High-rate data buffering in silicon nanophotonic devices

Abstract

Buffers represent one of the most important components in a communications router. The device must be able to store data packets for a substantial period of time and release the data within an acceptable delay when the switch is clear. Optical buffers—devices that store optically transmitted data—are considered key elements to achieve synchronized and contention-free traffic in the design of all-light-based communication networks. Conventional buffers use optical fiber delay lines, but since the delay is for a fixed amount of time, they are unable to guarantee contention-free connections in the switch or through a network. Hence, research on tunable optical delay lines is generating significant interest, especially with optical communications now gearing up for large-scale integration. Advances in silicon technology are making this material a choice candidate for future integrated photonics. On-chip delay lines based on silicon-on-insulator (SOI) photonic wire waveguides were recently demonstrated, consisting of up to 100 microring resonators cascaded in either coupled-resonator or all-pass filter (APF) configurations with error-free operation up to 5Gbps.1 This demonstration was a major milestone in the development of all-optical buffers for interconnects. Tunable delays in an SOI planar waveguide based on slow light induced by stimulated Raman scattering (SRS) have also been reported,2 as well as intensity-tunable group delays in siliconmicroresonators enhanced by SRS.3 The functional mechanism of a ring resonator-based optical delay line can be described as follows: When a probe beam is injected into a ring with a frequency matching the resonance of the ring, light is forced to circle multiple times, lengthening the delay. If beam frequency deviates from resonance, it will bypass the ring and no delay will occur. When a pump light, whose frequency is of a different resonance, is injected into the microring resonator, the absorbed energy is eventually converted to therFigure 1. (a) Scanning electron microscope image of a microring resonator and (b) its resonance spectrum.