Capacity Analysis and Receiver Design in the Presence of Fiber Nonlinearity
Doktorsavhandling, 2019

The majority of today's global Internet traffic is conveyed through optical fibers. The ever-increasing data demands have pushed the optical systems to evolve from using regenerators and direct-direction receivers to a coherent multi-wavelength network. Future services like cloud computing and virtual reality will demand more bandwidth, so much so that the so called capacity-crunch is anticipated to happen in near future. Therefore, studying the capacity of the optical system is needed to better understanding and utilizing the existing fiber network.

The characterization of the capacity of the dispersive and nonlinear optical fiber described by the nonlinear Schr{\"o}dinger equation is an open problem.
There are a number of lower bounds on the capacity which are mainly obtained based on the mismatched decoding principle or by analyzing simplified channels. These lower bounds either fall to zero at high powers or saturate. The question whether the fiber-optical capacity has the same behavior as the lower bounds at high power is still open. Indeed, the only known upper bound increases with the power unboundedly.

In this thesis, we first study how the fiber nonlinear distortion is modeled in some simplified channels and what is the influence of the simplifying assumptions on the capacity. To do so, the capacity of three different memoryless simplified models of the fiber-optical channel are studied. The results show that in the high-power regime the capacities of these models grow with different pre-logs, which indicates the profound impact of the simplifying assumptions on the capacity of these channels.

Next, we turn our attention to demodulation and detection processes in the presence of fiber nonlinearity. We study a two-user memoryless network. It is shown that by deploying a nonlinearity-tailored demodulator, the performance improves substantially compared with matched filtering and sampling. In the absence of dispersion, we show that with the new receiver, unlike with matched filtering and sampling, arbitrarily low bit error rates can be achieved. Furthermore, we show via simulations that performance improvements can be obtained also for a low-dispersion fiber.

Then, we study the performance of three different dispersion compensation methods in the presence of inter-channel nonlinear interference. The best performance, in terms of achievable information rate, is obtained by a link with inline per-channel dispersion compensation combined with a receiver that compensates for inter-channel nonlinearities.
Finally, the capacity analysis is performed for short-reach noncoherent channel, where the source of nonlinearity is not the fiber but a square-law receiver. Capacity bounds are established in the presence of optical and thermal noises. Using these bounds we show that optical amplification is beneficial at low signal-to-noise ratios (SNRs), and detrimental at high SNRs. We quantify the SNR regime for each case for a wide range of channel parameters.

perturbation theory.

Achievable rate

nonlinearity mitigation

noncoherent optics

dispersion compensation

fiber optics

channel capacity

information theory

in Room EA, Hörsalsvägen 11, Chalmers
Opponent: Prof. Joseph M. Kahn, Department of Electrical Engineering, Stanford University, Stanford, CA, USA.


Kamran Keykhosravi

Chalmers, Elektroteknik, Kommunikation, Antenner och Optiska Nätverk

K. Keykhosravi, G. Durisi, and E. Agrell, Bounds on the per-sample capacity of zero-dispersion simplified fiber-optical channel models,

Demodulation and Detection Schemes for a Memoryless Optical WDM Channel

IEEE Transactions on Communications,; Vol. 66(2018)p. 2994-3005

Artikel i vetenskaplig tidskrift

How to Increase the Achievable Information Rate by Per-Channel Dispersion Compensation

Journal of Lightwave Technology,; Vol. 37(2019)p. 2443-2451

Artikel i vetenskaplig tidskrift

K. Keykhosravi, E. Agrell, M. Secondini, and M. Karlsson, When to use optical amplification in noncoherent transmission: An information-theoretic approach

Advancements in the telecommunication industry have reformed people's lifestyle in the past few decades. Anyone connected to Internet can acquire or disseminate data with a click of a button. The massive volume of data is transferred almost exclusively through optical fibers, which connect continents, countries, and cities together. Optical fibers are also used in datacenters to transfer information bits in short distances with high speeds.

With the phenomenal growth of Internet and the advent of social media, Internet-of-things, and high-resolution movie streaming, the request for data transmission is rapidly increasing. It is predicted that the demand surpasses the limits of current optical systems in the near future. Therefore, it is essential to reconsider the design of conventional optical transmitters and receivers to maximize the performance of fiber-optic systems.

The core of optical fiber is a cylindrically-shaped medium slightly thicker than a human hair made from extremely transparent glass. The light is generated at the source via a laser, traverses the fiber, and is received at its destination. The information is coded into the intensity and/or the phase of the light at the transmitter and is decoded at the receiver. This process of data transmission is not perfect since the light's phase and intensity is disturbed through propagation via noise and interference. These impairments of optical systems limit the rate of data transmission through the fiber.

In this thesis, we study the capacity of fiber-optic channels, i.e., the maximum rate at which information can be transferred reliably through fiber-optic systems. First, an introduction is given to the physics, properties, and impairments of the optical fiber. Then, we compare multiple available models of fiber-optic channel and assess their accuracy. Next, we propose a method to mitigate the effects of nonlinear interference caused by a copropagating optical signal. In the next step, we compare the performance of three different multi-channel optical systems. Finally, we study the capacity of short-haul fiber-optic channels.

Fiberoptisk interferens är inte brus

Vetenskapsrådet (VR) (2013-5271), 2014-01-01 -- 2017-12-31.


Informations- och kommunikationsteknik






Grundläggande vetenskaper


C3SE (Chalmers Centre for Computational Science and Engineering)



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4604



in Room EA, Hörsalsvägen 11, Chalmers

Opponent: Prof. Joseph M. Kahn, Department of Electrical Engineering, Stanford University, Stanford, CA, USA.

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