  By considering gauge transformations on the macroscopic Maxwell's equations,
a two dimensional gauge field, with its pseudo magnetic field in the real
space, is identified as tilted anisotropy in the constitutive parameters. We
show that optical spin Hall effect and one-way edge states become possible
simply by using anisotropic media with broadband response. The proposed gauge
field also allows us to design an optical isolator based on the Aharonov-Bohm
effect. Our approach will be useful in spoof magneto-optics with arbitrary
magnetic fields mimicked by metamaterials with subwavelength unit cells. It
also serves as a generic way to design polarization-dependent devices.
