| Author: | Wang, Zhuo |
| Title: | Design and fabrication of few-mode fibers for space-division multiplexing in optical communications |
| Advisors: | Yu, Changyuan (EIE) Lu, Chao (EIE) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Optical fibers Optical communications Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Electronic and Information Engineering |
| Pages: | xxiii, 111 pages : color illustrations |
| Language: | English |
| Abstract: | Under the high growth rate of the demand for bandwidth resources, space-division multiplexing (SDM) is required to further increase the capacity of fiber-optic communication networks. In this work, novel optical fibers including multi-ring-core few-mode fiber (MRC-FMF), hollow-core antiresonant fiber (HC-ARF), and negative curvature structure assisted ring-core fiber (NC-RCF) were designed and optimized for SDM transmission. The finite element method (FEM) and analytical method were adopted for the simulations of fiber modal properties. The MRC-FMF and NC-RCF were fabricated and tested experimentally. A 7-ring-core fiber, of which each core can support 5 mode groups (including a fundamental mode group and 4 higher-order mode groups) in the C+L band (wavelength from 1.53 to 1.625 µm), was designed and fabricated. The coupling between mode groups under the influence of macro bending, core axis shift, and elliptical core was discussed. To balance the requirement of low inter-mode-group coupling, high mode purity, large ∆neff between mode groups, large effective mode area, low intra-mode-group differential mode group delay (DMGD), and low inter-core crosstalk (XTc) an optimized fiber design was proposed. The transmission losses of the fabricated fiber were measured at around 0.25 dB/km. The inter-mode-group crosstalk (XTmg) was measured by the method of power measurement. The XTmg remains lower than -9.11 dB after the propagation in the fabricated 23-km fiber. A HC-ARF supporting LP01 and LP11 modes in the wavelength band from 1.31 to 1.65 µm was designed. Using the core-cladding mode coupling effect, the ratios of confinement loss (CL) between the two guiding modes and the other higher-order modes can be increased larger than 150 which guarantees the high purity of the guided modes. The minimum CLs of LP01 and LP11 modes were estimated as 1.7 × 10−4 dB/m and 3.1 × 10−3 dB/m in the wavelength band from 1.53 to 1.565 µm, respectively. Fiber bending has a relatively weak influence on the fiber loss when the bending radius is 10 cm. The fabrication tolerance of the fiber was analyzed, and it was concluded that the tolerance of tube rotation angle, tube ellipticity, and tube thickness for the designed fiber are ±10°, [0.95, 1] and 1.11 ± 0.08 µm, respectively. A new kind of NC-RCF for stable orbital angular momentum (OAM) modes transmission was designed. Inspired by the HC-ARFs, antiresonant tubes were adopted to form a lower refractive index cladding structure surrounding a ring core. The fabrication of this NC-RCF was processed under the two-stage stack-and-draw method. Two rolls of NC-RCFs with different structural sizes were fabricated. The first roll of NC-RCF can support 4 orders of OAM modes, and the measured losses of the 1st to 4th order OAM modes were 0.30 dB/m, 0.36 dB/m, 0.37 dB/m, and 0.42 dB/m, respectively. The second roll of NC-RCF can only support two orders of OAM modes. The measured losses of OAM+1,1 and OAM+2,1 were 0.995 dB/m and 0.25 dB/m. |
| Rights: | All rights reserved |
| Access: | open access |
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