Employing optical code division multiple access technology in the all fiber loop vibration sensor system

A 1 × K coupler was adopted for the sensor system to divide a broadband light source into K light sources, which were then transmitted to various FBG encoders. The AFLVS was placed between the optical circulators of the various FBG encoders and multiple FBG arrays, and the stepping motor was directly placed on the fiber loops of the various AFLVSs. A signal generator was then used to input different frequencies into the stepping motors of the various sensors. After the light intensity for the reflectance spectrum, which was outputted by the FBG encoder, was modulated by the AFLVS, the modulated reflected signals were outputted to the K × K star coupler through the optical circulator and transmitted to the FBG decoders for the users. A balanced photodetector (BPD) was employed in this study to convert the light output of the FBG decoder into an electrical signal, and a digitizing oscilloscope was employed to conduct a Fourier transform on the BPD electrical signal output, thereby acquiring the vibration frequency of the test object. The results of the experiment are compared to a piezoelectric accelerometer. The comparison results indicate that the piezoelectric accelerometer is less sensitive when the frequency is lower than 90 Hz, whereas the AFLVS exhibits excellent measurement results at a low frequency ranging between 50 and 200 Hz.