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Quantum Electronics, IEEE Journal of

Issue 9 • Date Sept. 2000

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Displaying Results 1 - 12 of 12
  • In-well ambipolar diffusion in room-temperature InGaAsP multiple quantum wells

    Page(s): 1013 - 1015
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    Three-pulse transient amplitude grating experiments were performed using picosecond pulses at 1.525 /spl mu/m on room-temperature InGaAsP multiple quantum wells using a periodically poled LiNbO/sub 3/ (PPLN) optical parametric oscillator. An ambipolar diffusion coefficient of 7.2 cm/sup 2//s was measured from the diffraction efficiency decay rates. We deduce the presence of alloy scattering or an increase in interface scattering when comparing these results with those of similar experiments on GaAs-AlGaAs multiple quantum wells. View full abstract»

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  • Azimuthal mode discrimination in radially chirped concentric-circle-grating distributed feedback lasers

    Page(s): 1016 - 1025
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    We report a theoretical investigation analyzing the threshold modes of a concentric-circle-grating (CCG) distributed feedback laser with a radially chirped first-order Bragg grating. A numerical coupled-mode analysis of a chirped CCG laser shows improved azimuthal mode discrimination for chirped gratings with linear, quadratic, and square-root radial dependence. Negatively chirped gratings, in which the grating period decreases with radius, result in improved threshold discrimination between the circularly symmetric fundamental mode and higher order modes; positively chirped gratings, in which the grating period increases with radius, result in decreased threshold for higher order modes in general. Also, the intensity for the fundamental mode at the grating center can be reduced by an order of magnitude using linearly chirped gratings. View full abstract»

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  • Modeling self-pulsating DFB lasers with an integrated phase tuning section

    Page(s): 1026 - 1034
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (257 KB)  

    A theoretical model of a self-pulsating three-section DFB laser with an integrated phase tuning section is established. It is based on traveling wave equations and the standard carrier rate equations. Parameters of an existing device are used for applying the model. Key conditions and characteristics of self-pulsations (SPs) are modeled and compared with experimental results. The important role of phase tuning for turning on the SP is pointed out. The dependence of the SP regime on the detuning between the Bragg wavelengths in the laser and reflector is determined and the essential role of phase-readjustment is identified. Frequency tuning via the laser currents, as well as the pulse shape at various frequencies, is investigated. This allows us to identify the mechanism for frequency tuning. The model turns out to be a good tool to improve our knowledge of the self-pulsation effect and to design optimized devices. View full abstract»

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  • Ultrashort pulse generation by intracavity spectral shaping and phase compensation of external-cavity modelocked semiconductor lasers

    Page(s): 1035 - 1040
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (122 KB)  

    Intracavity spectral shaping and external chirp compensation techniques were employed to generate nearly transform-limited optical pulses with a temporal duration of 250 fs from an external-cavity modelocked semiconductor laser. It was also demonstrated that intracavity spectral shaping techniques can be used for artificially tailoring the chirp of the output pulses. View full abstract»

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  • Frequency-tunable optically pumped carbon monoxide laser

    Page(s): 1041 - 1052
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    Single-line frequency-tunable lasing was observed in an optically pumped, repetitively pulsed, room-temperature CO laser for the first time. The R(0) and R(7) ro-vibrational transitions in the (2,0) overtone of CO at 2.3 /spl mu/m were optically pumped with a high-energy optical parametric oscillator. Single-line lasing was observed on (2,1) P(2)-P(17) transitions and R(0)-R(11) transitions (covering wavelengths within the range 4.6-4.9 /spl mu/m) when using a diffraction grating as the spectrally selective reflector of the laser resonator. The observed CO laser pulse lengths were /spl sim/10/sup -7/ s with peak power up to 10/sup 4/ W. The influence of CO pressure, the addition of buffer gas (He, Ar), Q-factor of the laser resonator, and the pump pulse energy on CO laser pulse temporal characteristics and output energy spectral distribution was studied experimentally. View full abstract»

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  • High-repetition-rate operation of a segmented hollow-cathode Ne-Cu/sup +/ 249-nm laser

    Page(s): 1053 - 1057
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    A segmented hollow-cathode Ne-Cu/sup +/ 249-nm laser is operated at a pulse repetition rate of 500 Hz and a pulse duration of 30 /spl mu/s. The laser pulse has a risetime of 5 /spl mu/s and is delayed by 5 /spl mu/s on the leading edge of the current pulse. The fast evolution of the laser pulse results from a higher gas temperature at the start of each discharge pulse, and consequently during the pulse, due to the higher mean cathode temperature required to transfer the discharge power from cathode to anode. The higher gas temperature results in a faster diffusion of the sputtered copper atoms into the negative glow and in an increased rate coefficient for charge transfer, both of which increase the pumping rate for the laser transition. An initial overshoot in the discharge voltage gives rise to a sharp initial peak in the laser pulse. A significant sharp peak in the laser pulse immediately at the end of the current pulse indicates that an enhanced laser pulse of duration 10 /spl mu/s at a pulse repetition rate of 1 kHz may be achieved by appropriately shortening the current pulse duration. View full abstract»

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  • Gain characteristics of InGaN-GaN quantum wells

    Page(s): 1058 - 1064
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    A self-consistent approach is used to examine gain and radiative lifetimes in InGaN-GaN quantum-well structures. The effect of high built-in electric fields due to spontaneous polarization and the piezoelectric effect and the screening of these fields by carrier injection is examined. We study how the peak gain and radiative lifetime vary with injection density and well size. We also examine the blue shift in the peak gain energy with carrier injection. Implications for laser design are discussed. View full abstract»

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  • Temperature dependence of gain saturation in multilevel quantum dot lasers

    Page(s): 1065 - 1071
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    The temperature dependence of quantum dot (QD) optical gain is analyzed using a multilevel model and compared with experiment. The maximum gain is found to have a surprisingly strong temperature dependence that causes level switching and can limit laser performance in QD lasers. The model based on multiple discrete levels elucidates general design criteria that should be satisfied to obtain a stable threshold versus temperature in QD lasers. Good agreement is obtained between calculations and experiment for level switching in 1.3-/spl mu/m QD lasers. View full abstract»

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  • A time-domain computer simulator of the nonlinear response of semiconductor optical amplifiers

    Page(s): 1072 - 1080
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    We present a computer simulator of semiconductor optical amplifiers. The nonlinear input-output response of the device is characterized in terms of a complex gain, representing the accumulated gain and wavevector change of the propagating field across the active waveguide. We account for the gain saturation induced by stimulated recombination and by the perturbation of the carrier quasi-equilibrium distribution within the bands. A rigorous elimination of the spatial coordinate allows us to reduce the description of the amplifier dynamics to the solution of a set of ordinary differential equation for the complex gain. If the waveguide internal loss is negligible, the spatial inhomogeneity of the complex gain is implicitly yet exactly taken into account by the reduced model. The accuracy of the reduced model is the same for models based on the direct solution of the set of partial differential equations describing the interaction between the optical field and the active semiconductor waveguide, but the model is computationally much simpler. To preserve the input-output characteristics of the model, we include the amplified spontaneous emission noise in the device description by an equivalent signal applied to the device input and amplified by the saturated gain. At the expense of a minor increase of the program complexity, the waveguide internal loss may also be included. We report on the comparison between the output of the simulator and the results of four-wave mixing experiments in various pump-signal configurations. Good agreement is obtained. View full abstract»

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  • Influence of nonuniform carrier distribution on the polarization dependence of modal gain in multiquantum-well lasers and semiconductor optical amplifiers

    Page(s): 1081 - 1088
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    We investigate the modal gain seen by transverse-electric (TE) and transverse-magnetic (TM) modes of bulk and multiquantum-well (MQW) lasers given a nonuniform distribution of active region carriers. We find that the dependence of modal gain on the nonuniformity of carrier profile differs for TE and TM modes. This experimentally observable phenomenon is proposed as a measure of carrier density nonuniformity. We discuss the importance of the confinement picture for TE and TM modes, in the generalized presence of some asymmetry, in assuring injection-level independent polarization insensitivity in semiconductor lasers and optical amplifiers. View full abstract»

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  • Characteristics of Er-doped Al/sub 2/O/sub 3/ thin films deposited by reactive co-sputtering

    Page(s): 1089 - 1097
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    Er-doped Al/sub 2/O/sub 3/ thin films have been deposited by reactive co-sputtering onto thermally oxidized Si-wafers. The deposition process has been optimized with respect to the requirements originating from the application of these multilayer structures as integrated optical amplifiers for the third telecom window, i.e., the wavelength range 1.52-1.55 /spl mu/m. The films obtained at a substrate temperature of only 400/spl deg/C are amorphous and show a homogenous structure, without columns or grains. For slabguides, background losses smaller than 0.25 dB/cm have been obtained, even without any annealing. A relatively broad luminescence band, having an FWHM of /spl sim/55 nm around the 1.533-/spl mu/m wavelength, has been measured. From gain versus pumping power curves, an upconversion coefficient lower then 20/spl middot/10/sup -25/ m/sup 3//s has been derived, being half of the values reported up to now in the literature. Simulations based on experimentally determined material parameters and assuming a channel attenuation of 0.5 dB/cm indicate, for 0.24 at.% Er channel devices with an optimal channel length of 7.7 cm, an amplification of 8 dB at 1.533 /spl mu/m for a pump wavelength of 1.48 /spl mu/m, and a pump power of only 8.7 mW. View full abstract»

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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