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.
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
After amplification, the signal is transmitted over a 100-km SMF. It follows CD compensation,
reamplification, filtering and OTDM demultiplexing.
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
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
Keywords: Optical Time Division Multiplexing (OTDM), high-speed systems, DQPSK
Similar demonstrations are available in VPItransmissionMaker Optical Systems and on the VPIphotonics Forum.