High-speed detection at two micrometres with monolithic silicon photodiodes

With continued steep growth in the volume of data transmitted over optical networks there is a widely recognized need for more sophisticated photonics technologies to forestall a 'capacity crunch'(1). A promising solution is to open new spectral regions at wavelengths near 2 mu m and to exploit the long-wavelength transmission and amplification capabilities of hollow-core photonic-bandgap fibres(2,3) and the recently available thulium-doped fibre amplifiers(4). To date, photodetector devices for this window have largely relied on III-V materials(5) or, where the benefits of integration with silicon photonics are sought, GeSn alloys, which have been demonstrated thus far with only limited utility(6-9). Here, we describe a silicon photodiode operating at 20 Gbit s(-1) in this wavelength region. The detector is compatible with standard silicon processing and is integrated directly with silicon-on-insulator waveguides, which suggests future utility in silicon-based mid-infrared integrated optics for applications in communications.