Metasurface-Integrated Pattern-Preserved Fiber Mode Separator

Abstract

Traditional mode-division-multiplexing (MDM) configurations necessitate multiple steps of mode-conversion for signal relay in long-distance communication, suffering from bulky volume and higher losses due to their relatively long coupling regions induced by conversion steps. Hence, a pattern-preserved separator without a converting step will strongly improve the integration and efficiency of fiber communication networks. However, keeping fiber modes preservation in such a miniaturized communication system is still challenging due to the complexity of concurrently modulating the 2D structured light fields of overlapping modes. Here, an innovative MDM scheme utilizing a few-mode fiber (FMF) integrated with a metasurface designed through a partition-optimized strategy is presented, which achieves the spatial separation and preservation of three LP modes in the FMF without mode conversion and reduces the device size by two orders of magnitude. This polarization-insensitive scheme achieves a mode fidelity up to 92% across the C-band, which significantly reduces the channel crosstalk down to −15 dB after re-coupling. Moreover, the mode-combination capability and ultrahigh fidelity facilitate a trustworthy colourful image encryption transmission with a bit error rate (BER) to 0. These demonstrations indicate that the mode-preserved meta-fiber separator provides a new avenue for future large-scale integration of data multiplexing.