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In this paper, the performance of mid-link spectral inversion (MLSI)-based transmission is quantitatively compared to the performance for 'conventional' dispersion compensating fiber (DCF)-based transmission. Bit error rates (BER) are measured at optimized residual dispersion for all sixteen channels after 800km transmission in standard single mode fiber (SSMF). We show that for the MLSI-based configuration up to a decade of improvement in BER is obtained compared to the DCF based system. MLSI has the potential of lowering the cost of long haul transmission systems since instead of having multiple DCF modules per span only one spectral inverter is required for the whole transmission line. For spectral inversion, a polarization independent magnesium-oxide-doped periodically-poled lithium-niobate (MgO:PPLN) based subsystem was used.

We demonstrate the successful transmission of 10 channels with 224-Gb/s POLMUX-16QAM modulation (28 GBaud) on a 37.5-GHz wavelength grid. Using large-Aeff pure-silica-core fibers we show a 656-km transmission distance with a spectral efficiency of 5.6 b/s/Hz. We report a back-to-back performance penalty of 3.5 dB compared to theoretical limits at the forward-error correction (FEC) limit (bit-error rate of 3.8·10-3), and a margin of 0.5 dB in Q-factor with respect to the FEC-limit after 656 km of transmission.

We report a FPGA-based real time 23.9-Gb/s CO-OFDM transmitter with IQ-mixing with a 1024 point FFT, the largest FFT-size reported to date. For a BER of 10-3 a required OSNR of 10.8 dB is measured.

We demonstrate the successful transmission of five 448 Gb/s dual-carrier POLMUX 16QAM modulation (28 GBaud) on a 75-GHz wavelength grid. Using large Aeff pure-silica-core fibers we show a 984 km transmission distance with a spectral efficiency of 5.6 b/s/Hz, including three ROADM passes.

We compare the suitability of 43-Gb/s POLMUX-RZ-DPSK and POLMUX-RZ-DQPSK modulation for long-haul optical transmission. We experimentally demonstrate that the higher robustness against nonlinear impairments of 43-Gb/s POLMUX-RZ-DPSK allows for a ~40% increase in feasible transmission distance.

We demonstrate that coherent detection combined with digital signal processing can completely compensate for FBG induced phase-ripple. We report penalty free transmission of 40×111-Gb/s POLMUX-RZ-DQPSK over 1,425-km of SSMF with FBG for in-line dispersion compensation

The rise of coherent detection and digital signal processing is drastically changing the design of optical transmission systems. In this paper we review the challenges and opportunities offered by such receivers in the design of long-haul 100G systems.

We investigate the transmission performance of 111-Gb/s POLMUX-RZ-DQPSK modulation using either optical or electrical dispersion compensation. We show that after 2000-km LEAF transmission both link configurations have a comparable nonlinear tolerance.

We discuss the optimal filtering bandwidth for 42.8-Gbit/s RZ-DQPSK modulation through simulations and experiment. We verify that 42.8-Gbit/s RZ-DQPSK is tolerant to suboptimal filtering, and show that narrowband filtering can result in a sensitivity improvement.

Background There are a number of studies that suggest a relationship between decline of melatonin function and the symptoms of dementia. Objectives The review assessed the evidence of clinical effectiveness of melatonin in the treatment of symptoms of dementia. Relevant primary outcomes were cognition, mood, behaviour, functions of daily living, and safety of melatonin use and secondary outcomes were quality of life, morbidity, mortality and length of time to institutionalization and caregiver stress. Search methods The Specialized Register of the Cochrane Dementia and Cognitive Improvement Group (CDCIG), The Cochrane Library,MEDLINE, EMBASE, PsycINFO, CINAHL and LILACS were searched on 29 June 2009 using the terms: MELATONIN and N-ACETYL-5- METHOXYTRYPTAMINE. The CDCIG Specialized Register contains records from all major health care databases (The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL, LILACS) as well as from many trials databases and grey literature sources. The search of June 2009 retrieved several studies for consideration by the authors. Selection criteria All relevant, randomized controlled trials in which orally administered melatonin in any dosage was compared with a control group for the effect on managing cognitive, behavioral (excluding sleep), and mood disturbances of people with dementia of any degree of severity. Data collection and analysis Two to three reviewers independently assessed the retrieved articles for relevance and risk of bias, and extracted data from the selected studies. Statistically significant differences in end-points or changes in outcomes frombaseline to end of treatment between themelatonin and control groups were examined. Each study was summarized using a measure of effect (e.g. mean difference) and meta-analyses were conducted when appropriate. Main results Five studies met the inclusion criteria. The pooled estimates of MMSE cognitive and ADAS-cognitive change scores from three of these studies revealed non-significant cognitive effects for melatonin treatment. In two of these studies, significant improvements in psychopathological behaviours (e.g., decreased mood symptoms of depression, anxiety and apathy and decreased behavior symptoms of hallucinations, delusions, agitation, irritability, and appetite disturbances), were found from meta-analysis of the change scores from the NPI (7 weeks, 2.5 mg melatonin), and ADAS non-cognitive (4 weeks, 3 mg melatonin) scales. Sensitivity analyses found similar results to those of the original meta-analyses, and thus, supported the effect estimates for non-significant cognitive outcomes. Individual study estimates for treatment effect of 2.5 mg melatonin at one year demonstrated a significant worsening of mood (e.g. decrease in positive affect) as measured by the Philadelphia Geriatric Centre Affect Rating Scale (positive). The remainder of the treatment effects for mood, behavior, and function of daily living were non-significant. There were no reported adverse effects associated with melatonin use. Authors’ conclusions The analyses did not support the use of melatonin for treatment of cognitive impairment associated with dementia. Meta-analysis of psychopathologic behavior scale scores suggested that melatonin may be effective in treating these dementia-related disturbances. P L A I N L A N G U A G E S U M M A R Y Melatonin treatment may be effective for the treatment of dementia-related behavior disturbances There are a number of studies that suggest a relationship between decline of melatonin function and the symptoms of dementia. Metaanalysis was conducted on data from three randomised, placebo controlled trials that were designed to evaluate melatonin for managing dementia-related cognitive changes; data also were pooled from two of these trials that evaluated melatonin for managing mood and behavioral disturbances. Significantly improved outcomes were found from the meta-analysis of psychopathologic behavior and mood scale scores. Melatonin treatment may be effective for the treatment of dementia-related psychopathologic behavior disturbances. No evidence was found to support the effectiveness of melatonin for the treatment of cognitive impairment.

As the data rate of long-haul transmission links is increased, the design and realization of the transmission link becomes more difficult. As a result, more sophisticated methods are required to improve the transmission quality. The robustness of a transmission link can be increased and its structure greatly simplified by the use of mid-link optical phase conjugation (OPC). OPC is a promising technology to compensate for deterministic, phase related impairments (i.e. the Kerr effect and chromatic dispersion) in long-haul transmission systems. This thesis assesses the regenerative capabilities of OPC for the compensation of distortions that occur in modern transmission systems. The focus of the research is on transmission systems where OPC is employed to compensate for both chromatic dispersion and nonlinear impairments. The dispersion map (i.e. the dispersion as a function of the transmission distance) of such a transmission system is completely different from that of a conventional transmission system. The accumulated dispersion along the link of an OPCbased transmission system is significantly higher than that of a conventional transmission system. We investigated the influence of the dispersion map of OPC on nonlinear impairments using the non return-to-zero amplitude-shift-keying (NRZ-ASK) modulation format. As a result, it is shown that the peak powers that occur in the OPC transmission system are at a 10-Gbit/s/channel data rate significantly higher than the peak powers that occur in a conventional transmission system. The higher peak powers in the OPC based transmission system lead to an increased self-phase modulation (SPM) penalty. Through phase conjugation most of the SPM impairments are compensated for. However, when multiple wavelength division multiplexed (WDM) channels at narrow channel spacing are used for transmission, cross-phase modulation (XPM) is the dominating transmission impairment. Although XPM is principally a deterministic distortion, it must be treated as non-deterministic due to the dispersion of the transmission link. With simulations and experiments we show that because of this, the XPM compensation through OPC is marginal. At a 40 Gbit/s data rate, the peak powers that occur in the OPC-based transmission system are similar to those that occur in the conventional transmission system. In 40 Gbit/s WDM transmission systems the influence of XPM is relatively low. These transmission systems are rather limited by intra-channel nonlinear impairments such as SPM, intrachannel XPM (IXPM) and intrachannel FWM (IFWM). We show experimentally that in this case, the performance of the OPC transmission system is better than that of the conventional transmission system. When OPC is used to compensate for the chromatic dispersion, the OPC must be placed in the middle of the transmission link. This technique is often referred to as "midlink OPC". However, in some transmission links it is not possible to place the OPC exactly in the middle. Therefore, several configurations with a transmission length of 700 km to 900 km were assessed where the OPC was placed 100 km from the middle of the transmission link. In this experiment practically no bit-error ratio (BER) degradation was observed in the off-center configuration. Recently, strong interest has been shown in phase-shift keying modulation (PSK) formats such as differential phase-shift-keying (DPSK). DPSK’s main advantages over ASK are that it is more robust to narrowband optical filtering and has a 3 dB higher sensitivity in combination with balanced detection. However, unlike ASK signals PSK signals can be distorted by nonlinear phase noise (NPN). For long-haul transmission systems, the impact of NPN is so severe that the performance of DPSK is in some cases even worse than that of ASK. The impact of nonlinear phase noise is studied for 10.7-Gbit/s DPSK in an 800-km transmission link. In this experiment it is shown that impairments due to nonlinear phase noise can be significantly reduced using optical phase conjugation. The dependence of the location of the OPC within the transmission link is assessed as well. Allowing a penalty of 1 decade in BER from the optimum, the OPC-unit can be varied over a wide range, from nearly 1/3 to 2/3 of the transmission link. The combination of mid-link OPC is assessed with 21.4-Gbit/s return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) in an ultra long-haul transmission experiment. Error-free transmission after FEC is realized over 10,200 km for all 22 WDM channels. In this experiment, a single OPC-unit is used in the middle of the link to compensate for an accumulated chromatic dispersion of over 160,000 ps/nm. Along the transmission line, the dispersion accumulates in this experiment to more than 80,000 ps/nm. This is significantly higher than the maximum accumulated dispersion in the conventional transmission system (approximately 3,000 ps/nm). The high accumulated dispersion results in an extreme overlap of the pulses along the transmission line. With this experiment we show that despite the high dispersion, the feasible transmission distance of the OPC based transmission system is 44% greater than that obtained in the conventional transmission system. By doubling the data rate and keeping the 50-GHz channel spacing, a 0.8-bit/s/Hz spectral efficient WDM transmission system is realized. At 42.8-Gbit/s RZ-DQPSK, transmission over 5,000 km was realized with mid-link OPC. Compared to the feasible transmission distance obtained at 21.4-Gbit/s, the feasible transmission distance is reduced by about 50%. This reduction of transmission distance with 50% corresponds to the 3-dB OSNR penalty that is present between 21.4-Gbit/s and 42.8-Gbit/s RZ-DQPSK in the back-toback configuration. For the conventional transmission system, a greater reduction in the feasible transmission distance (factor of 2.4) is measured due to increased penalties that result from a combination of self phase modulation and nonlinear phase noise. Comparing the feasible transmission distance of the OPC to the conventional transmission system an improvement of 60% is observed in this experiment.

We experimentally compare the nonlinear tolerance ofDWDM 21.4-Gbit/s RZ-DQPSK and 21.4-Gbit/s POLMUX-RZ-DPSK modulation over an 800-km SSMF straight-line. We show that the small depolarization penalty of POLMUX-RZ-DPSK makes it a possible alternative to RZDQPSK modulation for next-generation transmission.

The transmission performance of optical phase conjugation (OPC) is assessed with a special focus on the combination with the RZ-DQPSK modulation format. We show that when OPC is employed, significant performance improvement is obtained compared to conventional DCF based transmission.

Long-haul transmission (>1,000 km) with 1.6-b/s/Hz spectral efficiency is shown for the first time. Using polarization-multiplexed RZ-DQPSK, we demonstrate 40 x 85.6-Gb/s transmission over 1,700 km (18 x 94.5 km) of standard-single-mode fiber with 1-dB Q-margin.

In this paper we experimentally confirm the impairment due to nonlinear phase noise degradation in ultra-long haul 2x 10Gbit/s DQPSK WDM transmission over 7.100 km of SSMF

We discuss the performance of a multichannel 2 3 10 Gbit/s polarization-multiplexed differential phaseshift keying transmission system. Through simulations and transmission experiments we find that, despite the constant power envelope of non-return-to-zero phase-shift keying modulation formats, polarization multiplexing strongly reduces the nonlinear tolerance and transmission performance at a 2 3 10 Gbit/s line rate with multichannel transmission. This results in a 10 dB power penalty when comparing single- and nine-channel transmission. Additionally, multichannel impairments in differential phase-shift keying and on–off keying are compared for 2 3 10 Gbit/s polarization-multiplexed transmission. © 2005 Optical Society of America

We discuss an improved detection scheme for differential phase shift keying (DPSK) and differential quadrature phase shift keying (DQPSK), based on multi-symbol phase estimation (MSPE) through electrical signal processing. Using a recursive electrical signal processing algorithm, close to homodyne performance is obtained without a local oscillator at the receiver. In the presence of only Gaussian noise the proposed scheme yields a O.SdB and 1.8dB sensitivity improvement over self-homodyne detection, for DPSK and DQPSK respectively. lt furthermore improves robustness against impairments due to the influence of a finite laser linewidth and nonlinear phase noise.

Differential-quadrature phase-shift-keying (DQPSK) can, unlike on-off-keying (OOK), be impaired by nonlinear phase noise (NPN). It has been shown that optical phase conjugation (OPC) is an effective compensation scheme for NPN resulting from the ASE of EDFAs (ASE-NPN). In this paper we discuss the influence of NPN resulting from modulator imperfections (MJ-NPN). We show that MI-NPN can be compensated for through OPC, though shifts the optimum location of the OPC towards the middle of the transmission link.

We show in an 800km SSMF transmission experiment, that mid-link spectral inversion can be employed to reduce the effect of nonlinear phase noise (Gordon-Mollenauer noise) on DPSK by over two decades in BER.

The impact of asymmetric placement of a spectral inverter is investigated in an 800km long transmission link. We show that for 42.7Gbit/s NRZ and duobinary modulation the impact is minor and can be neglected.

A polarization-diverse subsystem based on periodically poled lithium niobate waveguides is used as an optical phase conjugator for compensation for linear and nonlinear distortion. We show successful transmission formats of 13 3 40 Gbit/s on-return-to-zero mixed with 6 3 10 Gbit/s non-return-to-zero and 40-Gbit/s suobinary

We demonstrate the feasibility of a cost-effective 640 Gb/s (16×40 Gb/s) wavelength-division-multiplexed (WDM) transmission system over 800 km of conventional standard single-mode fiber (SSMF) without using in-line dispersion management. Instead for chromatic-dispersion compensation, a Magnesium-oxide-doped periodically poled lithium niobate (MgO : PPLN)-based polarization-diverse subsystem is used to phase conjugate all 16 channels. The transmission line uses all erbium-doped fiber amplifiers and has an amplifier spacing of 100 km. All channels launched were copolarized. To the best of our knowledge, this is the first WDM transmission experiment with a channel data rate of 40 Gb/s using a PPLN as chromatic-dispersion compensator.

We show that by combining mid-link spectral-inversion with the duobinary data modulation format, a robust, highly dispersion tolerant 40-Gbit/s transmission system is created.

We report on 160-Gbit/s all-optical demultiplexing on the basis of a monolithically integrated SOA-Mach-Zehnder interferometer with error-free operation at a base data rate of 10 Gbit/s and a BER of 10-8at 40 Gbit/s.