Controlling Light with Optical Metasurface on Demand

Dr. Ming Lun Tseng

Research Center for Applied Sciences, Academia Sinica, Taipei 11529  (d00245003@ntu.edu.tw)

Metasurfaces are two-dimensional photonic nanostructures composed of subwavelength resonators (called meta-atoms). The optical functionalities of metasurfaces can be tailored by designing the geometrical parameters of the unit cells. They have promised to advance photonics and optoelectronics due to their ultracompact sizes and great capabilities to control and manipulate light [1,2].

In this talk, I will report my research results on applications of metasurface devices for active light manipulation and color generation. In the first part I will discuss a novel spectroscopy method called coherent control spectroscopy [3-5] for actively controlling and characterizing the optical resonances of planar metasurface devices. The proposed method is based on the fact that multipole resonances of metasurfaces can be selectively enhanced or suppressed by moving it along a standing wave. By using this method, the absorption of an ultrathin metasurface device can be tuned from nearly perfect absorption to near zero [3]. Hidden high order resonances in multilayered metasurfaces such as magnetic Fano resonance and toroidal dipole resonance can be revealed and enhanced by using the coherent control spectroscopy as well [4,5]. In the second part of my talk I will discuss the applications of phase-change material Ge2Sb2Te5 for low-loss and tunable metasurface devices. Optical properties of GST can be reversibly tuned by switching its phase states [6]. By utilizing GST nanostructures as the unit cells of the metasurface, the optical properties of the metasurfaces such as resonance wavelength, output reflection angle can be continuously tuned [7].  It will be very useful in the applications of low loss and speedy tunable devices. Finally, I will discuss a novel metasurface device composed of Al nanoparticles that color can be continuously tuned across the visible spectrum [8]. An Al metasurface was fabricated on a highly stretchable and transparent substrate. By stretching the substrate in either of its two dimensions, the period and therefore the scattering color can be tuned across the full visible spectrum. The proposed two-dimensional design of the metasurface enables continuous color tuning while keeping the elastic modulation to a minimum (less than 35%).

References：

1. Advanced Materials 2013, 25 (8), 1118-1123. 

2. Laser & Photonics Reviews 2012, 6 (5), 702-707.

3. Applied Physics Letters 2014, 104 (14), 141102.

4. Physical Review Applied 2016, 5 (1), 014010.

5. Scientific Reports 2017, 7, 44488.

6. Optics Express 2011, 19 (18), 16975-16984.

7. Laser & Photonics Reviews 2016, 10 (6), 1063-1063.

8. Nano Letters 2017, 17 (10), 6034-6039.