Integrated Free Space-Optical Permutation Network

Permutation networks such as the Perfect Shuffle, the Banyan, and the Crossover network can be used in optical computing or photonic switching to implement parallel algorithms efficiently [1]. Many different implementations for these various networks have been proposed recently; see for example [2-4]. A very flexible way of implementing space-variant permutation networks is by using diffracitve lenslet arrays [5, 6]. The basic concept is to give each optical channel its own miniaturized optical system, consisting typically of two diffractive off-axis lenslets. By controling the angle under which the light beams travel, it is possible to realize arbitrary interconnect schemes. The optical setup for this is shown in Figure 1. Using lithographic techniques, all components in an array can be fabricated at the same time with high alignment precision. In order to achieve high efficiencies diffractive optical elements can be implemented as phase structures with multiple discrete phase levels [7, 8]. A 2-D cyclic shifter was demonstrated recently using lithographically fabricated lenslet arrays [9]. An experimental result is shown in Fig. 2.