Easy-to-build Wollaston-like polarization splitter with adjustable beam deviation and tunable chromatic dispersion
Two hundred years after its invention, the Wollaston polarizing beamsplitter has a new and enticing competitor. The key feature of the Wollaston is the small symmetrical splitting angle, which enables, for example, polarization analysis of an image onto a single detector array. But it is indispensable for polarizing interferometry in techniques such as differential interference contrast microscopy or snapshot Fourier-transform spectrometry. Acher and Richard report how two commercial geometric-phase lenses (GPLs) can be combined to yield Wollaston-like beamsplitting, but with the added advantage of a variable splitting angle. The low-cost GPL is a planar structure which diffracts light into two orthogonally polarized focused beams, but when used in pairs, collimated light is diffracted into two collimated beams with a divergence angle that can be tuned by varying the separation of the GPL centers. This provides a new flexibility for agile and compact manipulation and interferometry with polarized light. The high diffractive dispersion may not be attractive for some broadband applications, but this new functionality may provide inspiration for new methods for spectro-polarimetric optical manipulation.