Numerical Estimation of Spectral Properties of Laser Based on Rate Equations

Laser spectral properties are essential to evaluate the performance of optical communication systems. In general, the power spectral density of the phase noise has a crucial impact on spectral properties of the unmodulated laser signal. Here the white Gaussian noise and 1/f-noise are taken into the consideration. By utilizing the time-dependent realizations of the instantaneous optical power and the phase simultaneously, it is possible to estimate the power spectral density or alternatively the power spectrum of an unmodulated laser signal shifted to the baseband and thus estimate the laser linewidth. In this work, we report on the theoretical approach to analyse unmodulated real-valued high-frequency stationary random passband signal of laser, followed by presenting the numerical model of the distributed feedback laser to emulate the time-dependent optical power and the instantaneous phase, as two important time domain laser attributes. The laser model is based on numerical solving the rate equations using fourth-order Runge-Kutta method. This way, we show the direct estimation of the power spectral density and the laser linewidth, when time-dependent laser characteristics are known

Monitoring of polarization-based effects in fiber-optic transmission link caused by environmental variations

The fast transmission of signals around the globe is fundamental to the flow of information for our society. A long-haul transmission certainly represents one of the key advancements that shaped modern ways of communicating and offers a nearly instant access to any available data or a latest information. However, fiber-optic transmission typically suffers from a variety of physical impairments that degrade the signal quality, thus imposing limits on both, the achievable transmission capacity and data reach. Of particular concerns are stochastic fiber impairments, primarily represented by polarization mode dispersion (PMD). The PMD originates from a random birefringence caused by imperfect fiber circularity and other, both internal and external, effects, basically completely re-defining the light polarization state of output signal compared to its initial counterpart. The PMD is particularly critical as it restricts operation of fiber-optic links running at speeds higher than 10 Gbps. This, in turn, hinders fiber link re-adaption towards higher transmission bit rates in future, however. In this context, both in-line link monitoring and testing of PMD-based effects is of great importance within the recently used optical fiber links. However, polarization-based effects are also very sensitive to the environmental changes, substantially degrading transmitted optical signals and reducing link quality. In this work, we provide experimental characterization for PMD-based propagation effects in optical fibers influenced by wind gusts. The investigation was performed on commercially used fiber-optic link that runs through optical power ground wire cables. The 111-km-long optical link under study comprised installed optical fibers with available 88 channels. Here, we monitored environmental changes caused by wind conditions over several consecutive days with a 60 second time frame and sensed PMD impact on the link performance. Here, differential group delay (DGD) was chosen to be a key parameter, enabling for sensitive characterization of wind related link changes. Measured maximum DGD’s were 4 and 10 ps for wind speeds up to 5 and 20 m/s, respectively. In addition, experimentally measured data were used in numerical model to assess the optical link quality. For a low wind condition, we observed negligible quality degradation in the optical link, considering transmission bit rates of 10, 40, and 100 Gbps. Conversely, in case of strong wind condition, the optical link maintained a reliable operation only for established 10 Gbps, while significant link degradation was observed for bit rates of 40 and 100 Gbps. Our work shows promising way to effectively sense and monitor undesired environmental variations and their impact on polarization-based fiber link propagation effects, which in turn, can allow an instant link quality evaluation

High-speed operation of fiber-optic link impaired by wind gusts

The fast signal transmission is critical long-haul communication systems. They represent the key advancements, shaping information-communication technologies. Fiber-optic transmission suffers from many degradation effects, and of particular concern are stochastic fiber impairments represented by polarization mode dispersion (PMD). The PMD is critical as it limits link operation at data rates higher than 10 Gbps. In this work, we report on experimental measurements and theoretical analysis characterization for PMD-based propagation effects in optical fibers influenced by wind gusts. The study was performed on fiber-optic link that runs through 111-km-long optical power ground wire cables. Measured maximum of DGD was up to 10 ps for a wind speed of 20 m/s. This wind condition, the optical link maintained a reliable operation only for established 10 Gbps, while considerable link degradation was seen for data rates of between 40 and 100 Gbps

Subwavelength metamaterial for communications and sensing

Silicon photonics is considered a breakthrough technology with strong impact in areas as diverse as data center interconnection, high performance computing, the deployment of 5G future communication systems or lab-on-a-chip sensors. The emergence of sub-wavelength grating waveguides (SWG) has been fundamental to achieve advanced devices with unprecedented performance in integrated optics. In this talk we will focus on our recent progress in designing sub-wavelength engineered devices like ultra-broadband mode (de)multiplexers and converters [1], ultra-narrowband Bragg filters [2], sensing waveguides with enhanced sensitivity [3], or suspended silicon mid-infrared waveguides capable of covering the full transparency window of silicon [4], among other. This work was supported by the Ministerio de Economía y Competitividad, Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad (Proyecto TEC2016-80718-R), and the Universidad de Málaga (Campus de Excelencia Internacional Andalucía Tech).Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech

Spectral Transmission Characteristics of Andvanced Amplitude Modulation Formats

In this paper we focus our attention on numerical investigation of high-order amplitude modulation format in single-channel transmission systems utilizing different kinds of optical fibers. The aim is to show the spectral behavior of advanced amplitude modulated signals in view of fundamental parameters of fiber-optic system. The investigation is realized by solving the nonlinear Schrodinger equation (NLSE) through the pseudospectral split-step Fourier method (SSFM). The obtained results show that the advanced amplitude modulation formats are sensitive to nonlinear phenomenon and they are more desirable for using at short-haul networks

Impact of wind gust on high-speed characteristics of polarization mode dispersion in optical power ground wire cables

Polarization mode dispersion is recognized as a key factor limiting optical transmission systems, particularly those fiber links that run at bit rates beyond 10 Gbps. In-line test and characterization of polarization mode dispersion are thus of critical importance to evaluate the quality of installed optical fibers that are in use for high-speed signal traffics. However, polarization-based effects in optical fibers are stochastic and quite sensitive to a range of environmental changes, including optical cable movements. This, in turn, gives rise to undesired variations in light polarization that adversely impair the quality of the signal transmission in the link. In this work, we elaborate on experimental testing and theoretical analysis to asses changes of polarization mode dispersion in optical fibers that are caused by environmental variations, here wind gusts in particular. The study was performed on commercially harnessed optical fibers installed within optical power ground wire cables, taking into account different weather conditions. More specifically, we showed that changes caused by wind gusts significantly influence the differential group delay and the principal state of polarization in those optical fibers. For this, we experimentally measured a number of parameters to characterize light polarization properties. Measurements were carried out on C-band operated fiber-optic link formed by 111-km-long power ground wire cables and 88 spectral channels, with a test time step of 1 min during 12 consecutive days. Variations in differential group delay allowed for sensitive testing of environmental changes with measured maxims up to 10 ps under the worst wind conditions. Moreover, measured parameters were used in a numerical model to assess the quality of transmitted high-bit-rate optical signals as a function of wind conditions. The analysis revealed a negligible impact of wind on a 10 Gbps transmission, while substantial influence was noticed for higher bit rates up to 100 Gbps. These results show promises for efficient sensing of environmental changes and subsequent monitoring of the quality of recently used fiber-optic link infrastructures