Photonic integrated circuit (PIC)
A chip that integrates two or more photonic functions — waveguides, modulators, photodetectors, sometimes lasers — on a single semiconductor substrate. Analogous to electronic integrated circuits.
A photonic integrated circuit (PIC) integrates multiple optical functions on a single chip. Standard functions include passive waveguiding, splitting and combining (Y-branches, multimode interference (MMI) couplers, directional couplers), wavelength filtering (ring resonators, arrayed waveguide gratings), modulation (Mach–Zehnder, electro-absorption, ring-resonator modulators), photodetection, and in some platforms light generation (monolithic DFB lasers on InP, or III-V dies bonded to silicon).
Major material platforms:
| Platform | Index contrast | Typical | Native lasing | Foundry availability |
|---|---|---|---|---|
| Silicon-on-insulator (SOI) | High | 1–3 dB/cm | No | High (GlobalFoundries, IMEC, AIM) |
| Silicon nitride (SiN) | Low | 0.1 dB/cm | No | Moderate (LioniX, AIM, IMEC) |
| Indium phosphide (InP) | Moderate | 1.5–4 dB/cm | Yes | Limited (Smart Photonics, Fraunhofer HHI) |
| Lithium niobate on insulator (LNOI) | High | 0.05–0.5 dB/cm | No | Emerging |
| Heterogeneous III-V on Si | Moderate | varies | Yes (bonded) | Limited (proprietary) |
The choice of platform is driven by required loss, available active functions, modulation speed, and operating wavelength range. SOI dominates volume datacenter transceiver applications. SiN is used where ultra-low loss is required (long delay lines, frequency combs, biosensing). InP retains the largest market in coherent telecom because of its native lasing capability.
PIC characterization combines optical and electrical instrumentation: fiber alignment to grating couplers or edge couplers, swept tunable laser sources, optical power meters, electrical probes, and temperature control. Standard PIC workflows are covered in Active Fiber Alignment to Surface Grating Couplers and Waveguide Propagation Loss by the Cutback Method.