Abstract
We propose and experimentally demonstrate a novel simultaneous strain and temperature fiber optic sensor. The sensing head is formed by two concatenated ultra-short distributed Bragg reflector lasers that operate in single longitude mode with two polarization modes. The total length of the sensing head is only 18 mm. The two lasers generate two polarization mode beat notes in the radio-frequency range which show different frequency response to strain and temperature. Simultaneous strain and temperature measurement can be achieved by radio-frequency measurement. This approach has distinctive advantages of ease of interrogation and avoidance of expensive wavelength detection.
Highlights
There has been considerable interest in developing simultaneous strain and temperature fiber optic sensors
Many techniques based on fiber Bragg gratings have been reported for simultaneous strain and temperature measurement
Several approaches based on a single Bragg grating for simultaneous strain and temperature measurement was demonstrated, such as utilization of a single Bragg grating in birefringent fibers [5], superstructure Bragg grating [6], a single Bragg grating in tapered fiber [7], and a single Bragg grating straddling over the junction of two fibers [8]
Summary
There has been considerable interest in developing simultaneous strain and temperature fiber optic sensors. A number of schemes based on a sensing head formed by Bragg gratings in combination with other fiber optic devices have been demonstrated. A sensing head formed by a dual-polarization fiber grating laser was demonstrated [13], where the mean wavelength and polarization mode beat frequency of the laser were utilized to discriminate strain and temperature. The disadvantage of the second category is, the intensity detection undercuts multiplexing capability of fiber Bragg grating sensors. The high cost of the wavelength detection unit impedes further applications of fiber Bragg grating sensors. Because the beat frequency is in the radio-frequency range, this type of sensor has distinctive advantages of ease of interrogation and avoidance of expensive wavelength detection that is required in the passive fiber Bragg grating sensors. Simultaneous strain and temperature measurement can be achieved by monitoring the two beat frequencies
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