Free-Space Optical Communication Using an Optical Frequency Comb and Modulating Retroreflectors

The paper presents a high data rate optical communication method with a swarm of unmanned aerial vehicles (UAVs) by combining quantum-well modulating retrorefiectors (MRRs) and an optical frequency comb. The passive optical link between a laser station and UAV s using MRRs can reduce the mission complexity and power consumption at UAV sites. While increasing the laser power is a straightforward way to further decrease power consumption at UAV sites, the saturation power of the photodetector (PD) at the laser station site can set the lower limit of power consumption since one PD has to receive all lights from UAV s. We used multiple comb modes as independent data transfer carriers. We designed a simple optical system consisting of a quantum-well modulator (QWM), a diffraction grating, a lens, and a planar focal plane. We experimentally realized that around 100 modes can be used with a near-diffraction limit. Our simulation showed that using a comb can reduce power consumption at UAV sites compared to using a continuous-wave (CW) laser with some specific conditions. One of the applications of this method is a distributed interferometric antenna that observes the frequency range from radio frequencies to a few tens of GHz.