| 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
-
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
-
Ingår i: Microelectronics Journal. - : Elsevier BV. - 0026-2692. ; 40:2, s. 360-362
-
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-
-
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
-
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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| 11. |
- Berglind, Eilert, et al.
(författare)
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Plasmonic/metallic passive waveguides and waveguide components for photonic dense integrated circuits : a feasibility study based on microwave engineering
- 2010
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Ingår i: IET Optoelectronics. - : Institution of Engineering and Technology (IET). - 1751-8768. ; 4:1, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the potential for dense integration of photonic components, we analyse passive plasmonic/metallic waveguides and waveguide components at optical frequencies by using mostly microwave engineering approaches. Four figures of performance are formulated that are utilised to compare the characteristics of four different slab waveguides with zero frequency cut-off modes. Three of these are metallic based whereas the fourth one, which also serves as a reference, is dielectric based with high index-contrast. It is found that all figures of performance cannot be optimised independently; in particular there is a trade-off between the waveguide Q-value and the transversal field confinement. Microwave methods are used to design several photonic transmission line components. The small Q-value of the metallic waveguides is the main disadvantage when using materials and telecom frequencies of today. Hence plasmonic waveguides do not offer full functionality for some important integrated components, being severe for frequency-selective applications. To achieve a dense integration, it is concluded that new materials are needed that offer Q-values several orders of magnitude higher than metals.
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| 12. |
- Berrier, Audrey, et al.
(författare)
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Negative Refraction at Infrared Wavelengths in a Two-Dimensional Photonic Crystal
- 2004
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:073902
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first experimental evidence of negative refraction at telecommunication wavelengths by a two-dimensional photonic crystal field. Samples were fabricated by chemically assisted ion beam etching in the InP-based low-index constrast system. Experiments of beam imaging and light collection show light focusing by the photonic crystal field. Finite-difference time-domain simulations confirm that the observed focusing is due to negative refraction in the photonic crystal area.
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| 13. |
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| 14. |
- Bratkovsky, A. M., et al.
(författare)
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Properties of nanostructured metamaterials at optical frequencies
- 2008
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Konferensbidrag (refereegranskat)abstract
- A variety of metamaterials has been demonstrated recently that support backward waves and negative refraction (Negative Index Materials, NIM.) In particular, these materials enable sub-wavelength resolution that makes them even more interesting, especially in optical domain rather than at microwave frequencies where their unusual properties were known for decades. We describe below theoretical and experimental studies of the so-called 'fishnet' metal-spacer holearray metamaterials, which exhibit NIM behavior at optical frequencies, having unit cell size of a few 100s nm. We demonstrate experimentally that their refractive index can be modulated very fast and very strongly (from -2.4 to -1.5) around the communication wavelength of =1.55 um, in good agreement with the FDTD results. We also discuss a problem of loss compensation in those materials with hefty Ohmic losses by using gain media and local field enhancement in metallic nanoparticles ensembles that enable SERS.
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| 15. |
- Chacinski, Marek, et al.
(författare)
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50 Gb/s modulation and/or detection with a travelling-wave electro-absorption transceiver
- 2008
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Ingår i: 2008 Conference on Optical Fiber Communication/National Fiber Optic Engineers Conference. - 9781557528568 ; , s. 94-96
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Konferensbidrag (refereegranskat)abstract
- Electro-Absorption-Transceiver (EAT) structures used as efficient Travelling-Wave Electro-Absorption-Modulator (TWEAM) as well as Travelling-Wave-Photo-Detector (TWPD) are investigated. Clear eye-openings at 50Gb/s for modulation and for detection are presented. Transmission over 2.2km and 5km SSMF were achieved.
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| 16. |
- Chacinski, Marek, et al.
(författare)
-
Electroabsorption Modulators Suitable for 100-Gb/s Ethernet
- 2008
-
Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 29:9, s. 1014-1016
-
Tidskriftsartikel (refereegranskat)abstract
- The design of a traveling-wave electroabsorption modulator (TWEAM) has been improved to decrease the drive voltage. The absorption layer was optimized and together with a novel segmentation of microwave design was introduced to increase the active modulator length. The resulting -3-dBe bandwidth of fabricated devices was estimated to be 99 GHz. Extinction ratios of 10 dB back-to-back and 6.7 dB after transmission over 2.2-km long fiber were measured with an incident drive voltage of only 2 V peak to peak. This TWEAM performance is believed to constitute a new state of the art for modulators suitable for 100-Gb/s Ethernet with on-off keying.
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| 17. |
- Chacinski, Marek, et al.
(författare)
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ETDM Transmitter Module for 100-Gb/s Ethernet
- 2010
-
Ingår i: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1041-1135 .- 1941-0174. ; 22:2, s. 70-72
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Tidskriftsartikel (refereegranskat)abstract
- Performance of a packaged distributed-feedback travelling-wave electroabsorption modulator module for data transmission at 100 Gb/s is presented for the first time. Clearly open eye diagrams at 80 Gb/s with an extinction ratio ( ER) of 4.9 dB and 100 Gb/s with ER 4.2 dB ( limited by measurement setup) are demonstrated together with data transmission over 100-m-long standard single-mode fiber and over dispersion-compensated 10-km fiber link.
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| 18. |
- Chacinski, Marek, et al.
(författare)
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Modulation and chirp evaluation of 100 GHz DFB-TWEAM
- 2010
-
Ingår i: European Conference on Optical Communication, ECOC. - NEW YORK : IEEE.
-
Konferensbidrag (refereegranskat)abstract
- The modulation and chirp performance of an InGaAsP based monolithically integrated distributed feedback (DFB) laser and travelling wave electro-absorption modulator (TWEAM) designed for 100Gb/s operation is presented. Open eye-diagrams at 100Gb/s, and error free 50Gb/s BER (limited by measurement system) were achieved. The chirp factor varied between 1.5 and 0 for absorptions between 10% and 90%.
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| 19. |
- Chacinski, Marek, et al.
(författare)
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Monolithically Integrated 100 GHz DFB-TWEAM
- 2009
-
Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 7:16, s. 3410-3415
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Tidskriftsartikel (refereegranskat)abstract
- A monolithically integrated distributed feedback (DFB) laser and traveling-wave electro-absorption modulator (TWEAM) with >= 100 GHz -dBe bandwidth suitable for Non-return-to-zero (NRZ) operation with on-off keying (OOK) is presented. The steady-state, small-signal modulation response, microwave reflection, chirp characteristic, and both data operation and transmission were investigated. The DFB-TWEAM was found to be an attractive candidate for future short distance communication in high bitrates systems.
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| 20. |
- Chacinski, Marek, et al.
(författare)
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Monolithically Integrated DFB-EA for 100 Gb/s Ethernet
- 2008
-
Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 29:12, s. 1312-1314
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Tidskriftsartikel (refereegranskat)abstract
- The world's first monolithically integrated distributed feedback laser and electroabsorption (EA) modulator with an expected >= 100 GHz -3 dBe bandwidth suitable for 100 Gb/s operation with on-off keying is presented. The design of the EA modulator uses a traveling-wave structure with three active segments and a total active length of 180 mu m resulting in similar to 2.5 V peak-to-peak drive voltage for 10 dB optical extinction ratio and low electrical reflection.
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| 21. |
- Chacinski, Marek, et al.
(författare)
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Monolithically Integrated DFB-EAT for Transmission beyond 50 Gb/s
- 2008
-
Ingår i: ICTON MEDITERR WINTER CONFER. - New York : IEEE. - 9781424434848 ; , s. 211-214
-
Konferensbidrag (refereegranskat)abstract
- We demonstrate >= 60 GHz Electro-Absorption-Transceiver (EAT) composed of monolithically integrated Distributed-Feedback laser (DFB) with low drive voltage Electro-Absorption-Modulator. Clear eye-openings at 50 Gb/s for modulation and detection are presented. The device can be used as efficient and compact size transmitter or as detector in direct 80 Gb/s links. Transmission over 7.2 km long fibre with dispersion compensation is achieved.
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| 22. |
- Chen, Jiajia, et al.
(författare)
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Comparison of hybrid WDM/TDM passive optical networks (PONs) with protection
- 2008
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Ingår i: 34th European Conference on Optical Communication, 2008, ECOC 2008.
-
Konferensbidrag (refereegranskat)abstract
- We present the evolution of PON protection and compare reliability performance related to investment and management cost for some representative cases. Our results can indicate the most cost efficient architectures.
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| 23. |
- Chen, Jiajia, et al.
(författare)
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Novel Architectures of Asynchronous Optical Packet Switch
- 2007
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Ingår i: 33rd European Conference and Exhibition on Optical Communication ECOC’07, 2007. - : IEEE conference proceedings. - 9783800730421
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We propose two asynchronous optical packet switch architectures, with efficient contention resolution based on controllable optical buffers and tunable wavelength converters TWCs. Providing a few shared optical buffers significantly boosts the performance obtained by TWCs.
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| 24. |
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| 25. |
- Dai, Daoxin, et al.
(författare)
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Gain enhancement in a hybrid plasmonic nano-waveguide with a low-index or high-index gain medium
- 2011
-
Ingår i: Optics Express. - 1094-4087. ; 19:14, s. 12925-12936
-
Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation of a nano-scale hybrid plasmonic waveguide with a low-index as well as high-index gain medium is presented. The present hybrid plasmonic waveguide structure consists of a Si substrate, a buffer layer, a high-index dielectric rib, a low-index cladding, a low-index nano-slot, and an inverted metal rib. Due to the field enhancement in the nano-slot region, a gain enhancement is observed, i.e., the ratio partial derivative G/partial derivative g > 1, where g and G are the gains of the gain medium and the TM fundamental mode of the hybrid plasmonic waveguide, respectively. For a hybrid plasmonic waveguide with a core width of w(co) = 30nm and a slot height of h(slot) = 50nm, the intrinsic loss could be compensated when using a low-index medium with a moderate gain of 176dB/cm. When introducing the high-index gain medium for the hybrid plasmonic waveguide, a higher gain is obtained by choosing a wider core width. For the high-index gain case with h(slot) = 50nm and w(co) = 500nm, a gain of about 200dB/cm also suffices for the compensation of the intrinsic loss.
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| 26. |
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| 27. |
- Dai, Daoxin, et al.
(författare)
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Silicon hybrid plasmonic submicron-donut resonator with pure dielectric access waveguides
- 2011
-
Ingår i: Optics Express. - 1094-4087. ; 19:24, s. 23671-23682
-
Tidskriftsartikel (refereegranskat)abstract
- Characteristic analyses are given for a bent silicon hybrid plasmonic waveguide, which has the ability of submicron bending (e.g., R = 500nm) even when operating at the infrared wavelength range (1.2 mu m similar to 2 mu m). A silicon hybrid plasmonic submicron-donut resonator is then presented by utilizing the sharp-bending ability of the hybrid plasmonic waveguide. In order to enable long-distance optical interconnects, a pure dielectric access waveguide is introduced for the present hybrid plasmonic submicron-donut resonator by utilizing the evanescent coupling between this pure dielectric waveguide and the submicron hybrid plasmonic resonator. Since the hybrid plasmonic waveguide has a relatively low intrinsic loss, the theoretical intrinsic Q-value is up to 2000 even when the bending radius is reduced to 800nm. By using a three-dimensional finite-difference time-domain (FDTD) method, the spectral response of hybrid plasmonic submicron-donut resonators with a bending radius of 800nm is simulated. The critical coupling of the resonance at around 1423nm is achieved by choosing a 80nm-wide gap between the access waveguide and the resonator. The corresponding loaded Q-value of the submicron-donut resonator is about 220.
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| 28. |
- Dainese, Matteo, et al.
(författare)
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Directional coupler wavelength selective filter based on dispersive Bragg Reflection Waveguide
- 2006
-
Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 260:2, s. 514-521
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Tidskriftsartikel (refereegranskat)abstract
- A new type of wavelength selective filter, based on high differential dispersion between two coupled waveguides, is presented. The Bragg Reflection Waveguide displays high effective refractive index dispersion, due to the interaction of the guided mode with the two confining Bragg reflectors. When coupled with a weakly guided buried channel silica waveguide, a very narrow bandwidth filter (< 1 nm) can be easily produced, in a shorter length, with respect to directional couplers made with standard step index channel waveguides. The complete design methodology, fabrication and characterization are presented.
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| 29. |
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| 30. |
- Dainese, Matteo, et al.
(författare)
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Narrow band coupler based on one-dimensional Bragg reflection waveguide
- 2003
-
Ingår i: 2003 Optical Fiber Communication Conference. - 1557527466 ; , s. 44-46
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Konferensbidrag (refereegranskat)abstract
- A new configuration based on the coupling between a conventional low loss, weakly guiding channel waveguide and a Bragg reflection waveguide (BRW) was discussed. The strong difference between the dispersion of a Bragg reflection waveguide and a channel waveguide was used to create a narrow band coupler. The two-dimensional analysis of the BRW was generally based on the transfer matrix method. The structure consisted of a weakly guiding conventional Ge-doped silica waveguide on the top of which a BRW was stacked. The number of periods in the mirror between the BRW and the silica waveguide affected the coupling length and ultimately the bandwidth.
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| 31. |
- Dainese, Matteo, 1970-
(författare)
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Plasma assisted technology for Si-based photonic integrated circuits
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The last two decades have witnessed a large increase in capacity in telecommunication systems, thanks to the development of high bandwidth, fiber optic based networks. Nevertheless the continuing growth of Internet data traffic, fuelled by the development of numerous services like on-line commerce, video on demand, large audio/video files downloads, demands for a significant increase in the ability of the network nodes to manage incoming and outcoming data streams effectively and fast. The different functionalities that are needed include add/drop channel multiplexing, routing, signal reshaping and retiming, electrical/optical and optical/electrical conversion. This has stimulated a large effort towards the investigation of technologies for opto-electronic integration at a wafer level, in order to cope with all the required operations, while limiting overall costs. Among the different approaches proposed, one of the most promising is the “Silicon optical bench”, which relies on the well established VLSI technology for the microelectronics part and on planar lightwave circuits (PLCs) made either with silica-on-silicon waveguide technology (low index contrast) of amorphous silicon technology (high index contrast) on the integrated optics side. This thesis presents the development of new techniques and methodologies utilized in photonic device fabrication, which can be used to facilitate integration of temperature sensitive elements. The process is based on low temperature, plasma assisted, thick film deposition. First, a low temperature (300°C) deposition process based on Plasma assisted Chemical Vapour Deposition (PACVD) for the fabrication of silica based Planar Lightwave Circuits (PLC) is developed. The low thermal budget lends itself to monolithic integration with devices fabricated with different technologies. Absorption bands at around the wavelengths 1.48µm and 1.51µm caused by N-H and Si-H bonds within the material, respectively, had previously been thought to be intrinsic to the PACVD deposition method, when using N2O as oxidant gas of SiH4 and the other dopant precursors. The traditional method to eliminate these absorption bands was high temperature (>1000°C) annealing that seriously hinders device integration. An important achievement in this thesis is the improved suppression of these two absorption bands while keeping the whole fabrication temperature below 300°C and also having a high deposition rate. A complete fabrication process for silica planar lightwave circuits was also developed, by optimising the photolithography and etching step. Finally the effect of dopants like Ge and B on the optical properties of the deposited silica glass was investigated, with particular emphasis to the photosensitive properties of the material upon illumination in the near UV. UV trimming is shown to be a versatile method to selectively control polarization birefringence of devices. Transmission dips of above 50dB were achieved in photo-induced gratings in low temperature deposited B-Ge codoped waveguide cores, without the need for hydrogen loading or other sensitisation techniques. The application of a high refractive index like amorphous silicon is addressed for the realization of efficient Bragg reflectors, either as vertical cavity laser mirrors or as dispersive element for planar waveguides used in highly selective co-directional coupler filters. Applications of amorphous silicon as core material for photonic crystal devices are also shown. The investigations carried out in this thesis show that PACVD technology can provide low-loss and UV sensitive material suitable for realizing a variety of low cost integrated devices for future all optical networks.
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| 32. |
- Dainese, Matteo, et al.
(författare)
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Wavelength selective coupler based on Bragg Reflection Waveguide
- 2005
-
Konferensbidrag (refereegranskat)abstract
- Highly wavelength selective optical filters are essential components for channel management in modern Dense Wavelength Division Multiplexed communication systems with 50GHz channel spacing and below 0.4nm channel bandwidth. We have designed, fabricated and characterized a new type of wavelength selective directional coupler, based on the high differential dispersion between a Bragg Reflection Waveguide (BRW) and a conventional buried channel silica waveguide.The bandwidth of the device is inversely proportional to the length of the coupler as well as to the differential effective refractive index dispersion of the coupled modal fields, at the wavelength of phase matching. The BRW is made of a high index (amorphous) silicon core layer, surrounded vertically by two periodic Bragg reflectors with alternating layers of silica and silicon. The silica waveguide with a Ge-doped core, vertically stacked with the BRW, allows fiber incoupling loss below 1dB which is essentially the insertion loss of the device. The device is operating within the optical bandgap of the Bragg reflectors. Both the bandwidth and the coupling wavelength can be tuned during the fabrication process: the fields’ overlap and the coupling coefficient between the two waveguide modes are controlled by one of the Bragg reflectors (coarse control) and a spacer layer (fine control); the position of the coupling wavelength is mainly determined by the BRW core thickness.The devices were fabricated by depositing SiO2 and a-Si:H films on a 4” <100> oriented Si substrate, by plasma enhanced chemical vapor deposition, at a temperature of 250ºC. The 5µm wide vertical stack of BRW and silica waveguide were defined by lithography and etched in an inductively coupled plasma reactor. The 8.8µm thick coupler structure was covered with a 16µm thick silica cladding. The device can be easily integrated in a standard silica-based planar lightwave circuit.The measured filter suppression is 14dB and the FWHM is 0.29nm for only a 1.73mm long device, which is close to the estimated value of 0.31nm, and one of the lowest ever reported for this type of coupler.
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| 33. |
- Davanco, M., et al.
(författare)
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Directional coupler wavelength filters based on waveguides exhibiting electromagnetically induced transparency
- 2003
-
Ingår i: IEEE Journal of Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9197 .- 1558-1713. ; 39:4, s. 608-613
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Tidskriftsartikel (refereegranskat)abstract
- We describe the principle and analyze the operation of an integrated optics directional coupler filter based on coupling between a regular waveguide and one, that exhibits electromagnetically induced transparency. Bandwidth length products on the order of 2 pm x mm are obtainable, as an example, using this approach.
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| 34. |
- Eriksson, U., et al.
(författare)
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Design and fabrication of electroabsorption modulators for data rates up to 100 Gb/s
- 2004
-
Ingår i: Proc. Int. Conf. Transparent Opt. Netw.. - 0780383435 - 9780780383432 ; , s. 41-46
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Konferensbidrag (refereegranskat)abstract
- We present segmented transmission-line (TML) electroabsorption modulators (EAM) matched to 50 Ω. The devices show excellent high frequency performance up to 50 GHz, and exhibit a maximum model-extrapolated 3 dBe bandwidth of 90 GHz. Design considerations and optimization techniques for periodic segmented TML-EAMs are discussed. Also methods used for the device fabrication are presented.
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| 35. |
- Forsberg, Erik, et al.
(författare)
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Limits to modulation rates of electroabsorption modulators
- 2004
-
Ingår i: IEEE Journal of Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9197 .- 1558-1713. ; 40:4, s. 400-405
-
Tidskriftsartikel (refereegranskat)abstract
- We analyze the speed limitations of optical electroabsorption modulators. We argue that modulation rate limits are closely related to quantum mechanical adiabaticity. By analyzing the breakdown of the adiabatic approximation, analytical expressions for modulation limits are found. These expressions are numerically validated. Furthermore, we discuss the constraints on the allowable modulation rate set by losses from the quantum well and transition linewidth.
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| 36. |
- Fu, Ying, et al.
(författare)
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A lossless negative dielectric constant from quantum dot exciton polaritons
- 2008
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 8:5, s. 1551-1555
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Tidskriftsartikel (refereegranskat)abstract
- Prospects for a lossless negative dielectric constant material for optical devices are studied. Simulations show that with sufficient gain, a mixture of two semiconductor quantum dots (QDs) can produce an effective dielectric constant that is lossless and negative. This permits, in concept, arbitrarily small scaling of the optical mode volume, a major goal in the field of nanophotonics. The proposed implementation of a lossless negative dielectric constant material based on colloidal QDs opens a tractable path.
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| 37. |
- Fu, Ying, et al.
(författare)
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Nanoscale excitonic-plasmonic optical waveguiding by metal-coated quantum dots
- 2006
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Ingår i: Proceedings of International Symposium on Biophotonics, Nanophotonics and Metamaterials. - 9780780397736 ; , s. 426-431
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Konferensbidrag (refereegranskat)abstract
- A three-dimensional metal-coated semiconductor-quantum-dot (QD) nanoscale lattice structure is designed for optical waveguiding. It is based on three notions: i) Excitons are first photogenerated in the QDs by the incident electromagnetic field which is the optical wave to be guided: ii) The exciton-polariton effect in the QD structure induces an extra optical dispersion in the QDs: iii) The high contrast ratio between the optical dispersions of the QDs and the background material creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained for the incident wave in the lossless case, thus providing the fundamental basis of QDs for optical waveguide applications. Metal coating at the QD surface generates a surface plasmon spatially confined in the QD so that the exciton generation becomes enhanced for a better dielectric modulation.
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| 38. |
- Fu, Ying, et al.
(författare)
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Optical reflection from excitonic quantum-dot multilayer structures
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:18, s. 183117-
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Tidskriftsartikel (refereegranskat)abstract
- We study theoretically and experimentally the optical reflection from excitonic quantum-dot (QD) multilayer structures composed of InAs QDs in a GaAs substrate. Quantum mechanical and finite-difference time-domain numerical calculations indicate that the incident radiation in the optical reflectance measurement photoexcites the InAs QDs which then form excitonic dipoles. The excitonic dipole modifies significantly the dielectric constant of the QD, which results in a reflectance peak in the vicinity of the excitonic energy, as observed experimentally.
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| 39. |
- Fu, Ying, et al.
(författare)
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Optical transmission and waveguiding by excitonic quantum dot lattices
- 2006
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:11, s. 2441-2447
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Tidskriftsartikel (refereegranskat)abstract
- Metal-dielectric-metal configurations of optical waveguides have a very high laterally packaging density at the cost of high optical loss. Photonic crystals based on refractive-index-modulation materials have been used in optics, e.g., two materials having different refractive indices form a well-defined Bragg refraction mirror. Such a waveguide has lower loss but also lower packaging density. From the outset of these two notions, we propose a photonic-crystal device based on the exciton-polariton effect in a three-dimensional array of semiconductor quantum dots (QDs) for ultradense optical planar circuit applications. Excitons are first photogenerated in the QDs by the incident electromagnetic field, the exciton-polariton effect in the QD photonic crystal then induces an extra optical dispersion in QDs. The high contrast ratio between the optical dispersions of the QDs and the background therefore creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained at a specific wavelength in the lossless case, thus providing the fundamental basis for ultradense optical waveguide applications.
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| 40. |
- Fu, Ying, et al.
(författare)
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Radiative and nonradiative recombination of photoexcited excitons in multi-shell-coated CdSe/CdS/ZnS quantum dots
- 2009
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 86:3, s. 37003-
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal quantum dots (QDs) have been widely studied for nanophotonics and bioimaging applications for which the lifetime of their fluorescence is of critical importance. We report experimental and theoretical characterizations of dynamic optical properties of multi-shell-coated CdSe/CdS/ZnS QDs. Quantum-mechanical studies of fundamental optical excitations and Monte Carlo simulations of energy relaxation mechanisms indicate that the excitonic states are densely compacted in the QDs and are easily photoexcited by the laser pulse in the presence of nonradiative electron-phonon interactions. For spherical QDs, the decay time of spontaneous radiative emission of individual photoexcited excitonic states with zero angular momenta is found to be only tens of picoseconds. In our multi-shell QDs, high-energy excitonic states of nonzero angular momenta have to go through a number of nonradiative electron-phonon interaction steps in order to relax to zero-angular-momentum excitonic states for radiative emission, resulting in an effective fluorescence peak at about 2 ns in the photoncount-time relationship. This explains the measured long average fluorescence lifetime of 3.6 ns. Such a long lifetime facilitates the applications of colloidal QDs in areas such as QD-based solar cells, bioimaging and metamaterials.
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| 41. |
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| 42. |
- Gvozdic, D. M., et al.
(författare)
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Comparison of performance of n- and p-type spin transistors with conventional transistors
- 2005
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Ingår i: Journal of Superconductivity. - : Springer Science and Business Media LLC. - 0896-1107 .- 1572-9605. ; 18:3, s. 349-356
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Tidskriftsartikel (refereegranskat)abstract
- A spintronic device that has stimulated much research interest is the Datta-Das spin transistor. The mechanism behind it called the Rashba effect is that an applied voltage gives rise to a spin splitting. We propose ways to optimize this effect. The relevant spin splitting in k-space is predicted to increase with electric field at a rate that is more than two orders of magnitude larger for holes than for electrons. Furthermore, the almost negligible lattice-mismatch between GaAs and AlGaAs can be used to further enhance the advantage of hole-based spin transistors. Compared to present transistors we conclude that electron-based spin transistors will have problems to become competitive but hole-based ones are much more promising.
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| 43. |
- Holmstrom, Petter, et al.
(författare)
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Composite metal/quantum-dot nanoparticle-array waveguides with compensated loss
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:7, s. 073110-
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the dispersion properties of waveguides composed of near-field-coupled arrays of metal-clad quantum dots (QDs). The high optical loss incurred by operating the metal shells close to resonance is mitigated by using optical gain in the QDs. A condition for achieving loss compensated operation is given based on realistic material parameters and neglecting inhomogeneous broadening. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467845]
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| 44. |
- Holmstrom, P., et al.
(författare)
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Proposal of an optical modulator based on resonant tunneling and intersubband transitions
- 2001
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Ingår i: IEEE Journal of Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9197 .- 1558-1713. ; 37:2, s. 224-230
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Tidskriftsartikel (refereegranskat)abstract
- We propose and analyze an optical modulator based on intersubband transitions. The absorption is modulated by modulating the carrier density in the ground state of a quantum well (QW). Electrons are injected resonantly into this subband from a QW reservoir subband through a single barrier. When the two states are tuned out of resonance, the electrons are rapidly evacuated by means of the optical held, A waveguide based on surface plasmons is assumed in order to have a high optical mode overlap. Calculations are performed for a cascaded structure with four periods, assuming InGaAs-InAlAs QWs, The considered modulator structure operates at lambda =6.0 mum and is RC limited to 27 GHz, An extinction ratio of it is obtained with a low applied voltage of 0.6 V, At larger applied voltages, the absorption is bistable, Absorption at shorter/longer wavelengths can be obtained by using materials with a larger/smaller conduction band offset. We also assess resonant tunneling from a 2-D electron gas reservoir into an array of quantum dots and compare it to the 2-D-2-D tunneling resonance.
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| 45. |
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| 46. |
- Holmström, Petter, et al.
(författare)
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Dielectric function of quantum dots in the strong confinement regime
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 107:6
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Tidskriftsartikel (refereegranskat)abstract
- The complex dielectric function of quantum dots (QDs) with a core-shell structure is modeled in the strong confinement regime. These results should be useful for the design of negative epsilon optical metamaterials, where the gain due to QDs could be an essential ingredient. Using the dielectric function it is also shown that conventional expressions for the gain substantially overestimate it for narrow linewidths.
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| 47. |
- Holmström, Petter, et al.
(författare)
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Efficient electroabsorption for mid-infrared wavelengths using intersubband transitions
- 2008
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Ingår i: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - Bristol : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)abstract
- We have demonstrated efficient intersubband (IS) electroabsorption in InGaAs/InAlGaAs/InAlAs step quantum wells grown by metal-organic vapor phase epitaxy (MOVPE). An absorption modulation of 2300 cm(-1) at lambda=5.7 mu m due to Stark shift of the IS resonance was achieved with a low applied voltage swing of +/-0.5 V in a multipass waveguide structure. Two useful wavelength ranges of lambda approximate to 5.4-5.8 mu m and 6.3-6.6 mu m were obtained by considering the two flanks of the IS resonance. Based on the experimental results it is estimated that an electroabsorption modulator with a low peak-to-peak voltage of V-PP = 0.9 V can yield a modulation speed of f(3dB) = 120 GHz with the present material by using a strongly confining surface plasmon waveguide of 30 mu m length.
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| 48. |
- Holmström, Petter, et al.
(författare)
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Efficient infrared electroabsorption with 1 V applied voltage swing using intersubband transitions
- 2008
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 93:19
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Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated efficient intersubband electroabsorption in InGaAs/InAlGaAs/InAlAs step quantum wells grown by metal-organic vapor-phase epitaxy. An absorption modulation of 6 dB (Delta alpha=2300 cm(-1)) at lambda similar to 5.7 mu m due to Stark shift of the intersubband resonance was achieved at a low applied voltage swing of +/- 0.5 V in a multipass waveguide structure. The interface intermixing was estimated by comparing experimental and theoretical Stark shifts. It is predicted that the present material in a strongly confining surface plasmon waveguide can yield an electroabsorption modulator with a peak-to-peak voltage of V-pp=0.9 V and modulation speed of f(3dB)approximate to 130 GHz.
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| 49. |
- Holmström, Petter, et al.
(författare)
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Electro-optic switch based on near-field-coupled quantum dots
- 2014
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 115:4, s. 1093-1101
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of exciton polaritons in near-field-coupled quantum-dot (QD) chains is modeled by a density-matrix formalism. It is shown that at least for low-temperature operation it is possible using electronically controlled switching by the quantum-confined Stark effect in such QD chains to rival and outperform room-temperature CMOS electronics in footprint and switch energy, though not in speed.
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| 50. |
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