Method and apparatus for modulating an optical signal using polarization

The invention is directed toward the field of optical communications, and more particularly, to a method and apparatus for modulating an optical communication signal using a magnetic field to adjust polarization properties. A low-rate data transmission system and method are disclosed that use the Faraday effect to modulate the polarization state of light traveling in an optical fiber. The resulting change in polarization is used to communicate information over the fiber. The low-rate data transmission system includes a low-rate signal source producing current in a wire coil wrapped around an optical fiber. Information is conveyed in accordance with the present invention by the selectively introducing a polarization change into the light carried by the fiber. Generally, the source light at the input of the optical fiber can be randomly polarized and information is conveyed in accordance with the present invention by the presence or absence of a predefined polarization introduced into the light. The longitudinal magnetic field produced by a current in the coil rotates the plane of polarization of the light, in accordance with the well-known Faraday effect. When the current in the coil is modulated by the signal source, the resulting change in polarization communicates information over the fiber.