High-speed / High-capacity Systems

100Gbps ETDM System - Impact of Transmitter Electronics

Description

High-speed systems transmitting 100Gbps on a single wavelength is the next technological step for integrating Ethernet traffic into metro and long haul networks. Several modulation technologies are being investigated at the moment. 100Gbps transmission using binary modulation formats (NRZ, Duobinary or NRZ/VSB) might be easier to realize compared to approaches using multilevel modulation formats. Further on, they might be more attractive from an economic point of view due to the simplicity of their transmitter and receiver structures. However, binary formats show increased requirements on electrical and electro-optical components, as electrical signals with ~100GHz bandwidth must be managed. The increase of speed of electronics enables the multiplexing of signals in the electrical domain (ETDM), and thus, the implementation of high-speed ETDM channels.
This example shows how data channels can be multiplexed in the electrical time domain and how to model the electronics in an ETDM transmitter to represent impairments such as electrical bandwidth and clock imperfections.

Typical Results

The setup of an Electrical Time Division Multiplexing (ETDM) system with 4 channels at 25Gbps is represented in Figure 1. The ETDM 100Gbps signal is generated by 4 x 25Gbps tributaries and two 2:1-stage electronic multiplexers, consisting of ideal logical gates. The driver amplifier adjusts the signal delivered by the electronic multiplexer, which is in the order of millivolts, to the level required by the modulator (usually in the order of volts). A Mach-Zehnder modulator (MZM) is driven with the adjusted 100Gbps-signal. Electrical filters represent amplitude ripple and non-linear phase response of the amplifier and the electrical response of the MZM. Clock imperfections are modeled by adding a source with pseudo-random jitter to an ideal clock signal. Delays between the clock and data signals are represented by a deterministic delay (Figure 2). The impact of bandwidth limitation of the MZM is investigated by varying the bandwidth of the electrical filters. Simulation results are represented in Figure 3 and Figure 4, showing a penalty on the allowed OSNR.