4 X 20 Gbit/s mode division multiplexing over free space using vector modes and a q-plate mode (de)multiplexer

TL;DR

This paper demonstrates a high-capacity free space optical communication system using vector modes and a q-plate mode (de)multiplexer to transmit 80 Gbit/s over a short distance with low crosstalk and acceptable error rates.

Contribution

It introduces a q-plate based mode (de)multiplexer for vector modes and demonstrates 80 Gbit/s data transmission using four modes at 20 Gbit/s each.

Findings

Transmitted 80 Gbit/s over 1 meter with low mode crosstalk

Achieved bit error rates below FEC threshold with minimal power penalty

Demonstrated feasibility of mode division multiplexing with vector modes

Abstract

Vector modes are spatial modes that have spatially inhomogeneous states of polarization, such as, radial and azimuthal polarization. They can produce smaller spot sizes and stronger longitudinal polarization components upon focusing. As a result, they are used for many applications, including optical trapping and nanoscale imaging. In this work, vector modes are used to increase the information capacity of free space optical communication via the method of optical communication referred to as mode division multiplexing. A mode (de)multiplexer for vector modes based on a liquid crystal technology referred to as a q-plate is introduced. As a proof of principle, using the mode (de)multiplexer four vector modes each carrying a 20 Gbit/s quadrature phase shift keying signal on a single wavelength channel (~1550nm), comprising an aggregate 80 Gbit/s, were transmitted ~1m over the lab table with <-16.4 dB (<2%) mode crosstalk. Bit error rates for all vector modes were measured at the forward error correction threshold with power penalties < 3.41dB.