1,721,092 research outputs found
Mode Multiplexing Optical Communication System
No full textThe present invention generally relates to the field of the communication over an optical fiber. More in particular, the present invention concerns a communication system over a multi-mode optical fiber by means of the selection of a suitable sub-set of modes
Very high-capacity short-reach VCSEL systems exploiting multicarrier intensity modulation and direct detection
Full text linkMulticarrier intensity modulation of a bandwidth-limited long-wavelength VCSEL is exploited combined to direct detection to achieve very high capacity simple systems for short-reach applications. Tailored FDM subcarriers modulation and allocation allow to match the non-uniform frequency response of the system induced by the direct modulation and detection of the FDM signal and by the uncompensated SSMF propagation, overcoming the VCSEL bandwidth limitations. A whole transported throughput ranging from 34 Gb/s to 25 Gb/s from few hundreds meters to 20 km of SSMF propagation is experimentally demonstrated even by employing a 5-GHz band VCSEL source
Sistema di comunicazione ottico a multiplazione di modo
No full textViene descritto un sistema di comunicazione ottico (1). Il sistema di comunicazione ottico (1) comprende un trasmettitore ottico (2) ed una fibra ottica multi-modale sostanzialmente circolare (40). Il trasmettitore ottico comprende un generatore (10, 11, 20) di almeno due vortici circolari in spazio libero (CVSL1, CVSL2) e comprende un elemento ottico (30) configurato per ricevere gli almeno due vortici circolari in spazio libero ed accoppiarli ad una faccetta d’ingresso della fibra ottica. La fibra ottica è configurata per ricevere sulla faccetta d’ingresso gli almeno due vortici circolari in spazio libero ed è configurata per generare da questi almeno due corrispondenti vortici circolari guidati (CVFR1, CVFR2) aventi rispettive costanti di propagazione (β), in cui i valori delle costanti di propagazione ad una frequenza definita sono fra di loro diversi
VCSEL-VCSEL injection locking a 10 Gb/s per trasmissione su 40 km senza compensazione di dispersione
No full textIs the access network ready for Quantum Key Distribution?
No full textThe access network segment represents the end point for the provision of quantum key distribution (QKD) services, offering secure communication to the end users. Yet the integration of QKD into legacy passive optical networks (PONs) is very challenging due to the high losses of the passive optical distribution network (ODN) and the presence of upstream and downstream classical channels belonging to many coexisting PON standards, which are the source of scattered Raman noise photons. In this study we evaluate the sustainability of discrete variable QKD services in access networks supporting one or more PON standards, evidencing the necessity of ODN architectures able to enhance the QKD performance and facilitate the key-exchange over the legacy PON links
Gouy phase shift in nondiffracting Bessel beams
No full textThe results of a theoretical and experimental investigation of the Gouy effect in Bessel beams are presented. We point out that the peculiar feature of the Bessel beams of being nondiffracting is related to the accumulation of an extra axial phase shift (i.e., the Gouy phase shift) linearly dependent on the propagation distance. The constant spatial rate of variation of the Gouy phase shift is independent of the order of the Bessel beam, while it is a growing function of the transverse component of the angular spectrum wave-vectors, originated by the transverse confinement of the beam. A free-space Mach-Zehnder interferometer has been set-up for measuring the transverse intensity distribution of the interference between holographically-produced finite-aperture Bessel beams of order from zero up to three and a reference Gaussian beam, at a wavelength of 633 nm. The interference patterns have been registered for different propagation distances and show a spatial periodicity, in agreement with the expected period due to the linear increase of the Gouy phase shift of the realized Bessel beams
Mode-division multiplexing in fibre-optic communications based on orbital angular momentum
No full textThe 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
Adjustable-chirp VCSEL-to-VCSEL injection locking for 10-Gb/s transmission at 1.55 μm
No full text1.55-μm single-mode VCSEL frequency chirp behavior is investigated in under-threshold and above-threshold operating conditions for different VCSEL-to-VCSEL injection locking configurations with respect to free-running case. We experimentally evaluated the capability of adjusting the frequency chirp, reducing its value and inverting the sign. The control over the frequency chirp is obtained changing the wavelength detuning and power injection ratio between the VCSEL master and the VCSEL slave. Advantages of the chirp inversion are demonstrated for 10 Gb/s error-free propagation at 1.55-μm over 40-km standard single mode fiber without any dispersion compensation
Discrete-variable quantum key distribution services hosted in legacy passive optical networks [Invited]
Full text linkFiber-based quantum key distribution (QKD) systems are mature and commercialized, but their integration into existing optical networks is crucial for their widespread use, in particular in passive optical networks (PONs) if end-to-end quantum-secured communications are to be addressed. While discrete-variable QKD coexistence with classical channels is well-studied in point-to-point links, its performance in point-to-multipoint topologies like PONs has received less attention. We thus developed a numerical tool to estimate quantum-available bandwidth and maximum link lengths for QKD systems in single-fiber PON architectures in coexistence with GPON, XG-PON, NG-PON2, and HS-PON standards. The QKD channel performance is obtained by setting thresholds on the quantum bit error rate and the secret key rate, ultimately limited by spontaneous Raman scattering noise and high optical distribution network losses. We perform a comparison between the performance obtained assuming the asymptotic infinite-key generation rate or taking into account actual implementations in the finite-key regime. We evidence that proper design rules can be obtained as a function of both classical and quantum system parameters to support end-to-end quantum security services in existing optical networks
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