with numerical data obtained from the full-blown finite-difference time-domain simulations. Close agreement between the two suggests that our analytical model is suitable for rapid design optimization of MDM-waveguide-based compact photonic devices.

Improved transmission model for metal-dielectric-metal plasmonic waveguides with stub structure

A novel subwavelength surface plasmon polaritons optical filter based on an incompletely directional coupler is proposed and numerically simulated by using the finite difference time domain method with perfectly matched layer absorbing boundary condition. An analytical solution for the resonant condition of the structure is derived by means of the cavity theory. Both analytical and simulative results reveal that the resonant wavelengths are proportional to the length of the slit segment, inversely proportional to the antinode number of a standing wave in the segment, and are related to the slit width and the gap between the two slits. The analytical solution being consistent with the numerical simulation verifies the feasibility of the concept of the new filter structure.

A subwavelength coupler-type MIM optical filter.

Characteristics of a multiple-teeth-shaped plasmonic filter are analyzed. As an extension of this structure, an asymmetrical multiple-teeth-shaped structure is proposed and numerically simulated by using the finite difference time domain method with perfectly matched layer absorbing boundary condition. It is found that the asymmetrical structure can realize the function of a narrow-passband filter. The central wavelength of the passband linearly increases with the simultaneous increasing of d(1) and d(2).

A narrow-band subwavelength plasmonic waveguide filter with asymmetrical multiple-teeth-shaped structure.

Characteristics of double-sided teeth-shaped nanoplasmonic waveguide filters are systematically investigated. It is found that the asymmetrical double-sided teeth-shaped waveguide structure can realize the function of a two-wavelength filter, and its two wavelengths are linear with the depths of the two-sided teeth, respectively. It is also found that a staggered double-sided teeth-shaped structure exahibits a wide and sharp bandgap. Double-sided teeth-shaped filters are of ultracompact size, in the length of a few hundred nanometers. The finite-difference time-domain method is employed in the simulations. Our results may open a way to construct nanoscale waveguide filters for high-density nanoplasmonic integration circuits.

Systematical research on characteristics of double-sided teeth-shaped nanoplasmonic waveguide filters

A novel surface plasmon-polariton (SPP) refractive index sensor based on the coupling of a split waveguide mode with a cavity mode in the metal is proposed and studied in this paper. Both analytic and simulated results show that the resonant wavelength of the sensor has a linear relationship with the refractive index of materials under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of the resonant wavelength. The resolution of refractive index of the nanometeric sensor can reach as high as 10-6, given the wavelength resolution of 0.01 nm. It can be applied to high-resolution biosensor.

Qin Zhang

Papers

A subwavelength coupler-type MIM optical filter.

A narrow-band subwavelength plasmonic waveguide filter with asymmetrical multiple-teeth-shaped structure.

Systematical research on characteristics of double-sided teeth-shaped nanoplasmonic waveguide filters

A Novel Nanometeric Plasmonic Refractive Index Sensor