I place lasers and EML devices at #1 with very high conviction—they are the most direct optical bottleneck for the 800G/1.6T and co‑packaged ramps, because a weak light‑source supply chain constrains the entire module ramp; I rank optical signal processors at #2 as the power‑performance gate; indium‑phosphide substrate supply and epitaxial capacity sit at #3‑4 as the material every laser starts from; precision optical packaging is #5, the manufacturing‑yield gate.