Optical waveguides – With optical coupler – Switch
Patent
1998-02-17
2000-03-21
Ngo, Hung N.
Optical waveguides
With optical coupler
Switch
359252, 359253, G02B 626
Patent
active
060411511
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The combination of decreasing feature sizes and increasing chip sizes is leading to a communication crisis in the area of VLSI circuits and systems. It is generally realized that the exponential growth of semiconductor chip capabilities cannot continue indefinitely, and that fundamental limits exist. These limits arise not from difficulties associated with the reduction of gate areas and delays, but rather from the difficulties associated with the interconnections as dimensions are scaled downward and chip areas continue to increase. It is anticipated that the speeds of semiconductor circuits will soon be limited by the interconnection delays, rather than gate delays. Furthermore, the trend of increasing bit-rate introduces problems in conductor design, as the conductors must be treated as transmission lines for high frequencies. This problem has been designated as the communication bottleneck, and is affecting wide-bandwidth switching systems and high-throughput computer system architectures.
Improvements in manufacturing processes and material handling have allowed a constant reduction of feature sizes in integrated circuits. Additionally the number of transistors in application designs has increased steadily. As further chip integration and complexity is obtained, the chip I/O demand increases. Such high I/O densities become difficult with current bonding techniques such as solder bump bonding.
As the number of components and connections of systems increase, the difficulty in assembling and maintaining these systems increases too. Systems become impractical or excessively expensive to build. One problem encountered is the bandwidth required to move data between subsystems. Sufficient bandwidth cannot be supported by state of the art interconnection technology. One example is the lack of sufficient bandwidth on backplanes to support large broadband switching systems. One approach is to demultiplex high bandwidth signals to multiple lower bandwidth signals. However, if connections are to be maintained at their original rate, the designer is faced with maintaining the transmission line integrity from printed circuit board to printed circuit board. This is normally achieved by designing a backplane, circuit cards and connectors that are transmission lines. However, there is a limit to the number of connections that can be made this may.
Another disadvantage of electrical interconnection technology is excessive crosstalk. Any current flowing in a conductor induces a magnetic field. The result of this magnetic field is inductive coupling, and electrons in adjacent conductors will travel with this field and set currents circulating in the conductors. Capacitive coupling between striplines also causes crosstalk. To alleviate this problem, the electrical interconnection must be set at a distance large enough to prevent this signal from having any effect on system performance. This creates fundamental rules for circuit routing. Furthermore, electrical interconnect paths must reside near a ground plane to ensure that stray electric fields are properly terminated.
Electrical interconnections suffer from an additional problem of sensitivity to external electromagnetic interference. The fields that reside in the vicinity of the interconnection lines induce currents in them, causing erroneous signals in the lesser case to circuit damage in the worst case. Designers must shield integrated circuits by using conducting envelopes to prevent any field from entering the shielded volume. Special interconnection line design is required for lines that connect any shielded circuits. Shielding also worsens the problem of heat removal in the circuit, as ventilation is restricted.
Optical interconnections, rather than electrical, offer a solution to the problems plaguing conventional electrical interconnections. For example, optical interconnections offer a freedom from mutual coupling effects (i.e., cross talk) not afforded by conventional electronic interconnects. In addition, they offer in
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Marom Dan M.
Mendlovic David
Friedman Mark M.
Ngo Hung N.
Ramot University Authority for Applied Research & Industrial Dev
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