Photodetectors designed for the Extreme Ultraviolet (EUV) range with the Aluminum Gallium Nitride (AlGaN) active layer are reported. AlGaN layers were grown by Molecular Beam Epitaxy (MBE) on Si(111) wafers. Different device structures were designed and fabricated, including single pixel detectors and 2D detector arrays. Sensitivity in different configurations was demonstrated, including front- and backside illumination. The latter was possible after integration of the detector chips with dedicated Si-based readouts using high-density In bump arrays and flip-chip bonding. In order to avoid radiation absorption in silicon, the substrate was removed, leaving a submicron-thin membrane of AlGaN active layer suspended on top of an array of In bumps. Optoelectrical characterization was performed using different UV light sources, also in the synchrotron beamlines providing radiation down to the EUV range. The measured cut-off wavelength of the active layer used was 280 nm, with a rejection ratio of the visible radiation above 3 orders of magnitude. Spectral responsivity and quantum efficiency values

Many imaging techniques require highly sensitive optical systems including detectors capable of measuring extremely small fluctuations in the detected incident light. Such systems use a modulated light source (at frequencies up to 100's of kHz) in combination with optics that induce a change in the amplitude and/or phase of the modulation in response to changes in the sample being imaged. These signals are usually demodulated using a point detector and a lock-in amplifier. However, this technique is not suitable for the fast acquisition of 2D images. Using a modified active pixel sensor architecture, cameras with resolutions up to 256 x 256 pixels which are capable of demodulating optical signals with frequencies up to 1 MHz and have been designed and fabricated. Each demodulation pixel consists of a photodiode, a reset switch, four independently controlled shutter switches and four supplementary well-boosting capacitances that improve both linearity and signal to noise ratio. The reset and shutter switches are implemented with 5 V thick oxide transistors to maximize the dynamic range of the sensor. Demodulation is achieved by rapidly acquiring four images at 90 degree intervals of the modulation period, then applying simple post processing to extract the modulation amplitude, phase, and DC level of the optical signal. The camera outputs 16 parallel analogue channels and can deliver total pixel rates of up to 160 Mega pixels per second. In imaging systems where demodulation is not necessary, the camera can be clocked to behave as a conventional DC camera capable of taking four images with independent exposure periods allowing for advanced multi-parametric imaging.

In pump-probe type experiments the signal of interest is often a very small fraction of the overall light intensity reaching the detector. This is beyond the capabilities of conventional cameras due to the necessarily high light intensity at the detector and its limited dynamic range. To overcome these problems, phase-sensitive or lock-in detection with a single photodiode is generally used. In phase-sensitive detection, the pump beam is modulated and the probe beam is captured with a photodiode connected to a lock-in amplifier running from the same reference. This provides very narrowband detection and moves the signal away from low frequency noise. We have developed a linear array detector that can perform shot-noise limited lock-in detection in 256 parallel channels. Each pixel has four independent wells to allow phase-sensitive detection. The depth of each well is massively increased and can be controlled on a per-pixel basis allowing the gain of the sensor to be matched to the incident light intensity, improving noise performance. The array reduces the number of dimensions that need to be sequentially scanned and so greatly speeds up acquisition. Results demonstrating spectral parallelism in pump-probe experiments are presented where the a.c. amplitude to background ratio approaches 1 part in one million.

This paper describes Ma_Miss (Mars Multispectral Imager for Subsurface Studies), the miniaturized instrument for spectrometric and stratigraphic analysis of sub-soil developed by SELEX Galileo in the context of ESA ExoMars mission. The Ma_Miss experiment is coordinated by the Principal Investigator Angioletta Coradini (IFSI-INAF, Rome) and is funded by the Italian Space Agency (ASI). The exploration of Mars requires a detailed in-situ investigation of the Martian surface and sub-surface. Determining the composition of the Martian subsoil will provide a direct indication of the steps through which the sample material evolved along geological timescales. Ma_Miss is an instrument fully integrated in the Drill system (developed by SELEX Galileo) hosted by a Rover operating on Mars surface; Ma_Miss illuminates the wall of the drill borehole and acquires its reflectance signal in the Visible and Infrared (0.4-2.2 micron) range, analyzes it through a miniaturized spectrometer (20nm spectral resolution), and transmits the digital data to the Rover. The innovative instrument concept was driven by several key needs, related to challenging scientific requirements and extreme environmental constraints. Implementation of the concept has required a deep interdisciplinary concurrent development in order to solve critical aspects of engineering and manufacturing, covering miniaturized monolithic optics and novel concept for fiberoptic connectors capable to automatically mate/de-mate during the robotic assembly of the Drill elements on Mars.

Star cameras represent a well-known class of attitude determination sensors. At this time, they achieve excellent accuracy within arc-seconds. However their size, mass, power, and cost make current commercial versions unacceptable for use on nano-satellites. Here, the concept of developing a small star camera with very modest accuracy requirements for future nano-satellite missions is studied. A small commercial cmos sensor with minimal commercial optics is presented. The cmos imager has an active array area of 5.7 × 4.3mm, with a focal length of 6mm and an aperture ratio of 1.4. This camera's field-of-view is approximately 50 × 40 degrees and can capture stars of magnitudes smaller than 3 with acquisition times of 100ms. The accuracy of attitude determination methods using data collected by this camera was tested by taking photos of the night sky under terrestrial conditions. The camera attitude was determined using offline image processing and star field attitude determination algorithms. Preliminary attitude accuracy results were determined and they are presented.

Fiber Bragg grating (FBG) sensor networks have been intensively researched in optical sensor area and it developed in wavelength division multiplexing (WDM) and time division multiplexing (TDM) technologies which was adopted for its interrogating many optical sensors. In particular, WDM technology can be easily employed to interrogate FBG sensor however, the number of FBG sensors is limited. On the other hand, the TDM technique can extremely expand the number of sensor because the FBG sensors have same center wavelength. However, it suffers from a reduced sensor output power due to low reflectivity of FBG sensor. In this paper, we proposed and demonstrated the FBG sensor network based on code division multiple access (CDMA) with a rapid response and wide spectral dynamic range. The reflected semiconductor optical amplifier (RSOA) as a light source was directly modulated by the generated pseudorandom binary sequence (PRBS) code and the modulated signal is amplified and goes through FBG sensors via circulator. When the modulated optical signal experienced FBG sensor array, the optical signal which was consistent with center wavelength of FBGs is reflected and added from each sensors. The added signal goes into dispersion compensating fiber (DCF) as a dispersion medium. After through the DCF, the optical signal is converted into electrical signal by using photodetector (PD). For separate individual reflected sensor signal, the sliding correlation method was used. The proposed method improves the code interference and it also has advantages such as a large number of sensors, continuously measuring individual sensors, and decreasing the complexity of the sensor network.

We suggest a spectrometer demodulation method of FBG sensors for the possible uses in wind power generator's blade monitoring. High signal-to-noise ratio outputs and linear demodulation were obtained by combining a fiber laser light source and a spectrometer which used a holographic volume grating and a 512-pixel PD array. Preliminary experimental results are presented to show the feasibility of the suggested FBG demodulation system.

We report on the application of a silica on silicon based planar Bragg grating (PBG) evanescent field sensor as a refractive index biosensor. Our results demonstrate that typical biochemical reactions such as the binding between Biotin (vitamin H) and Streptavidin can be traced in real time on the sensor surface. For the detection of Streptavidin, Biotin was attached to the silanized surface of the planar Bragg grating sensor followed by the immobilization of Streptavidin with a concentration of 7.5nM, 15nM and 30nM, respectively. Real time monitoring capability is highlighted by interrupting the biochemical reaction by applying PBS solution and restarting the reaction several times showing a quasi instantaneous spectral response of the PBG sensor. In addition, applying the same bio-functionalized sensor we have investigated the detection of DNA hybridization. For this purpose, biotinylated single stranded DNA was linked to the sensor surface via Streptavidin. Using this functionalized PBG sensor surface, the DNA hybridization of unlabeled complementary single stranded DNA with a concentration of 5μM can be observed.

Optoelectronical components and devices based on organic materials offer a wealth of possibilities in terms of integration, miniaturization and potentially low-cost fabrication for relevant applications, notwithstanding a performance that may fall short of conventional state-of-the-art systems. In this context we report on progress towards the combination of surface plasmon resonance (SPR) sensing with a monolithically integrated optical sensor platform based on organic materials, including an organic light emitting diode, an optical polymer waveguide and an organic photo diode. Several according components have been developed and demonstrated recently and were exemplarily applied to fluorescence lifetime detection. Aiming at multianalyte performance we add SPR to this platform, which enables the sensitive, real-time and label-free detection of a wide range of analytes. The SPR detection scheme is based on a gold surface sustaining a surface plasmon mode which reacts sensitively to analyte-induced refractive index changes. Here, we report on the investigation of the sensor response of a 50 nm thick gold film on an 11 μm thick multimode polymer waveguide. The feasibility of this sensor concept is shown and its sensitivity is estimated from measuring the intensity transmitted trough the waveguide at a single wavelength. In addition, some further steps towards full integration are discussed.

An analytical study of the sensitivity enhancement of an angularly interrogated long range surface plasmon (LRSP) sensor, with a closed symmetric transducer structure consisting of a prism, Teflon and gold layers, is presented. The effects of the sensor design parameters, such as wavelength and the thicknesses of the gold and Teflon layers, on the angular (Sθ) and intrinsic (ISθ) sensitivities are studied for cover refractive indices varying from 1.33 to 1.37. The angular and intrinsic sensitivity calculations for the transverse mode TM mode are conducted for wavelengths ranging from 500 nm to 1000 nm. The best averaged angular and intrinsic sensitivity values are 246 degRIU^-1 and 251 RIU^-1 at 1000 nm, respectively; however, these values were achieved with different thickness combinations of the gold and Teflon layers supported by a BK7 triangular prism. The LRSP sensor's intrinsic sensitivity is better than the results calculated for prism-Teflon-gold LRSP configurations published in the literature. Although it is feasible to optimize the sensor's design parameters for high precision measurements of the bulk refractive index, the sensitivity of the LRSP on a very thin layer of the molecular formation must be investigated.

Metal nanoparticles exhibit a large potential for the development of innovative and cost-effective sensing devices. They fulfill key requirements for biosensors such as the potential for miniaturization as well as for high parallelization, and they are compatible with the molecular world for the required biofunctionalization approaches. Their optical properties based on the localized surface plasmon resonance (LSPR) are well adjustable from the UV- to the infrared spectral range using chemical synthesis. Due to the strong influence of the surrounding dielectrics on the resonant properties these particles offer a high potential for sensing of minimal changes in the surrounding media. Additionally, plasmon nanoparticles can induce a local field-enhancement and so a signal amplification such as for fluorescence or Raman-spectroscopy. In general, plasmon nanoparticles are well suited as label or as transducer for different optical detection techniques. We will give an overview about recent developments in this field, and will present different sensing strategies at single particle or ensemble level and based on planar or fiber-based systems aiming for ultrasensitive point-of care applications in bioanalytics.

We proposed an innovative phase interrogation method for localized surface plasmon resonance (LSPR) detection. To our knowledge, this is the first demonstration of LSPR biosensor by phase interrogation. LSPR is realized as the plasmonic resonance within confined metal nanoparticle. Nanoparticle couples the light by means of a non-radiative inter-band absorption, and a scattering from surface plasmon oscillation, the total contribution is the optical extinction of nanoparticles. Due to the variety of resonance types, LSPR is extensively studied in the field of biological sensing, imaging, and medical therapeutics. Generally, LSPR is probed by optical intensity variation of continuous wavelength, in other words, wavelength interrogation. LSPR sensitivity probed by this method is ranged from several tens nm/RIU to less than 1000nm/RIU depending on the nanostructure and metal species, which at least an order of magnitude less than conventional SPR biosensor in wavelength interrogation. In this work, an innovative common-path phase interrogation system is applied for LSPR detection. Phase difference in our home-made system is simply extracted through the correlation of optical intensity under different polarization without any heterodyne optical modulator or piezoelectric transducer, and thus low down the cost and complexity in optical setup. In addition, signal-to-noise ratio is substantially reduced since the signal wave and reference wave share the common path. In our preliminary results, LSPR resolution of Au nanodisk array is 1.74 x 10^-4 RIU by wavelength interrogation; on the other side, LSPR resolution of Au nanodisk array is 2.02x10^-6 RIU in phase interrogation. LSPR sensitivity is around one order of magnitude enhanced. In conclusion, we demonstrated that LSPR sensitivity can be further enhanced by phase interrogation.

A phase-sensitive optical low coherence interferometer is investigated experimentally to implement a new optical reference standard in the field of biology. This interrogation technique is associated to a planar cyclic resonant sensor such as an optical waveguide-based micro-cavity. The biological solution to be analyzed will be brought onto the surface of the sensor through a micro-fluidic cell. The aim of this association is to quantify low concentrations of analytes and to realize a real-time investigation of the kinetics of specific molecules with time and temperature for metrological applications, with better sensitivity and accuracy than existing techniques. This paper deals with the results of a feasibility study on the PS-OLCI technique as a new reference in the field of biology.

Raman spectroscopy is a powerful tool for chemical analysis. This technique can elucidate fundamental questions about the metabolic processes and intercellular variability on a single cell level. Therefore, Raman spectroscopy can significantly contribute to the study and use of microalgae in systems biology and biofuel technology. Raman spectroscopy can be combined with optical tweezers. We have employed microfluidic system to deliver the sampled microalgae to the Raman-tweezers. This instrument is able to measure chemical composition of cells and to track metabolic processes in vivo, in real-time and label-free making it possible to detect population variability in a wide array of traits. Moreover, employing an active sorting switch, cells can be separated depending on input parameters obtained from Raman spectra. We focus on algal lipids which are promising potential products for biofuel as well as for nutrition. Important parameter characterizing the algal lipids is the degree of unsaturation of the constituent fatty acids. We demonstrate the capacity of our Raman tweezers based sensor to sort cells according to the degree of unsaturation in lipid storage bodies of individual living algal cells.

Gamma ray radiation can change the refractive index of Ge-doped silica glass proportional to ray dose. These changes can shift the resonance frequencies of whispering gallery modes of microdisk. A fiber coupled microdisk has been used to design a Gamma-ray dose sensor. The 800MHz shift in resonance frequency of whispering gallery mode of microdisk, due to Gamma ray radiation has been used to detect Gamma dose in the range of 0 to 1MGy.

In this work we describe a method for immobilizing the hexahistidine-modified OPH (His₆-OPH) enzyme via sol-gel technology in a porous material while retaining its catalytic activity. The potential use of each bio-sensing material was checked by quantifying the enzymatic properties, such as the relative activity of the immobilized enzyme, its Michaelis- Menten equation parameters and its stability under extreme working conditions (pH, T). The bio-sensor material was also characterised by SEM as well as in terms of its reversibility and sensitivity.

The propagation of laser light in biological tissues is of growing importance in many medical and food applications. This problem is seriously studied in live science. The biological tissues consist of cells which dimensions are bigger than wavelength of visible light and display large compositional variations, inhomogeneities, and anisotropic structures. Therefore a Mie scattering of transmitted or backscattered light occurs and different polarization states arise. The changes of polarization state due to the multiple scattering of light in the biological cellular tissues also allow measure the freshness of processed victuals. The transmitted and backscattered laser light exhibits multiple scattering on the thin slice of sample. The phenomenon is different if the cellular tissues are living or dead. In the case of meat, there are temporal and dynamic changes not only as a result of chemical process, but also geometric deformations due to the water evaporation from intracellular and extracellular sites. The polarization measurement shows the changes in polarization orientation due to the muscle orientation and meat aging. Two types of measurements were provided: a) Measurement of polarized light reflected and twice transmitted forward and backward through the biological tissue samples - meat slice attached on sample holder mirror. b) Measurement of polarized light transmitted through the biological tissue sample. The relationship between polarization changes and meat freshness, and a dynamic temporal behavior of polarization states in the aged meat is reported.

The growing activity in the field of optical chemical sensors has resulted in numerous sensing schemes, new indicator dyes, various polymeric matrix, size and shapes and highly diversified methods of immobilization. The sensor characteristics are dependent upon the choice of indicator, polymer, immobilization technique, and also size. Sol-gel technology provides a low-temperature method for obtaining porous silicate glass matrices. It enables to obtain material in the form of films, powders, monoliths, fibres or nanoparticles. Organic reagents and molecular receptors can be easily immobilized in the matrices. Moreover, one of the unique features of the sol-gel process is that the properties of the final network structure, such as hydrophobicity, thickness, porosity, flexibility, reactivity and stability can be easily tailored by controlling the process conditions, the type and the size of the precursors and catalysis. Here we will report about several sensor designed over the years based on sol-gel materials for monitoring and controlling different parameters, such as heavy metals, amines, phosphates, organophosphates.

A new silole bearing an allyl group at silicon has been incorporated into previously-reported novel reactive polysiloxane coatings made from polymethylhydrosiloxane (PMHS) polymers crosslinked by the sol-gel process allowing subsequent functionalization by hydrosilylation of the SiH reactive groups. The thin films of crosslinked resin are covalently bonded to the glass substrate and contain a very low concentration of silole groups. They exhibit the aggregation-induced emission effect owing to restricted intramolecular rotation, and show enhanced sensitivity to nitroaromatic analytes because of the very low concentration of silole groups. The films can be used to test for nitroaromatics present not only in the vapour phase but also in many types of solvent because of the robust nature of the crosslinked network and covalent bonding to the substrate. They can be made in thicknesses ranging from 20 nm up to 1 μm. The silole groups are readily accessible, and the sensors can be regenerated by washing with solvents such as chloroform.

The paper deals with the preparation and characterization of whispering-gallery-mode silica spherical microresonators and with effects of liquid acetone, ethanol, and xerogel layers applied onto these microresonators on their resonance spectra. Microrespheres with diameters ranging from 320 to 360 μm have been prepared by heating a tip of a silica fiber with a hydrogen-oxygen burner. The microspheres were excited by a fiber taper or a bulk prism and their resonance spectra were measured. Values of the Q factor from 10⁴ to 10⁶ have been determined from these spectra. In experiments, it has been found that short contact of microspheres with acetone causes a shift of resonance dips due to surface effects caused by acetone. A decrease of the Q factor has been observed with a microresonator onto which a xerogel silica layer was applied by the sol-gel method. A very high decrease of the Q factor has been observed when the silica microresonator was brought in contact with liquid ethanol.

We present a new optical sensor for the detection of organophosphates by incorporating fluorescent indicator dye into sol-gel material. We used different configurations of immobilization matrices such as thin film and spherical nanoparticles. The sensor thin films were prepared by using acid-catalyzed sol-gel process and the spherical nanoparticles by modified Stöber method. The effects of configuration matrices on the sensor's characteristic were studied. The use of dye-doped nanoparticles improved the detection limit from 0.69 μM to 17 nM, response time from 600 s to 12 s, precision and sensitivity, but reduced the sensor's working rage from 6.9×10^-7 M - 6.9×10^-3 M to 1.75×10^-8M - 2.3×10^-7 M.

We present first results of a research project that has the goal to develop an analyzer for volatile organic compounds (VOCs) with extraordinarily high detection sensitivity and detection selectivity. Due to its high potential concerning these two key parameters, optical spectroscopy is employed. The new detection scheme is based on photoacoustic spectroscopy (PAS). PA detection utilizes the fact, that the excitation energy of light absorbing molecules is essentially transferred into kinetic energy of the surrounding molecules via inelastic collisions. This causes a local pressure increase in the absorbing gas. If the excitation source is modulated, a sound wave is generated that can be detected by a microphone and phase-sensitively measured using a lock-in amplifier. A considerable challenge of this project is represented by the broad and strongly overlapping absorption bands of the hydrocarbons. Discrimination of the VOCs is possible only by using a spectrally tunable monochromatic radiation source in combination with a sophisticated data analysis algorithm. Therefore, we apply an optical parametric oscillator (OPO) with spectral emission between 3 and 4 μm.

Recent advances in the development of trace gas sensors based on the use of quantum cascade lasers (QCLs) for the sensitive, selective detection, quantification and monitoring of small molecular gas species with resolved spectroscopic features will be described. High detection sensitivity at ppbv and sub-ppbv concentration levels require detection sensitivity, enhancement schemes such as multipass absorption cells, cavity enhanced absorption techniques, or quartz enhanced photo-acoustic absorption spectroscopy (QEPAS). These three spectroscopic methods can achieve minimum detectable absorption losses in the range from 10^-8 to 10^-11 cm^-1/√Hz. Two recent examples of real world applications of field deployable PAS and QEPAS based gas sensors will be reported, namely the monitoring of ammonia concentrations in exhaled human breath and major urban environments.

We demonstrate gas sensing in a relatively compact sensor unit in particular for weakly absorbing gases in real time. As a proof-of-concept, we built an oxygen sensor for the A-Band at 760 nm. A VCSEL laser was used as a laser source due to its mode stability and reduced cost compared to DFB lasers and Fabry-Perot lasers. In order to reduce as much as possible the sensor size, a hollow waveguide is used to guide the light and the gas to be analysed in a long path to enhance the sensitivity of the sensor. Two different types of hollow fibres were characterised with respect to their suitability for gas sensing, a photonic crystal fibre, also known as micro-structured optical fibre, and hollow metal-coated capillaries. Characteristics as attenuation, spectral transmission properties and filling time were analysed. At the end, a sensor device with coupling and detection unit was developed. The main advantage of our set-up is the possibility of using the same design for different gases by changing solely the laser, the detector and the coupling lens.

A colorimetric sensor that provides a direct visual indication of chemical contamination was developed. The detection is based on the color change of the reflected light after exposure to a gas or a liquid. The sensor is a combination of a chemically sensitive dye layer and a subwavelength grating structure. To enhance the perception of color change, a reference area sealed under a non-contaminated atmosphere is used and placed next to the sensor. The color change is clearly visible by human eyes. The device is based on photonic resonant effects; the visible color is a direct reflection of some incoming light, therefore no additional supplies are needed. This makes it usable as a standalone disposable sensor. The dye thin film is deposited by Plasma enhanced chemical vapor deposition (PECVD) on top of the subwavelength structure. The latter is made by combining a replication process of a Sol-Gel material and a thin film deposition. Lowcost fabrication and compatibility with environments where electricity cannot be used make this device very attractive for applications in hospitals, industries, with explosives and in traffic.

An innovative spectroscopic technique based on balancing and cancellation of modulated signals induced by two excitation sources. We used quartz enhanced photoacoustic spectroscopy (QEPAS) in a 2f wavelength modulation mode as an absorption sensing technique and employed a modulation cancelation approach for spectroscopic measurements of small temperature differences in a gas mixture and detection of broadband absorbers. We demonstrated measurement of small temperature differences in a C₂H₂/N₂gas mixture with a sensitivity of 30 mK in 17 sec and detection of hydrazine, a broadband absorbing chemical species, down to concentration of 1 part per million in volume in 1 sec. In both cases we used near-infrared laser diodes and selected overtone transitions.nuscrip

A porous silicon (PSi) based microarray has been integrated with a microfluidic system based on polydimethylsiloxane (PDMS) channels circuit, as a proof of concept device for the optical monitoring of selective label-free DNA-DNA interaction. Theoretical calculations, based on finite element method, taking into account molecular interactions, are in good agreement with the experimental results, and the developed numerical model can be used for device optimization. The functionalization process and the interaction between probe and target DNA has been monitored by spectroscopic reflectometry for each PSi element in the microchannels.

We report that pages with color illustrations elicit more homogeneous duration of fixations in 12 elementary school children. For six first graders, we compared the reading of the color cover and a greyscale illustrated text page of an abcbook. For six second grade pupils, we demonstrated a color and a greyscale fairytale book page. The fixations we recorded are concordant with the duration for preschoolers reported elsewhere. Average duration of fixations on a page with color elements are shorter than on greyscale ones, 425 (SE=13.4) and 461 (18.3) ms, respectively. The correlation analysis lends support that a color page is processed differently than its greyscale version. Fixation duration for color and greyscale condition was correlated neither for text (r=.567, p=.241) nor for images (r=.517, p=.294) for the second graders. Our research suggests that color elements on textbook pages encourage emergent readers to perform better in acquisition.

A relative humidity (RH) sensor measuring wide range of humidity variations based on a bent single mode optical fiber coated with Agarose is reported. When exposed to moisture the change in refractive index of the Agarose layer results in changes in the degree of coupling of the core mode to cladding modes and corresponding changes in the output power are observed in the transmission spectrum of the Agarose coated bent fiber. The sensor shows linear response in the range 25 %- 90 % RH. We show that humidity sensitivity of the sensor is wavelength dependant and high sensitivity is observed at higher wavelengths. The sensor response is fast, stable and reversible in nature.

Local chemical sensing in living cells by fluorescence methods with submicron spatial resolution is in the scope of biologist because of bringing new information about biochemical processes in living matter [1]. One of the most important monitored variables is pH. Despite of progress of novel submicron probes suitable for in-situ measurement in living cells [1] and biological micro samples [2] still there is a lack off suitable opto-chemical transducers sensitive around pH 5-7 limiting development of novel fluorescence sensors. Moreover, the interaction of the immobilized transducer with the matrix can strongly affect its fluorescence properties. In our contributition the 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) fluorescence pH transducer was incorporated into organosols based on tetraethylorthosilicate (TEOS), 3-glycidoxypropyltrimethoxysilane (GPTMS) and 3-aminopropyltriethoxysilane (APTES). Formed organosols were spin-coated onto Pyrex glass substrates and thermally treated at 140°C for 4 hours. Prepared thin layers were exposed to Britton-Robinson buffers with different pH ranging from 4 to 8 pH units. Optical properties of immobilized BCECF were investigated by the mean of absorption and fluorescence spectroscopy Acquired results were compared with the properties of BCECF solutions. It was found that all matrices reduce the sensitivity of the BCECF transducer comparing to the free solution. GPTMS and APTES contained layers exhibited better mechanical properties and increase the solubility of BCECF inside prepared layers comparing to layers prepared from pure TEOS.

On the base of the developed formalism for the determination of the optical response of a layer of nanoparticles with the account of interparticle interactions we calculated transmission spectra of such a layer in the dependence on the particle size, shape and concentration on the surface. These spectra were modeled versus the thickness of an additional layer covering the particles what allowed to determine the sensitivity of such kind of optical sensor. Such an analysis allows to find optimal parameters of the layer of particles to obtain maximal sensitivity of such kind of sensor.

Mid-infrared immersion lens photodiodes developed at the Ioffe Institute have high spectral selectivity (λmax/▵λ≈0.1...0.15) at different wavelengths -2.9, 3.3, 4.2 and 4.7 microns, the response time (up to 10^-9s) and detectivity (D* ≈ 10⁹-10¹¹, (cm√Hz)/W) being significantly higher than those of currently known detectors of thermal radiation[1].The analysis of the transfer function of the temperature sensors based on A3B5 photodiodes has shown that they permit implementing the methods of color and two-color pyrometry providing a significant decrease of the methodical error in optical temperature measurements associated with unknown values of object surface emissivity and uncontrollable changes in the environment transmission.

A highly ordered structure and a relatively simple method of obtaining porous anodic alumina (PAA) have been attracting the attention of researchers to the potentialities of using such material in various fields of science and technology. The PAA- technology is oriented to mass production, does not require the use of expensive modern lithography and evaporation equipment. The technology makes it possible to produce PAA layers in a wide thickness range (0.1 - 800 μm) and with a spatially ordered system of pores whose diameter and periodicity can be changed within the range from tens to hundreds of nanometers. By filling nanopores with conductive, semiconductive and dielectric materials or their combinations, possibilities arise of making micro-sensors based on various physical, chemical and biological effects. For numerous applications, there is a promising development direction associated with modification of PAA structures with nano-diamonds. To control the modification process and for subsequent use of films in energyabsorbing sensor systems, a real-time measurement is required of their thermal and physical parameters, and, in particular, the coefficient of thermal diffusion (CTD). In this report an optical method for determining CTD is developed which is based on an analysis of the spatialtemporal dynamics of the speckle field. The proposed method for measuring the coefficient of thermal diffusion is based on the measurement of an average speed of the speckle-field movement along the specimen surface. Due to statistical nature of speckles, their movement must be also described statistically. Our approach consists in the use of correlation functions describing the degree of change in a speckle-image of some element of the surface in the process of heating or cooling. The proposed method is fully optical, fast, non-invasive and can be customized for specific applications. Optical measurement of CTD has been carried out for PAA structures both modified and not modified with nano-diamonds. High resolution allows one to measure spatial inhomogeneities of thermophysical properties of PAA- films.

The measurement of pH in small objects (cells, drops of liquid etc.) using optical fluorescence-based sensors on optical fiber tapers is one of the most widely used optical techniques. In these sensors the diameter of the taper can play important role for collecting fluorescence from tested samples. This paper presents results of experimental measurements of fluorescence intensity of dye sensitive to pH in a solution that is excited by a blue laser. The fluorescence of the dye is collected by a taper tip. The fiber tips were prepared from a graded-index fiber with a core diameter of 50 μm. Measurements with taper tips of different diameters have allowed us to estimated a limited tip diameter necessary for collecting any fluorescence form the dye solution on a level of about 5μm.

This work presents a pyrometer for measurement of temperature of a substrate surface during the MBE growth of semiconductor heterostructures. The pyrometer sensor is based on a high-sensitivity low-noise photodiode sensor representing a microassemblage of a Si p-i-n photodiode with an electronic signal processing scheme using time-pulse modulation. The basic advantage of the proposed pyrometer is its high sensitivity, accuracy (not worse than 1.5^oC ) and reproducibility within the temperature interval 450-1200 ^oC for the operation speed 0.001-1 s under the condition of changing transmission of a vacuum chamber observation (pyrometric) window by up to 10 times. High accuracy and reproducibility of results has been achieved due to implementing the calibration principle against characteristic temperature points inherent in an object and received in situ on indirect measurements.

We propose a numerical analysis method for evaluating gradient-index (GRIN) optical fiber using the Monte Carlo method. GRIN optical fibers are widely used in optical information processing and communication applications, such as an image scanner, fax machine, optical sensor, and so on. An important factor which decides the performance of GRIN optical fiber is modulation transfer function (MTF). The MTF of a fiber is swayed by condition of manufacturing process such as temperature. Actual measurements of the MTF of a GRIN optical fiber using this method closely match those made by conventional methods. Experimentally, the MTF is measured using a square wave chart, and is then calculated based on the distribution of output strength on the chart. In contrast, the general method using computers evaluates the MTF based on a spot diagram made by an incident point light source. But the results differ greatly from those by experiment. In this paper, we explain the manufacturing process which affects the performance of GRIN optical fibers and a new evaluation method similar to the experimental system based on the Monte Carlo method. We verified that it more closely matches the experimental results than the conventional method.

Monte Carlo approach is applied to simulate light transmission and emission characteristics of a dielectric multimode waveguide of a semi-toroid shape, for range of geometrical and optical parameters of the system. The physical description of light transport is based on classical Fresnel formulas used to define probability of single photon transmission/reflection at the core/cladding boundary. Even positional and angular distribution of 'emitters' launching photons into the waveguide within cones defined by critical angle was employed to simulate propagation of all meridian and skew rays. No interference effects are included in the model. The calculated results allow for direct assessment of light leaks from and transport through the waveguide core in dependence on system parameters.

Extremely bent optical fiber (U-optrode) is applicable as a sensing head, signal of which is govern by refractive index and light scattering properties of the surrounding medium. The presented contribution aims to shows that when covered with properly selected polymeric transducers, the reliable and fast thermometers covering different temperature ranges can be constructed suitable for, e.g., measurements in environments with high level of electric or magnetic disturbances. Obviously, the bare optrodes can be also used as sensitive analytic tools for collecting information about thermallyinduced changes of optical and micro-structural properties of polymers.

In this paper an edge filter based on multimode interference in an integrated waveguide is optimized for a wavelength monitoring application. This can also be used as a demodulation element in a fibre Bragg grating sensing system. A global optimization algorithm is presented for the optimum design of the multimode interference device, including a range of parameters of the multimode waveguide, such as length, width and position of the input and output waveguides. The designed structure demonstrates the desired spectral response for wavelength measurements. Fabrication tolerance is also analysed numerically for this structure.

This paper deals with a steering-wheel microstructure optical fibre designed prepared and tested for detection of gaseous analytes. The inner structure of the steering-wheel microstructure fibre consists of a thin silica core that is surrounded by three cladding holes. Numerical simulations showed that the evanescent wave of the guided fundamental mode at a wavelength of 1550 nm penetrates into the cladding holes. The calculated overlap of the evanescent wave of guided mode with the cladding holes of 0.78% can suitably be employed for gaseous analytes detection. The prepared steeringwheel microstructure fibre was experimentally tested for detection of toluene vapors flowing in the cladding holes of the fibre. It has been proved that this type of microstructure fibre can be used for detection of gaseous analytes such as toluene in nitrogen or in air in concentrations of about 0.1 mol.%.

PIN photodiodes are semiconductor devices widely used in a huge range of applications, such as photoconductors, charge-coupled devices and pulse oximeters for medical applications. The possibility to combine and to integrate the fabrication of the sensor with its signal conditioning circuitry in a CMOS process allows device miniaturization in addition to enhance its properties lowering the production and assembly costs. This paper presents the design and characterization of silicon based PIN photodiodes integrated in a CMOS commercial process. A high-resistivity, low impurity substrate is chosen as the start material for the PIN photodiode array fabrication in order to fabricate devices with a minimum dark current. The dark current is studied, analyzed and measured for two different starting materials and for different geometries. A model previously proposed is reviewed and compared with experimental data.

The team of authors tries to provide information on the results of the fiber-optic DTS system application under long-term research of accumulation possibilities of thermal energy in the rock mass in this article. In 2006, was in Ostrava implemented the largest object in the Czech Republic, which is heated by heat pump system. It is a multi-purpose aula at VŠB-TU + CIT (Center for Information Technology). The installed heat pump system consists of ten heat pumps with a total output of 700kW and 110 wells about 140m deep. The applied research is conducted in two measuring polygons ("Big" and "Little" polygon). Simultaneously with fiber-optic DTS system is applied group of PT1000 temperature sensors and Geothermal Response Test (GERT). Fiber-optic DTS system is deployed inside polyethylene PE collector via a special sensory fiber optic cable. The ecological antifreeze mixture, based on the technical spirit, used for the collection and delivery of energy to the rock mass circulates inside of PE collector. PT1000 temperature sensors are placed at certain intervals on the outer side of the PE U-tube within the heat well. The result of application of the fiberoptic DTS system is information about the heat profile of wells, thermal conductivity of the geological environment and the impact of external changes in the thermal wells, along with the accumulation possibilities of thermal energy in the rock mass (over-summer period).

The fiber optic sensors have a great possibilities thanks to its sizes, features and usage possibilities in measurement engineering. Optical fiber is mostly used as a medium for the transfer of information, but if we consider an optical fiber as a sensor then the other usage can be found for example in medicine or biology. If the optical fiber is heated by sufficiently high temperature, the light signal starts to be emitted in the internal structure. This signal has a spectral characteristic, which can be used for evaluation of temperature thanks to quality analysis. The article will describe the evaluation of spectral characteristics for utilizationof optical fiber as fiber optic sensor for very high temperatures.

We present an inexpensive technique capable to interrogate multiplexed sensors based on ultra-low-reflective Bragg gratings written in a long standard telecom fiber. The technique is suitable for distributed detection and localization of disturbances in security and early warning systems for pipeline monitoring, in linear temperature sensors for fire detectors, etc. It is based on the correlation OTDR principle measuring cross-correlation between a noise-like probe signal and the signal reflected back from the sensing fiber. In order to simplify the sensor configuration, an unmodulated CW DFB diode laser was used as a light source. A noise-like probe signal was generated by conversion of phase noise of the DFB laser into intensity noise with a help of unbalanced Michelson interferometer. Results of the experimental verification of the proposed technique are presented.

A photoplethysmography (PPG) signal can provide very useful information about a subject's hemodynamic status in a hospital or home environment. A newly developed portable multi-spectral photoplethysmography device has been used for studies of 11 healthy subjects. The developed optical fiber biosensor comprises one multi-wavelength laser diode (405nm, 660nm and 780nm) and a single photodiode with multi-channel signal output processing and built in Li-ion accumulator; special software was created for visualization and measuring of the MS-PPG signals. ARM7TDMI-S LPC2148, NXP (founded by Philips) 32 bit processor with clock frequency of 60 MHz performs measurement and analysis of the signal.

We constructed a FBG (fiber Bragg grating) sensor system based on a fiber-optic Sagnac interferometer. A fiber-optic laser source is used as a strong light source to attain high signal-to-noise ratio. However the unstable output power and coherence noises of the fiber laser made it hard to separate the FBG signals from the interference signals of the fiber coils. To reduce noises and extract FBG sensor signals, we used a Gaussian curve-fitting and a wavelet transform. The wavelet transform is a useful tool for analyzing and denoising output signals. The feasibility of the wavelet transform denoising process is presented with the preliminary experimental results, which showed much better accuracy than the case with only the Gaussian curve-fitting algorithm.

Fiber Bragg grating (FBG) sensors are employed in a fiber-optic Sagnac interferometer sensor to measure multi-stress information of electric power systems. By using the hybrid sensor configuration, it was possible to measure the temperature and the vibration signal in an insulating transformer oil bath at the same time. A novel fiber-optic Sagnac interferometer design and a signal processing technique were used to separate the FBG sensor signals from the interference signal. The preliminary experimental results are presented to show the feasibility of the sensor system.

Laser beam profiling technology in the UV spectrum of light is evolving with the increase of excimer lasers and lamps applications, that span from lithography for VLSI circuits to eye surgery. The development of a beam-profiler, able to capture the excimer laser single pulse and process the acquired pixel current signals in the time period between each pulse, is mandatory for such applications. 1D and 2D array detectors have been realized on polycrystalline CVD diamond specimens. The fast diamond photoresponse, in the ns time regime, suggests the suitability of such devices for fine tuning feedback of high-power pulsed-laser cavities, whereas solar-blindness guarantees high performance in UV beam diagnostics, also under high intensity background illumination. Offering unique properties in terms of thermal conductivity and visible-light transparency, diamond represents one of the most suitable candidate for the detection of high-power UV laser emission. The relatively high resistivity of diamond in the dark has allowed the fabrication of photoconductive vertical pixel-detectors. A semitransparent light-receiving back-side contact has been used for detector biasing. Each pixel signal has been conditioned by a multi-channel read-out electronics made up of a high-sensitive integrator and a Σ-Δ A/D converter. The 500 μs conversion time has allowed a data acquisition rate up to 2 kSPS (Sample Per Second).

The task has been solved of acoustooptic interraction of Bessel light beams (BLB) in uniaxial crystal with plane acoustic wave. The process has been calculated of isotropic scattering of BLBs without change of the polarization state. The diffraction efficiency has been found out, and it has been shown to be closely one hundred percent. The studied acoustooptical process can be taken as a principle of the method of TH- and TE-polarized Bessel light beams obtaining, which differs by the possibility of manipulation in time by the polarization state.

The results of optical properties study of porous aluminum oxide films, fabricated by anodizing in a water solution of a sulfuric acid and modified by thermal annealing on air at temperature T≥800°C are reported. On the basis of the comparative analysis of the received data it is shown that a photoluminescence in near UV and visible regions for aluminum oxide anodized in a sulfuric acid solution originates from the divacancies of oxygen (F₂, F⁺₂ and F²⁺₂ centers) and sulfates - ions do not render essential influence on luminescent properties AOA in researched spectral area. For samples annealed at T = 1300 °C, intensive narrow strips determined *see abstract on paper* by the radiative transitions (²E → ⁴A₂) in ions of Mn4+ (678 nm) and Cr³⁺ (694 nm), replacing ions of Al³⁺ in octahedral positions of α-Al₂O₃

The properties of Bessel beams propagation and transformation in optical metamaterials are studied. The problem is solved by reflection and refraction of vectoral BLB containing embedded vortices on the boundary of a usual medium and metamaterial. The reflection and refraction coefficients of arbitrary Bessel beam are represented as superposition of linear combinations of reflection and refraction ones of TM- and TE- polarized Bessel beams. The possibility is established and conditions are determined for unidirectional and opposite directional propagation of Bessel light beams (BLBs) phase and the longitudinal component of its energy flux in metamaterials.

Silicon photodiode integrated with CMOS has been in extensive study for the past ten years due to its wide use in applications such as short-distance communication, VCD players, ambient light sensors and many other intelligent systems. In recent years, high speed blue-ray DVD is replacing conventional DVD due to its larger storage capacity and higher speed. In this work, the photodiode optimized for blue ray is fully integrated with standard 0.35um CMOS process and the bandwidth dependency upon thermal process and epitaxial material is investigated. It was found that the additional substrate thermal process can improve bandwidth for blue and red light but reduce bandwidth for infra-red. It is also found that higher level p-type epi doping does not impact bandwidth for blue light but reduces bandwidth for red and infra-red. The various mechanisms of bandwidth were discussed based on the experimental results. It indicated that the bandwidth of photodiodes depends on photo carriers travel time which can be explained by simple model of drift transport and diffusion transport. The design of photodiode should optimize the depletion region and reduce the carrier travel time.

Silica based microstructured holey fibers offer the possibility for filling with unconventional fiber materials. Of special interest are chalcogenide glasses due to their high refractive index and their nonlinear optical properties. We demonstrate two types of fibers: an index guiding fiber type with high-index glass core and silica cladding and a fiber with silica core surrounded by a periodic, hexagonal high-index glass structure giving antiresonant guiding properties. We prepared such fibers filled with arsenic sulphide glass and arsenic selenide glass by a pressurized infiltration technique. The manufacturing process is modelled on the basis of viscous glass flow parameters and is compared with experimental results obtained from the filled fibers. The propagation and spectral transmission properties of such fibers are measured and discussed.

We present the fabrication of tellurite TeO₂-ZnO-Na₂O (TZN) microstructured optical fibers (MOFs) with a suspended core and the characterization of their optical properties. The fibers are designed to develop an infrared supercontinuum generation using a sub-nJ femtosecond pulsed laser at 1.56μm. By pumping a 20 cm long fiber we generate a supercontinuum (SC) spanning over 800 nm in the 1-2 μm wavelength range. For a MOF with a core size of 2.2 μm the zero dispersion wavelength (ZDW) is at 1.45 μm. The effective area of TZN MOF is 3.5 μm² and the nonlinear coefficient is calculated to be 437 W^-1km^-1.

In this work we report our achievements in the elaboration and optical characterizations of low-losses suspended core optical fibers elaborated from As₂S₃ glass. For preforms elaboration, alternatively to other processes like the stack and draw or extrusion, we use a process based on mechanical drilling. The drawing of these drilled performs into fibers allows reaching a suspended core geometry, in which a 2 μm diameter core is linked to the fiber clad region by three supporting struts. The different fibers that have been drawn show losses close to 0.9 dB/m at 1.55 μm. The suspended core waveguide geometry has also an efficient influence on the chromatic dispersion and allows its management. Indeed, the zero dispersion wavelength, which is around 5 μm in the bulk glass, is calculated to be shifted towards around 2μm in our suspended core fibers. In order to qualify their nonlinearity we have pumped them at 1.995 μm with the help of a fibered ns source. We have observed a strong non linear response with evidence of spontaneous Raman scattering and strong spectral broadening.

For a suspended nanowire, the holes surrounding the core are expected to be as large as possible to propagate the light at wavelengths as long as possible. However, the fabrication of nanowire surrounded with large holes is still a challenge so far. In this paper, a method which involves pumping positive pressure of nitrogen gas in both the cane fabrication and fiber-drawing processes, is proposed. A suspended nanowire, with a core diameter of 480 nm and an unprecedented large diameter ratio of holey region to core (DRHC) of at least 62, is fabricated in the length of several hundred meters. Owing to the large holes, the confinement loss of the suspended nanowire is insignificant when the wavelength of light propagated in it is 1700 nm. Additionally, the tube-shaped glass cladding of the suspended nanowire shifts the singlemode cutoff wavelength to 810 nm, which is much shorter than the cutoff wavelength, 1070 nm, of a naked nanowire with the same diameter. A single-mode supercontinuum (SC) generation covering a wavelength range of 900-1600 nm is obtained under 1064 nm pump pulse with the peak power as low as 24 W. A single-mode third harmonic generation (THG) is observed by this nanowire under the pump of a 1557 nm femtosecond fiber laser. This work indicates that the suspended nanowire with large holes can provide high nonlinearity together with single-mode propagation, which leads to interesting applications in compact nonlinear devices.

Microstructured optical fibers (MOFs) represent a promising platform technology for new biosensing devices. Using MOFs with adapted cavity diameters of about 20 to 30 μm, they can be used to carry the biofluids of analytical interest. Such cavities with their walls coated by transducer material form in combination with adequate microfluidic chips a platform for fully integrated next generation plasmonic devices. This paper describes the use of a dynamic chemical nanoparticle layer deposition (NLD) technique to demonstrate the wet chemical deposition of gold and silver nanoparticles (NP) within MOFs with longitudinal, homogenously-distributed particle densities. The plasmonic structures were realized on the internal capillary walls of a three-hole suspended core fiber. Electron micrographs, taken of the inside of the fiber holes, confirm the even distribution of the NP. With the proposed procedure fiber lengths of several meters can be coated and afterwards cut up into small pieces of desired lengths. Accordingly, this procedure is highly productive and makes the resulting MOF-based sensors potentially cost efficient. In proof-of-principle experiments with liquids of different refractive indices, the dependence of the localized surface plasmon resonance (LSPR) on the surroundings was confirmed. Comparing Raman spectra of NP coated and uncoated MOFs, each filled with crystal violet, a significant signal enhancement demonstrates the usability of such functionalized MOFs for surfaceenhanced Raman spectroscopy (SERS) experiments.

We present two white-light spectral interferometric techniques for measurement of the chromatic dispersion of polarization modes in holey fibers over a broad spectral range (e.g. 500-1600 nm). First, a technique employing an unbalanced Mach-Zehnder interferometer with a fiber in the test arm is used to measure the wavelength dependence of the differential group effective index, or equivalently the chromatic dispersion of one polarization mode supported by the fiber. Second, a technique employing a tandem configuration of a Michelson interferometer and the optical fiber under test is used to measure the group modal birefringence in the fiber. From these measurements, the chromatic dispersion of the other polarization mode supported by the fiber is retrieved. We measured by these techniques the chromatic dispersion of polarization modes in three air-silica holey fibers and revealed the dependence of zero-dispersion wavelength on the geometry of the holey fiber.

We present experience with photonic crystal fiber (PCF) characterization during COST Action 299, focusing on phenomena causing errors and ways to mitigate them. PCFs developed at IPHT Jena (Germany) and UMCS Lublin (Poland), designed for single mode operation were coupled to test instruments by fusion splicing to intermediate lengths of telecom single mode fibers (SMF). PCF samples were short (0.5-100 m), with 20-70 dB/km attenuation at 1310 nm and 1550 nm. Optical Time Domain Reflectometer (OTDR) was best for measuring loss as most PCFs produced strong backscattering, while variable splice losses and difficulties with PCF cleaving for optical power measurements made cutback and insertion loss measurements inaccurate. Experience with PCF handling and cleaving is also reviewed. Quality of splices to fiber under test was critical. Excitation of higher order modes produced strong "noise" during measurements of polarization parameters like PMD or PDL. Multimode propagation and vibration-induced interference precluded testing of fine dependence of PMD on temperature or strain, causing random variations comparable to true changes of PMD. OTDR measurements were not affected, but testing of short fiber sections with very different backscattering intensities puts special demands on instrument performance. Temperature testing of liquid-infiltrated PCF was time-consuming, as settling of parameters after temperature change took up to 40 minutes. PCFs were fragile, breaking below 2% linear expansion, sometimes in unusual way when twisted.

This paper summarizes analytic results describing the spectral broadening associated with fiber modulation instability as described by analytic breather solutions of the nonlinear Schrodinger equation. These solutions allow the prediction of spectral properties of both noise-driven and induced modulation instability processes. In the latter case, the ability to describe MI with an analytic formalism allows the design of optimized experiments to generate ultrashort pulse trains from weakly-modulated initial fields. These results are examples of only a very small number of analytic descriptions of optical field propagation in highly nonlinear fiber.

We propose a rigorous electromagnetic analysis for a Photonic Crystal Fiber (PCF) geometry consisting of multiple hollow slits that go across the fiber core along the propagation axis z. The slits are regarded as invariant along the transverse dimension x but exhibit multiple sinusoidal bends in the y-z plane, which prevents the transversal profile being constant along the z axis. To analyze and characterize the electromagnetic behavior of the considered PCF geometry, we use a 2D Finite-Difference Time-Domain (FDTD) scheme assuming an ultrashort incident pulse with a polarization angle of 45 degrees as the excitation source. Our analysis focuses on three key aspects for the ultrashort pulse propagation through the slit array: pulse shaping and delay, spatiotemporal dispersion and birefringence features. Numerical FDTD simulations illustrate the effect of the slit array parameters on the previous magnitudes. Our results demonstrate that the proposed structure provides with a wide and deep control over the pulse propagation and wavefront.

The contribution of this work is a new flat-dispersion fiber operating at telecom wavelengths. The investigation of chromatic dispersion in PCFs is implemented by the study of modified highly-nonlinear PCF with flattened dispersion. Required dispersion properties, achieved by balancing material and waveguide dispersion contribution, should be done for wide spectrum of wavelengths. Flat dispersion could be used for dispersion compensation purposes in systems with wavelength division multiplex. The main attention is paid to photonic crystal fibers that exhibit unique properties, being the result of selective doping of rings of holes in the considered structures. It is shown from numerical results that flattened dispersion of -0.025 ps/nm/km from a wavelength of 1200 nm to 1700 nm is achieved using a highly nonlinear photonic crystal fiber. The systematic study includes the description of mutual relations between fiber chromatic dispersion and the structural or material parameters. The results are obtained by using the full-vectorial finite difference frequency domain method.

Recently, the generation of coherent, octave-spanning, and recompressible supercontinuum (SC) light has been demonstrated in optical fibers with all-normal group velocity dispersion (GVD) behavior by femtosecond pumping. In the normal dispersion regime, soliton dynamics are suppressed and the SC generation process is mainly due to self-phase modulation and optical wave breaking. This makes such white light sources suitable for time-resolved applications. The broadest spectra can be obtained when the pump wavelength equals the wavelength of maximum all-normal GVD. Therefore each available pump wavelength requires a specifically designed optical fiber with suitable GVD to unfold its full power. We investigate the possibilities to shift the all-normal maximum dispersion wavelength in microstructured optical fibers from the near infra red (NIR) to the ultra violet (UV). In general, a submicron guiding fiber core surrounded by a holey region is required to overcome the material dispersion of silica. Photonic crystal fibers (PCFs) with a hexagonal array of holes as well as suspended core fibers are simulated for this purpose over a wide field of parameters. The PCFs are varied concerning their air hole diameter and pitch and the suspended core fibers are varied concerning the number of supporting walls and the wall width. We show that these two fiber types complement each other well in their possible wavelength regions for allnormal GVD. While the PCFs are suitable for obtaining a maximum all-normal GVD in the NIR, suspended core fibers are well applicable in the visible wavelength range.

We report a detailed implementation of a 2-D finite element method that is applied to calculate the stimulated Brillouin scattering (SBS) characteristics in As₂Se₃-based chalcogenide photonic crystal fibers (PCF). The full modal analysis of SBS is performed in both real and ideal As₂Se₃-based PCF structures taking into account the contribution of the higher order acoustic modes. Our results include the calculations of the Brillouin gain spectrum (BGS), Brillouin gain coefficient (g_B), Brillouin frequency shift (BFS), and the Brillouin threshold (P_th). The Pth in the real As₂Se₃-based chalcogenide PCF is evaluated to be around 36 mW for only 1-m length compared to hundreds of milliwatts found in the long silica PCF. We calculate, in both structures, a Brillouin gain coefficient of the fundamental acoustic mode of ~5.59 10^-9 mW^-1 at λ=1.55 μm, around the acoustic frequency of 8.08 GHz, which is more than 600 times higher than that of fused silica fiber.

We have recently introduced a new approach in the utilisation and actuation of liquid matrices inside microstructured optical fibers, by infiltrating in their capillaries magnetically active fluids, namely, ferrofluids. The specific optofluidic approach provides the possibility of actuation of the infiltrated liquid by applying an external magnetic field, thus, exhibiting magnetofluidic capabilities. We apply this infiltration protocol in microstructured optical fiber Bragg gratings for developing magnetic field tunable/sensitive photonic devices and sensing probes. The material and implementation considerations related to this infiltration approach of viscous and opaque ferrofluids inside microstructured optical fibers, and the corresponding effects on the guiding and scattering behavior of the microstructured optical fiber Bragg gratings are presented and discussed. An updated review on this infiltrated microstructured optical fiber devices will be presented, focusing on the demonstration of simple magnetofluidic configurations such as "on-off" Bragg grating trimmers, "infiber" magnetometers, ferrofluidic defected Bragg reflectors and external magnetic field modulators. The design principles of such "in-fiber" magnetofluidic photonic devices will be analysed, along with their particular functionalities and application prospects; while in addition, the infiltration and fiber capillary functionalisation processes will be presented.

To open up new optical frequency resources available for optical communications, the concept of all-band photonics has been proposed, which is based on the utilization of broadband of optical frequencies from 1- to 2-μm waveband as a novel photonic band for photonic transmission. In this study, an ultra-broadband photonic transport system was developed by employing a long-distance holey-fiber transmission line to simultaneously use the new 1-μm waveband (Tband) and a conventional waveband. We successfully demonstrate the use of a photonic transport system to achieve simultaneous 3x10-Gbps error-free optical data transmissions for waveband division multiplexing of the 1-μm waveband, C-band, and L-band.

Photonic crystal fiber long-period gratings (PCF-LPGs) operating near the phase-matching turning point to achieve high sensitivity to the refractive index of gas and liquid analytes infiltrated into cladding air holes are designed by numerical optimization. The vectorial finite element method is employed for the modal analysis of an index-guiding PCF and the calculation of the phase matching curves. The geometrical parameters of PCF (pitch and diameter of air holes arranged in a periodic triangular array) are optimized by using the down-hill simplex technique to engineer the dispersion of modes coupled by a LPG to obtain the turning point in the phase-matching curve at a desired wavelength for a given analyte refractive index. The resonant wavelength is subsequently extremely sensitive to the analyte refractive index, however, its large shifts can be detected with a substantially reduced resolution because the resonance dip in the LPG transmission spectrum is very broad. On the other hand, the broad resonance provides a broadband operation of a PCF-LPG sensor and its high sensitivity to the refractive index can still be achieved by relying on changes in the coupling strength (and consequently in the transmission loss) rather than in the resonant wavelength of LPG. We consider coupling between the fundamental core mode and the first-order symmetric cladding mode. We also explore an alternative approach based on coupling between the fundamental core mode and the fundamental space-filling mode instead of the individual cladding mode. The PCF-LPG structure optimized for refractive-index sensing is also assessed for label-free biosensing.

Fibre Bragg grating (FBG) sensors have been fabricated in polymer photonic crystal fibre (PCF). Results are presented using two different types of polymer optical fibre (POF); first multimode PCF with a core diameter of 50μm based on poly(methyl methacrylate) (PMMA) and second, endlessly single mode PCF with a core diameter of 6μm based on TOPAS cyclic olefin copolymer. Bragg grating inscription was achieved using a 30mW continuous wave 325nm helium cadmium laser. Both TOPAS and PMMA fibre have a large attenuation of around 1dB/cm in the 1550nm spectral region, limiting fibre lengths to no longer than 10cm. However, both have improved attenuation of under 10dB/m in the 800nm spectral region, thus allowing for fibre lengths to be much longer. The focus of current research is to utilise the increased fibre length, widening the range of sensor applications. The Bragg wavelength shift of a grating fabricated in PMMA fibre at 827nm has been monitored whilst the POF is thermally annealed at 80°C for 7 hours. The large length of POF enables real time monitoring of the grating, which demonstrates a permanent negative Bragg wavelength shift of 24nm during the 7 hours. This creates the possibility to manufacture multiplexed Bragg sensors in POF using a single phase mask in the UV inscription manufacturing. TOPAS holds certain advantages over PMMA including a much lower affinity for water, this should allow for the elimination of cross-sensitivity to humidity when monitoring temperature changes or axial strain, which is a significant concern when using PMMA fibre.

We propose a tellurite core phosphate cladding composite microstructured optical fiber (MOF) with high nonlinearity and flattened dispersion for parametric amplification. To realize flattened dispersion, the structure parameters such as the tellurite core diameter, the air hole diameter and the distance between the centers of the two neighboring air holes are optimized. The ultraflat dispersion curve is obtained for tellurite core of 1.1μm, pitch of 1.2 μm and air hole diameter of 0.5 μm. In this case, the flattened dispersion with value between -4 and 0.5 ps/nm/km is obtained ranging from 1400 to 1600 nm. The nonlinear coefficient γ is as high as 2.5 m^-1W^-1 at 1.5 μm. The optical parametric gain bandwidth of nearly 200 nm can be achieved in composite tellurite/phosphate MOF with the length of 2.5 m and the pump power of 0.4 W.