An optical fiber has an absorbing jacket to absorb cladding modes in a very short distance along the optical fiber to prevent cladding modes from having a significant affect upon signal quality. The absorbing jacket cooperates with a form birefringent polarizing fiber, which radiates light of one polarization out of the core into the cladding, to provide light of a single polarization suitable for use in fiber optic sensing systems and communications systems whose operational characteristics are polarization dependent.