Optical nanostructures in 2D for wide-diameter and broadband beam collimation

Abstract

Eliminating curved refracting lensing components used in conventional projection, imaging and sensing optical assemblies, is critical to enable compactness and miniaturisation of optical devices. A suitable means is replacing refracting lenses with two-dimensional optical media in flat-slab form, to achieve an equivalent optical result. One approach, which has been the focus of intense research, uses a Veselago lens which features a negative-index metamaterial. However, practical implementations rely on resonance techniques, thus broadband operation at optical frequencies imposes significant technical challenges that have been difficult to overcome. Here, we demonstrate a highly-collimated, broadband, wide-diameter beam from a compact source in flat-slab form, based on light collimation using nanomaterials ordered in patterns and embedded into flexible polymers. These provide a highly anisotropic absorption coefficient due to patterns created by vertical carbon nanotube structures grown on glass, and the anisotropic electrical conductivity of the nanotubes. We show this nanostructure strongly absorbs unwanted off-axis light rays, whilst transmitting the desired on-axis rays, to achieve the required optical effect over broadband, from visible to short-infrared, thus circumventing some technical limitations of negative-index metamaterials. We further show a low substrate-temperature system for nanotube growth, allowing direct implementation into heat-sensitive large-area devices.

Low temperature growth of carbon nanotubes – A review

“…A unique capability of CVD method is that both vertical and horizontally aligned CNTs at predefined substrate locations can be grown (Fig. 5), which allows their direct integration in various applications, for example, interconnects, micro-electrode arrays and optical devices [37,79,91,102,[105][106][107][108][109][110][111]. Selective growth of metallic (m-SWCNTs) or semiconducting (s-SWCNTs) CNTs with controlled diameter, walls, chirality, alignment and density is still challenging.…”

Carbon nanotube micro-contactors on ohmic substrates for on-chip microelectromechanical probing applications at wafer level

“…Combining this low temperature growth method with conducting diffusion barrier layers enables us to fabricate devices onto conductive substrates, which are kept at temperatures (Figure 1b) that are compatible with CMOS manufacturing processes. 17,24,25,32,33…”

Protected catalyst growth of graphene and carbon nanotubes

“…Details about PTCVD (SNS 1000n) can be found elsewhere. [21,28,46,47] Briefly, in PTCVD, 8 lamps (1 kW each) in the optical-head deliver optical energy through a quartz window directly on the catalyst at the top surface of a sample in the reaction chamber, while the sample itself is placed on a water-cooled chuck to keep its bulk temperature low. In this arrangement, the top surface of the sample reaches the temperature between 600 -750 o C depending on the electrical power supplied to the lamps, whereas the corresponding bulk temperature remains between 375 -450 o C. A plot showing the top surface temperature of a sample measured by a thermocouple corresponding to the bulk temperature measured by a pyrometer at the backside of a sample, is given in Figure S7 of the SI.…”