6. Conclusion

width since large computational area will contribute to a longer simulation time and

The space must be exactly proportionate to the size of the optical waveguide. The thickness of PML required for the device operating at around 1.52 μm wavelength is 0.5 μm to provide better electromagnetic wave absorption at the boundary. Other parameters that contribute to the accuracy of the simulation are determined by the choice of the spatial grid or mesh size, where smaller grid spacing gave more accurate computation. In other words, the closer the resolution in simulation to the

During the second half of the computational process, the author has used other commercially available software to compute all the device structures. This software is found to be more accurate than the previous simulation tool. On the other hand, by using the same parameters in the crystal wave tool as previously used in fullwave, the simulation time has been reduced by a factor of five, and the result obtained is closer to the measured result as shown in one of the example in Figure 6. The comparison is made by using 12-period 1D PhC mirrors with diameters of 350 nm and periodic spacing of 360 nm. By looking at the band edge location of the measured result in Figure 6, the 2D FDTD crystal wave shows closer result (band edge) than the one computed using RSoft tools where the deviation of 83 nm is observed between the simulation and the measured result. But this is understood to be due to small deviation in the dimension of the structures produced after fabrica-

No further investigation is made in reference to the discrepancy between the different examples of commercial software, but the problem has been addressed to the relevant personnel. As a result, based on further tests carried out using different measurements run to compare the results with the simulation, the CrystalWave software have been chosen as the relevant tools that are well-suited to the design

An example showing a comparison between 2D FDTD computed using different simulations tools (RSoft and

actual device, the more accurate simulation will be established.

also consume more memory and power.

Photonic Crystals - A Glimpse of the Current Research Trends

tion process as real devices.

Figure 6.

102

crystal wave) with the measured result.

structures used throughout this present work.

In conclusion, the 2D simulation approach is used to produce preliminary designs for the device, together with the employment of an effective index approximation based on the waveguide properties of the base material structure discussed earlier. 2D simulation helps with obtaining a better understanding of the general behaviour of the device—but 3D simulation gives more accurate prediction of the results, at the expense of much greater time and energy consumption. Both 2D and 3D simulations were carried out using the commercial software using finitedifference time-domain (FDTD) approach. This chapter in particular demonstrated the detailed theoretical models of single-row PhC cavities embedded in narrow (typically 500 nm wide) photonic wire waveguides based on silicon-on-insulator (SOI). The device structures have been designed to operate in TE polarisation at wavelengths around 1550 nm. The compactness together with high reflectivity and possibilities for an active tuning capability make the device suitable as a basic building block for incorporation into integrated circuits where several functions are realised on a single chip—i.e. what are commonly known as high-density photonic integrated circuits (PICs). On the other hand, it may also be useful in providing one of the solutions for the design of compact filters for either coarse or dense wavelength division multiplexing situations, for high-speed switching and non-linear optics. For instance, FDTD approach used in this chapter has shown a significantly good agreement with the measured result—thus it can be used as a method to obtain a preliminary result before the actual design for fabrication is proposed.
