4.4 Nuttall apodized cascaded fiber Bragg grating

We will simulate the spectral characteristics of the cascaded Nuttall apodized fiber Bragg grating as in Figure 7.

In this simulation the modulation index, d<sup>n</sup> ¼ 0:0003 and grating length L = 5 mm. from Figure 7 we noted that as the number of cascade of fiber Bragg grating is increased the bandwidth is decreased and the side lobes are also decreased but reflectivity is decreased. We have obtained from simulation result for one unit of fiber Bragg grating the reflectivity, R = 99% and bandwidth = 0.08 nm but the side lobes is high, for two cascaded units from fiber Bragg grating the reflectivity, R = 99% and bandwidth =0.063 nm but side lobes in this case is decreased on one unit of fiber Bragg grating, for three cascaded units from fiber Bragg grating the reflectivity, R = 98% and bandwidth = 0.061 nm but side lobes is decreased and for four cascaded units from fiber Bragg grating the reflectivity, R = 98%, bandwidth = 0.059 nm and approximately no side lobes. Then we concluded that Reflectivity, R = 98%, bandwidth = 0.059 nm and the minimum side lobes is achieved at the fourth unit of cascaded fiber Bragg grating.
