**5. Conclusions**

62 Photonic Crystals – Innovative Systems, Lasers and Waveguides

In figure 20 it is showed the influence of the position of the defect layer upon the transmission of the 1D PC. If the defect layer is inserted after an even number of (AB) groups the transmission in the localized states is near 100%. If the defect layer is inserted

a) b)

c) d)

Fig. 21. The variation of the thickness of the B type layer a) dB=3 mm; b) dB=6 mm; c) dB=9

Now it is analyzed the influence of the thickness of the B type defect layer upon the optical transmission of the 1D PC. The defect layer is inserted after 8 (AB) groups. The variation of the thickness of the defect layer doesn't influence the optical transmission of the crystal but if it is varied the thickness of all B type layers in the crystal structure are obtained some

mm; d) the frequency of the localized state vs. the position of the defect

interesting results as it can be seen in the following graphics.

after an ode number of (AB) groups the transmission is low (under 30%).

The insertion of a double negative material defect layer in the structure of the onedimensional photonic crystal structure generates localized states. The optical transmission in these localized states and the value of the frequency at which the localized states are obtained depend on the thickness and position in which we have inserted the defect layer.

Analyzing the simulations results it is reached the conclusion that the best photonic crystal configurations are the following three:


From the results obtained it can be said that the studied structures can be used as optical filters.
