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At least 793 records · Page 44Linked to original sources
PubMed1997

Optical imaging of anatomical maps derived from magnetic resonance images using time-independent optical sources.

We present a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed.

Adipose Tissue↗
PubMed1989

Quantitative analysis of visual receptive fields of neurons in nucleus of the optic tract and dorsal terminal nucleus of the accessory optic tract in macaque monkey.

1. The visual receptive field properties of neurons in the nucleus of the optic tract (NOT) in the pretectum and the dorsal terminal nucleus (DTN) of the accessory optic tract were analyzed quantitatively in anesthetized, paralyzed macaque monkeys. 2. Visual latencies to reversals in direction of stimulus movement ranged from 40 to 80 ms [61 +/- 13.5 (SD) ms]. 3. All neurons increased their discharge rate during ipsiversive movement and decreased their ongoing activity during contraversive movement of single stimuli or whole-field random dot patterns. The population of neurons in the left NOT-DTN was excited most strongly by leftward movement pointing 4 degrees down; neurons in the right NOT-DTN were excited most strongly by rightward movement pointing 6 degrees down. The mean angle between the directions yielding the highest and the lowest discharge rate in the two populations of NOT-DTN neurons was 177 degrees. 4. The deviation of the preferred excitatory directions from the horizon in individual neurons varied with recording depth. Within the first 500 microns below the midbrain surface, neurons preferred near-horizontal directions, whereas neurons recorded more deeply preferred more oblique directions of stimulus movement. 5. The tuning widths of NOT-DTN neurons in the preferred excitatory direction were very broad. The mean halfwidth defined as the range of directions eliciting responses greater than 50% of the maximum was 127 +/- 25 degrees. 6. Moving a random dot pattern and a single bar of light simultaneously but in opposite directions caused NOT-DTN neurons to increase their discharge rate as soon as one of the two stimuli moved in the ipsiversive direction. The reduction in overall discharge rates when two stimuli moved in opposite directions indicates mainly inhibitory interactions. 7. All NOT-DTN neurons could be activated from both eyes. Interactions between the two eyes were modest and unspecific. Misalignment of the visual axes of the two eyes had no influence on response strength. 8. Optimal speeds of stimulus movement varied widely for different NOT-DTN neurons. The effective range of speeds to elicit direction-selective responses in the total population was very broad (0.1400 degrees/s. With oscillating horizontal stimulation, NOT-DTN neurons followed repetition rates up to 4 Hz at excursions of 40 degrees. Speeds greater than 500 degrees/s were either not effective or resulted in a suppression of ongoing activity in all directions of movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1979

Interaction of optic tract and visual wulst impulses on single units of the pigeon's optic tectum.

The influences of visual wulst and optic tract (OTr) stimulation on units recorded from the pigeon's optic tectum (OT) were studied. 127 tectal units were excited with short latency by a single OTr volley. Excitation was followed by a long-lasting inhibition. On 54 of the OTr-excited units, single-shock visual wulst stimulation exerted a long-lasting inhibitory effect. On 34 units, the effect was purely excitatory and, on 28 units, excitation was followed by prolonged inhibition. No effect was exerted by wulst stimulation on 24 units. These results are discussed in terms of convergence of wulst and retinal input on OT neurons, and the role of the integration of visual information from both peripheral and central origins is suggested for the OT neurons.

Animals↗
PubMed1996

Optical coherence tomography for optical biopsy. Properties and demonstration of vascular pathology.

BACKGROUND: Optical coherence tomography (OCT) is an recently developed medical diagnostic technology that uses back-reflected infrared light to perform in situ micron scale tomographic imaging. In this work, we investigate the ability of OCT to perform micron scale tomographic imaging of the internal microstructure of in vitro atherosclerotic plaques. METHODS AND RESULTS: Aorta and relevant nonvascular tissue were obtained at autopsy. Two-dimensional cross-sectional imaging of the exposed surface of the arterial segments was performed in vitro with OCT. A 1300-nm wavelength, superluminescent diode light source was used that allows an axial spatial resolution of 20 microns. The signal-to-noise ratio was 109 dB. Images were displayed in gray scale or false color, Imaging was performed over 1.5 mm into heavily calcified tissue, and a high contrast was noted between lipid- and water-based constituents, making OCT attractive for intracoronary imaging. The 20-microns axial resolution of OCT allowed small structural details such as the width of intimal caps and the presence of fissures to be determined. The extent of lipid collections, which had a low backscattering intensity, also were well documented. CONCLUSIONS: OCT represents a promising new technology for imaging vascular microstructure with a level of resolution not previously achieved with the use of other imaging modalities. It does not required direct contact with the vessel wall and can be performed with a catheter integrated with a relatively inexpensive optical fiber. The high contrast among tissue constituents, high resolution, and ability to penetrate heavily calcified tissue make OCT an attractive new imaging technology for intracoronary diagnostics.

Arteriosclerosis↗
PubMed1993

Enzymatic optical resolution of dibenzoxepins and its application to an optically active antiallergic agent with thromboxane A2 receptor antagonistic activity.

Methyl (+/-)-11-(2-hydroxyethyl)thio-6,11-dihydrodibenz[b,e]oxepin- 2- carboxylate (5) was enantio-selectively acylated with acetic anhydride in an organic medium by Lipase Amano P to give methyl (-)-11-(2-acetoxyethyl)thio-6,11-dihydrodibenz[b,e]oxepin-2- carboxylate (8), and the (+)-enantiomer by Lipase Sigma Type VII. Using Lipase Amano P, (+)- and (-)-(5) could be prepared with high optical purity (84-94% e.e.). These products were respectively converted to (+)- and (-)-KW-4099, which had antiallergic activity with complete retention of the optical purity.

Acylation↗
PubMed2002

Theoretical analysis of a noncollinear phase-matched optical parametric amplifier seeded by an optical parametric generation.

We have theoretically analyzed the characteristics of an optical parametric amplifier system seeded by an optical parametric generation. We investigated the influences of the energy, pulse duration, material dispersion, and the third-order nonlinear effect in beta-barium borate. The group-velocity mismatch (GVM) becomes the most important factor for the amplification of bandwidths. Even though tilting the wave front of the pump can decrease the GVM, it seems impossible to generate pulses smaller than 10-fs with 400-nm pumping. However, 10-fs pulses can be achieved with a 30-fs pump duration with pumping at 800 nm.

Journal Article↗
PubMed2002

Elasto-optics in double-coated optical fibers induced by axial strain and hydrostatic pressure.

Stresses, microbending loss, and refractive-index changes induced simultaneously by axial strain and hydrostatic pressure in double-coated optical fibers are analyzed. The lateral pressure and normal stresses in the optical fiber, primary coating, and secondary coating are derived. Also presented are the microbending loss and refractive-index changes in the glass fiber. The normal stresses are affected by axial strain, hydrostatic pressure, material properties, and thickness of the primary and secondary coatings. It is found that microbending loss decreases with increasing thickness, the Young's modulus, and the Poisson's ratio of the secondary coating but increases with the increasing Young's modulus and Poisson's ratio of the primary coating. Similarly, changes in refractive index in the glass fiber decrease with the increasing Young's modulus and Poisson's ratio of the secondary coating but increase with the increasing Young's modulus and Poisson's ratio of the primary coating. Therefore, to minimize microbending loss induced simultaneously by axial strain and hydrostatic pressure in the glass fiber, the polymeric coatings should be suitably selected. An optimal design procedure is also indicated.

Journal Article↗
PubMed2003

Fiber-optic power limiter based on photothermal defocusing in an optical polymer.

We describe the performance of a fiber-optic power-limiting component. The passive device is dynamically responsive to the input signal and has been shown to attenuate continuous-wave power with a dynamic range of up to 9 dB at 150 mW of input power at 1550 nm. The limiting threshold is approximately 30 mW from 1530 to 1565 nm and less than 10 mW at 1430 nm. The device is activated by a photothermal defocusing mechanism in an optical polymer fixed between two expanded core fibers that collimate light through the material. The magitude and threshold of the limiting response is dependent on the absorption properties of the polymer and the size of the gap between the two fiber endfaces. Simple model calculations have been made to predict the limiting response, and they agree reasonably well with the performance of the actual device.

Journal Article↗
PubMed2003

All-optical wavelength conversion in a GaInAsP/InP optical gate loaded with a Bragg reflector.

All-optical wavelength conversion employing a GaInAsP/InP nonlinear distributed-feedback waveguide switch is investigated. The device has the advantages of simple structure, compactness, polarity-noninverted operation, and feasibility of integration with other photonic devices such as semiconductor optical amplifier and modulators. We show that the device exhibits constant conversion efficiency around -9.2 dB in a signal-wavelength range of 1530-1560 nm. Furthermore, this device can potentially be made polarization independent.

Journal Article↗
PubMed2004

Tunable dual-wavelength optical short-pulse generation by use of a fiber Bragg grating and a tunable optical filter in a self-seeding scheme.

A simple self-seeding scheme is developed to generate tunable dual-wavelength optical short pulses in a flexible manner and with an increased wavelength-tuning range. The wavelength selection and tuning are achieved by simultaneous use of a fiber Bragg grating and a tunable optical filter. The side-mode suppression ratio of the output pulses is better than 30 dB over a wavelength-tuning range of 33.8 nm. The system is compact and convenient for dual-wavelength tuning.

Journal Article↗
PubMed2005

Microinterferometric optical phase tomography for measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices.

A new technique, microinterferometric optical phase tomography, is introduced for use in measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices. The method combines microscopy-based fringe-field interferometry with parallel projection-based computed tomography to characterize fiber index profiles. The theory relating interference measurements to the projection set required for tomographic reconstruction is given, and discrete numerical simulations are presented for three test index profiles that establish the technique's ability to characterize fiber with small, asymmetric index differences. An experimental measurement configuration and specific interferometry and tomography practices employed in the technique are discussed.

Journal Article↗
PubMed2005

All-optical 2 x 2 switching with two independent Yb3+ -doped nonlinear optical fibers with a long-period fiber grating pair.

We have demonstrated a new type of all-optical 2 x 2 switch by using two independent Yb3+ -doped nonlinear optical fibers with a long-period fiber grating pair and a 3-dB fiber coupler. A 400-Hz square-wave pulse train at approximately 1549.4 nm was fully switched between the two output ports up to 200 Hz by modulated pump signals at 976 nm with a maximum pump power of approximately 35 mW, where the extinction ratio at approximately 1549.4 nm between the on and the off states was approximately 17.5 dB.

Journal Article↗
PubMed2005

Robust determination of optical path difference: fringe tracking at the infrared optical telescope array interferometer.

We describe the fringe-packet tracking system used to equalize the optical path lengths at the Infrared Optical Telescope Array interferometer. The measurement of closure phases requires obtaining fringes on three baselines simultaneously. This is accomplished by use of an algorithm based on double Fourier interferometry for obtaining the wavelength-dependent phase of the fringes and a group-delay tracking algorithm for determining the position of the fringe packet. A comparison of data acquired with and without the fringe-packet tracker shows a factor of approximately 3 reduction of the error in the closure-phase measurement. The fringe-packet tracker has been able so far to track fringes with signal-to-noise ratios as low as 1.8 for stars as faint as mH = 7.0.

Journal Article↗
PubMed2005

Analysis of optical channel cross talk for free-space optical interconnects in the presence of higher-order transverse modes.

We analyze the effect of cross-talk noise on the performance of free-space optical interconnects (FSOIs). In addition to diffraction-caused cross talk, we consider the effect of stray-light cross-talk noise, an issue that, to the best of our knowledge, was not addressed previously. Simulations were performed on a microlens-based FSOI system using the modal composition and beam profiles experimentally extracted from a commercial vertical-cavity surface-emitting laser. We demonstrate that this cross-talk noise introduces significant degradation to interconnect performance, particularly for multitransverse-mode laser sources. A simple behavioral model is also developed that accurately approximates the cross talk noise for a range of optical sources and interconnect configurations.

Journal Article↗
PubMed2006

2004 Optical Society Of America's Topical Meeting on Optical Interference Coatings: Manufacturing Problem.

Results are presented for the second Optical Society of America's Optical Interference Coatings Manufacturing Problem. The participants were asked to produce multilayer coatings which, in the 450-650 nm spectral region and for light incident at 60 degrees, would have transmittances of 0.7 and 0.3 for p- and s-polarized light, respectively. Three different teams each submitted four solutions. Three different deposition processes were used to produce these coatings. The smallest average departure from the target transmission values was 0.79%. A number of interesting conclusions can be drawn from this exercise.

Journal Article↗
PubMed2006

Investigation of the effect of accumulation of thickness errors in optical coating production by broadband optical monitoring.

We present a theoretical approach enabling one to perform a preproduction investigation of the effect of accumulation of thickness errors in the course of optical coating production using broadband optical monitoring. On the basis of this approach we investigate and compare thickness errors that may be associated with such factors as random and systematic errors in measurement data, instabilities of deposition rates, and inaccuracies of on-line algorithms predicting termination instants for layer depositions.

Journal Article↗
PubMed2006

Acousto-optic parallel read/write head for optical disk data storage.

Parallel read and write of optical disks has traditionally used a static grating for read or a linear array of independent lasers for read and write. Depending on the implementation, these systems suffer from coherent cross talk, excessive space between spots, and an inability to independently track. We show that a dynamic acousto-optic grating can generate multiple parallel read/write spots on the disk, each of which can be independently modulated and tracked and all of which are incoherent in less that a bit period. The resulting disk pickup can potentially reach gigabit per second transfer rates with only a modest increase in the drive complexity.

Journal Article↗
PubMed2006

2R optical regenerator in As2Se3 chalcogenide fiber characterized by a frequency-resolved optical gating analysis.

We present a detailed analysis of a 2R optical regenerator based on self-phase modulation in As(2)Se(3) chalcogenide glass fiber using frequency-resolved optical gating (FROG). We obtain good agreement between the FROG measurements and theory, and confirm that the output pulses are near-transform limited. We show that two-photon absorption improves the profile of the power transfer function while not degrading the temporal performance.

Journal Article↗