| Popis: |
practical applications because of the non-absolute nature of the measuce-ment. As well, lack of common-mode rejection does not permit the accu-rate measurement of low-frequency strains. Another method uses a passive,wavelength demodulation system (WDS) to measure the narrow-band Braggspectrum[7}. In such a system, the back-reflected light from a Bragg gratingilluminated by a broadband source is split into two beams, one of which isspectrally filtered in direct proportion to its wavelength, while the other isused as an intensity reference to cancel out any fluctuations in the sensorsignal. An absolute strain resolution of 28j€, a dynamic range of 25.5dB,and a bandwidth of 250Hz have been reported using such a system[8].A common disadvantage of the demodulation systems developed to dateis the use of a spectrally broadband source to interrogate the Bragg gratingsensor. In such a system, the source spectrum is chosen to be broad enoughto cover the wavelength range over which the Bragg grating will be tuned,and a narrow spectral band corresponding to the Bragg grating center wave-length will be reflected. This method is relatively inefficient, as only a smallfraction of the total fiber-launched light will be reflected as the sensor signal.As well, for typical systems which use currently available LED or SLD lightsources, the low power of this reflected light (approximately 5OnW-400nW)limits the signal-to-noise ratio or bandwidth of the demodulation system.In this paper we report the development of a laser sensor which emitsat the Bragg grating wavelength and permits efficient interrogation of the |
