Correlation and power distribution of intercore crosstalk field components of polarization-coupled weakly coupled single-mode multicore fibres

The correlation and power distribution of intercore crosstalk (ICXT) field components of weakly coupled multicore fibers (WC-MCFs) are important properties that determine the statistics of the ICXT and ultimately impact the performance of WC-MCF optical communication systems. Using intensive numerical simulation of the coupled mode equations describing ICXT of a single-mode WC-MCF with intracore birefringence and linear propagation, we assess the mean, correlation, and power distribution of the four ICXT field components of unmodulated polarization-coupled homogeneous and quasi-homogeneous WC-MCFs with a single interfering core in a wide range of birefringence conditions and power distribution among the field components at the interfering core input. It is shown that, for homogeneous and quasi-homogeneous WC-MCFs, zero mean uncorrelated ICXT field components with similar power levels are observed for birefringence correlation length and birefringence beat length in the ranges of [0.5 m, 10 m] and [0.1 m, 10 m], respectively, regardless of the distribution of power between the four field components at the interfering core input.info:eu-repo/semantics/publishedVersio

Outage probability due to crosstalk from multiple interfering cores in PAM4 inter-datacenter connections

In this work, we propose to use four-level pulse amplitude modulation (PAM4) and multicore fibers (MCFs) to support very high capacity datacenter interconnect (DCI) links. The limitations imposed by inter-core crosstalk (ICXT) on the performance of 112 Gb/s up to 80 km-long optically amplified PAM4 inter-DCI links with intensity-modulation and direct-detection and full chromatic dispersion compensation in the optical domain are analyzed through numerical simulation for high and low skew-symbol rate product (SSRP). With only one interfering core, we show that those PAM4 inter-DCI links achieve an outage probability (OP) of 10−4 with a maximum ICXT level of −13.9 dB for high SSRP and require an ICXT level reduction of about 8.1 dB to achieve the same OP for low SSRP. Due to using full dispersion compensation, for an OP of 10−4, the maximum acceptable ICXT level shows only a 1.4 dB variation with the MCF length increase from 10 km to 80 km. When considering the ICXT induced by several interfering cores, the maximum ICXT level per interfering core for an OP of 10−4 decreases around 3 dB when doubling the number of interfering cores. This conclusion holds for high and low SSRP regimes. For two interfering cores, we show that a single interfering core with low SSRP is enough to induce a severe reduction of the maximum acceptable ICXT level.info:eu-repo/semantics/publishedVersio

Performance evaluation of direct-detection OFDM optical receivers with RF down-conversion

A new method based on the moment generating function is proposed to assess the performance of a direct-detection OFDM optical communication system with radio-frequency I/Q demodulation and its accuracy is validated by Monte Carlo simulation.info:eu-repo/semantics/acceptedVersio

Accuracy of Gaussian approach for the performance evaluation of direct-detection receiver with partially polarized noise

We investigate the accuracy of a Gaussian approach (GA) developed to estimate the performance of a direct-detection optical receiver with arbitrary optical and electrical filtering and in the presence of partially polarized noise due to polarization-dependent loss (PDL). The accuracy is assessed by comparison of the performance estimates obtained from the GA with the estimates obtained from a rigorous method (RM) based on the calculation of the moment-generating function of the current at the optical receiver output. We show that the GA has a good accuracy when considering the variation of the optical filter bandwidth, extinction ratio, degree of polarization of the noise (DOP), and angle between signal and noise polarizations. However, it fails to predict the receiver sensitivity within 2 dB of the RM when DOP is greater than 0.7 and signal and noise polarizations are orthogonal in the Jones space. Nevertheless, it is shown that the GA provides receiver sensitivity estimates with good accuracy in most cases of long-haul optical communication systems influenced by PDL, where the typical average DOP is below 0.15. Due to its simplicity, shorter computation time, and good accuracy, the GA is a good tool to assess the performance of such optical systems.info:eu-repo/semantics/acceptedVersio

On the use of the Gaussian approach for the performance evaluation of direct-detection OFDM receivers impaired by in-band crosstalk

The Gaussian approach (GA) is used to assess the impact of in-band crosstalk on the performance of direct-detection orthogonal frequency division multiplexing (OFDM) optical communication systems. The GA accuracy is compared with estimates of the bit error probability (BEP) and crosstalk penalty obtained using Monte Carlo (MC) simulation. The GA revealed a reduced accuracy when estimating the BEP. However, when estimating the 1 dB crosstalk penalty, the GA exhibited a good accuracy (less than 0.5 dB in comparison with the crosstalk level estimated using MC simulation), for 16-quadrature amplitude modulation (QAM) and 64-QAM mappings in the OFDM subcarriers. The GA leads to very discrepant estimates of the crosstalk penalty for high crosstalk levels.info:eu-repo/semantics/acceptedVersio

Outage probability due to intercore crosstalk from multiple cores in short-reach networks

The outage probability (OP) due to intercore crosstalk (ICXT) arising from multiple interfering cores in short-reach binary intensity modulation-direct detection optical links supported by homogeneous weakly-coupled multicore fibers is assessed through numerical simulation. The maximum acceptable ICXT level for a given OP is extracted from simulation results, for low and high skew-bit rate products (SBRPs). (i) For high SBRP, a 3 dB reduction of the maximum acceptable ICXT level per core for a given OP is observed when the number of interfering cores doubles. In this case, as a very large number ( ≫1 ) of bits of each interfering core is contributing to ICXT, the total detected ICXT tends to a Gaussian distribution that makes the maximum acceptable total ICXT level independent of the interfering core count. (ii) For low SBRP, the number of bits contributing to ICXT is similar to the interfering core count and the total detected ICXT assumes a set of discrete amplitudes, which deviates it from the Gaussian distribution. Hence, the reduction of the maximum acceptable ICXT level per core, when the number of interfering cores is doubled, is about 2 dB, and the maximum acceptable total ICXT level increases with the interfering core count, by around 3 dB, when the interfering core count increases from 1 to 8.info:eu-repo/semantics/acceptedVersio

Moment Generating Function for the Rigorous Performance Assessment of Direct-Detection Baseband OFDM Communication Systems

WOS:000312036100008 (Nº de Acesso Web of Science)“Prémio Científico ISCTE-IUL 2013”A new moment generating function (MGF) is proposed to assess rigorously the performance of optically preamplified receivers with direct-detection employing baseband orthogonal frequency division multiplexing (OFDM). By comparison with Monte Carlo simulation, the proposed MGF-based method shows very good accuracy when predicting the bit error probability for arbitrary optical and electrical filters, different numbers of OFDM subcarriers, and double sideband and single sideband optical OFDM signals. Its good accuracy when estimating the bit error probability in each individual subcarrier is also demonstrated. The new MGF-based method exhibits a significant improvement of accuracy when compared to the MGF-based method previously reported in the literature, especially for filter bandwidths not exceeding the OFDM signal bandwidth, which is the range corresponding to the optimum filter bandwidth

Transmission of PAM4 signals in ICXT-impaired intra-datacenter connections with PAM2 signal interference

Traffic in datacenters has been significantly increasing over the last few years. As a result, it is necessary to scale the connections of the datacenters to accommodate such an increase of traffic. The solution considered in this work is to use four-level pulse amplitude modulation (PAM4) and weakly-coupled multicore fibers (MCFs) to support intra-datacenter connections. However, transmission in weakly-coupled MCFs may be significantly degraded by inter-core crosstalk (ICXT). In this work, the impact of ICXT on the performance of PAM4 transmission in short-haul direct-detection links is evaluated considering two-level PAM (PAM2) signals in the interfering cores. The ICXT impact on the performance of the tested core with PAM4 transmission is evaluated using the bit error rate (BER), outage probability (OP) and eye-pattern analysis. Comparing to PAM2 transmission in the tested core, a 7.6 dB lower ICXT level is required to achieve an acceptable OP for a reference BER of 3.8×10−3 in the PAM4 linkinfo:eu-repo/semantics/publishedVersio

Exhaustive Gaussian Approach for performance evaluation of direct-detection OFDM systems employing square and cross QAM

An exhaustive Gaussian approach (EGA) is proposed to evaluate, through numerical simulation, the bit error ratio (BER) of direct-detection orthogonal frequency division multiplexing systems employing square and cross quadrature amplitude modulation. Excellent agreement between the BER estimates from the direct error counting (DEC) and the EGA is shown for different levels of optical signal-to-noise ratio and signal distortion. It is shown that the EGA requires about three orders of magnitude less in computation time than the DEC method for BER levels around 10-6, with the difference getting higher for lower BER levels.info:eu-repo/semantics/publishedVersio

Performance evaluation of wavelength division multiplexing photonic analogue-to-digital converters for high-resolution radar systems

The performance of the wavelength division multiplexing (WDM) photonic analogue-to-digital converter (ADC) used for digitization of high-resolution radar systems is evaluated numerically by using the peak signal-to-noise ratio (SNR) metric. Two different WDM photonic ADC architectures are considered for the digitization of radar signals with 5 GHz of bandwidth (spatial resolution of 3 cm), in order to provide a comprehensive study of the compromises present when deploying radar signals with high-resolution: 1) a four-channel architecture with each channel employing an ADC with 5 GSamples/s, and 2) an eight-channel architecture with each channel employing an ADC with 2.5 GSamples/s. For peak powers of the pulsed source between 10 and 20 dBm and a distance between the radar antenna and the sensing object of 2.4 meters, peak SNR levels between 29 and 39 dB are achieved with the eight-channel architecture, which shows higher peak SNR levels when compared with the four-channel architecture. For the eight-channel architecture and for the same peak powers of the pulsed source, peak SNR levels between 11 and 16 dB are obtained when the distance increases to 13.5 meters. With this evaluation using the peak SNR, it is possible to assess the performance limits when choosing a specific radar range, while keeping the same resolution.info:eu-repo/semantics/publishedVersio