During a shopping spree in Shenzhen I came across a booth that sells optical fiber network equipment. The one thing that caught my eye was a 1000Base Ethernet to SFP media converter. They were sold in pairs for 480RMB (roughly 62€) inlcuding the SFP transceivers. For 10RMB more I also bought a matchting 5m fiber cable. Back at home I tested the device with the laptop of a friend and shure enough, the converters and transceivers can hanle 1Gbit/s.

marble@archlinux ~ % cat /dev/zero | pv -r | nc 10.10.10.3 1337
[93.7MiB/s]

 (93.7MiB/s equals 786.0126 Mb/s - considereing the TCP/IP and Ethernet overhead this seems reasonable)

The power supplies for the converters supply 5V with up to 1A. So in theory one can run these from the USB jack of a modern laptop. One of my goals is to get network across (or through) a lake during a camping trip this summer.

Being willing to risk voiding the guarantee I opened up one of the devices.
The board seems to be double sided withno inner layers. Nexto some power supply chips the active components of the board are a 4 port Gbit Ethernet switch chip and a OTP microcontroller

QCA8334 Four-port Gigabit Ethernet Switch

http://www.inno-vative.com/uploadfile/cfile/upload/201481410155030.pdfCost-Effective A/D 8-bit OTP MCU

http://www.holtek.com.tw/documents/10179/11842/HT46R003Bv100.pdf

Before openening it up I expected no switch chip at all. Wikipedia has quite a good article about SFP tranceivers. Their interface consists of 20 pins. 9 for the power supply. 7 for control (Loss of Signal, detecting that a transceiver is plugged in etc.) and 2 differentials pairs for communication - TD and RD.

Since Ethernet also works with differential signals (although through current loops - hence the little transformer blocks nexto every Ethernet port) I though one couls simply wire them to the SFP port. Apparently not 😄.