Enhancement of Free-Space Optical Communication with Structured Frequency Combs

In recent years, optical frequency combs (OFCs) and structured light beams have demonstrated remarkable performance across various fields, namely sensing, metrology, and optical communications. To benefit the advantages of both techniques, we propose a novel approach for generating structured OFCs carrying designed transverse modes. More specifically, we shape the narrow line width laser source not only in the temporal domain but also in the spatial domain, so as to obtain an electro-optic frequency comb with customizable radial structures, including higher-order Bessel structures, Airy structures, and other designed modes. This versatile structured frequency comb source featuring high repetition rates, strong tunability, high output power, and an unprecedented degree of freedom exhibits high performance in free-space optical telecommunications. Along this line, we have experimentally assessed the bit error rates (BERs) of a 20 GBaud/s pulse amplitude modulation 4-level signal carried by different comb lines of the structured beam, even with a simulated turbulence communication environment. The experimental results indicate that the generated beam supports a communication capacity of up to 360 Gbit/s, while the 4-fold Bessel beam multicasting achieves a relatively low BER of less than 2.4 × 10^–2. Compared with traditional OFCs and structured beams, the proposed scheme simultaneously enables wavelength-division multiplexing, turbulence-resistance, self-healing, and multicasting, thus tremendously enhancing free-space telecommunications for various scenarios.