A selection of spectroscopy-based, fiber optic and micro-optic devices is presented. They have been designed and tested for monitoring the quality and safety of typical foodstuffs. The VIS-NIR spectra, considered as product fingerprints, allowed to discriminating the geographic region of production and to detecting nutritional and nutraceutic indicators.

Oral cancers are the serious health problem in developing as well as developed world, and more so in India and other south Asian countries. Survival rate of these cancers, despite advances in treatment modalities are one of the poorest which is attributed to lack of reliable screening and early detection methods. The hamster buccal pouch (HBP)carcinogenesis model closely mimics human oral cancers. Optical spectroscopy methods are sensitive enough to detect subtle biochemical changes and thus hold great potential in early detection of cancers. However, efficacy of these techniques in classifying of sequential evolution of tumors has never been tested. Therefore, in this study, we have explored the feasibility of Raman spectroscopic classification of different stages of cancers in hamster model. Strong vibrational modes of lipids (1440, 1654, and 1746 cm-1) are seen in control tissue spectra, whereas strong protein bands are seen in spectra of DMBA treated tissues. These differences were exploited to classify control and treated tissues using Linear Discriminant Analysis (LDA), Principle Component Analysis (PCA)-Limit test, Factorial Discriminant Analysis (FDA), Quadratic Discriminant Analysis (QDA), PLS-DA and non- linear decision tree methods. All these techniques have shown good classification between spectra of different stages of tumor evolution and results were further successfully verified by leave-one-out and single blinded methods. Thus findings of this study, first of its kind,demonstrate the feasibility of Raman spectroscopic detection of early changes in tumor evolution.

This paper details the design and fabrication of an integrated optical waveguide biosensor for antibody/antigen detection. SU-8 polymer is used as the core material to have a bi-conical tapered waveguide fabricated on a silicon substrate. PDMS is used as a buffer layer. The waist diameter of the biconical tapered waveguide has been optimized using Opti-BPM CAD software before fabrication. In addition, the fabrication technique employs simultaneous and single-step formation of the polymer waveguide structures for the guidance of light with V-grooves for low-cost passive alignment of glass optical fiber. The designed biosensor chip demonstrates sensing of FITC tagged goat anti human IgG (GaHIgG) and HIgG immobilized over the sensor surface was the bio receptor. The sensor uses the evanescent field that is present at the surface of the core for rapid and accurate sensing of antibody/antigen in the range of few micrograms per ml.

Mueller Matrix has the potential to extract vital information regarding subtle morphological changes that appear in human tissue in the early stages of cancer. In this report we have analyzed data of Muller Matrix imaging obtained from human cervical tissue. The depolarization power quantifies the increase in density of cells in epithelium layer during the progress of dysplasia. The early changes in dysplasia seen in the breakdown of ordered collagen fiber of the stromal region result in changes in birefringence property. The retardance parameter of Mueller Matrix decomposition displays these changes quantitatively. Analysis of retardance images performed on measurements obtained from the stromal region shows significant differences to discriminate dysplasia from normal tissue, where histopathology fails to diagnose. Further, the covariance map of depolarization power and their highest eigenvector from the epithelial layer are able to grade the two different stages of dysplastic conditions, grade I (GD1) and grade II (GD2) in human cervical tissue. This study can improve sensitivity of detection in clinics as a supplementary technique to histopathology.

We report the results of a comparative evaluation of in vivo fluorescence and Raman spectroscopy for diagnosis of oral neoplasia. The study carried out at Tata Memorial Hospital, Mumbai, involved 26 healthy volunteers and 138 patients being screened for neoplasm of oral cavity. Spectral measurements were taken from multiple sites of abnormal as well as apparently uninvolved contra-lateral regions of the oral cavity in each patient. The different tissue sites investigated belonged to one of the four histopathology categories: 1) squamous cell carcinoma (SCC), 2) oral sub-mucous fibrosis (OSMF), 3) leukoplakia (LP) and 4) normal squamous tissue. A probability based multivariate statistical algorithm utilizing nonlinear Maximum Representation and Discrimination Feature for feature extraction and Sparse Multinomial Logistic Regression for classification was developed for direct multi-class classification in a leave-one-patient-out cross validation mode. The results reveal that the performance of Raman spectroscopy is considerably superior to that of fluorescence in stratifying the oral tissues into respective histopathologic categories. The best classification accuracy was observed to be 90%, 93%, 94%, and 89% for SCC, SMF, leukoplakia, and normal oral tissues, respectively, on the basis of leave-one-patient-out cross-validation, with an overall accuracy of 91%. However, when a binary classification was employed to distinguish spectra from all the SCC, SMF and leukoplakik tissue sites together from normal, fluorescence and Raman spectroscopy were seen to have almost comparable performances with Raman yielding marginally better classification accuracy of 98.5% as compared to 94% of fluorescence.

Cell transfection is the process in which extra cellular nucleic acids such as DNA, RNA, Si-RNA can be deliberately injected into the cytoplasm of the cell. This technique of cell transfection forms a central tool in the hands of a cell biologist to explore the mechanism within the cell. In optical transfection a well focused laser spot alters the permeability of the cell membrane so as to allow the entry of extra-nuclear materials into the cell. Femto-second optical transfection have proved to be better than other laser based cell transfection, owing to the three dimensionally confined multi-photon effects on the cell membrane thereby leaving the rest of the cell unaffected. Even though the femto-second optical transfection has proved to be sterile, non-invasive and highly selective, it has to improve in terms of efficiency, and throughput to address real life problems. We report here a method to achieve significant enhancement in the efficiency of femto-second optical transfection. The protocol of the transfection procedure is modified by adding a suitable biochemical reagent - Nupherin-neuron - into the cell medium during the transfection, which can assist the delivery of DNA into the nucleus once the DNA gets injected into the cytoplasm of the cell. We achieved a 3 fold enhancement in the transfection efficiency with this modified protocol. Also we report for the first time the transfection of recently trypsinised cells with a very high transfection efficiency, which would pave way to the development of high throughput microfluidic optical transfection devices.

Tumor growth is characterized by increased metabolic activity. The light absorption profile of hemoglobin in dysplastic tissue is different from a normal tissue. Neovascularization is a hallmark of many diseases and can serve as a predictive biomarker for the detection of cancers. Spectroscopic techniques can provide information about the metabolic and morphological changes related to the progression of neoplasia. Diffuse reflectance spectroscopy (DRS) measures the absorption and scattering properties of a biological tissue and this method can provide clinically useful information for the early diagnosis of epithelial precancers. We used tissue simulating phantoms with absorbing and scattering molecules for the determination of total hemoglobin concentration, hemoglobin oxygen saturation and intensity difference between the deoxy and oxy hemoglobin bands. The results show promising approach for the differentiating normal and malignant states of a tissue.

We investigate the physics of an optically trapped red blood cell under physiological conditions. When a single, live red blood cell, is placed in an optical trap, the normal biconcave disk shaped cell is observed to undergo a folding action and thereby take up a rod like shape. If such an RBC has any shape anisotropies due to perturbation through malarial infection or hyperosmotic stress, it is observed to rotate in the linearly polarised laser field. Finally when such an optically trapped RBC is exposed to a shear flow, a tank treading like behaviour of the red blood cell membrane is visualised (wherein the RBC membrane revolves around the central body of the cell). The tank treading motion of a red blood cell held stationary in the optical trap allows for the dynamics to be viewed in a prolonged manner without the usage of earlier constraints such fast imaging system.

Laser induced breakdown at copper-water interface was used to synthesize Copper@CopperOxide nanocomposites in the colloidal form. The antibacterial activities of these nanoparticles were studied using UV-Vis and Raman spectroscopy.

Large flattened mode optical fiber with raised index ring around the outer edge of the fiber core has been fabricated through modified chemical vapour deposition process to raise the threshold for non-linear interaction in high power laser fiber. The conversion of the fundamental mode shape from a Bessel function to a top hat function, enhances the effective area of the core intersected by the mode without increasing the physical size of the core. The shape of the fundamental mode is observed to be strongly dependent on the width of the raised index ring from the modal analysis. Suitable fiber parameters have also been estimated through the modal field analysis. Fabrication process steps have been optimized to achieve the desired fiber parameters. Modal field distribution, transmission properties and bending loss of the fabricated fibers have been characterized.

An integrated optical 1x8 power splitter has been designed and fabricated using large cross-section single-mode rib waveguides (input/output) in SOI substrate. The fabricated devices have been characterized in terms of excess loss, insertion loss and uniformity in transmitted powers at each of the output ports. The corresponding typical values are found to be 7 dB, 15 dB, and 0.7 dB, respectively. A prototype 1x8 power splitter has been fiber pigtailed, packaged and also characterized. The characterization results suggest that such power splitter (with further improved design parameters) can be potentially useful in passive/active optical networks operating in the communication window of λ ~ 1550 nm.

A pulsed distributed feedback quantum cascade laser (QCL) operating near 957 cm^-1 was employed in wavelength modulation mode for spectroscopic trace gas sensing applications. The laser was excited with short current pulses (5-10 ns) with < 2% duty cycle. The pulse amplitude was modulated with a linear sub-threshold current ramp at 20 Hz resulting in a ~ 2.5 cm^-1 frequency scan, which is typically wider than what has been reported for these lasers, and would allow one to detect molecular absorption features with line widths up to 1 cm^-1. A demodulation approach followed by numerical filtering was utilized to improve the signal-to-noise ratio. We then superimposed a sine wave current modulation at 10 kHz onto the 20 Hz current ramp. The resulting high frequency temperature modulation of the distributed feedback (DFB) structure results in wavelength modulation (WM). The set-up was tested by recording relatively weak absorption lines of carbon dioxide. We demonstrated a minimum detectable absorbance of 10^-5 for this spectrometer. Basic instrument performance and optimization of the experimental parameters for sensitivity improvement are discussed.

A square lattice photonic crystal waveguide with dielectric pillars placed in a dielectric substrate with refractive indices 3.4 and 1.45 respectively, is investigated here. An equivalent transmission line model is utilized for wave propagation in the waveguide. Electrical modeling of a defect placed along the planar photonic crystal waveguide is done with an equivalent T section model. Using the scattering parameters for the equivalent T model, spectral characteristics of defects have also been investigated and compared with those obtained by finite domain time difference analysis.

Waveguide (WG) structures are patterned on polymeric thin films and on three-dimensional colloidal photonic crystals (PhC). Different techniques such as direct laser writing, electron beam lithography (EBL), optical lithography and femto-second laser writing are used to pattern the WG structures on PPR, polymethyl methacrylate (PMMA) and SU-8 photoresists. All these techniques are found to be successful in writing the WG structures on thin films. Air channel WGs are formed by EBL and direct laser writing techniques on PMMA and PPR, respectively. The air channel is further infiltrated with a higher index zinc oxide by sol-gel chemistry for guidance of light by total internal reflection. The structure written on SU-8 by optical lithography and on PMMA thin film by femto second laser writing resulted in the ridged WG structures where the guidance is possible by total internal reflection. The WG writing is also successfully carried out by electron beam lithography and femto second laser writing on PhCs fabricated from PMMA and polystyrene colloidal particles using inward growing self-assembly method. Unlike the earlier WG structures, the light guidance is possible due to photonic band gap effect in PhC WG, only for the wavelengths that lie within the stop band of the PhC. The quality of the written structures is characterized using images from scanning electron microscope, atomic force microscope and optical microscope. For optical characterization, a diode laser beam is successfully guided through the WG structure fabricated on PMMA PhC by EBL and on SU-8 thin film by optical lithography method.

We have fabricated straight line structures and Y-couplers in X-cut lithium niobate crystals using femtosecond laser pulses. A systematic characterization study was performed initially to determine the effects of pulse energy on feature size. The optimal parameters were determined from experiments and simulations obtained using a two dimensional split step beam propagation method. Later the waveguides and couplers were fabricated using these optimized parameters. We present our results on the physical and optical characterization of these structures.

Applications of polymer post processing of silicon on insulator (SoI) devices are demonstrated. Polymer overlays on SoI nanophotonic circuits are used, on the one hand, to improve optical antenna transception for an any-one-to-all array and, on the other hand, a similar photodefinable coating is used to passively tune the dispersive characteristics of waveguides embedded in photonic crystals. Discussion is given to the polymer formulation. Coating that requires infiltration into voids with dimension 100 nm and less demands optimized wetting properties from the pre-cured polymer-in-solution. Atomic Force and Scanning Electron micrographs and Zygo interferometer image illustrate the quality of the post-photo-definition, cured coatings. Transmission measurements show a 10 dB improvement in the received signal level for a coated versus uncoated antenna pair radiating and receiving at 1550 nm. Wavelength dependent transmission measurements on waveguides in photonic crystals demonstrate that tuning can be affected in post processing performed after foundry fabrication. Careful formulation of the polymer for nano infiltration allows for tuning without increased attenuation.

We report the angle dependent transmission spectral characteristics of 331 nm diameter polystyrene (PS) photonic crystals (PhCs) with large band gap depth and steeper band edges which allow one to identify different Bragg planes promptly. The spectral characteristics recorded in the clock-wise (CW) and anti clock-wise (ACW) directions follow the LK and LU paths in the first Brillouin zone (FBZ) of the face centered cubic (fcc) structure. We obtained 25% of the band gap depth for (220) plane in the LK path, which is the highest value reported till now to the best of our knowledge. Interestingly we observed that (200) plane features for lower angles and (111) plane features for higher angles in the LU path while in the LK path the dips follow the (111) plane fit completely from lower angles to higher angle of incidence and the possible reasons are discussed.

We report the first experimental demonstration of a high-power Ti:sapphire laser pumped by an efficient, compact and cost-effective continuous-wave (cw) fiber-laser-green source at 532 nm. The green source is obtained by direct singlepass second-harmonic-generation (SHG) of a Yb-fiber laser in MgO:sPPLT crystal, providing 11 W of green power in TEM₀₀ spatial profile. The Ti:sapphire laser is continuously tunable across 743-970 nm and can deliver an output power up to 2.7 W with a slope efficiency as high as 32.8% under optimum output coupling of 20%. The laser output has a TEM₀₀ spatial profile with M²<1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 hour.

We report a simple, compact and novel implementation for single-pass second-harmonic-generation (SP-SHG) of continuous-wave laser radiation based on a cascaded multi-crystal scheme, which can provide the highest conversion efficiency at any given fundamental power. By deploying a suitable number of identical 30-mm-long MgO:sPPLT crystals in a cascade, and a 30-W cw Yb-fiber laser at 1064 nm as the fundamental source, we demonstrate SP-SHG into the green with a conversion efficiency as high as 56% in the low as well as high-power regime, providing a 5.6 W of green output for 10 W and 13 W green output for 25.1 W of input pump power. The multi-crystal scheme permits substantial increase in cw SP-SHG efficiency compared to the conventional single-crystal scheme, without compromising performance with regard to power stability and beam quality.

We experimentally study two different tripod configurations using metastable ⁴He, with the probe perpendicular and parallel to the quantization axis, defined by an applied weak magnetic field. In the first case, the two dark resonances interact incoherently and merge together into a single transparency peak with increasing coupling power. In the second case, we observe destructively interfering double dark resonances leading to a narrow absorption dip at the line center. We confirm the results theoretically.

A left-handed plasmonic optical nanoantenna is presented to demonstrate blue light generation with the incident red light through second harmonic generation. Negative real values of permeability and permittivity with extremely low imaginary values for visible light is obtained by applying coupled dipole approximation. Near-field and far-field resonance spectrums reveal high directionality for the designed nano-antenna.

We generate two dimensional Airy beams using a cubic phase mask and study its propagation through photorefractive material experimentally. The diffraction free nature as well as the acceleration of Airy beams is observed. Using beam propagation method (BPM), we confirm the experimental results. We also study the effect of an applied electric field on the propagation of Airy beams through photorefractive materials numerically. It is observed that the applied field leads to interaction between the lobes of Airy beams.

Using femtosecond time resolved degenerate pump-probe mass spectrometry coupled with simple linearly chirped frequency modulated pulse, we elucidate that the dynamics of retro-Diels-Alder reaction of diclopentadiene (DCPD) to cyclopentadiene (CPD) in supersonic molecular beam occurs in ultrafast time scale. Negatively chirped pulse enhances the ion yield of CPD, as compared to positively chirped pulse. This indicates that by changing the frequency (chirp) of the laser pulse we can control the ion yield of a chemical reaction.

We present experimental results on the effect of incident beam polarization on the spectral and polarization characteristics of the output spectrum due to a single filament generated in BK7 glass using focused femtosecond laser pulses. It is observed that the spectral characteristics of the output spectrum are different both in the spectral content as well as the peak wavelength of the spectrum due to the two input laser polarizations (linear and circular). The polarization properties of the output spectrum due to a single filament for the two polarizations have also been studied.

Our recent work [Phys. Rev. A, 82, 013805 (2010)] clearly establishes a new regime of filamentation beyond the conventional "intensity clamping" by high-resolution spatial imaging of filaments. We present the corresponding measurements of the supercontinuum emission (SCE) from filaments in this regime produced by ultrashort (45 fs) sub- TW (up to 0.2 TW) Ti:Sapphire laser pulses focused air under tight (f/6) focusing geometry. The intimate connection between the spatial and spectral domains in the new regime is established by investigating the spectral broadening of SCE at peak intensities exceeding 10¹⁴ W/cm² pulses at the focus thus giving a more complete picture of this new regime in filamentary propagation of intense fs pulses.

We present designs of all-optical reversible logic gates, namely, Feynman, Toffoli, Peres and Feynman Double gates, based on switching of a near-IR (1310/1550 nm) signal by low-power control signals at 532 nm and 405 nm, in optically controlled bacteriorhodopsin protein-coated silica microcavities coupled between two tapered single-mode fibers.

We describe a novel real time optical 3D nanoscope scheme that can be applied for both metrology and inspection in various semiconductor fields. Since the proposed off-axis scheme based on a matched filter correlation method basically measure the phase information of a nano object, the proposed scheme has some benefits in terms of sensitivity in both 3D geometry measurement and defect inspection capability. In this study, the feasibility of the proposed scheme has been evaluated by combining the conical diffraction and wave propagation simulation codes.

A comparative study of biohashing technique using different feature extraction methods has been carried out. A basic biohashing technique involves two steps. First is the extraction of the features from the biometrics and second is the discretization of the obtained features with the random numbers. In this paper, two different data bases and two different feature extraction techniques have been studied. The first data base consists of self generated images and images from ORL and Indian face database and the second data base is taken from the standard Yale-B data base. The two different feature extraction techniques that have been used are the optics based joint transform correlator technique and the principle component analysis technique. Hamming distance has been used to discriminate the different populations. The performance of the techniques has been analyzed by using the false rejection ratio (FRR), false acceptance ratio (FAR) and the equal error rate (EER) in order to compare the effect of the different feature extraction methods on the biohashing technique.

We report the results of a study aimed at optimizing the cavity configuration of an actively Q-switched Erbium-doped fibre laser. We study the importance of extinction ratio of Acousto-Optic Modulator (AOM) on the cavity lasing performance and in turn the Q-switching efficiency. Two different configurations were studied with the aim of extracting the highest possible pulse energy without much pulse width variation. Finally, we report the use of our Q-switched laser to study non-linear interactions in a highly non-linear fibre (HNLF).

With a view to enhancing the performance of all-fiber amplifier using Er⁺³-doped triangular-lattice photonic crystal fiber (PCF), we performed a detailed study of the amplifying characteristics of the PCF host by varying all associated parameters towards achieving high gain and lower optimum doped fiber length (minimum length required to get the maximum level of gain). A finite difference (FD) mode- convergence analysis is used to determine the modal propagation characteristics in the structure, which is then used to solve a standard propagation and population rate equation. Our results show that a spectral gain of the amplifier as high as 51 dB and that too over a short length ~2.4 m of the active fiber is achievable by optimizing the gain dependent parameters and the transverse geometry of the fiber. Aimed at field-deployment of the amplifier as inline component, we optimize splicing/coupling loss (considering the mismatch of fundamental modes only) of this all-fiber device. Notably, the splice loss with standard telecom-grade SMF-28 fiber is minimized through an improved mode-matching of the design. These results are new in fiber amplifier research and would make useful contribution to realize high-performance PCF-based amplifiers and devices.

Theoretical simulation shows that APE:LiNbO₃ ridge waveguide can support a more tightly confined fundamental mode than that of conventional APE or Ti-indiffused channel waveguides. Successful demonstration of such waveguides on the surface of LiNbO₃ crystal will have potential impact in the area of nonlinear integrated optics. However, the fabrication process of ridge structures has appeared to be a challenging task. The ridge structures on the surface of X-cut LiNbO₃ crystal were fabricated by wet/dry etching process using various recipes and corresponding surface morphologies have been closely investigated.

We demonstrate a novel device consisting of two concatenated chirped long period fiber gratings (LPG) that exhibit multiple pass bands. Transmission spectra of single and dual chirped LPG were simulated theoretically and investigated experimentally show a qualitatively good match. The dual chirped LPGs with multiple pass bands in the transmission spectrum could find applications as WDM channel isolation filter.

The optical performances of the Fiber Bragg Gratings (FBG) all-optical switches are studied under the case of the cross-phase modulation (XPM). The expressions of the switching power threshold in the different detuning range are given. The influence of parameter about different detuning and couple ratio to the threshold of switching power and extinction ratio of devices is also studied.

We report on the realization and analysis of a 150 W peak-power passively Q-switched Yb-doped double-clad fiber laser with 30 μJ pulse energy, and 205 ns pulse duration using Cr⁴⁺:YAG saturable absorber. Analysis of the effect of mode area inside the saturable absorber on pulse characteristics has also been carried out.

We present analysis of thermal effects in high-power Yb-doped double-clad fiber laser. We have performed simulations using heat and rate equations to find the core temperature distribution, and variation in population density of energy levels along the fiber length with pump power to access the power scaling feasibility in experimental configurations.

Power penalty in N-channel WDM system due to stimulated Raman crosstalk is investigated in a typical configuration consisting of two periodically amplified single mode fibers (SMF) by Erbium-doped fiber amplifier (EDFA) and dispersion compensated by dispersion compensating fiber (DCF). Results show that minimum power penalty is in central wavelength region of WDM system and inclusion of EDFA and DCF increases power penalty. Power penalty in individual channels due to remaining N-1 channels has also been investigated. The dependence of power penalty due to stimulated Raman scattering (SRS) on average input power, interchannel separation and bit rate of the system has also been assessed.

Optical Reach (OR) is the maximum distance along a route of wavelength-routed optical network (WRON), over which an optical signal can travel without any optical/electrical/optical (O/E/O) regeneration. In the first phase, this paper determines the required maximum optical transmit power at source nodes to achieve a given network-wide OR for a specified maximum number of intermediate nodes in the WRON topology under consideration. Subsequently, the paper examines the impact of OR on dynamically-provisioned WRONs, considering transparent (without O/E/O) as well as translucent (with O/E/O) scenarios.

We present results for a broadband supercontinuum spanning almost two octaves (575 nm - 1600 nm) generated in an equiangular spiral photonic crystal fiber proposed earlier. The pump source is taken to be Yb - doped fiber laser at 1.06 μm. The fiber has two zero dispersion wavelength (at 885 nm and 1115 nm) with very high nonlinearity ( >5580 W^-1 km^-1 at 1060 nm).

We report a simple, inexpensive fabrication method to fabricate polymer microlens at the apex of optical fiber. When compared to other established protocols for fabricating microlensed fiber, this procedure allows simple and inexpensive microlensed fiber fabrication with high reproducibility. Also it is possible to tune the focal length and working distance of the fabricated lens in a wider range by controlling the curing parameters such as curing power, beam shape of the curing beam and curing time. The novel curing procedure, where a specially structured curing laser beam of wavelength 405nm was used for curing, is the key factor for this extended flexibility. Once cured, the UV curable adhesive used for fabricating these lenses had a very good transmission in visible and near-IR region, making it ideal for communication and biophotonics applications. This fabrication technique can be used in a variety of applications owing to its ability to achieve customized microlenses for specific applications.

We optimize the simultaneous oscillations at two frequencies in a class-A Vertical External Cavity Surface Emitting Laser (VECSEL). We perform this task by measuring the coupling constant between the two perpendicular polarized modes for different values of the transverse spatial separation between the two modes.

Fractal Zone plates and optical pin sieves are designed and their focusing properties are analyzed using scalar diffraction formula. It is found that these zone plates offer better control on beam parameters compared to Fresnel Zone plates. These zone plates are then fabricated on to quartz substrates using UV lithography and the results are confirmed.

Huge confinement of light over micro and nano structures is finding various applications in the field of photonics. In this letter the results obtained over two different kinds of confined structures viz., (i) Metallo-Dielectric colloidal structures (MDCS), obtained by immobilization of metallic gold (Au) nanoparticles on the dielectric silica network of inverse silica opal matrix and (ii) Rare-earth activated silica-hafnia film coated silica microresonator is presented in detail. The structural, optical and spectroscopic assessments of these systems are giving an evidence to have applications in the field of sensing and lasing. Preliminary results on MDCS used as surface enhanced Raman scattering (SERS) substrate shows an evidence that an increase of the Raman signal with respect to that observed for other metallic and dielectric structures.

An experimental method for determining the generalized Stokes parameters in analogy with its counterpart experimental scheme of determining the usual Stokes parameters is presented. The two-point (generalized) Stokes parameters are determined for unpolarized, linearly polarized and partially polarized broadband light beams generated respectively, using a two-mirror and two-beam-splitter assembly.

In this paper, we present an interferometric technique for full field polarization mapping using Fourier fringe analysis. Uniqueness of the technique lies in its high stability against surrounding vibration and capability of single shot measurement. Accuracy of the technique is verified by mapping of beam with known state of polarization and subsequently the technique is used to map polarization for various kinds of sample fields.

We present some of our initial experimental results from laser induced breakdown spectroscopy (LIBS) studies of few high energy materials such as a simple match stick (MS) and BKNO3 (BPN), and ammonium perchlorate (AP) using nanosecond (ns), picosecond (ps), and femtosecond (fs) pulses. The characteristic peaks of each sample in different time domains are analyzed. The merits and de-merits of ultrashort pulses in LIBS experiments for discrimination of high energy materials are highlighted.

The light extraction efficiency of GaN/InGaN based blue LED is improved by using hexagonal facets on n- and p- free surfaces and on substrate interfaces. Light interaction with patterned surfaces having hexagonal facets significantly improved the light extraction efficiency. The simulated results show that the light extraction efficiency is drastically improved from 18.08% to 89.27% by patterning the free surfaces.

Amorphous Te_xAs₄₀Se_60-x (x = 0, 10) thin films were prepared using thermal evaporation technique onto cleaned glass substrate at room temperature, and then exposed to UV-VIS light (having accordance with ASTM standards CIE 85 Table 4) using a Xenon lamp for two hours duration. Thicknesses of the films were measured using a stylus based surface profilometer. Structural analysis of the films was done using XRD measurements. Optical changes under UVVIS exposure were investigated by UV/VIS spectroscopy in wavelength range 300~900 nm. Changes in optical parameters are proposed for environmental monitoring applications. These results are compared with other range of photoexposures for some different Te-As-Se compositions in order to analyze their usability for various photonic applications.

We aim to study the nonlinear optical phenomena with femtosecond pulse propagation in liquid-core photonic crystal fibers filled with CS₂. In particular, we intend to study the effect of slow nonlinearity due to reorientational contribution of liquid molecules on broadband supercontinuum generation in the femtosecond regime using appropriately modified nonlinear Schrödinger equation. We show that the response of the slow nonlinearity enhances broadening of the pulse and changes the dynamics of the generated solitons. To analyse the quality of the pulse, the stability analysis and coherence of the SCG are studied numerically.

A liquid crystal infiltrated spiral photonic crystal fiber (LCSPCF) is presented here for electrical tuning of two zero dispersion wavelengths (ZDWs) in the present communication window. The proposed LCSPCF shows tunability of the ZDWs from 1433 nm to 2136 nm due to the rotation of the infiltrated LC mesogen induced by the external electric field. Therefore, the ZDW can easily be shifted towards the available pump wavelength for effective supercontinuum generation (SCG) over a broad wavelength region. By tuning the bandwidth (BW) in between the two ZDWs the extension of the generated supercontinuum (SC) spectrum can also be electrically controlled. This will help the SCG in our desired band with optimum power budget. Moreover, the index guiding mechanism of the proposed soft glass LCSPCF shows improvement over the narrow operational bandwidth and the low nonlinearity of the band-gap guided silica LCPCF. Additionally, the solid core of the proposed LCSPCF is less lossy than the previously proposed liquid crystal core PCF.

An analytical approximation for the modal field of a single mode index-guiding microstructured fiber is developed further to obtain the evolution of the far-field pattern of these fibers. Comparison with available experimental results is also included.

Nanoparticles of noble metals exhibit variety of colors in the visible light region due to a surface plasmon resonance. The size-induced properties of nanoparticles enable addition of flexibility to existing systems in many areas. To design a material with desired electrical and optical properties is the aim in many composite materials. In this paper, we report the preparation and characterization of silver nanoparticles in SiO₂, TiO₂ and ZrO₂ films and gold nanoparticles in TiO2 and ZrO₂ films. To analyze the dielectric characteristic of the metal-dielectric nanocomposite film, three kinds of matrices with a different refractive index were compared. Titanium dioxide (TiO₂) is one of the most promising photocatalysts and actively used in various practical applications. However, only a narrow band in the ultraviolet region of solar light, about 3-4%, is available for photocatalytic reaction. Therefore, the development of TiO₂ photocatalysts with higher photoelectric conversion efficiency for visible light is required. Plasmon-induced photocatalytic activity in the ultraviolet and visible light region was studied for the TiO₂ thin film dispersed with gold nanoparticles. Photocatalytic activity of Au/TiO₂ film was analyzed by degradation of stearic acid, and compared with non-doped TiO₂film.

In this work, we explore the sensing applications of Surface Plasmon Resonance (SPR) enhanced transmission of light through 1-D metal gratings on commonly available compact discs (CDs). We show that SPR on CDs (CD-SPR) can be used to build a simple and compact angular displacement measurement system with submicro- radian resolution. In addition we show that by controlling the azimuthal angle of the grating vector with respect to incident k-vector, it is also possible to measure angular displacement in two planes which is not possible with thin film SPR. The major advantage of this method is the compact form factor which will enable CD-SPR based angular measurement systems to be integrated into other experimental setups with the least burden.

We present a detailed analysis and recipe for designing a channel Bragg-plasmon coupled waveguide where the intermodal coupling between a bandgap-guided mode and surface plasmon mode substantially modifies the phase-velocity dispersion slope of supermodes. This leads to appreciably large group-velocity-dispersion with peak value of ≈4.33x10⁴ ps/km-nm close to the optical communication band as well as interaction bandwidth of about 765 pm for 1 cm long waveguide. We also found that bandgap guided Bragg modes exhibit stronger dispersive features than the plasmon modes around ~ 1.50 μm which is exactly opposite to what is usually observed in visible region. The impact of waveguide parameters such as channel width etc. on mode-coupling mechanism is also studied with significant emphasis on the propagation loss suffered by the supermodes of the structure.

One-dimensional (1D) surface plasmonic (SP) nanostructured cavity for the sub-wavelength confinement of light is proposed. Since, the significant spatial confinement of the plasmonic structure is needed for the miniaturization of the device, thin silver metal sheet is used to get plasmonic mode of the cavity. 1D plasmonic photonic crystal structure is designed by placing a silver substrate film(εm) below the photonic crystal waveguide of one dimensional array of air holes in Si (ε_d=11.56 or n_d=3.4) slab of finite thickness. TM mode with vertical electric field is investigated and it is observed that the mode remains dominant in the structure. Further, surface plasmonic nano cavity defect mode is studied by changing the cavity length which can be tuned for different wavelengths by changing the geometry of the structure.

Highly fluorescent colloidal silver nanoparticles were synthesized by using DNA as a stabilising agent. The absorption spectrum of silver nanoparticles showed the appearance of a broad surface plasmon resonance peak centered at 420nm at low and higher concentration of DNA. The photo luminescence study shows emission of silver nanoparticles is getting enhanced as concentration of DNA increases.

The results concerning propagation characteristics of plasmonic metal stripe waveguide using FEM analysis are presented. The metal stripe waveguide consists of a layer of gold (Au) which is 55nm thick and 1μm wide on a glass substrate with air at the interface excited at 800nm wavelength. Various characteristics like modal confinement, propagation length, and dispersion were investigated. Finite Element analysis (FEM) for hybrid modes is used to solve for various bound modes. These bound modes could be either symmetric or asymmetric in nature. The symmetric modes can be characterized by electric field maxima inside the metal. As a result these modes die down very fast and propagate distances of few micrometers. The asymmetric modes can be characterized by electric field maxima at the interface and can propagate distances of tens of micrometers. For lower width of metal, propagation length of 100μm or more can also be observed. It was also observed that with increase in metal width higher order bound modes get characterized. There exists a definite relation between number of such modes and width of the metal stripe for a given excitation wavelength. Such modes tend asymptotically towards the characteristic of surface Plasmon wave similar to that energized at a metal-air interface. Based on all these parameters various characteristics of metal stripe waveguide are analyzed.

We report our experimental observations of variation in on-off statistics and fluorescence intensity of single Rhodamine6G molecules in presence of resonantly driven surface plasmon of silver nanoparticle. Derived lifetimes from on-off statistics of fluorophore show that interaction between the fluorophore and the subwavelength metal nanoparticle improves photostability and enhances fluorescence intensity. This enhancement follows the trend predicted by the dipole-dipole interaction model.

A Surface Plasmon Resonance (SPR) biosensor that operates deep into the infrared (3-11 μm wavelengths) is potentially capable of biomolecule recognition based on both selective binding and characteristic vibrational modes. The goal is to operate such sensors at wavelengths where biological analytes are strongly differentiated by their IR absorption spectra and where the refractive index is increased by dispersion. This will provide enhanced selectivity and sensitivity, when biological analytes bind reversibly to biomolecular recognition elements attached to the sensor surface. This paper investigates potentially useful IR surface plasmon resonances hosts on lamellar gratings formed from various materials with plasma frequencies in the IR wavelength range. These materials include doped semiconductors, CuSnS, graphite and semimetal Bi and Sb. Theoretical results were compared with the experimental results. Penetration depth measurement from the experimental complex permeabilities values shows the tighter mode confinement than for usual Au giving better overlap with biological analytes.

Cahill-Glauber C(s)-correspondence is employed to construct Quasi-Probability Distribution Functions (QPDFs) for optical-polarization in phase space following equivalent description of polarization in Classical Optics. The proposed scheme provides pragmatic insights as compared to obscure SU (2) quasi-distributions on Poincare sphere. QPDF (Wigner function) of bi-modal quadrature coherent states is evaluated and numerically investigated to demonstrate the application.

The nearest-neighbor entanglement of the evolved state of an asymmetric quantum XY spin chain, in a transverse time-dependent field, exhibits criticalities (dynamical phase transitions) as the initial field parameter is varied at a given fixed time. After a discussion of the dynamical phase transition, we investigate the extent to which the role of an information-theoretic quantum correlation measure, called quantum discord, can be used to understand the entanglement dynamics in this spin model. We show that quantum discord can be associated with the collapse and revival of nearest-neighbor entanglement exhibited in the critical behavior. This behavior of quantum discord leads to the broader question of whether certain classes of measures of nonclassical correlation can help to understand the non-generic features of entanglement in a given system.

An approach based on fiber-coupled super-luminescent diodes (SLD) centered at two different wavelengths 1530 nm and 831 nm along with a spectrometer were used for analysis and monitoring of ammonia (NH3) and water vapor (H₂O) gas concentrations of the order of hundreds of ppm, respectively. It was studied experimentally and computationally verified. The proposed approach can allow multiple gas sensing in mixture of these for industrial and combustion monitoring.

We show the performance enhancement of a distributed temperature sensing system based on Raman scattering in optical fibers by using correlation codes. Specifically, we demonstrate experimentally that the use of Golay sequences provide an improvement in the signal to noise ratio by a factor of 10 dB, thereby providing an improvement in the temperature uncertainty by a factor of 2.5 over conventional technique.

We present a high sensitive temperature sensor based on a side-polished fiber (SPF) coupled to a tapered multimode overlay waveguide (MMOW). We have theoretically shown that the longitudinal tapering of the MMOW can be used to tune the desired wavelength range in the spectrum without any loss in the sensitivity.

Surface plasmon resonance based tapered fiber optic refractive index sensor incorporating an additional high index dielectric layer between metal and sensing medium using wavelength interrogation method is analyzed. The simulation is carried out for gold and silver metals. The simulation predicts, for a given taper ratio, the increase in the sensitivity of the sensor with increase in the thickness of the dielectric layer. The sensitivity also increases with the increase in the taper ratio. The advantages of additional layer of dielectric, in addition to the increase in sensitivity, are the protection of metallic layer from oxidation and the tuning of wavelength range of operation of the sensor.

We present the design of a novel optical fiber sensor probe which can be used for measuring the critical mole fractions of aqueous binary alcohol mixtures. The critical alcohol mole fractions we got are 0.3 for methanol and ethanol, 0.15 for 2-propanol and 0.05 and 0.1 for tert-butanol. The results obtained using the sensor probe also gives an evidence for micellization in tert-butanol water mixtures.

An extrinsic fabry-perot interferometric pressure sensor is fabricated using a cavity formed by a metal diaphragm and a single mode optical fiber. The compact sensor probe has been tested for static pressure response using diaphragms of different metals.

A fibre based Optical Coherence Tomography (OCT) system has been developed and characterized. A Micro Electro Mechanical System (MEMS) mirror was used to scan infrared beam over the sample. In this paper, we have presented the system, its specifications and the results obtained. In particular we discuss about the suitability of the MEMS mirror based OCT to image vibrating samples.

Quantitative tunable diode laser spectroscopy (TDLS) has established itself as a very powerful technique for the detection of gases in field applications such as industrial process control. Recent calibration-free techniques have made field measurements more robust. However, in many situations, the significant levels of laser intensity modulation gives rise to background signals that either limit detection sensitivity or distort the target signals, thereby making it difficult to extract useful information. This paper outlines the recent trends in calibration-free wavelength modulation spectroscopy (WMS) and focuses on the elimination of the undesirable effects of both linear as well as nonlinear intensity modulation. The approach is generic and should be useful with newer types of lasers that have shown significantly nonlinear power-current characteristics.

Fibre Bragg gratings are used as temperature or longitudinal strain sensors in a number of applications. Only a few studies are concerned with transversal stress applied to these sensors. We recently derived an analytical solution for the reflection spectra of shear strain loaded fibre Bragg gratings. The experimental verification of this theory is presented in this work. A fibre-coupled spectra analyzer based on a Fabry-Perot tuneable filter was set up in order to measure the predicted effect. The setup is able to split and measure simultaneously the spectra of the two polarisation main axes of birefringent fibres. The experimental observations are in agreement with predictions derived by mode coupling theory.

An airborne, high resolution, load tracking and structural health monitoring system for unmanned aerial vehicles is presented. The system is based on embedded optical fiber Bragg sensors interrogated in real time during flight at 2.5 kHz. By analyzing the recorded vibration signature it is now possible to identify and trace the dynamic response of an airborne structure and track its loads.

It is important to monitor temperature in Aluminum Conductor Steel Reinforced (ACSR) overhead power cables and also inspect for any cable defect. A stainless steel encased optical fiber sensor is incorporated in ACSR in place of steel core. Defects are simulated in the ACSR and the temperature is monitored. The results demonstrate that Raman Distributed Temperature Sensor (RDTS) is a promising technique for both temperature and defect monitoring in ACSR cables.

Single mode tapered fiber (SMTF) has been fabricated with core diameter of 8 μm and reduced cladding diameter up to 11 μm by hydrofluoric acid (HF) etching technique. To obtain the required cladding diameter, the time of etching has been optimized by using different HF concentrations. The mechanism as well as kinetics path of etching reaction on standard optical fiber is discussed. This study is related to surface catalyzed dissociation of HF followed by direct reaction with adsorbate molecules and the surface silicon oxide molecules. The etched tapered fibers are then packaged on quartz substrate to use as sensor element. Finally, the etched fiber is used as an element within chemical sensor based on evanescent field absorption. In this experiment, a 419-ppm cobalt nitrate solution is used for sensing.

Based on the platform of phase modulation scheme, we report here our studies on the detection of strain and temperature separately by fabricating a single-mode fiber based ineterferometric sensor. We configured a fiber optic version of Double-Slit type set-up as the basic interferometer using fused 3dB biconical tapered fiber coupler as the coherent optical power splitter. The influence of the measurand parameters, namely, temperature and strain inducing an effective relative phase along one arm of the interferometer fiber are observed in terms of fringe-shift that is measured with experimental precision. We deployed the sensor to investigate its accuracy in strain and temperature measurement in the backdrop of theoretical prediction. In both the cases separately, we have obtained the linear relation between fringe-shift and strain (or temperature). In strain measurement, an average sensitivity ~2.50x10⁶ m^-1 is achieved reproducibly, while in temperature measurement, a change in the temperature of 0.25°C has been detected repeatedly using this setup. Our experimentally measured data confirming the theoretically predicted values demonstrates the accuracy and efficacy of the experimental configuration as a useful sensor.

Slow light generation through four wave mixing is experimentally investigated in a non-linear semiconductor optical amplifier (SOA). The mechanism of slow-light generation is analyzed through gain saturation behavior of the SOA. The delay of the probe beam is controlled optically by pump-probe detuning. A delay of 260 ps is achieved for sinusoidal modulation at 0.5 GHz corresponding to a RF phase change of 0.26π.

We observe unique dynamics of optical solitons formed when an optical pulse experiences initially normal GVD with a monotonous dispersion slope. For negative (positive) third-order dispersion the blue (red) components of the spectrum form a soliton which attracts (repels) the red (blue) components of the spectrum and forces them to travel with its own velocity.

We have studied the coherence and population dynamics of Astaxanthin solution in methanol and acetonitrile by spectrally resolving their photon echo signals. Our experiments indicate that methanol has a much stronger interaction with the ultrafast dynamics of Astaxanthin in comparison to that of acetonitrile.

This paper presents the performance and compatibility of optical signal amplification using a high gain, low noise figure, Erbium-Doped Fiber Amplifier (EDFA) with linear Minimum Shift Keying (MSK) modulation format for the transmission of DWDM signals in optical communication system.