Patent ID: 7228026

Claim:
An optical multiplexer/demultiplexer comprising: a filter element for transmitting light in a transmission area; and at least one photoconductor arranged on each of two sides of the filter element; wherein first and second ones of the photoconductors are arranged in such a manner that light in the transmission area of the filter element is transmitted through the filter element from the first photoconductor to the second photoconductor; wherein the filter element includes a multilayer film in which a high refractive index layer comparatively high in refractive index and a low refractive index layer comparatively low in refractive index are stacked alternately with each other; wherein a thickness T of the filter element is defined as T=t ( H )• n (0)/ n ( H )+ t ( L )• n (0)/ n ( L ) where n( 0 ) is the refractive index of a medium around the filter element, n(L) the refractive index of the low refractive index layer, t(L) the physical thickness of the low refractive index layer as a whole, n(H) the refractive index of the high refractive index layer and t(H) the physical thickness of the high refractive index layer as a whole; and wherein an optical axis of the first photoconductor and an optical axis of the second photoconductor are shifted by an axial shift amount δ defined as δ= A (λ)• T •tan θ where θ is the angle of light incident to the filter element is normal to an entrance surface of the filter element, and A(λ) a coefficient changing with the wavelength λ of the light incident to the filter element.