09-07-2011, 03:33 PM
OPTICAL INTERCONNECTS
In order to support the continuing increase in processing capability of integrated circuits and the overall improvement in the performance of digital systems, a commensurate improvement in the capacity of the interconnects in required throughout the hierarchy of the system.A large digital system that is too complex to fit on a single chip must be partitioned into several modules. At different levels of the systems, the modules may consist of individual chips, multi chip modules on entire printed circuit boards. In general, as the processing capability of each module increases, the capacity of the interconnect that connects the module must also increase.The electrical interconnects have many limitations are there are frequency dependent loss, power consumption etc. Thus, optical interconnects is proposed for the purpose. The narrow- band nature of optical signals makes it relatively simple to construct high-quality, uniform transmission lines that operate at high data rates. The narrow-band nature eliminates frequency –dependent loss, also there is no power dissipation associated with it. Parallel optical interfaces can be conceived that consist of arrays of optoelectronic devices of the order of one thousand optical channels each ‘running at speeds around I Gbit/s and hence offering and overall capacity of 1 Gbit/s to a single integrated circuit. Although there are still unresolved difficulties in the areas of architectural design, manufacturing processes, simulation and packaging (as explained later), the technology has now developed to the point that it is possible to contemplate its use in commercial systems within a time-frame of 5-10 years. Fig 1st shows the concept of chip-to-chip communication using optics.The idea of using optical techniques to address the chip-to-chip interconnection problems has been around for a long time. However, it is only in the last few years that technology with a realistic promise of eventual commercial applications has emerged. Progress can be attributed to a shift away from trying to develop custom VSLI techniques with in-built optoelectronic capability, towards developing techniques to allow parallel arrays of separately fabricated optoelectronic devices to be tightly integrated with standard foundry VLSI electronics, e.g. CMOS
In order to support the continuing increase in processing capability of integrated circuits and the overall improvement in the performance of digital systems, a commensurate improvement in the capacity of the interconnects in required throughout the hierarchy of the system.A large digital system that is too complex to fit on a single chip must be partitioned into several modules. At different levels of the systems, the modules may consist of individual chips, multi chip modules on entire printed circuit boards. In general, as the processing capability of each module increases, the capacity of the interconnect that connects the module must also increase.The electrical interconnects have many limitations are there are frequency dependent loss, power consumption etc. Thus, optical interconnects is proposed for the purpose. The narrow- band nature of optical signals makes it relatively simple to construct high-quality, uniform transmission lines that operate at high data rates. The narrow-band nature eliminates frequency –dependent loss, also there is no power dissipation associated with it. Parallel optical interfaces can be conceived that consist of arrays of optoelectronic devices of the order of one thousand optical channels each ‘running at speeds around I Gbit/s and hence offering and overall capacity of 1 Gbit/s to a single integrated circuit. Although there are still unresolved difficulties in the areas of architectural design, manufacturing processes, simulation and packaging (as explained later), the technology has now developed to the point that it is possible to contemplate its use in commercial systems within a time-frame of 5-10 years. Fig 1st shows the concept of chip-to-chip communication using optics.The idea of using optical techniques to address the chip-to-chip interconnection problems has been around for a long time. However, it is only in the last few years that technology with a realistic promise of eventual commercial applications has emerged. Progress can be attributed to a shift away from trying to develop custom VSLI techniques with in-built optoelectronic capability, towards developing techniques to allow parallel arrays of separately fabricated optoelectronic devices to be tightly integrated with standard foundry VLSI electronics, e.g. CMOS