Plastic-clad Silica Optical Fibers Research Articles

Mode Coupling and Steady-State Distribution in Multimode Step-Index Organic Glass-Clad PMMA Fibers

Mode coupling and power diffusion in multimode step-index (SI) organic glass-clad (OGC) PMMA fiber is examined in this study using the power flow equation (PFE). Using our previously proposed approach we determine the coupling coefficient D for this fiber. When compared to standard multimode SI PMMA fibers, the multimode SI OGC PMMA fiber has similar mode coupling strength. As a result, the fiber length required to achieve the steady-state distribution (SSD) in SI OGC PMMA fibers is similar to that required in standard SI PMMA fibers. We have confirmed that optical fibers with a plastic core show more intense mode coupling than those with a glass core, regardless of the cladding material. These findings could be valuable in communication and sensory systems that use multimode SI OGC PMMA fiber. In this work, we have demonstrated a successful employment of our previously proposed method for determination of the coupling coefficient D in multimode SI OGC PMMA fiber. This method has already been successfully employed in the previous research of mode coupling in multimode SI glass optical fibers, SI PMMA fibers and SI plastic-clad silica optical fibers.

Influence of wavelength on the bandwidth of W-type plastic-clad silica optical fibers

The bandwidth and steady-state loss of multimode W-type plastic-clad silica optical fibers are investigated by solving the time-dependent power flow equation. The results show how the bandwidth of W-type plastic-clad silica optical fibers can be enhanced by shifting from the red to the infrared wavelength region for different intermediate layer widths and refractive indices of the outer cladding. Such characterization of these fibers is consistent with their manifest effectiveness in reducing modal dispersion and increasing bandwidth.

Analysis of Fiber Loss Mechanisms in Communication System to Simulate Different Attenuation

The fiber optic communication system can transmit data a rate of 10 GB/S or more, over a maximum possible distance with less attenuation. In this research a low loss optical fiber has been simulated. The simulation is done by MATLAB Software. This research deals with different loss mechanisms in optical fiber communication. A number of mechanisms are responsible for the signal attenuation within optical fibers. As the optical signal propagates over long stretch of fiber, it becomes attenuated because of absorption, scattering, fiber bends by material impurities, and other effects. The absorption loss at 1310 nm wavelength of light is significantly very low. It is also observed that the scattering loss decreases as the wavelength of light increases and the same case for bending loss; for link loss the fiber attenuation is increased gradually with the increasing fiber distance. In this research it is shown that the attenuation for multimode fiber is greater than single mode fiber at wavelength 1550 nm, attenuation level for 1550 nm wavelength is lower than 1310 nm wavelength. It is also shown that there are great attenuation between glass and plastic optical fiber and large attenuation between plastic and Plastic Clad Silica optical fiber. Different fiber types and their properties such as attenuation or loss are also observed. The performance improvement of the proposed different loss, such as absorption loss, rayleigh scattering, bending loss, link loss for different wavelength and different material within the various loss mechanisms in fiber optic communication is shown through simulations.

Controlling the bandwidth of W-type plastic-clad silica optical fibers

A new design of a multimode plastic-clad silica optical fiber that takes the characteristic W-shaped index profile is proposed. The bandwidth and steady-state loss are determined for such a W-type plastic-clad silica optical fiber for the different structural parameters of the fiber. We have shown that the bandwidth of a W-type plastic-clad silica optical fiber is significantly higher (up to 15 times at a fiber length of 2 km) than the bandwidth of the singly clad step index plastic-clad silica optical fiber.

Fiber Optic SPR-Based Uric Acid Biosensor Using Uricase Entrapped Polyacrylamide Gel

In this letter, we report a fiber optic biosensor based on surface plasmon resonance (SPR) for the detection of uric acid in aqueous samples. The sensing probe is prepared by successive coatings of silver and silicon layers over a small unclad length of the plastic clad silica optical fiber in the middle. Thereafter, the probe is dipped in a polyacrylamide gel containing enzyme uricase to immobilize it using a gel entrapment method. The sensor is characterized using a wavelength interrogation method. The SPR spectra corresponding to different concentrations of uric acid in the range of 0-0.9 mM are recorded. A red shift in the resonance wavelength is observed with an increase in the concentration of uric acid around the probe. In addition, the sensitivity of the proposed biosensor is studied in relation to parameters, such as concentration and pH of the uric acid solution. Finally, the sensor is highly selective and possesses better limit of detection and limit of quantification.

Transmitted Intensity Variations in a Plastic-Clad Silica Optical Fiber by Exposing to Gasoline Octane Numbers 87 and 92 at Different Temperatures

Transmitted Intensity Variations in a Plastic-Clad Silica Optical Fiber by Exposing to Gasoline Octane Numbers 87 and 92 at Different Temperatures

Use of the original silicone cladding of an optical fiber as a reagent-immobilization medium for intrinsic chemical sensors

It is demonstrated that extended-length sensors can be fabricated by the direct immobilization of suitable reagents into the original cladding of a plastic-clad silica (PCS) optical fiber. This cladding, a copolymer of vinyl-terminated poly(dimethylsiloxane) and poly(dimethylmethylhydrosiloxane), is an attractive immobilization matrix for a wide variety of reagents and opens up new avenues of sensor design. Unlike fibers with custom-drawn cladding, the new approach offers greater photo- and thermal stability and permits immobilization of several reagents in adjacent sections of a single fiber. Further, compared to room-termperature vulcanizable (RTV) silicone films used often in optical point sensors, the silicone cladding of a PCS optical fiber offers a number of advantages, including a dynamic fluorescence quenching constant for an immobilized fluorophore that is up to 3.4 times higher, tolerance to aggressive environments (e.g. highly alkaline solutions), lower rates of indicator leaching, high uniformity, and applicability to extended-length sensing. The homogeneity of the microenvironment of the fiber cladding, its resistance to aggressive alkaline solutions, and its ability to transport water vapor were probed by introducing a variety of reagents into the cladding, including a fluorescent ruthenium complex and acid-base and solvatochromic indicators. The new sensor-fabrication approach should find wide application, including detection of neutral species in gases and dissolved in water, and for spatial analyte mapping over extended, remote areas.

Oxygen detection by fluorescence quenching of tetraphenylporphyrin immobilized in the original cladding of an optical fiber

A new fiber-optic sensor for oxygen has been developed. Tetraphenylporphyrin (TPP), embedded into the original analyte- permeable cladding of a conventional low cost plastic-clad silica optical fiber, is excited by the evanescent-wave traveling in the fiber; the resulting fluorescence is captured back into the guided modes of the fiber and can be detected at either end. Oxygen in the surrounding medium quenches the fluorescence and is quantified by means of the Stern–Volmer expression. Excitation was achieved with an ultra-bright (13 000 mcd) yellow 590 nm light-emitting diode (LED), with emission monitored at 650 nm. The new sensor offers excellent precision (relative standard deviation (RSD) of 0.1–0.2%) over the range of measured oxygen partial pressures (55–760 torr), a response time of 1 s, a detection limit of 3.5 torr of oxygen, and a quenching constant of 7.5×10 −4 torr −1. Unlike earlier oxygen sensors, the new device is immune to changes in relative-humidity of measured gaseous samples. The short (10 ns) fluorescence lifetime of TPP and the possibility to fabricate continuous chemically sensitive fibers hundreds of meters long make the sensor attractive in applications that require spatially resolved oxygen mapping over large remote areas.

Near-ultraviolet evanescent-wave absorption sensor based on a multimode optical fiber.

Fiber-optic near-ultraviolet evanescent-wave sensors have been constructed, and their feasibility for practical applications has been demonstrated. The sensors, used for the detection of ozone near the 254-nm peak of the Hartley absorption band, were fabricated from coiled segments of low-cost multimode plastic-clad silica optical fibers. The sensing sections were produced alternatively by stripping only the protective jacket from the fiber to expose the gas-permeable silicone cladding or by stripping the jacket and the cladding to expose the bare-silica fiber core. Response characteristics are given, including sensitivity to ozone, reversibility, and aging effects. The useful lifetime was unacceptably short for the sensor that employed the bare-silica core, whereas the exposed-cladding sensor demonstrated good stability over the entire two-month period of investigation. The latter, more useful sensor demonstrated a linear response to ozone over the range 0.02-0.35 vol% and a reversible response with a time constant on the order of 1 min. Differences in ozone absorption spectra obtained in the transmission and evanescent-wave modes are discussed. Projected applications of the new exposed-cladding sensor include ozone determination in water-treatment processes and ozone production plants.

Kramers–Kronig analysis of molecular evanescent-wave absorption spectra obtained by multimode step-index optical fibers

Spectral distortions that arise in evanescent-wave absorption spectra obtained with multimode step-index optical fibers are analyzed both theoretically and experimentally. Theoretical analysis is performed by the application of Kramers-Kronig relations to the real and the imaginary parts of the complex refractive index of an absorbing external medium. It is demonstrated that even when the extinction coefficient of the external medium is small, anomalous dispersion of that medium in the vicinity of an absorption band must be considered. Deviations from Beer's law, band distortions, and shifts in peak position are quantified theoretically as a function of the refractive index and the extinction coefficient of the external medium; the effect of bandwidth for both Lorentzian and Gaussian bands is also evaluated. Numerical simulations are performed for two types of sensing sections in commonly used plastic-clad silica optical fibers. These sensors include an unclad fiber in contact with a lower-index absorbing liquid and a fiber with the original cladding modified with an absorbing species. The numerical results compare favorably with those found experimentally with these types of sensing sections.

Use of fluoroptic thermometer temperature sensing for high-resolution temperature-controlled NMR applications

Many NMR experiments, especially kinetic studies of biological transformations using cryoenzymology techniques as performed in this laboratory ( I-5)) require precise sample temperature control. Temperature measurement in a superconducting NMR system has traditionally required use of a dimetal thermocouple placed in the temperature control airstream near the point at which it enters the sample chamber. Such systems almost invariably cause distortion in the local magnetic field, even when thermocouples are prepared from supposedly nonmagnetic metals, and extensive tuning is usually required after thermocouple installation or adjustment. Another problem is the difficulty in correlating temperature inside the sample with that of the incident airstream. Sample heating due to absorption of decoupler energy and temperature deviations from measured values as temperature variance from ambient increases are common difficulties. A second thermocouple inserted directly into the sample tube can give true sample temperature, but tends to distort the magnetic field more drastically than external temperature sensors and as a rule cannot be used with a spinning sample, limiting resolution to lower nonspinning levels. A Luxtron fluoroptic thermometer recently purchased by our laboratory which uses ratio of emissions of fluorescent lines of rare earth phosphors in a sensor at the terminus of a plastic-clad silica optical fiber to determine temperature eliminates these problems. The nonmetallic, nonelectronic design of the sensor device makes the system ideal for temperature control in NMR studies, but use in a modern spectrometer in the manner required was not possible without substantial modifications of the normal configuration. The temperature measurement and control system described below was designed to provide instantaneous, accurate temperature measurements inside a spinning sample tube without degradation of sensitivity or resolution. Spectra were recorded on a Bruker WM-300 wide-bore spectrometer equipped with either a Bruker 5 mm 13C/‘H probe or a homemade 5 mm ‘H/13C probe. Temperature