GÉANT Association aims to establish a fibre infrastructure for the distribution of time and frequency throughout Europe, with the implementation planned within the Horizon Europe GN5-2 funding cycle. These new fibre links will complement existing connections performing predominantly coherent optical frequency transfers, forming a basis of comprehensive Europe-wide infrastructure. This presentation will explore how this emerging fibre network will facilitate novel scientific research initiatives in Europe.
Moreover, the development of a pan-European fibre infrastructure will unlock opportunities for pioneering research in applied and fundamental science. This encompasses studies such as geodesy e.g. for underground water monitoring or unification of height systems across Europe, earthquake monitoring, the search for dark matter, and urban activity surveillance.
Coherent high-speed optical systems have played a very significant role in the world of data transmission in the last 15 years, and transmission speeds from 1.2 Tb/s to 1.6 Tb/s per lambda are expected to enter the market very soon. Historically, legacy high-speed 10 Gb/s data transmission systems have used the simplest On-Off Keying (OOK) modulation scheme. Since data transmission systems have been gradually moving to coherent transmissions with advanced modulation schemes, the coexistence of slower signals using OOK modulation can have a significant impact on coherent data signals via the nonlinear effect of Cross-Phase Modulation (CPM). In this paper, we evaluate the Bit Error Rate (BER) and Optical Signal-to-Noise Ratio (OSNR) for legacy 10 Gb/s data signals transmitted together with high-speed coherent 200 Gb/s data signals for fiber distances ranging from 100 km to 800 km. This scenario is rather suitable for National Research and Educational Network (NREN) operators, where slow OOK and high-speed coherent data signals are transmitted on the predefined International Telecommunication Union (ITU) channel spacing, usually 100 GHz.
Hollow-core fibers (HCF) are increasingly being studied and evaluated for telecommunication, as well as sensing application. They seem to have many advantages compare to standard single-mode fibers (SMF), especially in the area of the cyber-security of optical fiber infrastructures and also information they carrying. In our research we mainly focus on cyber-security issues, especially acoustic sensing. In the paper we evaluate sensitivity of negative curve HCF using a Mach–Zehnder interferometry (MZI). Results are compared with SMF (G.657 in this case). Both fibers were in primary coating with similar length. Sensitivity measurements were conducted within the controlled environment of an anechoic chamber. Results show that both fibers are sensitive to acoustic vibration and with post-processing method based on de-noising of the measured signal, the sensitivity can be improved. The clarity of the captured speech signal was assessed using the Speech Transmission Index for Public Address (STIPA).
The paper introduces an innovative object classification method for urban environments, employing distributed acoustic sensing (DAS) to address the complexities of urban landscapes. Utilizing omnipresent optical telecommunication cables, our approach involves a modified convolutional neural network (CNN) with transfer learning, achieving up to 85% accuracy. This method reuses most of the original network for feature extraction, with a final layer customized for new urban datasets – initially trained at the Brno University of Technology and then adapted to city center data. The model effectively identifies urban elements like vehicles and pedestrians, showcasing the potential of DAS for real-time classification in urban management and planning.
In the ever-advancing realm of modern technology, the demand for unparalleled precision and stability in timekeeping and frequency control has surged to unprecedented heights. As our interconnected world rellies more than ever on intricate synchronization and seamless communication, the development of cutting-edge optical infrastructure has emerged as a cornerstone in meeting these exacting demands. There has been obvious increased continuous focus on precise time and frequency transmission dissemination at a national and international level recently. We would like to present the situation in the Czech Republic, our strategy, approach, and our experience with a non-commercial, costeffective solution that utilizes optical networks shared with other traffic. The presented solution provides accurate time and stable frequency at a lower operational cost, using the shared spectrum of the CESNET3 network infrastructure.
In the period following the COVID-19 outbreak, there continues to be a demand for high-speed data services and sufficient bandwidth. From a transport network perspective, a coherent system transmits data independent of the specific transmission wavelengths . However, it is desirable to address the transmission of slow signals (e.g., OOK) in the same fiber and their interaction between transmissions. Here, we assess the effect of a slow signal with a low modulation rate in a DWDM network on high-speed (super channel) 800G transmission. To evaluate the effect on high-speed transmission, the Q factor and ESNR parameters provided by the Ciena transmission system were analyzed. For the test setup and the combination of the coherent 800G signal with the standard DFB transceiver signal and 100 GHz spacing. The 800G signal required 112 GHz bandwidth for its transmission. For a path length of 200 km and for modulation rates of the OOK signal ranging from 100 Mbit to 4 Gbit, we found no significant effect on the evaluated parameters of the Q factor and ESNR of the transmitted 800 G signal. The more significant effect on the 800G signal is, the mutual power level of neighboring channels with different modulation types. To limit the mutual influence of adjacent signals, these signals must also be balanced according to their maximum (peak) power level in the transmitted spectrum.
Passive optical networks play an important role in access networks and in current 5G networks. Passive optical network (PON) recommendations are published for two sectors by the Institute of Electrical and Electronics Engineers (IEEE) and the International Telecommunication Union (ITU), covering transmission speeds from 1 to 100 Gbit with wavelength division multiplex (WDM). The recommendations of the ITU define different encapsulation methods for the Ethernet frame, and meeting these recommendations necessitates new tools for control and data transmission. We present a downstream frame bandwidth field analysis for the simple topology of an XG-PON with 2 ONUs. The main purpose is to prove that the current access networks do not rely only on Ethernet frame transmission.
This contribution focuses on experimental verification of the QKD system deployment in a multi-domain network environment managed by Czech and Polish National Research and Educational Network (NREN) operators. We demonstrate full functionality of such a solution for transmission of secret keys in boundary conditions, and with this we open up new possibilities for further use of extremely secure communication between two neighboring network entities, and the services built upon it. Moreover, we have shared the cross-border link among strong QKD service channels, accurate time, and classical data channels together with weak quantum channel to reduce the total number of optical fibers needed for transmission. To our knowledge, this is the first shared cross-border QKD transmission in the region of Central and Eastern Europe (CEE).
The main topic of this paper is the detection state of polarization changes to enhance data security in fiber cable paths. The changes are generated by fiber manipulation or movements, which suggest potential security threats. Our designed system detects these changes using a polarization beam splitter and a pair of photodetectors. The values are subtracted from each other, sampled, and sent for analysis. The software detector applies FFT onto the signal and normalizes the output. The last step compares the sum of the bottom eighth of the spectrum against the threshold.
KEYWORDS: Sensors, Polarization, Data acquisition, Fiber optics sensors, Optical fibers, Time division multiplexing, Telecommunications, Photodetectors, Single mode fibers, Signal attenuation
The paper describes the possibilities of using the detection of fast and slow changes in the state of polarization for the detection of vibrations by an optical single-mode (SM) fiber. The system consists of a polarization beam splitter and a balanced photodetector. This sensing system is cost-effective, which contributes to its use in real operation. On the basis of an experiment with buried fiber near the railroad, the possibility of detecting vibrations with this system was proved. It is possible with simple analyzes to recognize the types of trains and their speed.
Precise time and ultra-stable optical frequency transfers over fiber networks are deployed relatively often these days. When size of such infrastructure for precise time and frequency bidirectional transmission is becoming significant, aspects associated with infrastructure operational cost and time needed for deployment of time and frequency transmission must be considered. First can be decreased via fiber sharing with telecommunication traffic, however spectral allocation must be considered carefully to avoid mutual disturbance of time and frequency transmission versus data and allow future accommodation of growing demands. In text, we show and discuss alternative spectral bands to be used for time and frequency transmission. Time to deployment can be quite excessive especially when transmission must be established via multiple networks or network domains, also there is a chance of blocking. In case of precise time and optical radio frequency transmission it is possible to use conversion from optical to electrical and back to optical domain with wavelength change. This possibility removes danger of blocking and improves time to deployment for such services. We also address possibility to change wavelength or just extend reach by using simple re-amplify and reshape approach.
Article summarizes past and continuous development, and especially current state of Czech national research infrastructure for Clock Network Services and future development plans. The focus is on used transmission means and stabilization techniques, available and planned wavelength bands and also plans for geographic extensions.
In this paper we present the design of a layered technical textile blocks for measuring temperature and strain using FBG gratings. In addition to research into individual layers of technical textiles, we also deal with joining methods to ensure sufficient strength while maintaining the flexibility of the created textile block. The textile with dimensions of 1x1 meter is designed for use in critical infrastructure security, such as a protection of secured area. A unique, robust connector using GRIN lenses was designed to connect the individual blocks. This special connector has dimensions 30x10x4.5mm and insertion loss of about 5dB.
Optical fibers are becoming commonly used beside data transmissions for dissemination of ultra-precise and stable quantities or alternatively as distributed sensors of for example acoustic and mechanic vibrations, seismic waves, temperature etc. There have been developed methods for these transfers and their stabilization, allowing thus to achieve excellent performances. Such performance is bound with utilization of single physical medium for both ways of propagation. These methods are attractive both for very high-performance applications and as a secure alternative complementary to radio and satellite-based transfer methods. From economical point of view, sharing fibers with regular data traffic is an advantage, especially for longer distances and large infrastructures. Unfortunately, the most often used wavelengths are located almost in the middle of telecommunication band. Due to continuous data traffic growth and utilization of flexible spectral allocation, the collision in wavelength plan will occur more and more often. In this paper we overview alternative wavelengths suitable for these transfers, we also propose suitable methods for all-optical reach extension, by all-optical amplification. Shared line design allowing transfer of ultra-stable quantities in three different spectral bands is proposed and such design is evaluated.
The reach of any all-optical transmission is limited by attenuation of transmission path and other factors as signal to noise ratio, and it can be extended by all-optical amplification. Bidirectional single fibre transmission introduces an issue of bidirectional symmetrical amplifiers in order not to lose advantage of path symmetry. In case of time transfer, quasibidirectional amplification might be acceptable when supported by specific arrangements, e.g. as much as possible equal arrangement for disjoint segments of the path. Time transfer with best available accuracy or optical frequency transfers require single path optical amplifiers that are further considered. In this constitution, unfortunately, reflections together with Rayleigh back-scattering will create feedback. In case feedback is strong enough and discrete amplifier operates in high gain regime (about 20dB), the whole system will start to oscillate. It saturates the gain of amplifiers and also can generate errors, when lasing in a transmission band. In the article, we review possible all optical amplification methods including those allowing to use untraditional transmission bands (outside C band).
Long distance precise frequency and accurate time transfer methods based on optical fiber links have evolved rapidly in recent years, demonstrating excellent performance. They are attractive both for very high-performance applications and as a secure alternative complement to radio- and satellite-based methods. In this paper, we present development of infrastructure for such transmission containing 700+km of transmission lines, with planned cross border optical frequency connectivity. According to our knowledge, this will be the third such line globally. The infrastructure also shares fibers with existing data transmissions, both amplitude and phase modulated, which poses high demands on mutual isolation and insensitivity to cross talks.
In this paper, we propose and present verification of all-optical methods for stabilization of the end-to-end delay of an optical fiber link. These methods are verified for deployment within infrastructure for accurate time and stable frequency distribution, based on sharing of fibers with research and educational network carrying live data traffic. Methods range from path length control, through temperature conditioning method to transmit wavelength control. Attention is given to achieve continuous control for relatively broad range of delays. We summarize design rules for delay stabilization based on the character and the total delay jitter.
Since optical fibre is a standard medium for all current and new networks, these optical networks offer possibility for connecting new applications over long distances almost to anywhere. However with increasing number of applications, the large number of dedicated fibres will be necessary. This constitution is quite unpractical in terms of costs, however since wavelength division multiplexing enables transmission of multiple different signals over one fibre it is more than suitable to use this technology for cost reduction and network efficiency increase. Wavelength division multiplexing technology is common in data networks where parameters of all signals may be optimized (especially maximum optical power launched into the fibre) for simultaneous transmission. In case of non-data applications the situation is more difficult because each application is connected by different type of signal and with its own requirements for transmission parameters. Hence it is necessary to evaluate possible interactions before field deployment. In this paper we deal with possible interaction of a coherent 100 Gb/s dual polarisation QPSK data signal with new applications like accurate time and stable frequency transmission and high-power pulse signal used for distributed sensing. In laboratory setup we performed a measurement with a standard G.652D single mode optical fibre and also with G.655 fibre which can also be found in some networks and may be source of more nonlinear interactions. All signals were transmitted in a grid with 100GHz spacing according to ITU standard. Results confirmed our assumptions that 100GHz spacing is not large enough and also that G.655 optical fibre is prone to more non-linear interactions.
Currently, fibre networks are only way how to satisfy the ever growing needs for more bandwidth. Thanks to that the optical fibre can be found almost anywhere and new applications and services can be transmitted through the networks. Accurate time transfer, ultra-stable frequency transfer and fibre-optic sensors networks have been rather common. High speed data transmission, time and frequency transmission, and fibre-optic sensors must share the common fibre-optic infrastructure because it would not be economically feasible to build separate fibre networks for long distances. Each system has individual transmission requirements and is prone to another type of interference. Data transmission systems based on DP-QPSK or DP-xQAM use digital signal processing for signal recovering but it cannot fully compensate signal degradation due to polarization dependent loss and nonlinear effects which are the most dominant sources of signal degradation. Accurate time signals are slow and often OOK modulated, therefore may experience the degrading effect of chromatic dispersion. Ultra-stable frequency signals are not modulated at all information transmitted is the frequency of photons and such signals are continuous wave, but they suffer from phase noise also environmentally introduced, e.g. by vibrations. For phase sensitive OTDR sensor systems the high power pulses are necessary to use which may cause interference with other signals. For this reason, parallel and simultaneous transmission in DWDM spectral grids of standard data, time, frequency, and sensing signals is rather new and unexplored area of research.
The infrastructure essentialities for accurate time and stable frequency distribution are presented. Our solution is based on sharing fibers for a research and educational network carrying live data traffic with time and frequency transfer in parallel. Accurate time and stable frequency transmission uses mainly dark channels amplified by dedicated bidirectional amplifiers with the same propagation path for both directions of transmission. This paper targets challenges related to bidirectional transmission, particularly, directional nonreciprocities.
Phase-sensitive optical time-domain reectometry (Φ-OTDR) seems to be the most appropriate solution for acoustic vibration along standard optical fiber detection. In general the sensing system measures phase changes of the received Rayleigh back-scattered signal in the fiber. Since the back-scattered signal intensity is decreased about tens of decibels in comparison to the forward propagating pulse power level, the received signal power level is very low. That is why the main limiting parameter of the system is the power level of the back-scattered signal, which limits maximum achievable distance. For long reach sensing it is necessary to create high power optical pulses with short time-duration. Direct pulse amplification by erbium doped fiber amplifier (EDFA) is an issue because of the pulses low repetition rate. We have designed and verified a simple method using a holding beam for amplifying of pulses with low repetition rate by standard telecommunication EDFA booster instead of deployment of an expensive optical shutter. A second CW laser with a different wavelength for EDFA stabilization is used in our setup. Because a pulse losses its energy during propagation in the fiber and with longer distances by 1st order Raman amplifier (RA). In telecommunications this amplifier is used to compensate for fiber losses. The second setup uses remote amplification by remotely pumped erbium doped fiber (EDF) placed after a few tens of kilometers of sensing fiber. A pump laser is placed in the transmitter part of the system from where EDF is pumped. In this paper, we present an overview of few techniques for Φ-ODTR signals amplification and their verification by measurement.
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