Device Requirements for Optical Interconnects to Silicon Chips

TLDR

Optical interconnects promise higher density, lower energy, and faster timing, with a target of ~10 fJ/bit to satisfy low‑energy constraints. The study evaluates current interconnect performance and projects device requirements for optical solutions to meet future high‑performance silicon chip demands. The authors assess device options such as low‑capacitance photodetectors, compact wavelength splitters, dense on‑chip waveguides, radical laser modulators, and free‑space optics to meet the ~10 fJ/bit energy target and bandwidth needs. The authors conclude that these optical technologies could sustain the interconnect capacity scaling needed for future chips.

Abstract

We examine the current performance and future demands of interconnects to and on silicon chips. We compare electrical and optical interconnects and project the requirements for optoelectronic and optical devices if optics is to solve the major problems of interconnects for future high-performance silicon chips. Optics has potential benefits in interconnect density, energy, and timing. The necessity of low interconnect energy imposes low limits especially on the energy of the optical output devices, with a ~ 10 fJ/bit device energy target emerging. Some optical modulators and radical laser approaches may meet this requirement. Low (e.g., a few femtofarads or less) photodetector capacitance is important. Very compact wavelength splitters are essential for connecting the information to fibers. Dense waveguides are necessary on-chip or on boards for guided wave optical approaches, especially if very high clock rates or dense wavelength-division multiplexing (WDM) is to be avoided. Free-space optics potentially can handle the necessary bandwidths even without fast clocks or WDM. With such technology, however, optics may enable the continued scaling of interconnect capacity required by future chips.