Can a single-mode single optical fiber support full-duplex communication, or does it have to be two fibers, one for each direction?
Can a single optical fiber support full-duplex communication?
Yes. There are "BX" standards, e.g. 100BASE-BX, which use different wavelengths for send and receive. The transmit wavelength on one end needs to be the receive wavelength on the other end.
For example, Cisco has these transceivers:
1000BASE-BX10-D and 1000BASE-BX10-U SFP for Single-Fiber Bidirectional Applications
The 1000BASE-BX-D and 1000BASE-BX-U SFPs, compatible with the IEEE 802.3ah 1000BASE-BX10-D and 1000BASE-BX10-U standards, operate on a single strand of standard SMF.
A 1000BASE-BX10-D device is always connected to a 1000BASE-BX10-U device with a single strand of standard SMF with an operating transmission range up to 10 km.
The communication over a single strand of fiber is achieved by separating the transmission wavelength of the two devices as depicted in Figure 2: 1000BASE-BX10-D transmits a 1490-nm channel and receives a 1310-nm signal, whereas 1000BASE-BX10-U transmits at a 1310-nm wavelength and receives a 1490-nm signal. As shown, the presence of a wavelength-division multiplexing (WDM) splitter integrated into the SFP to split the 1310-nm and 1490-nm light paths.
Figure 4. Bidirectional Transmission of a Single Strand of SMF
A full duplex or Bidirection communication meaning that it can support both stations transmitting and receiving simultaneously.
To accomplish this, a single optical fiber with WDM technology is required for optical tommunication.
WDM stands for wavelength division multiplex. This multiplex method uses both 1310 nm and 1550 nm wavelengths.Two devices are used for connection via a single optical fiber just as seen in the picture. Device A transmits data at 1310 nm on the TX channel and device B receives data at the same wavelength on the RX channel. When the roles are reversed, 1550 nm is used in the other direction. Connection is therefore only possible between device A and device B. The devices are available as a set.
Note that Cisco 1000BASE-BX10-D and 1000BASE-BX10-U SFP is availble for Single-Fiber Bidirectional Applications.
Yes, if you have the right hardware.
Normally a seperate strand of fiber is used for each direction. This keeps the transcievers simple and allows the same transcievers to be used for both ends of the connection.
However you can now buy transcievers that allow full-duplex communication on a single fiber. These are known as "bidi" transcievers. They work by using two different wavelengths with splitter prisms inside the transcievers. You need to use an "upstream" transciever at one end of the fiber and a "downstream" transciever at the other.
For 1Gbps there was a standard for bidi transcievers, 1000BASE-BX10. I cannot find any evidence of a standard for 10 gigabit bidi optics despite some vendors selling their products as "10GBASE-BX" or "10GBASE-BR". So I would treat any 10 gigabit bidi transcievers as propietary.
Single strand fiber transmission use a single strand of glass (optical fiber) to send data in both directions, namely bidirectional (BiDi) transmission. In recent years, the mainstream single strand fiber transmission technology is based on two wavelengths traveling in opposite directions (also called TW BiDi transmission). This technology is achieved via wavelength division multiplexing (WDM) couplers, also known as diplexers, which combine and separate data transmitted over a single fiber based on the wavelengths of the light. Generally, this WDM coupler is integrated into a standard interface optical transceiver module. You can read more details here: http://www.fs.com/blog/single-strand-fiber-solution-is-it-right-for-you.html