Metasurface Demonstrates Nonreciprocal Light Reflection

Scientists have created a brand-new kind of optical metasurface that only allows light to reflect in one way. The researchers empirically proved nonreciprocal light reflection at wavelengths around 860 nm by utilizing an ultrathin nonlinear metasurface’s spatial and temporal phase manipulation. The novel metasurface may facilitate the creation of scalable, magnetic-free, nonreciprocal devices that can be integrated with other optical parts.

The magneto-optic effect is presently almost solely used in optical devices that support the unidirectional flow of light, such as isolators and circulators, making them bulky and challenging to integrate. It is the first optical metasurface that can violate optical reciprocity without using a large magnet and has controllable, ultrafast time-varying properties.

The near-infrared (NIR) block-shaped silicon nanoantennas with a high, nonlinear Kerr index make up the ultrathin metasurface, which is supported by a silver back-reflector plate. The researchers created an effective traveling-wave refractive index modulation on the nanoantennas using a heterodyne interference between two laser lines closely spaced in frequency. It resulted in an ultrafast space-time phase modulation with a large temporal modulation frequency of about 2.8 THz. The dynamic modulation method could be tuned flexibly to the spatial and temporal modulation frequencies. 

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