Diffractive microstructures for color separation and fusing

• US 5,682,265 A
• Filed: 02/18/1994
• Issued: 10/28/1997
• Est. Priority Date: 02/18/1994
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Farn, Michael W., Veldkamp, Wilfrid B.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US08/198,883
• Time in Patent Office: 1,348 Days
• Field of Search: 359/48, 359/558, 359/566, 359/569, 359/571, 359/615, 345/88, 345/151, 348/760, 348/761, 348/790, 348/791, 349/61
• US Class Current: 359/571
• CPC Class Codes: G02B 27/1013 for colour or multispectral image sensors, e.g. splitting an image into monochromatic image components on respective sensors spectral imaging systems G01J
• CPC Class Codes: G02B 27/1086 operating by diffraction only
• CPC Class Codes: G02B 27/123 The splitting element being a lens or a system of lenses, including arrays and surfaces with refractive power
• CPC Class Codes: G02B 5/1871 Transmissive phase gratings
• 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
• CPC Class Codes: G02B 5/1885 Arranged as a periodic array
• CPC Class Codes: G02B 5/203 having holographic or diffractive elements diffraction gratings per se G02B5/18; holographic elements per se G02B5/32; generating the spectrum using diffraction elements G01J3/18
• CPC Class Codes: G02F 1/133621 providing coloured light G02F1/133617, G02F1/133533 take precedence
• CPC Class Codes: G02F 1/133623 Inclined coloured light beams

Abstract

Optical apparatus for dispersing a visible light spectrum into primary color bands and directing each color band into a specific pixelated cell of a passive display. The apparatus includes an array of refractive microlenses arranged parallel to the plane of the passive display such as a liquid crystal display and a diffraction grating arranged parallel and in close proximity to the lens array. The microlenses focus visible light onto the display while the diffraction grating separates the visible light into primary color bands in different diffraction orders such that the colors are directed to and transmitted through the corresponding specific pixelated cells.

Claims

1. Optical apparatus for dispersing a visible light spectrum into primary color bands and directing each color band into a specified pixelated cell of a passive display comprising:

a display including pixelated cells;

an array of refractive microlenses arranged parallel to the plane of the display to receive visible light;

a diffraction grating arranged parallel, and in close proximity, to the array of refractive microlenses to separate the visible light into primary color bands,

wherein said microlenses focus the visible light onto the display, while said diffraction grating separates the visible light into the primary color bands in different diffraction orders such that each color band is directed to the specified pixelated cell for transmission therethrough,

wherein said diffraction grating comprises an optical material having a periodic echelle structure,

wherein each period has a profile of discrete optical thicknesses and each profile begins with an minimum optical thickness, and increases stepwise in optical thickness to a maximum optical thickness,

wherein said profiles are arranged such that the optical thickness of the profiles increases in the same direction across a surface of the optical material, with the maximum optical thickness of at least one profile abutting the minimum optical thickness of an adjacent profile, and

wherein the physical difference in depth between adjacent steps within said profile is ##EQU7## where λ

is the design wavelength and n is the index of refraction of the material.

2. Optical apparatus for dispersing a visible light spectrum into primary color bands and directing each color band into a specified pixelated cell of a passive display comprising:

a display including pixelated cells;

an array of refractive microlenses arranged parallel to the plane of the display to receive visible light;

a diffraction grating arranged parallel, and in close proximity to, the array of refractive microlenses to separate the visible light into primary color bands,

wherein said microlenses focus the visible light onto the display, while said diffraction grating separates the visible light into the primary color bands in different diffraction orders such that each color band is directed to the specified pixelated cell for transmission therethrough,

wherein said diffraction grating comprises an optical material having a periodic echelle structure,

wherein each period has a profile of discrete optical thicknesses and each profile begins with an minimum optical thickness, and increases stepwise in optical thickness to a maximum optical thickness,

wherein said profiles are arranged such that the optical thickness of the profiles increases in the same direction across a surface of the optical material, with the maximum optical thickness of at least one profile abutting the minimum optical thickness of an adjacent profile, and

wherein the physical difference in depth between adjacent steps is 1.14 μ

m.

3. Optical apparatus for dispersing a visible light spectrum into primary color bands and directing each color band into a specified pixelated cell of a passive display comprising:

a display including pixelated cells;

an array of refractive microlenses arranged parallel to the plane of the display to receive visible light;

a diffraction grating arranged parallel, and in close proximity, to the array of refractive microlenses to separate the visible light into primary color bands; and

said diffraction grating adapted to separate the visible light two-dimensionally,

wherein said microlenses focus the visible light onto the display, while said diffraction grating separates the visible light into the primary color bands in different diffraction orders such that each color band is directed to the specified pixelated cell for transmission therethrough.

4. Optical apparatus for dispersing a visible light spectrum into primary color bands and directing each color band into a specified pixelated cell of a passive display comprising:

a display including pixelated cells;

an array of refractive microlenses arranged parallel to the plane of the display to receive visible light; and

a diffraction grating arranged parallel and in close proximity to the array of refractive microlenses to separate the visible light into primary color bands,

wherein said microlenses focus the visible light onto the display, while said diffraction grating separates the visible light into the primary color bands in different diffraction orders such that each color band is directed to the specified pixelated cell for transmission therethrough, and

wherein the diffraction grating diffracts light into substantially complementary angles but not in complementary orders.