A microring resonator sensor device for sensitive detection of the explosive 1,3,5-trinitrotoluene (TNT) is presented. It is based on the combination of a silicon microring resonator and tailored receptor molecules.

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Femtosecond laser pulses were used for the direct point-by-point inscription of phase-shifted fiber Bragg gratings (FBGs) in a single fabrication step without postprocessing. An electro-optic amplitude modulator is used in the setup to generate a defined delay between two identical laser pulse trains for the grating inscription. The grating structure with a central phase shift is formed by focusing the modulated laser pulses into the core of a fiber, while the fiber is translated with a constant velocity. The induced phase shift leads to a narrow transmission band with a bandwidth considerably below 10 pm within the stop band of the FBG. The inscribed FBGs show a birefringence of 3.9×10(-5) whereas their temperature and strain sensitivities are 10.4  pm/K and 1.4  pm/μstrain, respectively. The fabrication process is fast and offers a high grade of flexibility for the control of all grating parameters.

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A novel fiber optical refractive index sensor based on gold nanoshells immobilized on the surface of an etched single-mode fiber including a Bragg grating is demonstrated. The nanoparticle coating induces refractive index dependent waveguide losses, because of the variation of the evanescently guided part of the light. Hence the amplitude of the Bragg reflection is highly sensitive to refractive index changes of the surrounding medium. The nanoshell functionalized fiber optical refractive index sensor works in reflectance mode, is suitable for chemical and biochemical sensing, and shows an intensity dependency of 4400% per refractive index unit in the refractive index range between 1.333 and 1.346. Furthermore, the physical length of the sensor is smaller than 3 mm with a diameter of 6 μm, and therefore offers the possibility of a localized refractive index measurement.