WO2017120730A1 - 用渐变孔径光学积分法测量单模光纤模场直径的新方法 - Google Patents

用渐变孔径光学积分法测量单模光纤模场直径的新方法 Download PDF

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WO2017120730A1
WO2017120730A1 PCT/CN2016/070567 CN2016070567W WO2017120730A1 WO 2017120730 A1 WO2017120730 A1 WO 2017120730A1 CN 2016070567 W CN2016070567 W CN 2016070567W WO 2017120730 A1 WO2017120730 A1 WO 2017120730A1
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optical
aperture
fiber
field diameter
integrator
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PCT/CN2016/070567
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French (fr)
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周瑾
周文俊
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周瑾
周文俊
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Priority to CN201680000896.0A priority Critical patent/CN106537086B/zh
Priority to PCT/CN2016/070567 priority patent/WO2017120730A1/zh
Publication of WO2017120730A1 publication Critical patent/WO2017120730A1/zh
Priority to US15/996,513 priority patent/US10132716B2/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/08—Measuring arrangements characterised by the use of optical techniques for measuring diameters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/02—Details
    • G01J1/04—Optical or mechanical part supplementary adjustable parts
    • G01J1/0407—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
    • G01J1/0437—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings using masks, aperture plates, spatial light modulators, spatial filters, e.g. reflective filters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/4257—Photometry, e.g. photographic exposure meter using electric radiation detectors applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/005—Diaphragms

Definitions

  • the invention belongs to the field of testing methods and measurement technologies in optical fiber communication, and is also related to high-end instrument equipment and measurement standards, and particularly relates to a method for measuring characteristic parameters of optical fibers, and is a method for measuring single mode fiber mode field diameter (MFD). New method.
  • Mode field diameter is one of the important characteristic parameters of single-mode fiber. It directly affects the fiber joint loss and bending resistance. It is a must-measure parameter in fiber optic cable production and application.
  • MFD Mode field diameter
  • Literature 1 Zhou Wenjun, Theoretical and Experimental Research on Mask Measurement System, Journal of Electronics, Vol. 17, No. 6, (November 1989), 61.
  • Literature 2 Single-mode fiber multi-parameter tester, registration number 902548, "Science and Technology Research Results Bulletin", (1992), National Science and Technology Commission of the People's Republic of China.
  • the object of the present invention is to overcome the contradiction between the measurement accuracy and the measurement speed which are common in the standard test method for the mode field diameter of a single mode fiber.
  • the invention proposes a new method for measuring the mode field diameter of a single mode fiber, which is called a gradient aperture optical integration method.
  • the present invention can be referred to simply as the optical integration method, because it is different from the previous standard methods to make the integral in the Pitman definition use the complicated processing of multiple sampling, first dividing and then synthesizing, but the integral is regarded as a whole, and the utilization is utilized. Ingeniously designed integrator, this integral is done optically; the invention can also be referred to simply as the gradient aperture method, which is equivalent to the aperture angle from 0 to 25° compared to the variable aperture method.
  • variable aperture method Infinite number of clear apertures that vary continuously. This is not possible with the variable aperture method that is now commonly used: one is that the number of apertures in the variable aperture method is limited (generally less than 20); the other is due to the aperture angle of 0 to 5°. The light-passing holes between them are difficult to process, so in the region where the optical power density is likely to be the largest, the measurement points taken are more limited, which also brings errors.
  • the present invention first converts the integral in the second definition of Pitman into the mean square value of the numerical aperture NA of the fiber exit; this mean square value It not only has obvious physical meaning, but also can be obtained by the optical power ratio measured by the measured optical fiber passing through and not passing through the gradual aperture optical integrator.
  • the measured mode field diameter is not only approximated, but the measurement speed is more than ten times faster than the variable aperture method.
  • the mode field diameter MFD can be expressed as follows:
  • the mode field diameter of the fiber can be calculated from equation (4). This completes the transformation of the integral expression of the complex mode field diameter to the simple four-step operation formula.
  • the denominator in the brackets of (3) is the total optical power of the outgoing light, which is set to P(o); the numerator in the brackets of (3) can also be seen for each exit angle ⁇
  • the optical power is modulated by the squared sin 2 ⁇ of the fiber's numerical aperture, so we can design a device to match the amount of light passing through it at the corresponding position, so that the total optical power through the device is in brackets in (3)
  • the molecules are equal and set to P(i). This gives you:
  • the symmetrical light-passing area is consistent with the corresponding numerical aperture, and its size varies continuously from 0 to sin 2 ⁇ max .
  • This device a gradient aperture optical concentrator, The following coordinate equation design can be
  • D is the vertical distance from the exit end of the fiber to the center of the optical integrator
  • ⁇ and ⁇ are the radial and angular angles of the polar coordinates.
  • R in the above formula is the maximum value ⁇ max of the integrator light-receiving region, where tan (12.5°) represents a tangent value of 12.5°.
  • An optical integrator designed and used in accordance with equations (7) and (8) is effective. According to the above method, the mode field diameter of the single mode fiber can be quickly and accurately measured by the formula (6); and the shape of the integrator can be made into a circle, a square, and a rectangle.
  • the gradient aperture optical integrator is placed coaxially and vertically with the optical axis of the optical imaging system; then the opposite aperture of the clear aperture optical integrator is used in the horizontal and vertical directions. The feature is that the received optical power is minimized by horizontal adjustment, and the received optical power is maximized by vertical adjustment. Through such repeated adjustments, the requirement that the fiber end of the tested fiber is also coaxial with the system is achieved.
  • the Fermat spiral and the corresponding mode field diameter calculation formula in the mask method can be obtained by simple operation of (7) and (6) (see Document 1). ).
  • the present invention can accurately, quickly and easily measure the mode field diameter of a single-mode fiber, obtain a numerical aperture rms of a fiber having a clear physical meaning, and is not difficult to measure the mode field.
  • the mode spectrum curve of the diameter as a function of wavelength. Can be widely used in measurement, production, engineering and even scientific research and teaching. Thanks to the precise measurement, a more standard measuring instrument can be manufactured; due to the high measuring speed, it can be made into an efficient automatic test instrument for industrial production, saving a lot of society.
  • the test instrument manufactured by applying the invention will have higher cost performance, thereby saving and creating more social wealth.
  • Figure 1 shows the working principle of the sliding gradient aperture optical integrator
  • Figure 2 shows the working principle of the rotary gradient aperture optical integrator
  • Figure 3 is a working principle diagram of a split-gradient aperture optical integrator
  • Figure 4 is a schematic diagram of the distance between the exit of the optical fiber and the integrator and the alignment adjustment
  • Figure 5 is a schematic view of a square gradient aperture optical integrator
  • Figure 6 is a schematic diagram of a circular gradient aperture optical integrator.
  • the components common to the existing standard test methods of the present invention are a light source, an imaging system, and a detection.
  • the receiving system whose function is to collect and measure the optical power of the light source emitted through the optical fiber.
  • the variable aperture method needs to ensure that the outgoing light is coaxially aligned with each of the light-passing holes, and then respectively measure the optical power collected after passing through nearly 20 through-holes with different radii.
  • the optical illuminator (abbreviated as integrator) used has a square shape and a circular shape.
  • Scheme 1 As shown in Figure 1, a square gradient aperture optical integrator is placed in the exiting optical path of the fiber and allowed to slide horizontally along a fixed parallel track. After adjusting the centering, P(i) can be measured; Then, the integrator 3 is slid out of the optical path to measure P(o), and the measured ratios of the two optical powers are substituted into the equation (6), and the mode field diameter of the fiber to be tested can be quickly obtained. Like the slide, the square integrator can slide in and out, as the name suggests, the sliding method. Specifically, 1 in Figure 1 is the light source, 2-bit fiber, 3 is the optical integrator, 4-bit optical imaging system, 5 is detector.
  • Solution 2 As shown in Fig. 2, a disc with two holes is placed in the optical path, and the centers of the two holes are placed on a concentric circle. A circular gradient aperture optical integrator 33 is embedded in one of the circular holes 31, and the other is a through hole. When installing the disc, make sure that the two circular holes on it can be rotated coaxially with the optical system. Then, the output end of the fiber to be tested is adjusted so as to be on the same axis; the disk 3 is rotated, and the circular gradient aperture optical integrator 32 and the through hole 31 are coaxial with the system, respectively, and P(i) and P(o), also the mode field diameter is derived from (6).
  • this solution is to measure the mode field diameter by rotating the disk 3 by 180 degrees, it is called a rotation method.
  • the contour of the optical integrator be the same as the contour of the circular hole, let the light of the fiber under test be emitted from the integrator, measure once and record P(i); then rotate the disc to rotate the circular hole to the last optical
  • the position of the integrator is such that the light of the fiber under test is emitted from the hole, and then a measurement is made and P(o) is recorded.
  • 1 is a light source
  • 3 is an optical integrator, that is, a circular optical integrator, a 4-bit optical imaging system
  • 5 is a detector.
  • the mode field diameter can be found. Since this method is to measure the mode field diameter of a single-mode fiber by splitting, it is called a spectroscopic method.
  • the spectroscopic method does not need to change the position of the gradient aperture optical integrator, and the mode field diameter of the optical fiber can be measured in real time, so the measurement speed is the fastest, and it is more convenient to produce corresponding engineering instruments.
  • the maximum effective radius R of the integrator must be as follows between the fiber end face and the vertical distance D from the center of the integrator:
  • the far field test range should not be less than ⁇ 12.5°.
  • the farther away from the center in the horizontal direction the larger the light-passing area is, and the opposite is true in the vertical direction; therefore, when adjusting in the coaxial alignment, it is only necessary to make the measured in the horizontal direction.
  • the optical power is the smallest, and the measured optical power is maximized in the vertical direction.
  • Fig. 5 is a square gradient aperture optical integrator
  • Fig. 6 is a circular gradient aperture optical integrator.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Testing Of Optical Devices Or Fibers (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Spectroscopy & Molecular Physics (AREA)

Abstract

一种测量单模光纤模场直径的方法，即渐变孔径光学积分法，简称为渐变孔径法或光学积分法，属于光纤通信领域中光纤参数测量方法。本方法依据皮特曼第二定义，将单模光纤模场直径表达式中的积分运算，变换为含有光纤数值孔径均方值的四则计算，采用渐变孔径光学积分器（3），利用平移、转动、分光三种方法之一即可精确测出单模光纤数值孔径的均方值，继而求得被测光纤的模场直径。对于单模光纤模场直径的测量，具有精确、快速、简便的特点，可广泛应用于计量标准、自动化测试设备及工程仪表等各个方面。

Description

用渐变孔径光学积分法测量单模光纤模场直径的新方法 技术领域
本发明属于光纤通信中的测试方法和测量技术领域，还与高端仪器设备和计量标准有关，特别涉及光纤特征参数的测量方法，是一种测量单模光纤模场直径(Mode Field Diameter，MFD)的新方法。
背景技术
模场直径(MFD)是单模光纤重要的特征参数之一，它直接影响着光纤的接头损耗，抗弯曲性能等重要特性，是光纤光缆生产，应用中的必测参数。现在世界上单模光纤产量已达数亿芯公里，其测量工作量之巨大可想而知。不断探寻更加迅速、精确地测量这些数据的方法，一直是业内科学工作者共同努力的目标。
对于模场直径的测量，现在国际标准和国内标准公认的有三种方法：即作为基准测试方法(Reference Test Method，RTM)的远场扫描法，作为替代测试法(Alternative test method，ATM)的可变孔径法和近场扫描法。这些标准测试法的依据都是皮特曼(Petermann)第二定义；该定义的主要表达式是二个积分之比，这些标准方法不是将这些积分作为一个整体来进行处理，而是将其分割成若干部分进行采样，然后再按相应公式组合起来，将皮特曼(Petermann)第二定义中的积分表达式近似为若干有限项级数的求和，这样处理显然会产生误差；要减小这个误差，就不得不分割和测量更多的项数，这就必然导致测量时间的增加(测量一个波长处的模场直径往往要花费几十秒、甚至几分钟的时间)，从而降低了测量速度。现有的标准测试法，至今都无法解决这个基本矛盾，只有另外探索新的途径，寻求新的测量方法。还有值得一提的是掩膜法(Mask Method)，尽管采用改进后的掩膜法(参见文献1)制成的仪器设备，也能快速、 准确地测量模场直径，而且测量精度优于0.05μm(参见文献2)，与用可变孔径法制成的仪器设备的精度相当；但由于这种方法的前提条件中，用到了几何光学的近轴近似处理，因此而失去了理论上的严谨性。
文献1：周文俊，Mask测量系统的理论与实验研究《电子学报》，第17卷，第6期，(1989年11月)，61页。
文献2：单模光纤多参数测试仪，登记号902548，《科学技术研究成果公报》，(1992年)，中华人民共和国国家科学技朮委员会。
发明内容
本发明的目的，是为了克服现在单模光纤模场直径的标准测试法中，共同存在的测量精度和测量速度不可兼得的矛盾。本发明提出了一种新的单模光纤模场直径的测量方法，称之为渐变孔径光学积分法。本发明可简称为光学积分法，是因为要区别于此前各种标准方法将皮特曼定义中的积分利用多次采样、先分割后合成的繁杂处理，而是将该积分看作一个整体，利用巧妙设计的积分器，通过光学方法完成这个积分；本发明还可简称为渐变孔径法，这是相对于可变孔径法而言，这种积分器就相当于其孔径张角从0到25°之间连续变化的、无数个通光孔径。这是现在普遍采用的可变孔径法不可能做到的：一个是可变孔径法的通光孔数目受到限制(一般少于20个)；另一个则是由于孔径张角在0到5°之间的通光孔难于加工，因此在这个光功率密度可能最大的区域，其所取测量点更受限制，这也会带来误差。
本发明首先将皮特曼第二定义中的积分转化为该光纤出射数值孔径NA的均方值；此均方值
Figure PCTCN2016070567-appb-000001
不但具有明显的物理意义，而且还可以由被测光纤出射光通过和不通过渐变孔径光学积分器，在这二种情况下分别测得的光功率比值求得。 这样测得的模场直径由于未作任何近似，不但精度高，而且测量速度超过可变孔径法测量速度十倍以上。
根据皮特曼定义，模场直径MFD可表示如下：
Figure PCTCN2016070567-appb-000002
式中F2(q)是远场功率分布；q＝sinθ/λ,其中θ是出射光的张角，λ是入射光的波长。将q＝sinθ/λ代入(1)式可以得到
Figure PCTCN2016070567-appb-000003
显然，(2)式括号中的积分表达式就是光纤数值孔径NA＝sinθ的均方值
Figure PCTCN2016070567-appb-000004
Figure PCTCN2016070567-appb-000005
将(3)代入(2)式得到
Figure PCTCN2016070567-appb-000006
只要我们求出了光纤的数值孔径的均方值
Figure PCTCN2016070567-appb-000007
由(4)式就可算得该光纤的模场直径。这样就完成了将模场直径复杂的积分表达式向简单四则运算公式的变换。
不难看出，(3)式括号中的分母正是出射光的总光功率，设为P(o)；从(3)式括号中的分子也可看到，对于每一个出射角θ处的光功率都会受到光纤数值孔径平方sin2θ的调制，因此我们可以设计一种器件使其在相应位置通光量的大小与之一致，使通过该器件的全部光功率与(3)式中括号中的分子相等，並设为P(i)。由此得到：
Figure PCTCN2016070567-appb-000008
将(5)式代入(4)式中可得：
Figure PCTCN2016070567-appb-000009
对于该器件，其对称的通光区各处都要与相应的数值孔径相一致，其大小从0到sin2θmax之间连续变化，我们将该器件称为渐变孔径光学积光器，按下面极座标方程设计即可
ρ＝D×[2φ/(π-2φ)]1/2          (7)
(7)式中D是光纤出射端面到光学积分器中心的垂直距离，ρ、φ则是极座标的矢径和幅角。为满足国际标准对于远场扫描角不得小于25度的规定，还必须满足下面条件
R＝ρmax≥D×tan(12.5°)      (8)
上式中的R是积分器通光区矢径的最大值ρmax，其中tan(12.5°)代表正切值12.5°。只要按照(7)公式和(8)公式设计和使用的光学积分器都是有效的。依照上面方法处理，由(6)式就能快速、精确地测得单模光纤的模场直径；而且该积分器的外形可以做成圆形、方形、长方形。渐变孔径光学积分器的使用中，要使渐变孔径光学积分器与光学成象系统的光轴同轴、且垂直放置；然后利用渐变孔径光学积分器通光区在水平方向和垂直方向的相反对称的特点，通过水平调节使接收到的光功率最小，通过垂直调节使接收到的光功率最大。通过这样几次反复调节来达到被测光纤出端也与系统同轴的要求。
此外，在近轴近似条件下，通过对(7)式、(6)式的简单运算就可以得到掩膜法中的费马(Fermat)螺线及相应的模场直径计算公式(参见文献1)。
有益效果：与现在的传统测量方法相比较，本发明能够精确、快速、简便地测量单模光纤的模场直径，得到具有明确物理意义的光纤数值孔径均方根，也不难测得模场直径随波长变化的模斑谱曲线。可广泛应用于计量、生产、工程乃至科研教学各个方面。由于测量精确，就可制造更加标准的计量仪器；由于测量速度快，可制成用于工业生产的高效自动測试仪器设备，节约大量的社 会劳动时间，提高劳动生产率；由于操作简便，则可设计成便于工程应用的测量仪表；我们知道光纤的色散与模斑谱有关，而光纤的数值孔径则与光纤的折射率分布相联，本发明可利用自身的这些优势介入到科研教学中，通过相互结合，彼此促进，可望催生功能更多的高效光纤综合测试仪，並进而推动光纤传输理论和测试方法的进展。此外，与现有的测量单模光纤模场直径的仪器设备相比，应用本发明制造的测试仪表将有更高的性价比，从而节省並创造更多的社会财富。
附图说明
图1滑动渐变孔径光学积分器工作原理图；
图2转动渐变孔径光学积分器工作原理图；
图3分光渐变孔径光学积分器工作原理图；
图4光纤出射光与积分器放置距离及对中调节示意图；
图5为方形渐变孔径光学积分器示意图；
图6为圆形渐变孔径光学积分器示意图。
具体实施方式
结合附图，对本发明如何实现精确、快速测量单模光纤模场直径，进一步具体说明如下：如图1-3所示，本发明与现有标准测试方法共有的构件是光源，成像系统及探测接收系统，其功能都是收集、测量光源通过光纤出射的光功率。与现在国内外普遍采用的传统法不同的是：可变孔径法需要保证出射光与每个通光孔共轴对中，然后分别测量通过近20个半径不同的通孔后收集到的光功率，再进行多项级数的求和计算；远场扫描则需要测量更多的点，经过更加繁杂的计算，才能得到一个近似的积分结果；本发明只需测量光纤出射光通过与不通过渐变孔径光学积分器这两种状态下收集到的光功率之比，按照(6)式经过简单 的计算就可以得到符合皮特曼第二定义的模场直径。本发明得到的效果是：既提高了模场直径的测量精度，又极大地提高了测量速度。
为了实现对于单模光纤模直径的测量，首先要测量单模光纤数值孔径NA＝sinθ的均方值
Figure PCTCN2016070567-appb-000010
下面用几个具体方案来简单说明，所用的光学积光器(简称为积分器)的外部形状有方形、圆形之别。
方案1：如图1所示，将方形渐变孔径光学积分器置于光纤的出射光路中，並使其能沿固定的平行轨道水平滑动，调节对中后就可测得P(i)；再让积分器3滑出光路，即可测得P(o)，将测得的这二个光功率比值代入(6)式，很快就可以得出被测光纤的模场直径。如同幻灯片一样，方形积分器可滑进、滑出，顾名思意谓之滑动法，具体地，图1中1为光源，2位光纤，3为光学积分器，4位光学成像系统，5为探测器。
方案2：如图2所示，将开有二个孔的圆盘置于光路中，並使这二个孔的圆心位于一个同心圆上。在一个圆孔31中嵌入圆形渐变孔径光学积分器33，另一个则为通孔。安装圆盘时，要保证其上的二个圆孔可通过转动与光学系统同轴。然后，调节被测光纤出端，使其也在此同一轴上；转动圆盘3，先后让圆形渐变孔径光学积分器32和通孔31与系统同轴，分别测出P(i)和P(o)，同样由(6)得出模场直径。由于这个方案是通过将圆盘3转动180度完成模场直径的测量，因此称为转动法。进一步描述，让光学积分器的轮廓与圆孔的轮廓一样，让被测光纤的光线从积分器中射出，测量一次并记录P(i)；然后转动圆盘，使圆孔转动到上一次光学积分器所在的位置，让被测光纤的光线从圆孔中射出，再进行一次测量并记录P(o)。具体地，图1中1为光源，2位光纤，3为光学积分器，即圆形的光学积分器，4位光学成像系统，5为探测器。
方案3：如图3所示，在光纤出射端与渐变孔径光学积分器之间，靠近光纤出射端处放置一片分束器6，且与系统中心轴成45度角。这样，透过分束器的一束光通过渐变孔径光学积分器后，将被光学系统会聚到探测器中，得到光功率P*(i)；另一束光则被分束器反射，並被聚于另一个探测器中，其功率为P*(o)。如果光纤出射光的总功率是P(o)，分束器6的透射和反射系数分别是kt和kr，则有
P*(i)＝ktP(i)        (9)
P＊(o)＝krP(o)       (10)
注意，这时光纤数值孔径均方值应为
Figure PCTCN2016070567-appb-000011
同样将之代入(6)式，即可求出模场直径。由于这个方法是通过分光来完成单模光纤模场直径的测量，故谓之分光法。分光法不需要改变渐变孔径光学积分器的位置，就能即时测出光纤的模场直径，因此测量速度最快，而且更便于由此制作相应的工程仪表。
应用渐变孔径光学积分法测量单模光纤的模场直径，都会涉及到光纤的定位和共轴对中调试问题。为了说明这些问题，图4、图5给出了简明的图示，这里需要强调二点：
(1)有关积分器放置的位置。根据(8)式，积分器的最大有效半径R，与光纤端面到积分器中心的垂直距离D之间必须满足如下关系：
R≥D×tan(12.5°)       (8)
这是国际标准和国家标准要求，远场测试范围不应小于±12.5°。
(2)根据积分器设计的特点，其沿水平方向偏离中心越远通光面积越大，沿垂直方向则完全相反；因此在共轴对中调节时，只需在水平方向上使测得的光功率最小，而在垂直方向使测到的光功率最大即可。
关于渐变孔径光学积分器，必须按照(7)式给出的极座标方程设计
ρ＝D×[2φ/(π-2φ)]1/2       (7)
根据(7)式设计的，二种不同外型的渐变孔径光学积分器示意在图5、6中。图5中的是方型渐变孔径光学积分器，图6为圆形渐变孔径光学积分器。

Claims (6)

  1. 一种用渐变孔径光学积分法测量单模光纤模场直径的新方法，其特征在于将单模光纤模场直径表达式的积分运算变化为一个四则计算，所推导出的模场直径表达式中只包含通光波长和被测光纤数值孔径均方根这二个可变参数；
    Figure PCTCN2016070567-appb-100001
    式中λ为工作波长，
    Figure PCTCN2016070567-appb-100002
    是光纤的数值孔径NA＝sinθ的均方值：
    Figure PCTCN2016070567-appb-100003
    (3)式中，F2(q)是出射光的远场分布，q＝sinθ/λ，θ则是出射光的张角，光纤数值孔径的均方值
    Figure PCTCN2016070567-appb-100004
    可由光纤出射光经过和不经过渐变孔径光学积分器这二种情况下，分别收集到的光功率之比来确定：
    Figure PCTCN2016070567-appb-100005
    式中P(i)是出射光经过渐变孔径光学积分器后，通过光学系统所收集到的光功率；P(o)则是出射光不经过渐变孔径光学积分器通过光学系统所收集到的光功率，因此得到
    Figure PCTCN2016070567-appb-100006
  2. 根据权利要求1所述的用渐变孔径光学积分法测量单模光纤模场直径的新方法，其特佂是采用方形渐变孔径光学积分器，通过水平滑动使光纤的出射光经过和不经过渐变孔径光学积分器，並测量在这二种情况下所收集到的光功率之比，利用(5)式即可确定该光纤数值孔径的均方值。
  3. 根据权利要求1所述的用渐变孔径光学积分法测量单模光纤模场直径的新方法，其特佂是采用圆形渐变孔径光学积分器，通过转动使光纤的出射光分别经过渐变孔径光学积分器和通孔，並测量在这二种情况下所收集到的光功率之比，代入(5)式确定该光纤数值孔径的均方值。
  4. 根据权利要求1所述的用渐变孔径光学积分法测量单模光纤模场直径的 新方法，其特佂是采用分束器，透过分束器的出射光经过渐变孔径光学积分器后收集到的光功率为P*(i)，经分束器反射的出射光通过透镜会聚到另一个探测器中，其功率为P*(o)，按照下式即可求得该被测光纤数值孔径的均方值：
    Figure PCTCN2016070567-appb-100007
    式中的kt、kr分别是分束器的透射和反射系数。
  5. 根据权利要求2、3、4所述的用渐变孔径光学积分法测量单模光纤模场直径的新方法，其特佂是，其中所使用的渐变孔径光学积分器的通光区域边界的极座标(ρ，φ)应该满足下面方程
    ρ＝D×[2φ/(π-2φ)]1/2               (7)
  6. 根据权利要求5所述的用渐变孔径光学积分法测量单模光纤模场直径的新方法，为正确设计和使用渐变孔径光学积分器，其最大有效矢径R必须满足下面公式
    R≥D×tan(12.5°)               (8)
    式中D是光纤出射端面到渐变孔径光学积分器之间的距离。渐变孔径光学积分器的使用中，要使渐变孔径光学积分器与光学成象系统的光轴同轴、且垂直放置；然后利用渐变孔径光学积分器通光区在水平方向和垂直方向的相反对称的特点，通过水平调节使接收到的光功率最小，通过垂直调节使接收到的光功率最大，通过这样几次反复调节来达到被测光纤出端也与系统同轴的要求。
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