Femtosecond laser written integrated passive mode-multiplexers

Abstract

Single-mode (SM) optical fibres are rapidly approaching their transmission capacity limit. Mode-division multiplexing (MDM) is considered as one of the most promising techniques to overcome this [1]. MDM refers to using few-mode optical fibres, where each mode is used as an individual data channel. Thereby the data transmission capacity can be scaled proportional to the number of modes. However, using few-mode fibres requires the selective multiplexing and demultiplexing of individual modes. Common approaches include long-period gratings, phase-plates and liquid-crystal spatial light modulators [2]. However these techniques either suffer from a complex optical setup, high losses or a limited spectral bandwidth. In contrast integrated optics offer low losses, excellent compatibility with fibres, compact and entirely passive setups as well as an inherent robustness. However, 3-dimensional waveguide circuits are required in order to multiplex and de-multiplex all orientation states of the LP modes, making the use of traditional planar lightwave circuits challenging [3]. Show more