Traditional Fiber Optics

There are basically two types of optical communications fiber design, each having many variations. The first type, called step-index fiber, is similar in construction to that described in Sec. 6.6 for traditional fiber optics, with several key differences (1) Communications fiber dimensions are generally much smaller. (The outside diameter is now a standard 125 p.m the core diameter can be as small as about 8 /xm.) (2) The refractive index difference (An) between core and cladding is much smaller, on the order of 1 percent, or less. (3) Much greater precision is required for the critical dimensions, including core concentricity within the fiber. 

The intrinsic sensors are based on the direct recognition of the chemicals by its intrinsic optical activity, such as absorption or fluorescence in the UV/Vis/IR region. In these cases, no extra chemical is needed to generate the analytical signal. The detection can be a traditional spectrometer or coupled with fiber optics in those regions. Sensors have been developed for the detection of CO, C02 NOx, S02, H2S, NH3, non-saturated hydrocarbons, as well as solvent vapors in air using IR or NIR absorptions, or for the detection of indicator concentrations in the UV/ Vis region and fluorophores such as quinine, fluorescein, etc. 

The speed of information transfer can be increased by switching from twisted pair cables to coaxial or fiber optics, however, these types of cables add to the installation costs. In the future, communications between sensors and multiplex boxes and the rest of the system may use a combination of technologies including traditional means such as twisted wire and coaxial and non-traditional methods such as infrared or radio wave. 

The potential applications of NIR OFCD determination of metal ions are numerous. The detection of metal contaminants can be accomplished in real-time by using a portable fiber optical metal sensor (OFMD). Metal probe applications developed in the laboratory can be directly transferred to portable environmental applications with minimal effort. The response time of the NIR probe is comparable to its visible counterparts and is much faster than the traditional methods of metal analysis such as atomic absorption spectroscopy, polarography, and ion chromatography. With the use of OFMD results can be monitored on-site resulting in a significant reduction in labor cost and analysis time. 

Ng and Assirelli have carried out a mixing study in batch stirred vessels with working volumes of 3 L to 20L using a fiber-optic UV-vis monitoring technique. Bromophenol blue sodium salt was used as a non-reactive tracer. The results on traditional Rushton turbines and 45° angled pitched blade turbines showed good agreement with a typical conductivity technique and a correlation proposed in literature. 

This CVD procedure is somewhat different from that used to deposit semiconductor layers. In the latter process, the primary reaction occurs on the substrate surface, following gas-phase decomposition (if necessary), transport, and adsorption. In the fiber optic process, the reaction takes place in the gas phase. As a result, the process is termed modified chemical vapor deposition (MCVD). The need for gas-phase particle synthesis is necessitated by the slow deposition rates of surface reactions. Early attempts to increase deposition rates of surface-controlled reactions resulted in gas-phase silica particles that acted as scattering centers in the deposited layers, leading to attenuation loss. With the MCVD process, the precursor gas flow rates are increased to nearly 10 times those used in traditional CVD processes, in order to produce Ge02-Si02 particles that collect on the tube wall and are vitrified (densified) by the torch flame. 

The combination of chemical and biological sensors with flow injection has been demonstrated. Both more-traditional-type sensors such as pH electrodes and newer sensors such as fiber optics and surface acoustic wave detectors have been incorporated into FIA systems with success. An advantage that FIA brings to the sensor field is the possibility of turning a moderately selective sensor into a selective sensor by incorporating into the FIA system some type of selectivity enhancement technique such as gas diffusion, dialysis, and reactors. Finally the FIA systems permit renewable systems since sensor surfaces and reaction cells can be washed, surface regenerated, and reagents replenished on demand. 

Biosensors based on the heat produced by enzyme/substrate reactions have traditionally used microcalorimeters (1), thermistors (2), and Peltier or other macro devices <3,A) The area has been reviewed by Guilbault (5). The size, response time, and thermal mass of these detectors suggests that thermally responsive microsensors need to be explored. The ideal sensor would be inexpensive, and require simple, low cost support electronics. A fiber optic based sensor (Part A), and a pyroelectric polymer film based sensor (Part B) are described below. 

The use of NIR with fiber optics has also been reported for online monitoring of fuel quality parameters, such as research octane number, motor octane numbei olefin, naphthene and aromatics content of gasoline. The online analysis of the fuel quality parameters was obtained without loss of precision and accuracy when compared with the traditional motor test. 

The Internet. According to the United Nations International Telecommunication Union (ITU), the number of Internet users across the world met the two billion mark in January 2011. Much like standard telephone service, the capacity, ease, and speed to the Internet has been greatly increased by the replacement of phone-based modem systems, cable modems, and digital subscriber line (DSL) by fiber-optics wired systems. Although fiber-optic connections directly to homes in the United States are not available in all areas, some companies use fiber-optic systems down major networking lines and then split to traditional copper wiring for houses. 

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