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RF MODULE

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ELEMENT SIZE,<br />

CORE<br />

SUBDOMAIN<br />

EFFECTIVE MODE<br />

INDEX<br />

neff5 1.450871 1.450871 1.450871 1.450871<br />

neff6 1.451135 1.451135 1.451135 1.451135<br />

It is evident from the table that the fundamental modes, corresponding to the two<br />

lowest eigenmodes with the highest effective mode indices, are nearly degenerate. It is<br />

also clear that the split of the degenerate fundamental modes that is expected due to<br />

the stress-induced anisotropic refractive index has been properly resolved with these<br />

mesh sizes. The convergence of the two fundamental modes is shown in the figure<br />

below.<br />

effective mode index n eff<br />

1.4512<br />

1.4512<br />

1.4511<br />

1.4511<br />

1.4511<br />

1.451<br />

1.451<br />

1.4509<br />

Now, run the model without the stress-induced birefringence.<br />

1 Change the refractive index of Subdomains 4, 5, and 6 to an isotropic index by<br />

selecting Isotropic from the Anisotropy list in the extended n edit field for the<br />

refractive index in the Subdomain Settings dialog box, and typing N as the refractive<br />

index.<br />

2 Solve the problem for a maximum element size of 2.5e-7 for Subdomain 6.<br />

274 | CHAPTER 4: OPTICS AND PHOTONICS MODELS<br />

1E-6 5E-7 2.5E-7 1.25E-7<br />

Computed value of effective mode index vs. mesh size h in core subdomain<br />

1.4509<br />

6 6.1 6.2 6.3 6.4 6.5<br />

−log10(h)<br />

6.6 6.7 6.8 6.9 7

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