The optically modulated signal is applied to each sensor located

The optically modulated signal is applied to each sensor located at different places (here, L1 to LN). Then, the wavelength band corresponding to each sensor is selected by each FBG and selleck kinase inhibitor enters the dispersion compensation fiber (DCF) as a wavelength-to-time conversion module of dispersive medium. The dispersive medium shows different propagation velocities according to the wavelength of the light. When a strain is applied to FBG 2 as shown in Figure 1, the corresponding wavelength shift (����) is converted into a time shift (�Ӧ���) in the appearance time of the autocorrelation peak. Finally, by reading the difference in arrival time, this technique can provide a wider dynamic range than the conventional methods reading the peak value.Figure 1.
Conceptual diagram of FBG-based sensor network using sliding correlation and DCF as a function of wavelength-to-time conversion.In general, a narrow optical source like a distributed feedback laser diode (DFB-LD) can be used in a CDMA sensor network. However, in this case, the maximum number of FBG sensors installed in a serial line is limited by the transmission coefficient of each FBG. We can slice the spectrum of the DFB-LD and assign one portion to each sensor. Nevertheless, this has a limitation in the available sliced spectrum. Furthermore, narrow wavelength spacing between the sensors might induce channel crosstalk. Therefore, we use a broadband light source like an RSOA to secure a large dynamic range according to the wavelength change.
RSOA is a special type of semiconductor optical amplifier (SOA), which has a high reflective (HR) coating on one facet and an anti-reflective (AR) coating on the other facet to produce a highly versatile gain medium. Although its waveguide structure is similar to a conventional SOA, the RSOA has a lot of different optical properties, such as low noise figure and high optical gain at low drive current. The scanning time of proposed sensor network is determined by:TS=n��f(1)where n is the bit length of the PRBS code and ��f is the frequency difference between the two PRBSs applied to the source and the mixer. Additionally, the autocorrelation pulse width is defined as:TW=2��f(2)Therefore, the maximum number of sensors available without inter-symbol interference is limited by the optical source bandwidth and the PRBS pattern length 2Ts/Tw (=n).
The scanning effect associated with the sliding correlation can be explained as follows: AV-951 to prevent autocorrelation of the unwanted pattern, a random signal (here a PRBS) is used. In a PRBS signal, example the probability of repeating the same pattern within one period of scan is almost zero. Hence, insofar as the reflected lights from all sensors are within one period of scan, each sensor can be identified with a random pattern. Moreover, by giving a slightly different frequency to one (here connected to the mixer), a scanning effect is given to each sensor.3.?Experiment and Results3.1.

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