Gate-tunable optical anisotropy in wafer-scale, aligned carbon nanotube films

Telecommunications and polarimetry both require the active control of the polarization of light. Currently, this is done by combining intrinsically anisotropic materials with tunable isotropic materials into heterostructures using complicated fabrication techniques owing to the lack of scalable materials that possess both properties. Tunable birefringent and dichromic materials are scarce and rarely available in high-quality thin films over wafer scales. Here we report semiconducting, highly aligned, single-walled carbon nanotubes (SWCNTs) over 4″ wafers with normalized birefringence and dichroism values of 0.09 and 0.58, respectively. The real and imaginary parts of the refractive index of these SWCNT films are tuned by up to 5.9% and 14.3% in the infrared at 2,200 nm and 1,660 nm, respectively, using electrostatic doping. Our results suggest that aligned SWCNTs are among the most anisotropic and tunable optical materials known and open new avenues for their application in integrated photonics and telecommunications. Using electrostatic doping, the real and imaginary parts of the refractive index along the extraordinary axis of semiconducting, highly aligned, single-walled carbon nanotubes over 4″ wafers can be tuned by up to 5.9% and 14.3% in the infrared at 2,200 nm and 1,660 nm, respectively.