Abstract

There are many applications which require the measurement of tensile strain at elevated temperatures. We have developed a fiber-optic sensor capable of operating up to 650°C. which can determine both temperature and strain from dual-wavelength cross-talk observations. The device consists of a pair of single-mode cores embedded in a common cladding and symmetrically positioned about the center of the fiber. When one core is illuminated with monochromatic light, complete energy exchange from one core to the other and back takes place in a beat length λ_B. The variation in core contrast at the end of a sensor of length L is a periodic function of the beat phase ϕ = πL/λ_B. A change in temperature or strain causes a change in λ_B and an expansion or contraction of the fiber; the net effect is a change in beat phase or cross talk. The change in beat phase will depend on the wavelength.

© 1984 Optical Society of America