Opt Express. 2023 Feb 27;31(5):8586-8594. doi: 10.1364/OE.482879.
Weakly-coupled mode division multiplexing (MDM) techniques supporting intensity modulation and direct detection (IM/DD) transmission is a promising candidate to enhance the capacity of short-reach applications such as optical interconnections, in which low-modal-crosstalk mode multiplexers/demultiplexers (MMUX/MDEMUX) are highly desired. In this paper, we firstly propose an all-fiber low-modal-crosstalk orthogonal combine reception scheme for degenerate linearly-polarized (LP) modes, in which signals in both degenerate modes are firstly demultiplexed into the LP mode of single-mode fibers, and then are multiplexed into mutually orthogonal LP and LP modes of a two-mode fiber for simultaneous detection. Then a pair of 4-LP-mode MMUX/MDEMUX consisting of cascaded mode-selective couplers and orthogonal combiners are fabricated with side-polishing processing, which achieve low back-to-back modal crosstalk of lower than -18.51 dB and insertion loss of lower than 3.81 dB for all the 4 modes. Finally, a stable real-time 4 modes × 4λ × 10 Gb/s MDM-wavelength division multiplexing (WDM) transmission over 20-km few-mode fiber is experimentally demonstrated. The proposed scheme is scalable to support more modes and can pave the way to practical implementation of IM/DD MDM transmission applications.
弱耦合模式分复用（MDM）技术支持强度调制和直接检测（IM/DD）传输，是增强短距离应用（如光互连）容量的有前途的候选技术，其中低模式串扰模式复用器/解复用器（MMUX/MDEMUX）是非常需要的。在本文中，我们首先提出了一种用于退化线性偏振（LP）模式的全光纤低模式串扰正交组合接收方案，其中两个退化模式中的信号首先被解复用为单模光纤的 LP 模式，然后被复用为双模光纤的相互正交的 LP 和 LP 模式，以便同时检测。然后，通过侧面抛光处理制造了一对由级联模式选择耦合器和正交组合器组成的 4-LP 模式 MMUX/MDEMUX，其背对背模式串扰低于-18.51dB，所有 4 个模式的插入损耗低于 3.81dB。最后，在 20km 少模光纤上实验演示了稳定的实时 4 模式×4λ×10Gb/s MDM 波分复用（WDM）传输。所提出的方案可扩展以支持更多模式，并为实现 IM/DD MDM 传输应用铺平道路。
