Interconnect technology has been progressed at a very fast pace for the past decade. The signaling rates have steadily increased from 100:Mb/s to 25Gb/s. In every generation of interconnect technology evolution, optics always seems to take over at first, however, at the end, the cost advantage of copper wins over. Because of this, optical interconnects are limited to longer distance links where the attenuation in copper cable is too large for the integrated circuits to compensate. Optical interconnect has long been viewed as the premier solution in compared with copper interconnect. With the release of Thunderbolt technology, we are entering a new era in consumer electronics that runs at 10Gb/s line rate (20Gb/s throughput per connector interface). Thunderbolt interconnect technology includes both active copper cables and active optical cables as the transmission media which have very different physical characteristics. In order for optics to succeed in consumer electronics, several technology hurdles need to be cleared. For example, the optical cable needs to handle the consumer abuses such as pinch and bend. Also, the optical engine used in the active optical cable needs to be physically very small so that we don't change the looks and feels of the cable/connector. Most importantly, the cost of optics needs to come down significantly to effectively compete with the copper solution. Two interconnect technologies are compared and discussed on the relative cost, power consumption, form factor, density, and future scalability.
The package integration of optical components with electronic integrated circuits
(ICs) for optical interconnects is a subject of much debate and will, to a large extent,
determine the performance of the optical interconnect system. In this paper we examine
the challenges of incorporating optical interconnects into a computer system; specifically
we cover several ways to integrate the optical components with a central processing
unit (CPU) or chipset.
Critical performance parameters such as the supported distance, power
consumption and the achievable bandwidth are all impacted by the electrical integration
between the IC and the optical components. Additional electrical link issues which also
have a large impact on the performance of the link will be discussed as well; these include
protocol related issues as well as signal integrity concerns, such as the jitter budget.
We will also discuss the performance of some of the competing electrical
technologies in order to provide a better understanding of the implementation challenge
facing the developers of optical interconnect technology. Rack to rack communications
are quickly moving to optical links, board to board communication is the next step and chip
to chip communication is still further out as the electrical solutions for this topology have a
great deal of headroom.