Optical data link

This page covers technologies to link two places or buildings via an optical data link.

Suitable places to use an optical link

It may be useful in places where...

• Outdoor Wi-Fi is not permitted by a county's radio legislation.
• A line-of-site link is possible.
• The two places to be linked are about 1.5 KM/1 Mile or less apart (with the Ronja system below).
• Cheap hardware is required.
• A system with no subscription-fee is required.
• There is only occasional dense fog.

Example locations

• School-to-school links in urban/suburban areas.
• School-to-school links between nearby villages.
• School to nearby ISP office link, where the phone lines don't support high-speed access.
• Commercial Building (Business, Radio station, etc) to ISP office link, where schools are allowed internet access and to pick up files on removable media (Sneakernet).
• Multi-stage optical links with relays from building-to-building to reach a school or village.
• Optical network involving many schools/buildings/houses and optionally, an ISP office.
• Across mountain valleys.
• Up a hill and down the other side using two systems.

Technologies

Ronja cheap home-made optical link

The Ronja (Reasonable Optical Near Joint Access) website describes how to build a 100 US Dollar optical data link to connect two buildings up to 1.4KM/0.87 Miles apart at 10Mbps. The 'Ronja About page' describes the system (see text and the 4 .pdf files) and the 'Ronja Home page' has the equipment details. The site has designs for Printed Circuit Boards. The software is free.

The system uses an LED and lens, not a laser, so is 'eye-safe'. There is one version using a visible red LED and another using an invisible infra-red LED. Both are invisible to anyone in the area who is not in the direct line between the two sender/receiver units.

The system uses cheap parts, but is labor-intensive for amateurs to build. There are enough OLPC schools for it to be worthwhile having some systems mass-produced.

See Wikipedia: RONJA and Ronja About page for more details and photos.

Other systems

Please add any similar systems here.

--Ricardo 16:31, 23 August 2007 (EDT)