Architectural approach to nanophotonics for information and communication systems

Abstract

To accommodate the continuously growing amount of digital data handled in information and communications systems [1], optics is expected to play a wider role in enhancing the overall system performance by performing certain functional behavior [2] in addition to merely serving as the communication medium. In this regard, for example, so-called all-optical packet switching has been thoroughly investigated. Also, the application of inherent optical features, such as parallelism, in computing systems has been investigated [3,4]. However, many technological difficulties remain to be overcome in order to adopt optical technologies in critical information and communication systems: one problem is the poor integrability of optical hardware due to the diffraction limit of light, which is much larger than the gate width in VLSI circuits, resulting in relatively bulky hardware configurations. Nanophotonics, on the other hand, which is based on local electomagnetic interactions between nanometer-scale elements, such as quantum dots, via optical near fields, provides ultra high-density integration since it is not constrained by the diffraction limit of light [5]. From an architectural perspective, this drastically changes the fundamental design rules of functional optical systems. Consequently, suitable architectures may be built to exploit this capability of the physical layer. In this chapter, we approach nanophotonics from a system architecture perspective, considering the unique physical principles provided by optical near-field interactions and the functionality required for practical applications. This chapter deals with two architectures utilizing several physical properties provided by nanophotonics. First in Sect. 2, we discuss a memory-based architecture in which a large lookup table is recorded by configuring the size and positions of quantum dots, as well as individually implementing the required logical operation mechanisms for each table entry. Two basic functions are derived from this architecture. One is a data gathering, or summation, mechanism suitable for similarity evaluation, which is discussed in Sect. 3. [Image presented] As an extension of this summation architecture, Sect. 3 also discusses digitalto-analog conversion by configuring the coupling strength between QDs. The other basic function is broadcasting where query data is distributed to multiple table entries, as described in Sect. 4. We present enabling architectures by appropriate use of resonant energy levels between quantum dots and inter-dot interactions via optical near-fields that are forbidden for far-field light. Experimental results are also shown using CuCl quantum dots. In Sect. 5, we discuss hierarchical systems that use the different natures of light exhibited in optical near fields and far fields. The overall structure of this chapter is outlined in Fig. 1. Through such architectural and physical insights, we seek nanophotonic information and communications systems that can overcome the integrationdensity limit imposed by the diffraction limit of light with ultralow-power operation as well as unique functionalities which are only achievable using optical near-field interactions.