Binbin Song

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.

Fiber-optic in-line magnetic field sensor based on the magnetic fluid and multimode interference effects

A compact magnetic field sensor has been proposed based on multimode interference effects. It consists of typical multimode interferometer (MMI) immersed into the magnetic fluid (MF) which is formed by a section of square no-core fiber (NCF) spliced between two single-mode fibers. The transmission spectral characteristics of this MMI have been analyzed, and the spectral magnetic response of the proposed sensor has been investigated by immersing the NCF into the MF environment. The transmission response of the interference maxima exhibits a sensitivity of −0.01939 dB/Oe in the relatively linear range. Due to its low cost and compactness, this sensor would find potential applications in the measurement of magnetic field.

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.

Laser-tuned whispering gallery modes in a solid-core microstructured optical fibre integrated with magnetic fluids

A laser-assisted tuning method of whispering gallery modes (WGMs) in a cylindrical microresonator based on magnetic-fluids-infiltrated microstructured optical fibres (MFIMOFs, where MF and MOF respectively refer to magnetic fluid and microstructured optical fibre) is proposed, experimentally demonstrated and theoretically analysed in detail. The MFIMOF is prepared by infiltrating the air-hole array of the MOF using capillary action effect. A fibre-coupling system is set up for the proposed MFIMOF-based microresonator to acquire an extinction ratio up to 25 dB and a Q-factor as large as 4.0 × 104. For the MF-infiltrated MOF, the light propagating in the fibre core region would rapidly spread out and would be absorbed by the MF-rod array cladding to induce significant thermal effect. This has been exploited to achieve a WGM resonance wavelength sensitivity of 0.034 nm/mW, which is ~20 times higher than it counterpart without MF infiltration. The wavelength response of the resonance dips exhibit linear power dependence, and owing to such desirable merits as ease of fabrication, high sensitivity and laser-assisted tunability, the proposed optical tuning approach of WGMs in the MFIMOF would find promising applications in the areas of optical filtering, sensing, and signal processing, as well as future all-optical networking systems.

Low temperature sensitive intensity-interrogated magnetic field sensor based on modal interference in thin-core fiber and magnetic fluid

A fiber-optic magnetic field sensor based on the thin-core modal interference and magnetic fluid (MF) has been proposed and experimentally demonstrated. The magnetic field sensor is spliced with a thin-core fiber (TCF) between two conventional single-mode fibers immersed into the MF. The transmission spectra of the proposed sensor under different magnetic field intensities have been measured and theoretically analyzed. The results show that the magnetic field sensitivity reaches up to −0.058 dB/Oe with the linear range from 75 Oe to 300 Oe. Due to the small thermal expansion of the TCF material, the attenuation wavelength and the transmission power remain almost unchanged as the temperature varies. The proposed magnetic field sensor has several advantages such as intensity-interrogation, low temperature sensitivity, low cost, compact size, and ease of fabrication. And particularly, the temperature cross-sensitivity could be effectively resolved, which makes it a promising candidate for strict temperature environments. Therefore, it would find potential applications in the magnetic field measurement.

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.

Simultaneous measurement of temperature and magnetic field based on a long period grating concatenated with multimode fiber

A dual-parameter measurement scheme based on a long-period fiber grating (LPFG) concatenated with a multimode fiber (MMF) has been proposed and experimentally demonstrated for simultaneous measurement of magnetic field and temperature. Splicing the LPFG with the etched MMF enables the coupling between the core modes and different cladding modes of the LPFG as well as the interferences between higher-order modes in the MMF. Due to different transmission mechanisms of the LPFG and mode interference, the proposed sensor shows transmission dip wavelength sensitivities of 0.02878 nm/Oe and −0.04048 nm/°C for multi-mode interference (MMI) and −0.0024 nm/Oe and 0.03929 nm/°C for the LPFG, respectively. By monitoring the opposite behaviors of resonance wavelength shift corresponding to the LPFG and MMI, the magnetic field and environmental temperature can be simultaneously measured. The spectral characteristics of the proposed sensor that could be tuned through control of both environmental temperature and applie...

Dual-Direction Magnetic Field Sensor Based on Core-Offset Microfiber and Ferrofluid

A fiber-optical sensor is proposed for dual-direction magnetic field measurement by cascading an optical microfiber with a core-offset section. Due to the relative direction difference between magnetic field and fiber axis, the refractive index of the magnetic fluid could be tuned accordingly. The transmission spectral characteristics change with the variation of applied magnetic field. Experimental results show that different relative directions turn out different linear responses. When the magnetic field is applied perpendicular or parallel to the fiber axis, the magnetic field sensitivities are -0.02534 and 0.01111 dB/Oe, respectively. The proposed sensor has several advantages, including low cost, ease of fabrication, compact structure, and cost-effective intensity interrogation. It is promising in the measurement of magnetic field vector, as well as multiparameter sensing.

Label-free in-situ real-time DNA hybridization kinetics detection employing microfiber-assisted Mach-Zehnder interferometer

A label-free DNA biosensor based on microfiber-assisted Mach-Zehnder interferometer (MAMZI) for in-situ real-time DNA hybridization kinetics detection has been proposed and experimentally demonstrated. A microfiber of hundreds of microns in length is fabricated by tapering a segment of standard single-mode fiber (SMF) to construct the U-shaped microcavity between the lead-in and lead-out SMFs. Thanks to the mode field mismatching between the SMF and microfiber, the incident guided mode light would separate into two beams that respectively propagate in the air microcavity and the microfiber. Consequently, interference between different light modes would occur at the joint between the microfiber and the lead-out SMF. Experimental results indicate that owing to the participation of opening cavity modes in the modal interference process, the interferometric spectrum of our proposed microcavity sensor is highly sensitive to the variation of environmental refractive index (RI), especially for the RI range around 1.34 which is useful for most biological applications. The microfiber functionalization is achieved by stepwise modifying the microfiber with monolayer Poly-l-lysine (PLL) and single-stranded DNA (ssDNA) probes to produce the sensitive surface that could uniquely attach specific target ssDNAs. The fiber surface functionalization as well as DNA hybridization processes have been experimentally investigated for different target ssDNA solutions in real time. The interferometric transmission spectrum shows large wavelength shift for different biological phases, and a detection limit conservatively down to 0.0001pmol/μL has been acquired by employing the U-shaped microcavity of 176.88μm in length. Our proposed DNA biosensor possesses several advantages such as compact size, ease of fabrication, and strong response for DNA hybridization, which make it a promising candidate for potential applications in such rapidly expanding areas as medical diagnosis, cancer screenings, medicine examination and environmental engineering, etc.