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.
Highlights
Mode division multiplexing (MDM) with Tbit/s transmission capacity over free-space and optical fibres[12,13]
In this paper, using a device referred to as an OAM mode sorter[24,25,26], we show that OAM modes can bemultiplexed over a multimode optical fiber with higher than -15 dB mode selectivity and without cascaded beam splitting’s 1/N insertion loss
Using a device referred to as an OAM mode sorter, we showed that OAM modes can bemultiplexed over a multimode optical fiber with higher than -15 dB mode selectivity and without the 1/N insertion loss of using cascaded beam splitters
Summary
A description of the OAM mode sorter’s principle of operation is schematically shown in Fig. 1 24,25. The OAM−1,0 and OAM+1,0 modes, each carrying a PDM-QPSK signal, were coupled to the few-mode optical fibre using an x− y− z translation stage and a 20X microscope objective. (a1)–(c1): Intensity profiles of OAM modes as generated by the OAM mode sorter at the few mode optical fibre (FMF) input (a1) OAM−1,0. (a4)–(c4) Intensity profiles at the FMF output when coupling one OAM mode at a time at the FMF input (a3) SMF1 on - OAM−1,0. The output was coupled into the SMFs of another SMF array corresponding to OAM−1,0 and OAM+1,0 modes resulting in two PDM-QPSK signals.
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