Re: Double transmission peak narrow band filter?

In article
<ffb7dab2-083d-4beb-abc6-334371b87f0e@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
mpate@xxxxxxxxxxx wrote:

Wild Bill
For the single you should have the air | HLHLHHLHLH | glass, as you
stated.
For a 2 cavity you will have air | HLHLHHLHLH L HLHLHHLHLH | glass.
The L layer in between is called a coupling layer.
If you want the band narrower just as more HL and LH to the outside.

I am going to look at this in more detail. Off hand, I am guessing this
amounts to what in electrical circuits is called coupling two resonant
circuits together. As the coupling coefficient gets increased, you go
from a single peak to critical coupling and into a double peak. This is
often used to shape pass bands. I do not see how you go on to separated
sharp transmission peaks.

The fundamental problem, as I see it, is that a single peak filter of
this kind works because there is only one wavelength at which you get
the equivalent of absentee layers formed by pairing of the quarter-wave
layers in the stacks around the true half wave absentee layer. I was
hoping that there is a clever way around this limitation.

Bill
.