A set of coupled mode equations for a multi-channel array acousto-optic interaction is put forward, and its solutions
are derived. The principal diffraction and inter-modulation of multi-channel acoustic waves and their effects on diffracted
light beams are analyzed. The multi-channel array Bragg acousto-optic device is made. The experimental results indicate
that the multi-channel acousto-optic modulators can modulate the light beam of every channel simultaneously.
In order to detect the liquid leak, many researchers present different methods. However, traditional detection methods are
electrical methods, which are costly and unsafe. In this study, we present a LPG sensing system for leak detection of oil
storage tanks. Since LPG is sensitive to external refractive index changes LPGs can be used as sensors to detect oil leak.
Temperature-independent micro-displacement measurement using a single fiber Bragg grating based on broadened reflection spectrum is proposed and experimentally demonstrated. The structure of specially designed bending cantilever beam (BCB) is proposed. The BCB induces axial strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflected optical power correspond to micro-displacement changes, insensitive to spatially uniform temperature variations. For a displacement variation of 20mm and a temperature change from 20°C to 100°C, the micro-displacement measurement deviation error is ±0.12mm without any temperature compensation. Through optical power detecting by a pin photodiode (PD), the micro-displacement sensor avoids complex demodulation process and potentially costs little.
Simultaneous measurement of temperature and force using a single fiber Bragg grating based on broadened reflection spectrum is proposed and demonstrated. The wavelength peak shift and the bandwidth broadening with the change of temperature and force allow discrimination between the temperature and force effects. Standard deviation errors of 1.8°C and 0.16N have been obtained with temperature and force ranges of up to 20~100°C and 0~8N, respectively.
Design and construction of temperature-insensitive fiber Bragg grating (FBG) liquid level sensor based on bending cantilever beam (BCB) is proposed and demonstrated. The BCB induces spatially gradient strain on the unique sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflected optical power are corresponded to liquid level changes, insensitive to spatially uniform temperature variations. In the liquid-level range of 500 mm and temperature change from 20oC to 80oC, the liquid level measurement fluctuates less than 2% without any temperature compensation. By a pin-photodiode (PD) optical power detecting, the liquid-level sensor avoids expensive and complex demodulation techniques and potentially costs low.
We discuss the two-stage approximation of coupled-mode equations and apply it to all-fiber acousto-optic modulator. We take advantage of the perturbed coupled-mode equations to discuss the form of coupled-mode equations for optical fiber when the term of two-stage approximation has been reserved. Then we discuss the two-stage approximation of all-fiber acousto-optic modulator.
A set of coupled wave equations of multi-channel all-fiber acousto-optic modulation is deduced. The solutions of equations are obtained. The novel 2-channel surface acoustic wave (SAW) all-fiber acousto-optic modulator is presented and developed. Experimental results show modulator performance agrees with theoretical analyses.
The general format of multifrequency acousto-optic coupled wave equation including normal and abnormal acousto-optic interaction is presented in this paper. The solutions of the equations for two independent ultrasonic wave signals in the Bragg limit are put forward. These include diffraction efficiency, compression, cross modulation and additional intermodulation intensities. Especially the differences between the abnormal and normal diffraction are pointed out and analysed. The experimental results are in good agreement with theoretical analyses.
A novel pressure sensor with FBG partly packaged by a metal tube is presented. The thermal-strain cross effect can be avoided. Moreover, its pressure sensitivity is -2.44×10-3/MPa with the range from 0 to 0.44 MPa, which is 1200 times as that of a bare fiber grating. The linearity of this sensor reaches 0.9986.
In this paper, a filter which is cascaded n-stage high-birefringence fiber loop mirrors is presented. The related theory is analyzed and an expression cascaded with n-stage high-birefringence fiber loop mirrors of output intensity is given. Since experiment results are consistent with simulation outcomes, our theory is proved. Compared with a single stage high-birefringence filter, the cascaded filter shows more complex transmission Characteristics. Therefore, this kind of filter is flexible transmission spectrum and low cost for manufacture.
We propose a novel temperature compensation method that HBF is mounted on a piece of organic glass. It can lessen its temperature sensitivity to 0.059 nm/K, which are two orders of magnitude lower than that of an uncompensated HBF loop mirror. It is feasible that HBF loop mirror packaged with a large thermal-expansion material is insensitive to ambient temperature perturbation. This technique is beneficial to the practicality of loop mirror filter based fiber sensors.
All-fiber frequency shifter of polarisation maintaining fiber is of great importance in fiber optics. Previous researchers generally studied one-pass all-fiber frequency shifter of polarisation maintaining fiber. This paper discusses multiple-pass all-fiber frequency shifting of polarisation maintaining fiber theoretically. The solutions of coupled-mode equations for polarisation maintaining fiber when the two orthogonal modes exist is discussed, and the multiple-pass frequency shifting is analyzed. The special issue of the two-pass frequency shifter where the linearly polarized light launching into one polarisation axis of the polarisation maintaining fiber is discussed.
Following the development of the optical data storage technology, an important issue of reliability should also be paid attention to. The designing core of the reliability test way is simulating the users’ circumstance and the transporting process. The normal simulating is important but the users’ playing situation is extreme irregular. So the normal simulating is not enough for reflecting the virtual operating status. Few long time playing experiments have been done previously. In fact such kind of long time playing experiment is most similar to the users’ playing situation, and the effect is compositive since such playing is influenced by current surges, electrostatic discharges, even dust. It seems simple but it is important. We use the optical pickup heads to make sets to play DVD disc continuously for long time, and monitor the image and effect regularly. In our experiment, the optical pickup heads have operated continuously for 6000 hours. It suggests that such kind of long time playing as an additional reliability testing means is necessary, especially for the DVD player’s manufacturing company.
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