Optical Networking
Certain optical communications hubs (eg Madge; or at least, they used to) have
at least two fibre ports: one for the input signal, and the other for the output.
There is a cheaper way, that costs about half the price of a normal link, as you
still need at least one fibre. But it is full duplex. However, it requires a
bit of additional hardware in the form of beamsplitters.
If you use a normal thin piece of glass (say, a microscope slide), to split the
beam, you will produce a secondary ghost beam from internal reflection, which
if the detector picks it up, may produce some sort of interference. If you can
half/silver the slide, that would make things better.
Unfortunately, you can't buy beamsplitters at say PC World or wherever you buy
your computer bits from, and they are quite likely to be hugely expensive.
However, if you have two old useless single speed CD drives at the bottom of a
box somewhere, the assembly containing the laser pickup has probably got a
rhomboid type prism inside it, which can be carefully removed (If it's not
welded in with that indestructible glue), to build up the beamsplitter.
Alternative Rhomboid type beamsplitter out of CD Drive, where the secondary ghost
beam is foiled by the prism geometry. This has been tried with a laser pointer
and it does seem to work. This orientation is for the left hand splitter above,
where the TX laser is on the left hand side.
If you have a bit of a browse through the UK Farnell catalogue, you will note
that they are selling full duplex single fibre modules (Damn !). A working link
costs about £250 (excluding the cost of fibre), as you need to buy two units with
different transmit/receive wavelengths, matched up. Apparantly, they have a 3dB
wavelength differentiating mirror and integral lenses to couple to the single
fibre, ! whatever. Surely some researcher somewhere will have tried the beamsplitter
trick !
