Dual-core tapered fibers sustain two distinguished polarization axes and in each polarization axis, two supermodes interfere with each other to form a sinusoidal pattern in the transmission spectrum. ...By monitoring the wavelength shift of troughs in the transmission spectrum of each polarization axis when physical parameters in the surrounding environment change, multiparameter sensing can be achieved. In this paper, the factors for enhancing measurement sensitivity and accuracy of dual-core tapered fiber-based sensors, including taper length, taper diameter, and distance between two cores, are investigated theoretically: long sensor length, small core diameter and small distance between two cores (large superposed area) in the dual-core geometrical structure lead to a high-sensitivity and high-accuracy measurement to the variations of the surrounding environment. Theoretical analysis also shows that the sensitivity of transverse strain is much larger than that of longitudinal strain with a large distinguished difference between the two axes. Based on the theoretical deduction, 5 cm long dual-core tapered silica fibers with a core diameter of 10μm and different core distances are fabricated, and the transmission spectra in two distinguished polarization axes are utilized for monitoring the variations of refractive index and strain simultaneously. High measurement sensitivities are obtained with sensitivities of 2263.5 nm/RIU, −1.72 pm/με from the transmission spectrum of one principal polarization axis of the dual-core fiber and 2167.1 nm/RIU and −2.25 pm/με from the transmission spectrum of the second polarization axis. Dual-core silica fiber tapers are simple, compact fiber sensors with high-sensitivity and high-accuracy dual-parameter measurement capabilities.
•Effect of dual-core geometric structure on sensitivity is studied theoretically.•Effect of dual-core geometric structure on sensitivity is studied experimentally.•High-sensitivity and high-accuracy measurement is achieved.
A novel surface plasmon resonance sensor based on a D-shaped, all-glass, endless single-mode photonic crystal fiber is experimentally demonstrated in this paper, which provides a new approach to ...realizing a high-performance photonic crystal fiber surface plasmon resonance sensor. In order to achieve the best performance, the side-polished position of the D-shaped photonic crystal fiber is theoretically and experimentally obtained. The proposed sensor can be used in wavelength and intensity interrogations simultaneously, and the experimental results of wavelength interrogation agree well with theoretical results. By combining the two interrogation methods, we present a two-feature interrogation method to improve the resolution. As a new interrogation method, the two-feature resolution is determined to be 6.53 × 10−5 RIU, which is higher than those of the wavelength and intensity interrogations.
A diaphragm-based Fapry-Perot interferometry (FPI) fiber optic sensor that uses a super luminescent emitting diode (SLED) source was designed and tested for on-line detection of the acoustic waves. ...The single-mode fiber (SMF) and a diaphragm use as sensors, SMF captured in a glass tube to form an extrinsic Fabry-Perot interferometer (FPI). Investigation fallouts show that this optical fiber acoustic-optics sensor is suitable and efficient for sensing acoustic signals by the vibrated diaphragm and the advantage fiber has a high bandwidth and sensitivity.
•A high SNR distributed optical fiber sensing system is achieved.•There is a corresponding relationship between the sensing distance and the optimal Raman pump power.•Both simulation and experiment ...analyze the probe light power and the system SNR distribution.•A BOTDR system assisted by first-order co-direction Raman pumping with window function is proposed.•The mathematical model of the window function is designed.
Raman amplification can extend the sensing distance of distributed Brillouin optical fiber sensor, and there is a corresponding relationship between the optimal Raman pump, the sensing distance, and the lanched probe power. We propose a scheme of co-directional Raman pumping Brillouin optical time-domain reflectometer (BOTDR) with window functions to make a better tradeoff between sensing distance and signal-to-noise ratio (SNR). The mathematical model of window functions is designed based on the relationship between the sensing distance and Raman pump power. Both simulations and experiments analyze the distributions of Brillouin scattering power, which are detected under the fixed Raman pump and processed by the window functions. We then obtain the Brillouin frequency shift (BFS) distribution curve by Lorentzian curve fitting. The experimental results show that the system SNR is increased by 3.3 dB at the near-end of the 78.8 km long sensing fiber. Moreover, the accuracy of temperature and strain at the far-end is enhanced by 2.75 °C and 389 με by using window functions, respectively.
We demonstrate the design and characterization of a distributed optical fiber sensing system based on Michelson interferometer of the phase sensitive optical time domain reflectometer (φ-OTDR) for ...acoustic measurement. Phase, amplitude, frequency response and location information can be directly obtained at the same time by using the passive 3×3 coupler demodulation. In order to simulate sound profiles of seismic or hydroacoustic imaging, experiments on detection of multiple piezoelectric transducers (PZT) are carried out. The result shows that our system can well demodulate different acoustic sources with different intensities.
•We demonstrate an φ-OTDR-interferometer system for distributed acoustic sensing.•Phase, amplitude and location of the event can be directly obtained simultaneously.•Same acoustic source with different intensities is well demodulated in experiment.•Different acoustic sources with different intensities are also well demodulated.•Demodulated amplitudes in different intensities show good linear property.
In this study, a distributed multi-channel fiber-optic sensor for simultaneous measurement of relative humidity (RH) and temperature with finer gauge length based on spatial-domain time-delayed ...multiplexing is proposed and experimentally demonstrated. Simultaneous acquisition of multi-channel signals can be realized by reconfiguring the system layout in a spatial-domain time-delayed multiplexing manner by re-routing the Rayleigh backscattered signals for split-channel processing using only extra delay fibers and couplers instead of any optical switches extending the acquisition time or acquisition unit increasing the system cost. Sensing units comprised of copper (Cu)-coated fiber and polyimide (PI)-coated fiber are used to extract the changes of RH and temperature in the environment simultaneously thanks to the distinct sensitivities on RH and temperature of the two fibers. Experimental results show that the sensing system is able to realize multi-channel simultaneous measurement of RH and temperature with gauge length up to 10 mm. Besides, the system is proved to have excellent stability and reliability in high humidity environments. This novel and simple sensing technique for multi-channel dual-parameter simultaneous measurement will provide new ideas for development of economical, reliable, and practical RH and temperature sensing network.
A low-cost way of achieving a high sensitivity optical fiber strain sensor by introducing higher-order interference modes using a torsional multimode fiber (MMF) instead of normal MMF based on ...single-mode–multimode–single-mode (SMS) structure is proposed and the coupling mechanism of twist fiber is investigated theoretically. The sensor is fabricated by simple process of heating and twisting a small region of MMF. According to this method, the shift of multimode interference spectrum caused by an axial strain will be greatly magnified. Different strain sensitivities can be easily realized by controlling the torsional number of circles. The experimental results indicated a high strain sensitivity of 42.5 pm/με at most.
•An optical strain sensor utilizing twist effect of multimode fiber is proposed.•The sensitivity to strain enlarges along with the degree of torsion increasing.•The sensitivity of 42.5 pm/με is achieved in experiment by 16 circles twist.•The sensor possesses the advantages of high sensitivity and low cost.
In this paper, an optical fiber interferometric sensor with improved phase generated carrier (PGC) demodulation algorithm is proposed to eliminate the influence of light intensity disturbance. ...Performance of sensor using proposed algorithm is analyzed and compared with sensor using differential-cross-multiplying (PGC-DCM) algorithm and PGC Arctangent (PGC-Arctan) algorithm, respectively. Experimental results show that distortion, but also harmonic distortion is well suppressed by the improved PGC algorithm. In experiment, the signal-to-noise and distortion ratio of sensor using the proposed algorithm achieve a gain of 16.4 and 10.8 dB over sensor using PGC-DCM and PGC-Arctan algorithm, respectively.
We present the fabrication of fiber Bragg gratings (FBGs) in a trench-assisted heterogeneous multicore fiber (MCF). Two obviously different Bragg reflection peaks are obtained due to the slight ...difference of refractive indices between the center core and the outer cores. To investigate the reflections of the two FBGs simultaneously, only a segment of multimode fiber is inserted between the lead-in single mode fiber and the MCF. The experimental results confirm that the curvature sensitivity of the FBG in the outer core is a sinusoidal function of the bending orientation angle. The maximum linear curvature sensitivity is about 0.128 nm/m−1. The cross sensitivity to temperature or externally applied axial strain can be eliminated by discriminating the different responses of FBGs inscribed in outer cores and the center core. Thus this MCF with FBGs can be utilized as a directional bending sensor. Moreover, the proposed sensor offers several advantages, such as low cost and flexibility in fabrication.
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