Passive speckle-suppressing diffusers and associated methods and illuminators

A passive speckle-suppressing diffuser, comprising:

• a microlens array for diffusing a light field originating from one or more coherent light beams;
• and
• a diffractive optical element (DOE) mounted in series with the microlens array and having a pixelated thickness distribution across a first planar surface of the DOE, characterized by a spatial variation across the diffractive optical element, to impose a spatially varying phase shift on the light field, the pixelated thickness distribution having no periodic spatial pattern with period less than 80 micrometers, such that the spatially varying phase shift suppresses speckle of the light field while minimizing introduction of distinct diffraction structure;
• wherein,
• (i) in a direction parallel to the first planar surface of the DOE, a length of a microlens of the microlens array is larger than a length of a pixel of the diffractive optical element,
• (ii) the pixelated thickness distribution is binary, such that each pixel of the pixelated thickness distribution is characterized by either a first thickness T1 or a second thickness T2<T1,
• (iii) pixels of the pixelated thickness distribution are arranged in an array of square super-pixels, each super-pixel consisting of N,×Ny pixels, Ny being an integer greater than one, each super-pixel being characterized by an average thickness, the average thicknesses of the super-pixels in the array varying across the array of super-pixels and attaining N2+1 different values, and
• (iv) N, is less than √{square root over (CAmin/(2·Cp),)} CAmin being minimum clear aperture of microlenses of the microlens array, C, being side length of the pixels.