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

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 (λ ∼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.

Mode Conversion for Mode Division Multiplexing at 850 nm in Standard SMF

“…MDM increases the fiber capacity by means of the parallel transmission of different information through the available spatial modes at a specific wavelength. Specialty fibers or freespace transmission are usually considered on the MDM experiments instead of the ubiquitous SSMF [4], [7].…”

“…Mode converters and multiplexers based on spatial light modulators or q-plates have been successfully used in MDM experiments [4], [7] but the devices based on fused fiber couplers offer a compact solution, with less losses and with direct integration with optical fiber. Both, symmetric (same fiber type) and asymmetric (different fiber type) fused fiber couplers have been proposed as mode converters and mode (de)multiplexers [8], [9].…”

Fiber propagation of vector modes

“…A key technique in achieving high-capacity optical communication is that of mode division multiplexing (MDM), which uses the spatial modes of light as information carriers [1], and has been shown promise in both free-space [2,3] and fiber [4,5]. To date there has been work on MDM with orbital angular momentum (OAM) [6], Bessel beams [7,8] and linearly polarized (LP) modes commonly used to describe fiber modes [9].…”

Data information transfer using complex optical fields: a review and perspective (Invited Paper)

“…The spatial mode multiplexing using different mode sets has been reported in waveguides, free space, and fiber [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] . We show here three examples of data-carrying spatial mode multiplexing.…”