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Photonic Devices and Applications based on Intersubband Transitions and Electromagnetically Induced Transparency
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
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: urn:nbn:se:kth:diva-4246ISBN: 978-91-7178-525-1 (print)OAI: oai:DiVA.org:kth-4246DiVA: diva2:11438
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
List of papers
1. A high-speed intersubband modulator based on quantum interference in double quantum wells
Open this publication in new window or tab >>A high-speed intersubband modulator based on quantum interference in double quantum wells
2002 (English)In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, E-ISSN 1558-1713, Vol. 38, no 2, 178-184 p.Article in journal (Refereed) Published
Abstract [en]

Calculations on a modulator based on quantum interference in AlGaAs/GaAs asymmetric double quantum wells (QWs) are performed. The modulation of the absorption is based on the anti-crossing behavior of the two lowest states in the coupled wells. At anti-crossing, the oscillator strengths of the transitions from these two lowest states to a higher state are changed in opposite directions. The width of the barrier between the wells should be thick enough to allow a large change in oscillator strength with applied field, yet thin enough so that the absorption peaks of the transitions are resolved. The QWs are designed so that one absorption peak has only a small energy shift for the transition used for modulation while the absorption varies rapidly with the applied voltage. A complete structure including a surface plasmon waveguide is proposed enabling calculations of modal absorption. Parameters important for the performance of the modulator are then determined. An extinction ratio of 10 dB at a wavelength of 8.4 mum is predicted for a device length of 18 mum and a peak-to-peak voltage of 0.9 V. The resistance-capacitance-limited 3-dB bandwidth is 130 GHz. The predicted performance compares very favorably with present interband modulators based on the quantum-confined Stark effect.

Keyword
anti-crossing; intersubband transition; optical modulator; quantum interference; quantum well
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6656 (URN)10.1109/3.980270 (DOI)000173483000009 ()
Note
QC 20100823Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
2. Design of intersubband optical modulators
Open this publication in new window or tab >>Design of intersubband optical modulators
2002 (English)In: Proceedings of the 26th International Conference on the Physicsof Semiconductors (26th ICPS), Edinburgh, Scotland, 2002, 2002, P126- p.Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6657 (URN)
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2010-09-03Bibliographically approved
3. High-speed optical modulator based on intersubband transitions in InGaAs/InAlAs/AlAsSb coupled quantum wells
Open this publication in new window or tab >>High-speed optical modulator based on intersubband transitions in InGaAs/InAlAs/AlAsSb coupled quantum wells
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.

Series
Conference proceedings - indium phosphide and related materials, ISSN 1092-8669
Keyword
Absorption, Electrooptical devices, Light modulators, Phase transitions, Semiconducting aluminum compounds, Semiconducting indium compounds
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6658 (URN)000183253000080 ()
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
4. Strong electroabsorption using intersubb and transitions in InGaAs/InAlGaAs/InAlAs step quantum wells
Open this publication in new window or tab >>Strong electroabsorption using intersubb and transitions in InGaAs/InAlGaAs/InAlAs step quantum wells
2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Article in journal (Other academic) Submitted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6659 (URN)
Note
QS 20120316Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
5. Intersubband absorption at 1.5-3.5 µm in GaN/AlN multiple quantum wells grown by molecular beam epitaxy on sapphire
Open this publication in new window or tab >>Intersubband absorption at 1.5-3.5 µm in GaN/AlN multiple quantum wells grown by molecular beam epitaxy on sapphire
Show others...
2007 (English)In: Physica status solidi, ISSN 0370-1972, Vol. 244, no 8, 2892-2905 p.Article in journal (Refereed) Published
Abstract [en]

Ten and twenty period multiple quantum well structures with 1.5-5.4 nm GaN wells and 1.2-5.1 nm AlN barriers were grown on sapphire by molecular beam epitaxy. Layer thicknesses were determined by X-ray diffraction measurements and simulations. Reciprocal space mapping showed that the relaxation of the quantum well layers was independent of the buffer layer thickness. Intersubband absorption was observed by Fourier transform infrared spectroscopy at λ ∼ 1.5-3.5 μm. Monolayer fluctuations in the quantum well width induced multiple peaks in spectra, which were well fitted to Lorentzian peaks of only 57 meV linewidth. Samples were very homogeneous as the absorption peak energy varied less than 1% along ∼4 cm on 2 inch wafers. The intersubband transition energies were calculated considering the conduction-band nonparabolicity, built-in fields, strain, and many-body effects. The calculation and comparison to the fitted Lorentzian peak energies indicated a moderate blueshift due to many-body effects. It was shown by both experiments and calculations that the AlN barrier width affects the intersubband transition energy.

Keyword
many-body corrections, optical-transitions, wavelength-range, gan, superlattices, parameters, exchange, diodes, layer
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6660 (URN)10.1002/pssb.200675606 (DOI)000248712800019 ()2-s2.0-34547784042 (Scopus ID)
Note

QC 20100903

Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2016-05-09Bibliographically approved
6. Investigation of intersubband absorption of GaN/AlN multiple quantum wells grown on different substrates by molecular beam epitaxy
Open this publication in new window or tab >>Investigation of intersubband absorption of GaN/AlN multiple quantum wells grown on different substrates by molecular beam epitaxy
Show others...
2007 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 301, no SPEC. ISS., 301-302 p.Article in journal (Refereed) Published
Abstract [en]

Ten period GaN/AlN multiple quantum well (MQW) structures were grown by plasma-assisted molecular beam epitaxy (MBE) on sapphire substrates and metal-organic vapour-phase epitaxy (MOVPE)-grown GaN templates. Samples were investigated by high-resolution X-ray diffraction (HR-XRD) and Fourier transform infrared (FT-IR) spectroscopy. Intersubband (IS) absorbances and FWHM of IS absorption peaks indicated that samples grown on the GaN templates had better characteristics, resulting in a FWHM as low as 93 meV at a peak energy of 700 meV.

Keyword
high-resolution X-ray diffraction, molecular beam epitaxy, quantum wells, nitrides
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6661 (URN)10.1016/j.jcrysgro.2006.11.258 (DOI)000246015800105 ()2-s2.0-33947321547 (Scopus ID)
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
7. Propagation of two-dimensional pulses in electromagnetically induced transparency media
Open this publication in new window or tab >>Propagation of two-dimensional pulses in electromagnetically induced transparency media
2004 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, no 6, 063809- p.Article in journal (Refereed) Published
Abstract [en]

The propagation in two dimensions of "optical" pulses in electromagnetically induced transparency media is analyzed. Results are presented for coupled Maxwell-Bloch equations with slowly varying envelope approximation, for both adiabatic and nonadiabatic situations. The possibility of changing the direction of the pulse by a switch of control beam direction is investigated in detail.

Keyword
quantum-well, light, coherence, storage, states
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6662 (URN)10.1103/PhysRevA.69.063809 (DOI)000222471400111 ()2-s2.0-4043173527 (Scopus ID)
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
8. All optical serial to parallel converter utilizing electromagnetically induced transparency
Open this publication in new window or tab >>All optical serial to parallel converter utilizing electromagnetically induced transparency
2004 (English)In: Proceedings of 30th European Conference on Optical Communication (ECOC2004), vol. 3, Stockholm, Sweden, 2004., 2004, 692-693 p.Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6663 (URN)
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2010-09-03Bibliographically approved
9. Limits on optical pulse compression and delay bandwidth product in electromagnetically induced transparency media
Open this publication in new window or tab >>Limits on optical pulse compression and delay bandwidth product in electromagnetically induced transparency media
2005 (English)In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 23, no 11, 3893-3899 p.Article in journal (Refereed) Published
Abstract [en]

Delay bandwidth products (DBPs) and physical pulselengths obtainable in media exhibiting electromagnetically induced transparency (EIT) are analyzed. The study is performed in stationary media as well as for dynamic storing of light pulses in such media. In the latter case; the dispersion inherent in storage and readout of the pulses is analyzed. It is shown that absorption and the group velocity dispersion (GVD) are limiting factors. Analytical expressions for the minimum compressed 'pulselength and DBP are derived, and these expressions show good agreement with simulations of pulse propagation in EIT media.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6664 (URN)10.1109/JLT.2005.857733 (DOI)000234116800053 ()
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
10. Delay bandwidth product of electromagnetically induced transparency media
Open this publication in new window or tab >>Delay bandwidth product of electromagnetically induced transparency media
2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, no 5, 053803- p.Article in journal (Refereed) Published
Abstract [en]

The limitations on the delay-bandwidth product (DBP) in an electromagnetically induced transparency medium are investigated analytically by studying the susceptibility of the system, derived through Lindblad's master equation, including dephasing. The effect of inhomogeneous broadening is treated. It is shown that the DBP for a given material is fundamentally limited by the frequency-dependent absorption, while the residual absorption limits the penetration length of a pulse. Simple expression for the optimal choice of parameters to maximize the DBP are derived. Also, the length of a device is presented as a function of DBP and control-field Rabi frequency. Supporting these results, numerical calculations are carried out through the Maxwell-Bloch equations in the slowly varying envelope approximation. The results are scalable, hence they apply to the case of atoms or molecules in a gas as well as quantum dots and wells.

Keyword
coherent population transfer, slow-light, optical buffers, atomic gas, propagation, ultraslow, dynamics, pulses
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6665 (URN)10.1103/PhysRevA.75.053803 (DOI)000246890400148 ()2-s2.0-34247875970 (Scopus ID)
Note
QC 20100903Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved

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