The generation and detection of a light beam which is deflected back and forth at a microwave rate in accordance with frequency modulation on the beam is considered. Deflection was achieved by sending the frequency modulated light through a dispersing element. The detection system consisted of a photocathode which emitted a transversely modulated electron beam into a transverse-field interaction circuit. General analyses were developed for the dispersion and electron beam-circuit interaction systems. The applicability of the instantaneous-frequency viewpoint was explored in detail, and a new condition for the validity of this viewpoint was derived. Phototube design procedures were formulated. Experiments demonstrated the dispersion and interaction mechanisms, including an unforeseen effect involving partial interception of the deflected light beam. The experiments supported the detailed theoretical analyses. An examination of the basic noise limitation revealed a significant advantage over certain other FM light detection systems. As optical modulation techniques improve, it is expected that this approach may represent a superior means of detection in optical communications systems. (Author).