TM Waveguide Modes Research Articles

Detection band expansion by independently tunable double resonances in a long-wavelength dual-color QWIP.

Multi-resonance light coupling management is a promising way to expand the operating spectral ranges of optoelectronic devices. The classical strategies are either lack of independent tunability for each resonance or involved with complex fabrication. Here, we propose a new scheme for expanding the operating spectral range of an optoelectronic device through a dual-color active material integrated with a simple resonant waveguide structure. The TM waveguide mode and the SPP mode of the resonant waveguide structure are regulated to match the two active regions of the dual-color material both spectrally and spatially. Applying this scheme to a long-wavelength infrared quantum well photodetector, the absorption efficiencies at the two peak detection wavelengths of the dual-color quantum wells are both enhanced by more than 10 times compared with the case of a standard 45° edge facet coupled device with the same detection material. The simple light coupling structure is easy to accomplish and compatible with focal plane arrays. For thermal radiation detection, the absorption efficiency of the 300 K blackbody radiation by our dual-color detector is 83.8% higher than that by a single-color detector with the optimized structural parameters. Moreover, either polarization sensitive or polarization insensitive detection could be achieved in this dual-color infrared quantum well photodetector by using anisotropic or isotropic gratings.

Characterization of higher harmonic modes in Fabry\u2013P\xe9rot microcavity organic light emitting diodes

Encasing an OLED between two planar metallic electrodes creates a Fabry–Pérot microcavity, resulting in significant narrowing of the emission bandwidth. The emission from such microcavity OLEDs depends on the overlap of the resonant cavity modes and the comparatively broadband electroluminescence spectrum of the organic molecular emitter. Varying the thickness of the microcavity changes the mode structure, resulting in a controlled change in the peak emission wavelength. Employing a silicon wafer substrate with high thermal conductivity to dissipate excess heat in thicker cavities allows cavity thicknesses from 100 to 350 nm to be driven at high current densities. Three resonant modes, the fundamental and first two higher harmonics, are characterized, resulting in tunable emission peaks throughout the visible range with increasingly narrow bandwidth in the higher modes. Angle resolved electroluminescence spectroscopy reveals the outcoupling of the TE and TM waveguide modes which blue-shift with respect to the normal emission at higher angles. Simultaneous stimulation of two resonant modes can produce dual peaks in the violet and red, resulting in purple emission. These microcavity-based OLEDs employ a single green molecular emitter and can be tuned to span the entire color gamut, including both the monochromatic visible range and the purple line.

Polarization-insensitive silicon nitride arrayed waveguide grating.

Next-generation passive optical networks require integrated, polarization-insensitive wavelength-division multiplexing solutions, for which the recently emerging low-loss silicon nitride nanophotonic platforms hold great potential. A novel polarization-insensitive arrayed waveguide grating (AWG) built with silicon nitride waveguides is presented in this Letter. Polarization insensitivity is obtained when both the channel spacing and the center wavelength of the two orthogonal polarization states (i.e., the TE and TM waveguide modes) are simultaneously aligned. In our design, the channel spacing alignment between the polarization states is obtained by optimizing the geometry of the arrayed waveguides, whereas the central wavelength polarization insensitivity is obtained by splitting the two polarization states and adjusting their angle of incidence at the input star coupler to compensate for the polarization mode dispersion of the AWG. A 100GHz 1×8 wavelength-division multiplexer with crosstalk levels below -16 dB is demonstrated experimentally.

Huygens' dipole for polarization-controlled nanoscale light routing

Structured illumination allows for satisfying the first Kerker condition of in-phase perpendicular electric and magnetic dipole moments in any isotropic scatterer that supports electric and magnetic dipolar resonances. The induced Huygens' dipole may be utilized for unidirectional coupling to waveguide modes that propagate transverse to the excitation beam. We study two configurations of a Huygens' dipole -- longitudinal electric and transverse magnetic dipole moments or vice versa. We experimentally show that only the radially polarized emission of the first and azimuthally polarized emission of the second configuration are directional in the far-field. This polarization selectivity implies that directional excitation of either TM or TE waveguide modes is possible. Applying this concept to a single nanoantenna excited with structured light, we are able to experimentally achieve scattering directivities of around 23 dB and 18 dB in TM and TE modes, respectively. This strong directivity paves the way for tunable polarization-controlled nanoscale light routing and applications in optical metrology, localization microscopy and on-chip optical devices.

Polarization-insensitive one-dimensional guided-mode resonance filter operating at conical mounting.

We report the design and implementation of a one-dimensional guided-mode resonance filter (1D-GMRF) aiming to achieve polarization insensitivity at conical mounting. (The incident plane is aligned neither perpendicularly nor parallelly to the grating bars.) The design guideline indicates that, at conical mounting, polarization insensitivity of the 1D-GMRF can be achieved by optimizing the grating parameters to excite the fundamental TE and the fundamental TM waveguide modes simultaneously. Moreover, it is revealed that, at conical mounting, the polarization-insensitive GMR position in the angle-resolved resonance spectra is azimuthal angle ϕ-dependent. The experimental results demonstrate that polarization insensitivity of the fabricated 1D-GMRF occurs at the resonance wavelength of ∼673 nm for the conical mounting of azimuthal angle ϕ≈30° and incident angle θ≈11.2°, which agree with the simulated results.

Radiation of charged particle bunches in corrugated waveguides with small period

Bunch radiation in periodical waveguides was mainly analyzed for situations when wavelengths are comparable to the structure period (Smith-Purcell emission). However, it is also interesting to study long wave radiation with wavelengths which are much greater than the structure period. In this paper, the electromagnetic field is analyzed using the method of equivalent boundary conditions. According to this approach, the exact boundary conditions on the complex periodic surface are replaced with certain equivalent conditions which must be fulfilled on the smooth surface. We consider a vacuum circular waveguide with a corrugated conductive wall (corrugation has rectangular form). The charge moves along the waveguide axis. The period and the depth of corrugation are much less than the waveguide radius and wavelengths under consideration. Expressions for the full field components and the wave field components are obtained. It is established that radiation consists of the only one TM waveguide mode which is excited if the charge velocity is more than certain limit value. Dependencies of the frequency and amplitude of the mode on the charge velocity and parameters of corrugation are analyzed. It is demonstrated that typical amplitude of waveguide mode from the ultra relativistic bunch has the same order as one in the ordinary regular waveguides with dielectric filling. In order to verify the method applied in this work we have simulated the electromagnetic field using the CST Particle Studio. For this purpose, we have considered the charged particle bunch with negligible thickness and Gaussian longitudinal distribution. It has been shown that the coincidence between theoretical and simulated results is good. This fact confirms that the theory based on the equivalent boundary conditions adequately describe the radiation process in the situation under consideration. The obtained results can be useful for development of methods of the electromagnetic radiation generation and technique of the wakefield acceleration of charged particles.

High-resolution-scanning waveguide microscopy: spatial refractive index and topography quantification.

We report on a high-resolution metal-clad waveguide scanning microscopic method with a diffraction-limited resolution. This microscope can be operated in both TM and TE waveguide modes with radially and azimuthally polarized beams, respectively, and allows both refractive index and topography of dielectric objects to be evaluated at high resolution and sensitivity. We emphasize the performance of this microscopic method from calibrated 3D polymer microstructures with rectangular, disk, and ring shapes.

Transverse magnetic field impact on waveguide modes of photonic crystals.

This Letter presents a theoretical and experimental study of waveguide modes of one-dimensional magneto-photonic crystals magnetized in the in-plane direction. It is shown that the propagation constants of the TM waveguide modes are sensitive to the transverse magnetization and the spectrum of the transverse magneto-optical Kerr effect has resonant features at mode excitation frequencies. Two types of structures are considered: a non-magnetic photonic crystal with an additional magnetic layer on top and a magneto-photonic crystal with a magnetic layer within each period. We found that the magneto-optical non-reciprocity effect is greater in the first case: it has a magnitude of δ∼10-4, while the second structure type demonstrates δ∼10-5 only, due to the higher asymmetry of the claddings of the magnetic layer. Experimental observations show resonant features in the optical and magneto-optical Kerr effect spectra. The measured dispersion properties are in good agreement with the theoretical predictions. An amplitude of light intensity modulation of up to 2.5% was observed for waveguide mode excitation within the magnetic top layer of the non-magnetic photonic crystal structure. The presented theoretical approach may be utilized for the design of magneto-optical sensors and modulators requiring pre-determined spectral features.

Modified TM and TE waveguide modes and reflectivity by graphene layer in coupled-graphene-metal multilayer structure in sub-terahertz frequency

In this paper we focus on the dispersion characteristics of TM and TE waveguide modes and the reflectivity of plane waves, incident on the four-layer structure consisting of air/graphene monolayer/dielectric buffer layer/metal substrate. The TM waveguide modes split up into two branches for small frequencies, one of the branches (cutoff waveguide branch) undergoes cutoff at a certain cutoff buffer thicknesses. There is no splitting of TE waveguide modes. However, these modes can be converted into short-range waves for smaller buffer thickness with subsequent modes cutoff depending on frequency and graphene electron concentration. Reflection coefficients of the TM polarized incident electromagnetic waves from air on the multi-layer structure vanish in the vicinity of cutoff buffer thicknesses. It is demonstrated that waveguide mode propagation constants and reflectivity in the multilayer structure can be considerably influenced by the presence of a graphene layer in the vicinity of the cutoff thicknesses of the waveguide modes.

Properties of the fundamental TM waveguide mode in the narrow metal/dielectric/metal waveguide

We derive analytic expressions of the propagation length and the effective index of the fundamental TM waveguide mode in the limit of the small waveguide width by using the exact mode equation in the one dimensional metal/dielectric/metal waveguide, and results from approximate analytic expressions are compared with the direct numerical solution of the exact mode equation. In addition, we compare the coupled waveguide mode with the linear superposition mode in the metal/dielectric/metal waveguide by using the FDTD method with the Lorentz–Drude model for silver. It provides a physical understanding of properties of the fundamental TM waveguide mode in the narrow metal/dielectric/metal waveguide.

WHAT PERYTONS ARE NOT, AND MIGHT BE

Chirped radio pulses known as perytons are consistent with plasma propagation, but an astronomical origin has been excluded. This paper considers several physical processes as possible explanations. TE and TM waveguide modes have dispersion relations formally similar to those of plasmas, and emission at the plasma frequency of a plasma recombining by two-particle processes also produces a chirp δt∝ω−2, but these hypotheses fail quantitatively. The chirp might be approximately fitted to three-body recombination, cyclotron radiation in exponentially decaying fields, or to the resonance of a distributed LC circuit whose component conductors move. Constraints are placed on these possible processes, but no specific source has been identified.

Achromatic THz wave plate composed of stacked parallel metal plates

We propose a simple achromatic terahertz wave plate composed of stacked parallel metal plates with a hole array. It consists of an ensemble of designed parallel plate waveguides; the high and low propagation speeds of waves in TE and TM waveguide modes with the same group velocity cause a constant phase difference over a wide frequency region. Using that wave plate, we obtained intense single- and multi-cycle THz pulses with circular polarization.

低杂波电流驱动天线耦合的三维模型

通过数值计算对低杂波波导阵天线的耦合特性进行了模拟。采用三维天线耦合模型，考虑了波导沿环向及极向都为有限尺度，以及TE与TM模式的相互耦合。用数值积分的方法计算等离子体表面阻抗，利用此边界条件及波导口处电磁场的连续性。计算各波导在TE10主模2.45 GHz频率的低杂波信号的激励下，各TE与TM波导模式的反射系数。然后计算天线辐射的低杂波频率的功率谱分布。 The coupling performance of grills for lower hybrid frequency is obtained by digital simulation. The three dimensional model is adopted, namely considering the finite poloidal and toroidal sizes of the grills and coupling between TE modes and TM modes. The plasma surface impedance is estimated by digital integral method, and this boundary condition and the electromagnetic field continuity at the grills’ mouth are used. Under the main mode of 2.45 GHz lower hybrid frequency excited in the grills, the reflection factors of the TE and TM waveguide modes can be calculated. Then we obtain the lower hybrid frequency power spectrum distribution sent by the antennas.

Proposed electrically-pumped, III–V-metal hybrid plasmonic lasers

We propose an electrically-pumped hybrid plasmonic laser through the integration of a semiconductor quantum well laser with a thin metal film. Due to the coupling between the TM waveguide mode in the III–V active layer and the LRSPP mode around the metal thin film, light can be confined in both regions and optical gain can be provided by the active layer. We have shown that the quasi-odd supermode is the preferred lasing mode because of its larger confinement factor and lower modal loss compared to the quasi-even supermode. Through optimizing the gap distance between the active region and the metal film, we can obtain low threshold and a large amount of optical energy confined around the metal film for the hybrid plasmonic laser.

Mode-selective excitation of laser-written dielectric-loaded surface plasmon polariton waveguides

We experimentally demonstrate mode-selective excitation of laser-written dielectric-loaded surface plasmon polariton waveguides. The waveguide structures are fabricated by two-photon polymerization of spin-coatable epoxy-based resist on a metal covered glass slide. The waveguides are excited by illuminating the waveguide ends with a strongly focused Gaussian laser beam with a wavelength of 632.8 nm and adjustable polarization. The guiding properties are investigated in the far field by imaging the leakage radiation of the waveguide modes from the metal-substrate interface. It is observed that different TE and TM waveguide modes can be selectively excited with high precision. Simultaneous excitation of the plasmonic TM00 and TM01 modes leads to mode beating and oscillation of the guided intensity between the two sides of the waveguides. In Y-splitters, this simultaneous excitation of the first two TM modes can be used to control the splitting ratio at the exit ports of the splitter.

Spectroscopy of silica layers containing Si nanocrystals: Experimental evidence of optical birefringence

We report an unusual case of spectral filtering by a silica waveguide containing Si nanocrystals (Si-nc’s) deposited on a silica plate. For a number of Si-rich silica (SiOx) slab waveguides annealed at 1100°C, the TE and TM waveguide mode cutoff positions are found in the inversed order with respect to the classical waveguide theory for an isotropic material. Using the cutoff and m-line spectra, this unusual behavior was explained assuming an optical birefringence of the material. For the highest Si content (x∼1.5), we estimated a maximal positive birefringence of ∼8%. The cutoff spectrum simulated with the optical parameters extracted from the m-line measurements corresponds well to the cutoff spectrum directly obtained by measuring waveguided luminescence. This agreement shows that the spectral filtering effect of silica layers containing Si-nc can be described within the quantitative model of delocalized waveguide modes. The possible origin for the observed birefringence is discussed.

Wave-mode dispersions in a relativistic electron beam with ion-channel guiding

An analysis of the eigenmodes of a cylindrical metallic waveguide partially filled with a relativistic electron beam, and guided with an ion channel, is presented. The analysis is performed in the rest frame of the beam with self-fields taken into account. Dispersion relations for five families of electrostatic and EM modes are derived and solved numerically to study the characteristics of azimuthally symmetric TM and TE waveguide modes, betatron modes, and space-charge modes. A strong dependence of the frequencies of these electromagnetic-electrostatic waves on the ratio of the radius of the waveguide to the beam radius is revealed. The physical insight given to the electrostatic modes, at large and small wavelengths, equally applies to the Trivelpiece-Gould modes in an electron beam with axial magnetic field guiding. Interactions between the dispersion curves of different modes are used to find the infinite-space dispersion relation from the finite-radius dispersion relation and to explain the transition from a weak to strong ion channel.

Multimode waveguide mode surface plasmon coupling: a sensitivity and device realizability study

The coupling of p-polarized waveguide modes into waveguide-surface plasmon coupled modes is a promising concept to combine the features of propagating waveguide modes with the resonant field enhancement of surface plasmons and the unique possibility to functionalize the metal surface by self-assembled monolayers (SAMs) via sulfur chemistry. Recently we have demonstrated a waveguide device which allows to couple two TM waveguide modes to the surface plasmon and were able to characterize a new binding matrix with respect to the thickness and the refractive index. The noise and the sensitivity of this device needs further improvement. Therefore we present a sensitivity and device realizability study in order to optimize the technique of multimode waveguide mode surface plasmon coupling for the determination of the thickness and the refractive index of ultrathin layers binding to a metal surface.

Measuring the refractive indices of conjugated polymer films with Bragg grating outcouplers

Photoluminescence trapped inside a polymer film can be scattered out with a Bragg grating. The refractive index in the plane of the film and in the normal direction can be determined as a function of wavelength by measuring the scattering angles of the TE- and TM-waveguide modes. For the polymer poly[2-methoxy-5-(3′,7′-dimethyloctloxy)-paraphenylenevinylene], which is commonly used in light-emitting diodes, the refractive index in the plane of the film drops from 2.0 to 1.8 as the wavelength increases from 600 to 750 nm, while the refractive index in the normal direction is relatively constant at 1.57.

Competition of TE- and TM-waveguide modes in formation of spontaneous gratings and hexagons in the AgCl–Ag films by P-polarized laser beam

We studied the formation of spontaneous gratings in thin light-sensitive AgCl–Ag films irradiated with a P-polarized laser beam. We observed a competition between the waveguide TE 0- and TM 0-modes in the process of grating formation within a certain range of the angles of incidence. This competition results in a hexagon consisting of small grating vectors. The build-up process is studied by means of the small-angle scattering method.