The low cost and mass integration potential of CMOS integrated circuits create an attractive opportunity for investigating
CMOS as an optical platform. Although silicon, as an indirect band gap material, is known for inefficient
electroluminescence, silicon-based optical transmission is still a much sought after capability. This paper shows the
potential of an all silicon transmission system for both clock and data transmission.
By utilizing silicon light emitting diodes operating in avalanche, it is shown that a switching speed of above hundred
megahertz is possible. The transmitter consists of an array of light sources, with metal light directors for improved
external quantum efficiency. The array is pulsed across an optical fibre and received by an avalanche photodiode and
amplifier module. Spectral results of the received signal confirm an optical component in excess of 100 MHz, were the
off-chip driver circuitry and the photodiode receiver currently limit the bandwidth of the system.
As the requirements for wideband data transmission are more stringent than for a narrow band clock signal, the
transmission system was tested as a baseband digital communication system, with transmission speeds of up to 176 kbps.
We also present eye diagrams of the received signal to prove the success of the transmission system, where transmission
speed is limited to detectable optical levels versus allowable in-band noise.
A refinement on these principles might lead to CMOS as a contender in high speed clock transmission as well as an
alternative to III-V devices for low cost optical transmission systems.