We developed two underwater fluorimeters (VIS&UV) for in-situ assessments of aquatic fluorescence constituents. Two prototypes had been developed to assess chlorophyll a and BOD5, respectively, and were deployed under a buoy platform for long-term field tests. Design considerations include exciting light use efficiency, weak fluorescence signal detection, ambient light suppression, corrosion resistance and anti-biofouling. The prototypes demonstrated excellent linearity in response to fluorescence emissions in laboratory calibrations and good environment suitability during the field tests. We had obtained a large amount of observational data and maintenance experience.
This study mainly compares two optimized interrogation techniques for an interferometric fiber-optic surface plasmon resonance (SPR) sensor. For this sensor, both SPR and interference effects are excited in a single fiber structure and they can be applied for dual-parameter measurement. On the other hand, the interference fringe patterns are mixed into the SPR transmission spectra, and the novel interrogation technique should be evaluated. In this study, two optimized interrogation techniques are proposed and their performances are compared. For the first one, the non-linear least square method is used to filter out the interference components and only retain the SPR signal. For the second one, the wavelength-distributed spectra are converted into the spatial frequency-distributed spectra, hence SPR components and the interference components can be discussed individually. The advantages and disadvantages of the two interrogation techniques are discussed thoroughly.
We propose and demonstrate an interferometric sensor based on visibility modulation. In the interferometric sensor, a section of
polarization maintain (PM) fiber is spliced into one arm as the sensing head. Due to the interference between the two beams in the two
arms, respectively, an interferometric fringe can be obtained. The birefringence of the PM fiber splits the beam in the sensing arm,
yielding a visibility envelop in the interferometric fringe. Strain applied on the PM fiber can be demodulated by measuring the
visibility change in a given wavelength. Experimental result shows that the sensor can achieve resolution of up to 28 nano-strain. This
demodulation scheme is immunity to the wavelength shift and power fluctuation of OSA, thus improving the accuracy of the sensor.
This type of sensor can be improved by using a wavelength-swept laser or a mode-locked fiber laser.
This paper develops a promising low-priced optical fiber arcing detection system for measuring pantograph-catenary contact-loss. The system collects the ultraviolet light by UV lens. The filter cuts off visible light to reducing environmental disturbance. Ultraviolet light of arcing is transformed to visible one by fluorescent material, which is packaged on the fiber endface and has a high transforming efficiency in ultraviolet band. This optical fiber arcing detection system is equipped with self-checking pulsed light to monitoring the status of the detection system. The arcing energy is estimated by the relationship between the intensity of ultraviolet light and the output voltage signal.
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