Optimal Filtering of Spatial Modes of Light

A single-mode optical fiber (SMF) acts as an ideal spatial filter, in principle providing 100% transmission of a single mode of light while completely attenuating all other spatial modes. Structured transverse modes of light in general cannot be the fundamental mode of an optical fiber and thus cannot be filtered in this way. We show that a series of lenses and structured masks can act as an efficient mode filter for preparing or detecting arbitrary spatial modes of light, finding near-ideal SMF-like behavior for higher-order Hermite-Gaussian (HG) modes. Other spatial modes, including the simple case of an HG00 mode, are more challenging to filter, requiring a greater number of masks and lenses to achieve a similar degree of undesired mode rejection. We draw parallels between this problem and probabilistic state preparation by quadrature measurement in continuous-variable quantum information processing.

This work is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).