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At least 937 records · Page 52Linked to original sources
PubMed2006

Negligible birefringence in dual-mode ion-exchanged glass waveguide gratings.

Polarization dependence of UV-written Bragg gratings in buried ion-exchanged glass waveguides is investigated. A polarization-dependent shift in Bragg wavelength of less than 0.02 nm is measured, both for the even and the odd modes of a laterally dual-mode waveguide. The measured wavelength shift corresponds to a waveguide birefringence of the order of 10(-5), which is negligible for most applications in optical communications. It is observed that the UV-induced birefringence is small, within the limits of the measurement accuracy. The thermal stability of the fabricated gratings is also very good. The results are of particular importance for devices considered here since they require a polarization-independent mode-converting waveguide Bragg grating. Polarization-independent performance of these gratings enables the fabrication of a new class of integrated optical devices for telecommunication applications.

Journal Article↗
PubMed2000

Prospects for treating acquired pendular nystagmus with servo-controlled optics.

PURPOSE: To determine whether a device featuring electronically controlled motor-driven prisms can reduce oscillopsia and improve acuity in patients with acquired pendular nystagmus (APN). METHODS: A device was developed that senses eye movements and, by the use of motor-driven prisms, oscillates the image of the world in lockstep with the pathologic nystagmus, to negate its deleterious visual effects. Unlike existing optical and surgical treatments for nystagmus, the device negates only the pathologic movements. Voluntary and normal reflex eye movements required for normal vision are unaffected. The benefits of the device were assessed by its impact on acuity in five patients with medication-refractory APN. RESULTS: All patients reported decreases in oscillopsia when the device was in operation. Averaged across patients, the device increased the percentage of time in which retinal image velocity was within +/-4 degrees/sec from 12.8% to 33.3%. Acuities improved in four of five patients, by an average of 0.21 logMAR units. CONCLUSIONS: The symptoms of pendular nystagmus can be treated with a servomechanical device. Further refinements in the device should result in greater improvements in acuity, and a portable, wearable version is feasible using existing technologies.

Adult↗
PubMed2004

Quasi-group-velocity matching using integrated-optic structures.

We propose a device to compensate for group-velocity mismatch (GVM) effects that limit the efficiency-bandwidth product in nonlinear frequency-mixing devices. Integrated wavelength-dependent delay lines are introduced periodically in a waveguide containing a series of quasi-phase-matching (QPM) gratings. Appropriate choice of the time delays can compensate for GVM. We have demonstrated a two-stage device in a periodically poled lithium niobate waveguide. Two approximately 150-fs-long pulses generated 6 ps apart by second-harmonic generation in two QPM gratings were resynchronized by a fixed delay line, and their relative phase was fine controlled by temperature tuning. This technique, which can be iterated to more than two segments, permits optical frequency mixers with a higher efficiency-bandwidth product than would be possible in a single grating short enough to avoid GVM effects.

Journal Article↗
PubMed2006

All-optical switching, bistability, and slow-light transmission in photonic crystal waveguide-resonator structures.

We analyze the resonant linear and nonlinear transmission through a photonic crystal waveguide side-coupled to a Kerr-nonlinear photonic crystal resonator. First, we extend the standard coupled-mode theory analysis to photonic crystal structures and obtain explicit analytical expressions for the bistability thresholds and transmission coefficients which provide the basis for a detailed understanding of the possibilities associated with these structures. Next, we discuss limitations of standard coupled-mode theory and present an alternative analytical approach based on the effective discrete equations derived using a Green's function method. We find that the discrete nature of the photonic crystal waveguides allows a geometry-driven enhancement of nonlinear effects by shifting the resonator location relative to the waveguide, thus providing an additional control of resonant waveguide transmission and Fano resonances. We further demonstrate that this enhancement may result in the lowering of the bistability threshold and switching power of nonlinear devices by several orders of magnitude. Finally, we show that employing such enhancements is of paramount importance for the design of all-optical devices based on slow-light photonic crystal waveguides.

Journal Article↗
PubMed2006

Quality assessment of confocal microscopy slide based systems: performance.

BACKGROUND: All fluorescence slide-based cytometry detections systems basically include the following components: (1) an excitation light source, (2) intermediate optics, and (3) a detection device consisting of a CCD camera or a PMT. The optical principles employed is slide-based systems are similar to those of confocal microscopes (CLSM). METHODS: The following tests evaluated confocal equipment performance: dichroic reflectivity, field illumination, lens performance, laser power output, spectral registration, axial resolution, PMT reliability, and system noise. RESULTS: Quality assurance tests provide a basis to determine if the equipment is operating correctly. Laser power, PMTs function, dichroic reflection, spectral registration, axial registration, system noise and sensitivity, lens performance and laser stability were tested colocalization of UV and visible peaks of a bead should be less than 210 nm. Interference contrast optics decrease fluorescence resolution. CONCLUSIONS: QA tests that assess CLSM system performance are also applicable to other slide-based systems. By utilization this type of testing approach, the subjective nature of assessing the CLSM may be eliminated. These tests serve as guidelines for other investigators to ensure that their machines are providing data that is accurate with the necessary resolution, sensitivity and precision.

Animals↗
PubMed2006

Experience with the optical access trocar for safe and rapid entry in the performance of laparoscopic gastric bypass.

BACKGROUND: In laparoscopic surgery, serious complications caused by the blind insertion of trocars are well known. The open technique is compromised by the leakage of carbon dioxide and can also be time consuming, especially in morbidly obese patients. Our aim was to determine whether the optical access trocar can be used to establish a safe and rapid entry during laparoscopic gastric bypass. METHODS: The data on a single surgeon's experience with 370 laparoscopic gastric bypass procedures during a 4-year period were reviewed. The Optiview trocar was used for all except the initial 21 patients. The entry time for the optical trocar was measured in 10 patients. RESULTS: Of the 370 patients undergoing laparoscopic gastric bypass from November 2000 to September 2004, the initial 21 were treated using the standard Veress needle to create the pneumoperitoneum. The next 22 were treated using the Veress needle to create the pneumoperitoneum, followed by insertion of the optical access trocar in the left upper quadrant as the initial trocar. From this point to the present, the optical access trocar has been inserted without the use of a Veress needle. There have been no trocar-related bowel or vascular injuries in the entire series. The mean optical trocar insertion time was 28 +/- 1.2 s. CONCLUSIONS: This is the first laparoscopic gastric bypass series to report the results of its experience with the optical access trocar. This device provides a safe and rapid technique for placement of the initial trocar for laparoscopic gastric bypass. Insertion of the optical trocar with a 10-mm laparoscope into the left upper quadrant is our procedure of choice for obtaining the pneumoperitoneum in this patient population.

Adult↗
PubMed1992

Precision radiation therapy for optic nerve sheath meningiomas.

A more precise radiation therapy technique to treat unilateral optic nerve sheath meningioma is presented. It uses an immobilization device to align the ipsilateral optic nerve with a vertical axis and employs three small half-beam blocked fields to deliver radiation to a small conformal volume, thereby reducing the dose to the optic chiasm and the contralateral optic nerve. Three patients were successfully treated with this technique, and a fourth patient with optic nerve glioma was also treated in a similar fashion and was included in this study. The new technique irradiates a much smaller volume of tissue to high dose levels: 58 cm3 is irradiated to the 80% isodose level and only 18 cm3 to the 95% level. In contrast, the opposed lateral technique irradiates 171 and 73 cm3 to these levels, respectively. Thus, a considerable reduction in the volume of normal tissue irradiated was accomplished. Doses to the pituitary and contralateral optic nerve were 4% of the treatment dose for the new technique, whereas these doses were 40% and 100% for opposed laterals and 10% and 3% for wedged pair, respectively. The average setup error for this technique was very small, 50% of the setups measured were less than 1 mm off, and 92.5% were less than 3 mm off. However, for the conventional setups without a mask, only 21% of the setups were less than 1 mm off and 55% less than 3 mm off. We recommend this technique for localized unilateral optic nerve sheath meningioma and other optic nerve lesions that may require radiation therapy.

Cranial Nerve Neoplasms↗
PubMed1999

Complex spike activity of Purkinje cells in the ventral uvula and nodulus of pigeons in response to translational optic flow.

The complex spike (CS) activity of Purkinje cells in the ventral uvula and nodulus of the vestibulocerebellum was recorded from anesthetized pigeons in response to translational optic flow. Translational optic flow was produced using a "translator" projector: a mechanical device that projected a translational optic flowfield onto the walls, ceiling, and floor of the room and encompassed the entire binocular visual field. CS activity was broadly tuned but maximally modulated in response to translational optic flow along a "best" axis. Each neuron was assigned a vector representing the direction in which the animal would need to translate to produce the optic flowfield that resulted in maximal excitation. The vector is described with reference to a standard right-handed coordinate system, where the vectors, +x, +y, and +z represent, rightward, upward, and forward translation of the animal, respectively. Neurons could be grouped into four response types based on the vector of maximal excitation. +y neurons were modulated maximally in response to a translational optic flowfield that results from self-motion upward along the vertical (y) axis. -y neurons also responded best to translational optic flow along the vertical axis but showed the opposite direction preference. The two remaining groups responded best to translational optic flow along horizontal axes: -x + z neurons and -x-z neurons. In summary, our results suggest that the olivocerebellar system dedicated to the analysis of translational optic flow is organized according to a reference frame consisting of three approximately orthogonal axes: the vertical axis, and two horizontal axes oriented 45 degrees to either side the midline. Previous research has shown that the rotational optic flow system, the eye muscles, the vestibular semicircular canals and the postural control system all share a similar spatial frame of reference.

Animals↗
PubMed2002

Compact wavelength division multiplexers and demultiplexers.

Compact devices for wavelength division multiplexing and demultiplexing, believed to be novel, are presented. These devices are based on planar optics configurations, comprising multiplexed diffractive optical elements. The principle, design, and recording of these planar devices are described, including the fact that the recording is done at a single wavelength in the green region. Experimental procedures and results for planar devices that can handle three wavelengths in the visible as well as in the near infrared are presented.

Journal Article↗
PubMed2005

Design and preliminary analysis of a study to assess intra-device and inter-device variability of fluorescence spectroscopy instruments for detecting cervical neoplasia.

INTRODUCTION: A study was designed to assess variability between different fluorescence spectroscopy devices. Measurements were made with all combinations of three devices, four probes, and three sets of standards trays. Additionally, we made three measurements on the same day over 2 days for the same combination of device, probe, and standards tray to assess reproducibility over a day and across days. MATERIALS AND METHODS: The devices consisted of light sources, fiber-optics, and cameras. We measured thirteen standards and present the data from the frosted cuvette, water, and rhodamine standards. A preliminary analysis was performed with the data that were wavelength calibrated and background subtracted; however, the system has not been corrected for systematic intensity variations caused by the devices. Two analyses were performed on the rhodamine, water, and frosted cuvette standards data. The first one is based on first clustering the measurements and then looking for association between the 5 factors (device, probe, standards tray, day, measurement number) using chi-squared tests on the cross-tabulation of cluster and factor level. This showed that only device and probe were significant. We then did an analysis of variance to assess the percent variance explained by each factor that was significant from the chi-squared analysis. RESULTS: The data were remarkably similar across the different combinations of factors. The analysis based on the clusters showed that sometimes devices alone, probes alone, but most often combinations of device and probe caused significant differences in measurements. The analysis showed that time of day, location of device, and standards trays do not vary significantly; whereas the devices and probes account for differences in measurement. We expected this type of significance using unprocessed data since the processing corrects for differences in devices. However, this analysis on raw data is useful to explore what combination of device and probe measurements should be targeted for further investigation. This experiment affirms that online quality control is necessary to obtain the best excitation-emission matrices from optical spectroscopy devices. CONCLUSION: The fact that the device and probe are the primary sources of variability indicates that proper correction for the transfer function of the individual devices should make the measurements essentially equivalent.

Analysis of Variance↗
PubMed1979

[Microscopic, micro-chemical and fluorescent optical findings in endometrium with a copper-T intrauterine device in situ (author's transl)].

The uteri of ten patients who wore a copper-T for several months up to two years were examined immediately following hysterectomy by conventional microscopic techniques, fluorescent optical techniques after Acridin-Orange-Fluorochromization and by histo-chemical techniques for copper. With none of these methods changes in the endometrium could be found which explained the effect of the copper-T to inhibit implantation. Since practically any morphological change from the normal was absent it is suggested that the inhibiting effect on pregnancy of the copper intra-uterine devices is due to biochemical changes of the intra-uterine environment.

Adult↗
PubMed2005

Refractive-index profiling of azimuthally asymmetric optical fibers by microinterferometric optical phase tomography.

Accurate nondestructive refractive-index profiling is needed in the modeling, design, and manufacturing of optical fibers and fiber devices. Most profile measurement techniques cannot correctly characterize fibers with small or irregular refractive-index variations over their cross sections. Microinterferometric optical phase tomography (MIOPT) is a technique that allows measurement of fiber refractive-index profiles exhibiting such variations. We present the first demonstration, to our knowledge, of MIOPT. The profile of a polarization-maintaining fiber is measured by MIOPT and shown to be in agreement with (destructive) fiber end-face measurements. MIOPT is also applied to the limiting case of a symmetric single-mode fiber.

Journal Article↗
PubMed1989

Optically-based chemical and biochemical sensors for the detection of some drugs and biological compounds.

The development of new methods for determining at a very low level a large spectrum of substances affecting the behaviour of living organisms is still a challenging goal. For such a purpose, chemical sensors which can be defined as the intimate combination of a sensitive and specific layer with a transducer, are undoubtedly among the more promising devices. In this field, optical sensors are expanding rapidly, mainly based on absorption, fluorescence, chemi- and bioluminescence. Beside pH and gases, drugs (anticonvulsant, antitumour, anaesthetic...) and other compounds of biological interest can be determined with specifically designed optical sensors, for instance immunosensors. Special attention will be given to optical biosensors with emphasis on chemi- and bioluminescence-based devices which are highly selective and ultrasensitive. When co-immobilizing various auxiliary enzymes in the sensing layer, the potentialities of such devices can be greatly extended as demonstrated by promising results recently obtained in our group.

Biosensing Techniques↗
PubMed2003

Delay and dispersion characteristics of a frequency-domain optical delay line for scanning interferometry.

The reflective frequency-domain optical delay line employing a diffraction grating, a lens, and a tiltable mirror has emerged as a device particularly suitable for interferometry and optical coherence tomography. The device is comprehensively described, both theoretically and experimentally, in the context of interferometry. The variations of phase and group delay produced by the device as well as its dispersive properties are described and demonstrated experimentally.

Interferometry↗
PubMedDate not supplied

[Equipment for measuring the optical density of wide-format x-ray films].

For qualitative estimation of the dynamics of medical treatment in the patients with pulmonary diseases a device has been produced based on measuring the optical density of X-ray films. This device comprises the optical part of the microphotometer MF-2, a modified microscope stand, with its moving mechanism, electronic circuit with a logarithmic amplifier, control circuit and a double-coordinate-recorder.

Absorptiometry, Photon↗
PubMed2004

Cell micropatterning using photopolymerization with a liquid crystal device commercial projector.

Photopolymerization has been widely used for surface micropatterning. The technique often requires photomasks and light sources with appropriate energies or filters. For rapid prototyping of surface photo-micropatterning, we have developed a novel device by modifying a commercially available liquid crystal device projector. In place of the image expansion unit of the projector, we attached an image reduction unit, an adjustable stage, and an optical monitoring unit. The device projected computer-generated images onto surfaces and subjected these patterns to photopolymerization. Micropatterned images can be easily prepared with various software run on personal computers. With the developed photopolymerization device, micropatterning of poly(ethylene glycol) (PEG) was achieved with PEG-diacrylate and a visible light photopolymerization initiator, camphorquinone. Selective cell adhesion control was also achieved on the micropatterned surfaces.

Animals↗
PubMed2003

Image-based tracking of optically detunable parallel resonant circuits.

In this work strategies for the robust localization of parallel resonant circuits are investigated. These strategies are based on the subtraction of two images, which ideally differ in signal intensity at the positions of the devices only. To modulate their signal amplification, and thereby generate the local variations, the parallel resonant circuits are alternately detuned and retuned during the acquisition. The integration of photodiodes into the devices permits their fast optical switching. Radial and spiral imaging sequences are modified to provide the data for the two images in addition to those for a conventional image in the same acquisition time. The strategies were evaluated by phantom experiments with stationary and moving catheter-borne devices. In particular, rapid detuning and retuning during the sampling of single profiles is shown to lead to a robust localization. Moreover, this strategy eliminates most of the drawbacks usually associated with image-based tracking, such as low temporal resolution. Image-based tracking may thus become a competitive (if not superior) alternative to projection-based tracking of parallel resonant circuits.

Catheterization↗