Introduction: Beyond Einstein's Dream. Riding the Photons
Light is a manifestation of the electromagnetic field as the main vector of information for man to know the world and the universe. It presents multiple symmetries, currents and related conserved quantities, or »degrees of freedom«, that can be used to gain knowledge of nature, from the quantum realm to the classical domain.
In the International Year of Light and Light-Based Technologies 2015, the UPPSALA-KARLSRUHE INSTALLATION at ZKM’s GLOBALE exhibition »Infosphere« invites visitors to experience the twisted MIMO.
Adding a twist to spatial information – an action that opens new possibilities to interact with unseen properties of light, transferring information wirelessly in a new and efficient way. By riding the photon, we obtain more information that we currently have about stars and galaxies, which is encoded into light: For this, the orbital angular momentum (OAM), an extrinsic property of the photon is used, as well as vorticity, the spin that is intrinsic and related to polarization. Spin is like the 24-hour rotation of the earth around its own axis, while orbital angular momentum looks more like the revolution of the earth around the sun.
Often waves with OAM carry a vortex, a twist in phase that structures, or »sculpts«, spatial information into a wave front that is preserved during its propagation. When we start riding a photon, we start manipulating and sculpting light, interacting with the universe in a way that has never been done before. We can share information and knowledge across large distances through new forms of frequency re-use, manipulate particles at small scales and sculpt materials at nanoscales. This opens up a new era, from astronomical scales to nanoscales: STRUCTURED LIGHT.
In the UPPSALA-KARLSRUHE INSTALLATION, frequency re-use occurs by using an electromagnetic vortex that is generated by the reflection of a radio wave onto the spiral staircase mask and from a standard wave emitted from a small dipole antenna in the same frequency band and polarization state. The spatial information encoded in the vortex wave and the spatial properties of the geometric distribution of all the antennas make it possible to double the frequency: it is a MIMO (multiple-input-multiple-output) multichannel setup based on radio vorticity. This draws on the spatial information encoded on two electromagnetic waves for frequency re-use.
Two receiving antennas located in different positions are connected to each other to detect the spatial information of the two channels. One antenna is fixed, while the other can be moved mechanically to capture either the twisted wave or the standard wave.
Visitors can experience this »invisible« spatial information by moving one of the receiving antennas, which tunes it between the two video channels carried by the two electromagnetic waves. Visitors also interact with these waves when they walk across the space where the invisible waves propagate, thereby disturbing the waves. Their bodies cause reflections, absorptions, and refractions, similarly to what Heinrich Hertz did in 1887, but in this case interacting with and experiencing twisted light! The result is seen directly in random changes and interference on the two channels.
Authors: Fabrizio Tamburini and Freddy Paul Grunert