用镜子做交换机：谷歌的光路交换（OCS）是怎么回事？

系列第三期：谷歌的光路交换（OCS）。谷歌在数据中心网络和 TPU 超级计算机里，用一台会“转镜子”的交换机代替了传统的电交换机。 Episode 3 of the series (Chinese narration, Chinese captions burned in): how Google's optical circuit switch "Palomar" steers light with two arrays of MEMS micro-mirrors — no packet processing, no O/E/O — and why that let Google remove the spine layer of Jupiter and wire 4,096 TPU v4 chips into one reconfigurable supercomputer. Chapters 00:00 开场 · Cold open 00:55 片头 · Title 01:02 一、传统的交换机为什么又贵又费电 · Why electrical switches are hot and costly 02:48 二、大块流量其实很稳定 · Big flows barely move 04:13 三、Palomar：一台用镜子做的交换机 · A switch made of mirrors 06:26 　对准：850 nm 监测光 · Closed-loop alignment 09:02 四、代价：镜子转得太慢 · The price: mirrors are slow 10:16 五、Jupiter：拿掉脊交换机 · Removing the spine 11:35 六、TPU v4：几千颗芯片，一台超级计算机 · One machine from 4,096 chips 13:25 　坏了就绕过去 · Routing around failures 15:07 　按需改变形状 · Reshaping the torus 16:00 七、为什么别人很难照搬 · Why it is hard to copy 19:00 八、回到 Astera：三种路线 · Three roads 21:17 下期预告 · Next: co-packaged optics Key numbers Palomar: 136×136 ports (128 + 8 spare) · insertion loss typically ‹ 2 dB · ms-scale switching · max 108 W Jupiter (2022): ~30% lower cost · ~40% lower power · ~30% higher throughput · ~10% faster flow completion · ~50× less downtime TPU v4 (2023): 4,096 chips · 4×4×4 cubes · 48 OCS · OCS ‹ 5% of system cost, ‹ 3% of power · twisted torus 1.3–1.6× all-to-all Sources · Google, "Mission Apollo: Landing Optical Circuit Switching at Datacenter Scale" (2022) · Google, "Jupiter Evolving" (SIGCOMM 2022) and the Google Cloud blog (Aug 2022) · Google, "TPU v4: An Optically Reconfigurable Supercomputer for Machine Learning…" (ISCA 2023) · Open Compute Project blog: OCS subproject announcement (July 2025) · Google: Ironwood, 7th-generation TPU (2025) Some details are physics-based illustrations and are marked 示意 on screen. Technology explainer, not investment advice. Made entirely in code (HTML/SVG/Three.js rendered with HyperFrames). AI-synthesised narration; ~10 s of AI-generated footage in the cold open (labelled on screen). Previous: 一条链路值多少钱？——Astera Labs · Next: co-packaged optics / optical I/O #谷歌 #光路交换 #OCS #TPU #数据中心 #OpticalCircuitSwitch #googlegemini