定义：
在时域上的复用技术

时分复用指的是不同的光信号被合在一起传输，然后基于不同的到达时间再将不同信号分离开来的技术。在光纤通信系统中，交叠在一起的载有不同信号的脉冲列可以在一根光纤中同时传输。这种利用不同信道一同传输的方法可以在不增加信号速率的情况下增加其传输容量。但是每比特信号之间的时间间隙需要减小。通过使用一列超短脉冲（而不是连续光）作为调制器的输入可以克服调制器的带宽带来的限制。 

图 1： 时分复用技术示意图。两个交叠的脉冲组成一个新的脉冲序列。在通信系统中可以利用“1”（存在）和“0”（被抑制）代表脉冲。 对于用于光时分复用的数据发射器有特殊的要求：短的脉冲长度和低的定时抖动。此外，消光比需要很高，也就是说：在信号光之间的时间间隙上应该保持一个很低的功率水平因为这一背景可能会对其它信道产生干扰。 

除了时分复用技术，还可以采用另一种复用技术是波分复用，其不同的信道是通过波长而不是到达时间区分的。 
在分布式光纤传感器中，光时分复用技术指的是传感器中的信号根据其到达时间来探测其位置。这些系统通常采用的是超短脉冲。

Acronym: TDM, OTDM

Definition: a multiplexing technique operating in the time domain

More general term: optical multiplexing

Opposite term: wavelength 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.

Figure 1: Schematic of optical time division multiplexing. Two interleaving pulse sequences are combined to a single pulse train. In a communications system, each pulse may represent a “1” bit (if present) or a “0” (if suppressed).

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. During signal propagation in an optical fiber, for example, the temporal spreading by effects like chromatic dispersion must be limited, or at least redone before detection with suitable dispersion compensation.

In the context of distributed fiber-optic sensors [2], 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.

An alternative to time division multiplexing is wavelength division multiplexing, where the channels are distinguished by wavelength rather than by arrival time.

Bibliography