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Accepted papers to appear in an upcoming issue

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Singular laser beams nanofocusing with dielectric nanostructures: theoretical investigation

Alexey Porfirev, Sergey Degtyarev, Andrey Ustinov, and Svetlana Khonina

Doc ID: 271989 Received 21 Jul 2016; Accepted 20 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: We show that near-field nanoscale focusing is feasible using not only metallic but also dielectric sharp-edged structures. Based on vector Rayleigh–Sommerfeld integrals, we prove that the effect of an enhancement of the longitudinal electromagnetic field component occurs in the vicinity of the incident field phase discontinuities due to abrupt jumps in the optical element’s microrelief. Using a finite-element method, we simulate diffraction of the electromagnetic field using sharp edges of metallic and high-contrast dielectric structures. The resulting focal spot size is shown to be near directly proportional to the structure tip’s curvature radius. We propose a focusing arrangement that contains a radiation collector in the form of a conic axicon and a nanofocuser in the form of a nanosphere on the axicon’s apex. Using the finite-element method, we demonstrate that the proposed setup enables light to be confined to a thin focal spot with the size λ/373 for a silicon nanosphere with a radius of 2 nm.

Large enhancement of optical limiting effects in anisotropic two-photon absorbers by radially polarized beams

Gu Bing, Guanghao Rui, Yuxiong Xue, jun He, and Yiping Cui

Doc ID: 273723 Received 15 Aug 2016; Accepted 20 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: We report the large enhancement of optical limiting effects by exploiting the anisotropy of two-photon absorber and manipulating the polarization distribution of the light field simultaneously. After modeling the polarization-orientation dependence on the two-photon absorption (TPA) coefficient, we demonstrate the enhanced TPA effect on an anisotropic two-photon absorber using radially polarized beams (RPBs) and exploit for the intriguing applications in the Z-scan technique and optical limiter. Numerical results reveal that both the sensitivity of the Z-scan technique and the optical limiting effect on an anisotropic two-photon absorber using RPBs have great enhancement compared with those on an isotropic two-photon absorber and using linearly polarized Gaussian beams. The presented work opens up new avenues for the enhancement of polarization-dependent nonlinear optical effects, which have potential applications in two-photon lithography, polarization-sensitive photodetectors, and multi-photon photoluminescence imaging.

A complete analytical model of tunable Alexandrite lasing under diode end-pumping with experimental comparison

William Kerridge-Johns and Michael Damzen

Doc ID: 273999 Received 18 Aug 2016; Accepted 20 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: A complete analytical model is formulated to support understanding and underpin experimental development of laser action in the promising diode end-pumped Alexandrite system. Closed form solutions are found for output power, threshold and slope efficiency that for the first time incorporate the combined effects of laser ground state absorption (GSA) and excited state absorption (laser ESA), along with pump excited state absorption (pump ESA), in the case of an end-pumping geometry. Comparison is made between model predictions and experimental results from a fibre-delivered diode end-pumped Alexandrite laser system, showing the impact of wavelength tuning, crystal temperature, laser output coupling, and intracavity loss. The model is broadly applicable to other quasi-three-level lasers with combined laser and pump ESA. A condition for bistable operation is also formulated.

Control of ultrafast plasmon pulses by spatiotemporally phase-shaped laser pulses

Fumihiko Kannari, Yuta Masaki, and Yasuhiro Kojima

Doc ID: 267001 Received 25 May 2016; Accepted 20 Oct 2016; Posted 21 Oct 2016  View: PDF

Abstract: We propose a novel method to spatiotemporally control ultrafast plasmon pulses generated at metal nanostructures using spatially and temporally phase-shaped ultrafast laser pulses. Excitation laser pulses designed by the superposition of high-order Hermite-Gaussian modes can localize the plasmon excitation at desired areas in nanostructures, and at the same time the temporal plasmon evolution is determined by the excitation pulse shape and the local plasmon response function. We numerically demonstrate this control scheme for local plasmons at the Au nanostructures and a surface plasmon polariton waveguide.

Ultra-narrowband perfect terahertz absorber based on a metal and insulator stacked structure

Hu Quan Li and Jing Nie

Doc ID: 269805 Received 08 Jul 2016; Accepted 19 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: Electromagnetic field absorber with ultra-narrow relative bandwidth (<1%) and extremely high peak absorbance (>90%) is a challenge nowadays in terahertz frequency. In this paper, we proposed an insulator-metal-insulator-metal stacked structure with nearly unity peak absorbance (~99%) and 0.77% relative bandwidth as an ultra-narrowband perfect terahertz absorber. Even though the composite structure contains high reflective metal layers, however, thanks to the introduction of top insulator, the terahertz field can tunnel through the upper gold film at some functional tunneling bands. As a result, the energy at the Fabry-Pérot (FP) resonance of the metal-insulator-metal substructure is strongly absorbed due to an enhancement effect. The perfect absorption (>99%) and ultra-narrowband width properties make the design promising in terahertz devices such as absorber, filter, narrowband THz emitter, etc.

Plasmonic Photoconductive Antennas with Rectangular and Stepped Rods: A Theoretical Analysis

Gholamreza Dadashzadeh and Mohammadreza Khorshidi

Doc ID: 273073 Received 03 Aug 2016; Accepted 18 Oct 2016; Posted 21 Oct 2016  View: PDF

Abstract: Photoconductive antennas (PCAs) have extensive industrial applications as terahertz (THz) emitters. It is an established belief that the existence of periodic metallic structures at the edges of the antenna electrodes, as is the case in plasmonic PCAs, can remarkably improve the antenna performance. In this paper, we start with introducing a theoretical model for the analysis of plasmonic PCAs, with considering the effect of screening electric field as well. The results of the model, applied to a plasmonic PCA with periodic rectangular rods, agree well with the experimental measurements. Finally, guided by the theoretical model, a plasmonic PCA with buried stepped rods is proposed for improved performance in THz radiation power and in generated current. The enhancements turn out to be the consequence of two welcoming phenomena: First, according to the theoretical model (as well as independent finite element simulations), for the PCA with buried stepped rods, the power transmitted into the low-temperature-grown GaAs (LT-GaAs) substrate is 70% in the THz wavelength range and complete at optical wavelength of 0.8 μm, 40% enhancement in the optical power transmission as compared to the rectangular rods. Second, in comparison with the rectangular rods, a larger portion of the carriers are generated in the vicinity of the rods corners, which favorably contributes well to the current generation but does not contribute much to the unwanted screening electric field.

Engineered aperiodically-poled nonlinear crystal for High-power second-harmonic generation

Saeed Ghavami Sabouri and Alireza Khorsandi

Doc ID: 269676 Received 30 Jun 2016; Accepted 17 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: We demonstrate the use of an engineered aperiodic periodically-poled (APP) crystal grating to generate a high-efficiency second-harmonic radiation of about 66% at 50 W of fundamental power at room-temperature. By embedding several phase compensators (PCs) along the propagation direction, it is shown that such structure is capable of compensating thermal de-phasing and Gouy phase shift without the need to controllable oven for the crystal. Compared to a temperature-optimized conventional PP crystal, an APP device can generate the SHG light by a factor of about two times. Moreover, a multi-path structure of an APP is theoretically investigated to decrease the sensitivity of the device to the pumping power variation. Eventually, the acceptance bandwidth of an APP scheme is found to be enhanced by 3.3 C and 0.5 C compared with the temperature-optimized PP crystal.

Quasi-analytical solutions of hybrid platform and the optimization of highly sensitive thin-film sensors for terahertz radiation

Piyawath Tapsanit, Masatsugu Yamashita, Chiko Otani, and Teruya Ishihara

Doc ID: 270876 Received 19 Jul 2016; Accepted 17 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: We present quasi-analytical solutions (QANS) of hybrid platform (HP) comprising metallic grating (MG) and stacked-dielectric layers for terahertz (THz) radiation. The QANS are validated by finite difference time domain simulation. It is found that the Wood’s anomalies induce the high-order spoof surface plasmon resonances in the HP. The QANS are applied to optimize new perfect absorber for THz sensing of large-area thin film with ultrahigh figure of merit reaching fifth order of magnitude for the film thickness 0.0001p (p:MG period). The first-order Wood's anomaly of the insulator layer and the Fabry-Perot in the slit's cavity account for the resonance of the perfect absorber. The QANS and the new perfect absorber may lead to highly sensitive and practical nano-film refractive index sensor for THz radiation.

Generation of unipolar pulses in a circular Raman-active medium excited by few-cycle optical pulses

Anton Pakhomov, Rostislav Arkhipov, Ihar Babushkin, Yurii Tolmachev, Nikolay Rosanov, and Mikhail Arkhipov

Doc ID: 270391 Received 12 Jul 2016; Accepted 17 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: We study theoretically a new possibility of unipolar pulses generation in Raman-active medium excited by a series of few-cycle optical pulses. We consider the case when the Raman-active particles are uniformlydistributed along the circle, and demonstrate a possibility to obtain a unipolar rectangular video pulses with an arbitrarily long duration, ranging from a minimum value equal to the natural period of the low frequency vibrations in the Raman-active medium.

Optical Bound States in Slotted High-Contrast Gratings

Meng Lu, Yifei Wang, Jiming Song, and Liang Dong

Doc ID: 274386 Received 25 Aug 2016; Accepted 17 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: This paper investigates the optical bound states in the continuum (BIC) supported by a slotted high-contrast grating (sHCG) structure. The sHCG structure consists of a periodic array of silicon ridges with a slot in each ridge. Given that the BICs are perfectly confined, their spectral locations are identified using a finite-element method formulated from a generalized eigenvalue problem. The real eigenvalues represent the wavelengths of BIC modes and the associated eigenvectors correspond to the electric field distributions. In the spectral and angular vicinity of the BICs, the leaky waveguide modes are studied using the rigorous coupled-wave analysis. The combination of the full-wave eigenvalue solver and the coupled-wave analysis provides an ideal setting for investigating the optical BICs of periodic structures for various applications. For example, the simulation results show that the sHCG structures can support symmetry-protected bound states with zero in-plane wave vector as well as high-quality-factor (high-Q) resonances for both TE and TM polarizations. By adjusting the slot, the BIC mode can be turned into high-Q modes and the linewidth of the mode is determined by the degree of asymmetry.

Theoretical study on the characteristics of intracavity frequency doubling of diode-pumped cesium vapor laser

Fei Chen, dongdong xu, Qi Pan, Yang He, deyang Yu, and Kuo Zhang

Doc ID: 270595 Received 14 Jul 2016; Accepted 15 Oct 2016; Posted 20 Oct 2016  View: PDF

Abstract: Rate equations for intracavity frequency doubling of diode-pump cesium vapor laser (Cs-DPAL) are established and the characteristics are studied theoretically. The optimal length of nonlinear crystal with relatively small effective nonlinear coefficient is very large, because the stimulated emission section of Cs-DPAL is very large which leads to a smaller effective saturated power intensity. For intracavity frequency doubling of Cs-DPAL in quasi two-level limit, the optimal length of nonlinear crystal is slightly shorter than the Cs-DPAL with assumption of very rapid transition between the 62P3/2 to 62P1/2 level and a qualitative interpretation is given. The second harmonics (SH) power by intracavity frequency doubling of Cs-DPAL is also limited by the relatively slower collisional transfer rate between the 62P3/2 to 62P1/2 level for higher pump power intensity.

Temporal smooth effects in parametric amplification process

Wenkai Li, Yun Chen, Yanyan Li, Yi Xu, Xiaoyang Guo, Jun Lu, XinLiang Wang, Shuai Li, Yuxin Leng, and Fenxiang Wu

Doc ID: 268326 Received 13 Jun 2016; Accepted 14 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: We theoretically investigate the smooth effects on the signal temporal phase and intensity in the optical parametric amplification (OPA) process. The theoretical model was set up based on the coupled second-order three-wave nonlinear propagation equations in the plane-wave limit, using the phase and intensity modulation to mimic the input noises of signal. The analytical and numerical results indicate that the walk-off between signal and idler plays a dominant role in the temporal smooth process of OPA, and the smooth process by walk-off and broad bandwidth parametric amplification can be achieved simultaneously. Compare to walk-off smooth mechanism, the gain saturation just can smooth the temporal intensity fluctuation. Meanwhile, equations to estimate the maximum smoothable modulation cycle are provided.

Three-state interactions determine the second-order nonlinear optical response

Javier Perez-Moreno

Doc ID: 272568 Received 27 Jul 2016; Accepted 11 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: Using the sum-rules, the sum-over-states expression for the diagonal term of first hyperpolarizability can be expressed as the sum of three-state interaction terms. We study the behavior of a generic three-state term to show that is possible to tune the contribution of resonant terms by tuning the spectrum of the molecule. When extrapolated to the off-resonance regime, the three-state interaction terms are shown to behave in a similar manner as the three-level model used to derive the fundamental limits. We finally show that most results derived using the three-level ansatz are general, and apply to molecules where more than three levels contribute to the second-order nonlinear response or/and far from optimization.

Generation of Continuous-variable Spatial Cluster Entangled States in Optical Mode Comb

Rongguo Yang, JingJing Wang, Jing Zhang, Kui Liu, and Jiangrui Gao

Doc ID: 273143 Received 04 Aug 2016; Accepted 10 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: Cluster entangled states are often used as the fundamental resources for one-way quantum computation. In this paper, we put forward a scheme of generating the spatial cluster entangled states of Laguerre-Gaussian modes in a large-Fresnel-number degenerate optical parametric oscillator operating below threshold with type I phase matching, which is pumped by two spatial Laguerre-Gaussian modes with same frequency. The nonlinear parametric process of each pump modes satisfies the conservation of momentum, energy and orbit angular momentum. Eleven-partite spatial cluster entangled states of Laguerre-Gaussian modes can be produced in optical mode comb under feasible experimental condition, which can be demonstrated by using the entanglement criterion proposed by van Loock and Furusawa.

A path to Ultralarge Nonlinear-Optical Susceptibilities

Mark Kuzyk

Doc ID: 274111 Received 19 Aug 2016; Accepted 07 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: The search for new materials with ever-larger nonlinear-optical susceptibility is fueled by the promise of new applications. While much progress has been made, no new paradigms have been discovered that lead to significantly larger nonlinear susceptibilities when size has been taken into account. The next breakthrough requires a step back to consider the fundamental requirements for increasing the strength of light-matter interactions. In essence, the problem at hand is to understand how to get the most out of a system of fixed size that contains a given number of electrons. The intrinsic nonlinearity takes into account size so that the origin of what makes a large nonlinear response can be identified. Only then can a recipe be articulated for making the system larger in a way that scales optimally so that ultralarge nonlinear susceptibilities can become a reality.

Hybrid quantum systems for enhanced nonlinear optical susceptibilities

Sean Mossman, Dennis Sullivan, and Mark Kuzyk

Doc ID: 272191 Received 27 Jul 2016; Accepted 07 Oct 2016; Posted 11 Oct 2016  View: PDF

Abstract: Significant effort has been expended in the search for materials with ultra-fast nonlinear-optical susceptibilities, but most fall far below the fundamental limits. This work applies a theoretical materials development program that has identified a promising new hybrid made of a nanorod and a molecule. This system uses the electrostatic dipole moment of the molecule to break the symmetry of the metallic nanostructure that shifts the energy spectrum to make it optimal for a nonlinear-optical response near the fundamental limit. The structural parameters are varied to determine the ideal configuration, providing guidelines for making the best structures.

Diameter Dependent Shielding Effectiveness and Terahertz Conductivity of Multi-walled Carbon Nanotubes

Rajib Mitra, Debanjan Polley, Anjan Barman, and Kumar Neeraj

Doc ID: 278139 Received 04 Oct 2016; Accepted 07 Oct 2016; Posted 14 Oct 2016  View: PDF

Abstract: In the present contribution we have experimentally demonstrated the diameter dependence of terahertz (THz) shielding and THz conductivity of multi-walled carbon nanotubes (MWNT) and performed detailed theoretical analysis to extract the mechanism of shielding at different MWNT diameter. Self-standing films of three different types of MWNT having the same average length but different outer tube diameter (namely MWNT_7nm, MWNT_25nm and MWNT_40nm) are prepared by vacuum filtration technique. Shielding effectiveness (SE) of these films in the frequency range of 0.4-2.2 THz are measured at room temperature and the results are analyzed using a theoretical model. Shielding due to absorption (SEA) turns out to be the dominant shielding mechanism for the MWNT_7nm and MWNT_25nm films, while the contribution of shielding due to reflection (SER) dominates for the MWNT_40nm films in the smaller frequency region (< 0.8 THz). Considering the films as a composite of MWNT and air gaps, we have modelled the dielectric properties of the films using a combination of Maxwell-Garnett (MG) effective medium theory (EMT) and Drude-Lorentz (DL) model. THz conductivity is found to be increasing with increasing MWNT diameter due to the increasing number of Drude like free electrons. No systematic dependence of the THz conductivity peak (TCP) frequency has been observed on the diameter of the tubes which negates the idea of curvature induced band gap as the sole origin of the much debated TCP in carbon nanotubes. Our results reveal intriguing aspects on THz response of MWNT films as a function of MWNT diameter.

Thermally managed Z-scan methods investigation of the size-dependent nonlinearity of Graphene Oxide in various solvents

Anthony Johnson, Paul Burkins, Robinson Kuis, ISAAC BASALDUA, Siva Swaminathan, Dajie Zhang, and Sudhir Trivedi

Doc ID: 274009 Received 17 Aug 2016; Accepted 06 Oct 2016; Posted 06 Oct 2016  View: PDF

Abstract: Thermally managed Z-scan using a modified chopper was compared to the utilization of a pulsepicker with the common calibration material Carbon Disulfide and then extended to Graphene Oxide (GO) in different solvents. GO in distilled water using femtosecond laser excitation yielded a value of (-2.7 ± .4) x 10-15 cm2/W for nanometer particles and (-1.6 ± .6) x 10-15 cm2/W for micrometer-sized particles. Open aperture Z-scan results using the modified chopper show a change from saturable absorption to reverse saturable absorption due to thermal contributions.

Modulation instability induced by higher-order nonlinear dispersions in nonlinear positive-negative index couplers with exponential saturable nonlinearity

Mohamadou Alidou, Aboukar NO LAST NAME GIVEN, and Alim Dia

Doc ID: 264583 Received 04 May 2016; Accepted 04 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: We study the modulational instability (MI) in positive-negative couplers with higher-order effects and exponential saturable nonlinearity. Special attention is paid tothe influence of self-steepening (SS); intrapulse Raman scattering and second-order nonlinear dispersion (SOND) on the MI gain. The results show that saturable nonlinearity can be used to control the generation of sidebands through the coupler. We show that in normal dispersion regime, the instability gain exists even if theperturbation frequency ($\Omega$) is zero. The instability gain at $\Omega=0$ is nil, when the dispersion is anomalous. We find that the magnitude and sign of SOND exert strong influences on MI sideband. Moreover, by adjusting the various parameters such as SS, intrapulse Raman scattering, and SOND we obtain new instability regions.These results can be helpful to understand the generation of soliton-like exitaction in nonlinear oppositely coupler and can be potentially useful for future experiments.

Enhancing quantum entanglement by combinations of photon additions and photon subtractions

Yang Yang

Doc ID: 265317 Received 16 May 2016; Accepted 04 Oct 2016; Posted 05 Oct 2016  View: PDF

Abstract: We investigate the entanglement enhancement of the two-mode squeezed vacuum state using various combinations of photon additions and photon subtractions. We suppose that a sequence of $N$ operations are performed on each mode of the two-mode squeezed vacuum state, each operation being photon addition or photon subtraction, then there are $2^N$ possible combinations of operations in total. We calculate the entanglement for all the photon-added/subtracted states generated by all possible combinations for $N=2$, $N=3$ and $N=4$ respectively and deduce that the combination of operations alternating between photon addition and photon subtraction enhances the entanglement most effectively, while adding or subtracting $N$ photons repeatedly enhances the entanglement least effectively.

Theory for optical detection of picosecond shearacoustic gratings

O. Matsuda, Mansour Kouyate, Thomas Pezeril, and Vitalyi Goussev

Doc ID: 272608 Received 28 Jul 2016; Accepted 03 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: Theoretical formalism describing the heterodyne detection of planeinhomogeneous shear acoustic waves by probe laser-induced gratings isdeveloped. Inhomogeneous plane shear acoustic wave is a purely shearwave with plane phase front and mechanical displacement vector whichis sinusoidally spatially modulated in magnitude. It could begenerated by laser-induced gratings and could be useful for theacoustic testing of sub-micrometer thick membranes and coatings in theGHz frequency range. The theory reveals the potential advantages anddisadvantages of this wave application in non-destructive testing ofmaterials and fundamental research from the point of view of thefeasibility of their experimental detection.

Low loss and high-performance mid-infrared plasmon waveguiding in substrate-mediated graphene-coated nanowires

Yaser Hajati and Morteza Hajati

Doc ID: 274091 Received 18 Aug 2016; Accepted 03 Oct 2016; Posted 04 Oct 2016  View: PDF

Abstract: In this paper, we theoretically show that low loss and high-performance mid-infrared plasmon waveguiding can be achieved by introducing a thin low-index buffer layer between graphene-coated nanowire and silicon substrate. It is found that introduction of the buffer layer can mediate the coupling between the nanowire and substrate and can effectively suppress the leaky radiation to the substrate. According to the results, by choosing ultra-small buffer thickness and gap distance and also by optimizing the nanowire and graphene parameters, a low propagation loss (0.312 dB/µm) and improved figure of merit (FOM) can be realized simultaneously. Our findings are important for the optimum design of substrate-mediated graphene-coated nanowire waveguides.

High-contrast self-imaging with ordered optical elements

Ali Naqavi, Hans Peter Herzig, and Markus Rossi

Doc ID: 264917 Received 16 May 2016; Accepted 02 Oct 2016; Posted 03 Oct 2016  View: PDF

Abstract: Creating arbitrary light patterns finds applications in various domains including lithography, beam shaping, metrology, sensing and imaging. We study the formation of high-contrast light patterns that are obtained by transmission through an ordered optical element based on self-imaging.By applying the phase-space method, we explain phenomena such as the Talbot and the angular Talbot effects. We show that the image contrast is maximum when the source is either a plane wave or a point source, and it has a minimum for a source with finite spatial extent. We compare these regimes and address some of their fundamental differences. Specifically, we prove that increasing the source divergence reduces the contrast for the plane wave illumination but increases it for the point source. Also, we show that to achieve high contrast with a point source, tuning the source size and its distance to the element is crucial.We furthermore indicate and explore the possibility of realizing highly complex light patterns by using a periodic transmission element. These patterns can have more spots in the far field than the number of diffraction orders of the periodic element. We predict that the ultimate image contrast is smaller for a point source compared to a plane wave.Our simulations confirm that the smallest achievable spot size in the image is imposed by diffraction regardless of the imaging regime. Our research can be applied to similar domains e.g. quantum systems.

Design guidelines for nanoparticle chemical sensors based on splitting mode SOI planar micro-cavities

Carlo Edoardo Campanella, Clarissa Martina Campanella, Monika Dunai, and Luigi Calabrese

Doc ID: 273264 Received 09 Aug 2016; Accepted 02 Oct 2016; Posted 03 Oct 2016  View: PDF

Abstract: In this paper we report on the design guidelines for optical systems based on splitting mode micro-cavities. These guidelines are applied to Silicon on Insulator (SOI) technology with the aim of optimizing chemical sensing platforms for revealing the specific presence of nanoparticles. In particular, through the analysis of the splitting mode sensing principle, we point out the characteristics a cavity should respect in order to be used as single nanoparticle sensor, and we identify some standard planar SOI geometries, i.e. ring and disk shaped resonant cavities, as candidates for mode splitting based nanoparticle chemical sensing. Moreover, we also envisage a hybrid SOI planar cavity, obtained by properly combining the physical features of SOI micro-ring and micro-disk, as a perfect candidate for improved performance in mode splitting nanoparticle chemical SOI sensors. With a Limit of Detection (LOD) of 30 nm, the hybrid configuration allows a theoretical resolution comparable to those achieved by ultra-high quality factor resonators in low loss Silica technology.

Alternative Bridging Architecures in Organic Nonlinear Optical Materials: Comparison of π and χ type structures

Bruce Robinson, Meghana Rawal, Kerry Garrett, Lewis Johnson, Werner Kaminsky, Evgheni Jucov, Tatiana Timofeeva, Bruce Eichinger, Andreas Tillack, Delwin Elder, Larry Dalton, and David Shelton

Doc ID: 273715 Received 12 Aug 2016; Accepted 02 Oct 2016; Posted 03 Oct 2016  View: PDF

Abstract: Organic non-linear optical (ONLO) chromophores are used to make electro-optic devices. Traditional ONLO chromophores use a π-conjugated bridge to couple electron acceptor and donor moieties. We have explored whether other types of conjugation can be used to make high performance ONLO chromophores. We have found that cross-conjugated bridge structures, when other parameters are kept the same, can exhibit comparable hyperpolarizabilities. Experimental hyperpolarizabilities of prototypical cross-conjugated chromophores, measured by hyper-Raleigh scattering (HRS), are comparable to their π-conjugated analogues, in contrast with the prediction of several electronic structure calculation methods. This opens new synthetic routes to other types of chromophores which may provide enhanced performance.

First principal study on electro-optical properties of new structure photodetectors based on graphene nanoribbons

Mehran Balarastaghi, Vahid Ahmadi, and ghafar darvish

Doc ID: 274920 Received 30 Aug 2016; Accepted 02 Oct 2016; Posted 03 Oct 2016  View: PDF

Abstract: In this paper, we propose photodetectors based on sandwiched graphene nanoribbons and investigate their optical and electrical characteristics. Here we combine three narrow armchair graphene nanoribbons (AGNRs) in a way that two AGNRs with the same width, sandwich another AGNR with a different width and smaller length. Some of these structures produce sharp peaks in their absorption spectrum that increase selectivity in some frequencies. Some of the peaks shift to mid- infrared and so are useful in various optical communication windows. These structures also increase the absorption coefficient at some wavelengths up to 90-fold. The responsivity peak shows a maximum of about 52 percent increase. We also show that some of these structures can reduce dark current by about three times. Finally, we demonstrate the effect of channel length on dark current in these devices.

Multifunctional all-dielectric nano-optical systems using collective multipole Mie resonances: Towards on-chip integrated nanophotonics

Swarnabha Chattaraj and Anupam Madhukar

Doc ID: 274309 Received 22 Aug 2016; Accepted 01 Oct 2016; Posted 03 Oct 2016  View: PDF

Abstract: We present an analysis of the optical response of a class of on-chip integrated nano-photonic systems comprising all-dielectric building block based multifunctional light manipulating units (LMU) integrated with quantum dot (QD) light sources. The multiple functions (such as focusing excitation light, QD emission rate enhancement, photon guidance, and lossless propagation) are simultaneously realized using the collective Mie resonances of dipole and higher order multipole modes of the dielectric building blocks (DBBs) constituting a single structural unit, the LMU. Using analytical formulation based on Mie theory we demonstrate enhancement of the excitation light simultaneously with the guiding and propagation of the emitted light from a QD emitter integrated with the DBB based LMU. The QD-DBB integrated structures can serve as the basic element for building nano-optical active circuits for optical information processing in both classical and quantum realms.

Modulation Instabilities in Equilateral Three-Core Optical Fibers

Kin Chiang, Jin Hua Li, Huan Zhou, and Shao Rong Xiao

Doc ID: 269355 Received 28 Jun 2016; Accepted 30 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: Modulation instabilities (MIs) of the continuous-wave (CW) states in equilateral three-core fibers are analyzed in detail. For the symmetric CW state, conventional MI characteristics similar to those of two-core fibers are obtained. For the antisymmetric CW state, however, new MI characteristics are found. In the normal dispersion regime, there are in general two MI bands, one of which is generated above a critical total power and quickly becomes the dominant band as the total power increases. This critical power increases with the coupling coefficient almost linearly and decreases rapidly to almost zero as the coupling-coefficient dispersion (CCD) of the fiber increases. In the anomalous dispersion regime, there are two main MI bands. The lower-frequency band, which is similar to the MI band of a single-core fiber, is independent of the coupling coefficient and the CCD. In contrast, the higher-frequency band depends sensitively on the coupling coefficient and the CCD. The lower-frequency band is always stronger than the higher-frequency band, though their strengths are comparable when the values of the coupling coefficient and the CCD are small. Simulation results based on solving the nonlinear coupled-wave equations agree well with the MI analysis.

Dispersion-optimized multi-cladding silicon nitride waveguides for nonlinear frequency generation from ultraviolet to mid infrared

Jose Chavez Boggio, Alejandro Ortega-Moñux, Daniele Modotto, Tino Fremberg, Daniel Bodenmüller, Enrique Silvestre, Domenico Giannone, Tobias Hansson, Stefan Wabnitz, Lars Zimmermann, and Martin Roth

Doc ID: 273144 Received 05 Aug 2016; Accepted 30 Sep 2016; Posted 30 Sep 2016  View: PDF

Abstract: Nonlinear frequency conversion spanning from the ultraviolet to the mid-infrared (beyond 2.4 µm) is experimentally demonstrated in multi-cladding silicon nitride (SiXNY) waveguides. By adjusting the waveguide cross-section the chromatic dispersion is flattened, which enhances both the efficiency and the bandwidth of the nonlinear conversion. How accurately the dispersion is tailored is assessed through chromatic dispersion measurements and an experiment/simulation comparison of the dispersive waves wavelength locations. Undesirable fluctuations of both the refractive index and the dimensions of the waveguide during the fabrication process result in a dispersion unpredictability of at least 20 ps/nm/km. Finally, the manipulation of the effective refractive index allows for multiple third harmonic generated (THG) tones spanning from 381 to 715 nm

End-fire coupling efficiencies of surface plasmons for silver, gold, and plasmonic nitride compounds: erratum

Caitlin Fisher, Lindsay Botten, Chris Poulton, Ross McPhedran, and C. Martijn de Sterke

Doc ID: 274510 Received 19 Sep 2016; Accepted 27 Sep 2016; Posted 05 Oct 2016  View: PDF

Abstract: We correct the errors made in the field-overlap derivation in the Appendix of "End-fire coupling efficiencies of surface plasmons for silver, gold, and plasmonic nitride compounds" [J. Opt. Soc. Am. B 33(6), 1044–1054 (2016)].

Understanding search behavior via search landscape analysis in design optimization of optical structures

Sacha Verweij and Shanhui Fan

Doc ID: 264384 Received 02 May 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Search algorithms play a crucial role in systematic design optimization of optical structures. We demonstrate how search landscape analysis sheds light on the behavior of search algorithms in this context and thereby leads to valuable insight. Specifically, we present a case study in which search landscape analysis demystifies the surprisingly-good performance of a simple stochastic local search algorithm --- restarted iterative best improvement --- on a challenging design optimization problem --- combinatorial design optimization of a multi-spatial-mode photonic crystal waveguide bend that preserves modal content. Moreover, the search landscape analysis leads to insight potentially valuable in design optimization of a broad class of optical structures.

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