Effect of carrier reshaping and narrow MUX-DEMUX filtering in 0.8 bit/s/Hz WDM RZ-DPSK transmission

Effect of the carrier shape in the ultra high dense wavelength division multiplexing (WDM) return to zero differential phase shift keying (RZ-DPSK) transmission has been examined through numerical optimization of the pulse form, duty cycle and narrow multiplex/de-multiplex (MUX/DEMUX) filtering parameters. © 2007 Springer Science+Business Media, LLC.

Performance comparison of SSMF and ultra wave fibers for ultra-long-haul 40-Gb/s WDM transmission

We experimentally compare the performance of standard single-mode fiber (SSMF) and UltraWave fiber (UWF) for ultra-long-haul (ULH) 40-Gb/s wavelength- division- multiplexing transmissions. We used the carrier-suppressed return-to-zero amplitude-shift-keying (CSRZ-ASK) and the carrier-suppressed return-to-zero differential-phase-shift-keying (CSRZ-DPSK) formats, which are particularly well-adapted to 40-Gb/s pulse-overlapped propagation. We demonstrate that transmission distance well beyond 2000 km can be reached on UWF with both the CSRZ-ASK and CSRZ-DPSK formats, or on SSMF with the CSRZ-DPSK format only, thus indicating that SSMF-based infrastructure of incumbent carriers can be upgraded at 40-Gb/s channel rates to ULH distances. © 2007 IEEE.

Optical regeneration using self-phase modulation and quasi-continuous filtering

We propose a scheme for 211 optical regeneration based on self-phase modulation in fiber and quasi-continuous filtering. Numerical simulations demonstrate the possibility of increasing the transmission reach from 3500 to more than 6000 km at 10 Gb/s using 100-km spans. Spectral broadening is shown to be small using this technique, indicating its suitability for wavelength-division-multiplexing regeneration.

Spectral density enhancement using coherent WDM

It is shown by numerical simulations that a significant increase in the spectral density of a 40-Gb/s wavelength-division-multiplexing (WDM) system can be obtained by controlling the phase of adjacent WDM channels. These simulations are confirmed experimentally at 40 Gb/s using a coherent,comb source. This technique allows the spectral density of a nonreturn-to-zero WDM system to be increased from 0.4 to 1 b/s/Hz in a single polarization. Optical filter optimization is required to minimize power crosstalk, and appropriate strategies are discussed in this letter. Index Terms-Filtering, optical communication terminals, phase control, wavelength-division multiplexing (WDM).

Investigation of the effect of an increased supervisory signal power in a high-loss loopback monitoring system

We present experimental results for the effect of an increased supervisory signal power in a high-loss loopback supervisory system in an optically amplified wavelength division multiplexing (WDM) transmission line. The study focuses on the investigation of increasing the input power for the supervisory signal and the effect on the co-propagating WDM data signals using different channel spacing. This investigation is useful for determining the power limitation of the supervisory signal if extra power is needed to improve the monitoring. The study also shows the effect of spacing on the quality of the supervisory signal itself because of interaction with adjacent data signals.

Investigation of the effect of an increased supervisory signal power in a high-loss loopback monitoring system

We present experimental results for the effect of an increased supervisory signal power in a high-loss loopback supervisory system in an optically amplified wavelength division multiplexing (WDM) transmission line. The study focuses on the investigation of increasing the input power for the supervisory signal and the effect on the co-propagating WDM data signals using different channel spacing. This investigation is useful for determining the power limitation of the supervisory signal if extra power is needed to improve the monitoring. The study also shows the effect of spacing on the quality of the supervisory signal itself because of interaction with adjacent data signals.

Impact of the fiber type and dispersion management on the performance of a NRZ 16 x 40 Gb/s DWDM transmission system

We examine the impact of the fiber type and dispersion management on the performance of a 16 × 40 Gb/s dense wavelength-division-multiplexing nonreturn-to-zero transmission system. The transmission line is composed of G.652 or G.655 fiber with periodic dispersion compensation and hybrid Raman erbium-doped fiber amplifier amplification.

Dual-polarization multi-band optical OFDM transmission and transceiver limitations for up to 500 Gb/s uncompensated long-haul links

A number of critical issues for dual-polarization single- and multi-band optical orthogonal-frequency division multiplexing (DPSB/ MB-OFDM) signals are analyzed in dispersion compensation fiber (DCF)-free long-haul links. For the first time, different DP crosstalk removal techniques are compared, the maximum transmission-reach is investigated, and the impact of subcarrier number and high-level modulation formats are explored thoroughly. It is shown, for a bit-error-rate (BER) of 10-3, 2000 km of quaternary phase-shift keying (QPSK) DP-MBOFDM transmission is feasible. At high launched optical powers (LOP), maximum-likelihood decoding can extend the LOP of 40 Gb/s QPSK DPSB- OFDM at 2000 km by 1.5 dB compared to zero-forcing. For a 100 Gb/s DP-MB-OFDM system, a high number of subcarriers contribute to improved BER but at the cost of digital signal processing computational complexity, whilst by adapting the cyclic prefix length the BER can be improved for a low number of subcarriers. In addition, when 16-quadrature amplitude modulation (16QAM) is employed the digital-toanalogue/ analogue-to-digital converter (DAC/ADC) bandwidth is relaxed with a degraded BER; while the 'circular' 8QAM is slightly superior to its 'rectangular' form. Finally, the transmission of wavelength-division multiplexing DP-MB-OFDM and single-carrier DP-QPSK is experimentally compared for up to 500 Gb/s showing great potential and similar performance at 1000 km DCF-free G.652 line. © 2014 Optical Society of America.

Quasi-pilot aided phase noise estimation for coherent optical OFDM systems

In this letter, a novel phase noise estimation scheme has been proposed for coherent optical orthogonal frequency division multiplexing systems, the quasi-pilot-aided method. In this method, the phases of transmitted pilot subcarriers are deliberately correlated to the phases of data subcarriers. Accounting for this correlation in the receiver allows the required number of pilots needed for a sufficient estimation and compensation of phase noise to be reduced by a factor of 2 in comparison with the traditional pilot-aided phase noise estimation method. We carried out numerical simulation of a 40 Gb/s single polarization transmission system, and the outcome of the investigation indicates that by applying quasi-pilot-aided phase estimation, only four pilot subcarriers are needed for effective phase noise compensation. © 2014 IEEE.

Volterra-based reconfigurable nonlinear equalizer for coherent OFDM

A reconfigurable nonlinear equalizer (RNLE) based on inverse Volterra series transfer function is proposed for dual-polarization (DP) and multiband coherent optical orthogonal frequency-division multiplexing (OFDM) signals. It is shown that the RNLE outperforms by 2 dB the linear equalization in a 260-Gb/s DP-OFDM system at 1500 km. The RNLE improves the tolerance to inter/intraband nonlinearities, being independent on polarization tributaries, modulation format, signal bit rate, subcarrier number, and distance. © 1989-2012 IEEE.

Nonlinear spectral management:linearization of the lossless fiber channel

Using the integrable nonlinear Schrodinger equation (NLSE) as a channel model, we describe the application of nonlinear spectral management for effective mitigation of all nonlinear distortions induced by the fiber Kerr effect. Our approach is a modification and substantial development of the so-called eigenvalue communication idea first presented in A. Hasegawa, T. Nyu, J. Lightwave Technol. 11, 395 (1993). The key feature of the nonlinear Fourier transform (inverse scattering transform) method is that for the NLSE, any input signal can be decomposed into the so-called scattering data (nonlinear spectrum), which evolve in a trivial manner, similar to the evolution of Fourier components in linear equations. We consider here a practically important weakly nonlinear transmission regime and propose a general method of the effective encoding/modulation of the nonlinear spectrum: The machinery of our approach is based on the recursive Fourier-type integration of the input profile and, thus, can be considered for electronic or all-optical implementations. We also present a novel concept of nonlinear spectral pre-compensation, or in other terms, an effective nonlinear spectral pre-equalization. The proposed general technique is then illustrated through particular analytical results available for the transmission of a segment of the orthogonal frequency division multiplexing (OFDM) formatted pattern, and through WDM input based on Gaussian pulses. Finally, the robustness of the method against the amplifier spontaneous emission is demonstrated, and the general numerical complexity of the nonlinear spectrum usage is discussed. © 2013 Optical Society of America.

Femtosecond laser microstructuring through optical fibre end faces:inscription of surface gratings and sub-surface splitters

We present the results of femtosecond laser microstructuring of optical fibres by direct access of the fibre end face, both at the surface and several hundred microns into the fibre, to realise one-and two-dimensional grating structures and optical fibre splitters, respectively. We show the versatility of this simple but effective inscription method, where we demonstrate classic multiple slit diffraction patterns and show the potential for coarse wavelength division multiplexing for sensor signals. A key advantage for the fibre splitter is that the inscription method avoids the use of oil immersion that compensate for the fibre curvature in the standard side writing method. © 2012 SPIE.

Design of ultra-narrow WDM filters using the transmission response function of fibre Bragg gratings

We have demonstrated the feasibility of error-free DWDM 8×40 Gb/s transmission over an 800 km SMF/DCF link with 0.8 bit/s/Hz spectral efficiency without polarization multiplexing.

Application of long period gratings sensors to respiratory function monitoring

A series of in-line curvature sensors on a garment are used to monitor the thoracic and abdominal movements of a human during respiration. These results are used to obtain volumetric tidal changes of the human torso showing reasonable agreement with a spirometer used simultaneously to record the volume at the mouth during breathing. The curvature sensors are based upon long period gratings written in a progressive three layered fibre that are insensitive to refractive index changes. The sensor platform consists of the long period grating laid upon a carbon fibre ribbon, which is encapsulated in a low temperature curing silicone rubber. An array of sensors is also used to reconstruct the shape changes of a resuscitation manikin during simulated respiration. The data for reconstruction is obtained by two methods of multiplexing and interrogation: firstly using the transmission spectral profile of the LPG's attenuation bands measured using an optical spectrum analyser; secondly using a derivative spectroscopy technique.

Comparison of bit error rate estimation methods for QPSK CO-OFDM transmission

In this letter, we experimentally study the statistical properties of a received QPSK modulated signal and compare various bit error rate (BER) estimation methods for coherent optical orthogonal frequency division multiplexing transmission. We show that the statistical BER estimation method based on the probability density function of the received QPSK symbols offers the most accurate estimate of the system performance.