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At least 397 records · Page 22Linked to original sources
PubMed2006

Measuring optical fiber length by use of a short-pulse optical fiber ring laser in a self-injection seeding scheme.

A method for measuring the length of an optical fiber by use of an optical fiber ring laser pulse source is proposed and demonstrated. The key element of the optical fiber ring laser is a gain-switched Fabry-Perot laser diode operated in a self-injection seeding scheme. This method is especially suitable for measuring a medium or long fiber, and a resolution of 0.1 m is experimentally achieved. The measurement is implemented by accurately determining the pulse frequency that can maximize the output power of the fiber ring laser. The measurement results depend only on the refractive index of the fiber corresponding to this single wavelength, instead of the group index of the fiber, which represents a great advantage over both optical time-domain reflectometry and optical low-coherence reflectometry methods.

Journal Article↗
PubMed2001

Optical properties of an isotrophic optically active medium at oblique incidence.

The optical properties of an isotropic optically active medium at oblique incidence have been investigated. It was found that the amount of transmitted light converted from p polarization to s polarization and vice versa, through an isotropic optically active medium, is independent of the state of incident polarization. Though the optical rotation through the optically active medium is same for p and s polarization at normal incidence, it becomes different at oblique incidences.

Journal Article↗
PubMed2003

Three-dimensional optical-transfer-function analysis of fiber-optical two-photon fluorescence microscopy.

The three-dimensional optical transfer function is derived for analyzing the imaging performance in fiber-optical two-photon fluorescence microscopy. Two types of fiber-optical geometry are considered: The first involves a single-mode fiber for delivering a laser beam for illumination, and the second is based on the use of a single-mode fiber coupler for both illumination delivery and signal collection. It is found that in the former case the transverse and axial cutoff spatial frequencies of the three-dimensional optical transfer function are the same as those in conventional two-photon fluorescence microscopy without the use of a pinhole.However, the transverse and axial cutoff spatial frequencies in the latter case are 1.7 times as large as those in the former case. Accordingly, this feature leads to an enhanced optical sectioning effect when a fiber coupler is used, which is consistent with our recent experimental observation.

Journal Article↗
PubMed2005

Gaussian-optics-based optical modeling and characterization of a Fabry-Perot microcavity for sensing applications.

A generalized study has been carried out on the modeling of a Fabry-Perot microcavity for sensing applications. Different analytical models on transmission characteristics of a Fabry-Perot microcavity are established by using plane-wave-based techniques, such as the Macleod characteristic matrix technique, the transfer matrix technique, and Smith's technique. A novel Gaussian-optics-based model for a Fabry-Perot microcavity illuminated by a laser beam is then developed and validated. The influence of laser beam waist on microcavity optical response is investigated, and the required minimal beam waist size is explored to ensure a useful optical response for sensing applications that can be accurately predicted by plane-wave optics. Also, the perturbations of microcavity performance induced by different types of microcavity mirror imperfections are discussed, based on the novel optical model. The prototype of the proposed Fabry-Perot microcavity for sensing applications has been successfully fabricated and characterized.

Journal Article↗
PubMed2004

Controllable photoinduced optical attenuation in a single-mode optical fiber by irradiation of a femtosecond pulse laser.

Novel optical attenuation fibers were fabricated by the irradiation of a focused infrared femtosecond pulsed laser onto the core of a silica glass single-mode optical fiber. Optical attenuation at a wavelength of 1.55 microm proportionally increased with increasing numbers of irradiation points and was controllable under laser irradiation conditions. The single-mode property of the waveguide and the mode-field diameter of the optical fiber were maintained after irradiation of the femtosecond laser. It is suggested that the attenuation results from optical scattering at photoinduced spots formed inside the fiber core.

Journal Article↗
PubMed2005

Experimental demonstration of 10 Gbit/s transmission with an optical backplane system using optical slots.

A practical optical backplane system was prepared with transmitter-receiver processing boards and an optical backplane made from polymeric-waveguide-embedded optical printed-circuit boards. Optical slots were used as connection components between the transmitter-receiver processing boards and the backplane board to permit easy and repeatable insertion and extraction of the boards with micrometer precision. We report 10 Gbit/s data transmission between an optical backplane and the transmitter-receiver processing boards.

Journal Article↗
PubMed1981

Anterior ischemic optic neuropathy. V. Optic disc edema an early sign.

Four unusual patients had bilateral anterior ischemic optic neuropathy (AION). In all four cases, AION developed in the first eye with the classic presentation. The fellow eye had symptomless optic disc edema (ODE) with no subjective or objective visual loss initially, but the classic AION clinical picture developed later on. The findings indicate that symptomless ODE may precede the visual loss in AION and could constitute the earliest sign of this disease. Since ODE in AION is due to axoplasmic flow stasis that, by itself, does not produce visual loss (this is produced by disruption of visual impulse transmission), this would suggest that mild optic nerve head ischemia interferes with axoplasmic flow without disrupting the visual impulse; however, more severe ischemia would disrupt both. Possible effects of various grades of acute optic nerve head ischemia are discussed.

Aged↗
PubMed1990

Optic nerve head extracellular matrix in primary optic atrophy and experimental glaucoma.

Unilateral glaucomatous optic neuropathy and optic nerve transections were produced in cynomolgus monkeys, and the optic nerve heads were examined by light and electron microscopic immunohistochemistry. Glaucomatous nerve heads showed increased labeling for collagen type IV along the margins of beams in the lamina cribrosa, due to accumulation of basement membrane-like materials. We also noted material in the pores of the laminar beams that labeled with antibodies to collagen types I, III and IV, but not elastin. In transected eyes, increased type IV labeling of laminar beam margins resulted solely from redundant astrocyte basement membranes. Extracellular matrix deposition within laminar pores was not observed following optic nerve transection; hence this may be a selective response to elevated intraocular pressure. This response may alter the biochemical composition of the lamina cribrosa and its function in patients with elevated intraocular pressure.

Animals↗
PubMed1990

Extracranial optic nerve decompression for traumatic optic neuropathy.

We examined 14 patients with acute, unilateral optic nerve injury after blunt head trauma. In each patient the optic canal was decompressed through an ipsilateral external ethmoidectomy. The patients also received treatment with dexamethasone during the perioperative period. There was no morbidity or mortality. Eleven of the 14 patients improved, including 3 of the 5 who could not perceive light preoperatively. Transethmoid-sphenoid optic canal decompression is a safe and effective treatment for indirect optic nerve trauma.

Adult↗
PubMed1997

Diffusion-weighted imaging of the human optic nerve: a new approach to evaluate optic neuritis in multiple sclerosis.

The apparent diffusion coefficient (ADC) in the optic nerve was measured from diffusion-weighted magnetic resonance imaging using an intravoxel incoherent motion (IVIM) sequence. The subjects were seven normal volunteers and eight patients with multiple sclerosis (MS) with a total of four optic nerves with acute neuritis and nine nerves with chronic neuritis. The mean ADC (4.18 +/- 1.13 x 10(-3) mm2/s, n = 9) in the optic nerves with chronic neuritis was significantly higher than that in normal volunteers (1.56 +/- 0.675 x 10(-3) mm2/s, n = 14) and that in the nerves with acute neuritis (0.94 +/- 0.43 x 10(-3) mm2/s n = 4) (P < 0.001). The ADC is useful in assessing MS foci in the optic nerves.

Adolescent↗
PubMed1996

Long time echo STIR sequence magnetic resonance imaging of optic nerves in optic neuritis.

Magnetic resonance images of optic nerves were obtained in 20 patients with acute optic neuritis (ON), and assessed by means of clinical, visual field and visual evoked potential evaluations; the imaging was repeated 1 year later. The results of the conventional Short Tau Inversion Recovery (STIR) sequence obtained using short time echo (STE-STIR: 22 msec) were compared with those of the long time echo sequence (LTE-STIR: 80 msec). The conventional STE-STIR sequence revealed lesions in 57.2% cases of acute ON and in 42.9% of the optic nerves affected by previous ON; the LTE-STIR sequence was diagnostic in 95.2% of acute ON cases and in 85% of patients with previous ON. The calculated length of the optic nerve lesions was significantly longer in the images obtained using the LTE-STIR sequence than in those obtained using conventional STE-STIR sequences.

Adult↗
PubMed1988

Size of the optic nerve scleral canal and comparison with intravital determination of optic disc dimensions.

Diameters, area, and form of the optic nerve scleral canal were measured in 107 freshly enucleated, unfixed, human donor eyes. Macrophotographs of the sectioned posterior fundus pole were provided with a millimeter scale and evaluated planimetrically. They revealed a surprising variation: area: 2.59 +/- 0.72 mm2 (minimum 0.68 mm2, maximum 4.42 mm2); minimal diameter: 1.67 +/- 0.72 mm; maximal diameter: 1.92 +/- 0.32 mm. The mean form factor was 0.92 +/- 0.11 and the quotient of minimal to maximal diameter 0.86 +/- 0.11, indicating a slightly oval nearly round form. The coefficients of variation of the method's reproducibility were 0.005 for intraobserver and 0.02 for interobserver determination. The size values of these optic nerve scleral canals were not significantly (Wilcoxon-Mann-Whitney test) different from than those of 100 unselected optic discs that had been determined intravitally using Littmann's method. This indicates the reliability of Littmann's method for the intravital measurement of the optic nerve head in absolute dimensions.

Adult↗
PubMedDate not supplied

Bilateral, nearly simultaneous anterior ischemic optic neuropathy complicated by diabetes and bilateral, small, crowded optic discs.

BACKGROUND: Bilateral simultaneous anterior ischemic optic neuropathy (AION) is uncommon. We report a case of bilateral and nearly simultaneously occurring AION. CASE: A 61-year-old man was referred to our hospital with bilateral optic disc edema. OBSERVATIONS: Visual field testing demonstrated inferior nasal defect OD and inferior defect OS. Fluorescein angiography showed a delay of dye filling in the superior part of the optic disc in both eyes. The patient had poorly controlled diabetes. A mild increase in erythrocyte sedimentation rates and creactive protein was observed, but the results of temporal artery biopsy were negative. His optic discs were small and lacked biological cups, which has been identified as a risk factor for developing AION. CONCLUSIONS: The complications of the structural anomaly, also known as "disc at risk," and diabetes might have caused the bilateral and nearly simultaneously occurring AION.

Blood Pressure↗
PubMedDate not supplied

Is all nondefinable optic atrophy Leber's hereditary optic neuropathy?

Leber's hereditary optic neuropathy has been considered a bilateral, sequential hereditary optic neuropathy occurring overwhelmingly in young men. Until recently the diagnosis has been based on clinical criteria: severe loss of vision associated with central scotomas and classic ophthalmoscopic findings (circumpapillary telangiectatic microangiopathy, pseudoedema of the disk with absence of staining on fluorescein angiography, tortuous vessels in the early stages and eventually optic disk pallor). In 1988 a genetic mutation associated with Leber's hereditary optic neuropathy affecting mitochondrial DNA was recognized. Subsequently other mutations have been discovered as well. The ability to identify these patients technically has allowed us to recognize cases that do not fit our previous clinical criteria. One such case is presented and the question asked is whether the findings are related to the clinical course.

Child↗
PubMed2004

Mechanical and optical characteristics of a new fiber optical system used for cardiac contraction measurement.

In order to obtain a better physiological performance and a closer restoration of the regular rhythm of failing hearts, a new fiber optical sensor system for the measurement of cardiac contraction has been developed. It consists of an opto-electrical unit and a sensing fiber which has to be positioned in the heart. The objective of this new fiber optic sensor system is to use the inotropic information to adjust a stimulation algorithm in single or multichamber pacing or to detect arrhythmia in insufficient heart function. In this study, the mechanical and optical characteristics of different fibers are investigated. The relationship between the attenuation (with an achieved numerical maximum of 0.3 dB), the bending diameter and the angle of bending is determined in a range of 20-160 mm. The most suitable fiber for the application in cardiological problems is determined (WT8 fiber), for which the sensitivity is analyzed. Additionally, power spectra are calculated from WT8 fiber signals obtained from pig hearts, working under physiological conditions. The maximal frequency response was 23 Hz. It is concluded that the fiber optical measurement of cardiac contraction is not only feasible and reproducible, but the WT8 fiber also shows optimal behavior in the range of parameters occurring in the heart chambers. Nevertheless, in order to restrict the measured signal reliably to bending processes within the chambers only, it is concluded that a special combined fiber has to be constructed with a high sensitivity only at its terminal section within the heart.

Algorithms↗
PubMed2005

Optic nerve diffusion tensor imaging in optic neuritis.

Diffusion tensor magnetic resonance imaging (DT-MRI) provides in vivo information about the pathology of multiple sclerosis lesions. Increases in mean diffusivity (MD) and reductions in fractional anisotropy (FA) have been found and may represent axonal disruption. The optic nerve is an ideal structure for study by DT-MRI but previous clinical studies did not obtain the full diffusion tensor necessary to calculate MD and FA. In this study, a technique that was specifically developed to achieve full diffusion tensor measurements from the optic nerve (zonal oblique multislice (ZOOM) echoplanar imaging) was applied to 25 patients with a single unilateral episode of optic neuritis at least one year previously, and 15 controls. The intraorbital nerves were segmented on non-diffusion-weighted images and the regions of interest transferred to MD, FA, and eigenvalue maps to obtain quantitative data. Quantitative visual testing and electrophysiology were also performed. In affected nerves, mean MD and mean orthogonal eigenvalue lambda( perpendicular) were elevated, and mean FA reduced compared with clinically unaffected contralateral nerves (P < 0.001) and control nerves (P < 0.001). The mean principal eigenvalue lambda\\ was significantly increased in affected nerves compared to contralateral unaffected nerves (P = 0.04) but not compared to control nerves (P = 0.13). There was no association of clinical measures of visual function in affected eyes with the DT-MRI parameters but there was a significant correlation of the whole field visual evoked potential (VEP) amplitude with MD (r = -0.57, P = 0.006) and lambda( perpendicular) (r = -0.56, P = 0.007). These findings suggest that optic nerve DT-MRI measures provide an indication of the structural integrity of axons.

Adult↗
PubMed1985

The pattern of optic nerve fiber loss in anterior ischemic optic neuropathy.

Postmortem quantification of the remaining optic nerve fibers in three eyes with nonarteritic anterior ischemic optic neuropathy showed that the loss of fibers was complete in the superior half of each nerve and included loss of peripheral fibers in the other half. The fibers with the greatest resistance to atrophy were found in the middle of the nerve cross section. The pattern was similar to that found in a previous example of anterior ischemic optic neuropathy and unlike that found in glaucoma or other optic neuropathies studied in similar fashion.

Aged↗
PubMed1992

Optic disk cupping and electrocardiographic abnormalities in an American pedigree with Leber's hereditary optic neuropathy.

We examined the clinical characteristics of affected and unaffected members of an American black family with the 11778 mitochondrial DNA mutation associated with Leber's hereditary optic neuropathy. Thirty-six individuals from four generations were included. All maternally related subjects were shown to be essentially homoplasmic for the 11778 mitochondrial DNA mutation in blood. Paternally related subjects did not carry this mutation. Patients affected with optic neuropathy had optic nerve head cupping. Loss of unmyelinated axons from the prelaminar optic nerve may be responsible for cupping in these patients. Electrocardiographic analysis of subjects carrying the 11778 mitochondrial DNA mutation disclosed statistically significant (P = .02) prolongation of the corrected OT interval as compared to control subjects. While the clinical significance of this magnitude of corrected QT prolongation is unknown, it may represent a systemic manifestation of the 11778 mutation. No electrocardiographic evidence of preexcitation syndromes was seen.

Adolescent↗