Large-scale optical compression of free-space using an experimental three-lens spaceplate

Recently introduced, spaceplates achieve the propagation of light for a distance greater than their thickness. In this way, they compress optical space, reducing the required distance between optical elements in an imaging system. Here we introduce a spaceplate based on conventional optics in a 4-$f$ arrangement, mimicking the transfer function of free-space in a thinner system - we term this device a three-lens spaceplate. It is broadband, polarization-independent, and can be used for meter-scale space compression. We experimentally measure compression ratios up to 15.6, replacing up to 4.4 meters of free-space, three orders of magnitude greater than current optical spaceplates. We demonstrate that three-lens spaceplates reduce the length of a full-color imaging system, albeit with reductions in resolution and contrast. We present theoretical limits on the numerical aperture and the compression ratio. Our design presents a simple, accessible, cost-effective method for optically compressing large amounts of space.