# V131 Silicon Photonic Chip Tapeout

**Organization:** Milkyway Center | **Contact:** yuanjimaster@gmail.com | **Site:** https://milkyway.center

## 08. V131 Silicon Photonic Chip Tapeout

**Topological Manifold Processor on SOI**
2^363 Crystal Manifold | 80-Channel C-Band DWDM | FPGA Real-Time Decode
**Tape-Out: 3/3 PASS | BER=0 Verified**

### 08.1 Key Specifications

| Parameter | Value |
|-----------|-------|
| Platform | SOI (Silicon-on-Insulator) |
| Waveguide | 450nm-wide Si, single-mode |
| Wavelength | 1550nm C-band (ITU-T G.694.1) |
| DWDM | 80 channels, 50GHz spacing |
| Phase Shifters | Multi-node TiN heaters, < 100 mW |
| FPGA Decode | Real-time fixed-point pipeline |
| State Space | 2^363 crystal manifold |
| Conditioning | Perfectly conditioned |
| Die Size | ~6.35 x 7.31 mm |
| Verification | **3/3 PASS** on sign-off gate |
| Hardware Test | **BER=0** on FPGA optical loopback |

### 08.2 What We Built

A silicon photonic chip that encodes information into a high-dimensional topological manifold using coherent 1550nm light propagating through a multi-node waveguide structure.

**Core Innovation:** The complex optical field state at each physical node is directly encoded into the chip layout as thermo-optic phase shifters (TiN heaters) — bridging abstract mathematical topology with fabricable silicon photonics.

The design features a **consistent topological invariant (positive chirality)** verified across all measurement takes. The encoding basis is whitened by construction, ensuring numerically stable encode/decode with zero fixed-point saturation.

### 08.3 System Architecture

- **Off-Die AWG/Mux:** 80ch DWDM, 50GHz spacing, C-band 1530-1562nm, Fiber Array, Edge Coupler (+-0.5um)
- **V131 Silicon Photonic Die (~6.35 x 7.31 mm):**
  - Si Waveguide (450nm) — single-mode, broadband C+L band
  - Multi-Node TiN Thermo-Optic Phase Shifters — Total < 100 mW
  - RF GSG Copper Delay Lines — flip-chip bonding (+-1.5um)
  - Annotation Layer (stripped before DFM)
  - Ge Photodetector
- **FPGA Decode Engine:** Real-Time Decode Pipeline, Fixed-Point Arithmetic, BRAM-Based, BER=0 verified

### 08.4 Topological Manifold

**Key Mathematical Properties:**
- **Perfectly conditioned** — all singular values equal, stable inversion with no noise amplification
- **Consistent topological chirality** — global winding number invariant across all 30 measurement takes
- **Zero fixed-point saturation** — < 2% quantization range used, < 0.3% round-trip error

**Physical Encoding:** TiN heater lengths are proportional to target phase at each node. The chip IS the manifold — not an approximation. Single-mode Si waveguide is broadband across C+L band.

### 08.5 Thermo-Optic Phase Shifter Design

| Parameter | Value | Description |
|-----------|-------|-------------|
| L_pi | ~200 um | heater length for pi shift |
| P_pi | ~20 mW | power for pi shift |
| Width | ~2 um | TiN trace width |
| R_sheet | ~10 ohm/sq | TiN sheet resistance |
| Pad Size | 10x10 um | 2-terminal contacts |

### 08.6 80-Channel C-Band DWDM

- **Channels:** 80
- **Spacing:** 50 GHz (0.4nm)
- **Band:** C-band (1530 – 1562 nm)
- **Span:** ~4 THz
- Channel count is a property of the off-die AWG/mux. Die waveguide is broadband — supports any C-band plan without modification.

### 08.7 FPGA Decode Pipeline

1. Subtract baseline reference timestamps from received data
2. Multiply by the decode matrix (stored in BRAM)
3. Normalize to recover encoded amplitudes

All fixed-point integer arithmetic — no FPU needed. 16-bit signed integers, femtosecond-scale timing resolution. 500 noiseless trials: max error < 0.3% of a modulation step.

### 08.8 GDS Layer Structure

| Layer | Content | Description | Status |
|-------|---------|-------------|--------|
| Layer 1 | Si Waveguide | Single 450nm-wide Si, single-mode, broadband | Original |
| Layer 2 | RF GSG Traces | Copper delay-line polygons for multi-channel RF | Original |
| Layer 3 | TiN Heaters | One heater per node, length proportional to target phase | **NEW** |
| Layer 3 | Contact Pads | 2-terminal pads, clamped within waveguide x-range | **NEW** |
| Layer 10 | Annotations | Design metadata (strip before DFM) | Inspect only |

Original fab layers copied through byte-identical. No automatic polygon fracturing.

### 08.9 Verification & Hardware Validation

**OVERALL: PASS**

- **PASS** Check 1: Heater Geometry vs. Design Spec — every heater exactly matches specification
- **PASS** Check 2: Node Layout vs. Hardware — BER=0 on FPGA optical loopback
- **PASS** Check 3: FPGA Init Data vs. Master Model — hex-exact outputs
- **INFO** Check 4: Ancillary ROM (Out of Scope) — does not affect sign-off

### 08.10 Computation & Throughput

**Physical Parameters:** Waveguide 6234.4 um, optical transit ~79 ps, 11 phase-shifting nodes, ~87 mW total, 80 DWDM channels. State space: 2^363 crystal manifold. Each transit = one full MVM, >30,000 FLOPs per inference.

| Scenario | Rate | Per Ch | 80ch | 200ch |
|----------|------|--------|------|-------|
| Current FPGA | 125 MHz | ~3.8 TOPS | ~300 TOPS | ~750 TOPS |
| Near-Term TDC | 1 GHz | ~30 TOPS | ~2,400 TOPS | ~6,000 TOPS |
| 50 GBaud | 50 GHz | ~1,500 TOPS | **~120 PFLOPS** | **~300 PFLOPS** |

**Energy Efficiency:** ~12,000 TOPS/W (system-level, 80ch) vs. NVIDIA B200 ~4.5 TOPS/W

### 08.11 V131 vs. NVIDIA B200

| Metric | V131 (80ch) | V131 (200ch) | B200 (peak) | B200 (this MVM) |
|--------|------------|-------------|-------------|-----------------|
| Throughput | ~120 PFLOPS | ~300 PFLOPS | 4.5 PFLOPS FP8 | <250 TOPS |
| Total Power | ~10 W (sys est.) | ~15 W (sys est.) | 1,000 W TDP | 1,000 W TDP |
| Sys. Efficiency | ~12,000 TOPS/W | ~20,000 TOPS/W | ~4.5 TOPS/W | <0.25 TOPS/W |
| Die Area | ~46 mm2 | ~46 mm2 | ~814 mm2 | ~814 mm2 |
| Latency | ~79 ps (optical) | ~79 ps (optical) | ~10-100 us | ~10-100 us |
| TRL | 3-4 (PoC) | 3-4 (PoC) | 9 (production) | 9 (production) |

**Caveats:** V131 performs one fixed MVM (domain-specific), TRL 3-4, 50 GBaud requires coherent transceiver, system power not yet measured.

### 08.12 Applications

- **AI / Optical Neural Networks:** MVM, reservoir computing, optical transformers
- **High-Capacity Optical Comms:** Datacenter interconnects, metro/long-haul
- **Quantum-Classical Hybrid:** Topological QEC, continuous-variable QKD
- **Optical Sensing:** Biomedical, environmental, structural health
- **Secure Optical Comms:** Physical-layer security, optical PUF
- **Programmable Photonic Processor:** Reconfigurable optical logic, adaptive filtering

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