The temporal signal: Temporal signal varies with time. It is used to identify patterns, or changes in audio signals, video frames, or sensor readings. In optics, it is used for shaping, filtering, or differentiating light signals to data transmission or image processing.
The metasurface is very thin material that can manipulate electromagnetic waves in ways that normal materials can't. At the nanoscale, metasurfaces can change how light bends and focuses.
Nonlocal metasurface: It manipulates light in ways that depend on the light's current position and where the light has been before. It detects changes over time in a light signal. study shows that they can efficiently perform operations like first-order differentiation of signals.
Here metasurfaces material is TiO2-coated glass substrates is used. The Fourier transform of an input signal is calculated then multiplying it by the metasurface transfer function calculated and then applying the inverse Fourier transform.
The transfer function tω dictates how the metasurfaces affect different frequency components of the impinging pulse.
is represented in Fourier space by the multiplicative operation (below)
where s(w) is the Fourier transform of s(t).
metasurface with a transfer function
signal Sin(t) ( a square pulse) is encoded in the envelope of an electromagnetic wave impinging on a metasurface. The envelope of the transmitted wave is the first-order derivative of the input pulse.
Assuming electric field pulse created by the pulse shaper is given by the sum of two gaussian pulses,
CCT Cross-Correlation Trace : CCT helps determine how the output signal produced by the metasurface correlates with the input signal. By comparing these signals, researchers can evaluate how effectively the metasurface performs differentiation.
CCT of the input field
CCT of output field
Reference: https://www.nature.com/articles/s44310-024-00039-0:
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