Proc. SPIE. 11048, 17th International Conference on Optical Communications and Networks (ICOCN2018)
KEYWORDS: Signal to noise ratio, Optical filters, Phase shift keying, Fiber optics sensors, Data acquisition, Frequency modulation, Sensing systems, Signal detection, Radar signal processing, Pulsed laser operation, Compressed sensing
We reported a new method based on additive random sampling (ARS) and non-linear frequency modulation (NLFM) to enhance the frequency response of long-range phase-sensitive optical time-domain reflectometry (φ-OTDR) system. Using the NLFM interrogation pulse, the side-lobe suppression ratio (SLSR) and signal-to-noise ratio (SNR) of the demodulated traces are improved, and phase signal detection with less than 3m spatial resolution is achieved over 50 km sensing range. By modulating the NLFM laser pulse intervals, we realize the ARS and the uniform sampling alternately for every sensing point of the long interrogation fiber, and therefore the frequency domain aliasing is avoided. We test the proposed system by detected a 20 kHz harmonic signal, and this signal is well identified and reconstructed over 50 km sensing range.
In this paper, we proposed a new method to generate OAM beams based on modal interference principle in two mode fiber. Micro-waveguides were specially designed to excite and combine the high order mode for realizing the two-mode interference in the two-mode fiber. Advanced femtosecond laser processing technology was employed to inscribed the micro-waveguides at the two ends of the two-mode fiber. After optimizing the waveguide size, an in-line interferometer was successfully realized with a low insertion loss of 1.3 dB and a contrast of higher than 22 dB. Finally, the experimental results demonstrated that the left- and right-handed circularly polarized fundamental mode was successfully converted into the ±1-order OAM beams.
In this paper, an egg-shaped microbubble is proposed and analyzed firstly, which is fabricated by the pressure-assisted arc discharge technique. By tailoring the arc parameters and the position of glass tube during the fabrication process, the thinnest wall of the fabricated microbubble could reach to the level of 873nm. Then, the fiber Fabry–Perot interference technique is used to analyze the deformation of microbubble that under different filling pressures. It is found that the endface of micro-bubble occurs compression when the inner pressure increasing from 4Kpa to 1400KPa. And the pressure sensitivity of such egg-shaped microbubble sample is14.3pm/Kpa. Results of this study could be good reference for developing new pressure sensors, etc.
We demonstrated an ultrasensitive temperature sensor based on a unique fiber Fabry-Perot interferometer (FPI). The FPI was created by means of splicing a mercury-filled silica tube with a single-mode fiber (SMF). The FPI had an air cavity, which was formed by the end face of the SMF and that of the mercury column. Experimental results showed that the FPI had an ultrahigh temperature-sensitivity of up to -41 nm/°C, which was about one order of magnitude higher than those of the reported FPI-based fiber tip sensors. Such a FPI temperature sensor is expected to have potential applications for highly-sensitive ambient temperature sensing.
We investigated experimentally liquid crystal (LC) filled photonic crystal fiber’s temperature responses at different temperature ranging from 30 to 80°C. Experimental evidences presented that the LC’s clearing point temperature was 58°C, which is consistent with the theoretical given value. The bandgap transmission was found to have opposite temperature responses lower and higher than the LC’s clearing point temperature owing to its phase transition property. A high bandgap tuning sensitivity of 105 nm/°C was achieved around LC’s clearing point temperature.
We proposed and experimentally demonstrated four kinds of high-sensitivity gas pressure sensors based on in-fiber devices, including a sub-micron silica diaphragm-based fiber-tip, a polymer-capped Fabry-Perot interferometer, an inflated long period fiber grating and a twin core fiber-based Mach-Zehnder interferometer, which have sensitivities of 1036, 1130, 1680, 9600 pm/MPa, respectively.
An improved arc discharge technique was demonstrated to inscribe high-quality LPFGs with a resonant attenuation of - 28 dB and an insertion loss of 0.2 dB by use of a commercial fusion splicer. Such a technique avoids the influence of the mass which is prerequisite for traditional technique. Moreover, no physical deformation was observed on the LPFG surface. Compared with more than 86 grating periods required by traditional arc discharge technique, only 27 grating periods were required to inscribe a compact LPFG by our improved arc discharge technique.
We demonstrated a high-sensitivity strain sensor based on an in-line Fabry-Perot interferometer with an air cavity whose was created by splicing together two sections of standard single mode fibers. The sensitivity of this strain sensor was enhanced to 6.02 pm/με by improving the cavity length of the Fabry-Perot interferometer by means of repeating arc discharges for reshaping the air cavity. Moreover, such a strain sensor has a very low temperature sensitivity of 1.06 pm/°C, which reduces the cross-sensitivity problem between tensile strain and temperature.
A compact and high sensitivity curvature sensor based on twin core fiber (TCF) coupler is proposed and demonstrated
experimentally in the curvature range from 0 to 9.30 m-<sup>1</sup>. The TCF coupler is formed by splicing a section of 86.85 mm
TCF between two single mode fibers (SMFs). A nonlinear blue-shift of the wavelength was observed when increasing
the curvature. In the range from 3 m<sup>-1</sup> to 9.30 m-<sup>1</sup>, the minimum and maximum sensitivity are - 2.5 nm/m<sup>-1</sup> and - 14.7
nm/m<sup>-1</sup>, respectively. The dynamic range can be tailored by proper selection of the TCF length and the resonance dips.
A novel side-leakage PCF with high birefringence is designed and fabricated by introducing a linear side-leakage region
into both sides of the elliptical Ge-doped core. A curvature sensor using the homemade side-leakage PCF based Sagnac
interferometer is proposed and demonstrated experimentally. Experimental result shows that a high bending sensitivity
of 10.798nm/m<sup>-1</sup> can be achieved when the linear side-leakage region is in the vertical with the direction of curvature.
With the measuring matrix obtained from sensor's sensitivity matrix by measuring the wavelength shifts of two dip in
the transmission spectrum, this sensor can also realize simultaneous measurement of curvature and temperature.