Feature: Communications


Figure 5: Mode separation after an arbitrary mode mixing


a. Representation of two free space beams (A and B) that arrive at the receiver after an unknown linear transformation performed by a randomly- orientated phase mask acting on two orthogonal modes (Mode 1 is HG00 and Mode 2 is 45°-rotated HG10-like).


b. The shape of the beams A and B can be identified by observing the backward far-field intensity pattern radiated by the 2D optical antenna array when the photonic processor is configured to couple beam A with WG1 (b1) and beam B with WG2 (b2). Circles indicate the position of zero-order diffraction;


c. BER measurements of 10Gbit/s OOK channels simultaneously transmitted on the overlapped beams A and B and separated by the photonic processor.


light is injected at ports WG1 and WG2, respectively. We find very good matching with the shape of the HG10-like mode as well as the HG11-like mode (both rotated by 45°). Te good mode separation is confirmed when the photonic processor is used as a two-beam mode-diversity receiver in a data transmission link, where each mode carries a


10Gbit/s intensity-modulated OOK signal. Figure 4d shows the BER curves versus


OSNR measured on the data channels separated by the mode-diversity receiver. With respect to the reference curves, given by the BER curves of Mode 3 (blue squares) and Mode 4 (red squares) when they are individually transmitted in the absence


24 July/August 2023 www.electronicsworld.co.uk


of the other mode, no OSNR penalty is observed when both data channels are transmitted and they are sorted out by the photonic processor at the output ports. Te results validate the effectiveness of the photonic processor separating generic pairs of orthogonal modes emerging from a free- space-mode converter.


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