US 6,271,968 B1Granted

Cut-off filters

AssigneeNational Research Council of Canada

InventorsJ. A. Dobrowolski, Li Li

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Abstract

A cut-off filter is based on the use of light at non-normal angles of incidence and on the use of coating materials with a large dispersion of the optical constants. The filter has a pair of optical media respectively defining an inlet port and an outlet port and having an inclined interface such that a light beam passing between the inlet and outlet ports strikes the interface at a non-normal angle of incidence. An active core is sandwiched between the optical media at the interface. In one embodiment, the active core has a refractive index which has high dispersion in the vicinity of the predetermined cut-off wavelength and an extinction coefficient which is high on the cut-off side and low on the transmission side. The angle of incidence α is selected such that total internal reflection occurs at the predetermined wavelength λ to bring about a sharp cut-off in the transmittance of the filter at the predetermined wavelength.

Claims21

Dependent claims

An optical filter with a sharp cut-off at a predetermined wavelength λ, comprising:

a pair of optical media respectively defining an inlet port and an outlet port and having an inclined interface such that a light beam passing between said inlet and outlet ports strikes said interface at a non-normal angle of incidence α;
a functional core comprising at least one material sandwiched between said optical media at said interface, said functional core having a complex refractive index of the form n−ik, wherein n and k are optical constants, n being the real refractive index, k being the extinction coefficient, and wherein the real refractive index n is highly dispersive in one wavelength region, and the extinction coefficient k is highly dispersive in another wavelength region adjacent said one wavelength region, said extinction coefficient having a high value on the cut-off side of said predetermined wavelength;
and
wherein said angle of incidence α is selected such that light at said predetermined wavelength strikes said interface at a critical angle whereby total internal reflection at said predetermined wavelength occurs in said functional core and on the cut-off side of said predetermined wavelength transmission is inhibited by a high value of said extinction coefficient.

1 more element

Dependencies are inferred from the claim text.