  The Stokes-parameter operators and the associated Poincare sphere, which
describe the quantum-optical polarization properties of light, are defined and
their basic properties are reviewed. The general features of the Stokes
operators are illustrated by evaluation of their means and variances for a
range of simple polarization states. Some of the examples show polarization
squeezing, in which the variances of one or more Stokes parameters are smaller
than the coherent-state value. The main object of the paper is the application
of these concepts to bright squeezed light. It is shown that a light beam
formed by interference of two orthogonally-polarized quadrature-squeezed beams
exhibits squeezing in some of the Stokes parameters. Passage of such a primary
polarization-squeezed beam through suitable optical components generates a pair
of polarization-entangled light beams with the nature of a two-mode squeezed
state. The use of pairs of primary polarization-squeezed light beams leads to
substantially increased entanglement and to the generation of EPR-entangled
light beams. The important advantage of these nonclassical polarization states
for quantum communication is the possibility of experimentally determining all
of the relevant conjugate variables of both squeezed and entangled fields using
only linear optical elements followed by direct detection.
