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

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× gapGaAs 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 PicoJool2:29 Inventing the active optical cable5:03 Engineering mindset, copper limits8:43 Why VCSELs13:45 Scale-up and bit error rate20:09 Unconstrained vs constrained supply21:53 Indium phosphide bottleneck25:49 VCSEL design and foundry handoff31:59 Product road map, 200G launch34:16 Path to 3.2T and 12.8T40:10 Ordering a million VCSELs45:10 Ramp timing and training new engineersFollow Chipstrat:Newsletter: https://www.chipstrat.comX: https://x.com/chipstratFollow Vik:Newsletter: https://www.viksnewsletter.com/X: https://x.com/vikramskrFollow Semi Doped:Get more of Austin and Vik daily, free!Sign up: https://daily.semidoped.com/