CN110260920A - Temperature and refractive index dual sampling device based on directional coupler and long-period fiber grating - Google Patents
Temperature and refractive index dual sampling device based on directional coupler and long-period fiber grating Download PDFInfo
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Abstract
本发明涉及一种基于定向耦合器与长周期光纤光栅的温度和折射率双参量传感器，属于光纤传感技术领域。包括光源、单模光纤、一段双芯光纤、探测器；双芯光纤的同一个纤芯与两侧单模光纤的纤芯对准熔接；双芯光纤两个纤芯材料相同，均为单模，纤芯间距小于20微米，两个纤芯满足相位匹配条件，连接两端单模光纤的纤芯上刻有长周期光纤光栅，为通光纤芯。两纤芯可发生能量耦合构成定向耦合器。光栅产生的共振峰随外界折射率和温度改变而发生漂移，定向耦合器共振峰的变化仅由外界温度变化引起，从而实现折射率与温度的同时测量。本发明传感器制作简单，器件小易于集成，可同时进行双参数测量，灵敏度高，具有温度自补偿能力，应用前景广阔。
The invention relates to a temperature and refraction index dual-parameter sensor based on a directional coupler and a long-period fiber grating, and belongs to the technical field of fiber optic sensing. Including light source, single-mode optical fiber, a section of dual-core optical fiber, and detector; the same core of the dual-core optical fiber is aligned and welded with the cores of the single-mode optical fibers on both sides; the two core materials of the dual-core optical fiber are the same, both are single-mode , the core spacing is less than 20 microns, the two cores meet the phase matching conditions, and the core connecting the two ends of the single-mode fiber is engraved with a long-period fiber grating, which is a pass-through fiber core. The energy coupling between the two cores can form a directional coupler. The resonant peak generated by the grating drifts with the change of the external refractive index and temperature, and the change of the resonant peak of the directional coupler is only caused by the change of the external temperature, thereby realizing the simultaneous measurement of the refractive index and temperature. The sensor of the invention is simple to manufacture, small in size and easy to integrate, can simultaneously measure two parameters, has high sensitivity, has temperature self-compensation capability, and has broad application prospects.
Description
技术领域technical field
本发明涉及一种基于定向耦合器与长周期光纤光栅的温度和折射率双参量传感器，属于光纤传感技术领域。The invention relates to a temperature and refraction index dual-parameter sensor based on a directional coupler and a long-period fiber grating, and belongs to the technical field of fiber optic sensing.
背景技术Background technique
光纤传感技术的出现，使新型传感器用光作为敏感信息载体，具有光学测量和光信号传输等独特优点，同时具有高灵敏度，可快速测量，大信息容量，强适应性(耐高温、抗腐蚀、抗电磁干扰等)，适宜集成等优势。利用光波分复用、时分复用以及空分复用技术，一根光纤可同时传输多路信号。与计算机技术和遥测技术配合，还可实现远距离，实时在线测量等，其应用前景十分广泛。The emergence of optical fiber sensing technology makes the new sensor use light as a sensitive information carrier, which has unique advantages such as optical measurement and optical signal transmission, and has high sensitivity, fast measurement, large information capacity, and strong adaptability (high temperature resistance, corrosion resistance, Anti-electromagnetic interference, etc.), suitable for integration and other advantages. Using optical wavelength division multiplexing, time division multiplexing and space division multiplexing technologies, one optical fiber can transmit multiple signals at the same time. Cooperating with computer technology and telemetry technology, it can also realize long-distance, real-time online measurement, etc., and its application prospect is very wide.
多芯光纤(空分复用)可以提高光的传输容量，基于多芯光纤的传感器具有很多优良特性，比如体积小、结构紧凑、集成度高、易于实现多参量测量。基于多芯光纤的传感元件已经成为光纤传感领域的研究热点之一。双芯光纤是结构最简单的多芯光纤，利用双芯光纤可以实现定向耦合器、复用/解复用器、双芯光纤分波/合波器、滤波器、传感器等。Multi-core fiber (space division multiplexing) can improve the transmission capacity of light. Sensors based on multi-core fiber have many excellent characteristics, such as small size, compact structure, high integration, and easy multi-parameter measurement. Sensing elements based on multi-core optical fibers have become one of the research hotspots in the field of optical fiber sensing. The dual-core optical fiber is the simplest multi-core optical fiber, and the dual-core optical fiber can be used to realize directional couplers, multiplexers/demultiplexers, dual-core fiber splitters/combiners, filters, sensors, etc.
光纤光栅具有阻带宽、灵敏度高、耐腐蚀、抗电磁辐射等特点，已成为目前最具代表性的光纤无源器件之一。而长周期光纤光栅将纤芯模耦合到正向传输的包层模，比布拉格光纤光栅更容易感知外界物理量的变化，由于其对环境折射率敏感而被作为研制折射率传感器的重要结构。目前，折射率传感器除被直接用于液体折射率测量外，还大量应用于对气体浓度、有机物浓度(有机农药、食品添加剂等)或生化元素含量(蛋白质、病毒等)的间接检测。此类应用对折射率测量的精度要求极高，所以温度串扰引入的测量误差成为限制其最终检测精度的一个重要因素。Fiber Bragg Grating has the characteristics of wide band stop, high sensitivity, corrosion resistance, and electromagnetic radiation resistance, and has become one of the most representative optical fiber passive devices at present. The long-period fiber grating couples the core mode to the forward-transmitting cladding mode, which is easier to perceive the change of the external physical quantity than the fiber Bragg grating. Because of its sensitivity to the environmental refractive index, it is used as an important structure for the development of refractive index sensors. At present, in addition to being directly used to measure the refractive index of liquids, the refractive index sensor is also widely used in the indirect detection of gas concentration, organic substance concentration (organic pesticides, food additives, etc.) or biochemical element content (protein, virus, etc.). Such applications have extremely high requirements on the accuracy of refractive index measurement, so the measurement error introduced by temperature crosstalk becomes an important factor limiting the final detection accuracy.
本发明利用一种双芯光纤构成的定向耦合器与长周期光纤光栅相结合来实现对环境折射率和温度的双参量测量。由于双芯光纤的芯间距很小，在满足相位匹配条件时可以实现纤芯间的能量耦合。由于包层的阻隔，这种纤芯之间的能量耦合对外界折射率变化不敏感，所以定向耦合器共振耦合形成的共振峰仅对温度变化敏感。而长周期光纤光栅将纤芯模耦合到包层模中，包层模对外界折射率变化极为敏感，故长周期光纤光栅形成的共振峰对外界折射率变化和温度变化均敏感。检测过程中，可由定向耦合器产生的共振峰实现对温度变化的检测，并为长周期光纤光栅的折射率测试过程提供温度补偿，进而得到排除温度串扰的折射率监测结果，有效解决了折射率测量过程中的串扰问题，实现折射率与温度的同时测量。该传感器制作简单，器件小易于集成，可同时进行双参数测量，具有温度自补偿能力，具有高的折射率测量精度。The invention combines a directional coupler composed of a double-core optical fiber and a long-period optical fiber grating to realize the dual-parameter measurement of the ambient refractive index and temperature. Since the core spacing of the dual-core fiber is very small, the energy coupling between the cores can be achieved when the phase matching conditions are met. Due to the barrier of the cladding, the energy coupling between the cores is not sensitive to the change of the external refractive index, so the resonant peak formed by the resonant coupling of the directional coupler is only sensitive to the temperature change. The long-period fiber grating couples the core mode to the cladding mode, and the cladding mode is extremely sensitive to changes in the external refractive index, so the resonance peak formed by the long-period fiber grating is sensitive to changes in the external refractive index and temperature. During the detection process, the resonance peak generated by the directional coupler can be used to detect the temperature change, and provide temperature compensation for the refractive index test process of the long-period fiber Bragg grating, and then obtain the refractive index monitoring result that excludes temperature crosstalk, effectively solving the problem of refractive index. The problem of crosstalk in the measurement process is realized, and the simultaneous measurement of the refractive index and temperature is realized. The sensor is simple to manufacture, small in size and easy to integrate, can simultaneously measure two parameters, has temperature self-compensation capability, and has high measurement accuracy of refractive index.
发明内容Contents of the invention
本发明的目的是为了解决温度串扰引入的测量误差而提供一种基于定向耦合器与长周期光纤光栅的温度和折射率双参量传感器。The object of the present invention is to provide a temperature and refraction index dual-parameter sensor based on a directional coupler and a long-period fiber grating in order to solve the measurement error caused by temperature crosstalk.
本发明的目的是这样实现的：一种基于定向耦合器与长周期光纤光栅的温度和折射率双参量传感器；包括光源、单模光纤、一段双芯光纤、单模光纤、探测器；光源位于最左侧，右边依次是单模光纤、一段双芯光纤、单模光纤、探测器，探测器位于最右侧；在光源一侧，单模光纤的纤芯与双芯光纤的一个纤芯对准熔接，在探测器一侧，双芯光纤的同一个纤芯与单模光纤的纤芯对准熔接；双芯光纤长度为耦合长度的奇数倍，双芯光纤的包层直径为125微米，两个纤芯材料相同，均为单模，纤芯间距小于20微米，两个纤芯满足相位匹配条件，连接两端单模光纤的纤芯上刻有长周期光纤光栅，为通光纤芯。The object of the present invention is achieved like this: a kind of temperature and refractive index dual-parameter sensor based on directional coupler and long-period fiber grating; Comprising light source, single-mode optical fiber, a section of double-core optical fiber, single-mode optical fiber, detector; On the far left, on the right are single-mode fiber, a section of double-core fiber, single-mode fiber, detector, and the detector is on the far right; Quasi-splicing, on the detector side, the same core of the dual-core fiber is aligned with the core of the single-mode fiber for fusion splicing; the length of the dual-core fiber is an odd multiple of the coupling length, and the cladding diameter of the dual-core fiber is 125 microns. The two core materials are the same, both are single-mode, the distance between the cores is less than 20 microns, the two cores meet the phase matching conditions, and the cores connecting the single-mode fibers at both ends are engraved with long-period fiber gratings, which is a pass-through fiber core.
本发明还包括这样一些结构特征：The present invention also includes such structural features:
所述双芯光纤为全固态实心光纤，两个纤芯关于光纤轴线对称分布。The dual-core optical fiber is an all-solid solid optical fiber, and the two cores are symmetrically distributed about the axis of the optical fiber.
所述双芯光纤为全固态实心光纤，两个纤芯一个位于中心，另一个是偏芯。The dual-core optical fiber is an all-solid solid optical fiber, one of the two cores is located at the center, and the other is an eccentric core.
所述双芯光纤为孔助光纤，包层有一个大尺寸偏心空气孔，光纤的一个纤芯位于包层中心，另一纤芯位于与中心纤芯距离最近的空气孔内壁，孔助双芯光纤空气孔的直径为30-50微米，悬挂纤芯的尺寸大于中心纤芯的尺寸，两个纤芯在某一波长下满足相位匹配条件。The dual-core optical fiber is a hole-assisted optical fiber, and the cladding has a large-sized eccentric air hole. One core of the optical fiber is located in the center of the cladding, and the other core is located on the inner wall of the air hole closest to the central core. The hole-assisted dual-core The diameter of the fiber air hole is 30-50 microns, the size of the suspended fiber core is larger than the size of the central fiber core, and the two fiber cores meet the phase matching condition at a certain wavelength.
所述双芯光纤为经过载氢处理的双芯光纤。The dual-core optical fiber is a hydrogen-loaded dual-core optical fiber.
所述长周期光纤光栅的加工方法是高频CO2激光器单侧曝光法。The processing method of the long-period fiber grating is a high-frequency CO 2 laser single-side exposure method.
所述长周期光纤光栅的加工方法是激光器逐点曝光法。The processing method of the long-period fiber grating is a point-by-point laser exposure method.
所述双芯光纤的空气孔中注有增敏材料。The air hole of the double-core optical fiber is injected with a sensitivity-increasing material.
与现有技术相比，本发明的有益效果是：本发明利用双芯光纤纤芯间的共振耦合与长周期光纤光栅产生的纤芯模式与包层模式的耦合作为传感原理，测量折射率时可以有效避免温度串扰问题，提高折射率测量精度，又可实现折射率与温度的同时测量。本发明器件结构简单，易与单模光纤互联，定向耦合器和光栅是并联结构，器件紧凑，集成度高。本发明利用孔助双芯光纤构造传感器件时，可通过在空气孔中注入增敏材料来提高温度灵敏度，实现更高精度的温度与折射率测量。Compared with the prior art, the beneficial effect of the present invention is: the present invention uses the resonant coupling between the cores of the dual-core optical fiber and the coupling of the core mode and the cladding mode produced by the long-period fiber grating as the sensing principle to measure the refractive index It can effectively avoid the temperature crosstalk problem, improve the measurement accuracy of the refractive index, and realize the simultaneous measurement of the refractive index and temperature. The device of the invention has a simple structure and is easy to be interconnected with a single-mode optical fiber. The directional coupler and the grating are in parallel structure, and the device is compact and highly integrated. When the invention utilizes the hole-aided dual-core optical fiber to construct the sensor device, the temperature sensitivity can be improved by injecting the sensitizing material into the air hole, and higher-precision temperature and refractive index measurement can be realized.
附图说明Description of drawings
图1是基于实双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器示意图；Figure 1 is a schematic diagram of a temperature and refractive index dual-parameter sensor based on a real dual-core fiber directional coupler and a long-period fiber grating;
图2(a)是实双芯光纤结构图；图2(b)是孔助双芯光纤结构图；Fig. 2 (a) is a structural diagram of a real dual-core optical fiber; Fig. 2 (b) is a structural diagram of a hole-assisted dual-core optical fiber;
图3(a)是在实双芯光纤中写入长周期光纤光栅时激光方位图；图3(b)是在孔助双芯光纤写入长周期光纤光栅时激光方位图；Fig. 3(a) is the laser azimuth diagram when writing long-period fiber grating in real dual-core fiber; Fig. 3(b) is the laser azimuth diagram when writing long-period fiber grating in hole-assisted dual-core fiber;
图4是基于孔助双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器示意图。Fig. 4 is a schematic diagram of a temperature and refractive index dual-parameter sensor based on a hole-assisted dual-core fiber directional coupler and a long-period fiber grating.
具体实施方式Detailed ways
下面结合附图与具体实施方式对本发明作进一步详细描述。The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.
本发明的目的是这样实现的：一种基于光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器是由光源、单模光纤4、一段双芯光纤6、单模光纤5、探测器依次相连而成。双芯光纤长度为耦合长度的奇数倍，双芯光纤6的包层3直径为125微米，两个纤芯1和2材料相同，均为单模，纤芯间距小于20微米，纤芯1和纤芯2需满足相位匹配条件，且一个纤芯上刻有长周期光纤光栅7。两个纤芯1和2可以关于光纤轴线对称分布，也可以一个位于中心，另一个是偏芯。双芯光纤两端单模光纤的纤芯需要与双芯光纤中同一个纤芯对准熔接。长周期光纤光栅7刻写在双芯光纤6的通光纤芯上，用于激发芯模与包层模之间的耦合。双芯光纤需进行载氢处理来提高光纤光敏性，从而在制备长周期光纤光栅时激发更高阶的包层模式，提高折射率响应灵敏度。可以利用不同的双芯结构进行器件优化，长周期光纤光栅的加工方法可以但不限于高频CO2激光器单侧曝光法和激光器逐点曝光法。双芯光纤可以为全固态实心光纤，也可以为孔助光纤12，即包层9有一个大尺寸偏心空气孔10，光纤的一个纤芯11位于包层中心，另一纤芯8位于与中心纤芯距离最近的空气孔内壁，孔助双芯光纤空气孔的直径为30-50微米，悬挂纤芯的尺寸大于中心纤芯的尺寸，两个纤芯在某一波长下满足相位匹配条件。可以通过在空气孔中注入增敏材料来提升器件温度灵敏度。基于光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器，其工作原理是：光从单模光纤4注入双芯光纤6的纤芯1，由于纤芯1与纤芯2满足相位匹配条件，所以光会在两芯间来回耦合。在出射端，纤芯1中的光进入单模光纤5，并被探测器检测。由于长周期光纤光栅的存在，满足长周期光纤光栅共振条件的光将被耦合到双芯光纤的包层中。所以探测器接收到的光谱同时包含定向耦合器产生的共振峰和长周期光纤光栅产生的共振峰。在进行折射率测试时，长周期光纤光栅产生的共振峰对外界折射率变化和温度变化均产生响应。环境折射率的改变引起包层模式有效折射率的改变，从而引起长周期光纤光栅产生共振峰的漂移。同时，温度的变化会引起双芯光纤纤芯和包层折射率发生变化，也会导致长周期光纤光栅产生共振峰的漂移。但是，定向耦合器产生的共振峰对外界折射率变化不产生响应，仅对温度变化产生响应。温度变化引起双芯光纤纤芯和包层的折射率发生变化，进而导致两纤芯间耦合系数的变化，最终引起定向耦合器产生的共振峰发生漂移。所以可以通过定向耦合器共振峰的漂移检测温度变化，进一步为长周期光纤光栅产生的共振峰进行温度补偿，得到排除温度串扰的折射率测量结果。即实现了折射率测量中温度串扰的排除与温度和折射率的同时测量。The object of the present invention is achieved like this: a kind of temperature and the refractive index dual parameter sensor based on optical fiber directional coupler and long-period fiber grating are composed of light source, single-mode optical fiber 4, a section of double-core optical fiber 6, single-mode optical fiber 5, detection connected in sequence. The length of the dual-core optical fiber is an odd multiple of the coupling length. The diameter of the cladding 3 of the dual-core optical fiber 6 is 125 microns. The materials of the two cores 1 and 2 are the same, both of which are single-mode. The fiber core 2 needs to meet the phase matching condition, and a long-period fiber grating 7 is engraved on one fiber core. The two cores 1 and 2 can be distributed symmetrically with respect to the fiber axis, or one can be located at the center and the other can be eccentric. The cores of the single-mode fiber at both ends of the dual-core fiber need to be aligned with the same core in the dual-core fiber for fusion splicing. The long-period fiber grating 7 is written on the clear core of the dual-core fiber 6, and is used to excite the coupling between the core mode and the cladding mode. The double-core fiber needs to be treated with hydrogen to improve the photosensitivity of the fiber, so as to excite higher-order cladding modes when preparing long-period fiber gratings, and improve the sensitivity of the refractive index response. Different dual-core structures can be used for device optimization, and the processing methods of long-period fiber gratings can be, but not limited to, high-frequency CO 2 laser single-side exposure method and laser point-by-point exposure method. The dual-core optical fiber can be an all-solid solid optical fiber, or a hole-assisted optical fiber 12, that is, the cladding 9 has a large-sized eccentric air hole 10, and one core 11 of the optical fiber is located at the center of the cladding, and the other core 8 is located at the center of the cladding. The core is closest to the inner wall of the air hole, the diameter of the air hole of the hole-assisted dual-core fiber is 30-50 microns, the size of the suspended core is larger than the size of the central core, and the two cores meet the phase matching condition at a certain wavelength. The temperature sensitivity of the device can be enhanced by injecting sensitizing materials into the air holes. The temperature and refractive index dual-parameter sensor based on the fiber directional coupler and long-period fiber grating, its working principle is: light is injected into the core 1 of the dual-core fiber 6 from the single-mode fiber 4, because the core 1 and the core 2 meet the phase Matching conditions, so light will couple back and forth between the two cores. At the exit end, the light in the core 1 enters the single-mode fiber 5 and is detected by a detector. Due to the existence of the long-period fiber grating, the light satisfying the resonance condition of the long-period fiber grating will be coupled into the cladding of the dual-core fiber. Therefore, the spectrum received by the detector contains both the resonant peaks produced by the directional coupler and the resonant peaks produced by the long-period fiber grating. During the refractive index test, the resonant peak generated by the long period fiber grating responds to both the external refractive index change and the temperature change. The change of the ambient refractive index causes the change of the effective refractive index of the cladding mode, which causes the shift of the resonant peak of the long-period fiber grating. At the same time, changes in temperature will cause changes in the refractive index of the core and cladding of the dual-core fiber, and will also cause the shift of the resonance peak of the long-period fiber grating. However, the resonance peak generated by the directional coupler does not respond to external refractive index changes, but only responds to temperature changes. The temperature change causes the refractive index of the core and cladding of the dual-core fiber to change, which in turn leads to a change in the coupling coefficient between the two cores, and finally causes the resonance peak generated by the directional coupler to shift. Therefore, the temperature change can be detected by the drift of the resonant peak of the directional coupler, and further temperature compensation can be performed for the resonant peak generated by the long-period fiber Bragg grating, and the refractive index measurement result that excludes temperature crosstalk can be obtained. That is to say, the elimination of temperature crosstalk in the measurement of the refractive index and the simultaneous measurement of the temperature and the refractive index are realized.
下面结合附图给出本发明的实施例。Embodiments of the present invention are given below in conjunction with the accompanying drawings.
实施例1：Example 1:
结合图1、图2(a)和图3(a)，图1是基于实双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器示意图；图2(a)是实双芯光纤结构图；图3(a)是在实双芯光纤中写入长周期光纤光栅时激光方位图。一种基于实双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器是由光源、单模光纤4、一段双芯光纤6、单模光纤5、探测器依次相连而成。双芯光纤6的两个纤芯1和2材料相同，均为单模，两个纤芯1和2关于光纤轴线对称分布，纤芯间距为15微米。在光源一侧，单模光纤4的纤芯与双芯光纤6的纤芯1对准进行熔接。双芯光纤6的长度为耦合长度的奇数倍。在探测器一侧，利用相同的方法将纤芯1与单模光纤5的纤芯进行熔接。将熔接好的样品置于常温高压载氢罐中进行载氢处理，一周后取出。将取出的样品放置在高频CO2激光器平台，两端由可旋转夹具夹紧。调整可旋转夹具，使纤芯1正对高频CO2激光器。采用高频CO2激光单侧曝光法在双芯光纤纤芯1上写入长周期光纤光栅7，完成器件制备。定向耦合器和长周期光纤光栅形成的两个共振峰都随温度变化发生偏移，首先可确定两共振峰各自的温度特性。在进行折射率测试时，由于温度和折射率均发生改变，长周期光纤光栅形成的共振峰受温度和折射率变化共同影响发生偏移，而定向耦合器形成的共振峰仅对温度变化响应。根据定向耦合器共振峰的变化情况可以检测出温度的变化量，并对长周期光纤光栅共振峰进行温度补偿，得到纯粹的折射率变化量。进而排除折射率测量过程中的温度串扰，实现温度和折射率的同时测量。Combining Figure 1, Figure 2(a) and Figure 3(a), Figure 1 is a schematic diagram of a temperature and refractive index dual-parameter sensor based on a real dual-core fiber directional coupler and a long-period fiber grating; Figure 2(a) is a real dual-core sensor Core fiber structure; Figure 3(a) is the laser orientation diagram when writing long-period fiber gratings in a real dual-core fiber. A temperature and refractive index dual-parameter sensor based on a real dual-core optical fiber directional coupler and a long-period optical fiber grating is formed by sequentially connecting a light source, a single-mode optical fiber 4, a section of dual-core optical fiber 6, a single-mode optical fiber 5, and a detector. The two cores 1 and 2 of the dual-core optical fiber 6 are made of the same material and are both single-mode. The two cores 1 and 2 are symmetrically distributed about the fiber axis, and the distance between the cores is 15 microns. On the light source side, the core of the single-mode fiber 4 is aligned with the core 1 of the dual-core fiber 6 for fusion splicing. The length of the dual-core optical fiber 6 is an odd multiple of the coupling length. On the detector side, the same method is used to fuse the core 1 and the core of the single-mode fiber 5 . The welded samples were placed in a normal temperature and high pressure hydrogen tank for hydrogen loading treatment, and were taken out after one week. The removed sample is placed on a high-frequency CO2 laser platform, and both ends are clamped by rotatable clamps. Adjust the rotatable fixture so that core 1 is facing the high-frequency CO2 laser. A long-period fiber grating 7 is written on the core 1 of a dual-core fiber by using a high-frequency CO 2 laser single-side exposure method to complete the device preparation. The two resonant peaks formed by the directional coupler and the long-period fiber grating shift with the temperature change, and the temperature characteristics of the two resonant peaks can be determined first. During the refractive index test, due to the change of temperature and refractive index, the resonance peak formed by the long period fiber grating is affected by the temperature and the refractive index change and shifts, while the resonance peak formed by the directional coupler only responds to the temperature change. According to the change of the resonant peak of the directional coupler, the temperature change can be detected, and the temperature compensation is performed on the resonant peak of the long-period fiber grating to obtain the pure refractive index change. Furthermore, the temperature crosstalk in the process of measuring the refractive index is eliminated, and the simultaneous measurement of temperature and refractive index is realized.
实施例2：Example 2:
结合图2(b)、图3(b)和图4，图2(b)是孔助双芯光纤结构图；图3(b)是在孔助双芯光纤写入长周期光纤光栅时激光方位图；图4是基于孔助双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器示意图。一种基于孔助双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器，与实施例1不同的是，传感单元由双芯光纤6换为一段具有大直径空气孔的孔助双芯光纤12。孔助双芯光纤12的一个纤芯11位于包层9的中心，光纤包层9中有一个空气孔10，另一纤芯8位于空气孔10内壁且距离纤芯11最近处。孔助双芯光纤12的空气孔10直径为45微米，纤芯11直径为9微米，纤芯8直径为13微米，纤芯与包层折射率差为0.005，两个纤芯间距18微米，在波长2000纳米时耦合长度为3.5毫米。长度为31.5毫米的孔助双芯光纤12与单模光纤14正对熔接，使单模光纤纤芯与孔助双芯光纤中心纤芯11正对。采用高频CO2激光单侧曝光法在孔助双芯光纤12的纤芯11上写入长周期光纤光栅13。光栅制备时，将空气孔10旋转至中心纤芯11下方，如图3(b)所示。完成器件制备。Combining Figure 2(b), Figure 3(b) and Figure 4, Figure 2(b) is the structural diagram of the hole-assisted dual-core fiber; Figure 3(b) is the laser when the hole-assisted dual-core fiber is written into the long-period fiber grating Orientation diagram; Figure 4 is a schematic diagram of a temperature and refractive index dual-parameter sensor based on a hole-assisted dual-core fiber directional coupler and a long-period fiber grating. A dual-parameter sensor for temperature and refractive index based on a hole-assisted dual-core optical fiber directional coupler and a long-period fiber grating. The difference from Embodiment 1 is that the sensing unit is replaced by a dual-core optical fiber 6 with a large-diameter air hole. The hole assists the dual-core optical fiber 12. One core 11 of the hole-assisted dual-core optical fiber 12 is located at the center of the cladding 9 , and there is an air hole 10 in the fiber cladding 9 , and the other core 8 is located at the inner wall of the air hole 10 and is closest to the core 11 . The air hole 10 of the hole-assisted dual-core optical fiber 12 has a diameter of 45 microns, the diameter of the core 11 is 9 microns, the diameter of the core 8 is 13 microns, the difference between the refractive index of the core and the cladding is 0.005, and the distance between the two cores is 18 microns. The coupling length is 3.5 mm at a wavelength of 2000 nm. The hole-assisted dual-core optical fiber 12 and the single-mode optical fiber 14 with a length of 31.5 mm are welded facing each other, so that the core of the single-mode optical fiber is opposite to the center core 11 of the hole-assisted dual-core optical fiber. A long-period fiber grating 13 is written on the core 11 of the hole-assisted dual-core optical fiber 12 by using a high-frequency CO 2 laser single-side exposure method. When preparing the grating, the air hole 10 is rotated below the central core 11, as shown in FIG. 3(b). Complete device preparation.
实施例3：Example 3:
结合图2(b)和图4，图2(b)是孔助双芯光纤结构图；；图4是基于孔助双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器示意图。一种基于孔助双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感器，与实施例2不同的是，在长度为31.5毫米的孔助双芯光纤12与单模光纤14进行正对熔接之前，可以在孔助双芯光纤12的空气孔10中注入折射率为1.35的折射率匹配液，然后进行熔接。该传感器的温度灵敏度将被提高。Combining Figure 2(b) and Figure 4, Figure 2(b) is a structural diagram of a hole-assisted dual-core fiber; Figure 4 is a temperature and refractive index dual-parameter sensor based on a hole-assisted dual-core fiber directional coupler and a long-period fiber grating schematic diagram. A temperature and refractive index dual-parameter sensor based on a hole-assisted dual-core optical fiber directional coupler and a long-period fiber grating. The difference from Embodiment 2 is that the hole-assisted dual-core optical fiber 12 and the single-mode optical fiber 14 with a length of 31.5 mm Before performing the facing fusion splicing, a refractive index matching liquid with a refractive index of 1.35 may be injected into the air hole 10 of the hole-assisted dual-core optical fiber 12, and then fusion splicing is performed. The temperature sensitivity of the sensor will be improved.
综上，本发明提供了一种基于双芯光纤定向耦合器与长周期光纤光栅的温度和折射率双参量传感，传感器是由光源、单模光纤、一段双芯光纤、单模光纤、探测器依次相连而成。双芯光纤两纤芯的中心间距小于20微米，两个纤芯满足相位匹配条件且一个纤芯上刻有长周期光纤光栅。由于两纤芯距离近且满足相位匹配条件，两纤芯可以发生能量耦合构成定向耦合器。通光纤芯中的光能量被耦合到另一纤芯中，由于包层将纤芯与外界隔离，纤芯间的互耦对外界折射率变化并不敏感，仅对温度变化敏感。而双芯光纤通光纤芯上的长周期光纤光栅使通光纤芯的纤芯模式与包层模式耦合，被激发的高阶包层模式对外界折射率变化敏感，因此光栅产生的共振峰会随外界折射率和温度改变而发生漂移。定向耦合器共振峰的变化仅由外界温度变化引起，其共振峰可实现对折射率测量过程中温度变化的测定，并为长周期光纤光栅在折射率测试过程中提供温度补偿，实现折射率与温度的同时测量。该传感器制作简单，器件小易于集成，可同时进行双参数测量，灵敏度高，具有温度自补偿能力。In summary, the present invention provides a dual-parameter sensing of temperature and refractive index based on a dual-core fiber directional coupler and a long-period fiber grating. The sensor is composed of a light source, a single-mode fiber, a section of dual-core fiber, a single-mode fiber, a detection connected in sequence. The distance between the centers of the two cores of the dual-core optical fiber is less than 20 microns, the two cores meet the phase-matching condition and one core is engraved with a long-period fiber grating. Since the distance between the two cores is close and the phase matching condition is met, the energy coupling between the two cores can form a directional coupler. The light energy in the passing fiber core is coupled to another fiber core. Since the cladding isolates the fiber core from the outside world, the mutual coupling between the fiber cores is not sensitive to changes in the external refractive index, but only to temperature changes. However, the long-period fiber grating on the pass-through fiber core of the dual-core fiber couples the core mode and the cladding mode of the pass-through fiber core, and the excited high-order cladding mode is sensitive to the change of the external refractive index, so the resonance peak generated by the grating varies with the external environment. Drift occurs with changes in refractive index and temperature. The change of the resonant peak of the directional coupler is only caused by the change of the external temperature, and its resonant peak can realize the determination of the temperature change during the refractive index measurement process, and provide temperature compensation for the long-period fiber grating during the refractive index test process, and realize the refractive index and Simultaneous measurement of temperature. The sensor is simple to manufacture, small in size and easy to integrate, capable of simultaneous dual-parameter measurement, high in sensitivity, and capable of temperature self-compensation.
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