Showing papers in "Optics Letters in 2006"
TL;DR: The diffraction phase microscopy method combines the principles of common path interferometry and single-shot phase imaging and is characterized by subnanometer path-length stability and millisecond-scale acquisition time.
Abstract: We have developed diffraction phase microscopy as a new technique for quantitative phase imaging of biological structures. The method combines the principles of common path interferometry and single-shot phase imaging and is characterized by subnanometer path-length stability and millisecond-scale acquisition time. The potential of the technique for quantifying nanoscale motions in live cells is demonstrated by experiments on red blood cells.
784 citations
TL;DR: A new approach to known-plaintext attack on an optical encryption scheme based on double random phase keys that can be accessed with the help of the phase retrieval technique is demonstrated.
Abstract: We demonstrate a new approach to known-plaintext attack on an optical encryption scheme based on double random phase keys. With this attack an opponent can access both random phase keys with the help of the phase retrieval technique. This demonstration shows that an optical encryption scheme based on double random encoding is vulnerable to known-plaintext attack.
608 citations
TL;DR: Digital holographic microscopy is applied to perform optical diffraction tomography of a pollen grain for the first time, with a precision of 0.01 for the refractive index estimation and a spatial resolution in the micrometer range.
Abstract: For what we believe to be the first time, digital holographic microscopy is applied to perform optical diffraction tomography of a pollen grain. Transmission phase images with nanometric axial accuracy are numerically reconstructed from holograms acquired for different orientations of the rotating sample; then the three-dimensional refractive index spatial distribution is computed by inverse radon transform. A precision of 0.01 for the refractive index estimation and a spatial resolution in the micrometer range are demonstrated.
555 citations
TL;DR: To the best of the knowledge, this is the best figure of merit reported for any negative-index photonic metamaterial to date.
Abstract: We fabricate and characterize a low-loss silver-based negative-index metamaterial based on the design of a recent theoretical proposal. Comparing the measured transmittance and reflectance spectra with theory reveals good agreement. We retrieve a real part of the refractive index of Re(n)= -2 around 1.5 microm wavelength. The maximum of the ratio of the real to the imaginary part of the refractive index is about three at a spectral position where Re(n)= -1. To the best of our knowledge, this is the best figure of merit reported for any negative-index photonic metamaterial to date.
517 citations
TL;DR: The LCORR takes advantage of the high sensitivity, small footprint, and low sample consumption with the ring resonator, as well as the efficient fluidic sample delivery with the capillary, and will open an avenue to future multiplexed sensor array development.
Abstract: We have demonstrated a novel sensor architecture based on a liquid-core optical ring-resonator (LCORR) in which a fused silica capillary is utilized to carry the aqueous sample and to act as the ring resonator. The wall thickness of the LCORR is controlled to a few micrometers to expose the whispering gallery mode to the aqueous core. Optical characterization with a water-ethanol mixture shows that the spectral sensitivity of the LCORR sensor is approximately 2.6 nm per refractive index unit. A model based on Mie theory is established to explain the experimental results. The LCORR takes advantage of the high sensitivity, small footprint, and low sample consumption with the ring resonator, as well as the efficient fluidic sample delivery with the capillary, and will open an avenue to future multiplexed sensor array development.
469 citations
TL;DR: This work develops a scheme based on a simple criterion taken from perturbation theory that is the only one that attains quadratic convergence with resolution for arbitrarily sloped interfaces and compares it with other published FDTD smoothing methods.
Abstract: Finite-difference time-domain (FDTD) methods suffer from reduced accuracy when modeling discontinuous dielectric materials, due to the inhererent discretization (pixelization). We show that accuracy can be significantly improved by using a subpixel smoothing of the dielectric function, but only if the smoothing scheme is properly designed. We develop such a scheme based on a simple criterion taken from perturbation theory and compare it with other published FDTD smoothing methods. In addition to consistently achieving the smallest errors, our scheme is the only one that attains quadratic convergence with resolution for arbitrarily sloped interfaces. Finally, we discuss additional difficulties that arise for sharp dielectric corners.
463 citations
TL;DR: Buffered Fourier domain mode locking (FDML), a technique for tailoring the output and multiplying the sweep rate of FDML lasers, is described and the role of the laser source in dynamic range versus sensitivity performance in optical coherence tomography (OCT) imaging is investigated.
Abstract: We describe buffered Fourier domain mode locking (FDML), a technique for tailoring the output and multiplying the sweep rate of FDML lasers. Buffered FDML can be used to create unidirectional wavelength sweeps from the normal bidirectional sweeps in an FDML laser without sacrificing sweep rate. We also investigate the role of the laser source in dynamic range versus sensitivity performance in optical coherence tomography (OCT) imaging. Unidirectional sweep rates of 370 kHz over a 100 nm range at a center wavelength of 1300 nm are achieved. High-speed, swept-source OCT is demonstrated at record speeds of up to 370,000 axial scans per second.
443 citations
TL;DR: A method of chosen-plaintext attack on lensless double-random phase encoding (L-DRPE) in the Fresnel domain is demonstrated, showing that a lensless optical encryption scheme based on DRPE is vulnerable to chosen- Plaintext attack.
Abstract: We demonstrate a method of chosen-plaintext attack on lensless double-random phase encoding (L-DRPE) in the Fresnel domain. With this attack an opponent can access two encryption keys with help of the impulse functions as chosen plaintexts. This shows that a lensless optical encryption scheme based on DRPE is vulnerable to chosen-plaintext attack. Cryptoanalysis also indicates that the security worry originates from the linearity of the encryption and decryption mechanism of the L-DRPE scheme. One of the interesting features of the proposed attack is that the decryption process is lossless. Numerical simulations show good agreement with theoretical analysis.
388 citations
TL;DR: In this paper, the authors show that equivalent circuits offer a qualitative and even quantitative simple explanation for the behavior of various types of left-handed (or negative-index) metamaterials and apply this unifying circuit approach in accounting for the features and in optimizing the structure employing parallel metallic bars on the two sides of a dielectric film.
Abstract: We show that equivalent circuits offer a qualitative and even quantitative simple explanation for the behavior of various types of left-handed (or negative-index) metamaterials. This allows us to optimize design features and parameters while avoiding trial and error simulations or fabrications. In particular, we apply this unifying circuit approach in accounting for the features and in optimizing the structure employing parallel metallic bars on the two sides of a dielectric film.
354 citations
TL;DR: A novel algorithm of two-step PSI, with an arbitrary known phase step, by which a complex object field can be reconstructed with only two interferograms is proposed and is applied to an information security system based on double random-phase encoding in the Fresnel domain.
Abstract: Conventional phase-shifting interferometry (PSI) needs at least three interferograms. A novel algorithm of two-step PSI, with an arbitrary known phase step, by which a complex object field can be reconstructed with only two interferograms is proposed. This algorithm is then applied to an information security system based on double random-phase encoding in the Fresnel domain. The feasibility of this method and its robustness against occlusion and additional noise attacks are verified by computer simulations. This approach can considerably improve the efficiency of data transmission and is very suitable for Internet use.
337 citations
TL;DR: A new detection scheme for Fourier domain optical coherence microscopy that exhibits high transverse resolution along an axially extended focal range is reported on.
Abstract: We report on a new detection scheme for Fourier domain optical coherence microscopy that exhibits high transverse resolution along an axially extended focal range. Nearly constant transverse resolution of ∼1.5 μm along a focal range of 200 μm is experimentally verified with a maximum sensitivity of 105 dB. A broad-bandwidth Ti:sapphire laser allowed for an axial resolution of 3 μm in air.
TL;DR: A high spectral resolution, 2D nanohole-array-based surface plasmon resonance sensor that operates at normal or near normal incidence--facilitating high spatial resolution imaging--is presented and the potential of this system of O(10(-6)) RIU under optimal conditions is estimated.
Abstract: A high spectral resolution, 2D nanohole-array-based surface plasmon resonance sensor that operates at normal or near normal incidence--facilitating high spatial resolution imaging--is presented. The angular and spectral transmittance of the structure is modified from a Fano type to a pure Lorentzian line shape with a parallel and orthogonal polarizer-analyzer pair. This change leads to a linewidth narrowing that maximizes the sensor resolution, which we show to be of O(10−5) refractive index units (RIU). We estimate the potential of this system of O(10−6) RIU under optimal conditions.
TL;DR: The fabrication and characterization of a new type of hollow-core photonic crystal fiber based on large-pitch kagome lattice lattice cladding is reported, with broad optical transmission bands covering the visible and near-IR parts of the spectrum with relatively low loss and low chromatic dispersion.
Abstract: We report the fabrication and characterization of a new type of hollow-core photonic crystal fiber based on large-pitch (∼12μm) kagome lattice cladding. The optical characteristics of the 19-cell, 7-cell, and single-cell core defect fibers include broad optical transmission bands covering the visible and near-IR parts of the spectrum with relatively low loss and low chromatic dispersion, no detectable surface modes and high confinement of light in the core. Various applications of such a novel fiber are also discussed, including gas sensing, quantum optics, and high harmonic generation.
TL;DR: It is shown that heterodyne CARS microscopy permits the detection of weak vibrational resonances that are otherwise overshadowed by the strong interference of the nonresonant background.
Abstract: We have achieved rapid nonlinear vibrational imaging free of nonresonant background with heterodyne coherent anti-Stokes Raman scattering (CARS) interferometric microscopy. This technique completely separates the real and imaginary responses of nonlinear susceptibility chi(3) and yields a signal that is linear in the concentration of vibrational modes. We show that heterodyne CARS microscopy permits the detection of weak vibrational resonances that are otherwise overshadowed by the strong interference of the nonresonant background.
TL;DR: In this article, the authors proposed a terahertz imaging system that includes a source for generating radiation having one or more frequencies in a range of about 0.1 THz to about 10 THz and a two-dimensional detector array comprising a plurality of radiation detecting elements that are capable of detecting radiation in that frequency range.
Abstract: The present invention generally provides a terahertz (THz) imaging system that includes a source for generating radiation (e.g., a quantum cascade laser) having one or more frequencies in a range of about 0.1 THz to about 10 THz, and a two-dimensional detector array comprising a plurality of radiation detecting elements that are capable of detecting radiation in that frequency range. An optical system directs radiation from the source to an object to be imaged. The detector array detects at least a portion of the radiation transmitted through the object (or reflected by the object) so as to form a THz image of that object.
TL;DR: The development of a miniature, flexible, fiber-optic scanning endoscope for two-photon fluorescence imaging using a tubular piezoelectric actuator for achieving two-dimensional beam scanning and a double-clad fiber for delivery of the excitation light and collection of two-Photon Fluorescence.
Abstract: We report on the development of a miniature, flexible, fiber-optic scanning endoscope for two-photon fluorescence imaging. The endoscope uses a tubular piezoelectric actuator for achieving two-dimensional beam scanning and a double-clad fiber for delivery of the excitation light and collection of two-photon fluorescence. Real-time imaging of fluorescent beads and cancer cells has been performed.
TL;DR: A simple subwavelength-diameter plastic wire, similar to an optical fiber, for guiding a terahertz wave with a low attenuation constant is reported, with direct free-space coupling efficiency as high as 20% can be achieved by use of an off-axis parabolic mirror.
Abstract: We report a simple subwavelength-diameter plastic wire, similar to an optical fiber, for guiding a terahertz wave with a low attenuation constant. With a large wavelength-to-fiber-core ratio, the fractional power delivered inside the lossy core is reduced, thus lowering the effective fiber attenuation constant. In our experiment we adopt a polyethylene fiber with a 200 µm diameter for guiding terahertz waves in the frequency range near 0.3 THz in which the attenuation constant is reduced to of the order of or less than 0.01 cm−1. Direct free-space coupling efficiency as high as 20% can be achieved by use of an off-axis parabolic mirror. Furthermore, all the plastic wires are readily available, with no need for complex or expensive fabrication.
TL;DR: It is demonstrated that relatively large gold particles (R(b)=50 nm) indeed yield a sixfold enhancement in trapping efficiency and detection sensitivity as compared to similar-sized polystyrene particles, however, optical absorption by gold at the most common trapping wavelength induces dramatic heating.
Abstract: Gold nanoparticles appear to be superior handles in optical trapping assays. We demonstrate that relatively large gold particles (R(b)=50 nm) indeed yield a sixfold enhancement in trapping efficiency and detection sensitivity as compared to similar-sized polystyrene particles. However, optical absorption by gold at the most common trapping wavelength (1064 nm) induces dramatic heating (266 degrees C/W). We determined this heating by comparing trap stiffness from three different methods in conjunction with detailed modeling. Due to this heating, gold nanoparticles are not useful for temperature-sensitive optical-trapping experiments, but may serve as local molecular heaters. Also, such particles, with their increased detection sensitivity, make excellent probes for certain zero-force biophysical assays.
TL;DR: The current findings are the first in vivo demonstration of this relationship, and show that specific characteristics of aged skin such as the ratio of extracellular matrix components collagen and elastin can be evaluated by in vivo AF and SHG measurements using near-IR femtosecond laser pulses.
Abstract: Changes of dermal collagen and elastin content are characteristic for skin aging as well as for pathological skin conditions. To evaluate these changes, we used in vivo multiphoton laser tomography to measure two-photon excited autofluorescence (AF) and second harmonic generation (SHG). We tested 18 patients of all ages and calculated the SHG-to-AF aging index of dermis (SAAID). We observed a negative relationship between the SAAID and age, which was accelerated for the female (n=7) subgroup. The current findings are the first in vivo demonstration of this relationship, and they show that specific characteristics of aged skin such as the ratio of extracellular matrix components collagen and elastin can be evaluated by in vivo AF and SHG measurements using near-IR femtosecond laser pulses.
TL;DR: A novel design for an all-fiber bandpass filter based on a multimode interference reimaging phenomenon that has achieved low insertion loss with adequate bandwidth and isolation for coarse wavelength-division multiplexing is presented.
Abstract: A novel design for an all-fiber bandpass filter based on a multimode interference reimaging phenomenon is presented. The filter has achieved low insertion loss with adequate bandwidth and isolation for coarse wavelength-division multiplexing. The filter can easily be made with any central wavelength that is compatible with the single-mode fiber used for its construction. The measured filter performance matches the theoretical predictions well. The filter can have broad applications in fiber-optic telecommunications, spectroscopy, and sensing.
TL;DR: A novel all-fiber refractometer sensor is proposed, which is based on multimode interference in the multimode fiber core section sandwiched between two single-mode fibers, based on wide-angle beam propagation method in the cylindrical coordinate.
Abstract: A novel all-fiber refractometer sensor is proposed, which is based on multimode interference in the multimode fiber core section sandwiched between two single-mode fibers. A wide-angle beam propagation method in the cylindrical coordinate is employed as the modeling tool for simulation and design of the proposed refractometer sensor. The design for a refractometer is presented that shows that the refractometer would have an estimated resolution of 5.4 x 10(-5) for refractive indices from 1.33 to 1.45 and of 3.3 x 10(-5) for refractive indices from 1.38 to 1.45 through the choice of an appropriate length of the multimode fiber core section.
TL;DR: This achromatic wave plate demonstrates a huge frequency bandwidth (upsilonmax/upsilonmin approximately 7), and therefore can be applied to terahertz time domain spectroscopy and polarimetry.
Abstract: Phase retarders usually present a strong frequency dependence. We discuss the design and characterization of a terahertz achromatic quarter-wave plate. This wave plate is made from six birefringent quartz plates precisely designed and stacked together. Phase retardation has been measured over the whole terahertz range by terahertz polarimetry. This achromatic wave plate demonstrates a huge frequency bandwidth (upsilonmax/upsilonmin approximately 7), and therefore can be applied to terahertz time domain spectroscopy and polarimetry.
TL;DR: Double-slit interference is shown to be affected by the azimuthal phase dependence of a Laguerre-Gaussian beam, providing new insight into the helical phase structure of the LaguERre- Gaussian beam and has potential applications for measuring the orbital angular momentum of an arbitrary wavefront.
Abstract: The interference of Laguerre-Gaussian beams carrying orbital angular momentum was demonstrated in Young's double-slit geometry. Double-slit interference is shown to be affected by the azimuthal phase dependence of a Laguerre-Gaussian beam. This interference provides new insight into the helical phase structure of the Laguerre-Gaussian beam and has potential applications for measuring the orbital angular momentum of an arbitrary wavefront.
TL;DR: Distributed strain sensing with millimeter-order spatial resolution is demonstrated in optical fibers based on Brillouin optical correlation domain analysis and a novel beat lock-in detection scheme is introduced to suppress background noises coming from the reflection of BrillouIn pump waves.
Abstract: Distributed strain sensing with millimeter-order spatial resolution is demonstrated in optical fibers based on Brillouin optical correlation domain analysis. A novel beat lock-in detection scheme is introduced to suppress background noises coming from the reflection of Brillouin pump waves. The Brillouin frequency shifts of 3 mm fiber sections are successfully measured with a theoretical spatial resolution of 1.6 mm.
TL;DR: Experimental characterizations of the MOSPR sensor have shown an increase in the limit of detection by a factor of 3 in changes of refractive index and in the adsorption of biomolecules compared with standard sensors.
Abstract: The characteristics of a novel magneto-optic surface-plasmon-resonance (MOSPR) sensor and its use for the detection of biomolecules are presented. This physical transduction principle is based on the combination of the magneto-optic activity of magnetic materials and a surface-plasmon resonance of metallic layers. Such a combination can produce a sharp enhancement of the magneto-optic effects that strongly depends on the optical properties of the surrounding medium, allowing its use for biosensing applications. Experimental characterizations of the MOSPR sensor have shown an increase in the limit of detection by a factor of 3 in changes of refractive index and in the adsorption of biomolecules compared with standard sensors. Optimization of the metallic layers and the experimental setup could result in an improvement of the limit of detection by as much as 1 order of magnitude.
TL;DR: The operation of a passively mode-locked fiber ring laser made of purely normal dispersive fibers is reported and it is shown that the operation of the laser can be well described by an extended Ginzburg-Landau equation model that governs the soliton dynamics of fiber lasers.
Abstract: We report on the operation of a passively mode-locked fiber ring laser made of purely normal dispersive fibers. Self-started mode locking can still be achieved in the laser by use of the nonlinear polarization rotation technique, and the mode-locked pulse has large pulse energy, strong frequency chirp, and a mode-locked spectral width limited by the effective laser gain bandwidth. Furthermore, we show that the operation of the laser can be well described by an extended Ginzburg-Landau equation model that governs the soliton dynamics of fiber lasers.
TL;DR: In this article, a metal slot waveguide on silicon with a predicted confinement substantially below the optical wavelength was proposed, and a standard silicon dielectric waveguide with a coupling efficiency of approximately 2.5 dB per facet.
Abstract: We demonstrate propagation losses of less than 0.8 dB/µm in a metal slot waveguide on silicon with a predicted confinement substantially below the optical wavelength (~1.55 µm). We also show compact and efficient coupling of the high-confinement metal slot waveguide with a standard silicon dielectric waveguide with a coupling efficiency of approximately 2.5 dB per facet.
TL;DR: Magnetic metamaterials composed of 35 nm minimum feature-size gold split-ring resonators with a fundamental magnetic resonance at a wavelength of 900 nm are presented.
Abstract: We present magnetic metamaterials composed of 35 nm minimum feature-size gold split-ring resonators with a fundamental magnetic resonance at a wavelength of 900 nm. Corresponding calculations reveal excellent agreement with the experiments and show that the limits of size scaling have been reached.
TL;DR: Optical bistability in a micrometer-sized silicon ring resonator based on the free-carrier dispersion effect in silicon is demonstrated and applications include sequential logic operations for all-optical routing.
Abstract: We demonstrate optical bistability in a micrometer-sized silicon ring resonator based on the free-carrier dispersion effect in silicon. We measure the transfer function of the resonator showing a hysteresis loop with an input optical power of less than 10 mW. The influence of the thermal optical effect, which is minimized in the experiment by use of nanosecond pulses, is evaluated theoretically. Applications include sequential logic operations for all-optical routing.
TL;DR: It is demonstrated that LSTCA can significantly suppress the influence of the laser speckle from the stationary structure, such as the skull, and thus reveal the blood flow and morphology of blood vessels through the laser Speckle images recorded from the intact rat skull.
Abstract: We discovered that laser speckle temporal contrast analysis (LSTCA) is able to access the two-dimensional (2D) cerebral blood flow velocity and vessel structure through the intact rat skull. It is demonstrated that LSTCA can significantly suppress the influence of the laser speckle from the stationary structure, such as the skull, and thus reveal the blood flow and morphology of blood vessels through the laser speckle images recorded from the intact rat skull.