|An optical fiber is positioned next to several cuvettes sample and LEDs.When one of the LEDs is turned on, its light is absorbed by the sample in the cuvette; some of this absorbed light finds its way into the fiber and is guided to a detector. This procedure can be repeated at any of the other sources in the array, providing multiple independent measurements along the fiber. (Drawing: S&ST)
Los Angeles, CA--The Physics Club of Los Angeles Harbor College, in conjunction with Science & Sensors Technologies (S&ST), is developing and testing a new type of optical-fiber configuration that accepts light at many defined points along the fiber for sensing applications.
This type of technology was created by Claudio Oliveira Egalon more than 20 years ago while he was working under contract for NASA Langley Research Center (Hampton, VA), according to a press release issued by S&ST. Since then, he has been developing and protecting this technology and now holds the title to several US and overseas patents on this configuration. Egalon found that a strong signal can be coupled from a light source into the fiber using side illumination. He also found that these side-illuminated fiber sections act like small sensing points with a length equal to the size of the source. When combined with sources that have diameters of 0.2 in., it is possible to create an array of at least 20 different sensing points within a 4-in.-long fiber. “And these are rather conservative estimates," says Egalon.
“It is like watering the surface of a pipe and have the water conveyed to one of the pipe’s extremities," says Egalon, who is an LA Harbor faculty member and the president of S&ST. “By the same way that perforated pipes in a French drain can convey water from their outer surfaces, optical fibers can also be modified to transmit light incident from their side.”
This large number of sensing points provides a high degree of redundancy, allowing this device to be used in hostile environments where sensor failure, damaging, and fouling are expected to happen, according to S&ST. This redundancy can also be used to improve measurement precision and specificity. For instance, when this sensor is used to measure a single parameter with its multiple sensing points, multiple independent measurements are obtained: this decreases the standard deviation of this measurement, increasing its precision and, consequently, its accuracy. Similarly multiple independent measurements of different parameters can also increase the sensor specificity, decreasing, or even eliminating, the interference produced by certain chemical species. Unlike regular spectrometric techniques, which require one detection system per sample, this new optical-fiber configuration requires a single detection system that can be positioned at either end of the fiber, eliminating several units of the most expensive element: the detection system.
'Similar to the human nervous system'
In conventional axially illuminated fiber sensors, evanescent waves interact with the sample; however, the amount of power in the evanescent region is minute and, in order to obtain any useful signal, an expensive source and detection system is required. “Then there is also the problem of probing multiple sensitive points along the fiber,” says Egalon. “Scientists have proposed the use of time-of-flight measurements of light pulses, however the speed of the light is too fast for any electronics to resolve any sensitive points near by each other and, at the end, the cost of the instrumentation required becomes prohibitive.” In contrast, with the side-illuminated sensor, it is possible to develop devices that are similar to the human nervous system with its vast network of nerve fibers having several sensitive points scattered in an almost continuous fashion throughout the human body, according to S&ST.
Recently, Egalon was awarded an SBIR Phase II grant from the US Department of Agriculture (USDA), to continue development of the technology. In the Summer of 2012, formed the LA Harbor’s Physics Club with several of his former students including Michael Matta, Delbert Lavezzari, Robert Insley, Luis Elias, Ray Duenas, Paul Delgado, Carolyn Jarring, Marie Frances Quiday, and others. The group developed an optical-fiber-based colorimeter that uses multiple cuvettes; a prototype was built and data was generated for a paper presented at Pittcon 2013 in Philadelphia, PA. Because multiple measurements from different cuvettes placed along the fiber length can be made with a single detection system, considerable savings are realized if compared with regular optical instrumentation that requires one detection system, or even spectrometer, for every sample.
Cutting-edge research at a community college
“But most importantly,” says Egalon, “this work shows that with the right ideas, support, knowledge, and technology, it is perfectly possible to conduct cutting-edge research in a community-college setting."
For more info, contact Claudio Oliveira Egalon at address: [email protected], or see www.scisensorstec.com