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Evidence for accumulated sidewall damage in dry etched photonic crystals
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0002-4606-4865
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2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Article in journal (Other academic) Submitted
Place, publisher, year, edition, pages
2008.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-8378OAI: oai:DiVA.org:kth-8378DiVA: diva2:13683
Note
QS 20120314Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2017-12-14Bibliographically approved
In thesis
1. InP-based photonic crystals: Processing, Material properties and Dispersion effects
Open this publication in new window or tab >>InP-based photonic crystals: Processing, Material properties and Dispersion effects
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Photonic crystals (PhCs) are periodic dielectric structures that exhibit a photonic bandgap, i.e., a range of wavelength for which light propagation is forbidden. The special band structure related dispersion properties offer a realm of novel functionalities and interesting physical phenomena. PhCs have been manufactured using semiconductors and other material technologies. However, InP-based materials are the main choice for active devices at optical communication wavelengths. This thesis focuses on two-dimensional PhCs in the InP/GaInAsP/InP material system and addresses their fabrication technology and their physical properties covering both material issues and light propagation aspects.

Ar/Cl2 chemically assisted ion beam etching was used to etch the photonic crystals. The etching characteristics including feature size dependent etching phenomena were experimentally determined and the underlying etching mechanisms are explained. For the etched PhC holes, aspect ratios around 20 were achieved, with a maximum etch depth of 5 microns for a hole diameter of 300 nm. Optical losses in photonic crystal devices were addressed both in terms of vertical confinement and hole shape and depth. The work also demonstrated that dry etching has a major impact on the properties of the photonic crystal material. The surface Fermi level at the etched hole sidewalls was found to be pinned at 0.12 eV below the conduction band minimum. This is shown to have important consequences on carrier transport. It is also found that, for an InGaAsP quantum well, the surface recombination velocity increases (non-linearly) by more than one order of magnitude as the etch duration is increased, providing evidence for accumulation of sidewall damage. A model based on sputtering theory is developed to qualitatively explain the development of damage.

The physics of dispersive phenomena in PhC structures is investigated experimentally and theoretically. Negative refraction was experimentally demonstrated at optical wavelengths, and applied for light focusing. Fourier optics was used to experimentally explore the issue of coupling to Bloch modes inside the PhC slab and to experimentally determine the curvature of the band structure. Finally, dispersive phenomena were used in coupled-cavity waveguides to achieve a slow light regime with a group index of more than 180 and a group velocity dispersion up to 10^7 times that of a conventional fiber.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xv, 115 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:7
Keyword
Photonic crystals, indium phosphide, photonic bandgap, Bloch modes, slow light, dispersion, coupled cavity waveguides, chemically assisted ion beam etching, lag effect, cavities, optical losses, carrier transport, carrier lifetimes, negative refraction, photonic bandstructure
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4734 (URN)978-91-7178-969-3 (ISBN)
Public defence
2008-05-30, N1, Electrum 3, Kista, 10:00
Opponent
Supervisors
Note
QC 20100712Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-07-12Bibliographically approved
2. Design, Simulation and Characterization of Some Planar Lightwave Circuits
Open this publication in new window or tab >>Design, Simulation and Characterization of Some Planar Lightwave Circuits
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Optical devices based on planar lightwave circuit (PLC) technology have the advantages of small size, high reliability, possibility for large scale production, and potential integration with electronics. These devices are widely employed in optical telecommunications, sensing, data storage, imaging, and signal processing. This thesis focuses on some selected PLC based devices, such as power splitters, demultiplexers, triplexers and polarization beam splitters.

First, the basic principle of the waveguides and the simulation methods for PLC devices are discussed. A novel effective index method is introduced to reduce a two-dimensional structure to a one-dimensional one, and can be implemented for arbitrarily shaped waveguides. Numerical methods, such as finite-difference mode solver, beam propagation method, finite-difference time-domain method are introduced to analysis the mode profile of the waveguides, and the propagation properties of light in PLC devices.

Multimode interference (MMI) couplers are widely used in many PLCs, such as power splitters, ring lasers, optical switches, and wavelength division multiplexers/demultiplexers. In this work, concepts for improving the self-imaging quality of MMI couplers are analyzed and new designs are proposed. A significant improvement in performance together with compact sizes were obtained with taper sections at the input/output of MMI couplers based on SOI, and deeply etched ridges in MMI couplers based on SiO2. A polarization insensitive dual wavelength demultiplexer based on sandwiched MMI waveguides was presented.

Novel devices including triplexers and polarization beam splitters were realized by using photonic crystal (PhC) structures. Two stages of directional couplers based on PhC waveguides are cascaded to form an ultracompact triplexer. The special decoupling property of the PhC waveguide based directional coupler was utilized in the design. A novel polarization beam splitter was realized by combining a MMI coupler and a PhC which works as a polarization sensitive reflector.

Finally, fabrication and optical characterization of an ultra-compact directional coupler and PhC structures in InP are presented. In a single etching step, by using the lag-effect in inductively coupled plasma reactive ion etching, a compact directional coupler (55 μm) is demonstrated. Carrier life times in PhC structures etched by chemically assisted ion beam etching were investigated, for emitter and switching applications.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xiv, 84 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:9
Keyword
planar lightwave circuit, waveguide, coupler, multimode interference, photonic crystal waveguide, (de)multiplexer, triplexer, polarization beam splitter, dry etching, carrier life time.
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-4760 (URN)978-91-7178-989-1 (ISBN)
Public defence
2008-06-09, sal N2, Electrum 3, Isafjordsgatan 28, Kista, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100909Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-09-09Bibliographically approved

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