Visible to the public Confinement

SoS Newsletter- Advanced Book Block


In photonics, confinement is important to loss avoidance. In quantum theory, it relates to energy levels. The articles cited here cover both concepts and were presented or published in the first half of 2014.

  • Hasan, D.; Alam, M.S., "Ultra-Broadband Confinement in Deep Sub-Wavelength Air Hole of a Suspended Core Fiber," Lightwave Technology, Journal of, vol.32, no. 8, pp. 1434, 1441, April 15, 2014. doi: 10.1109/JLT.2014.2306292 We demonstrate low loss (0.4043 dB/Km at 1.55 mm) deep sub-wavelength broadband evanescent field confinement in low index material from near IR to mid IR wavelengths with the aid of an specialty optical fiber whilst achieving at least 1.5 dB improvement of figure of merit over the previous design. Plane strain analysis has been conducted to foresee fiber material dependent fabrication challenges associated with such nanoscale feature due to thermal stress. Size dependence of air hole is explained rigorously by modifying the existent slot waveguide model. We report significant improvement of field intensity, interaction length, bandwidth and surface sensitivity over the conventional free standing nanowire structure. The effect of metal layer thickness on surface plasmon resonance sensitivity is explored as well. A method to obtain strong evanescent field in such structure for medical sensing is also demonstrated. The proposed technique to enhance sub-wavelength confinement is expected to be of potential engineering merits for optical nanosensors, atomic scale waveguide for single molecule inspection and ultra-low mode volume cavity.
    Keywords: fibre optic sensors;nanomedicine;nanophotonics;nanosensors;nanowires;optical fibre fabrication; optical fibre losses; optical materials; surface plasmon resonance thermal stresses; atomic scale waveguide; bandwidth; conventional free standing nanowire structure; deep subwavelength air hole; fiber material dependent fabrication; field intensity; figure of merit; gain 1.5 dB; interaction length; low index material; low loss deep subwavelength broadband evanescent field confinement; medical sensing; metal layer thickness ;mid IR wavelengths; nanoscale feature; optical nanosensors; plane strain analysis; single molecule inspection; size dependence; slot waveguide model; specialty optical fiber; strong evanescent field; subwavelength confinement; surface plasmon resonance sensitivity; surface sensitivity; suspended core fiber; thermal stress; ultrabroadband confinement; ultralow mode volume cavity; wavelength 1.55 mum; Indexes; Materials; Optical fiber devices; Optical fiber dispersion; Optical fibers; Optical surface waves; Characteristic decay length; evanescent sensing; field intensity; slot waveguide; sub-wavelength confinement ;suspended core fiber(ID#:14-2729)
  • Paul, U.; Hasan, M.; Rahman, M.T.; Bhuiyan, AG., "Effect of QD Size And Band-Offsets On Confinement Energy In Inn QD Heterostructure," Electrical Information and Communication Technology (EICT), 2013 International Conference on, pp.1,4, 13-15 Feb. 2014. doi: 10.1109/EICT.2014.6777897 Detailed theoretical analysis of how QD size variation and band-offset affects the confinement energy of InN QD is presented. Low dimensional structures show a strong quantum confinement effect, which results in shifting the ground state away from the band edge and discrete eigen-states. Graphically solving 1D Schrodinger ground quantized energy levels of electrons were computed and using Luttinger-Khon 4x4 Hamiltonian matrix ground quantized energy level of holes were determined. Our results allow us to tune dot size and band-offset to obtain required bandgap for InN based low dimensional device design.
    Keywords: III-V semiconductors; Schrodinger equation; energy gap; ground states ;indium compounds; semiconductor heterojunctions; semiconductor quantum dots; InN; Luttinger-Khon 4x4 Hamiltonian matrix ground quantized energy level; band edge; band gap; band-offset effects; confinement energy; discrete eigenstates graphically solving 1D Schrodinger ground quantized energy levels; ground state; low dimensional device design; quantum confinement effect; quantum dot heterostructure; quantum dot size effect; quantum dot size variation; theoretical analysis; Charge carrier processes; Energy states; Equations; Materials; Mathematical model; Optoelectronic devices; Quantum dots; Confinement energy; Indium Nitride; Quantum dots (QD) (ID#:14-2730)
  • Tripathi, Neeti; Yamashita, Masaru; Uchida, Takeyuki; Akai, Tomoko, "Observations on Size Confinement Effect In B-C-N Nanoparticles Embedded In Mesoporous Silica Channels," Applied Physics Letters, vol. 105, no.1, pp.014106,014106-4, Jul 2014. doi: 10.1063/1.4890000 Fluorescent B-C-N/silica nanoparticles were synthesized by solution impregnation method. Effect of B-C-N particle size on the optical properties was investigated by varying the silica pore sizes. Formation of B-C-N nanoparticles within the mesoporous matrix is confirmed by x-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. Furthermore, a remarkable blue-shift in emission peak centres with decreasing pore size in conjugation with band gap modification, ascribed to the size confinement effect. A detailed analysis of experimental results by theoretically defined confinement models demonstrates that the B-C-N nanoparticles in the size range of 3-13 nm falls within the confinement regime. This work demonstrated the experimental evidence of the size confinement effect in smaller size B-C-N nanoparticles.
    Keywords: (not provided) (ID#:14-2731)
  • Lingyun Wang; Youmin Wang; Xiaojing Zhang, "Integrated Grating-Nanoslot Probe Tip for Near-Field Subwavelength Light Confinement and Fluorescent Sensing," Selected Topics in Quantum Electronics, IEEE Journal of, vol.20, no.3, pp.184,194, May-June 2014. doi: 10.1109/JSTQE.2014.2301232 We demonstrate a near-field sub-wavelength light confinement probe tip comprised of compact embedded metallic focus grating (CEMFG) coupler and photonic crystal (PhC) based l/4 nano-slot tip, in terms of its far-field radiation directivity and near-field sub-wavelength light enhancement. The embedded metallic grating coupler increases the free space coupling at tilted coupling angle of 25deg with over 280 times light intensity enhancement for 10 mm coupler size. Further, 20 nm air slot embedded in single line defect PhC waveguide are designed, using the impedance matching concept of the l/4 "air rod", to form the TE mode light wave resonance right at the probe tip aperture opening. This leads to the light beam spot size reduction down to l/20. The near-field center peak intensity is enhanced by 4.2 times from that of the rectangular waveguide input, with the total enhancement factor of 1185 from free space laser source intensity. The near-field fluorescence excitation and detection also demonstrate its single molecular enhanced fluorescence measurement capability.
    Keywords: diffraction gratings; fluorescence; integrated optics; nanophotonics; nanosensors; optical couplers; optical sensors; optical waveguides; photonic crystals; rectangular waveguides; TE mode light wave resonance; air rod; air slot; compact embedded metallic focus grating coupler; coupler size; far-field radiation directivity; fluorescent sensing; free space coupling; free space laser source intensity; impedance matching; integrated grating-nanoslot probe tip; light beam spot size reduction ;light intensity enhancement; near-field center peak intensity; near-field fluorescence excitation; near-field sub-wavelength light confinement probe tip; near-field sub-wavelength light enhancement; near-field subwavelength light confinement; photonic crystal based l/4 nanoslot tip; probe tip aperture opening; rectangular waveguide input; single line defect PhC waveguide; single molecular enhanced fluorescence measurement capability; size 10 mum; tilted coupling angle; Couplers; Couplings; Etching; Gratings; Metals; Optical waveguides; Probes; l/4 nano-slot; Metallic grating; light confinement; near-field; photonic crystal; single molecule fluorescence detection (ID#:14-2732)
  • Ali, M.S.; Islam, A; Ahmad, R.; Siddique, AH.; Nasim, K.M.; Khan, M.AG.; Habib, M.S., "Design Of Hybrid Photonic Crystal Fibers For Tailoring Dispersion And Confinement Loss," Electrical Information and Communication Technology (EICT), 2013 International Conference on, pp. 1, 4, 13-15 Feb. 2014 doi: 10.1109/EICT.2014.6777861 This paper presents the proposal of a hybrid cladding photonic crystal fiber offering flat dispersion and low confinement operating in the Telecom bands. Simulation results reveal that near zero ultra flattened dispersion of 0 +- 1.20 ps/( is obtained in a 1.25 to 1.70 mm wavelength range i.e. 450 nm flat band along with low confinement losses which is less than 10-2 dB/km at operating wavelength 1.55 mm. Moreover, the sensitivity of the fiber dispersion properties to a +-1% to +-5% variation in the optimum parameters is studied for practical conditions.
    Keywords: holey fibres; optical fibre dispersion; optical fibre losses; photonic crystals; Telecom bands; design; fiber dispersion properties; flat dispersion; hybrid cladding photonic crystal fiber; low confinement losses; wavelength 1.25 mum to 1.70 mum; Chromatic dispersion; Optical fiber communication; Optical fiber dispersion; Optical fibers; Photonic crystal fibers; Refractive index; chromatic dispersion; confinement loss; effective area; photonic crystal fiber (ID#:14-2733)
  • Ghasemi, M.; Choudhury, P.K., "Effect Due To Down-Tapering On The Hybrid Mode Power Confinement In Liquid Crystal Optical Fiber," Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON), 2014 11th International Conference on, pp.1,4, 14-17 May 2014. doi: 10.1109/ECTICon.2014.6839753 The paper presents analysis of the wave propagation through down-tapered three-layer liquid crystal optical fiber in respect of power confinement due to the hybrid modes supported by the guide. The inner two regions are homogeneous and isotropic dielectrics whereas the outermost layer being composed of radially anisotropic liquid crystal material. It has been found that the guide supports relatively very high amount of power in the liquid crystal region, which indicates the possible use of such microstructures in varieties of optical applications. The effects on confinement due to the positive and the negative (illustrating the taper type) values of taper slopes are reported.
    Keywords: dielectric materials; liquid crystals; micro-optics; optical fibres; down-tapering; homogeneous dielectrics; hybrid mode power confinement; hybrid modes; isotropic dielectrics; liquid crystal optical fiber; power confinement; radially anisotropic liquid crystal material; taper slopes; wave propagation; Dielectrics; Equations ;Liquid crystals; Optical fiber dispersion; Optical fibers; Liquid crystal fibers; complex mediums; electromagnetic wave propagation (ID#:14-2734)
  • Janjua, B.; Ng, T.K.; Alyamani, AY.; El-Desouki, M.M.; Ooi, B.S., "Enhancement of Hole Confinement by Monolayer Insertion in Asymmetric Quantum-Barrier UVB Light Emitting Diodes," Photonics Journal, IEEE, vol.6, no.2, pp.1,9, April 2014. doi: 10.1109/JPHOT.2014.2310199 We study the enhanced hole confinement by having a large bandgap AlGaN monolayer insertion (MLI) between the quantum well (QW) and the quantum barrier (QB). The numerical analysis examines the energy band alignment diagrams, using a self-consistent 6 x 6 k *p method and, considering carrier distribution, recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates), under equilibrium and forward bias conditions. The active region is based on AlaGa1-aN (barrier)/AlbGa1-bN (MLI)/AlcGa1-cN (well)/AldGa1-dN (barrier), where b d a c. A large bandgap AlbGa1 - bN mono layer, inserted between the QW and QB, was found to be effective in providing stronger hole confinement. With the proposed band engineering scheme, an increase of more than 30% in spatial overlap of carrier wavefunction was obtained, with a considerable increase in carrier density and direct radiative recombination rates. The single-QW-based UV-LED was designed to emit at 280 nm, which is an effective wavelength for water disinfection.
    Keywords: Auger effect; III-V semiconductors; aluminium compounds; electron-hole recombination; gallium compounds; k.p calculations; light emitting diodes; monolayers; semiconductor quantum wells; wave functions; wide band gap semiconductors; AlGaN; Auger recombination rates; MLI; Shockley-Reed-Hall recombination rates; asymmetric quantum-barrier UVB light emitting diodes; carrier density; carrier distribution; carrier wavefunction; direct radiative recombination rates; energy band alignment diagrams; enhanced hole confinement; hole confinement; monolayer insertion; numerical analysis; radiative recombination rates; recombination rates ;self-consistent 6 x 6 k *p method; water disinfection; Aluminum gallium nitride; Charge carrier density; Charge carrier processes; III-V semiconductor materials; Light emitting diodes; Radiative recombination ;Light emitting diodes (LEDs);energy barrier; semiconductor quantum well; thin insertion layer; ultraviolet; water disinfection; wavefunction overlap (ID#:14-2735)
  • Qijing Lu; Fang-Jie Shu; Chang-Ling Zou, "Extremely Local Electric Field Enhancement and Light Confinement in Dielectric Waveguide," Photonics Technology Letters, IEEE, vol.26, no.14, pp.1426, 1429, July15, 15 2014. doi: 10.1109/LPT.2014.2322595 Extremely local electric field enhancement and light confinement are demonstrated in dielectric waveguides with corner and gap geometry. Classical electromagnetic theory predicts that the field enhancement and confinement abilities are inversely proportional to radius of rounded corner (r) and gap (g), and shows a singularity for infinitesimal r and g. For practical parameters with r = g = 10 nm, the mode area of opposing apex-to-apex fan-shaped waveguides can be as small as 4 x 10-3 A0 (A0 = l2/4), far beyond the diffraction limit. The lossless dielectric corner and gap structures offer an alternative method to enhance light-matter interactions without the use of metal nanostructures, and can find applications in quantum electrodynamics, sensors, and nanoparticle trapping.
    Keywords: light diffraction; optical waveguide theory; apex-to-apex fan-shaped waveguides; classical electromagnetic theory; corner geometry; dielectric waveguide; diffraction limit; extremely local electric field enhancement; gap geometry; gap radius; gap structures; light confinement; light-matter interactions; lossless dielectric corner; nanoparticle trapping; quantum electrodynamics; rounded corner radius; sensors; Antennas; Dielectrics; Electric fields; Optical waveguides; Plasmons; Waveguide discontinuities; Dielectric waveguides; nanophotonics; optical waveguides (ID#:14-2736)
  • Kai-Jun Che, "Waveguide modulated photonic molecules with metallic confinement," Transparent Optical Networks (ICTON), 2014 16th International Conference on , vol., no., pp.1,3, 6-10 July 2014 doi: 10.1109/ICTON.2014.6876649 Abstract: Photonic molecules based on the evanescent wave have been displayed unique physical characteristics, such as quality factor enhancement of optical system and mode transition between different order modes etc. Waveguide, as basic photonic element, is introduced for indirect optical interaction and guided emission of photonics molecules. Due to that the metal can effectively confine the photons in a fixed space and facilitates the high density device package as optical insulator, the optical characteristics of photonic molecules with metallic confinement, including the mode and emission characteristics, are investigated by electromagnetic analysis, combined with finite difference time domain simulations. The results show the metal dissipation of odd and even state split since they have different morphologies at coupling area and the guided emission is strongly determined by the metal-dielectric confined waveguide. Moreover, non-local optical interaction between two whispering gallery circular resonators through a waveguide coupled in radial direction is proposed for breaking the small depth of evanescent permeation. Strong optical interaction is found from the even state and interaction intensity is relative to the features of waveguide.
    Keywords: Q-factor; finite difference time-domain analysis; optical resonators; optical waveguides; coupling area; electromagnetic analysis; evanescent permeation; evanescent wave; even state; finite difference time domain simulations; guided emission ;high density device package; interaction intensity; metal dissipation; metal-dielectric confined waveguide; metallic confinement; mode transition; nonlocal optical interaction; odd state; optical insulator; photonic molecules; quality factor enhancement; waveguide modulated photonic molecules; whispering gallery circular resonators; Integrated optics; Optical coupling; Optical resonators; Optical surface waves; Optical waveguides; Photonics; Stimulated emission; guided emission; metallic confinement; n on-local optical interaction; photonic molecules (ID#:14-2737)
  • Hegde, Ganesh; Povolotskyi, Michael; Kubis, Tillmann; Charles, James; Klimeck, Gerhard, "An Environment-Dependent Semi-Empirical Tight Binding Model Suitable For Electron Transport In Bulk Metals, Metal Alloys, Metallic Interfaces, And Metallic Nanostructures. II. Application--Effect Of Quantum Confinement And Homogeneous Strain On Cu Conductance," Journal of Applied Physics, vol.115, no.12, pp.123704, 123704-5, Mar 2014. doi: 10.1063/1.4868979 The Semi-Empirical tight binding model developed in Part I Hegde et al. [J. Appl. Phys. 115, 123703 (2014)] is applied to metal transport problems of current relevance in Part II. A systematic study of the effect of quantum confinement, transport orientation, and homogeneous strain on electronic transport properties of Cu is carried out. It is found that quantum confinement from bulk to nanowire boundary conditions leads to significant anisotropy in conductance of Cu along different transport orientations. Compressive homogeneous strain is found to reduce resistivity by increasing the density of conducting modes in Cu. The [110] transport orientation in Cu nanowires is found to be the most favorable for mitigating conductivity degradation since it shows least reduction in conductance with confinement and responds most favorably to compressive strain.
    Keywords: (not provided) (ID#:14-2738)
  • Padilla, J.L.; Alper, C.; Gamiz, F.; Ionescu, AM., "Assessment of field-induced quantum confinement in heterogate germanium electron-hole bilayer tunnel field-effect transistor," Applied Physics Letters, vol.105, no.8, pp.082108, 082108-4, Aug 2014. doi: 10.1063/1.4894088 The analysis of quantum mechanical confinement in recent germanium electron-hole bilayer tunnel field-effect transistors has been shown to substantially affect the band-to-band tunneling (BTBT) mechanism between electron and hole inversion layers that constitutes the operating principle of these devices. The vertical electric field that appears across the intrinsic semiconductor to give rise to the bilayer configuration makes the formerly continuous conduction and valence bands become a discrete set of energy subbands, therefore increasing the effective bandgap close to the gates and reducing the BTBT probabilities. In this letter, we present a simulation approach that shows how the inclusion of quantum confinement and the subsequent modification of the band profile results in the appearance of lateral tunneling to the underlap regions that greatly degrades the subthreshold swing of these devices. To overcome this drawback imposed by confinement, we propose an heterogate configuration that proves to suppress this parasitic tunneling and enhances the device performance.
    Keywords: (not provided) (ID#:14-2739)
  • Puthen Veettil, B.; Konig, D.; Patterson, R.; Smyth, S.; Conibeer, G., "Electronic Confinement In Modulation Doped Quantum Dots," Applied Physics Letters, vol.104, no. 15, pp. 153102, 153102-3, Apr 2014. doi: 10.1063/1.4871576 Modulation doping, an effective way to dope quantum dots (QDs), modifies the confinement energy levels in the QDs. We present a self-consistent full multi-grid solver to analyze the effect of modulation doping on the confinement energy levels in large-area structures containing Si QDs in SiO2 and Si3N4 dielectrics. The confinement energy was found to be significantly lower when QDs were in close proximity to dopant ions in the dielectric. This effect was found to be smaller in Si3N4, while smaller QDs in SiO2 were highly susceptible to energy reduction. The energy reduction was found to follow a power law relationship with the QD size.
    Keywords: (not provided) (ID#:14-2740)
  • Li Wei; Aldawsari, S.; Wing-Ki Liu; West, B.R., "Theoretical Analysis of Plasmonic Modes in a Symmetric Conductor-Gap-Dielectric Structure for Nanoscale Confinement," Photonics Journal, IEEE, vol.6, no.3, pp.1, 10, June 2014. doi: 10.1109/JPHOT.2014.2326677 A hybrid plasmonic waveguide is considered as one of the most promising architectures for long-range subwavelength guiding. The objective of this paper is to present a theoretical analysis of plasmonic guided modes in a symmetric conductor-gap-dielectric (SCGD) system. It consists of a thin metal conductor symmetrically sandwiched by two-layer dielectrics with low-index nanoscale gaps inside. The SCGD waveguide can support ultra-long range surface plasmon-polariton mode when the thickness of a low-index gap is smaller than a cutoff gap thickness. For relatively high index contrast ratios of the cladding to gap layers, the cutoff gap thickness is only a few nanometers, within which the electric field of the guided SCGD mode is tightly confined. The dispersion equations and approximate analytical expressions of the cutoff gap thickness are derived in order to characterize the properties of the guided mode. Our simulation results show that the cutoff gap thickness can be tailored by the metal film thickness and the indices of the cladding and gap materials. The geometrical scheme for lateral confinement is also presented. Such a structure with unique features of low-loss and strong confinement has applications in the fabrication of active and passive plasmonic devices.
    Keywords: metallic thin films; nanophotonics; optical waveguides; plasmonics; polaritons; surface plasmons; cutoff gap thickness; dispersion equations; electric field; hybrid plasmonic waveguide; low-index nanoscale gaps; metal film thickness; nanoscale confinement; plasmonic guided modes; surface plasmon-polariton mode; symmetric conductor-gap-dielectric structure; theoretical analysis; thin metal conductor; two-layer dielectrics; Equations; Films; Indexes; Metals; Optical waveguides; Plasmons; Propagation losses; Surface plasmons; guided wave; integrated optics; waveguides (ID#:14-2741)
  • Barbagiovanni, E.G.; Lockwood, D.J.; Rowell, N.L.; Costa Filho, R.N.; Berbezier, I; Amiard, G.; Favre, L.; Ronda, A; Faustini, M.; Grosso, D., "Role of Quantum Confinement In Luminescence Efficiency Of Group IV Nanostructures," Journal of Applied Physics, vol.115, no.4, pp. 044311, 044311-4, Jan 2014. doi: 10.1063/1.4863397 Experimental results obtained previously for the photoluminescence efficiency (PLeff) of Ge quantum dots (QDs) are theoretically studied. A log-log plot of PLeff versus QD diameter (D) resulted in an identical slope for each Ge QD sample only when EG(D2+D)1. We identified that above D 6.2 nm: EGD1 due to a changing effective mass (EM), while below D 4.6 nm: EGD2 due to electron/hole confinement. We propose that as the QD size is initially reduced, the EM is reduced, which increases the Bohr radius and interface scattering until eventually pure quantum confinement effects dominate at small D.
    Keywords: (not provided) (ID#:14-2742)
  • Ishizaka, Yuhei; Nagai, Masaru; Saitoh, Kunimasa, "Strong Light Confinement In A Metal-Assisted Silicon Slot Waveguide," Optical Fibre Technology, 2014 OptoElectronics and Communication Conference and Australian Conference on, pp.103,105, 6-10 July 2014. A metal-assisted silicon slot waveguide is presented. Numerical results show that the proposed structure achieves a strong light confinement in a low-index region, which leads to the improvement of the sensitivity in refractive index sensors.
    Keywords: Metals; Optical waveguides; Optimized production technology; Refractive index; Sensitivity; Sensors; Silicon (ID#:14-2743)
  • Park, Y.; Hirose, Y.; Nakao, S.; Fukumura, T.; Xu, J.; Hasegawa, T., "Quantum Confinement Effect In Bi Anti-Dot Thin Films With Tailored Pore Wall Widths And Thicknesses," Applied Physics Letters, vol. 104, no. 2, pp.023106,023106-4, Jan 2014. doi: 10.1063/1.4861775 We investigated quantum confinement effects in Bi anti-dot thin films grown on anodized aluminium oxide templates. The pore wall widths (wBi) and thickness (t) of the films were tailored to have values longer or shorter than Fermi wavelength of Bi (lF = 40 nm). Magnetoresistance measurements revealed a well-defined weak antilocalization effect below 10 K. Coherence lengths (Lph) as functions of temperature were derived from the magnetoresistance vs field curves by assuming the Hikami-Larkin-Nagaoka model. The anti-dot thin film with wBi and t smaller than lF showed low dimensional electronic behavior at low temperatures where Lph(T) exceed wBi or t.
    Keywords: (not provided) (ID#:14-2744)


Articles listed on these pages have been found on publicly available internet pages and are cited with links to those pages. Some of the information included herein has been reprinted with permission from the authors or data repositories. Direct any requests via Email to SoS.Project (at) for removal of the links or modifications to specific citations. Please include the ID# of the specific citation in your correspondence.