Showing papers in "Optics Express in 2001"
TL;DR: A fully-vectorial, three-dimensional algorithm to compute the definite-frequency eigenstates of Maxwell's equations in arbitrary periodic dielectric structures, including systems with anisotropy or magnetic materials, using preconditioned block-iterative eigensolvers in a planewave basis is described.
Abstract: We describe a fully-vectorial, three-dimensional algorithm to compute the definite-frequency eigenstates of Maxwell's equations in arbitrary periodic dielectric structures, including systems with anisotropy (birefringence) or magnetic materials, using preconditioned block-iterative eigensolvers in a planewave basis. Favorable scaling with the system size and the number of computed bands is exhibited. We propose a new effective dielectric tensor for anisotropic structures, and demonstrate that O Delta x;2 convergence can be achieved even in systems with sharp material discontinuities. We show how it is possible to solve for interior eigenvalues, such as localized defect modes, without computing the many underlying eigenstates. Preconditioned conjugate-gradient Rayleigh-quotient minimization is compared with the Davidson method for eigensolution, and a number of iteration variants and preconditioners are characterized. Our implementation is freely available on the Web.
2,861 citations
TL;DR: An improved method of polarization sensitive optical coherence tomography is presented that enables measurement and imaging of backscattered intensity, birefringence, and fast optic axis orientation simultaneously with only one single A-scan per transverse measurement location.
Abstract: We present an improved method of polarization sensitive optical coherence tomography that enables measurement and imaging of backscattered intensity, birefringence, and fast optic axis orientation simultaneously with only one single A-scan per transverse measurement location. While intensity and birefringence data are obtained in a conventional way, the optic axis orientation is determined from the phase difference recorded in two orthogonal polarization channels. We report on accuracy and precision of the method by measuring birefringence and optic axis orientation of well defined polarization states in a technical object and present maps of birefringence and, what we believe for the first time, of optic axis orientation in biological tissue.
491 citations
TL;DR: Several applications of microstructured optical fibers are presented and their modal characteristics are studied by using Bragg gratings inscribed into photosensitive core regions designed into the air-silica microstructure to enable a number of functionalities including tunability and enhanced nonlinearity.
Abstract: We present several applications of microstructured optical fibers and study their modal characteristics by using Bragg gratings inscribed into photosensitive core regions designed into the air-silica microstructure. The unique characteristics revealed in these studies enable a number of functionalities including tunability and enhanced nonlinearity that provide a platform for fiber device applications. We discuss experimental and numerical tools that allow characterization of the modes of the fibers.
438 citations
TL;DR: A low-loss and highly birefringent polarization maintaining photonic crystal fiber has been fabricated and the fiber loss and modal bireFringence at 1550 nm were 1.3 dB/km and 1.4x10 -3 , respectively.
Abstract: A low-loss and highly birefringent polarization maintaining photonic crystal fiber has been fabricated. The fiber loss and modal birefringence at 1550 nm were 1.3 dB/km and 1.4×10-3, respectively.
435 citations
TL;DR: The light-propagation characteristics of OmniGuide fibers, which guide light by concentric multi-layer dielectric mirrors having the property of omnidirectional reflection, are presented, promising that the properties of silica fibers may be surpassed even when nominally poor materials are employed.
Abstract: We present the light-propagation characteristics of OmniGuide fibers, which guide light by concentric multi-layer dielectric mirrors having the property of omnidirectional reflection. We show how the lowest-loss TE01 mode can propagate in a single-mode fashion through even large-core fibers, with other modes eliminated asymptotically by their higher losses and poor coupling, analogous to hollow metallic microwave waveguides. Dispersion, radiation leakage, material absorption, nonlinearities, bending, acircularity, and interface roughness are considered with the help of leaky modes and perturbation theory, and both numerical results and general scaling relations are presented. We show that cladding properties such as absorption and nonlinearity are suppressed by many orders of magnitude due to the strong confinement in a hollow core, and other imperfections are tolerable, promising that the properties of silica fibers may be surpassed even when nominally poor materials are employed.
396 citations
TL;DR: In this paper, the first microstructured polymer optical fiber is described and both experimental and theoretical evidence is presented to establish that the fibre is effectively single moded at optical wavelengths.
Abstract: The first microstructured polymer optical fibre is described. Both experimental and theoretical evidence is presented to establish that the fibre is effectively single moded at optical wavelengths. Polymer-based microstructured optical fibres offer key advantages over both conventional polymer optical fibres and glass microstructured fibres. The low-cost manufacturability and the chemical flexibility of the polymers provide great potential for applications in data communication networks and for the development of a range of new polymer-based fibre-optic components.
376 citations
TL;DR: This analysis includes a thorough description of the dependence of the fiber geometrical dispersion on the structural parameters of a PCF and established a well-defined procedure to design specific predetermined dispersion profiles.
Abstract: We present a systematic study of group-velocity-dispersion properties in photonic crystal fibers (PCF’s). This analysis includes a thorough description of the dependence of the fiber geometrical dispersion on the structural parameters of a PCF. The interplay between material dispersion and geometrical dispersion allows us to established a well-defined procedure to design specific predetermined dispersion profiles. We focus on flattened, or even ultraflattened, dispersion behaviors both in the telecommunication window (around 1.55 µm) and in the Ti-Za laser wavelength range (around 0.8 µm). We show the different possibilities of obtaining normal, anomalous, and zero dispersion curves in the above frequency domains and discuss the limits for the existence of the above dispersion profiles.
359 citations
TL;DR: The plasmon resonances of interacting silver nanowires with a 50 nm diameter are investigated and a dramatic field enhancement between the particles is observed, where the electric field amplitude reaches a hundredfold of the illumination.
Abstract: We investigate the plasmon resonances of interacting silver nanowires with a 50 nm diameter. Both non–touching and intersecting configurations are investigated. While individual cylinders exhibit a single plasmon resonance, we observe much more complex spectra of resonances for interacting structures. The number and magnitude of the different resonances depend on the illumination direction and on the distance between the particles. For very small separations, we observe a dramatic field enhancement between the particles, where the electric field amplitude reaches a hundredfold of the illumination. A similar enhancement is observed in the grooves created in slightly intersecting particles. The topology of these different resonances is related to the induced polarization charges. The implication of these results to surface enhanced Raman scattering (SERS) are discussed.
333 citations
TL;DR: A model-based iterative image reconstruction scheme that employs adjoint differentiation methods to minimize the difference between measured and predicted data is developed and reported on, the first three-dimensional, volumetric, tomographic localization of vascular reactivity in the brain.
Abstract: We report on the first three-dimensional, volumetric, tomographic localization of vascular reactivity in the brain. To this end we developed a model-based iterative image reconstruction scheme that employs adjoint differentiation methods to minimize the difference between measured and predicted data. The necessary human-head geometry and optode locations were determined with a photogrammetric method. To illustrate the performance of the technique, the three-dimensional distribution of changes in the concentration of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin during a Valsalva maneuver were visualized. The observed results are consistent with previously reported effects concerning optical responses to hemodynamic perturbations.
294 citations
TL;DR: It is shown that this technique can be efficiently used for obtaining quantitative information from the intensity and the phase distributions of the reconstructed field at different locations along the propagation direction.
Abstract: In this paper, we have investigated on the potentialities of digital holography for whole reconstruction of wavefields. We show that this technique can be efficiently used for obtaining quantitative information from the intensity and the phase distributions of the reconstructed field at different locations along the propagation direction. The basic concept and procedure of wavefield reconstruction for digital in-line holography is discussed. Numerical reconstructions of the wavefield from digitally recorded in-line hologram patterns and from simulated test patterns are presented. The potential of the method for analysing aberrated wave front has been exploited by applying the reconstruction procedure to astigmatic hologram patterns.
278 citations
TL;DR: Correcting the temporal variation in the eye's wave aberration increases the Strehl ratio of the point spread function nearly 3 times, and increases the contrast of images of cone photoreceptors by 33% compared with images taken with only static correction of the eyes' higher order aberrations.
Abstract: We measured the improvement in retinal image quality provided by correcting the temporal variation in the eye's wave aberration with a closed-loop adaptive optics system This system samples the eye's wave aberration at rates up to 30 Hz Correction of the eye's aberrations can be completed in 025-05 seconds, resulting in residual rms wave-front errors as low as 01 microns for 68 mm pupils Real-time wave-front measurements were used to determine how effectively the spatial and temporal components of the eye's wave aberration were corrected The system provides dynamic correction of fluctuations in Zernike modes up to 5 th order with temporal frequency components up to 08 Hz Temporal performance is in good agreement with predictions based on theory Correction of the temporal variation in the eye's wave aberration increases the Strehl ratio of the point spread function nearly 3 times, and increases the contrast of images of cone photoreceptors by 33% compared with images taken with only static correction of the eye's higher order aberrations
TL;DR: A novel method for multimodality medical image fusion is proposed using wavelet transform and fusion rule is proposed and used for calculating the wavelet transformation modulus maxima of input images at different bandwidths and levels.
Abstract: Medical image fusion has been used to derive useful information from multimodality medical image data. In this research, we propose a novel method for multimodality medical image fusion. Using wavelet transform, we achieved a fusion scheme. A fusion rule is proposed and used for calculating the wavelet transformation modulus maxima of input images at different bandwidths and levels. To evaluate the fusion result, a metric based on mutual information (MI) is presented for measuring fusion effect. The performances of other two methods of image fusion based on wavelet transform are briefly described for comparison. The experiment results demonstrate the effectiveness of the fusion scheme.
TL;DR: A numerical dispersion compensation technique for Partial Coherence Interferometry (PCI) and Optical Coherence Tomography (OCT) based on numerical correlation of the depth scan signal with a depth variant kernel is presented.
Abstract: Dispersive samples introduce a wavelength dependent phase distortion to the probe beam. This leads to a noticeable loss of depth resolution in high resolution OCT using broadband light sources. The standard technique to avoid this consequence is to balance the dispersion of the sample by arranging a dispersive material in the reference arm. However, the impact of dispersion is depth dependent. A corresponding depth dependent dispersion balancing technique is diffcult to implement. Here we present a numerical dispersion compensation technique for Partial Coherence Interferometry (PCI) and Optical Coherence Tomography (OCT) based on numerical correlation of the depth scan signal with a depth variant kernel. It can be used a posteriori and provides depth dependent dispersion compensation. Examples of dispersion compensated depth scan signals obtained from microscope cover glasses are presented.
TL;DR: A highly efficient cladding pumped single transverse mode holey fiber laser has been demonstrated, allowing continuous-wave output powers in excess of 1W with efficiencies of more than 80%.
Abstract: We have fabricated an ytterbium doped all-glass double-clad large mode area holey fiber. A highly efficient cladding pumped single transverse mode holey fiber laser has been demonstrated, allowing continuous-wave output powers in excess of 1W with efficiencies of more than 80%. Furthermore both Q-switched and mode-locked operation of the laser have been demonstrated.
TL;DR: Dark-field imaging in the terahertz fre-quency regime is investigated with the intention to enhance image contrast through the analysis of scattering and diffraction signatures and the capability of the technique for tumor detection is addressed.
Abstract: We investigate dark-field imaging in the terahertz (THz) frequency regime with the intention to enhance image contrast through the analysis of scattering and diffraction signatures. A gold-on-TPX test structure and an archived biomedical tissue sample are examined in conventional and dark-field transmission geometry. In particular, the capability of the technique for tumor detection is addressed.
TL;DR: This paper compares tandem scanning reflected light confocal microscopy and multi-photon excitation microscopy for the observation of human skin in vivo and identifies the relative merits of these two techniques.
Abstract: This paper compares tandem scanning reflected light confocal microscopy and multi-photon excitation microscopy for the observation of human skin in vivo. Tandem scanning confocal light microscopy based on a white light source can provide video-rate image acquisition from the skin surface to the epidermal-dermal junction. Multi-photon excitation is induced by a 80 MHz pulse train of femtosecond laser pulses at 780 nm wavelength. This nonlinear microscopic technique is inherently suitable for deep tissue fluorescence imaging. The relative merits of these two techniques can be identified by comparing movies of optical sections obtained from the forearm skin of the same volunteer.
TL;DR: Vector field calculations of the electric fields near focus for both linear and radially polarized illumination show that a high NA parabolic mirror allows an easy orientation of the polarization of the illuminating light in all spatial directions.
Abstract: We explore the diffraction limited focusing and confocal imaging properties of a high NA parabolic mirror for confocal imaging and spectroscopy of nanoparticles and single molecules. Vector field calculations of the electric fields near focus for both linear and radially polarized illumination are discussed and show that the optical field can be similar tightly focused as in the case of a high NA objective lens. Furthermore they show that a high NA parabolic mirror allows an easy orientation of the polarization of the illuminating light in all spatial directions. The simulation of confocal imaging of single molecules is discussed and yields, that the use of radially polarized excitation light gives an easy access to their orientations.
TL;DR: A method of synthesizing arbitrary views from IP images captured by the HDTV camera is proposed, founded on the 4-D data space Representation of light rays, which has the potential to improve the quality of images rendered by computer graphics techniques.
Abstract: Integral photography (IP), which is one of the ideal 3-D photographic technologies, can be regarded as a method of capturing and displaying light rays passing through a plane. The NHK Science and Technical Research Laboratories have developed a real-time IP system using an HDTV camera and an optical fiber array. In this paper, the authors propose a method of synthesizing arbitrary views from IP images captured by the HDTV camera. This is a kind of image-based rendering system, founded on the 4-D data space representation of light rays. Experimental results show the potential to improve the quality of images rendered by computer graphics techniques.
TL;DR: The classic problem of high numerical aperture focusing from an immersion lens to a glass-air interface is given particular attention and it is found that the use of radially and azimuthally polarized illumination for this type of imaging provides an impressive lateral confinement of the fields over a wide range of interface positions.
Abstract: Cylindrical vector beams have been proposed and demonstrated for applications ranging from microscopy to high energy physics. In this paper, we analyze the three-dimensional field distributions of radial and azimuthal beams focused near a dielectric interface. We give particular attention to the classic problem of high numerical aperture focusing from an immersion lens to a glass-air interface and find that the use of radially and azimuthally polarized illumination for this type of imaging provides an impressive lateral confinement of the fields over a wide range of interface positions.
TL;DR: An approach for converting reflection coefficients of any structure into colors, taking into account human color perception, is described, applied to the study of the colors reflected by Morpho rhetenor butterflies wings.
Abstract: We describe an approach for converting reflection coefficients of any structure into colors, taking into account human color perception. This procedure is applied to the study of the colors reflected by Morpho rhetenor butterflies wings. The scales of these wings have a tree-like periodic structure which is modeled with the help of a rigorous lamellar grating electromagnetic theory. In this way, we are able to determine the colors reflected by the wing under various illumination conditions.
TL;DR: This paper shows that calibration of the emitter strength and detector efficiency/gain can be done successfully in a linear reconstruction model with simulated continuous-wave data and is general for frequency and time domain data.
Abstract: In order for diffuse optical tomography to realize its potential of obtaining quantitative images of spatially varying optical properties within random media, several potential experimental systematic errors must be overcome One of these errors is the calibration of the emitter strength and detector efficiency/gain While in principle these parameters can be determined accurately prior to an imaging experiment, slight fluctuations will cause significant image artifacts For this reason, it is necessary to consider including their calibration as part of the inverse problem for image reconstruction In this paper, we show that this can be done successfully in a linear reconstruction model with simulated continuous-wave data The technique is general for frequency and time domain data
TL;DR: Comparison of its predictions to the calculated properties of the exact structure indicates that the ring structures emulate homogeneous rings of lower refractive index resulting in the ring structured fibres behaving approximately as cylindrically layered fibres.
Abstract: Recent developments in polymer microstructured optical fibres allow for the realisation of microstructures in fibres that would be problematic to fabricate using glass-based capillary stacking. We present one class of such structures, where the holes lie on circular rings. A fibre of this type is fabricated and shown to be single moded for relatively long lengths of fibre, whereas shorter lengths are multimoded. An average index model for these fibres is developed. Comparison of its predictions to the calculated properties of the exact structure indicates that the ring structures emulate homogeneous rings of lower refractive index resulting in the ring structured fibres behaving approximately as cylindrically layered fibres.
TL;DR: A Monte Carlo model was used to analyze the propagation of polarized light in linearly birefringent turbid media, such as fibrous tissues, and videos of spatially distributed polarization states of light backscattered from or propagating in bireFringent media are presented.
Abstract: A Monte Carlo model was used to analyze the propagation of polarized light in linearly birefringent turbid media, such as fibrous tissues. Linearly and circularly polarized light sources were used to demonstrate the change of polarizations in turbid media with different birefringent parameters. Videos of spatially distributed polarization states of light backscattered from or propagating in birefringent media are presented.
TL;DR: The study indicates that high bend transmission can be achieve with the addition of a low- Q resonant cavity; however, similar or even better performance can be achieved with a structure that combines a corner mirror with a phase retarder.
Abstract: We present an evaluation of the parameters involved in designing low-loss right-angle waveguide bends based on a high index contrast materials system. We apply the finite difference time domain method (FDTD)to several two-dimensional bend structures and study the effects of varying the bend geometry. Such a study is relevant for the understanding of bend mechanisms and for the optimization and fabrication of high-density high-contrast integrated optical components. The study indicates that high bend transmission can be achieved with the addition of a low-Q resonant cavity; however, similar or even better performance can be achieved with a structure that combines a corner mirror with a phase retarder. The use of a double corner mirror structure is shown to further increase the bend transmission, with little increase in bend area.
TL;DR: This study shows that diffuse optical tomography has the potential to be used for detection and monitoring of bone and joint diseases such as osteoporosis and arthritis.
Abstract: We present what is believed to be the first absorption and scattering images of in vitro and in vivo bones and joints from continuous-wave tomographic measurements. Human finger and chicken bones embedded in cylindrical scattering media were imaged at multiple transverse planes with Clemson multi-channel diffuse optical imager. Both absorption and scattering images were obtained using our nonlinear, finite element based reconstruction algorithm. This study shows that diffuse optical tomography (DOT) has the potential to be used for detection and monitoring of bone and joint diseases such as osteoporosis and arthritis.
TL;DR: The major features seen in quantum mechanical simulations, including the double-ionization jets, are reproduced when using a classical ensemble of two-particle trajectories.
Abstract: We compare quantum mechanical and fully classical treatments of electron dynamics accompanying strong field double ionization. The major features seen in quantum mechanical simulations, including the double-ionization jets, are reproduced when using a classical ensemble of two-particle trajectories.
TL;DR: Upon comparison with a rigorous electromag-netic analysis technique, specifically, the finite difference time-domain method (FDTD), it is found that the scalar-based design method is surprisingly valid for DOE's having sub-wavelength features.
Abstract: We have designed high-efficiency finite-aperture diffractive optical elements (DOE's) with features on the order of or smaller than the wave-length of the incident illumination. The use of scalar diffraction theory is generally not considered valid for the design of DOE's with such features. However, we have found several cases in which the use of a scalar-based design is, in fact, quite accurate. We also present a modified scalar-based iterative design method that incorporates the angular spectrum approach to design diffractive optical elements that operate in the near-field and have sub-wavelength features. We call this design method the iterative angular spectrum approach (IASA). Upon comparison with a rigorous electromag-netic analysis technique, specifically, the finite difference time-domain method (FDTD), we find that our scalar-based design method is surprisingly valid for DOE's having sub-wavelength features.
TL;DR: This work investigates into the causes of the loss of the fabricated HALFs, and shows that a GeO2-doped core, in addition to the low power fraction, is desirable for low loss.
Abstract: Hole-assisted lightguide fiber (HALF) is a microstructured fiber comprising a material index profile for waveguiding and air holes for modifying optical properties. Anomalous dispersion larger than those of the conventional fibers can be realized without severe degradation in optical loss, because of low power fraction in the holes and structural simplicity. We investigate into the causes of the loss of the fabricated HALFs, and show that a GeO2-doped core, in addition to the low power fraction, is desirable for low loss. The fabricated HALF exhibits a loss as low as 0.41 dB/km and a large anomalous dispersion of +35 ps/nm/km at 1550 nm wavelength.
TL;DR: A non-scanning instrument that simultaneously acquires full spectral information from every pixel within its 2-D field of view during a single integration time (typically, 2 seconds) allows for the analysis of physiological responses within living biological specimens.
Abstract: Multispectral imaging has significantly enhanced the analysis of fixed specimens in pathology and cytogenetics. However, application of this technology to in vivo studies has been limited. This is due in part to the increased temporal resolution required to analyze changes in cellular function. Here we present a non-scanning instrument that simultaneously acquires full spectral information (460 nm to 740 nm) from every pixel within its 2-D field of view (200 im x 200 im) during a single integration time (typically, 2 seconds). The current spatial and spectral sampling intervals of the spectrometer are 0.985 im and 5 nm, respectively. These properties allow for the analysis of physiological responses within living biological specimens.
TL;DR: It is interesting to note that the epithelia and stromal intensities are comparable at 365, 460 nm; however, at 440, 525 nm, the epithelial intensity is more than a factor of two less that that of the stroma for all tissue types.
Abstract: We characterized the fluorescence intensity distribution within the epithelia and stroma of frozen human cervical tissues at the following excitation-emission wavelength pairs: 440, 525 nm and 365, 460 nm. The intensities at both excitation-emission wavelength pairs are significantly lower in the epithelia of severely dysplastic tissues, relative to that in normal and inflammatory tissues. Furthermore, there are small differences in (1) the epithelial intensity of severe dysplasia and mild dysplasia at 440, 525 nm and (2) the stromal intensity of inflammatory and severely dysplastic tissues at 365, 460 nm. A comparison of the ratio of intensities at 440, 525 nm and 365, 460 nm between the epithelia of each tissue type indicates that this ratio is lowest in severely dysplastic tissues. It is interesting to note that the epithelial and stromal intensities are comparable at 365, 460 nm; however, at 440, 525 nm, the epithelial intensity is more than a factor of two less that that of the stroma for all tissue types.