Nowadays, there are several kinds of multiplexing technology pushing the development of network speed based on fiber optical cabling. They are time division multiplexing(TDM) technology, space division multiplexing (SDM) technology and wavelength division multiplexing(WDM) technology. 

Time division multiplexing(TDM) technology

Time division multiplexing is a way of transmitting more data by using smaller and smaller time increments and multiplexing the signal with a lower data rate into a higher speed composite signal. By time division multiplexing, lower speed electrical signals are interleaved in time and are transmitted over a faster composite optical path. Thus, the resulting higher data rate will be several times as much as the individual input rate.

There are many examples of this. By using this parallel electrical signal, combine in the multiplexer, and transmit serially in the optical fiber to achieve the Ethernet rate. For instance, 10Gbps Ethernet has four channel options, each channel accounts for a quarter of the rate of 2.5Gbps.

Today, Ethernet has a maximum rate of 25Gbps for each channel. If we look to the future, 50Gbps channel rate has already been in development.

With the higher rates, more bits can be obtained via each symbol by using more complex multi-level coding schemes. This indicates that the maximum speed limit has been reached, then alternative technology is needed to increase the speed of the composite channel.

Space division multiplexing (SDM) technology

Space division multiplexing, commonly referred to as parallel fiber, is a way of adding one or more channels by adding one or more optical fibers to a composite link. In this case, a channel is actually another fiber. This is an alternative to the above-mentioned time division multiplexing channels in which the signals are combined by time in the same fiber. There are many instances of applying this technology in the industry. For example, the 40G SR4 provides a 40 Gbps rate in a multimode fiber by using four channels or fibers, In other words, there are four channels in each direction. This is exactly what the “4” mean in "SR4", 4 channels, 10Gbps for each one.

The standard of using 10 10Gbps channels to provide 100Gbps solutions is called SR10. The second generation 100G will increase the channel rate to 25Gbps, four channels can provide 100G, then combining time-division multiplexing with parallel fiber technology, will be able to achieve higher speed.

Wavelength division multiplexing(WDM) technology

Wavelength division multiplexing is a technique of simultaneously transmitting signals by multiplexing and separating of multiplexers by multiple channels separated by wavelengths (colors) of different lights. As the name suggests, the wavelength band used for transmission is divided into multiple segments, each of which can be used as a channel for communication. It is possible to squeeze multiple channels out as a small spectrum. A common version for long-haul, single-mode systems is called dense wavelength division multiplexing or coarse wavelength division multiplexing. In multimode systems, short wavelength division multiplexing is emerging. 

With the help of short wavelength division multiplexing, it’s more likely to add channels to single strand of fiber by using a low-cost shortwave near the 850nm range. An example of the current market is Cisco's 40G BD or Bi-Di. Bi-Di represents bidirectional, and the signal is bi-directionally transmitted in each fiber, and it is using two different wavelengths that distinguish between possible reflections. This kind of technology uses 20Gbps of each wavelength in two fibers to achieve 40Gbps rate in two fiber cores by using a duplex LC connector.