Li Han Chen

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.

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.

A Temperature-Insensitive Twist Sensor by Using Low-Birefringence Photonic-Crystal-Fiber-Based Sagnac Interferometer

An optical fiber twist sensor is proposed by using solid core low birefringence photonic crystal fiber (LB-PCF)-based Sagnac interferometer. The twist effects on the fiber are theoretically analyzed. The results show that the dip wavelength of the transmission spectrum shifts with the twist angle with a high sensitivity and resolution of 1.00 nm/0 and 0.010 , respectively. The sensor is also insensitive to environmental temperature change with an ultralow thermal dependent coeffiecient of -0.5 pm/0C.

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.

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.

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.

Chitosan-Coated Polarization Maintaining Fiber-Based Sagnac Interferometer for Relative Humidity Measurement

A relative humidity fiber sensor based on polarization maintaining (PM) fiber Sagnac interferometery configuration is presented. The proposed sensor is functionalized with a thin layer of a moisture-sensitive natural polymer chitosan, whose degree of swelling varies as a function of relative humidity. The sensing scheme used in this study is based on the strain effect induced on the PM fiber to modulate its birefringence property through the swelling effect of chitosan. To optimize the sensors response, the experiments were first conducted to evaluate the effect of chitosan concentration on the PM fiber, followed by investigating effects of chemically etched PM fiber and analyzing modified chitosan sensing film effect on the sensors performance. As observed from the results, the optimized sensor exhibits a sensitivity of 81 pm/%RH for the relative humidity ranging from 20% RH to 95% RH with an uncertainty of ±2.04% RH.

Fiber Optic Refractometer Based on Cladding Excitation of Localized Surface Plasmon Resonance

A fiber optic refractometer based on a novel configuration to excite localized surface plasmon resonance is demonstrated. The fiber sensor consists of a short segment of photonic crystal fiber (PCF) fusion spliced between multimode fibers. Evanescent field of cladding modes excite gold nanoparticles (AuNPs) immobilized on the PCF surface. The proposed sensor offers ease of fabrication, when normalized transmitted intensity is used to quantify external bulk refractive index (RI), sensitivity of -731%/RIU, limit of detection of 1.76×10-5 RIU can be achieved with high linearity (r2=0.9988) over RI range from 1.33 to 1.43 RIU.

Layer-By-Layer (Chitosan/Polystyrene Sulfonate) Membrane-Based Fabry–Perot Interferometric Fiber Optic Biosensor

A label-free, layer-by-layer (LBL) modified, fiberoptic interferometry biosensor for real-time affinity-based protein sensing applications has been proposed. The proposed sensor allows real-time protein adsorption detection by monitoring interference wavelength shifts, which offers better dynamic range and stability in comparison to current detection of changes in optical intensity. With a label-free sensing mechanism, it eliminates issues of progressive leaching of indicators, expensive and time-consuming labeling procedures and undesirable nonspecific interactions with target proteins. The unique Fabry-Perot cavity consists of an LBL coating layer of nanometre thickness deposited on the distal ends of a hollow core cavity spliced to a standard single-mode optical fiber (SMF). This novel configuration allows the LBL sensing element to be enclosed by similar mediums, on both sides of the LBL multilayer film coat, thus surrounded by identical properties such as the same refractive index that improves the sensitivity of the proposed sensor. Furthermore, the LBL coat consisting of chitosan and polysodium styrene sulfonate, commonly used in drug delivery and cell culture, indicates good biocompatibility for future in vivo biomedical applications such as immunosensing and DNA hybridization detections.

Miniature temperature sensor with germania-core optical fiber

A miniature all-fiber temperature sensor is demonstrated by using a Michelson interferometer formed with a short length of Germania-core, silica-cladding optical fiber (Ge-fiber) fusion-spliced to a conventional single-mode fiber (SMF). Thanks to the large differential refractive index of the Ge-fiber sensing element, a reasonably small free spectral range (FSR) of 18.6 nm is achieved even with an as short as 0.9 mm Ge-fiber that may help us increase the measurement accuracy especially in point sensing applications and, at the same time, keep large measurement temperature range without overlapping reading problem. Experimental results show that high sensitivity of 89.0 pm/°C is achieved and the highest measurement temperature is up to 500°C.