A vibration optic fiber sensing system with tunable sensitivity based on Sagnac interference is proposed and demonstrated. In virtue of the linear Sagnac interference structure, vibration sensitivity adjustment could be realized by changing the delay fiber length. The phase modulation depth on sensing fiber induced by intrusion disturbance is heavily influenced by the delay fiber length, which reflected in the intensity detected by the AC photo-detector, thus enabling the vibration sensitivity adjustment in optical sensing system. The relationship between the amplitude of intrusion disturbance and delay fiber length shows a sinusoidal function in absolute value.
The aperture-field mapping is very important to diagnosing the amplitude and phase distribution of the antenna under test( AUT). Since such measurements need to be done without influence to the actual field distribution near the aperture, traditional metallic near-field probes, such as horn antennas, waveguide slots, et al, are irrespective. Miniature electrooptic E-field sensors offer good possibility for such near-field or very near-field measurements, because of its small size and little perturbation to the AUT. Moreover these devices have high resolution and reduced dimensions. In this paper, we have present a simple photonic microwave probe to measure the electric field vector distribution at a distance shorter than one wavelength from the aperture plane of a antenna. The photonic E-field probe is a type of pigtailed electro-optic sensor and consists of an electro-optic crystal supported by a quartz sleeve. The probe is all-dielectric, without any metallic materials. Those physical and electrical features make the photonic sensor attractive when used as a probe for near-field antenna measurements. A patch antenna with a resonant frequency at 6.5GHz was designed and fabricated. Both amplitude and phase distribution of the two tangential E-field components are mapped by using the present photonic probe. Simulation was carried out as well, and compared with the experimental measurements. The result shows great correspondence for amplitude distribution between simulations and experiments, as well as for the phase distribution except for some random tiny fluctuations. The methods to improve the stability of measurement system are briefly discussed.
We present an optical fiber voltage sensor by Michelsion interferometer (MI) employing a Fabry-Perot (F-P) interferometer and the DC phase tracking (DCPT) signal processing method. By mounting a MI fabricated by an optical fiber coupler on a piezoelectric (PZT) transducer bar, a dynamic strain would be generated to change the optical path difference (OPD) of the interferometer when the measured voltage was applied on the PZT. Applying an F-P interferometer to demodulate the optical intensity variation output of the MI, the voltage can be obtained. The experiment results show that the relationship between the optical intensity variation and the voltage applied on the PZT is approximately linear. Furthermore, the phase generate carrier (PGC) algorithm was applied to demodulate the output of the sensor also.
A tunable intracavity fiber laser has been widely used for gas sensing. In order to design a better performance sensor by use of this tunable intracavity fiber laser, the influence factors, including output power such as pump power, intracavity loss, output splitting ratio, and emission wavelength, are investigated based on a theoretical model using the propagation equation. The tunable intracavity fiber laser is set up, and the effects of pump power, intracavity loss, output splitting ratio, and emission wavelength are measured. The experimental results indicate that the theoretical analysis is in good agreement with the experimental measurements; in the process of designing the sensor, the intracavity loss and splitting ratio should be given more attention.
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