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High-speed optical modulator based on intersubband transitions in InGaAs/InAlAs/AlAsSb coupled quantum wells
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
2003 (English)In: Conference Proceedings - International Conference on Indium Phosphide and Related Materials, 2003, 308-311 p.Conference paper, Published paper (Refereed)
Abstract [en]

We investigate theoretically an optical modulator based on intersubband transitions in InGaAs/InAlAs/AlAsSb coupled quantum wells with an operating wavelength of 1.55 mum. We show that such a modulator has the potential to outperform conventional electroabsorption and electro-optic modulators with a combination of high speed, moderate voltage swing, negative chirp and high saturation power. The modulator studied here is predicted to have a RC-limited speed of 90 GHz with 10 dB extinction ratio at a peak-to-peak voltage of 2.0 V.

Place, publisher, year, edition, pages
2003. 308-311 p.
Series
Conference proceedings - indium phosphide and related materials, ISSN 1092-8669
Keyword [en]
Absorption, Electrooptical devices, Light modulators, Phase transitions, Semiconducting aluminum compounds, Semiconducting indium compounds
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6658ISI: 000183253000080OAI: oai:DiVA.org:kth-6658DiVA: diva2:11430
Conference
2003 International Conference Indium Phosphide and Related Materials; Santa Barbara, CA; 12 May 2003 through 16 May 2003
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2010-09-03Bibliographically approved
In thesis
1. Photonic Devices and Applications based on Intersubband Transitions and Electromagnetically Induced Transparency
Open this publication in new window or tab >>Photonic Devices and Applications based on Intersubband Transitions and Electromagnetically Induced Transparency
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Although photonic devices have experienced a rapid development lately, there is still room for substantial improvements in performance. From a telecommunications perspective, improvements in speed, size, integration and power consumption are desired. There is also a general interest in photonic devices with new functionalities. Being a key component in fiber-optic systems, high-speed optical modulators often initiate the development towards higher bit-rates. The technology of current state-of-the-art modulators has matured suggesting new paths of development. In this thesis we investigate the potential of modulators based on intersubband (IS) transitions in quantum wells (QWs). Specific QW designs are suggested and complete modulator structures are simulated. IS absorption is also experimentally characterized. Absorption linewidth is critical for IS modulator performance since narrow linewidth implies high bandwidth and/or small driving voltage. High material quality is important, since linewidth is typically limited by well-width fluctuations and interface roughness.

A mid-IR AlGaAs/GaAs-modulator is proposed having a RC-limited bandwidth of 130 GHz and a peak-to-peak voltage of 0.9 V. Experimentally, Stark shift is measured in InAlAs/InAlGaAs/InGaAs step QWs at λ ~ 6 μm predicting that an IS modulator based on this material would have a bandwidth of 90 GHz and a peak-to-peak voltage of 0.9 V. IS absorption at 1.55 μm requires material combinations with high conduction-band offset. Simulations of an InGaAs/InAlAs/AlAsSb-modulator predict a bandwidth of 90 GHz and a peak-to-peak voltage of 2.0 V. Experimental studies of IS absorption in AlN/GaN QWs are presented. IS absorption at 1.5-3.4 μm with linewidth below 100 meV is measured for well widths between 15-54 Å. Subpeaks corresponding to well-width fluctuations on the monolayer scale are identified with linewidths of ~60 meV. Agreement between theoretical calculations and measured spectra is encouraging. Theoretical simulations together with measured absorption linewidths suggest that high performance IS modulators operating at 1.55 μm are realizable.

Photonic devices with new functionalities are addressed by investigating electromagnetically induced transparency (EIT) theoretically and considering potential applications based on EIT. Simulations of two-dimensional pulse-propagation based on the Maxwell-Bloch equations are performed with a focus on storing and reading out optical pulses. We explicitly formulate the phase-matching conditions for reading out stored pulses in a new direction and propose a serial-to-parallel converter based on this.

For slow-light devices, e.g. optical buffers, we identify and analyze two main limitations on the medium bandwidth; the frequency dependent absorption and the group velocity dispersion. Since large bandwidth and large delay are contradictory requirements, the delay bandwidth product is considered. Analytical expressions are derived and analyzed and verified by simulations on pulse propagation. Insertion of parameters relevant for semiconductors indicates that development of materials with long coherence times are necessary for realizing optical buffers based on EIT.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xiii, 55 p.
Series
Trita-ICT/MAP, 2006:5
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4246 (URN)978-91-7178-525-1 (ISBN)
Public defence
2007-01-17, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2010-09-03Bibliographically approved

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