RESUMEN
An in-line Mach-Zehnder interferometer based on a multimode-fiber-assisted tapered open-cavity (TOC) is proposed. Light field distributions of the TOC were investigated using beam propagation method with different offsets and diameters of the taper waist. Bias and uniform taper (BT and UT)-based structures were fabricated and compared using one- and two-step arc-discharge methods, and comprehensive tests were then conducted considering axial-strain. The experimental results show that the UT structure has more than -45 pm/µÉ linear wavelength shift with the applied axial-strain. Owing to its compact size and low cost, the proposed sensor is promising for axial-strain-related high-precision engineering applications.
RESUMEN
The polarization-maintaining fiber-based Sagnac loop interferometer (PSLI) is frequently applied in directional torsion measurement, but may suffer from a large temperature cross talk. In this study, a novel method was proposed for fabrication of side-tapered PSLI by a two-step arc-discharge technique at the splicing point. The energy distribution of the taper region was characterized, and comprehensive tests were performed in terms of torsion and temperature. The experimental results showed that, through bias twisting, the measuring areas were effectively gapped and highly sensitive torsion and temperature responses were gained simultaneously. With a small wavelength shift, the torsion sensitivity reached 13.54 dB/rad in the range from -30 to 30 rad/m. Moreover, the temperature sensitivity was found to be -1.579nm/∘C, with a near-zero intensity fluctuation. Therefore, the sensor fabricated herein successfully achieves simultaneous measurement of directional torsion and temperature with high sensitivity and ultralow cross talk. The proposed scheme has the merits of practicality, low cost, and ease of operation, and is very promising for multiparameter engineering monitoring.
RESUMEN
In this paper, we report a novel in-fiber Mach-Zehnder interferometer based directional torsion sensor, in which a section of two-mode fiber is sandwiched between two single mode fibers by over core-offset splicing technique. The variety of fringe visibility demonstrates the strong dependence on offset and fiber length. For the first time the near zero visibility at 0° rotating state is obtained by fine offset-modulation. The experimental results show that, with 0° turning point, the counter-clockwise to the clockwise direction can be recognized by the reversal from peak to dip of fringes. Moreover, a competitive sensitivity of 21.485 dB/(rad/cm) is gained with high linearity and low-temperature crosstalk in the range from -40 rad/m to 40 rad/m. Without any pre-twisting, our fiber torsion sensor is small size, ease of fabrication, cost efficiency and very potential in the applications of industrial and artificial intelligence.
RESUMEN
In this paper, an in-line Mach-Zehnder interferometer embedded in a fiber Bragg grating (FBG) is fabricated by a tiny offset-core splicing technique and inserted into a fiber ring laser to effectively improve the detection limit and discrimination of sensing. Through fine power adjustment, the stable operation of dual-wavelength lasing is completed in a single FBG for the first time to our knowledge, and simultaneous measurement of refractive index (RI) and ambient temperature is achieved with high discrimination due to the RI immunity of the FBG. The experimental results indicate that the sensitivities of RI and temperature are -30.57 nm/RIU and 131.1 pm/°C, respectively, with very low intensity drift. Furthermore, the over 20 times improvement of the RI detection limit is obtained owing to the large extinction ratio (>30 dB) and small linewidth (≤0.13 nm).
RESUMEN
A novel in-fiber Mach-Zehnder interferometer based on cascaded up-down-taper (UDT) structure is proposed by sandwiching a piece of polarization maintaining fiber between two single-mode fibers (SMF) and by utilizing over-fusion splicing method. The dual up tapers respectively act as fiber splitter/combiner, the down taper acts as an optical attenuator. The structure parameters are analyzed and optimized. A larger interference fringe extinction ratio ~15 dB is obtained to achieve refractive index (RI) sensing based on intensity demodulation. The experimental results show that the RI sensitivity is -310.40 dB/RIU with the linearity is improved to 0.99 in the range of 1.3164-1.3444. The corresponding resolution can reach 3.22 × 10-5 RIU, which is 6.8 times higher than wavelength demodulation. The cross sensitivity which caused by temperature fluctuation is less than 1.4 × 10-4.
RESUMEN
In this paper, a novel in-line modal interferometer for refractive index (RI) sensing is proposed and experimentally fabricated by cascading single-taper and multimode-double- cladding-multimode (MDM) fiber structure. Owing to evanescent field in taper area, the ultra-sensitive and linear intensity-responses to the varied surrounding RI are gained in both single- and double-pass structures. Moreover, the crosstalk from temperature can be effectively discriminated and compensated by means of the RI-free nature of MDM. The experimental results show that the RI sensitivities in single- and double-pass structures, respectively, reach 516.02 and 965.46 dB/RIU (RIU: refractive index unit), both with the slight wavelength shift (~0.2 nm). The temperature responses with respect to wavelength and intensity are 68.9 pm°C-1/0.103 dB°C-1 (single-pass structure) and 103 pm°C-1/0.082 dB·°C-1 (double-pass structure). So the calculated cross-sensitivity of intensity is constrained within 8.49 × 10-5 RIU/°C. In addition, our sensor presents high measurement-stability (~0.99) and low repeatability error (<4.8‱). On account of the ~620 µm size of taper, this compact sensor is cost-efficient, easy to fabricate, and very promising for the applications of biochemistry and biomedicine.
RESUMEN
In this paper, a comprehensive passive torsion measurement is performed firstly in a 40-cm-long polarization maintaining fiber-based Sagnac interferometer (PMF-SI), and the non-linear torsion response is found and investigated. Then, a fiber laser torsion sensor (FLTS) with a dual-ring-cavity structure is proposed and experimentally demonstrated, in which the PMF-SI is utilized as the optical filter as well as the sensing unit. In particular, the highly sensitive linear range is adjusted through fine phase modulation, and owing to the flat-top feature of fringes, an ~83.6% sensitivity difference is effectively compressed by the generated lasing. The experimental results show that, without any pre-twisting, the ultra-wide linear response from -175 to 175 rad/m is gained, and the torsion sensitivities are 2.46 and 1.55 nm/rad with high linearity (>0.99) in the clockwise and anti-clockwise directions, respectively. Additionally, a high extinction ratio (>42 dB) and small line-width (~0.14 nm) are obtained in the proposed FLTS, and the corresponding detection limit reaches 0.015 rad/m.
RESUMEN
The principle and the characteristics of the bias-scanning based tunable localized surface plasmon resonance (LSPR) sensors for environmental refractive index have been theoretically and numerically investigated in detail. The sensors exhibit linear negative-shifts in the scattering-bias spectral position when the refractive index of the surrounding medium increases. By bias-scanning, a single-wavelength measurement for sensing the environmental refractive index can be realized effectively. In addition, we demonstrate that the sensing performance of the designed sensor can be adjusted by nano-scale manipulations of metal nanoparticles' sizes and shapes. The proposed devices may pave the way for the development of electrochemical sensors that can convert spectrum scanning into bias scanning.
RESUMEN
A novel intensity demodulated refractive index (RI) sensor is theoretically and experimentally demonstrated based on the front-tapered single-mode-multimode-single-mode (FT-SMS) fiber structure. The front taper is fabricated in a section of multimode fiber by flame-heated drawing technique. The intensity feature in the taper area is analyzed through the beam propagation method and the comprehensive tests are then conducted in terms of RI and temperature. The experimental results show that, in FT-SMS, the relative sensitivity is -342.815 dB/RIU in the range of 1.33~1.37. The corresponding resolution reaches 2.92 × 10-5 RIU, which is more than four times higher than that in wavelength demodulation. The temperature sensitivity is 0.307 dB/°C and the measurement error from cross-sensitivity is less than 2 × 10-4. In addition, fabricated RI sensor presents high stability in terms of wavelength (±0.045 nm) and intensity (±0.386 dB) within 2 h of continuous operation.
RESUMEN
We report the observation of hybrid optoelectronic bistability in a fiber Bragg grating (FBG) by use of an electro-optically tuned cw fiber laser in which another wavelength-matched FBG is employed to constitute a tunable resonant cavity. The potential application of such a device as a fiber-optic sensor is also discussed.