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Holographic diffuser

  • US 6,285,503 B1
  • Filed: 08/25/1997
  • Issued: 09/04/2001
  • Est. Priority Date: 08/25/1997
  • Status: Expired due to Fees
First Claim
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1. A method for the preparation of holographic diffusers applicable to light source with multiple wave lengths, comprising the following steps:

  • preparing a substrate made of a plurality of units;

    determining a thickness of the holographic diffuser, a unit area of said holographic diffuser, and sizes of said units;

    calculating etching depths according to phase distribution matrices Φ

    n of light having wavelengths λ

    n passing through said diffuser by;

    (a) using a random number generator to generate initial etching depths do and amplitude values A1 for optical field function Ψ

    1=A1*exp(iφ

    1) in the spatial frequency domain;

    (b) calculating a phase distribution matrix φ

    1 in the spatial frequency domain from the initial etching depths to obtain an optical field function Ψ

    1=A1*exp(iφ

    1) in the spatial frequency domain;

    (c) performing an inverse Fourier transform on optical field function Ψ

    1 to obtain the optical field a1*exp(iΦ

    1) and the phase distribution matrix Φ

    1 in the spatial domain for a first wavelength λ

    1, to obtain adjusted etching depths;

    (d) using the phase distribution matrix Φ

    1 and the adjusted etching depths, to calculate a new phase distribution matrix Φ

    2 at a second wavelength λ

    2 in the spatial domain;

    (e) obtaining a second optical field in the spatial domain a1*exp (iΦ

    2), performing a Fourier transform on said second optical field to obtain an optical field function Ψ

    2=A2*exp(iφ

    2) for wavelength λ

    2 in the spatial frequency domain;

    (f) adjusting amplitude coefficients A2 of optical field function Ψ

    2 to permit a desired amplitude of light having wavelength λ

    2 to pass through said diffuser and therefore provide a desired mixing effect, thereby obtaining an adjusted amplitude A2′ and

    an amplitude adjusted optical field function Ψ

    2

    ;

    (g) performing an inverse Fourier transform of the amplitude-adjusted optical field function Ψ

    2

    for wavelength λ

    2 to obtain the optical field a2*exp(iΦ

    2

    ) and an adjusted phase distribution matrix Φ

    2

    in the spatial domain to obtain a new set of adjusted etching depths;

    (h) using the phase distribution matrix Φ

    2′ and

    the new set of adjusted etching depths, to calculate a new phase distribution matrix Φ

    3 at a third wavelength λ

    3 in the spatial domain;

    (i) obtaining a third optical field in the spatial domain a2*exp (iΦ

    3), performing a Fourier transform on said third optical field to obtain an optical field function Ψ

    3=A3*exp(iφ

    3) for the wavelength λ

    3 in the spatial frequency domain;

    (j) adjusting amplitude coefficients of A3 of optical field function Ψ

    3 to permit a desired amplitude of light having wavelength λ

    3 to pass through said diffuser and therefore provide a desired mixing effect, thereby obtaining an adjusted amplitude A3′ and

    an amplitude adjusted optical field function Ψ

    3

    ;

    (k) performing an inverse Fourier transform on amplitude-adjusted optical field function Ψ

    3

    for wavelength λ

    3 to obtain the optical field a3*exp(iΦ

    3

    ) in the spatial domain;

    (l) repeating steps (h)-(k) for wavelengths λ

    4 to λ

    n where n is the number of wavelengths to be diffused by said diffuser;

    (m) repeating steps (h)-(k) for wavelengths λ

    n to λ

    1 to form an iterative operation loop and obtain a set of final adjusted depths based on the final adjusted phase distribution matrix in the spatial domain;

    determining patterns of masks according to the final adjusted depths di so obtained;

    preparing masks according to patterns so determined; and

    etching said substrate with said masks.

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