Optical Waveguides and Resonant Cavities

Optics Express, 2010

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.

Selected Topics in …, 2008

Future ultracompact photonic integrated circuits (PICs) will rely on high-index-contrast dielectric materials, which permit a strong confinement of the optical field in the diffraction limit as well as low propagation losses. This is the case of PICs implemented on a silicon-on-insulator (SOI) platform. To achieve confinement beyond the diffraction limit, plasmonic waveguides (based on metal-dielectric interfaces) have been recently proposed. This new kind of waveguide provides a strong enhancement of the field in the metal-dielectric interface, which is of paramount importance for nonlinear functionalities or sensing. Plasmonic waveguides can also be built on SOI wafers. Thus, it can be reasonably thought that high index contrast as well as plasmonic waveguides can coexist in future ultradense PICs. In this paper, a theoretical and numerical study on the performance of several dielectric and plasmonic waveguides is presented. Thanks to their plasmon-coupled supported modes, ultracompact devices as hybrid ring resonators can be devised and integrated with silicon photonic circuits.

Advances in OptoElectronics, 2011

A TM-pass/TE-stop polarizer consisting of a metal film sandwiched between dielectric gratings is investigated using the finite-difference time-domain method. At normal incidence with respect to the grating plane, a transmissivity of more than 94% and a reflectivity of more than 98% are obtained at m for the TM and TE waves, respectively. The extinction ratio is more than 17 dB over a wavelength range of 1.50 m to 1.75 m. A high extinction ratio is maintained at oblique incidence, although the wavelength range shifts towards longer wavelengths. The TM-pass/TE-stop operation is also achieved with a modified structure, in which a dielectric grating is sandwiched between metal films.

The combination of a thin dielectric grating with a thin metal film is shown to reveal the existence of multiple plasmons, some are short range and others long range both represented by resonant dips in the reflectivity. Usually the plasmons come in pairs, where one is excited at the substrate metal interface while the other at the grating metal interface. One of these dips is sensitive to the refractive index (RI) of the medium adjacent to the metal surface while the other to that near the grating interfaces. Using an optimum design it is possible to obtain high sensitivity to the RI variations of one of the adjacent media but not to the other, hence a self-referenced biosensor can be built using this design. Two configurations are shown to reveal unique features in the angular mode: 1) the possibility of using both angular and intensity sensitivity to detect variations in the RI of the analyte, 2) the possibility of using the excited multiple sharp plasmons that cause multiple resonances (dips) in the reflectivity, where part of these resonances are red-shifted due to variations in the RI of the analyte, while the others are blue shifted. Hence, by measuring the shift of one with respect to the other the angular sensitivity is improved, 3) multiple dips can be used for reference, and 4) high figure of merit is obtained. The thin dielectric grating is shown to have two roles, one to provide the momentum matching whereas the other is to act effectively as a dielectric layer underneath the metal film to enable the excitation of both the long and short range surface plasmons.

2015

The Insulator-Metal-Insulator-Insulator (IMII) plasmonic structures present a great interest for the optical photonics devices. In this paper we present an analyze for coupling of light into plasmonic structures which contains a dielectric waveguide. We obtained the characteristic equation for the wave guides in the IMII structure by solving the Helmholtz equations in four homogeneous media. The characteristic equations for three and four layers have similar forms as established. Subsequently, the numerical simulations for TM waveguide modes and the coupling by a prism with the refractive index lower then waveguide were done. It was showed that, the TM0 mode is confined to the metal interface and can’t be exited. Resonance coupling into higher waveguide modes may be realized for some film thicknesses.

2021

Optics Letters, 2015

In this Letter, we study numerically diffraction gratings for surface plasmon polaritons. Investigated plasmonic gratings consist of a periodic set of dielectric ridges located on the metal surface. The grating period is comparable with the wavelength of the incident wave. The simulation results obtained within the rigorous coupled-wave analysis framework have shown that the SPP diffraction on a plasmonic grating with parasitic scattering suppression is remarkably close to the diffraction of a TE-polarized plane wave on a conventional grating. A compact and efficient reflecting plasmonic grating is considered as an example. The presented results can be used for the design of high-efficiency two-dimensional optical elements for steering surface plasmon propagation.

Quantum Electron, 2000

Abstract: We have designed, fabricated and characterized surface plasmon waveguides for near infrared light in the telecommunications spectrum. These waveguides exhibit losses of -1.2dB/µm and can guide light around 0.5 µm bends. Light can also be efficiently coupled ...

IEEE Sensors Journal, 2019

We configure and analyze a nanostructured device that hybridizes grating modes and surface plasmon resonances. The model uses an effective index of refraction that considers the volume fraction of the involved materials, and the propagation depth of the plasmon through the structure. Our geometry is an extruded low-order diffraction grating made of dielectric nano-triangles. Surface plasmon resonances are excited at a metal/dielectric interface, which is separated from the analyte by a high-index dielectric layer. The optical performance of the refractometric sensor is highly competitive in sensitivity and figure of merit (FOM) because of the the ultra-narrow spectral response (below 0.1 nm). Moreover, it is operative within a wide range of the index of refraction (from 1.3 till 1.56), and also works under normal incidence conditions.

Journal of Optics, 2011

A novel nanostructure grating with broadband reflection is proposed and analyzed in this paper. The grating is based on a hybrid plasmonic slot waveguide that consists of a vertical dielectric-slot incorporated at the gap between the upper silicon rib and the metal substrate. The structure could provide an ultra-tight mode confinement in the cross-section while maintaining a relatively low propagation loss. By exploiting the superior modal properties, an ultra-compact and broadband Bragg grating is presented, which shows the capability of efficient wavelength selection near the telecom bandwidths. The waveguide-based Bragg grating could be used as a filter in telecommunication systems and could be a promising candidate for future integrated photonic circuits.