Overview
An Optical Frequency Comb Generator (OFCG) is utilized in optical communication systems to generate a series of discrete, equally spaced frequency lines (or “teeth” on a frequency “comb” when veiwed on a spectrum analyzer) which are used to carry data. For example, the base frequency might be at 350Thz, with “teeth” plus and minus a range of 3 Thz with a spacing of 17 GHz. This creates multiple, parallel channels (subcarriers) from a single laser source, facilitating the transmission of multiple data streams simultaneously, thereby increasing the overall data rate.
These subcarriers should be strong or have enough value to ensure the signal is above the noise level, flat or carry a similar power level to one another, and have a fixed but adjustable spacing between one another to avoid inter-channel interference while still allowing for adjustment of the distance as appropriate for the application. OFCGs use IFFTs to convert or synthesizes the individual frequency-domain components into a time-domain signal or waveform, and FFTs to convert the signal back into the frequency domain and allow it to be compiled into a data stream.
OFCGs have applications outside of FSO and communications in general, with increases in efficiency opening up new potential applications. [2] Originally, OFCGs were developed for counting cycles in optical atomic clocks, due to the much higher oscillation of light frequencies versus electronics. [3] In the case of FSO applications, OFCGs can potentially reduce the total energy usage of the system due to greater system efficiency. [4]
References
Mohsin, Marwa & Murdas, Ibrahim. (2022). Design an Outdoor Light Fidelity (Li-Fi) System Based on All-Optical OFDM Architecture. International Journal of Intelligent Engineering and Systems. 15. 2022. 10.22266/ijies2022.0630.16.
[2] Hu, Y., Yu, M., Buscaino, B. et al. High-efficiency and broadband on-chip electro-optic frequency comb generators. Nat. Photon. 16, 679–685 (2022). https://doi.org/10.1038/s41566-022-01059-y
[3] Fortier, T., Baumann, E. 20 years of developments in optical frequency comb technology and applications. Commun Phys 2, 153 (2019). https://doi.org/10.1038/s42005-019-0249-y
[4] Ullah, Rahat, et al. “High-Capacity Free Space Optics-Based Passive Optical Network for 5G Front-Haul Deployment.” Photonics. Vol. 10. No. 10. MDPI, 2023.