Coherent optical communication systems have traditionally met the challenge of sustained growth in traffic demand by increasing the data rate on single wavelength channels. However continually increasing baud rates has become prohibitively challenging and expensive while increasing the constellation size quickly limits the transmission reach. For these reasons, coherent channels based on multiple parallel wavelengths are emerging to facilitate continued bandwidth growth and to keep pace with ethernet optics. Today, dual-wavelength channels are implemented with individual lasers, however as channel counts increase using integrated comb lasers can offer additional benefits over individual lasers.
Integrated comb lasers deliver multiple coherent wavelengths from a single chip or package. In high capacity core networks, since all of the wavelengths are frequency locked, intra channel guard bands can be minimized or eliminated allowing capacity to be maximised. And because the wavelengths are all phase related, the DSP can be simplified, and transmission impairments can be compensated. On the other hand, in edge aggregation networks where cost and power are more critical a single comb-based terminal located at the hub can distribute fractions of the line rate as individual optical carriers to slower receivers while remaining compatible with standard optical line systems (OLS) in terms of WDM grid and routing options. Reductions in cost, size, power and complexity offered by integrated comb lasers in comparison to multiple individual lasers also make them a compelling solution for this use case.