Optical Fiber Array Research Articles

Compact collimated fiber optic array diagnostic for railgun plasmas

We developed and tested a compact collimated 16 channel fiber optic array diagnostic for studying the light emission of railgun armature plasmas with approximately millimeter spatial and submicrosecond temporal resolution. The design and operational details of the diagnostic are described. Plasma velocities, oscillation, and dimension data from the diagnostic for the Livermore fixed hybrid armature experiment are presented and compared with one-dimensional simulations. The techniques and principles discussed allow the extension of the diagnostic to other railgun and related dense plasma experiments.

Multitip-Localized Enhanced Raman Scattering from a Nanostructured Optical Fiber Array

An optical fiber bundle composed of ∼6000 individual 3 μm core diameter fibers has been chemically etched to form a regular array of sharp tips, resulting in the confinement of the light reaching the tip apexes of the fibers as demonstrated by near-field optical microscopy. After coating this nanostructure with a gold thin film (30 nm thick), spatially resolved Raman experiments have been performed to detect a benzenethiol monolayer adsorbed on the covering gold film. High intensity Raman spectra were observed and localized at the extremities of the tips, demonstrating a surface enhanced Raman scattering (SERS) effect induced by the strong curvature of the metallized tip apexes. The Raman enhancement factor of the nanostructure has been investigated and an average enhancement factor of 2.7 × 104 was measured. This opens new avenues for the use of such optical fibers for in situ and endoscopic Raman measurements on complex systems.

Multiplexed Fiber Optic Twin-sensor Array based on a Combination of Mach-Zehnder and Michelson Interferometers

A multiplexed white light interferometric fiber optic twin-sensor array is designed and demonstrated. In this sensing system, based on a combination of Mach-Zehnder and Michelson interferometers, an optical path matching technique is used to demodulate each twin sensor. The twin-sensor array consists of 2 × N sensing elements linked by a 3 dB coupler. While one of the twin sensors is used to measure strain, the other one compensates the variation caused by the temperature. The multiplexing capacity of the sensing scheme is analyzed and an experimental result with a 2 × 3 twin-sensor array is demonstrated and tested.

Measurement of Two-Dimensional Photon Beam Distributions Using a Fiber-Optic Radiation Sensor for Small Field Radiation Therapy

In this study, we fabricated a fiber-optic radiation sensor with an organic scintillator to measure the high-energy photon beam from a clinical linear accelerator, and a two-dimensional fiber-optic sensor array to measure high-resolution and real-time dose distributions for small field radiotherapy dosimetry. The scintillating lights generated from each organic sensor probe embedded and arrayed in a water phantom are guided by 10 m plastic optical fibers to the light-measuring device. Two-dimensional photon beam distributions in a water phantom were measured for photon beams with different energies and field sizes. Also, percent depth dose curves for 6 and 15 MV photon beams were obtained.

Evaluation of Multiwavelength Culture Fluorescence for Monitoring the Aroma Compound 4-Hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF) Production

Fluorescence spectra of a 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF) fermentation culture broth were combined with measurable process variables for off-line and on-line process monitoring. Culture broth fluorescence in UV and visible ranges was acquired by a fiber optic LCD array spectrometer. Process dynamics was followed on-line using a fiber optic probe attached to an external recirculation loop of the bioreactor. Partial least squares and stepwise regression methods were used to correlate measurable process parameters with the components of the fluorescence spectra. Both methods provided adequate approximation of yeast density, HEMF, glucose, and ethanol concentrations from fluorescence spectra. HEMF production was observed during the oxido-reductive growth phase when there was a lack of measurable oxygen in the culture broth and an excess of glucose. The addition of glucose resulted in the rapid production of HEMF and other metabolite intermediates such as ethanol, acetate, and glycerol.

Detection of Single-Molecule DNA Hybridization Using Enzymatic Amplification in an Array of Femtoliter-Sized Reaction Vessels

Improving the sensitivity of DNA biosensors is extremely important in clinical diagnostics, gene therapy, and a variety of other biomedical studies. In this regard, we have developed a highly sensitive single molecule DNA assay platform with a 1fM experimental detection limit using enzymatic amplification in an array of femtoliter-sized reaction wells. To validate the utility of this technology in our study, we employed a fiber optic array to create thousands of femtoliter-sized reaction wells, each specifically functionalized with oligonucleotide probes capable of capturing biotinylated target DNA. After hybridization, the fiber was incubated with streptavidin-labeled enzyme solution. The bound single enzyme molecules were confined to individual reaction vessels containing excess fluorogenic substrate and catalyzed the production of a sufficient number of fluorescent product molecules to generate a detectable signal. At low target DNA concentrations with relatively short incubation times, only a small percentage of the capture sites bind target DNA, enabling a binary readout of target concentration from the high-density fiber array. This simple binary readout-based scheme is easy to perform and exhibits a high signal-to-noise ratio in the presence of trace amounts of DNA target. Furthermore, it also should be possible to extend this technology to protein detection by modifying the reaction wells with specific capture antibodies. We expect this assay to be useful in a number of biomedical applications where accurate and highly sensitive target analysis is critical.

Diagnosis of rhinosinusitis with a colorimetric sensor array

A variety of electronic nose technologies are currently commercially available or under evaluation at research institutions. Sensors include conducting polymers, polymer composites, acoustic wave, metal oxide and optical fiber arrays. Reactive, metalloporphyrin dyes have also been used as colorimetric sensor arrays (CSAs). We hypothesized that a CSA array could be used to distinguish exhaled gas from patients with chronic bacterial sinusitis versus those without. Exhaled gas was selectively sampled from the nasal passages using a nasal CPAP (continuous positive airway pressure) mask and pumped across an array of 36 metalloporphyrin sensor dots printed on a paper sensor cartridge, which was photographed at 2 min intervals during the sampling period for a total of 12 min. Changes in the red, green and blue values for each of the senor dots were recorded for each time interval. Eleven patients with sinusitis were compared to nine control patients. A leave-one-out classification test was carried out using binary logistic regression, which employed the principal component projections of data as features. The classification rate was as high as 90% accurate at 2, 4 and 6 min, following exposure using 12 principal components. Classification accuracy fell off when more principal components were used and at longer time intervals following exposure. Chronic sinusitis is typically a clinical diagnosis and the etiologic organisms include both Gram-positive and Gram-negative bacteria. Accurate classification at 90% is very encouraging and warrants further investigation.

Tunable Fabry–Perot-resonator-based fiber-optic white-light interferometric sensor array

A tunable Fabry-Perot-resonator-based fiber-optic white-light interferometric quasi-distributed sensing system permitting absolute length measurement in a remote reflective sensor array is proposed and demonstrated. The sensor reflective signals characteristics have been analyzed, and the relationship between light signal intensities and sensors number was given for multiplexing potential evaluation. The proposed sensing scheme will be useful for the measurement of strain distribution. An important application could be deformation sensing in smart structures. Experimentally, a four-sensor array has been demonstrated.

Nonlinear localization of light in disordered optical fiber arrays

Light propagating through optical fiber arrays tends to localize in only a few center cores. The recent experiments in two-dimensional single-mode optical fiber arrays suggest that an interplay of deterministic and random linear and nonlinear effects might be responsible for this localization. We study this phenomenon, both analytically and numerically, in a hexagonal optical fiber array similar to that used in the experiments. Our analysis reveals that Anderson localization is evident in the linear and intermediate regimes, where a larger fraction of initial energy is returned to the center fiber due to the stochastic effects. For very high levels of input energy, the system is strongly nonlinear, with the randomness amplifying the Kerr localization.

Performance Evaluation of One-dimensional Fiber-optic Radiation Sensor for Measuring High Energy Electron Beam Using a Charge-coupled Device

In this study, we have fabricated one-dimensional fiber-optic radiation sensor array for high energy electron beam therapy dosimetry. Fiber-optic radiation sensor comprises an organic scintillator as a sensing volume, optical fiber as a light guider and photo-detector as a light measuring device. Usually, photomultiplier tube or photodiode is used as a photo-detector however we have tried to use a charge-coupled device as a scintillating light measuring system for one-dimensional fiber-optic radiation sensor array. This system can take an image of the proximal ends of one-dimensional fiber-optic sensor array and can measure light intensities of individual image of optical fibers simultaneously using simple imaging software. Charge-coupled device as a light measuring detector has many advantages which are easy in multi-dimensional measurements, high spatial resolution and relatively low cost. We have measured one-dimensional electron beam distributions in a PMMA phantom with different energies and field sizes of electron beam using a fiber-optic sensor and a charge-coupled device. Also, the percentage depth dose curves for high energy electron beams are obtained.

MEASUREMENTS OF HIGH ENERGY X-RAY DOSE DISTRIBUTIONS USING MULTI-DIMENSIONAL FIBER-OPTIC RADIATION DETECTORS

In this study, we have fabricated multi-dimensional fiber-optic radiation detectors with organic scintillators, plastic optical fibers and photo-detectors such as photodiode array and a charge-coupled device. To measure the X-ray dose distributions of the clinical linear accelerator in the tissue-equivalent medium, we have fabricated polymethylmethacrylate phantoms which have one-dimensional and two-dimensional fiber-optic detector arrays inside. The one-dimensional and two-dimensional detector arrays can be used to measure percent depth doses and surface dose distributions of high energy X-ray in the phantom respectively.

A Model‐free Method for Damage Locating and Quantifying in a Beam‐like Structure Based on Dynamic Distributed Strain Measurements

Abstract: A damage locating algorithm with no requirement for a detailed structural analytical model has been proposed in our previous research, named a modal macro‐strain vector (MMSV) method by directly using the modal parameters extracted from dynamic macro‐strain data recorded by a long‐gage fiber optic sensors array distributed throughout the full or some partial areas of beam‐like structures. This article is devoted to generalizing the originally proposed algorithm based on the correlation of modal parameters among the distributed fiber optic sensors to develop a method for both damage locating and quantifying. After a brief review of the distributed sensing techniques, the generalized method is proposed based on the originally proposed MMSV‐based algorithm. Numerical case studies are performed to locate and quantify damage under different designed cases to verify the effectiveness and universality of the method. Experimental investigations on a simple beam under hammer impulsive excitation at different locations with arbitrary amplitudes are then carried out to verify the accuracy of the proposed method. An innovative idea on data interpretation and feature extraction is described. On the basis of the experimental and numerical investigations, an integrated model‐free scheme for damage locating and quantifying is finally summarized for proposal.

Microchip Spots Rare Tumor Cells in Blood

TUMORS SHED CELLS INTO THE BLOOD of patients with cancer, but researchers have long sought a reliable way to detect these rare cells. Now, however, investigators atMassachusetts GeneralHospitalinBostonreportsuccessful tests with a unique microchip-based device thatcanefficientlyandselectively separatecirculating tumorcells fromperipheral blood samples (Nagrath S et al. Nature. 2007;450[7173]:1235-1239). The technology has been used to identify these cells in the blood of patients with various types of metastatic cancer and to effectively monitor individuals’ responses to therapy. Ultimately, the inventors hope, the device will someday enable physicians to characterize and monitor cancer status in patients in a noninvasive way. While the presence of circulating cancer cells seems to correlate with prognosis in some studies, however, it remains to be seen whether the detection of these cells has any clinical benefit. Patients with metastatic cancer have as few as one circulating tumor cell per 10 hematologic cells in their blood. In previous work, researchers have used flow cytometry, immunomagnetic beads, high-throughput optical imaging systems, and fiber optic array scanning to detect these cells. However, in the work reported by the Boston-based investigators, the new chip technology is more streamlined and isolates greater numbers of viable cells, according to senior author Mehmet Toner, PhD, who is director of Massachusetts General Hospital’s BioMicroElectroMechanical Systems Resource Center. “The beauty of the technology is its simplicity—it uses whole blood with no preprocessing and it’s gentle on the cells,” Toner said. In addition, the device can handle large volumes of blood, unlike other techniques that are limited to microliter amounts of liquid. Other researchers note additional qualities of the device. “The data show that it’s far more sensitive than earlier technologies, and it purifies these rare circulating tumor cells, which is ex-

A Simple Method of H/He Influx Ratio Measurement as a Monitor for Machine Operation in LHD

In order to observe edge neutral recycling for fusion machine operation, the absolute values of Hα and HeI emissions have been usually analyzed with measurement of edge density and temperature. On the other hand, it is known that the temperature and density dependences of each line can be negated by taking the ratio between the two lines. The intensity ratio of Hα (6563 A) to HeI (5876 A or 6678 A) visible spectral lines is adopted, and the results are presented here instead of the method usually used for monitoring the edge particle recycling and the effect of wall conditioning in LHD. The ionization events per photon were calculated for both emissions using a collisional-radiative model, and the ratio of H+ flux (≡ H0 influx) to He+ flux (≡ He0 influx) was obtained. The Hα and HeI (5876 A) emissions in LHD have been measured using a monitor assembly with an interference filter and optical fiber array. The H+ /He+ flux ratio has been thus evaluated by integrating the Hα and HeI emissions from a 10-channel toroidal array. As an example of the measurement, all discharges performed during the past 9 years in LHD have been analyzed. The present method shows that the aftereffects of the H2 and He glow discharge cleaning for vacuum wall conditioning on the LHD discharges become clearly visible. The replacement of deposited atoms on the carbon divertor plates was also analyzed. It is found that the replacement is completed by 40-50 shot repetition of discharges. These results indicate the effectiveness of the present method as a good monitor for fusion machine operation.

近年の物理探査の技術動向―時空間スケールの重要性―

Geophysical exploration technologies have been developed through several innovative steps in the history. Data acquisition and processing technologies evolved since 1960s. Since 1980s, these technologies started to be integrated first to reservoir description, then to reservoir modeling (characterization), and recently to reservoir management technologies. These developments have taken place due to the recent tendency to have their target structures in smaller scale or more complex than it used to be. We may summarize these technical developments as follows : a) 3D to 4D data acquisition to realize reservoir management, b) 4-C marine data acquisition (tri-component geophone and pressure gauge), c) single sensor acquisition supported by well-developed multi-channel signal processing techniques for true amplitude recovery without any instrumental spatial filtering, d) new acquisition technologies such as fiber-optic sensor arrays. We believe that further new development would surely be attempted to satisfy the needs to visualize underground structure, to understand what is on-going for the state of natural resources under development, and to enhance our management capabilities to control the production from existing reservoir.

Composite Optical Bend Loss Sensor for Pressure and Shear Measurement

A composite optical bend loss sensor for measuring 3-D forces has been developed. The sensor is composed of two optic fiber meshes which are embedded into a polydimethylsiloxane (PDMS) slab. The sensor consists of an array of optical fibers lying in perpendicular rows and columns sandwiched inside an elastomeric pad. A map of normal and shear stress is constructed based on observed macrobending through the intensity attenuation from physical deformation of two adjacent perpendicular fibers. Due to the new addition of the composite design and acrylic holder, the stability of the present sensor is found to be significantly better than our previously reported microfabricated optical bend loss sensor. In this paper, we will report the results of an optical bend loss simulation using the beam propagation method based on a series of images captured by a CCD camera on the fiber's bending curvatures. The result from the simulation will be compared with the results obtained from the experiment. Other results include vertical force and shear measurements at a single pressure point of the sensor. A force image algorithm is used to map the force distribution detected by the sensor. Here, we will present the results of six different shape patterns and two force magnitudes on each shape using a neural network system. We will also present a radio frequency sensor module, which we developed for the composite optical bend loss sensor for remote sensing.

Three-dimensional integral display using plastic optical fibers

A novel approach to an integral imaging system using a pliable plastic optical fiber array is proposed. The proposed system has the advantage that it can utilize a light source for three-dimensional (3D) images at an arbitrary location because the point light sources are formed by the plastic fiber array with flexible optical paths. Two-dimensional images can also be expressed in the proposed system. The light efficiency of this system is high compared with previous point light source array integral imaging systems. The feasibility of the proposed method is explained and demonstrated with experiments.

Development of One-dimensional Fiber-Optic Radiation Sensor for Measuring Dose Distributions of High Energy Photon Beams

The purpose of this study was to develop a method for measuring the one-dimensional dose distribution of a high-energy photon beam using a miniaturized high-resolution fiber-optic radiation sensor array. The measurements were made by thin plastic optical fibers with organic scintillating fiber sensor probes that emit the visible wavelength of light. The scintillating light is guided to a silicon photodiode array by plastic optical fibers in order to convert light output to an electrical signal. The one-dimensional spatial dependence of photon beam is measured by a one-dimensional fiberoptic sensor array in a poly(methyl methacrylate) (PMMA) phantom. It is shown that this fiber-optic radiation sensor has better spatial resolution than a conventional ionization chamber and much less time is required to measure one-dimensional dose distribution in the high radiation fields. The real-time and the high spatial resolution measurements due to the small detector volume make this system suitable for dosimetry in radiation therapy.

Subsurface and transcutaneous Raman spectroscopy and mapping using concentric illumination rings and collection with a circular fiber-optic array.

Different spatial separations between an illumination ring and a bundle of 50 collection fibers focused to collect light in the center of the ring were used to investigate the recovery of subsurface Raman spectra. The depth of Raman signal recovery and the preservation of spatial information in the recovered signal were investigated using polymer blocks stacked in different geometries. The illumination rings were then combined into a single data set to increase variation in the signal. Multivariate data analysis was used to recover the Raman spectra of the subsurface component. The Raman spectrum of a Delrin target was recoverable at depths up to 22.6 mm of overlying Teflon. Spatial information was lost at approximately 6.5 mm below the Teflon surface. The same protocols were used to recover canine bone spectra transcutaneously at depths up to 5 mm below the skin's surface. The recovered bone spectra were validated by exposed bone measurements.

Two-dimensional optical splitters with polymer optical fibre arrays

A novel approach for optical beam distribution into two-dimensional (2D) fibre arrays using 2D Dammann gratings is investigated. We report for the first time experimental results of a 2D optical power distribution into 2 × 2 polymer optical fibre arrays using a Dammann grating. This paper focuses on the design and fabrication of the diffractive optical element (DOE) along with investigating the coupling performance of the system. This grating may be applicable to a fibre to the home (FTTH) network as it can support sufficient channels with good output uniformity together with low polarization-dependent loss (PDL). Using an appropriate optimization algorithm, the optimum profile for the Dammann gratings can be calculated. The gratings are then fabricated on indium-doped tin oxide (ITO) glass using electron-beam lithography. This method shows that it can achieve low PDL and good uniformity together with acceptable insertion loss.