Patent ID: 7573639

Claim:
A terahertz band optical filter having a bandpass characteristic in a terahertz band comprising: a dielectric multilayer periodic structure, the dielectric multilayer periodic structure including: at least two cavity layers, each cavity layer comprising a low refractive index medium and having an optical path length of an integer multiple of a ½ wavelength of a passband center frequency; a single-layer coupling layer located between each of the at least two cavity layers so as to form a multi-cavity structure, each coupling layer having an optical path length of a ¼ wavelength of the passband center frequency and comprising a high refractive index medium having a refractive index ratio of 2 or more with respect to the low refractive index medium; and matching layers disposed at either end of the multi-cavity structure, each matching layer including a layer of a high refractive index medium and a layer of a low refractive index medium, the matching layers having different dielectric constants, and each of the matching layers having an optical path length of an integer multiple of a ¼ wavelength of the passband center frequency.