A device functions as a polarization beam combiner and an isolator. When light
is transmitted in a first propagation direction, a second beam is displaced towards
a first beam. The second beam has a polarization orthogonal to the polarization
of the first beam, and the second beam is substantially parallel to the first beam.
The polarizations of the first and second beams are rotated by a same first amount
in a first rotation direction and then rotated by the same first amount in a second
opposite rotation direction. The first and second beams are combined by displacing
the second beam towards the first beam. The combined beam is polarized along a
first plane and second plane, which is orthogonal to the first plane. When light
is transmitted in a second opposite propagation direction, the device is used to
provide optical isolation.
