Biomedical subjects

Moshe Horowitz

Publications and source records attributed to Moshe Horowitz.

9 recordsLinked to original sources

PubMed2006

Analysis and design of nonlinear fiber Bragg gratings and their application for optical compression of reflected pulses.

We demonstrate a novel split-step solution for analyzing nonlinear fiber Bragg gratings. The solution is used for designing nonlinear fiber Bragg gratings with a low reflectivity. The structure of the grating is designed according to the profiles of the incident and reflected pulses. We demonstrate our method for nonlinear compression of a pulse reflected from a fiber Bragg grating. The method allows us to obtain compressed pulses with a very low wing intensity.

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PubMed2006

To biopsy or not to biopsy: an 82-year-old patient with a retroperitoneal mass and severe low back pain.

An 82-year-old patient was admitted to our ward due to disabling severe low back pain. Computed tomography of the spine revealed a retroperitoneal space-occupying lesion encroaching on two adjacent lumbar vertebrae and causing destruction of the cortex of their anterior aspect. The patient was scheduled for a biopsy of the mass. Magnetic resonance (MR) of the lumbar spine, however, suggested that the mass was most probably an aortic aneurysm. The biopsy was cancelled and the patient was referred for surgical intervention. MR is indicated in the evaluation of a solid mass causing vertebral destruction in order to achieve an accurate preoperative diagnosis and prevent a hazardous invasive procedure.

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PubMed2006

Reconstruction of long-period fiber gratings from their core-to-core transmission function.

In order to reconstruct the structure of a long-period grating, both the complex core-to-core transmission function and the complex core-to-cladding transmission function should be known. However, in practice, only the core-to-core transmission function of the grating can be measured. We demonstrate theoretically the reconstruction of long-period gratings from only the core-to-core transmission function. The reconstruction is performed by extracting the complex core-to-cladding transmission function of the grating from its core-to-core transmission function. Generally, the extraction is not unique; however, we show that by writing an additional grating in cascade to the interrogated grating, a unique reconstruction can be obtained. In weak long-period gratings, only the amplitude of the core-to-core transmission function is needed to reconstruct the grating. The results of our work can enable the experimental reconstruction of long-period gratings from their transmission function as well as the development of novel distributed sensors.

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PubMed2005

Experimental reconstruction of a long-period grating from its core-to-core transmission spectrum.

We demonstrate, for the first time to our knowledge, reconstruction of the structure of a long-period grating from its measured core-to-core transmission spectrum intensity. The reconstruction is obtained by writing an auxiliary grating in cascade to the interrogated grating. Our reconstruction technique is based on using the Hilbert transform and a phase-retrieval algorithm. Using our method, we have reconstructed the structure of a uniform long-period grating with a 47% coupling efficiency.

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PubMed2005

Reconstruction of a fiber Bragg grating from noisy reflection data.

We develop a novel method that enables one to reconstruct the structure of highly reflecting fiber Bragg gratings from noisy reflection spectra. When the reflection spectrum is noisy and the grating reflectivity is high, noise in the Bragg zone of the reflection spectrum is amplified by the inverse scattering algorithms and prevents the reconstruction of the grating. Our method is based on regularizing the reflection spectrum in frequencies inside the Bragg zone by using the data on the grating spectrum outside the Bragg zone. The regularized reflection spectrum is used to reconstruct the grating structure by means of inverse scattering. Our method enables one to analyze gratings with a high reflectivity from a spectrum that contains a high level of noise. Such gratings could not be analyzed by using methods described in previous work [IEEE J. Quantum Electron. 39, 1238 (2003)].

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PubMed2005

[Transient lower limbs paralysis--a rare presenting symptom of Sjögren's syndrome].

Sjögren's syndrome is commonly presented with eye and mouth dryness caused by an autoimmune destruction of lacrimal and salivary glands. Kidney involvement is not common but may appear in patients with long standing disease. We present a patient with Sjögren's syndrome whose first manifestation of the disease was related to type 1 renal tubular acidosis (RTA) causing severe hypokalemia with lower limb paralysis. The uneven distribution of limb weakness necessitated the exclusion of cord compression.

Acidosis↗

PubMed2004

Inverse scattering algorithm for reconstructing lossy fiber Bragg gratings.

We demonstrate an inverse scattering algorithm for reconstructing the structure of lossy fiber Bragg gratings. The algorithm enables us to extract the profiles of the refractive index and the loss coefficient along the grating from the grating transmission spectrum and from the reflection spectra, measured from both sides of the grating. Such an algorithm can be used to develop novel distributed evanescent-wave fiber Bragg sensors that measure the change in both the refractive index and the attenuation coefficient of the medium surrounding the grating. The algorithm can also be used to analyze and to design fiber Bragg gratings written in fiber amplifiers. A novel method to overcome instability problems in extracting the parameters of the lossy grating is introduced. The new method also makes it possible to reduce the spectral resolution needed to accurately extract the grating parameters.

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PubMed2004

Optical imaging with a directional detector.

We demonstrate a new optical imaging technique based on a directional detector that measures the intensity of light waves that propagate only in a narrow angular window around a specific direction. Light waves that propagate in other directions do not significantly affect the detector output. The directional detector is obtained by illuminating the interrogated object with a high-coherence light source and measuring the interference between the light wave reflected from the object and a reference wave. By measuring the intensity of the interference pattern with an optical detector that has a finite width and moving the object by use of a rotation stage, one can obtain the angular directionality of the filter. The use of coherent detection in the directional detector makes it possible to increase the sensitivity of the system. The directional detector was analyzed theoretically and demonstrated experimentally for a Gaussian beam scattered from a conducting cylinder. The interference enabled us to theoretically increase the angular resolution by a factor of approximately 10 and experimentally by a factor of 8.5. A configuration for using a directional detector array to reconstruct a two-dimensional object is suggested. Since the directional detector makes it possible to reduce the effect of diffraction and scattering, reconstruction techniques based on nondiffracting sources, as implemented in x-ray tomography, may be used.

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PubMed2003

Measuring temperature profiles in high-power optical fiber components.

We demonstrate a new method for measuring changes in temperature distribution caused by coupling a high-power laser beam into an optical fiber and by splicing two fibers. The measurement technique is based on interrogating a fiber Bragg grating by using low-coherence spectral interferometry. A large temperature change is found owing to coupling of a high-power laser into a multimode fiber and to splicing of two multimode fibers. Measurement of the temperature profile rather than the average temperature along the grating allows study of the cause of fiber heating. The new measurement technique enables us to monitor in real time the temperature profile in a fiber without the affecting system operation, and it might be important for developing and improving the reliability of high-power fiber components.

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