Signal Multiplexing
Multiplexing is defined as the process of combing multiple signals together in order to share a transportation medium. Two popular multiplexing techniques for fiber optic communication systems are Time Domain Multiplexing (TDM) and Wavelength Division Multiplexing (WDM). Multiplexing saves the number of fibers needed to transmit signals.
TDM
Time domain multiplexing; Figure 1, is accomplished in the electrical domain. Multiple parallel signals are simultaneously applied to a multiplexor that will only allow each input signal to transmit through the communication link at certain times. Since multiplexing is done in the time domain, TDM can be used with multimode fiber. Since the output bit rate is an addition of all the input signals plus some overhead, the output data rate quickly becomes large. Timing and latency issues are to be considered when using a TDM network.
 |
| Figure 1: Time domain multiplexing block diagram. Multiple input signals are sequentially transmitted. Multiplexing is accomplished in the electrical domain |
WDM
Wavelength Division Multiplexing, figure 2, is done entirely in the optical domain. Input electrical signals are each assigned a wavelength, which are combined on one fiber for transmission and separated before being received. Each electrical input signal can operate at an independent bit rate and will not interfere with any of the other input signals. Wavelength division multiplexing is available in multiple channels. We offers an economical 1310nm/1550nm WDM solution consisting of two wavelengths only. Also available are 4, 8, 12 and 16 channel CWDM systems that have a 20nm channel spacing. 8, 16, 24, 32, and 40 channel dense wavelength division multiplexing systems are also now available for high signal capacity networks.
 |
| Figure 2: A 4 Channel Wavelength Division Multiplexing Block Diagram. Multiple input signals are combined optically, each signal having its own bit rate. |
