In this paper, an edge filter demodulation of fiber Bragg grating (FBG) displacement measuring scheme using long
period grating (LPG) is reported and demonstrated. The system consists of a 3dB coupler, a sensing FBG, a LPG and a
photo-detector. As the sensing element, FBG can convert the displacement information into the shift of the Bragg
wavelength, and then the wavelength information is converted into power using edge filter demodulation. The
experimental results show that there is good linear relation between the output power detected by the photo-detector and
the displacement in the measurable ranges 0-3.6mm. The displacement sensitivity is 9.24pw/mm.
A novel method of demodulation for fiber Bragg sensor is presented. An experimental system is built up in which HBF
Sagnac LM is used as the edge filter. We achieve linear demodulation whith a bandwith of 3.6nm. We have also
experimentally demonstrated that packaged HBF can compensate the temperature shift of the HBF Sagnac LM filter. The
shift of wavelength for an uncompensated HBF Sagnac LM is approximately 2.3nm/°C,and that of the compensated HBF
Sagnac LM is 0.005nm/°C,which is much less than that of the uncompensated HBF Sagnac LM filter.
A new method of tuning fiber Bragg grating by electromagnetic force is proposed. The wavelength shift of the fiber Bragg grating is 1.16nm in the range of the current intensity from 0 to 85.5mA. The researches indicate that the system has advantages of simple configuration and high sensitivity.
A technique for temperature compensation in fiber grating vibration sensor is reported. By special design, it causes reversed strain on two FBGs and has temperature effects cancelled. After discussion about the factors affecting the sensitivity and the width of frequency band, it is experimentally proved that the total variation in wavelength difference within temperature of -15 ~ 50°C is nearly 0. When the input vibration frequency is up to 800Hz and the drive power is as low as 2mw, the output waveform is still distortionless.
A novel optical add-drop multiplexer (OADM) based on Mach-Zehnder interferometer and fiber Bragg grating (FBG) is proposed. In the structure, the Mach-Zehnder interferometer acts as an optical switch. The OADM can add/drop one of the multi input channels or pass the channel directly by adjusting the difference of the two arms of the interferometer. The channel isolation is more than 20dB.
In this paper a four-channel OADM based on fiber gratings with smart temperature stable sets was implemented. It solved the conflict between the tunable capability and the temperature stability of the center wavelength. Using a cantilever beam method, the tunable range of 1nm is obtained. Within the temperature range -20°C ~+ 60°C, the center wavelength shift is less than 0.004 nm/°C and the thermal stability is 6.75 times as that without thermal stable sets. The wavelength spacing is 0.8 nm, which accords with ITU-T G.692 recommendation. 35 dB of the adjacent isolation in the OADM is obtained, which is the best one reported as we known.
A new approach for displacement sensing based on chirp effect of fiber Bragg grating under strain-gradient is proposed and demonstrated in this paper. Strain gradient chirp of fiber Bragg grating is realized by attaching the grating slantways on a side face of a simple cantilever beam. The strain gradient, which is formed along the grating when the free of the beam is curved, produces a linear variation in the grating pitch .The theoretical formulae are derived and the experimental results are given. Because bandwidth of the grating is temperature-insensitive, the cross talk between displacement and temperature is avoided. This device has many characteristics, such as simple configuration, good noise immunity, and good linearity (about 0.9992). It is promising to be used into in-process displacement measurement.
A novel of bend sensor is demonstrated firstly. The device uses a simple support beam composing of two beams with a metal line winded on each beam and multimode fiber of a few meters in length which is placed between two beams having metal teeth profile such that the fiber experiences multiple bends. The experiment shows that the microbend loss of the multimode optical fiber is sensitive to the simple support beam bend curvature. The microbend loss with curvatures from 0 to 4.4m-1 is examined. The microbend loss with curvature is nonlinear, with a minimum detectable curvature change of 0.0175m-1.
A direct current sensor based on all-fiber Mach-Zehnder interferometer is demonstrated in this paper. The phases of interferometric lights in the interferometer is modulated by heat effect when current flowing through a thin metal tube. The charactersistics of current sensing are studied experimentally. Adopting the wavelength scale method, in the case of elimination of environmental perturbation, the wavelength changing range is 32nm when the current changes from 0 to 1.8A. The shifting wavelength is linear to the power and the linear fitting is 0.9987. The tuning efficiency is approximately 19.47nm/W.
Three kinds of add-drop multiplexers (OADMs) based on fiber gratings and circulators are proposed and demonstrated. There are significant homodyne crosstalk reduction of about 24.4dB, 39.3dB and 23.6dB, 24.6dB on the dropped and added channels, respectively, for the best proposed lI-type structure and III-type structure as compared with the conventional I-type structure.
Based on the microbend characteristics of the multimode optical fiber (MMF), a novel twisted fiber torsion angle sensor is demonstrated firstly. The experimental principle and the basic formula have been analyzed and given. The experiment shows that the microbend loss of the multimode optical fiber is sensitive to the torsion angle. In the range of torsion angle from 0 degree(s) to 90 degree(s) the sensitivity is about 1dB/degree. The experimental results are well agreement with the theoretical ones.
A direct current voltage sensor based on all-fiber Mach- Zehnder interferometer is demonstrated, which utilizes electrostriction effect of Piezoelectric Translator. The character of voltage sensing is studies experimentally. Adopting the wavelength scale method, in the case of elimination of environmental perturbation, the wavelength changing range is 3.86nm when the voltage changes from -58v to 58v. The tuning sensitivity and the linear fitting are 0.033nm/v and 0.9985, respectively.
A novel technique for fiber Bragg grating sensor is introduced. The sensor is successfully used to measure wavelength-shift induced to strain and temperature. The experiment results agree with the theory and indicate that the sensor has good linear response capacity and high intensity signal and signal to noise ratio.