160-Gbps OTDM System with Clock Recovery

  • Description

    High-speed systems at 100 Gbps 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 a few picoseconds' width) and low-data-rate transmitters of, for example, 40 Gbps. Both take the advantage of employing a single optical source for all channels, thus increasing the channel speed in comparison to the Wavelength Division Multiplexing (WDM) technology. This application example shows the implementation of an Optical-Time-Division Multiplexed (OTDM) system. Four DQPSK channels at 40 Gbps are multiplexed in the time domain after optical modulation producing a 160-Gbps 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 40 Gbps and then time-delayed, so that their pulses interleave when combined (Figure 1).
    After amplification, the signal is transmitted over a 100-km SMF. It follows CD compensation, reamplification, filtering and OTDM demultiplexing. Figure 2 shows the calculated BER for one 40-Gbps DQPSK channel versus OSNR for different launch powers.
    The demultiplexer 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.

  • Further Information

    Keywords: Optical Time Division Multiplexing (OTDM), high-speed systems, DQPSK

    Similar demonstrations are available in VPItransmissionMaker Optical Systems and on the VPIphotonics Forum.

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