End-to-end Deep Learning for VCSEL’s Nonlinear Digital Pre-Distortion

We propose a novel optimization method for a Neural Network based Digital Pre-Distorter (DPD), applied in Intensity Modulation-Direct Detection transmission systems leveraging Multi-Modal Fiber and Vertical-Cavity Surface-Emitting Laser. We train the DPD using End-to-end Deep Learning of the optical link, together with a Direct Learning Approach leveraging experimental measurements for modeling the transmission channel. The optimization considers VCSEL amplitude constraints, the use of an FFE at the receiver side, and the presence of a receiver non-flat Colored Gaussian Noise (CGN). We verify our optimized DPD on an experimental setup transmitting a 92 Gbps PAM-4 modulated signal. We achieve, for BER=0.01, a performance gain of more than 1 dB in terms of Optical Path Loss with respect to the best performing non-pre-distorted scenario

Experimental VCSEL Digital Twin modeling for net 100 Gb/s/λ nonlinear Digital Pre-Distortion

We experimentally model a VCSEL-based optical transmitter for high speed intra data center interconnects using a convolutional neural network digital twin. The device is able to effectively reproduce the VCSEL linear and nonlinear distortions on PAM4 signals transmitted at 107.2 Gbps, thus enabling the optimization of nonlinear VCSEL-MMF digital pre-distorters

Optimization of 50G-PON APD-based receivers

In this paper, we approach the optimization of IM-DD systems leveraging APD-based receivers and Feed-Forward Equalization (FFE) at the receiver side (RX). We review the role of APD-based receivers in recent evolutions of IEEE and ITU-T standards for high-speed Passive Optical Networks (PON) and in particular in 50G-PON as discussed in the recently approved Recommendation ITU-T G.9804.3. We analyze different optimization methods for PAM-2 (NRZ) and PAM-4 modulation formats, based on grid search methods and analytical closed-form solutions for decision thresholds and PAM-4 internal levels. We develop our study on a simulated optical IM-DD system, transmitting at a Baud Rate R s =50 GBaud (i.e., 50 Gbps for NRZ, 100 Gbps for PAM-4). We assess power budget gain in terms of Optical Path Loss (OPL) with respect to nominal thresholds and levels, determining that optimizations are effective (i.e., approximately 1 dB OPL gain) when the system has moderate bandwidth limitations (B3dB>0.5⋅Rs). Our study can be of interest in the future for a better definition of the TDEC parameter for APD-based receivers

Nonlinear Pre-distortion through a Multi-rate End-to-end Learning Approach over VCSEL-MMF IM-DD Optical Links

We experimentally demonstrate a nonlinear digital pre-distorter for PAM-M shaping in VCSEL+MMF IM-DD links able to operate at a generic baud rate using a fractional sample-per-symbol Neural Network. We focus on efficient and practical multi-rate operation, signal amplitude constraints, and linear equalizer at the receiver

A Multi-Rate Approach for Nonlinear Pre-Distortion Using End-to-End Deep Learning in IM-DD Systems

Modern intra-data center (IDC) interconnects leverage robust and low-cost intensity modulation (IM) and direct detection (DD) optical links, based on multimode fibers (MMFs) and vertical-cavity surface-emitting lasers (VCSELs). Current solutions, based on on-off keying (OOK) modulations, reach up to 25-50 Gbps per lane over nearly 100 meters. The actual target for IDCs is to increase VCSEL-MMF links capacity up to 100 Gbps, using PAM-4 on the same devices. To counteract the consequent linear and nonlinear distortions affecting the transmitted signals, an effective solution is to exploit digital signal processing (DSP). In this manuscript, we propose a novel method to optimize a nonlinear artificial neural network (ANN) digital pre-distorter (DPD), based on End-to-end (E2E) learning, that, trained jointly with a Feed-Forward Equalizer (FFE), fulfills physical amplitude constraints and handles different ratio between the sampling rates incurring along with an optical IM-DD system. We indeed propose an E2E ANN system operating simultaneously at different sampling frequencies. We moreover propose in our training method a substitution to the time-domain injection of the receiver noise in the system with an additive regularization term in the FFE gradient loss. We experimentally show the advantages of our proposed DPD comparing the bit error rate (BER) performance against the same scenario without DPD. We assess the gain in terms of Gross Bit Rate and Optical Path Loss (OPL), at given BER targets, for different fiber lengths

Estimation Accuracy of Polarization State from Coherent Receivers for Sensing Applications

We experimentally investigate on the intrinsic accuracy in fiber State of Polarization estimation from the DSP of commercial coherent tranceivers, in terms of angular uncertainty on the Poincaré’s sphere vs. received OSNRs, for sensing applications. We then demonstrate how using a moving average enhances accuracy

APLICAÇÃO DE INDICADORES DE DESEMPENHO NOS MUNICÍPIOS COM MAIOR ORÇAMENTO DAS MESORREGIÕES DO RS

As demonstrações contábeis constituem o principal meio de divulgação das informações das entidades públicas, as quais são analisadas com o emprego de indicadores de desempenho, visando evidenciar a gestão dos recursos públicos. Este estudo objetiva realizar a análise de indicadores de desempenho nas demonstrações contábeis dos municípios com maior orçamento de cada uma das sete mesorregiões do estado do Rio Grande do Sul, nos anos 2018, 2019 e 2020. Caracteriza-se como uma pesquisa aplicada, descritiva e quantitativa, por meio de levantamento de dados nas demonstrações contábeis dos municípios selecionados, os quais foram analisados pela análise interpretativa. Como resultados deste estudo pode-se destacar que Caxias do Sul demonstra que parte das disponibilidades estão comprometidas com as obrigações, que não sobrou receitas correntes para aplicar em investimentos e que foram utilizados recursos de anos anteriores para realização das despesas. Passo Fundo evidencia que não tem disponibilidades para pagamento da dívida fundada, que sobrou receitas correntes para realizar investimentos e que parte dos recursos foram utilizados para pagamento da dívida. Pelotas demonstra que as disponibilidades estão comprometidas com as obrigações. Porto Alegre apresenta os maiores valores no indicador receita tributária per capita. Santa Maria e Santa Cruz do Sul demonstram que tem disponibilidade de recursos para pagamento das dívidas, que parte das receitas de capital são operações de crédito e que parte dos gastos são com despesas obrigatórias. E Uruguaiana aponta que parte dos recursos foram aplicados em investimentos e parte comprometido com pagamento da dívida

Evidence of an interaction between FXR1 and GSK3β polymorphisms on levels of Negative Symptoms of Schizophrenia and their response to antipsychotics

Introduction: Genome Wide Association Studies (GWAS) have identified several genes associated with schizophrenia (SCZ) and exponentially increased knowledge on the genetic basis of the disease. Additionally, products of GWAS genes interact with neuronal factors coded by genes lacking association, such that this interaction may confer risk for specific phenotypes of this brain disorder. In this regard, FXR1 (Fragile-X mental-retardation-syndrome-related 1) gene has been GWAS associated with SCZ. FXR1 protein is regulated by Glycogen Synthase Kinase-3 (GSK3), which has been implicated in pathophysiology of SCZ and response to Antipsychotics (APs). rs496250 and rs12630592, two eQTLs of FXR1 and GSK3 respectively, interact on emotion stability and amygdala/PFC activity during emotion processing. These two phenotypes are associated with Negative Symptoms (NS) of SCZ suggesting that the interaction between these SNPs may also affect NS severity and responsiveness to medication. Methods: To test this hypothesis, in two independent samples of patients with SCZ, we investigated rs496250 by rs12630592 interaction on NS severity and response to APs. We also tested a putative link between APs administration and fxr1 expression, as already reported for GSK3 expression. Results: We found that rs496250 and rs12630592 interact on NS severity. We also found evidence suggesting interaction of these polymorphisms also on response to APs. This interaction was not present when looking at positive and general psychopathology scores. Furthermore, chronic olanzapine administration led to a reduction of FXR1 expression in mouse frontal cortex. Discussion: Our findings suggest that, like GSK3 , FXR1 is affected by APs while shedding new light on the role of the FXR1/GSK3 pathway for NS of SCZ

Italian natural history museums on the verge of collapse?

The Italian natural history museums are facing a critical situation, due to the progressive loss of scientific relevance, decreasing economic investments, and scarcity of personnel. This is extremely alarming, especially for ensuring the long-term preservation of the precious collections they host. Moreover, a commitment in fieldwork to increase scientific collections and concurrent taxonomic research are rarely considered priorities, while most of the activities are addressed to public events with political payoffs, such as exhibits, didactic meetings, expositions, and talks. This is possibly due to the absence of a national museum that would have better steered research activities and overall concepts for collection management. We here propose that Italian natural history museums collaborate to instate a “metamuseum”, by establishing a reciprocal interaction network aimed at sharing budgetary and technical resources, which would assure better coordination of common long-term goals and scientific activities