[1] [1] General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, Standardization Administration of the People's Republic of China. Specifications for optical fibre test methods-part 20: measurement methods and test procedures for dimensions- fiber geometry: GB 15972.20–2008[S]. Beijing: Standards Press of China, 2008.

[2] [2] Chen L, Chen J B, Lu R H. Automatic measurement of optical fiber geometric parameters[J]. Acta Optica Sinica, 2001, 21(10): 1245–1248.

[3] [3] Yin A E, Jiang Z X, Zhang Y L. Refracted near-field technique for the measurement of optical fiber refractive index profiles[J]. Acta Optica Sinica, 1989, 9(2): 181–185.

[4] [4] Gao Y C. Simulation of measuring the optical fiber refractive index profiles by refraction near-field method[D]. Harbin: Harbin Engineering University, 2012.

[5] [5] Sun H G, Chu J R, Zhong L S, et al. Measurement of refrac-tive-index profile of plastic optical fibers[J]. Optical Fiber & Electric Cable, 2001(4): 12–16.

[6] [6] Jia H Z, Li Y L, Hu M L. Fabrication methods of fiber gratings[J]. Laser Technology, 2001, 25(1): 23–26.

[7] [7] Wu Z H. The research about measurement system of six-angle fiber geometrical dimension on the basis of CCD and image processing[D]. Taiyuan: Taiyuan University of Technology, 2006.

[8] [8] Ma L D. Research on effective mode area measurement of photonic crystal fiber[D]. Qinhuangdao: Yanshan University, 2016.

[9] [9] Hameed M F O, Obayya S S A. Modal analysis of a novel soft glass photonic crystal fiber with liquid crystal core[J]. Journal of Lightwave Technology, 2012, 30(1): 96–102.

[10] [10] Rosa L, Coscelli E, Poli F, et al. Thermal modeling of gain competition in Yb-doped large-mode-area photonic-crystal fiber amplifier[J]. Optics Express, 2015, 23(14): 18638–18644.

[11] [11] Yang Y. Research on detecting optical fiber geometric para-meter based on machine vision[D]. Harbin: Harbin Engineering University, 2011.

[12] [12] Ling F C, Kang M, Lin X. Improved Canny edge detection algorithm[J]. Computer Science, 2016, 43(8): 309–312.

[13] [13] Guo M, Hu L L, Zhao J T. Surface defect detection method of ceramic bowl based on Kirsch and Canny operator[J]. Acta Optica Sinica, 2016, 36(9): 0904001.

[14] [14] Wang W H, Jiang M X, Zhao W D. Edge detection algorithm based on improved Canny operator[J]. China Sciencepaper, 2017, 12(8): 910–915.

[15] [15] WangW G,Wang S R, Xu Z F, et al. Optimal ellipse fitting algorithm of least square principle based on boundary[J]. Computer Technology and Development, 2013, 23(4): 67–70.

[16] [16] Xiong F G, Li X, Han X. A method of ellipse fitting based on total least squares[J]. Microelectronics & Computer, 2017, 34(1): 102–105.

[17] [17] Cao J L, Li J F. Improved ellipse fitting algorithm based on Letts criterion[J]. Journal of Computer Applications, 2017, 37(1): 273–277.

[18] [18] Gander W, Golub G H, Strebel R. Least–squares fitting of circles and ellipses[J]. BIT Numerical Mathematics, 1994, 34(4): 558–578.

[19] [19] Mitchell D R G, Van den Berg J A. Development of an ellipse fitting method with which to analyse selected area electron dif-fraction patterns[J]. Ultramicroscopy, 2016, 160: 140–145.

[20] [20] He C C, Yang J, Song H Y, et al. Effect of cutting tool aging on the geometric size measurement of single mode fiber[J]. Mod-ern Transmission, 2016(1): 56–61.

[21] [21] Liu W, Tang C H, Ma X M, et al. Measurement of geometric parameters of defective fiber ends[J]. Study on Optical Com-munications, 2013, 39(6): 35–38.