Passive Speckle-Suppressing Diffuser with Pixelated Phase Element
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Solution Overview
Problem
Coherent light sources, such as lasers, often produce speckle patterns due to constructive and destructive interference, which can be undesirable in applications like near-infrared imaging and depth sensing, and existing methods to reduce speckle often require active movement or complex manufacturing processes.
Innovation Solution
A passive speckle-suppressing diffuser comprising a microlens array and a diffractive optical element with a pixelated thickness distribution that imposes a spatially varying phase shift on the light field, eliminating speckle without introducing distinct diffraction structures, and is suitable for cost-effective mass production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a coherent light source is used to achieve high efficiency and power output, then energy efficiency is improved, but speckle patterns appear on illuminated objects
Solution Approach 1:
The optical system is segmented into multiple functional components: a microlens array that divides the coherent light into multiple beams, and a diffractive optical element with pixelated thickness distribution that further segments and randomizes the light paths. This segmentation approach maintains the advantages of coherent light while eliminating speckle through statistical averaging of multiple independent light paths
Solution Approach 2:
A diffractive optical element with pixelated thickness distribution serves as an intermediary between the coherent light source and the illuminated object. This intermediary component introduces controlled phase variations that decohere the light without requiring active movement, thereby suppressing speckle while preserving the high energy efficiency of coherent light sources
2Object-affected harmful factors
If an active diffuser is moved to suppress speckle, then speckle is reduced, but device complexity and power consumption increase
Solution Approach 1:
Instead of actively moving the diffuser to suppress speckle, the invention inverts the approach by using a passive diffractive optical element with a specifically designed pixelated thickness distribution. This static structure achieves speckle suppression through its inherent optical properties rather than through movement, thereby reducing device complexity and power consumption
Solution Approach 2:
The mechanical system of actively moving or spinning diffusers is replaced with a static diffractive optical element. The speckle suppression function is achieved through the optical phase modulation properties of the pixelated thickness distribution rather than through mechanical motion, eliminating the need for motors, control systems, and power consumption associated with active movement
3Object-affected harmful factors
If a diffractive optical element with periodic pattern is used, then diffraction structure is introduced, but speckle suppression is compromised
Solution Approach 1:
The diffractive optical element employs an asymmetric, non-periodic pixelated thickness distribution rather than a regular periodic pattern. This asymmetric structure prevents the formation of distinct diffraction orders and grating lobes while still providing the phase modulation necessary for speckle suppression through statistical averaging
Solution Approach 2:
Each pixel in the diffractive optical element has a locally optimized thickness value that contributes to the overall speckle suppression function. The local quality of each pixel (its specific thickness) is varied according to a non-periodic pattern, ensuring that no regular diffraction structure emerges while maintaining effective phase randomization across the entire aperture
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses speckle in coherent light fields, providing a compact, robust, and power-efficient solution suitable for various applications, including near-infrared imaging and depth sensing, without the need for active movement or complex manufacturing.
Implementation Method 1
refracting a light field originating from the one or more coherent light beams, through a microlens array, to diffuse the light field
Implementation Method 2
a diffractive optical element mounted in series with the microlens array and having a pixelated thickness distribution, characterized by a spatial variation across the diffractive optical element, to impose a spatially varying phase shift on the light field
Data Source
AI summary
A passive speckle-suppressing diffuser includes a microlens array for diffusing a light field originating from one or more coherent light beams, and a diffractive optical element mounted in series with the microlens array and having a pixelated thickness distribution, 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 may be configured such that the spatially varying phase shift suppresses speckle of the light field while minimizing introduction of distinct diffraction structure. A method for passive speckle-suppressing diffusion a light field originating from one or more coherent light beams may include refracting the light field, through a microlens array, to diffuse the light field, and imposing a spatially varying phase shift on the light field to decohere the light field without introducing any first-order diffraction components deflected beyond angle spread introduced by the microlens array.