Patent ID: 7184215

Claim:
An optical filter comprising: a mirror formed from q number of layers comprising a plurality of first dielectric layers having a first index of refraction, a plurality of second dielectric layers having a second index of refraction, and a composite layer having a third index of refraction that is between the first index of refraction and the second index of refraction, formed at a third layer and a q- 2 layer, wherein said composite layer is formed by a high refractive index material being clad with two separate low refractive index materials; wherein a plurality of said first dielectric layers have an integer quarter wave optical thickness and at least one of said first dielectric layers has a non-integer quarter wave optical thickness, wherein a plurality of said second dielectric layers have an integer quarter wave optical thickness and at least one of said second dielectric layers has a non-integer quarter wave optical thickness, and wherein the layers are arranged at least with layer 1 and layer q being first dielectric layers having a high index of refraction, layer 2 and layer q- 1 being second dielectric layers having a low index of refraction, layer 3 and layer q- 2 being third dielectric layers having an intermediate index of refraction, layer 4 and layer q- 3 being second dielectric layers having the low index of refraction, and layer 5 and layer q- 4 being first dielectric layers having the high index of refraction.