  The spin Hall effect of light, a spin-dependent transverse splitting of light
at an optical interface, is intrinsically an incident-polarization-sensitive
phenomenon. Recently, an approach to eliminate the polarization dependence by
equalizing the reflection coefficients of two linear polarizations has been
proposed, but is only valid when the beam waist is sufficiently larger than the
wavelength. Here, we demonstrate that an interface, at which the reflection
coefficients of the two linear polarizations are the same and so are their
derivatives with respect to the incident angle, supports the
polarization-independent spin Hall shift, even when the beam waist is
comparable to the wavelength. In addition, an isotropic-anisotropic interface
that exhibits the polarization-independent spin Hall shift over the entire
range of incident angles is presented. Monte-Carlo simulations prove that spin
Hall shifts are degenerate under any polarization and reaches a half of beam
waist under unpolarized incidence. We suggest an application of the
beam-waist-scale spin Hall effect of light as a tunable beam-splitting device
that is responsive to the incident polarization. The spin Hall shift that is
independent of the incident polarization at any incident angle will facilitate
a wide range of applications including practical spin-dependent devices and
active beam splitters.
