Let us first consider asymmetric PQW structure [(AB).
According to TMM, the total transfer matrix for asymmetric PQW structure is expressed as 
3) leads to the result for symmetric PQW structure.
With the same parameters in Figure 2, we combine two PCs to form the PQW structure.
For the symmetric PQW structure, the blue curves illustrate that the peak frequency as well as the peak height remain nearly unchanged as P changes.
On the other hand, the effect of P-value is more salient in asymmetric PQW structure (red curves).
With the PQW structures, by properly choosing the geometric and dielectric parameters, a large number of multi-channel filter mode can be achieved, which may have potential application as narrow band filters.
These results show that the PQW structures have been used to achieve multi-channel filter modes in the photonic band gap region.