Attojoule Optoelectronics for Low-Energy Information Processing and Communications: a Tutorial Review (1609.05510v3)

Abstract: Optics offers unique opportunities for reducing energy in information processing and communications while resolving the problem of interconnect bandwidth density inside machines. Such energy dissipation overall is now at environmentally significant levels; the source of that dissipation is progressively shifting from logic operations to interconnect energies. Without the prospect of substantial reduction in energy per bit communicated, we cannot continue the exponential growth of our use of information. The physics of optics and optoelectronics fundamentally addresses both interconnect energy and bandwidth density, and optics may be the only scalable solution to such problems. Here we summarize the corresponding background, status, opportunities, and research directions for optoelectronic technology and novel optics, including sub-femtojoule devices in waveguide and novel 2D array optical systems. We compare different approaches to low-energy optoelectronic output devices and their scaling, including lasers, modulators and LEDs, optical confinement approaches (such as resonators) to enhance effects, and the benefits of different material choices, including 2D materials and other quantum-confined structures. Beyond the elimination of line charging by the use optical connections, the next major interconnect dissipations are in the electronic circuits for receiver amplifiers, timing recovery and multiplexing. We can address these through the integration of photodetectors to reduce or eliminate receiver circuit energies, free-space optics to eliminate the need for timing and multiplexing circuits (while solving bandwidth density problems), and using optics generally to save power by running large synchronous systems. One target concept is interconnects from ~ 1 cm to ~ 10 m that have the same energy (~ 10fJ/bit) and simplicity as local electrical wires on chip.

• The paper demonstrates how integrating optical interconnects can achieve attojoule-level energy reductions, addressing the energy challenges in modern computing.
• It outlines novel methodologies using lasers, modulators, and resonators to leverage quantum impedance conversion and precise timing.
• It offers actionable research directions for utilizing emerging materials and nanoscale technologies to enhance energy efficiency and bandwidth density.

Attojoule Optoelectronics for Low-Energy Information Processing and Communications

The paper "Attojoule Optoelectronics for Low-Energy Information Processing and Communications" by David A. B. Miller explores the potential of optics to significantly lower energy consumption in information processing and communications. As the energy demands of these technologies grow, reducing energy per bit is crucial to sustaining their growth and avoiding environmental impacts. This tutorial review provides in-depth analysis, technological implications, and future research directions in optoelectronics, offering solutions that address both energy and bandwidth density issues.

Current computing systems are facing severe energy efficiency challenges, particularly in the domain of interconnects, which now surpass logic operations as primary energy consumers in systems. Notably, up to 80% of energy within electronics on silicon chips is used for inter- and intra-chip communication. The transition from high-energy electrical interconnects to low-energy optical ones presents a compelling opportunity to curtail this trend. Optoelectronics, with its minimal line charging dissipation and substantial potential for reducing interconnect energy, emerges as a promising solution, particularly as the potential to improve electrical options diminishes.

The paper emphasizes the immense role optics could play by presenting several technologically viable approaches, including lasers, modulators, and LEDs. With innovations such as sub-femtojoule (attojoule) devices and integrated optoelectronics, optics offers an escape from current energy constraints. Leveraging optical confinement through resonators and exploring new materials, such as two-dimensional quantum-confined structures, can further optimize energy efficiencies.

Analyses within the review identify two fundamental benefits optics provides: quantum impedance conversion and exceptional timing precision. These allow for significant system simplifications, enabling energy-efficient synchronous system operations even over extended distances. By focusing on optical techniques for clock delivery and re-timing via optical pulses, optics could eliminate energy-intensive electronic circuitry like line coding, CDR, and SERDES, which are traditionally used to manage timing inaccuracies in electrical interconnections.

Practical implementations suggest the use of free-space optical systems for high-density chip interconnections, which can handle multiple channels through advanced optics like Dammann gratings. Simulation and example calculations propose a realistic approach to realizing densely packed arrays with scale-specific adjustments, underscoring scalability and addressing manufacturing challenges.

Miller's work highlights the feasibility of achieving substantial attojoule optoelectronic energy reductions. It critically notes that without integrating optics, the desired exponential growth in information usage may be unattainable due to the unsustainable energy demands of traditional electronics. Future research, driven by advances in nanoscale integration, photodetector design, and efficient mode coupling, is expected to push the boundaries of current optoelectronic technologies, driving them closer to mainstream adoption.

In conclusion, this detailed examination not only addresses the theoretical and practical aspects of optoelectronics but also suggests a strategic direction for research, underpinning the necessity of optics in resolving intrinsic energy challenges in burgeoning digital information systems. Through concerted efforts to overcome technical barriers, optics can be a transformative force in the continuation of Moore's Law and the sustainable advancement of technological infrastructures.