Skew-lens image rotator.

We construct combinations of three skew ideal lenses whose mapping between object and image space corresponds to a rotation of the object space around a common intersection line of all included lenses. The angle of image rotation Δθ can be set arbitrarily within a range (0, 2π) by tuning the parameters of the lenses. The resulting skew-lens image rotator could form the basis of novel applications, e.

Ray-optical transformation optics with ideal thin lenses makes omnidirectional lenses.

We present the theory of ray-optical transformation optics (RTO) with ideal thin lenses and show that ideal-thin-lens RTO devices are omnidirectional lenses. Key to designing such devices are two theorems, the loop-imaging theorem, and the edge-imaging theorem, which ensure that the interior physical space is distorted in the same way for all viewing directions. We discuss the possibility of realising such devices using lens holograms or Fresnel lenses, as both are in principle capable of changing the directions of rays incident from a specific point precisely like an ideal thin lens, thereby enabling macroscopic and broad-band RTO devices that work for at least one viewing position.

Optics. Spatially structured photons that travel in free space slower than the speed of light.

That the speed of light in free space is constant is a cornerstone of modern physics. However, light beams have finite transverse size, which leads to a modification of their wave vectors resulting in a change to their phase and group velocities. We study the group velocity of single photons by measuring a change in their arrival time that results from changing the beam's transverse spatial structure.