Rigorous mode theory and analysis of few-mode fibers

Abstract

The research and development of fibers has a long history over half a century. Although the transmission capacity of single-mode fibers has reached 10 Tbps order owing to some breakthroughs, it is approaching the limit of about 100 Tbps owing to nonlinearity and the fiber fuse. To overcome this problem, a new approach utilizing the space-division multiplexing and mode-division multiplexing has been proposed and demonstrated. However, in mode-division multiplexing, even when a mode multi/demultiplexer is used, accurate mode discrimination has been difficult and multiple-input multiple-output (MIMO) signal processing has always been used to identify the input mode channel. This is because the accurate analysis of mode propagation has not been sufficiently investigated. In this review, the history of the mode theory of optical fibers is briefly reviewed and the recent progress of mode theory and related experimental results are introduced.

Predictable and unpredictable phenomena in optical fibers for space-division/mode-division multiplexing transmission: statistical analysis of coupling and mysterious behavior of modes

“…11(a) is in good agreement with the theoretical interference between the TMH group of true eigenmodes Fig. 10 Cross-sectional structures of (a) 4-LP-mode 12-core fiber and (b), (c) 4-LP-mode 19-core fiber [15]. Copyright (2018) The Japan Society of Applied Physics ) [45].…”

“…In this fiber, the ellipticity of each core and the major and minor axes of the ellipse were obtained from microscopic bright-and dark-field images. The average value of the measured ellipticity was as small as 2.0% and the maximum value was 3.9% [15].…”

“…It consists of a tunable laser, a selective LP mode exciter (rotatable halfwave and rotatable phase plates), and an NFP observation system (rotatable polarizer and infrared camera). The angle of the polarizer was measured clockwise from the negative x-axis [15,49]. Fig.…”

“…10(b) by the microscopic observation of the cross section, as shown in Fig. 10(c) [15]. The input and output ends of the fiber were also observed using a microscope, and the numbering of the cores in the arrangement defined in Fig.…”

“…In the very early stage of research on MCFs, it was assumed that the crosstalk is due to the coupling between cores with a constant mode coupling coefficient [10] and that the coupled Fig. 1 Progress of multi-core fibers and few-mode fibers [15]. Copyright (2018) The Japan Society of Applied Physics Fig.…”