US 5,847,877 AGranted

Diffractive optical element

AssigneeOlympus Optical Co., Ltd.

InventorsAyami Imamura, Tetsuya Ishii

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Abstract

A diffractive optical element including a first layer made of a first optical material having high refractive index and low dispersion, and a second layer made of a second optical material having low refractive index and high dispersion. The first and second layers are stacked together. The outer surfaces of the first and second layers are substantially smooth, while the connecting surfaces of the first and second layers are substantially contoured to follow a relief pattern. To satisfy a preferred operating wavelength range of 400 nm to 700 nm, a glass selected from the group consisting of BSM7, BSM81, BSL7, BAL5, BAL50, BAL22, LAL11, LAL12, LAL18, YGH51, LAH57 and LAH75 may be used as the first optical material, and a silicate glass containing certain amounts (e.g., 2 to 25 mol %) of Tl.sub.2 O may be used as the second optical material.

Claims9

Dependent claims

A diffractive optical element comprising a plurality of layers including at least one boundary surface formed by adjacent layers made of different optical materials and at least one relief pattern formed in said at least one boundary surface,

wherein at least first and second adjacent layers between which said relief pattern is formed are made of optical materials having refractive indices n.sub.1 (.lambda.) and n.sub.2 (.lambda.), which are refractive indices of one of said optical materials having a high refractive index and low dispersion and one of said optical materials having a low refractive index and high dispersion, respectively, and which satisfy the following conditions:
n.sub.1 (.lambda.)>n.sub.2 (.lambda.) and ##EQU15## wherein .lambda..sub.1 is a short wavelength of 400 nm, .lambda..sub.2 is a long wavelength of 700 nm, and .lambda. is an arbitrary wavelength between said short and long wavelengths, .lambda..sub.1 and .lambda..sub.2, and
wherein the relief pattern is formed such that a depth d and a pitch T of recesses of relief pattern satisfy the following condition:
##EQU16##

1 more element

Dependencies are inferred from the claim text.