What Is Co-Packaged Optics (CPO)?

Co-packaged optics (CPO) is an advanced packaging architecture that integrates silicon photonics optical engines into the same package as a switch, accelerator, or compute ASIC. Instead of plugging an optical transceiver into the faceplate of a switch, CPO places the optical-to-electrical conversion directly beside the chip, on a shared interposer or substrate. The result is a dramatically shorter electrical interconnect distance, lower power consumption, and much higher bandwidth density.

In a CPO module, a photonic integrated circuit (PIC) containing waveguides, modulators, and photodetectors is bonded together with electrical driver and transimpedance amplifier (TIA) dies. This optical engine then communicates with the host ASIC through fine-pitch RDL and micro-bumps over a distance measured in millimeters rather than tens of centimeters. For network architects building AI-scale fabrics, CPO represents the most credible path to 800G, 1.6T, and 3.2T port speeds without hitting a power wall.

Why CPO Emerged: The AI Data Center Bottleneck

Artificial intelligence workloads, especially large language model training and inference, have rewritten the rules for data center networking. A single AI training cluster can contain tens of thousands of accelerators, and every accelerator pair needs a low-latency, high-bandwidth connection through the network fabric. Under this load, conventional pluggable optics runs into three hard limits:

  • Power density. An 800G pluggable transceiver plus its electrical driver circuitry can draw 15-30 watts per port. At hyperscale port counts, optics can consume 30-50 percent of total network power, power that AI clusters would rather spend on compute.
  • Signal integrity. At 112 Gbps and 224 Gbps per lane, electrical signals lose integrity over long PCB traces. Designers must add expensive equalization, retiming, and DSP in the SerDes, which burns silicon area and more power.
  • Faceplate bandwidth limits. A switch can only fit a finite number of QSFP-DD or OSFP ports on its front panel, capping total bandwidth precisely when AI fabrics demand more.

CPO was developed to break these limits. By moving the optical engine into the package, CPO shortens electrical paths to millimeters, reduces per-port power by roughly 30-50 percent, and multiplies bandwidth density. For AI data centers where power and floor space are the binding constraints, co-packaged optics is not an incremental improvement, it is an architectural necessity.

CPO vs. Pluggable Optical Transceivers

The table below compares co-packaged optics with traditional pluggable optical transceivers across the dimensions that matter most to data center architects.

Attribute Pluggable Transceiver Co-Packaged Optics
Optical engine location Faceplate module (QSFP-DD / OSFP) Inside the package, beside the ASIC
Electrical reach 10-30 cm PCB trace Millimeters on interposer
Power per port 15-30 W (with SerDes) Approx. 5-10 W
Bandwidth density Limited by faceplate ports Scales with package area
Signal integrity Hard at 112/224 Gbps per lane Short links, relaxed equalization
Serviceability Hot-swappable in the field Not field-replaceable
Maturity Mature, volume deployed Early production, ramping fast

The trade-off is straightforward: pluggable optics remain flexible and easy to service, but CPO wins decisively on power, density, and cost-per-bit at hyperscale, exactly the metrics that determine whether an AI data center can keep scaling.

The Wafer-Level and Advanced Packaging Behind CPO

Co-packaged optics is fundamentally a packaging problem. Every CPO design depends on wafer-level processes and advanced packaging technologies originally developed for chiplets, HBM stacks, and high-performance computing.

Silicon Photonics Optical Engines

At the heart of every CPO module is a silicon photonics PIC fabricated on standard silicon wafers using mature CMOS-compatible processes. The PIC integrates grating couplers, waveguides, high-speed modulators, and photodetectors on a single die, delivering optical functionality at semiconductor economics. This photonics die is co-packaged with electrical driver and TIA dies to form a complete optical engine, the building block that makes CPO manufacturable at scale.

2.5D and 3D Co-Packaging of Chiplets and Optical Engines

Most CPO architectures use 2.5D packaging: the switch ASIC, optical engines, and supporting chiplets sit side by side on a shared interposer, connected through fine-pitch RDL and micro-bumps, and are mounted on a package substrate. Emerging 3D approaches stack photonics and electronics vertically to shrink footprint and shave latency further. In both cases the interposer is the critical link, it must carry thousands of high-speed signals with ultra-low loss, low crosstalk, and controlled thermal expansion that matches both silicon photonics and the switch die.

TGV Glass Interposers

Glass interposers with through-glass vias (TGV) are becoming a preferred platform for CPO. Glass offers outstanding high-frequency electrical performance, a coefficient of thermal expansion that can be tuned to match silicon photonics, and the surface quality needed for ultra-fine line-and-space RDL. For engineers evaluating interposer options, TGV glass wafer substrates from GINECHIP are engineered specifically for these co-packaging and photonics applications.

RDL and Bumping for Optical Engine Interconnect

Redistribution layers and micro-bumping are what physically connect the tightly packed I/O of optical engines and chiplets to the interposer and package. Fine-pitch RDL lowers signal loss, supports dense escape routing, and enables the heterogeneous integration CPO demands. GINECHIP provides RDL and bump wafer services for exactly these co-packaging flows, from design support to full-wafer processing.

How GINECHIP Supplies the Enabling Substrates and Processes

GINECHIP positions itself as a one-stop supplier for the substrates and wafer-level processes that make co-packaged optics possible. From the raw wafer to the finished interposer, GINECHIP covers the critical steps of the CPO supply chain:

  • TGV glass interposers, through-glass via wafers with excellent RF performance and CTE matching for photonics co-packaging.
  • RDL and bump processing, fine-pitch redistribution and micro-bumping that connect optical engines, chiplets, and switch ASICs.
  • Silicon wafer substrates, high-quality silicon wafers for silicon photonics PIC fabrication and interposer manufacturing.
  • Advanced packaging solutions, end-to-end wafer-level packaging capabilities for 2.5D and 3D co-packaging of chiplets and optical engines.

By controlling these substrate and process steps, GINECHIP helps chipmakers, OSATs, and system vendors accelerate their CPO roadmaps with qualified, production-ready materials and shorter qualification cycles.

Get in Touch with GINECHIP

Co-packaged optics is redefining how AI data centers scale, and the substrate is where the entire architecture comes together. Whether you need TGV glass interposers, RDL and bump processing, or silicon wafer substrates for a CPO or silicon photonics program, GINECHIP has the materials and process expertise to support you. Contact the GINECHIP team today to discuss your requirements, request samples, or get a quotation.