<svg viewBox="0 0 760 470" xmlns="http://www.w3.org/2000/svg" font-family="-apple-system,Segoe UI,Roboto,sans-serif">
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  <text x="380" y="28" fill="#e6edf3" font-size="21" font-weight="700" text-anchor="middle">Optical Interconnect — Light Replaces Copper</text>
  <text x="380" y="48" fill="#8b98a5" font-size="12" text-anchor="middle">silicon photonics: modulate laser → waveguide/fiber → detect — Tbps bandwidth, fJ/bit energy</text>

  <!-- === TOP: Optical link (TX → fiber → RX) === -->
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  <text x="380" y="83" fill="#e6edf3" font-size="11" text-anchor="middle" font-weight="600">Optical Link (one lane, co-packaged with ASIC)</text>

  <!-- TX side -->
  <!-- Laser -->
  <rect x="50" y="100" width="55" height="30" rx="3" fill="#2a1a0a" stroke="#f59e0b" stroke-width="1.2"/>
  <text x="77" y="114" fill="#fbbf24" font-size="8" text-anchor="middle">Laser</text>
  <text x="77" y="126" fill="#a1701a" font-size="7" text-anchor="middle">CW (1310nm)</text>

  <!-- Light arrow from laser -->
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  <!-- Modulator -->
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  <text x="162" y="112" fill="#c4b5fd" font-size="8.5" text-anchor="middle">Modulator</text>
  <text x="162" y="126" fill="#8b98a5" font-size="7" text-anchor="middle">MZI or ring</text>
  <!-- Data input -->
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  <text x="162" y="82" fill="#93c5fd" font-size="7" text-anchor="middle">data in (elec)</text>

  <!-- Waveguide on-chip -->
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  <text x="240" y="108" fill="#c4b5fd" font-size="7.5" text-anchor="middle">Si waveguide</text>

  <!-- Fiber coupling -->
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  <text x="297" y="118" fill="#6ee7b7" font-size="6.5" text-anchor="middle">coupler</text>

  <!-- Fiber (the long link) -->
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  <text x="377" y="108" fill="#6ee7b7" font-size="8" text-anchor="middle">fiber / waveguide</text>
  <text x="377" y="140" fill="#6b7684" font-size="7.5" text-anchor="middle">meters to km (no repeater for short reach)</text>

  <!-- RX side -->
  <!-- Fiber coupling -->
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  <text x="457" y="118" fill="#6ee7b7" font-size="6.5" text-anchor="middle">coupler</text>

  <!-- Photodetector -->
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  <text x="515" y="112" fill="#93c5fd" font-size="8.5" text-anchor="middle">Photodetector</text>
  <text x="515" y="126" fill="#8b98a5" font-size="7" text-anchor="middle">Ge PD</text>

  <!-- TIA -->
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  <text x="582" y="114" fill="#8b98a5" font-size="7.5" text-anchor="middle">TIA</text>
  <text x="582" y="126" fill="#6b7684" font-size="6.5" text-anchor="middle">amplify</text>

  <!-- CDR + digital out -->
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  <text x="637" y="118" fill="#8b98a5" font-size="7.5" text-anchor="middle">CDR</text>
  <line x1="662" y1="115" x2="690" y2="115" stroke="#60a5fa" stroke-width="1"/>
  <text x="700" y="118" fill="#93c5fd" font-size="7">data out</text>

  <!-- Connections -->
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  <!-- TX/RX labels -->
  <text x="130" y="148" fill="#fbbf24" font-size="8" text-anchor="middle">TX (electrical → optical)</text>
  <text x="570" y="148" fill="#93c5fd" font-size="8" text-anchor="middle">RX (optical → electrical)</text>

  <!-- WDM annotation -->
  <text x="380" y="185" fill="#a78bfa" font-size="8.5" text-anchor="middle">WDM: multiplex 4-16 wavelengths per fiber → 4-16 Tbps per fiber pair</text>

  <!-- === BOTTOM LEFT: Why optical wins === -->
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  <text x="195" y="218" fill="#e6edf3" font-size="10" text-anchor="middle" font-weight="600">Optical vs Electrical (why switch)</text>

  <text x="50" y="238" fill="#34d399" font-size="9">Energy: 1-5 pJ/bit (optical) vs 10-20 pJ (elec SerDes)</text>
  <text x="50" y="254" fill="#34d399" font-size="9">Distance: km without repeater (vs cm for copper)</text>
  <text x="50" y="270" fill="#34d399" font-size="9">Density: 100+ lanes per fiber (WDM)</text>
  <text x="50" y="286" fill="#34d399" font-size="9">No crosstalk, no impedance matching</text>
  <text x="50" y="304" fill="#f87171" font-size="9">Challenge: laser integration, thermal sensitivity</text>
  <text x="50" y="318" fill="#6b7684" font-size="8.5">Crossover point: >1m reach, optical wins on pJ/bit</text>

  <!-- === BOTTOM RIGHT: Co-packaged optics === -->
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  <text x="552" y="218" fill="#e6edf3" font-size="10" text-anchor="middle" font-weight="600">Co-Packaged Optics (CPO)</text>

  <text x="395" y="238" fill="#8b98a5" font-size="9">Put photonics ON the switch/GPU package</text>
  <text x="395" y="254" fill="#8b98a5" font-size="9">(not pluggable — directly bonded)</text>
  <text x="395" y="274" fill="#fbbf24" font-size="9" font-weight="600">Players:</text>
  <text x="395" y="290" fill="#8b98a5" font-size="8.5">Ayar Labs: optical I/O chiplets</text>
  <text x="395" y="304" fill="#8b98a5" font-size="8.5">Lightmatter: photonic interconnect fabric</text>
  <text x="395" y="318" fill="#8b98a5" font-size="8.5">Intel: integrated photonics on package</text>
  <text x="590" y="274" fill="#8b98a5" font-size="8.5">Broadcom: CPO switch</text>
  <text x="590" y="290" fill="#8b98a5" font-size="8.5">TSMC: photonics</text>
  <text x="590" y="304" fill="#8b98a5" font-size="8.5">roadmap</text>

  <!-- === BOTTOM: The scaling argument === -->
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  <text x="380" y="353" fill="#e6edf3" font-size="10" text-anchor="middle" font-weight="600">Why AI Needs Optical Now</text>

  <text x="50" y="373" fill="#8b98a5" font-size="9">100K GPU cluster: 400K+ cables, each 400 Gbps → petabits/s aggregate</text>
  <text x="50" y="389" fill="#8b98a5" font-size="9">Electrical SerDes at 200G/lane hitting power wall (~7 pJ/bit × Pbps = megawatts in I/O alone)</text>
  <text x="50" y="405" fill="#34d399" font-size="9">Optical at 1-2 pJ/bit saves 5x power at the same bandwidth — critical at datacenter scale</text>

  <!-- Key numbers -->
  <text x="380" y="430" fill="#e6edf3" font-size="9.5" text-anchor="middle" font-weight="600">Silicon photonics: CMOS-compatible, fabricated on 300mm wafers at GlobalFoundries/Tower/TSMC</text>
  <text x="380" y="446" fill="#8b98a5" font-size="9" text-anchor="middle">Timeline: pluggable today (800G ZR) → CPO next (2026-28) → fully optical fabric (2030+)</text>

  <text x="380" y="464" fill="#6b7684" font-size="11" text-anchor="middle">Light is the only way to move petabits per second without melting the building — copper has hit its wall.</text>
</svg>
```tical I/O** is the practice of moving data into and out of a chip or package over light instead of over copper wires. Today almost all chip-to-chip communication uses electrical SerDes driving signals down metal traces, but copper attenuates high-frequency signals badly over distance, so electrical links are stuck with short reach and rising energy cost as data rates climb. Optical I/O converts the electrical bits to modulated light, sends them across an optical fiber or waveguide, and converts them back — trading copper's reach-and-energy wall for the near-lossless, high-bandwidth physics of photons. For large AI systems trying to wire together thousands of accelerators, it is increasingly seen as the way past the interconnect bottleneck.\n\n```svg\n<svg viewBox="0 0 700 384" xmlns="http://www.w3.org/2000/svg" font-family="-apple-system,Segoe UI,Roboto,sans-serif">\n  <rect x="0" y="0" width="700" height="384" fill="#0d1117"/>\n  <text x="350" y="30" fill="#e6edf3" font-size="20" font-weight="700" text-anchor="middle">Optical I/O — Moving Data In and Out of a Chip with Light</text>\n  <text x="350" y="52" fill="#8b98a5" font-size="12" text-anchor="middle">replace copper SerDes with photons to break the reach × bandwidth × energy wall at the package edge</text>\n  <text x="40" y="84" fill="#cbd5e1" font-size="12" font-weight="700">Why switch to light: electrical copper dies over distance</text>\n  <text x="130" y="102" fill="#f87171" font-size="12" text-anchor="middle">electrical (copper)</text>\n  <polyline points="48,118 54,123 60,126 66,126 72,122 78,116 84,112 90,110 97,112 103,116 109,121 115,124 121,124 127,122 133,119 139,115 145,113 151,113 157,115 163,119 169,121 175,123 181,122 188,120 194,117 200,115 206,114 212,115 218,117 224,119 230,120" fill="none" stroke="#f87171" stroke-width="1.6" opacity="0.85"/>\n  <text x="139" y="140" fill="#6b7684" font-size="12" text-anchor="middle">reach ~1m, high energy/bit</text>\n  <text x="470" y="102" fill="#34d399" font-size="12" text-anchor="middle">optical (fiber)</text>\n  <line x1="378" y1="118" x2="560" y2="118" stroke="#34d399" stroke-width="2.2"/>\n  <text x="469" y="140" fill="#6b7684" font-size="12" text-anchor="middle">reach m–km, low energy/bit, huge BW density</text>\n  <line x1="250" y1="118" x2="360" y2="118" stroke="#8b98a5" stroke-width="1.6"/>\n  <path d="M353 121 L360 118 L353 115" stroke="#8b98a5" stroke-width="1.6" fill="none"/>\n  <text x="305" y="112" fill="#9fb4c6" font-size="12" text-anchor="middle">convert e→o</text>\n  <text x="40" y="172" fill="#cbd5e1" font-size="12" font-weight="700">An optical I/O link — electrons in, photons across, electrons out</text>\n  <rect x="40" y="188" width="70" height="44" rx="7" fill="#141a2e" stroke="#818cf8" stroke-width="1.5"/>\n  <text x="75" y="208" fill="#a5b4fc" font-size="12" font-weight="700" text-anchor="middle">chip</text>\n  <text x="75" y="222" fill="#8b98a5" font-size="12" text-anchor="middle">SerDes/driver</text>\n  <rect x="140" y="188" width="74" height="44" rx="7" fill="#2a1420" stroke="#fbbf24" stroke-width="1.5"/>\n  <text x="177" y="207" fill="#fcd34d" font-size="12" font-weight="700" text-anchor="middle">modulator</text>\n  <text x="177" y="221" fill="#8b98a5" font-size="12" text-anchor="middle">ring / MZM</text>\n  <line x1="110" y1="210" x2="140" y2="210" stroke="#3f5169" stroke-width="1.5"/>\n  <path d="M133 213 L140 210 L133 207" stroke="#3f5169" stroke-width="1.5" fill="none"/>\n  <rect x="140" y="262" width="74" height="30" rx="6" fill="#1a0f26" stroke="#c084fc" stroke-width="1.5"/>\n  <text x="177" y="281" fill="#d8b4fe" font-size="12" text-anchor="middle">laser (ELS)</text>\n  <line x1="177" y1="262" x2="177" y2="234" stroke="#c084fc" stroke-width="1.5"/>\n  <path d="M180 241 L177 234 L174 241" stroke="#c084fc" stroke-width="1.5" fill="none"/>\n  <line x1="214" y1="204" x2="430" y2="204" stroke="#f472b6" stroke-width="1.5" opacity="0.9"/>\n  <line x1="214" y1="208" x2="430" y2="208" stroke="#fbbf24" stroke-width="1.5" opacity="0.9"/>\n  <line x1="214" y1="212" x2="430" y2="212" stroke="#34d399" stroke-width="1.5" opacity="0.9"/>\n  <line x1="214" y1="216" x2="430" y2="216" stroke="#38bdf8" stroke-width="1.5" opacity="0.9"/>\n  <text x="322" y="194" fill="#9fb4c6" font-size="12" text-anchor="middle">one fiber, many wavelengths (WDM)</text>\n  <text x="322" y="234" fill="#6b7684" font-size="12" text-anchor="middle">each color = an independent channel</text>\n  <rect x="430" y="188" width="74" height="44" rx="7" fill="#0f1c17" stroke="#34d399" stroke-width="1.5"/>\n  <text x="467" y="207" fill="#6ee7b7" font-size="12" font-weight="700" text-anchor="middle">detector</text>\n  <text x="467" y="221" fill="#8b98a5" font-size="12" text-anchor="middle">Ge PD + TIA</text>\n  <rect x="534" y="188" width="70" height="44" rx="7" fill="#141a2e" stroke="#818cf8" stroke-width="1.5"/>\n  <text x="569" y="208" fill="#a5b4fc" font-size="12" font-weight="700" text-anchor="middle">chip</text>\n  <text x="569" y="222" fill="#8b98a5" font-size="12" text-anchor="middle">recover bits</text>\n  <line x1="504" y1="210" x2="534" y2="210" stroke="#3f5169" stroke-width="1.5"/>\n  <path d="M527 213 L534 210 L527 207" stroke="#3f5169" stroke-width="1.5" fill="none"/>\n  <rect x="40" y="300" width="300" height="70" rx="8" fill="#0b1220" stroke="#233043" stroke-width="1.2"/>\n  <text x="56" y="320" fill="#cbd5e1" font-size="12" font-weight="700">Optics march toward the die</text>\n  <rect x="56" y="332" width="64.6" height="26" rx="5" fill="#101826" stroke="#60a5fa" stroke-width="1.5"/>\n  <text x="88.3" y="349" fill="#60a5fa" font-size="12" text-anchor="middle">pluggable</text>\n  <line x1="120.6" y1="345" x2="134.6" y2="345" stroke="#8b98a5" stroke-width="1.3"/>\n  <path d="M127 348 L135 345 L127 342" stroke="#8b98a5" stroke-width="1.3" fill="none"/>\n  <rect x="138.6" y="332" width="107.80000000000001" height="26" rx="5" fill="#101826" stroke="#c084fc" stroke-width="1.5"/>\n  <text x="192.5" y="349" fill="#c084fc" font-size="12" text-anchor="middle">co-packaged (CPO)</text>\n  <line x1="246.4" y1="345" x2="260.4" y2="345" stroke="#8b98a5" stroke-width="1.3"/>\n  <path d="M253 348 L260 345 L253 342" stroke="#8b98a5" stroke-width="1.3" fill="none"/>\n  <rect x="264.4" y="332" width="91.60000000000001" height="26" rx="5" fill="#101826" stroke="#34d399" stroke-width="1.5"/>\n  <text x="310.2" y="349" fill="#34d399" font-size="12" text-anchor="middle">in-package OIO</text>\n  <rect x="360" y="300" width="300" height="70" rx="8" fill="#0b1220" stroke="#233043" stroke-width="1.2"/>\n  <text x="376" y="320" fill="#cbd5e1" font-size="12" font-weight="700">The figures of merit</text>\n  <text x="376" y="337" fill="#8b98a5" font-size="13">energy: pJ/bit (aim well below electrical SerDes)</text>\n  <text x="376" y="351" fill="#8b98a5" font-size="13">shoreline bandwidth density: Tbps per mm of die edge</text>\n  <text x="376" y="365" fill="#8b98a5" font-size="13">reach: meters to kilometers, not centimeters</text>\n</svg>\n```\n\n**The motivation is that electrical links are hitting a wall.** A PCB trace or cable loses more signal the faster you push it, so beyond roughly a meter an electrical link needs heavy equalization and burns significant energy per bit — and the bandwidth you can cram through the edge of a package (the "shoreline" or beachfront) is capped by how many copper pairs physically fit. Light does not attenuate the same way: an optical fiber carries enormous bandwidth over meters to kilometers at low loss, and many wavelengths can share one fiber. Optical I/O attacks reach, bandwidth density, and energy per bit all at once.\n\n**A link is a chain of electrical-to-optical conversions.** On the transmit side, a modulator (often a compact silicon ring resonator, or a Mach-Zehnder modulator) imprints the electrical data onto a beam of light supplied by a laser. The modulated light travels down a fiber or on-chip waveguide. On the receive side, a photodetector (typically germanium on silicon) turns the light back into current, and a trans-impedance amplifier recovers the electrical bits. The laser light itself usually comes from an external laser source (ELS) rather than being generated on the die, because efficient lasers are hard to build in silicon.\n\n**Wavelength-division multiplexing is the bandwidth multiplier.** Because light of different colors does not interfere, many independent data channels can ride the same fiber at once, each on its own wavelength, using an array of ring resonators tuned to different colors. This WDM trick is what lets a single fiber carry terabits per second, and it is central to why optical I/O achieves such high bandwidth per millimeter of die edge compared with copper.\n\n**The figures of merit are energy, shoreline density, and reach — not just raw speed.** Optical I/O is judged on picojoules per bit (it must beat electrical SerDes to be worth the complexity), on shoreline bandwidth density measured in terabits per second per millimeter of die edge, and on reach. Where electrical links top out around a meter, optical links keep their signal over meters to kilometers, which is exactly what disaggregated, rack-scale systems need.\n\n**Packaging is marching the optics toward the die.** The progression runs from pluggable optical transceivers at the faceplate, to co-packaged optics (CPO) that place the optical engine right next to the switch or accelerator ASIC on the same substrate, to fully in-package optical I/O where the optical interface is a chiplet sitting beside the compute die. Each step shortens the electrical path to the optics, cutting energy and boosting density — which is why CPO and in-package optical I/O are among the most watched technologies for next-generation AI fabrics.\n\n| Element | Job |\n|---|---|\n| Modulator (ring / MZM) | imprint electrical data onto light |\n| Laser source (ELS) | supply the optical carrier |\n| Fiber / waveguide + WDM | carry many wavelengths far, at low loss |\n| Photodetector + TIA | convert light back to electrical bits |\n| Packaging (pluggable→CPO→in-package) | move optics closer to the die |\n\nRead optical I/O through a *beat-the-copper-wall* lens rather than a *faster-cable* lens: the point is not simply speed but escaping the reach, energy, and shoreline-density limits that cap electrical SerDes at the package edge. Once the optical engine moves onto the package and light replaces copper for chip-to-chip links, bandwidth stops falling off with distance — which is precisely what lets an AI cluster grow from a board into a rack into a fabric without the interconnect becoming the bottleneck.\n