Four structurally different business models compete at the optical-assembly layer, each with different economics. I see the neutral contract assembler, Fabrinet, own no products so any customer feels safe. Lumentum keeps laser‑attach know‑how in‑house, Coherent spans from substrate to system, and Applied Optoelectronics integrates upward with its own lasers. None of these models is obviously superior—trust favors neutral assembler, capture favors integrators—and independent research treats their coexistence as proof assembly layer itself is the scarce resource, not any single configuration.