Optical data transmission at 44Tb/s and 10 bits/s/Hz spectral density over standard fibre with a single micro-comb source chip
Micro-combs - optical frequency combs generated by integrated micro-cavity
resonators – offer the full potential of their bulk counterparts, but in an
integrated footprint. The discovery of temporal soliton states (DKS –
dissipative Kerr solitons) as a means of mode-locking micro-combs has enabled
breakthroughs in many fields including spectroscopy, microwave photonics,
frequency synthesis, optical ranging, quantum sources, metrology and more. One
of their most promising applications has been optical fibre communications where
they have enabled massively parallel ultrahigh capacity multiplexed data
transmission. Here, by using a new and powerful class of micro-comb
called “soliton crystals”, we achieve unprecedented data transmission over
standard optical fibre using a single integrated chip source. We demonstrate a line
rate of 44.2 Terabits per second (Tb/s) using the telecommunications C-band at
1550nm with a spectral efficiency – a critically important performance metric -
of 10.4 bits/s/Hz. Soliton crystals exhibit robust and stable generation and
operation as well as a high intrinsic efficiency that, together with a low soliton
micro-comb spacing of 48.9 GHz enable the use of a very high coherent data modulation
format of 64 QAM (quadrature amplitude modulated). We demonstrate error free
transmission over 75 km of standard optical fibre in the laboratory as well as in
a field trial over an installed metropolitan optical fibre network. These
experiments were greatly aided by the ability of the soliton crystals to
operate without stabilization or feedback control. This work demonstrates the capability
of optical soliton crystal micro-combs to perform in demanding and practical optical
communications networks.