Towards higher scalability of hybrid optical CDMA network

A novel approach for improving the number of simultaneous users in a hybrid OCDMAOTDMA network is proposed and analysed. OCDMA system is based on two-dimensional wavelength-hopping time-spreading codes with multi-wavelengths picosecond carriers. The scalability increase was achieved by adding a third dimension to separate OCDMA user groups within OTDMA time slots by assigning them into different wavelength bands. We have shown this will scale-up the system capacity proportionally to the number of assigned wavelength bands. A self-clocking all-optical time gate was then demonstrated as an effective means for suppressing the growing detrimental multi access interference noise resulted from this capacity increase

Chiral microstructures (spirals) fabrication by holographic lithography

We present an optical interference model to create chiral microstructures (spirals) and its realization in photoresist using holographic lithography. The model is based on the interference of six equally-spaced circumpolar linear polarized side beams and a circular polarized central beam. The pitch and separation of the spirals can be varied by changing the angle between the side beams and the central beam. The realization of the model is carried out using the 325 nm line of a He-Cd laser and spirals of sub-micron size are fabricated in photoresist.Comment: 6 page

Investigation of 2D-WH/TS OCDMA system performance under the influence of PMD

The impact of a differential group delay (DGD) and polarization mode dispersion (PMD) on multi-wavelength picosecond code carriers used by two-dimensional wavelength-hopping time-spreading coding schemes in optical code division multiple access (2D-WH/TS OCDMA systems is investigated. Based on experimental data collected over ten days on a 111 km long commercially used fiber link PMD and DGD parameters are determined and used to find the code carriers temporal broadening. This information is then used to calculate the 2D-WH/TS OCDMA system performance degradation as a function of varying number of simultaneous users for different DGD

Investigation of 2d-wh/ts ocdma code stability in systems with soa-based device

This paper investigates for the first time how the implementation of semiconductor optical amplifier (SOA)-based devices in photonic networks can negatively impact the integrity of two-dimensional wavelength-hopping time-spreading (2D-WH/TS) optical code-division multiple access (OCDMA) codes based on multi-wavelength picosecond code carriers. It is demonstrated and confirmed by simulations that the influence of an SOA under driving currents of 50 mA to 250 mA causes a 0.08 to 0.8 nm multi-wavelength picosecond code carriers’ wavelength redshift. The results obtained are then used to calculate the degradation of OCDMA system performance in terms of the probability of error Pe and the decrease in the number of simultaneous users. It is shown that, when the SOA-induced 0.8 nm code carriers redshift becomes equal to the code carries wavelength channel spacing, the (8,53)-OCDMA system performs only as a (7,53)-OCDMA system, and the number of simultaneous users drops from 14 to 10 or 84 to 74 with the forward error correction (FEC) Pe of 10 −9, respectively. The impact of the 0.8 nm redshift is then shown on a (4,53)-OCDMA system, where it causes a drop in the number of simultaneous users from 4 to 3 or 37 to 24 with the FEC Pe of 10 −9, respectively

Pulse-power-detection analysis of incoherent O-CDMA systems under the influence of fiber temperature fluctuations

In this paper, a pulse-shift technique, which divides every time slot (or chip) into equal-width sub-chips, is used to model the effect of fiber temperature fluctuations in incoherent optical code-division multiple-access (O-CDMA) systems. With the advance in all-optical thresholding technology, power detection of ultrashort optical pulses is possible. This paper also formulates a new pulse-power-detection model for incoherent OCDMA and applies it to the analysis of the pulse-shift technique as a case study. Numerical studies and computer simulations are presented to validate the new analytical model. Our study presents a more realistic theoretical model of all-optical thresholding in incoherent O-CDMA and results in better performance than the conventional pulse-energy-detection model

On the use of SOA-based tunable dispersion compensator in ultrafast incoherent fiber-optic CDMA systems undertemperature variation

The use of semiconductor-optical-amplifier-based tunable dispersion compensator (SOA-TDC) in ultrafast incoherent fiber-optic code-division multiple-access (FO-CDMA) systems with picosecond multiwavelength codes has recently been demonstrated. In this paper, results on the SOA-TOC’s capability of compensating for fiber chromatic dispersion and distorted autocorrelation function caused by fiber temperature variation (FTV) in such a FO-CDMA system with a long fiber link are reported. The deleterious effects of FTV to the system performance are quantified in terms of “chip granularity” and studied by applying a recent multiple-QoS performance-analytical model

Variable weight code division multiple access system for monitoring vibration of unequally distributed points

The ever-growing demand for more accurate structural health monitoring of large scale facilities such as modern high-speed railways and bridges have resulted in the development of optical sensor networks (OSN), which help eliminate the disadvantages of conventional electric sensors, the most significant of which are sensitivity to electromagnetic interferences and larger sizes. The existing fibre optic infrastructures that are implanted mainly for communication purposes are not widely used by OSNs, due to the lack of appropriate multiplexing techniques. This study proposes an optical code division multiple access (OCDMA) system for support vibration sensing of unequally distributed points. The proposed system takes the advantages of spectral amplitude encoding (SAC) technique in providing differentiated services in physical layer by varying code weights. Simulation results monitoring three vibration sensor nodes with different distances are presented in the paper. The simulation and mathematical analysis indicate the suitability and simple implementation of the proposed system for supporting vibration sensing with high accuracy

On the performance of the effects of temperature variation in ultrafast incoherent fiber-optic CDMA systems with SOA-based tunable dispersion compensator

Recent studies show that temperature variation in ultrafast incoherent fiber-optic code-division multiple-access (FO-CDMA) systems using picosecond multiwavelength codes is a realistic problem even though dispersion-compensating fiber is utilized. The phenomenon creates distortions in auto- and cross-correlation functions and then worsens system performance. A physical-layer mitigation approach has been reported by using a recently demonstrated semiconductor-optical-amplifier-based tunable dispersion compensator to fully recover the auto-correlation peaks. Applying the concept of 'chip granularity' to account for the effects of temperature variation to the cross-correlation functions, this paper formulates a new performance-analytical model for such FO-CDMA systems. The model also supports adjustable quality-of-services through code weight control

Association of cerebral small vessel disease burden and health-related quality of life after acute ischemic stroke

Objective: Cerebral small vessel disease (SVD) is associated with increased mortality, disability and cognitive decline, depression in stroke survivors. This study examined the association between SVD burden, defined by a combination of SVD markers, and health-related quality of life (HRQoL) in acute ischemic stroke. Methods: Patients admitted with acute ischemic stroke of any etiology were prospectively screened between January 2010 to December 2014 and enrolled in the study if they met study entry criteria. HRQoL was evaluated with the 12-item Stroke Specific Quality of Life (SSQoL) at 3 months after the onset of acute ischemic stroke. SVD was ascertained by the presence of any of the SVD markers including lacune, white matter hyperintensities (WMH), cerebral microbleeds (CMB) and enlarged perivascular spaces (EPVS) in the basal ganglia or their combinations on brain magnetic resonance imaging (MRI). The presence of each individual marker scored 1 point and was summed up to generate an ordinal “SVD score” (0–4) capturing total SVD burden. Linear regression was used to determine the associations between SVD burden and HRQoL. Results: Of the743 acute ischemic stroke patients that formed he study sample (mean age: 66.3 ± 10.6 years; 41.7% women), 49.3%, 22.5%, 16.0%, 9.2% and 3.1% had SVD scores of 0, 1, 2, 3 and 4, respectively. After adjusting for demographic, clinical and imaging variables, the SVD score was independently associated with lower overall score of SSQoL (B = − 1.39, SE = 0.56, p = 0.01), and its domains of mobility (B = − 0.41, SE = 0.10, p \u3c 0.001) and vision (B = − 0.12, SE = 0.06, p = 0.03). Acute infract volume (B = − 1.44, SE = 0.54, p = 0.01), functional independence (B = 5.69, SE = 0.34, p \u3c 0.001) and anxious (B = − 1.13, SE = 0.23, p \u3c 0.001) and depressive symptoms (B = − 3.41, SE = 0.22, p \u3c 0.001) were also the significant predictors of the overall score of SSQoL. Conclusion: The brain’s SVD burden predicts lower HRQoL, predominantly in domains of mobility and vision at 3 months after acute ischemic stroke. The evaluation of SVD burden could facilitate developing individual treatment strategies

Maternal protein-energy malnutrition during early pregnancy in sheep impacts the fetal ornithine cycle to reduce fetal kidney microvascular development

This paper identifies a common nutritional pathway relating maternal through to fetal protein-energy malnutrition (PEM) and compromised fetal kidney development. Thirty-one twin-bearing sheep were fed either a control (n=15) or low-protein diet (n=16, 17 vs. 8.7 g crude protein/MJ metabolizable energy) from d 0 to 65 gestation (term, ∼ 145 d). Effects on the maternal and fetal nutritional environment were characterized by sampling blood and amniotic fluid. Kidney development was characterized by histology, immunohistochemistry, vascular corrosion casts, and molecular biology. PEM had little measureable effect on maternal and fetal macronutrient balance (glucose, total protein, total amino acids, and lactate were unaffected) or on fetal growth. PEM decreased maternal and fetal urea concentration, which blunted fetal ornithine availability and affected fetal hepatic polyamine production. For the first time in a large animal model, we associated these nutritional effects with reduced micro- but not macrovascular development in the fetal kidney. Maternal PEM specifically impacts the fetal ornithine cycle, affecting cellular polyamine metabolism and microvascular development of the fetal kidney, effects that likely underpin programming of kidney development and function by a maternal low protein diet