ABSTRACT
The field of optical signal processing has had a long and checkered history. Decades of research have been devoted to photonic implementation of either analog or digital models of computation, yet neither approach has been scalable to complex computational systems. Optical logic devices, such as the self-electro-optic-effect device (SEED) [1], were investigated with the goal of making self-contained, optical computing systems. Neural-inspired systems soon followed, based on using vertical light-emitting lasers or spatial light modulators together with free-space holographic routing (i.e., [2–5]). Many researchers imagined an optical computer would look much like the picture illustrated in Fig. 14.1(a), in which a three-dimensional holographic cube would be programmed to route signals between arrays of light-emitting devices. Although optical logic devices later developed into the switches/routers that form our telecommunications infrastructure today, optical computing did not achieve the same level of success. Researchers realized that electronic scaling laws could continue to address interconnectivity and speed bottlenecks in traditional processors for many years to come. The ceaseless march of Moore’s law meant that even if optical computing systems displayed a significant advantage over their electronic counterparts, the latter would soon be able to match and then exceed their performance in just a couple years. Neural-inspired photonic systems. (a) Initially, researchers believed that optical neural computers would involve the use of holography and free space optics to implement interconnects (reproduced from <xref ref-type="bibr" rid="ref14_5">[5]</xref>). Unfortunately, this vision did not pan out. (b) A renewed take at the problem involves an on-chip implementation with optical waveguides, microring filters, lasers/modulators, and electronic control systems as described here. This approach uses wavelength division multiplexing (WDM) to superimpose many virtual interconnections between processors. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315370590/694adb39-a3ab-4859-b5dd-cd1ca150afbf/content/fig14_1.tif"/>
