Modulation Techniques For Deep-Space Pulse-Position Modulation (PPM) Optical Communication

JPL is actively pursuing the use of optical communications with deep-space probes using the extremely energy-efficient pulse-position modulation (PPM) format. We are studying and developing the critical technologies for this, including the use of different modulation schemes for efficiently producing laser pulses over a broad range of repetition rates. Diode-pumped Nd:YAG is envisioned to be the source, and two principal types of modulation are available: Q-switching and cavity dumping. These two techniques are discussed, and numerical calculations of cavity dumping are described.