Coupling analysis of non-circular-symmetric modes and design of orientation-insensitive few-mode fiber couplers

• Published in: Optics communications Vol. 383; pp. 42 - 49
• Main Authors: Li, Jiaxiong, Du, Jiangbing, Ma, Lin, Li, Ming-Jun, Jiang, Shoulin, Xu, Xiao, He, Zuyuan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2017
• Subjects: Few-mode fiber couplers; Mode multiplexer/demultiplexer and mode-division multiplexing; Non-circular-symmetric modes; Non-circular-symmetric modes; Mode multiplexer/demultiplexer and mode-division multiplexing; Few-mode fiber couplers
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2016.08.051

We study the coupling between two identical weakly-coupled few-mode fibers based on coupled-mode theory. The coupling behavior of non-circular-symmetric modes, such as LP11 and LP21, is investigated analytically and numerically. By carefully choosing the fiber core separation and coupler length, we can design orientation-insensitive fiber couplers for non-circular-symmetric modes at arbitrary coupling ratios. Based on the design method, we propose an orientation-insensitive two-mode fiber coupler at 850nm working as a mode multiplexer/demultiplexer for two-mode transmission using standard single-mode fiber. Within the band from 845 to 855nm, the insertion losses of LP01 and LP11 modes are less than 0.03dB and 0.24dB, respectively. When the two-mode fiber coupler is used as mode demultiplexer, the LP01/LP11 and LP11/LP01 extinction ratios in the separated branches are respectively above 12.6dB and 21.2dB. Our design method can be extended to two-mode communication or sensing systems at other wavelengths. •We demonstrate the design of orientation-insensitive few-mode fiber couplers.•We propose an orientation-insensitive LP01/LP11 mode MUX/DeMUX at 850 nm.