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Quantum Electronics, IEEE Journal of

Issue 2 • Date Feb 2001

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Displaying Results 1 - 18 of 18
  • A very low-loss wide-angle Y-branch with a composite diamond-like microprism

    Page(s): 231 - 236
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    A very low-loss wide-angle symmetric Y-branch with a low-index composite diamond-like microprism (CDM) is proposed. The CDM is composed of a diamond-like microprism (DM) and a post-compensating microprism (PM). The former is designed to compensate the phase-front mismatch at the branching point, and it will improve the field mismatch by this diamond-like shape; the latter is used to reduce the coupling between the branches. After complete phase-front compensation of the CDM; the simulated normalized transmission will maintain 96.4% even if the branching angle is up to 200. Besides, the design rules of the indices of CDM are remarkably readily derived and efficient. This structure will also provide various advantages of simple shape, relative insensitivity to fabrication errors, and flexible selection of prism index. Furthermore, detailed examinations of the design parameters have been discussed relative to the transmission characteristics View full abstract»

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  • Jitter dynamics of a gain switched semiconductor laser under self-feedback and external optical injection

    Page(s): 254 - 264
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    We investigate the jitter dynamics of a gain switched laser diode (LD) under the influence of strong optical injection due either to multiple reflections from an external cavity mirror, or from another LD. A numerical technique that considers both the spontaneous emission noise and multiple reflections from external optical components is implemented. At all times, the LD exhibits multi-longitudinal mode operation with a Gaussian-shaped spectral line profile that is centered around a fixed dominant output wavelength. We separately consider three (strong) optical injection conditions: 1) coherent self-feedback; 2) incoherent self-feedback; and 3) coherent, external continuous-wave (CW) optical injection. Incoherent self-feedback results in a reduction, by an order of magnitude, in both the intensity and timing jitter (0.5 ps), while maintaining the average peak power and pulsewidth. Eye pattern results show an opening of at least 90 %, which represents an improvement by a factor of two over the same LD that operates without optical injection. The external CW injection condition approaches that of incoherent self-feedback only at high external injection. Coherent self-feedback does not produce any significant change in the LD performance View full abstract»

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  • High average and high peak brightness slab laser

    Page(s): 296 - 303
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    A high average and high peak brightness Nd:YAG MOPA laser system composed of a laser-diode-pumped Nd:YAG master oscillator, flash-lamp-pumped slab power amplifiers and a phase conjugated mirror was developed. The system demonstrates an average output power of 235 W at a repetition rate of 320 Hz and a peak power of 30 MW at a pulse duration of 24 ns with M2=1.5. Both an average brightness of 7×109 W/cm2·sr and a peak brightness of 1×1015 W/cm2·sr are achieved simultaneously. The system design rules that we confirmed suggest that by replacing lamp pumping in the amplifier with laser-diode pumping, an average output power of ~1 kW can be obtained at ~1 kHz with a higher average brightness of ~3×1010 W/cm2·sr and a higher peak brightness of ~3×1015 W/cm2·sr View full abstract»

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  • Analysis of lateral-mode behavior in broad-area InGaN quantum-well lasers

    Page(s): 265 - 273
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    A wave-optical model that is coupled to a microscopic gain theory is used to investigate lateral mode behavior in group-III nitride quantum-well lasers. Beam filamentation due to self-focusing in the gain medium is found to limit fundamental-mode output to narrow stripe lasers or to operation close to lasing threshold. Differences between nitride and conventional near-infrared semiconductor lasers arise because of band structure differences, in particular, the presence of a strong quantum-confined Stark effect in the former. Increasing mirror reflectivities in plane-plane resonators to reduce lasing threshold current tends to exacerbate the filamentation problem. On the other hand, a negative-branch unstable resonator is found to mitigate filament effects, enabling fundamental-mode operation far above threshold in broad-area lasers View full abstract»

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  • On the synthesis of fiber Bragg gratings by layer peeling

    Page(s): 165 - 173
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    Two methods for grating synthesis which have appeared in the literature recently are compared directly. In particular, we point out the similarity between the two; both algorithms are based on propagation of the fields through the structure with simultaneous evaluation of the coupling coefficient according to simple causality arguments (layer-peeling algorithms). The first published method (the discrete layer-peeling algorithm) is reformulated in a simpler, more efficient way, and it is shown that its implementation can be made exact. For mathematical comparison, a derivation of the second method (the continuous layer-peeling algorithm) is presented. The methods are compared both mathematically and numerically. We find that the discrete layer-peeling algorithm is significantly faster and can be more stable than its continuous counterpart, whereas the continuous algorithm offers some advantages in flexibility View full abstract»

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  • Proposal of an optical modulator based on resonant tunneling and intersubband transitions

    Page(s): 224 - 230
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    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 field. 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-InIAs QWs. The considered modulator structure operates at λ=6.0 μm and is RC limited to 27 GHz. An extinction ratio of 4 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 View full abstract»

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  • Performance of waveguide-based two-dimensional photonic-crystal mirrors studied with Fabry-Perot resonators

    Page(s): 237 - 243
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    As a step toward the use of photonic crystals in optoelectronic devices, we present a thorough study of 2-D photonic-crystal mirrors etched into a GaAs-AlGaAs planar waveguide. Fabry-Perot resonators are fabricated to deduce the reflectivity, transmission, losses, as well as the penetration lengths of these mirrors. The guided photoluminescence of InAs quantum dots embedded in GaAs is used to obtain the transmission spectra of these cavities. The varying thickness between the mirrors allows a scan across the whole bandgap spectral range. Quality factors (up to 200) and peak transmissions (up to 0.3) are measured showing that mirrors of four rows of holes have 88% reflectivity, 6% transmission and 6% losses. Losses are also related to a two-dimensional transfer matrix method calculation including a recently introduced scheme to account for losses View full abstract»

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  • Long wavelength vertical-cavity semiconductor optical amplifiers

    Page(s): 274 - 281
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    This paper overviews the properties and possible applications of long wavelength vertical-cavity semiconductor optical amplifiers (VCSOAs). A VCSOA operating in the 1.3-μm wavelength region is presented. The device was fabricated using wafer bonding; it was optically pumped and operated in reflection mode. The reflectivity of the VCSOA top mirror was varied in the characterization of the device. Results are presented for 13 and 12 top mirror periods. By reducing the top mirror reflectivity, the amplifier gain, optical bandwidth, and saturation output power were simultaneously improved. For the case of 12 top mirror periods, rye demonstrate 13-dB fiber-to-fiber gain, 0.6 nm (100 GHz) optical bandwidth, a saturation output power of -3.5 dBm and a noise figure of 8.3 dB. The switching properties of the VCSOA are also briefly investigated. By modulating the pump laser, we have obtained a 46-dB extinction ratio in the output power, with the maximum output power corresponding to 7-dB fiber-to-fiber gain. All results are for continuous wave operation at room temperature View full abstract»

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  • Amplified spontaneous emission in dye-doped sol-gel amplifiers

    Page(s): 189 - 198
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    Transversely pumped dye doped slab waveguides are investigated. A set of coupled-rate equations for the excited-state population and for the amplified spontaneous emission (ASE) power, at all wavelengths, is presented. The equations are solved numerically for the steady-state case. The results describe the dependence of ASE output power on pumping power, the spectral narrowing process, and the effect of waveguiding. The theoretical calculations are compared with the results of experiments, and good agreement is found View full abstract»

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  • Optical spectroscopy and diode-pumped laser performance of Nd3+ in the CNGG crystal

    Page(s): 304 - 313
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    We have exploited the broad absorption and emission bandwidth of the laser crystal Ca3(NbGa)2-xGa3O12 doped with Nd3+ to develop a tunable and mode locked diode-pumped 1.06 μm laser. We also present the fluorescence and excitation spectra at different crystal temperatures from 10 to 298 K. The spontaneous transition probabilities, the branching ratios, and the radiative lifetime are calculated by means of the Judd-Ofelt theory and compared with the experimental results. The stimulated emission cross-sections of the most important transitions have been calculated and compared with laser results. Employing a 2-W laser diode as a continuous-wave pump source, we have been able to tune the emission wavelength in the range 1053-1074 nm. Active mode-locking yielding pulses of 9.6, 18, and 19.7 ps at the three main emission peaks of 1058.6, 1061.2, and 1065.3 nm, respectively. was also demonstrated View full abstract»

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  • Impact of gain dispersion on the spatio-temporal dynamics of multisection lasers

    Page(s): 183 - 188
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    We present a refined model for multi-section lasers, introducing an additional equation for material polarization in the well-known traveling wave model. We investigate the polarization-induced changes in the spectral properties of the optical waveguide. Finally, we show the relevance of this model for a more realistic simulation of the complicated dynamical behavior of multi-section distributed feedback (DFB) lasers, such as fast self-pulsations, multi-stability, and hysteresis effects due to mode competition View full abstract»

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  • Atmospheric thermal lens induced by high-power CO2 laser beams in laser materials processing

    Page(s): 218 - 223
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    The atmospheric thermal lens induced by high-power CO2 laser beams in laser materials processing and its influence on beam propagation and focus are studied in this paper. It is found in experiments that the atmospheric thermal lens is generated when the air in the beam propagation path is stationary. But it can be eliminated by blowing air with a certain pressure into the beam's guidance system. Also, the behavior of the beam's propagation under the case of the thermal lens deviates from Gaussian theory. This deviation is calculated by the linear and nonlinear models of the atmospheric thermal lens under the conditions of a large beam diameter and high power intensity. In addition, the influence of the thermal lens on the beam's focus size and position is also discussed in this paper View full abstract»

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  • Laser diode injected intracavity-doubled Ti:sapphire laser for single-mode tunable UV sources

    Page(s): 290 - 295
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    Intracavity frequency doubling of a pulsed Ti:sapphire laser is shown to be well described by multimode rate equations nonlinearly coupled through the homogeneous gain linewidth of the amplifying medium. Hole burning in the fundamental wave spectrum is observed at the phase-matched frequency and is explained well by theory in terms of the dynamic depletion of the fundamental waves phase-matched to the nonlinear output mirror. The doubling conversion efficiency is shown to be greatly improved by injection seeding at the same frequency as the “spectral hole” with a low power continuous-wave-tunable laser diode. This leads, for the first time to our knowledge, to single-mode UV-tunable (380-410 nm) emission using this technique. Finally, the source is shown to exhibit a minimum yield at the coincidence between injection and exactly phase-matched wavelengths while maintaining high efficiency when injecting a few nanometers away from the phase-matching maximum View full abstract»

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  • Characteristics of Q-switched cladding-pumped ytterbium-doped fiber lasers with different high-energy fiber designs

    Page(s): 199 - 206
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    We theoretically and experimentally analyze Q-switched cladding pumped ytterbium-doped fiber lasers designed for high pulse energies. We compare the extractable energy from two high-energy fiber designs: (1) single- or few-moded low-NA large mode area (LMA) fibers and (2) large-core multimode fibers, which may incorporate a fiber taper for brightness enhancement. Our results show that the pulse energy is proportional to the effective core area and, therefore, LMA fibers and multimode fibers of comparable core size give comparable results. However, the energy storage in multimode fibers is mostly limited by strong losses due to amplified spontaneous emission (ASE) or even spurious lasing between pulses. The ASE power increases with the number of modes in a fiber. Furthermore, spurious feedback is more difficult to suppress with a higher NA, and Rayleigh back-scattering increases with higher NA, too. These effects are smaller in low-NA LMA fibers, allowing for somewhat higher energy storage. For the LMA fibers, we found that facet damage was a more severe restriction than ASE losses or spurious lasing. With a modified laser cavity, we could avoid facet damage in the LMA fiber, and reached output pulse energies as high as 2.3 mJ, limited by ASE. Theoretical estimates suggest that output pulse energies around 10 mJ are feasible with a larger core fiber, while maintaining a good beam quality View full abstract»

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  • Thermal, stress, and thermo-optic effects in high average power double-clad silica fiber lasers

    Page(s): 207 - 217
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    Yb:glass fiber lasers have matured to the point where the average power scaling of such devices to the kilowatt level and beyond can be realistically pursued. In this paper, we present a comprehensive study of thermal, stress, and average power scaling in double-clad silica fiber lasers. We show that careful management of thermal effects in fiber lasers will determine the efficiency and success of scaling-up efforts View full abstract»

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  • Modeling of GaN optoelectronic devices and strain-induced piezoelectric effects

    Page(s): 244 - 253
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    Modeling of nitride-based LEDs and laser diodes requires a fast modular tool for numerical simulation and analysis. It is required that the modeling tool reflects the primary physical processes of current injection, quantum well (QW) bound-state dynamics, QW capture, radiative, and nonradiative transitions. The model must also have the flexibility to incorporate secondary physical effects, such as induced piezoelectric strain fields due to lattice mismatch and spontaneous polarization fields. A 1-D model with a phenomenological well-capture process, similar to that developed by Tessler and Eisenstein, has been implemented. The radiative processes are calculated from first principles, and the material band structures are computed using k·p theory. The model also features the incorporation of such effects as thermionic emission at heterojunctions. Shockley-Read-Hall recombination, piezoelectric strain fields, and self-consistent calculation of the QW bound states with dynamic device operation. The set of equations underlying the model is presented, with particular emphasis on the approximations used to achieve the previously stated goals. A sample structure is analyzed, and representative physical parameters are plotted. The model is then used to analyze the effects of incorporation of the strain-induced piezoelectric fields generated by lattice mismatch and the spontaneous polarization fields. It is shown that these built-in fields can accurately account for the blue-shift phenomena observed in a number of different GaN LEDs View full abstract»

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  • Power, efficiency, and thermal characteristics of type-II interband cascade lasers

    Page(s): 282 - 289
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    High-performance mid-infrared type-II interband cascade lasers have been demonstrated under continuous-wave (CW) conditions with record-high wall-plug efficiencies (>14%) and output powers (>100 mW/facet) above 77 K. Device characteristics of these type-II interband cascade lasers are investigated systematically in terms of their output powers and efficiencies. Also, by comparing the temperature dependence of the threshold currents under pulsed and CW conditions, the thermal resistance and maximum heat sink temperature for CW operation are estimated for several mesa sizes. The limiting factors due to device heating for high-power/high-efficiency operation are identified and discussed in connection with device dimensions and packaging for the purpose of assessing further improvements View full abstract»

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  • Parametric study of small-signal gain in a slit nozzle, supersonic chemical oxygen-iodine laser operating without primary buffer gas

    Page(s): 174 - 182
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    A detailed experimental study of the gain and temperature in the cavity of a supersonic chemical oxygen-iodine laser (COIL) is carried out to find optimal values of the flow parameters corresponding to the maximum gain. It is found that high gain (>0.7%/cm) can be obtained in a COIL operating without primary buffer gas and, hence, having a high gas temperature (>250 K) in the cavity. The measurements are performed for slit nozzles with different numbers and positions of iodine injection holes. Using a diode laser-based diagnostic, the gain is studied as a function of the molar flow rates of various reagents, with optical axis position along and across the flow, and Mach number in the cavity. Maximum gain of 0.73%/cm is obtained at chlorine and secondary nitrogen flow rates of 15 mmole/s and 7 mmole/s, respectively, for a slit nozzle with transonic injection of iodine. The gain is found to be strongly inhomogeneous across the flow. For a slit nozzle with iodine injection in the diverging part of the nozzle, the values of the maximum gain are smaller than for nozzles with transonic injection. Opening a leak downstream of the cavity in order to decrease the Mach number and increase the cavity pressure results in a decrease of the gain and dissociation fraction. The gain is a nonmonotonic function of the iodine flow rate, whereas the temperature increases with increasing iodine flow. An analytical model is developed for calculating in slit nozzles the iodine dissociation fraction F and the number N of O2 (1Δ) molecules lost in the region of iodine dissociation per I2 molecule 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