Light is made up of individual photons and exibit properties of both a particle and a wave. Photons are massless but also the fastest stuff in the Universe. Nothing travels faster than light (3x10^8 m/s^2). Light exhibits several measurable properties which include direction, electric field, magnetic field, and polarization.
This paper talks about using interference from 2 coherent light sources (lasers) together with filters to force light into traveling into an infinite loop called a mobius strip.
One interesting implication of the success of this experiment is the possible relationship between light and the electron. Science doesn't understand what the electron really is. Electrons exhibit many properties of light. They behave a bit more like a particle but also exhibit wave-like characteristics. But unlike, photons, electrons travel slower than light and exhibit a small bit of mass.
The possible relationship between photons and electrons some suggest is not QED (Quantum Electrodynamics) where the Universe is made up of a set of fundamental particles, is that electrons amd other particles are made up of light tied into a knot. In other words, light that propagates in a straight line is massless, but photons that travel in a tight loop in resonance with the Compton wavelength of fundamental particles, exhibit mass.
The photon structure function theory goes a step further suggesting that quark-antiquark pairs which decay into hadrons (ie protons) can be generated by scattering electrons with high energy photons. This theory suggests that that all matter is made up of light.