Wenlei Yang

Combining Two Types of Gratings for Simultaneous Strain and Temperature Measurement

A new optical fiber sensor made of tapered and CO2-laser-notched long-period fiber gratings (LPFGs) is proposed for the simultaneous measurement of strain and temperature. Experiments are run to verify the feasibility of using the proposed sensor for the simultaneous measurement of strain and temperature. Experimental results indicate that after the two LPFGs are connected with each other, the sensitivity of CO2-LPFG to strain deceases from 1.7 to 0 pm/με, and the sensitivity of the tapered LPFG remains unchanged; it is -1.4 and -1.5 pm/με. The sensitivity of resonance wavelength 1280, 1412, and 1545 nm to temperature are 80 pm/°C, 67 pm/°C, and 69 pm/°C. Simultaneous strain and temperature experiments prove the stability of proposed sensor. It is therefore strongly believed that the proposed sensor can be used to achieve simultaneous measurement of strain and temperature.

A Curvature Sensor Based on Twisted Single-Mode–Multimode–Single-Mode Hybrid Optical Fiber Structure

An optical fiber curvature sensor based on a twisted multimode fiber (MMF) sandwiched between two single-mode fibers (SMF) is proposed and investigated theoretically and experimentally. The measured transmission spectrum exhibits good agreement with theoretical predictions. Compared with a traditional single-mode–multimode–single-mode fiber structure sensor, the proposed configuration offers a higher average curvature sensitivity of –2.42 nm/m^–1 over a curvature measurement range of 0–1.7390 m^–1 and –7.09 dB/m^–1 at an operating wavelength of 1537 nm. The temperature sensitivity of this sensor has been determined as 0.01 nm/°C over a wavelength range of 1535–1550 nm and circa 0.007 dB/°C at the wavelength of 1537 nm, over a measured temperature range of 21–121 °C.

Modal Interferometer Using Three-Core Fiber for Simultaneous Measurement Strain and Temperature

A structure made of tapered three-core fiber and CO₂ laser notch long-period fiber grating is proposed in this paper. By adjusting the taper waist diameter of a three-core fiber, this structure is made suitable for simultaneous strain and temperature measurements. The effectiveness of the proposed structure in realizing simultaneous measurement sensitivity is verified by measuring the sensitivities of the two peaks at the variation of the wavelength and the depth difference. Experimental results indicate that the wavelength sensitivities of the two peaks are -2.96 nm mε^-1, 42.9 pm °C^-1 and -1.52 nm mε^-1, 47.4 pm °C^-1 for strain and temperature, respectively, and the depth sensitivities of two peaks can reach 2.5 dB mε^-1, 0.007 dB °C^-1 and -2.8 dB mε^-1, -0.013 dB°C^-1. It can therefore be concluded that the proposed structure can be realized by adjusting the taper waist diameter of a three-core fiber for simultaneous strain and temperature measurements.

Packaged Optical Add-Drop Filter Based on an Optical Microfiber Coupler and a Microsphere

In this letter, a packaged add-drop filter composed of a silica microsphere resonator with a diameter of 80 μm and an optical microfiber coupler with a waist diameter of 1 μm is investigated. A one-step fabrication process using UV curable epoxy is shown to stabilize the coupling between the microsphere and the microfiber coupler, which is used for the add and drop ports. The packaged microsphere-microfiber coupler device has a high Q-factor of 1 × 107 in the add-drop filter configuration. This device has excellent features, such as improved ease of fabrication, multiple resonant peaks, and high mechanical stability.

Passive photonic integrated ratiometric wavelength monitor with resolution better than 15 pm

This paper presents a compact and low-loss photonic integrated device consisting of a Y-branch and a pair of multimode interferometers (MMI) for a ratiometric wavelength monitoring around 1550 nm on silicon-on-insulator (SOI) technique. Two MMIs are designed in terms of width and length to achieve overlapping but opposite slope spectral responses used as two edge filters over a wavelength measurement range from 1500 nm to 1600 nm. The developed integrated photonic ratiometric structure demonstrates a suitable discrimination range for a high-speed passive wavelength measurement, with a high resolution better than 15 pm over a 100 nm wavelength range.

High Sensitive Directional Torsion Sensor Based on a Segmented Long-Period Fiber Grating

A segmented long period fiber grating (LPFG)-based torsion sensor with both high sensitivity and ability to discriminate torsion direction is proposed and experimentally investigated. The sensor is made up of three spatial orthogonal short LPFGs by using a CO2 laser notched method. Experimental results show that the torsion sensitivities can reach −0.54 and 0.33 dB/(rad/m) in dip depth and 0.30 and −0.14 nm/(rad/m) in resonance wavelength for clockwise and counterclockwise, respectively, in a single polarization state. Torsion rate and torsion direction can be measured simultaneously by the sensor. Moreover, the temperature sensitivity of the sensor has been determined as 0.067 nm/°C. Therefore, the proposed segmented-LPFG would have great potential applications in engineering and fiber sensors.

Simultaneous measurement of temperature and strain based on composite long-period fiber grating

Long period fiber grating is a kind of transmission type optical fiber grating. Due to the advantages such as low insertion loss, wide bandwidth, low-level reflection, high sensitivity, low cost and ease of compactness, LPFGs have been widely applied in optical fiber sensing and optical fiber communication. The Mode coupling of LPFG is the coupling between the fiber core mode and the cladding mode in the same transmission direction. If the ordinary LPFG is combined with bitaper or taper, we can effectively change the original LPFGs transmission spectrum to obtain the composite LPFG, which can stimulate new resonant peaks in the original wavelength-dependent transmission loss of the grating basis, thus applying to the dual-parameter simultaneously measuring field. We report a novel all-fiber narrow-bandwidth intermodal Mach– Zehnder interferometer (MZI) based on a long-period fiber grating (LPFG) combined with a fiber bitaper. The LPFG is written by high-frequency CO2 laser pulses, and the bitaper is connected in series with the LPFG, forming the Mach– Zehnder interferometer (MZI). Experimental results indicate that the MZI has good temperature sensitivity, The temperature sensitivity of the two loss peaks are 55.35pm/°C and 48.18pm/°C respectively. The strain sensitivity of the two loss peaks are 3.35pm/με and -4.925pm/με respectively. By using the different temperature and strain response characteristics of the loss peaks, the temperature and strain measurement can be realized simultaneously. the proposed device has good repeatability and stability, which would be a promising candidate for precise dual-parameter sensing application.

High temperature sensitivity fiber sensor based on M-Z interferometer fabricated by suspended dual-core hollow fiber

We successfully fabricate and demonstrate a type of in-line M-Z interferometer by using single mode fiber and suspended dual-core hollow fiber. We fuse one section of dual-core hollow fiber (about 5-10cm length used as interferometer arms) with two part of single mode fiber by arc discharging on their cross sections. After this new M-Z interferometer’s fabrication and related experiments, we improved it by absorbing drops of alcohol in its dual-core hollow body which can do much of contributions to its sensitivity. With bunches of temperature experiments conducted, we find this new interferometer has a good temperature sensitivity highly as 1.751nm/°C (from 20 to 100 °C) and interferometer with alcohol inside has a better temperature sensitivity highly as 3.015nm/ °C (from 20 to 60 °C) respectively.

A direction detective asymmetrical twin-core fiber curving sensor

Long period fiber gratings (LPFGs), which can couple the core mode to the forward propagating cladding modes of a fiber and have the advantage of small additional loss, no backward reflection, small size, which is widely used in optical fiber sensors and optical communication systems. LPFG has different fabricating methods, in order to write gratings on the twin-core at the same time effectively, we specially choose electric heating fused taper system to fabricate asymmetric dual-core long period fiber grating, because this kind of method can guarantee the similarity of gratings on the twin cores and obtain good geometric parameters of LPFG, such as cycle, cone waist. Then we use bending test platform to conduct bending test for each of the core of twin-core asymmetric long period fiber grating. Experiments show that: the sensitivity of asymmetrical twin-core long period fiber grating’s central core under bending is -5.47nm·m, while the sensitivity of asymmetric twin-core long period fiber grating partial core changed with the relative position of screw micrometer. The sensitivity at 0°, 30°, 90° direction is -4.22nm·m, -9.84nm·m, -11.44nm·m respectively. The experiment results strongly demonstrate the properties of rim sensing of asymmetrical twin-core fiber gratings which provides the possibility of simultaneously measuring the bending magnitude and direction and solving the problem of cross sensing when multi-parameter measuring. In other words, we can detect temperature and bend at the same time by this sensor. As our knowledge, it is the first time simultaneously measuring bend and temperature using this structure of fiber sensors.