Showing papers in "Optics Communications in 2014"

The third-order nonlinear optical susceptibility of gold

Abstract: We critically analyze reported measured values of the third-order nonlinear optical susceptibility χð3Þ of bulk gold. Reported values of this quantity span a range of more than three orders of magnitude. Much of this variation results from the use of different measurement procedures which are sensitive to different contributions to the nonlinear optical response. For example, values measured through use of thirdharmonic generation or non-degenerate four-wave mixing tend to be significantly lower than those obtained from measurements of the intensity-dependent refractive index. We ascribe this behavior to the fact that the first two processes respond only to “instantaneous” nonlinearities, whereas the nonlinear refractive index has a contribution from the much stronger but much slower “hot electron,” or “Fermi-smearing” mechanism, which has a response time of the order of picoseconds. The data also reveal that the hot-electron contribution has a strong dependence on laser wavelength, because of the turn-on of the 5d to 6sp transition at about 550 nm. It is hoped that the compilation presented here will prove useful in establishing what value of χ ð3Þ is most appropriate for adoption under various laboratory conditions.

Multi-hole fiber based surface plasmon resonance sensor operated at near-infrared wavelengths

Abstract: We propose a surface plasmon resonance (SPR) sensor based on a single mode optical fiber with six air holes. A thin gold film and a TiO2 film are deposited on the walls of air holes. Due to high refractive index of TiO2 the proposed sensor can operate at near-infrared (IR) wavelengths. The characteristics of the sensor were numerically investigated based on the finite-element method (FEM). The numerical results indicate that the optical loss spectrum of SPR sensor can be tuned easily by changing the thicknesses of gold and TiO2 layers. The refractive-index resolution of 2.7×10−5 (sensitivity S≈370/RIU) for aqueous analytes can be achieved.

Gallium arsenide (GaAs) quantum photonic waveguide circuits

Abstract: Integrated quantum photonics is a promising approach for future practical and large-scale quantum information processing technologies, with the prospect of on-chip generation, manipulation and measurement of complex quantum states of light. The gallium arsenide (GaAs) material system is a promising technology platform, and has already successfully demonstrated key components including waveguide integrated single-photon sources and integrated single-photon detectors. However, quantum circuits capable of manipulating quantum states of light have so far not been investigated in this material system. Here, we report GaAs photonic circuits for the manipulation of single-photon and two-photon states. Two-photon quantum interference with a visibility of 94.9±1.3% was observed in GaAs directional couplers. Classical and quantum interference fringes with visibilities of 98.6±1.3% and 84.4±1.5% respectively were demonstrated in Mach–Zehnder interferometers exploiting the electro-optic Pockels effect. This work paves the way for a fully integrated quantum technology platform based on the GaAs material system.

All-optical NOR and NAND gates based on photonic crystal ring resonator

Abstract: We report a new configuration of all-optical logic gates based on two-dimensional (2D) square lattice photonic crystals (PCs) composed of silicon (Si) rods in Silica (SiO 2 ). The proposed device is composed of cross-shaped waveguide and two photonic crystal ring resonators (PCRRs) without nonlinear materials and optical amplifiers. The gate has been simulated and analyzed by finite difference time domain (FDTD) and plane wave expansion (PWE) methods. The simulation results show that the proposed all-optical logic gates could really function as NOR and NAND logic gates. This new device can potentially be used in large-scale optical integration and on-chip photonic logic integrated circuits.

On the numerical simulation of Kerr frequency combs using coupled mode equations

Abstract: It is demonstrated that Kerr frequency comb generation described by coupled mode equations can be numerically simulated using Fast Fourier Transform methods. This allows broadband frequency combs spanning a full octave to be efficiently simulated using standard algorithms, resulting in orders of magnitude improvements in the computation time.

Perfect absorber metamaterials: Peak, multi-peak and broadband absorption

Abstract: We investigated the absorption in a sandwich model of absorber metamaterial (MM) which consists of periodic metallic dishes at the front and metallic plane at the back, separated by dielectric substrate. First, single perfect-absorption (PA) peaks were achieved by studying the influence of parameters in the unit cell of the MM. The electromagnetic properties were presented to understand the mechanism of the PA at resonance frequency. In order to yield a multi-peak absorption, the dishes were designed in different sizes and appropriately arranged on the front side of MM. For the furthermost purpose of our work, customizing broadband absorption was performed by adjusting the dishes sizes. Utilizing the symmetrical geometry of dishes, polarization-insensitivity of the broadband absorption was gained. Finally, the influence of the angle of incidence wave on the broadband absorption was examined.

Perfect metamaterial absorber with polarization and incident angle independencies based on ring and cross-wire resonators for shielding and a sensor application

Abstract: We report the design, characterization and experimental verification of a perfect metamaterial absorber (MA) based on rings and cross wires (RCWs) configurations that operate in the microwave regime. The suggested MA provides perfect absorption with incident angle and polarization independencies which can be used for various shielding applications. Maximum absorption rate is 99.9 % at 2.76 GHz for simulation and 99.4 % at 2.82 GHz for experiment, respectively. The experimental results of the fabricated prototype are in good agreement with the numerical simulations. We also present a numerical analysis in order to explain physical interpretation of MA mechanism in detail. Moreover, a sensor application of the proposed MA is introduced to show additional feature of the model. As a result, proposed MA enables myriad potential applications in S band radar and medical technologies.

Design of all-optical logic gates avoiding external phase shifters in a two-dimensional photonic crystal based on multi-mode interference for BPSK signals

Abstract: In this paper several new structures of all-optical logic gate in a two-dimensional photonic crystal (PC) based on multi-mode interference (MMI) are proposed and designed. 3 π /2 phase shift is introduced between two input ports in the photonic crystal devices through different lengths of the waveguide of two input ports, which makes the logic gates to be directly used for logic operations of binary-phase-shift-keyed (BPSK) signals. XOR, XNOR, OR and NAND logic gates are realized. In order to simulate the performance of the proposed logic gates, the plane wave expansion method (PWEM) and finite difference time domain (FDTD) method are employed. Numerical results reveal that the contrast ratio between Logic 1 and Logic 0 logic-levels is more than 21 dB for XOR, 17 dB for XNOR, and 13 dB for OR and NAND logic operations in the whole C-Band (1530–1565 nm). This kind of structure does not adopt nonlinear optical properties, and hence, the power consumption of the device is very low and the size of the device is very small. Therefore, the proposed logic gate has the potential to constitute photonic integrated components that will be used in all-optical signal processing, photonic computing and all-optical networks.

Implementation of full-adder and full-subtractor based on electro-optic effect in Mach–Zehnder interferometers

Abstract: The optical switching phenomena has been studied and its efficient application to construct the full-adder/subtractor (A/S) has been projected. The paper constitutes the mathematical description of proposed device and thereafter compilation using MATLAB. The analysis of various factors such as crosstalk, extinction ratio, power imbalance and transition loss has been presented. The desirable device parameter has been examined in order to obtain the optimum best influencing parameter. The work is carried out by simulating the proposed device with Beam propagation method and using the observed results to study the characteristics of influencing parameters in consideration with the device parameters.

Judd–Ofelt analysis and spectral properties of Dy3+ ions doped niobium containing tellurium calcium zinc borate glasses

Abstract: Niobium containing tellurium calcium zinc borate (TCZNB) glasses doped with different concentrations of Dy 3+ ions were prepared by the melt quenching method and their optical properties have been studied. The Judd–Ofelt (J–O) intensity parameters Ω t ( t =2, 4 and 6) were calculated using the least square fit method. Based on the magnitude of Ω 2 parameter the hypersensitivity of 6 H 15/2 → 6 F 11/2 has also been discussed. From the evaluated J–O intensity parameters as well as from the emission and lifetime measurements, radiative transition properties such as radiative transition probability rates and branching ratios were calculated for 4 F 9/2 excited level. It is found that for Dy 3+ ion, the transition 4 F 9/2 → 6 H 13/2 shows highest emission cross-section at 1.0 mol% TCZNB glass matrix. From the visible luminescence spectra, yellow to blue ( Y / B ) intensity ratios and chromaticity color coordinates were also estimated. The TCZNB glasses exhibit good luminescence properties and are suitable for generation of white light.

Design and characterization of a 30-GHz bandwidth low-power silicon traveling-wave modulator

Abstract: We present the design and characterization of a silicon PN junction traveling-wave Mach–Zehnder modulator near 1550 nm wavelength. The device shows 30 GHz bandwidth at 1 V reverse bias, with a 2.7 V-cm V π L π and accordingly a 9-V small-signal V π . The insertion loss of the phase shifter is 3.6 dB±0.4 dB. The device performance metrics in combination show significant improvement compared to the state-of-the-art in the sense that lower phase shifter loss and higher bandwidth are achieved for the same V π or vice versa. We demonstrated low modulation power of 640-fJ/bit at 40 Gb/s with a 1.6- V pp differential-drive and 0-V DC bias, raising the prospect of direct compatibility with CMOS drive-voltages. Critical design tradeoffs are analyzed and design models are validated with measurement results. We proposed a new figure-of-merit (FOM) V π L π R pn C 2 pn as the junction design merit for high-speed traveling-wave modulators, and utilized 6 implants to achieve an optimal FOM with lower insertion loss. Several key RF design issues are addressed for the first time using simulation and measurement results. In particular, we discussed bandwidth extension using mismatched termination and closely matched experimental results. A bandwidth-limiting RF multi-mode behavior is noted, which also exists in other results in the literature; we suggested a widely applicable design remedy.

Silicon-on-sapphire waveguides design for mid-IR evanescent field absorption gas sensors

Abstract: Major trace gases have absorption lines in mid-IR. We propose silicon-on-sapphire waveguides at mid-IR for gas sensing based on evanescent field absorption. This can provide a general platform for multipurpose sensing of different types of gases in a reusable fashion. Three types of waveguides (strip, rib and slot) are investigated on their geometrical dependence of evanescent-field ratio (EFR) and propagation loss to serve as the proposed gas sensor. Slot waveguide provides the highest EFR (>25%) in mid-IR with moderate dimension, but its fabrication can be more challenging and its high loss (~10 dB/cm) impairs the sensing resolution and necessitates higher input power in longer waveguides. Strip and rib waveguides can achieve similar EFR with smaller dimensions. We analyze the detection of CO2 in atmosphere based on its mid-IR absorption peak at ~4.23 µm as a case study. Numerical analysis based on up-to-date commercial mid-IR detector parameters shows that a resolution of 2 ppm, 5 ppm and 50 ppm can be achieved in cooled InSb, room-temperature HgCdTe and room-temperature PbSe detectors respectively by using 1 cm waveguides. Effect of waveguide loss also has been investigated.

Toward fJ/bit optical communication in a chip

Abstract: This article reviews our recent studies of ultralow-power nanophotonics devices toward implementing a dense optical communication network in a processor chip A photonic crystal nanocavity that has a very large Q/V is a very promising tool for reducing the energy consumption and footprint related to this goal We demonstrate that, to fully exploit this merit, it is essential to introduce appropriate cavity designs and device structures tailored for each device type In this article, we report several examples of photonic-crystal nanocavity devices that exhibit record low consumption energy/power and explain how we have achieved the performance that we describe These results indicate that current technology enables us to integrate a large number of various wavelength-sized photonic devices with extremely low energy consumption, which will lead to fJ/bit-level optical communication in a chip

Photonic crystal structures for light trapping in thin-film Si solar cells: Modeling, process and optimizations

Abstract: In this paper, we present our efforts on studying light trapping in thin-film silicon solar cells using photonic crystal (PC) based structures. Specifically, we propose a photonic backside texture combining periodic gratings and a distributed Bragg reflector (DBR). The mechanisms of this integrated photonic design are theoretically studied and compared with conventional PCs. We experimentally fabricate the texture using lithographic and self-assembled method on thin-film single crystalline Si (c-Si) and micro-crystalline Si (μc-Si) cells. We analyze the effects of the photonic textures on different cells and demonstrate the performance improvements. A numerical method is developed to explore the optimal multiscale textured surface and investigate light trapping limits in the wave optics regime. Using a detailed balance analysis, we show that it is possible to reach over 20% efficiency for 1.5 μm Si cells through optimal device design and fabrication.

Hybrid amorphous silicon (a-Si:H)–LiNbO3 electro-optic modulator

Abstract: Here we report the demonstration of a GHz-speed Lithium Niobate (LiNbO3) modulator that uses an amorphous Silicon waveguide to strongly confine light. The compact (

A pixel based multi-focus image fusion method

Abstract: The lenses used in computer vision systems by nature provide limited depth of field, so digital cameras are incapable of acquiring an all-in-focus image of objects at varying distances in a scene. To obtain an all-in-focus image of such scenes from their differently focused images, this paper proposes a novel spatial domain multi focus image fusion technique. The developed technique, firstly, computes the point spread functions (PSF) of the source images. Next, the images are artificially blurred by convolving them with the estimated PSFs. Then, the artificially blurred images are used to determine the sharpest pixels of the source images. Finally, the all-in-focus image of the scene is constructed by gathering the sharpest pixels of the source images. Experiments are carried out on several multi-focus image sets. The proposed method and other well-known image fusion methods are compared in terms of visual and quantitative evaluation. The results obtained show the feasibility of the developed technique.

Curvature sensor based on two cascading abrupt-tapers modal interferometer in single mode fiber

Abstract: A curvature sensor based on two cascading abrupt-tapers modal interferometer in a single mode fiber (SMF) is proposed and experimentally demonstrated in this paper. The device consists of two cascading abrupt-tapers with different sizes, manufactured by CO2 laser in a standard SMF. The cladding modes will be excited in the first abrupt-taper section, partly coupled with the core mode. After propagation of these coupled modes, they will recombine at the second abrupt-taper section. The experimental results show that the optimum visibility of interference fringe can be got only when the two abrupt-tapers are at different sizes. If we bend the proposed modal interference, part of the cladding modes will be leaked out, making the interference pattern having a shift. Thus it can be used to measure curvature. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivities are −13.176 nm/m−1 in the measurement ranges of 4.8 m−1 to 6.38 m−1. As the curvature continues to increase, ranging from 6.38 m−1 to 7.98 m−1, the sensitivity is doubled to −25.946 nm/m−1. Moreover, this curvature sensor can be seen low sensitive to either the external refractive index or the temperature when employing in a relatively stable environment. The proposed curvature sensor is simple-fabricated and inexpensive, which is very suitable for curvature measurement in practical applications.

A hybrid-system approach for W state and cluster state generation

Abstract: Here we demonstrate an efficient scheme for W state and cluster state generation based on the hybrid-system where nitrogen-vacancy centers are coupled to microcavities. In our proposed scheme, entanglement between solid-state qubits can be generated with the assistance of an ancillary photon. We also discuss the efficiency of the entanglement generation protocols and generalize them to multi-qubit cases. With current and near-future technology, the entanglement of nitrogen-vacancy centers can be achieved and our scheme can further be used for quantum information processing and long-distance quantum communication.

The sensing characteristics of plasmonic waveguide with a single defect

Abstract: A novel two-dimensional nanoscale structure for sensing which consists of a metal–insulator–metal (MIM) waveguide with a defect, is designed and numerically simulated by using the finite element method (FEM). Both of the refractive index sensing characteristics and the temperature sensing characteristics of the structure are analyzed systematically by investigating the transmission spectrum. The numerically simulated results show that the dip positions of the transmission spectrum have linear relationships with the refractive index of the material under sensing and the ambient temperature, respectively. Based on the relationships, the refractive index of the material under sensing or the ambient temperature can be obtained from the dip wavelength shift detection. When the width and the height of the defect are set to be 50 nm, 300 nm, respectively, the refractive index sensitivity can be obtained as high as 1736 nm RIU −1 and the temperature sensitivity is about 0.51 nm/°C with a FOM of 9.79. This work has a certain significance for designing nanoscale refractive index sensors and temperature sensors.

Symbol synchronization and sampling frequency synchronization techniques in real-time DDO-OFDM systems

Abstract: In this paper, we propose and experimentally demonstrate a symbol synchronization and sampling frequency synchronization techniques in real-time direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) system, over 100-km standard single mode fiber (SSMF) using a cost-effective directly modulated distributed feedback (DFB) laser. The experiment results show that the proposed symbol synchronization based on training sequence (TS) has a low complexity and high accuracy even at a sampling frequency offset (SFO) of 5000-ppm. Meanwhile, the proposed pilot-assisted sampling frequency synchronization between digital-to-analog converter (DAC) and analog-to-digital converter (ADC) is capable of estimating SFOs with an accuracy of

Linear and nonlinear intra-conduction band optical absorption in (In,Ga)N/GaN spherical QD under hydrostatic pressure

Abstract: Linear, third-order nonlinear and total optical absorption coefficients of intra-conduction band 1s–1p transition with hydrogenic shallow-donor impurity in wurtzite (In,Ga)N/GaN spherical quantum dot are reported. Hydrostatic pressure effect is investigated within the framework of single band effective-mass approximation using a combination of Quantum Genetic Algorithm (QGA) and Hartree–Fock–Roothaan (HFR) method. The results show that the pressure has a great influence on optical absorption coefficients of QDs. A blue-shift of the resonant peak is observed while the maximum of the amplitude of optical absorption coefficients decreases under hydrostatic pressure effect. A good agreement is shown compared with results of the finding.

Plasmonic wavelength demultiplexers based on tunable Fano resonance in coupled-resonator systems

Abstract: We investigate a plasmonic waveguide system using a 2-dimension finite element method, which consists of a metal-insulator-metal waveguide coupled with a stub resonator and a baffle. Numerical simulations results show that the sharp and asymmetric Fano-line shapes can be created by placing a baffle into the waveguide, and the main dependent factors of Fano-like spectra response are discussed. Based on the above results, we design three kinds of plasmonic waveguides with possible applications in wavelength demultiplexing. An analytic model based on the transfer matrix formalism is utilized to describe and explain this phenomenon. These results could be applied for developing ultra-compact wavelength division multiplexing devices in highly all-optical integration system.

Optical bistability and multistability via biexciton coherence in semiconductor quantum well nanostructure

Abstract: In this paper, we report theoretical investigation of controlling the optical bistability (OB) and optical multistability (OM) in a GaAs quantum well inside a unidirectional ring cavity. In this scheme quantum interference is raised by a control pulse that couples to a resonance of a biexcitons. It is shown that many-particle interactions which are natural in semiconductors can be used to creation of quantum coherence. In this case optical bistability and multistability can be controlled by biexciton energy renormalization which resulted from many-particle coulomb interactions.

A circuit method to integrate metamaterial and graphene in absorber design

Abstract: We theoretically investigate a circuit analog approach to integrate graphene and metamaterial in electromagnetic wave absorber design. In multilayer graphene-metamaterial (GM) absorbers, ultrathin metamaterial elements are theoretically modeled as equivalent loads which attached to the junctions between two transmission lines. Combining with the benefits of tunable chemical potential in graphene, an optimized GM absorber is proposed as a proof of the circuit method. Numerical simulation results demonstrate the effectiveness of the circuit analytical model. The operating frequency of the GM absorber can be varied in terahertz frequency, indicating the potential applications of the GM absorber in sensors, modulators, and filters.

Modeling the spatial shape of nondiffracting beams: Experimental generation of Frozen Waves via holographic method

Abstract: In this paper we experimentally implement the spatial shape modeling of nondiffracting optical beams via computer generated holograms reconstructed optically by spatial light modulators. The results reported here are an experimental confirmation of the so-called Frozen Wave method, developed a few years ago. Optical beams of this type have potential applications in optical tweezers, medicine, atom guiding, remote sensing, etc.

Target tracking in nonuniform illumination conditions using locally adaptive correlation filters

Abstract: An accurate method for tracking the position and orientation of a moving target in nonuniformly illuminated and noisy scenes is proposed. The approach employs a filter bank of space-variant correlation filters which adapt their parameters accordingly with local statistics of the observed scene in each frame. When a scene frame is captured, a fragment of interest is extracted from the frame around predicted coordinates of the target location. The fragment is firstly preprocessed to correct the illumination. Afterwards, the location and orientation of the target are estimated from the corrected fragment with the help of the filter bank. The performance of the proposed system in terms of tracking accuracy is tested in nonuniformly illuminated and noisy scene sequences. The obtained results are discussed and compared with those of similar state-of-the-art techniques for target tracking in terms of objective metrics.

A development of two-dimensional birefringence distribution measurement system with a sampling rate of 1.3 MHz

Abstract: A two-dimensional birefringence distribution measurement system with a sampling rate of 1.3 MHz is proposed. A polarization image sensor is developed as core device of the system. It is composed of a pixelated polarizer array made from photonic crystal and a parallel read out circuit with a multi-channel analog to digital converter specialized for two-dimensional polarization detection. By applying phase shifting algorism with circularly-polarized incident light, birefringence phase difference and azimuthal angle can be measured. The performance of the system is demonstrated experimentally by measuring actual birefringence distribution and polarization device such as Babinet–Soleil compensator.

Improved empirical mode decomposition based denoising method for lidar signals

Abstract: Based on the physical significance of intrinsic mode functions (IMFs) and the noise component removed from the empirical mode decomposition (EMD) method, the denoising process of the lidar (CE370-2, Cimel) backscattering signal is analyzed in detail. Two parameters, typical range (TR) and low-frequency fraction (LFF) are suggested as the reference principles to decide how many high-frequency IMFs should be removed as noise. TR represents the major spatial range of each IMF, which increases with the decrease in the frequency of IMFs; LFF represents the relative value of the low-frequency component of the removed component, which increases as more IMFs are removed. The simulated signals show that the cloud layer altitudes and intensities impact little on the noise reduction processes. Based on an appropriate amount of lidar data, thresholds for TR and LFF are provided, respectively, for various weather conditions: 0.330 and 0.276 for clear sky conditions, 0.460 and 0.517 for cloudy conditions, 0.331 and 0.316 for dusty conditions, and 0.327 and 0.310 for polluted conditions. These thresholds are applied to the automatic data-denoising algorithm. Only 3.9% of the data encounters a numerical calculation error for the clear sky conditions, and the percentage increases to 8.5% for cloudy conditions, which is also acceptable. It turns out that the automatic EMD denoising method has a better denoising performance than that of the wavelet method.

Analysis of PolSK based FSO system using wavelength and time diversity over strong atmospheric turbulence with pointing errors

Abstract: Free space optics (FSO) or wireless optical communication systems is an evolving alternative to the current radio frequency (RF) links due to its high and secure datarates, large license free bandwidth access, ease of installation, and lower cost for shorter range distances. These systems are largely influenced by atmospheric conditions due to wireless transmission; requirement of line of sight (LOS) propagation may lead to alignment problems in turn pointing errors. In this paper, we consider atmospheric turbulence and pointing errors are the major limitations. We tried to address these difficulties by considering polarization shift keying (PolSK) modulated FSO communication system with wavelength and time diversity. We derived the closed form expressions for estimation of the average bit error rate (BER) and outage probability, which are vital system performance metrics. Analytical results are shown considering different practical cases.

Implementation of sequential logic circuits using the Mach-Zehnder interferometer structure based on electro-optic effect

Abstract: The electro-optic effect is one of the most important phenomena in Mach–Zehnder (MZI) interferometer structure. The Mach–Zehnder interferometer structure working on the principle of electro-optic effect behaves as the powerful optical switching device. The paper contains the discussion of electro-optic effect based MZI structure. The proper feedback mechanism with the delay unit provides the responses of optical clocked D flip-flop. The paper includes the detailed mathematical description of optical clocked D flip-flops with the MATLAB simulation result. Based on the proposed optical D-flip flop, it is possible to construct some sequential circuits such as synchronous shift registers and ripple counters. Finally, the paper includes the detailed discussion of optical sequential circuits such as synchronous shift register and ripple counter and its implementation using the MATLAB simulation. However, the concept of proposed optical clocked D flip-flop is implemented using the OptiBPM software for the proper verification of the discussed schemes. The Basic building block structures are analyzed to check the optimum performance parameters such as crosstalk, power imbalance, extinction ratio and transition losses, in order to obtain the appropriate Ti-thickness and switching voltage.