Localized Waveguide Research Articles

Optical transmission resonances tuned by external static magnetic field in an n-doped semiconductor grating with subwavelength slits

Transmission behavior of light through a grating consisting of n-doped semiconductor with subwavelength slits under the application of external static magnetic fields is investigated. As dielectric constant of n-doped semiconductor can be substantially altered by applied magnetic field, in the Voigt configuration and for TM-polarized illumination, two transmission resonance peaks associated with localized waveguide modes of slits are significantly shifted toward the lower frequency regime with the increase of the applied magnetic field. These characteristics can be assigned to a reduction of effective plasma frequency of n-doped semiconductor under the applied magnetic field. Our findings may provide possibility for achieving tunable transmission resonance spectrum.

Two different transmission tunnels of light through double-layer gold nanoholearrays

We numerically simulate the enhancement of optical transmission through the double-layergold nanohole arrays by using the finite-difference time-domain (FDTD) method. Theoptical transmission originates not only from the localized waveguide resonance but alsofrom the well-recognized surface plasmon resonance due to the periodicity. Thetransmission characteristic of the two different resonance modes is also revealed clearly byanalyzing the maps of electric field and electromagnetic energy distribution. In addition, wealso show clearly the wave transport characteristics between the two-layer gold films.

Light reflection from a metal surface with subwavelength cavities

The interaction of light with the localized/delocalized system, i.e., a metal surface with rectangular cavities of finite depth, has been studied. Reflection spectrum has been measured in the optical frequencies, and resonant minima have been observed. We have developed an analytical model, which agrees well with the experiment. The localized waveguide resonance and delocalized surface resonance have been identified and discussed. The results may be useful for manipulating the coupling between light and matters.

Microwave physics and photonics

Microwave physics is an important line of research, combining many fields in radiophysics. Along with the development of methods for generation, amplification, and processing of electromagnetic waves, it initiated practical development and fabrication of artificial media of new type—metamaterials with a negative refractive index. A ray refracted at a boundary of such a medium, in contrast to refraction in conventional materials, lies at the same side of the normal as the incident ray. Metamaterials with negative refraction find application, in particular, in design of antennas, waveguides, and lenses of new type. They also make it possible to transform real objects into invisible ones. They add unusual properties to open cavities: if a layer of a medium with negative refraction is placed between plane mirrors, localized waveguide modes can be excited. Surface waves propagating along the interface between an anisotropic metamaterial and vacuum acquire new dispersion properties. In multiferroics, possessing simultaneously ferromagnetic and ferroelectric properties, specific magnetoelectric effects arise. It is noteworthy that metamaterials based on nanostructured elements have already been developed in the optical range.

New all-optical logic gates based on the local nonlinear Mach-Zehnder interferometer

We propose new all-optical logic gates containing a local nonlinear Mach-Zehnder interferometer waveguide structure. The light-induced index changes in the Mach-Zehnder waveguide structure make the output signal beam propagate through different nonlinear output waveguides. Based on the output signal beam propagating property, various all-optical logic gates by using the local nonlinear Mach-Zehnder waveguide interferometer structure with two straight control waveguides have been proposed to perform XOR/NXOR, AND/NAND, and OR/NOR logic functions.

Enhanced transmission through metal-film hole arrays and the surface plasmon resonance

In this paper，we show that the enhanced transmission and the surface plasmon distribution through a thin gold film with a periodic array of subwavelength holes with the finite-difference time-domain (FDTD) method. The transmission spectra exhibit two different surface plasmon resonance features: the localized waveguide resonance and the well-recognized photonic crystal resonance. For the localized waveguide resonance，the tangential electric field component Ey is seen to be concentrated entirely in the rectangular air hole region. And for the photonic crystal resonance，the tangential electric field components Ey is nonzero only on the two sides of the rectangular hole region. With the aid of the SP，light can form a strong focal spot at the bottom of the metal.

A Real-Time Precision Characterization Technique for Low-Loss Optical Polymeric Waveguide and Lightwave Circuits

An optical polymer waveguide is a key passive component for the optical interconnection. Design, fabrication, and characterization of high-performance waveguides have critical importance for the success of optoelectronic integration. In addition, defect effects, coupling, leakages, crosstalk, etc. are great concerns for the lightwave circuits. We present herein a fast, nondestructive, sensitive, real-time technique for detailed investigation of the propagation properties of planar optical waveguides and lightwave circuits. We use this technique to measure low-loss polymer waveguides on printed circuit board (PCB) substrates, and we have measured propagation losses of 0.065 dB/cm at 850 nm and 0.046 dB/cm at 980 nm. To the best of our knowledge, these are among the lowest losses reported to date for polymer waveguides on PCB substrates. A high-sensitivity CCD camera with a built-in integration function is utilized to observe the light streak in two dimensions through a two-lens imaging system. A few seconds to a few tens of seconds is needed for one complete measurement, compared with the sliding prism method, which requires several hours, and the cutback method, which requires even longer times. This technique can be used to evaluate not only the overall performance of a waveguide but also the local waveguide performance, as well as perform in-situ investigation of propagation properties (defect effect, bending effect, coupling, leakage, etc.). It can be extended to monitor the process of waveguide fabrication and alignment control during assembly for lightwave circuit integration.

The surface plasmon resonance of metal-film nanohole arrays

In this paper we investigated the enhanced transmission and surface plasmon resonance through a thin gold film with a periodic array of subwavelength nanoholes. Both freestanding gold-film nanohole arrays and gold-film nanohole arrays deposited on a gallium arsenide (GaAs) substrate are considered. Periodic arrays of nanoholes exhibit two different surface plasmon resonance features: localized waveguide resonance and the well-recognized photonic crystal resonance. The tangential electric field component E y is nonzero only in the hole region for a freestanding gold-film nanohole array, but it can exist in the hole region and in the metallic region for a gold-film nanohole array deposited on a GaAs substrate.

Numerical investigation of the transmission enhancement through subwavelength hole array

The transmission characteristics of a metallic film with subwavelength periodic square hole arrays are investigated by using the three-dimensional finite-difference time-domain (3D-FDTD) method. The influences of the hole size, the refractive index of substrate, the refractive index of filled medium, the thickness of film as well as the incident angle on the characters of transmission spectra are studied. It is found that the transmission can be enhanced by filling the holes with higher refractive index medium. This enhancement can be explained by the collaboration of localized waveguide resonance with surface plasmon resonance.

Cointegration of Gate-All-Around MOSFETs and Local Silicon-on-Insulator Optical Waveguides on Bulk Silicon

In this work we present a bulk silicon technology platform able to cointegrate gate-all-around (GAA) MOSFETs and local SOI waveguides with pentagonal cross section. Wire diagonals of 100-800 nm are obtained using a lithographic resolution of 0.8 mum. Well-functioning triangular multigate MOSFETs are reported, and tested up to 150 degC. A significant increase is observed in the low-field mobility mu0 for small devices (Weffles500 nm), which is attributed to local volume inversion in the corners. Preliminary characterization of the optical waveguides is carried out, showing optical losses of a few dB/cm. The processing is entirely CMOS compatible, does not require access to advanced lithography equipment, and is based on a silicon bulk substrate. Thus, this technology might serve as the basis for a low-cost, high-performance optical signaling platform

Enhanced transmission through arrays of subwavelength holes in gold films coated by a finite dielectric layer

Enhanced transmissions through a gold film with arrays of subwavelength holes are theoretically studied, employing the rigid full vectorial three dimensional finite difference time domain method. Influence of air-holes shape to the transmission is firstly studied, which confirms two different resonances attributing to the enhanced transmission: the localized waveguide resonance and periodic surface plasmon resonances. For the film coated with dielectric layers, calculated results show that in the wavelength region of interest the localized waveguide resonant mode attributes to sensing rather than the periodic gold-glass surface plasmon mode. Although the detected peak is fairly broad and the shift is not too pronounced, we emphasize the contribution for sensing from the localized waveguide resonant mode, which may opens up new ways to design surface plasmon based sensors.

Array waveguide evanescent ribbon coupler for card-to-backplane optical interconnects

A flexible array waveguide evanescent coupler for card-to-backplane optical interconnects is presented. The proposed technique eliminates traditional 90 degrees out-of-plane turns and local waveguide termination of multidrop bus architectures that hinder conventional card-to-backplane optical interconnections. Evanescent coupling between array waveguide ribbons has been successfully demonstrated. Further experiments have been performed to quantify array waveguide coupling length versus transfer efficiency and waveguide misalignment tolerance. Preliminary optical interconnect testing has demonstrated 2.5GHz operation of the coupler ribbons. The successful high-speed coupling confirms the effectiveness of the proposed method for high-speed computing systems.

Enhanced Transmission through Periodic Arrays of Subwavelength Holes: The Role of Localized Waveguide Resonances

By using the rigid full-vectorial three-dimensional finite-difference time-domain method, we show that the enhanced transmission through a metallic film with a periodic array of subwavelength holes results from two different resonances: (i) localized waveguide resonances where each air hole can be considered as a section of metallic waveguide with both ends open to free space, forming a low-quality-factor resonator, and (ii) well-recognized surface plasmon resonances due to the periodicity. These two different resonances can be characterized from electromagnetic band structures in the structured metal film. In addition, we show that the shape effect in the enhanced transmission through the Au film with subwavelength holes is attributed to the localized waveguide resonance.

Modeling sound progation in shallow water including dynamic internal wave fields

Shallow-water acoustic fields are dominated by effects due to multiple interactions with the bottom. Particularly at low frequencies, the acoustic field can be modeled as a sum of normal modes that satisfy local waveguide properties. For a point source in the water column, the acoustic field is characterized in depth and range by constructive and destructive interference of the propagating modes in range. When including a range-dependent sound-speed field in the water column, such as that caused by internal waves, mode coupling occurs which can impact the observed interference pattern. In previous work, these effects have been considered by modeling acoustic propagation through a moving solibore, or by con- sidering fixed 2D realizations of the sound-speed field. In this work, acoustic fields are generated for the case of a propagating internal wave field. In this case, the modal source function and local normal modes are constantly changing. The impact of these changes on the resulting modal interference pattern is examined for frequencies between 50 and 1000 Hz. In addition, fields are compared as would be measured on fixed versus synthetic aperture horizontal arrays. [Work supported by an ONR Ocean Acoustics Entry-Level Faculty Award.]

Analytical solution for the field in photonic structures containing cubic nonlinearity

In this work, we consider the exact solution of the stationary cubic nonlinear equation in a semi-infinite nonlinear medium in contact with a one-dimensional photonic crystal. Two kinds of analytical solutions are found for an arbitrary magnitude of the nonlinearity: a standing-wave-like one containing the inverse elliptic function Eli(ϕ∣m), and a one-wave-type solution for transmitted TE-polarized waves. An approximate two-wave solution is proposed to describe the field propagation through the nonlinear film covering the photonic crystal. It is shown that the problem of a mixed linear–nonlinear structure may be reduced to a transcendental kernel equation determining the field inside the nonlinear part of the medium. The light reflection from a Si/SiO2 layered structure in contact with an optically nonlinear medium is calculated. The angular-frequency photonic band diagram and power dependency are investigated. Local interface waveguide modes are considered.

Specific solutions of the generalized Korteweg-de Vries equation with possible physical applications

Abstract Solutions for a type of generalized Korteweg-de Vries equation which should have physical impact will be determined here. These types of solutions should have applications in the study of intrinsic localized modes optical waveguide arrays and fluid dynamics. It is shown that trigonometric and hyperbolic solutions can be obtained by matching powers and coefficients of the independent terms in the equation after the assumed solution has been substituted. As well, solutions to the equation in terms of more complicated Jacobe elliptic functions are determined.

Tailoring the Ultrafast Dephasing of Quasiparticles in Metallic Photonic Crystals

The ultrafast dephasing of waveguide-plasmon polaritons in metallic photonic crystal slabs is investigated in the femtosecond regime by second-order nonlinear autocorrelation. We find a drastic modification of the dephasing rates due to interaction between localized particle plasmons and optical waveguide modes and subsequent modification of the photonic density of states. In the strong coupling regime our measurements give clear evidence for the appearance of ultrafast polaritonic beat phenomena. All experimental results agree well with theoretical simulations based on a coupled damped harmonic oscillator model.

Lower‐stratospheric Rossby wave trains in the southern hemisphere: A case‐study for late winter of 1997

AbstractBehaviour of quasi‐stationary circulation anomalies observed in the lower stratosphere of the extratropical southern hemisphere during austral late winter of 1997 is studied. The anomalies are defined as daily low‐pass‐filtered departures from the circulation varying slowly with the seasonal cycle. A wave‐activity flux and refractive index for stationary Rossby waves are utilized in the analysis, each of which is defined locally for the zonally varying westerlies. Subseasonal fluctuations in the lower stratosphere were often associated with zonally confined wave trains emanating upward from localized, quasi‐stationary anomalies in the troposphere, including blocking ridges. The three‐dimensional propagation of the waves was found sensitive to the structure of a local waveguide. Upward injection of Rossby‐wave activity into the stratosphere tended to occur slightly upstream or just beneath of a lower‐stratospheric waveguide associated with the developed polar‐night jet (PNJ), which led to the subsequent formation of a well‐defined wave train downstream along that jet. The distribution of the lower‐stratospheric subseasonal variability thus exhibits significant zonal asymmetries, reflecting those in the PNJ structure and the distribution of tropospheric disturbances. Seasonal evolution of the PNJ and that of the tropospheric intraseasonal variability substantially modulated the lower‐stratospheric activity of subseasonal fluctuations. Copyright © 2004 Royal Meteorological Society

Waveguide-Plasmon Polaritons: Strong Coupling of Photonic and Electronic Resonances in a Metallic Photonic Crystal Slab

Strong coupling between localized particle plasmons and optical waveguide modes leads to drastic modifications of the transmission of metallic nanowire arrays on dielectric waveguide substrates. The coupling results in the formation of a new quasiparticle, a waveguide-plasmon polariton, with a surprisingly large Rabi splitting of 250 meV. Our experimental results agree well with scattering-matrix calculations and a polariton-type model. The effect provides an efficient tool for photonic band gap engineering in metallodielectric photonic crystal slabs. We show evidence of a full one-dimensional photonic band gap in resonant plasmon-waveguide structures.

Waveguides and waveguide arrays formed by incoherent light in photorefractive materials

We report on experimental observations of nonlinear optical waveguides and waveguide arrays formed by incoherent light in photorefractive materials. Such waveguides are made possible by creating partially spatially incoherent solitons in a noninstantaneous self-focusing photorefractive medium. In addition to planar, Y-junction, and circular waveguides, we report the first demonstration of pixel-like spatial solitons from partially incoherent light. An array of as many as 56×56 soliton pixels is readily realized by launching a spatially modulated incoherent beam into the self-focusing photorefractive medium. These solitons are stable and robust, forming a steady-state two-dimensional waveguide array in which optical coupling and control of local waveguide channels can be achieved. These experiments bring about the possibility of controlling high-power laser beams with low-power incoherent light sources as well as the possibility for optically inducing three-dimensional reconfigurable photonic lattices in a bulk medium.