Yaofei Chen

Optical fiber magnetic field sensor based on single-mode–multimode–single-mode structure and magnetic fluid

An optical fiber magnetic field sensor based on the single-mode-multimode-single-mode (SMS) structure and magnetic fluid (MF) is proposed and demonstrated. By using a piece of no-core fiber as the multimode waveguide in the SMS structure and MF sealed in a capillary tube as the magnetic sensitive media, which totally immersing the no-core fiber, an all-fiber magnetic sensor was fabricated. Interrogation of the magnetic field strength can be achieved either by measuring the dip wavelength shift of the transmission spectrum or by detecting the transmission loss at a specific wavelength. A demonstration sensor with sensitivities up to 905 pm/mT and 0.748 dB/mT was fabricated and investigated. A theoretical model for the design of the proposed device was developed and numerical simulations were performed.

Magnetic Field Sensor Based on U-Bent Single-Mode Fiber and Magnetic Fluid

In this paper, an all-fiber magnetic field sensor based on a U-bent single-mode fiber and magnetic fluid (MF) is proposed and investigated. Because of the tunable refractive index and absorption coefficient of MF, the transmission spectrum will change with the magnetic field strength (H), which can be used to demodulate H through the wavelength shift or the intensity change. The influence of the diameter of the U shape to the performance of the sensor is investigated and discussed. In the experiments, the highest sensitivities achieved with wavelength and intensity demodulation are 0.374 nm/Oe and -0.4821 dB/Oe, respectively. The reproducibility of the sensor is studied as well.

U-bent single-mode–multimode–single-mode fiber optic magnetic field sensor based on magnetic fluid

A magnetic field sensor based on a U-bent single-mode–multimode–single-mode (SMS) fiber structure and magnetic fluid (MF) is presented and demonstrated experimentally. The U-bent and straight sensors are compared, and the influence of the diameter of the no-core fiber (NCF) on the sensitivity of the U-bent sensor is investigated. The experimental results show that the sensitivity of the sensor can be improved by bending the NCF and decreasing the NCF diameter. The following magnetic field sensitivities have been achieved: 3185.2 pm/mT and 5.6 dB/mT, based on dip wavelength and transmission loss demodulations, respectively.

An All-Fiber Optic Current Sensor Based on Ferrofluids and Multimode Interference

In this paper, an all-fiber optical current sensor based on ferrofluids and a singlemode-multimode-singlemode structure (SMS) with a piece of no-core fiber as the multimode section was proposed and experimentally investigated. The transmittance of the SMS that is sealed in a capillary with ferrofluids is highly sensitive to the surrounding magnetic field. Because the strength of the magnetic field is proportional to the current in the electric line, so the current can be measured. A demonstration sensor was fabricated and experimentally characterized. A sensitivity of 2.12 dB/A was achieved.

Simultaneous Measurement of Refractive Index and Temperature Using a Cascaded FBG/Droplet-Like Fiber Structure

A simple and compact sensor based on a cascaded fiber Bragg grating (FBG)/droplet-like fiber structure is proposed for simultaneous measurement of refractive index (RI) and temperature. The sensor can be easily constructed by mechanically bending a section of coating-stripped single-mode fiber at an FBGs pigtail. In the transmission spectrum, two kinds of dips induced by FBG and droplet-like structure are observed. The central wavelength of the dip caused by droplet-like structure is susceptible to both of surrounding RI and temperature, while that caused by FBG is only dependent on temperature. A sensor with a 9.5-mm diameter of droplet-like structure is fabricated and experimentally studied. The experimental results demonstrate the feasibility of the proposed sensor and show that sensor possesses a high RI sensitivity of 157.8891 nm/RIU for the RI range from 1.3330 to 1.3785 and a temperature sensitivity of 10.3 pm/°C.

Reflective all-fiber current sensor based on magnetic fluids

A reflective all-fiber current sensor based on magnetic fluid (MF) is reported. The MF is used as the cladding of a piece of no-core fiber which is spliced between two sections of singlemode fiber to form a singlemode-multimode-singlemode structure. An intensity based interrogation scheme with a superluminescent diode as the light source and the dual-balanced detection method is used in the sensing system. The influence of the direction of the magnetic field on the sensitivity of the sensor is also experimentally investigated and analyzed.

Magnetic-Fluid-Coated Photonic Crystal Fiber and FBG for Magnetic Field and Temperature Sensing

A novel optical fiber sensor for simultaneous measurement of magnetic field and temperature is proposed and demonstrated. The sensor consists of a cascaded photonic crystal fiber (PCF) interferometer and fiber Bragg grating (FBG). The interferometer and the FBG are sealed in a capillary tube filled with magnetic fluid. The transmission spectrum of the sensor contains both the information of the interferometer and the FBG. The FBG is only sensitive to the temperature but the PCF interferometer is also sensitive to the magnetic field, which in turn can be used for the simultaneous measurement of magnetic field and temperature. A sensor was fabricated and investigated experimentally.

Highly efficient Er/Yb-codoped fiber amplifier with an Yb-band fiber Bragg grating

In this Letter, a high-power Er/Yb-codoped fiber amplifier (EYDFA) with a high-reflection Yb-band fiber Bragg grating (FBG) at the pump end is experimentally investigated. The FBG was inscribed on a piece of double-clad fiber with a center wavelength of 1032 nm. Due to the selective reflection of the backward Yb-band amplified spontaneous emission (Yb ASE) by the FBG, a co-pump-propagating Yb-band auxiliary signal was generated. Because of the stimulated amplification and reabsorption of the auxiliary signal, the Yb ASE was dramatically suppressed and the pump conversion efficiency (PCE) of the EYDFA was notably improved. An output power of 6.48 W was achieved at a pump power of 16.5 W, which is equivalent to a PCE of ∼39%. The slope efficiency relative to applied pump power was ∼40%. The maximum output power was improved ∼20% because of the introduction of the FBG.

Wavelength Dependence of the Sensitivity of All-Fiber Refractometers Based on the Singlemode–Multimode–Singlemode Structure

In this paper, the wavelength dependence of the sensitivity of all-fiber refractometers based on the singlemode-multimode-singlemode fiber structure, in which a piece of no-core fiber (NCF) is used to serve as the multimode section, is investigated via numerical simulations and experiments. We found that the sensitivity of a refractometer is linearly proportional to the wavelength of the dip/peak in the transmission spectrum that is chosen to measure the refractive index (RI) change. Because the wavelength shift is larger for a dip/peak at a longer wavelength than at a shorter wavelength, a linear spectral chirp will occur in the transmission spectrum when the surrounding RI changes. We also found that the sensitivity significantly increases with the decrease in the diameter of the NCF and is independent of its length. The experimental results agree well with the numerical predictions.

Fiber loop ring-down cavity integrated U-bent single-mode-fiber for magnetic field sensing

A novel magnetic field sensing system based on the fiber loop ring-down technique is proposed in this paper. In the fiber loop, a U-bent single-mode-fiber structure coated with magnetic fluid (MF) serves as the sensing head, and an erbium-doped fiber amplifier (EDFA) is introduced to compensate for the intrinsic loss of the cavity. The ring-down time of the system varies with the change of applied magnetic field due to the tunable absorption coefficient and refractive index of the MF. Therefore, measurement of the magnetic field can be realized by monitoring the ring-down time. The experimental results show that the performance of the system is extremely dependent on the interrogation wavelength, because both the gain of the EDFA and the loss of the sensing head are wavelength dependent. We found that at the optimal wavelength, the ratio of the gain to loss attained its maximum. The sensing system was experimentally demonstrated and a sensitivity of −0.5951  μs/Oe was achieved.