Integrated photonic devices in III-V semiconductors for optical communications

The success of the internet in stimulating new services has resulted in an exponentially growing demand for transmission capacity with a compound annual growth rate as high as 40-60% per annum [1]. Such a rapid growth rate cannot be accommodated by simple scaling of existing equipment practices: not only the cost but also the size and power consumption would be prohibitive. Technical innovation has provided the solution: optical fibre links in the core network now routinely run at 10 Gbit/s per wavelength, providing a total capacity in the region of 1 Tbit/s on a single fibre through the deployment of wavelength division multiplexing (WDM), whilst data rates of 40 Gbit/s and 100 Gbit/s per wavelength are increasingly employed. With the adoption of advanced modulation formats and coherent systems, 100 Gbit/s can now be transmitted over fibre infrastructure that was designed for 10 Gbit/s [2], while tunable lasers and reconfigurable optical add-drop multiplexers (ROADMs) allow network operators to reroute traffic in a highly flexible and dynamic manner, allowing optimum use of their assets. Optical terminal equipment in modern systems is accordingly much more complex than was possible hitherto, whilst size, power and cost have been continuously reduced. An important enabling factor in achieving these objectives is the availability of monolithic photonic integrated circuit (PIC) technology.