Theoretic Study of Cascaded Fiber Bragg Grating DOI: http://dx.doi.org/10.5772/intechopen.83020

In this simulation the modulation index, d<sup>n</sup> ¼ 0:0003 and grating length L = 5 mm. From Figure 9 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 = 96% and bandwidth =0.013 nm but the side lobes is high, for two cascaded units from fiber Bragg grating the reflectivity, R = 93% and bandwidth =0.0092 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 = 90% and bandwidth =0.0084 nm but side lobes is decreased and for four cascaded units from fiber Bragg grating the reflectivity, R = 87%, bandwidth =0.0081 nm and approximately no side lobes. Then we concluded that Reflectivity, R = 87%, bandwidth =0.0081 nm and the minimum side lobes is achieved at the fourth unit of cascaded fiber Bragg grating.


#### Table 1.

Comparison between reflectivity, R and bandwidth for different cascaded units of apodized fiber Bragg grating.

fiber Bragg grating the reflectivity, R = 95%, bandwidth =0.0096 nm and approximately no side lobes. Then we concluded that Reflectivity, R = 95%, bandwidth =0.0096 nm and the minimum side lobes is achieved at the fourth unit of cascaded

1.5495 1.5496 1.5497 1.5498 1.5499 1.55 1.5501 1.5502 1.5503 1.5504 1.5505

Wavelength, um

x 10-6

One FBG Two FBG Three FBG Four FBG

x 10-6

One FBG Two FBG Three FBG Four FBG

We will simulate the spectral characteristics of the cascaded proposed apodized

1.5495 1.5496 1.5497 1.5498 1.5499 1.55 1.5501 1.5502 1.5503 1.5504 1.5505

Wavelength, um

4.6 Proposed apodized cascaded fiber Bragg grating

Reflectivity spectrum for four stage proposed apodized fiber Bragg grating.

Reflectivity spectrum for four stage sinc apodized fiber Bragg grating.

Fiber Optic Sensing - Principle, Measurement and Applications

fiber Bragg grating.

Figure 8.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Refelectivity, R

fiber Bragg grating as in Figure 9.

0

Figure 9.

18

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Refelectivity, R
