Study On The Characteristics Of Coherent Control In Metamaterial All-optical Devices

Metamaterial is a kind of composite structure with sub-wavelength artificial micro-structural units arranged periodically,which does not exist in nature.The electromagnetic metamaterials with only one or several layers of periodic or aperiodic unit structures in the direction of electromagnetic wave propagation are called metasurfaces.Metasurfaces have been used in many applications,such as negative refraction,gradient phase,broadband chirality,anomalous refraction,photoelectric switches,sensors,polarization control and so on.At present,the coherent modulation technology in metasurface has been paid more and more attention.At the same time,with the arrival of the bottleneck of electronic bit rate and the high energy consumption and slow response time of nonlinear effects,there is an urgent need to develop all-optical metasurface devices with ultrafast and low energy consumption to solve the aforementioned problems.In this thesis,we demonstrate the coherent control characteristics of metamaterial all-optical devices.The ultrafast all-optical switch is realized by using the asymmetric split-ring slit metasurface coherent control,and the dual-band all-optical logic gate is realized by using the metal-dielectric-metal three-layer complementary split-ring metasurface coherent control.We have designed an ultrafast metamaterial all-optical switch,whose basic structural unit is an asymmetric open-ring aperture,allowing for the modulation of the transmission and absorption of a signal beam by another coherent control beam.The all-optical switch is composed of a gold film with asymmetric split-ring apertures on a silicon substrate.The device utilizes the interaction between two coherent light beams on a nanostructured metamaterial with a thickness of only 50 nm,effectively controlling the transmission of continuous pulses in the 1200-1800 nm communication band and the absorption of short pulses with a pulse duration of 80 fs.The metamaterial can achieve an output control of over 90% under continuous light illumination.When the pulse duration is 80 fs,the switch contrast ratio is greater than 3:1,and the modulation bandwidth is greater than 12.5 THz.The switching time can be as short as femtoseconds.We have designed a dual-band all-optical logic gate device based on a metamaterial superstructure that induces a Pseudo-Anapole effect.By combining coherent control principles,the device achieves coherent perfect absorption and coherent perfect transmission at wavelengths of 1310 nm and 1550 nm.At 1310 nm,the device provides a total coherent absorption intensity that can be modulated from 0.39 % to 94.65 %,and a total coherent output intensity that can be tuned from 5.3% to 99.6%.At 1550 nm,the device provides a total coherent absorption intensity that can be modulated from 0.74 % to91.1 %,and a total coherent output intensity that can be tuned from 8.9 % to 99.26 %.By controlling the phase difference between the coherent light beams,the total output can be modulated,and appropriate threshold intensities can be set to achieve logic gate control.At1310 nm,the contrast ratios of the AND gate and XOR gate are 6.8 d B and 17 d B,respectively.At 1550 nm,the contrast ratios of the AND gate and XOR gate are 6.4 d B and14.8 d B,respectively.