Varying 400G proposals present test challenges

Companies beginning to deploy 100G data-communications systems are simultaneously facing the need to develop next-generation 400G systems—and even 1-Tb/s systems—as well. To achieve higher speeds, instead of increasing the symbol rate of a single carrier, one approach is to transmit signals in parallel by using multiple carriers at lower individual rates. Such multicarrier systems are called superchannels.

Robert A. Marsland, Jr., Ph.D., product line manager for optical products at Tektronix, said challenges facing developers looking to adapt superchannel technology include variations in current proposals for implementing coherent optical systems—proposals vary considerably with regard to number of carriers, carrier spacing, and modulation format used. Consequently, he said, developers need test and measurement equipment that offers the flexibility to support any combination of system parameters.

Marsland, who came to Tektronix with its acquisition of Optametra, cited several examples of how vendors are looking to achieve high data rates, including 400 Gb/s using two channels and DP-16QAM, 500 Gb/s using five or 10 channels and DP-QPSK modulation; 1 Tb/s using 10 channels and DP-QPSK modulation, and 1.5 Tb/s suing eight channels and DP-16QAM. “There is no industry consensus on how to build superchannels,” he said in a phone interview.

To support developers investigating multiple combinations of channel count, channel spacing, and modulation capability, Marsland said, Tektronix is offering a software option dubbed MCS on its OM-Series coherent light-wave signal analyzers, which in turn are tightly integrated with Tektronix DPO70000D Series 33-GHz oscilloscopes and DSA8300 Series 70-GHz sampling oscilloscopes. (View a product summary here.) Marsland said the instruments and new software option support unlimited user-definable superchannel definitions and reduced test times.

The software can present integrated multicarrier measurement results that facilitate channel-to-channel comparisons. Users can view eye diagrams, constellation diagrams, and optical spectrum plots, and channels can be superimposed for easy comparison.

The software also supports test automation. With multiple carriers defined in a multicarrier setup table (no carrier fixed grid is imposed, so carrier width can vary from carrier to carrier), a single run command initiates all testing.

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