High-capacity free-space optical communications using wavelength- and mode-division-multiplexing in the mid-infrared region

TLDR

The mid‑infrared region’s atmospheric absorption properties have attracted interest for high‑capacity free‑space optical communications. The study experimentally demonstrates wavelength‑division‑multiplexing and mode‑division‑multiplexing in a ~0.5 m mid‑IR free‑space link. The authors multiplex three ~3.4 µm wavelengths, each carrying two orbital‑angular‑momentum beams, generate and detect the WDM channels in the C‑band, convert them to mid‑IR and back via difference‑frequency generation, and estimate system penalties of ~2 dB (conversion), ~1 dB (WDM), and ~0.5 dB (MDM). The experiment achieves a total capacity of 300 Gbit/s and demonstrates that multiplexing can yield a ~30‑fold increase in data capacity for a mid‑IR free‑space link.

Abstract

Due to its absorption properties in atmosphere, the mid-infrared (mid-IR) region has gained interest for its potential to provide high data capacity in free-space optical (FSO) communications. Here, we experimentally demonstrate wavelength-division-multiplexing (WDM) and mode-division-multiplexing (MDM) in a ~0.5 m mid-IR FSO link. We multiplex three ~3.4 μm wavelengths (3.396 μm, 3.397 μm, and 3.398 μm) on a single polarization, with each wavelength carrying two orbital-angular-momentum (OAM) beams. As each beam carries 50-Gbit/s quadrature-phase-shift-keying data, a total capacity of 300 Gbit/s is achieved. The WDM channels are generated and detected in the near-IR (C-band). They are converted to mid-IR and converted back to C-band through the difference frequency generation nonlinear processes. We estimate that the system penalties at a bit error rate near the forward error correction threshold include the following: (i) the wavelength conversions induce ~2 dB optical signal-to-noise ratio (OSNR) penalty, (ii) WDM induces ~1 dB OSNR penalty, and (iii) MDM induces ~0.5 dB OSNR penalty. These results show the potential of using multiplexing to achieve a ~30X increase in data capacity for a mid-IR FSO link.