Diffractive optical element

• US 5,227,915 A
• Filed: 06/25/1991
• Issued: 07/13/1993
• Est. Priority Date: 02/13/1990
• Status: Expired due to Fees

• Current Assignee: Holo Ltd.
• Original Assignee: Holo Ltd.
• Inventors: Grossinger, Israel, Kedmi, Joseph
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US07/722,372
• Time in Patent Office: 749 Days
• Field of Search: 350/162.16, 350/162.22, 350/452, 350/162.2, 359/575, 359/573, 359/565, 359/566, 359/569
• US Class Current: 359/565
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08

Abstract

A diffractive optical element and a method to produce same is disclosed. The optical element comprises a base and at least first and second phase zones wherein the first phase zone comprises a first multiplicity of steps and the second phase zone comprises a second multiplicity of steps and wherein the first multiplicity and the second multiplicity of steps are different. The method to produce the diffractive optical element of the present invention includes the step of defining a collection of masks for creating stepped phase zones wherein at least one of the collection of masks partially masks out at least one phase zone such that the at least one phase zone will be partially etched.

Claims

1. A binary mask for use in creating a diffractive optical element through a binary masking process, with the completed diffractive optical element having a pattern including at least two phase zones each having a plurality of corresponding descending steps, said mask comprising:

regions of masked and unmasked regions configured such that during a forming step utilizing that mask, the height of at least a portion of one existing step in one phase zone is changed while the height of the entire corresponding step in another phase zone is unchanged whereby in the completed diffractive optical element, the number of steps in said one phase zone will be different than the number of steps in said another phase zone.

2. In a method of fabricating a diffractive optical element including the steps of generating a set of binary masks and using the masks consecutively in a lithographic process to produce a completed pattern including at least two phase zones each having a plurality of corresponding descending steps wherein the improvement comprises at least one forming step wherein the height of at least a portion of one existing step in one phase zone is changed while the height of the entire corresponding step in another phase zone is unchanged whereby in the completed pattern, the number of steps in said one phase zone will be different than the number of steps in said another phase zone.

3. A method of fabricating a diffractive optical element on a substrate, with the completed diffractive optical element having a pattern including at least two phase zones each having a plurality of corresponding descending steps, comprising the steps of:

a) coating the substrate with a layer of photoresist;

b) placing a first mask on said layer of photoresist;

c) exposing said photoresist through said mask thereby producing the mask pattern on the photoresist;

d) etching said substrate in accordance with the mask pattern; and

e) repeating steps a through d each time using a different mask to create said pattern and wherein at least one mask is configured such that during the associated etching step, the etching is performed on at least a portion of one existing step in one phase zone to create two steps while the height of the corresponding step in another phase zone is unchanged whereby in the completed diffractive optical element, the number of steps in said one phase zone will be greater than the number of steps in said another phase zone.