Design and fabrication of a Gaussian fan-out optical interconnect

A phase-retrieval algorithm is described and used to optimize the phase profile of a multilevel phase grating that achieves a two-dimensional Gaussian fan-out. Binary-optics technology is used to fabricate a surface-relief structure that implements this optimized phase profile. The results of the fabrication process are summarized, and the experimental measurements on the fan-out element are presented. Differences between theory and experiment arise from scalar-theory approximations used in the design algorithm. In order to illustrate the scalar-theory limitations, a rigorous formulation is used to analyze the diffraction efficiency and the reconstruction error of a representative binary surface-relief phase grating as a function of the period-to-wavelength ratio. The analysis serves to show qualitatively the effects of the period-to-wavelength ratio on the performance of free-space optical interconnects designed with a scalar-theory formalism.