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    Dual-wavelength demodulation technique for interrogating a shortest cavity in multi-cavity fiber-optic Fabry–Pérot sensors
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    Abstract:
    This paper demonstrates, for the first time, a novel demodulation technique that can be applied for interrogating a shortest cavity in multi-cavity Fabry–Pérot (F–P) sensors. In this demodulation technique, using an amplified spontaneous emission (ASE) light source and two optical fiber broadband filters, the interference only occurs in a shortest F–P cavity that is shorter than the half of the coherence length. Using a signal calibration algorithm, two low-coherence interference optical signals with similar coherence lengths were calibrated to obtain two quadrature signals. Then, the change in the cavity length of the shortest F–P cavity was interrogated by the two quadrature signals and the arctangent algorithm. The experimental results show that the demodulation technique successfully extracted 1 kHz and 500 Hz vibration signals with 39.28 µm and 64.84 µm initial cavity lengths, respectively, in a multi-cavity F–P interferometer. The demodulation speed is up to 500 kHz, and the demodulation technique makes it possible for multi-cavity F–P sensors to measure dynamic and static parameters simultaneously. The results show that the demodulation technique has wide application potential in the dynamic measurement of multi-cavity F–P sensors.
    A spectrometer is insufficient to resolve all emission lines from a single quantum dot. A custom-made Fabry-Perot Interferometer mechanically linked to an actively stabilized Shearing Interferometer is used as a stable and tunable narrow-band filter.
    Shearing (physics)
    Shearing interferometer
    This paper introduces a dual-path Mach-Zehnder interferometer for determining refractive index and geometrical thickness of an optical plate. In this interferometer, two parallel incident beams are separated into two interference pairs which are then recombined to generate two interference signals. An optical plate is placed on the path of one wave of an interference pair, so the phase difference of the interference signals is a function of the plate, and the interferometer is thus able to determine the index and thickness of the plate. A setup constructed to realize the proposed interferometer is described. And the experimental results of applying this setup agree the validity of the interferometer.
    Interferometric visibility
    Optical path length
    Optical path
    Intensity interferometer
    A description is given of a simple piezoelectrically scanned Fabry?Perot interferometer based on a commercially available (unscanned) IT-28-30 interferometer. The proposed construction ensures a high thermal stability of the Fabry?Perot resonator because of the mutual compensation of the thermal expansions of the separate elements of the interferometer.
    This work provides the information for fabricating Fabry-Perot Interferometer sensors and their performances. The Fabry-Perot Interferometer sensors developed here will be used for the detection of flaws in aircraft structures. The sequel also contains discussion of the experimental setups for the Ultrasonic technique and the Fabry-Perot Interferometer.
    Citations (1)
    The experimental fabrication of a Fabry-Perot interferometer for the x-ray region is reported. Based on state of the art thin film deposition technology at Osmic Inc., challenging requirements for making the interferometer for x-rays have been met.
    Deposition
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    The construction of Fabry-Perot interferometer is very simple and it has been already utilized in different measurement systems. The result of displacement measurement is obviously influenced by the tilt angles of measurement mirror, if a Fabry-Perot interferometer is utilized for displacement measurement. Hence, the measuring range of current systems is rather small (less than 1 mm). The goal of this investigation is to develop a Fabry-Perot interferometer for large travelling range (till 60 mm) by aid of compensation of tilt angles with an angular sensor, piezo translators, control mechanism and self-designed software. To verify the measuring characteristic of the self-developed Fabry-Perot interferometer, some comparison measurements have been performed. A commercial laser interferometer serves as reference standard and the differences between Fabry-Perot interferometer and the commercial Laser interferometer are measured. Through experimental tests, the differences are less than 0.3 m in the full measurement range. The results show that the Fabry-Perot interferometer can meet the measuring requirement with high accuracy of sub-micrometer order and large measurement range.
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    A new type of Fabry-Perot Interferometer (FPI) which exploits the multiplex advantage is presented. The Multiplex Fabry-Perot Interferometer (MFPI) has one etalon plate that is fixed while the other is moved over a large optical distance thus producing an interferogram similar to that obtained with a Michelson Interferometer. The result is an instrument which has the ability to examine large spectral regions at high resolution using the inversion techniques normally applied to a Michelson Interferometer while retaining the small size of an FPI. The MFPI is a compact rugged high resolution instrument that will be useful for the remote sensing of minor species.
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