The various arguments for introducing optical interconnections to silicon CMOS chips are summarized, and the challenges for optical, optoelectronic, and integration technologies are discussed. Optics could solve many physical problems of interconnects, including precise clock distribution, system synchronization (allowing larger synchronous zones, both on-chip and between chips), bandwidth and density of long interconnections, and reduction of power dissipation. Optics may relieve a broad range of design problems, such as crosstalk, voltage isolation, wave reflection, impedence matching, and pin inductance. It may allow continued scaling of existing architectures and enable novel highly interconnected or high-bandwidth architectures. No physical breakthrough is required to implement dense optical interconnects to silicon chips, though substantial technological work remains. Cost is a significant barrier to practical introduction, though revolutionary approaches exist that might achieve economies of scale. An Appendix analyzes scaling of on-chop global electrical interconnects, including line inductance and the skin effect, both of which impose significant additional constraints on future interconnects.

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Rationale and challenges for optical interconnects to electronic chips

Nonlinear Optical Crystals: A Complete Survey

Conditions are determined for which optical interconnects can transmit information at a higher data rate and consume lc3s power than the equivalent electrical interconnections. The analysis is performed for free-space optical intrachip communication links. Effects of scaling circuit dimensions, presence of signal fan-out, and the use of light modulators as optical signal transmitters are also discussed.

Comparison between optical and electrical interconnects based on power and speed considerations

In this review paper, we present radiation effects on silica-based optical fibers. We first describe the mechanisms inducing microscopic and macroscopic changes under irradiation: radiation-induced attenuation, radiation-induced emission and compaction. We then discuss the influence of various parameters related to the optical fiber, to the harsh environments and to the fiber-based applications on the amplitudes and kinetics of these changes. Then, we focus on advances obtained over the last years. We summarize the main results regarding the fiber vulnerability and hardening to radiative constraints associated with several facilities such as Megajoule class lasers, ITER, LHC, nuclear power plants or with space applications. Based on the experience gained during these projects, we suggest some of the challenges that will have to be overcome in the near future to allow a deeper integration of fibers and fiber-based sensors in radiative environments.

Radiation Effects on Silica-Based Optical Fibers: Recent Advances and Future Challenges

This is a board to transport and convert optical outgoing free-space signals from a spatial light modulator which comprises: at least one detector to process the outgoing free-space signal; at least one signal transmitter to process the outgoing free-space signal; and at least one outgoing optical signal carrier to carry a converted outgoing signal. Other methods and devices are disclosed.

Optical signal free-space conversion board

This paper introduces new applications and design trade-offs anticipated for free-space optical interconnections of VLSI chips. New implementation s of VLSI functions are described that use the capability of making optical inputs at any point on a chip and take advantage of greater flexibility in on-chip signal routing. These include n-port addressable memories, CPU clock phase distribution, hardware multipliers, and dynamic memory refresh, as well as enhanced testability. Fault tolerance and production yields may be improved by reprogramming the optical imaging system to circumvent defective elements. These attributes, as well as those related to performance alone, will affect the design methodology of future VLSI ICs. This paper focuses on identifying the design issues, their possible solutions, and their impact on VLSI design techniques and, finally, presents some preliminary measurements on various system components.

Holographic optical interconnects for VLSI

Strain-free electro-optic effect in single crystal barium titanate as function of temperature between 10 and 120 degrees C

The Strain-Free Electro-Optic Effect in Single-Crystal Barium Titanate

The design of a dc electric field meter capable of measuring the magnitude and direction of the electric field at an arbitrary location above the ground plane is described. The meter is based on measuring induced charge on a split cylindrical electrode pair which is rotated around its axis of symmetry. Data readout is by fiber-optic cable using pulse frequency encoding. The sensing head is electrically isolated. Initial results are reported from a series of tests at General Electric's High Voltage Transmission Research Facility, Pittsfield, MA. The electric field was measured in a large test cage and under a dc test line. Measurement of field magnitude and direction around a human subject standing under the conductor was demonstrated.

dc electric field meter with fiber‐optic readout

Results are presented concerning the effects of temperature on the transmission properties of various optical fibers including a silicone plastic clad, an acrylic plastic clad, and CVD step-index fibers both with and without polyurethane jackets Results are presented for the normalized transmitted power vs temperature, the index of refraction vs temperature, and induced attenuation coefficients vs temperature The data show that the intrinsic transmission of a CVD fiber is independent of temperature over the -110 to +150 C range Plastic clad fused silica fibers are subject to transmission losses at lower temperatures due to changes in the optical index of the cladding polymer Acrylic-clad and plastic-clad silica fibers also show transmission losses at lower temperatures, but to lesser extents

Effect of temperature on optical fiber transmission

A semiconductor laser diode was mode locked in an external cavity when synchronously pumped with 90-ps current pulses. Transform-limited optical pulses with a 10-ps pulse width and a peak power of 160 mW were produced. Operating characteristics of such a system are described.

Alan R. Johnston

Papers

Holographic optical interconnects for VLSI

The Strain-Free Electro-Optic Effect in Single-Crystal Barium Titanate

dc electric field meter with fiber‐optic readout

Effect of temperature on optical fiber transmission

Picosecond pulse generation from a synchronously pumped mode‐locked semiconductor laser diode