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Quantum Electronics, IEEE Journal of

Issue 8 • Date Aug. 2007

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Displaying Results 1 - 21 of 21
  • Table of contents

    Publication Year: 2007 , Page(s): 623 - 624
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  • Consideration of the Actual Current-Spreading Length of GaN-Based Light-Emitting Diodes for High-Efficiency Design

    Publication Year: 2007 , Page(s): 625 - 632
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1469 KB) |  | HTML iconHTML  

    Based on the proposed experimental method, the current spreading length of GaN-based light-emitting diodes (LEDs) was measured and analyzed for practical device design. In this study, Thompson's and Guo's models, which are categorized according to vertical series resistance (in particular, p-type contact resistance), were used to extract device parameters. It was shown that the measured current spreading length strongly depends on the injected current density. For LEDs fabricated with low-resistance p-type contacts, this behavior could be explained in terms of the accelerated current crowding with higher current densities occurring as a result of the reduced voltage drop across the junction, which is in good agreement with Thompson's relation. However, for LEDs fabricated with high-resistance p-contacts, unlike Guo's prediction, the measured current spreading length also showed a strong dependence on the injected current density. This was attributed to thermal heating at the p-contact, resulting in the reduction of the voltage drop across the p-contact and so junction voltage, which is also in agreement with Thompson's model. Based on the measured parameters and the design rule, efficient p-type reflectors, namely, hybrid reflectors were designed. Compared with conventional ones, LEDs fabricated with the hybrid reflectors exhibited better output power at a reasonable forward voltage, indicating that the proposed method is effective in understanding the actual current spreading and hence the practical design of high-efficiency LEDs. View full abstract»

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  • Analysis and Demonstration of Mach–Zehnder Polymer Modulators Using In-Plane Coplanar Waveguide Structure

    Publication Year: 2007 , Page(s): 633 - 640
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1065 KB) |  | HTML iconHTML  

    Analysis, design, and experimental demonstration of polymer Mach-Zehnder (MZ) modulators with a newly proposed in-plane coplanar waveguide (CPW) electrode are presented in this paper. Compared to the conventional CPW electrode, the new in-plane CPW configuration significantly enhances the overlap factor between microwave and optical wave by 40% from the theoretical calculations. Different from polymer modulators using the traditional microstrip electrodes, this structure can suppress dc bias voltage drift and widen modulation bandwidth. Using CLD1/APC and AJL8/APC electrooptic polymers, MZ modulators using the in-plane CPW are fabricated and tested. The measured Vpi's of the MZ with 15-mum gap spacing and 2 cm electrode length are 5.4 and 9.5 V at 1.55 mum for the AJL8/APC and CLD1/APC devices, respectively. The evaluated Upsi33's are 46 pm/V for the AJL8/APC and 26 pm/V for the CLD1/APC MZ. The dc bias stability is tested and compared for both the microstrip and the in-plane CPW electrode modulators. Experimental results show that the in-plane CPW modulator greatly improves the bias stability. From the microwave measurement, the microwave signal loss of the modulator using the in-plane CPW is much reduced to 0.2 dB/cmradicGHz, while 0.7 dB/cmradicGHz using the microstrip. View full abstract»

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  • Electrorefractive Coupled Quantum Well Modulators: Model and Experimental Results

    Publication Year: 2007 , Page(s): 641 - 650
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1012 KB) |  | HTML iconHTML  

    Theoretical modeling of InP coupled-quantum-well electroabsorptive and electrorefractive modulators is presented. Key mathematical transformations are developed that allow efficient computation of electrorefraction for a complex multiparameter coupled quantum well structure. The model is realized in the Mathematica platform and is used to simulate the impact of well and barrier composition and thickness on Mach-Zehnder modulator performance. The advantage of using coupling between quantum wells is quantified and in addition, it is shown that linewidth broadening is a key input to the model and has a critical impact on modulator performance. The model is compared to experimental data from phase modulators and Mach-Zehnder intensity modulators. View full abstract»

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  • Optimized Asymmetric Double Quantum Well for High Electric-Field-Sensitivity Electroabsorption: Excitonic Mixing Effects

    Publication Year: 2007 , Page(s): 651 - 654
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (535 KB) |  | HTML iconHTML  

    Asymmetric double quantum wells (ADQWs) are optimized to exhibit maximum optical modulation sensitivity by varying the barrier width, barrier position, and well width. Anticrossing of the two lowest excitons in ADQWs significantly enhances the modulation sensitivity. Consideration of exciton mixing is crucial to obtain accurate estimates of the effects. For a given linewidth of the excitonic peaks, we find optimum structural parameters that exhibit maximum modulation sensitivity. Values dalpha / dE ~ 6.51 x 104 kV-1of of at 4.2 K and ~1.25 x 103 kV-1of at 298 K are predicted in GaAs-based ADQWs. The result provides new design guidelines in fabricating high-sensitivity QW electroabsorption modulators. View full abstract»

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  • Analysis of 2-D Surface-Emitting ROW-DFB Semiconductor Lasers for High-Power Single-Mode Operation

    Publication Year: 2007 , Page(s): 655 - 668
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1437 KB) |  | HTML iconHTML  

    A detailed analysis of 2D surface-emitting active-photonic-crystal (APC) lasers composed of a resonant-optical-waveguide (ROW) array and Pi-phaseshifted second-order distributed feedback/distributed Bragg reflector (DFB/DBR) gratings, made atop the ROW-array elements, is performed. Coupled-mode theory and the transfer-matrix method are used for analysis in the longitudinal direction, and 2D rigorous array modeling is used for analysis in the lateral direction. The gratings, beside their usual functions (i.e., feedback and outcoupling), act as strong lateral-mode (i.e., array-mode) selectors by exploiting the array-modes' different field-intensity overlap with the element regions, at the in-phase-mode resonance. The in-phase array mode is strongly favored to lase at and around its (lateral) resonance due both to better longitudinal-field overlap with the active-grating (i.e., DFB) region and to much lower interelement loss than the other array modes. The loss in the interelement regions that suppresses lasing of the nonresonant modes is due to strong absorption to both the metal contact (i.e., Au) as well as to the semiconductor/metal grating layers (i.e., GaAs-Au) in the element regions. The intermodal discrimination can be further enhanced by introducing strong free-carrier absorption in the interelement regions. For 20-element arrays with 700 mum/600 mum DFB/DBR gratings, emitting at 0.98 mum and of 100-mum-wide lateral dimension, the intermodal discrimination, DeltaJth, is high (~500 A/cm2) at the in-phase-mode resonance, and > 70 A/cm2 as the regrown interelement-region thickness t is varied (during fabrication) over a 0.02-mum range. The external differential quantum efficiency reaches 58%, and the guided-field intensity profile is virtually uniform in both the lateral and longitudinal directions. For 40-element devices, the projected CW power in a single, diffraction-limited lobe is 2.4 W at 10 x threshold. For 20-e- lement arrays with intentionally introduced free-carrier absorption in the interelement regions, DeltaJth is very high (~6500 A/cm2) at the in-phase-mode resonance, and >70 A/cm2 as t is varied over a 0.035-mum range. The projected single-mode, diffraction-limited continuous-wave power, from 40-element devices at 10x threshold, is similar: 2.4 W. View full abstract»

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  • Pump Uniformity and Temperature Profile Measurements in a Planar Waveguide Nd:YAG Laser by a Beam Deflection Method

    Publication Year: 2007 , Page(s): 669 - 675
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (659 KB) |  | HTML iconHTML  

    A planar waveguide laser using a large-core Nd:YAG waveguide and face-pumping by diode bars has produced a multimode power up to 160 W, with direct-contact water-cooling across the largest faces of the waveguide in the lateral direction. A method is reported that measures the nonuniform heat dissipation in the waveguide core and nonuniform water-cooling through deflection of a helium-neon laser beam passing through the waveguide claddings. Temperature gradients resulting from the varying heat transfer coefficient to the coolant are quantified, together with lateral thermal lens effects associated with edge-cooling and nonuniform pumping. The heat flux in the claddings is compared for two different waveguide structures, giving information on multipass face-pumping efficiency and uniformity. View full abstract»

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  • Characterization and Modeling of Broad Spectrum InAs–GaAs Quantum-Dot Superluminescent Diodes Emitting at 1.2–1.3 μm

    Publication Year: 2007 , Page(s): 676 - 686
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB) |  | HTML iconHTML  

    High-power broadband superluminescent diodes (SLDs) emitting in the 1.2-1.3-mum region are demonstrated using InAs-GaAs quantum dots (QDs). The highest output powers of ~30-50 mW are achieved using 18 QD layers with p-doped GaAs spacers. At these high powers the device operates in a regime of broad bandwidth (~100 nm) with a spectral dip of ~5 dB between two separate peaks originated by the QD ground and excited states. Spectral calculations performed with a traveling-wave rate equation model show excellent agreement with the experimental data and provide design rules for optimizing the output spectrum. SLD characteristics are presented for two different device structures consisting of tilted and bent waveguides. The latter allows the achievement of higher output powers at lower currents. The coherence properties and the temperature characteristics are also discussed in detail. View full abstract»

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  • Subwavelength Microdisk and Microring Terahertz Quantum-Cascade Lasers

    Publication Year: 2007 , Page(s): 687 - 697
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1858 KB) |  | HTML iconHTML  

    We report on the emission characteristics of microcavity quantum-cascade lasers emitting in the terahertz frequency range based on circular-shaped microresonators. Strong mode confinement in the growth and in-plane directions are provided by a double-plasmon waveguide and due to the strong impedance mismatch between the gain material and air. This allows laser emission from devices with overall dimensions much smaller than the free-air emission wavelength (lambda > 100 mum). Hence, for the smallest microdisks we achieved a threshold current as low as 13.5 mA (350 A/cm2) in pulsed-mode operation at 5 K and stable single-mode emission up to 95 K in continuous-wave mode operation. We have observed dynamical frequency pulling of the resonator mode on the gigahertz scale, as a consequence of the gain shift due to the quantum-confined Stark effect. Thus, we were able to estimate the peak gain of the material to 27 cm-1. The smallest microcavities exhibited a strong dependence on the exact placement of the bond wire which resulted in single- as well as double-mode emission. Finite-difference time-domain simulations were performed in order to identify the modes of the recorded spectra. They confirm that most of the observed spectral features can be attributed to the lasing emission of whispering-gallery modes. View full abstract»

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  • Nonradiative Recombination in Multiple Layer In(Ga)As Quantum-Dot Lasers

    Publication Year: 2007 , Page(s): 698 - 703
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB) |  | HTML iconHTML  

    The segmented contact technique has been used to study the effects on nonradiative recombination of stacking multiple quantum-dot layers. As the number of stacked layers is increased a shift in the balance of dots in the bimodal dot distribution is observed due to a reduction in the number in the smaller dot size subset. This is attributed to an increase in the density of defect islands, as the number of layers is increased, that preferentially take material from the smaller dots, and lead to an increased level of nonradiative recombination per layer at low injection level. A second nonradiative process is apparent at higher injection level, which is related to the population of the small dot size subset. Spontaneous radiative efficiency was improved in a five-layer sample where the large to small dot size energy separation and relative density of the large dot size subset were increased. View full abstract»

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  • Mode-Hop-Free, Optical Frequency Tunable 40-GHz Mode-Locked Fiber Laser

    Publication Year: 2007 , Page(s): 704 - 708
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (390 KB) |  | HTML iconHTML  

    We have successfully achieved a mode-hop-free, optical frequency tunable 3-ps 40-GHz mode-locked fiber laser by installing an optical etalon in a 6.8-m laser cavity. The laser frequency was continuously tuned over 1 GHz without mode hopping by tuning the etalon peak frequency. The oscillation wavelength was also tuned over 1535-1560 nm by tuning an optical bandpass filter installed in the laser cavity. View full abstract»

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  • Demonstration and Performance Assessment of Large Format InP–InGaAsP Quantum-Well Infrared Photodetector Focal Plane Array

    Publication Year: 2007 , Page(s): 709 - 713
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (433 KB) |  | HTML iconHTML  

    There have been various studies showing that InP-InGaAs quantum-well infrared photodetectors (QWIPs) are potential alternatives to AlGaAs-GaAs QWIPs in the long wavelength infrared (LWIR) band, especially for applications requiring high responsivity. Being on InP substrate, this material system also offers lattice matched mid-wavelength infrared (MWIR)/LWIR dual band QWIP stack when it is used with the AlInAs-InGaAs system. It is desirable to extend the cut-off wavelength of InP based LWIR QWIPs to , which can be accomplished by replacing the QW material with InGaAsP. In this paper, we report the first InP-InGaAsP QWIP focal plane array (FPA). The 640 512 FPA displayed remarkably low noise equivalent temperature difference (NETD) with very short integration times (46 mK at 66 K with and f/1.5 optics). The results show that these QWIPs can be operated with high responsivity (1 A/W) while offering bias adjustable gain in a wide range where the detectivity is almost constant at a reasonably high level. View full abstract»

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  • CW Gain Characteristics of Linear Optical Amplifiers

    Publication Year: 2007 , Page(s): 714 - 721
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1018 KB) |  | HTML iconHTML  

    The operation of the linear optical amplifier is described in terms of the two mutually orthogonal optical waves in the cavity of a vertical-cavity surface-emitting laser (VCSEL) when operated above threshold. Both photon populations induce stimulated emission from the same quantum-well population and the amplifier gain is constant due to the clamped value of stimulated lifetime (gain) in the VCSEL. An analytical description is developed for both the constant gain region when the VCSEL is above threshold and for the region of gain compression at higher input power. The maximum gain is found to occur at the cavity mode position. Experimental data are found to be well matched by the calculated results. View full abstract»

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  • Modeling of Actively Q-Switched Intracavity Raman Lasers

    Publication Year: 2007 , Page(s): 722 - 729
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    The normalized space-dependent rate equations are deduced assuming the intracavity photon densities and initial population-inversion density to be of Gaussian spatial distributions in the diode-pumped actively Q-switched intracavity Raman lasers. Numerical calculations are carried out to investigate the influences of these normalized variables on the pulse parameters of the first Stokes. The rate equations under the planewave approximation are also normalized and solved numerically, and the results show the obvious discrepancies from those of the space-dependent theory. The spontaneous Raman scattering factor in rate equations are deduced in detail for the first time, and the oscillating threshold of the first Stokes inside the resonator is deduced analytically. A sample calculation for an actively Q-switched self-Raman laser is presented to demonstrate the use of the curves and related formulas. View full abstract»

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  • Specific Features of XGM in QD-SOA

    Publication Year: 2007 , Page(s): 730 - 737
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1422 KB) |  | HTML iconHTML  

    The peculiarities of a cross-gain modulation (XGM) in quantum-dot semiconductor optical amplifier (QD SOAs) related to the inhomogeneous broadening are theoretically studied. We have solved numerically the electron rate equations for the QD SOA model including an excited state, a ground state and a continuum wetting layer (WL), and the propagation equations for the pump and the signal lightwaves. It is shown that XGM in QD SOA is possible for a comparatively large detuning close to the inhomogeneous broadening because in such a case QDs with substantially different resonant frequencies interact directly through WL. View full abstract»

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  • Special issue on nano-optoelectronics and applications

    Publication Year: 2007 , Page(s): 738
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    Freely Available from IEEE
  • Special issue on nanosensor technology

    Publication Year: 2007 , Page(s): 739
    Save to Project icon | Request Permissions | PDF file iconPDF (153 KB)  
    Freely Available from IEEE
  • Special issue on in vivo sensors for medicine

    Publication Year: 2007 , Page(s): 740
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    Freely Available from IEEE
  • IEEE Journal of Quantum Electronics information for authors

    Publication Year: 2007 , Page(s): 741
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    Freely Available from IEEE
  • [Front cover]

    Publication Year: 2007 , Page(s): 742
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    Freely Available from IEEE
  • IEEE Journal of Quantum Electronics publication information

    Publication Year: 2007 , Page(s): 743
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    Freely Available from IEEE

Aims & Scope

The IEEE Journal of Quantum Electronics is dedicated to the publication of manuscripts reporting novel experimental or theoretical results in the broad field of the science and technology of quantum electronics..

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Meet Our Editors

Editor-in-Chief
Aaron R. Hawkins
Brigham Young University