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Accepted papers to appear in an upcoming issue

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An electro-optic controllable TE/TM polarization convertor based on the GaN/Al₀.₃Ga₀.₇N superlattice waveguide

Tao Wang and Guangming He

Doc ID: 331000 Received 07 May 2018; Accepted 20 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: An electro-optic controllable TE/TM polarization convertor based on the GaN/Al₀.₃Ga₀.₇N superlattice waveguide is proposed for actively controlling the output polarization state. We use the highly accurate and efficient full vector mode matching method to evaluate its performance. The result indicates that the output polarization state can be actively controlled in a full 0º~90º range by applying the adjustable voltage on this polarization convertor, and that a full TE↔TM conversion can also be realized by applying no voltage, with a conversion efficiency of 99.9% and an insertion loss of 0.03 dB. We further investigate the deviation effect of the etching width or the operating wavelength on TE↔TM conversion. In order to counteract deterioration on conversion efficiency brought in by the deviation, a simple compensation method is presented by actively adjusting the voltage to certain value.

Temporal dynamics of light-written waveguides in unbiased liquid crystals

Alessandro Alberucci, Jisha Pannian, Stefan Nolte, and Raouf Barboza

Doc ID: 330644 Received 30 Apr 2018; Accepted 19 Jun 2018; Posted 20 Jun 2018  View: PDF

Abstract: The control of light by light is one of the main aims in modern photonics. In this context, a fundamental cornerstone is the realization of light-written waveguides in real time,resulting in all-optical reconfigurability of communication networks. Light-written waveguides are often associated with spatial solitons, that is, non-diffracting waves due to anonlinear self-focusing effect in the harmonic regime.From an applicative point of view, it is important to establish the temporal dynamics for the formation of such light-written guides. Here we investigate theoretically the temporal dynamics in nematic liquid crystals (NLCs), a material where spatial solitons can be induced using CW lasers with few milliWatts power.We fully address the role of the spatial walk-off and the longitudinal nonlocality in the waveguide formation. We show that, for powers large enough to induce light self-steering, the beam undergoes several fluctuations before reaching the stationary regime, in turn leading to a much longer formation time for the light-written waveguide.

Robust Increase of the Optical Forces in Waveguide Based Optical Tweezers Using V Groove Structure

Amir Habibzadeh-Sharif and Mahdi Sahafi

Doc ID: 326355 Received 26 Mar 2018; Accepted 19 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: Waveguide-based optical tweezers have significant advantages for particle trapping and transporting in optofluidic chips due to their simple fabrication process. However, for effective trapping of nanoparticles, a high power input field should be applied, which limits their applications. Here, we numerically show that a silicon on insulator (SOI) based V groove waveguide has a much higher capability to trap nanoparticles compared with the traditional waveguides. According to the calculations, the trapping force exerted by the V-groove waveguide to a 5 nm radius nanoparticle can be 14 times greater than that of the strip waveguide. The scattering force is 5 times larger in the same conditions. This structure would be very useful to be integrated into a lab on a chip system to form a particle delivery and analysis device.

Optical corral using a standing-wave Bessel beam

Keith Bonin and Chad McKell

Doc ID: 328104 Received 12 Apr 2018; Accepted 19 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: Here we create a series of optical corrals and calculate their potential energy profile. A standing wave Bessel beam is used to form traps in 1D (along the optical axis), and corrals in 2D, in planes perpendicular to the optical axis at the antinode regions of the standing waves. These optical corrals are formed by an axicon-generated Bessel beam that is retro-reflected back onto itself. We report on Mie calculations of the 2D optical corral and then compare the resulting probability distributions to those observed for latex particles of diameters 100, 200, and 300 nm. The experimental radial probability density function of tracked particles closely mimics the theoretical optical structure of a Bessel standing-wave corral. The Bessel standing-wave corrals we have characterized are being developed to measure rotational diffusion and torques on micro- and nanorods to help understand microfluidic behavior. The maximum forces on our small beads in the diffraction-free central zone of the Bessel beam standing wave are F_|| = 0.5 pN and F_perp = 0.1 pN.

A Lie algebraic approach to a nonstationary atom-cavity system

Jose Recamier, carlos gonzalez gutierrez, Octavio Sánchez, Ricardo Roman, and Manuel Berrondo

Doc ID: 328955 Received 20 Apr 2018; Accepted 19 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: In this work we study the generation of photons inside an ideal cavity with resonantly oscillating boundaries in the presence of a two-level atom. We make use of Lie algebraic techniques to obtain an approximate time-evolution operator and evaluate not only the resonant and dispersive regimes but also explore different regions of parameters. We have found a very good agreement between our approximate results and those obtained by numerical means.

Ultrathin omnidirectional, broadband visible absorbers

Shangliang Wu, Yan Ye, Minghui Luo, and Linsen Chen

Doc ID: 328028 Received 10 Apr 2018; Accepted 18 Jun 2018; Posted 20 Jun 2018  View: PDF

Abstract: A broadband and omnidirectional absorber based on asymmetric multi-cavity resonance is presented in the visible range. This device is realized by adapting a lossless silicon nitride layer on top, a sandwiched amorphous silicon layer and a sliver mirror at bottom. Its average optical absorption is 0.95 (0.90, experiment) for wavelengths from 400 nm to 700 nm and still over 0.84 (0.80, experiment) with the incident angle increase to 60°. Besides, only deposition method is involved in its fabrication, providing a promise avenue for large scale applications. Finally, photophysical properties of this absorber at the actual solar cell device level are investigated, where high short-circuit current density and photo-conversion efficiency is obtained even the amorphous silicon layer thinning to 22 nm. Therefore, the demonstrated absorber has great potential for applications as solar cell and thermal emitters.

Extended coupled Lorentz oscillator model and analogue of electromagnetically-induced transparency in coupled plasmonic structures

Jing Zhang, Y. G. Xu, Jie Zhang, Pingping Ma, MengQiao Zhang, and Yongfang Li

Doc ID: 323233 Received 13 Feb 2018; Accepted 17 Jun 2018; Posted 20 Jun 2018  View: PDF

Abstract: We report a new extended coupled Lorentz oscillator (ECLO) model by adding a coupled phase factor for the first time, in contrast to the conventional coupled Lorentz oscillator (CLO) model for describing the analogue of electromagnetically-induced transparency (EIT) in a dimer, which is composed by two identically broken eccentric silver nanorings (ESNRs) arranged in an asymmetric manner. Based on the finite element method (FEM), the distribution features of the absorption spectra, the charges, and the electric field of the ESNRs are numerically simulated under the action of applied light field. Importantly, The ECLO model reveals the physical mechanism of the spectra feature and the EIT-like. Our findings indicate that the destructive interference effect plays a key role in the generation of the EIT-like. The theoretical analyses are in good agreement with the numerical results.

Numerical Investigations on Polymer-Based Bent Couplers: Refractive Index Modulation, Offset Tolerance, Curvature, and Curing Time

Monali Suar, Maik Rahlves, Bernhard Roth, and Eduard Reithmeier

Doc ID: 326623 Received 21 Mar 2018; Accepted 15 Jun 2018; Posted 20 Jun 2018  View: PDF

Abstract: A diffusion-based material model is implemented and linked to the Crank Nicholson beam propagation method to carry out numerical investigations on self-written bent waveguide couplers on polymer basis. Such couplers are established in a photopolymer mixture when two opposing Gaussian laser beams with offset or gap along their propagation axes are traversed through the medium and the beams, eventually, get self-trapped. In this work, numerical investigations of the processes involved with respect to temporal dynamics of refractive index modulation and the corresponding intensity profiles are presented. We also show that compensation of misalignments or gaps is possible as the coupling length of the structure increases. Furthermore, we report and analyze the curing time and curvature of the bent couplers which are regulated by control of model parameters such as propagation distance between opposing beams, component concentrations, and the value of the rate constant during the simulation process.

Silicon-wire delayed interferometric WDM filters operating in broadband spectral range

Seok-Hwan Jeong and Yu Tanaka

Doc ID: 330249 Received 24 Apr 2018; Accepted 15 Jun 2018; Posted 20 Jun 2018  View: PDF

Abstract: We present a novel broadband operating multistage delayed interferometric optical demultiplexer (DI-DeMUX). The devices were proposed, theoretically analyzed through transfer matrix method based on coupled mode theory, and fabricated by 300-mm wafer-scale ArF-immersion lithography process technology. By employing the Mach-Zehnder interferometer based wavelength-insensitive couplers and optimizing the phase relation between cascade-connected multistage DIs, it was experimentally demonstrated that the operating spectral range of the proposed DI-DeMUX was extended to be >120-nm for various kinds of channel spacing and channel count.

Enhancing the Spectral Reflectance of Refractory Metals by Multilayer Optical Thin-Film Coatings

Muhammed Kecebas and Ibrahim Sendur

Doc ID: 326050 Received 16 Mar 2018; Accepted 14 Jun 2018; Posted 14 Jun 2018  View: PDF

Abstract: Good thermomechanical properties of refractory metals, including Tungsten, Tantalum, Molybdenum and Niobium, makes them attractive candidates for operation in extreme environments. In addition, their ability to reflect thermal radiation in the infrared region beyond 1.5 µm makes them attractive for use as reflective surfaces in extreme environments. These refractory metals, however, have relatively poor reflectivity in the visible and near-infrared spectral regions making them absorb incident thermal radiation. Average absorption percentages of these metals at the 300-1500 nm spectrum is in the range of 40-50%. In this manuscript, we propose and demonstrate that by periodic thin-film dielectric coatings deposited over refractory metals, the absorption of thermal radiation can be drastically reduced. Various thin-film optical filter designs are investigated to engineer and improve the spectral reflectivity of refractory metals in the visible and near-infrared spectral regions without deteriorating the performance beyond 1.5 µm. TiO2, Al2O3 and SiO2 are used as materials, which are dielectrics that do not absorbed incident radiation in visible and near-infrared, with high melting points and Young’s modules. Our results indicate that combination of several periodic segments, designed at different wavelengths around which high reflectivity is desired, can be utilized to generate high reflectivity in broadband spectrum. Bandwidth and magnitude of the reflectivity over the spectrum are highly dependent on materials, number of segments, and number of layers in the segments of the filters.

State-preparation-and-measurement tomography of a two-qubit system

Mark Beck, Meghan Feldman, Gabriel Juul, and Steven Van Enk

Doc ID: 327236 Received 02 Apr 2018; Accepted 14 Jun 2018; Posted 14 Jun 2018  View: PDF

Abstract: We experimentally demonstrate that loop state-preparation-and-measurement (SPAM) tomography is capable of detecting correlated errors in a two-qubit system. We prepare photon pairs in a state that approximates a Werner state, which may or may not be entangled. By performing measurements with multiple different detector settings we are able to detect correlated errors between two single-qubit measurements performed in different locations. No assumptions are made concerning either the state preparations or the measurements, other than that the dimensions of the states and the positive-operator-valued measures describing the detectors are known. This demonstrates that loop SPAM tomography is a useful technique for detecting errors that would degrade the performance of multiple-qubit quantum information processors.

Nuclear-spin polarization of atoms by chirped laser pulses: application to the muonium

Rakesh Mohan Das, Katsuhiko Ishida, Masahiko Iwasaki, and Takashi Nakajima

Doc ID: 320667 Received 31 Jan 2018; Accepted 14 Jun 2018; Posted 14 Jun 2018  View: PDF

Abstract: We theoretically show that the use of chirped laser pulses with an appropriatebandwidth is more favorable to achieve a higher degree of nuclear-spin polarization of atoms/ions. The physical origin of this is identified as multiple pump-dumpprocesses during the single chirped laser pulse. As a specific example, we consider the case of muonium ($\mu^+e^-$, lifetime 2.2 $\mu$s). By numerically solving a set of density matrix equations, we find that a chirped 1 ns pulsewith a narrow bandwidth instead of a broad bandwidth efficiently induces a resonant pump and following dump processes within a single laser pulse, thereby transferring the angular momentum of the circularly-polarized pump pulse to the atoms, which leads to the higher degree of nuclear-spin polarization. For muoniums at rest, a single chirped 1 ns pulse with a 4 GHz bandwidth and peak intensity of $2\times10^{6}$ W/cm$^2$ leads to $43\%$ of nuclear-spin polarization, which is to be compared with $33\%$ of nuclear-spin polarization by the transform-limited 1 ps pulse or chirped 1 ns pulse with a 400 GHz bandwidth for both. We also find that an introduction of the chirp does not help under the presence of significant Doppler broadening. This means that the use of chirped laser pulses is beneficialfor the atomic beam at the cross-beam geometry where the influence of Doppler broadening is negligible, and similarly, if a slow muonium beam is realized in the future to nearly eliminate Doppler broadening, then chirped laser pulses would be useful to attain the higher degree of nuclear-spin polarization.

Adopting Image Theorem for Rigorous Analysis of PEC-backed Array of Graphene Ribbons

Mahdi Rahmanzadeh, Ali Abdolali, Amin Khavasi, and Hamid Rajabalipanah

Doc ID: 324910 Received 26 Feb 2018; Accepted 13 Jun 2018; Posted 14 Jun 2018  View: PDF

Abstract: Analytical and numerical study of graphene ribbons has become a prime focus of recent researches due to their potential applications in tunable absorption, wavefront manipulation, polarization conversion, and so on. In this paper, an accurate analysis of PEC-backed array of graphene ribbons (PAGR) is presented based on the well-known electromagnetic (EM) image theorem, where the induced currents are theoretically derived under a TM-polarized incident wave. For the first time, the proposed analysis rigorously incorporates the EM coupling effects between the PEC back plate and the subwavelength array of graphene ribbons. It is proved that the strong interaction between the PEC back plate and graphene ribbons drastically affects the results, especially in ultra-thin PAGR structures, whereas it was neglected in the previous works. As a proof-of-principle, an ultra-thin graphene-assisted absorber (=0.05λ0) exhibiting tunable absorption at terahertz (THz) regime is theoretically designed to verify the proposed analytical scheme. Unlike the previous studies, this paper reveals a more general, valid and reliable analysis of PEC-backed graphene ribbons and can be simply extended to 2D geometries of PEC-backed graphene metasurfaces.

Design and Optimization of a Slotted-PhC Waveguide based TE-pass Polarization Filter

chandra prakash, Mrinal Sen, Haraprasad Mondal, and Kamanashis Goswami

Doc ID: 327122 Received 28 Mar 2018; Accepted 13 Jun 2018; Posted 13 Jun 2018  View: PDF

Abstract: A TE-pass polarization filter based on a slotted photonic crystal waveguide structure is proposed for application in photonic integrated circuits. The silicon slab based structure is fabrication-compatible with the standard silicon-on-insulator process technologies. Different structural parameters; such as - r/a ratio of the photonic crystal sections, slab-height, slot-width, slot-length etc.; are optimized for improved performance. Moreover, the conversion efficiency of a mode of W1-waveguide to that of slot-waveguideis analyzed for different starting positions of the slot in order to achieve a high extinction ratio of TE wave over the TM wave. A 3D Finite Difference Time Domain (FDTD) simulation methodology, which has been verified against an earlier experimental study made by some researchers on another structure, is adopted to evaluate the transmittance of the structure. It shows that the polarization filter, with a footprint of merely 6.28 × 4.35 μm², offers an extinction ratio in the order of 22 dB this corresponds to an effective extinction ratio of 3.5 dBμm-¹ considering the total length (or 6.5 dBμm-¹ considering only the slot length). TE-transmittance of the device is calculated as ~ -3 dB at the wavelength 1550 nm.

Comparison of spatiotemporal contrasts of pulsed-beams in un-, 1D- and 2D-focusing fields and enhancement of the on-axis temporal contrast at the focus

Zhaoyang Li, Noriaki Miyanaga, and Junji Kawanaka

Doc ID: 330168 Received 23 Apr 2018; Accepted 13 Jun 2018; Posted 14 Jun 2018  View: PDF

Abstract: With the rapid development of ultra-intense femtosecond lasers, the measurement and then the improvement of the temporal contrast (ratio of signal to noise) become more and more important, which have already aroused wide concern. Recently, due to the technical limit, the temporal contrast usually is measured in the un-focusing or 1D-focusing field, however such lasers are utilized in the 2D-focusing field for relativistic or even higher intensities. Herein, we theoretically compared the spatiotemporal contrasts of pulsed-beams in the un-focusing, 1D-focusing and 2D-focusing fields while common temporal and spatiotemporal distortions are being considered. The result shows the near-field spatiotemporal distortion of a pulsed-beam would degrade its spatiotemporal contrast at the focus, however which cannot be detected in the un-focusing field. Meanwhile, different from the traditional view, the on-axis temporal contrast at the focus can be enhanced by introducing a suitable slowly-varying spatiotemporal coupling in the near-field, e.g., a suitable low spatial frequency deformation at the second or the third grating in the grating compressor.

Tunable and enhanced spin Hall effect of light in layered nanostructures containing graphene

Min Cheng, Ping Fu, Xiaoteng Tang, Shengyu Chen, Xiyao Chen, Yingting Lin, and Shangyuan Feng

Doc ID: 328897 Received 20 Apr 2018; Accepted 12 Jun 2018; Posted 14 Jun 2018  View: PDF

Abstract: We investigate theoretically the photonic spin Hall effect (SHE) in layered nanostructure containing graphene. When the propagating wave exists in the nanostructure containing graphene, it is found that near the transmission resonance of the nanostructure, the giant photonic SHE of the reflected beam is present. When the evanescent wave exists in the nanostructure containing graphene, we show that the photonic SHE of the reflected and transmitted beam can both be enhanced near tunneling resonance. Through manipulating the voltage applied to graphene via an exterior gate, the corresponding large transverse displacement of light beam from photonic SHE near resonance can be easily regulated. By combing with the weak measurement method, it is expected that these phenomena may lead to some potential application for developing new nanophotonic devices

Divergence angle rotation in rotary coherent media

Rafi Din, Qing He, Bakhat Amin Bacha, Iftikhar Ahmad, and Guo Ge

Doc ID: 330123 Received 23 Apr 2018; Accepted 12 Jun 2018; Posted 14 Jun 2018  View: PDF

Abstract: We investigate the behavior of a linearly polarized pulseinteracting to a multilevel rotary chiral medium. Due to the strong chirality induced by electromagnetic fields together with Fizeau effect, the two spatially split (left- and right-circularly polarized) components of the incident pulse show typical dual rotation. We find that the angle between the two components, the divergence angle, rotates in the spinning direction of the rotary medium. In addition, the chirality and rotation of the medium is controlled by external sources so we can manipulate the exact position of the divergence angle. A possible experimental realization of the model is also discussed. The scheme can be useful for metamaterial applications, accurate position control of the transmitted images and an efficient modulation of the probe pulse.

A novel mid-infrared nonlinear silicon hybrid waveguide with high figure of merit

Shiming Gao, Zhihua Tu, Qiang Jin, and Xibin Li

Doc ID: 327443 Received 02 Apr 2018; Accepted 09 Jun 2018; Posted 12 Jun 2018  View: PDF

Abstract: Mid-infrared (MIR) integrated waveguides with strong local field enhancement and relatively low loss have shown their potential in nonlinear optical applications. We present a novel highly nonlinear silicon hybrid waveguide by setting an insulator-metal-insulator structure with DDMEBT and silver materials into the silicon slot. The mode field is strongly confined in the DDMEBT layers via surface plasmon polariton effect. Two rectangular silicon nanobridges are used to further confine the optical field and reduce the loss simultaneously. The waveguide dimensions are optimized to get a figure of merit (FOM) as high as 2.2 W-1m-2 at 2.1 μm and a zero-dispersion wavelength of 2.06 μm. In a 6.6-mm-long waveguide, the maximum four-wave mixing (FWM) efficiency of -15.4 dB and the bandwidth of 536 nm (1.876-2.412 μm) can be simultaneously obtained pumped by a 2.1-μm source with a power of only 150 mW. Our designed waveguide exhibits excellent overall performance for nonlinear optical applications such as all-optical signal processing in MIR band.

Role of optical losses in metal-organic framework thin film based gas sensors

Madhuri Kumari, Boyang Ding, Marina Roxburgh, Lyall Hanton, and Richard Blaikie

Doc ID: 328010 Received 10 Apr 2018; Accepted 09 Jun 2018; Posted 12 Jun 2018  View: PDF

Abstract: The optical responses of thin film sensors based on metal-organic framework (MOF) materials can be further enhanced by incorporating them into optical resonators. This work presents the first experimental demonstration of humidity sensing using optically lossy MOF integrated thin-film cavities that have sub-wavelength dimensions. Both experimental and simulated results reveal that the interaction between optical loss (the absorption part of the refractive index) in the MOF and the resonance in the cavity plays a crucial role in the sensing behaviour.

Spectroscopic studies of dye-doped porous alumina membranes

Cansu On, Ekembu Tanyi, Mikhail Pashchanka, Jonathan Skuza, Vanessa Peters, and Mikhail Noginov

Doc ID: 327825 Received 06 Apr 2018; Accepted 06 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: We have studied spectroscopic properties of nanoporous alumina membranes impregnated with rhodamine 6G (R6G) dye molecules. At small dye concentrations, the reflectance spectra feature one minimum, corresponding to the absorption band of R6G. With increase of the dye concentration, the reflectance dip splits into two and the energy difference between the two minima increases. A similar behavior is shared by the emission spectral band. We explain these observations in terms of strong coupling of closely situated dye molecules inside the channels. At the same time, the experimentally observed angular dependence of the reflectance spectrum is consistent with a long-range collective behavior of dye molecules across an array of dye-impregnated channels.

A novel three-port graphene-based electromagnetic circulator in the THz and infrared frequency range with a very low-loss and wideband response

Vahid Nikkhah, Ahmad Bakhtafrouz, Mohsen Maddahali, and Somayeh Kaviani Dazeki

Doc ID: 319411 Received 09 Jan 2018; Accepted 05 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: In this paper, the design process of a novel three port graphene-based circulator in THz and infrared frequencies is presented. This new structure consists of three 120◦ rotational symmetry branches of graphene-based single mode waveguides coupled to a cavity resonator at the center. To achieve the nonreciprocity response in this structure, anisotropy property of the graphene has been utilized in the cavity resonator. Owing to low insertion loss, wide bandwidth (∼ 15%), and small footprint (∼subwavelengthdimension) and simple configuration of our design, it is superior to other structures reported in the literature. The propagation loss of the graphene in the waveguide and energy loss in the graphene patch resonator have been efficiently controlled, and insertion loss is maintained near ∼ 1.8dB. Also, due to the extremely confined hybrid SPP modes and large wavenumber (∼120k0) of these modes, the proposed configuration has a very small footprint. For verification of the method of design, two circulators at 17(THz) and 33(THz) are designed in this manuscript and the reported results demonstrate the excellent performance of the presented configuration.The structures were simulated using FEM method by commercial COMSOL Multiphysics EM solver while the graphene is considered as a surface sheet which carries surface current density.

Multidirectional Smoothing by Spectral Dispersion Scheme Based on Hybrid Dispersion Grating

Bin Zhang, Zheqiang Zhong, Jian wang, and pengcheng Hou

Doc ID: 325589 Received 08 Mar 2018; Accepted 05 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: A hybrid dispersion grating consisting of several segments of different groove types and groove densities is designed to disperse the laser beam and eventually to redistribute the speckles of the laser beam in different directions (linear, radial and azimuthal). The elaborately designed redistribution of the speckles significantly improves the irradiation uniformity of the focal spot. As the focal spot is smoothed in at least two of the three directions, the scheme using the hybrid dispersion grating is called multidirectional smoothing by spectral dispersion. Results indicate that, the performance and feasibility of the multidirectional smoothing scheme are better than the smoothing scheme based on a linear grating or a star grating.

Design and development of aluminum nanoring arrays for realizing dual mode operation plasmonic color filters

Fatemeh Fouladi Mahani, Arash Mokhtari, and Mahdiyeh Mehran

Doc ID: 326865 Received 26 Mar 2018; Accepted 05 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: In this paper, engineering the optical characteristics of aluminum nanoring arrays has been investigated aiming to achieve a practical design approach to realize dual mode plasmonic color filters. In addition to designing a set of subtractive and additive color filters with appropriate properties, an improved approach has also been proposed in order to design different additive/subtractive filters at arbitrary wavelengths. The proposed structures show great optical efficiencies while offering narrow-band characteristics and a good color purity. They are CMOS-compatible, cost-effective, easy-to-fabricate, highly tunable, and polarization insensitive. Moreover, they offer potential applications in displays, CMOS image sensors, color printing, and multispectral imaging.

Femtosecond Pulse Trains through Dual-Pumping of Optical Fibers: Role of Third-Order Dispersion

Aku Antikainen and Govind Agrawal

Doc ID: 327833 Received 06 Apr 2018; Accepted 04 Jun 2018; Posted 05 Jun 2018  View: PDF

Abstract: Generation of high-repetition-rate, femtosecond, soliton pulse trains through dual-wavelength pumping of a dispersion-decreasing fiber is studied numerically. The achievable shortest pulse width is found to be limited by third-order dispersion that has a significant effect on the pulse-compression dynamics. The output wavelength is red shifted because of intrapulse Raman scattering and depends heavily on third-order dispersion, whose positive values lead to the most red shifted solitons (>25%) of the input pump center wavelength). The proposed scheme allows the generation of ultrashort pulse trains at tunable high repetition rates with a wide range of output wavelengths and pulse durations through dispersion engineering. The resulting frequency combs extend over a wide bandwidth with a tunable spacing between the comb lines.

Azimuthal-segmented linear zone plate: 1D beam structuring and topological charge detecting

Arash Sabatyan and Maryam Fatehi

Doc ID: 326225 Received 16 Mar 2018; Accepted 01 Jun 2018; Posted 04 Jun 2018  View: PDF

Abstract: Unique linear structured light beams carrying fractional vortex dipoles in the shape of either transverse elliptical or transverse bottle-like beam are presented and studied. These beams are generated using a novel diffractive element produced by a given combination of two phase-shifted spiral linear zone plates with equal but opposite helicities. The impact of the topological charge upon the beams is surveyed and demonstrated that the size of the beams is quietly controlled by the charge. As an interesting application, we demonstrate that the element may be simply used to measure the topological charge of a vortex optical beam. On the other hand, when the element is illuminated by a vortex beam, the focused pattern is modulated so the number and direction of the modulated fringes easily reveal the sign and modulus of topological charge. The experimental results verify well the simulation works.

Near-IR second harmonic generation vs mid-IR optical parametric oscillation in multigrating and fan-out PPMgO:LN structures pumped by repetitively-pulsed 2-μm Tm3+:Lu2O3-ceramics laser

Dmitry Kolker, Oleg Antipov, Vladimir Shur, Andrey Akhmatkhanov, Sergey Larin, and Dmitry Kal'yanov

Doc ID: 328445 Received 16 Apr 2018; Accepted 01 Jun 2018; Posted 04 Jun 2018  View: PDF

Abstract: Mid-infrared optical parametric oscillators based on multigrating and fan-out periodically-poled MgO-doped LiNbO3 (PPMgO:LN ) crystals pumped with repetitively-pulsed Tm3+:Lu2O3-ceramics laser at 1966 nm were experimentally studied. The 983 nm wavelength second harmonic generation of the pumping beam was found to be competing with the parametric oscillations in PPMgO:LN crystals. Double-resonant optical parametric oscillations near degeneracy point at 3.93 μm were observed in multigrating PPMgO:LN crystal, but were not detected in the fan-out PPMgO:LN structure due to pump-power depletion by second harmonic generation. The efficient second harmonic generation with the average power up to 4.66 W at 983 nm was achieved in the fan-out PPMgO:LN crystal.

Quantum noise of Raman amplification in a fiber transmission line

Kyo Inoue

Doc ID: 314001 Received 21 Nov 2017; Accepted 31 May 2018; Posted 04 Jun 2018  View: PDF

Abstract: Raman amplification in a fiber transmission line is described in terms of quantum mechanics. The motion of the light field operator is derived on the basis of the Heisenberg equation that includes Raman interaction and the propagation loss, and then physical quantities, such as mean amplitude, mean photon number, and their variances, are evaluated. The obtained results are equivalent to conventional classical expressions, which provides a logical quantum mechanical base for the conventional phenomenological treatment, except for the intrinsic quantum noise or the vacuum fluctuation that appears owing to the quantum mechanical treatment.

Direction dependent propagation of high-power femtosecond pulses through large-mode-area tapered fiber

Gyanendra Kumar, MOHD REHAN, Vipul Rastogi, Dmitry Korobko, and Alexej Sysoliatin

Doc ID: 326820 Received 26 Mar 2018; Accepted 31 May 2018; Posted 04 Jun 2018  View: PDF

Abstract: We propose a design of a large mode area W-fiber tapered fiber for the direction dependent propagation of high power femtosecond pulses at 1550 nm wavelength. In the down-tapered case (forward-propagation), the fiber supports propagation of 40 kW, 85 fs Gaussian pulse with small variations in the pulse shape over 5 m distance. In up tapered (backward-propagation) case, the pulse is significantly disperses to nearly 1000 fs. Such a fiber would be useful for delivering of ultra-short high peak power pulses while simultaneously working as an isolator.

'Au Nanowire-VO2 Spacer-Au Film' based Optical Switches

Arun Thomas, Priten Savaliya, Kamal Kumar, Akanksha Ninawe, and Anuj Dhawan

Doc ID: 325146 Received 06 Mar 2018; Accepted 31 May 2018; Posted 31 May 2018  View: PDF

Abstract: We present a novel optical switch which consists of a 1-D array of Au nanowires present on a vanadium dioxide (VO2) thin film layer, which is further present on top of an underlying Au film. The optical switching action in this nanostructure arises from the semiconductor-to-metal transition of the VO2 spacer layer ⎯ i.e. upon phase transition of VO2 from its semiconductor state to its metallic state ⎯ which can be induced by the application of heat, infra-red light, or voltage. The phase transition of the VO2 layer results in a change in the reflectance signal from the 'Au Nanowire-VO2 Spacer-Au Film' nanostructure. The differential reflectance signal, i.e. difference in the reflection spectra from this nanostructure when the VO2 spacer layer is present in its metallic and the semiconductor states, was calculated using RCWA simulations and employed as a measure of switchability. We demonstrate that switchability, as well as the wavelength at which the maximum differential reflectance is observed (i.e. the optimal switching wavelength), can be tuned over a wide spectral regime by changing the structural parameters of these optical switches. Ultra-fast switching can be achieved using these optical switches, as the phase transition in the VO2 film spacer occurs at femto-second time-scales. These optical switches can be easily fabricated using the currently available nanofabrication capabilities.

Using ZnO nanosheets grown by electrodeposition in random lasers as scattering centers: The effects of sheet size and presence of mode competition

Abbas Ghasempour Ardakani and Peymaneh Rafieipour

Doc ID: 325896 Received 13 Mar 2018; Accepted 30 May 2018; Posted 31 May 2018  View: PDF

Abstract: In this paper, a single mode random laser is fabricated based on zinc oxide (ZnO) nanosheets. ZnO nanosheets are grown on a FTO glass substrate using electrodeposition technique. We use Rhodamine 6G solution as the random laser gain medium while optical feedback is provided by light multi-scattering from ZnO nanosheets. We investigate experimentally the effects of changing the electrolyte concentration used in electrodeposition on emission properties of random lasers based on ZnO nanosheets. It is demonstrated here that size and shape of nanosheets and their related random lasing emission properties change with electrolyte concentration. Our results reveal that the random lasing emission from ZnO nanosheets can become multi-mode and discrete modes appear in the emission spectrum for pumping energies larger than the threshold pumping energy. It is demonstrated that by increasing the electrolyte concentration, the threshold pumping energy corresponding to the lasing mode decreases first. This effect is attributed to the enhancement of quality factors of random lasing cavities and increase of their numbers with increasing the electrolyte concentration, due to the increase of sheet size and their sharpness. With further increase of electrolyte concentration, the emission spectrum becomes double mode. Following the appearance of more than one lasing mode in the emission spectrum, mode competition and cross gain saturation effects between the excited modes lead to an increase in threshold as well as a decrease in intensity. We measure the threshold pumping energy for each lasing mode excited in the system. Our results also show that the double mode random lasing emission from ZnO nanosheets strongly depends on the region of sample which is illuminated by the pumping laser.

The Relationship between Morphology and Transparency in Glass-Ceramic Materials

Nicholas Borrelli, Charlene Smith, and Alexandra Mitchell

Doc ID: 320833 Received 31 Jan 2018; Accepted 10 May 2018; Posted 15 May 2018  View: PDF

Abstract: This paper is an attempt to understand and interpret the optical scattering in composite materials. It focuses on phase-separated glasses and glass-ceramics that maintain transparency at high crystal content. Two approaches aimed at understanding optical scattering are investigated for each example material: 1) a single particle approach and 2) a correlation function approach based on the spatial distribution of the refractive index profile of the material pioneered by P. Debye. Both methods have shortcomings: the single particle approach cannot take the material’s morphology into account whereas it is non-trivial to determine the correlation function. Regardless, the preferred approach is determined for each of the materials investigated. It is shown that optical scattering in glass ceramics can be controlled to produce a transparent material if the glass ceramic has a bulk fine-grained structure without an easily recognized ‘grain size’.

Light scattering in glass-ceramics: revision of the concept

Mikhail Shepilov, Olga Dymshits, and Alexander Zhilin

Doc ID: 322870 Received 13 Feb 2018; Accepted 19 Apr 2018; Posted 20 Apr 2018  View: PDF

Abstract: Transparency of glass-ceramics is limited by light scattering connected with their structure (nano(micro)-sized crystals distributed within the residual glass). We digitized and analyzed graphical data on transparency of glass-ceramics presented in literature and demonstrated that, for most glass-ceramics, wavelength dependence of scattering coefficient is described by the power law with the constant exponent (-p). The values of p are often markedly greater than the Rayleigh value 4 and may be as much as 9. This conclusion is extremely important for the development of new materials and contradicts the generally accepted opinion that p ≤ 4 for glass-ceramics. Similar behavior of light scattering was observed earlier in phase-separated glasses and is known as anomalous light scattering.

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