Experimental Designs for Efficient Free - Space Multi - Spatial - Mode Optical

In optical communications, two measures of efficiency are commonly at odds. The first is the photon information efficiency (in bits/photon) which measures the information that each detected photon conveys; the second is the spectral efficiency (in bits/s/Hz) which measures the bit rate achieved under limited bandwidth. One interesting communication protocol which can simultaneously obtain high information efficiency without sacrificing spectral efficiency, however, is spatial pulseposition-modulation (spatial-PPM), in which information is encoded into the spatial modes of light and sent through free space between transmitter and receiever. This thesis aims to lay the groundwork for an experimental design to achieve efficient spatial-PPM free-space optical communication using 1550 nm light at the single photon level. We focus on presenting and evaluating a transmitter-receiever design by giving a precise characterization of its operation, properties, and limitations. Thesis Supervisor: Franco N.C. Wong Title: Senior Research Scientist