Page 94 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioTechnology

P1: GNB Final Pages
Encyclopedia of Physical Science and Technology EN005F-954 June 15, 2001 20:48

Fiber-Optic Chemical Sensors 807

FIGURE 4 Optical fiber bundle fabrication and use for imaging. (a) Fiber bundles are constructed from thousands of
individual single fibers that are fused together. (b) Coherent bundles can be used for imaging.

other fiber-optic chemical sensor applications, fiber-optic requirements for the application, for example, the use of
bundles comprising thousands of identical single fibers nontoxic agents and biocompatible materials for clinical
(each with a diameter of a few micrometers) are employed, applications. There are two basic configurations for fiber-
as shown in Fig. 4a. The fibers can be bundled in a coherent optic chemical sensors: (a) A single fiber is used to trans-
or random fashion and used to enhance light transmission. mit the light from the light source to the sample region
In coherent fiber bundles, the position of each fiber on one and back to the detector, as shown in Fig. 1. (b) Multi-
end is identical to its position on the other end. These ple fibers are used, one to transmit the light to the sample
coherent fiber bundles are mostly used for imaging appli- region and the rest to transmit light from the sample re-
cations as shown in Fig. 4b. The coherent fibers allow each gion to the detector, as shown in Figs. 5a and 5b. For the
individual fiber to transmit light in an addressable manner second configuration, the most common format is a bifur-
from one end of the bundle to the other. In some recent ap- cated fiber. Bifurcated fibers are fabricated by fusing two
plications, these bundles are used for imaging and sensing fibers together on one end, leaving the other ends free. The
simultaneously. fused side is used for the sensing and the other ends of the
fiber are connected to the light source and to the detector,
as shown in Fig. 5c.
B. Fiber-Optic Chemical Sensor
Design and Instrumentation
1. Light Sources
Each fiber-optic chemical sensor system design depends
intimately on the nature of the analytes detected, the par- The light sources used for fiber-optic chemical sensors
ticular conditions at the measurement site, and the specific should provide sufficient light intensity within the sensor