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Showing papers in "Optics Express in 2013"


Journal ArticleDOI
TL;DR: It is shown that strong photoluminescence emission is caused by the transition from an indirect band gap semiconductor of bulk material to a direct bandgap semiconductor in atomically thin form.
Abstract: We mechanically exfoliate mono- and few-layers of the transition metal dichalcogenides molybdenum disulfide, molybdenum diselenide, and tungsten diselenide. The exact number of layers is unambiguously determined by atomic force microscopy and high-resolution Raman spectroscopy. Strong photoluminescence emission is caused by the transition from an indirect band gap semiconductor of bulk material to a direct band gap semiconductor in atomically thin form.

1,290 citations


Journal ArticleDOI
TL;DR: A graphene based perfect absorber is demonstrated and the properties of graphene wire medium and graphene fishnet metamaterials are investigated and both narrowband and broadband tunable absorbers are demonstrated.
Abstract: In this paper we present the efficient design of functional thin-film metamaterial devices with the effective surface conductivity approach. As an example, we demonstrate a graphene based perfect absorber. After formulating the requirements to the perfect absorber in terms of surface conductivity we investigate the properties of graphene wire medium and graphene fishnet metamaterials and demonstrate both narrowband and broadband tunable absorbers.

526 citations


Journal ArticleDOI
TL;DR: An optical model for light field microscopy based on wave optics, instead of previously reported ray optics models is presented, and a 3-D deconvolution method is presented that is able to reconstruct volumes at higher spatial resolution, and with better optical sectioning, than previously reported.
Abstract: Light field microscopy is a new technique for high-speed volumetric imaging of weakly scattering or fluorescent specimens It employs an array of microlenses to trade off spatial resolution against angular resolution, thereby allowing a 4-D light field to be captured using a single photographic exposure without the need for scanning The recorded light field can then be used to computationally reconstruct a full volume In this paper, we present an optical model for light field microscopy based on wave optics, instead of previously reported ray optics models We also present a 3-D deconvolution method for light field microscopy that is able to reconstruct volumes at higher spatial resolution, and with better optical sectioning, than previously reported To accomplish this, we take advantage of the dense spatio-angular sampling provided by a microlens array at axial positions away from the native object plane This dense sampling permits us to decode aliasing present in the light field to reconstruct high-frequency information We formulate our method as an inverse problem for reconstructing the 3-D volume, which we solve using a GPU-accelerated iterative algorithm Theoretical limits on the depth-dependent lateral resolution of the reconstructed volumes are derived We show that these limits are in good agreement with experimental results on a standard USAF 1951 resolution target Finally, we present 3-D reconstructions of pollen grains that demonstrate the improvements in fidelity made possible by our method

472 citations


Journal ArticleDOI
TL;DR: This work presents an adjoint-based optimization for electromagnetic design that embeds commercial Maxwell solvers within a steepest-descent inverse-design optimization algorithm, and finds that convergence is much faster, within a larger design space.
Abstract: We present an adjoint-based optimization for electromagnetic design. It embeds commercial Maxwell solvers within a steepest-descent inverse-design optimization algorithm. The adjoint approach calculates shape derivatives at all points in space, but requires only two “forward” simulations. Geometrical shape parameterization is by the level set method. Our adjoint design optimization is applied to a Silicon photonics Y-junction splitter that had previously been investigated by stochastic methods. Owing to the speed of calculating shape derivatives within the adjoint method, convergence is much faster, within a larger design space. This is an extremely efficient method for the design of complex electromagnetic components.

469 citations


Journal ArticleDOI
TL;DR: X-ray diffraction measurements show that synthesized Cu( 2)O thin films grow on c-sapphire substrate with preferred (111) orientation, and the performance of Cu(2)O films is poorer compared to that ofCu(2),O using RF power of 0.1 V.
Abstract: Cuprous oxide (Cu2O) films synthesis by radical oxidation with nitrogen (N2) plasma treatment and different RF power at low temperature (500°C) are studied in this paper. X-ray diffraction measurements show that synthesized Cu2O thin films grow on c-sapphire substrate with preferred (111) orientation. With nitrogen (N2) plasma treatment, the optical bandgap energy is increased from 1.69 to 2.42 eV, when N2 plasma treatment time is increased from 0 min to 40 min. Although the hole density is increased from 1014 to 1015 cm−3 and the resistivity is decreased from 1879 to 780Ωcm after N2 plasma treatment, the performance of Cu2O films is poorer compared to that of Cu2O using RF power of 0. The fabricated ZnO/Cu2O solar cells based on Cu2O films with RF power of 0 W show a good rectifying behavior with a efficiency of 0.02%, an open-circuit voltage of 0.1 V, and a fill factor of 24%.

398 citations


Journal ArticleDOI
TL;DR: A novel on-chip two-mode division multiplexing circuit using a tapered directional coupler-based TE(0)&TE(1) mode multiplexer and demultiplexer on the silicon-on-insulator platform is demonstrated.
Abstract: We demonstrate a novel on-chip two-mode division multiplexing circuit using a tapered directional coupler-based TE(0)&TE(1) mode multiplexer and demultiplexer on the silicon-on-insulator platform. A low insertion loss (0.3 dB), low mode crosstalk (< -16 dB), wide bandwidth (~100 nm), and large fabrication tolerance (20 nm) are measured. An on-chip mode multiplexing experiment is carried out on the fabricated circuit with non return-to-zero (NRZ) on-off keying (OOK) signals at 40 Gbit/s. The experimental results show clear eye diagrams and moderate power penalty for both TE(0) and TE(1) modes.

373 citations


Journal ArticleDOI
TL;DR: Recent progress in terahertz wireless communications using telecom-based photonics technologies towards 100 Gbit/s is reviewed.
Abstract: There has been an increasing interest in the application of terahertz (THz) waves to broadband wireless communications. In particular, use of frequencies above 275 GHz is one of the strong concerns among radio scientists and engineers, because these frequency bands have not yet been allocated at specific active services, and there is a possibility to employ extremely large bandwidths for ultra-broadband wireless communications. Introduction of photonics technologies for signal generation, modulation and detection is effective not only to enhance the bandwidth and/or the data rate, but also to combine fiber-optic (wired) and wireless networks. This paper reviews recent progress in THz wireless communications using telecom-based photonics technologies towards 100 Gbit/s.

371 citations


Journal ArticleDOI
TL;DR: This work uses mechanical translation of a coded aperture for code division multiple access compression of video to discuss the compressed video's temporal resolution and present experimental results for reconstructions of > 10 frames of temporal data per coded snapshot.
Abstract: We use mechanical translation of a coded aperture for code division multiple access compression of video. We discuss the compressed video’s temporal resolution and present experimental results for reconstructions of > 10 frames of temporal data per coded snapshot.

354 citations


Journal ArticleDOI
TL;DR: This work systematically study the influence of particle geometry and dielectric environment on the resonant behavior of dielectrics resonators in the visible to near-IR spectral range, and shows that the directional radiation profiles of the ED and MD modes in resonators on a substrate are similar to those of point-dipoles close to a substrate.
Abstract: High-performance integrated optics, solar cells, and sensors require nanoscale optical components at the surface of the device, in order to manipulate, redirect and concentrate light. High-index dielectric resonators provide the possibility to do this efficiently with low absorption losses. The resonances supported by dielectric resonators are both magnetic and electric in nature. Combined scattering from these two can be used for directional scattering. Most applications require strong coupling between the particles and the substrate in order to enhance the absorption in the substrate. However, the coupling with the substrate strongly influences the resonant behavior of the particles. Here, we systematically study the influence of particle geometry and dielectric environment on the resonant behavior of dielectric resonators in the visible to near-IR spectral range. We show the key role of retardation in the excitation of the magnetic dipole (MD) mode, as well as the limit where no MD mode is supported. Furthermore, we study the influence of particle diameter, shape and substrate index on the spectral position, width and overlap of the electric dipole (ED) and MD modes. Also, we show that the ED and MD mode can selectively be enhanced or suppressed using multi-layer substrates. And, by comparing dipole excitation and plane wave excitation, we study the influence of driving field on the scattering properties. Finally, we show that the directional radiation profiles of the ED and MD modes in resonators on a substrate are similar to those of point-dipoles close to a substrate. Altogether, this work is a guideline how to tune magnetic and electric resonances for specific applications.

335 citations


Journal ArticleDOI
TL;DR: This work has built a light-sheet microscope that uses remote focusing with an electrically tunable lens (ETL) and achieves flexible volume imaging at much higher speeds than previously reported.
Abstract: The in-vivo investigation of highly dynamic biological samples, for example the beating zebrafish heart, requires high-speed volume imaging techniques. Light-sheet microscopy is ideal for such samples as it records high-contrast images of entire planes within large samples at once. However, in order to obtain images of different planes, it has been necessary to move the sample relative to the fixed focal plane of the detection objective lens. This mechanical movement limits speed, precision and may be harmful to the sample. We have built a light-sheet microscope that uses remote focusing with an electrically tunable lens (ETL). Without moving specimen or objective we have thereby achieved flexible volume imaging at much higher speeds than previously reported. Our high-speed microscope delivers 3D snapshots of sensitive biological samples. As an example, we imaged 17 planes within a beating zebrafish heart at 510 frames per second, equivalent to 30 volume scans per second. Movements, shape changes and signals across the entire volume can be followed which has been impossible with existing reconstruction techniques.

331 citations


Journal ArticleDOI
TL;DR: 1-to-8 wavelength (de-)multiplexer devices based on a binary tree of cascaded Mach-Zehnder-like lattice filters, and manufactured using a 90 nm CMOS-integrated silicon photonics technology, demonstrate that they combine a flat pass-band over more than 50% of the channel spacing with low insertion loss.
Abstract: We present 1-to-8 wavelength (de-)multiplexer devices based on a binary tree of cascaded Mach-Zehnder-like lattice filters, and manufactured using a 90 nm CMOS-integrated silicon photonics technology. We demonstrate that these devices combine a flat pass-band over more than 50% of the channel spacing with low insertion loss of less than 1.6 dB, and have a small device size of approximately 500 × 400 µm. This makes this type of filters well suited for application as WDM (de-)multiplexer in silicon photonics transceivers for optical data communication in large scale computer systems.

Journal ArticleDOI
TL;DR: A figure-of-merit is proposed to fairly compare the performance of Brillouin distributed sensing systems and offers the research community and potential users the possibility to evaluate with an objective metric the real performance gain resulting from any proposed configuration.
Abstract: A thorough analysis of the key factors impacting on the performance of Brillouin distributed optical fiber sensors is presented. An analytical expression is derived to estimate the error on the determination of the Brillouin peak gain frequency, based for the first time on real experimental conditions. This expression is experimentally validated, and describes how this frequency uncertainty depends on measurement parameters, such as Brillouin gain linewidth, frequency scanning step and signal-to-noise ratio. Based on the model leading to this expression and considering the limitations imposed by nonlinear effects and pump depletion, a figure-of-merit is proposed to fairly compare the performance of Brillouin distributed sensing systems. This figure-of-merit offers to the research community and to potential users the possibility to evaluate with an objective metric the real performance gain resulting from any proposed configuration.

Journal ArticleDOI
TL;DR: In this paper, a few-layer TI: Bi2Se3 (2-4 layer thickness) is firstly fabricated by the liquid-phase exfoliation method, and has a low saturable optical intensity of 53 MW/cm2 measured by the Z-scan technique.
Abstract: Passive Q-switching of an ytterbium-doped fiber (YDF) laser with few-layer topological insulator (TI) is, to the best of our knowledge, experimentally demonstrated for the first time. The few-layer TI: Bi2Se3 (2–4 layer thickness) is firstly fabricated by the liquid-phase exfoliation method, and has a low saturable optical intensity of 53 MW/cm2 measured by the Z-scan technique. The optical deposition technique is used to induce the few-layer TI in the solution onto a fiber ferrule for successfully constructing the fiber-integrated TI-based saturable absorber (SA). By inserting this SA into the YDF laser cavity, stable Q-switching operation at 1.06 μm is achieved. The Q-switched pulses have the shortest pulse duration of 1.95 μs, the maximum pulse energy of 17.9 nJ and a tunable pulse-repetition-rate from 8.3 to 29.1 kHz. Our results indicate that the TI as a SA is also available at 1 μm waveband, revealing its potential as another broadband SA (like graphene).

Journal ArticleDOI
Yuanquan Wang1, Yiguang Wang1, Nan Chi1, Jianjun Yu1, Huiliang Shang1 
TL;DR: This work proposes and experimentally demonstrate a novel full-duplex bi-directional subcarrier multiplexing (SCM)-wavelength division multiplexed (WDM) visible light communication (VLC) system based on commercially available red-green-blue (RGB) light emitting diode (LED) and phosphor-based LED (P-LED) with 575-Mb/s upstream transmission.
Abstract: We propose and experimentally demonstrate a novel full-duplex bi-directional subcarrier multiplexing (SCM)-wavelength division multiplexing (WDM) visible light communication (VLC) system based on commercially available red-green-blue (RGB) light emitting diode (LED) and phosphor-based LED (P-LED) with 575-Mb/s downstream and 225-Mb/s upstream transmission, employing various modulation orders of quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM). For the downlink, red and green colors/wavelengths are assigned to carry useful information, while blue chip is just kept lighting to maintain the white color illumination, and for the uplink, the low-cost P-LED is implemented. In this demonstration, pre-equalization and post-equalization are also adopted to compensate the severe frequency response of LEDs. Using this scheme, 4-user downlink and 1-user uplink transmission can be achieved. Furthermore, it can support more users by adjusting the bandwidth of each sub-channel. Bit error rates (BERs) of all links are below pre-forward-error-correction (pre-FEC) threshold of 3.8x 10−3 after 66-cm free-space delivery. The results show that this scheme has great potential in the practical VLC system.

Journal ArticleDOI
TL;DR: In this article, the authors study the properties of nonlinear interference noise (NLIN) in fiber-optic communications systems with large accumulated dispersion, and derive the true NLIN power and verify that the NLIN is not additive Gaussian, but rather it depends strongly on the data transmitted in the channel of interest.
Abstract: We study the properties of nonlinear interference noise (NLIN) in fiber-optic communications systems with large accumulated dispersion. Our focus is on settling the discrepancy between the results of the Gaussian noise (GN) model (according to which NLIN is additive Gaussian) and a recently published time-domain analysis, which attributes drastically different properties to the NLIN. Upon reviewing the two approaches we identify several unjustified assumptions that are key in the derivation of the GN model, and that are responsible for the discrepancy. We derive the true NLIN power and verify that the NLIN is not additive Gaussian, but rather it depends strongly on the data transmitted in the channel of interest. In addition we validate the time-domain model numerically and demonstrate the strong dependence of the NLIN on the interfering channels' modulation format.

Journal ArticleDOI
TL;DR: Recent new methods in wideband signal processors including high-resolution, arbitrary response, low noise, programmable processing, beamforming, and ultra-wide continuous filter tunability, are presented.
Abstract: Photonic signal processing offers the advantages of large time-bandwidth capabilities to overcome inherent electronic limitations. In-fibre signal processors are inherently compatible with fibre optic microwave systems that can integrate with wireless antennas, and can provide connectivity with in-built signal conditioning and electromagnetic interference immunity. Recent methods in wideband and adaptive signal processing, which address the challenge of realising programmable microwave photonic phase shifters and true-time delay elements for phased array beamforming; ultra-wideband Hilbert transformers; single passband, widely tunable, and switchable microwave photonic filters; and ultra-wideband microwave photonic mixers, are described. In addition, a new microwave photonic mixer structure is presented, which is based on using the inherent frequency selectivity of the stimulated Brillouin scattering loss spectrum to suppress the carrier of a dual-phase modulated optical signal. Results for the new microwave photonic mixer demonstrate an extremely wide bandwidth operation of 0.2 to 20 GHz and a large conversion efficiency improvement compared to the conventional microwave photonic mixer.

Journal ArticleDOI
TL;DR: Through the analysis of membrane deformation within geometrical constraints, it is shown that by selecting appropriate lens dimensions, even larger focusing dynamic ranges can be achieved.
Abstract: Focus tunable, adaptive lenses provide several advantages over traditional lens assemblies in terms of compactness, cost, efficiency, and flexibility. To further improve the simplicity and compact nature of adaptive lenses, we present an elastomer-liquid lens system which makes use of an inline, transparent electroactive polymer actuator. The lens requires only a minimal number of components: a frame, a passive membrane, a dielectric elastomer actuator membrane, and a clear liquid. The focal length variation was recorded to be greater than 100% with this system, responding in less than one second. Through the analysis of membrane deformation within geometrical constraints, it is shown that by selecting appropriate lens dimensions, even larger focusing dynamic ranges can be achieved.

Journal ArticleDOI
TL;DR: It is shown how a combination of metal nanobrick and nanocross elements allows one to fully control the phase of reflected light for two orthogonal polarizations simultaneously, in relation to birefringent metal-backed metasurfaces.
Abstract: We numerically study the optical properties of metal-insulator-metal resonators and metasurfaces, emphasizing the presence of gap-surface plasmon (GSP) resonances and their connection to the optical response. In relation to birefringent metal-backed metasurfaces, we show how a combination of metal nanobrick and nanocross elements allows one to fully control the phase of reflected light for two orthogonal polarizations simultaneously. The approach is exemplified by the design of a gradient birefringent metasurface that reflects two orthogonal polarization states into +2 and −3 diffraction order, respectively, with a reflectivity up to ∼ 80% and in a broad wavelength range around the design wavelength of 800 nm. Finally, we introduce the concept of metascatterers, which are wavelength-sized polarization-sensitive scatterers.

Journal ArticleDOI
TL;DR: This paper demonstrates the light transmission in a spectral range of 2.5 to 7.9 µm through a silica negative curvature hollow core fiber (NCHCF) with a cladding consisting of eight capillaries with a separation between the cladding capillary was introduced to remove the additional resonances in the transmission bands.
Abstract: In this paper we demonstrate the light transmission in a spectral range of 2.5 to 7.9 µm through a silica negative curvature hollow core fiber (NCHCF) with a cladding consisting of eight capillaries. A separation between the cladding capillaries was introduced to remove the additional resonances in the transmission bands. The measured optical loss at 3.39 µm was about 50 dB/km under a few modes waveguide regime.

Journal ArticleDOI
TL;DR: An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor platform was demonstrated for detection of carbon monoxide and nitrous oxide and the presence of water vapor increases the detected CO and N2O QEPAS signal levels as a result of enhancing the vibrational-translational relaxation rate of both target gases.
Abstract: An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor platform was demonstrated for detection of carbon monoxide (CO) and nitrous oxide (N2O). This sensor used a state-of-the art 4.61 μm high power, continuous wave (CW), distributed feedback quantum cascade laser (DFB-QCL) operating at 10°C as the excitation source. For the R(6) CO absorption line, located at 2169.2 cm−1, a minimum detection limit (MDL) of 1.5 parts per billion by volume (ppbv) at atmospheric pressure was achieved with a 1 sec acquisition time and the addition of 2.6% water vapor concentration in the analyzed gas mixture. For the N2O detection, a MDL of 23 ppbv was obtained at an optimum gas pressure of 100 Torr and with the same water vapor content of 2.6%. In both cases the presence of water vapor increases the detected CO and N2O QEPAS signal levels as a result of enhancing the vibrational-translational relaxation rate of both target gases. Allan deviation analyses were performed to investigate the long term performance of the CO and N2O QEPAS sensor systems. For the optimum data acquisition time of 500 sec a MDL of 340 pptv and 4 ppbv was obtained for CO and N2O detection, respectively. To demonstrate reliable and robust operation of the QEPAS sensor a continuous monitoring of atmospheric CO and N2O concentration levels for a period of 5 hours were performed.

PatentDOI
TL;DR: In this article, a low-loss and wavelength insensitive Y-junction for submicron silicon waveguides was proposed using FDTD and particle swarm optimization (PSO).
Abstract: A compact, low-loss and wavelength insensitive Y-junction for submicron silicon waveguides. The design was performed using FDTD and particle swarm optimization (PSO). The device was fabricated in a 248 nm CMOS line. Measured average insertion loss is 0.28±0.02 dB across an 8-inch wafer. The device footprint is less than 1.2 μm×2 μm, orders of magnitude smaller than MMI and directional couplers.

Journal ArticleDOI
TL;DR: The near-perfect absorptions of dual, triple and quad peaks are persistent with polarization independence, and the effect of angle of incidence for both TE and TM modes was also elucidated.
Abstract: We propose multi-band metamaterial absorbers at microwave frequencies. The design, the analysis, the fabrication, and the measurement of the absorbers working in multiple bands are presented. The numerical simulations and the experiments in the microwave anechoic chamber were performed. The metamaterial absorbers consist of an delicate arrangement of donut-shape resonators with different sizes and a metallic background plane, separated by a dielectric. The near-perfect absorptions of dual, triple and quad peaks are persistent with polarization independence, and the effect of angle of incidence for both TE and TM modes was also elucidated. It was also found that the multiple-reflection theory was not suitable for explaining the absorption mechanism of our investigated structures. The results of this study are promising for the practical applications.

Journal ArticleDOI
TL;DR: The concept, analysis, and design of series switches for graphene-strip plasmonic waveguides at near infrared frequencies are presented and the performance of the switch is evaluated versus different parameters of the structure, including surrounding dielectric media, electrostatic gating and waveguide dimensions.
Abstract: The concept, analysis, and design of series switches for graphene-strip plasmonic waveguides at near infrared frequencies are presented. Switching is achieved by using graphene's field effect to selectively enable or forbid propagation on a section of the graphene strip waveguide, thereby allowing good transmission or high isolation, respectively. The electromagnetic modeling of the proposed structure is performed using full-wave simulations and a transmission line model combined with a matrix-transfer approach, which takes into account the characteristics of the plasmons supported by the different graphene-strip waveguide sections of the device. The performance of the switch is evaluated versus different parameters of the structure, including surrounding dielectric media, electrostatic gating and waveguide dimensions.

Journal ArticleDOI
TL;DR: The radiative properties of metamaterial nanostructures made of two-dimensional tungsten gratings on a thin dielectric spacer and an opaque tungsen film from UV to mid-infrared region as potential selective solar absorbers will facilitate the design of novel highly efficient solar absorber to enhance the performance of various solar energy conversion systems.
Abstract: In this work, we numerically investigate the radiative properties of metamaterial nanostructures made of two-dimensional tungsten gratings on a thin dielectric spacer and an opaque tungsten film from UV to mid-infrared region as potential selective solar absorbers. The metamaterial absorber with single-sized tungsten patches exhibits high absorptance in the visible and near-infrared region due to several mechanisms such as surface plasmon polaritons, magnetic polaritons, and intrinsic bandgap absorption of tungsten. Geometric effects on the resonance wavelengths and the absorptance spectra are studied, and the physical mechanisms are elucidated in detail. The absorptance could be further enhanced in a broader spectral range with double-sized metamaterial absorbers. The total solar absorptance of the optimized metamaterial absorbers at normal incidence could be more than 88%, while the total emittance is less than 3% at 100°C, resulting in total photon-to-heat conversion efficiency of 86% without any optical concentration. Moreover, the metamaterial solar absorbers exhibit quasi-diffuse behaviors as well as polarization independence. The results here will facilitate the design of novel highly efficient solar absorbers to enhance the performance of various solar energy conversion systems.

Journal ArticleDOI
TL;DR: Earlier theories in the Clemmow's prescription for transformation of the electromagnetic field in hyperbolic media are summarized and a review of recent developments in this active research area is provided.
Abstract: Hyperbolic materials enable numerous surprising applications that include far-field subwavelength imaging, nanolithography, and emission engineering. The wavevector of a plane wave in these media follows the surface of a hyperboloid in contrast to an ellipsoid for conventional anisotropic dielectric. The consequences of hyperbolic dispersion were first studied in the 50’s pertaining to the problems of electromagnetic wave propagation in the Earth’s ionosphere and in the stratified artificial materials of transmission lines. Recent years have brought explosive growth in optics and photonics of hyperbolic media based on metamaterials across the optical spectrum. Here we summarize earlier theories in the Clemmow’s prescription for transformation of the electromagnetic field in hyperbolic media and provide a review of recent developments in this active research area.

Journal ArticleDOI
Abstract: The third order nonlinear optical property of Bi2Se3, a kind of topological insulator (TI), has been investigated under femto-second laser excitation. The open and closed aperture Z-scan measurements were used to unambiguously distinguish the real and imaginary part of the third order optical nonlinearity of the TI. When excited at 800 nm, the TI exhibits saturable absorption with a saturation intensity of 10.12 GW/cm2 and a modulation depth of 61.2%, and a giant nonlinear refractive index of 10−14 m2/W, almost six orders of magnitude larger than that of bulk dielectrics. This finding suggests that the TI: Bi2Se3 is indeed a promising nonlinear optical material and thus can find potential applications from passive laser mode locker to optical Kerr effect based photonic devices.

Journal ArticleDOI
TL;DR: A method to retrieve and correct position errors during the image reconstruction iterations and improve both the quality of the retrieved object image and the position accuracy requirement while acquiring the diffraction patterns is proposed.
Abstract: Accurate knowledge of translation positions is essential in ptychography to achieve a good image quality and the diffraction limited resolution. We propose a method to retrieve and correct position errors during the image reconstruction iterations. Sub-pixel position accuracy after refinement is shown to be achievable within several tens of iterations. Simulation and experimental results for both optical and X-ray wavelengths are given. The method improves both the quality of the retrieved object image and relaxes the position accuracy requirement while acquiring the diffraction patterns.

Journal ArticleDOI
Elsa Garmire1
TL;DR: Applications of NLO are categorized into three areas: improving lasers, interaction with materials, and information technology: coherent light of different wavelengths; multi-photon absorption for plasma-materials interaction; advanced spectroscopy and materials analysis; and applications to communications and sensors.
Abstract: An overview is presented of the impact of NLO on today’s daily life. While NLO researchers have promised many applications, only a few have changed our lives so far. This paper categorizes applications of NLO into three areas: improving lasers, interaction with materials, and information technology. NLO provides: coherent light of different wavelengths; multi-photon absorption for plasma-materials interaction; advanced spectroscopy and materials analysis; and applications to communications and sensors. Applications in information processing and storage seem less mature.

Journal ArticleDOI
TL;DR: In this paper, the authors introduce the idea of discontinuous electric and magnetic fields at a boundary to design and shape wavefronts in an arbitrary manner, and show how to arbitrarily refract a beam using a set of impedance and admittance surfaces.
Abstract: We introduce the idea of discontinuous electric and magnetic fields at a boundary to design and shape wavefronts in an arbitrary manner. To create this discontinuity in the field we use orthogonal electric and magnetic currents which act like Huygens source to radiate the desired wavefront. These currents can be synthesized either by an array of electric and magnetic dipoles or by a combined impedance and admittance surface. A dipole array is an active implementation to impose discontinuous fields while the impedance/admittance surface acts as a passive one. We then expand on our previous work showing how electric and magnetic dipole arrays can be used to cloak an object demonstrating novel cloaking and anti-cloaking schemes. We also show how to arbitrarily refract a beam using a set of impedance and admittance surfaces. Refraction using the idea of discontinuous fields is shown to be a more general case of refraction than using simple phase discontinuities.

Journal ArticleDOI
TL;DR: A computational method which utilizes the full parameter space to design linear nanophotonic devices which are fully three-dimensional and multi-modal, exhibit novel functionality, have very compact footprints, exhibit high efficiency, and are manufacturable is developed.
Abstract: In contrast to designing nanophotonic devices by tuning a handful of device parameters, we have developed a computational method which utilizes the full parameter space to design linear nanophotonic devices. We show that our method may indeed be capable of designing any linear nanophotonic device by demonstrating designed structures which are fully three-dimensional and multi-modal, exhibit novel functionality, have very compact footprints, exhibit high efficiency, and are manufacturable. In addition, we also demonstrate the ability to produce structures which are strongly robust to wavelength and temperature shift, as well as fabrication error. Critically, we show that our method does not require the user to be a nanophotonic expert or to perform any manual tuning. Instead, we are able to design devices solely based on the user's desired performance specification for the device.