Performance analysis of long band passive optical network using amplifier spontaneous noise and fiber Bragg gratings

Long band (L-Band) passive optical networks (PONs) are attracting a lot of attention these days, thanks to rising capacity demands. Because of PONs requesting more and more channels, fault detection/monitoring is critical. Fault detection in the conventional band (C-Band) employing reflecting Fiber Bragg Gratings (FBGs) and a probe signal integrating an additional amplified spontaneous noise (ASEN) source has been frequently demonstrated. However, interference occurs when ASEN and transmitter signals are in the same wavelength band, and adding additional ASEN sources to the network raises the overall cost. So, in L-Band PONs, a cost-effective, low-complexity fault detection/monitoring system is required. Therefore, in this work, a fault detection/monitoring system for L-Band PON using C-Band ASEN from inline erbium doped fiber amplifier (EDFA) and dual purpose FBG, i.e. (1) ASEN reflection for fault monitoring and (2) dispersion compensation is proposed. A 4 × 10 Gbps L-Band PON is investigated over 40 km feeder fiber (FF) and 1 km drop fibers (DFs) that serve 32 optical network units (ONUs)/different input powers, dispersion values, and laser linewidths in terms of reflective power of FBGs, eye opening factor, and bit error rate (BER), respectively.

Gain flattened and C/L band amplified spontaneous emission noise re-injected L-band EDFA

Explosive increase in internet services put peer pressure on conventional band grid (1530–1570 nm) and therefore L-band wide wavelength grid is required to cater the ever-increasing demands. In this work, accentuation is given to enhance the gain flattening of ultradense (25 GHz) L-band WDM system using single stage EDFA amplifier when ultralow power is launched from 16 and 32 channels. High gain and gain flattening is achieved by incorporating three fiber Bragg gratings (FBGs) for amplified spontaneous noise reinjection. Maximum Amplified spontaneous emission (ASE) is emerged at 1565 nm for the 1575.69–1579 nm input wavelengths (16 channels) and 1572.58–1579 nm (32 channels) at −55 dBm ultra low carrier powers. To optimize different parameters of L-band EDFA, different physical parameters such as core radius, EDF link lengths, and launched powers are varied, and results are analyzed in terms of lateness. Maximum gain is found out to be 34.12 dB at optimal physical parameters of the EDF with gain flatness of ±0.45 dB in case of 16 channels and ±1.41 in case of 32 channels.

Diurnal modulation of multivesicular release controls the efficiency of information transmission at a sensory synapse

Sensory circuits adapt to changes in the external world or the animal's internal state through the actions of neuromodulators. Synapses are key sites at which neuromodulators act but it is not known how they alter the amount of information transmitted. We investigated this question in the context of the diurnal regulation of visual processing in larval zebrafish, focusing on ribbon-type synapses of retinal bipolar cells. We demonstrate that contrast-sensitivity peaks in the afternoon accompanied by an average four-fold increase in the Shannon information transmitted at individual active zones. This increase reflects higher synaptic gain, lower spontaneous noise, reduced variability of stimulus-evoked release and improved temporal precision. Simultaneously, an increase in the probability of multivesicular events with larger information content increases the efficiency of information transmission (bits per vesicle) by factors of 2-3. The neuromodulator dopamine contributes to all these changes in synaptic function, although ON and OFF visual channels are differentially affected. Multivesicular release is a property of synapses in many parts of the brain and this study demonstrates that potentiation by neuromodulators can both increase the amount of information that is transmitted and the efficiency of transmission, revealing a previously unknown mechanism for adjusting neural processing.

Modeling Neural Variability in Deep Networks with Dropout

ABSTRACTConvolutional neural networks (CNNs) have been used to model the biological visual system. Compared to other models, CNNs can better capture neural responses to natural stimuli. However, previous successes are limited to modeling mean responses; while another fundamental aspect of cortical activity, namely response variability, is ignored. How the CNN models capture neural variability properties remains unknown. Previous computational neuroscience studies showed that the response variability can have a functional role, and found that the correlation structure (especially noise correlation) influences the amount of information in the population code. However, CNN models are typically deterministic, so noise (and correlations) in CNN models have not been studied. In this study, we developed a CNN model of visual cortex that includes neural variability. The model includes Monte Carlo dropout, namely a random subset of units is silenced at each presentation of the input image, inducing variability in the model. We found that our model captured a wide-range of neural variability findings in electrophysiology experiments, including that response mean and variance scale together, noise correlations are small but positive on average, both evoked and spontaneous noise correlation are larger for neurons with similar tuning, and the noise covariance is low-dimensional. Further, we found that removing the correlation can boost trial-by-trial decoding performance in the CNN model.

Serotonergic Modulation of Spontaneous and Evoked Transmitter Release in Layer II Pyramidal Cells of Rat Somatosensory Cortex

As axons from the raphe nuclei densely innervate the somatosensory cortex, we investigated how serotonin (5-HT) modulates transmitter release in layer II pyramidal cells of rat barrel cortex. In the presence of tetrodotoxin and gabazine, 10 μM 5-HT caused a waxing and waning in the frequency of miniature excitatory postsynaptic currents (mEPSC) with no effect on amplitude. Specifically, within 15 min of recording the mEPSC frequency initially increased by 28 ± 7%, then dropped to below control (−15 ± 3%), before resurging back to 27 ± 7% larger than control. These changes were seen in 47% of pyramidal cells (responders) and were mediated by 5-HT2C receptors (5-HT2CR). Waxing resulted from phospholipase C activation, IP3 production, and Ca2+ release from presynaptic stores. Waning was prevented if PKC was blocked. In contrast, in paired recordings, the unitary EPSC amplitude was reduced by 50 ± 3% after 5-HT exposure in almost all cases with no significant effect on paired-pulse ratio and synaptic dynamics. This sustained EPSC reduction was also caused by 5-HT2R, but was mediated by presynaptic Gβγ subunits likely limiting influx through CaV2 channels. EPSC reduction, together with enhanced spontaneous noise in a restricted subset of inputs, could temporarily diminish the signal-to-noise ratio and affect the computation in the neocortical microcircuit.

Frequency Encoded All Optical Tri-state Logic Gates NOT and NAND Using Semiconductor Optical Amplifier Based Interferometric Switches

All optical tri-state frequency encoded logic gates NOT and NAND are proposed and numerically investigated using TOAD based interferometric switch for the first time to the best of our knowledge. The optical power spectrum, extinction ratio, contrast ration, and amplified spontaneous noise are calculated to analyze and confirm practical feasibility of the gates. The proposed device works for low switching energy and has high contrast and extinction ratio as indicated in this work.

Bit Error Rate Analysis of Hybrid Buffer-Based Switch for Optical Data Centers

Data centers are very critical elements which store and distribute data over the Internet. current data centers heavily rely on electronics, and thus require vast amount of power and speed is limited. These limitations can be tackled using optical technology. In general optical devices consume lesser amount of power, and support very high data rates. In this paper, a hybrid buffer-based optical packet switch which can be used in data centers as aggregated or core switches is discussed. The physical layer analysis is presented and performance is measured in terms of bit error rate (BER) obtained at various power levels. The analysis is carried out in presence of crosstalk of various components and for acceptable BER≤10–9, minimum power required for all optical, all electronic and hybrid buffer is evaluated. Finally power penalty is also evaluated which is required to overcome the effect of amplified spontaneous noise (ASE) and components crosstalk.