Interrogation system for a miniature all-fiber optic sensor using the temperature control of a DFB laser diode, and reference fiber Bragg grating

摘要

This paper describes an efficient system for the interrogation of miniature all-fiber optic sensors, such as Fabry-Perot interferometers or Bragg gratings that change their spectral characteristics within a narrow wavelength band, under the influence of the measured parameter. The signal interrogation is performed by sweeping the laser diode's wavelength over the narrow spectral band containing information about the measured parameter. The optical source consists of a standard telecommunication distributed feedback laser diode with integrated elements for thermal control. The laser diode's sensitivity to temperature is used to cyclically sweep the emitted wavelength for approximately 3 nm. This allows for integration of FBGs and all-fiber FP interferometers with resonator lengths between 0.3 and 1 mm. The interrogation system further includes a wavelength reference, which was formed by a Bragg gratings pair that was temperature stabilized by the miniature Peltier element. The responses of both the optical sensor and the reference Bragg gratings are simultaneously recorded in time during the temperature-induced wavelength sweep. These characteristics are further digitally processed to eliminate any amplitude fluctuations and noise. The peaks in both recorded spectral characteristics are then used to calculate the value of the measured parameter, like for example, strain or temperature. There is, therefore, no need for additional wavelength measurements, which simplifies the presented system. The proposed system is built from standard opto-electronic devices and is, therefore, simple, easy to manufacture and cost-effective. The system was tested using a 1 mm long sensing all-fiber Fabry-Perot interferometer for temperature measurements, and standard Bragg gratings for temperature and strain sensing. The achieved temperature repeatability was better than 0.5 ℃, while the strain reparability proved to be about 10 iz. The proposed system is thus appropriate for various industrial and other applications, requiring cost-effective measurements with optical sensors.