Cascaded Mode-Division-Multiplexing and Time-Division-Multiplexing Passive Optical Network Based on Low Mode-Crosstalk FMF and Mode MUX/DEMUX

We propose cascaded mode-division-multiplexing and time-division-multiplexing passive optical network (MDM-TDM-PON) based on low mode-crosstalk few-mode fiber (FMF) and all-fiber mode multiplexer/demultiplexer (MUX/DEMUX), in which optical network units communicate with the optical line terminal utilizing different time slots and specific optical linearly polarized spatial modes. An MDM optical distribution network (ODN) is cascaded with multiple conventional TDM ODNs to effectively extend a larger scale of current commercial PON systems based on TDM. The upgrade from TDM-PON to the cascaded MDM-TDM-PON is simple and cost-effective. No multiple-input–multiple-output (MIMO) digital signal processing is required to eliminate the mode crosstalk. The all-fiber mode MUX/DEMUXs are composed of mode selective couplers, which simultaneously multiplex or demultiplex multiple modes. We experimentally demonstrate MDM-PON transmission over 10 and 55 km two-mode FMFs and cascaded MDM-TDM-PON transmission over a 10-km two-mode FMF and a 10-km standard single-mode fiber with 10-Gb/s optical on–off keying (OOK) signal and direct detection.