A long-period grating (LPG) fiber optic sensor has been developed for monitoring the relative humidity levels and toxic chemicals, especially the chemical warfare agents. The principle of operation of this sensor is based on monitoring the refractive index changes exhibited by the reactive coating applied to the surface of the LPG region in response to analytes. Specific interaction of the analyte with the thin film polymer coating produces as the output a wavelength shift that can be correlated with the concentration of the analyte. Thin polymer coating for relative humidity sensor is made of carboxymethylcellulose (CMC) covalently bound to the surface of the fiber. Coating for chemical warfare agent detection employs metal nanoclusters imbedded in polyethylenimine (PEI) for specific reaction. The relative humidity level can be determined from 0% to 95% and the level of toxic chemicals can be determined is at least on the scale of 1 ppm. This small-size and low-cost LPG fiber optic sensor exhibited high sensitivity, rapid response, repeatability and durability. The goal of developing relative humidity sensor is to produce a fiber optic sensor-based health monitoring system for building, while the chemical sensor has found its application in point detection network for chemical warfare agent monitoring.
A novel system incorporating optical fiber long-period grating (LPG)-based sensors for rapid detection of biological targets is presented to address the current need for highly responsive, inexpensive, instrumentation for in-situ subsurface bioremediation technologies. With the appropriate configuration, the LPG sensor is able to measure key environmental parameters. The sensor allows for highly sensitive, real-time, refractive index measurements and by applying affinity coatings to the fiber surface, specific binding of molecules can be accomplished using swellable polymers or ligand-based affinity coatings. Advantages of the sensors have are that they are highly responsive, low profile, and can be serially multiplexed within a single-ended probe-like arrangement. This arrangement can be utilized either locally for site characterization or as a distributed sensor to map contaminant levels at multiple depths over a large area. The performance advantages make optical fiber sensors ideal for detection of environmental targets in drinking water, groundwater, soil, and other complex samples. This paper presents recent long-period grating-based sensor results that demonstrate the potential for bioremediation as well as a variety of other chemical and biological sensing applications.
A novel near-infrared diode laser having sensitivity to change of absorption and refractive index at its surface- sensitive region is presented. This semiconductor laser utilizes an AlGaAs single quantum well structure emitting at a wavelength of 950 nm, and its dimensions are 1 mm X 0.5 mm X 0.2 mm. One of the cladding layers is thinned such that the evanescent wave in the quantum well interacts with a surface-sensitive region on the laser. A theoretical model of laser sensitivity toward changes in absorption of a dye- doped polymer coating is formulated. Experimental data using the surface-sensitive diode laser for sensing ammonia and adsorbed monolayers of molecular films are presented. The output power, threshold current and wavelength are shown to be affected by the changes in the adsorbed coating.
An optical fiber fluorescence sensor system capable of compensating fiber bending loss is presented. The system utilized a modulated light-emitting diode and digital-signal processing chips to enhance the measurement of fluorescence signals. A fiber-optic oxygen sensor system suitable for measuring oxygen levels in gas and in aqueous media was developed, and the capability of the system to alleviate fiber bending loss was demonstrated. The signal-to-noise ratio of the system was found to exceed 30 dB using inexpensive components.