Composite Right/Left-Handed Metasurface In The Mid-infrared

Artificial periodic metamaterials have opened a new area in the field of optics and attracted a lot of attention in recent decades.Metamaterials consist of periodic or non-periodic structural units which are smaller than the free-space wavelength.Metamaterials can exhibit exotic properties that do not exist in natural materials.Particularly,left-handed materials with simultaneously negative value of permittivity ? and permeability ? have attracted great attention in the scientific community.With rapid advances of left-handed materials,scientists proposed the concept of composite right/left-handed(CRLH)transmission-line metamaterials which can also realize the left-handed property.Subsequently,many experiments on this subject have been conducted.Since the CRLH transmission line possesses advantageous properties such as low loss,broad bandwidth and non-linear phase constant,a variety of novel Radio-Frequency(RF)devices and microwave antennas based on the concept of CRLH transmission line have been invented in recent years.This thesis firstly applied the microwave concept of CRLH transmission line to the mid-infrared range which is of great importance for the development of optoelectronic devices.This work develops a new mid-infrared metasurface and lays a foundation for further development of new infrared devices.The main contents and contributions in this paper are listed below:First,based on HFSS simulations,a new mid-infrared CRLH metasurface is proposed.It consists of a bottom copper film,a layer of silicon oxide and a top “U” shaped antenna array.Eigenmode and Driven Modal simulations show that the designed metasurface has left-handed and right-handed metasurface modes simultaneously in the mid-infrared region.Next,the designed CRLH metasurface has been successfully fabricated.The main fabrication methods include using electron beam evaporation to evaporate copper on a silicon substrate and patterning the “U” shaped antenna array on the silicon oxide by using electron beam lithography.Some technical challenges,for example the peeling of silicon oxide film from gold surface and the patterning of small size antennas,have been overcome in this paper.Finally,the measured results based on FTIR demonstrate that our sample has CRLH metasurface modes in the mid-infrared.We established an angle-variable FTIR measurement system,and the measured reflection spectra show that our sample has left-handed modes between 19 THz and 21 THz and right-handed modes between 45 THz and 50 THz.In addition,this work has analyzed the loss mechanism of metasurface modes.The analysis indicates the material losses from the silicon oxide and metals as the dominant factor for the loss of left-handed modes and the leaky-wave radiation as the one for the right-handed modes.In order to explain the measured CRLH property,a transmission-line circuit model with extracted values of capacitances and inductances were presented,which intuitively explains the mode behavior in our CRLH metasurface.