Single-mode fibres with low loss and a large transmission bandwidth are a key enabler for long-haul high-speed optical communication and form the backbone of our information-driven society. However, we are on the verge of reaching the fundamental limit of single-mode fibre transmission capacity. Therefore, a new means to increase the transmission capacity of optical fibre is essential to avoid a capacity crunch. Here, by employing few-mode multicore fibre, compact three-dimensional waveguide multiplexers and energy-efficient frequency-domain multiple-input multiple-output equalization, we demonstrate the viability of spatial multiplexing to reach a data rate of 5.1 Tbit s −1 carrier −1 (net 4 Tbit s −1 carrier −1 ) on a single wavelength over a single fibre. Furthermore, by combining this approach with wavelength division multiplexing with 50 wavelength carriers on a dense 50 GHz grid, a gross transmission throughput of 255 Tbit s −1 (net 200 Tbit s −1 ) over a 1 km fibre link is achieved. W ith the persistent exponential growth in Internet-driven traffic, the backbone of our information-driven society, based on single-mode fibre (SMF) transmission, is rapidly approaching its fundamental capacity limits 1 . In the past, capacity increases in SMF transmission systems have been achieved by exploiting various dimensions, including polarization and wavelength division multiplexing, in tandem with advanced modulation formats and coherent transmission techniques 2 . However, the impending capacity crunch implies that carriers are lighting up dark fibres at an exponentially increasing rate to support societal capacity demands 3 . To alleviate the corresponding costs and increased energy requirements associated with the linear capacity scaling from using additional SMFs, spatial division multiplexing (SDM) within a single fibre can provide a solution 4,5 . By introducing an additional orthogonal multiplexing dimension, the capacity, spectral and energy efficiency, and therefore the cost per bit, can be decreased, which is vital for sustaining the business model of major network stakeholders. To fulfil the SDM promise, a new paradigm is envisaged that allows up to two orders of magnitude capacity increase with respect to SMFs 6 . SDM is achieved through multiple-input multiple-output (MIMO) transmission, employing the spatial modes of a multimode fibre (MMF) 7 , or multiple single-mode cores, as channels 8-13 . Recently, a distinct type of MMF, the few-mode fibre (FMF), has been developed to co-propagate three or six linear polarized (LP) modes 14-17 . Driven by rapid enhancements in high-speed electronics, digital signal processing (DSP) MIMO techniques can faithfully recover mixed transmission channels 18 , allowing spectral efficiency increases as spatial channels occupy the same wavelength. State-of-the-art single-carrier FMF transmission experiments have demonstrated capacity increases in a single fibre by exploiting six spatial modes, achieving 32 bit s −1 Hz −1 spectral efficiency 17 . By using multicore transmissi...

Probabilistic shaping based on constant composition distribution matching (CCDM) has received considerable attention as a way to increase the capacity of fiber optical communication systems. CCDM suffers from significant rate loss at short blocklengths and requires long blocklengths to achieve high shaping gain, which makes its implementation very challenging. In this paper, we propose to use enumerative sphere shaping (ESS) and investigate its performance for the nonlinear fiber optical channel. ESS has lower rate loss than CCDM at the same shaping rate, which makes it a suitable candidate to be implemented in real-time high-speed optical systems. In this paper, we first show that finite blocklength ESS and CCDM exhibit higher effective signal-to-noise ratio than their infinite blocklength counterparts. These results show that for the nonlinear fiber optical channel, large blocklengths should be avoided. We then show that for a 400 Gb/s dual-polarization 64-QAM WDM transmission system, ESS with short blocklengths outperforms both uniform signaling and CCDM. Gains in terms of both bit-metric decoding rate and bit-error rate are presented. ESS with a blocklength of 200 is shown to provide an extension reach of about 200 km in comparison with CCDM with the same blocklength. The obtained reach increase of ESS with a blocklength of 200 over uniform signaling is approximately 450 km (approximately 19%).

In this paper, a new four-dimensional 64-ary polarization ring switching (4D-64PRS) modulation format with a spectral efficiency of 6 bit/4D-sym is introduced. The format is designed by maximizing the generalized mutual information (GMI) and by imposing a constant-modulus on the 4D structure. The proposed format yields an improved performance with respect to state-of-the-art geometrically shaped modulation formats for bit-interleaved coded modulation systems at the same spectral efficiency. Unlike previously published results, the coordinates of the constellation points and the binary labeling of the constellation are jointly optimized. When compared with polarization-multiplexed 8-ary quadrature-amplitude modulation (PM-8QAM), gains of up to 0.7 dB in signal-to-noise ratio are observed in the additive white Gaussian noise (AWGN) channel. For a long-haul nonlinear optical fiber system of 8, 000 km, gains of up to 0.27 bit/4D-sym (5.5% data capacity increase) are observed. These gains translate into a reach increase of ap- proximately 16% (1, 100 km). The proposed modulation format is also shown to be more tolerant to nonlinearities than PM-8QAM. Results with LDPC codes are also presented, which confirm the gains predicted by the GMI.Index Terms-Achievable information rates, binary labeling, generalized mutual information, mutual information, forward error correction, multidimensional constellations, signal shaping.

Achievable information rates are used as a metric to design novel modulation formats via geometric shaping. The proposed geometrically shaped 256-ary constellation achieves SNR gains of up to 1.18 dB.

Low-loss all-fiber photonic lantern (PL) mode multiplexers (MUXs) capable of selectively exciting the first six fiber modes of a multimode fiber (LP₀₁, LP_11a, LP_11b, LP_21a, LP_21b, and LP₀₂) are demonstrated. Fabrication of the spatial mode multiplexers was successfully achieved employing a combination of either six step or six graded index fibers of four different core sizes. Insertion losses of 0.2-0.3 dB and mode purities above 9 dB are achieved. Moreover, it is demonstrated that the use of graded index fibers in a PL eases the length requirements of the adiabatic tapered transition and could enable scaling to large numbers.

No abstract

We present a new technique allowing the fabrication of large modal count photonic lanterns for space-division multiplexing applications. We demonstrate mode-selective photonic lanterns supporting 10 and 15 spatial channels by using graded-index fibres and microstructured templates. These templates are a versatile approach to position the graded-index fibres in the required geometry for efficient mode sampling and conversion. Thus, providing an effective scalable method for large number of spatial modes in a repeatable manner. Further, we demonstrate the efficiency and functionality of our photonic lanterns for optical communications. Our results show low insertion and mode dependent losses, as well as enhanced mode selectivity when spliced to few mode transmission fibres. These photonic lantern mode multiplexers are an enabling technology for future ultra-high capacity optical transmission systems.

No abstract