Aleksejs Udalcovs

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.

Schemes for Compensation of Chromatic Dispersion in Combined HDWDM Systems

Schemes for Compensation of Chromatic Dispersion in Combined HDWDM Systems The authors seek best ways to realize chromatic dispersion (CD) compen-sation schemes for differently modulated optical signals in high-speed mixed data rate HDWDM systems. The research is based on OptSim 5.1. simulation software, which numerically solves nonlinear Schrödinger equation using the split-step Fourier method. It is shown that the CD compensation scheme is crucial for the performance evaluation in combined HDWM transmission channels. Therefore, a scheme of the type is proposed that is suited best for a very complicated combined fiber optical transmission system. It is also found that asymmetrical CD compensation schemes in pre- and post-compensation modules are the most efficient, allowing the best BER in a channel to be achieved. Hromatiskās Dispersijas Kompensācijas Metožu Izpēte Kombinētām Hdwdm Sistēmām Autori ir izpētījuši vispiemērotākās hromatiskās dispersijas (CD) kompen-sācijas shēmas realizāciju ātrdarbīgā HDWDM sistēmā ar dažādi modulētiem optiskajiem signāliem un jauktu pārraides ātrumu. Šī pētījuma pamatā ir OptSim 5.1 simulācijas programmatūras izmantošana, kura, skaitliski, izmantojot sadale-solis Furjē metodi, risina nelineāro Šrēdingera vienādojumu. Darbā ir parādīts, ka hromatiskās dispersijas kompensācijas shēmai ir izšķiroša loma, lai uzlabotu kom-binētas HDWDM sistēmas veiktspēju. Lai palielinātu pārraides ātrumu kanālā četras reizes, ir nepieciešams pielietot dispersijas pārvaldības stratēgiju. Līdz ar to, tika atrasts vispiemērotākais hromatiskās dispersijas kompensācijas risinājums samērā sarežgītas kombinētas šķiedru optikas pārraides sistēmas gadījumā. Tika atklāts, ka asimetrisko hromatiskās dispersijas kompensācijas shēmu izmantošana pirms- un pēc-kompensācijas moduļos ir visefektīvākā un ļauj sasniegt vislabākās iespējamās BER vērtības sistēmas kanālos.

Laser Frequency Noise in Coherent Optical Systems: Spectral Regimes and Impairments

Coherent communication networks are based on the ability to use multiple dimensions of the lightwave together with electrical domain compensation of transmission impairments. Electrical-domain dispersion compensation (EDC) provides many advantages such as network flexibility and enhanced fiber nonlinearity tolerance, but makes the system more susceptible to laser frequency noise (FN), e.g. to the local oscillator FN in systems with post-reception EDC. Although this problem has been extensively studied, statistically, for links assuming lasers with white-FN, many questions remain unanswered. Particularly, the influence of a realistic non-white FN-spectrum due to e.g., the presence of 1/f-flicker and carrier induced noise remains elusive and a statistical analysis becomes insufficient. Here we provide an experimentally validated theory for coherent optical links with lasers having general non-white FN-spectrum and EDC. The fundamental reason of the increased susceptibility is shown to be FN-induced symbol displacement that causes timing jitter and/or inter/intra symbol interference. We establish that different regimes of the laser FN-spectrum cause a different set of impairments. The influence of the impairments due to some regimes can be reduced by optimizing the corresponding mitigation algorithms, while other regimes cause irretrievable impairments. Theoretical boundaries of these regimes and corresponding criteria applicable to system/laser design are provided.

Digital mobile fronthaul employing differential pulse code modulation with suppressed quantization noise

A differential pulse code modulation (DPCM) based digital mobile fronthaul architecture is proposed and experimentally demonstrated. By using a linear predictor in the DPCM encoding process, the quantization noise can be effectively suppressed and a prediction gain of 7~8 dB can be obtained. Experimental validation is carried out with a 20 km 15-Gbaud/λ 4-level pulse amplitude modulation (PAM4) intensity modulation and direct detection system. The results verify the feasibility of supporting 163, 122, 98, 81 20-MHz 4, 16, 64, 256 QAM based antenna-carrier (AxC) containers with only 3, 4, 5, 6 quantization bits at a sampling rate of 30.72MSa/s in LTE-A environment. Further increasing the number of quantization bits to 8 and 9, 1024 quadrature amplitude modulation (1024 QAM) and 4096 QAM transmission can be realized with error vector magnitude (EVM) lower than 1% and 0.5%, respectively. The supported number of AxCs in the proposed DPCM-based fronthaul is increased and the EVM is greatly reduced compared to the common public radio interface (CPRI) based fronthaul that uses pulse code modulation. Besides, the DPCM-based fronthaul is also experimentally demonstrated to support universal filtered multicarrier signal that is one candidate waveform for the 5th generation mobile systems.

Power efficiency vs. spectral efficiency and transmission distance in 2.5–10–40 Gbps backbone optical networks

This paper aims to revealing the interrelation between channel spacing, transmission distance, and power efficiency on WDM system level of backbone optical network which configuration in based on the concept of Mixed-Line Rate (MLR). In such MLR network, three different types of wavelengths could co-propagate over the same optical fiber: 2.5 Gbps Non-Return-to-Zero (NRZ) On-Off Keying (OOK), 10 Gbps NRZ-OOK, and 40 Gbps NRZ-Differential Phase-Shift Keying (DPSK). It is found that depending on spectral efficiency power costs per transmitted bps can be reduced more than eight times for the same transmission distance.

Real-time 100 Gbps/lambda/core NRZ and EDB IM/DD transmission over multicore fiber for intra-datacenter communication networks

A BiCMOS chip-based real-time intensity modulation/direct detection spatial division multiplexing system is experimentally demonstrated for both optical interconnects. 100 Gbps/λ/core electrical duobinary (EDB) transmission over 1 km 7-core multicore fiber (MCF) is carried out, achieving KP4 forward error correction (FEC) limit (BER < 2E-4). Using optical dispersion compensation, 7 × 100 Gbps/λ/core transmission of both non-return-to-zero (NRZ) and EDB signals over 10 km MCF transmission is achieved with BER lower than 7% overhead hard-decision FEC limit (BER < 3.8E-3). The integrated low complexity transceiver IC and analog signal processing approach make such a system highly attractive for the high-speed intra-datacenter interconnects.

High-speed optical interconnects with integrated externally modulated laser

The cloud services together with the huge size datasets are driving demand for bandwidth in datacenters [1]. The 400 Gbps client-side links are demanding cost efficient solution: to reduce the number of lanes and increase the bandwidth for a single lane. The intensity modulation and direct-detection systems together with integrated semiconductor lasers and modulators appear as promising solution in four optical lanes at 100G since it reduces complexity, power consumption and costs [2]. However, it requires silicon and InP opto-electronic components with more than 70 GHz bandwidth [3]. In this talk, we report on a cost-efficient integrated externally modulated laser (EML) with high bandwidth for record high-speed intensity modulation and direct detection system demonstration with up to 100G OOK, PAM4/8 and duobinary signaling, as well as analog modulations e.g. DMT, paving the way for high speed multilevel modulation formats [4–6]. Related techniques including digital signal processing algorithms for timing recovery, adaptive/static equalization are also discussed in terms of practical implementation and complexity. In addition, techniques constructively using time domain super-Nyquist image induced aliasing for mitigating modulator driver nonlinearity for high speed DMT transmission will be presented [6], [7].

Ultra-Broadband High-Linear Integrated Transmitter for Low Complexity Optical Interconnect Applications

We report on a high-speed optical transmitter using InP-based integrated externally modulated laser for optical interconnect applications with up to 30 dB static extinction ratio and over 100 GHz 3 dB bandwidth with 2 dB ripple. It is evaluated with up to 116 Gbit/s on-off keying, 4-pulse amplitude modulation (PAM) and up to 105 Gbit/s 8-PAM optical signals with different digital equalization implementations. Low number of taps is required for a high and stable performance. Results reveal that digital equalization significantly boosts the passive optical interconnect scalability.

“High-speed optical and wireless transmission - challenges and achievements”

The cloud services together with the huge size datasets are driving demand for bandwidth in datacenters. The 400 Gbps client-side links are demanding a solution. The intensity modulation and direct-detection systems together with integrated semiconductor lasers and modulators appear as promising solution in four optical lanes at 100 Gbps net rate in order to reduce complexity, size, power consumption and cost.