Measurement of optical fiber geometry parameters by gray distribution fitting with Gaussian function

Li Yiming; Tu Jiankun; Xiang Huazhong; Jiang Bin; Zheng Gang

doi:10.12086/oee.2020.190247

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Li Y M, Tu J K, Xiang H Z, et al. Measurement of optical fiber geometry parameters by gray distribution fitting with Gaussian function[J]. Opto-Electron Eng, 2020, 47(4): 190247. doi: 10.12086/oee.2020.190247

Citation:

Li Y M, Tu J K, Xiang H Z, et al. Measurement of optical fiber geometry parameters by gray distribution fitting with Gaussian function[J]. Opto-Electron Eng, 2020, 47(4): 190247. doi: 10.12086/oee.2020.190247

Measurement of optical fiber geometry parameters by gray distribution fitting with Gaussian function

1.
Shanghai Engineering Research Center of Interventional Medical Device, Key Laboratory of Ministry of Education for Applied Optical Instruments, University of Shanghai for Science and Technology, Shanghai 200093, China
2.
Shanghai Cable Research Institute, Shanghai 200093, China

Fund Project: Supported by National Natural Science Foundation for Young Scientists of China (61605114)

More Information

^*Corresponding author: Zheng Gang, E-mail:gangzheng@usst.edu.cn

Received Date 15 May 2019

Revised Date 26 August 2019

Published Date 01 April 2020

Abstract

Abstract

The geometry parameters of optical fiber affect the optical transmission and mechanical properties, which are the important indexes to measure the quality of fiber. Near-field light distribution method is recommended in GB15972.20-2008 for the measurement of geometry parameters. In order to distinguish the boundary between fiber core and cladding, the method needs to illuminate the fiber. The end face of the fiber core is a bright spot with unclear edge, so the true edge of the core and cladding cannot be accurately judged. In this paper, the distribution of mode field in optical fiber is analyzed. Theoretically, the solution of electromagnetic vector of mode field satisfies Bessel function, but Gaussian function can also be used under approximate conditions. Therefore, Gaussian function is used to fit the distribution of the fiber core in this paper, and the real edge of the fiber core and cladding can be obtained from the Gaussian function after fitting. This method is a further improvement on the measurement method of GB15972.20-2008. The experimental results show that when the cutting effect of the fiber is not good or the imaging quality is poor, the Gaussian function method fitting with mode distribution can still ensure the repeatability of the measurement and the stability of the measured data.
- optical fiber geometry parameters /
- mode distribution /
- Gaussian function /
- edge detect

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References

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Overview

Overview

Overview: The geometry parameters of optical fiber affect the optical transmission and mechanical properties of optical fiber. The near-field optical distribution method is a measurement method recommended in GB15972.20-2008. The main parameters to be measured include the diameter of cladding and core, the roundness of cladding and core, and the concentricity of cladding and core. In order to distinguish the boundary between fiber core and cladding, the fiber core should be illuminated during the measurement of the geometry parameters. Actually, the end face of fiber core is a bright spot with unclear edges, so it is impossible to accurately judge the true edges of fiber core, which will bring errors to the measurement of geometry parameters of fiber core. In this paper, the distribution of optical mode field in fiber was analyzed. Theoretically, the solution of electromagnetic vector of optical fiber mode field satisfies Bessel function, but Gaussian function can also be used to approximately describe the distribution of optical fiber mode field.

Therefore, Gaussian function was used to fit the gray distribution of fiber core, and the true edge of fiber core was obtained from the Gaussian function. Gaussian function fitting method mainly includes the following three steps. The first step is to obtain the image of the end face of the optical fiber by CCD and conduct appropriate image preprocessing. The image contrast is stronger and more conducive to subsequent gray data extraction by image preprocessing. The second step is to find the best Gaussian function by the fitting with gray data of the image. 3D fitting with all the gray data of fiber core end face can effectively filter out error data and reflect the true mode field distribution of fiber core. The third step is to find the true edge of the fiber core through the best-fitting Gaussian function, and fit the edge data with elliptical curves. Finally, the geometry parameters of the fiber core will be obtained. For the measurement of cladding geometry parameters, because of the high contrast of the edge, Canny operator can be directly used to extract the edge of the cladding. The cladding geometry parameters with high precision can be obtained by elliptical curves fitting.

The real edge of optical fiber core can be accurately obtained by Gaussian function fitting, and the error points in the image can be effectively filtered through fitting, so as to improve the measurement accuracy of optical fiber geometry parameters. Taking fiber core data as an example, the data of diameter and roundness measured by the standard instrument are 8.420 μm and 0.670%, respectively. When cutting effect of fiber end face or lighting condition is poor, the instrument data change to 9.044 μm and 1.457%, while the data measured in this paper are 8.425 μm and 0.480%, respectively.