Optical interconnect

Abstract: In this paper III-V on silicon-on-insulator (SOI) het- erogeneous integration is reviewed for the realization of near infrared light sources on a silicon waveguide platform, suitable for inter-chip and intra-chip optical interconnects. Two bonding technologies are used to realize the III-V/SOI integration: one based on molecular wafer bonding and the other based on DVS- BCB adhesive wafer bonding. The realization of micro-disk lasers, Fabry-Perot lasers, DFB lasers, DBR lasers and mode- locked lasers on the III-V/SOI material platform is discussed. Artist impression of a multi-wavelength laser based on micro- disk cavities realized on a III-V/SOI heterogeneous platform and a microscope image of a realized structure.

Abstract: Optical fiber links have become ubiquitous for links at the metropolitan and wide area distance scales, and have become common alternatives to electrical links in local area networks and cluster networks. As optical technology improves and link frequencies continue to increase, optical links will be increasingly considered for shorter, higher-bandwidth links such as I/O, memory, and system bus links. For these links closer to processors, issues such as packaging, power dissipation, and components cost assume increasing importance along with link bandwidth and link distance. Also, as optical links move steadily closer to the processors, we may see significant differences in how servers, particularly high-end servers, are designed and packaged to exploit the unique characteristics of optical interconnects. This paper reviews the various levels of a server interconnect hierarchy and the current status of optical interconnect technology for these different levels. The potential impacts of optical interconnect technology on future server designs are also reviewed.

Abstract: One of the current challenges in photonics is developing high-speed, power-efficient, chip-integrated optical communications devices to address the interconnects bottleneck in high-speed computing systems. Silicon photonics has emerged as a leading architecture, in part because of the promise that many components, such as waveguides, couplers, interferometers and modulators, could be directly integrated on silicon-based processors. However, light sources and photodetectors present ongoing challenges. Common approaches for light sources include one or few off-chip or wafer-bonded lasers based on III-V materials, but recent system architecture studies show advantages for the use of many directly modulated light sources positioned at the transmitter location. The most advanced photodetectors in the silicon photonic process are based on germanium, but this requires additional germanium growth, which increases the system cost. The emerging two-dimensional transition-metal dichalcogenides (TMDs) offer a path for optical interconnect components that can be integrated with silicon photonics and complementary metal-oxide-semiconductors (CMOS) processing by back-end-of-the-line steps. Here, we demonstrate a silicon waveguide-integrated light source and photodetector based on a p-n junction of bilayer MoTe2, a TMD semiconductor with an infrared bandgap. This state-of-the-art fabrication technology provides new opportunities for integrated optoelectronic systems.

Abstract: An architectural approach for very-high-capacity wide-area optical networks is presented, and a proposed program of research to address key system and device issues is described. The network is based on dense multiwavelength technology and is scalable in terms of the number of networked users, the geographical range of coverage, and the aggregate network capacity. Of paramount importance to the achievement of scalability are the notions of wavelength reuse and wavelength translation. A distributed optical interconnect that is wavelength-selective and electronically controllable, permitting the same limited set of wavelengths to be reused among other access stations, is employed. By exercising the wavelength-selective switches, the wavelength-routed connectivity between stations can be reconfigured as needed. A multihop overlay network involving wavelength translation and self-routing fast packet switches permits full connectivity, if desired among the access stations at the individual virtual circuit level. Using just eight wavelengths, such a network could in principle interconnect a population of 100 million users over a nationwide geography with an expected delay equal to that of 12 hops. >