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Quantum Electronics, IEEE Journal of

Issue 11 • Date Nov. 1996

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Displaying Results 1 - 20 of 20
  • Transverse-mode control of vertical-cavity surface-emitting lasers

    Page(s): 1950 - 1958
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    Transverse-mode control of vertical-cavity surface-emitting lasers (VCSELs) has been investigated. A theoretical model takes into account the distributions of carriers, optical field, and temperature. Using a method of finding self-consistent solutions for the carrier diffusion, optical field, and thermal conduction equations, we have studied the influence of current spreading, injected current density, gain-guided aperture, and window diameter on the transverse modes. The calculated results agree well with those of experiments and show that the transverse-mode evolution of VCSELs depends on the changes of gain and refractive index induced by carriers and heating; decreasing temperature rise and profile width, current spreading, and gain-guided aperture dimension, increasing homogeneity of the injected carriers at the lasing region, and decreasing window diameter are effective methods to suppress high-order transverse modes. View full abstract»

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  • High-coupling-efficient 1.3-μm laser diodes with good temperature characteristics

    Page(s): 1959 - 1964
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    We have proposed uniformly beam-expanded structures based on the advanced concept for realizing high coupling efficiency and good temperature characteristics. Beam expansion (optical confinement reduction) by narrowing the core layer width as well as a carrier confinement are strongly enhanced by adopting a larger bandgap InGaAsP for MQW barriers and separate confinement heterostructure layers. These laser diodes (LD's) were fabricated by the conventional buried heterostructure laser process, which is very important in reducing the cost. Our results have proven the effectiveness of our proposition. The LD's with high coupling efficiency (-3.2 dB) and good temperature characteristics have been achieved even using the simple approach of reducing optical confinement. The threshold currents at 25 and 85°C are 9.3 and 39.4 mA, respectively. The slope efficiency at 25°C is 0.39 W/A and still high (0.26 W/A) even at 85°C View full abstract»

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  • Time-resolved plasma diagnostic by laser-diode spectroscopy

    Page(s): 1874 - 1881
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    A tunable diode laser has been used as a light source for line-of-sight absorption and Doppler-shift measurements. We have applied the method to perform plasma diagnostics in a magneto plasma dynamic (MPD) pulsed propulsor device and of an Ar+ laser tube plasma. Spectrally resolved argon absorption lineshapes of transitions of neutral and single ionized argon were recorded. A high temporal resolution (a few microseconds) is achieved by fast tuning the laser frequency at a repetition rate greater than 100 kHz. From the recorded spectra, we deduce the dynamics of the neutral components of the plasma in the thruster. We also demonstrate the possibility of direct ion diagnostics by the observation of ionic transitions, using red diode lasers in an Ar+-laser commercial tube View full abstract»

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  • Experimental studies on output, spatial, and spectral characteristics of a microdroplet dye laser containing Intralipid as a highly scattering medium

    Page(s): 1864 - 1873
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    Lasing characteristics of Rhodamine 6G dye-doped microdroplets containing highly scattering fat emulsion Intralipid-10% are studied experimentally. Noteworthy findings are that well-defined lasing threshold can be observed and one order or more magnitude enhancement of emission intensity with suitable (optimum) conditions of the Intralipid mixing ratio, in comparison with original neat-dye lasing microdroplets. We present and discuss the measured results of input-output intensities for different dye concentrations and dye-Intralipid mixing ratios in this high-gain laser dye-soft scatterer system and microscope images of spatial distribution of light emission from both the microdroplets containing neat-dye and dye-Intralipid mixture. It was found that almost no-lasing neat-dye microdroplets, which have either much higher or much lower dye concentration, can achieve lasing by substituting suitably certain amounts of the Intralipid, causing multiple light scattering. Spectral measurements of lasing outputs from the Rhodamine 6G dye-Intralipid microdroplets show the tendency of the disappearance of the well-known mode structures, owing to the morphology-dependent resonances of this microspherical cavity inherent to the neat-dye microdroplets. It is our belief that the present results make this novel method of dye-Intralipid microsystem very attractive for a variety of future applications, including diagnostic tools for highly sensitive detection and identification of small quantity objects and species embedded or hidden in highly scattering media, such as biological tissues and cellular structures View full abstract»

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  • Practical aspects of lasing without inversion in various media

    Page(s): 1882 - 1896
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    A rigorous density-matrix-based theory of lasing based on optically induced or autoionization-induced coherence between the levels is developed. The balance equations are obtained, and the conditions for lasing threshold are derived as a function of pumping strength and relaxation rates. Connection between the lasing without inversion and Raman and parametric processes is established. The main conclusion is that true CW lasing without inversion can indeed be obtained but only in a system where pumping and relaxation rates are favorable for attaining conventional lasing with population inversion. Practical implications of it, especially for the intersubband lasers, are discussed View full abstract»

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  • A fiber-optic autocollimation refractometric method for dispersion measurement of bulk optical materials using a widely tunable fiber Raman laser

    Page(s): 1897 - 1902
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    A simple and highly sensitive fiber-optic autocollimation method for refractive-index dispersion measurement of solid-state and liquid bulk optical materials is presented. The method is based on the use of a double-pass multimode fiber Raman laser which generates widely tunable emission in a broadband (0.54-1.01 μm) continuous spectral range at pumping with the second harmonic of a Q-switched Nd:YAG laser. The optical fiber is used in a specific multifunctional regime where, because of its micrometric core dimensions, it serves simultaneously as a point laser source for the formation of a collimated input emission, as a highly sensitive receiver of the autocollimation backreflectance, and as a medium for nonlinear frequency conversion and generation of a broad-band continuum spectrum. The experimental results obtained in the refractive-index dispersion measurements are fitted to the Sellmeier dispersion equation and used to determine the material dispersion and additional dispersive characteristics of the test optical material View full abstract»

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  • Polarization-dependent refractive-index change induced by superlattice disordering

    Page(s): 1922 - 1931
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    A model of the polarization-dependent refractive-index change that accompanies superlattice disordering is proposed for the first time. Calculated results agree well with experimental results in terms of the amount and direction of the refractive-index changes. In the GaAs-AlAs system, a simple diffusion model that considers the diffusion of group III atoms explains the experimental results. In a InGaAs-InP system, it is assumed that group V atoms mainly induce disordering, and the difference between the diffusion constant in wells and that in barriers is taken into account. The refractive-index changes induced by superlattice disordering are useful for fabricating polarization control devices and integrated optical circuits View full abstract»

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  • Tuning characteristics of monolithic passively mode-locked distributed Bragg reflector semiconductor lasers

    Page(s): 1965 - 1975
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    Tuning characteristics of multicontact passively mode-locked distributed Bragg reflector (DBR) semiconductor lasers are investigated in terms of center wavelengths and pulse repetition frequencies. It is shown that the center wavelength of the pulses can be tuned over a wide range by changing the refractive index of the Bragg reflector section either by means of carrier injection or by thermal effects while maintaining the pulses to be nearly transform-limited. Tuning of the pulse repetition rates is realized by using four different approaches, i.e., current injection to a passive phase-control section, varying of the reverse bias to the absorber, varying of the injection current to the gain region, and thermal effects. Injecting current into the phase-control region results in a tuning range of more than 400 MHz while maintaining the pulses at transform-limited condition. Varying the reverse bias voltage to the absorber is shown to be an alternative to achieve large repetition rate tuning, by which a tuning range of 600 MHz is obtained. By combining these tuning schemes, a total tuning range of more than 1 GHz is realized View full abstract»

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  • Room-temperature CW laser operation at ~1.55 μm (eye-safe range) of Yb:Er and Yb:Er:Ce:Ca2Al2SiO7 crystals

    Page(s): 2004 - 2009
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    Room-temperature CW laser operation at 1.55 μm of Yb:Er:Ca2Al2SiO7 (CAS) single crystal pumped at 940 nm and 975 nm has been achieved for the first time. Introduction of a third doping ion, Ce3+, decreases the Er 3+4I11/2 excited-state lifetime and improves the laser properties. For Yb:Er:Ce:CAS single crystal, a maximum of 20 mW output power is produced for 285 mW absorbed power. With this material, a low threshold of 20 mW and a relatively high slope efficiency of ~5.5% are obtained. Preliminary results indicate possible improvement in the near future. Experimental threshold values and laser properties of CAS crystals with various compositions are in good agreement with calculations, performed using the rate-equations modeling. Comparison with a Yb:Er:phosphate glass laser is also presented View full abstract»

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  • Effect of grating phase difference on single-mode yield in complex-coupled DFB lasers with gain and index gratings

    Page(s): 1937 - 1949
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    In complex-coupled DFB lasers with both index and gain gratings, I have studied the effect of the phase difference between index and gain gratings on the single-mode yield considering the threshold gain difference (side-mode suppression ratio) and the optical field uniformity (spatial hole burning). I have obtained the optimum values of: (1) the phase difference ΔΩ between index and gain gratings, (2) the coupling strength (ℵL)i of gain grating, and (3) the coupling strength (ℵL)r of index grating, in order to obtain a high single-mode yield regardless of the relative positions of both facets, The used theory is based on the coupled-mode theory and includes the spatial hole burning correction and the standing wave effect. ΔΩ=π/4 (and 3π/4) DFB lasers with HR-AR facets have the highest single-mode yield and should have ~0.6⩽(ℵL)i⩽~1.5 and (ℵL)r<~1.25 in order to obtain above 50% yields. Even above 90% yields can be obtained with the range of ~1.1⩽(ℵL)i⩽~1.4 and ~0.5⩽(ℵL)r ⩽~0.85. The superior yield characteristics of ΔΩ=π/4 (and 3π/4) DFB lasers, which is above 2.4 times higher than that of ΔΩ=0 (and π) DFB lasers, comes from their better field intensity uniformity. The results presented in this paper provide insight into the variation of the threshold gain difference and the optical field uniformity with ΔΩ, (ℵL)r, (ℵL)i, and (ρl, ρr) View full abstract»

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  • Tunneling-time properties in type II quantum resonant structures

    Page(s): 1932 - 1936
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    A tunneling-time calculation method has been developed for unbiased and biased type II quantum resonant structures. The tunneling-time properties of asymmetric quantum resonant structures has been studied for both type II staggered and misaligned heterostructures View full abstract»

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  • Theory and simulations of tunable two-mirror and three-mirror resonant-cavity photodetectors with a built-in liquid-crystal layer

    Page(s): 1903 - 1915
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    Integrated, tunable resonant-cavity photodetectors with a built-in liquid-crystal layer structure are described. Two structures, a single resonant-cavity (Fabry-Perot) configuration and a three-mirror resonant-cavity configuration, are investigated theoretically. A quantum efficiency formula for the three-mirror resonant-cavity configuration is derived and performance simulations and optimization for both configurations are presented. Additionally, a new performance measure referred to as the efficiency-linewidth joint criterion (ELJC) is defined for reasonable and convenient performance estimations. It is shown that a wide wavelength tuning range can be easily achieved for both configurations. Although it is hard to obtain a linewidth as narrow as 2 nm for the single resonant-cavity configuration, the three-mirror resonant-cavity configuration can achieve narrower linewidth and high quantum efficiency when optimized. This type of device may prove useful for wavelength division multiplexing (WDM) applications View full abstract»

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  • Tunable dual-wavelength picosecond optical pulses generated from a self-injection seeded gain-switched laser diode

    Page(s): 1976 - 1980
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    A novel scheme to generate dual-wavelength picosecond optical pulses has been demonstrated. The pulses are obtained by self-injection seeding of a gain-switched laser diode simultaneously at two different wavelengths. Optical feedback is provided by a partially reflecting fiber mirror. Single-mode pulses at alternate wavelengths around 1.3 μm have been generated. The pulse width varies from about 40 to 50 ps. The output wavelengths can be tuned by changing the electrical modulation frequency. Spacing between the wavelengths can also be controlled by adjusting the length of the dispersive fiber cavity. Our experimental data are in good agreement with the calculated results View full abstract»

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  • 3.5-mm-square InGaAs p-i-n photodiodes and their application to optical-axis arrangement between 1.3-μm laser diodes and a SMF

    Page(s): 1916 - 1921
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    InGaAs p-i-n photodiodes (PD) with 3.5-mm×3.5-mm-large photosensitive area have been fabricated using chlorine-vapor-phase-epitaxial (C-VPE) growth. They showed high responsivity of 0.95 A/W (λ=1.3 μm) and 1.2 A/W (λ=1.55 μm) and good homogeneity in the whole area. Long-term reliability was confirmed through high-temperature aging tests at 150°C up to 5200 hours. A PD with two pairs of parallel electrodes (PE-PD) was applied to optical-axis arrangement between 1.3-μm laser diodes (LD's) and a single mode fibre (SMF). The beam position of a LD was detected in error within ±20 μm using PE-PD prior to coupling of a LD beam into a SMF. Total inspection time was reduced to one third the original time View full abstract»

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  • Jitter reduction through feedback for picosecond pulsed InGaAsP lasers

    Page(s): 1988 - 1994
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    Following a comparison of picosecond-pulse generation techniques, feedback schemes are reported for the generation of picosecond pulse trains with improved jitter for both multicontact and conventional single-contact InGaAsP-InP lasers. Subpicosecond jitter is achieved for Q-switched laser sources using a novel optoelectronic feedback scheme. The use of resonant electrical feedback is shown to improve the timing jitter of gain-switched pulses by up to six times. Pulse-to-pulse timing jitter as low as 250 fs is demonstrated for a hybrid of optical and electrical feedback schemes. Limits for timing jitter in diode lasers are established for optoelectronic, electrical, and optical feedback schemes, and the key picosecond pulse generation schemes are compared in terms of timing jitter for the first time View full abstract»

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  • 100-mW high-power angled-stripe superluminescent diodes with a new real refractive-index-guided self-aligned structure

    Page(s): 1981 - 1987
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    We have developed 100-mW high-power angled-stripe superluminescent diodes with a new angled-stripe real refractive-index guided self-aligned structure. The structure has a GaAlAs optical confinement layer on a planar active layer and an inclined current injection stripe by 5° with respect to the facet normal. The structure gives small internal loss (~10 cm-1) and facet power reflectivity less than the order of 10-6. As a result, the output power as high as 105 mW at a low operating current of 270 mA is obtained with less than 3% spectral modulation and 10.5 nm full width at half maximum (FWHM) spectral width View full abstract»

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  • Optimization of fiber-coupled laser-diode end-pumped lasers: influence of pump-beam quality

    Page(s): 2010 - 2016
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    A general model has been developed for the optimization of fiber-coupled laser-diode pumped lasers by including the effect of pump-beam quality into the mode-overlap integrals. The numerical results of the mode-overlap integrals have been fitted to an analytical function of pump spot size, laser mode size and the parameter β, which is in terms of laser-diode beam quality and properties of the active medium. This analytical function allowed us to obtain explicit formulae for the threshold pump power, the slope efficiency, and the optimum pump spot size. With these formulae, the optimum mode size and the maximum output efficiency can be easily calculated for arbitrary values of β and input power. From the numerical results, we obtained an analytical expression to relate the required input power and pump-beam quality to the desired output efficiency and properties of an active medium. The present model provides a straightforward procedure to design the laser resonator and the optical coupling system for optimization. To illustrate the utility of the present model, a Nd:YAG laser pumped by fiber-coupled laser diodes is considered and optimized View full abstract»

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  • Theory of gain spectra for quantum cascade lasers and temperature dependence of their characteristics at low and moderate carrier concentrations

    Page(s): 1995 - 2003
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    We have developed a theory describing the operation of lasers based on intersubband transitions in a quantum well. The theory combines a first-principles description of the intersubband lineshape and the optical gain with kinetic models for carrier heating. The theory is consistent with the experimental data available and suggests new ways of improving the laser design for room-temperature operation with high output power. At low carrier concentrations, it is possible to achieve positive values of the gain at room temperature even in the absence of an overall population inversion between quantum-well subbands. For higher (but still moderate) concentrations, the theory predicts a peculiar dependence of the output wavelength on the pump current, including a regime where the lasing wavelength switches “digitally” between two stable values View full abstract»

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  • pH temporal jumps and spatial inhomogeneities in acid-base dye lasers

    Page(s): 1858 - 1863
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    The possibility of obtaining temporal jumps and inhomogeneous spatial distributions of the concentration of free protons during the laser emission of a dye laser composed by two acid-base species is shown using the numerical resolution of the corresponding set of balance equations. The differences of behavior between the case of equilibrium or nonequilibrium in the excited state are stated. The possible generation of transient photoelectrochemical effects is discussed 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