| 221. |
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| 222. |
- Karlsson, Magnus, 1967
(author)
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Modulational instability in lossy optical fibers
- 1995
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In: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 12:11, s. 2071-2077
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Journal article (peer-reviewed)abstract
- The modulational instability in an optical fiber, with loss taken into account, is analytically investigated. It is demonstrated how the linearized equation for perturbation can be solved exactly in terms of Bessel functions, and qualitative differences from previous analytic approaches are pointed out. Finally, the limits imposed by this instability on optical communication systems are discussed. The use of this theory in system design is examined.
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| 223. |
- Karlsson, Magnus, 1967, et al.
(author)
-
Multidimensional Modulation and Coding
- 2016
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In: 2016 Optical Fiber Communications Conference and Exhibition (Ofc).
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Conference paper (peer-reviewed)abstract
- We discuss how error-correction coding and modulation can be cooptimized, how modulation formats can be interpreted as codes, and the roles of soft and hard decision decoding.
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| 224. |
- Karlsson, Magnus, 1967, et al.
(author)
-
Multidimensional Modulation and Coding in Optical Transport [Invited]
- 2017
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In: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 35:4, s. 876-884
-
Journal article (peer-reviewed)abstract
- This paper reviews the performance of optimized modulation formats in 2, 4, and 8 dimensions. We present performance (lower bounds) for higher dimensions by exploiting known performance of binary block codes. Ultimately, the achievable information rates of given modulation formats and receiver types are limited by the mutual information and generalized mutual information. We exemplify how these metrics can be used for system performance as well as to quantify the performance differences between four types of systems; using hard or soft decision on bits or symbols.
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| 225. |
- Karlsson, Magnus, 1967
(author)
-
Multidimensional modulation formats for optical communication
- 2016
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In: 21st OptoElectronics and Communications Conference, OECC 2016 - Held Jointly with 2016 International Conference on Photonics in Switching, PS 2016, Niigata, Japan, 3-7 July 2016. - 9784885523052
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Conference paper (peer-reviewed)abstract
- We review the research on multidimensional modulation formats for coherent optical transmission systems. Examples of lattice-based formats in 4 and 8 dimensions are given, and a number of performance metrics are discussed.
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| 226. |
- Karlsson, Magnus, 1967, et al.
(author)
-
Multidimensional Optimized Optical Modulation Formats
- 2016
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In: Enabling Technologies for High Spectral-efficiency Coherent Optical Communication Networks, Ch. 2. - : Wiley. - 9781118714768 ; , s. 13-64
-
Book chapter (other academic/artistic)abstract
- This chapter overviews the relatively large body of work (experimental and theoretical) on modulation formats for optical coherent links. It first gives basic definitions and performance metrics for modulation formats that are common in the literature. Then, the chapter discusses optimization of modulation formats in coded systems. It distinguishes between three cases, depending on the type of decoder employed, which pose quite different requirements on the choice of modulation format. The three cases are soft-decision decoding, hard-decision decoding, and iterative decoding, which loosely correspond to weak, medium, and strong coding, respectively. The chapter also discusses the realizations of the transmitter and transmission link properties and the receiver algorithms, including DSP and decoding. It further explains how to simply determine the transmitted symbol from the received 4D vector, without resorting to a full search of the Euclidean distances to all points in the whole constellation.
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| 227. |
- Karlsson, Magnus, 1967, et al.
(author)
-
Multilevel pulse-position modulation for optical power-efficient communication
- 2011
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In: Optics Express. - 1094-4087 .- 1094-4087. ; 19:26, s. B799-B804
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Journal article (peer-reviewed)abstract
- A family of modulation formats is derived by combining pulse-position modulation (PPM) with multilevel dual-polarization signal constellations. With 16-PPM, gains of up to 5.4 dB are obtained over dual-polarization QPSK, at the cost of reduced spectral efficiency.
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| 228. |
- Karlsson, Magnus, 1967
(author)
-
Nonlinear Propagation of Optical Pulses and Beams
- 1994
-
Doctoral thesis (other academic/artistic)abstract
- The propagation of optical beams and pulses under the influence of nonlinear effects is characterized by a rich variety of phenomena and many potentially important applications. We analyse two main topics in this context: nonlinear beam propagation, and nonlinear pulse propagation in optical fibers. The propagation of an optical beam is characterized by diffractive broadening. For Kerr-media, in which the refractive index increases with beam intensity, at a certain intensity, the beam may induce its own waveguide and propagate without broadening. For higher intensities, the nonlinearly induced refractive index causes self-focusing and in some cases even collapsing singularities. We demonstrate in this work that an analytical variational approach describes the dynamics of nonlinear beam propagation very well, in particular with respect to the phase modulation dynamics, which previous approaches are found to describe erroneously. The collapse can be removed by allowing the refractive index to saturate. Beam dynamics in saturable nonlinear media is therefore an important issue. Using the variational method, we manage to reproduce the essential features from numerical simulations, and to give a complete picture of optical beam dynamics in saturable nonlinear media. Another important effect in nolinear media is the modulational instability, which is well-known to break up broad beams into filaments. However, this instability can occur only in nonlinear focusing media. Considering a pulsed beam with a defocusing-in-time and focusing-in-space nonlinearity, we show that temporal breakup is possible due to the spatial instability, despite the fact that a purely temporal modulation is stable.
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| 229. |
- Karlsson, Magnus, 1967
(author)
-
Optical beams in saturable self-focusing media
- 1992
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In: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 46:5, s. 2726-2734
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Journal article (peer-reviewed)abstract
- An approximate analytical analysis of two-dimensional optical beams propagating in saturable self-focusing media is carried out. In particular, the radial shape and the phase shift of the stationary self-trapped fundamental mode are investigated in detail. The dynamic variations of the beamwidth and the phase shift for nonstationary propagation are also analyzed. The predictions of the analytical model are compared with numerical results for stationary propagation and show good agreement. © 1992 The American Physical Society.
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| 230. |
- Karlsson, Magnus, 1967
(author)
-
Optical fiber-grating compressors utilizing long fibers
- 1994
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In: Optics Communications. - : Elsevier BV. - 0030-4018. ; 112:1-2, s. 48-54
-
Journal article (peer-reviewed)abstract
- The properties of optical fiber-grating compressors have been investigated numerically, considering fibers ten times longer than in previous studies. It is found that such long fibers yield substantially better compression than the previously investigated short ones. Also considerde are the sensitivity of pulse shape on the compression by using Gaussian-, parabolic- and sech- shaped pulses as initial conditions. © 1994.
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