A fiber-Bragg-grating sensor interrogation system using a in-fiber Fabry-Pérot interferometer (IFFPI) is presented. The
IFFPI was formed by splicing together a conventional single-mode fiber and a photonic crystal fiber with simple arcdischarge
technique. The ellipsoidal air-cavity between the two fibers forms Fabry-Pérot cavity. The diffraction loss can
be very low due to the focusing of reentrant and very short cavity length, thus resulting in high visibility and long period.
The IFFPI is used as the filter component of the interrogation system. The resolving wavelength can achieve 2pm by
using an Er-doped ring FBG laser in the experimental system. The advantages of this system are an all-fiber design,
temperature insensitivity, quasistatic and dynamic operation, potential high speed and large range demodulation.
An all-fiber liquid level sensor based on core-offset attenuator is proposed and demonstrated. The interference fringe is
affected by the fraction of the length of the interferometeric arm that is surrounded by the liquid. The experiments show
that for a liquid level variation of 30mm, the maximum difference of attenuation changes about 3dB. Also in the linear
region, a sensitivity of 0.84dB/mm is achieved. For a temperature range from 30°C to 80°C, the measured liquid level
fluctuates less than 1% without any temperature compensation. The liquid level sensor we reported in this paper appears
more robust and repeatable, and its ease of fabrication makes it a low cost alternative to existing fiber liquid level sensor.
In this work, an absolute distance measurement method based on the self-mixing interference is presented. The
principles of the method used three-mirror cavity equivalent model are studied in this paper, and the
mathematical model is given. Wavelength modulation of the laser beam is obtained by saw-tooth modulating the
infection current of the laser diode. Absolute distance of the external target is determined by Fourier analysis
method. The frequency of signal from PD is linearly dependent on absolute distance, but also affected by
temperature and fluctuation of current source. A dual-path method which uses the reference technique for
absolute distance measurement has been proposed. The theoretical analysis shows that the method can eliminate
errors resulting from distance-independent variations in the setup. Accuracy and stability can be improved.
Simulated results show that a resolution of ±0.2mm can be achieved for absolute distance ranging from 250mm to
500mm. In the same measurement range, the resolution we obtained is better than other absolute distance
measurement system proposed base on self-mixing interference.
An optical MEMS pressure sensor based on multi-layer circular diaphragm has been analyzed by utilizing the shell theory and characteristic matrix methods. Finite element methods are used to analyze the deflection of circular diaphragm with the residual stress effect considered. Simulation results are given by using FEM software tools ANSYS. The analytic expressions for the absolute reflectance of multi-layer circular diaphragm structure are derived. The results are valid for the most optical MEMS pressure sensors based on Fabry-Perot interferometer.