We realized mode-division multiplexing(MDM) transmission by using orthogonal LP modes with negligible modal crosstalk, for the first time. A 2x10Gbps MDM transmission was achieved over a 10km two-mode fiber with sufficiently low power penalty.
IntroductionThe network traffic in optical fiber communication systems has increased rapidly and will continue to grow in the near future. Large transmission capacity experiments of more than 60 Tbps per fiber have been reported, which were realized by utilizing both a wavelength-division multiplexing (WDM) system and a multi-level modulation format [1,2]. However, it has been discussed that these technology had difficult to realize a much larger capacity of more than 100 Tbps per fiber with these technologies because of limitations for the input power and bandwidth of optical amplifiers [3]. Recently, multi-core fiber and mode-division multiplexing (MDM) transmission have been studied in order to overcome these limitations [4][5][6]. They can realize a much larger transmission capacity when combined with conventional WDM, polarization-division multiplexing (PDM) and multi-level modulation technologies.MDM transmission has received particular attention since it allows us to increase greatly the number of signals per fiber core. With MDM transmission, several individual signals are transmitted in propagation modes at a certain wavelength through a certain core. A mode multiplexer/demultiplexer (MUX/DEMUX) can be realized by optical devices without digital signal processing in the electrical domain. Although the several mode MUX/DEMUX have been proposed [7][8][9], the transmission performance of MDM transmission systems has remained unclear.In this paper, we demonstrate the first MDM transmission to use orthogonal LP modes in two-mode fiber. We designed our mode MUX/DEMUX by controlling the interaction parameters of fiber couplers. We achieved a 2 x 10 Gbps MDM transmission over a 10 km-long two-mode fiber with negligible modal crosstalk. Our experimental results reveal the possibility of realizing a large transmission capacity using MDM.
In optical fiber networks it is important to monitor water which seeps into splice enclosures. The fibers have residual stress at splicing points and, when water is present, this adversely affects fiber lifetime.We developed a water sensor with optical fiber which has a simple structure for monitoring water at splicing points. This water sensor causes optical loss due to fiber bending when water seeps into splicing enclosures. The design method using a fiber bending model and sensor performance are described.
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