Jan Bohata

Experimental verification of long-term evolution radio transmissions over dual-polarization combined fiber and free-space optics optical infrastructures.

This paper describes the experimental verification of the utilization of long-term evolution radio over fiber (RoF) and radio over free space optics (RoFSO) systems using dual-polarization signals for cloud radio access network applications determining the specific utilization limits. A number of free space optics configurations are proposed and investigated under different atmospheric turbulence regimes in order to recommend the best setup configuration. We show that the performance of the proposed link, based on the combination of RoF and RoFSO for 64 QAM at 2.6 GHz, is more affected by the turbulence based on the measured difference error vector magnitude value of 5.5%. It is further demonstrated the proposed systems can offer higher noise immunity under particular scenarios with the signal-to-noise ratio reliability limit of 5 dB in the radio frequency domain for RoF and 19.3 dB in the optical domain for a combination of RoF and RoFSO links.

10 Gbps all-optical relay-assisted FSO system over a turbulence channel

Relay-assisted free space optics (FSO) communications becomes one of the promising solutions to improve the FSO link capabilities by implicitly reducing the transmission distance and exploiting distance-dependent fading variance of turbulence. Highly motivated by the capabilities of the system, this paper presents bit error rate (BER) performance of an all-optical 10-Gbps FSO relay based system using amplify-and-forward signaling is investigated through numerical simulations and experimental implementation. Results show that BER improves up to several orders of magnitudes when using relay based links over the same turbulent distance.

Long-Term Polarization Mode Dispersion Evolution and Accelerated Aging in Old Optical Cables

Today’s optical networks are composed of thousands of kilometers of aging optical cables. Many of these cables are located in harsh environments, which contribute to induced birefringence of the fibers and a corresponding increase of polarization mode dispersion (PMD). This letter introduces derived statistics from the longest-known running evaluation of a PMD measuring campaign and an investigation into how higher optical power affects these aging systems. Results indicate strong seasonal dependence of PMD on temperature for an optical cable test bed exposed to atmospheric changes, leading to a 16% increase of a mean PMD value in summer. This fluctuation causes bit error rate limits to be exceeded for 10 and 40 Gbps non-return-to-zero signals, which is a critical issue for applications where high reliability is required. Moreover, due to the high optical power load within old optical infrastructures, a more than 0.15 dB increase of relative loss per year in tested routes, compared with reference routes, has been observed.

Analyses of dual polarization WDM and SCM Radio over Fiber and Radio over FSO for C-RAN architecture

In this paper, the transmission schemes for Centralized Radio Access Network Architecture (C-RAN) based on combination of two technologies - Radio over Fiber (RoF) and Radio over FSO (RoFSO) are simulated and experimentally verified. The proposed setups are optimized for Long Term Evolution (LTE) with 20 MHz bandwidth using 64 Quadrature amplitude modulation in terms of Error Vector Magnitude (EVM). At the first, the measurements of Polarization Division Multiplexing using combination of RoF a RoFSO (PDM-RoF/FSO) is compared with simulation models. This is further extended by combination of PDM-Wavelength Division Multiplexing (WDM)-RoF/FSO and PDM-Subcarrier Multiplexing (SCM)-RoF/FSO, respectively. Results indicate better performance of PDM-SCM-RoF/FSO than WDM RoF/RoFSO in terms of launch power to reach EVM limit.

Outdoor atmospheric influence on polarization mode dispersion in optical cables

Oscillation of phenomena birefringence under atmospheric conditions is reported. Paper contains measured values of polarization mode dispersion from long term monitoring scenario and gives illustration about measuring of long time installed cables. Several commonly utilizing measuring techniques were used to determine birefringent properties of the fibers. Results are correlated with temperature changes during different terms to achieve proper comprehensive conception of progress.

Reliability of aircraft multimode optical networks

Abstract. Results from tests and analyses of multimode optical fibers for an avionic optical network under a variety of stress conditions are presented. Experiments revealed vibrational and temperature changes of distinct multimode fibers. Results lead to the discussion of influenced insertion losses and especially reduced bandwidth corresponding to modal distribution changes. It was determined that these crucial parameters could affect system reliability when an airplane network intersects thermal and vibrational variable environments.

Fundamental investigation of extending 4G-LTE signal over MMF/SMF-FSO under controlled turbulence conditions

In this paper, we propose a hybrid radio over multi-mode/single-mode fibre and free space optics (RoMMF/SMF-FSO) system to enhance the 4th generation-long term evolution (4G-LTE) signal performance when used in local area access networks. A single mode fibre pigtailed gradient index lens is used to minimise the modal effect of the optical link at different turbulence strengths. The proposed system is characterised in terms of the system transfer function, error vector magnitude (EVM), and optical launch power (OLP). Results demonstrate the robustness of the proposed scheme in terms of increased available passband bandwidth by 2 GHz and improving the transmission shape by reducing the system transfer function ripple by more than 5 dB. Successful transmission of the 4G-LTE signal is achieved over a MMF/SMF-FSO channel with a 1.5 dB power penalty under the higher turbulence level (i.e., Rytov variance of 0.1).

Characterization of dual-polarization analogue radio over fiber fronthaul for LTE C-RAN architecture

In this paper the results from extended measurement of dual-polarization (DP) analogue radio over fiber (RoF) in a long term evolution (LTE) cloud radio access network (C-RAN) architecture are presented. This technique is proposed for fiber connections between central offices and remote base stations. Investigation of various optical fiber length is carried out to determine the best system performance in terms of error vector magnitude (EVM) and bit error rate. Maximal achieved distance for the case of LTE bandwidth of 20 MHz is 50 km displaying permissible EVM value of 8.5 % at the radio frequency of 2.6 GHz when using 64 QAM modulation scheme.

Optimized mode-field adapter for low-loss fused fiber bundle signal and pump combiners

In our contribution we report novel mode field adapter incorporated inside bundled tapered pump and signal combiner. Pump and signal combiners are crucial component of contemporary double clad high power fiber lasers. Proposed combiner allows simultaneous matching to single mode core on input and output. We used advanced optimization techniques to match the combiner to a single mode core simultaneously on input and output and to minimalize losses of the combiner signal branch. We designed two arrangements of combiners’ mode field adapters. Our numerical simulations estimates losses in signal branches of optimized combiners of 0.23 dB for the first design and 0.16 dB for the second design for SMF-28 input fiber and SMF-28 matched output double clad fiber for the wavelength of 2000 nm. The splice losses of the actual combiner are expected to be even lower thanks to dopant diffusion during the splicing process.

Channel characterization of a last-mile access radio over combined fibre and free-space optics system

In this paper, we characterize a radio over fibre and radio over free space optic system for the last mile access network in urban areas and as a solution to the cellular backhaul networks. Special focus is put on the performance of such systems under the atmospheric turbulence. We show that the proposed system performance is almost the same for the entire frequency range of 0.4-4 GHz under the weak or no turbulence regimes. Finally we show that for proposed system with BPSK and QPSK at different RF carrier frequencies the turbulence effect has marginal impact.