  The WALOP-South instrument will be mounted on the 1 m SAAO telescope in South
Africa as part of the PASIPHAE program to carry out a linear imaging
polarization survey of the Galactic polar regions in the optical band. Designed
to achieve polarimetric sensitivity of $0.05~\%$ across a $35\times35$
arcminute field of view, it will be capable of measuring the Stokes parameters
I, q and u in a single exposure in the SDSS-r broadband and narrowband filters
between $0.5~{\mu}m - 0.7~{\mu}m$. For each measurement, four images of the
full field corresponding to linear polarization angles of 0 deg, 45 deg, 90 deg
and 135 deg in the instrument coordinate system will be created on four
detectors from which the Stokes parameters can be found using differential
photometry. In designing the optical system, major challenges included
correcting for the dispersion introduced by large split angle Wollaston Prisms
used as analysers as well as other aberrations from the entire field to obtain
imaging quality PSF at the detector. We present the optical design of the
WALOP-South instrument which overcomes these challenges and delivers near
seeing limited PSFs for the entire field of view.
