Lin Htein

Microstructured Optical Fiber Sensors

In this paper, a review of microstructured optical fiber (MOF) sensors is given. Various kinds of MOFs are described and their sensing applications are summarized. Two main types of MOF sensors in terms of grating based and interferometry based are reviewed. In particular, several types of microstructured optical fibers designed for sensing applications in our works are demonstrated, including the measurement of physical parameters, e.g., pressure, strain, torsion, temperature, and the detection of biomedical parameters such as refractive index and microfluidic flow rate. The basic design principles of MOF sensors based on fiber Bragg grating and interferometers are given. Comparisons of the performances of the fibers and sensors are also conducted according to the relevant topics.

Hydrostatic pressure sensor based on fiber bragg grating written in single-ring suspended fiber

We present a novel optical fiber consisting of a suspended-fiber with core and cladding diameter of ~ 5 and 30 μm and a supporting ring with thickness of ~ 9 μm. The outer diameter of the fiber was 125 μm and a fiber Bragg grating (FBG) with a length of 1-mm was inscribed on it. Hydrostatic pressure was measured by monitoring the Bragg wavelength shifts of 9-mm long single-ring suspended fiber. Pressure sensitivity was measured to be –18.92 pm/MPa, which is about five times higher than FBG on standard single-mode fiber.

Highly sensitive miniature fluidic flowmeter based on an FBG heated by Co2+-doped fiber

In this paper, we present a miniature fluidic flow sensor based on a short fiber Bragg grating inscribed in a single mode fiber and heated by Co2+-doped multimode fibers. The proposed flow sensor was employed to measure the flow rates of oil and water, showing good sensitivity of 0.339 nm/(m/s) and 0.578 nm/(m/s) for water and oil, flowing at v = 0.2 m/s. The sensitivity can be increased with higher laser power launched to the Co2+-doped multimode fibers. A small flow rate of 0.005 m/s and 0.002 m/s can be distinguished for a particular phase of water or oil, respectively, at a certain laser power (i.e. ~1.43W). The flow sensor can measure volume speed up to 30 L/min, which is limited by the test rig. The experimental results show that the sensor can discriminate slight variation of flow rates as small as 0.002m/s.

Large dynamic range pressure sensor based on two semicircle-holes microstructured fiber

This paper presents a sensitive and large dynamic range pressure sensor based on a novel birefringence microstructured optical fiber (MOF) deployed in a Sagnac interferometer configuration. The MOF has two large semicircle holes in the cladding and a rectangular strut with germanium-doped core in the center. The fiber structure permits surrounding pressure to induce large effective index difference between the two polarized modes. The calculated and measured group birefringence of the fiber are 1.49 × 10−4, 1.23 × 10−4, respectively, at the wavelength of 1550 nm. Experimental results shown that the pressure sensitivity of the sensor varied from 45,000 pm/MPa to 50,000 pm/MPa, and minimum detectable pressure of 80 Pa and dynamic range of better than 116 dB could be achieved with the novel fiber sensor. The proposed sensor could be used in harsh environment and is an ideal candidate for downhole applications where high pressure measurement at elevated temperature up to 250 °C is needed.

Highly Sensitive Small Pressure Monitoring Using Hyperelastic Silicone-Cladding/Silica-Core Composite Optical Fiber

We have fabricated a composite optical fiber with hyperelastic silicone cladding and silica core, and demonstrated a simple and highly sensitive pressure sensor based on the light coupling between two such composite fibers twisted together. The hyperelastic silicone has very low Youngs modulus which makes the fiber deformation easier even under small pressure and hence improves the light coupling and pressure sensitivity. Both simulation and experiment show that the light coupling based pressure sensor using the composite fibers is very sensitive to small pressure (e.g., several newtons) compared with those using conventional silica fibers and polymethyl methacrylate resin polymer fibers, which almost have no response to small pressure. With excellent sensitivity and fast response time (

Ultrasensitive pressure sensor realized with two-semicircle hole fiber based on Sagnac interferometer

\ll 1\;{\rm{s}}

Bragg grating in novel two-core holey fiber for simultaneous measurement of pressure and temperature

), both static and dynamic side pressure have been successfully detected. The sensing configuration is simple without any complicated structures and would be a cost-effective candidate for highly sensitive small pressure monitoring.

Miniature FBG-based fluidic flowmeter to measure hot oil and water

In this paper, we demonstrate a novel microstructure optical fiber designed for pressure measurement with ultrahigh sensitivity. The fiber has a cross-sectional structure of two-semicircle holes with a modal birefringence of −1×10−4 The demonstrated sensitivity of hydrostatic pressure is −44 nm/MPa, which is about 13 times higher than previously reported result.

Flow sensor based on heated-FBG by multiple pump lasers

A novel holey fiber with two suspended Ge-doped cores was successfully developed for simultaneous measurement of pressure and temperature. The diameters of the cores are 4.2 μm and 6 μm, with cladding diameters of 23.8 μm and 37.4 μm, respectively. Pressure sensitivities of the two-core holey fiber were measured to be −16.98 pm/MPa and −14.84 pm/MPa whereas temperature sensitivities were 12.41 pm/°C and 12.51 pm/°C.

Enhanced broadband upconversion emission and 23 dB optical gain at 780 nm in Tm3+/Nd3+ codoped optical fiber

In this paper, we present a miniature fluidic flowmeter based on a packaged FBG and laser-heated fibers. The flow rates of water and hydraulic oil were measured by utilizing the proposed flowmeter. The measured results exhibited good sensitivity of 0.339 nm/(m/s) for water and 0.578 nm/(m/s) for oil flow. Experimental results showed that the sensitivity of the fluidic flow sensor is depending on the heat capacity of the fluids, where the fluid with higher heat capacity has higher sensitivity and lower detection limit at the same measurement condition. The real-time flow rates measured by the proposed sensor and a commercial flowmeter installed in the test rig were also compared, demonstrating good agreement with correlation coefficient of 0.9974.