**6. Conclusions**

324 Photonic Crystals – Innovative Systems, Lasers and Waveguides

Fig. 22(b) shows the spectrum of S-parameters. It is very similar to S-parameters graph presented in Fig. 20(b). In Fig. 22(b), within the frequency band of 199-208 GHz, S21 and S11 are higher and less than -5 dB and -15 dB, respectively. Since the structure was designed for 90o rotation, higher polarization extinction ratio was expected in comparison with the polarization rotator with 26o angle of rotation. The S-parameter plot in Fig. 22(b) has large fluctuation and it is not as smooth as the S-parameter shown in Fig. 20(b). These fluctuations

Snap shots of Ex and Ey components at f=205 GHz is presented in Fig. 23. Fig. 23(a) shows that the TE10 mode has launched Ey –fields in the left side and it is well-confined inside the input taper and then couples into the defect line of the PC slab waveguide. On the other hand, Ex–field component in Fig. 23(b) is weak at the left (input) side of the defect line; the color bar shows that it is one order of magnitude smaller than Ey component. As Ey –field mode propagates inside the defect line of PC slab waveguide based polarization rotator, it gradually rotates and converts to Ex component. At the other end of the PC slab waveguide, Ex component seems to be one order of magnitude larger than Ey. At the output taper, Ex will expose to the geometry variation of the taper resulting in reverse polarization conversion. Thus, the polarization conversion efficiency

(a)

(b)

Fig. 23. Snap shots of (a) Ey and (b) Ex componnets obtained using 3D-FDTD analysis.

are due to the numerical noise of 3D-FDTD analysis.

would decrease.

The focus of this chapter was on design and fabrication of PC slab waveguide based polarization processor devices. A summary of the key achievements are highlighted as following:

