Evolution of optical pulses in fiber lines with lumped nonlinear devices as a mapping problem

We analyze the steady-state propagation of optical pulses in fiber transmission systems with lumped nonlinear optical devices (NODs) placed periodically in the line. For the first time to our knowledge, a theoretical model is developed to describe the transmission regime with a quasilinear pulse evolution along the transmission line and the point action of NODs. We formulate the mapping problem for pulse propagation in a unit cell of the line and show that in the particular application to nonlinear optical loop mirrors, the steady-state pulse characteristics predicted by the theory accurately reproduce the results of direct numerical simulations.

Autosoliton propagation and mapping problem in optical fiber lines with lumped nonlinear devices

A theoretical model is developed to describe the propagation of ultrashort optical pulses in fiber transmission systems in the quasilinear regime, with periodically inserted in-line nonlinear optical devices.

Autosoliton propagation and mapping problem in optical fiber lines with lumped nonlinear devices

A theoretical model is developed to describe the propagation of ultrashort optical pulses in fiber transmission systems in the quasilinear regime, with periodically inserted in-line nonlinear optical devices. © 2005 The American Physical Society.

Evolution of optical pulses in fiber lines with lumped nonlinear devices as a mapping problem

We analyze the steady-state propagation of optical pulses in fiber transmission systems with lumped nonlinear optical devices (NODs) placed periodically in the line. For the first time to our knowledge, a theoretical model is developed to describe the transmission regime with a quasilinear pulse evolution along the transmission line and the point action of NODs. We formulate the mapping problem for pulse propagation in a unit cell of the line and show that in the particular application to nonlinear optical loop mirrors, the steady-state pulse characteristics predicted by the theory accurately reproduce the results of direct numerical simulations. © 2005 Springer Science+Business Media, Inc.

Development of a neurotoxicity test-system, using human post-mitotic, astrocytic and neuronal cell lines in co-culture

Astrocytes are essential for neuronal function and survival, so both cell types were included in a human neurotoxicity test-system to assess the protective effects of astrocytes on neurons, compared with a culture of neurons alone. The human NT2.D1 cell line was differentiated to form either a co-culture of post-mitotic NT2.N neuronal (TUJ1, NF68 and NSE positive) and NT2.A astrocytic (GFAP positive) cells (∼2:1 NT2.A:NT2.N), or an NT2.N mono-culture. Cultures were exposed to human toxins, for 4 h at sub-cytotoxic concentrations, in order to compare levels of compromised cell function and thus evidence of an astrocytic protective effect. Functional endpoints examined included assays for cellular energy (ATP) and glutathione (GSH) levels, generation of hydrogen peroxide (H2O2) and caspase-3 activation. Generally, the NT2.N/A co-culture was more resistant to toxicity, maintaining superior ATP and GSH levels and sustaining smaller significant increases in H2O2 levels compared with neurons alone. However, the pure neuronal culture showed a significantly lower level of caspase activation. These data suggest that besides their support for neurons through maintenance of ATP and GSH and control of H2O2 levels, following exposure to some substances, astrocytes may promote an apoptotic mode of cell death. Thus, it appears the use of astrocytes in an in vitro predictive neurotoxicity test-system may be more relevant to human CNS structure and function than neuronal cells alone. © 2007 Elsevier Ltd. All rights reserved.

Monitoring long distance WDM communication lines using a high-loss loopback supervisory system

In this paper, we present experimental results for monitoring long distance WDM communication links using a line monitoring system suitable for legacy optically amplified long-haul undersea systems. This monitoring system is based on setting up a simple, passive, low cost high-loss optical loopback circuit at each repeater that provides a connection between the existing anti-directional undersea fibres, and can be used to define fault location. Fault location is achieved by transmitting a short pulse supervisory signal along with the WDM data signals where a portion of the overall signal is attenuated and returned to the transmit terminal by the loopback circuit. A special receiver is used at the terminal to extract the weakly returned supervisory signal where each supervisory signal is received at different times corresponding to different optical repeaters. Therefore, the degradation in any repeater appears on its corresponding supervisory signal level. We use a recirculating loop to simulate a 4600 km fibre link, on which a high-loss loopback supervisory system is implemented. Successful monitoring is accomplished through the production of an appropriate supervisory signal at the terminal that is detected and identified in a satisfactory time period after passing through up to 45 dB attenuation in the loopback circuit. © 2012 Elsevier B.V. All rights reserved.

Monitoring long distance WDM communication lines using a high-loss loopback supervisory system

In this paper, we present experimental results for monitoring long distance WDM communication links using a line monitoring system suitable for legacy optically amplified long-haul undersea systems. This monitoring system is based on setting up a simple, passive, low cost high-loss optical loopback circuit at each repeater that provides a connection between the existing anti-directional undersea fibres, and can be used to define fault location. Fault location is achieved by transmitting a short pulse supervisory signal along with the WDM data signals where a portion of the overall signal is attenuated and returned to the transmit terminal by the loopback circuit. A special receiver is used at the terminal to extract the weakly returned supervisory signal where each supervisory signal is received at different times corresponding to different optical repeaters. Therefore, the degradation in any repeater appears on its corresponding supervisory signal level. We use a recirculating loop to simulate a 4600 km fibre link, on which a high-loss loopback supervisory system is implemented. Successful monitoring is accomplished through the production of an appropriate supervisory signal at the terminal that is detected and identified in a satisfactory time period after passing through up to 45 dB attenuation in the loopback circuit. © 2012 Elsevier B.V. All rights reserved.

Dispersionless low-loss miniature slow light delay lines based on optical fibers

A miniature slow light delay line with the record large delay time, small transmission loss, dispersion, and effective speed of light is proposed and demonstrated using the SNAP (Surface Nanoscale Axial Photonics) technology. © 2014 OSA.

Reduction of nonlinear intrachannel effects by channel asymmetry in transmission lines with strong bit overlapping

We have examined the statistics of simulated bit-error rates in optical transmission systems with strong patterning effects and have found strong correlation between the probability of marks in a pseudorandom pattern and the error-free transmission distance. We discuss how a reduced density of marks can be achieved by preencoding optical data.

Optimisation of optical regeneration at 40 Gbit/s in dispersion-managed transmission lines with modified synchronous modulators

Numerical optimisation of a 40 Gbit/s dispersion-managed soliton transmission system with in-line synchronous intensity modulation is performed. Using a time-saving numerical approach, superiority of the modified synchronous modulation over conventional synchronous modulation is demonstrated and an optimal operational regime is found.

Optical regeneration at 40 Gb/s in dispersion-managed transmission lines with in-line synchronous modulators

Numerical optimization is performed of the 40-Gb/s dispersion-managed (DM) soliton transmission system with in-line synchronous intensity modulation. Stability of DM soliton transmission results from a combined action of dispersion, nonlinearity, in-line filtering, and modulation through effective periodic bandwidth management of carrier pulses. Therefore, analysis of the multiparametric problem is typically required. A two-stage time-saving numerical optimization procedure is applied. At the first step, the regions of the stable carrier propagation are determined using theoretical models available for DM solitons, and system parameters are optimized. At the second stage, full numerical simulations are undertaken in order to verify the tolerance of optimal transmission regimes. An approach developed demonstrates feasibility of error-free transmission over 20 000 km in a transmission line composed of standard fiber and dispersion compensation fiber at 40 Gb/s.

Optimization of dispersion-managed optical fiber lines

We present various approaches to the optimization of optical fiber lines and discuss the ranges of validity of such methods. An effective scheme for upgrading of existing transmission lines using dispersion-management with optimization of the pre- and postcompensating fiber is examined. The theory and numerical methods are illustrated in application to the Upgrade of a specific installed Deutsche Telekom fiber line.

Transglutaminase overexpression sensitizes neuronal cell lines to apoptosis by increasing mitochondrial membrane potential and cellular oxidative stress

'Tissue' transglutaminase (tTG) selectively accumulates in cells undergoing apoptosis both in vivo and in vitro. Considering the central role played by mitochondria in apoptosis, we investigated the relationships existing amongst tTG expression, apoptosis and mitochondrial function. To this aim we studied the mechanisms of apoptosis in a neuronal cell line (SK-N-BE (2)) in which the tTG-expression was driven by a constitutive promoter. Furthermore, a tet-off inducible promoter was also used in 3T3 fibroblastic cells used as control. Both cell lines, when expressing tTG, appeared 'sensitized' to apoptosis. Strikingly, we found major differences in the morphological features of mitochondria among cell lines in the absence of apoptotic stimuli. In addition, these ultrastructural characteristics were associated with specific functional features: (i) constitutively hyperpolarized mitochondria and (ii) increased reactive oxygen intermediates production. Importantly, after mitochondrial-mediated apoptosis by staurosporine, a rapid loss of mitochondrial membrane potential was found in tTG cells only. Taken together, these results seem to suggest that, via hyperpolarization, tTG might act as a 'sensitizer' towards apoptotic stimuli specifically targeted to mitochondria. These results could also be of pathogenetic relevance for those diseases that are characterized by increased tTG and apoptotic rate together with impaired mitochondrial function, e.g. in some neurodegenerative disease.

Further preliminary assessment of three human glioma cell lines as models of human astrocytic toxicity in vitro

Three human astroglioma lines U251-MG, U373-MG and CCF-STTG1 have been evaluated further as possible models for astrocytotoxicity (GFAP and IL-6 release). The effects of bacterial lipopolysaccharide, chloroquine diphosphate and acrylamide were studied on GFAP expression and LPS, chloroquine diphosphate, ethanol, trimethyltin chloride (TMTC) and acrylamide were examined on interleukin-6 (IL-6) release in the U373-MG line only. At 4-h LIPS elevated GFAP (17.0±5.0% P < 0.05) above control in the U251-MG cell line only. Chloroquine diphosphate over 4 h in the U251-MG line resulted in an increase in GFAP-IR to 20.3 ±4.2% and 21.1 ± 4.1 % above control levels 0.1 µM (P< 0.05) and 1 µM (P< 0.05) respectively. CQD was associated with decreases in MTT turnover, particularly after 24 h incubation. With the U373-MG line, LPS (0.5 µg/ml) increased IL-6 expression 640% above control (P < 0.001), whilst chloroquine diphosphate (100 µM), ethanol (10mM) and TMTC chloride (1 µM) also increased IL-6. It is possible that batteries of astrocytic human glioma cell lines may be applicable to the sensitive evaluation of toxicants on astrogliotic expression markers such as GFAP and IL-6.

A comparison of the apoptotic and cytotoxic effects of hexanedione derivatives on human non-neuronal lines and the neuroblastoma line SH-SY5Y

The effects of the alpha-diketone derivatives 2,3- and 3,4-hexanediones were investigated in three non-neuronal cell lines (MCF7, HepG2 and CaCo-2) as well as in the neuroblastoma line, SH-SY5Y. The MTT reduction assay was employed to determine the necrotic effects of the alpha-diketones and the neurotoxin 2,5-hexanedione over 4, 24 and 48 hr exposures. Flow cytometry was also used to study the effects of the three isomers on the cell cycle of the SH-SY5Y line only. With 2,5-hexanedione, the mean MTT IC50 decreased more than 10-fold from 4 to 48 hr. The toxicities of both alpha-diketones were similar, with a more than 18-fold increase in sensitivity of the SH-SY5Y at 24 hr compared to that of 4 hr. With flow cytometry at 48 hr, SH-SY5Y apoptosis with 2,5-hexanedione rose throughout the concentration range evaluated (0-30 mM) while 2,3- and 3,4-hexanediones showed apoptosis over the concentration range 1-1.6 mM, with 3,4-hexanedione being the more potent compared to the 2,3-isomer. At 1.6 mM nearly all the cells had entered apoptosis in the presence of the 3,4-isomer, (94.9 ± 1.4%) but only 57.5 ±4.1% of the 2,3-isomer-treated cells had reached that stage. The 2,3-and 3,4-isomers in diets alone may not pose a serious threat to human health. Further studies may be necessary to evaluate the effects of other dietary components on their toxicity. These alpha-diketones also display a degree of toxic selectivity towards neuroblastoma cells, which may have therapeutic implications.