Diffractive optical element

• US 6,781,756 B1
• Filed: 09/29/2000
• Issued: 08/24/2004
• Est. Priority Date: 08/29/1995
• Status: Expired due to Term

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Ishii, Tetsuya
• Primary Examiner(s): CHANG, AUDREY Y
• Application Number:
  US09/672,455
• Time in Patent Office: 1,425 Days
• Field of Search: 359/576, 359/569, 359/566, 359/565, 359/571
• US Class Current: 359/576
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence

Abstract

A diffractive optical element including a stack of first, second and third optical regions or a stack of first, second, third and fourth optical regions, a first relief pattern formed between the first and second optical regions, and a second relief pattern formed between the second and third or between the third and fourth optical regions. The first and second relief patterns have substantially identical pitch distributions and are substantially aligned in a direction of an optical axis. Depths of the first and second relief patterns are set such that a wavelength dependency of diffraction efficiency can be decreased over a wavelength range to be used. It is possible to manufacture in a simple manner at a low cost a diffractive optical element in which undesired flares and ghosts are suppressed.

Claims

1. A diffractive optical element comprising:

a first optical region made of a first optical material which is substantially transparent to light within a wavelength range to be used and has a refractive index n₁;

a second optical region made of a second optical material which is substantially transparent to said light but is different from said first optical material and has a refractive index n₂;

a third optical region made of a third optical material which is transparent to said light but is different from said second optical material and has a refractive index n₃, said first, second and third optical regions being arranged to be brought into contact with each other or being arranged close to each other;

a first relief pattern formed in a boundary surface between said first and second optical regions and having a first pitch distribution and a first depth; and

a second relief pattern formed in a boundary surface between said second and third optical regions and having a second pitch distribution and a second depth, said second pitch distribution being substantially identical with said first pitch distribution of the first relief pattern, wherein

said first and second pitch distributions and first and second depths of the first and second relief patterns are set to diffract said light,

said first and second relief patterns are arranged such that tops and bottoms of the first relief pattern are aligned with tops and bottoms of the second relief pattern, respectively viewed in a direction of an optical axis, and

said refractive indices n₁, n₂ and n₃ of the first, second and third optical materials satisfy the following condition;

n₁, n₃>

n₂.

2. A diffractive optical element comprising:

a first optical region made of a first optical material which is substantially transparent to light within a wavelength range to be used and has a refractive index n₁;

a second optical region made of a second optical material which is substantially transparent to said light but is different from said first optical material and has a refractive index n₂;

a third optical region made of a third optical material which is transparent to said light but is different from said second optical material and has a refractive index n₃, said first, second and third optical regions being arranged to be brought into contact with each other or being arranged close to each other;

a first relief pattern formed in a boundary surface between said first and second optical regions and having a first pitch distribution and a first depth; and

a second relief pattern formed in a boundary surface between said second and third optical regions and having a second pitch distribution and a second death, said second pitch distribution being substantially identical with said first pitch distribution of the first relief pattern, wherein

said first and second pitch distributions and first and second depths of the first and second relief patterns are set to diffract said light,

said first and second relief patterns are arranged such that tops and bottoms of the first relief pattern are aligned with tons and bottoms of the second relief pattern viewed in a direction of an optical axis,

said refractive indices n₁, n₂ and n₃ of the first, second and third optical materials satisfy a condition of n₁, n₃>

n₂, and

when an average refractive index of a composite relief pattern structure constituted by said first and second relief patterns is n₀, a thickness of the diffractive element is D and a smallest pitch of the first and second relief patterns is T, the following condition is satisfied;

3. A diffractive optical element comprising:

a first optical region made of a first optical material which is substantially transparent to light within a wavelength range to be used and has a refractive index n₁;

a second optical region made of a second optical material which is substantially transparent to said light but is different from said first optical material and has a refractive index n₂;

a third optical region made of a third optical material which is transparent to said light but is different from said second optical material and has a refractive index n₃, said first, second and third optical regions being arranged to be brought into contact with each other or being arranged close to each other;

a first relief pattern formed in a boundary surface between said first and second optical regions and having a first pitch distribution and a first depth; and

a second relief pattern formed in a boundary surface between said second and third optical regions and having a second pitch distribution and a second depth, said second pitch distribution being substantially identical with said first pitch distribution of the first relief pattern, wherein

said first and second pitch distributions and first and second depths of the first and second relief patterns are set to diffract said light,

said first and second relief patterns are arranged such that tops and bottoms of the first relief pattern are aligned with tops and bottoms of the second relief pattern, respectively viewed in a direction of an optical axis,

said refractive indices n₁, n₂ and n₃ of the first, second and third optical materials satisfy a condition of n_{1, n3}>

n₂; and

when a shortest wavelength of the wavelength range to be used is λ

₁, a longest wavelength of the wavelength range to be used is λ

₂, and a middle wavelength between λ

₁ and λ

₂ is λ

₀=(=(λ

₁+λ

₂)/2), the following condition is satisfied;

4. A diffractive optical element comprising:

a first optical region made of a first optical material which is substantially transparent to light within a wavelength range to be used and has a refractive index n₁;

a second optical region made of a second optical material which is substantially transparent to said light but is different from said first optical material and has a refractive index n₂;

a third optical region made of a third optical material which is transparent to said light but is different from said second optical material and has a refractive index n₃, said first, second and third optical regions being arranged to be brought into contact with each other or being arranged close to each other;

a first relief pattern formed in a boundary surface between said first and second optical regions and having a first pitch distribution and a first depth; and

a second relief pattern formed in a boundary surface between said second and third optical regions and having a second pitch distribution and a second depth, said second pitch distribution being substantially identical with said first pitch distribution of the first relief pattern, wherein

said first and second pitch distributions and first and second depths of the first and second relief patterns are set to diffract said light,

said first and second relief patterns are arranged such that tops and bottoms of the first relief pattern are aligned with bottoms and tops of the second relief pattern, respectively viewed in a direction of an optical axis, and

said refractive indices n₁, n₂ and n₃ of the first, second and third optical materials satisfy the following condition;