Donglin Yan

Highly sensitive twist sensor employing Sagnac interferometer based on PM-elliptical core fibers

A highly sensitive optical fiber twist sensor has been proposed by employing a Sagnac interferometer based on polarization-maintaining elliptical core fibers (PM-ECFs). The twist effects have been theoretically analyzed and experimentally demonstrated. Based on the photoelastic effect, the resonance wavelength linearly shifts with the increment of twist and the wavelength shift is also dependent on the torsion direction. The maximum torsion sensitivities reach 18.60nm/(rad/m) for clockwise (CW) torsion direction and 15.83nm/(rad/m) for anticlockwise (ACW) torsion direction, respectively. To eliminate the temperature cross-sensitivity effect, a sensor matrix for simultaneous measurement of twist and temperature has also been obtained. Moreover, theoretical and experimental investigations indicate that by optimizing the refractive index difference between the core and cladding, core ellipticity and cladding diameter, the twist sensitivity could be further improved.

Loss-Based Magnetic Field Sensor Employing Hollow Core Fiber and Magnetic Fluid

An inline optical fiber magnetic field sensor based on hollow core fiber (HCF) wall integrated with magnetic fluid tuned by magnetic field was proposed by sandwiching a length of HCF between two single mode fibers with offset joints. Intermodal interference is present in the HCF wall, mode propagation, as well as mode field distribution within the HCF wall have been simulated, and the contrast ratio of the interference fringes in response to the variation of the applied magnetic field has been theoretically analyzed and experimentally observed. The maximum sensing sensitivity of -0.02173 dB/Oe within the linear magnetic intensity range from 150 to 300 Oe has been achieved.

Liquid-filled photonic-crystal-fiber-based multimodal interferometer for simultaneous measurement of temperature and force

In this paper, a multimodal interferometer based on the liquid-filled photonic crystal fiber (PCF) has been proposed and experimentally demonstrated for simultaneous measurement of temperature and force. Experimental results show that different spectral minima have distinctive sensitivities to the temperature and force. The proposed interferometer shows the temperature sensitivities of -9.214 nm/°C, -24.757 nm/°C, and -12.543/°C and the force sensitivities of 0 nm/N, 4.978 nm/N, and 0 nm/N, respectively, for the three selected spectral minima. The sensing matrices are thus established and simultaneous measurement of temperature and force has been experimentally demonstrated. The proposed liquid-filled PCF-based multimodal interferometer would find potential applications in multiple-parameter sensing owing to its high sensitivity, compactness, ease of fabrication, and low cost.

Magnetically controllable wavelength-division-multiplexing fiber coupler

In this paper, a magnetically controllable wavelength-division-multiplexing (WDM) fiber coupler has been proposed and experimentally demonstrated. A theoretical model has been established to analyze the influences of the weak as well as strong couplings to the wavelength tunability of this coupler. Experimental results show that the operation wavelength tunability of the proposed WDM coupler could be fulfilled for an applied magnetic field intensity range of 0 Oe to 500 Oe, and particularly it possesses high operation performances within the magnetic field intensity ranging from 25 Oe to 125 Oe when additional transmission loss and isolation are both considered. Within this range, the two selected channels show the wavelength tunability of 0.05 nm/Oe and 0.0744 nm/Oe, respectively, and the isolation between the two branches is higher than 24.089 dB. Owing to its high isolation, good splitting ratio stability, and high wavelength tunability, the proposed controllable WDM coupler is anticipated to find potential applications in such fields as fiber laser, fiber sensing and fiber-optic communications. Moreover, the fiber coupler integrated with the magnetic fluid would be valuable for the design of magnetically controllable mode-division-multiplexing devices.

Laser-Induced Thermal Effect for Tunable Filter Employing Ferrofluid and Fiber Taper Coupler

In this letter, an all-optically tunable filter based on laser-induced thermal effect has been proposed by employing a fiber taper coupler immersed in the magnetic fluids. Tunable spectral characteristics of the optically controlled fiber filter have been theoretically analyzed and experimentally investigated. Experimental results indicate that as the pump power varies from 0 to 216.1 mW, and the proposed filter shows a large wavelength shift of 58.2 nm. Moreover, it exhibits a nonlinear spectral shift behavior in response to the applied pump light intensity with good spectral repeatability. With such desirable advantages as compactness, ease of fabrication, and high spectral tunability, our proposed all-optically tunable filter would be a promising candidate for fiber laser and amplification, fiber-optic sensing, and optical fiber communications applications.

Tuning of whispering gallery modes in a magnetic-fluid-infiltrated silica capillary based on lateral pumping scheme

An all-optical tuning method of whispering gallery modes (WGMs) in a silica capillary based on lateral pumping scheme has been proposed and experimentally demonstrated by exploiting the photo-thermal effect of magnetic fluids (MFs) infiltrated into a micro-capillary. The WGMs are coupled from a tapered fiber perpendicular to the silica capillary. Experimental results indicate that the microresonator integrated with MFs shows a Q-factor of 1.2867 × 104 and its optical tunability reaches 0.0382 nm/(mW mm−2) under 532 nm laser illumination. Compared with the one infiltrated with pure water, our proposed capillary shows an optical tuning sensitivity increase of about 4270 times. The experimental results on the WGM resonance wavelength sensitivity for the capillaries with different diameters are in accordance with our simulation outcome using radially dependent heat conducting equation. Further experimental studies indicate that the proposed microresonator possesses a good spectral reversibility. Moreover, the dynamic response experiment shows that the rise and fall time of this microresonator is about 231 ms and 255 ms, respectively. The above intriguing features make the proposed WGM resonator a promising candidate for potential applications in optical filtering, microfluidic sensing, and signal processing as well as reconfigurable devices for future all-optical networks.

Ultrahigh sensitive twist sensor employing Sagnac interferometer based on PM-elliptical core fibers

An ultrasensitive optical fiber twist sensor is proposed by employing a Sagnac interferometer based on polarization-maintaining elliptical core fibers (PM-ECFs). The twist effects are theoretically analyzed and experimentally demonstrated. Based on the photoelastic effect, the wavelength shift in response to twist rate turns out linear tendency and is torsion-direction-dependent. The maximum torsion sensitivity reaches 18.59593nm/(rad/m) (or 0.67582nm/°) for clockwise (CW) torsion direction and 15.83073nm/(rad/m) for anticlockwise (ACW) torsion direction, respectively. Furthermore, it is further improved up to 1.675 nm/° by rotating two ends of PM-ECF simultaneously. The prominent advantage of ultrasensitivity keep it meritorious in the applications of spaceflight and constructional engineering.