We describe a reproducible method of fabricating adiabatic tapers with 3–4μm diameter. The method is based on a heat-and-pull rig, whereby a CO2 laser is continuously scanned across a length of fiber that is being pulled synchronously. Our system relies on a CO2 mirror mounted on a geared stepper motor in order to scan the laser beam across the taper region. We show that this system offers a reliable alternative to more traditional rigs incorporating galvanometer scanners. We have routinely obtained transmission losses between 0.1 and 0.3dB indicating the satisfactory production of adiabatic tapers. The operation of the rig is described in detail and an analysis on the produced tapers is provided. The flexibility of the rig is demonstrated by fabricating prolate dielectric microresonators using a microtapering technique. Such a rig is of interest to a range of fields that require tapered fiber fabrication such as microcavity-taper coupling, atom guiding along a tapered fiber, optical fiber sensing, and th...

An inexpensive heat-and-pull rig for fiber taper fabrication

Visible Light Communications: Theory and Applications

All-optical amplify-and-forward (OAF) relaying technique can amplify and filter the attenuated optical signal in optical domain, and thus is regarded as a simple way to extend the transmission distance of free-space optical (FSO) communication systems. At the relaying node, however, the incident background radiation and the amplified spontaneous emission noise of the deployed erbium-doped fiber amplifier will deteriorate the optical signal-to-noise, therefore causing the degradation of the system's bit error ratio (BER). In this paper, we perform simulations and experiments on FSO system with on-off keying (OOK) and differential phase-shift keying (DPSK) signals, focusing on the receiving sensitivity loss (RSL) of the OAF-assisted dual-hop system. Taking the BER level of ${10^{ - 7}}$ as the reference, we find that the DPSK system suffers more than 8 dB RSL at the data rate of 5 Gb/s in simulation, while the OOK system gets less than 1 dB RSL at the same data rate. In the following experiments, the obtained results exhibit that RSL of DPSK system is nearly 10 dB, which of OOK system is less than 1.5 dB, shown similarly property to the simulations.

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Performance Comparison of All-Optical Amplify-and-Forward Relaying FSO Communication Systems With OOK and DPSK Modulations

Vehicular ad-hoc network (VANET) is a promising technology to realize communications among vehicles in intelligent transportation systems. Conventional VANET utilizes radio frequency (RF) for vehicle to vehicle communications. However, as the vehicle density increases, RF-based VANET suffers from limited bandwidth and unavoidable interference. Visible light communication (VLC) is emerging as a complement candidate, which possesses the advantages of wide spectrum, high power efficiency and low interference, but also has the drawback of limited communication range. Therefore, the hybrid VLC/RF structure is beneficial to an efficient and reliable VANET. Since there are usually no center infrastructures in VANET and different vehicles could have different preferences, the distributed and non-cooperative topology control (TC) should be investigated for the establishment of VLC and RF links among various vehicles to satisfy some properties, e.g., interference level, power consumption, connectivity and delay requirements. Conventional TC schemes designed particularly for RF-based ad-hoc network can not be applied directly due to the distinctive features of VLC and RF links. In this paper, the TC problem for the hybrid VLC/RF VANET is modeled as a potential game. When considering the different features of the two kinds of links, a distributed TC algorithm is proposed to handle the TC game, in which the RF and VLC transmitting power of each vehicle is locally adapted based on the vehicle’s local knowledge about the VANET topology and can converge to a Nash Equilibrium state.

Topology Control in Hybrid VLC/RF Vehicular Ad-Hoc Network

Fifth generation (5G) mobile communication systems have entered the stage of commercial deployment, providing users with new services, improved user experiences as well as a host of novel opportunities to various industries. However, 5G still faces many challenges. To address these challenges, international industrial, academic, and standards organizations have commenced research on sixth generation (6G) wireless communication systems. A series of white papers and survey papers have been published, which aim to define 6G in terms of requirements, application scenarios, key technologies, etc. Although ITU-R has been working on the 6G vision and it is expected to reach a consensus on what 6G will be by mid-2023, the related global discussions are still wide open and the existing literature has identified numerous open issues. This paper first provides a comprehensive portrayal of the 6G vision, technical requirements, and application scenarios, covering the current common understanding of 6G. Then, a critical appraisal of the 6G network architecture and key technologies is presented. Furthermore, existing testbeds and advanced 6G verification platforms are detailed for the first time. In addition, future research directions and open challenges are identified to stimulate the on-going global debate. Finally, lessons learned to date concerning 6G networks are discussed.

On the Road to 6G: Visions, Requirements, Key Technologies, and Testbeds

Serially DF relayed hybrid FSO/MMW links with Weibull fading, M-turbulence and pointing errors

Experimental characterization of SNSPD receiver technology for deep space FSO under laboratory testbed conditions

Autonomous vehicles are sophisticated self-sufficient systems which employ hundreds of sensors. To improve road safety, the number of Advanced Driver Assistance Systems (ADAS) steadily increases. Consequently, the applied systems are growing in complexity and connectivity. The network architecture within vehicles, however, is only adapted and extended to support emerging high-bandwidth applications while redesigning the whole network would yield many benefits. As a result, modern wiring harnesses are too complex, heavy and prone to errors.In this paper, existing bus systems are analysed for their capabilities to handle sophisticated network traffic which will emerge in autonomous vehicles. Furthermore, problems are identified and discussed, and a potential solution based on optical technologies is presented. This solution combines existing optical technologies in a novel way to cope with the upcoming bandwidth requirements of autonomous vehicles, while keeping the costs to a minimum.

Approach for an Optical Network Design for Autonomous Vehicles

Free Space Optical (FSO) systems offer tremendous channel capacity, which can significantly contribute to the bandwidthhungry next generation networks. FSO technology is certainly highly vulnerable to atmospheric Mie scattering, which leads to severe degradation of the established optical communication link. To address this key-issue, the current paper is focused on detailed investigation of the fog effect using artificially built fog environment. Low-visibility conditions are adjusted within a 50 m long corridor covered with PVC and including two artificial fog machines and a signal flare. The Particle Size Distributions (PSDs) of the simulated fog are measured with a sophisticated and so-called “Spraytec” device provided by Malvern Instruments Company. Once the main characteristics of the artificial fog are assessed, the measurements are compared with an empirical estimated fog model using modified gamma function. The comparison is accomplished in terms of theoretically defined PSDs where both radiation as well as advection fog modelling are taken into account. In order to calculate the relevant FSO channel attenuation only based on our measured fog PSDs, Mie theory is applied. For this purpose, Mie scattering efficiencies of a fog water sphere with arbitrary radius and refractive index are shown and examined. Respectively, apart from the presented figures with comparison of various PSDs, also the specific attenuation in dependence on fog particles size is introduced and discussed. Taking into account that particle density of the artificial fog can be manually setup in accordance with the applied theoretical models, our simulations offer attenuation up to 210 dB/km in the presence of continental moderate and dense fog effects. Consequently, we have the possibility to simulate significantly well various fog conditions in artificially simulated environment.

Estimation of Mie scattering influence for the FSO channel under artificially simulated fog conditions

Free space optics (FSO) is a wireless optical communication technology enabling extremely high data transmission rates, which can be used for a wide range of emerging applications. Nevertheless, FSO system reliability can be easily deteriorated in the presence of various weather-induced disruptions. The main two atmospheric effects influencing FSO links are fog and turbulence. Their investigation is based on real data and simulations—separately performed for two different locations in Austria. Based on the aforementioned weather-induced disruption analysis and existing knowledge about the link margin of the selected FSO communication measurement scenario, both outage probability and availability parameters are evaluated. Considering these outcomes, the most prominent and well-established atmospheric mitigation techniques for FSO technologies are explained. To address these techniques, a special emphasis is placed on two emerging applications: modern deep space communications as well as vehicle-to-vehicle (V2V) wireless optical communications. Both are examined based on their susceptibility to the investigated weather-induced disruptions. In order to improve the deep space FSO system resilience against long-distance and atmospheric effects, an approach using the superconducting nanowire single-photon detector (SNSPD) technology is considered. Furthermore, a hybrid V2V communication solution based on radio frequency (RF) and FSO is described.

Hristo Ivanov

Papers

Serially DF relayed hybrid FSO/MMW links with Weibull fading, M-turbulence and pointing errors

Experimental characterization of SNSPD receiver technology for deep space FSO under laboratory testbed conditions

Approach for an Optical Network Design for Autonomous Vehicles

Estimation of Mie scattering influence for the FSO channel under artificially simulated fog conditions

Free Space Optics System Reliability in the Presence of Weather-Induced Disruptions