| 1. |
- Lewen, R., et al.
(författare)
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High frequency characterization of a GaInAs/InP electronic waveguide T-branch switch
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2398-2402
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Tidskriftsartikel (refereegranskat)abstract
- We report comprehensive microwave measurements on a T-branch switch; a GaInAs/InP electron waveguide based structure. The study includes a small signal model of the device where limitations of high frequency operation are discussed. An example of large signal operation where the nonlinearity of the device is exploited by operating the T-branch switch as a frequency multiplier is demonstrated.
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| 2. |
- Aggerstam, Thomas, et al.
(författare)
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GaN/AlN multiple quantum well structures grown by MBE on GaN templates for 1.55 mu m intersubband absorption
- 2007
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Ingår i: Quantum Sensing and Nanophotonic Devices IV. - : SPIE. - 9780819465924 ; 6479, s. 64791E-
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Konferensbidrag (refereegranskat)abstract
- We have used MBE to grow MQW structures on MOVPE GaN/sapphire templates. The MQW devices are intended for high speed intersubband electroabsorption modulator devices operating at 1.55-mu m. The GaN/AlN multiple quantum well material was systematically studied regarding the surface morphology, structural characterization and optical property by atomic force microscopy, X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The intersubband resonance energy was also calculated considering many-body effects in n-type doped structures. The multiple quantum well structure showed superior performance in terms of linewidth when grown on GaN templates as compared on sapphire. GaN quantum well and AlN barriers with a thickness of 3.3 and 4.2 nm respectively resulted in FWHM of the intersubband absorption peak as low as 93 meV at an absorption energy of 700 meV. This is promising for intersubband modulator applications.
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| 3. |
- Akram, Nadeem, 1971-
(författare)
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Photonic devices with MQW active material and waveguide gratings : modelling and characterisation
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research work presented in this thesis deals with modelling, design and characterisation of passive and active optical waveguide devices. The rst part of the thesis is related to algorithm development and numerical modelling of planar optical waveguides and gratings using the Method of Lines (MoL). The basic three-point central-di erence approximation of the δ2=δx2 operator used in the Helmholtz equation is extended to a new ve-point and seven-point approximation with appropriate interface conditions for the TE and TM elds. Di erent structures such as a high-contrast waveguide and a TM surface plasmon mode waveguide are simulated, and improved numerical accuracy for calculating the optical mode and propagation constant is demonstrated. A new fast and stable non-paraxial bi-directional beam propagation method, called Cascading and Doubling algorithm, is derived to model deep gratings with many periods. This algorithm is applied to model a quasi-guided multi-layer anti-resonant reecting optical waveguide (ARROW) grating polarizing structure. In the second part of the thesis, our focus is on active optical devices such as vertical-cavity and edge-emitting lasers. With a view to improve the bandwidth of directly modulated laser, an InGaAsP quantum well with InGaAlAs barrier is studied due to its favorable band o set for hole injection as well as for electron con nement. Quantum wells with di erent barrier bandgap are grown and direct carrier transport measurements are done using time and wavelength resolved photoluminescence upconversion. Semi-insulating regrown Fabry-Perot lasers are manufactured and experimentally evaluated for light-current, optical gain, chirp and small-signal performance. It is shown that the lasers having MQW with shallow bandgap InGaAlAs barrier have improved carrier transport properties, better T0, higher di erential gain and lower chirp. For lateral current injection laser scheme, it is shown that a narrow mesa is important for gain uniformity across the active region. High speed directly modulated DBR lasers are evaluated for analog performance and a record high spurious free dynamic range of 103 dB Hz2=3 for frequencies in the range of 1-19 GHz is demonstrated. Large signal transmission experiment is performed at 40 Gb/s and error free transmission for back-to-back and through 1 km standard single mode ber is achieved.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Andersson, Thorvald, 1946, et al.
(författare)
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Macroscopic defects in GaN/AlN multiple quantum well structures grown by MBE on GaN templates
- 2009
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Ingår i: Microelectronics Journal. - : Elsevier BV. - 0026-2692. ; 40:2, s. 360-362
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Tidskriftsartikel (refereegranskat)abstract
- We have used MBE to grow in AlN/GaN superlattices, with different number of periods, on 2.5-mu m-thick MOVPE-GaN templates to study the development of defects such as surface deformation due to strain. After growth the samples were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), XRD and Fourier transform infrared spectroscopy (FT-IR). The strain increased with the number of quantum wells (QWs) and eventually caused defects such as microcracks visible by optical microscopy at four or more QW periods. High-resolution TEM images showed shallow recessions on the surface (surface deformation) indicating formation of microcracks in the MQW region. The measured intersubband (IS) absorption linewidth from a four period structure was 97 meV, which is comparable with the spectrum from a 10 period structure at an absorption energy of similar to 700 meV. This indicates that the interface quality of the MQW is not substantially affected by the presence of cracks.
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| 8. |
- Arve, Per, et al.
(författare)
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Propagation of two-dimensional pulses in electromagnetically induced transparency media
- 2004
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 69:6, s. 063809-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Berglind, Eilert, et al.
(författare)
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Microwave engineering approach to metallic based photonic waveguides and waveguide components
- 2006
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Ingår i: Proceedings of International Symposium on Biophotonics, Nanophotonics and Metamaterials. - 9780780397736 ; , s. 247-251
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Konferensbidrag (refereegranskat)abstract
- Approaches from microwave engineering are used to analyze metallic waveguides and wave-guiding circuits and to point out the usefulness of these techniques in photonics applications, for design of components and to achieve higher densities of integration in integrated photonics circuits than is the case today. It is also find that the losses are severe for certain applications.
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| 10. |
- Berglind, Eilert, et al.
(författare)
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On the Possibilities to Create a Negative Permittivity Metamaterial with Zero Imaginary Part of the Permittivity at a Specific Frequency-Electrical Network Theory Approach
- 2012
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 48:4, s. 507-511
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Tidskriftsartikel (refereegranskat)abstract
- A permittivity function suggested in the literature describing a material that exhibits negative permittivity and no loss at a specific frequency (and losses at other frequencies) is analyzed using electrical network theory. An equivalent circuit of the polarization admittance consisting of RLC components is derived. Further, a proof is given showing that if the admittance is lossless at a specific frequency, then all components with losses (resistances) in the circuit have to be short circuited or blocked or virtually disconnected at this frequency by the use of ideal lossless resonant LC circuits. However, in the literature, inductors in metamaterials are associated with inherently lossy metal nanoparticles, hence invalidating the suggested permittivity function unless a lossless inductor at optical frequencies is found or proved possible.
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