Optical fiber sensors are proposed to detect static
and dynamic collector strain for high-speed railway pantograph
achieving electromagnetic immunity, nonelectrically conducting
and small size. The implemented scheme based on a Michelson’s
interferometer with a 3x3 coupler allows local strain measurement
insensitive to temperature variations with high reliability
guaranteed by the employment of standard 1550 nm optical communications
components. By a test rig to experimentally simulate
the pantograph-catenary contact-force the sensor performance is
compared with typical electric measurement
Directly modulated long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered for the implementation of sliceable bandwidth/bitrate variable transceivers for very high capacity transmission (higher than 50 Gb/s per wavelength) in metropolitan area systems characterized by reduced cost, power consumption, and footprint. The impact of the frequency chirp measured for InP VCSELs with different kinds of design (high-bandwidth very short cavity and widely-tunable with micro electro-mechanical systems (MEMS) top mirror) is analyzed in case of discrete multitone (DMT) direct modulation in combination with 25-GHz wavelength selective switch (WSS) filtering. The maximum transmitted capacity for both dual side- and single side-band DMT modulation is evaluated as a function of the number of crossed nodes in a mesh metro network, comparing VCSEL based transmitters performance also with the case of external electro-absorption modulator use. Finally, the maximum reach achieved based on the received optical signal to noise ratio (OSNR) and the fiber span length is discussed. The results confirm the possibility to use directly-modulated long-wavelength VCSELs for the realization of sliceable bandwidth/bitrate variable transmitters targeting 50-Gb/s capacity per polarization, also in the presence of 5 crossed WSSs for reaches of hundreds of kilometers in multi-span Erbium-doped fiber amplified (EDFA) metro links supported by coherent detection.
The experimental demonstration of a free-space optical transmission system with orbital angular momentum (OAM) division multiplexing is reported. Two beams have been multiplexed with different values of the azimuthal index, and hence carrying different OAM, at a wavelength of 1550 nm. a binary intensity modulation at 1.25 Gbit/s has been applied to each OAM channel and an interferometer with Dove prisms has been exploited for OAM demultiplexing
Application of few-mode transmission (FMT) in transport optical network is currently under scrutiny, especially for metro networks, where shorter distances and pressing traffic increase (e.g., due to a growing need for metro datacenter interconnection) represent promising conditions for FMT deployment. In this paper, we analyze, from a network-level perspective, the benefits introduced by FMT in metro networks. We consider the application in a flexi-grid network of a FMT system employing hybrid optical/digital mode demultiplexer and low-complexity MIMO-based digital signal processing (DSP). Under this system model, we derive the reach values associated to different modulation formats, baud rates, and number of modes. For the first time to the best of our knowledge, we formulate using linear programming the routing, modulation format, baud rate, and mode assignment problem, for two different switching policies (spatially flexible and spatially and spectrally flexible switching). Using our proposed modes, we identify the configurations that ensure minimum spectrum occupation or minimum cost of installed transceivers, and contrast them to the benchmark case of single-mode transmission.
The possibility of using optical vortices with different values of topological charge l, and hence with different values of the orbital angular momentum (OAM), for mode-division multiplexing in optical fibres is here investigated. Two OAM modes with l equal to 0 and 1, respectively, are multiplexed in a few-mode fibre and then demultiplexed after a fibre propagation of 200 m. Such modes are spatially separated at the two output ports of a Mach–Zehnder interferometer with mutually 90°-rotated Dove prisms in the two arms. It is also shown how to generalize this demultiplexing scheme, which is all-optical, passive and in principle without splitting losses, in order to deal with a higher number of vortices propagating in the fibre. Therefore the proposed mode-division multiplexing technique based on OAM modes is very promising for increasing the capacity of fibre-optic transmission systems in an energy-saving efficient way, without the high power consumption of modal demultiplexing exploiting real-time electronic post-processing.
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