RESUMO
High-speed broadband services require optical fibres in access networks, in which multiple subscribers are connected to service providers, to satisfy the continuously growing bandwidth demand. The primitive signaling scheme used in access networks enables the use of low-cost equipment but diminishes the bandwidth available to end-users. Thus, current technology will be unable to support future broadband demands. Coherent communication systems offer significantly improved power- and bandwidth-efficiency, but require fundamental simplifications to become economically viable for access networks. Here, we demonstrate a promising simplified coherent receiver exhibiting a robust performance against polarisation fluctuations over an installed fibre network. It enables the realisation of high-order modulation formats and offers high sensitivities, achieving a four-fold increase in the supported number of subscribers and approximately doubling the transmission distance compared to the recently standardized access technology. The proposed solution indicates that digital coherent technology can be feasible and transform the access networks, enabling ubiquitous new services and applications with uncontended, multi-gigabits/user broadband connections.
RESUMO
A major cause of faults in optical communication links is related to unintentional third party intrusions (normally related to civil/agricultural works) causing fiber breaks or cable damage. These intrusions could be anticipated and avoided by monitoring the dynamic strain recorded along the cable. In this work, a novel technique is proposed to implement real-time distributed strain sensing in parallel with an operating optical communication channel. The technique relies on monitoring the Rayleigh backscattered light from optical communication data transmitted using standard modulation formats. The system is treated as a phase-sensitive OTDR (ΦOTDR) using random and non-periodical non-return-to-zero (NRZ) phase-shift keying (PSK) pulse coding. An I/Q detection unit allows for a full (amplitude, phase and polarization) characterization of the backscattered optical signal, thus achieving a fully linear system in terms of ΦOTDR trace coding/decoding. The technique can be used with different modulation formats, and operation using 4 Gbaud single-polarization dual PSK and 4 Gbaud dual-polarization quadrature PSK is demonstrated. As a proof of concept, distributed sensing of dynamic strain with a sampling of 125 kHz and a spatial resolution of 2.5 cm (set by the bit size) over 500 m is demonstrated for applied sinusoidal strain signals of 500 Hz. The limitations and possibilities for improvement of the technique are also discussed.
RESUMO
Plasmonic crystals, which consist of periodic arrangements of surface features at a metal-dielectric interface, allow the manipulation of optical information in the form of surface plasmon polaritons. Here we investigate the excitation and propagation of plasmonic beams in and around finite size plasmonic crystals at telecom wavelengths, highlighting the effects of the crystal boundary shape and illumination conditions. Significant differences in broad plasmonic beam generation by crystals of different shapes are demonstrated, while for narrow beams, the propagation from a crystal onto the smooth metal film is less sensitive to the crystal boundary shape. We show that by controlling the boundary shape, the size and the excitation beam parameters, directional control of propagating plasmonic modes and their behaviour such as angular beam splitting, focusing power and beam width can be efficiently achieved. This provides a promising route for robust and alignment-independent integration of plasmonic crystals with optical communication components.
RESUMO
The use of single-sideband subcarrier modulation (SCM) with Nyquist (N) pulse shaping for cost-effective spectrally-efficient wavelength division multiplexed transmission with direct detection is described. Transmission of digitally pre-compensated 7 × 11 GHz-spaced QPSK SCM channels at 14 Gb/s per channel is experimentally demonstrated over distances of up to 800 km of uncompensated standard single-mode fiber (SSMF) (13440 ps/nm chromatic dispersion).
RESUMO
The paper investigates the performance of a blind symbol synchronisation technique for optical OFDM systems based on virtual subcarriers. The test-bed includes a real-time 16-QAM OFDM transmitter operating at a net data rate of 30.65 Gb/s using a single OFDM band with a single FPGA-DAC subsystem and demonstrates transmission over 23.3 km SSMF with direct detection at a BER of 10(-3). By comparing the performance of the proposed synchronisation scheme with that of the Schmidl and Cox algorithm, it was found that the two approaches achieve similar performance for large numbers of averaging symbols, but the performance of the proposed scheme degrades as the number of averaging symbols is reduced. The proposed technique has lower complexity and bandwidth overhead as it does not rely on training sequences. Consequently, it is suitable for implementation in high speed optical OFDM transceivers.
RESUMO
Ultrashort pulse propagation in high gain optical fiber amplifiers with normal dispersion is studied by self-similarity analysis of the nonlinear Schrödinger equation with gain. An exact asymptotic solution is found, corresponding to a linearly chirped parabolic pulse which propagates self-similarly subject to simple scaling rules. The solution has been confirmed by numerical simulations and experiments studying propagation in a Yb-doped fiber amplifier. Additional experiments show that the pulses remain parabolic after propagation through standard single mode fiber with normal dispersion.
