hollow core PBG fiber (number of supported defect modes)

Hello all,

I would like to evaluate the number of modes (and their respective group 
velocities) supported by the defect of a hollow core PBG fiber.

However, I am not certain how to proceed with MPB.

I am planning to proceed like this:

Preliminary step:
Identify the band gaps of the structure without the defect.
Determine Target-freqs associated to the largest band gap.

Inverse problem solution at the target-freqs in the structure with the 
defect
Solving only one k-point: Gamma (0 0 kz)


I am planning to iterate in function of the target-freq from the lower 
band to the upper-band frequency of the band gap, In order to see how 
many different frequency will converge.

Is it the good approach or there is any better approach.

Thanks for your help
Regards
Stef