Stokes Vector Modulation for Terabit-Class Data Center Networks

Cuny College Of Staten Island, Staten Island NY

Investigators

Abstract

Data centers have become the nerve centers of the modern information-driven economy, relying on large networks of fiber-optic links operating at data rates up to 10 gigabits per second. Going forward, these fiber-optic links must scale to higher speeds at an acceptable cost in both dollars and in watts, but today's solutions, using on-off keyed signaling and power-sensing receivers, will not meet cost and dissipation targets as rates exceed 40 gigabits per second. Neither will fiber-optic transceivers developed for telecommunication networks, as these require complex receivers, expensive lasers in both transmitter and receiver, and power-hungry digital signal processing. To close the performance gap, this research program will investigate fiber-optic links in which the polarization of the transmitted light is switched to carry the data. Polarization shift keying and Stokes vector modulation (which switches both the polarization and amplitude) can transmit multiple bits of data per transmitted symbol, greatly accelerating the link's data rate while maintaining tolerance to fiber loss and other signal impairments. Research tasks will include theoretical study of noise impacts, optimization of advanced transmitter and receiver designs, simulation of polarization-modulated communication links, and experimental study in a lab testbed that incorporates dynamic optical networking. The timely and practical focus of this project will offer graduate and undergraduate students excellent opportunities to develop into productive practitioners in communications, fiber optics, and data center design. Beyond its direct impact on the student researchers, the program will offer additional educational benefits to the broader community by presenting lab tours and demonstrations to college and high-school students who might otherwise lack an opportunity to experience modern fiber-optic technology. Finally, by advancing the state of the art in data center technology, the project will contribute to economic growth as well as helping to keep the U.S. innovation pipeline well-filled. The primary technical objective of this research program is to advance the understanding of multi-dimensional modulation techniques based on polarization-shift keying and Stokes vector modulation, as applied to fiber-optic transceivers for terabit-class data center networks (i.e., photonic networks in which each wavelength channel carries about 1 terabit per second of data). Such research is critically needed because no existing technique has been found that offers both the data throughput and the cost needed to support Big Data applications in the 2020-2030 timeframe. Scaling of massive data centers to meet future demands will require a radical shift in optical data link technology. Current development based on pulse amplitude modulation will not be able to reach the 1 terabit per second level, because it is based on a one-dimensional symbol space. Coherent lightwave systems developed for long-distance telecommunications offer multi-dimensional symbol spaces, but they are too costly and power-hungry, and their slow setup times will inhibit the rapid dynamic networking needed for data center networks. Polarization-based modulation formats can provide 2-D, 3-D, or even 4 D symbol spaces using direct (i.e. non-coherent) detection, once critical challenges are overcome. This program will study fundamental issues of symbol constellations and noise mapping into Stokes space, as well as low-complexity digital signal processing and multiple-input, multiple-output techniques to enhance both receivers and transmitters. Alternative Stokes vector receiver designs will be compared theoretically and experimentally for both unimpaired link budgets and impairment tolerance. In support of dynamic topologies, performance under rapid optical switching/routing will be directly tested. At all stages, the work will be socialized through publications, presentations, and bilateral collaborations, while preparing students to enter the industrial and academic communities.