Micro-device for coupling, multiplexing and demultiplexing using elliptical-core two-mode fiber

We propose and demonstrate experimentally a fiber optic micro-device that is capable of tunably splitting, multiplexing, and demultiplexing optical signals using elliptical-core two-mode optical fiber. A crosstalk of 15 dB with an insertion loss of 1.2 dB was obtained

Elliptical-core two mode fiber sensors and devices incorporating photoinduced refractive index gratings

Results of experiments performed using germanium-doped, elliptical core, two-mode optical fibers whose sensitivity to strain was spatially varied through the use of chirped, refractive-index gratings permanently induced into the core using Argon-ion laser light are presented. This type of distributed sensor falls into the class of eighted-fiber sensors which, through a variety of means, weight the strain sensitivity of a fiber according to a specified spatial profile. We describe results of a weighted-fiber vibration mode filter which successfully enhances the particular vibration mode whose spatial profile corresponds to the profile of the grating chirp. We report on the high temperature survivability of such grating-based sensors and discuss the possibility of multiplexing more than one sensor within a single fiber

Optical Fiber Methods for Autoclave and Epoxy Cure Monitoring

The fabrication process of recently developed advanced technology hybrid structures has placed a demand on methods to monitor the state of cure of resins and epoxies commonly used in composite materials. Such monitoring allows in-situ process control insuring homogeneous structural integrity. Furthermore, fabrication costs can be reduced by avoiding the need to over cure“ the composite specimens. Existing techniques such as differential scanning calorimetry (DSC), optical spectroscopy, and dielectric spectroscopy lack the in-situ capabilities required to monitor localized cure state. Other methods, including ultrasonic wave monitoring, are absolute in nature, require frequent calibration, and involve complex measurement systems for monitoring localized cure state [1–3]. We propose to expand upon a principle recently suggested by M. A. Afromowitz, in which optical waveguides made out of the hybrid resin material itself are embedded within the specimen to be monitored [4]. Such implementation exploits some of the advantages of fiber optic sensing techniques, while avoiding the incorporation of “foreign materials” which might cause inhomogeneities in the composite structure

Strong long-period fiber gratings recorded at 352 nm

We describe long-period grating inscription in hydrogenated telecom fibers by use of high-intensity femto-second 352 nm laser pulses. We show that this technique allows us to fabricate high-quality 30 dB gratings of 300 μm period and 2 cm length by use of a three-photon absorption mechanism. © 2005 Optical Society of America

Design and fabrication of an intrinsically gain flattened Erbium doped fiber amplifier

We report design and subsequent fabrication of an intrinsically gain flattened Erbium doped fiber amplifier (EDFA) based on a highly asymmetrical and concentric dual-core fiber, inner core of which was only partially doped. Phase-resonant optical coupling between the two cores was so tailored through optimization of its refractive index profile parameters that the longer wavelengths within the C-band experience relatively higher amplification compared to the shorter wavelengths thereby reducing the difference in the well-known tilt in the gains between the shorter and longer wavelength regions. The fabricated EDFA exhibited a median gain ?28 dB (gain excursion below $\pm$2.2 dB within the C-band) when 16 simultaneous standard signal channels were launched by keeping the I/P level for each at ?20 dBm/ channel. Such EDFAs should be attractive for deployment in metro networks, where economics is a premium, because it would cut down the cost on gain flattening filter head

Advances and new applications using the acousto-optic effect in optical fibers

This work presents a short review of the current research on the acousto-optic mechanism applied to optical fibers. The role of the piezoelectric element and the acousto-optic modulator in the excitation of flexural and longitudinal acoustic modes in the frequency range up to 1.2 MHz is highlighted. A combination of the finite elements and the transfer matrix methods is used to simulate the interaction of the waves with Bragg and long period gratings. Results show a very good agreement with experimental data. Recent applications such as the writing of gratings under the acoustic excitation and a novel viscometer sensor based on the acousto-optic mechanism are discussed

Research activities arising from the University of Kent

In this paper I describe research activities in the field of optical fiber sensing undertaken by me after leaving the Applied Optics Group at the University of Kent. The main topics covered are long period gratings, neural network based signal processing, plasmonic sensors, and polymer fiber gratings. I also give a summary of my two periods of research at the University of Kent, covering 1985–1988 and 1991–2001

Infective endocarditis causing acute aortic regurgitation

Interesting echocardiographic features in a case o f acute onset aortic regurgitation due to infective endocarditis of bicuspid aortic valve are reported. Early closure of mitral valve (ECMV) recog-nised by echocardiography confirmed the clinical diagnosis of acute inset aortic regurgitation. Aortic root echocardiogram showed ec-centric diastolic closure line of bicuspid aortic leaflets and multiple echoes on aortic leaflets due to bacterial vegetations