Operation of modern-day technology requires an ever-increasing use of broadband frequency signals. This, in turn, has grown the demand for reliable, efficient methods of signal transmission that prevent interference and are more efficient in their use of the scarcely available frequency spectrum. These requirements are constrained, however, by reciprocity–a law of physics that forces the transmission of light to be identical in opposite directions.

Expansion of urban, suburban and exurban land in the United States over the past several decades has led to neighborhoods in very different parts of the country featuring patterns of roads, residential lots, commercial areas and aquatic features that are more similar to each other than the native ecosystems they replaced.