Precision Glass Processing for Co-Packaged Optics

From optical coupling to embedded photonics: enable scalable CPO with LPKF NEXAR Direct Write

As CPO moves optical interfaces closer to the compute die, the demands on packaging precision, alignment, and optical quality increase sharply. LPKF's NEXAR Direct Write technology turns glass into a high-performance photonic integration platform providing reliable coupling, passive alignment, and optical routing, at production scale.

The CPO Packaging Challenge

Integrating optical and electrical functions at the package level introduces precision requirements conventional substrates can't meet:

Optical interfaces sensitive to surface defects at the sub-micron level
Active alignment adding several minutes per unit, incompatible with production volumes
Electrical interconnects reaching bandwidth and power limits at 400G and beyond
Minimal thermal expansion ensuring stable optical coupling
Glass structuring methods introducing microcracks that compromise optical and mechanical performance

Glass as the CPO Substrate of Choice

Glass uniquely supports the convergence of optical and electrical interconnects within a single platform:

Optical transparency for photonic integration and waveguide formation
Low CTE for alignment stability across operating temperatures
Compatibility with both TGV electrical routing and embedded optical structures
Panel-level scalability for high-volume CPO manufacturing

LPKF Capabilities at a Glance

Precision glass structuring across the full CPO process flow:

Crack-free precision cleaving for optically flat coupling interfaces

Monolithic passive alignment features with sub-micron positional accuracy

Embedded waveguide formation through refractive index modification

Single-process integration of TGVs, alignment structures, and optical paths

Consistent process performance from prototype to panel-scale production

Critical Glass Processing Capabilities for Co-Packaged Optics

Edge Coupling Through Precision Glass Cleaving

The Optical Interface Starts at the Edge

The lateral edge of a glass substrate is where light enters the package. Any microcrack, thermal damage zone, or geometric inconsistency at that surface translates directly into coupling loss and it can't be corrected downstream.

Mechanical dicing and laser ablation both compromise the edge in different ways. LIDE avoids surface contact entirely. It defines a subsurface modification path, and the fracture follows it precisely producing optically flat, crack-free cleaved surfaces without post-process polishing, at consistent geometry across every substrate in a production run.

NEXAR Direct Write based Cleaving for Edge Coupling

Process flow: from glass blank to PIC-ready cavity wall

LIDE structuring

Subsurface laser processing pre‑defines the waveguide path inside the glass.
A groove / notch at the future cleave edge localizes the break.
The waveguide is routed up to the planned cavity wall position.
This ensures controlled crack propagation and predictable, optical‑grade geometry.

Cleavage

Mechanical stress is applied so the glass cleaves exactly along the LIDE track.
This produces an optically flat, crack‑free cavity wall with tightly controlled waviness and roughness, without post‑polishing.

Component placement

A photonic integrated circuit (PIC) or edge‑coupler is positioned directly against the cleaved wall.
The smooth, well‑defined surface acts as a stable, low‑loss optical interface for CPO integration.

Passive Alignment Features for Optical Assembly

Minutes Per Device vs. Designed-In Accuracy

Active alignment works but at several minutes per unit, it doesn't scale to CPO production volumes. Passive alignment is the answer. Reference structures built into the substrate that position every component correctly, by design or geometry.

LPKF NEXAR Direct Write technology generates these features directly into the glass volume. No secondary material, no bonding interface, no thermal mismatch. Sub-micron accuracy across fiber arrays, photonic IC die, and edge-coupler interfaces all within a single process sequence. Assembly becomes a placement step, not a tuning exercise.

Embedded Waveguides for Co-Packaged Optical Routing

3D Optical Routing Within the Glass Volume

In co-packaged optics, waveguides are the optical interconnect backbone routing light between fibers, photonic ICs, and connector structures within the package itself.

At 400G and beyond, electrical interconnects fall short on energy and bandwidth, while 2D waveguides remain constrained to planar X-Y routing neither scales with the integration density CPO demands.

LPKF's NEXAR Direct Write locally modifies the refractive index within the glass volume, forming 3D waveguides through direct laser writing, no material removal, no layer constraints. Light propagates in X, Y, and Z: vertical transitions, crossings, and fan-outs in a single maskless process. High positional accuracy enables precise coupling toward connector structures and embedded photonic ICs within the same glass carrier.

Ready to Build Your CPO Glass Platform?

From HPC platforms to AI clusters, co-packaged optics is no longer a roadmap item. LPKF NEXAR Direct Write delivers precision at every layer — cleaved interface, alignment feature, waveguide path. Discuss your substrate architecture with LPKF's experts.

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