Showing papers in "IEEE Journal of Quantum Electronics in 1985"
IBM1
1,793 citations
TL;DR: In this article, the quantum well self-electrooptic effect devices with a CW laser diode as the light source were shown to have bistability at room temperature with 18 nW of incident power, or with 30 ns switching time at 1.6 mW with a reciprocal relation between switching power and speed.
Abstract: We report extended experimental and theoretical results for the quantum well self-electrooptic effect devices. Four modes of operation are demonstrated: 1) optical bistability, 2) electrical bistability, 3) simultaneous optical and electronic self-oscillation, and 4) self-linearized modulation and optical level shifting. All of these can be observed at room-temperature with a CW laser diode as the light source. Bistability can be observed with 18 nW of incident power, or with 30 ns switching time at 1.6 mW with a reciprocal relation between switching power and speed. We also now report bistability with low electrical bias voltages (e.g., 2 V) using a constant current load. Negative resistance self-oscillation is observed with an inductive load; this imposes a self-modulation on the transmitted optical beam. With current bias, self-linearized modulation is obtained, with absorbed optical power linearly proportional to current. This is extended to demonstrate light-by-light modulation and incoherent-to-incoherent conversion using a separate photodiode. The nature of the optoelectronic feedback underlying the operation of the devices is discussed, and the physical mechanisms which give rise to the very low optical switching energy (∼4 fJ/ μm2) are discussed.
533 citations
TL;DR: In this article, a line broadening up to 25 GHz in a singlemode semiconductor laser with relatively strong optical feedback is reported and theoretically analyzed, based on the view that coherence collapse is maintained due to optical-feedback-delay effects, in which quantum fluctuations play no role of importance.
Abstract: Line broadening up to 25 GHz in a single-mode semiconductor laser with relatively strong optical feedback is reported and theoretically analyzed. Measurements of the coherence function were performed using a Michelson interferometer and demonstrate that the coherence length decreases by a factor 1000 (to approximately 10 mm) due to optical feedback. A self-consistent theoretical description is given, which is based on the view that coherence collapse is maintained due to optical-feedback-delay effects, in which quantum fluctuations play no role of importance. A connection with recently suggested chaotic behavior is made. The theoretical results obtained are in good qualitative and reasonable quantitative agreement with measurements.
480 citations
TL;DR: In this paper, a theoretical and experimental investigation of injection locking of semiconductor lasers is presented, taking into account the dependence of refractive index on the carrier density expressed by the linewidth enhancement factor α.
Abstract: We present a theoretical and experimental investigation of injection locking of semiconductor lasers. The theoretical analysis takes into account the dependence of refractive index on the carrier density expressed by the linewidth enhancement factor α. Locking conditions and dynamic stability are analyzed. The nonzero value of α results in an increased locking bandwidth, where only part of the range corresponds to a dynamically stable state. Asymmetric characteristics are obtained for the locked power and phase as a function of frequency detuning between the master and slave laser. Outside the stable range, light injection gives rise to beat phenomena and intensity pulsations. The theoretical results were confirmed by experiments on 830 nm CSP lasers and 1.3 μm BH lasers. The experiments include the first measurements of locking bandwidth characteristics reported for 1.3 μm lasers. Power spectra are recorded under locked and near-locked conditions and compared with theory. The 1.3 μm lasers are found to have a better dynamic stability than 830 nm lasers. Even so, the stability problems may exclude the particular application of injection locking where phase modulation is generated for coherent transmission.
432 citations
TL;DR: In this article, the effect of radiation losses on the mode selectivity of DFB laser with second-order gratings was studied, and it was shown that interference of the radiation due to first-order diffraction of oppositely propagating guided waves cancels the radiation loss at one of the edges of the spectrum gap.
Abstract: We present a theoretical study of the effect of radiation losses on the mode selectivity of DFB lasers with second-order gratings. For a second-order grating, interference of the radiation due to first-order diffraction of oppositely propagating guided waves cancels the radiation loss at one of the edges of the spectrum gap. This provides threshold gain discrimination of order 10 cm-1against one of the two dominant modes occurring near the edges of the gap. This should allow fabrication of DFB lasers with properties that are nearly independent of the positions of the facets relative to the grating corrugations, which are uncontrolled. By applying antireflection coatings to the two ends, differential quantum efficiencies close to those of conventional Fabry-Perot lasers should be achievable.
333 citations
TL;DR: In this article, the authors investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers, and reveal the existence of gain saturation with current in structures with a small number of wells, pointing to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.
Abstract: We investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers. These include a basic derivation of the laser gain, the linewidth enhancement factor α, and the differential gain constant in single and multiple QW structures. The results reveal the existence of gain saturation with current in structures with a small number of wells. They also point to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.
269 citations
TL;DR: In this article, the density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments, which is given theoretically by the k. p method and is calculated for various semiconductor materials.
Abstract: The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by the k . p method and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region are calculated. It is found that the linear gain is larger for longer wavelength lasers and that the gain-suppression is much larger for longer wavelength lasers, which results in that single-mode operation is more stable in long-wavelength lasers than in shorter-wavelength lasers, in good agreement with the experiments.
265 citations
TL;DR: In this article, the authors examined the possibilities of further extending the bandwidth of semiconductor lasers and discussed the issues related to application of these lasers in actual systems, but they did not consider the application of such lasers in real-world systems.
Abstract: Recent progress on semiconductor lasers having a very high direct modulation bandwidth of beyond 10 GHz will be described. Issues related to application of these lasers in actual systems will be addressed. Possibilities of further extending the bandwidth of semiconductor lasers will be examined.
254 citations
TL;DR: In this article, the authors derived the gain/current curves for a single quantum well and the optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers.
Abstract: Gain/current curves for a single quantum well are calculated. The optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers are derived in terms of this gain curve. The limiting performance of MQW lasers is found to be better than that of graded refractive index (GRIN) lasers, assuming comparable efficiencies and spontaneous emission linewidths. The optimum threshold current for an MQW laser with a 7 μm cavity and 90 percent facet reflectivity is \sim50 \mu A/μm.
253 citations
TL;DR: The dispersion relations for TE polarized waves guided by thin dielectric (planar integrated optics) films, surrounded on one or both sides by media with intensity-dependent refractive indexes, are solved numerically and interpreted in this paper.
Abstract: The dispersion relations for TE polarized waves guided by thin dielectric (planar integrated optics) films, surrounded on one or both sides by media with intensity-dependent refractive indexes, are solved numerically and interpreted. Comparisons are made between these nonlinear guided waves and the usual integrated optics modes associated with linear media. For media characterized by self-defocusing nonlinearities, increasing guided wave power leads to a decrease in the guided wave effective index and to mode cutoffs characterized either by finite or diverging total guided wave powers. For self-focusing media, the effective index increases with increasing power. New wave solutions are obtained with power thresholds and anomalous power-dependent field distributions. These characteristics are illustrated by numerical calculations for a specific material system and possible applications to optical devices are discussed.
192 citations
TL;DR: In this paper, the authors measured the intensity of an injection-locked 1.54 μm InGaAsP laser and found that the change in intensity across the locking range is quite asymmetric, with a shape that agrees well with the theory of Lang.
Abstract: Measurements of the intensity of an injection locked 1.54 μm InGaAsP laser are reported. The change in intensity of the locked laser across the locking range is quite asymmetric, with a shape that agrees well with the theory of Lang. A linewidth parameter of \alpha = 6 \pm 1 was determined from the magnitude of the locking range. The injection locked laser was found to be unstable on the high frequency end of the locking range. The physical origin of this instability is explained in terms of a laser intensity change altering the phase of the laser field relative to that of the injected field.
TL;DR: In this article, the authors show that wavelength excursions with magnitudes as large as 6 A are seen to occur in single frequency lasers (both C3and DFB) during a transition from one power level to another.
Abstract: Wavelength excursions with magnitudes as large as 6 A are seen to occur in single frequency lasers (both C3and DFB) during a transition from one power level to another. The wavelength shifts briefly toward shorter wavelengths and then back to the equilibrium value during turn-on and toward longer wavelengths and back during turn-off. These excursions, which are well explained by a model in which the carrier density is temporarily driven out of equilibrium by a change in injection current, last for hundreds of picoseconds or about one half of the relaxation resonance period. This time dependent behavior gives rise to a dramatic degradation of lightwave system performance with increasing bit rate. Laser structures which heavily damp the relaxation resonance peak are seen to exhibit the least chirp and to perform best in high speed transmission systems.
TL;DR: In this article, the authors used two-photon absorption, self-defocusing, and optically-induced melting in GaAs to limit 1 μm picosecond pulsed radiation.
Abstract: We have used two-photon absorption, self-defocusing, and optically-induced melting in GaAs to limit 1 μm picosecond pulsed radiation. The contribution to the limiting action from each of these mechanisms is discussed and demonstrated. Additionally, we measure a two-photon absorption coefficient of 26 cm/GW, which is in good agreement with the smallest values reported in the literature. A pulse-width study of the nonlinear absorption was conducted to isolate the effects of two-photon-generated free-carrier absorption. Results indicate that, even though the number of free-carriers is sufficient to severely defocus the incident beam, free-carrier absorption does not measurably contribute to the nonlinear absorption.
TL;DR: In this paper, basic spectroscopy of Co:MgF 2, a determination of the gain cross section, the efficiency and temporal behavior under pulsed excitation, and performance in the Q-switched mode are discussed.
Abstract: The Co:MgF 2 laser, tunable over the range from 1.5 to 2.3 μm, has been investigated under a variety of operating conditions. Included in this paper are reports on basic spectroscopy of Co:MgF 2 , a determination of the gain cross section, the efficiency and temporal behavior under pulsed excitation, and performance in the Q -switched mode. In addition, operation with thermoelectric cooling and CW oscillation at the multiwatt power level are discussed. Equations covering laser-pumped lasers are derived and comparisons between experiments and theory are presented.
TL;DR: In this article, a new optical modulator has been fabricated which uses the recently discovered electroabsorption effect in MQW's and optical pulses 131 ps long were generated when the device was driven with 122 ps electrical pulses.
Abstract: A new optical modulator has been fabricated which uses the recently discovered electroabsorption effect in MQW's. Optical pulses 131 ps long were generated when the device was driven with 122 ps electrical pulses. The input-output characteristics of the device show that it has low insertion loss with reasonable modulation depth and drive voltage.
Journal Article•
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TL;DR: In this article, the fundamental mechanisms that limit the performance of a given technology are quantified, and a figure of merit, the product of bit rate times maximum repeater spacing, is estimated.
Abstract: This paper presents an introduction to the principles of lightwave system engineering. The treatment is historical rather than categorical-lightwave systems are described in terms of their evolution through four generations of technology, from a first generation operating at 0.85 μm wavelength over multimode fiber to a fourth generation employing coherent techniques at 1.55 μm. Basic engineering considerations such as fiber dispersion and receiver sensitivity are introduced early, then refined as the discussion progresses toward higher-performance, more sophisticated systems. The fundamental mechanisms that limit the performance of a given technology are quantified, and a figure of merit, the product of bit rate times maximum repeater spacing, is estimated. Values of this product range from about 2 Gbits/s . km for first-generation technology to roughly 900 Gbits/s . km for coherent systems.
TL;DR: In this paper, a parallel development of the semiclassical and quantum statistics of multispatiotemporal mode direct, homodyne, and heterodyne detection using an ideal (except for its subunity quantum efficiency) photon detector is presented.
Abstract: A parallel development of the semiclassical and quantum statistics of multispatiotemporal mode direct, homodyne, and heterodyne detection using an ideal (except for its subunity quantum efficiency) photon detector is presented. Particular emphasis is placed on the latter two coherent detection Configurations. The primary intent is to delineate the semiclassical theory's regime of validity and to show, within this regime of validity, how the quantum theory's signal quantum noise, local oscillator quantum noise, the quantum noise incurred because of subunity detector quantum efficiency, plus (for heterodyning only) image band quantum noise produce the quantitative equivalent of the semiclassical theory's local oscillator shot noise. The effects of classical fluctuations on the local oscillator, and the recently suggested dual-detector arrangement for suppressing these fluctuations, are treated. It is Shown that previous studies of this arrangement have neglected a potentially significant noise contribution.
TL;DR: In this article, the authors review performance achievements for a variety of pulsed and CW laser configurations including singlemode, multimode, and mode-locked resonators, high-power amplifiers, and zig-zag slabs.
Abstract: Some major recent developments in alexandrite laser research are reviewed. Emphasis is placed on key material characteristics, and their relationship to laser performance. Alexandrite's favorable thermomechanical properties and high capacity for energy storage have led to laser performance levels that, in certain areas, exceed those of established solid-state laser sources. Here we review performance achievements for a variety of pulsed and CW laser configurations including single-mode, multimode, and mode-locked resonators, high-power amplifiers, and zig-zag slabs. In these configurations, operating performance levels have been demonstrated that are comparable to those of older, more familiar solid-state laser technologies. Alexandrite's broad tunability offers additional advantages. Together with nonlinear frequency conversion processes, alexandrite lasers provide high-brightness output over most of the UV, visible, and near IR.
TL;DR: In this paper, the authors present two methods for calculating the thermally induced stress, focusing, and depolarization in a pumped zigzag-slab solid-state laser.
Abstract: This paper presents two methods for calculating the thermally induced stress, focusing, and depolarization in a pumped zigzag-slab solid-state laser. A computer program capable of detailed calculations of thermal effects in the general case is described. An approximate analysis of slab thermal effects in many cases allows calculation of these effects without use of the computer model directly. The analysis predicts that slabs of square cross section can be designed to have low depolarization and thermal focusing compared to Nd:YAG laser rods.
TL;DR: In this article, a comparison between optical bistability in laser amplifiers and in passive Fabry-Perot cavities is presented, showing that amplifiers have advantages of lower input intensity requirements and reduced sensitivity to wavelength by comparison with passive cavities.
Abstract: A comparison is presented between optical bistability in laser amplifiers and in passive Fabry-Perot cavities. The basis for comparison is afforded by a new analysis of optical amplifiers which encompasses the cases of passive refractive and absorptive bistability as special limiting cases. The results indicate that amplifiers have advantages of lower input intensity requirements (by a factor of 103) and reduced sensitivity to wavelength by comparison with passive cavities; experimental results indicate an input power of -30 dBm is required for active bistability. Facet coating requirements for active and passive optimum configurations are also discussed.
TL;DR: The arsenic composition depends on electron and hole ionization coefficients, α and β, in this article, where α is the electron ionization coefficient and β is the hole ionisation coefficient.
Abstract: The arsenic composition dependences of electron and hole ionization coefficients, α and β, in
TL;DR: In this article, a simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given.
Abstract: A simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser, and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given. The dynamic spectral width of a DSM laser is determined by the modulated optical shape and the linewidth enhancement factor α. The spectral width caused by the dynamic wavelength shift is shown to be larger by ( 1 + \alpha^{2} )1/2than that caused by the sideband of the signal of the intensity modulation. Furthermore, the maximum transmission bandwidth of a conventional single-mode fiber with a DSM laser is expressed by using the parameter α and the chromatic dispersion of the fiber. The product of the maximum bit rate and the square root of the fiber length at the wavelength of 1.55 μm is estimated to be about 25 Gbit/s . km1/2.
TL;DR: In this article, a comprehensive theory of the behavior of electromagnetic waves in a potential device that consists of a thin, opticaliy linear film, bounded by dissimilar semi-infinite nonlinear materials with frequency and wavenumber independent parameters is presented.
Abstract: This paper contains a comprehensive theory, supported by many numerical examples, of the behavior of electromagnetic waves in a potential device that consists of a thin, opticaliy linear film, bounded by dissimilar semiinfinite nonlinear materials with frequency- and wavenumber-independent parameters. The relationship between the electric field amplitudes on the respective boundaries of the film leads to an elegant analysis that results in physical quantities being derived without a quantitative knowledge of the nonlinear fields. Guided and surface waves are precisely differentiated from each other, and it is shown that the linear cutoff criterion generalizes, when nonlinearity is added, to a novel changeover condition. The nonlinear eigenvalue equations are used to give the guided/surface mode index in terms of the optical power density at one of the interfaces. The power flow down the guide is then calculated both as a function of the interfacial optical power density and as a function of the mode index. These are shown to lead to two different sets of dispersion curves labeled with power flow down the guide or the optical power density at the interface. Finally, by assuming that the nonlinear media are lossy, optical hysteresis is shown to be possible.
TL;DR: In this paper, the effects of phase slip on gain threshold and mode discrimination in a distributed feedback laser were investigated with attention given to the practical aspects of today's semiconductor lasers in the 1.5 μm region.
Abstract: The effects of a periodicity interruption (phase slip) in distributed feedback lasers are investigated with attention given to the practical aspects of today's semiconductor lasers in the 1.5 μm region. We find that effects on gain threshold and mode discrimination should be large and favorable if the size and placement of a phase slip are correct.
TL;DR: In this article, the authors studied the mechanism and the dynamics of degenerate four-wave mixing in a nematic liquid crystal film, where nanosecond laser pulses are used to generate an index grating associated with the changes in the density and in the order parameter.
Abstract: We have studied the mechanism and the dynamics of degenerate four-wave mixing in a nematic liquid crystal film. Nanosecond laser pulses are used to generate an index grating associated with the changes in the density and in the order parameter. We have measured and analyzed the contributions from these two mechanisms, their interference effects rise and decay time constants, and have also performed a detailed analysis of the diffraction efficiency. This study quantitatively characterizes the potential usefulness of nematie films for four-wave mixing based applications.
TL;DR: In this paper, the characteristics of the amplified pulses have been investigated as a function of wavelength, pulse duration, and the pressure in the gain medium, using a high-power pulse compression technique.
Abstract: Picosecond pulses, generated by semiconductor switching (2-40 ps), have been regeneratively amplified to an energy density of ∼1.5 J/cm2in a multiatmosphere CO 2 laser. The characteristics of the amplified pulses have been investigated as a function of wavelength, pulse duration, and the pressure in the gain medium. Using a high-power pulse compression technique, 10 μm pulses as short as 600 fs have been obtained.
TL;DR: In this paper, bistability in semiconductor lsaer injection locking is demonstrated for the first time in the output versus frequency detuning curve, using DFB lasers for both injecting and injected lasers in order to maintain a single longitudinal mode operation, even at a near laser threshold.
Abstract: Experimental observations of bistability in semiconductor lsaer injection locking are demonstrated for the first time in the output versus frequency detuning curve. This is accomplished using DFB lasers for both injecting and injected lasers in order to maintain a single longitudinal mode operation, even at a near laser threshold. The essential mechanism giving rise to the bistability is the carrier density dependence of the refractive index in the active region. Bistability in injected laser output is also observed when the injecting laser drive current changes.
TL;DR: In this article, the authors reported measurements of the distribution of 90° radiation loss along the length of an optically pumped distributed feedback resonator having a second-order grating and nonreflecting ends.
Abstract: We report measurements of the distribution of 90° radiation loss along the length of an optically pumped distributed feedback resonator having a second-order grating and nonreflecting ends. The loss is strong at the ends, but nearly cancels at the center due to destructive interference of the scattered radiation from the oppositely propagating waves forming the lasing mode. This is the first observation of this interference effect, which provides an important source of single mode selection in distributed feedback lasers with second-order gratings.
TL;DR: The growth, spectroscopy, and lasing of titanium-doped sapphire are discussed in this paper, with particular attention paid to the problems of achieving high-quality laser material and to the identification and elimination of defects that currently limit Ti:Al 2 O 3 laser performance.
Abstract: The growth, spectroscopy, and lasing of titanium-doped sapphire are discussed. Particular attention is given to the problems of achieving high-quality laser material and to the identification and elimination of defects that currently limit Ti:Al 2 O 3 laser performance.
TL;DR: In this article, the spectral dependence of material gain and spontaneous emission in semiconductor laser amplifiers has been analyzed and it has been shown that for reflectivities below about 1 percent, increased spontaneous emission imposes more stringent limits on current density than realized hitherto.
Abstract: We present results of a new model of semiconductor laser amplifiers which differs from previous analyses in that it includes the spectral dependence of material gain and spontaneous emission. The implications of low facet reflectivities are explored in some detail. For reflectivities below about 1 percent, the increased spontaneous emission imposes more stringent limits on current density than realized hitherto. If thermal runaway is to be avoided and gains in the range of 20-30 dB are to be achieved without excessive currents, then facet reflectivities on the order of 0.1-1 percent are probably optimal. Another consequence of including the spectral dependence is that wavelengths longer than that corresponding to the unsaturated gain peak are predicted to experience enhanced amplification at high input powers by comparison to shorter wavelengths.