Jixuan Wu

Magnetic field tunability of optical microfiber taper integrated with ferrofluid.

Optical microfiber taper has unique propagation properties, which provides versatile waveguide structure to design the tunable photonic devices. In this paper, the S-tapered microfiber is fabricated by using simple fusion spicing. The spectral characteristics of microfiber taper integrated with ferrofluid under different magnetic-field intensities have been theoretically analyzed and experimentally demonstrated. The spectrum are both found to become highly magnetic-field-dependent. The results indicate the transmission and wavelength of the dips are adjustable by changing magnetic field intensity. The response of this device to the magnetic field intensity exhibits a Langvin function. Moreover, there is a linear relationship between the transmission loss and magnetic field intensity for a magnetic field intensity range of 25 to 200Oe, and the sensitivities as high as 0.13056dB/Oe and 0.056nm/Oe have been achieved, respectively. This suggests a potential application of this device as a tunable all-in-fiber photonic device, such as magneto-optic modulator, filter, and sensing element.

Multi-mode interferometer-based twist sensor with low temperature sensitivity employing square coreless fibers

An all-fiber twist sensor based on multimode interferometer (MMI) has been proposed and fabricated by splicing both ends of a section of square no-core fiber (NCF) with a single mode fiber. We have investigated the transmission spectral characteristics of the square fiber under different applied twisting angles. Within a torsion angle range of -360°~360°, the wavelength and transmission sensitivities are 1.28615 nm/(rad × m(-1)) and 0.11863%/ (rad × m(-1)), respectively. Moreover due to the trivial thermal expansion coefficient of pure silica fiber, the proposed twist sensor has a low temperature sensitivity, which is desirable to solve the temperature cross sensitivity.

Two-Dimensional Magnetic Field Vector Sensor Based on Tilted Fiber Bragg Grating and Magnetic Fluid

A two-dimensional (2D) magnetic field vector sensor is proposed and experimentally demonstrated. A theoretical model is established to analyze the physical mechanism in detail. The transmission response of the sensor depends on the angle (θ) between the magnetic orientation and the polarization direction of tilted fiber Bragg grating (TFBG) and the intensity of magnetic field (H) when keeping θ constant and exhibits a sinuous behavior when keeping H constant. When -θ_c <; θ <; θ_c and π - θ_c <; θ <; π + θ_c, the transmission increases with the increment of H, while it decreases when θ_c <; θ <; π - θ_c or π + θ_c <; θ <; 2π - θ_c. The resonance peak in the transmission spectrum does not shift with the change of H within the experimental error. The experimental results are in good agreement with our theoretical analysis. 2D magnetic field vector sensor could be achieved by employing rotators to change the orientation of the sensor head. Our proposed TFBG-based sensing system would find potential applications in magnetic field vector sensing and refractive index sensing for polarized liquids.

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.

Magnetic-field sensor based on core-offset tapered optical fiber and magnetic fluid

A magnetic field sensor based on an asymmetrical fiber modal Mach–Zehnder interferometer (MMZI) is achieved by cascading tapered fiber with the core-offset structure. The MMZI is sealed by the magnetic fluid and its spectral dependence on magnetic field has been investigated. The results show that the transmission variations of the two dips are about 8 dB and 10 dB for a magnetic intensity range from 0 Oe to 400 Oe, respectively. The highest magnetic sensitivity reaches 0.03407 dB Oe−1. The proposed sensor based on the intensity demodulation is cost-effective and robust; therefore, the device is beneficial to the magnetic field sensing applications and other magneto-optical tunable photonics devices.

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.

Low-temperature cross-talk magnetic-field sensor based on tapered all-solid waveguide-array fiber and magnetic fluids

A compact fiber-optic magnetic-field sensor based on tapered all-solid waveguide-array fiber (WAF) and magnetic fluid (MF) has been proposed and experimentally demonstrated. The tapered all-solid WAF is fabricated by using a fusion splicer, and the sensor is formed by immersing the tapered all-solid WAF into the MF. The transmission spectra have been measured and analyzed under different magnetic-field intensities. Experimental results show that the acquired magnetic-field sensitivity is 44.57 pm/Oe for a linear magnetic-field intensity range from 50 to 200 Oe. All-solid WAF has very similar thermal expansion coefficient for high- and low-refractive-index glasses, so mode profile is not affected by thermal drifts. Also, magnetically induced refractive-index changes into the ferrofluid are of the order of ∼5×10(-2), while the corresponding thermally induced refractive-index changes into the ferrofluid are expected to be lower. The temperature response has also been detected, and the temperature-induced wavelength shift perturbation is less than 0.3 nm from temperature of 26.9°C-44°C. The proposed magnetic-field sensor has such advantages as low temperature sensitivity, simple structure, and ease of fabrication. It also indicates that the magnetic-field sensor based on tapered all-solid WAF and MF is helpful to reduce temperature cross-sensitivity for the measurement of magnetic field.

Magnetic Field Tunability of Square Tapered No-Core Fibers Based on Magnetic Fluid

A magnetic-field-tuned photonics device based on magnetic fluid (MF) and a square tapered no-core fiber (NCF) sandwiched between two single-mode fibers (SMFs) has been demonstrated experimentally and theoretically. The enhanced evanescent field effect in the NCF is achieved by tapering the square NCF utilizing a fusion splicer. The spectral dependence of the proposed device on the applied magnetic-field intensity has been investigated. The results indicate that the multimode interference spectrum exhibits a blue-shift with the increment of the magnetic-field intensity. A maximal sensitivity of -18.7 pm/Oe is obtained for a magnetic field strength ranging from 25 to 450 Oe. The proposed tunable device has several advantages, including low cost, ease of fabrication, simple and compact structure, and high sensitivity. Therefore, the magnetic-field-tuned square tapered NCF is expected to find potential applications in the fields of optical fiber sensors, as well as fiber communications.

Temperature-insensitive optical fiber refractometer based on multimode interference in two cascaded no-core square fibers.

A temperature-insensitive optical fiber refractometer, based on multimode interference in no-core square fibers, has been proposed and experimentally demonstrated. The refractometer is formed by a single-mode fiber sandwiched between two segments of no-core square fibers through cleaving and fusion splicing. The transmission spectra characteristic of refractive index (RI) and environmental temperature have been investigated. Experimental results show that a transmission dip exhibits a redshift as large as about 25 nm when the ambient RI increases from 1.3424 to 1.4334. Within the RI range of 1.4033 to 1.4334, the RI sensitivity reaches 474.8189  nm/RIU. A temperature sensitivity of 0.00639  nm/°C is experimentally acquired between 20°C and 85°C, showing a low temperature cross-sensitivity of about 1.35×10⁻⁵  RIU/°C. The proposed refractometer has several advantages, such as low cost, simple structure, and compact size. Therefore, it is also expected to be employed in chemical and multi-parameter sensing applications.

Magnetic field tunability of square tapered no-core fibers

A magnetic-field-tuned photonics device based on magnetic fluid (MF) and a square tapered no-core fiber (NCF) sandwiched between two single-mode fibers (SMFs) has been proposed. The enhanced evanescent field effect in the NCF is achieved by tapering the square NCF utilizing a fusion splicer. The spectral dependence of the proposed device on the applied magnetic-field intensity has been investigated. The results indicate that a maximal sensitivity of -18.7pm/Oe is obtained for a magnetic field strength ranging from 25Oe to 450Oe. The proposed tunable device has several advantages, including low cost, ease of fabrication, compact structure, and high sensitivity.