The tunability for an optical notch filter by means of bending is studied. We consider a curved fourlayer slab waveguide as a model for a bent D-type singlemode optical fiber with a thin semiconductor film on its planar surface. We obtain characteristic transmission curves with minima at specific wavelengths, which can be shifted by varying the bending radius. In the limit of large curvature radius our results are in qualitative agreement with experimental results for straight filters.