photonic integrated circuit fabrication

Photonic integrated circuit fabrication uses semiconductor foundry methods to build optical waveguides, modulators, detectors, splitters, and multiplexers on a chip. **A PIC foundry is manufacturing light paths, not just transistors.** The process must control waveguide geometry, optical loss, coupling efficiency, thermal tuning, and alignment to fibers or lasers. Silicon photonics often reuses CMOS-style process discipline, but the yield problem includes both electrical and optical behavior. | PIC element | What the foundry controls | Design consequence | |---|---|---| | Waveguide | Width, thickness, sidewall roughness | Sets loss, phase, and mode behavior | | Modulator | Junction, heater, or material stack | Sets bandwidth and drive power | | Detector | Germanium or III-V integration quality | Sets responsivity and dark current | | Coupler and package | Fiber attach, grating, edge coupling | Often determines system-level yield | **PIC success depends on co-design.** The layout, process, package, thermal plan, and test strategy must be developed together because an optically good die can still fail if coupling, calibration, or packaging is weak.