Essentially what the UC San Diego researchers did was to develop a system (frequency comb) that acts a bit like a concert conductor, which is the person responsible for tuning multiple instruments in an orchestra to the same pitch at the beginning of a concert.

The engineers then used this comb to synchronize the frequency variations of the different streams of optical information (optical carriers), which can compensate in advance for the crosstalk interference (this will be familiar to those who have been reading about FTTC / VDSL2 Vectoring technology on copper cables) that can occur between multiple communication channels within the fibre optic cable. The frequency comb also ensures that the crosstalk interference is reversible.

Source: Scientists Have Broken One of the Biggest Limits in Fibre Optic Networks – ISPreview UK