  We propose a compact snapshot monocular depth estimation technique that
relies on an engineered point spread function (PSF). Traditional approaches
used in microscopic super-resolution imaging such as the Double-Helix PSF
(DHPSF) are ill-suited for scenes that are more complex than a sparse set of
point light sources. We show, using the Cram\'er-Rao lower bound, that
separating the two lobes of the DHPSF and thereby capturing two separate images
leads to a dramatic increase in depth accuracy. A special property of the phase
mask used for generating the DHPSF is that a separation of the phase mask into
two halves leads to a spatial separation of the two lobes. We leverage this
property to build a compact polarization-based optical setup, where we place
two orthogonal linear polarizers on each half of the DHPSF phase mask and then
capture the resulting image with a polarization-sensitive camera. Results from
simulations and a lab prototype demonstrate that our technique achieves up to
$50\%$ lower depth error compared to state-of-the-art designs including the
DHPSF and the Tetrapod PSF, with little to no loss in spatial resolution.
