Dynamic control of polarization mismatch and coma aberrations in rod-GRIN assemblies

We describe the use of stacked electrically tunable liquid crystal lenses (TLCLs), along with rod gradient index (GRIN) fixed focus lenses, for endoscopic applications. Architectural and driving conditions are found for the optimization of total aberrations of the assembly. Particular attention is devoted to the coma and polarization aberrations. The coma aberration is reduced by stacking two TLCLs with "opposed" pre-tilt angles (all molecules are in the same plane), and then two such doublets are used with cross oriented molecules (in perpendicular planes) to reduce the polarization dependence. The obtained adaptive rod-GRIN lens enables a focus scan over 80μm (with exceptionally low RMS aberrations ≤0.16μm), making possible the high-quality observation of neurons at various depths.