Temperature-compensated fiber optic external cavity strain sensors and an intensity-based fiber optic sensor system

A temperature compensated fiber optic sensor for measuring strain in a host structure, comprising:

• an elongated optical fiber having a first flat end comprising a reflecting surface;
• an elongated wire having a first flat end comprising a reflecting surface;
• a connecting sleeve for connecting said optical fiber with said elongated wire such that said first end of said optical fiber is in spaced, facing and parallel relationship with said first end of said elongated wire to define a gap D between said ends, said connecting sleeve being bonded to said host structure;
• a capillary tube encasing that part of the sensor comprising the elongated wire;
• said capillary tube being sealed at one end and being bonded, at its other end, at a capillary wire bonding point to said connecting sleeve;
• said optical fiber being bonded to said connecting sleeve at an optical fiber bonding point spaced from said first end of said optical fiber;
• said capillary tube bonding point being spaced from said optical fiber bonding point by a distance L comprising the sensor length;
• said elongated wire being bonded to said connecting sleeve at an elongated wire bonding point spatted from said first end of said elongated wire;
• said elongated wire bonding point being spaced from said first end of said elongated wire by a distance L.sub.w comprising the wire length of said sensor;
• the material of said wire being selected such that:
• C.sub.host L=C.sub.wire L.sub.w
• wherein:
• C.sub.host =thermal expansion coefficient of said host structure;
• and
• C.sub.wire =thermal expansion coefficient of said elongated wire.

A temperature compensated fiber optic sensor for measuring strain in a host structure, comprising:

• an elongated optical fiber having a first flat end comprising a reflecting surface;
• an elongated wire having a first flat end comprising a reflecting surface;
• a connecting sleeve for connecting said optical fiber with said elongated wire such that said first end of said optical fiber is in spaced, facing and parallel relationship with said first end of said elongated wire to define a gap D between said ends, said connecting sleeve being bonded to said host structure;
• wherein, the reflecting surface of said elongated wire comprises a temperature sensitive reflector.

A temperature compensated fiber optic sensor for measuring strain in a host structure, comprising:

• an elongated single mode optical fiber having a first flat end comprising a bandpass filter;
• an elongated wire having a first flat end comprising a reflecting surface;
• and
• a connecting sleeve for connecting said optical fiber with said elongated wire such that said first end of said optical fiber is in spaced, facing and parallel relationship with said first end of said elongated wire to define a gap between said ends, said connecting sleeve being bonded to said host structure.

A method of sensing strain or temperature comprising the steps of:

• i) providing a temperature compensated fiber optic sensor, comprising an elongated optical fiber having a first flat end comprising a bandpass filter, an elongated wire having a first flat end comprising a reflecting surface, and a connecting sleeve for connecting said optical fiber with said elongated wire such that said first end of said optical fiber is in spaced, facing and parallel relationship with said first end of said elongated wire to define a gap between said ends, said connecting sleeve being bonded to said host structure;
• ii) connecting a broadband light source to said optical fiber to direct light to said sensor;
• iii) splitting return light from said single mode fiber to feed two opto-detectors;
• and
• iv) detecting spectral changes in said sensor by analyzing and processing information signals received from said opto-detectors.