Quaternary modulation formats for 100-Gbps optical links

Abstract

The demand for 100 Gb/s optical links is rapidly spreading across all levels of the optical networking infrastructure. Many of the first deployments will be in the local area network (LAN) and metro-core and regional network environments. To address needs in LAN, the upcoming IEEE standard (IEEE P802.3ba) seeks 100 Gb/s over distances up to 40km. Furthermore metro-core/regional dense wavelength division multiplexing (DWDM) architectures require reach of several hundred km and the ability to pass through ten or more ROADMs. However, a number of fundamental challenges remain including the selection of appropriate modulation formats that are robust to a variety of nonlinearities, are sufficiently spectrally efficient, and able to withstand the strong optical filtering of cascaded ROADMs. Here we compare a variety of single-carrier quaternary modulation formats, each providing 2 bits/symbol/polarization and each likely to provide some advantages at 100Gb/s. Each format is presented with an appropriate MZM-based transmitter, and constrained by practical signal fidelity limitations that also enable comparison to experimental results from our 100G testbed. We primarily examine direct detection for cost-sensitive metro networks; however we also quantify the performance of coherent receivers, where applicable. Simulation results demonstrate the relative OSNR penalty (at a pre-FEC BER of 10 -3 ) for a range of launch powers and adjacent channel formats.

Continuous phase modulation parameter optimization for DWDM systems

“…4) follow similar trends, where the quaternary schemes degrade in the region of h=0. 3. It is noted that partial response quaternary schemes are typically capable of achieving higher minimum distance than full response systems, however they operate with lower SE than that required by this application.…”

“…The transmitter can generally be constructed with DACs on the I and Q branches of a nested MZM modulator which must operate with adequate resolution at nearly twice the baud rate. Some full response systems can be implemented without DACs [3]. The optimal demodulator requires a coherent optical receiver (dual-pol for maximum data rate), as well as a Viterbi decoder with a traceback length of N. Due to this complexity, the use of full response CPM systems is favorable for complexity since optimal reception is achieved with lower N, however, partial response systems can achieve higher minimum distance.…”