Vjaceslavs Bobrovs

Mixed Chromatic Dispersion Compensation Methods for Combined HDWDM Systems

The authors have investigated the most efficient realization of mixed chromatic dispersion (CD) compensation schemes for high speed combined high density wavelength division multiplexing (HDWDM) systems. This research is performed with OptSim 5.1 simulation software. In this research it is shown that chromatic dispersion compensation scheme has a crucial role for guaranteed performance in combined HDWM transmission channels. Dispersion management strategy is needed when increasing the bit rate per channel by a factor of four. Therefore, the most efficient CD compensation scheme must be found for realized combined fiber optical transmission system. Authors have revealed that implementation of asymmetrical CD compensation schemes in pre-compensation and post-compensation modules are the most efficient and that it enables the best possible channels bit error ratio (BER) values.

Spectral and energy efficiency considerations in mixed-line rate WDM networks with signal quality guarantee

Mixed-Line Rate (MLR) is a cost efficient solution to cope with the rapidly increasing and heterogeneous Internet traffic. In a MLR-based scenario wavelength channels are organized in groups (i.e., sub-bands), each of which consisting of channels operating at the same rate, e.g., it is possible to have on the same fiber link subbands operating at 10 Gbps, 40 Gbps, and 100 Gbps. In order to increase spectral efficiency one can reduce not only the channel spacing within a sub-band but also the frequency spacing between sub-bands operating at different rates, i.e., the sub-band spacing. On the other hand smaller sub-band spacing may: (i) negatively impact the transparent optical reach of wavelength channels due to the higher inter-channel crosstalk levels, and consequently (ii) increase the network power consumption because of the need of more signal regeneration. This paper aims at assessing the trade-off between spectral efficiency and the power consumption in a WDM transport network, when a certain quality of transmission needs to be guaranteed at the receiving node. This is accomplished by evaluating a number of spectral efficient MLR solutions, where the number of wavelength channels allocated to each sub-band is varied while keeping the required Bit Error Rate (BER) level at the receiving node fixed. Results show that the width of each sub-band plays a central role in determining the power consumption of an end-to-end connection.

Latency causes and reduction in optical metro networks

The dramatic growth of transmitted information in fiber optical networks is leading to a concern about the network latency for high-speed reliable services like financial transactions, telemedicine, virtual and augmented reality, surveillance, and other applications. In order to ensure effective latency engineering, the delay variability needs to be accurately monitored and measured, in order to control it. This paper in brief describes causes of latency in fiber optical metro networks. Several available latency reduction techniques and solutions are also discussed, namely concerning usage of different chromatic dispersion compensation methods, low-latency amplifiers, optical fibers as well as other network elements.

Investigation of spectrally efficient transmission for unequally channel spaced WDM systems with mixed data rates and signal formats

The authors have investigated the frequency plan of channels central wavelengths allotment for wavelength division multiplexing (WDM) systems with the mixed data rates and optical signal formats. Such mixed-WDM fiber-optic transmission system (FOTS) is offered as a model for the designing of a next generation of backbone optical networks. Since the necessity for transmission of different signal formats (even with mixed per channel bitrates) over single optical fiber may arise in the nearest future as a result of telecom networks infrastructure development effort which goal is a larger systems carrying capacity (data throughput). These frequency plans were drawn applying unequal frequency intervals which values were found using the principle of intermediate value applied for channel spacings defined in ITU - T Recommendation G.694.1. The obtained more accurate frequency grid of channel central wavelength allows increase the utilization of transmission band and spectral efficiency. It is found that the improvement in transmission spectral efficiency of investigated mixed WDM system highly depends on its initial configuration - i.e. equal channel spacing value that is used for channel separation and the number of channel with the higher per channel bitrate (i.e. 40 Gbit/s) comparing with bitrate in the remaining channels (i.e. 10 Gbit/s). In general, it is revealed that for some of investigated mixed-WDM systems the transmission spectral efficiency can be increased up to 42 percent by applying proposed flexed frequency grid for channel central wavelengths.

Efficient Wavelength Filters for DWDM Systems

Efficient Wavelength Filters for DWDM Systems The authors investigate the best parameters of optical filters for dense wavelength division multiplexing (DWDM) systems. The investigation is based on the OptSim 5.0 simulation software using the method for solving a complex set of differential equations taking into account the optical and electrical noise as well as linear and nonlinear effects. It is shown that the bandwidth of optical filter extends as the data transmission speed increases, and that the most efficient are Supergaussian and Raised Cosine optical band-pass filters. It is also revealed that an ASK-RZ 40 Gbit/s data transmission system is impossible to realize with a channel interval less than 50 GHz because of wide spectral density and lower chromatic dispersion tolerance of this modulation format. Efektīvākie Viļņa Garuma Filtri DWDM Sistēmām Autori ir noskaidrojuši labākos optiskā filtra parametrus blīvām viļņgarumdales blīvēšanas (DWDM) sistēmām. Pētījumi ir realizēti ar OptSim 5.0 simulācijas programmatūru, kuras izmantotā aprēķinu metode balstās uz sarežgītu diferenciālvienādojumu risināšanu, ņemot vērā optisko un elektrisko troksni, lineāros un nelineāros optiskos efektus. Pētījumā parādīts, ka optiskā filtra joslas platums palielinās līdz ar datu pārraides ātrumu, un noskaidrots, ka Supergausa un Pacelta Kosinusa optiskie joslas filtri ir efektīvākie. Savukārt, ASK-RZ 40 Gbit/s datu pārraides sistēmu nav iespējams realizēt ar kanālu intervālu, kas mazāks par 50 GHz, tā plašā jaudas spektrālā blīvuma un zemās hromatiskās dispersijas noturības dēļ.

Hybrid optical amplifiers for flexible development in long reach optical access system

In this paper the authors have investigated the performance improvement in long reach optical access system with hybrid optical amplifiers. The apparent options of optical amplification in wavelength division multiplexing systems include the distributed Raman amplifiers, erbium doped fiber amplifiers, and semiconductor optical amplifiers. In our case distributed Raman amplifier is located at the mid-span reach extender which allows for remote amplification in passive network nodes by distributing a Raman pump together with the data signals. In the case of only distributed Raman amplifier in long reach optical access system wavelength division multiplexing exploitation is inefficient. Combining the advantages of different amplifiers allows fast gain dynamics, simultaneous large bandwidth amplification, and the ability to provide gain at any wavelength. Degradation of optical signal quality is evaluated in 10 Gbit/s long reach wavelength division multiplexing optical access system with hybrid distributed Raman-erbium doped fiber amplifier and distributed Raman-semiconductor optical amplifier.

Investigation of high-speed AWG filtered spectrum-sliced WDM PON system

This paper contains the investigation of 8-channel wavelength-division-multiplexed passive optical network by using spectrum-sliced amplified spontaneous emission (ASE) source as a seed light with arrayed-waveguide gratings (AWGs). There are investigated the impact of signal filtering for Gaussian and Flat-top type AWGs on the overall optical systems performance. It is shown that Gaussian type AWGs with channel interval 100 GHz are not suitable for SS-WDM PON systems with high data rate - 2.5 Gbit/s because of wide spectral shape and high channel crosstalk. Numerically it is proved that best solution for 8 channel SS-WDM PON system which provides high performance over the passive fiber optical link length up to 10 km with BER <; 1·10-10 are AWGs with Flat-top spectral shape. It has been investigated that Flat-top AWG unit shows high OSNR because of its amplitude transfer function that provides excellent channel separation and filtering at the same time passing sufficient high optical power from spectrally sliced ASE broadband light source.

Comparison of chromatic dispersion compensation techniques for WDM-PON solution

The upper transmission range of the wavelength division multiplexing passive optical network (WDM-PON) can be restricted by chromatic dispersion (CD). This paper contains the investigation of till 16-channel WDM-PON system with efficient CD pre-compensation and post-compensation methods. It is shown that CD offset has a marginal role for guaranteed optical link downstream performance and maximum length of high-speed WDM-PON system. The results show that employment of extra 7 km long dispersion compensating fiber (DCF) placed in central office (pre-compensation configuration) enhances the WDM-PON network link length by 19.3% (from 57 km up to 68 km), but if extra 2 km long DCF fiber is used in remote terminal (post-compensation configuration) link length can be extended up to 5.3% (from 57 km to 60 km). It was found that usage of fiber Bragg grating (FBG) in central office (pre-compensation configuration) improves network reach up to 26.3% (from 57 km up to 72 km), but using this FBG for CD post-compensation in remote terminal network reach can be improved by 15.8% or 9 km in length - from 57 km to 66 km. Basis on the results authors recommend to use FBG as the best solution for CD compensation in pre-compensation configuration (before SMF line) in future high speed long-reach DWDM-PON systems.

Frequency Arrangement For 700 MHz Band

Abstract The 694-790 MHz (700 MHz) band was allocated by the 2012 World Radiocommunication Conference (WRC-12) in ITU Region 1 (Europe included), to the mobile service on a co-primary basis with other services to which this band was allocated on the primary basis and identified for the International Mobile Telecommunications (IMT). At the same time, the countries of Region 1 will be able also to continue using these frequencies for their broadcasting services if necessary. This allocation will be effective immediately after 2015 World Radiocommunication Conference (WRC-15). In order to make the best possible use of this frequency band for mobile service, a worldwide harmonized frequency arrangement is to be prepared to allow for large economies of scale and international roaming as well as utilizing the available spectrum in the best possible way, minimizing possible interference between services, facilitating deployment and cross-border coordination. The authors analyze different possible frequency arrangements and conclude on the frequency arrangement most suitable for Europe.

Performance improvement of high speed spectrum-sliced dense WDM-PON system

This paper contains the investigation of reach improvement of dense wavelength-division-multiplexed passive optical network (DWDM-PON) using spectrum-sliced amplified spontaneous emission (ASE) source as a seed light. It is shown that flat-top AWG unit provides excellent channel separation and filtering at the same time passing sufficient high optical power from spectrally sliced ASE broadband light source. The maximum reach of the spectrum-sliced dense wavelength-division-multiplexed passive optical network (SS-DWDM PON) system with data transmission speed 2.5 Gbit/s can be fairly limited by chromatic dispersion (CD) because of large optical bandwidth per channel compared to the bit rate. And therefore, dispersion degrades the performance of a SS-DWDM PON system more than it is observed in conventional laser-based system. This paper contains the investigation of improved high speed 8-channel spectrum-sliced DWDM PON system with efficient CD compensation methods like dispersion compensating fiber (DCF) and fiber Bragg grating (FBG). In this research it is shown that CD compensation has an important role for guaranteed downstream optical link performance and maximum link length of high speed SS-DWDM PON system. Results show that FBG used for CD compensation in high speed spectrum-sliced dense WDM PON systems provides better accumulated CD compensation and increase link length up to 150% while DCF fiber provides up to 130% network reach improvement.