Vadakke Matham Murukeshan

Cure monitoring of smart composites using Fiber Bragg Grating based embedded sensors

A sensor embedded in the composite laminate can act as a temperature transducer during the composite cure mechanism. Once the composite is cured, the same sensor can be used to provide the information about the mechanical changes that influence the performance of the material. Fiber Bragg Grating (FBG) sensor is one such sensor which one can use for the composite cure monitoring. We present here the results obtained with an associated FBG sensor system for the cure monitoring of smart composites. The performance of the embedded FBG sensor smart composite specimens under 3- and 4-point bending conditions are also being investigated. Finally, the performance analysis has been extended to cantilever specimens.

Compact SOI nanowire refractive index sensor using phase shifted Bragg grating

The phase shifted vertical side wall gratings are designed and numerically simulated on a submicron SOI waveguide to obtain the performance characteristics needed for an integrated refractive index sensor. The gratings are designed to obtain narrow band width, high transmittivity and sharp line shape in the resonant transmission so that the sensor sensitivity can be improved. The proposed sensor is easy to fabricate and will provide a linear response over a wide wavelength range with a compact structure dimension which is suitable for label free biosensing applications. The detection limit of the sensor is investigated through both wavelength shift and intensity measurement method and the performance parameter is compared with other silicon based structures like Mach-Zehnder interferometer, ring resonator and surface corrugated Bragg grating.

Formulation and implementation of a phase-resolved fluorescence technique for latent-fingerprint imaging: theoretical and experimental analysis

A theoretical and experimental study of the imaging of latent fingerprints by a phase-resolved fluorescence technique along with associated signal-processing analysis is described. The system configuration is optimized by incorporation of a novel approach of homodyne-assisted even-step phase shifting in a signal-processing concept. The excitation laser source and gain of the detection device, which are modulated at megahertz frequency followed by sensitive signal-processing concepts, are employed to separate the fingerprint fluorescence from background fluorescence. Experiments are carried out with fingerprints deposited upon different types of substrate surfaces. Later, a quantitative image-quality assessment is carried out, which confirms the improvement in the quality of the phase-resolved fingerprint image. Imaging of older fingerprints with better contrast is also carried out with the proposed novel technique.

Excitation of gap modes in a metal particle-surface system for sub-30 nm plasmonic lithography

In this Letter, a near-field optical excitation of gap modes in a metal particle-surface system for patterning periodic nanostructure is proposed and numerically demonstrated using the finite-difference time-domain method. It is observed that high-density sub-30 nm periodic structures were achievable by employing an aluminium nanosphere-silver surface system. A 2D resist profile cross section using the modified cellular automata model, which was obtained through this proposed configuration, is also presented.

An optical crossconnect (OXC) using drawbridge micromirrors

Abstract The free-space optical crossconnect (OXC) is one of the key components for all-optical networking. Different configurations of micromachined drawbridge mirrors are developed to enable optical switching action in free-space with the advantages of accurate angular alignment, large working distance, high switching speed, long-term reliability operation and small switch element size. A prototype 4×4 optical crossconnect OXC having the size of about 4 mm ×4 mm is demonstrated. The OXC is scalable to large port numbers. Factors such as optical crossconnect architectures, insertion losses and mirror motion types are investigated for the design of optical crossconnects having large port numbers.

Analysis on the nature of thermally induced deformation in human dentine by electronic speckle pattern interferometry (ESPI)

OBJECTIVE To examine the in-plane and out-of-plane response of human dentine to thermal loads in real time. METHODS An Electronic Speckle Pattern Interferometry (ESPI) system sensitive to both the in-plane and out-of-plane displacements was configured and used in conjunction with an advanced fringe processing technique. Specimens were prepared from freshly extracted lower central incisor teeth and were separately mounted on a thermal block to apply thermal loads from room temperature (25 degrees C) to 60 degrees C. The real time speckle patterns were acquired using a digital camera. These digital fringe patterns were subjected to further image processing to enhance the quality of fringes. The resultant images were later analyzed to study the out-of-plane and in-plane displacement gradients in the facio-lingual plane of the dentine. RESULTS The out-of-plane deformations were observed in the plane perpendicular to the long axis of the tooth, while the in-plane deformations occurred in the plane parallel to the long axis of the tooth. CONCLUSION The ESPI analysis revealed whole-field and distinct thermal response in human dentine in-plane and out-of-plane. The cervical dentine experienced distinct and conspicuous displacement to the temperature changes.

Discrete and Fine Wavelength Tunable Thermo-Optic WSS for Low Power Consumption

Broadband wavelength tunability is demonstrated in a microring resonator (MRR)-based thermo-optic wavelength selective switch (TO-WSS) with low power consumption and low thermal crosstalk. Instead of direct tuning a single MRR spectrum, the discrete and fine wavelength tunability in a Vernier configured TO-WSS has been used to achieve single wavelength selection over a high free spectral range (FSR). With the observed discrete tunability (7.3 mW/FSR) and fine tunability (5 mW/nm) of the WSS, the power requirement for full band tuning can be reduced to 32.7% of that of a single ring tuning.

{\rm C}{+}{\rm L}

A prototype tunable laser of /spl sim/2 mm/spl times/1.5 mm size has been developed for wavelength-division-multiplexing (WDM) application. This device is an integrated micromachined polysilicon three-dimensional (3-D) mirror with a single-mode Fabry-Perot laser diode and an antireflection-coated optical fiber. The micromirror can be driven to move laterally by an electrostatic comb-drive that changes the external cavity length of laser diode enabling wavelength tuning. A wavelength-tunable range of 16 nm is obtained using a driving voltage within /spl plusmn/3 V at a bias voltage of 10 V.

Band Tunability

Microlens-ended fibers could find great usefulness in future biomedical applications, particularly in endoscopic imaging applications. In this context, this paper focuses on microlens-attached specialty optical fibers such as imaging fiber that can be used for probe imaging applications. Stand-alone self-aligned polymer microlenses have been fabricated by microcompression molding. The fabrication parameters have been optimized for different materials, such as poly(methyl methacrylate) (PMMA), polycarbonate (PC Lexan 123R), Zeonor 1060R (ZNR), and Topas COC. A comparison study of the focusing and spatial resolution of the fabricated lenses is performed prior to employing them for fiber-optic fluorescence imaging applications.

A novel integrated micromachined tunable laser using polysilicon 3-D mirror

This work presents a theoretical study of using the interference of multiple counter-propagating evanescent waves as a lithography technique to print periodic two dimensional features. The formulation of the three dimensional Cartesian space expression of an evanescent wave is presented. In this work, the evanescent wave is generated by the total internal reflection of a plane wave at the interface between a incident dielectric material and a weakly absorbing transmission medium. The influences of polarization, incident angle and the phase shifting of the incident plane waves on the evanescent wave interference are studied. Numerical simulation results suggest that this technique enables fabrication of periodic two dimensional features with resolution less than one third the wavelength of the irradiation source.