Optical Interposer is silicon-based optical routing layer with integrated modulators and detectors for photonic chip-to-chip communication — optical routing substrate. Architecture silicon waveguides route signals; integrated electro-optic modulators; photodiodes detect. Waveguides sub-wavelength (~400×200 nm) silicon guides enable single-mode, compact routing. Modulators Mach-Zehnder or microring resonators encode signals. Photodiodes Ge or Si detectors on same substrate. Light Source external laser (telecom) or heterogeneous III-V bonded source. Coupling efficient input/output coupling via grating couplers or butt-coupling. Bandwidth >25 GHz per channel demonstrated. Channels WDM: 4-16 wavelengths tested. Power sub-pJ/bit achievable for optical links. Eye Diagram high-speed testing validates signal quality. BER bit-error-rate testing measures reliability. Wavelength 1310/1550 nm (telecom) or 850 nm (data-center). Thermo-Optic refractive index varies with temperature. Active tuning compensates. Crosstalk waveguide spacing reduces coupling between channels. Routing Density thousands of channels possible. Integration optical interposer + electrical logic/memory. Tight integration. Chiplet Communication optical links between chiplets enable new architectures. Prototypes published >100 Gbps/channel, >1 Tbps aggregate. Standards JEDEC developing chiplet optical interfaces. Reliability long-term reliability of optical components unproven. Optical interposers enable revolutionary bandwidth for heterogeneous systems.