C. E. Lee

Optical-fiber Fabry-Perot embedded sensor

A reflectively monitored optical-fiber Fabry-Perot interferometer was embedded in a graphite-epoxy composite material. Its performance as a temperature sensor was demonstrated from 20 to 200 degrees C. The change in relative phase shift with temperature, Deltaø/øDeltaT, was measured to be 8.0 x 10(-6)/ degrees C for this embedded sensor. This value is 4% lower than for one employing a similar fiber in an air ambient. A thermal expansion coefficient for the composite material in the direction of the fiber axis is estimated from these data to be 2.1 x 10(-7)/ degrees C.

Performance of a fiber-optic temperature sensor from −200 to 1050°C

A reflectively monitored Fabry-Perot temperature sensor is characterized over a 1250 degrees C temperature range. Dielectric mirrors for the interferometer are incorporated into a continuous length of single-mode fiber by a fusionsplicing technique. The change in optical phase per unit temperature is nearly constant above room temperature but decreases at lower temperatures. Phase-shift data for the germania-doped silica fiber used in these experiments are compared with calculations based on previously reported information on the temperature dependence of refractive index and length in bulk fused silica.

FIBER-OPTIC PRESSURE SENSORS FOR INTERNAL COMBUSTION ENGINES

Two designs incorporating embedded fiber Fabry-Perot interferometers as strain gauges were used for monitoring gas pressure in internal combustion engines. Measurements on a Diesel engine, a gasoline-fueled engine, and a natural-gas engine are reported.

Fiber optic application for thermal switching in vanadium dioxide films

Large thermally induced changes in the end-interface reflectance and transmittance of silica fibers coated with vanadium dioxide films have been observed.

Metal-embedded fiber-optic Fabry–Perot sensors

The sensing of temperature and of ultrasonic pressure with fiber-optic Fabry-Perot interferometers embedded in aluminum is demonstrated. The metal parts are cast in air by using graphite molds. Breakage of the fibers at the air-metal interface during the casting process is avoided through the use of stainless-steel stress-relief tubes. The optical phase in an embedded interferometer is found to be 2.9 times more sensitive to temperature change than for the same interferometer in air, in good agreement with model calculations. An embedded interferometer has also been used to detect ultrasonic waves over the frequency range of 0.1-8 MHz.

Optical fiber Fabry-Perot sensors for smart structures

Fiber Fabry-Perot interferometers (FFPIs) utilizing internal mirrors have been developed to sense temperature, strain, acoustic waves and other physical perturbations in structural materials, and have been successfully embedded in composites and in metals. The construction, performance and application of the FFPI sensors to smart structures are described.

Programmable fiber optic signal processor

Signal storage in a single-mode optical fiber with programmable time delay is described. The reflectivity monitored delay line contains three Fabry-Perot interferometers arranged in serial fashion. By thermally tuning two of the interferometers for near-zero reflectance and the third for relatively high ( Omega 14%) reflectance, any of three possible time delays can be selected. Generation of programmable binary sequences is also demonstrated.<<ETX>>

Internal mirror optical fiber couplers

A description is given of a way of making mirrored fiber couplers, and test results on both multimode and single-mode taps are reported. The couplers were produced by a fusion splicing process similar to that used for making mirrors oriented normal to the axis in multimode and single-mode fibers. These mirrored fibers serve as compact directional couplers with low excess optical loss ( approximately=0.2 dB for multimode and 0.5 dB for single mode at 1.3 mu m) and excellent mechanical properties. The reflectance is found to be wavelength dependent and strongly polarization dependent, as expected.<<ETX>>

Etalon-based fiber optic sensors

Progress in the development of fiber sensors with the Fabry-Perot interferometer (etalon) configuration is reviewed. Fabrication methods and performance results for intrinsic and extrinsic sensors are presented. Application of these devices in measuring temperature, strain, ultrasonic pressure, and gas pressure in internal combustion engines is described. Techniques by which the fiber Fabry-Perot sensors have been successfully embedded in composites and metals are indicated.

In-line Fiber Fabry-Perot Interferometer with High-Reflectance Internal Mirrors

Operation of fiber Fabry-Perot interferometer (FFPI) temperature sensors from -200°C to +1050°C has been demonstrated [1]. These sensors used internal mirrors produced by a fusion splicing technique. Internal-mirror FFPIs have been embedded in graphite-epoxy composites and polymers, where they were used to sense temperature [2] and ultrasonic pressure [3].