Ri-Qing Lv

Magnetic Fluid-Filled Optical Fiber Fabry–Pérot Sensor for Magnetic Field Measurement

Magnetic fluid is a new type of optical functional material, which has interesting optical characteristics under an external magnetic field. In this letter, the magneto-optical characteristic of the magnetic fluid was adopted to form a novel fiber-optic magnetic field sensor. The sensor probe was composed of an extrinsic fiber Fabry-Pérot interferometer and magnetic fluid. The refractive index of the magnetic fluid would be changed with the increase of magnetic field. Preliminary experiment was carried out to verify the feasibility of the sensor. The magnetic field measurement sensitivity was 0.0431 nm/Gs in the experiment. The measurement resolution was better than 0.5 Gs at the measurement range from 0 to 400 Gs. The sensor has the advantages of simple structure, compact size, and easy fabrication.

Tunable Characteristics and Mechanism Analysis of the Magnetic Fluid Refractive Index With Applied Magnetic Field

The tunable refractive index of the magnetic fluid (MF) is a unique optical property, which has attracted a lot of research interest in recent years. In this paper, a method based on the Fresnel reflection at the fiber end face is presented. Experimental measurements are carried out to investigate the magnetic field (intensity and direction) and temperature-dependent refractive index of the MF. For a given concentration, with the increase of the magnetic field intensity, the nMF increases gradually when H//Light, while decreases when H⊥Light. The effect of temperature on nMF is relatively insignificant with the sensitivity of -8 × 10-5/°C. In addition, the mechanism is analyzed from the point of the microstructure by the Monte Carlo method.

Magnetic Field Sensor Based on Photonic Crystal Fiber Taper Coated With Ferrofluid

A novel and compact magnetic field sensor based on a tapered photonic crystal fiber (PCF) coated with ferrofluid is proposed. It consists of a section of tapered PCF, which is spliced between two single-mode fibers with a waist diameter of 24 μm. The ferrofluid is filled in the capillary to coat the PCF taper. Experimentally, the refractive index (RI) of the ferrofluid increased under increasing magnetic field intensity (H) with a sensitivity of 4 × 10-5 RIU/Gs and the RI sensitivity in the evanescent held is 401 nm/RIU. Therefore, the interference spectrum is shifted as the change of H ranged from 100 to 600 Gs with a sensitivity of 16.04 pm/Gs and resolution of 0.62 Gs. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference beyond what conventional magnetic field sensors can offer.

Fiber Optic Fabry-Perot Magnetic Field Sensor With Temperature Compensation Using a Fiber Bragg Grating

Based on the characteristic of magnetic-controlled refractive index, magnetic fluid was used as a sensitive medium in fiber optic Fabry-Perot (F-P) cavity. Combined with the temperature sensing property of fiber Bragg grating (FBG), a novel fiber optic F-P magnetic field sensor with temperature compensation was proposed. The sensor probe has the advantages of simple structure, low cost, and high magnetic field measurement accuracy. Magnetic field and temperature can be simultaneously measured by the proposed sensor. Sensing mechanism and experimental results indicated that the temperature cross effect on magnetic field measurement can be effectively compensated using a FBG. The maximal magnetic field intensity is up to 600 Gs with a sensitivity of 0.04 nm/Gs and measurement resolution is 0.5 Gs.

Magnetic Field Measurement Based on the Sagnac Interferometer With a Ferrofluid-Filled High-Birefringence Photonic Crystal Fiber

A compact optical fiber magnetic field sensor based on the principle of the Sagnac interferometer is proposed. Different from the conventional ones, a ferrofluid-filled high-birefringence photonic crystal fiber (HB-PCF) is inserted into the Sagnac as a magnetic field sensing element. The refractive index of the ferrofluid filled in the cladding air holes of the HB-PCF will change with respect to the applied magnetic field, and subsequently, the birefringence of the HB-PCF will change, which will affect the shifts of the output interference spectrum in Sagnac. Experiments are carried out to verify the simulation model and the results indicate that the interference spectrum exhibits a red shift with the increment in the magnetic field intensity. The sensitivity of the proposed sensor is up to 0.073 nm/mT for a magnetic field intensity ranging from 10 to 40 mT, while the resolution is 0.001 mT. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference beyond what conventional magnetic field sensors can offer.

Simultaneous Measurement of Magnetic Field and Temperature Based on Magnetic Fluid-Infiltrated Photonic Crystal Cavity

A method for simultaneous measurement of magnetic field and temperature with high sensitivity and high precision was realized according to magnetic fluid (MF)-infiltrated photonic crystal cavity, where two different types of MF were, respectively, infiltrated into certain air holes adjacent to a waveguide to form two cascaded cavities. As the refractive index (RI) of MF is dependent on external magnetic field and temperature, the two independent resonant dips of cascaded cavities that can be simultaneously monitored at the output spectrum of the waveguide would all shift with the change of external magnetic field or temperature. Using finite-difference time-domain method, the RI sensitivity of the proposed cavity was firstly analyzed and optimized, and then the linear relationships between the shifts of two resonant wavelengths and external magnetic field/temperature were calculated. Finally, combined with the dual-wavelength matrix method, the magnetic field detection limit could reach to 1.333 × 10-4 T with the uncertainty of ±0.22 × 10-4 T (coverage factor k = 2) and detection range from 0 to 0.06 T. Simultaneously, the temperature detection limit could reach to 0.301 K with the uncertainty of ±0.051 K (k = 2) and detection range from 250 to 340 K.

Highly Sensitive Airflow Sensor Based on Fabry–Perot Interferometer and Vernier Effect

A novel highly sensitive airflow sensor based on Fabry-Perot interferometer (FPI) and Vernier effect is proposed and demonstrated. The sensor is fabricated by splicing a section of hollow-core fiber (HCF) between a lead-in single mode fiber (SMF) and a section of SMF, which is almost one-fifteenth the length of the HCF. Airflow changes the cavity length of the FPI, which leads to the shift of the reflection spectrum. The reflection beam from the last end of the SMF is utilized to generate the Vernier effect, which enlarges the shift of the spectrum for 9.57 times than that of a single FPI. According to the experimental results, when the airflow ranges from 0 to 7 m/s, the spectrum of the sensor shifts as high as 7.9 nm which is almost eight times more than that of the self-heating sensor based on silver-coated FBG. And the highest airflow velocity sensitivity of the sensor can reach 1.541 nm/(m/s) in the region of 3 m/s ~ 7 m/s. Besides, the sensor has a series of advantages such as fast response, low cost, compact size, and reflection measurement.

Small and Practical Optical Fiber Fluorescence Temperature Sensor

A small optical fiber temperature sensor employing the fluorescence lifetime of Mn4+ doped oxyfluoride germanate phosphor was presented and experimentally demonstrated, which has a fairly good temperature measurement precision. The performance of the fluorescent materials for temperature measurement was compared and analyzed. A small temperature sensing probe with a diameter of 1.8 mm was proposed. For the first time, the integrated tee-light-path structure was put forward, the transmission and separation of excitation light and fluorescence in only a single optical path was realized. Experimental results showed that standard deviation errors of 0.45 °C were obtained within the temperature range from 0 °C to 90 °C.

Enhancement of RI Sensitivity Through Bending a Tapered-SMF-Based Balloon-Like Interferometer

An all-fiber sensitivity-enhanced refractive index (RI) balloon-like interferometer based on a tapered single-mode fiber (SMF) is proposed and experimentally investigated. The tapered fiber is designed into a balloon-like shape to form a modal interferometer which is sensitive to external environmental RI solutions. Compared with the untapered-SMF-based modal interferometer with an optimal sensitivity of 187.73 nm/RIU which also has been investigated in this paper, the tapered-SMF-based balloon-like interferometer has an improvement in RI sensitivity. Further, a serial of balloon-like interferometers based on tapered fiber with different bending radii are fabricated to explore the RI sensitivity properties on account of bending. Experimental results show that by bending the tapered-SMF-based balloon-like interferometer, the RI sensitivity has been enhanced further, and a higher sensitivity of 404.9 nm/RIU is achieved, which exhibits great potential in areas related in RI sensing.

AN OPTICAL FIBER TEMPERATURE SENSOR BASED ON AN ETHANOL FILLED FABRY-PEROT CAVITY

Optical fiber Fabry-Perot interferometers have been widely used as sensors. A novel anhydrous ethanol-filled optical fiber Fabry-Perot temperature sensor was reported in this article. Based on the characteristics of the temperature-controlling refractive index, the ethanol may serve as a sensitive medium for a sensor. According to the experimental results, the refractive index of the ethanol was changed by approximately 0.02617 when the temperature increased from 16°C to 74°C. A cavity length of 94 μm was used to demonstrate the feasibility of this sensor. The resonance wavelength of the sensor shifted about −0.42 nm/°C. The novel optical fiber Fabry-Perot temperature sensor was simple, compact, sensitive, and immune to electromagnetic interferences.