About the research area Optical communications
There is an ever present need from society for more bandwidth. This manifests probably most significantly in services such as video conferencing, television, and video-on-demand transmitted over the internet, but also in massive data transfers required with and within data centers for backup, storage and data processing in the ”cloud”.
The dramatic evolution of the wavelength-division multiplexed fiber-optical transmission systems in the mid-90s in combination with earlier significant hardware improvements has paved the way for today´s global data infrastructure. However, while up until now photonic technology competence has sufficed for optical link design, an increasing amount of communication theory competence is now required, as the potential gains made by hardware improvements becomes costlier, or even infeasible.
n the Communication Systems Group, we collaborate with the Photonics Laboratory at the Department of Microtechnology and Nanoscience, achieving results that none of the groups could have reached alone. Roughly, the Photonics Laboratory provides the photonics expertise, including knowledge of lasers, fibers, detectors, and amplifiers, while Communication Systems provides expertise in digital communication theory, including coding, modulation, detection, and estimation. The research is carried out within the research center FORCE
(Fiber-Optic Communications Research Center) at Chalmers.
Currently, we are launching new methods to increase the capacity of existing optical links, by optimizing the transmitter and receiver algorithms. This might extend the distances between access points in fiber-to-the-home applications, or increase the amount of data transmitted over long distance links, thus reducing expenses, equipment, energy consumption and – in the long term – the environmental impact. The new technology is an enabler for new cloud-based mobile services, for example navigation, translation and entertainment.
Nonlinear distortion in fiber-optical transmission
One main track in our present research aims to understand and mitigate nonlinear distortion in fiber-optical transmission. These effects cause the signal quality to decrease dramatically if the transmitted power is increased above a certain limit, which is fundamentally different from linear systems such as wireline and wireless links, whose performance improves continuously (within reasonable limits) with increasing power. Therefore, transmission and detection methods designed for such systems do not necessarily perform well in optical systems. Based on mathematical models of the nonlinear distortion, we develop new methods optimized for these kinds of impairments, which perform significantly better than traditional algorithms.
> Advanced modulation and coding
In this project, we analyze multilevel modulation formats suitable for coherent, optical transmission. Modulation formats are optimized under ideal conditions as well as considering realistic optical impairments, such as self-phase modulation and transmitter/receiver saturation...
> Coded modulation
Coded modulation (CM) refers to a system where an encoder is combined with a higher order modulator with more than one bit per symbol to increase the spectral efficiency. Examples of encoders can be simple block codes or convolutional codes, to more advanced encoders like turbo codes...
> Adaptive optical networks
Global internet traffic is expected to increase fourfold in the next five years. This traffic will be highly time-varying and has led to the introduction of flexible, so-called "elastic," optical networks. In such networks, light-paths are set up and optically routed from sources to destinations with no intermediate electro-optic conversions...
> Technologies for spatial-division multiplexing: The next frontier in optical communications
Optical fiber communication systems constitute the backbone of Internet. In this project, we propose to analyze and demonstrate concepts to reach substantially higher transmission throughput than in todays optical communication systems. This is essential, as the currently used technology approach, using single-mode optical fibers...
> Towards flexible and energy-efficient datacentre networks
The growing popularity of cloud and multimedia services is increasing the traffic volume that datacentres need to handle, leading to serious bottlenecks in datacentre networks in terms of both capacity and energy consumption. Reducing the power required by the inter- and intra-rack communication inside the datacentre...
> Optical fiber interference is not noise
Optical fiber networks are indispensable for our society’s information infrastructure. The demands for high-capacity, reliable communications will continue to increase for many years, due to new emerging services such as cloud processing and telepresence. This project addresses one of the fundamental bottlenecks in the development of next-generation optical networks, namely interference...
> MIMOptics: Multi-mode coherent fiber-optical communications
Our society’s demand for increasing data rates is continuing unabated, today mainly to support streaming video and cloud computing. According to a conservative estimate from Cisco, the global Internet traffic increases 29% per year, leading to a ten-fold increase by 2022...
> Energy-efficient optical fibre communication
Optical communication links and networks are essential for the Internet backbone as well as for interconnects used in data centres and high-performance computing systems. Therefore, the energy consumption in optical transmission systems is an increasingly important problem within our information society...
> Coding for optical communications in the nonlinear regime (COIN)
The rapid increase in data traffic in the past years and traffic forecasts will lead to capacity exhaust in the optical fibre communications infrastructure which carries over 95% of all data services. The optical fibre channel is nonlinear, that is, its properties, namely its refractive index, is dependent on optical intensity, and at high power densities, ...
> Coherent receiver syncronization
Synchronization refers to processing at the receiver-side of a digital communication link, in order to recover optimal sampling times and compensate for frequency and phase offsets induced by physical components. In optical communication systems, the design of synchronization algorithms is especially challenging due to extremely high baud rates, minimal dedicated processing capabilities, stringent latency constraints, and hardware deficiencies...
> Theory for intensity-modulated links
With the rapidly increasing demand for large-scale fiber-to-the-home, the cost of transmission equipment is crucial. In this project, we develop communication theory for links consisting of a low-cost laser diode (e.g., a vertical-cavity surface-emitting laser, VCSEL) in the transmitter, whose intensity but not phase can be modulated. Similarly, the receiver is a photo diode that detects the intensity of the received lightwave... > Power-efficient terabit/s transmission
Fiber optic communications has, and will play, a pivotal role in our future, being a major enabling technology in our increasingly Internet-centric society. The aggregated data rates in e.g. Internet cross-connects are now so high that terabit/s transmission systems and line cards are being required, and solutions for e.g. terabit Ethernet are being discussed.