Fiber Optic Sensors For Detection of Toxic and Biological Threats

Abstract

Protection of public and military personnel from chemical and biological warfare agents is an urgent and growing national security need. Along with this idea, we have developed a novel class of fiber optic chemical sensors, for detection of toxic and biological materials. The design of these fiber optic sensors is based on a cladding modification approach. The original passive cladding of the fiber, in a small section, was removed and the fiber core was coated with a chemical sensitive material. Any change in the optical properties of the modified cladding material, due to the presence of a specific chemical vapor, changes the transmission properties of the fiber and result in modal power redistribution in multimode fibers. Both total intensity and modal power distribution (MPD) measurements were used to detect the output power change through the sensing fibers. The MPD technique measures the power changes in the far field pattern, i.e. spatial intensity modulation in two dimensions. Conducting polymers, such as polyaniline and polypyrrole, have been reported to undergo a reversible change in conductivity upon exposure to chemical vapors. It is found that the conductivity change is accompanied by optical property change in the material. Therefore, polyaniline and polypyrrole were selected as the modified cladding material for the detection of hydrochloride (HCl), ammonia (NH3), hydrazine (H4N2), and dimethyl-methl-phosphonate (DMMP) {a nerve agent, sarin stimulant}, respectively. Several sensors were prepared and successfully tested. The results showed dramatic improvement in the sensor sensitivity, when the MPD method was applied. In this paper, an overview on the developed class of fiber optic sensors is presented and supported with successful achieved results.

Integrated Optical Gas Sensors on Silicon-on-Insulator Platform

“…Optical gas sensors can be realized either with direct light -gas interaction or with the aid of transducer chemical coatings on optical circuits [1,4]. Gas sensitive chemical coatings significantly reduce the very long interaction length that would have been required if a direct spectroscopy of gases were used.…”

“…Robustness, multiplexing of sensor arrays, safety, remote sensing and low power consumption are among the interesting features about the optical sensors [1].…”

Sensing application of an optical fiber dip coated with L-Cystein ethyl ester hydrochloride capped ZnTe quantum dots

“…Recently, quantum dots embedded coating on optical fibers have been developed to detect gases [1,2], pH [3], temperature [4], humidity [5,6] and bimolecules [7,8]. There are various schemes described in literature, for optical fiber sensors such as Bent optical fiber sensor [9], tapered optical fiber sensors and cladding removed optical fiber sensor [10].…”

Estudo da aplicabilidade do polipirrol no desenvolvimento de um sensor óptico de umidade.

“…Trabalhos desenvolvidos sobre sensores ópticos são feitos principalmente utilizando fibras ópticas [6,7,8], embora estas sejam mais utilizadas para trabalhar na área de telecomunicações, também apresentam vantagens para serem usadas em monitoramento, controle, sensoriamento e medição. Quando usadas em sensoriamento, elas são chamadas de FOS (Fiber Optic Sensor -segundo a sigla em inglês).…”

“…Laktimur e El-Sheriff em [6,7,65] desenvolveram um sensor de gás usando a técnica de revestimento modificado. Usando esta técnica, eles removeram uma parte do revestimento de uma fibra óptica multimodo e a substituíram (à parte do revestimento da fibra removida) pelo polipirrol dopado.…”