Traditional electrical interconnects suffer frequency-dependent attenuation. Inside networking and computing infrastructure (large data centres), these losses limit the length of electrical interconnect to as little as a few metres at modern data rates. Moreover, at high frequencies electrical interconnect and connectors act as both transmit and receive antennae, and therefore experience significant crosstalk. Crosstalk limits the density with which high-speed electrical interconnect can be packed
By contrast, signals propagating on optical fibres exhibit relatively little frequency-dependent loss and practically no crosstalk. Counteracting these benefits are the challenges of converting high-speed electrical signals to/from optical signals. Our research strives to address these challenges by developing low-power compact CMOS circuits for optical interfaces at serial data rates of 100+ Gb/s.
Although the fiber itself may offer a near-ideal medium for optical signal transmission, the optoelectronic devices at either end of the fiber (photodetector, laser, modulator, etc.) can be significant impairments. Firstly, the devices’ electro-optical conversion is inherently inefficient, so the electrical signal induced at the receiver is a small fraction of the electrical signal in the transmitter. Optoelectronic devices also introduce frequency-dependent loss, although unlike the frequency-dependent losses of copper interconnect, this characteristic doesn’t depend upon the length of the interconnect. Finally, nonlinearity of the optoelectronic devices can come into play. Our research strives to overcome these unique challenges using low-cost and low-power CMOS circuits, thus allowing high-performance computing and networking infrastructure to benefit from optical interconnects.
Our recent past work in this area has yielded exciting results up to 40Gb/s. Shown below is one of several prototype optical transmitters developed and tested in our lab. Future work is underway to extend data rates to 100+ Gb/s.