Meta-programmable analog differentiator

Abstract

We present wave-based signal differentiation with unprecedented fidelity and flexibility by purposefully perturbing overmoded random scattering systems such that zeros of their scattering matrices lie exactly at the desired locations on the real frequency axis. Our technique overcomes limitations of hitherto existing approaches based on few-mode systems, both regarding their extreme vulnerability to fabrication inaccuracies or environmental perturbations and their inability to maintain high fidelity under in-situ adaptability. We demonstrate our technique experimentally by placing a programmable metasurface with hundreds of degrees of freedom inside a 3D disordered metallic box. Regarding the integrability of wave processors, such repurposing of existing enclosures is an enticing alternative to fabricating miniaturized devices. Our over-the-air differentiator can process in parallel multiple signals on distinct carriers and maintains high fidelity when reprogrammed to different carriers. We also perform programmable higher-order differentiation. Conceivable applications include segmentation or compression of communication or radar signals and machine vision.

Quad-Band Polarization-Insensitive Square Split-Ring Resonator (SSRR) with an Inner Jerusalem Cross Metamaterial Absorber for Ku- and K-Band Sensing Applications

“…MTM properties depend on the geometry of the unit cell structure with a stable structural composition. These extraordinary physical properties make MTMs appropriate for numerous applications, such as sensing [2,3], imaging [4], metamaterial coding [5], lensing [6], reflect arrays [7], terahertz applications [8], invisible clocks [9], antennae [10][11][12], absorbers [13], programable analog differentiators [14], etc. The perfect or near-perfect metamaterial absorber has the ability to absorb a specific frequency by preventing reflection and transmission of electromagnetic (EM) waves at a given frequency [15][16][17][18][19].…”

Metasurface-enabled on-chip multiplexed diffractive neural networks in the visible

“…Metasurfaces are novel planar optical elements consisting of subwavelength resonators for manipulating the wavefront of light 32 , 33 . Optical analog computing based on ultra-thin metasurfaces attracted much attention in recent years, which enables the miniaturization of free-space and bulky systems to perform continuous mathematical operations 34 , including differentiator 35 , integrator 36 , convolutional operator 37 , and equation solver 38 , etc. Researchers also explored different degrees of freedom, such as space 39 , frequency 35 , 40 , and polarization 41 to achieve parallel signal processing.…”

“…Optical analog computing based on ultra-thin metasurfaces attracted much attention in recent years, which enables the miniaturization of free-space and bulky systems to perform continuous mathematical operations 34 , including differentiator 35 , integrator 36 , convolutional operator 37 , and equation solver 38 , etc. Researchers also explored different degrees of freedom, such as space 39 , frequency 35 , 40 , and polarization 41 to achieve parallel signal processing. However, diffractive ONNs, which are driven by matrix multiplications 19 of discrete spatial channels, are currently not fully explored in terms of utilizing physical parametric degrees of freedom.…”

Parallel wave-based analog computing using metagratings

“…Among them, the Green’s function (GF) method in which a specific-purpose computing operation is directly realized in the real space, without transforming back and forth from the spatial to the spectral domain [ 14 ], affords compactness and avoids possible challenges in error propagation and alignment issues. The applicability of the GF method to execute signal processing has been verified in a series of proposals via spin hall effect of light [ 24 ], disordered and complex scattering system [ 7 , 25 , 26 ], layered structures [ 18 , 27 ], topological insulators [ 28 , 29 ], plasmonic arrays [ 5 ], bianisotropic metasurfaces [ 10 , 17 ], and so on. Nevertheless, prior GF-based studies still face two different challenges: (i) parallel realization of mathematical operators has been only addressed by using bulky structures [ 7 , 16 ] and array of subwavelength meta-atoms with complex geometries [ 30 , 31 ] and thus, they are still subject to implementation difficulties arising from high fabrication precision demands; (ii) although reflective optical processing for normal incidences is a good alternative for complex oblique illumination setups, it still needs additional optical components to separate the processed signal from the input one [ 10 ].…”

“…The applicability of the GF method to execute signal processing has been verified in a series of proposals via spin hall effect of light [ 24 ], disordered and complex scattering system [ 7 , 25 , 26 ], layered structures [ 18 , 27 ], topological insulators [ 28 , 29 ], plasmonic arrays [ 5 ], bianisotropic metasurfaces [ 10 , 17 ], and so on. Nevertheless, prior GF-based studies still face two different challenges: (i) parallel realization of mathematical operators has been only addressed by using bulky structures [ 7 , 16 ] and array of subwavelength meta-atoms with complex geometries [ 30 , 31 ] and thus, they are still subject to implementation difficulties arising from high fabrication precision demands; (ii) although reflective optical processing for normal incidences is a good alternative for complex oblique illumination setups, it still needs additional optical components to separate the processed signal from the input one [ 10 ]. Further efforts to tackle these barriers must be accompanied with the use of more powerful architectures to implement spatial optical signal processing.…”