Showing papers in "Journal of Modern Optics in 2017"
TL;DR: In this paper, the authors review the various collective effects that occur when light interacts with an ensemble of atoms and explain why some collective effects depend on the atomic density, and others on the optical depth.
Abstract: Cooperative scattering has been the subject of intense research in the last years. In this article, we discuss the concept of cooperative scattering from a broad perspective. We briefly review the various collective effects that occur when light interacts with an ensemble of atoms. We show that some effects that have been recently discussed in the context of ‘single-photon superradiance’, or cooperative scattering in the linear-optics regime, can also be explained by ‘standard optics’, i.e. using macroscopic quantities such as the susceptibility or the diffusion coefficient. We explain why some collective effects depend on the atomic density, and others on the optical depth. In particular, we show that, for a large and dilute atomic sample driven by a far-detuned laser, the decay of the fluorescence, which exhibits superradiant and subradiant dynamics, depends only on the on-resonance optical depth. We also discuss the link between concepts that are independently studied in the quantum-optics community an...
115 citations
TL;DR: This computational imaging technique can retrieve an image from sub-Nyquist measurements, and the background noise is easily cancelled to give excellent image quality.
Abstract: We propose and demonstrate a computational imaging technique that uses structured illumination based on a two-dimensional discrete cosine transform to perform imaging with a single-pixel detector. A scene is illuminated by a projector with two sets of orthogonal patterns, then by applying an inverse cosine transform to the spectra obtained from the single-pixel detector a full-colour image is retrieved. This technique can retrieve an image from sub-Nyquist measurements, and the background noise is easily cancelled to give excellent image quality. Moreover, the experimental set-up is very simple.
104 citations
TL;DR: In this article, a non-linear optical demulitiplexer with defect rods made of doped glass which has high Kerr coefficient is proposed. But the defect rods are not employed in the optical decoder.
Abstract: In this paper, we are going to design and propose a novel structure for all optical decoder. The proposed structure is composed of optical power splitters and a four-port optical switch. The four-port optical switch simply is a non-linear optical demulitiplexer. For achieving non-linear behaviour for the demultiplexer, we will employ defect rods made of doped glass which has high Kerr coefficient. The final structure has three input ports and four output ports. Port E acts as enable port, which will be used activating or deactivating the total structure. A and B are the control ports, by which one can control when the structure is active, which port of the structure to be active. The optical intensity of the input ports required appropriate operation of the structure is about 20 W/μm2. The maximum switching frequency of the proposed structure is 2 GHz. Reduced input optical intensity is the main characteristics of the present work. Numerical methods such as plane wave expansion and finite differen...
96 citations
TL;DR: In this paper, a silicon strip waveguide at 3.39μm was proposed for CH4 gas sensing based on the evanescent field absorption, which can provide the highest EFR>55% with adequate dimensions.
Abstract: Trace gases such as H2O, CO, CO2, NO, N2O, NO2 and CH4 strongly absorb in the mid-IR (>2.5 μm) spectral region due to their fundamental rotational and vibrational transitions. CH4 gas is relatively non-toxic, however, it is extremely explosive when mixed with other chemicals in levels as low as 5% and it can cause death by asphyxiation. In this work, we propose a silicon strip waveguide at 3.39 μm for CH4 gas sensing based on the evanescent field absorption. These waveguides can provide the highest evanescent field ratio (EFR)>55% with adequate dimensions. Moreover, EFR and sensitivity of the sensor are highly dependent on the length of the waveguide up to a certain limit. Therefore, it is always a compromise between the length of the waveguide and EFR in order to obtain greater sensitivity.
66 citations
TL;DR: Based on the hybrid cladding design, a singlemode photonic crystal fiber (PCF) is proposed to achieve an ultra-high birefringence and large negative dispersion coefficient using finite-element method.
Abstract: Based on the hybrid cladding design, a single-mode photonic crystal fibre (PCF) is proposed to achieve an ultra-high birefringence and large negative dispersion coefficient using finite-element method. Simulation results reveal that with optimal design parameters, it is possible to achieve an ultra-high birefringence of 2.64 × 10−2 at the excitation wavelength of 1.55 μm. The designed structure also shows large dispersion coefficient about −242.22 to −762.6 ps/nm/km over the wavelength ranging from 1.30 to 1.65 μm. Moreover, residual dispersion, effective dispersion, effective area, confinement loss and nonlinear coefficient of the proposed PCF are discussed thoroughly.
64 citations
TL;DR: In this article, the authors describe simulation and experimental methods for designing a D-shaped surface plasmon resonance (SPR) sensor, which consists of two set-up approaches.
Abstract: This paper describes simulation and experimental methods for designing a D-shaped surface plasmon resonance (SPR) fibre sensor. The sensor consists of two set-up approaches. Finite element method is used in simulation on the fibre sensor device. Two experimental methods for detecting relative intensity are used by varying the wavelength of the optical signal sources and the thickness of gold layer coated on the D-shaped fibre. In the first method, the sensor device works by detecting the relative intensity of two optical signal sources having different wavelengths. In the second set-up, the relative intensity between two D-shaped fibres coated with different thicknesses of gold is measured when a single signal source is launched at the input. The difference in intensities of the signal outputs is used to estimate the refractive index at the sensing region. A prototype SPR D-shaped fibre sensor has been fabricated and the experimental results show good agreement with simulation.
57 citations
TL;DR: In this article, the coupled sine-Gordon equation was used to describe the propagation of an optical pulse in a fiber waveguide, and the Jacobi elliptic, hyperbolic and trigonometric function solutions were derived with the help of the extended Jacobi elliptic function expansion method.
Abstract: The coupled sine-Gordon equation, which can be used to describe the propagation of an optical pulse in fibre waveguide, has been investigated analytically. The hyperbolic and trigonometric function solutions are constructed by the extended G′/G-expansion method, and then the Jacobi elliptic, hyperbolic and trigonometric function solutions are derived with the help of the extended Jacobi elliptic function expansion method.
54 citations
TL;DR: In this paper, two different forms of the conformable fractional Benjamin-Bona-Mahony (BBM) equations were analyzed by an analytical method and the extended Jacobi's elliptic function expansion scheme was used to extract explicit solitons.
Abstract: This paper deals with two different forms of the conformable fractional Benjamin–Bona–Mahony (BBM) equations by an analytical method. These physical models have important applications for describing the propagation of optical pulses in non-linear media. The conformable fractional symmetric BBM equation and the conformable time fractional Equal-width (EW) equation are considered. The extended Jacobi’s elliptic function expansion scheme are used to extract explicit solitons.
49 citations
TL;DR: A modified gain coefficient filter based Dark channel prior (DCP) for single image dehazing is proposed to solve the problems of colour distortion, edge preservation, and halo artefacts.
Abstract: Haze reduces the visibility of outdoor images. The majority of existing dehazing techniques perform poorly whenever objects are similar to airlight, and no shadow is cast on them. Also, existing approaches still suffer from the problems of colour distortion, edge preservation, and halo artefacts. To solve these issues, a modified gain coefficient filter based Dark channel prior (DCP) for single image dehazing is proposed. To reduce the colour distortion, restoration model of DCP is also redefined. The experimental results indicate that the proposed technique provides better results as compared with existing approaches.
48 citations
TL;DR: In this article, an ultra-short polarization beam splitter based on dual-core photonic crystal fiber with square lattice is proposed, where an ideal coupling length and coupling length ratio can be achieved by changing the pitch in two polarizations and the ellipticity.
Abstract: An ultra-short polarization beam splitter based on dual-core photonic crystal fibre with square lattice is proposed. Numerical results show that an ideal coupling length and coupling length ratio can be achieved by changing the pitch in two polarizations and the ellipticity. The length of splitter is 93.3μm, the bandwidth is about 70 nm as the extinction ratio lower than -20dB at the wavelength of 1.55μm. The characteristic of the short length is rare in previous literatures which could widely apply to integrated optical communication systems.
44 citations
TL;DR: In this article, the underlying mechanisms and optimal conditions for paint removal by laser ablation are thoroughly investigated on the basis of ablation morphologies and combining experiments with numerical modeling, and the authors suggest that laser paint removal is dominated by the laser vaporization effect, thermal stress effect and laser plasma effect.
Abstract: Paint removal by laser ablation is favoured among cleaning techniques due to its high efficiency. How to predict the optimal laser parameters without producing damage to substrate still remains challenging for accurate paint stripping. On the basis of ablation morphologies and combining experiments with numerical modelling, the underlying mechanisms and the optimal conditions for paint removal by laser ablation are thoroughly investigated. Our studies suggest that laser paint removal is dominated by the laser vaporization effect, thermal stress effect and laser plasma effect, in which thermal stress effect is the most favoured while laser plasma effect should be avoided during removal operations. Based on the thermodynamic equations, we numerically evaluated the spatial distribution of the temperature as well as thermal stress in the paint and substrate under the irradiation of laser pulse at 1064 nm. The obtained curves of the paint thickness vs. threshold fluences can provide the reference stand...
TL;DR: In this article, a rib waveguide structure with non-linear coefficient as high as 18,250 W−1,km−1 at 2.5μm was proposed for ultra broadband mid-infrared supercontinuum generation across molecular fingerprint region.
Abstract: We report a dispersion-engineered As2Se3 chalcogenide glass rib waveguide structure for ultra broadband mid-infrared supercontinuum generation across molecular ‘fingerprint region’. The proposed rib waveguide structure offers non-linear coefficient as high as 18,250 W−1 km−1 at 2.5 μm. Supercontinuum spectrum spanning 2–15 μm, which not only covers the both atmospheric transparent windows (3–5 μm and 8–13 μm) in the mid-infrared domain but also covers the important molecular ‘fingerprint domain’, is obtained using only 4 mm-long rib waveguide structure. To the best of our knowledge, such broadband mid-infrared supercontinuum spectrum in As2Se3-based chalcogenide waveguide geometry is reported for the first time. The proposed design of rib waveguide has potential for robust, integrated and low-cost supercontinuum sources in various applications including frequency comb generation, chemical sensing, food quality control and early cancer diagnostics.
TL;DR: This paper builds a model of the trust relaying QKD network for easily analysing and understanding this network, and proposes a dynamical routing scheme for this network that demonstrates the validity and effectiveness of the proposed routing scheme.
Abstract: Quantum key distribution (QKD) technology can establish unconditional secure keys between two communicating parties. Although this technology has some inherent constraints, such as the distance and point-to-point mode limits, building a QKD network with multiple point-to-point QKD devices can overcome these constraints. Considering the development level of current technology, the trust relaying QKD network is the first choice to build a practical QKD network. However, the previous research didn’t address a routing method on the trust relaying QKD network in detail. This paper focuses on the routing issues, builds a model of the trust relaying QKD network for easily analysing and understanding this network, and proposes a dynamical routing scheme for this network. From the viewpoint of designing a dynamical routing scheme in classical network, the proposed scheme consists of three components: a Hello protocol helping share the network topology information, a routing algorithm to select a set of sui...
TL;DR: In this article, the authors have focused on finding more applications of WSN in multimedia technologies, i.e. audio, video and digital images, and have focused towards findings more applications in WSN.
Abstract: Wireless Sensor Networks (WSN) is widely deployed in monitoring of some physical activity and/or environmental conditions. Data gathered from WSN is transmitted via network to a central location for further processing. Numerous applications of WSN can be found in smart homes, intelligent buildings, health care, energy efficient smart grids and industrial control systems. In recent years, computer scientists has focused towards findings more applications of WSN in multimedia technologies, i.e. audio, video and digital images. Due to bulky nature of multimedia data, WSN process a large volume of multimedia data which significantly increases computational complexity and hence reduces battery time. With respect to battery life constraints, image compression in addition with secure transmission over a wide ranged sensor network is an emerging and challenging task in Wireless Multimedia Sensor Networks. Due to the open nature of the Internet, transmission of data must be secure through a process known a...
TL;DR: In this article, the optical solitons to the non-linear Shrodinger's equation with spatio-temporal dispersion were investigated and two types of nonlinear media were studied.
Abstract: In this work, we investigate the optical solitons to the non-linear Shrodinger’s equation with spatio-temporal dispersion. There are two types of non-linear media studied in this paper. They are Ke...
TL;DR: In this article, the optical characteristics of sodium polyacrylate in the terahertz frequency range were investigated and the material dispersion effect on object visualisation was discussed.
Abstract: We present measurements of optical characteristics of sodium polyacrylate in the terahertz frequency range and discuss how material dispersion affects object visualisation in terahertz imaging. We demonstrate how important is to take into account the material dispersion for phase and relief reconstruction of the investigated object.
TL;DR: In this article, both the exchange and correlation energies due to Coulomb and spin-orbit interactions in a monolayer silicene with a buckled honeycomb lattice are calculated.
Abstract: Both the exchange and correlation energies due to Coulomb and spin-orbit interactions in a monolayer silicene with a buckled honeycomb lattice are calculated. We use Lindhard formalism for the polarizability. Many-body effects in such Dirac-like materials are studied with an emphasis on the influence of on-site potential difference Δz between two sublattices. Our calculations have shown that the presence of an energy bandgap Δσ,ξ=|σξΔSO-Δz| leads to a reduced exchange energy, which has some potential applications, such as, tunability of entanglement of electrons for quantum information devices. Since silicene acquires two energy gaps associated with up- and down-pseudospin, we can adjust its electronic properties in a wider range by varying these two bandgaps as compared to graphene. Another way to tune silicene electronic properties is through impurity doping. Our numerical results demonstrate the dependence of exchange and correlation energies on the energy bandgaps, doping and temperature under...
TL;DR: In this article, a hyper-spectral polarization imaging system based on a non-collinear, acousto-optic tunable filter (AOTF) and a linear polarizer is described.
Abstract: The present paper describes a hyper-spectral polarization imaging system based on a non-collinear, acousto-optic tunable filter (AOTF) and a linear polarizer. The paper begins with an analysis of the equivalent relationship of the AOTF to describe the principle of polarization detection of this system. Appropriate parameters of hardware components are assigned later. This system, being electronically controllable and tunable, can not only ensure the precision of imaging but also obtain hyper-spectral polarization signatures. The prototype has two optional working modes, namely, hyper-spectral polarization imaging and hyper-spectral intensity imaging. Moreover, parameters of this system – such as diffraction efficiency, spectral resolution and modulation precision – are tested using a halogen tungsten lamp and an optical fibre spectrometer. The results indicate that this instrument is compact, vibration-insensitive, robust and precisely controllable. The system designed in this paper has further ap...
TL;DR: In this paper, various dispersion compensation units are presented and evaluated in a 10-Gb/s NRZ transmission system over 100-km-long singlemode fiber is used and three chirped FBGs are optimized individually to yield pulse width reduction percentage (PWRP) of 8666, 7996, 6242% for linear, square root, and cube root, respectively.
Abstract: Various dispersion compensation units are presented and evaluated in this paper These dispersion compensation units include dispersion compensation fiber (DCF), DCF merged with fiber Bragg grating (FBG) (joint technique), and linear, square root, and cube root chirped tanh apodized FBG For the performance evaluation 10 Gb/s NRZ transmission system over 100-km-long single-mode fiber is used The three chirped FBGs are optimized individually to yield pulse width reduction percentage (PWRP) of 8666, 7996, 6242% for linear, square root, and cube root, respectively The DCF and Joint technique both provide a remarkable PWRP of 9445 and 9696%, respectively The performance of optimized linear chirped tanh apodized FBG and DCF is compared for long-haul transmission system on the basis of quality factor of received signal For both the systems maximum transmission distance is calculated such that quality factor is ≥ 6 at the receiver and result shows that performance of FBG is comparable to that of
TL;DR: In this article, a plasmonic filter based on a metal-insulator-metal structure is analyzed for band-rejection applications, where a square ring is used in proximity to the waveguide in order to resonate with some transmitted wavelengths and drop them to prevent from propagation towards the output.
Abstract: A novel high-performance plasmonic filter based on a metal–insulator–metal structure is analysed for band-rejection applications. A square ring is used in proximity to the waveguide in order to resonate with some transmitted wavelengths and drop them to prevent from propagation towards the output. The effect of the structural parameters of square ring resonator is studied deploying the finite difference time domain method and the possibility of tuning the rejected wavelength is investigated in detail. The simulation results demonstrate that the rejected wavelength has a red-shift with increase in the size of the ring’s dimensions. A further study is carried out considering narrowing the bandwidth. To improve the quality factor of the proposed filter, a small ring within the resonator is introduced that considerably decreases the bandwidth of the peak with respect to its central wavelength.
TL;DR: Using direct search algorithms for solving the quantum optimization problem, the authors demonstrate on model systems that with specifically tailored Gaussian-form laser pulses one can achieve a very good control over the dynamics in complicated quantum systems.
Abstract: Using direct search algorithms for solving the quantum optimization problem, we demonstrate on model systems that with specifically tailored Gaussian-form laser pulses one can achieve a very good control over the dynamics in complicated quantum systems. We show that by manipulating a very limited number of laser-pulse parameters, one is able to control the charge migration process in molecules. In particular, by combining two identical Gaussian laser pulses with an appropriate delay between them, one can stop the pure electronic, few-femtosecond oscillation of the charge, redistributing it along the molecule of propiolic acid.
TL;DR: Numerical simulations demonstrate that the proposed image encryption scheme is feasible, secure and capable of resisting common classical attacks.
Abstract: An image encryption scheme is proposed by combining the random fractional discrete cosine transform (RFrDCT) with the dependent scrambling and diffusion (DSD). The application of the randomization, irrational choice and vectorization of fractional orders and the randomization of generating sequences improves the key-sensitivity and thus enlarges the key space greatly. Both the locations and the values of RFrDCT transformed coefficients are changed during the stage of DSD to further enhance the security of image encryption scheme. Numerical simulations demonstrate that the proposed image encryption scheme is feasible, secure and capable of resisting common classical attacks.
TL;DR: In this article, a (2+1)-dimensional Bogoyavlenskii-Kadontsev-Petviashili equation was investigated in a fluid, plasma or ferromagnetic thin film.
Abstract: In this paper, we investigate a (2+1)-dimensional Bogoyavlenskii–Kadontsev–Petviashili equation in a fluid, plasma or ferromagnetic thin film. Through the Bell polynomials, Hirota method and symbolic computation, the one- and two-kink-soliton solutions are derived. Backlund transformation, Lax pair and conservation laws are presented. Elastic collisions including the oblique, parallel, unidirectional and bidirectional collisions between the two-kink solitons are discussed. In addition, the relation between the velocities and wave numbers of the two-kink solitons are analysed. When wave numbers bj>0,νjx, the velocities in the x axis, increase with wave numbers aj increasing. With bj increasing, νjx increase when aj4-3bj2>0, while decrease when aj4-3bj2<0. νjy, the velocities in the y axis, increase with aj increasing and bj decreasing.
TL;DR: In this article, a Co3O4 nanocubes are embedded into a polyethylene oxide film to produce a high nonlinear optical response, which is useful for SA application.
Abstract: We demonstrate a Q-switched Erbium-doped fibre laser (EDFL) utilizing cobalt oxide (Co3O4) nanocubes film based saturable absorber (SA) as a passive Q-switcher. Co3O4 nanocubes are embedded into a polyethylene oxide film to produce a high nonlinear optical response, which is useful for SA application. It has saturation intensity and modulation depth of 3 MW/cm2 and 0.35%, respectively. The proposed laser cavity successfully generates a stable pulse train where the pulse repetition rate is tunable from 29.8 to 70.92 kHz and the pulse-width reduces from 10.9 to 5.02 μs as the 980 nm pump power increases. This result indicates that the Co3O4 is excellent for constructing an SA that can be used in producing a passively Q-switched fibre laser operating at a low pump intensity. To the best of our knowledge, this is the first demonstration of Co3O4 film based fibre laser.
TL;DR: In this paper, a single-shot phase-shifting triple-interferometer (PSTI) is developed for analysis of characteristics of transparent structures and optical path difference (OPD) measurements.
Abstract: Considering the deficiency of time elapsed for phase-stepping interferometric techniques and the need of developing non-contact and on-line measurement with high accuracy, a single-shot phase-shifting triple-interferometer (PSTI) is developed for analysis of characteristics of transparent structures and optical path difference (OPD) measurements. In the proposed PSTI, coupled three interferometers which generate four interference patterns, and a polarizer array is used as phase shifters to produce four spatially separated interferograms with π/2-phase shifts, which are recorded in a single capture by a camera. The configuration of the PSTI allows dynamic measurements (4D measurements) and does not require vibration isolation. We have applied the developed system to examine the size and OPD of cells, and the slope of thin films
TL;DR: In this article, the authors show that for the generation of Brunel harmonics at all frequencies, the subcycle ionization dynamics is of critical importance, and that such harmonics disappear at low pump intensities when the ionisation dynamics depends only on the slow envelope (so-called multiphoton ionization regime).
Abstract: Brunel radiation appears as a result of a two-step process of photo-ionization and subsequent acceleration of electron, without the need of electron recollision. We show that for generation of Brunel harmonics at all frequencies, the subcycle ionization dynamics is of critical importance. Namely, such harmonics disappear at the low pump intensities when the ionization dynamics depends only on the slow envelope (so-called multiphoton ionization regime) and not on the instantaneous field. Nevertheless, if the pump pulse contains incommensurate frequencies, Brunel mechanism does generate new frequencies even in the multiphoton ionization regime.
TL;DR: In this article, the authors present coherent control of above-threshold photoemission from a tungsten nanotip achieving nearly perfect modulation, where electron emission is significantly enhanced or depressed during temporal overlap.
Abstract: In this article, we present coherent control of above-threshold photoemission from a tungsten nanotip achieving nearly perfect modulation. Depending on the pulse delay between fundamental (1560nm) and second harmonic (780nm) pulses of a femtosecond fiber laser at the nanotip, electron emission is significantly enhanced or depressed during temporal overlap. Electron emission is studied as a function of pulse delay, optical near-field intensities, DC bias field and final photoelectron energy. Under optimized conditions modulation amplitudes of the electron emission of 97.5% are achieved. Experimental observations are discussed in the framework of quantum-pathway interference supported by local density of states simulations.
TL;DR: In this paper, the effects of tissue turbulence on the propagation of an optical spherical wave are analyzed in weakly turbulent soft tissue and the variation of the scintillation index versus the wavelength is also investigated.
Abstract: Effects of the tissue turbulence on the propagation of an optical spherical wave are analysed. For this purpose, scintillation index of an optical spherical wave which is propagating in a soft tissue is formulated and evaluated in weakly turbulent soft tissue. Scintillation index of the optical spherical wave is examined against the changes in the tissue parameters which are the tissue length between the optical spherical wave source and the detector, random variations in the refractive index of the tissue and the outer scale of the tissue turbulence. According to our graphical outputs, it is observed that increase in the random variations of the refractive index of the tissue results in an increase in the scintillation index at a certain realization of the turbulence spectrum. On the other hand, larger outer scales and longer tissue lengths yield larger scintillations. The variation of the scintillation index of the optical spherical wave versus the wavelength is also investigated. It is found th...
TL;DR: In this article, the electron photoemission from isolated nanoparticles of different materials in few-cycle laser fields at intensities where the Coulomb field of the ionized electrons and residual ions significantly contribute to the electron acceleration process was investigated.
Abstract: The excitation of nanoscale near-fields with ultrashort and intense laser pulses of well-defined waveform enables strongly spatially and temporally localized electron emission, opening up the possibility for the generation of attosecond electron pulses. Here, we investigate the electron photoemission from isolated nanoparticles of different materials in few-cycle laser fields at intensities where the Coulomb field of the ionized electrons and residual ions significantly contribute to the electron acceleration process. The dependences of the electron cut-off energy on the material’s dielectric properties and electron binding energy are investigated systematically in both experiments and semi-classical simulations. We find that for sufficiently high near-field intensities the material dependence of the acceleration in the enhanced near-fields is quenched by many-particle charge-interaction.
TL;DR: In this paper, the authors studied the bandwidth improvement of reflection-mode linear to circular polarization converters (RMCPs) based on multi-layer rectangular patches, which can be used for different ranges of frequencies without losing generality.
Abstract: In this paper, bandwidth improvement of reflection-mode linear to circular polarization converters (RMCPs) is studied. The proposed RMCP is based on multi-layer rectangular patches. Equivalent transmission line circuit of multi-layer reflection-mode polarization converters is used for designing the proposed metamirror. In addition, the approximate equation of axial ratio (AR) of the reflected wave is obtained from the structures containing rectangular patches on each layer. Polarization converters containing multi-layer rectangular patches can be utilized for different ranges of frequencies. However, the frequency range of 2–8 THz is considered in this paper without losing generality. The incident wave is assumed to be linearly polarized with 45° polarization angle. AR equation is used for initial optimization of the dimensions of rectangular patches to obtain the widest possible bandwidth of RMCPs with two- and three-layer patches. Secondary optimization is applied after specifying largest dimens...