A Mach–Zehnder interferometer based on S-taper embedded in long-period grating (LPG) for simultaneous measurement of strain and temperature is proposed. The LPG is written using CO2 laser in a single-mode fiber. Then an S-taper is made by putting the LPG in a fusion splicer and applying off-axis pull at the middle point. The spectral characteristics of strain and temperature are investigated theoretically and experimentally. The experimental results show that the maximum strain sensitivity is 53.6 pm / με within a strain range of 0 to 373.13 με. In additionally, the proposed sensor has a maximum temperature sensitivity of 70 pm / ° C when the temperature varies from 30°C to 90°C. Further analysis shows that this sensor could be applied for simultaneous measurement of strain and temperature.
An intensity-interrogated fiber-optic magnetic field sensor functionalized with magnetic fluids is proposed and experimentally demonstrated by encapsulating an S-taper concatenated with down-fusion taper in a silica capillary. The down-fusion taper serves as a higher order mode exciter, whereas the S-taper is employed to couple the cladding modes back into the fiber core, and so an interferometric spectrum could be acquired for sensing interrogation. Spectral characteristics of the proposed sensor dependent on magnetic field intensity and environmental temperature are investigated in detail. Experiment results show that the maximum magnetic field sensitivity reaches −0.02336 dB / Oe within a specific range of 25 to 200 Oe, and the temperature sensitivity reaches 0.07116 dB / ° C within a temperature range of 26°C to 46°C. By exploiting the distinction between magnetic field intensity and temperature sensitivities of peak 1 and dip 1 that are selected for intensity interrogation, temperature cross-sensitivity issue can be resolved.
A microwave photonic filter (MPF) based on four-wave mixing (FWM) is proposed and experimentally demonstrated. Two single-frequency laser beams produce the four-wave-mixing effect in a highly nonlinear fiber and generate a multiwavelength optical signal output. The multiwavelength optical signal is used to generate the multitaps of the MPF. The wavelength spacing of the multiwavelength optical source is equal to the frequency difference of the two input laser beams. By changing the frequency difference of the two input laser beams, wavelength spacing of the multiwavelength optical source output can be continuously tuned in the range of 0.36 to 1.6 nm. Thus the center frequency of the filter can be continuously tuned within the range of 6.914 to 30.729 GHz.
An optical fiber magnetic field sensor using intermodal interferometer coated by magnetic fluid (MF) is proposed. The interferometer consists of down-taper and spherical structure formed on the standard single-mode fiber (SMF) by a fusion splicer. Since the refractive index (RI) of the MF is sensitive to external magnetic field, the interferometer coated by MF can be used for magnetic field sensing. Two interference valleys of the interferometer integrated with ferrofluid under different magnetic field intensities have been experimentally analyzed. The experimental results show that there is a linear relationship between the valley wavelength shift and magnetic field intensity for a range of 0 to 20 mT, and the maximum sensitivity reaches up to −0.195 nm/mT. In the range of 0 to 12 mT, the variation of transmission loss at valley wavelength with a magnetic field has a maximum sensitivity of 0.106 dB/mT.
An all-fiber sensor for simultaneous measurement of temperature and microdisplacement is presented and demonstrated. The sensor head is fabricated by a peanut structure Mach–Zehnder interferometer (MZI) cascaded with a fiber Bragg grating (FBG). Experimental results show that the temperature sensitivities of the MZI (dip1) and the FBG (dipFBG) are 0.0909 and 0.0121 nm/°C, respectively. The microdisplacement sensitivities are −0.0233 and 0.0122 nm/μm, respectively. The simultaneous measurement of the temperature and microdisplacement is demonstrated based on the sensitive matrix. With the advantages of low cost and easy fabrication, this sensor has potential applications in security, construction, and energy.
A dual-parameter optical fiber sensor is proposed and demonstrated. It is based on an intermodal interferometer (IMI) with an inline embedded fiber Bragg grating (FBG). The IMI is formed by cascading a taper structure and a spherical-shaped structure through a segment of a single-mode fiber. Due to the different wavelength shifts of the IMI and FBG to temperature and liquid level, simultaneous measurement can be achieved. Experimental results indicate a good linear relation between the wavelength shift and external parameters (temperature and liquid level). The sensitivities of 0.066 nm/°C and −0.133 nm/mm are achieved experimentally for temperature and liquid level, respectively. The interesting properties of the sensor include good operation linearity, compact size, and high sensitivity.
The paper conducts a research on a new type of long period fiber grating with a local micro-structured defect, we analyze and simulate its spectral characteristics by the coupled mode theory and transfer matrix method. Gaining this new type of long period fiber grating method is etching a long period fiber grating by the hydrofluoric acid (HF). This method will etch the local couple of long period fiber grating. The result shows that with the change of the etching depth, length and the position of the defect state, it will open a transmission window and break up into two transmission peaks in the spectra of the stop-band of long period fiber grating, the depth of the two transmission peaks have some relationship with the etching depth, length and the position of the defect state. When the corrosion depth is shallow, the depth of the left peak is higher than the right peak, with the increase of the corrosion depth, the depth of right peak gradually is increasing and over the left peak, the two peaks will return to the state of a single peak, if the corrosion depth continues to increase. With the increase in the length of the corrosion, the depth of the left transmission peak is greater than the right peak, with the continued increase of the corrosion length, the right peak’s depth will gradually increase and over the left peak, if the corrosion length continues to increase, showing that the depth of the two peaks are equal, however, compared with previous cycles the transmission peaks depth decreases. With the change of the corrosion position LTH off the center, the transmittance of the peak’s depth gradually decreases. This research offers a theoretical basis for making the new type of local micro-structured long period fiber grating and achieving double parameters sensing applications.
A novel FBG obliquity sensor is proposed. In this sensor one half of the FBG is stick to the fixed end of a
cantilever, and the other half remains at freedom state. The difference of the center reflection wavelength of the
two half of the FBG changes linearly with the sine of the obliquity from 0284 to 0393(linear degree 0.9956) . In
this sensor cross sensitivity is alSo eliminated by the different strain coherent of the two half FBG. If combined
with another sensor of the same structure, the sensing of two dimensional obliquity is achieved. The research
demonstrates that the new sensor system has the advantages of simple and compact structure, easy manipulation,
low cost, light weight, etc.
We bring forward a novel FBG sensor multiplexing technique based on Petri Net theory and the wavelength/spatial-division multiplexing technique. With this technique, the FBG sensing system not only avoid frequently switching and improve the average response speed, but also is able to enact data acquisition rule according to the priority (PRI), the delay time and the wavelength shift of FBG sensors. Therefore, the smart FBG sensors multiplexing system is more rational and smarter than the conventional WDM/SDM multiplexing technique. To validate the feasibility and advantage of the multiplexing technology, a FBG strain sensing system and theory simulation were proposed. The resolution power of the sensing system is 1με. The average delay time of the technique is lower one magnitude order than the conventional ones.
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