Awad S. Gerges

Coherence tuned fiber optic sensing system, with self-initialization, based on a multimode laser diode

In this paper we study the potential of using multimode laser diodes as an alternative to low coherence length sources normally used white light fiber optic interferometric sensors. A simple theoretical model is introduced to demonstrate the autocorrelation function of such sources. An experimental setup of two interferometers in tandem was used to study the coherence properties of the multimode laser diode Mitsubishi ML-4406 and then to demonstrate the possibility of using it in coherence tuned multiplexing systems. The main advantage of using such sources is to launch more optical power into the monomode fiber and hence to improve the system resolution.

High-sensitivity fiber-optic accelerometer.

We describe a novel accelerometer in which the sensing element is a weighted diaphragm. The displacement of the diaphragm produced by acceleration is measured using a miniature hemispherical air-spaced Fabry-Perot interferometer, of which one mirror is mounted on the diaphragm. The interferometer is illuminated by a diode laser and addressed through a monomode optical fiber.

Practical fiber-optic-based submicro-g accelerometer free from source and environmental perturbations

We describe a novel accelerometer in which the sensing element is a weighted diaphragm designed to have minimal cross coupling. The displacement of the diaphragm, produced by acceleration, is measured by using two miniature hemispherical air-spaced Fabry-Perot interferometers, one constructed on either side of the diaphragm. The output of the two interferometers is processed such that the detrimental effects caused by wavelength drift of the source and variation in temperature of the sensor are reduced by 45.8 and 27.3 dB, respectively, compared with those of a single interferometer.

A hemispherical air cavity fibre Fabry-Perot sensor

Abstract We describe here a novel form of sensor, based on fiber optic technology, in which the sensing element is a miniature hemispherical air cavity Fabry Perot interferometer. The optical properties of the air cavity were analysed theoretically. A simple technique was used to form the sensing element. Finally the properties of the air cavity as an optical interferometer were investigated experimentally.

Image continuity at different levels of zoom for fringe patterns

Fringe patterns are raw output data from many measurement systems including laser interferometers and moiré systems. For instruments with a range of zoom levels to measure the object at different scales, a technique (algorithm) is needed to combine and/or compare data to obtain information at different levels of details. A technique to keep the continuity of output images both at different levels of zoom and within the same level of zoom is developed and demonstrated. Image registration is used to correlate images, find relative zoom values, and obtain shift between images in the lateral plane. Fringe patterns from a moiré system and a laser interferometer are used as images to be stitched and demonstrate the technique. Interferomteric fringes are used to find the required parameters to inter-relate locations and scale of the fringe patterns at different levels of zoom. The calculated parameters are scale and translation in both directions; these parameters make it possible to locate the coordinates of the region that the measurement system is zoomed in on, related to the area with lower magnification and relative locations of images within the same level of zoom. Results show that this technique is capable of finding the scale and shift parameters within the resolution of one pixel and therefore can restore continuity between images at different levels of zoom.

A fibre-optic based high temperature probe illuminated by a multimode laser diode

Abstract A remote fibre-optic based temperature sensor capable of operating above 1000°C, based upon a hemispherical solid etalon is described. A coherence tuned receiving interferometer is used to demodulate the signal. By illuminating the system with a multimode laser diode, significant improvements in the signal to noise ratio have been achieved when compared with illumination via a conventional low coherence-length source.

Image continuity at different levels of zoom for Moiré techniques

Moiré technique is a technique used for 2D and 3D imaging and surface characterization. Moiré systems may have a range of zooms to image an object at different levels of details or Moiré images may be combined (or compared) with images from other interferometers. So, it is needed to inter-relate images together in order to keep the continuity of the images at different levels of zoom or images from different types of interferometers. This paper uses image registration techniques to correlate images and find scale and translation between two images. Image registration is widely used in medical imaging and range imaging to relate two different images from a single object or scene. In this work, only interferograms from two successive levels of zooms of a Moiré system are used. Saved interferograms are correlated using one of the affine algorithms which are used in image registration and then relative scale and shift are calculated. Calculation of these parameters makes it possible to locate the position of area that the Moiré system is zoomed in, related to the area with lower zoom level. Simulation results show that this technique is applicable and successful in finding the scale and shift parameters and therefore can keep the continuity between images at different levels of zoom.

Biological imaging with high dynamic range using compressive imaging technique

Scenes in real world have dynamic range of radiation that cannot be captured by conventional cameras. High dynamic range imaging is a technique to capture detail images where, in the field of image, intensity variation is extreme. This technique is very useful for biological imaging where the samples have very bright and very dark regions and both parts have useful information. In this article we propose a novel high dynamic range imaging technique based on compressive imaging that uses one single detector instead of camera (array of detectors) to capture an image. Combination of high dynamic range imaging and compressive imaging benefits from imaging with high dynamic range of radiation and advantages of compressive sampling; namely, imaging at regions of optical spectrum where conventional cameras are not readily available and single detectors are available. Additionally, as its name suggests, this technique requires less number of samples (compared to raster scanning). Our experimental results show that high dynamic range compressive imaging system is capable of capturing images with large intensity contrast.

A combined fiber Bragg grating and interferometric based sensor

A novel combined fiber Bragg grating (FBG) and interferometric based sensor is proposed and demonstrated. The sensor is based on two overlapped Michelson interferometers working at different wavelengths in a Sagnac loop and two FBGs used as wavelength selective mirrors. The advantage of the system is that it combines the benefit of point measurement with FBG and the high sensitivity of long gauge interferometric sensor.

New Trends in Wide Bandgap Semiconductors: Synthesis of Single Crystalline Silicon Carbide Layers by Low Pressure Chemical Vapor Deposition Technique on P-Type Silicon (100 and/or 111) and their Characterization

We report the growth of SiC layers on low cost p-type silicon (100 and/or 111) substrates maintained at constant temperature (1050 - 1350oC, ∆T=50oC) in a low pressure chemical vapor deposition reactor. Typical Fourier transform infrared spectrum showed a dominant peak at 800 cm-1 due to Si-C bond excitation. Large area x-ray diffraction spectra revealed single crystalline cubic structures of 3C-SiC(111) and 3C-SiC(200) on Si(111) and Si(100) substrates, respectively. Cross-sectional views exposed by scanning electron microscopy display upto 104 µm thick SiC layer. Energy dispersive spectroscopy of the layers demonstrated stiochiometric growth of SiC. Surface roughness and morphology of the films were also checked with the help of atomic force microscopy. Resistivity of the as-grown layers increases with increasing substrate temperature due to decrease of isolated intrinsic defects such as silicon and/or carbon vacanies having activation energy 0.59 ±0.02 eV.