Hui Ding

All-fiber magnetic-field sensor based on microfiber knot resonator and magnetic fluid

All-fiber magnetic-field sensor based on a device consisting of a microfiber knot resonator and magnetic fluid is proposed for the first time in this Letter. Sensor principles and package technology are introduced in detail. Experimental results show that the resonance wavelength of the proposed sensor regularly varies with changes to the applied magnetic field. When the magnetic field is increased to 600xa0Oe, the wavelength shift reaches nearly 100xa0pm. Moreover, the sensor responding to the 50xa0Hz alternating magnetic field is also experimentally investigated, and a minimal detectable magnetic-field strength of 10xa0Oe is successfully achieved.

A Stable Evanescent Field-Based Microfiber Knot Resonator Refractive Index Sensor

An evanescent field-based microfiber knot resonator (MKR) refractive index sensor with long-term stability was proposed in this letter. To protect the microfiber from the mechanical and optical degradation and at the same time preserve the large evanescent waves, a dip-coating technique was presented to coat the MKR and a thin coating in the submicrometer thickness range was experimentally fabricated. The temporal stability of the coated MKR and its sensing properties in refractive index were, respectively, investigated. The results indicated that the coated MKR did not degrade over a long time, and the minimal detectable refractive index of (2 times 10 ^{-4}) was successfully achieved.

Temperature Insensitive Magnetic Field Sensor Based on Ferrofluid Clad Microfiber Resonator

In this letter, an inherently temperature insensitive magnetic field sensor based on microfiber knot resonator with ferrofluid as cladding was theoretically and experimentally demonstrated. It was theoretically shown that the thermal property of the proposed sensor could be effectively suppressed by selecting the optimal microfiber diameter. On the basis of that, a sensor with its microfiber diameter of 2.92 μm was experimentally fabricated and its temperature sensitivity was demonstrated to be as low as 0.17 pm/°C with the temperature ranging from 20 °C to 80 °C. The results take a step forward toward the development of thermal stable devices based on the microfiber resonators.

Investigation of evanescent coupling between tapered fiber and a multimode slab waveguide

A tapered fiber-slab waveguide coupler (TFSC) is proposed in this paper. Both the numerical analysis based on the beam propagation method and experiments are used for investigating the dependencies of TFSC transmission features on their geometric parameters. From the simulations and experimental results, the rules for fabricating a TFSC with low transmission loss and sharp resonant spectra by optimizing the configuration parameters are presented. The conclusions derived from our work may provide helpful references for optimally designing and fabricating TFSC-based devices, such as sensors, wavelength filters, and intensity modulators.

Magnetic Field Sensor Based on Microfiber Sagnac Loop Interferometer and Ferrofluid

We demonstrate a novel compact optical magnetic field sensor composed of a single-mode microfiber sagnac loop interferometer (SMSLI) and ferrofluid (FF). The refractive index of FF cladding in the twist area of SMSLI is changed with the externally applied magnetic field, which makes the dip-wavelength of the SMSLI transmission spectra shift. The experimental results show that the transmission spectrum of the proposed sensor shifts regularly with the change of externally applied magnetic field intensity. When the magnetic field intensity increased from 0 to 600 Oe, the dip-wavelength of transmission spectrum shifted nearly 200 pm. In addition, a minimal detectable magnetic field strength of the sensor responding to the 50-Hz alternating magnetic field was demonstrated to be ~3 Oe experimentally.

INVESTIGATION OF THE THERMAL PROPERTIES OF OPTICAL MICROFIBER KNOT RESONATORS

The dependence of optical microfiber knot resonators (MKRs) thermal properties on the geometry parameters is theoretically and experimentally investigated in this article. According to the simulated and experimental results, the thermal properties of MKRs are synthetically determined by the microfiber diameter, refractive index, and thermo-optic coefficients of the external medium. Also, the rules for reinforcing or suppressing the thermal effects of MKRs and MKR-based devices by selecting matched configuration parameters are presented. A good agreement between the simulated and experimental results is obtained. The conclusions derived from our work would provide helpful guidelines in designing MKR-based devices with desired thermal properties to satisfy different requirements in applications.

AN ALL-FIBER GAS SENSING SYSTEM USING HOLLOW-CORE PHOTONIC BANDGAP FIBER AS GAS CELL

An all-fiber compact gas sensing system using a hollow-core photonic bandgap fiber (HC-PBF) as a gas cell is proposed in this paper. Compared with the present reported microstructured optical-fiber gas cells, the HC-PBF gas cell proposed here has relatively lower transmission loss and much simpler construction. The total transmission loss through the HC-PBF gas cell is demonstrated experimentally to be as low as 1.5 dB and the time taken for gas to get into the 90-cm-cell, under the free diffusion condition, is approximately 11 min. Combining the HC-PBF gas cell with a tunable fiber laser, an all-fiber gas sensing system is developed. The properties of the proposed system are demonstrated experimentally by detection of carbon monoxide (CO) and acetylene (C2H2). Approximately linear relationships between the system responses and the concentrations of the detected gases are experimentally demonstrated. The minimal detectable concentration of CO of 300 ppm and C2H2 of 5 ppm are also achieved respectively by the experiments.

Demonstration of a refractometric sensor based on an optical micro-fiber three-beam interferometer

With diameter close to the wavelength of the guided light and high index contrast between the fiber and the surrounding, an optical micro-fiber shows a variety of interesting waveguiding properties, including widely tailorable optical confinement, strong evanescent fields and waveguide dispersion. Among various micro-fiber applications, optical sensing has been attracting increasing research interest due to its possibilities of realizing miniaturized fiber optic sensors with small footprint, high sensitivity, and low optical power consumption. Typical micro-fiber based sensing structures, including Michelson interferometer, Mach-Zenhder interferometer, Fabry-Perot interferometer, micro-fiber ring resonator, have been proposed. The sensitivity of these structures heavily related to the fraction of evanescent field outside micro-fiber. In this paper, we report the first theoretical and experimental study of a new type of refractometric sensor based on micro-fiber three-beam interferometer. Theoretical and experimental analysis reveals that the sensitivity is not only determined by the fraction of evanescent field outside the micro-fiber but also related to the values of interferometric arms. The sensitivity can be enhanced significantly when the effective lengths of the interferometric arms tends to be equal. We argue that this has great potential for increasing the sensitivity of refractive index detection.

A novel magnetic field sensor based on the combination use of microfiber knot resonator and magnetic fluid

In this paper, a novel all-fiber magnetic field sensor based on a device consisting of microfiber knot resonator (MKR) and magnetic fluid (MF) is proposed for the first time. MF is infused into a homemade sealed cell containing a partially embedded MKR in low-index polymer as sensing element. Experimental results show that the resonance wavelength of the proposed sensor regularly varies with changes of the applied magnetic field. When the magnetic field increases to 22mT, the wavelength shift reaches nearly 200pm.

Microfiber knot resonator based electric field sensor

ABSTRACT An optical fiber electric field sensor was constructed by coating a microfiber based knot resonator with propylene carbonate, a liquid electrooptic material. The Kerr electrooptic effect of propylene carbonate changed the refractive index of the liquid in the presence of an electric field and shifted the fringe pattern of the resonator. The electric field was demodulated by monitoring the fringe shift. The sensor was used to characterize sinusoidal electric fields with magnitudes from 200–4000u2009V/cm and a pulsed field with a 200u2009µs duration time. This work may provide practical applications for the characterization of electric fields.