We have a 10 gb fiber run between 2 buildings about a mile apart and will not be able to purchase any more fiber. I was told I could use four "10 gigabit bidi's" to allow 2 separate ethernet connections over the same pair of fiber. These connections will be going to two separate, adjacent switches on each end. I need more information about this as my internet searches have not resulted in any good information about these devices.
SnapOverflow
What you're probably looking for is CWDM. This allows you to transmit and receive on the same strand of fiber on different wavelengths of light. You would need to purchase a CWDM mux and compatible transceivers for your routers. This is the cheaper version for transmitting and receiving a 1gb link over a single strand of fiber without requiring a CWDM mux. I have only used this method for gig links and haven't been able to find any CWDM 10gig compatible transceivers.
CWDM usually refers to 1G Ethernet or 1/2/4 G Fibre Channel. To pass 10GE you will want some sort of EWDM or possibly a passive DWDM setup. You will end up with single mode LR optics that emit light at a certain specific wavelength which connect to a passive device that, in turn, connects to your inter-site fiber. At the other side the wavelengths will break out to connect to your remotes.
The EWDM solution I mentioned is Cisco (http://www.cisco.com/en/US/docs/interfaces_modules/transceiver_modules/installation/note/78_17894.html) and can handle up to 8 10GE (and another 8 CWDM links) on a single pair of strands, but there are plenty of other comparable solutions out there. The big money is in the optics themselves rather than the actual multiplexer.