Optical fiber sensor

Abstract

An optical fiber sensor including an optical fiber for transmitting first and second linearly polarized laser beams in respective two modes having mutually perpendicular polarization planes, a light transmitter/receiver portion for producing the linearly polarized beams having different frequencies, and directing the beams to the optical fiber for propagation of the beams toward a distal end of the fiber, and a sensor head portion optically connected to the distal end of the fiber. The transmitter/receiver portion receives a reference and a measuring beam which have been returned through the fiber. The head portion receives the first and second beams from the distal end of the fiber, and splits the received beams into the reference and measuring beams, such that each of the reference and measuring beams consists of two components having mutually perpendicular polarization planes. The head portion causes at least the measuring beam to be influenced by an external subject, combines the reference and measuring beams, and returns the combined beams to the transmitter/receiver portion. The head portion includes a device for rotating by 90 degrees the polarization planes of the two components of one of the reference and measuring beams, in opposite directions, before the reference and measuring beams are combined and returned in the second direction.