Coherent Transmission Technology Research Articles

Spatially disaggregated model for self-channel interference in mixed fiber optical network segments

Coherent transmission technology is widely diffused in backbone optical uncompensated transmission (UT) network segments. In metro and access network segments instead, intensity-modulated direct detected channels at 10 Gbps requiring inline dispersion compensation units (DCUs) are still largely used. While the transition to coherent technology is foreseen in the dispersion managed (DM) network segment, in the meantime, it would be handy to route coherent channels through DM network segments to fully exploit deployed hardware and available spectrum and improve network flexibility. In this scenario, self-channel interference (SCI) exhibits strongly coherent accumulation due to the presence of DCUs, which is not well modeled by traditional analytical models for non-linear interference estimation used for path feasibility assessment. In this paper, we propose a semi-analytical model able to fill this gap. We show that our proposed model is able to provide a quick, conservative estimation of the SCI noise on both UT and DM systems, including optical line system configurations with mixed fiber types.

Optical Single-Sideband Transmitters

Optical single-sideband (SSB) transmission technique fills the gap between intensity-modulation/direct-detection (IM/DD) and digital coherent transmission technologies. It provides a cost-effective solution to overcome the transmission distance limitation induced by fiber chromatic dispersion in IM/DD system at the expense of increased complexity of the transmitter (Tx) structure and receiver-side signal processing. This makes optical SSB system become a promising candidate for cost- and latency-sensitive datacenter interconnects. Previous research on optical SSB system mainly focused on improving the spectral efficiency and receiver sensitivity, whereas the increased complexity and cost of optical SSB Tx were overlooked. In this paper, we present a comprehensive review of the recent advances in the optical SSB Tx. First, we evaluate three conventional optical SSB Tx schemes based on optical filter, in-phase/quadrature modulator, and dual-drive Mach-Zehnder modulator. We then introduce the recently proposed optical SSB Tx schemes based on electro-absorption modulation lasers (EMLs), including the double-sided EML, two-segment EML, and the dually modulated EML. Compared with the conventional optical SSB Tx solutions, the EML-based schemes exhibit obvious friendliness to monolithic integration. Besides, we investigate the practical ways to add optical carrier with optical SSB signal and efficient implementation of the Hilbert transform, which are two practical issues in the optical SSB Tx. Finally, we explore the capability of monolithic integration of optical SSB Tx with state-of-the-art material platforms. Our comparison made among these schemes can provide a guideline for the selection of proper Tx scheme for specific optical SSB systems.

High-performance coherent optical modulators based on thin-film lithium niobate platform

The coherent transmission technology using digital signal processing and advanced modulation formats, is bringing networks closer to the theoretical capacity limit of optical fibres, the Shannon limit. The in-phase/quadrature electro-optic modulator that encodes information on both the amplitude and the phase of light, is one of the underpinning devices for the coherent transmission technology. Ideally, such modulator should feature a low loss, low drive voltage, large bandwidth, low chirp and compact footprint. However, these requirements have been only met on separate occasions. Here, we demonstrate integrated thin-film lithium niobate in-phase/quadrature modulators that fulfil these requirements simultaneously. The presented devices exhibit greatly improved overall performance (half-wave voltage, bandwidth and optical loss) over traditional lithium niobate counterparts, and support modulation data rate up to 320 Gbit s−1. Our devices pave new routes for future high-speed, energy-efficient, and cost-effective communication networks.

Planning constraints of low grazing altitude GEO-LEO laser links based on in-orbit data

Part of the operational concept for laser communication networks such as the European data relay system is planning constraints. In addition to hard constraints such as angular range of the actuators, there is also the atmosphere, which has a gradual increasing impact as the distance between laser beam path and earth decreases. The shortest distance between the laser beam path and the surface of the earth is called “grazing altitude.” The atmosphere impacts spatial acquisition as well as communication performance. In-orbit measurement data of geostationary orbit–low-Earth orbit (GEO-LEO) links between two laser communication terminals (LCT) developed by TESAT-Spacecom, Germany, in the frame of Alphasat TDP1 optical GEO-relay demonstration program are presented. Planning constraint guidelines are formulated based on the observed influence. TESAT-Spacecom’s LCTs use a highly sensitive and high-performance coherent transmission technology and a beaconless spatial acquisition system.

A review of high-speed coherent transmission technologies for long-haul DWDM transmission at 100g and beyond

Over the past five years, coherent transmission technologies have delivered more than an order of magnitude improvement in the capacity- reach product for long-haul DWDM transmission systems. This article provides a working definition of "coherent transmission" based on current market realities; provides a functional model for beyond 100G coherent systems, and then examines five key technologies that will deliver beyond 100G: evolving transmitter technologies, including Nyquist pulse shaping and nonlinear compensation of transmitter devices; nonlinear compensation for the propagation effect; further advances in FEC technology; flexible grid DWDM and coherent super-channels. In each case we explain the factors in terms of optical or electronic component performance that are most likely to result in system performance limitations, and discuss engineering strategies to mitigate those limitations.

대용량 광통신 부품 기술 동향

스마트 기기, 클라우드 서비스, 광가입자망 등의 보급에 따른 멀티미디어 기반의 대용량 인터넷 트래픽의 급속한 증가로 통신 수요는 연 40%이상씩 증가하고 있다. 이러한 대역폭 증가를 수용하기 위해서 광통신용 광부품의 진화도 각 계층별로 빠르게 진행되고 있다. 가입자망에서는 변조속도 증가와 더불어 파장다중방식의 도입이 시작되고 있고, 매트로망에서는 보다 효율적인 망 운용을 위해 차세대 ROADM에 대한 개발이 진행중이며, 장거리 통신에서는 코히어런트 통신 기반의 새로운 변조방식이 도입되어 스팩트럼 효율을 향상시키고 있다. 본 논문에서는 이러한 폭발적인 통신 대역폭 증가 요구에 따른 광통신망의 진화와 이를 수용하기 위한 고속화, 효율화, 저전력화로 발전하고 있는 핵심 광부품에 대해 살펴본다. With the explosive growth of internet data traffic due to the FTTH penetration, prevalence of smart devices and cloud network service, the demand for higher bandwidth is ever increasing with the pace of more than 40% annual growth. To accommodate ultra high bandwidth traffic, optical components in each hierarchy have progressed rapidly. WDM has begun to be deployed along with higher bandwidth service in the access network. Next-generation ROADM is under development for efficient network management in the metro network. For long-haul transmission, an advanced modulation scheme based on coherent transmission technology has been adopted to enhance spectral efficiency. In this paper, core components to meet the demands of high speed, high efficiency and low power consumption will be reviewed.

Massive Terminal Dispersion Compensation Enabling Nondispersion-Managed Submarine Links With First Generation Coherent Transponders

We numerically and experimentally investigate the limits of terminal-based optical dispersion compensation for nondispersion-managed systems, using coherent transmission technology. The resulting residual dispersion is ~50 000 ps/nm, which is within the digital signal processing compensation range of first generation coherent transponders.

Temporal Solitonic Crystals and Non-Hermitian Informational Lattices

Clusters of temporal optical solitons--stable self-localized light pulses preserving their form during propagation--exhibit properties characteristic of that encountered in crystals. Here, we introduce the concept of temporal solitonic information crystals formed by the lattices of optical pulses with variable phases. The proposed general idea offers new approaches to optical coherent transmission technology and can be generalized to dispersion-managed and dissipative solitons as well as scaled to a variety of physical platforms from fiber optics to silicon chips. We discuss the key properties of such dynamic temporal crystals that mathematically correspond to non-hermitian lattices and examine the types of collective mode instabilities determining the lifetime of the soliton train. This transfer of techniques and concepts from solid state physics to information theory promises a new outlook on information storage and transmission.