Time Division Multiplexing
Time division multiplexing is a technique where several optical signals are combined, transmitted together, and separated again based on different arrival times. In an optical fiber communication system, interleaving pulse trains can carry different data channels in a single fiber [1, 3]. The use of multiple channels allows increased overall data transmission capacities without increasing the data rates of the single channels, or transmission of data of different users simultaneously. However, the time slot per bit must be reduced. Even if the bandwidth of the data modulator is limited, this can be done by using a train of ultrashort pulses (rather than a continuous optical wave) as the input of the modulator.
Special requirements of data transmitters for optical time division multiplexing are a short pulse duration and a low timing jitter. Also, the extinction ratio should be high, i.e. each combined channel should exhibit a very low power level between the bit slots, because such a background could otherwise interfere with other channels. For combining the signals, one typically requires some kind of optical delay lines.
An alternative to time division multiplexing is wavelength division multiplexing, where the channels are distinguished by wavelength rather than by arrival time.
In the context of distributed fiber-optic sensors , optical time division multiplexing means that signals are assigned to certain locations in the sensor via their arrival times. Such systems usually operate with ultrashort pulses.
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