High-Channel FAU for CPO: Why Pitch Consistency Beats Channel Count
CPO engines are pushing fiber array unit channel counts well past 100. Wioptic runs 36, 40, 72 and 154-channel FAU as standard configurations for this. The number that actually decides whether the part works in the engine isn't the channel count — it's whether core pitch holds steady from channel 1 to the last channel.
A fiber array unit is the mechanical interface between a fiber ribbon and a photonic chip. Fibers are seated into a precision V-groove substrate, bonded, and the end face polished so every core sits on a known pitch at a known angle — turning an alignment problem with N degrees of freedom into one part that is actively aligned once and then fixed. That description doesn't change as channel count goes up. What changes is how much room there is for error before the part stops working.
Why 36, 40, 72 and 154 keep showing up
These aren't round numbers picked for a datasheet. They track the port and lane counts that current co-packaged optics engine designs are landing on as radix scales climb — and they're the standard high-channel-count configurations Wioptic runs in regular production for CPO customers, alongside the PM, lens-integrated and isolator-integrated FAU variants built on the same platform.
Channel count, pitch, polish angle, substrate material, fiber type and connector are all set per order on top of these standard counts — a 154-channel starting point is a production baseline, not a ceiling.
The failure mode that channel count alone doesn't show you
On Wioptic's standard V-groove fiber array line, pitch tolerance is published as graded by channel count — ±0.3 µm through 8 channels, ±0.5 µm to 32, ±0.7 µm to 64, and ±1.0 µm at 96 and 128 — and the reason given is straightforward: the tolerance reflects error accumulated over the length of the array. That's the same physics at work in a high-channel FAU. A systematic pitch error that is invisible across the first 8 channels does not stay invisible across 154.
Why the pitch gets tracked channel-by-channel, not sampled at the end
For the 36/40/72/154-channel builds, core pitch is measured and tracked channel-by-channel through production, rather than checked at a handful of points at final test. That distinction matters more as channel count goes up: a drift that starts at channel 20 and grows slowly is still within any reasonable spot-check tolerance at channel 40, and only shows up as a problem once you reach channel 100 or beyond. Catching it mid-process, channel by channel, means a drifting build gets corrected or scrapped before it becomes 154 channels of finished part.
Configuring a high-channel FAU
Beyond the standard 36/40/72/154-channel counts, the same platform carries the rest of the FAU line — polarization-maintaining builds with per-channel axis reference, lens-array integration for active or passive coupling, and isolator die-bonding on automated placement equipment. Channel count, pitch, polish angle, substrate material, fiber type and connector are all built to your drawing; lens array or isolator integration can be added as a bonded sub-assembly.
| Configuration | What's specified |
|---|---|
| High-channel-count FAU | 36 / 40 / 72 / 154 standard counts, core pitch tracked channel-by-channel |
| PM FAU | 15-channel, 127 µm pitch, ±0.7 µm pitch tolerance, axis angle to ±1° |
| Lens-integrated FAU | 250 or 500 µm lens pitch, active or passive coupling |
| Isolator-integrated FAU | Automated die-bonding, >99% coupling yield in volume |
If your engine's channel count sits outside these standard counts, that's a starting point for a conversation, not a limit — send the drawing and we'll quote the configuration.