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Medical diagnostics in the recent past has seen the challenging trend to come up with dual and multi-modality imaging for implementing better diagnostic procedures. The changes in tissues in the early disease stages are often subtle and can occur beneath the tissue surface. In most of these cases, conventional types of medical imaging using optics may not be able to detect these changes easily due to its penetration depth of the orders of 1 mm. Each imaging modality has its own advantages and limitations, and the use of a single modality is not suitable for every diagnostic applications. Therefore the need for multi or hybrid-modality imaging arises. Combining more than one imaging modalities overcomes the limitation of individual imaging method and integrates the respective advantages into a single setting. In this context, this paper will be focusing on the research and development of two multi-modality imaging platforms. The first platform combines ultrasound and photoacoustic imaging for diagnostic applications in the eye. The second platform consists of optical hyperspectral and photoacoustic imaging for diagnostic applications in the colon. Photoacoustic imaging is used as one of the modalities in both platforms as it can offer deeper penetration depth compared to optical imaging. The optical engineering and research challenges in developing the dual/multi-modality platforms will be discussed, followed by initial results validating the proposed scheme. The proposed schemes offer high spatial and spectral resolution imaging and sensing, and is expected to offer potential biomedical imaging solutions in the near future. Published version

This article reviews different waveguide based architectures forlabel-free detection of biomolecules. Working principles of various configurationsare discussed with an emphasis on their sensing principle and sensitivity. Later part of the article demonstrates a silicon waveguide Bragg grating resonator array as a highly sensitive refractive index sensor device for multiplexed detection of multi-analytes. Main features of the sensor element are discussed through numerical simulation, and proof-of concept device is demonstrated through micro fabrication. The proposed configuration of silicon waveguide based sensor array is expected to find potential application in portable chip based devices as highly sensitive multiplexed biosensors. Published version

Noninvasive medical imaging techniques have high potential in the field of ocular imaging research. Angle closure glaucoma is a major disease causing blindness and a possible way of detection is the examination of the anterior chamber angle in eyes. Here, a simple optical method for the evaluation of angle-closure glaucoma is proposed and illustrated. The light propagation from the region associated with the iridocorneal angle to the exterior of eye is considered analytically. The design of the gel assisted probe prototype is carried out and the imaging of iridocorneal angle is performed on an eye model. Published version

Visual access to physically inaccessible parts has become the forefront of research and development in medical diagnostics tools and procedures. Flexible and thin endoscopes with fiber bundle as an image conduit serves this purpose. However, when the light passes through the core of the fiberlet, it is blocked by the inter fiberlet gap. This structural limitation creates special honeycomb like pattern overlaying the image captured with the image fiber assisted probes, known as the comb structure or fiber pixelation. It obstructs the perception of the original image sacrificing resolution and contrast and inhibits the use of object recognition and tracking algorithms. Generally, comb structure removal or depixelation methods are employed to remove honeycomb pattern from an image. In the recent past, several depixelation techniques have been proposed albeit using different set of pixilated images by different researchers. It is quite difficult to make a comparison of their performances based on such images, as they adopt different images for different particular framework of their study. In this context, a basic database of such images is the need of the hour to meet the growing diagnostic needs in the medical and industrial arena. This paper in this context proposes and details a Comb Structure Affected Image database (CSAI) to meet the objective. Images are generated considering the image fiber specifications and the characteristics at different targeted optical imaging modalities delineated by resolution scales. The proposed database is designed to have a set of synthetically generated pixelated images of test patterns of different scales, sizes and shapes. Published version

The optical fiber phase modulator is an important component in fiber opiie interferometers f sensors, where the modulation is achieved by physically varying the parameters such as the refractive index or the length of the optical fiber. The fiber optic phase modulator is normally realised by wrapping a fiber on piezo-electric transducer (PZT), usually of cylindrical form. It is difficult to rely purely on published data of piezoelectric constants, because the performance depends critically on the dimensions of the cylinder and the type and compositions of the PZT material. Hence, it is essential that the phase modulator is calibrated before being put to an application. The paper contains description of existing theories of phase modulation, comparison of experimental results with theoretical predictions, and phase dependance on ambient temperature

The desert beetle or namib beetle has inspired the scientific community for decades due to its water collecting, harvesting and frost control capabilities. The exact and robust bio-mimicry of this surface is challenging and essential for a better understanding of surface processes and to align them with the significant applications. This paper realizes the fabrication of such structures by a novel concept of integrating the shape engineered spindle speckles with photo-lithography. The uniformly shaped spindle speckle patterns are achieved using a 'diffuser-lens-aperture' optical configuration. It is demonstrated that the fabricated structures that mimic the desert beetle skin are exhibiting excellent super hydrophobic properties. The obtained results also indicate that these structures can be tailored for open air fluidic channels in lab-on-chip and clinical applications.

Ocular imaging technology that holds promise for both fundamental investigation and clinical detection of glaucoma is still a challenging research area. A direct view of the trabecular meshwork (TM) with high resolution is not generally possible because the iridocorneal angle region is obstructed by the sclera overlap. The best approach to observe the aqueous outflow system (AOS) is therefore to view from the opposite angle. In this research work, we developed two imaging systems for the high resolution ex vivo studies of the AOS inside porcine eye, based on a Gaussian illuminated and a digitally scanned Bessel–Gauss beam light sheet fluorescence configurations. The digitally scanned Bessel–Gauss beam is able to overcome the trade-off between the length and thickness of the Gaussian light sheet to give better imaging performance. It has adequate spatial resolution to resolve critical anatomical structures such as the TM, thereby enabling objective information about the AOS. This non-contact and non-invasive imaging methodology with excellent safety profile is expected to be well received by vision researchers and clinicians in the evaluation and management of glaucoma.

Over the past few years, plasmon-resonant nanorods of gold (AuNRs) have been used as the contrast agent in optical imaging and for photothermal applications. However, most of these studies were limited to AuNRs whose spectral peaks fall below 1000 nm. Recently, optical coherence tomography (OCT) imaging around 1300 nm has become one of the niche research areas due to its potential for many diagnostics imaging applications. In this paper, we have investigated plasmon-resonant AuNRs with higher aspect ratio as a potential contrast agent in OCT and for photothermal applications around the 1300 nm window. The AuNRs with an aspect ratio of 8.8, and longitudinal plasmon-resonance peak at 1320 nm have been used for the study. The AuNR used in the study has an average dimension of 88 nm (length) × 10 nm (diameter), and an effective size (R eff) of 11.8 nm. The optical extinction of plasmon-resonant AuNRs has been characterized by OCT using a new cross-correlation approach. The extinction cross-section estimated using the OCT method is in good agreement with the values obtained via finite difference time domain-method and UV–vis–NIR spectroscopy. Both the simulation and phantom based experimental studies have shown that AuNRs exhibit a large absorption to scattering cross-section ratio, making them ideal for absorption based contrast enhancement in OCT imaging around 1300 nm. Ex vivo studies on the pig adipose tissue also illustrate the efficiency of AuNRs with identified aspect ratio as a potential photothermal agent around 1300 nm.

In this paper, we report a methodology to fabricate high resolution periodic grating features using high index prism based interferometer and i-line laser source. Features with sub-60 nm half pitch size were fabricated on i-line resist in an immersion medium using a prism of high index 1.939.

We demonstrate a novel multifunctional optical system that is capable of trapping, imaging, position sensing, and fluorescence detection of micrometer-sized fluorescent test particles using hollow-core photonic crystal fiber (HC-PCF). This multifunctional optical system for trapping, position sensing, and fluorescent detection is designed such that a near-IR laser light is used to create an optical trap across a liquid-filled HC-PCF, and a 473 nm laser is employed as a source for fluorescence excitation. This proposed system and the obtained results are expected to significantly enable an efficient integrated trapping platform employing HC-PCF for diagnostic biomedical applications. Published version

In this paper, we report a novel concept and methodology to fabricate high resolution periodic features using i-line laser source and multiple converging lenses. This configuration reduces the number of optical elements by employing a converging two-lens system to direct the beams on to the sample instead of conventional multiple mirror assembly that is normally associated with multiple beam interference configurations. A simple optical configuration using a 60° prism, 364 nm laser source and two converging lenses are employed to implement immersion lithography concept to achieve four beam interference. Square lattice patterns with pitch size of 210±8 and 240±6 nm are recorded on a positive photo resist using this technique.

Nanoparticles have great potential towards optical investigations in biological tissues which include imaging applications as well as therapeutic applications. However the effectiveness of these techniques is greatly governed by the optical properties of the nanoparticles. In this context this work performs computational investigations in determining the scattering and absorption efficiencies of spherical nanoparticles for a variety of nanoparticle dimensions and compositions over a wavelength band ranging from 380nm - 1064nm. The simulation results show that the optical response of the nanoparticles greatly varies with the material property, the radii of the particle as well as the laser wavelength and the results obtained aids in the selection of suitable nanoparticle for specific biomedical applications.

Achievable resolution of nano-rings, fabricated using commonly employed conventional mask based photolithography, is limited by diffraction of light. In this work conventional photolithography is modified to incorporate the phenomenon of surface plasmons to overcome the diffraction limit and thus to fabricate nano rings. Here, an embedded-amplitude mask based surface plasmon lithography is numerically investigated to conceptalize a noval methodology to fabricate the proposed nano-ring structure. Results of FDTD simulation shows sharp transmission peaks at the hole edges which could be recorded using suitable thinned photoresist to obtain nano ring structures.

Microlens-ended fibers, which have found tremendous interest in the recent past, find potential biomedical applications, in particular, in endoscopic imaging. The work presented in this paper focuses on the stand-alone microlenses along with custom-fabricated specialty optical fiber, such as imaging fiber, for probe imaging applications. Stand-alone self-aligned microlenses have been fabricated employing microcompression molding and then attached at the end facet of imaging fiber. A detailed characterization of the fabricated microlens is carried and it demonstrates appropriate focusing ability, high fluorescence collection efficiency and imaging ability for biomedical applications. The surface roughness of the microlens is found to be 25 nm with a minimum spot size of 38 μm. The probe imaging system is found to be able to image the fluorescence microspheres of 10 μm size. The collection efficiency of the fiber probe with lens found to be enhanced by three times approximately.

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.

In this paper, we experimentally demonstrate and compare single-exposure multiple-beam interference lithography based on conventional laser interference, evanescent wave interference, and surface plasmon interference. The proposed two-beam and four-beam interference approaches are carried out theoretically and verified experimentally, employing the proposed configurations so as to realize the patterning of one- and two-dimensional periodic features on photoresists. A custom-fabricated grating is employed in the configuration in order to achieve two- and four-beam interference.

This paper illustrates the design and fabrication of wavelength filters using resonant cavity which is constructed out of a phase shifted vertical side wall grating. The resonant cavity is analyzed as a Fabry-Perot resonator and the variation in cavity quality factor (Q) and transmission with respect to various grating parameters is studied. It is observed that a high Q-factor together with a high transmittivity can be obtained for this wavelength filter through optimization in grating length and reduction in the out of plane loss. Multiple phase shifts are applied in the grating to get a coupled cavity configuration so that channel isolation and spectral shape is improved. The channel wavelengths in a DWDM ITU grid C band (100GHz spacing) is simulated by varying the phase shift length of the gratings and good channel isolation with constant Q -factor and transmittivity is observed for the spectrum. The paper also explains the effective fabrication process flow for this structure on a silicon wafer through e-beam lithography and Reactive Ion Etching (RIE).

In this paper, a maskless single step multiple (two and four) beams surface plasmon interference lithographic configuration is proposed and illustrated experimentally so as to obtain interference pattern with resolution several orders less than the illumination source wavelength. This technique utilizes a custom made prism layer configuration to pattern both one dimensional (grating line) and two dimensional (dot array) periodic nanostructures on the recording medium. Both aluminum and silver metal films are used for the experimental study. Large area patterns of grating lines and dot arrays with feature size ≈ 90 nm were experimentally obtained using an exposure radiation of 364 nm wavelength.

Optical (Photo) lithography has played a significant role in almost every aspects of modern micro-fabrication technology in the recent years. It has initiated transistor revolution in electronics and optical component developments in photonics. Advances in this field have allowed scientists to improve the resolution of the conventional photolithographic techniques, which is restricted by the diffraction limit [Okazaki, 1991]. To overcome this problem and to reduce the critical dimension, several solutions were introduced. New research suggests that we may be able to develop new low cost photolithographic technique beyond the diffraction limit. The minimum critical dimension (half-pitch resolution) achievable by photolithography (Optical projection lithography) is given by 1 / half pitch CD k NA λ − = , where λ is the incident source wavelength, NA is the numerical aperture of projection optics of the system and 1 k is a constant value as a indication of the effectiveness of the wavefront engineering techniques. To reduce the half-pitch resolution, critical dimension equation demands either to decrease the wavelength of illumination light source or to increase the numerical aperture of projection system. Or in short, fabrication of sub-100nm features generally imposes the requirement of shorter wavelength laser sources. In this context, the critical challenges that hinder the resolution enhancement approaches are (i) lack of availability of suitable ultra-short wavelength lasers, and (ii) the unavailability of suitable optics and materials such as photoresist for use at suitable wavelengths. Recently, techniques like extreme ultraviolet lithography (EUV) [Gwyn et al., 1998] and Xray lithography [Silverman, 1998] have been proposed for nanofabrication overcoming the diffraction limit. Here, the illumination wavelength is reduced to the extreme UV (smaller wavelength) to get smaller features. Another reported technique is the immersion lithography in which numerical aperture of the imaging system is increased by inserting high index fluids (prism or liquid) between last optical component and wafer surface [Wu, et al., 2007]. But this technique is either limited by air absorption or availability of high index fluids. Approaches such as electron-beam lithography can also be used to overcome diffraction limit, but these are serial process and cannot be used for high throughput [Chen et al., 2005]. Imprint lithography is another option to improve the resolution beyond the diffraction limit [McAlpine et al., 2003]. Nanometer scale features are possible by stamping a

In this paper, bandgap characteristics of transversely probed hollow-core photonic crystal fibers (HC-PCFs) are numerically investigated by FDTD analysis. The transmission characteristic of the transverse trapping beam is described using concept of photonic partial bandgap. The field and intensity distribution are monitored at the central hollow-core for both TE and TM modes illuminated in the Г-M direction. From the numerical results obtained, it is found that photonic stop bands are formed in the transmission spectrum. It is inferred that such partial bandgap studies are important for the application of HC-PCFs in the well-known area of optical tweezers where an efficient trapping can be performed inside the hollow-core.

A promising maskless surface-plasmon-interference nanoscale lithographic technique is proposed and demonstrated experimentally in this paper. One-dimensional (grating-type) and two-dimensional (pillar-type) nanocale features were patterned on the photoresist layer using a 364 nm illumination wavelength source with a single exposure, by employing a custom-made prism layer configuration. Large-area patterns of grating lines and pillars with feature size approximately 90 nm were realized experimentally using this configuration.

We propose the silicon-on-insulator (SOI) based, phase shifted vertical side wall grating as a resonant transmission filter suitable for dense wavelength division multiplexing (DWDM) communication channels with 100 GHz channel spacing. The gratings are designed and numerically simulated to obtain a minimum loss in the resonant cavity by adjusting the grating parameters so that a high transmittivity can be achieved for the resonant transmission. The resonant grating, which is designed to operate in the DWDM International Telecommunication Union (ITU) grid C band of optical communication, has a high free spectral range of 51.7 nm and a narrow band resonant transmission. The wavelength selectivity of the filter is improved through a coupled cavity configuration by applying two phase shifts to the gratings. The observed channel band width and channel isolation of the resonant transmission filter are good and in agreement with the ITU specifications.

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.

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.

In this paper, fabrication of nano-scale 3-D features by total internal reflection generated single exposure counter propagating multiple evanescent waves interference lithography (TIR-MEWIL) in a positive tone resist is investigated numerically. Using a four incident plane waves configuration from an 364nm wavelength illumination source, the simulated results indicate that the proposed technique shows potential in realizing periodic surface relief features with diameter as small as 0.08lambda and height-to-diameter aspect ratio as high as 10. It is also demonstrated that the sensitivity of multiple evanescent waves' interference depends on the polarization and phase of the incident plane waves, and can be tailored to obtain different geometry features. A modified cellular automata algorithm has been employed to simulate three-dimensional photoresist profiles that would result from exposure to the studied evanescent waves interference configurations.

We present the implementation of a fluorescence lifetime imaging microscopy (FLIM) system for cellular characterisation. FLIM system can be used as an investigative tool to identify minor biochemical changes in cellular abnormalities. These subtle changes could possibly alter cellular fluorescence properties such as emission wavelength and lifetime. In this study, the fluorescence lifetime of haematoxylin and eosin (H&E)-stained tissues were investigated using a wide-field time-domain FLIM system. The transient response of epithelial fluorescence was investigated and the lifetime extracted using a bi-exponential model. It was found that the fluorescence lifetimes of eosin can be correlated to the tissue histology. The preliminary result suggests that tumor-associated molecules are retained in the tissues even after tissue fixation and staining. The developed FLIM system was successfully applied to detect the histological changes in the tissue samples. Optimization of system parameters is also discussed.

Disease detection in body cavities, such as the detection of abnormal growths in the colon path, has been illustrated here using an image fiber guided catheter based multispeckle modality endoscopic system. An all fiber-optic approach for the illumination and imaging of the inner cavity walls is adopted here. An endoscope probe to carry the illumination fibers as well as the imaging lens–image fiber unit is designed and custom fabricated in order to operate the probe in its various direction sensitive configurations. This is facilitated by the selection of suitable optical elements such as beam combiner and biprism at the probe proximal end. Experimental investigations were carried out using the endoscope system employing phantom model of colon as the test specimen that has normal and abnormal (representing growth) regions and the obtained results indicated the system effectiveness in identifying the abnormal growths at an early stage.

Random textures have proven to be a better option for light localization and energy harvesting in solar cells. On the other hand, plasmonic structures are significant in localizing the fields into submicron domains. We propose a layered structure design that contains the random dielectric medium with a plasmonic nanopillars array as a back reflector, followed by demon- strating its efficient light trapping ability through simulation means. This structure has shown significant enhancement in the broadband absorption of the light spectrum in the wavelength range UV-IR and a higher extinction in the near-infrared wavelengths. The structure also shows the dependence of reflection on the nanopillar height as well as localization in the nano- pillar region. The broadened and red shifted plasmonic nanopillar resonances (transverse and longitudinal) in a high-index medium are shown as the reasons for enhanced broadband absorption. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1. JNP.9.093061)

A spatial-scanning pushbroom hyperspectral imaging (HSI) system incorporating a video camera (VC) which is not only used for direct video imaging but also for the selection of the region of interest within the VC’s full field-of-view is presented. Using a VC for these two applications brings many benefits to a pushbroom HSI system, such as a minimized data acquisition time and smaller data storage requirement. A detailed description of the system followed by the methods and formulas used for calibration and electronic hardware interfacing were discussed and analyzed using United States Air Force resolution chart, chicken breast tissue, and fluorescent targets as test samples. The proposed concepts and developed system can find potential biomedical imaging applications and can be extended to endoscopic imaging applications as well.

A near-IR tunable external-cavity laser that uses an electro-optic deflector and a reflection grating as a tunable filter is demonstrated. The deflector is an electronically reconfigurable nonpixelated nematic liquid-crystal device. By controlling the voltage applied to the electro-optic deflector, a tuning range of 12 nm and a side-mode suppression higher than 30 dB are obtained.

A flexible fiber optic endoscope system for investigations in medical cavities using specially designed probe distal and proximal ends so as to facilitate speckle correlation analysis and simultaneous cavity imaging is presented in this paper. The design of the endoscope probe and associated detection system facilitating the analysis of deformation components and their derivatives in cavity surfaces is discussed. The distal end of the probe consists of a single fiber optic port for illumination and an imaging lens-image fiber unit for imaging the reflected speckle pattern from the cavity surface. An optical component selection unit is designed and used at the probe proximal end, for switching between deformation and derivative configurations. Theoretical analysis regarding speckle fringe formation on curved surfaces, for out-of-plane and shear configurations are discussed. Preliminary experimental investigations using the developed probe on inner surfaces of curved phantom tissue specimens are carried out for the abnormal growth detection and the results are analyzed. The obtained experimental results are compared with the developed theory. This probe system and its associated concepts may later lead into the improvements of currently used surgical assisted endoscopic techniques for early cancer diagnosis.

Fluorescence lifetime imaging (FLIM) in frequency domain enables the mapping of the spatial distribution of fluorescence lifetimes of a specimen. FLIM can provide unique information about fluorophores and hence is widely used in biology and for medical diagnostics. In this paper, a theoretical analysis for the fluorescence lifetime determination of latent fingerprint samples is described, which is followed by the feasibility study of using FLIM in frequency domain for latent fingerprints detection. Experiments are carried out with fingerprint on green paper substrate and postcard substrate treated with certain fluorescent powder. The total phase lag and demodulation factor are calculated to determine the lifetimes pixel by pixel. The resulting fluorescence lifetime image of fingerprint revealed an improvement in the contrast, and was able to detect the latent fingerprint clearly.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.

In this paper, we present the design of an endoscope probe, which can image the inner cavity walls as well as collect fluorescence emission from the same cavity inner surfaces, for disease diagnosis in body cavities. The probe makes use of a single coherent laser illumination / excitation source for both modalities. An imaging lens at the probe end collects the fluorescence emission as well as the image from the test surface. Two types of imaging lens are used in the probe and their fluorescence collection efficiencies and imaging capabilities are compared with each other. An eyepiece at the end of the probe directs the transmitted light into a CCD camera / Monochromator through selected filters to display the image / analyze the emission spectrum. The developed probe has been tested in a phantom colon model, where cancerous growths and fluorophores are simulated, so as to illustrate the probe diagnostic efficiency.

This article presents a total concentration method for two-dimensional wet chemical etching. The proposed procedure is a fixed-grid approach. It is analogous to the enthalpy method used for modeling melting/solidification problems. The governing equation is formulated using the total concentration of the etchant. It includes the reacted and the unreacted concentrations of the etchant. The proposed governing equation includes the interface condition. The reacted concentration is used to capture the etchant-substrate interface implicitly. Since the grids are fixed, a diffusion problem remains a diffusion problem unlike the moving grid approach where the diffusion problem becomes the convection-diffusion problem due to the mesh velocity. For demonstration purposes, the finite volume method is used to solve for the transient concentration distribution of etchant. In this article, two-dimensional diffusion-controlled wet chemical etching processes are modeled. The results obtained from the proposed total concentration method are compared with available “analytic” solutions and solutions from moving-grid approach.Copyright © 2005 by ASME

A theoretical model, which describes both the spatial distributions of photons in fluorescence endoscopic images forthe detection of cancerous cells in the intracavities of human body, specifically gastrointestinal path is presented inthis paper. The design concept of the image probe, which was developed for collecting the low fluorescent emissionusing an excitation laser source and imaging done through a novel imaging lens scheme will be discussed with itsadvantages and limitations in comparison with the existing imaging schemes. Finally, a quantitative analysis doneby varying the different parameters affecting the tissue fluorescence is discussed in this paper.Key words : Endoscopy, Imaging lens, Fluorescent imaging. 1. INTRODUCTION Minimally invasive treatment is becoming central to medicine, both improving results and reducing recovery timesand costs. In some cases it is guided by external imaging means [1], such as fluoroscopy, ultrasound, computedtomography (CT), magnetic resonance (MR), etc ., but often it is critical to have the internal optical view providedby an endoscope. Endoscopes are long and narrow optical systems intended for the observation of technical andmedical intra cavities. Several studies have been done in the area of endoscopic imaging [1-6]. There are rigid andflexible endoscopes available for this purpose and both have found wide acceptance in medical fields [5,6]. Rigidand flexible endoscopes differ in their image-transmitting scheme, based on which most endoscopes are divided intothree distinct subsystems: the objective, the relay and the eyepiece. Of the three, the relay system, which starts fromthe tip of the endoscope to transfer the image, whose length varies according to the application is used to classify theentire endoscope system [7]. In rigid endoscopes, image is transferred by means of relay rod lenses with spherical surfaces where as in flexibleendoscopes, an ordered fiber bundle is used for this purpose [6]. For practical purposes, flexible endoscopes provideunlimited length and the demands on design and performance of endoscopic instruments, including very smalldiameters and extreme flexibility have increased over the last decade. Fiberoptic endoscopes permit visualization ofnormally accessible areas within the body and without pain or discomfort for patients. And a flexible endoscope isessential due to the fact that rigid endoscopes have limited use in digestive endoscopy [8]. A flexible endoscope isconsidered to be a more appropriate tool for minimally invasive inspection and surgery as it enters the body throughnatural openings [9]. In such cases more care should be taken in selecting appropriate biocompatible materials, asthey are supposed to interact with living tissue without any kind of conflict or collateral effect, for the endoscopeouter covering so as to ensure seldom hazards to the body tissue sites [10]*Address for correspondence

A theoretical model, which describes both the spatial distributions of photons in fluorescence endoscopic images for the detection of cancerous cells in the intracavities of human body, specifically gastrointestinal path is presented in this paper. The design concept of the image probe, which was developed for collecting the low fluorescent emission using an excitation laser source and imaging done through a novel imaging lens scheme will be discussed with its advantages and limitations in comparison with the existing imaging schemes. Finally, a quantitative analysis done by varying the different parameters affecting the tissue fluorescence is discussed in this paper.

Recent research in diagnostic imaging and sensing focuses on deriving complementary information from the diagnosed site. From that perspective it is imperative to devise new imaging platforms where multiple distinct modalities are used either simultaneously or sequentially. Increased efforts have been devoted towards establishing such multi-modal imaging systems, which house and operate more than two imaging modalities within a single instrumentation set-up. In this context, we propose a novel multi-modal imaging platform using non-ionizing radiation that has been successfully conceptualized, established and experimentally demonstrated. This proposed GRIN lensed fiber-optic microscope and linear array transducer based PAUSFI (photoacoustic, ultrasound and fluorescence imaging) system makes use of non-ionizing radiation sources to map optical and acoustic heterogeneities (complementary information) along the depth of the tissue at multi-scale resolution (microscopic to mesoscopic). The fiber-optic assembly enables the system to perform minimally invasive remote light delivery and high resolution fluorescence and photoacoustic imaging of inaccessible areas of intact tissues or intra body cavities. It is expected that the proposed multi-modal imaging system could open up niches in bio-imaging research in the near future.

In interferometric fringe pattern analysis, specular and speckle fringe patterns are the two main divisions. While specular fringes are characterized by quality fringes with high spatial resolution, speckle (that obtains due to the diffuse scattering of the coherent radiation from an optically rough surface) fringe patterns, which contain high frequency carrier (as noise), are characterized by noisy fringes. This paper concentrates on this aspect and the matlab based filtering methods to improve quality of speckle fringe patterns by developing the appropriate software. Further, the newly developed software Macurv will be presented which can give the second order derivative (curvature) fringe information . A software with several functions is written using Matlab. The objective of the software is to provide a more effective way for post-processing of the speckle interferometric fringes. The algorithm and functions of the developed software Macurv will be explained.

Dynamic analysis of structures and machines provide valuable information on the performance and reliability of structures. In this paper, we present the development of a Fiber Optic Polarimetric Sensor (FOPS*) for dynamic and impact loading. The sensor monitors the change in the state of polarization of the light beam traversing the fiber under dynamic loading. The dynamic response of three different sensing optical fibers - high birefringence (bow-tie) fiber, low birefringence fiber and an ordinary communication grade single mode fiber are evaluated. The studies were carried out by embedding the optical fibers in a glass fiber reinforced plastic (GFRP) specimen and the performances of the three different systems were compared.

Tele-shearographic system based on bulk optics shearing and optical fiber based illumination have been used for the Non-Destructive Testing (NDT)of aircraft/composite laminates. This paper describes the application of this system and a detailed experimental analysis to assess defects in Carbon Fiber Reinforced Plastic (CFRP) composite laminates by analyzing the fringe patterns. CFRP laminates and honeycomb panels have been studied using the this system in various optical configurations. This technique provides the full-field, non-contact method for Non-Destructive Evaluation (NDE) of composite specimens. A Comparative study between digital shearography and other NDTechniques are also discussed in this paper.

Human tooth structure in the oral environment is affected by considerable thermal fluctuations while consuming hot and cold, fluids and food materials. This paper describes the use of digital moire interferometric technique and Electronic Speckle Pattern correlation Interferometry (ESPI) to study the behavior of the functionally adapted dentine materials to thermal loads in its own plane and out of plane. Further, this study also highlights the advantage of optical techniques with enhanced sensitivity and spatial resolution to examine the whole-field thermal property gradients in an anisotropic biological material such as human dentine.

With the emergence of new trends in optical communication and sensing syste, the importance and need for novel concepts such as diffractive gratings that can be implemented on a microscale has become a thrust area of research. In this paper, we compare various grating structures and their suitability for MEMS applications. The design approach, analysis and integration into optical systems are discussed in the context of both fiber and planar waveguide technology. Also, the differences and similarities among these methodologies using silicon micromachining are brought out. Parameters of interest, such as efficiency of micro-grating structures and ambient effects that influence the performance of the devices/systems are also discussed.