Al Yuen, CEO of PicoJool, talks with Austin about using VCSELs for scale-up optical interconnects in AI data centers. Al explains why gallium arsenide (GaAs) supply is unconstrained while indium phosphide (InP) is limited, and how PicoJool can leverage existing supply chains to ship in the millions per month. They cover the roadmap from 1.6T to 12.8T, the trade-offs among 8×200G, 16×100G, and 32×50G, and the push to train the next generation of photonics engineers.

The spec that changed is error rate. AI needs error-free links (10⁻¹⁰–10⁻¹² vs Ethernet's old 10⁻⁶) because GPUs act as one system — one error stalls the whole job.
Single-mode optics can't hit the volume. Built for ~100K city-to-city links; datacenters need millions/month — a 10–50× gap
GaAs vs InP is the whole supply story. VCSELs run on unconstrained GaAs; single-mode on constrained InP. 1M units: 8–10 weeks vs a sold-out 8–18 months.
One platform, three flavors to 1.6T: 8×200G "fast and narrow," 16×100G LPO low-power, 32×50G NRZ "slow and wide" — pick on power, cost, and BER.
12.8T needs no new tech — just more of the same: 64 channels (4×16 array in a finger-sized connector) × 200G, scaling channels, bi-di wavelengths, and lane speed.
Capacity isn't the time consuming part — qualification is. WIN runs ~1,000 wafers/week at ~240K VCSELs each, so 1M units = ~10 wafers. The wait is tier-1 (>6 mo) and tier-2 (~3 mo) quals.

Chapters:
0:00 Meet Al Yuen and PicoJool
2:29 Inventing the active optical cable
5:03 Engineering mindset, copper limits
8:43 Why VCSELs
13:45 Scale-up and bit error rate
20:09 Unconstrained vs constrained supply
21:53 Indium phosphide bottleneck
25:49 VCSEL design and foundry handoff
31:59 Product road map, 200G launch
34:16 Path to 3.2T and 12.8T
40:10 Ordering a million VCSELs
45:10 Ramp timing and training new engineers

Follow Chipstrat:
Newsletter: https://www.chipstrat.com
X: https://x.com/chipstrat

Follow Vik:
Newsletter: https://www.viksnewsletter.com/
X: https://x.com/vikramskr

Follow Semi Doped:
Get more of Austin and Vik daily, free!
Sign up: https://daily.semidoped.com/

PicoJool's Al Yuen: The Case for GaAs VCSELs in Scale-Up Interconnects

Semi Doped

PicoJool's Al Yuen: The Case for GaAs VCSELs in Scale-Up Interconnects