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Theoretical Investigation on Propagation and Coupling of Nonreciprocal Electromagnetic Surface Waves
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis aims at revealing the fundamental guiding and coupling properties of nonreciprocal electromagnetic surface waves on magneto-optical or gyromagnetic media and designing novel applications based on the properties.

We introduce the background in the first chapter. We then describe the concept of nonreciprocity and the main calculation method in the second chapter. In the third chapter, we show that one-way waves can be sustained at the edge of a gyromagnetic photonic crystal slab under an external magnetic field. We also investigate the coupling between two parallel one-way waveguides. We reveal the condition for effective co-directional and contra-directional coupling. We also notice that the contra-directional coupling is related to the concept of a “trapped rainbow”.

In the fourth chapter, we address the concept of a “trapped rainbow”. It aims at trapping different frequency components of the electromagnetic wave packet at different positions in space permanently. In previous structures, the entire incident wave is reflected due to the strong contra-directional coupling between forward and backward modes. To overcome this difficulty, we show that utilizing nonreciprocal waveguides under a tapered external magnetic field can achieve a truly “trapped rainbow” effect at microwave frequencies. We observe hot spots and relatively long duration times around critical positions through simulations and find that such a trapping effect is robust against disorders.

Lastly, in the fifth chapter, we study the one-way waves in a surface magnetoplasmon cavity. We find that the external magnetic field can separate the clockwise and anti-clockwise cavity modes into two totally different frequency ranges. This offers us more choices, both in the frequency ranges and in the one-way directions, for realizing one-way components. We also show the waveguide-cavity coupling by designing a circulator, which establishes the foundation for potential applications.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. , xii, 62 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2016:094
Keyword [en]
wave propagation, coupling, magneto-optical, gyromagnetic, photonic crystal, nonreciprocity, one-way, trapped rainbow
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-190792ISBN: 978-91-7729-055-1OAI: oai:DiVA.org:kth-190792DiVA: diva2:952842
Public defence
2016-09-09, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, VR 621-2011-4620
Note

QC 20160816

Available from: 2016-08-16 Created: 2016-08-15 Last updated: 2016-08-16Bibliographically approved
List of papers
1. One-way edge mode in a gyromagnetic photonic crystal slab
Open this publication in new window or tab >>One-way edge mode in a gyromagnetic photonic crystal slab
2012 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 19, 4110-4112 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate that one-way electromagnetic modes could be sustained by the edge of a gyromagnetic photonic crystal slab of triangular lattice under an external dc magnetic field. The applied magnetic field breaks the time-reversal symmetry of the three-dimensional system, and thus the original degeneracy point in k space, at which two dispersion surfaces intersect, is lifted, resulting in a photonic band gap below the light cone. At this band gap, the one-way mode is localized horizontally to the slab edge, while confined by the index contrast in the vertical direction.

Keyword
Applied magnetic fields, DC magnetic field, Degeneracy point, Dispersion surface, Electromagnetic modes, Index contrasts, K space, Photonic crystal slab, Slab edges, Three dimensional systems, Time reversal symmetries, Triangular lattice, Vertical direction
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-104701 (URN)10.1364/OL.37.004110 (DOI)000309542900062 ()2-s2.0-84867155082 (ScopusID)
Note

QC 20121112

Available from: 2012-11-12 Created: 2012-11-09 Last updated: 2016-08-16Bibliographically approved
2. Interaction Between Two One-Way Waveguides
Open this publication in new window or tab >>Interaction Between Two One-Way Waveguides
2012 (English)In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, E-ISSN 1558-1713, Vol. 48, no 8, 1059-1064 p.Article in journal (Refereed) Published
Abstract [en]

The interaction between two (parallel) one-way waveguidesformed by photonic crystals is investigated theoretically. It is shown that when thetwo waveguides support modes propagating in opposite directions, they can effectively interact with each other only within a narrow guiding region where their propagation constants are nearly zero. In this coupling window, the waveguides are contra-directionally coupled and the efficiency grows monotonously with the coupling length, reaching 100% as the coupling length is large enough. When the one-waywaveguides support the modes propagating in the same direction, they may be efficiently coupled through the whole guiding regime, and their coupling exhibits the same behavior as the conventional uniform waveguides. The coupling between theone-way waveguides is first analyzed with the coupled-mode approximation and then verified by rigorous numerical simulation. 

Place, publisher, year, edition, pages
IEEE, 2012
Keyword
coupling, nonreciprocity, one-way waveguides, photonic crystals
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-190012 (URN)10.1109/JQE.2012.2202215 (DOI)000305572600001 ()2-s2.0-84862565201 (ScopusID)
Note

QC 20160815

Available from: 2016-07-29 Created: 2016-07-29 Last updated: 2016-08-16Bibliographically approved
3. Truly trapped rainbow by utilizing nonreciprocal waveguides
Open this publication in new window or tab >>Truly trapped rainbow by utilizing nonreciprocal waveguides
2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, 30206Article in journal (Refereed) Published
Abstract [en]

The concept of a “trapped rainbow” has generated considerable interest for optical data storage and processing. It aims to trap different frequency components of the wave packet at different positions permanently. However, all the previously proposed structures cannot truly achieve this effect, due to the difficulties in suppressing the reflection caused by strong intermodal coupling and distinguishing different frequency components simultaneously. In this article, we found a physical mechanism to achieve a truly “trapped rainbow” storage of electromagnetic wave. We utilize nonreciprocal waveguides under a tapered magnetic field to achieve this and such a trapping effect is stable even under fabrication disorders. We also observe hot spots and relatively long duration time of the trapped wave around critical positions through frequency domain and time domain simulations. The physical mechanism we found has a variety of potential applications ranging from wave harvesting and storage to nonlinearity enhancement.

Place, publisher, year, edition, pages
Nature Publishing Group, 2016
Keyword
trapped rainbow, nonreciprocity, one-way, slow light
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-190013 (URN)10.1038/srep30206 (DOI)000380200100001 ()2-s2.0-84979593598 (ScopusID)
External cooperation:
Funder
Swedish Research Council, 621-2011-4620
Note

QC 20160815

Available from: 2016-07-29 Created: 2016-07-29 Last updated: 2016-08-30Bibliographically approved
4. One-way surface magnetoplasmon cavity and its application for nonreciprocal devices
Open this publication in new window or tab >>One-way surface magnetoplasmon cavity and its application for nonreciprocal devices
2016 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 41, no 4, 800-803 p.Article in journal (Refereed) Published
Abstract [en]

We theoretically analyze surface magnetoplasmon modes in a compact circular cavity made of magneto-optical material under a static magnetic field. Such a cavity provides two different methods for the surface wave to circulate in a unidirectional manner around the cavity, which offers more freedom, both in the one-way direction and in the frequency range, for designing nonreciprocal photonic components. We also show the interaction between this one-way cavity and waveguides through the example of a circulator, which lays the fundamental groundwork for potential nonreciprocal devices.

Place, publisher, year, edition, pages
Optical Society of America, 2016
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-183311 (URN)10.1364/OL.41.000800 (DOI)000369942900037 ()26872192 (PubMedID)2-s2.0-84962175657 (ScopusID)
Note

QC 20160309

Available from: 2016-03-09 Created: 2016-03-07 Last updated: 2016-08-16Bibliographically approved

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