Optical fiber sensor

An optical fiber sensor fo detecting a change in a transmission parameter of a measuring beam, based on the measuring beam and a reference beam, comprising:

• a single optical fiber capable of transmitting a light beam in two transmission modes having mutually perpendicular polarization planes, such that the polarization planes of said two transmission modes are maintained;
• a light transmitter/receiver portion for generating said light beam for producing said measuring and reference beams and directing said light beam to said optical fiber so that said light beam is transmitted through said optical fiber in one of said two transmission modes in a first direction from a proximal end of the optical fiber to a distal end thereof, said light transmitter/receiver portion being operable to detect said change in said transmission parameter of said measuring beam, based on said measuring and reference beams which have been returned through said optical fiber in said two transmission modes in a second direction from said distal end toward said proximal end;
• a sensor head portion operable to receive said light beam transmitted through said optical fiber in said first direction, and splitting said light beam into said measuring and reference beams, said sensor head portion causing said transmission parameter of at least said measuring beam to be influenced by a change of an external subject, and returning said measuring and reference beams to said light transmitter/receiver portion through said optical fiber in said second direction;
• and
• said sensor head portion including adjusting means for adjusting said measuring and reference beams prior to incidence upon said distal end of said optical fiber, so that the measuring and reference beams are returned through said optical fiber in said second direction in said two transmission modes, as two linearly polarized beams having mutually perpendicular polarization planes and a phase difference of 90.degree..

An optical fiber sensor for detecting a change in a transmission parameter of a measuring beam, based on the measuring beam and a reference beam, comprising:

• a first and a second optical fiber capable of transmitting a light beam;
• a light transmitter/receiver portion for generating said measuring and reference beams and directing the measuring and reference beams to said first and second optical fibers so that the measuring and reference beams are transmitted through said first and second optical fibers, respectively, in a first direction from a proximal end of each of said first and second optical fibers to a distal end of said each optical fiber, said light transmitter/receiver portion being operable to detect said change in said transmission parameter of said measuring beam, based on said measuring and reference beams which have been returned through said second and first optical fibers, respectively, in a second direction from said distal end toward said proximal end;
• a sensor head portion operable to receive said measuring and reference beams transmitted in said first direction through said first and second optical fibers, respectively, and causing said transmission parameter of at least said measuring beam to be influenced by a change of an external subject, said sensor head portion returning said measuring and reference beams to said light transmitter/receiver portion in said second direction through said second and first optical fibers, respectively;
• and
• said sensor head portion including guiding means for directing said measuring and reference beams so that said measuring and reference beams are transmitted through said second and first optical fibers, respectively, in said second direction.