Multiplexed fiber Fabry-Perot temperature sensor system using white-light interferometry

A novel monitoring system for a fiber Fabry-Perot interferometer (FFPI) temperature sensor has yielded a resolution of 0.013 degrees C (0.0025 fringe). Light from a broadband source passes through a scanned Michelson interferometer and is reflected from a FFPI to produce a fringe pattern, the temporal position of which is proportional to a change in the optical length of the fiber interferometer. A second Michelson interferometer with a distributed-feedback laser source is used to correct for variations in the translation rate of the motor-driven scanning mirror. Coherence multiplexing of three such sensors has also been demonstrated.     

基于蓝宝石晶片的光纤法布里-珀罗高温传感器

提出并研制了一种基于蓝宝石晶片的光纤法布里-珀罗(法珀)高温传感器.该传感器采用斜端面蓝宝石光纤作传输波导,蓝宝石晶片作法珀干涉仪,"陶瓷插芯-陶瓷套管"结构做为传感器的固定结构.通过傅里叶变换-最小均方差联合算法解调传感器的反射光谱,实现了20℃~1 000℃范围内的温度测量,测试准确度为±2.5℃.该传感器具有体积小、成本低、制作简单以及重复性高的优点,可用于高温环境下稳定、精确的温度测量.     

Highly sensitive bend sensor based on Mach-Zehnder interferometer using photonic crystal fiber

Optical fiber bend sensor with photonic crystal fiber (PCF) based Mach-Zehnder interferometer (MZI) is demonstrated experimentally. The results show that the PCF-based MZI is sensitive to bending with a sensitivity of 3.046 nm/m⁻¹ and is independent on temperature with a sensitivity of 0.0019 nm/°C, making it the best candidate for temperature insensitive bend sensors. To that end, another kind of bend sensor with higher sensitivity of 5.129 nm/m⁻¹ is proposed, which is constructed by combining an LPFG and an MZI with zero offset at the second splice mentioned above.     

Parallel demodulation system and signal-processing method for extrinsic Fabry-Perot interferometer and fiber Bragg grating sensors

A parallel demodulation system for extrinsic Fabry-Perot interferometer (EFPI) and fiber Bragg grating (FBG) sensors is presented that is based on a Michelson interferometer and combines the methods of low-coherence interference and Fourier transform spectrum. Signals from EFPI and FBG sensors are obtained simultaneously by scanning one arm of a Michelson interferometer, and an algorithm model is established to process the signals and retrieve both the wavelength of the FBG and the cavity length of the EFPI at the same time, which are then used to determine the strain and temperature.     

High-pressure and high-temperature characteristics of a Fabry-Perot interferometer based on photonic crystal fiber

A fiber-optic Fabry-Perot interferometer was constructed by splicing a short length of photonic crystal fiber to a standard single-mode fiber. The photonic crystal fiber functions as a Fabry-Perot cavity and serves as a direct sensing probe without any additional components. Its pressure and temperature responses in the range of 0-40 MPa and 25°C-700°C were experimentally studied. The proposed sensor is easy to fabricate, potentially low-cost, and compact in size, which makes it very attractive for high-pressure and high-temperature sensing applications.     

Generation of longitudinal modes in an active Fabry-Perot fiber interferometer pumped by a low-power single-frequency semiconductor laser

The results of experiments on taking beat spectra at the exit of a stationary (modulator-free) fiber Mach-Zender interferometer are presented. The interferometer is excited by a single-frequency semicon-ductor laser with an output power varying from 0.65 to 2.00 mV and a line-width of less than 20 kHz. The observed line beat spectrum is explained based on the fact that the extended (several kilometers long) arm of the interferometer serves as an active fiber Fabry-Perot interferometer. In this case, the effects of enhancement of stimulated Mandel’shtam-Brillouin scattering in the fiber and the Fresnel reflection of light from the end faces of the fiber play a decisive role. Remarkably, these effects are observed at a low (less than 0.3 mW) power deposited into the fiber. The features of beat signals are considered, and the feasibility of applying this effect in high-sensitive field and displacement optical sensors is indicated.     

一种测量高温中间包的蓝宝石光纤温度计

介绍了一种测量高温的蓝宝石光纤温度计.蓝宝石单晶光纤由于其极好的高温物理化学性能,适用于高温下光纤测温应用,可用作辐射型光纤温度传感器.蓝宝石光纤温度计采用激光加热小基座法生长出端部掺Cr3+的蓝宝石光纤荧光温度传感头.用激光加热小基座,把对荧光有温度反应的材料如红宝石晶体光纤生长在蓝宝石光纤上,制成具有结构紧凑,耐高温,功能稳定的传感探头.通过荧光寿命的检测,可以测量所对应的温度.根据表面温度,可以依据温度场得到内部温度,用于测量连铸炉中的中间包钢水温度,并给出了温度计的实验系统以及原始实验数据.实验数据表明,此结果精度高,可实现非接触测量.     

Temperature characteristics of a core-mode interferometer based on a dual-core photonic crystal fiber

A core-mode Fabry–Perot (FP) interferometer is constructed by using a dual-core photonic crystal fiber (DCPCF). The FP cavity is formed by a single piece of DCPCF, which can also serve as a direct sensing probe without any additional components. We theoretically and experimentally studied its temperature responses in the range of 40–480 °C. The temperature sensitivity is 13 pm/°C which matches the theoretical results. Since the temperature sensitivity of the proposed sensor is independent on cavity length, precise control of the length of FP cavity or photonic crystal fiber is not required. The sensor size can be as short as 100–200 μm, and its fabrication only involves splicing and cleaving, which make the sensor production very cost-effective. The proposed FP interferometric sensor based on a DCPCF can find applications in high-temperature measurement especially those that need accurate point measurement with high sensitivity.     

Accurate monitoring of an interferometric fiber-optic sensor with a multimode semiconductor laser

A technique for monitoring interferometric sensors by correlation of the optical signal from the sensor with the signal from a phase-modulated reference interferometer is described. The technique is applied to temperature measurement with a fiber Fabry-Perot sensing head. We extend the 7 degrees C unambiguous measurement range obtained with a 1.3-mum laser diode as the light source to 43 degrees C by adding a second laser diode emitting at 1.55mum . Experimentally, a rms phase-measurement error of +/-0.28rad , corresponding to a temperature error of +/-0.32 degrees C , was achieved with a low-quality multimode Fabry-Perot laser. The phase error was improved to +/-0.14rad , corresponding to a temperature error of +/-0.16 degrees C , by use of a distributed-feedback laser diode.     

Photonic crystal fiber tip interferometer for refractive index sensing

In this paper we present an interferometer based on photonic crystal fiber (PCF) tip ended with a solid silica-sphere for refractive index sensing. The sensor is fabricated by splicing one end of the holey PCF to a single mode fiber (SMF) and applying arc at the other end to form a solid sphere. The sensor has been experimentally tested for refractive index and temperature sensing by monitoring its wavelength shift. Measurement results show that the sensor has the resolution of the order of 8.7×10(-4) over the refractive index range of 1.33-1.40, and temperature sensitivity of the order of 10 pm/°C in the range of 20-100 °C.     

基于空芯光子晶体光纤的微小型非本征光纤法布里-珀罗干涉应变传感器

报道了一种用空芯光子晶体光纤制作的法布里-珀罗腔体,利用光纤熔接方法将该法布里-珀罗腔体和两根普通通信单模光纤熔接起来构成的微小型光纤法布里-珀罗干涉应变传感器。这种干涉传感器制作过程仅应用了切割和熔接手段,光纤材料单一,因此受温度变化的影响小。另外,该类型传感器的干涉腔长度对干涉信号强度影响不大,其干涉腔长度可至数厘米。因此,这类传感器将在大容量、准分布式传感系统中具有极大的潜在应用价值。     

Fiber grating sensors for high-temperature measurement

Two fiber grating sensors for high-temperature measurements are proposed and experimentally demonstrated. The interrogation technologies of the sensor systems are all simple, low cost but effective. In the first sensor system, the sensor head is comprised of one fiber Bragg grating (FBG) and two metal rods. The lengths of the rods are different from each other. The coefficients of thermal expansion of the rods are also different from each other. The FBG will be strained by the sensor head when the temperature to be measured changes. The temperature is measured based on the wavelength-shifts of the FBG induced by the strain. In the second sensor system, a long-period fiber grating (LPG) is used as the high-temperature sensor head. The LPG is very-high-temperature stable CO₂-laser-induced grating and has a linear function of wavelength–temperature in the range of 0–800 °C. A dynamic range of 0–800 °C and a resolution of 1 °C have been obtained by either the first or the second sensor system. The experimental results agree with theoretical analyses.     

Fiber in-line Mach-Zehnder interferometer constructed by selective infiltration of two air holes in photonic crystal fiber

A fiber in-line Mach-Zehnder interferometer is fabricated through selective infiltrating of two adjacent air holes of the innermost layer in the solid core photonic crystal fiber, assisted by femtosecond laser micromachining. The liquid infiltrated has higher refractive index than that of the background silica, and, hence, the two rods created can support a guide mode with lower effective refractive index than that of silica. The interference is produced by the fiber fundamental mode and the guide mode. The free spectral range (FSR) of the interferometer is found to be dependent on the photonic crystal fiber length, and a large FSR corresponds to a short photonic crystal fiber length. Such an interferometer device is robust and exhibits extremely high temperature sensitivity (～7.3?nm/°C for the photonic crystal fiber length of 3.4?cm) and flexible operation capability.     

基于飞秒激光加工的微纳高温光纤振动传感器

报道了一种基于飞秒激光加工的微纳高温振动传感器。通过熔接形成单模光纤-空芯光纤-单模光纤的结构,利用单模光纤和空芯光纤在熔接面形成的菲涅尔反射,构成外腔式法布里-珀罗干涉仪(EFPI)。用飞秒激光烧蚀空芯光纤,形成悬臂梁结构。末端的单模光纤作为质量块,在受到振动时带动悬臂梁振动,使悬臂梁产生微弯,进而使EFPI腔长发生变化。实验结果表明,传感器的工作区域为20~300Hz,在100Hz时,0~3.01g范围内测得加速度分辨率为5×10-4 g,加速度响应灵敏度为129.6nm/g。传感器受温度影响小,腔长的温度交叉响应仅为0.225nm/℃,传感器可耐950℃高温冲击。     

Reflection interferometer based on the Troitsky thin film for frequency selection in fiber lasers

A two-mirror multiple-beam interferometer with a noninverted response function in reflection is used for the frequency selection and tuning in fiber lasers. The simplest version of the interferometer is based on a thin metal (Troitsky) film. Such a reflection interferometer corresponds to an external (with respect to a fiber) two-mirror cavity that consists of a spherical highly reflective (99.8%) mirror and a plane mirror represented by the thin metal film deposited on the fiber end face. Tuning to the selected frequency is performed due to a variation in the distance between the mirrors.     

High-temperature fiber optic imaging

An experimental demonstration of fiber optic imaging inside a furnace at 1000°C is described, A low-resolution sapphire fiber optic video system was designed, fabricated, and tested for basic performance in a small tube furnace. The imaging fiber bundle was assembled using 100 high-quality sapphire fibers aligned and bonded at each end. Experiments to achieve a high-temperature cladding are described. Reference imaging experiments at room temperature were performed with the sapphire fiber bundle and a commercial glass fiber bundle of comparable sue. Imaging experiments at 1000°C are described and discussed.     

一种光纤干涉式高压电流传感器的设计

设计了一种结构简单的光纤干涉式电流传感器，给出了其数学模型，并用实验验证了该系统的可靠，与其它光纤电流感器相比，该传感器高压侧无需电源，特殊的光路使得它的测量范围大大增加，并且对缓变的干扰信号（如温度）不敏感。     

飞秒激光制作微型光纤干涉传感器的研究进展

飞秒激光脉冲持续时间短、峰值功率高,在对物质进行处理过程中热作用区域小、加工精度高,已成为一种制作高性能、新结构光子器件的重要方法。简单介绍了飞秒脉冲激光微加工的方法和特性,归纳了飞秒激光直写技术在光纤干涉型传感器制作方面的研究进展,包括微型光纤Fabry-Perot干涉传感器和微型光纤Mach-Zehnder干涉传感器,重点介绍了这些光纤传感器的结构、特性和潜在应用。对用该技术制作的微型光纤干涉传感器进行了总结和展望。     

Simultaneous measurement of refractive index and temperature based on a reflection-mode long-period grating and an intrinsic Fabry-Perot interferometer sensor

We have demonstrated a single fiber probe for simultaneous measurement of external refractive index and temperature based on two interferometers: a reflection-mode long-period grating (LPG) for refractometry and an intrinsic Fabry-Perot interferometer (IFPI) for temperature measurement. Since the output signal of the combined structure is a superposition of signals produced by both sensors, which have different spatial frequencies, the original signals needed for the index and temperature measurements can be separated and recovered through digital filters.     

具有有源闭合腔的光纤光栅传感系统地址查询技术

基于熔融拉锥技术研制的3 dB宽带耦合器的光纤环形镜的工作原理,提出了一种新型的具有有源闭合腔装置的光纤光栅传感系统。在用作闭合共振腔端镜的环形镜中写入十个波分复用光纤光栅传感元,利用共振腔中接入的法布里-珀罗滤波器,通过控制电压对传感光栅的波长扫描,实现对传感地址的查询。用非平衡的迈克耳孙扫描干涉仪将传感光栅的波长漂移信息变为相移信息,实现传感信号的解调。系统传感灵敏度的实验值为1.5835°/10-6ε,与理论值(1.6662°/10-6ε)基本吻合。