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...

In general, a sensor is used to monitor a single parameter only, and in many cases, a reference sensor is necessary to compensate the effect of temperature. Here, we demonstrate that a single supermode interferometer is capable of monitoring two parameters simultaneously. Said interferometer was fabricated with a segment of strongly coupled multicore fiber fusion spliced at the end of a standard single mode fiber. The free end of the multicore fiber was flat, thus, it behaved as a low reflectivity mirror whose reflection depended on the external refractive index. The reflection spectrum of our supermode interferometer consisted of well-defined periodic maxima and minima whose values and position varied when the interferometer was exposed to refractive index and temperature changes. In the Fourier domain, the changes of the interference pattern can be decoded easily. We demonstrate that the supermode interferometer here proposed can be useful to measure the thermo-optic coefficient of a sample. An important advantage of the device reported here is that the length of the multicore fiber is not determinant on the performance of the sensor. In addition, the device can be reused multiple times.

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