Excitation Of Waveguide Modes Research Articles

Excitation of Hybrid Plasmonic Waveguide Modes by Colloidal Quantum Dots

Quantum information technologies will greatly benefit from efficiently coupled quantum emitter–waveguide systems. Hybrid plasmonic waveguide modes are relatively low-loss confined modes, which prov...

Excitation of Plasmon Waveguide Mode by Counterpart Coaxial Split Ring Resonators

The improvement of excitation efficiency from free space to the longitudinal propagating plasmonic-guided wave attracts growing researchers’ interests recently. In this work, a coupling structure composed of counterpart coaxial split ring resonators and a plasmonic stripe waveguide was proposed to investigate the characteristics of the plasmonic waveguide mode excitation by using finite-difference time-domain (FDTD) method. Results showed that an extremely wide spectrum bandwidth about 930 nm which covered the communication region from 1070 nm to 2 μm was achieved and the excitation efficiencies at resonant wavelengths of 1235 nm and 1636 nm reached 36.1% and 24.5%, respectively. And the coupling wavelength can be modulated by rotating the outer split ring. Our research provides potential applications for next-generation plasmonic integrated chips and functional devices.

Cherenkov-transition radiation in a waveguide partly filled with a strongly magnetized plasma

We analyze the electromagnetic field of a small bunch that uniformly moves in a circular waveguide and transverses a boundary between an area filled up with a strongly magnetized cold plasma and a vacuum area. Such plasma is described with a diagonal dielectric permittivity tensor. The investigation of the waveguide mode components is performed analytically and numerically. The Cherenkov radiation in the filled area of the waveguide and the Cherenkov-transition radiation (CTR) in the vacuum area are under investigation. The conditions of excitation of CR and the CTR peculiarities are obtained. Typical graphics for the field of the excited waveguide mode are presented.

Enhanced sensitivity of fiber optic evanescent wave absorption-based concentration sensor by shining a Bessel–Gauss beam and effect of fiber bending on the sensor response: a theoretical analysis

We present a theoretical perspective on the notion of a highly sensitive multimode fiber optic evanescent wave absorption-based sensor by exploiting a zero-order Bessel–Gauss beam to determine the concentration of sodium chloride (NaCl) from its aqueous solution. The phenomenon of excited waveguide modes inside the sensor structure has been assessed by using a classical wave-optic model. By harnessing the advantages of the Bessel–Gauss beam, the difference in transmitted output power is evaluated for various concentrations of NaCl, ranging from 0 to 360 g/L. To corroborate our theoretical predictions, the computer-aided simulation in Mode Solutions software has been performed on the proposed sensing configuration. In contrast to the conventional concentration sensor using Gaussian beam, the projected scheme yields a maximum 14.40-fold superior sensitivity of 0.072 dB / gL − 1 with a commendable sensing resolution of ∼0.013 g / L. Also, attention has been paid to the Bessel–Gauss beam shined U-bent fiber-optic absorption-based concentration sensor, where the sensor response has been numerically investigated for different bending radii, and it is concluded that the sensitivity can be enhanced appreciably by gently reducing the bending radius. Due to ultrahigh sensitivity, the present paradigm is very much alluring and evocative, establishing pivotal implication in chemical and biological sensing fields.

Multiple compound Tamm waves with Uller–Zenneck wave characteristics guided by dissipative dielectric defect in periodic multilayered isotropic dielectric material

A canonical problem configured in three different arrangements of periodic multilayered isotropic dielectric material layers with a dissipative dielectric defect, to guide multiple compound Tamm waves with Uller–Zenneck wave characteristics, was formulated and solved. The numerical solutions showed multiple Tamm waves guided at a fixed wavelength along the dissipative defect with same polarization state. These waves propagate with different phase speeds, different propagation distances, different field localizations, and different field profiles. The results identified excitation of symmetric and anti-symmetric solutions of p-polarized Tamm waves and p- and s-polarized waveguide modes. The high phase speed solutions ceased to exist beyond a certain limit of dissipative dielectric defect thickness, but the low phase speed solutions were computed for a wide range of dissipative dielectric defect thickness. The Tamm waves were compounded when the thickness of defect is very small and transmuted into waveguide modes for increasing thickness of dissipative dielectric defect because most of the energy is then strongly confined to the dissipative dielectric defect. The excitation of multiple Tamm waves and waveguide modes at a given dissipative dielectric defect thickness and fixed wavelength can be considered for multi-channel optical communication and sensing applications.

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.

Analysis of Graphene-Based Multilayer Comb-Like Absorption System Based on Multiple Waveguide Theory

We propose the monolayer graphene with a periodic stack of the dielectric materials to achieve comb-like absorption enhancement. The number of absorption peaks corresponds to the stacked period number of two dielectric materials. The simulation and theoretical results illustrate that the appearance of multiple absorption peaks is attributed to the excitation of multiple waveguide modes confirmed by using the multiple waveguide theory. The perfect absorption peaks at any desired wavelength in the visible range can be tuned by carefully optimizing the structural parameters and the stacked period number of two dielectric materials.

Ultra-sensitive biosensor with hybrid coupling between molybdenum disulfide thin film and photonic waveguide mode

Abstract Coupling between planar waveguide modes (WGMs) with monolayer molybdenum disulfide (MoS2) is analyzed. A low quality factor waveguide is attached with MoS2 to generate a broad resonance. While another high quality factor waveguide provides an extra sharper resonance. Fano resonance (FR) arising from the coupling between the excited WGMs is discussed and confirmed through numerical calculation. Electric field distributions at the resonance position are also presented to verify the existence of FR. It is demonstrated that the FR shape can be engineered by the structural parameters and applied in the ultrasensitive biosensor to enhance the intensity sensitivity. A maximal sensitivity of 9630 RIU−1 is obtained under the optimal condition. Our research reveals the potential application prospect in optical sensing and detection with high sensitivity based on coupling between waveguide modes with MoS2.

Spin‐Selective and Wavelength‐Selective Demultiplexing Based on Waveguide‐Integrated All‐Dielectric Metasurfaces

AbstractA novel approach for the design of a spin‐selective directional coupler and spin‐selective wavelength demultiplexing device by integrating an all‐dielectric metasurface into a silicon nitride waveguide is proposed and demonstrated. Taking advantage of the intrinsic chirality of the electromagnetic field inside the waveguide, the propagation direction of the excited waveguide mode can be easily controlled by the spin and wavelength of the incident light. The coupling efficiency of the spin‐selective directional coupler toward one side can reach ≈51.6% at 1836 nm. In addition, the working wavelengths, coupling efficiency, peak width, and mode type can be easily tailored by adjusting the geometric parameters of the waveguide and the antenna arrays. This study may provide a further step in the development of photonic integrated circuits, integrated quantum optics, chiral optics, and high‐bit‐rate telecommunication applications.

The Effect of Fast Normal Mode Structure and Magnetopause Forcing on FLRs in a 3‐D Waveguide

AbstractThis paper investigates the excitation of waveguide modes in a nonuniform dipole equilibrium and, further, their coupling to field line resonances (FLRs). Waveguide modes are fast compressional ultralow frequency (ULF) waves, whose structure depends upon the magnetospheric equilibrium and the solar wind driving conditions. Using magnetohydrodynamic simulations, we consider how the structure of the excited waveguide mode is affected by various forms of magnetopause driving. We find that the waveguide supports a set of normal modes that are determined by the equilibrium. However, the particular normal modes that are excited are determined by the structure of the magnetopause driver. A full understanding of the spatial structure of the normal modes is required in order to predict where coupling to FLRs will occur. We show that symmetric pressure driving about the noon meridian can excite normal modes which remain around to drive resonances for longer than antisymmetric driving. Further, the critical quantity in terms of efficient coupling is the magnetic pressure gradient aligned with the resonance.

Enhanced light trapping in thin-film silicon solar cells with concave quadratic bottom gratings.

We present a theoretical crystalline silicon thin-film solar cell with concave quadratic bottom gratings using parametric design of the gratings and systematically perform optoelectronic simulations of the proposed grating structures. Numerical results reveal that the concave quadratic grating structure leads to a desirable enhancement of light absorption in the near-IR region (750-1100nm), and this enhancement is dominated by TE-polarized light. The mechanisms of light absorption enhancement under TE-polarized light are based on the hybrid effect of optical waveguide modes and Fabry-Perot modes. Moreover, research results indicate that the concave quadratic grating structure has excellent light-focusing effects, which is conducive to the excitation of optical waveguide modes. The study findings can be utilized to improve the efficiency of thin-film solar cells based on grating structures.

Bloch Surface Wave Photonic Device Fabricated by Femtosecond Laser Polymerisation Technique

We applied femtosecond laser polymerisation technique to fabricate a novel Bloch surface wave integrated photonic device with a compact coupling scheme. The device consisted of a waveguide, coupling and decoupling gratings and focusing and defocusing triangles. We manufactured an array of devices with varying geometrical parameters of waveguide. Excitation and propagation of Bloch surface wave waveguide modes were studied by direct and back focal plane imaging. The obtained results prove that the maskless and flexible femtosecond laser polymerisation technique may be applied for fabrication of Bloch-surface-wave based integrated photonics.

Reversed Cherenkov-transition radiation in a waveguide partly filled with a left-handed medium

We analyze the electromagnetic field of a charged particle that moves uniformly in a circular waveguide and crosses a boundary between a vacuum area and an area filled with a left-handed medium exhibiting resonant frequency dispersion. The investigation of the waveguide mode components is performed analytically and numerically. The reversed Cherenkov radiation in the filled area of the waveguide and the reversed Cherenkov-transition radiation (RCTR) in the vacuum area are analyzed. The conditions for the excitation of RCTR are obtained. It is shown that the number of modes of RCTR is always finite; in particular, under certain conditions, the RCTR is composed of the first waveguide mode only. Plots of the typical fields of the excited waveguide mode are presented.

Photovoltaic absorber with different grating profiles in the near-infrared region.

We theoretically introduce a Si-based photovoltaic absorber with different grating profiles, which demonstrates a desirable enhancement of light absorption in the near-infrared region by increasing the degree of the grating's profile function. The mechanisms of light absorption enhancement originate from the synergetic effect of optical waveguide modes, light scattering, and Fabry-Perot resonances. Moreover, numerical results indicate that the convex grating structure is more conducive to the excitation of optical waveguide modes compared with the concave grating structure. The research findings can be utilized to guide the design of thin-film solar cells based on grating structures.

High-performance near-field thermophotovoltaics for waste heat recovery

The US industries reject nearly 20–50% of the consumed energy into the environment as waste heat. Harvesting this huge amount of heat can substantially improve the energy usage efficiency. For waste heat in the medium temperature range (~ 500–900K), traditional solid-state waste heat recovery techniques like thermoelectric generators and thermophotovoltaics (TPVs) are still suffering from relatively low efficiency or power density. In this work, we analyze a near-field TPV system consisting of a plasmonic emitter (indium tin oxide) and a narrow-bandgap photovoltaic cell (InAs) that are brought to deep sub-wavelength distances for high-efficiency and high-power-density waste heat recovery. We show that despite the inclusion of realistic nonradiative recombination rates and sub-bandgap heat transfer, such a near-field TPV system can convert heat to electricity with up to nearly 40% efficiency and 11W/cm2 power density at a 900K emitter temperature, because of the spectral reshaping and enhancement by the thermally excited surface plasmons and waveguide modes. Thus, we show that for waste heat recovery, near-field TPV systems can have performances that significantly exceed typical thermoelectric systems. We propose a modified system to further enhance the power density by using a thin metal film on the cell, achieving a counterintuitively “blocking-assisted” heat transfer and power generation in the near-field regime.

Free space excitation of coupled Anderson-localized modes in photonic crystal waveguides with polarization tailored beam

We experimentally demonstrate free space excitation of coupled Anderson-localized modes in photonic crystal (PhC) line-defect waveguides (W1) with polarization tailored beams. The corresponding light beam is tightly focused on a pristine W1, and out-of-plane scattering is imaged. By integrating the scattering spectra along the guide, at the W1 modal cut-off, Anderson-localized cavities are observed due to residual W1 fabrication-disorder. Their spectral lines exhibit high quality Q factors up to 2 × 105. The incident beam polarization and scattering intensities of the localized modes characterize the efficiency of free-space coupling. The coupling is studied for linearly and radially polarized input beams and for different input coupling locations along the W1 guide. The proposed coupling scheme is particularly attractive for excitation of PhC waveguide modes and Anderson-localized cavities by beam steering and scanning microscopy for sensing applications.

Absorption enhancement and total absorption in a graphene-waveguide hybrid structure

We propose a graphene/planar waveguide hybrid structure, and demonstrate total absorption in the visible wavelength range by means of attenuated total reflectance. The excitation of planar waveguide mode, which has strong near field enhancement and increased light interaction length with graphene, plays a vital role in total absorption. We analyze the origin and physical insight of total absorption theoretically by using an approximated reflectance, and show how to design such hybrid structure numerically. Utilizing the tunability of doped graphene, we discuss the possible application in optical modulators. We also achieve broadband absorption enhancement in near-IR range by cascading multiple graphene-waveguide hybrid structures. We believe our results will be useful not only for potential applications in optical devices, but also for studying other two-dimension materials.

Considering Symmetry Properties of InP Nanowire/Light Incidence Systems to Gain Broadband Absorption

Geometrically designed III-V nanowire arrays are promising candidates for disruptive optoelectronics due to the possibility of obtaining a strongly enhanced absorption resulting from nanophotonic resonance effects. With normally incident light on such vertical nanowire arrays, the absorption spectra exhibit peaks that originate from excitation of HE1m waveguide modes in the constituent nanowires. However, the absorption spectra typically show dips between the absorption peaks. Conventionally, such weak absorption has been counteracted by either making the nanowires longer or by decreasing the pitch of the array, both alternatives effectively increasing the volume of absorbing material in the array. Here, we first study two approaches for compensating the absorption dips by exciting additional Mie resonances: 1) oblique light incidence on vertical InP nanowire arrays and 2) normal light incidence on inclined InP nanowire arrays. We then show that branched nanowires offer a novel route to achieve broadband absorption by taking advantage of simultaneous excitations of Mie resonances in the branches and guided HE1m modes in the stem. Finite element method calculations show that the absorption efficiency is enhanced from 0.72 for vertical nanowires to 0.78 for branched nanowires under normal light incidence. Our work provides new insight for the development of novel efficient photovoltaics with high efficiency and reduced active material volume.

Electric field enhancement with plasmonic colloidal nanoantennas excited by a silicon nitride waveguide.

We investigate the feasibility of CMOS-compatible optical structures to develop novel integrated spectroscopy systems. We show that local field enhancement is achievable utilizing dimers of plasmonic nanospheres that can be assembled from colloidal solutions on top of a CMOS-compatible optical waveguide. The resonant dimer nanoantennas are excited by modes guided in the integrated silicon nitride waveguide. Simulations show that 100-fold electric field enhancement builds up in the dimer gap as compared to the waveguide evanescent field amplitude at the same location. We investigate how the field enhancement depends on dimer location, orientation, distance and excited waveguide mode.

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.