Mode Field Analysis of Single-mode Multi-core Optical Fibers based on Scalar Coupled Mode Theory

• Main Authors: Yi-ling Li, 李翊鈴
• Other Authors: Hung-Wen Chung
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/55973305676970651525

碩士 === 國立中山大學 === 光電工程學系研究所 === 104 === The recent trend in optical fiber communication is moving toward developing the multi-core fiber (MCF) with each fiber core supporting either a single mode or multi modes. It will effectively increase the bandwidth of the communications system. However, for the single-mode MCF as we reduce the cladding spacing between each core the coupling among each core increases. This will result in undesirable signal crosstalk coming from adjacent fiber cores. It is interesting to note that present theoretical prediction of the coupling strength of a single-mode MCF is a few orders of magnitude larger than experimentally measured values. We can only speculate that the coupling strength is reduced partly due to random fluctuation of relative phases among neighboring cores and partly due to polarization variation among fiber bores. Since the cross sectional area of a MCF is of several hundred/thousand wavelength square, it is impossible to conduct mode field analysis of these MCFs using commercial software using traditional mode-solving techniques such as the finite-element method or beam propagation method. In this paper, considering the small index contrast in the MCF we propose to develop a rigorous scalar coupled-mode theory (CMT) to analyze mode fields of a given single-mode MCF. The global MCF mode fields are then represented by some linear combination of linear polarized fiber mode field attributed to each single individual fiber core. In the end we have implemented Matlab codes for the MCF under CMT formulation. This program not only computes every eigen-mode of the global MCF waveguide structure it also allows us to study the mode field evolution of the single-mode MCF. As we initially turn on one of the fiber core we are able to observe that the energy gradually spread across all fiber cores according to the governing equation. When combined with new broadband MCF optical amplifiers we may see another ten-fold increase in the capacity of the optical fiber communication system with a minimum increase in cost.