Optical chemical sensors using polythiophene derivatives as active layer for detection of volatile organic compounds

Several studies on polythiophene gas sensors, based mainly on electrochemical and gravimetric principles can be found in the literature. However, other principles of gas detection, such as optical and thermal, are still little studied. Optical sensing is suitable for remote detection and offers great versatility at low cost. Here,we report on the use of thin films of seven polythiophene derivatives as active layer in optical sensors for the detection of six volatile organic compounds (n-hexane, toluene, tetrahydrofuran, chloroform, dichloromethane and methanol) and water vapor, in concentration range of 500-30,000 ppm. The results showed that it is possible to use different polythiophene derivatives to differentiate VOCs by optical sensing. Differentiation can be performed based on the presence or not of response to an analyte and the sensitivity value of the sensors for the analytes. Another important feature is the lack of the effect of humidity on the response of most films, which could be a major drawback in the application of these sensors. (C) 2011 Elsevier B.V. All rights reserved.

Temperature Sensing Using Colloidal-Core Photonic Crystal Fiber

We report on a temperature sensor based on the monitoring of the luminescence spectrum of CdSe/ZnS nanocrystals, dispersed in mineral oil and inserted into the core of a photonic crystal fiber. The high overlap between the pump light and the nanocrystals as well as the luminescence guiding provided by the fiber geometry resulted in relatively high luminescence powers and improved optical signal-to-noise ratio (OSNR). Also, both core end interfaces were sealed so as to generate a more stable and robust waveguide structure. Temperature sensitivity experiments indicated a 70 pm/degrees C spectral shift over the 5 degrees C to 90 degrees C range.

Design of a Comb Generator for High Capacity Coherent-WDM Systems

This paper presents a theoretical model developed for estimating the power, the optical signal to noise ratio and the number of generated carriers in a comb generator, having as a reference the minimum optical signal do noise ratio at the receiver input, for a given fiber link. Based on the recirculating frequency shifting technique, the generator relies on the use of coherent and orthogonal multi-carriers (Coherent-WDM) that makes use of a single laser source (seed) for feeding high capacity (above 100 Gb/s) systems. The theoretical model has been validated by an experimental demonstration, where 23 comb lines with an optical signal to noise ratio ranging from 25 to 33 dB, in a spectral window of similar to 3.5 nm, are obtained.

Optimal Code Set Selection and Security Issues in Spectral Phase-Encoded Time Spreading (SPECTS) OCDMA Systems

In this paper, we perform a thorough analysis of a spectral phase-encoded time spreading optical code division multiple access (SPECTS-OCDMA) system based on Walsh-Hadamard (W-H) codes aiming not only at finding optimal code-set selections but also at assessing its loss of security due to crosstalk. We prove that an inadequate choice of codes can make the crosstalk between active users to become large enough so as to cause the data from the user of interest to be detected by other user. The proposed algorithm for code optimization targets code sets that produce minimum bit error rate (BER) among all codes for a specific number of simultaneous users. This methodology allows us to find optimal code sets for any OCDMA system, regardless the code family used and the number of active users. This procedure is crucial for circumventing the unexpected lack of security due to crosstalk. We also show that a SPECTS-OCDMA system based on W-H 32(64) fundamentally limits the number of simultaneous users to 4(8) with no security violation due to crosstalk. More importantly, we prove that only a small fraction of the available code sets is actually immune to crosstalk with acceptable BER (<10(-9)) i.e., approximately 0.5% for W-H 32 with four simultaneous users, and about 1 x 10(-4)% for W-H 64 with eight simultaneous users.

Effects of laser focusing and fluence on the analysis of pellets of plant materials by laser-induced breakdown spectroscopy

The effects of laser focusing and fluence on LIBS analysis of pellets of plant leaves was evaluated. A Q-switched Nd:YAG laser (5ns, 10Hz, 1064nm) was used and the emission signals were collected by lenses into an optical fiber coupled to a spectrometer with Echelle optics and ICCD. Data were acquired from the accumulation of 20 laser pulses at 2.0 mu s delay and 5.0 mu s integration time gate. The emission signal intensities increased with both laser fluence and spot size. Higher sensitivities for Ca, K, Mg, P, Al, B, Cu, Fe, Mn, and Zn determinations were observed for fluences in the range from 25 to 60Jcm(-2). Coefficients of variation of site-to-site measurements were generally lower than 10% (n=30 sites, 20 laser pulses/site) for a fluence of 50Jcm(-2) and 750 mu m spot size. For most elements, there is an indication that accuracy is improved with higher fluences. (C) 2012 Elsevier B.V. All rights reserved.

Novel Sealing Technique for Practical Liquid-Core Photonic Crystal Fibers

In this letter, we describe a simple and effective technique to prevent evaporation in liquid-core photonic crystal fibers (PCFs). The technique consists of using a micropipette to deploy a micro-droplet of an ultraviolet curable polymer adhesive in both core inputs. After it is cured, the adhesive creates sealing polymer plugs with quite satisfactory insertion loss (overall optical transmission of about 15%). Processed fibers remained liquid-filled for at least six weeks. From a practical point of view, we conducted a supercontinuum generation experiment in a water-core PCF to demonstrate a 120-minute spectral width stability and the ability to withstand at least 3-mW average power at the sealed fiber input. Similar experiments carried out with nonsealed fibers produced supercontinuum spectra lasting no longer than 10 minutes, with average powers kept below 0.5 mW to avoid thermally induced evaporation.

Red and infrared light distribution in blood.

Low level laser therapy (LLLT) is used in several applications, including the reduction of inflammatory processes. It might be used to prevent the systemic inflammatory response syndrome (SIRS), which some patients develop after cardiopulmonary bypass (CPB) surgery. The objectives of this study were to investigate light distribution inside blood, in order to implement the LLLT during CPB, and, through this study, to determine the best wavelength and the best way to perform the treatment. The blood, diluted to the same conditions of CPB procedure was contained inside a cuvette and an optical fiber was used to collect the scattered light. Two wavelengths were used: 632.8 nm and 820 nm. Light distribution in blood inside CPB tubes was also evaluated. Compared to the 820 nm light, the 632.8 nm light is scattered further away from the laser beam, turning it possible that a bigger volume of blood be treated. The blood should be illuminated through the smallest diameter CPB tube, using at least four distinct points around it, in only one cross section, because the blood is kept passing through the tube all the time and the whole volume will be illuminated.

Nerve fiber layer in glaucomatous hemifield loss: a case-control study with time- and spectral-domain optical coherence tomography

Purpose: To evaluate the retinal nerve fiber layer measurements with time-domain (TD) and spectral-domain (SD) optical coherence tomography (OCT), and to test the diagnostic ability of both technologies in glaucomatous patients with asymmetric visual hemifield loss. Methods: 36 patients with primary open-angle glaucoma with visual field loss in one hemifield (affected) and absent loss in the other (non-affected), and 36 age-matched healthy controls had the study eye imaged with Stratus-OCT (Carl Zeiss Meditec Inc., Dublin, California, USA) and 3 D OCT-1000 (Topcon, Tokyo, Japan). Peripapillary retinal nerve fiber layer measurements and normative classification were recorded. Total deviation values were averaged in each hemifield (hemifield mean deviation) for each subject. Visual field and retinal nerve fiber layer "asymmetry indexes" were calculated as the ratio between affected versus non-affected hemifields and corresponding hemiretinas. Results: Retinal nerve fiber layer measurements in non-affected hemifields (mean [SD] 87.0 [17.1] mu m and 84.3 [20.2] mu m, for TD and SD-OCT, respectively) were thinner than in controls (119.0 [12.2] mu m and 117.0 [17.7] mu m, P<0.001). The optical coherence tomography normative database classified 42% and 67% of hemiretinas corresponding to non-affected hemifields as abnormal in TD and SD-OCT, respectively (P=0.01). Retinal nerve fiber layer measurements were consistently thicker with TD compared to SD-OCT. Retinal nerve fiber layer thickness asymmetry index was similar in TD (0.76 [0.17]) and SD-OCT (0.79 [0.12]) and significantly greater than the visual field asymmetry index (0.36 [0.20], P<0.001). Conclusions: Normal hemifields of glaucoma patients had thinner retinal nerve fiber layer than healthy eyes, as measured by TD and SD-OCT. Retinal nerve fiber layer measurements were thicker with TD than SD-OCT. SD-OCT detected abnormal retinal nerve fiber layer thickness more often than TD-OCT.