WO2017012393A1 - 一种光纤预制棒掺杂元素分布的原位检测方法和装置 - Google Patents

一种光纤预制棒掺杂元素分布的原位检测方法和装置 Download PDF

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Publication number
WO2017012393A1
WO2017012393A1 PCT/CN2016/081478 CN2016081478W WO2017012393A1 WO 2017012393 A1 WO2017012393 A1 WO 2017012393A1 CN 2016081478 W CN2016081478 W CN 2016081478W WO 2017012393 A1 WO2017012393 A1 WO 2017012393A1
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optical fiber
laser
fiber preform
distribution
point
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PCT/CN2016/081478
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English (en)
French (fr)
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李祥友
李嘉铭
郭连波
曾晓雁
陆永枫
陈启蒙
吴宝业
喻惠武
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华中科技大学
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Publication of WO2017012393A1 publication Critical patent/WO2017012393A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited

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  • the invention belongs to the field of optical detection technology and relates to a high-resolution, non-contact, non-vacuum and multi-element optical fiber preform doping element distribution in-situ detection method and device.
  • Active fibers in fiber lasers and amplifiers need to be doped with rare earth ions such as yttrium (Yb), europium (Er), thallium (Tm), and thallium (Tb) at the core; anti-irradiation fibers need to be reduced in core Coloring element ionic iron (Fe), chromium (Cr), manganese (Mn), copper (Cu), cobalt (Co), nickel (Ni), lead (Pb) concentration, while doping element ⁇ in the core (Ce And nitrogen (N), doping fluorine (F) and colored ions in the cladding; in the fiber temperature sensor, doping ⁇ (Nd) or ⁇ (Ho) elements can have a good linear relationship between fiber absorption and temperature In the polarizing device, the core doped erbium (Tb) and cerium (Ce) elements give the fiber a strong optical rotation characteristic. In recent years, various types of doped optical fibers, especially those based on rare earth doping, have been widely used in the
  • MCVD Modified Chemical Vapor Deposition
  • VAD Vapor phase Axial Deposition
  • OLED Outside Chemical Vapor Deposition
  • PCVD Plasma Activated Chemical Vapor Deposition
  • the doping element ion distribution in the fiber is closely related to the preform bar shrinkage process.
  • the difference of parameters such as ion concentration distribution and ion volatilization of each element may result in performance difference of the drawn fiber. Therefore, the detection of the concentration distribution of each doping element in the cross section of the optical fiber preform has a very important guiding role in optimizing the preparation process of the optical fiber, controlling the mode of the optical fiber, and controlling the optical quality of the optical fiber, thereby providing a high performance and high quality special optical fiber. Strong support and security.
  • the conventional preform element analysis methods mainly include refractive index measurement, electron probe method, X-ray fluorescence spectrometry, atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and the like.
  • the refractive index measurement can only estimate the overall distribution of doping elements by the refractive index distribution, and cannot obtain the information of each element distribution.
  • This method is suitable for detecting single element doped optical fiber preforms, and prefabricated for multi-element co-doped optical fibers. The stick does not apply.
  • the electron probe method not only needs to spray the conductive layer on the optical fiber preform sample before the measurement, but also causes interference to the lower concentration doping element, and requires a vacuum environment, and the operation is too complicated and takes too long.
  • X-ray fluorescence spectroscopy is only suitable for measuring elements with an atomic number greater than 11, and X-ray focusing ability is limited, making it difficult to achieve high-resolution analysis.
  • Atomic absorption spectrometry can only measure more than 70 kinds of elements in the periodic table of elements. Common elements such as phosphorus and sulfur cannot be measured, and the elements are different. The excitation light source must be replaced, and simultaneous all-element measurement cannot be realized. Inductively coupled plasma atomic emission spectrometry is currently the most commonly used analytical method, but it needs to dissolve the glass material in hydrofluoric acid first, which will produce highly toxic silicon tetrafluoride gas. For high content, it needs to be diluted first. Therefore, the in-situ analysis of the optical fiber preform cannot be achieved, and the distribution of the element content cannot be obtained.
  • Commonly used fiber preforms range in diameter from a few millimeters to a dozen millimeters, with a core diameter of approximately 1 mm, which places higher demands on component analysis techniques.
  • the invention provides an in-situ detection method and device for doping element distribution of an optical fiber preform, aiming at solving the problems existing in the conventional preform component analysis technology and realizing in-situ high-precision detection of the doping element distribution of the optical fiber preform.
  • the invention provides an in-situ detection method for doping element distribution of an optical fiber preform, which focuses a pulsed laser on a surface to be measured on the surface of the optical fiber preform to form a spot size of several to several tens of micrometers, and instantaneously in the laser At the focus point, ablation and plasma are generated, the plasma of the point to be measured is collected, coordinate information of the point to be measured and element concentration information are obtained, and the coordinate information of the plurality of different points to be measured and the element concentration information are used to obtain the optical fiber preform. Accurate doping element concentration distribution spectrum.
  • the invention provides an in-situ detecting device for doping element distribution of an optical fiber preform, characterized in that the device comprises a laser system, an optical path system, a spectrum acquisition system and a control analysis system; and the laser system is used for generating a bombardment optical fiber preform surface
  • the pulsed laser beam at the point to be measured causes the plasma to be measured to generate a plasma
  • the optical path system is used to shape and focus the laser beam, and to illuminate and image the surface morphology of the sample
  • the spectral acquisition system is used to collect the plasma emission including the test
  • the coordinate information of the point and the characteristic spectral signal of the element concentration information are converted into electrical signals for transmission to the control analysis system
  • the control analysis system is used to control the operation of the laser system and the spectral acquisition system, and the characteristic spectral signals provided by the spectral acquisition system
  • the treatment is performed to obtain a doping element concentration distribution spectrum of the precision required for the optical fiber preform.
  • the invention provides an in-situ detection method and device for doping element distribution of an optical fiber preform, and adopts the characteristics of good laser directivity and high peak pulse power to realize high resolution and non-contact distribution of doping elements of the optical fiber preform.
  • the present invention has the following technical features:
  • the invention utilizes the characteristics of good directivity and high energy density of the laser, and uses a high-focus objective lens to focus the laser beam on an analysis point on the surface of the sample to be tested, forming several to A few tens of micrometers of spot size instantaneously ablate at the laser focus and produce a plasma. By collecting the emitted light of the plasma, the element types and their contents in the plasma are quickly analyzed.
  • the present invention can realize high-resolution, non-contact, non-vacuum, multi-element in-situ detection of the preform, and obtain the concentration distribution of the doping element ions. Due to the ease of integration and environmental adaptability of the present invention, real-time on-line detection of doping element distribution can be realized at the fiber preform production site.
  • the present invention combines the data of the element type and content of each analysis point with the coordinates of the point position to generate a high-resolution multi-element type and concentration profile;
  • the present invention uses a transmissive illumination device to make the preform core and the cladding more clear;
  • the present invention utilizes median filtering to have an ideal ability to remove salt and pepper noise for bad point noise, and processes the measured original concentration spectrum of the doping element concentration distribution, and the interaction between the laser and the surface of the preform sample in the experiment. Randomly generated dead point data is removed;
  • the doping element concentration profile is subjected to Fourier transform to obtain a frequency domain map. Since various types of noise and fluctuations introduced during the measurement process are in the high frequency portion of the frequency domain diagram, the low-frequency filter is used to attenuate the high-frequency portion, and the low-frequency component due to the change in the element concentration is retained. Then, the processed frequency domain map is inversely Fourier transformed to obtain a more realistic doping element concentration profile.
  • the disclosed method and apparatus use laser induced plasma to detect the doping element distribution of the fiber preform cross section, with high resolution, multi-element simultaneous analysis, non-contact, micro-loss, fast real-time, in-situ detection
  • the advantages can be used as the basis for judging the advantages and disadvantages of the preform in the production process of the optical fiber preform, thereby providing a key guiding role for the improvement of the doping concentration of the optical fiber preform and the production process.
  • FIG. 1 is a schematic flow chart of an in-situ detection method for doping element distribution of an optical fiber preform according to the present invention
  • FIG. 2 is a schematic diagram of data processing of an in-situ detection method for doping element distribution of an optical fiber preform according to the present invention
  • FIG. 3 is a schematic view of an in-situ detecting device for doping element doping of an optical fiber preform according to the present invention
  • FIG. 4 is a schematic diagram showing the results of a one-dimensional line scan of a fiber preform cross section by the method and apparatus provided by the present invention
  • FIG. 5 is a schematic diagram showing the results of scanning a two-dimensional surface of an optical fiber preform by the method and apparatus provided by the present invention.
  • the method of the invention utilizes the focused pulsed laser to ablate trace substances at a certain point on the surface of the sample to be tested for analysis, to achieve high resolution, multi-element simultaneous analysis, non-contact, micro-loss, fast real-time, original
  • the purpose of the bit detection is that it can be used in industrial fields without the need for a vacuum environment.
  • the experimental process of the embodiment of the present invention specifically includes the following process:
  • the preform sample is sliced and polished to make the upper and lower surfaces parallel;
  • the focused pulsed laser is used to bombard the point to be measured on the surface of the preform to generate a plasma
  • the plasma spectrum is collected, transmitted to a computer for analysis and stored;
  • Step 4 changing the bombardment position of the pulsed laser on the surface of the preform, and repeating steps 2 and 3;
  • step 5 the coordinate information and the element concentration information of all the analysis points are combined into a concentration distribution original spectrum map
  • the data processing process of the embodiment of the present invention specifically includes the following process:
  • step 51 the raw spectrum of the doping element concentration distribution obtained in the experiment is subjected to median filtering to remove the dead point spectral data;
  • step 52 the spectral domain image of the spectral distribution after removing the dead point is subjected to Fourier transform to obtain a frequency domain image;
  • step 53 the frequency domain image is subjected to low-pass filtering processing to attenuate or even eliminate the high frequency portion where the noise and the fluctuation introduced by the experiment are located;
  • the low-pass filtered frequency domain image is subjected to inverse Fourier transform to obtain an ideal spatial distribution map of the doping element concentration.
  • the in-situ detection device for the doping element distribution of the optical fiber preform mainly includes a laser system, an optical path system, a spectrum acquisition system, and a control analysis system.
  • the laser system is used to generate a pulsed laser beam of high power density, providing the ablation energy required by the analysis device.
  • the laser system specifically includes a laser 1 and a laser attenuator 2.
  • the laser 1 exit port and the laser attenuator 2 are on the same horizontal optical path.
  • the laser 1 can produce a stable high power density laser pulse output, and the laser attenuator 2 is used to adjust the laser pulse energy.
  • the optical path system is used to shape and focus the laser beam, as well as to illuminate and image the surface morphology of the sample.
  • the optical path system specifically includes a diaphragm 3, a first transflective mirror 4, a coaxial surveillance camera 5, a second transflective mirror 7, a selectable high power focusing mirror 8, and a transmissive illumination panel 21.
  • the aperture 3, the first half mirror 4 and the second half mirror 7 and the laser 1 exit port are in the same water Pingguang Road.
  • the first half half mirror 4 and the second half mirror 7 are placed at an angle of 45 degrees with respect to the horizontal light path direction.
  • the laser beam is shaped by the aperture 3 and transmitted downwardly through the second half mirror 7 and focused by the optional high magnification objective lens 8 onto the surface of the preform sample 9.
  • the transmissive illumination panel 21 is encapsulated by LEDs and frosted glass, placed under the preform sample 9 for transmission illumination, and the surface image information of the preform sample 9 is reflected by the second half mirror 7 and the first half mirror 4, Finally, the coaxial monitoring camera 5 collects and transmits the corresponding signals to the computer 13.
  • the spectral acquisition system is used to acquire a characteristic spectral signal emitted by the plasma and convert the electrical signal to a computer.
  • the spectral acquisition system may specifically include a light collector 6, an optical fiber 11, and a spectrometer 12.
  • the characteristic light signal emitted by the plasma is collected by the light collector 6 and coupled into the fiber 11 for transmission to the spectrometer 12.
  • the grating in spectrometer 12 splits the optical signal from the optical fiber 11 along the wavelength domain and converts it from ICCD to electrical signal for transmission to computer 13.
  • the control analysis system acts as a general console and signal analysis system for controlling laser switching, spectrometer measurement behavior, displacement platform movement, and monitoring sample surface morphology and analyzing signals from the spectrometer.
  • the system specifically includes a computer 13 and a digital synchronization controller 14.
  • the computer 13 achieves timing control of the laser 1, spectrometer 12, and three-dimensional displacement platform 10 throughout the analysis system by controlling the synchronous triggering behavior of the digital synchronization controller 14.
  • the computer 13 obtains imaging information on the surface of the sample, spectral signals, and concentration distribution information of each element by collecting signals from the coaxial monitoring camera 5 and the spectrometer 12.
  • the laser 1 is connected to the digital synchronizing controller 14 via a laser synchronizing signal transmission line 18; the spectrometer 12 is coupled to the digital synchronizing controller 14 via a spectrometer synchronizing signal transmission line 17; the three-dimensional displacement platform 10 controls the signal transmission line 19 and the digital synchronizing controller 14 via a three-dimensional displacement platform.
  • the coaxial surveillance camera 5 is coupled to the computer 13 via an image transmission cable 15; the spectrometer 12 is coupled to the computer 13 via a spectrometer data transmission line 20.
  • the first half of the half mirror 4 faces the laser 1 with an antireflection film on one side and an antireflection film on the other side.
  • the optional high power focusing objective 8 selects the corresponding high power focusing mirror in accordance with the desired spatial resolution.
  • Computer 13 As a total console and signal analysis system, the laser 1 is controlled by the Q-switch, the measurement behavior of the spectrometer 12, and the three-dimensional displacement platform 10 is moved. The three-dimensional displacement platform 10 moves the surface of the preform sample 9 on the focal plane of the selectable high power focusing mirror 8, and the laser pulse can be subjected to line sweeping or surface scanning on the surface of the preform sample 9, and the spectral signals are processed by computer analysis.
  • Computer software has the functions of online monitoring, finding element peaks, qualitative analysis and quantitative analysis.
  • the preform sample 9 was first sliced. Turn on the laser 1, the coaxial surveillance camera 5, the three-dimensional displacement platform 10, the spectrometer 12, the computer 13 and the digital synchronization controller 14 power, turn on the various control and analysis software in the computer 13, complete the spectrometer 12 cooling and calibration, and set the digital synchronization control 14 Timing parameters.
  • the preform sample 9 is placed on the transmission illumination panel 21, and the transmission illumination panel 21 is turned on.
  • the position of the preform sample 9 is monitored in the computer 13, and the three-dimensional displacement platform 10 is controlled by software, the surface height of the preform sample 9 is first adjusted to the focal plane of the high-focus objective lens 8, and the preform sample 9 is moved to the analysis. Starting point location.
  • the laser energy is adjusted by the laser attenuator 2.
  • the light emitted by the plasma passes through the optional high-magnification focusing objective lens 8 and the second half-reflecting mirror 7, is collected by the light collector 6, and coupled into the optical fiber 11 for transmission to the spectrometer 12.
  • the spectrometer 12 converts the optical signal received from the plasma into a spectral signal by spatial dispersion and converts it into an electrical signal, which is sent by the spectrometer data transmission line 20 to the computer 13 for data analysis.
  • the three-dimensional displacement stage 10 moves the preform sample 9 to the next analysis point, and repeats steps (3) and (4).
  • the cross-section of the preform sample 9 can be subjected to one-dimensional scanning or two-dimensional scanning as needed.
  • Computer 13 records each analysis point Coordinate information and element concentration information, and the data is integrated to obtain the original spectrum of the one-dimensional or two-dimensional element concentration distribution of the preform sample 9. ;
  • Fig. 4 is a schematic diagram showing the results of one-dimensional element distribution
  • Fig. 5 is a schematic diagram showing the results of two-dimensional element distribution.
  • the in-situ detection method and device for doping element distribution of an optical fiber preform according to the present invention can fully satisfy the high-resolution, multi-element simultaneous analysis required for preform analysis, non-contact, Micro-loss, fast real-time, in-situ detection and other requirements, and provide two options of one-dimensional analysis and two-dimensional analysis to meet the different needs of preform detection.

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Abstract

一种光纤预制棒掺杂元素分布的原位检测方法和装置，该方法将脉冲激光聚焦至光纤预制棒表面的待测点，形成几个至几十个微米的光斑尺寸，瞬间在激光聚焦点处烧蚀并产生等离子体，采集待测点的等离子体，得到待测点的坐标信息和元素浓度信息，利用多个不同待测点的坐标信息和元素浓度信息得到光纤预制棒所需精度的掺杂元素浓度分布光谱图，然后利用中值滤波器和频域滤波器改善分析结果。该装置包括激光器系统、光路系统、光谱采集系统和控制分析系统。

Description

一种光纤预制棒掺杂元素分布的原位检测方法和装置 【技术领域】
本发明属于光学检测技术领域，涉及了一种高分辨率、非接触、非真空和多元素的光纤预制棒掺杂元素分布的原位检测方法和装置。
【背景技术】
早期的光纤制备中，人们都在想方设法去除光纤中的各类杂质元素来提高石英光纤的纯度，从而降低光纤的损耗。上世纪80年代，英国的南安普顿大学的Payne等首先发现掺杂稀土元素的光纤有激光振荡和光放大的现象。S.B.Poole和J.E.Townsend等人发现通过严格控制纤芯和包层中掺杂离子的含量和种类可使光纤具有抗辐照、抗光子暗化等特殊性能。对于特定掺杂元素的光纤，只要通过改变元素掺杂浓度比例或者掺杂浓度分布，也能带来许多新的特性。光纤激光器和放大器中的有源光纤需要在纤芯处掺杂镱(Yb)、铒(Er)、铥(Tm)、铽(Tb)等稀土元素离子；抗辐照光纤需要在减小纤芯着色元素离子铁(Fe)、铬(Cr)、锰(Mn)、铜(Cu)、钴(Co)、镍(Ni)、铅(Pb)浓度的同时，在纤芯掺杂元素铈(Ce)和氮(N)，在包层掺杂氟(F)和着色离子；光纤温度传感器中，掺杂钕(Nd)或钬(Ho)元素可以使光纤吸收与温度之间具有良好的线性关系；偏振器件中，纤芯掺铽(Tb)和铈(Ce)元素使光纤具有强旋光特性。近年来，各类掺杂光纤特别是基于稀土掺杂的光纤器件已经广泛应用于传感、材料加工、医疗以及国防等领域。
国际上生产石英光纤预制棒的方法有十多种，其中常用的方法主要有以下四种：改进的化学气相沉积法(Modified Chemical Vapor Deposition，MCVD)、轴向气相沉积法(Vapor phase Axial Deposition，VAD)、棒外化学气相沉积法(Outside Chemical Vapor Deposition，OVD)和等离子体激活化学气相沉积法(Plasma activated Chemical Vapor Deposition，PCVD)。合 理设计并优化纤芯内各掺杂元素离子的浓度分布，不仅能优化掺杂元素离子作用特性，改善光纤折射率分布，实现模式控制，而且还能大幅提高光纤损伤阈值及斜率效率，实现抗光子暗化性能的提升，消除掺杂元素离子浓度淬灭现象。光纤中的掺杂元素离子分布与预制棒缩棒过程密切相关，缩棒过程中，各元素离子浓度分布、离子挥发情况等参数的不同会导致拉制出的光纤存在性能差异。因此，光纤预制棒横截面的各掺杂元素浓度分布的检测对光纤制备工艺的优化、光纤模式的调控、光纤光学质量的控制具有非常关键的指导性作用，从而为生产高性能优质特种光纤提供强有力的支持和保障。目前传统的预制棒元素成分分析方法主要有折射率测定法、电子探针法、X射线荧光光谱法、原子吸收光谱法、电感耦合等离子体原子发射光谱法等。
然而，折射率测定法只能通过折射率分布来推测掺杂元素的总体分布，无法得到每个元素分布信息，该方法适合检测单一元素掺杂的光纤预制棒，对于多元素共掺的光纤预制棒并不适用。电子探针法不仅需要在测量前对光纤预制棒样品进行喷涂导电层，对浓度较低的掺杂元素带来干扰，并且需要真空环境，操作过于复杂，耗时过长。X射线荧光光谱法只适合于测量原子序数大于11的元素，而且X射线聚焦能力有限，难以实现高分辨率分析。原子吸收光谱法只能测定元素周期表中的七十多种元素，如磷和硫等常用元素无法测定，而且测定元素不同，必须更换激发光源灯，无法实现同时全元素测量。电感耦合等离子体原子发射光谱法是目前最常用的分析方法，但它需要先将玻璃材料溶于氢氟酸，会生成剧毒的四氟化硅气体，对于含量高的元素还需要先稀释，因此无法实现对光纤预制棒的原位分析，也无法获得其元素含量的分布情况。
常用的光纤预制棒直径从几毫米到十几个毫米不等，其中纤芯直径大约为1毫米，这对成分分析技术提出了更高的要求。
【发明内容】
本发明提出了一种光纤预制棒掺杂元素分布的原位检测方法和装置，目的在于解决传统预制棒成分分析技术存在的难题，实现对光纤预制棒掺杂元素分布的原位高精度检测。
本发明提供的一种光纤预制棒掺杂元素分布的原位检测方法，该方法将脉冲激光聚焦至光纤预制棒表面的待测点，形成几个至几十个微米的光斑尺寸，瞬间在激光聚焦点处烧蚀并产生等离子体，采集待测点的等离子体，得到待测点的坐标信息和元素浓度信息，利用多个不同待测点的坐标信息和元素浓度信息得到光纤预制棒所需精度的掺杂元素浓度分布光谱图。
本发明提供的一种光纤预制棒掺杂元素分布的原位检测装置，其特征在于，该装置包括激光器系统、光路系统、光谱采集系统和控制分析系统；激光器系统用于产生轰击光纤预制棒表面的待测点脉冲激光束，使待测点产生等离子体；光路系统用于对激光束整形和聚焦，以及对样品表面形态的照明和成像；光谱采集系统用于采集等离子体发射的包含待测点的坐标信息和元素浓度信息的特征光谱信号，并转换成电信号传输到控制分析系统；控制分析系统用于控制所述激光器系统和光谱采集系统工作，并对光谱采集系统提供的特征光谱信号进行处理，得到光纤预制棒所需精度的掺杂元素浓度分布光谱图。
本发明提出了一种光纤预制棒掺杂元素分布的原位检测方法和装置，利用激光方向性好，脉冲峰值功率高的特点，对光纤预制棒掺杂元素的分布实现高分辨率、非接触、非真空、多元素的快速原位检测。具体而言，本发明具有以下技术特点：
(1)本发明利用激光的方向性好，能量密度大的特点，配合使用高倍聚焦物镜，将激光束聚焦到待测预制棒样品表面某个分析点，形成几个至 几十个微米的光斑尺寸，瞬间在激光聚焦点处烧蚀并产生等离子体。通过收集等离子体的发射光，快速分析出等离子体内元素种类及其含量。
(2)与传统的检测技术相比，本发明对预制棒可以实现高分辨率、非接触、非真空、多元素的原位检测，获得掺杂元素离子的浓度分布。由于本发明的易集成性与环境适应性，可以在光纤预制棒生产现场对其掺杂元素分布实现实时在线检测。
(3)本发明将每个分析点的元素种类及含量的数据与该点位置坐标组合，生成高分辨率多元素种类和浓度分布图；
(4)本发明使用透射照明装置，使预制棒纤芯与包层成像时更加清晰；
(5)本发明利用中值滤波对坏点噪声具有非常理想的去除椒盐噪声的能力，将测量后的掺杂元素浓度分布原始光谱图进行处理，将实验中由于激光与预制棒样品表面相互作用随机产生的坏点数据进行去除；
(6)本发明中数据处理过程将掺杂元素浓度分布图进行傅立叶变换，得到频域图。由于各类噪声和测量过程中引入的波动皆处于频域图中高频部分，利用低通滤镜将高频部分进行衰减，保留由于元素浓度变化引起的低频分量。然后将处理后的频域图进行傅立叶反变换得到更接近真实的掺杂元素浓度分布图。
综上所述，本发明所公开的方法和装置利用激光诱导等离子体检测光纤预制棒截面掺杂元素分布，具有高分辨率、多元素同时分析，非接触、微损、快速实时、原位检测等优点，可以作为光纤预制棒生产过程中判断预制棒优劣的依据，从而为光纤预制棒掺杂浓度和生产工艺的改进提供关键的指导性作用。
【附图说明】
附图是为提供对本发明进一步的理解，它们被收录并构成本申请的一部分，附图示出了本发明的实施例，并与本说明书一同起到解释本发明原 理的作用。
图1是本发明的光纤预制棒掺杂元素分布原位检测方法的流程示意图；
图2是本发明的光纤预制棒掺杂元素分布原位检测方法的数据处理示意图；
图3是本发明的光纤预制棒掺杂元素分布原位检测装置的示意图；
图4是本发明提供的方法和装置对光纤预制棒截面一维线扫描结果示意图；
图5是本发明提供的方法和装置对光纤预制棒截面二维面扫描结果示意图。
其中：1.激光器；2.激光衰减器；3.光阑；4.第一半透半反镜；5.同轴监控摄像头；6.光收集器；7.第二半透半反镜；8.可选择式高倍聚焦物镜；9.预制棒样品；10.三维位移平台；11.光纤；12.光谱仪；13.计算机；14.数字同步控制器；15.图像传输线；16.数字同步信号传输线；17.光谱仪同步信号传输线；18.激光器同步信号传输线；19.三维位移平台控制信号传输线；20.光谱仪数据传输线；21.透射照明面板。
【具体实施方式】
下面结合附图对本发明的具体实施方式作详细说明。在此需要说明的是，对于这些实施方式的说明用于帮助理解本发明，但并不构成对本发明的限定。此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
本发明方法利用聚焦后的脉冲激光在待测预制棒样品表面某个点可以烧蚀出微量物质用于分析，以达到高分辨率、多元素同时分析，非接触、微损、快速实时、原位检测的目的，并且可以在工业现场使用，无需真空环境。
如图1所示，本发明实施例的实验过程具体包括下述过程：
第1步，将预制棒样品切片后抛光，使其上下表面平行；
第2步，利用聚焦的脉冲激光轰击预制棒表面的待测点，产生等离子体；
第3步，采集等离子体光谱，传输至计算机分析并存储；
第4步，改变脉冲激光在预制棒表面的轰击位置，并重复第2步和第3步；
第5步，将所有分析点的坐标信息和元素浓度信息组合成浓度分布原始光谱图；
如图2所示，本发明实施例的数据处理过程具体包括下述过程：
第51步，将实验中得到的掺杂元素浓度分布原始光谱图进行中值滤波，去除坏点光谱数据；
第52步，将去除坏点后的光谱分布空间域图像进行傅立叶变换得到频域图像；
第53步，将频域图像进行低通滤波处理，将噪声和实验引入的波动所处的高频部分减弱甚至消除；
第54步，将低通滤波处理后的频域图像进行傅立叶反变换，获得理想的掺杂元素浓度空间域分布图。
如图3所示，本发明实例提供的光纤预制棒掺杂元素分布的原位检测装置，主要包括激光器系统、光路系统、光谱采集系统和控制分析系统。
激光器系统用于产生高功率密度的脉冲激光束，提供分析装置所需的烧蚀能量。本实例中，激光器系统具体包括激光器1和激光衰减器2。激光器1出光口和激光衰减器2处在同一水平光路上。激光器1可以产生稳定的高功率密度激光脉冲输出，激光衰减器2用于调节激光脉冲能量。
光路系统用于对激光束整形和聚焦，以及对样品表面形态的照明及成像。本实例中，光路系统具体包括光阑3、第一半透半反镜4、同轴监控摄像头5、第二半透半反镜7、可选择式高倍聚焦镜8和透射照明面板21。光阑3、第一半透半反镜4和第二半透半反镜7和激光器1出光口处在同一水 平光路上。第一半透半反镜4和第二半透半反镜7相对于水平光路方向成45度角放置。激光光束通过光阑3整形后经过第二半透半反镜7反射向下传输并通过可选择式高倍聚焦物镜8聚焦到预制棒样品9表面。透射照明面板21由LED和毛玻璃封装而成，放置在预制棒样品9下面进行透射照明，预制棒样品9表面图像信息通过第二半透半反镜7和第一半透半反镜4反射，最后通过同轴监控摄像头5收集并将相应信号传输至计算机13。
光谱采集系统用于采集等离子体发射的特征光谱信号，并转换电信号传输到计算机。本实例中，光谱采集系统具体可包括光收集器6、光纤11和光谱仪12。等离子体发射的特征光信号通过光收集器6收集并耦合进光纤11后中，传输至光谱仪12。光谱仪12中的光栅将来自光11纤的光信号沿波长域分光并由ICCD转换成电信号传输至计算机13。
控制分析系统作为总控制台和信号分析系统，用来控制激光器开关、光谱仪测量行为、位移平台移动方式，并监控样品表面形态以及分析来自光谱仪的信号。本实例中，该系统具体包括计算机13和数字同步控制器14。计算机13通过控制数字同步控制器14的同步触发行为，实现对整个分析系统中激光器1、光谱仪12和三维位移平台10的时序控制。计算机13通过采集来自同轴监控摄像头5和光谱仪12的信号，分别得到样品表面成像信息、光谱信号及其各元素浓度分布信息。
激光器1通过激光器同步信号传输线18与数字同步控制器14相连；光谱仪12通过光谱仪同步信号传输线17与数字同步控制器14相连；三维位移平台10通过三维位移平台控制信号传输线19与数字同步控制器14相连；同轴监控摄像头5通过图像传输线缆15与计算机13相连；光谱仪12通过光谱仪数据传输线20和计算机13相连。
第一半透半反镜4面向激光器1一面为增透膜，另一面为增反膜。可选择式高倍聚焦物镜8按照所需空间分辨率选择相应的高倍聚焦镜。计算机 13作为总控制台和信号分析系统，控制激光器1调Q开关、光谱仪12的测量行为、三维位移平台10移动方式。三维位移平台10使预制棒样品9表面在可选择式高倍聚焦镜8的焦平面上移动，激光脉冲可以在预制棒样品9表面进行线扫面或面扫描，光谱信号由计算机分析处理。计算机软件具有在线监测、寻找元素谱峰、定性分析和定量分析等的功能。
本发明装置的具体操作步骤如下：
(1)准备工作。首先将预制棒样品9切片。开启激光器1、同轴监控摄像头5、三维位移平台10、光谱仪12、计算机13和数字同步控制器14电源，打开计算机13中各个控制和分析软件，完成光谱仪12降温及校准，设置数字同步控制14的时序参数。
(2)将预制棒样品9放置在透射照明板21上，打开透射照明板21电源。在计算机13中监控预制棒样品9的位置，并使用软件控制三维位移平台10，先将预制棒样品9的表面高度调整到高倍聚焦物镜8的焦平面上，再将预制棒样品9移动到分析起点位置。通过激光衰减器2调节激光器能量。
(3)通过计算机13控制激光器1输出，该激光脉冲一次通过激光衰减器2、光阑3、第一半透半反镜4、第二半透半反镜7、可选择式高倍聚焦物镜8，聚焦到预制棒样品9上表面，激发出等离子体。
(4)等离子体发射的光经过可选择式高倍聚焦物镜8和第二半透半反镜7，被光收集器6收集并耦合进光纤11中传输至光谱仪12。光谱仪12将接收到来自等离子体的光信号通过空间色散的方式转换为光谱信号并转换为电信号，由光谱仪数据传输线20输送给计算机13进行数据分析。
(5)三维位移平台10将预制棒样品9移动至下一个分析点处，重复步骤(3)(4)。通过控制三维位移平台10的运动方式，可以根据需要将预制棒样品9的截面进行一维扫描或二维扫描。计算机13记录每个分析点的 坐标信息和元素浓度信息，并将数据整合处理后得到预制棒样品9的一维或二维元素浓度分布原始光谱图。；
(6)将以上步骤得到的掺杂元素浓度分布原始光谱图进行中值滤波处理，将实验中由于激光与预制棒样品表面相互作用随机产生的坏点数据进行去除；
(7)将步骤(6)处理后的掺杂元素浓度分布图进行傅立叶变换，得到频域图。由于各类噪声和测量过程中引入的波动皆处于频域图中高频部分，利用低通滤镜将高频部分进行衰减，保留由于元素浓度变化引起的低频分量。然后将低通滤波后的频域图进行傅立叶反变换得到更接近真实的掺杂元素浓度分布图。图4为一维元素分布结果示意图，图5为二维元素分布结果示意图。
综上所述，采用本发明所示的一种的光纤预制棒掺杂元素分布的原位检测方法和装置，完全能够满足预制棒分析所需的高分辨率、多元素同时分析，非接触、微损、快速实时、原位检测等要求，并且提供了一维分析和二维分析两个选项，以适应预制棒检测的不同需求。
以上所述为本发明的一种较佳实施例而已，但本发明并不局限于该实施例和附图所公开的内容。所以凡是不脱离本发明所公开的精神下完成的等效或修改，都落入本发明保护的范围。

Claims (5)

  1. 一种光纤预制棒掺杂元素分布的原位检测方法，该方法将脉冲激光聚焦至光纤预制棒表面的待测点，形成几个至几十个微米的光斑尺寸，瞬间在激光聚焦点处烧蚀并产生等离子体，采集待测点的等离子体，得到待测点的坐标信息和元素浓度信息，利用多个不同待测点的坐标信息和元素浓度信息得到光纤预制棒所需精度的掺杂元素浓度分布光谱图。
  2. 根据权利要求1所述的光纤预制棒掺杂元素分布的原位检测方法，其特征在于，所述的待测光纤预制棒样品在检测前切片并抛光，使上下表面平行。
  3. 根据权利要求1或2所述的光纤预制棒掺杂元素分布的原位检测方法，其特征在于，对所述坐标信息和元素浓度信息的处理过程如下：
    第1步 将所有待测点的坐标信息和元素浓度信息组合成组合成浓度分布原始光谱图；
    第2步 对原始光谱图进行中值滤波，去除坏点光谱数据；
    第3步 将去除坏点的光谱图进行傅立叶变换至频域；
    第4步 再利用频域低通滤波器去除参数波动带来的各类噪声；
    第5步 将第4步得到的结果进行反傅立叶变换，得到更真实的元素浓度分布图。
  4. 一种光纤预制棒掺杂元素分布的原位检测装置，其特征在于，该装置包括激光器系统、光路系统、光谱采集系统和控制分析系统；激光器系统用于产生轰击光纤预制棒表面的待测点脉冲激光束，使待测点产生等离子体；光路系统用于对激光束整形和聚焦，以及对样品表面形态的照明和 成像；光谱采集系统用于采集等离子体发射的包含待测点的坐标信息和元素浓度信息的特征光谱信号，并转换成电信号传输到控制分析系统；控制分析系统用于控制所述激光器系统和光谱采集系统工作，并对光谱采集系统提供的特征光谱信号进行处理，得到光纤预制棒所需精度的掺杂元素浓度分布光谱图。
  5. 根据权利要求3所述的原位检测装置，其特征在于，
    所述激光器系统具体包括激光器和激光衰减器；激光器出光口和激光衰减器处在同一水平光路上；
    所述光路系统包括光阑、第一半透半反镜、同轴监控摄像头、第二半透半反镜、可选择式高倍聚焦镜和透射照明面板，光阑、第一半透半反镜和第二半透半反镜和激光器出光口处在同一水平光路上，第一半透半反镜和第二半透半反镜相对于水平光路方向成45度角放置，激光光束通过光阑整形后经过第二半透半反镜反射向下传输并通过可选择式高倍聚焦物镜聚焦到预制棒样品表面；透射照明面板由LED和毛玻璃封装而成，放置在预制棒样品下面进行透射照明，预制棒样品表面图像信息通过第二半透半反镜和第一半透半反镜反射，再通过同轴监控摄像头收集并将相应信号传输至计算机；
    所述光谱采集系统包括光收集器和光谱仪，光收集器用于收集等离子体发射的特征光信号，所述光谱仪通过光纤与光收集器相连，光谱仪将接收的特征光信号沿波长域分光并转换成电信号传输至计算机；
    所述控制分析系统包括计算机和数字同步控制器，计算机通过控制数字同步控制器的同步触发行为，实现对激光器、光谱仪和用于放置光纤预制棒的三维位移平台的时序控制；计算机通过采集来自同轴监控摄像头和光谱仪的信号，分别得到样品表面成像信息、光谱信号及其各元素浓度分布信息。
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