Mode division multiplexing using an orbital angular momentum mode sorter and MIMO-DSP over a graded-index few-mode optical fibre

Abstract

Mode division multiplexing (MDM)– using a multimode optical fiber’s N spatial modes as data channels to transmit N independent data streams – has received interest as it can potentially increase optical fiber data transmission capacity N-times with respect to single mode optical fibers. Two challenges of MDM are (1) designing mode (de)multiplexers with high mode selectivity (2) designing mode (de)multiplexers without cascaded beam splitting’s 1/N insertion loss. One spatial mode basis that has received interest is that of orbital angular momentum (OAM) modes. In this paper, using a device referred to as an OAM mode sorter, we show that OAM modes can be (de)multiplexed over a multimode optical fiber with higher than −15 dB mode selectivity and without cascaded beam splitting’s 1/N insertion loss. As a proof of concept, the OAM modes of the LP11 mode group (OAM−1,0 and OAM+1,0), each carrying 20-Gbit/s polarization division multiplexed and quadrature phase shift keyed data streams, are transmitted 5km over a graded-index, few-mode optical fibre. Channel crosstalk is mitigated using 4 × 4 multiple-input-multiple-output digital-signal-processing with <1.5 dB power penalties at a bit-error-rate of 2 × 10−3.

Controllable all-fiber generation/conversion of circularly polarized orbital angular momentum beams using long period fiber gratings

“…Therefore, in the current study, it is necessary to find the relation between the LP modes and the CP-OAM modes. Each LP mode group in fibers has four unstable transverse electric field distributions [7,24]:…”

“…Conventionally, in optical fibers, the linearly polarized (LP) mode basis is widely used because the modes forming this basis are more readily excited and detected than the eigenmodes [7,[19][20][21]. Recently, OAM modes stably propagating in fiber-based transmission links have also shown the potential applications in optical communication.…”

“…Zhang et al [18] generated the OAM ±2 modes composed of HE 31 even ± iHE 31 odd in a four-mode fiber (4MF) by using an acoustically induced fiber grating. However, these published works lack analysis in the photonics spin of the generated OAM beams, which is not only a fundamental physical question but also a crucial factor in multiplexing [7] and micro-particles manipulation system [21][22][23].…”

“…A beam of light carrying OAM possesses a phase φ(l,ϕ) = exp(ilϕ) in the transverse plane, where ϕ is the azimuth angle and l is the topological charge number. As the unique characteristics of the OAM light beam were found, a number of attempts to generate and manipulate the OAM beams were proposed based on discrete free space optical systems [6][7][8][9][10][11] and optical fiber components [12][13][14][15][16][17][18].…”

“…As one of the most fundamental physical quantities in classical and quantum electrodynamics, orbital angular momentum (OAM) of light has initiated widespread interest in many areas, including optical tweezers [1], atom manipulation [2][3][4], nanoscale microscopy [5], quantum information processing, and large-capacity optical communication [6][7][8]. A beam of light carrying OAM possesses a phase φ(l,ϕ) = exp(ilϕ) in the transverse plane, where ϕ is the azimuth angle and l is the topological charge number.…”