Usb3-fiber

USB3-over-Fiber Link

USB3 SuperSpeed carried over an optical fiber link, using a DS100BR111 redriver into a 10GbE SR SFP+ optical module. A single symmetric PCB serves both ends of the link — host-side and remote-side roles are selected by jumpers. The MCP2221A provides the SFP+ management (I²C) interface and GPIO for TX_DISABLE / RX_LOS. No microcontroller, no firmware, no EEPROM.

Built as the remote front-end for an SDR receiver: put the ADC at the antenna and stream USB3 back to the shack over fiber.

How it works

USB3-A connector        ┌───────────────┐        SFP+ cage
(SuperSpeed pairs) ─────►│  DS100BR111   │◄─────► (optical module) ──► fiber
                        │ (pin-strapped, │
                        │   3.3V)        │
                         └───────────────┘
                                │ SDA/SCL
                          ┌───────────┐
                          │ MCP2221A  │── USB micro-B ── laptop (SFP+ mgmt)
                          └───────────┘

Each fiber link needs two identical boards — one at the antenna, one at the shack — with jumpers JP1/JP2 selecting the role. The USB3 path is fully symmetric: the DS100BR111 is bidirectional and the SFP+ module handles both TX and RX in one cage.

Central hypothesis

This prototype exists to test one thing:

A 10GbE SR SFP+ optical module will transport USB3 SuperSpeed signalling intact — LFPS bursts, link training, electrical-idle transitions, spread-spectrum clocking, and receiver detection — without modifying the module or the USB3 endpoints.

It has been done in the amateur-radio and USB-extension communities, but it is guaranteed by no specification. See docs/USB3_Fiber_Link_Minimal_Circuit.md for the architecture, channel assignment, and the failure modes this board is built to probe.

Repository layout

Requirements

• KiCad 10.0 (latest stable 10.0.4) — the project baseline.

Building the manufacturing outputs

From the repo root, with kicad-cli (KiCad 10):

kicad-cli sch erc   usb3_fiber.kicad_sch --output erc.rpt
kicad-cli pcb drc   usb3_fiber.kicad_pcb --output drc.rpt   # honors .kicad_dru
kicad-cli sch export pdf     usb3_fiber.kicad_sch --output schematic.pdf
kicad-cli sch export bom     usb3_fiber.kicad_sch --output bom.csv
kicad-cli pcb export gerbers usb3_fiber.kicad_pcb --output gerbers/
kicad-cli pcb export drill   usb3_fiber.kicad_pcb --output gerbers/
kicad-cli pcb export pos     usb3_fiber.kicad_pcb --output cpl.csv
kicad-cli pcb export step    usb3_fiber.kicad_pcb --output usb3_fiber.step

Fabrication

4-layer FR4, ENIG, controlled impedance (100 Ω differential on the high-speed pairs), targeting JLCPCB's standard 4-layer process. Full stackup, impedance, and drill/feature constraints are in docs/fab_specification.txt.

Downloads

Latest release (see all releases):

• 📄 Schematic (PDF)
• 🧩 Assembly drawing (PDF) — top + bottom component placement
• 📐 Fabrication drawing (PDF) — overview/spec, per-layer, and drill maps
• 🛠 Gerbers — JLCPCB-ready (zip)
• 📦 Full fabrication + design package (zip) — Gerbers, drill, BOM, CPL, schematic PDF, assembly + fabrication drawings, STEP

Packages are built and version-stamped by CI. Versioning is semantic (vMAJOR.MINOR): dev publishes v0.x pre-releases, and promotion to main cuts production releases (v1.0, then v2.0, …). The version and git hash are stamped into the title block and bottom silkscreen at build time, and named in each release's title/tag. The download links above resolve to the newest production release; during the pre-1.0 phase (only v0.x pre-releases so far), grab the assets from the specific pre-release on the Releases page. See docs/RELEASE_STRATEGY.md for how versions and releases work (a new version is cut only when the design changes).

Status

Prototype. This is an unproven design intended to validate the central hypothesis above. The current revision is whatever the latest release is — it's stamped into the board, not hardcoded here.

License

CERN-OHL-P v2 (CERN Open Hardware Licence Version 2 – Permissive, SPDX CERN-OHL-P-2.0).