High-Speed Dielectric Waveguide Communication Links

Dielectric waveguide interconnects show great potential for high-speed communication at distances up to a few meters, due to the high bandwidth that is intrinsically available at mm-wave frequencies. However, existing links have fallen short of reaching their full data rate at distances higher than a meter, mainly because of the detrimental effect of dispersion within the fiber. In addition, while first-generation dielectric waveguide links were able to use simple, binary modulation schemes such as On-Off Keying, this is no longer sufficient to meet the increasing demands of today’s systems.

A CMOS ASK transceiver has been developed and optimized for the targeted fiber. The circuits were designed for high bandwidth and high power/low loss, allowing for high data rate and large communication range. Enhanced linearity of the transceiver enables the use of modulation schemes with a higher spectral efficiency such as 4-ASK. In addition, application of equalization techniques such as FFE (Feed-forward Equalization) or a non-linear Volterra equalizer, can drastically increase the maximum data rate achievable over the link. Finally, the use of advanced error-correcting codes relaxes the SNR (Signal-to-Noise Ratio) requirements for a given Bit Error Rate by several dB, at negligible coding overhead. This, in turn, leads to an increased communication range. In this way, 50 Gb/s was achieved over fibers up to 3 meters.

A more advanced iteration of the transceiver targets 100 Gb/s communication over up to 7 meters. By using a multi-band architecture, the dispersion requirements of the waveguide are relaxed. Improved linearity of the circuits allows multi-level amplitude modulation in each band, making the link compatible with modern Ethernet standards. Non-coherent linear detection obviates the need for a power-hungry PLL and greatly simplifies the design.