Marcin Kowalczyk

Instability of the Multimode Fiber Frequency Response Beyond the Baseband for Coherent Sources

Fluctuations of the multimode fiber (MMF) frequency response beyond the baseband are observed experimentally when highly coherent light sources are used. This behavior is caused by the variation of the mode group powers caused by the relative modal phase fluctuation combined with spatial filtering at elements such as nonideal connectors. The observed effect may have vital influence on subcarrier multiplexing systems operation outside the baseband of the MMF. The effect is investigated both theoretically and experimentally.

Transmission Beyond 100 Mbit/s Using LED Both as a Transmitter and Receiver

In this letter, the experimental operation of a wireless transmission link employing identical LEDs both as transmitter and receiver is demonstrated. The transmitted signal is a simple, two-level pulse amplitude modulation. Digital equalization at the receiver is applied to overcome the bandwidth limitation of the link. Transmission throughput exceeding 100 Mbit/s is reported, even if the receiving red LED operates in the photovoltaic mode.

Substantial OBI Noise Reduction in MM Fiber Network

Optical beat interference is one of the major problems impairing upstream transmission in passive optical networks. In this letter, a theoretical study indicates that if single mode fibers are replaced with multimode fibers, the interference is reduced at least by the factor of N, where N is the number of modes propagating. In the experiment carried with two types of lasers, a reduction of beating noise ~10 dB is observed. Even greater reduction is expected in the first transmission window.

Influence of reverse bias on the LEDs properties used as photo-detectors in VLC systems

Continuous increasing share of light emitting diodes (LEDs) in a lighting market, which we observe during the last couple years, opens new possibilities. Especially, when we talk about practical realization the concept of visible light communications (VLC), which gains on popularity recently. The VLC concept presupposes utilization of illumination systems for a purpose of data transmission. It means, the emitters, in this case the LEDs, will not of a light source only, but also the data transmitters. Currently, most of the conducted researches in this area is concentrated on achievement of effective transmission methods. It means a transmission only in one direction. This is not enough, when we talk about the fully functional transmission system. Ensuring of feedback transmission channel is a necessary also. One of the ideas, which was postulated by authors of this article, is using for this purpose the LEDs in a double role. A utilization of LEDs as photo-detectors requires a reverse polarization, in contrast to a forward bias, which has a place when they work as light emitters. Ensuring of proper polarization get significant meaning. The article presents the investigations results on the influence of reverse bias on photo-receiving properties of LEDs used as light detectors. The conducted research proved that an improvement of sensitivity and bandwidth parameters are possible by application of appropriate value of the reverse voltage in a receiver.

Multimode Fiber Passive Optical Network for IEEE 802.11 Signal Distribution

In this paper, we present a novel concept of the IEEE 802.11n signal distribution over a multimode fiber passive optical network. In the study we provide a theory on the sources of potential interference in such a network, namely optical beat interference and modal noise, and ways to mitigate them. We demonstrate a passive optical distribution network deployed in a real environment of the facultys building. Our deployment utilizes custom designed remote antenna units. In the paper, we provide a series of network throughput measurements in different scenarios. These results confirm the correctness of our solution and show its excellent performance. The latter proves the network to be optically transparent. The distribution network does not downgrade the transmission rate when compared to the sole radio access point, and in addition it significantly increases the overall radio coverage.

Volterra Kernel Estimation of White Light LEDs in the Time Domain

In this paper, we present a time domain method for extracting coefficients of nonlinear Volterra-series kernels for white light-emitting diodes (LED) used both for illumination and visible light communications. We show that this method may have several advantages over the thus far more popular frequency domain method. We successfully apply the measured kernel coefficients up to the 3rd order for the modeling of nonlinear distortion impact on advanced modulation formats: pulse amplitude modulation, carrierless amplitude phase and orthogonal frequency division multiplexing. The impact of blue filtering on dynamic nonlinearity is also presented.

WiFi Signal Distribution over Multimode Fiber PON

For the first time we present a successful deployment of WiFi distribution system employing RAUs over MMF PON. We show experimental data confirming network operation in a real environment condition (faculty building).

Sound and light intensity meter in a form of application on mobile phone

The aim of this article is to present fully - functional meter of sound and light intensity in a form of application on mobile phones controlled by Android OS (operating system). The solution distinguishes itself from other solutions of this type due to many unique features, which make that the meter is itself a sophisticated measurement platform. Not only it allows to measure these physical quantities in real time and shows it on a plot, but also it is able to gather measuring points on external server for further analysis. Moreover, the tool was extended to additional measurement modes, which are placing points on the map using GPS (i.e. creating noise maps) or mapping them on the plane simulating the room. Saving the data and adding a location factor to measures allows deeper analysis of issues related to these quantities, e.g. noise intensity in cities.

Channel modeling and characterization for VLC indoor transmission systems based on MMC ray tracing method

The article presents methodology of obtaining the channel impulse responses (CIRs) on a way of numerical calculation for optical wireless transmission systems working indoor, including also those which work in scope of visible spectrum of light (VLC), based on the modified Monte Carlo ray tracing algorithm (MMC), which allows to determine them with really good quality for any room conditions in a short time. The influence of transmission channel is one of the most important factors, which is taken into consideration when design of wireless transmission systems is done. Using of the CIR is commonly applicable technique for this purpose. Based on the channel impulse response we can among others analyze and predict the link performance in the presence of noise and other factors, which can have significant impact on it final performance.

On the modeling of lighting LED dynamic nonlinearity

In this paper, we attempted to match an analytical model to the observed dynamic nonlinearity of the optical power versus driving current characteristic of lighting LED. Among the models tested were the (generalized) Wiener model, the Hammerstein model, and a variant of the generalized Wiener-Hammerstein model. Unfortunately, it turned out that neither model fits the data obtained from LED power versus current dynamic measurements.