High Speed Multi-Level Drivers for Spectrally Efficient Optical Transmission Systems (for external publication)

High spectral efficiency modulation is key to addressing the optical network capacity challenge. Typical implementations of transmitters for advanced modulation formats use high-resolution Silicon Digital-to-Analog Converters, complemented by high-bandwidth linear amplifiers to drive the electro-optic modulator. To overcome this set-up's limitations, both in speed and complexity, an alternative approach has been proposed and realized by Bell Labs, based on a Multi-Level Driver, which operates at symbol rates up to 50 GBaud with swings of a few Volts, sufficient to drive various common electro-optic modulators. Over the past 2 years, Multi-Level Drivers have enabled various Bell Labs optical system experiments relying on the high signal quality achieved and the rate flexibility offered. The circuit architecture, the technology, and the assembly of these drivers are described in this paper, and the various system experiments are summarized. The relevance for future products is discussed.