Experimental Demonstration of a 100-Gbit/s 16-QAM Free-Space Optical Link Using a Structured Optical “Bottle Beam” to Circumvent Obstructions

We experimentally demonstrate a free-space optical (FSO) communication link using an optical "bottle" beam to help circumvent obstructions. At the transmitter, an optical "bottle" beam is generated by spatially structuring a Gaussian beam with a transmitter beam diameter of 7 mm. During propagation, the energy of the "bottle" beam evolves in a three-dimensional (3-D) shell which creates a "bottle"-like low-intensity region, allowing the beam to circumvent an obstruction located inside this region. Subsequently, the beam evolves back to its original shape and propagates in its original direction. In our demonstration, we use a 100-Gbit/s, 16 quadrature amplitude modulation (16-QAM) data signal. Experimental results show that a "bottle" beam with a "bottle" size of 5 mm could help circumvent a circle-shaped obstruction with a diameter of ∼4.5 mm and suffers ∼10-dB less obstruction-induced power penalty as compared to a Gaussian beam. Additionally, we experimentally tailor the size and location of the "bottle" by changing the structuring pattern at the transmitter. Results after tailoring show that: (i) the beam with a larger "bottle" size could circumvent a larger obstruction but suffers more power loss when using a limited-size receiver aperture, and (ii) the location of the "bottle" in the propagation direction could be tuned to circumvent an obstruction more optimally at varying locations as compared to the case where the locations of the "bottle" and obstruction are not matched.