Research of M-PAM and Duobinary Modulation Formats for Use in High-Speed WDM-PON Systems

The exponential growth of Internet data traffic and progress of Information and Communication Technology (ICT) sector pushes hard the telecommunication infrastructure for upgrading the transmission data rate. Wavelength division multiplexed passive optical networks (WDM-PONs) can be the next generation solution for nowadays problems which are related to transmission capacity. Next-generation WDM-PON systems based on mixed wavelength transmitters are expected to become more cost-efficient at high per user data rates, e.g., over 10 Gbit/s per channel. Important advantage of this technology is to set various channel spacing and use different modulation formats to increase spectral efficiency in the same time and provide different transmission speeds for end user, based on pay-as-you-grow approach. Therefore, several modulation formats like non-return to zero (NRZ) also called 2-level pulse-amplitude modulation (PAM-2), four level PAM or PAM-4 and Duobinary (DB) are investigated to understand their limitations, advantages and disadvantages to be further used in next generation PON systems to increase its capacity and spectral efficiency

Evaluation of Parametric and Hybrid Amplifier Applications in WDM Transmission Systems

Over the past two decades, a rapid expansion of the amount of information to be transferred has been observed. This tendency is explained by the rapid increase of Internet and other service users, as well as with the increasing availability of these services. This rapid growth in the amount of globally transmitted data is also associated with the expansion of the range of services offered, including such resource-consuming services as high-resolution video transmission, videoconferencing, and cloud computing, as well as with increasing popularity of such services. To satisfy this constantly increasing demand for higher network capacity, fiber optical transmission systems have been studied and applied with a growing intensity. Currently, optical transmission systems with wavelength-division multiplexing (WDM) have attracted much attention, as this technology allows using the available optical fiber resources more effectively than alternative technologies

Fiber Bragg Grating Sensors Integration in Fiber Optical Systems

Fiber Bragg grating (FBG) sensors are a progressive passive optical components, and used for temperature, strain, water level, humidity, etc. monitoring. FBG sensors network can be integrated into existing optical fiber network infrastructure and realized structural health monitoring of roads, bridges, buildings, etc. In this chapter, the FBG sensor network integration in a single-channel and multi-channel spectrum sliced wavelength division multiplexed passive optical network (SS-WDM-PON) is presented and assessed. The operation of both the sensors and data transmission system, over a shared optical distribution network (ODN), is a challenging task and should be evaluated to provide stable, high-performance mixed systems in the future. Therefore, we have investigated the influence of FBG temperature sensors on 10 Gbit/s non-return-to-zero on–off keying (NRZ-OOK) modulated data channels optical transmission system. Results show that the crosstalk between both systems is negligible. The successful operation of both systems (with BER < 2 × 10−3 for communication system) can be achieved over ODN distances up to 40 km

Cladding-Pumped Er/Yb-Co-Doped Fiber Amplifier for Multi-Channel Operation

The Institute of Solid State Physics, University of Latvia, as a Center of Excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2. We express our gratitude to rer. nat. Nicoletta Haarlammert from Fraunhofer Institute for Applied Optics and Precision Engineering IOF for the refractive index measurements of ytterbium/erbium-co-doped fibers. This work is supported by the European Regional Development Fund project No. 1.1.1.1/18/A/068.Cladding-pumped erbium (Er3+)/ytterbium (Yb3+)-co-doped fiber amplifiers are more advantageous at high output powers. However, this amplification technique also has potential in telecom-related applications. These types of amplifiers have complex properties, especially when considering gain profile and a pump conversion efficiency. Such metrics depend on the doped fiber profile, absorption/emission spectra, and the input signal power. In this context, we design, build and characterize an inhouse prototype of cladding-pumped Er3+/Yb3+-co-doped fiber amplifier (EYDFA). Our goal is to identify the EYDFA configuration (a co-doped fiber length, pump power, input signal power) suitable for signal amplification in a multichannel fiber-optic transmission system with a dense wavelength allocation across the C-band (1530–1565 nm). Our approach involves experimentally determining the Er3+/Yb3+-co-doped fiber’s parameters to be used in a simulation setup to decide on an initial EYDFA configuration before moving to a laboratory setup. An experimental EYDFA prototype is tested under different conditions using a 48-channel dense wavelength division multiplexing (DWDM, 100 GHz) system to evaluate the absolute gain and gain uniformity. The obtained results allow the cladding pump amplifier’s suitability for wideband signal amplification to be assessed. The developed prototype provides > 21 dB of gain with a 12 dB ripple within 1534–1565 nm. Furthermore, we show that the gain profile can be partially flattened out by using longer EYDF spans. This enhances signal amplification in the upper C-band in exchange for a weaker amplification in the lower C-band, which can be marginally improved with higher pump powers. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.ERDF project No. 1.1.1.1/18/A/068; the Institute of Solid State Physics, University of Latvia, as a Center of Excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Linear Regression vs. Deep Learning for Signal Quality Monitoring in Coherent Optical Systems

Error vector magnitude (EVM) is a metric for assessing the quality of m-ary quadrature amplitude modulation (mQAM) signals. Recently proposed deep learning techniques, e.g., feedforward neural networks (FFNNs) -based EVM estimation scheme leverage fast signal quality monitoring in coherent optical communication systems. Such a scheme estimates EVM from amplitude histograms (AHs) of short signal sequences captured before carrier phase recovery (CPR). In this work, we explore further complexity reduction by proposing a simple linear regression (LR) -based EVM monitoring method. We systematically compare the performance of the proposed method with the FFNN-based scheme and demonstrate its capability to infer EVM from an AH when the modulation format information is known in advance. We perform both simulation and experiment to show that the LR-based EVM estimation method achieves a comparable accuracy as the FFNN-based scheme. The technique can be embedded with modulation format identification modules to provide comprehensive signal information. Therefore, this work paves the way to design a fast-learning scheme with parsimony as a future intelligent OPM enabler

The Lossless Adaptive Binomial Data Compression Method

In this paper, we propose a new method for the binomial adaptive compression of binary sequences of finite length without loss of information. The advantage of the proposed binomial adaptive compression method compared with the binomial compression method previously developed by the authors is an increase in the compression rate. This speed is accompanied in the method by the appearance of a new quality—noise immunity of compression. The novelty of the proposed method, which makes it possible to achieve these positive results, is manifested in the adaptation of the compression ratio of compressible sequences to the required time, which is carried out by dividing the initial set of binary sequences into compressible and incompressible sequences. The method is based on the theorem proved by the authors on the decomposition of a stationary Bernoulli source of information into the combinatorial and probabilistic source. The last of them is the source of the number of units. It acquires an entropy close to zero and practically does not affect the compression ratio at considerable lengths of binary sequences. Therefore, for the proposed compression method, a combinatorial source generating equiprobable sequences is paramount since it does not require a set of statistical data and is implemented by numerical coding methods. As one of these methods, we choose a technique that uses binomial numbers based on the developed binomial number system. The corresponding compression procedure consists of three steps. The first is the transformation of the compressible sequence into an equilibrium combination, the second is its transformation into a binomial number, and the third is the transformation of a binomial number into a binary number. The restoration of the compressed sequence occurs in reverse order. In terms of the degree of compression and universalization, the method is similar to statistical methods of compression. The proposed method is convenient for hardware implementation using noise-immune binomial circuits. It also enables a potential opportunity to build effective systems for protecting information from unauthorized access