Copper interconnects rely on direct electrical conduction over twinaxial or micro coaxial cables, providing low latency, minimal unit cost, and zero power consumption over short reaches under 3 meters. Optical interconnects convert electrical SerDes signals into optical pulses via lasers and photodiodes, delivering essentially distance-agnostic bandwidth, immune to EMI, across extended rack and data center reaches from 5 to over 1000 meters.
High-Speed Physical Layers: Evaluating Copper vs. Optical Interconnect Architectures
Channel Attenuation and Reach Limitations
As single-lane SerDes speeds scale to 112G and 224G PAM4, copper conductors experience extreme attenuation caused by skin effect and dielectric absorption. Passive Direct Attach Copper (DAC) cables are physically limited to reaches of 1 to 2 meters at 224G due to insertion loss exceeding physical DSP equalization limits. Optical fibers (single-mode SMF or multi-mode MMF) exhibit near-zero frequency-dependent attenuation over rack distances, shifting channel loss constraints entirely to the electro-optical transceiver conversion stage.
Power Dissipation and Thermal Density
Direct Electrical Links: Passive copper links consume zero direct electrical power at the cable assembly itself, keeping thermal dissipation isolated entirely to the host SerDes IC.
Electro-Optical Conversion: Optical modules (pluggable optics, active optical cables, or Co-Packaged Optics) require transimpedance amplifiers (TIA), laser drivers, and VCSELs or silicon photonics Mach-Zehnder modulators. This introduces 3W to 18W of thermal power consumption per transceiver port.
Latency Overhead: Copper propagation delay is governed strictly by the dielectric constant (approximately 4.5 ns/m). Optical links add SerDes retimer processing, FEC framing, and electro-optical conversion delays.
Technical Performance Matrix
Max Reach at 112G/224G — Copper DAC: ~1.0m to 2.0m / Optical: 10m to 10km+
Media Type — Copper: Twinaxial copper cable / Optical: Multi-mode (MMF) or single-mode (SMF) fiber
Power Consumption — Copper: 0 watts (passive) / Optical: 3.5W to 20+ W per end
EMI Immunity — Copper: Shielding dependent / Optical: 100% galvanic and EMI immune
Cable Weight & Radius — Copper: Heavy, thick wire gauge (26-30 AWG) / Optical: Ultra-thin, flexible, light fiber cables
Design Selection Criteria
Specify Copper Interconnects for intra-rack top-of-rack switch-to-server connections, backplanes, and direct chip-to-chip links where cable runs are under 2 meters and zero power consumption is required. Specify Optical Interconnects for inter-rack, row-to-row, hyperscale data center backbones, or long-reach AI compute clusters where link distances exceed copper insertion loss limits.