The set of paraxial optical systems is the manifold of the group of symplec
tic matrices. The structure of this group is nontrivial: It is not simply c
onnected and is not of an exponential type. Our analysis clarifies the orig
in of the metaplectic phase and the inherent limitations for optical map fr
actionalization. We describe, for the first time to our knowledge, an image
girator and a cross girator whose geometric and wave implementations are o
f interest. (C) 2000 Optical Society of America [S0740-3232(00)00102-2] OCI
S codes: 080.2730, 000.3870.