Self Adaptive Programmable Optical Processor for FSO turbulence mitigation

In a Free Space Optics (FSO) link, there are several phenomena that can affect and degrade the performance of the channel. Among them, atmospheric turbulence plays a relevant role and today is the main obstacle in the implementation of high bitrates reliable FSO communication systems. The effect of turbulence on optical beams can be described as a random phase and amplitude modulation which results in a beam profile affected by scintillation.

This random modulation reduces the coupling efficiency with the receiver and causes deep fading in the signal after the photodetector. These effects can be mitigated using a multi-aperture receiver; the distorted wavefront is sampled in several points where each portion of the optical signal has its own amplitude and phase. By increasing the number of apertures, the fading probability reduces.

The sampled optical signals originating from each aperture have random and uncorrelated amplitude and phase and they must be recombined coherently, but their phase randomly change in time because of turbulence, with a bandwidth several hundreds of Hz.

In this work, the incoming optical beam is sampled by an integrated optical phased array antenna with 16 elements and each sample is coherently combined by means of a Programmable Optical Processor (POP). The dynamic adaptive control layer can compensate the fluctuations of the incoming phase front and stabilize the link at 10 Gbit/s. The experiments are conducted indoor emulating the atmospheric turbulence with realistic intensities. The results demonstrate the effectiveness of the approach in terms of performance and footprint compared with other solutions.

An invited speaker presentation byProfessor Andrea Melloni, the Photonic Devices Group in the Dipartimento di Elettronica, Informazione e Bioingegneria at the Politecnico di Milano.

He is driven by the opportunity of a brainstorming on an emergent area and the networking with relevant scientists in this specific field and he foresees the trend of Multi-physics and multidisciplinary. Photonics cannot be considered alone anymore but in an holist way with electronics, thermal management, control theory, etc. etc.

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