  Optical interconnect is a potential solution to attain the large bandwidth
on-chip communications needed in high performance computers in a low power and
low cost manner. Mode-division multiplexing (MDM) is an emerging technology
that scales the capacity of a single wavelength carrier by the number of modes
in a multimode waveguide, and is attractive as a cost-effective means for high
bandwidth density on-chip communications. Advanced modulation formats with high
spectral efficiency in MDM networks can further improve the data rates of the
optical link. Here, we demonstrate an intra-chip MDM communications link
employing advanced modulation formats with two waveguide modes. We demonstrate
a compact single wavelength carrier link that is expected to support 2x100 Gb/s
mode multiplexed capacity. The network comprised integrated microring
modulators at the transmitter, mode multiplexers, multimode waveguide
interconnect, mode demultiplexers and integrated germanium on silicon
photodetectors. Each of the mode channels achieves 100 Gb/s line rate with 84
Gb/s net payload data rate at 7% overhead for hard-decision forward error
correction (HD-FEC) in the OFDM/16-QAM signal transmission.
