Passband-shifting filters through postgrowth modification of filter optical thickness.

We describe a postgrowth method to produce passband filters with different center wavelengths from a single growth run by irreversibly changing the refractive index of a layer or a series of layers within the filter. This leads to a new type of filter, the passband-shifting filter, whose center wavelength can be irreversibly shifted from lambda0 to lambda0 - deltalambda after the filter has been grown. The passband shift can be controlled exactly by proper design of the multilayer. We present the theory behind passband-shifting-filter design along with transfer-matrix simulations and preliminary experimental results for a two-cavity filter, using lateral oxidation of AlxGa1-x As-based materials to effect the passband shift.