Free-Space Optical Communication Based on Mode Diversity Reception Using a Nonmode Selective Photonic Lantern and Equal Gain Combining

Abstract

This paper experimentally investigates the performance of free-space optical (FSO) communication based on mode diversity reception (MDR) using nonmode selective photonic lantern (NSPL) and equal gain combining (EGC). By employing a mode demultiplexer and combining technology in the receiver, the bit error rate (BER) and outage performance of FSO communication system can be significantly improved. However, different from diversity system with multiple receive apertures, the branches in mode diversity system are non-independent fading signals, which are influenced by not only atmospheric but also the modal crosstalk of mode demultiplexer. Therefore, we take into consideration the difference of mode demultiplexer and study four schemes for FSO mode diversity reception system: 1) NSPL with equal gain combining (NSPL-EGC), 2) NSPL with maximal ratio combining (NSPL-MRC), 3) mode selective photonic lantern with equal gain combining (MSPL-EGC), and 4) mode selective photonic lantern with equal gain combining (MSPL-MRC). Experimental results show that NSPL-EGC is the most suitable scheme for MDR with low implementation complexity, and the performance difference is less than 1 dB compared with the one using MRC at BER= 3.8×10 -3 under turbulence from weak to strong.

Experimental demonstration of coherent receiver with photonic lantern and digital signal processing

“…( 1) for successful realization of the maximal ratio combining the DSP algorithm should be able to adiabatically follow and adjust for the drift of 𝑆𝑁𝑅 𝑖 and the net channel power 𝑃 𝑐ℎ (𝑖) for each PL output channel in real time. Note that though in the equal gain equalization (EGC) all the weight coefficients 𝐶 𝑖 = 1, which simplifies the DSP, the combined signal SNR for EGC [21] stays lower than the SNR for the maximal ratio combined signal given by Eq. (A12) unless both the 𝑆𝑁𝑅 𝑖 and the net channel power 𝑃 𝑐ℎ (𝑖) remain the same for all N channels, in which case the SNR for EGC coincides with the SNR for the maximal ratio combining.…”

The application of photonic lanterns in free space optical communications

“…A photonic lantern offers a potentially simpler alternative to the commonly used adaptive optic systems as demonstrated in Refs. [13][14][15][16]. Not only can photonic lanterns transition light from a multi-mode input into a single mode fiber, they also can provide information about the shape of the wavefront [17].…”