Patent ID: 6285503
Filing Date: 2001-09-04
Classification: G02B,G03H

Abstract:
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 .PHI..sub.n of light having wavelengths .lambda..sub.n passing through said diffuser by:(a) using a random number generator to generate initial etching depths d.sub.o and amplitude values A1 for optical field function .PSI..sub.1 =A1*exp(i.phi..sub.1) in the spatial frequency domain;(b) calculating a phase distribution matrix .phi..sub.1 in the spatial frequency domain from the initial etching depths to obtain an optical field function .PSI..sub.1 =A1*exp(i.phi..sub.1) in the spatial frequency domain;(c) performing an inverse Fourier transform on optical field function .PSI..sub.1 to obtain the optical field a1*exp(i.PHI..sub.1) and the phase distribution matrix .PHI..sub.1 in the spatial domain for a first wavelength .lambda..sub.1, to obtain adjusted etching depths;(d) using the phase distribution matrix .PHI..sub.1 and the adjusted etching depths, to calculate a new phase distribution matrix .PHI..sub.2 at a second wavelength .lambda..sub.2 in the spatial domain;(e) obtaining a second optical field in the spatial domain a1*exp (i.PHI..sub.2), performing a Fourier transform on said second optical field to obtain an optical field function .PSI..sub.2 =A2*exp(i.phi..sub.2) for wavelength .lambda..sub.2 in the spatial frequency domain;(f) adjusting amplitude coefficients A2 of optical field function .PSI..sub.2 to permit a desired amplitude of light having wavelength .lambda..sub.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 .PSI..sub.2 ';(g) performing an inverse Fourier transform of the amplitude-adjusted optical field function .PSI..sub.2 ' for wavelength .lambda..sub.2 to obtain the optical field a2*exp(i.PHI..sub.2 ') and an adjusted phase distribution matrix .PHI..sub.2 ' in the spatial domain to obtain a new set of adjusted etching depths;(h) using the phase distribution matrix .PHI..sub.2 ' and the new set of adjusted etching depths, to calculate a new phase distribution matrix .PHI..sub.3 at a third wavelength .lambda..sub.3 in the spatial domain;(i) obtaining a third optical field in the spatial domain a2*exp (i.PHI..sub.3), performing a Fourier transform on said third optical field to obtain an optical field function .PSI..sub.3 =A3*exp(i.phi..sub.3) for the wavelength .lambda..sub.3 in the spatial frequency domain;(j) adjusting amplitude coefficients of A3 of optical field function .PSI..sub.3 to permit a desired amplitude of light having wavelength .lambda..sub.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 .PSI..sub.3 ';(k) performing an inverse Fourier transform on amplitude-adjusted optical field function .PSI..sub.3 ' for wavelength .lambda..sub.3 to obtain the optical field a3*exp(i.PHI..sub.3 ') in the spatial domain;(l) repeating steps (h)-(k) for wavelengths .lambda..sub.4 to .lambda..sub.n where n is the number of wavelengths to be diffused by said diffuser;(m) repeating steps (h)-(k) for wavelengths .lambda..sub.n to .lambda..sub.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 d.sub.i so obtained; preparing masks according to patterns so determined; and etching said substrate with said masks.