To fight against the explosives-related threats in defense and homeland security applications, a smarter sensing device
that not only detects but differentiates multiple true threats from false positives caused by environmental interferents is
essential. A new optical detection system is proposed to address these issues by using the temporal and spectroscopic
information generated by the surface plasmon coupling emission (SPCE) effect. Innovative SPCE optics have been
designed using Zemax software to project the fluorescence signal into clear "rainbow rings" on a CCD with subnanometer
wavelength resolution. The spectroscopic change of the fluorescence signal and the time history of such
changes due to the presence of a certain explosive analyte are unique and can be used to identify explosives. Thanks to
high optical efficiency, reporter depositions as small as 160-μm in diameter can generate a sufficient signal, allowing a
dense array of different reporters to be interrogated with wavelength multiplexing and detect a wide range of explosives.
We have demonstrated detection and classification of explosives, such as TNT, NT, NM, RDX, PETN, and AN, with
two sensing materials in a prototype.
We demonstrate the rapid detection of explosive vapors based on a fiber-based optical Fabry-Pérot (FP) gas sensor. The
sensing probe of the FP sensor is composed of a thin metal layer and a vapor-sensitive polymer layer that are deposited
sequentially on a cleaved fiber endface to form an FP cavity. The interference spectrum generated from the reflected
light at the metal-polymer and polymer-air interfaces changes upon the absorption of gas analyte. By monitoring the
interference shift, we are able to obtain quantitative and knetic information of the interaction between the analyte and the
polymer layer. We further assemble the FP sensor with a short fused silica capillary into a sensor module, and employ it
in a gas chromotgraphy (GC) system for selevtive rapid on-column detection. In this report, we specifically target 2, 4-
dinitrotoluene (DNT) and 2, 4, 6-trinitrotoluene (TNT) for their obvious defense applications. This work could lead to a
portable sensor capable of detecting low concentrations of DNT, TNT, and other explosive chemicals.
A versatile, compact, and sensitive fiber-based optical Fabry-Pérot (FP) gas sensor is reported in this paper. The sensor
probe is composed of a silver layer and a vapor-sensitive polymer layer that are deposited on the cleaved fiber endface to
form an FP cavity sequentially. The interference spectrum generated from the reflected light at the silver-polymer and
polymer-air interfaces changes upon the absorption of gas analytes. This structure enables using polymer of any
refractive index (RI) as the sensing layer, which significantly enhances the sensor versatility. Two polymers of
polyethylene glycol (PEG) 400 (RI=1.465-1.469) and Norland Optical Adhesive (NOA) 81 (RI=1.53-1.56) are used as
the gas sensing polymer to demonstrate the feasibility of the FP sensor, and show drastically different sensor response to
various gas analytes. In addition, we assemble the FP sensor with a short fused silica capillary into a sensor module, and
employ it in the gas chromotgraphy (GC) system to investigate its capability as a GC detector for rapid on-column
detection.
We develop a novel chemical vapor sensing platform based on optofluidic ring resonator (OFRR) for rapid and on-column
detection and analysis of a wide range of chemical vapors. The OFRR is a thin-walled fused-silica capillary with
a diameter of ~100 μm and a few centimeters in length. The circular cross-section of the OFRR defines a ring resonator
that supports high-Q (>106) whispering gallery modes or circulating waveguide modes (WGMs). Polymer thin film is
coated on the OFRR capillary interior surface as a vapor sensitive material. The unique structure of the OFRR achieves
dual-use of the capillary as the gas delivery channel and as the sensing transducer, avoiding the necessity of building
extra gas detection chambers commonly seen in chemical vapor sensors. When vapor molecules pass through the OFRR,
the interaction between vapor molecules and the polymer causes polymer refractive index and thickness to change,
which leads to a WGM spectral shift. Therefore, by monitoring the WGMs spectrum in time, the quantitative and kinetic
information regarding vapor molecule-polymer interaction is acquired. The rapid detection of methanol and hexane
vapors representing polar and nonpolar analytes respectively are demonstrated with OFRR vapor sensors. Owing to the
unique multipoint on-column detection capability, the OFRR vapor sensor is studied for the development of the micro-
GC gas analyzer. Efficient separation and rapid detection are achieved by a few centimeters long OFRR capillary coated
with a stationary phase polymer. We further explore the capability of OFRR micro-GC for more challenging explosive
detection. The OFRR vapor sensing platform is a promising candidate for the development of rapid, sensitive, simple,
portable, and cost-effective micro-gas sensors.
Whispering-gallery mode (WGM) resonators such as microspheres, microcylinders, and microrings have been proposed for telecommunication and sensing applications for decades. However, several challenges, such as the robustness of the optical coupling and sample delivery means, were often found in the path of developing them for the real world sensing applications. In this paper, a robust microring platform based on integrated lightwave circuit technology and a tunable laser interrogation system has been demonstrated as high-resolution refractive index and pressure measurement system. By using a "two-point" interrogation scheme and a microring with Q factor of about 24,000, a refractive index sensitivity of about 145 nm/RIU (TM mode) and 205 nm/RIU (TE mode) for two different polarizations and a limit of detection on the order of 10-7 RIU have been demonstrated. For the high-pressure measurement applications, a pressure resolution of 0.05 psia has been achieved.
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