CN106940300A - A kind of liquid refractivity characteristic research method - Google Patents

A kind of liquid refractivity characteristic research method Download PDF

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CN106940300A
CN106940300A CN201710166312.3A CN201710166312A CN106940300A CN 106940300 A CN106940300 A CN 106940300A CN 201710166312 A CN201710166312 A CN 201710166312A CN 106940300 A CN106940300 A CN 106940300A
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lpfg
mach
refractive index
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fiber
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祝连庆
李达
何巍
闫光
刘锋
董明利
娄小平
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Beijing Information Science and Technology University
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    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41Refractivity; Phase-affecting properties, e.g. optical path length
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Abstract

A kind of liquid refractivity characteristic research method based on Mach once moral filtering and LPFG, it is characterised in that including step 1:The system of processing that infrared femtosecond laser makes LPFG has been built using devices such as femto-second laser, three-D displacement platform, wideband light source and spectroanalysis instruments;Step 2:Making of the resonance wavelength for 1548.5nm LPFG is completed using the femtosecond laser system of processing built;Step 3:The making of fiber Mach -Zehnder interferometer is completed by way of fibre core dislocation welding using optical fiber splicer;Step 4:Mach-Zehnder interferometer is linked together with LPFG, LPFG transmitted spectrum is filtered;Step 5:The system constituted using Mach-Zehnder interferometer and LPFG is completed to liquid refractivity characteristic research.

Description

一种液体折射率特性研究方法A Research Method of Liquid Refractive Index Characteristics

技术领域technical field

本发明涉及光纤传感器领域,尤其涉及基于马赫-曾德滤波和长周期光纤光栅的液体折射率特性方向的研究方法。The invention relates to the field of optical fiber sensors, in particular to a research method for the direction of liquid refractive index characteristics based on Mach-Zehnder filtering and long-period optical fiber gratings.

背景技术Background technique

光纤传感器具有质量轻、体积小、耐高温、抗腐蚀、抗电磁干扰和灵敏度高等优点。目前利用光纤传感测量液体折射率的方法有法布里珀罗干涉法[2]、马赫-曾德干涉法(MZI)、迈克尔逊干涉法和长周期光纤光栅(Long period fiber grating,LPFG)等。传统的长周期光纤光栅制作方法如紫外曝光掩模板法、高频CO2激光逐点写入法和腐蚀刻槽等在光纤载氢处理、高温稳定性、机械强度和灵敏度等方面都具有不同程度的缺陷。飞秒激光制作的LPFG,具有高灵敏度和耐高温等优势。Optical fiber sensors have the advantages of light weight, small size, high temperature resistance, corrosion resistance, electromagnetic interference resistance and high sensitivity. At present, there are Fabry-Perot interferometry [2], Mach-Zehnder interferometry (MZI), Michelson interferometry and long period fiber grating (Long period fiber grating, LPFG) methods to measure the refractive index of liquids using optical fiber sensing. Wait. Traditional long-period fiber grating fabrication methods, such as ultraviolet exposure mask method, high-frequency CO2 laser point-by-point writing method, and etching groove, etc., have varying degrees of limitations in terms of hydrogen-carrying fiber processing, high-temperature stability, mechanical strength, and sensitivity. defect. The LPFG made by femtosecond laser has the advantages of high sensitivity and high temperature resistance.

利用飞秒激光制作LPFG与全光纤型MZI的制作是近年来国内外研究的热点。2011年Li B等人采用紫外飞秒激光逐点刻写方法实现了谐振波长为1476nm,栅区长度为25mm的LPFG制备,并将LPFG用于液体折射率传感测试,观察到随着折射率的增加,LPFG的透射波长发生蓝移。2012年苗飞等人利用飞秒激光制作出栅区长度为40mm的LPFG并对该LPFG的高温传感特性进行了研究。2013年张琪等人利用单模光纤和长周期光纤光栅制作了锥体光纤-长周期光纤光栅-锥体光纤型全光纤MZI;2014年杨凯等人利用单模光纤采用锥腰扩大熔接技术制作了同轴式液封MZI。2015年Ahmed F等人利用飞秒激光首次在无掺杂的纯硅光纤中制作了光栅长度为26.97mm的LPFG,并对LPFG的高温和折射率特性进行分析,发现随着折射率的增加谐振波长发生蓝移。2016年卞继城等人在保偏光纤中通过电弧放电和熔接推挤的方式制作了MZI温度传感器,温度灵敏度为0.0998nm/℃。综上所述,研究纤芯错位熔接法制作MZI和飞秒制备高折射率灵敏度、短栅区的LPFG具有重要意义。The fabrication of LPFG and all-fiber MZI by using femtosecond laser is a research hotspot at home and abroad in recent years. In 2011, Li B et al. used the ultraviolet femtosecond laser point-by-point writing method to realize the preparation of LPFG with a resonance wavelength of 1476nm and a gate length of 25mm, and used LPFG for liquid refractive index sensing tests. increase, the transmission wavelength of LPFG is blue-shifted. In 2012, Miao Fei et al. used a femtosecond laser to fabricate an LPFG with a gate length of 40 mm and studied the high-temperature sensing characteristics of the LPFG. In 2013, Zhang Qi et al. used single-mode fiber and long-period fiber grating to make a cone fiber-long-period fiber grating-cone fiber type all-fiber MZI; in 2014, Yang Kai et al. used single-mode fiber to expand the fusion splicing technology with cone waist Made a coaxial liquid seal MZI. In 2015, Ahmed F et al. used a femtosecond laser to fabricate an LPFG with a grating length of 26.97mm in an undoped pure silicon fiber for the first time, and analyzed the high temperature and refractive index characteristics of the LPFG, and found that the resonance increases with the increase of the refractive index. The wavelength is blue shifted. In 2016, Bian Jicheng et al. fabricated an MZI temperature sensor in a polarization-maintaining fiber by means of arc discharge and fusion splicing, with a temperature sensitivity of 0.0998nm/°C. In summary, it is of great significance to study the fabrication of MZI by core dislocation fusion splicing and femtosecond fabrication of LPFG with high refractive index sensitivity and short gate region.

发明内容Contents of the invention

本发明提出了一种基于马赫-曾德滤波和长周期光纤光栅的液体折射率特性研究方法,其特征在于,包括步骤1:利用飞秒激光器、三维位移平台、宽带光源和光谱分析仪等器件搭建了红外飞秒激光制作长周期光纤光栅的加工系统;步骤2:利用搭建的飞秒激光加工系统完成谐振波长为1548.5nm的长周期光纤光栅的制作;步骤3:利用光纤熔接机通过纤芯错位熔接的方式完成光纤马赫曾德干涉仪的制作;步骤4:将马赫曾德干涉仪与长周期光纤光栅连接在一起,对LPFG的透射光谱进行滤波;步骤5:利用马赫曾德干涉仪与长周期光纤光栅组成的系统完成对液体折射率特性研究。The present invention proposes a method for researching liquid refractive index characteristics based on Mach-Zehnder filter and long-period fiber grating, which is characterized in that it includes step 1: using devices such as femtosecond lasers, three-dimensional displacement platforms, broadband light sources, and spectrum analyzers A processing system for making long-period fiber gratings with an infrared femtosecond laser was built; Step 2: Use the built femtosecond laser processing system to complete the production of long-period fiber gratings with a resonance wavelength of 1548.5nm; Step 3: Use a fiber fusion splicer to pass through the fiber core The production of the optical fiber Mach-Zehnder interferometer is completed by dislocation fusion; step 4: connect the Mach-Zehnder interferometer with the long-period fiber grating, and filter the transmission spectrum of the LPFG; step 5: use the Mach-Zehnder interferometer and The system composed of long-period fiber gratings completes the research on the refractive index characteristics of liquids.

优选地,所述步骤1中的激光器中心波长800nm、脉冲宽度120fs、重复频率1kHz的钛蓝宝石飞秒激光器;采用的显微物镜的放大倍数为100倍、数值孔径为0.70;光谱分析仪的工作波长范围1200nm~2400nm,最小分辨精度为0.02nm。Preferably, the titanium sapphire femtosecond laser with a center wavelength of 800nm, a pulse width of 120fs, and a repetition rate of 1kHz in the step 1; the magnification of the microscopic objective lens used is 100 times, and the numerical aperture is 0.70; the work of the spectrum analyzer The wavelength range is 1200nm~2400nm, and the minimum resolution accuracy is 0.02nm.

优选地,所述步骤2中的长周期光纤光栅的周期为400,占空比为0.5,谐振强度为7dB,半高宽为6.3nm。Preferably, the period of the LPFG in step 2 is 400, the duty cycle is 0.5, the resonance strength is 7dB, and the half maximum width is 6.3nm.

优选地,所述步骤3中的光纤熔接机的放电时间为2500ms,预熔时间为180ms;马赫曾德干涉仪的干涉光谱对比度为10dB。Preferably, the discharge time of the fiber fusion splicer in step 3 is 2500ms, and the pre-melting time is 180ms; the interference spectrum contrast of the Mach-Zehnder interferometer is 10dB.

优选地,所述步骤4中的长周期光纤光栅经马赫曾德干涉滤波器滤波后的谐振波的半高宽为5.6nm。Preferably, the FWHM of the resonant wave filtered by the Mach-Zehnder interference filter of the long-period fiber grating in step 4 is 5.6 nm.

优选地,所述步骤5中的测量系统分别对酒精、蔗糖和NaCl溶液的折射率特性进行测试,三种溶液的折射率灵敏度分别为01.78nm/RIU、132.67nm/RIU和138.80nm/RIU。Preferably, the measurement system in step 5 tests the refractive index properties of alcohol, sucrose and NaCl solutions respectively, and the refractive index sensitivities of the three solutions are 01.78nm/RIU, 132.67nm/RIU and 138.80nm/RIU respectively.

应当理解,前述大体的描述和后续详尽的描述均为示例性说明和解释,并不应当用作对本发明所要求保护内容的限制。It should be understood that both the foregoing general description and the following detailed description are exemplary illustrations and explanations, and should not be used as limitations on the claimed content of the present invention.

附图说明Description of drawings

参考随附的附图,本发明更多的目的、功能和优点将通过本发明实施方式的如下描述得以阐明,其中:With reference to the accompanying drawings, more objects, functions and advantages of the present invention will be clarified through the following description of the embodiments of the present invention, wherein:

图1示出了根据本发明的基于光纤纤芯错位熔接法制作的MZI的结构示意图;Fig. 1 shows the structural representation of the MZI made based on the optical fiber core dislocation fusion splicing method according to the present invention;

图2示出了飞秒激光制作LPFG加工系统图;Fig. 2 shows femtosecond laser to make LPFG processing system diagram;

图3示出了长周期光纤光栅结构图;(a)LPFG栅区刻写轨迹示意图;(b)LPFG栅区显微结构图;Fig. 3 shows the structure diagram of long period fiber grating; (a) Schematic diagram of writing track of LPFG grid area; (b) microstructure diagram of LPFG grid area;

图4示出了基于飞秒激光制作的LPFG透射光谱图;Fig. 4 shows the LPFG transmission spectrogram made based on femtosecond laser;

图5示出了基于纤芯错位熔接制备的MZI;(a)光纤1和光纤2纤芯错位熔接显微图;(b)光纤2和光纤3纤芯错位熔接显微图;(c)MZI透射干涉光谱;Figure 5 shows the MZI prepared based on core dislocation fusion; (a) micrograph of fiber 1 and fiber 2 core dislocation fusion; (b) micrograph of fiber 2 and fiber 3 core dislocation fusion; (c) MZI Transmission interference spectrum;

图6示出了基于MZI滤波的LPFG测量折射率实验系统图;Fig. 6 shows the LPFG measurement experimental system diagram of refractive index based on MZI filtering;

图7示出了MZI与LPFG连接后的透射光谱;(a)MZI连接LPFG前后的光谱图;(b)LPFG谐振波长附近的透射光谱;Figure 7 shows the transmission spectrum after the MZI is connected with the LPFG; (a) the spectrograms before and after the MZI is connected to the LPFG; (b) the transmission spectrum near the resonance wavelength of the LPFG;

图8示出了LPFG的酒精溶液折射率特性曲线;(a)不同折射率下的LPFG的透射光谱;(b)LPFG的谐振波长与折射率的拟合曲线;Fig. 8 shows the alcohol solution refractive index characteristic curve of LPFG; (a) the transmission spectrum of the LPFG under different refractive indices; (b) the fitting curve of the resonant wavelength and the refractive index of LPFG;

图9示出了LPFG的NaCl溶液折射率特性曲线;(a)不同折射率下的LPFG的透射光谱;(b)LPFG的谐振波长与折射率的拟合曲线;Fig. 9 shows the NaCl solution refractive index characteristic curve of LPFG; (a) the transmission spectrum of LPFG under different refractive indices; (b) the fitting curve of the resonant wavelength and the refractive index of LPFG;

图10示出了LPFG的蔗糖溶液折射率特性曲线;(a)不同折射率下的LPFG的透射光谱;(b)LPFG的谐振波长与折射率的拟合曲线。Fig. 10 shows the characteristic curve of the refractive index of LPFG in sucrose solution; (a) the transmission spectrum of LPFG under different refractive indices; (b) the fitting curve of the resonant wavelength and the refractive index of LPFG.

具体实施方式detailed description

通过参考示范性实施例,本发明的目的和功能以及用于实现这些目的和功能的方法将得以阐明。然而,本发明并不受限于以下所公开的示范性实施例;可以通过不同形式来对其加以实现。说明书的实质仅仅是帮助相关领域技术人员综合理解本发明的具体细节。The objects and functions of the present invention and methods for achieving the objects and functions will be clarified by referring to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it can be implemented in various forms. The essence of the description is only to help those skilled in the relevant art comprehensively understand the specific details of the present invention.

在下文中,将参考附图描述本发明的实施例。在附图中,相同的附图标记代表相同或类似的部件,或者相同或类似的步骤。Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

本发明设计并搭建了基于800nm红外飞秒激光制作LPFG的加工系统,制作了栅区长度为3.2mm的LPFG;通过光纤纤芯错位熔接的方式制作了全光纤结构的MZI,与长周期光纤光栅连接对LPFG的谐振波长进行滤波。利用基于MZI滤波的LPFG分别对酒精溶液、NaCl溶液和蔗糖溶液的折射率传感特性进行分析。实验发现随着折射率增加,长周期光纤光栅的透射波长向长波方向移动,具有较高的折射率灵敏度。The present invention designs and builds the processing system based on 800nm infrared femtosecond laser to make LPFG, and makes the LPFG with the gate area length of 3.2mm; makes the MZI of all-fiber structure through the dislocation welding of the fiber core, and the long-period fiber grating The connection filters the resonant wavelength of the LPFG. The refractive index sensing characteristics of alcohol solution, NaCl solution and sucrose solution were analyzed by LPFG based on MZI filter. Experiments have found that with the increase of the refractive index, the transmission wavelength of the long-period fiber grating moves to the long-wave direction, which has a higher refractive index sensitivity.

具体步骤如下:Specific steps are as follows:

1理论分析1 Theoretical analysis

图1是基于光纤纤芯错位熔接法制作的MZI的结构示意图。该MZI是利用熔接机通过光纤纤芯错位熔接的方法制作两个纤芯失配衰减器,光纤1纤芯中的光经过第一个纤芯失配衰减器后进入到光纤2中,一部分在光纤纤芯中传播,另一部分进入到包层中传输。光纤2的纤芯和包层中传输的光通过第二个光纤纤芯失配衰减器后,会有一部分光耦合到光纤3的纤芯中传输。由于光纤2的纤芯模和包层模的相位差异产生不同的干涉光强,对应透射光谱上不同的峰值,形成干涉光谱。Fig. 1 is a schematic structural diagram of an MZI fabricated based on optical fiber core dislocation fusion splicing. The MZI uses a fusion splicer to make two core mismatch attenuators through the method of optical fiber core dislocation fusion. The light in the fiber 1 core enters the fiber 2 after passing through the first core mismatch attenuator, and part of it is in the The fiber propagates in the core, and the other part enters the cladding for transmission. After the light transmitted in the core and cladding of the optical fiber 2 passes through the second optical fiber core mismatch attenuator, part of the light will be coupled into the core of the optical fiber 3 for transmission. Due to the phase difference between the core mode and the cladding mode of the optical fiber 2, different interference light intensities are generated, corresponding to different peaks on the transmission spectrum, forming an interference spectrum.

马赫-曾德干涉仪的传输光强为:The transmitted light intensity of the Mach-Zehnder interferometer is:

式中:I1和I2分别表示为光纤2的纤芯模和包层模耦合到光纤3纤芯中的光强;λ为光纤中传输光的波长;L表示光纤2的长度;为光纤2纤芯模和第j模包层模的有效折射率。纤芯模和j阶包层模的相位差为:In the formula: I 1 and I 2 respectively represent the light intensity of the core mode and cladding mode of fiber 2 coupled to the core of fiber 3; λ is the wavelength of light transmitted in the fiber; L represents the length of fiber 2; with is the effective refractive index of the fiber 2 core mode and the jth cladding mode. The phase difference between the core mode and the j-order cladding mode is:

其中,Δneff为纤芯模和第j包层模的有效折射率差。Among them, Δn eff is the effective refractive index difference between the core mode and the jth cladding mode.

当相位差满足时,干涉光强最弱,其中k为整数,此时透射光谱中波谷对应的波长为:When the phase difference satisfies When , the interference light intensity is the weakest, where k is an integer, and the wavelength corresponding to the trough in the transmission spectrum is:

根据耦合模理论,LPFG是光纤中前向传输的纤芯模和前向传输的包层模之间的耦合,其透射谱中的谐振波长满足以下相位匹配条件:According to the coupled-mode theory, LPFG is the coupling between the forward-propagating core mode and the forward-propagating cladding mode in the fiber, and the resonant wavelength in its transmission spectrum satisfies the following phase matching conditions:

其中,λLP为LPFG透射谱的谐振波长,分别是纤芯基模和j阶包层模的有效折射率,Λ为光栅周期。由于外界折射率的变化会导致有效折射率的变化,引起长周期光纤光栅的透射谱上谐振波长的漂移,因此LPFG可用于液体折射率传感测试。Among them, λ LP is the resonant wavelength of LPFG transmission spectrum, with are the effective refractive indices of the core fundamental mode and the j-order cladding mode, respectively, and Λ is the grating period. Since the change of the external refractive index will lead to the change of the effective refractive index, which will cause the shift of the resonant wavelength on the transmission spectrum of the long-period fiber grating, the LPFG can be used for the liquid refractive index sensing test.

2长周期光纤光栅与马赫-曾德干涉仪制备2 Fabrication of long period fiber grating and Mach-Zehnder interferometer

2.1长周期光纤光栅制备2.1 Fabrication of long period fiber gratings

基于飞秒激光直写法制作长周期光纤光栅的系统组成如图2所示。刻写系统使用的激光器中心波长800nm、脉冲宽度120fs、重复频率1kHz的钛蓝宝石飞秒激光器。激光器出射的红外激光首先经过半波片、偏振片、衰减片和高反镜,然后通过100倍的显微物镜将光斑聚焦在由光纤夹具固定的HI-1060的光纤上,光纤夹具固定在高精度三维运动平台上。采用JDSU公司生产的宽带光源(Broadband light source,BBS)作为测试光源,该光源的出射波长范围为1530nm~1600nm。光谱分析仪为日本YOKOGAWA公司的AQ6375光谱分析仪(Optical spectrum analyzer,OSA),工作波长范围1200nm~2400nm,最小分辨精度为0.02nm。在加工过程中利用光谱分析仪实时观测光纤光栅的透射光谱,通过软件控制三维运动平台的移动和Shutter的闭合从而完成长周期光纤光栅的制作。The composition of the system for fabricating long-period fiber gratings based on the femtosecond laser direct writing method is shown in Figure 2. The writing system uses a titanium sapphire femtosecond laser with a center wavelength of 800nm, a pulse width of 120fs, and a repetition rate of 1kHz. The infrared laser emitted by the laser first passes through a half-wave plate, a polarizer, an attenuation plate and a high-reflection mirror, and then focuses the light spot on the HI-1060 optical fiber fixed by the optical fiber clamp through a 100-fold microscope objective lens. The optical fiber clamp is fixed on the high Precision 3D motion platform. The Broadband light source (BBS) produced by JDSU Company was used as the test light source, and the output wavelength range of the light source was 1530nm-1600nm. The optical spectrum analyzer is AQ6375 optical spectrum analyzer (OSA) from Japan YOKOGAWA Company, the working wavelength range is 1200nm-2400nm, and the minimum resolution accuracy is 0.02nm. In the process of processing, a spectrum analyzer is used to observe the transmission spectrum of the fiber grating in real time, and the movement of the three-dimensional motion platform and the closing of the shutter are controlled by software to complete the production of the long-period fiber grating.

飞秒激光通过逐线写入的方式对光纤进行加工,其刻写轨迹如图3(a)所示。设置飞秒激光的加工速度为10μm/s,功率为50μw,光栅周期Λ=400μm,,逐点划线间距a=40μm,单周期内刻写长度b=200μm,占空比为0.5,图3(b)为LPFG的栅区结构显微图。The femtosecond laser processes the optical fiber by writing line by line, and its writing track is shown in Figure 3(a). Set the processing speed of the femtosecond laser to 10 μm/s, the power to 50 μw, the grating period Λ=400 μm, the interval between dots and dashes a=40 μm, the writing length b=200 μm in a single period, and the duty cycle to be 0.5, as shown in Figure 3( b) Micrograph of the gate structure of LPFG.

实验中,刻写8个周期,LPFG的透射光谱如图4所示,该LPFG在1548.5nm处谐振峰峰值深度为7dB,半高全宽(full width at half maximum,FWHM)为6.3mm。光纤栅区长度小于约为3.2mm,刻写时间小于3min。In the experiment, 8 cycles were written, and the transmission spectrum of the LPFG is shown in Figure 4. The depth of the resonance peak of the LPFG at 1548.5nm is 7dB, and the full width at half maximum (FWHM) is 6.3mm. The length of the optical fiber grating region is less than about 3.2 mm, and the writing time is less than 3 minutes.

2.2全光纤马赫-曾德干涉仪制备2.2 Fabrication of all-fiber Mach-Zehnder interferometer

实验中设计采用光纤纤芯错位熔接的方式制备MZI,结构示意图如图1所示。其中,MZI由三根HI1060光纤构成。其制作流程为:将光纤2去掉涂覆层并用光纤切割刀将端面切平,采用光纤熔接机(Fujikura FSM-80s)分别与光纤1和光纤3错位熔接。为了实现光纤纤芯错位熔接,光纤熔接机的参数为:对芯方式为手动对芯,预熔时间为180ms,预熔功率为标准+10,放电时间为2500ms。熔接过程中手动控制光纤错位间距,鉴于HI1060光纤的纤芯直径为5.3,为了保证MZI干涉光谱有较高的对比度和较高的透射光强,手动设置纤芯的错位间距约2,完成MZI的制作。图5(a)为左右两个纤芯错位熔接的显微图。将制作完成的MZI一端连接JDSU公司生产的光谱范围为1530nm~1600nm的宽带光源,输出端连接日本YOKOGAWA公司的AQ6375光谱分析仪,MZI的透射光谱如图5(b)所示,图中可以看出,该MZI的干涉条纹对比度为10dB。In the experiment, the MZI was prepared by dislocation fusion splicing of optical fiber cores. The schematic diagram of the structure is shown in Figure 1. Among them, MZI is composed of three HI1060 optical fibers. The production process is as follows: remove the coating layer from the optical fiber 2, cut the end face flat with an optical fiber cutter, and then use an optical fiber fusion splicer (Fujikura FSM-80s) to splice the optical fiber 1 and the optical fiber 3 in dislocation respectively. In order to achieve dislocation fusion of optical fiber cores, the parameters of the optical fiber fusion splicer are: the core alignment method is manual alignment, the pre-melting time is 180ms, the pre-melting power is standard +10, and the discharge time is 2500ms. During the fusion splicing process, the dislocation distance of the fiber is manually controlled. Since the core diameter of the HI1060 fiber is 5.3, in order to ensure that the MZI interference spectrum has a high contrast and a high transmitted light intensity, the dislocation distance of the fiber core is manually set to about 2 to complete the MZI. make. Fig. 5(a) is a micrograph of dislocation welding of the left and right cores. Connect one end of the completed MZI to a broadband light source with a spectral range of 1530nm to 1600nm produced by JDSU Company, and connect the output end to the AQ6375 spectrum analyzer of Japan YOKOGAWA Company. The transmission spectrum of MZI is shown in Figure 5(b), which can be seen in the figure It is shown that the interference fringe contrast of the MZI is 10dB.

3液体折射率传感实验3 Liquid Refractive Index Sensing Experiment

实验将基于错位熔接制作的MZI与LPFG连接在一起,对LPFG的透射光谱经行滤波。利用LPFG分别对不同折射率的酒精、NaCl和蔗糖三种溶液的进行测量,实验系统如图6所示。该系统由宽带光源、光谱分析仪、MZI、LPFG和NaCl溶液、酒精溶液、蔗糖溶液和载玻片等装置组成。将LPFG固定在载玻片上,在LPFG上滴加不同折射率的溶液,用光谱仪实时观测其透射光谱。为了避免每次测量完成时LPFG上残留液体对实验的影响,每次测量完成后,用无水乙醇对LPFG进行擦拭,等待LPFG的谐振波长与空气中的原始谐振波长一致时在进行下一组折射率实验。整个实验过程在温度为20℃的超净间里完成,避免了温度变化对透射光谱的影响。In the experiment, the MZI fabricated based on dislocation welding was connected with LPFG, and the transmission spectrum of LPFG was filtered. LPFG was used to measure the three solutions of alcohol, NaCl and sucrose with different refractive indices. The experimental system is shown in Figure 6. The system consists of broadband light source, spectrum analyzer, MZI, LPFG and NaCl solution, alcohol solution, sucrose solution and slide glass and other devices. Fix LPFG on a glass slide, drop solutions with different refractive indices on LPFG, and observe its transmission spectrum in real time with a spectrometer. In order to avoid the influence of residual liquid on the LPFG on the experiment when each measurement is completed, wipe the LPFG with absolute ethanol after each measurement, and wait for the resonant wavelength of the LPFG to be consistent with the original resonant wavelength in the air before proceeding to the next set Refractive index experiment. The whole experimental process was completed in a clean room with a temperature of 20°C, which avoided the influence of temperature changes on the transmission spectrum.

将红外飞秒激光制作的LPFG与纤芯错位熔接法制作的MZI连接在一起,通过光谱仪观测其在空气中的透射光谱,图7(a)是MZI连接LPFG前后的透射光谱对比图。从图中虚线框中的光谱图可以看出,连接LPFG后,MZI的透射光谱在LPFG谐振波长处出现明显的变化。7(b)为MZI与LPFG连接时波长在LPFG谐振峰附近的光谱图。从图中可以看出,LPFG的谐振峰的谐振强度为9dB,半高宽为5.6nm,相较于图4,谐振峰的质量有较为明显的改善。The LPFG made by the infrared femtosecond laser is connected with the MZI made by the core dislocation fusion method, and its transmission spectrum in air is observed by a spectrometer. Figure 7(a) is a comparison of the transmission spectrum before and after the MZI is connected to the LPFG. It can be seen from the spectrogram in the dotted box in the figure that after connecting the LPFG, the transmission spectrum of the MZI changes significantly at the resonance wavelength of the LPFG. 7(b) is the spectrogram of the wavelength near the resonance peak of LPFG when MZI is connected with LPFG. It can be seen from the figure that the resonance intensity of the resonance peak of LPFG is 9dB, and the full width at half maximum is 5.6nm. Compared with Figure 4, the quality of the resonance peak has been significantly improved.

3.1LPFG的酒精溶液折射率传感实验3.1 Refractive index sensing experiment of LPFG in alcohol solution

利用蒸馏水和无水乙醇配置了浓度为5%、10%、15%、20%和25%的酒精溶液,将蒸馏水和上述五种浓度的酒精溶液分别滴到LPFG上,其中几种液体的折射率变化范围为1.3331~1.3414,用光谱仪观测其透射光谱的变化。图8(a)为不同折射率的酒精溶液下长周期光纤光栅的透射光谱,可以看出,随着酒精溶液的折射率增加,LPFG的谐振波长向长波方向移动,谐振峰发生红移。图8(b)是酒精溶液折射率与LPFG谐振波长关系拟合曲线。LPFG谐振波长对酒精溶液折射率响应灵敏度为301.78nm/RIU,拟合曲线的线性度为0.9917。Alcohol solutions with concentrations of 5%, 10%, 15%, 20% and 25% were prepared with distilled water and absolute ethanol, and the distilled water and the above five concentrations of alcohol solutions were dropped on the LPFG respectively, and the refraction of several liquids The change range of the rate is 1.3331~1.3414, and the change of the transmission spectrum is observed with a spectrometer. Figure 8(a) is the transmission spectrum of the LPFG in alcohol solutions with different refractive indices. It can be seen that as the refractive index of the alcohol solution increases, the resonance wavelength of the LPFG moves to the long-wave direction, and the resonance peak red shifts. Figure 8(b) is a fitting curve of the relationship between the refractive index of the alcohol solution and the resonance wavelength of the LPFG. The response sensitivity of LPFG resonance wavelength to the refractive index of alcohol solution is 301.78nm/RIU, and the linearity of the fitting curve is 0.9917.

3.2LPFG的NaCl溶液折射率传感实验3.2 Refractive index sensing experiment of LPFG in NaCl solution

实验用胶头滴管分别将蒸馏水和浓度为3%、6%、9%、12%和15%的NaCl溶液滴加到载玻片上的LPFG上,其中液体的折射率变化范围为1.3331~1.3609,通过光谱分析仪对不同折射率的NaCl溶液中LPFG的透射光谱进行观测。NaCl溶液不同折射率下LPFG的透射光谱如图9(a)所示,随着NaCl溶液折射率的增大,LPFG的谐振波长向长波方向漂移。图9(b)为NaCl溶液折射率与LPFG谐振波长的关系拟合曲线。可以看出基于MZI滤波的LPFG的折射率响应灵敏度为138.80nm/RIU,拟合曲线的线性度为0.9915。Add distilled water and NaCl solutions with concentrations of 3%, 6%, 9%, 12% and 15% to the LPFG on the glass slide with a rubber dropper, and the refractive index of the liquid ranges from 1.3331 to 1.3609 , the transmission spectra of LPFG in NaCl solutions with different refractive indices were observed by a spectrum analyzer. The transmission spectra of LPFG under different refractive indices of NaCl solution are shown in Fig. 9(a). As the refractive index of NaCl solution increases, the resonance wavelength of LPFG shifts to the long-wave direction. Fig. 9(b) is a fitting curve of the relationship between the refractive index of NaCl solution and the resonance wavelength of LPFG. It can be seen that the refractive index response sensitivity of LPFG based on MZI filtering is 138.80nm/RIU, and the linearity of the fitting curve is 0.9915.

3.3LPFG的蔗糖溶液折射率传感实验3.3 Refractive index sensing experiment of LPFG in sucrose solution

为了测量LPFG对蔗糖溶液折射率的特性,选用蒸馏水和浓度为3%、6%、9%、12%和15%的蔗糖溶液分别滴到LPFG上,其液体折射率分别为1.3331、1.3386、1.3441、1.3497、1.3552和1.3607。利用光谱仪实时观测其透射光谱的变化,图10(a)为不同折射率的蔗糖溶液中LPFG的透射光谱图。图中可以看出随着折射率的增加,LPFG的透射峰发生红移。图10(b)为蔗糖溶液的折射率与LPFG谐振峰波长拟合曲线。LPFG的蔗糖溶液折射率响应灵敏度为132.67nm/RIU,线性拟合度为0.9938。In order to measure the characteristics of LPFG on the refractive index of sucrose solution, distilled water and sucrose solutions with concentrations of 3%, 6%, 9%, 12% and 15% were respectively dropped on LPFG, and the liquid refractive indices were 1.3331, 1.3386, 1.3441 , 1.3497, 1.3552 and 1.3607. A spectrometer was used to observe the change of its transmission spectrum in real time, and Fig. 10(a) is a transmission spectrum diagram of LPFG in sucrose solutions with different refractive indices. It can be seen from the figure that the transmission peak of LPFG red shifts with the increase of the refractive index. Fig. 10(b) is a fitting curve of the refractive index of the sucrose solution and the resonance peak wavelength of LPFG. The sensitivity of LPFG's response to the refractive index of sucrose solution was 132.67nm/RIU, and the linear fitting degree was 0.9938.

本发明的有益效果为:The beneficial effects of the present invention are:

利用飞秒激光器和三维位移平台等装置搭建了长周期光纤光栅刻写系统,制作了谐振波长为1548.5nm,谐振强度为7dB,栅区长度为3.2mm的LPFG;通过纤芯错位熔接的方法制作了对比度为10dB的马赫-曾德干涉仪,对LPFG的透射光谱进行滤波,使LPFG的谐振峰的半高全宽从6.3nm降低到5.6nm。实验中,基于MZI滤波的LPFG在酒精溶液、NaCl溶液和蔗糖溶液中的折射率灵敏度分别为301.78nm/RIU、132.80nm/RIU和132.67nm/RIU,线性拟合度分别为0.9917、0.9915和0.9938。因此,设计的基于马赫-曾德滤波和长周期光纤光栅的光纤传感器可用于液体折射率测量。A long-period fiber grating writing system was built using femtosecond lasers and three-dimensional displacement platforms, and an LPFG with a resonance wavelength of 1548.5nm, a resonance intensity of 7dB, and a gate length of 3.2mm was produced; the fiber core was dislocated and welded. The Mach-Zehnder interferometer with a contrast ratio of 10dB filters the transmission spectrum of the LPFG, reducing the full width at half maximum of the resonant peak of the LPFG from 6.3nm to 5.6nm. In the experiment, the refractive index sensitivities of LPFG based on MZI filtering in alcohol solution, NaCl solution and sucrose solution were 301.78nm/RIU, 132.80nm/RIU and 132.67nm/RIU, respectively, and the linear fitting degrees were 0.9917, 0.9915 and 0.9938, respectively. . Therefore, the designed optical fiber sensor based on Mach-Zehnder filter and long period fiber grating can be used for liquid refractive index measurement.

结合这里披露的本发明的说明和实践,本发明的其他实施例对于本领域技术人员都是易于想到和理解的。说明和实施例仅被认为是示例性的,本发明的真正范围和主旨均由权利要求所限定。Other embodiments of the invention will be apparent to and understood by those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The description and examples are considered exemplary only, with the true scope and spirit of the invention defined by the claims.

Claims (6)

1.一种基于马赫-曾德滤波和长周期光纤光栅的液体折射率特性研究方法,其特征在于,包括1. A method for researching liquid refractive index characteristics based on Mach-Zehnder filter and long-period fiber grating, characterized in that, comprising 步骤1:利用飞秒激光器、三维位移平台、宽带光源和光谱分析仪等器件搭建了红外飞秒激光制作长周期光纤光栅的加工系统;Step 1: Using femtosecond laser, three-dimensional displacement platform, broadband light source and spectrum analyzer to build a processing system for making long-period fiber gratings with infrared femtosecond laser; 步骤2:利用搭建的飞秒激光加工系统完成谐振波长为1548.5nm的长周期光纤光栅的制作;Step 2: Use the built femtosecond laser processing system to complete the fabrication of long-period fiber gratings with a resonance wavelength of 1548.5nm; 步骤3:利用光纤熔接机通过纤芯错位熔接的方式完成光纤马赫曾德干涉仪的制作;Step 3: Use the optical fiber fusion splicer to complete the production of the optical fiber Mach-Zehnder interferometer by dislocation fusion of the fiber core; 步骤4:将马赫曾德干涉仪与长周期光纤光栅连接在一起,对LPFG的透射光谱进行滤波;Step 4: Connect the Mach-Zehnder interferometer with the long-period fiber grating to filter the transmission spectrum of the LPFG; 步骤5:利用马赫曾德干涉仪与长周期光纤光栅组成的系统完成对液体折射率特性研究。Step 5: Use the system composed of the Mach-Zehnder interferometer and the long-period fiber grating to complete the research on the refractive index characteristics of the liquid. 2.根据权利要求1所述的方法,其特征在于:所述步骤1中的激光器中心波长800nm、脉冲宽度120fs、重复频率1kHz的钛蓝宝石飞秒激光器;采用的显微物镜的放大倍数为100倍、数值孔径为0.70;光谱分析仪的工作波长范围1200nm~2400nm,最小分辨精度为0.02nm。2. The method according to claim 1, characterized in that: the titanium sapphire femtosecond laser of laser central wavelength 800nm, pulse width 120fs, repetition frequency 1kHz in the said step 1; the magnification of the microscopic objective lens that adopts is 100 times, the numerical aperture is 0.70; the working wavelength range of the spectrum analyzer is 1200nm-2400nm, and the minimum resolution accuracy is 0.02nm. 3.根据权利要求1所述的方法,其特征在于:所述步骤2中的长周期光纤光栅的周期为400,占空比为0.5,谐振强度为7dB,半高宽为6.3nm。3. The method according to claim 1, characterized in that: the period of the long-period fiber grating in the step 2 is 400, the duty cycle is 0.5, the resonance strength is 7dB, and the full width at half maximum is 6.3nm. 4.根据权利要求1所述的方法,其特征在于:所述步骤3中的光纤熔接机的放电时间为2500ms,预熔时间为180ms;马赫曾德干涉仪的干涉光谱对比度为10dB。4. The method according to claim 1, characterized in that: the discharge time of the optical fiber fusion splicer in the step 3 is 2500ms, and the pre-melting time is 180ms; the interference spectrum contrast of the Mach-Zehnder interferometer is 10dB. 5.根据权利要求1所述的方法,其特征在于:所述步骤4中的长周期光纤光栅经马赫曾德干涉滤波器滤波后的谐振波的半高宽为5.6nm。5. The method according to claim 1, characterized in that: the FWHM of the resonant wave filtered by the Mach-Zehnder interference filter of the long-period fiber grating in the step 4 is 5.6 nm. 6.根据权利要求1所述的方法,其特征在于:所述步骤5中的测量系统分别对酒精、蔗糖和NaCl溶液的折射率特性进行测试,三种溶液的折射率灵敏度分别为01.78nm/RIU、132.67nm/RIU和138.80nm/RIU。6. The method according to claim 1, characterized in that: the measuring system in the step 5 tests the refractive index properties of alcohol, sucrose and NaCl solutions respectively, and the refractive index sensitivities of the three solutions are respectively 01.78nm/ RIU, 132.67nm/RIU and 138.80nm/RIU.
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