Wei Chang Wong

Magneto-optical fiber sensor based on magnetic fluid

A novel tilted fiber Bragg grating (TFBG)-based magnetic field sensor by incorporating magnetic fluid is proposed and experimentally demonstrated. It is based on the refractive index change of magnetic fluid with external magnetic field. Magnetic field strength measurement is successfully achieved within a range from 0 to 196 Gauss by monitoring extinction ratio of the TFBGs cladding mode resonance, which is sensitive to surrounding refractive index.

Magneto-optical fiber sensor based on bandgap effect of photonic crystal fiber infiltrated with magnetic fluid

A magnetic field sensor based on combination of the magnetic fluid and the tunable photonic bandgap effect of photonic crystal fiber is proposed. The magnetic fluid with higher refractive index (>1.45) is prepared and filled into the air-holes of photonic crystal fiber to convert the index guiding fiber into photonic bandgap fiber. The proposed sensor takes full advantage of the ultrahigh sensitivity characteristic of photonic bandgap fiber and achieves a high sensitivity and resolution of 1.56 nm/Oe and 0.0064 Oe, respectively, which are 2-3 orders of magnitude better than other sensors based on magnetic fluid.

Temperature-Insensitive Magnetic Field Sensor Based on Nanoparticle Magnetic Fluid and Photonic Crystal Fiber

A novel magnetic field sensor based on the magnetic fluid and Mach-Zehnder interferometer is proposed. The sensor takes advantage of the tunable refractive index property of the magnetic fluid and the modal interference property of the collapsed photonic crystal fiber. The achieved sensitivity and resolution of the sensor are 2.367 pm/Oe and 4.22 Oe, respectively. The magnetic field sensor is insensitive to the temperature variation with a temperature coefficient of 3.2 pm/°C.

Photonic Crystal Fiber Strain Sensor Based on Modified Mach–Zehnder Interferometer

In this paper, a novel strain sensor is proposed and demonstrated by employing a modified photonic crystal fiber (PCF)-based Mach-Zehnder interferometer, in which a collapsed region is introduced at the middle point of the PCF to improve the extinction ratio. Experimental results show that this proposed structure has a high sensitivity of 11.22 over a range of 1.28 and high-temperature stability.

Highly sensitive fiber loop ringdown strain sensor using photonic crystal fiber interferometer

A highly sensitive strain sensor is demonstrated by introducing a photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI) in a cavity ringdown fiber loop as a sensing element. The MZI is fabricated by splicing a short length of PCF between two single-mode fibers with collapsed air holes over a short region at two splicing points, which allows coupling between core and cladding modes inside the PCF. By measuring the decay constants of the fiber ringdown loop under different applied strains, a high strain sensitivity of ~0.21 μs⁻¹/εm and a minimum detectable strain of ~3.6 με are obtained. As a benefit from the ultralow thermal dependence of PCF, the maximum temperature-induced measurement error could be reduced to ~0.24 με.

Highly sensitive miniature photonic crystal fiber refractive index sensor based on mode field excitation.

A highly sensitive miniature photonic crystal fiber refractive index sensor based on field mode excitation is presented. The sensor is fabricated by melting one end of a photonic crystal fiber into a rounded tip and splicing and collapsing the other end with a single-mode fiber. The rounded tip is able to induce cladding mode excitation, which resulted in an additional phase delay. Linear response of 262.28 nm/refractive index unit in the refractive index range of 1.337 to 1.395 is obtained for the physical length of a 953 μm sensor. The sensor is also shown to be insensitive to environmental temperature.

Temperature Sensing Based on Ethanol-Filled Photonic Crystal Fiber Modal Interferometer

A modal interferometer made of a short ethanol-filled photonic crystal fiber (PCF) combined with a fully collapsed splicing with single-mode fibers (SMFs) is proposed for temperature measurement. Two fully collapsed splicing regions between the ethanol-filled PCF and SMFs excite and recombine two interfering modes in the ethanol-filled PCF. The interference spectrum of the ethanol-filled PCF is more sensitive to temperature than that of original PCF. By monitoring one peak wavelength shift of the ethanol-filled PCF modal interference spectrum, the temperature sensitivity reaches up to -0.35 nm/°C for a 3.25-cm long ethanol-filled PCF.

Photonic crystal fiber interferometric pH sensor based on polyvinyl alcohol/polyacrylic acid hydrogel coating.

We present a simple photonic crystal fiber interferometer (PCFI) that operates in reflection mode for pH measurement. The sensor is made by coating polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel onto the surface of the PCFI, constructed by splicing a stub of PCF at the distal end of a single-mode fiber with its free end airhole collapsed. The experimental results demonstrate a high average sensitivity of 0.9 nm/pH unit for the 11 wt.% PVA/PAA coated sensor in the pH range from 2.5 to 6.5. The sensor also displays high repeatability and stability and low cross-sensitivity to temperature. Fast, reversible rise and fall times of 12 s and 18 s, respectively, are achieved for the sensor time response.

Mach–Zehnder Photonic Crystal Interferometer in Cavity Ring-Down Loop for Curvature Measurement

Abstract-An all-fiber Mach-Zehnder interferometer curvature sensor fabricated by collapsing both ends of a photonic crystal fiber connected to a single-mode fiber is described. The interferometer is inscribed into the cavity ring-down loop and shows high sensitivity of 0.7311(μs)^-1 · m and high repeatability when a curvature of 0.4135 to 0.8122 m^-1 is applied. High correlation value of 0.997 is obtained with low standard error of 1.05%. This corresponds to a minimum detectable curvature of 4.849 × 10^-3 m^-1. The proposed sensor also displays low sensitivity to temperature with a value of 0.0008(μs ·° C)^-1.

High Extinction Ratio Magneto-Optical Fiber Modulator Based on Nanoparticle Magnetic Fluids

A novel magneto-optical fiber modulator with a high extinction ratio (ER) based on a polarization interference structure is proposed. A magnetic fluid (MF) film and a section of a polarization-maintaining fiber (PMF) are inserted into the structure to generate a suitable sinusoidal interference spectrum for light modulation. The MF film leads to a spectrum shift under external magnetic field due to its magnetically controllable birefringence, whereas the PMF is used to control the period of the interference spectrum. In this experiment, magneto-optical modulation with a high ER of 38 dB is demonstrated.