Optical Fiber-based System Research Articles

Monitoring of Bond in FRP Retrofitted Concrete Structures

Debonding failure of the concrete cover in reinforced concrete beams retrofitted with fiber reinforced polymer (FRP) composites is a brittle phenomenon which in most cases occurs in an abrupt manner. A complete understanding of bond requires information about the relationship between the local bond stress and slip. Bond-slip defines the constitutive relationship of the interface, and it provides means for computation of ultimate strength and distribution of the bond stress. For FRP composites interface slip is very small even at the ultimate stage prior to failure. For this reason, the study of local bond in the earlier studies did not include slip. This article presents a fiber optic based method for measurement of local slip at the interface between concrete and FRP as well as for prediction of bond failure in reinforced concrete members. Since bond failure in FRP retrofitted concrete is a brittle phenomenon, development of effective means to predict the failure prior to occurrence plays an important role in structural health monitoring of such structures. Therefore, the scope of the study includes two types of tests, namely pull out tests and beam flexure tests. In general, the measured interface slip between concrete substrate and FRP at ultimate load stage is <60 μm. The fiber optic based system is capable of measuring the interface slip with a resolution of 1 μm. In flexure, the long gauge distributed sensors are able to predict the debonding and peeling of the FRP fabric from the concrete beam through deformation reversals. A numerical model based on finite element analysis of the beams is developed to verify the capabilities of the fiber optic sensor through computation of principal stresses at the interface.

Tiny mirrors for huge telescopes

Observing the formation of early galaxies helps us understand our origins. The light coming from these faraway objects is very faint and shifted to the infrared. Multi-object spectroscopy (MOS) is the central method for studying many isolated objects simultaneously, using a slit mask in the focal plane of the telescope for blocking spoiling sources and background light. Today these masks are static perforated sheets or complex fiber-opticbased systems. In the future, microelectromechanical systems (MEMS) could provide a remote controllable, reconfigurable slit mask, increasing the scientific efficiency of MOS. In the framework of studies on the future European Extremely Large Telescope (E-ELT), we are developing a micromirror array (MMA)-based reflective slit mask. Another MEMS solution, a microshutter-based slit mask, is being developed for the James Webb Space Telescope by Moseley and colleagues at NASA.1 However, we believe that MMAs are an appropriate solution for extremely large telescopes (ELTs), as they have a large focal plane (in the meter range). Because we work with reflected light, the electric wiring and mounting of the MEMS can be realized under the MMA. These integrated MMA building blocks can be used as ‘paving stones’ to cover large surfaces nearly seamlessly. Figure 1 shows the basic concept of a MOS using an MMA as a slit mask. The mirrors at the locations of the objects of interest are tilted (ON state), and the light is sent toward the spectrograph. All the other mirrors remain unactuated (OFF state) and send the light of the spoiling sources back to the telescope. The ratio of wanted to unwanted light must be 3000:1 or better. Thus a mechanical tilt angle of at least 20◦ is needed.2 This tilt angle must be uniform across the whole array, so that the light of all selected objects goes through the entrance pupil of the spectrograph. In order not to disturb the wavefront of the reflected light, the mirror must remain optically flat (λ/20) during operation. For infrared applications, it must be in a cryogenic environment. Figure 1. In the multi-object spectroscopy microelectromechanical systems (MOS-MEMS) setup, the micromirror array in the focal plane of the telescope selects the light from the objects of interest and sends it to the spectrograph.

Evaluation of a fiberoptic-based system for measurement of optical properties in highly attenuating turbid media

BackgroundAccurate measurements of the optical properties of biological tissue in the ultraviolet A and short visible wavelengths are needed to achieve a quantitative understanding of novel optical diagnostic devices. Currently, there is minimal information on optical property measurement approaches that are appropriate for in vivo measurements in highly absorbing and scattering tissues. We describe a novel fiberoptic-based reflectance system for measurement of optical properties in highly attenuating turbid media and provide an extensive in vitro evaluation of its accuracy. The influence of collecting reflectance at the illumination fiber on estimation accuracy is also investigated.MethodsA neural network algorithm and reflectance distributions from Monte Carlo simulations were used to generate predictive models based on the two geometries. Absolute measurements of diffuse reflectance were enabled through calibration of the reflectance system. Spatially-resolved reflectance distributions were measured in tissue phantoms at 405 nm for absorption coefficients (μa) from 1 to 25 cm-1 and reduced scattering coefficients () from 5 to 25 cm-1. These data and predictive models were used to estimate the optical properties of tissue-simulating phantoms.ResultsBy comparing predicted and known optical properties, the average errors for μa and were found to be 3.0% and 4.6%, respectively, for a linear probe approach. When bifurcated probe data was included and samples with μa values less than 5 cm-1 were excluded, predictive errors for μa and were further reduced to 1.8% and 3.5%.ConclusionImprovements in system design have led to significant reductions in optical property estimation error. While the incorporation of a bifurcated illumination fiber shows promise for improving the accuracy of estimates, further study of this approach is needed to elucidate the source of discrepancies between measurements and simulation results at low μa values.

A Fiberoptic-based System for Integrating Photosynthetically Active Radiation in Plant Canopies

This report describes a system for integrating photosynthetically active radiation (PAR) using fiberoptics. Many photoelectric sensors or 1-m-long line sensors that integrate individual interception points for spatial averaging were replaced with fiberoptics, which integrate interception points. Depending on the positioning of optical fibers and the amount of fibers terminated at a PAR sensor, whole-plant, canopy layer, and individual leaf light interception can be determined. The use of fiberoptics has the added advantage of being very small in comparison to the bulk of a typical quantum sensor. The fiberoptic-based system potentially is a more accurate, less expensive method to integrate PAR throughout plant canopies than PAR sensors.

A fiber optic-based system for behavioral eyeblink measurement in a MRI environment

We previously described a reliable system to control the timing of multiple stimuli and to detect behavioral eyeblink responses in fMRI studies of learning in animals. Here, we report a significant advancement of the original system, which incorporates a fiber-optic probe in order to avoid the interference associated with the application of pulsed field gradients during MR imaging, particularly echo planar imaging. Eyeblink responses recorded with our fiber-optic probe and modified detection circuit demonstrate the ability of our new system to acquire behavioral data free of gradient-induced artifacts, thereby eliminating the need for low-pass filtering. This fiber optic-based system should be applicable to both animal and human imaging experiments.

Fiber optical liquid level sensor under cryogenic environment

Abstract This paper reports a preliminary experimental investigation and characterization of an optical fiber-based liquid level detection system for applications in cryogenic environment. The sensor system comprises a multiplexed array of point liquid probes. Two different designs of the probe were fabricated and tested. Probe tests were conducted in water–air, liquid–gas nitrogen environments. The multiplexing of multiple liquid probes using an optical time domain reflectometer (OTDR) device was successfully demonstrated. In addition, response time of the liquid probe was measured and compared experimentally.

Effect of multiaccess interference on code synchronization using a sequential detector in an optical CDMA LAN

The performance of a sequential detection code synchronization scheme in the presence of multi-access interference and receiver noise for a noncoherent, optical fiber-based CDMA system is investigated. The mean acquisition time of the synchronizer is derived using the Markov flow-graph technique. The results emphasize the need to optimize the sequential detector threshold to the number of active users on the network to maximize the performance of the synchronizer.

Optical Fiber-Based Wave Mixing as a Convenient and Sensitive Laser Analytical Tool for Condensed-Phase Analytes

A fiber-optic degenerate four-wave mixing (D4WM) probe for the measurement of small absorptions in liquid-phase samples is described. Laser D4WM is a nonlinear laser spectroscopic technique that has proven to be highly sensitive for the detection of trace analytes in condensed-phase media. A significant improvement in the forward-scattering optical arrangement of D4WM is demonstrated by using optical fibers for both laser light input and output. There is considerable flexibility inherent in the design since the system may be used in three configurations: (1) the simplest case of transmitting the signal radiation by optical fiber to the detection electronics, (2) the case of guiding the excitation beams to the analyte by polarization-maintaining optical fibers, and (3) the combination of both. The optical fiber-based D4WM system is shown to be an effective and sensitive laser analytical spectroscopic method for trace analysis, offering advantages such as detection in very small probe volumes, remote and in situ analysis, and convenient and efficient optical alignment enhancements obtained by the use of optical fibers.

In situ visualization and photoablation of individual neurons using a low cost fiber optic based system

This paper describes a low-cost system for in situ visualization and photoablation of single neurons. The system includes a fiber optics light source equipped with a filter port, a blue excitation filter and a yellow barrier filter, and a light guide which terminates with a focusing lens. This system is inexpensive, easy to use, and requires minimal maintenance. Given its price, this system is readily accessible and has the potential of becoming standard equipment for in situ visualization and killing of individual neurons.

In situ visualization and photoablation of individual neurons using a low cost fiber optic based system

This paper describes a low-cost system for in situ visualization and photoablation of single neurons. The system includes a fiber optics light source equipped with a filter port, a blue excitation filter and a yellow barrier filter, and a light guide which terminates with a focusing lens. This system is inexpensive, easy to use, and requires minimal maintenance. Given its price, this system is readily accessible and has the potential of becoming standard equipment for in situ visualization and killing of individual neurons.

Compound parabolic concentrator probe for efficient light collection in spectroscopy of biological tissue

We describe a compound parabolic concentrator (CPC)-based probe for enhanced signal collection in the spectroscopy of biological tissues. Theoretical considerations governing signal enhancement compared with conventional collection methods are given. A ray-tracing program was used to analyze the throughput of CPC's with shape deviations and surface imperfections. A modified CPC shape with 99% throughput was discovered. A 4.4-mm-long CPC was manufactured and incorporated into an optical fiber-based near-infrared Raman spectrometer system. For human tissue samples, light collection was enhanced by a factor of 7 compared with collection with 0.29-NA optical fibers.

An easily constructed device for removal of laser plume and bodily fluid leakage from the biopsy ports of endoscopes

endoscopes has broadened the spectrum of potential clinical use and extended it beyond that of choledocholithiasis alone. Currently, retrograde cholangioscopy has been found to be of value in the diagnosis and therapy of pancreaticobiliary lesions. ~ Both intrahepatic and more distal ductal calculi may be treated under direct vision by the passage of lithotripters (laser or electrohydraulic). 1°-12 Furthermore, cholangioscopy permits the visual assessment and sampling of suspicious intraluminal and mucosal-based lesions seen under fluoroscopy. 6 However, present fiberoptic-based systems are fragile and with time yield images of deteriorating quality. In recent years the development of the video chip for use in standard endoscopic equipment has largely overcome the problem of poor image quality. However, such technology has proved difficult to extend to endoscopes of small caliber. The XCHF-B200 prototype endoscope used in this study would seem to represent the next generation of cholangioscopes. However, a larger operating channel will be a prerequisite for therapeutic intervention.