Fig. 5: Experimental implementation. | Communications Physics

Fig. 5: Experimental implementation.

From: Leveraging the orthogonality of Zernike modes for robust free-space optical communication

Fig. 5

Schematic of the free-space optical communication system: (a) a collimated laser beam is incident on a reflective ferroelectric LCSLM (LCSLM1). LCSLM1 displays singlex binary holograms sent by PC1 at a rate of 1440 Hz. The user information is encoded as ϕRMS of Zernike modes present in the +1 order beam diffracted from the singlex binary hologram. The beam after traveling the free space is incident on another reflective LCSLM (LCSLM2) that displays an appropriate type-K multiplex hologram via PC2. The resulting +1 order focal spots are captured by a digital camera connected to PC2 that decodes the user information. In this implementation, the two LCSLMs, although not essentially required, are kept in optically conjugate planes. More details of the experimental implementation is found in the “Methods” section. Experimental focal spot patterns (for a plane incident wavefront) of the type-K sensor corresponding to (b) base-9 encoding scheme (using sensor modes Z6 and Z11), (c) base-25 encoding scheme (using sensor modes Z5 and Z11), and (d) base-27 encoding scheme (using sensor modes Z5, Z6, and Z11). (e) Experimental type-K sensor outputs over several camera frames, in the presence of turbulence introduced by a table fan, before external perturbation compensation and (f) after external perturbation compensation. The table fan is positioned at the left of the camera so that the resulting wind affects the information carrying beam over the entire stretch starting from the beam splitter BS to the camera. (g) Screen shot of the oscilloscope showing the display timings of LCSLM1 at 1440 Hz and the timings of user wavefront generation at an interval of tw. Also seen is the schematic of the sequence of reference and information carrying wavefronts from the transmission station, over a duration of 16.67 ms.

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