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  • 1.
    Akram, Nadeem
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lateral current injection (LCI) multiple quantum-well 1.55 mu m laser with improved gain uniformity across the active region2004In: Optical and quantum electronics, ISSN 0306-8919, E-ISSN 1572-817X, Vol. 36, no 9, p. 827-846Article in journal (Refereed)
    Abstract [en]

    A simulation study of lateral current injection 1.55 mum laser with strain-compensated multiple quantum-well (MQW) active region (InGaAsP well, InGaAlAs barrier) is presented using self-consistent 2D numerical simulations. The effects of different mesa width and p-doping in the QWs on the carrier and gain uniformity across the active region are explored. A high p-doping in the quantum wells is found to increases the carrier and gain non-uniformity across the active region. The QW region close to the n-contact side does not provide much gain at high optical powers. An asymmetric optical waveguide design is proposed to help reduce the gain non-uniformity across the active region. By shifting the optical modal peak toward the p-side, the modal overlap between the gain region and the optical mode is improved and a more even carrier and gain distribution is obtained. However, due to reduced bandgap of the quaternary InGaAsP p-cladding, an enhanced electron leakage out of the QWs into the p-cladding degrades the laser efficiency and increases the threshold current. Transient time - domain simulations are also performed to determine the small-signal modulation response of the laser promising a simulated high modulation bandwidth suitable for direct-modulation applications.

  • 2.
    Akram, Nadeem
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Photonic devices with MQW active material and waveguide gratings: modelling and characterisation2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    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.

  • 3.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Experimental characterization of high-speed 1.55 mu m buried heterostructure InGaAsP/InGaAlAs quantum-well lasers2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, no 2, p. 318-327Article in journal (Refereed)
    Abstract [en]

    Detailed experimental characterization is performed for 1550 nm semi-insulating regrown buried heterostructure Fabry-Perot (FP) lasers having 20 InGaAsP/InGaAlAs strain-balanced quantum wells (QWs) in the active region. Light-current-voltage performance, electrical impedance, small-signal response below and above threshold, amplified spontaneous emission spectrum below threshold and relative intensity noise spectrum are measured. Different laser parameters such as external differential quantum efficiency eta(d), background optical loss alpha(i), K-factor, D-factor, characteristic temperature T-0, differential gain dg/dn, gain-compression factor epsilon, carrier density versus current, differential carrier lifetime tau(d), optical gain spectrum below threshold, and chirp parameter alpha are extracted from these measurements. The FP lasers exhibited a high T-0 (78-86.5 degrees C) and very high-resonance frequency (23.7 GHz). The results indicate that appropriately designed lasers having a large number of InGaAsP well/InGaAlAs barrier QWs with shallow valence-band discontinuity can be useful for un-cooled high-speed direct-modulated laser applications.

  • 4.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    High-Speed Performance of 1.55 µm Buried Hetero-Structure Lasers with 20 InGaAsP/InGaAlAs Quantum-Wells2006In: 2006 European Conference on Optical Communications Proceedings, ECOC 2006, IEEE , 2006, p. 1-2Conference paper (Refereed)
    Abstract [en]

    1550 nm re-grown FP lasers having 20 InGaAsP/InGaAlAs strain-balanced QWs exhibit low threshold current density, high T0 (78.0 #x000B0;C) and high resonance frequency (24 GHz) indicating that a large number of shallow barrier QWs are attractive for un-cooled high-speed direct-modulation applications.

  • 5.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Marcinkevičius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    The effect of barrier composition on the vertical carrier transport and lasing properties of 1.55-mu m multiple quantum-well structures2006In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, E-ISSN 1558-1713, Vol. 42, no 7, p. 713-714Article in journal (Refereed)
    Abstract [en]

    In this paper, the effect of barrier bandgap and composition on the optical performance of 1.55-mu m InGaAsP/In-GaAsP and InGaAsP/InGaAlAs multiple quantum-well structures and Fabry-Perot lasers is evaluated experimentally. Direct vertical carrier transport measurements were performed through strain-compensated multiple quantum-well (MQW) test structures using femto-second laser pulse excitation and time-resolved photoluminescence up-conversion method. MQW test structures were grown with different barrier composition (InGaAsP and InGaAlAs) and barrier bandgap (varied from lambda(g) = 1440 to 1260 nm) having different conduction band Delta E-c and valence band discontinuity Delta E-v, while keeping the same InGaAsP well composition for all the structures. The ambipolar carrier transport was found to be faster in the structures with lower valence band discontinuity Delta E-v. Regrown semi-insulating buried heterostructure Fabry-Perot (SIBH-FP) lasers were fabricated from similar QWs and their static light-current-voltage characteristics (including optical gain and chirp spectra below threshold) and thermal characteristics were measured. Lasers with InGaAlAs barrier showed improved high-temperature operation, higher optical gain, higher differential gain, and lower chirp, making them suitable candidates for high-bandwidth directly modulated uncooled laser applications.

  • 6.
    Akram, Nadeem
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Influence of electrical parasitics and drive impedance on the laser modulation response2004In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 16, no 1, p. 21-23Article in journal (Refereed)
    Abstract [en]

    In this letter, we analyze the effects of electrical parasitics and drive impedance on the laser modulation response. It is found that for lasers with small active-region volume, e.g., vertical-cavity surface-emitting lasers, the finite drive impedance and/or the laser parasitic capacitance can significantly enhance the damping of the laser resonance peak at low bias. This is due to the voltage fluctuations across the laser diode active layer during modulation. It is also shown that the real pole of the small-signal response transfer function corresponding to the laser parasitic cutoff frequency is not fixed but decreases with the increased bias level.

  • 7.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Silfvenius, Christofer
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Design optimization of InGaAsP-InGaAlAs 1.55 mu;m strain-compensated MQW lasers for direct modulation applications2004In: Indium Phosphide and Related Materials, 2004. 16th IPRM. 2004 International Conference on, IEEE , 2004, p. 418-421Conference paper (Refereed)
    Abstract [en]

    A comprehensive simulation study of InGaAsP (well)/InGaAlAs(barrier) 1.55 mu;m strain-compensated MQW lasers is presented. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and strain of the barriers and p-doping in the active region. Some preliminary results are also presented for the manufactured lasers using these QWs indicating a good material platform.

  • 8.
    Akram, Nadeem
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Silfvenius, Christofer
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Design optimization of InGaAsP-InGaAlAs 1.55 mu m strain-compensated MQW lasers for direct modulation applications2004In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 19, no 5, p. 615-625Article in journal (Refereed)
    Abstract [en]

    In this paper, a simulation study of InGaAsP(well)/InGaAlAs(barrier) 1.55 mum strain-compensated multi-quantum well (MQW) lasers is presented. Due to a large conduction band discontinuity in this material system, a higher material gain and differential gain can be obtained from such a quantum well (QW) as compared to a traditional InGaAsP/InGaAsP quantum well. The deeper electron well should also improve elevated temperature operating characteristics and reduce the electron spillover from QWs. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and the strain in the barriers. A large number of quantum wells can be uniformly pumped, reducing the carrier density in each individual well. A uniform and low carrier density in all the wells help reduce the total Auger recombination current. High p-doping in the active region is shown to enhance the carrier and gain non-uniformity in the MQWs. A simulated high modulation bandwidth has been demonstrated, promising directly modulated lasers as a low-cost source for short to medium distance (1-10 km) high speed optical links.

  • 9.
    Jamid, H. A.
    et al.
    Electrical Engineering Department, King Fahd Univ. Petrol. and Minerals, Saudi Arabia.
    Akram, Nadeem
    Electrical Engineering Department, King Fahd Univ. Petrol. and Minerals, Saudi Arabia.
    A new higher order finite-difference approximation scheme for the method of lines2001In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 19, no 3, p. 398-404Article in journal (Refereed)
    Abstract [en]

    A new 5-point and a 7-point nonuniform mesh finite-difference scheme is introduced to approximate the second-derivative operator. The scheme is applied using the method of lines. The necessary interface conditions for the TE and TM fields at an index discontinuity are appropriately included in the derivation. This scheme can model lossy dielectrics as well as metallic layers in a unified way. Numerical results are given for the fundamental TE and TM modes of a high-contrast waveguide and for a metal/dielectric single interface TM surface-plasmon mode showing excellent convergence behavior to the analytical results.

  • 10.
    Jamid, H. A.
    et al.
    Department of Electrical Engineering, King Fahd Univ. of Petrol./Minerals, Saudi Arabia.
    Akram, Nadeem
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Analysis of antiresonant reflecting optical waveguide gratings by use of the Method of Lines2003In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, no 18, p. 3488-3494Article in journal (Refereed)
    Abstract [en]

    The modal spectral response of an antiresonant reflecting optical waveguide (ARROW) with periodic corrugations or grating is calculated for both shallow and deep gratings with the Method of Lines. The effect of the ARROW layer thickness and the grating depth on the spectral response is studied. It is found that when the ARROW-layer thickness is close to resonance, the ripples in the reflection spectra become smooth and the peak reflectivity drops. This is attributed to the large increase in the leakage loss of the ARROW waveguide near resonance. The ARROW grating is characterized by modal reflectivity spectra, which exhibit a strong polarization discrimination property, in favor of the TE polarization.

  • 11.
    Jamid, H. A.
    et al.
    Department of Electrical Engineering, King Fahd University of Petroleum and Minerals, Saudi Arabia.
    Akram, Nadeem
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Analysis of deep waveguide gratings: an efficient cascading and doubling algorithm in the method of lines framework2002In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 20, no 7, p. 1204-1209Article in journal (Refereed)
    Abstract [en]

    In this work, a computationally fast, numerically stable, and memory-efficient cascading and doubling algorithm is proposed within the method of lines framework to model long planar waveguide gratings having thousands of periods in the propagation direction. This algorithm can model 2(n) grating periods in n calculational steps and needs N-2 matrices for N sample points in the problem space. It can model periodic, quasi-periodic, symmetric, and asymmetric, gratings efficiently. Different deep waveguide gratings are modeled using this scheme and results for the fundamental TE mode spectral reflectivity are compared with published results showing excellent agreement.

  • 12.
    Kjebon, Olle
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Akram, Nadeem
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    40 Gb/s transmission experiment using directly modulated 1.55 mu m DBR lasers2003In: Conference Proceedings - International Conference on Indium Phosphide and Related Materials, 2003, p. 495-498Conference paper (Refereed)
    Abstract [en]

    Directly modulated two section 1.55 mum InGaAsP DBR lasers were used for 40 Gb/s error free operation back-to-back and through 1 km of standard single mode fiber.

  • 13.
    Kjebon, Olle
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Carlsson, C.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Akram, Nadeem
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Experimental evaluation of detuned loading effects on distortion in edge emitting DBR lasers2002In: International Topical Meeting on Microwave Photonics, 2002, 2002, p. 125-128Conference paper (Refereed)
    Abstract [en]

    Detuned loading in directly modulated DBR lasers has been evaluated. IMD3 was measured, yielding a spurious free dynamic range for frequencies 1-19 GHz.

  • 14. Tångring, I.
    et al.
    Wang, S. M.
    Gu, Q. F.
    Wei, Y. Q.
    Sadeghi, M.
    Larsson, A.
    Zhao, Q. X.
    Akram, M. Nadeem
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Strong 1.3-1.6 mu m light emission from metamorphic InGaAs quantum wells on GaAs2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 17, p. 171902-Article in journal (Refereed)
    Abstract [en]

    We demonstrate strong 1.3-1.6 mu m photoluminescence (PL) from InGaAs quantum wells (QWs) grown on alloy graded InGaAs buffer layers on GaAs by molecular beam epitaxy. The epistructures show quite smooth surfaces with an average surface roughness less than 2 nm. The PL intensity is comparable with those from InAs quantum dots and InGaAs QWs on GaAs, and InGaAsP QWs on InP at similar wavelengths, but stronger than those from GaInNAs QWs (at least 10 times higher at around 1.5-1.6 mu m). The excellent optical quality implies that the metamorphic approach could be a promising alternative to GaInNAs(Sb) QWs for 1.55 mu m lasers on GaAs.

1 - 14 of 14
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