Chemical Sensor Based on a Long-Period Fibre Grating Modified by a Functionalized Polydimethylsiloxane Coating

A chemical sensor based on a coated long-period grating has been prepared and characterized. Designer coatings based on polydimethylsiloxane were prepared by the incorporation of diphenylsiloxane and titanium cross-linker in order to provide enhanced sensitivity for a variety of key environmental pollutants and optimal refractive index of the coating. Upon microextraction of the analyte into the polymer matrix, an increase in the refractive index of the coating resulted in a change in the attenuation spectrum of the long-period grating. The grating was interrogated using ring-down detection as a means to amplify the optical loss and to gain stability against misalignment and power fluctuations. Chemical differentiation of cyclohexane and xylene was achieved and a detection limit of 300 ppm of xylene vapour was realized.

Experimental characterization of continuous-variable entanglement

We present an experimental analysis of quadrature entanglement produced from a pair of amplitude squeezed beams. The correlation matrix of the state is characterized within a set of reasonable assumptions, and the strength of the entanglement is gauged using measures of the degree of inseparability and the degree of Einstein-Podolsky-Rosen (EPR) paradox. We introduce controlled decoherence in the form of optical loss to the entangled state, and demonstrate qualitative differences in the response of the degrees of inseparability and EPR paradox to this loss. The entanglement is represented on a photon number diagram that provides an intuitive and physically relevant description of the state. We calculate efficacy contours for several quantum information protocols on this diagram, and use them to predict the effectiveness of our entanglement in those protocols.

Implications of high power losses in IR femtosecond laser inscribed fibre Bragg gratings

We report on high power issues related to the reliability of fibre Bragg gratings inscribed with an infrared femtosecond laser using the point-by-point writing method. Conventionally, fibre Bragg gratings have usually been written in fibres using ultraviolet light, either holographically or using a phase mask. Since the coating is highly absorbing in the UV, this process normally requires that the protective polymer coating is stripped prior to inscription, with the fibre then being recoated. This results in a time consuming fabrication process that, unless great care is taken, can lead to fibre strength degradation, due to the presence of surface damage. The recent development of FBG inscription using NIR femtosecond lasers has eliminated the requirement for the stripping of the coating. At the same time the ability to write gratings point-by-point offers the potential for great flexibility in the grating design. There is, however, a requirement for reliability testing of these gratings, particularly for use in telecommunications systems where high powers are increasingly being used in long-haul transmission systems making use of Raman amplification. We report on a study of such gratings which has revealed the presence of broad spectrum power losses. When high powers are used, even at wavelengths far removed from the Bragg condition, these losses produce an increase in the fibre temperature due to absorption in the coating. We have monitored this temperature rise using the wavelength shift in the grating itself. At power levels of a few watts, various temperature increases were experienced ranging from a few degrees up to the point where the buffer completely melts off the fibre at the grating site. Further investigations are currently under way to study the optical loss mechanisms in order to optimise the inscription mechanism and minimise such losses.

Chemical Sensor Based on a Long-Period Fibre Grating Modified by a Functionalized Polydimethylsiloxane Coating

A chemical sensor based on a coated long-period grating has been prepared and characterized. Designer coatings based on polydimethylsiloxane were prepared by the incorporation of diphenylsiloxane and titanium cross-linker in order to provide enhanced sensitivity for a variety of key environmental pollutants and optimal refractive index of the coating. Upon microextraction of the analyte into the polymer matrix, an increase in the refractive index of the coating resulted in a change in the attenuation spectrum of the long-period grating. The grating was interrogated using ring-down detection as a means to amplify the optical loss and to gain stability against misalignment and power fluctuations. Chemical differentiation of cyclohexane and xylene was achieved and a detection limit of 300 ppm of xylene vapour was realized.

Investigations on selected chalcogenide glasses towards the realization of photonic devices

Among various optical sensing schemes, infrared spectroscopy is a powerful tool for detecting and determining the composition of complex organic samples since vibrational finger prints of all biomolecules and organic species are located in this window. This spectroscopic technique is simple, reliable, fast, non-destructive, cost-effective while having low sensitivity. Use of metallic nanoparticles in association with a good IR transparent sensing substrate, is one of the promising solutions to enhance the sensitivity. Chalcogenide glasses are promising substrate material because of their extended optical transmission window starting from the visible to the far infrared range up to 20 μm, high refractive index usually between 2 and 3 and high optical nonlinearity, which make them good candidates as IR sensors and optical ultrafast nonlinear devices. These glasses are favorable sensor materials for the infrared spectral range because of their high IR transparency to allow for low optical loss at wavelengths corresponding to the characteristic optical absorption bands of organic molecules, high refractive index for tight confinement of optical energy within the resonator structure, processibility into thin film form, chemical compatibility for adhesion of silver nano particles and thin films and resistance to the chemical environment to be sensed. Molecules adsorbed to silver island structures shows enhanced IR absorption spectra and the extent of enhancement is determined by many factors such as the size, density and morphology of silver structures, optical and dielectric properties of the substrate material etc.

Global flash multifocal electroretinogram : early detection of local functional changes and its correlations with optical coherence tomography and visual field loss in diabetic eyes

Purpose: To investigate the correlations of the global flash multifocal electroretinogram (MOFO mfERG) with common clinical visual assessments – Humphrey perimetry and Stratus circumpapillary retinal nerve fiber layer (RNFL) thickness measurement in type II diabetic patients. Methods: Forty-two diabetic patients participated in the study: ten were free from diabetic retinopathy (DR) while the remainder suffered from mild to moderate non-proliferative diabetic retinopathy (NPDR). Fourteen age-matched controls were recruited for comparison. MOFO mfERG measurements were made under high and low contrast conditions. Humphrey central 30-2 perimetry and Stratus OCT circumpapillary RNFL thickness measurements were also performed. Correlations between local values of implicit time and amplitude of the mfERG components (direct component (DC) and induced component (IC)), and perimetric sensitivity and RNFL thickness were evaluated by mapping the localized responses for the three subject groups. Results: MOFO mfERG was superior to perimetry and RNFL assessments in showing differences between the diabetic groups (with and without DR) and the controls. All the MOFO mfERG amplitudes (except IC amplitude at high contrast) correlated better with perimetry findings (Pearson’s r ranged from 0.23 to 0.36, p<0.01) than did the mfERG implicit time at both high and low contrasts across all subject groups. No consistent correlation was found between the mfERG and RNFL assessments for any group or contrast conditions. The responses of the local MOFO mfERG correlated with local perimetric sensitivity but not with RNFL thickness. Conclusion: Early functional changes in the diabetic retina seem to occur before morphological changes in the RNFL.

Dielectric function and optical conductivity of TiOx (0.8loss spectroscopy

Reflection electron energy-loss spectra are reported for the family of compounds TiOx over the entire homogeneity range (0.8 < a: < 1.3). The spectra exhibit a plasmon feature on the low-energy side, while several interband transitions are prominent at higher energies. The real and imaginary parts of dielectric functions and optical conductivity for these compounds are determined using the Kramers-Kronig analysis. The results exhibit systematic behavior with varying oxygen stoichiometry.

Optimization of efficiency-loss figure of merit in carrier-depletion silicon Mach-Zehnder optical modulator.

In this paper we study the optimization of interleaved Mach-Zehnder silicon carrier depletion electro-optic modulator. Following the simulation results we demonstrate a phase shifter with the lowest figure of merit (modulation efficiency multiplied by the loss per unit length) 6.7 V-dB. This result was achieved by reducing the junction width to 200 nm along the phase-shifter and optimizing the doping levels of the PN junction for operation in nearly fully depleted mode. The demonstrated low FOM is the result of both low V(π)L of ~0.78 Vcm (at reverse bias of 1V), and low free carrier loss (~6.6 dB/cm for zero bias). Our simulation results indicate that additional improvement in performance may be achieved by further reducing the junction width followed by increasing the doping levels.

Low loss and low crosstalk multimode polymer waveguide crossings for high-speed optical interconnects

Multimode polymer waveguide crossings exhibiting the lowest reported excess loss of 0.006dB/crossing and crosstalk values as low as -30dB are presented. Their potential for use in high-speed dense optical interconnection architectures is demonstrated. © 2007 Optical Society of America.

Optical waveguide propagation loss measurement using multiple reflections method

Optical waveguide propagation loss measurement method based on optical multiple reflections detection is presented in this paper. By using a precision reflectometer, uncertain influence on waveguide propagation loss measurement caused by fiber-waveguide coupling can be eliminated effectively and the waveguide net propagation loss can be measured accurately. To demonstrate this, the propagation loss of a Silicon-on-Insulator (SOI) rib waveguide fabricated by RIE is measured with the obtained value being 4.3 dB/cm. This method provides a non-destructive means for evaluating waveguide propagation loss. (c) 2005 Elsevier B.V. All rights reserved.

Loss of superfluidity in a Bose-Einstein condensate on an optical lattice via a novel classical phase transition

We predict the loss of superfluidity in a Bose-Einstein condensate (BEC) trapped in a combined optical and axially-symmetric harmonic potentials during a resonant collective excitation initiated by a periodic modulation of the atomic scattering length a, when the modulation frequency equals twice the radial trapping frequency or multiples thereof. This classical dynamical transition is marked by a loss of superfluidity in the BEC and a subsequent destruction of the interference pattern upon free expansion. Suggestion for future experiment is made. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Strong infrared spectral broadening in low-loss As-S chalcogenide suspended core microstructured optical fibers

We report the fabrication and characterization of the first guiding chalcogenide As(2)S(3) microstructured optical fibers (MOFs) with a suspended core. At 1.55 mu m, the measured losses are approximately 0.7 dB/m or 0.35 dB/m according to the MOF core size. The fibers have been designed to present a zero dispersion wavelength (ZDW) around 2 mu m. By pumping the fibers at 1.55 mu m, strong spectral broadenings are obtained in both 1.8 and 45-m-long fibers by using a picosecond fiber laser. (C) 2010 Optical Society of America