High Performance Bianisotropic Metasurfaces: Asymmetric Transmission of Light

It is experimentally shown that bianisotropic metasurfaces allow for extreme polarization control of light with high performance. A metasurface providing asymmetric transmission (i.e., polarization conversion) of circularly polarized light is reported at a wavelength of $1.5\mu \mathrm{m}$. The experimental transmittance and extinction ratio are 50% and $20:1$, which represents an order of magnitude improvement over previous optical structures exhibiting asymmetric transmission. The metasurface consists of patterned gold sheets that are spaced at a subwavelength distance from each other. The same design and fabrication processes can be used in the future to completely control the phase, amplitude, and polarization of light.

Figure 1

An artistic rendering of the asymmetric circular polarizer converting right-handed circularly polarized light from region 1 to left-handed circularly polarized light in region 2. However, right-handed circularly polarized light is completely reflected when incident from region 2.

Figure 2

Unit cell design. (a) Analytic model of a unit cell comprising the asymmetric circular polarizer. (b) Perspective view of the designed unit cell. Exact dimensions of the Au patterns are provided in the Supplemental Material [27].

Figure 3

Fabrication of the asymmetric circular polarizer. (a) Fabrication process involves sequential patterning of each 2 nm/28 nm thick Ti/Au layer using electron-beam lithography and liftoff, followed by spin coating of a 200 nm thick SU-8 dielectric layer. Three metallic layers are patterned using the process, resulting in an overall thickness of 430 nm. (b) SEM picture of the first Au sheet $({\mathbf{Y}}_{s1})$. The second sheet can be seen below the first, although it is less clear. (c) SEM picture of the second Au sheet $({\mathbf{Y}}_{s2})$. The third sheet can be seen below it. (d) SEM picture of the third Au sheet $({\mathbf{Y}}_{s3})$.

Figure 4

Measured and simulated Jones matrix of the metasurface on (a) linear and (b) logarithmic scales. Solid lines correspond to simulation, whereas circles correspond to measurements. Error bars denote 1 standard deviation in the measured data. It can be seen that the metasurface provides high transmission of 50% for the left-handed circular when the right-handed circular is incident. In addition, all other elements of the Jones matrix in the circular polarization basis are below 2.5% at the operating wavelength of $1.5\mu \mathrm{m}$.