High-speed / High-capacity Systems

160Gbps OTDM System with Clock Recovery

Description

High-speed systems at 100Gbps and higher on a single wavelength are feasible by means of Time Division Multiplexing (TDM). The two choices are Electronic Time Division Multiplexing (EDTM) and Optical Time Division Multiplexing (OTDM). ETDM systems may be limited by electronics, whereas OTDM works with optical short pulses (with few picoseconds width) and low data rate transmitters of e.g. 40Gbps. Both take the advantage of employing a single optical source for all channels, and thus, increasing the channel-speed in comparison to Wavelength Division Multiplexing (WDM) technology. This application example shows the implementation of an Optical Time Division Multiplexed (OTDM) system. Four DQPSK-channels at 40Gbps are multiplexed in the time domain after optical modulation producing a 160Gbps signal.

Typical Results

The OTDM transmitter consists of a short pulse source with a 1-to-4 splitter. The four channels are DQPSK modulated at 40Gbps and then time delayed, so that their pulses interleave when combined (Figure 1).
After amplification, the signal is transmitted over 100km SMF. It follws CD-compensation, re-amplification, filtering and OTDM demultiplexing. Figure 2 shows the calculated BER for one 40Gbps DQPSK channel versus OSNR for different launch powers.
The de-multiplexer uses EA modulators as optical gate to extract the desired channel. These optical gates are driven by a clock recovery module which generates clock signals extracted from the data signal. The nonlinear characteristic of the EA modulators ensures a sharp gating function (Figure 3). Once the desired channel is selected, the signal is detected by a DQPSK receiver; the received electrical eye diagram of the in-phase (I) component is represented in Figure 4.