Andis Supe

This research aims to analyse and compare the Matter protocol versus other IoT-related protocols to highlight similarities, advantages and compatibility regarding hardware and software. We demonstrate the decoding of the Matter network traffic using virtual devices and Wireshark. A comparative analysis is performed between Matter integration over Thread and Wi-Fi networks. The proposed environment provides a basis for testing the OpenThread Border Router, Matter security mechanisms, and cluster analysis.

This research aims to demonstrate a machine learning (ML) algorithm-based indoor air quality (IAQ) monitoring and forecasting system for a public sector building use case. Such a system has the potential to automate existing heating/ventilation systems, therefore reducing energy consumption. One of Riga Technical University’s campus buildings, equipped with around 128 IAQ sensors, is used as a test bed to create a digital shadow including a comparison of five ML-based data prediction tools. We compare the IAQ data prediction loss using Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) error metrics based on real sensor data. Gated Recurrent Unit (GRU) and Kolmogorov–Arnold Networks (KAN) prove to be the most accurate models regarding the prediction error. Also, GRU proved to be the most efficient model regarding the required computation time.

Monitoring of optical signal polarization state in optical fiber networks can provide a variety of information for infrastructure owners. There is a rather limited choice of available techniques for monitoring the change in a polarization state of an optical signal over the transmission line. Mostly, as the typical measurement, the total optical line polarization mode dispersion (PMD) is determined, or the instantaneous change in polarization state at the line input or output is measured. But that does not allow determining the location and cause of sudden polarization changes in an optical fiber. The authors propose a polarization monitoring technique using a traditional commercially-used optical time-domain reflectometer (OTDR) with additional circuitry to generate polarization-dependent measurement traces. Such a technique can potentially be used for continuously tracking a physical impact on an optical fiber link.

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.

Space-division multiplexing (SDM) attracts attention to cladding-pumped optical amplifiers, but they suffer from a low pump power conversion efficiency. To address this issue, ytterbium (Yb³⁺) and erbium (Er³⁺) co-doping is considered as an effective approach. However, it changes the gain profile of Er³⁺-doped fiber amplifiers and induces the gain difference between optical wavelengths in the C-band, significantly limiting the effective band of the dense wavelength-division multiplexed (DWDM) system. This paper is devoted to a detailed study of a cladding-pumped Er³⁺/Yb³⁺ co-doped fiber amplifier (EYDFA) through numerical simulations aiming to identify a configuration, before assembling a similar EYDFA in our laboratory premises that ensures the desired performance. The simulation model is based on a commercial double cladding EYDF whose parameters are experimentally extracted and fed to the EYDFA setup for the system-level studies. We investigate the wavelength dependence of the amplifier’s characteristics (absolute gain, gain uniformity, noise figure) and bit error rate (BER) performance for several DWDM channels and their optical power. The obtained results show that a 7 m long EYDF and co-propagating pump direction is preferable for the EYDFA with a 3 W pump source at 975 nm and with the given gain medium characteristics for WDM applications. For instance, it ensures a gain of 19.7–28.3 dB and a noise figure of 3.7–4.2 dB when amplifying 40 DWDM channels with the input power of −20 dBm per channel. Besides, we study EYDFA gain bandwidth and the maximum output power when operating close to the saturation regime and perform a sensitivity analysis showing how the doped fiber’s absorption and emission cross-sections impact the amplification process through energy transfer from Yb³⁺ to Er³⁺. Finally, we quantify the power penalty introduced by the EYDFA; the results show that it is not higher than 0.1 dB when amplifying 40 × 10 Gbps non-return-to-zero on-off keying signals from −20 dBm/channel.

In this paper we present results from the study of optical signal amplification using Raman assisted fiber optical parametric amplifier with considerable benefits for S-band telecommunication systems where the use of widely used erbium-doped fiber amplifier is limited. We have created detailed models and performed computer simulations of combined Raman and fiber optical parametric amplification in a 16-channel 40 Gbps/channel wavelength division multiplexed transmission system. Achieved gain bandwidth, as well as transmission system parameters—signal-to-noise ratio and bit-error-ratio—were analyzed by comparing the Raman assisted fiber optical parametric amplifier to the single pump fiber optical parametric amplifier. Results show that the 3 dB gain bandwidth in the case of combined amplification is up to 0.2 THz wider with 1.9 dB difference between the lowest and highest gain.

Optical Fiber Communication widely implements Dense Wave Division Multiplexing (DWDM) technique in order to accommodate large number of channels within a limited bandwidth. But, this technology suffers a serious degradation in signal quality due to inter-channel interference. Optical Kerr Effect, in addition to this, worsens the situation. This paper deals with minimization of Four Wave Mixing (FWM) impact, one of the Optical Kerr effects, by using variable channel spacing instead of conventional fixed channel spacing technique. FWM effect generates spurious components at multiple frequencies, whose effective amplitude can be reduced using different channel spacing. Bit Error Rate (BER) observed for different length of fiber has been analyzed with an aim to estimate the difference between variable channel spacing algorithms. Obtained results have shown that BER of 10-11 can be reached with 153.7 km long fiber for fixed channel spacing while the usage of variable channel spacing method keeps the same BER level with 160.5 km long fiber.

The effective non-linear parameter of a highly non-linear optical fiber was measured using the four-wave mixing effect. A value of γ = 10.6 W^–1/km was obtained for a small wavelength separation between pump and signal waves, whereas for a large wavelength separation, a value of = 8γ/9 = 9.4 W^–1/km was found. This value corresponds to an average of the Kerr non-linearity over the Poincaré sphere, since the polarization of both the pump and signal waves become uncorrelated in the last case. A theoretical model is proposed to describe the variation of the effective non-linear parameter with the wavelength separation between pump and signal waves, which is in good agreement with the experimental data.

The main goal of this paper is to investigate the ability of a single-pump fiber optical parametric amplifier with linearly polarized pumping radiation to provide binary polarization shift keying to intensity on-off keying modulation format conversion in a single channel optical transmission system. The amplifier produced up to 14.8 dB of on-off gain, and it was demonstrated that such level of amplification is sufficient to provide modulation format conversion, while maintaining acceptable quality of the converted signal. It was found that due to fiber birefringence the original state of polarization needs to be recovered at the input of the amplifier, otherwise, drop in amplification and converted signal discrepancies will occur.