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A fiber-optic strain gauge system for use in structural monitoring and smart-structure applications is described. The strain gauge uses a fiber-optic Bragg grating sensor to measure strain and a passive, wavelength demodulation system to determine the wavelength of the narrow-band, backreflected spectrum from the grating sensor. The fiber-optic strain gauge system permits the measurement of both static and dynamic strains with a noise-limited resolution of 0.44 microstrain/√Hz, a measurement dynamic range of 27.8 dB, and a bandwidth of 250 Hz.

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Smart materials and adaptive structures will require structurally integrated fiber optic sensing systems that can operate in practical situations including harsh environments. The intracore fiber optic Bragg grating has considerable potential to serve as the sensor of choice for this emerging field. However, its role has been impeded by the lack of a simple, passive and fast method of determining the wavelength of its narrow back-reflected optical signal. We report on the development of just such a wavelength demodulation system that is inexpensive and easily implemented with a minimum of equipment. Furthermore, we shall show that this approach lends itself to the development of an optoelectronic chip that could process many fiber optic sensors, yet be small enough to be integrated within the structural interface and thereby address the interconnect problem-potentially one of the most critical facing the development of practical smart structures.