Compound Metaoptics for Independent Amplitude and Phase Control
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Solution Overview
Problem
Single phase-only metasurfaces cannot independently control both the phase and power density distributions of a transmitted electromagnetic wave, leading to speckle noise in holographic images, and existing reflectionless metasurfaces fail to demonstrate amplitude and phase control without absorption and polarization losses.
Innovation Solution
A compound metaoptic comprising two spatially separated metasurfaces, where the first metasurface refracts electromagnetic radiation without reflection or loss, changing the power density distribution, and the second metasurface corrects the phase to match a target distribution, both exhibiting bianisotropic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single phase-only metasurface is used, then the phase profile of the incident wavefront can be reshaped, but the local power density distribution cannot be independently controlled
Solution Approach 1:
The single metasurface is segmented into two separate metasurfaces spaced by a distance d. The first metasurface controls the phase profile while the second metasurface controls the amplitude profile, allowing independent control of both phase and amplitude that cannot be achieved with a single metasurface
Solution Approach 2:
The solution transitions from a two-dimensional single metasurface to a three-dimensional compound metaoptic with separation distance d along the propagation direction. This additional spatial dimension enables independent control of phase and amplitude by placing different functional elements at different positions along the propagation axis
2Manufacturing precision
If a phase-only metasurface is used for holographic imaging, then the phase distribution can be controlled, but speckle noise appears due to uncontrolled amplitude fluctuations
Solution Approach 1:
The holographic imaging function is segmented between two metasurfaces: the first metasurface imparts the desired phase distribution for image formation, while the second metasurface independently controls the amplitude distribution to suppress speckle noise by eliminating random amplitude fluctuations
Solution Approach 2:
The compound metaoptic structure acts as an intermediary system between the incident wave and the target image, providing dual control over phase and amplitude to achieve speckle-free holographic imaging
3Loss of energy
If reflectionless and lossless conditions are imposed on the metasurface, then transmission efficiency is maintained, but amplitude and phase control cannot be achieved simultaneously
Solution Approach 1:
The reflectionless and lossless constraints are applied to each metasurface individually, allowing each to maintain high transmission efficiency. The segmentation enables the first metasurface to handle phase control while the second handles amplitude control, achieving both functions simultaneously without sacrificing transmission efficiency
Solution Approach 2:
By changing the spatial separation parameter d between the two metasurfaces and optimizing their respective unit cell designs, the system achieves independent amplitude and phase control while maintaining reflectionless and lossless operation at each interface
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
Enables independent control of amplitude and phase distributions, suppressing speckle noise and achieving high transmission efficiency with subwavelength pixelation, scalable from microwave to visible wavelengths.
Implementation Method 1
The first metasurface is configured to receive electromagnetic radiation incident thereon and operates to refract the electromagnetic radiation onto the second metasurface
Implementation Method 2
The second metasurface is configured to receive the refracted electromagnetic radiation from the first metasurface and operates to correct the phase of the electromagnetic radiation to match a target phase distribution
Implementation Method 3
Metasurfaces are two-dimensional arrays of sub-wavelength polarizable inclusions, which aggregately manipulate an electromagnetic wave. These inclusions, or unit cells, are arranged in single- or few-layer stacks and are electrically or optically thin
Data Source
AI summary
A compound metaoptic is presented. The compound metaoptic is comprised of at least two phase-discontinuous metasurfaces, which can convert an incident light beam to an aperture field with a desired magnitude, phase, and polarization profile. Each of the constitutive metasurfaces is designed to exhibit specific refractive properties, which vary along the metasurface. Furthermore, due to its transmission-based operation, the metaoptic can operate without lenses and be low profile: potentially having a thickness on the order of a few wavelengths or less. A systematic design procedure is also presented, which allows conversion between arbitrary complex-valued field distributions without reflection, absorption or active components. Such compound metaoptics may find applications where a specific complex field distribution is desired, including displaying holographic images and augmented or virtual reality systems.