High-speed detection at two micrometres with monolithic silicon photodiodes

A silicon detector that is capable of long-wavelength photodetection at multi-gigabit per second data rates could prove useful for unlocking a new wavelength window for optical communications. 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 μm 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 , 7 , 8 , 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.