KEYWORDS: Light emitting diodes, Modulation, Sensors, Resonators, Light sources, Absorption, Gas lasers, Photoacoustic spectroscopy, Signal to noise ratio, Near infrared
Due to the lack of an economic midinfrared laser, especially wavelength around 3 μm, light sources are critical to trace gas sensing for the gases without absorption in the near-infrared zone. We present a trace ethane photoacoustic (PA) sensor using a midinfrared light-emitting diode (MIR LED). MIR LEDs are very attractive sources for PA technology since they are relatively high power spectral density, easy modulation, low power consumption, and low cost. The proposed PA system with a 3.36-μm MIR LED shows good linearity to ethane concentration and reaches a detection limit of 10 parts per million by volume easily. Ideas of further enhancement of the sensitivity are discussed.
To overcome the accuracy limits of fringe counting method for a F-P interferometer and the complexity of a higher
resolution demodulation system such as phase generated carrier (PGC), where a residual amplitude modulation always
exists in frequency modulation, this paper presents a fiber F-P displacement sensor based on double-interferometer phase
demodulation, which eliminates the modulation of lightsource. Comparing to the reported double-fiber F-P structure, our
design has no strict requirement for a specific phase difference between the two optical paths. Experimental results
demonstrate a good linearity of 1.1% and a resolution of ±3 μm within a measuring range of 0-0.5 mm.
This paper presents a liquid level sensor with a double-fiber Fabry-Perot (F-P) cavity and a diaphragm serving as the
sensing element. The end surfaces of the two fibers that integrated in a ferrule serve as the front surfaces of the F-P cavities,
and the diaphragm (one of the standard components of a manometer) as the rear surface. The random difference in position
between the two fiber ends makes a phase difference between the two F-P interferometers, and is used to interpret the
direction of the pattern shifts with the variation of the F-P cavity length, which leads to a much lower technological
requirement for the cavity manufacture and a more stable sensor. A prototype is fabricated to demonstrate the design, and
the experimental results show a system accuracy of 1/2 fringe, refer to a height-resolution of 1mm.
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