[5] Russian mathematician Victor Veselago predicted that a material with simultaneously negative electric and magnetic polarization responses would yield a negative refractive index (an isotropic refractive index of −1), a "left-handed" medium in which light propagates with opposite phase and energy velocities.
[6] Traditional curved glass lenses can bend light coming from many angles to end up at the same focal point on a piece of photographic film or an electronic sensor.
[2] Flat lenses employ metamaterials, that is, electromagnetic structures engineered on subwavelength scales to elicit tailored polarization responses.
Negative refractive indices that are isotropic in two and three dimensions at microwave frequencies have been achieved in resonant metamaterials with centimetre-scale features.
[3] With the advances in micro- and nanofabrication techniques, continued miniaturization of conventional optical lenses has been requested for applications such as communications, sensors, and data storage.
Specifically, smaller and thinner micro lenses are needed for subwavelength optics or nano-optics with small structures, for visible and near-IR applications.
Also, the linear optical absorption of GO increases as the reduction of GO deepens, which results in transmission contrast between GO and rGO and therefore provides an amplitude modulation mechanism.
[clarification needed] Thereafter, the focal length can be reduced to as small as 0.8 μm, which would potentially increase the NA and the focusing resolution.
The first flat lens used a thin wafer of silicon 60 nanometers thick coated with concentric rings of v-shaped gold nanoantennas to produce photographic images.
[2] Nanoantennas introduce a radial distribution of phase discontinuities, thereby generating respectively spherical wavefronts and nondiffracting Bessel beams.
[4] In 2015 a refined version used an achromatic metasurface to focus different wavelengths of light at the same point, employing a dielectric material rather than a metal.
Transmission through the metamaterial can be turned on and off using higher frequency light as a switch, allowing the lens to act as a shutter with no moving parts.