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 hollowcore 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.The advantages of silicon photonics, which have been well documented for traditional communication wavelengths around 1.3 and 1.5 µm (refs 8,9), extend to operation in the mid-infrared (MIR) region 10 . Silicon photonic components are fabricated using complementary metal-oxide semiconductor (CMOS)-compatible technologies, with the potential for integration with electronic control. Recently, groups have demonstrated several silicon-based components operating in the MIR wavelength range of 2-20 μm, including low-loss waveguides, couplers, splitters and multiplexers 11 , as well as some with hybrid active functionality 12,13 . However, photodetectors that are compatible with silicon waveguides, are capable of detection beyond 2 μm, and operate at the bandwidths required by future optical communication networks remain elusive. The sig-

Abstract-The bandwidth bottleneck looming for traditional electronic interconnects has driven the consideration of optical communications technologies as realized through the complementary metal-oxide-semiconductor-compatible silicon nanophotonic platform. Within the silicon photonics platform, silicon microring resonators have received a great deal of attention for their ability to implement the critical functionalities of an on-chip optical network while offering superior energy-efficiency and small footprint characteristics. However, silicon microring-based structures have a large susceptibility to fabrication errors and changes in temperature. Integrated heaters that provide local heating of individual microrings offer a method to correct for these effects, but no largescale solution has been achieved to automate their tuning process. In this context, we present the use of dithering signals as a broad method for automatic wavelength tuning and thermal stabilization of microring resonators. We show that this technique can be manifested in low-speed analog and digital circuitry, lending credence to its ability to be scaled to a complete photonic interconnection network.Index Terms-Frequency locked loops, multi-processor interconnection, optical interconnects, optical resonators.

Abstract:Recently the 2μm wavelength region has emerged as an exciting prospect for the next generation of telecommunications. In this paper we experimentally characterise silicon based plasma dispersion effect optical modulation and defect based photodetection in the 2-2.5μm wavelength range. It is shown that the effectiveness of the plasma dispersion effect is dramatically increased in this wavelength window as compared to the traditional telecommunications wavelengths of 1.3μm and 1.55μm. Experimental results from the defect based photodetectors show that detection is achieved in the 2-2.5μm wavelength range, however the responsivity is reduced as the wavelength is increased away from 1.55μm. Kaertner, and T. M. Lyszczarz, "CMOS-compatible all-Si high-speed waveguide photodiodes with high responsivity in near-infrared communication band," IEEE Photon.

A defect-enhanced silicon photodiode and heater are integrated with and used to thermally stabilize a microring modulator. These optoelectronic components are interfaced with external control circuitry to create a closed-looped feedback system for thermally stabilizing the microring modulator. The thermal stabilization system enables the microring modulator to provide error-free 5-Gb/s modulation while being subjected to thermal fluctuations that would normally render it inoperable.

We have fabricated monolithic silicon avalanche photodiodes capable of 10 Gbps operation at a wavelength of 1550 nm. The photodiodes are entirely CMOS process compatible and comprise a p-i-n junction integrated with a silicon-on-insulator (SOI) rib waveguide. Photo-generation is initiated via the presence of deep levels in the silicon bandgap, introduced by ion implantation and modified by subsequent annealing. The devices show a small signal 3 dB bandwidth of 2.0 GHz as well as an open eye pattern at 10 Gbps. A responsivity of 4.7 ± 0.5 A/W is measured for a 600 µm device at a reverse bias of 40 V.