External laser source (ELS)
Beginner
Keeping the lasers in their own plug-in box, away from the hot switch chip, and piping their light in through fiber.
Novice
A pluggable module that holds only lasers. It sends steady, unmodulated light over fiber to the co-packaged optical engines, which imprint the data onto it. Lasers are the part most likely to fail and they dislike heat, so keeping them replaceable and cool helps.
Expert
Continuous-wave lasers in a front-panel form factor (for example the OIF ELSFP). Costs optical loss in the fiber and connectors, made up with higher laser power, but separates the laser from ASIC heat and keeps it field-replaceable.