Showing papers on "Semiconductor optical gain published in 1999"

Demonstration of optical synchronization of chaotic external-cavity laser diodes

Abstract: An experimental demonstration of optical synchronization of chaotic external-cavity semiconductor laser diodes is reported for what is believed to be the first time. It is shown that at an optimum coupling strength between the master and the slave lasers high-quality synchronization can be obtained.

Low-loss Al-free waveguides for unipolar semiconductor lasers

Abstract: A promising waveguide design for midinfrared (λ=5–20 μm) unipolar semiconductor lasers is proposed and demonstrated in (Al)GaAs quantum cascade structures. In the latter, the active region is embedded between two GaAs layers, with an appropriate doping profile which allows optical confinement, with low waveguide losses and optimal heat dissipation. Low internal cavity losses of 20 cm−1 have been measured using different techniques for lasers with emission wavelength at ∼9 μm. At 77 K, these devices have peak output power in excess of 550 mW and threshold current of 4.7 kA/cm2.

Determination of single-pass optical gain and internal loss using a multisection device

Abstract: We describe a technique for the measurement of optical gain and loss in semiconductor lasers using a single, multisection device. The method provides a complete description of the gain spectrum in absolute units and over a wide current range. Comparison of the transverse electric and transverse magnetic polarized spectra also provides the quasi-Fermi-level energy separation. Measurements on AlGaInP quantum well laser structures with emission wavelengths close to 670 nm show an internal loss of 10 cm−1 and peak gain values up to 4000 cm−1 for current densities up to 4 kA cm−2.

Polarization switching of a vertical-cavity semiconductor laser as a Kramers hopping problem

Abstract: We report stochastic polarization switching in vertical-cavity semiconductor lasers, with residence times that vary by 8 orders of magnitude for a single such laser by changing its switch current with a hot-spot technique. In spite of the potentially complicated polarization dynamics of these lasers, the experimental results agree with Kramers hopping in a 1D double-well potential initiated by quantum fluctuations. We confirm the validity of this surprisingly simple theoretical model by independent measurements of the potential barrier between the wells and the spontaneous emission noise strength.

Double-locked laser diode for microwave photonics applications

Abstract: Semiconductor lasers subjected to near-resonant external optical injection can exhibit strong oscillations of the output power due to a dynamic instability in the coupling of the gain medium to the circulating optical field. The oscillation frequency depends on the operating point of the injected laser and the strength and frequency offset of the injected optical signal. Adding a reference current modulation to the dc-bias current can induce the oscillation frequency of the optical power to become locked to the reference. Tunable, locked output from 9.5 to 17.1 GHz is demonstrated, with a linewidth below the 1-kHz resolution limit of the measurement apparatus.

Demonstration of phase correlation in multiwavelength mode-locked semiconductor diode lasers.

Abstract: Wideband spectral phase correlation is demonstrated from a multiwavelength mode-locked semiconductor laser. By use of frequency-resolved optical gating techniques, significant phase correlation was observed between multiple intracavity oscillating wavelengths, with wavelength separations of ?1 nm. The resultant temporal characteristics show a substantial modulation owing to the spectral coupling induced by intracavity-generated four-wave mixing. This result may lead to novel methods for directly generating ultrafast subpicosecond optical pulse sequences with spectrally tailored amplitude and phase characteristics from actively mode-locked semiconductor lasers.

Improved theory of the refractive-index change in quantum-well lasers

Abstract: An improved theory of the change of the real part of the dielectric function in quantum-well lasers is presented. New formulas for the intraband component are given, which allow for the first time to take into account all possible optical transitions on equal footing. As an application, the dependence of the change of the effective index on the modal gain is investigated.

Room-temperature gain at 1.3 μm in PbS-doped glasses

Abstract: We report on room-temperature optical gain at the ground exciton transition of PbS quantum-dot-doped glasses while optical pumping into the next-higher exciton resonance. The material gain in the quantum dots is as large as 80 cm−1. The dot-size selective excitation provides tunability of the optical gain. This is demonstrated by tuning the gain from 1317 to 1352 nm by changing the pump wavelength from 900 to 980 nm.

Epitaxially-stacked multiple-active-region 1.55μm lasers for increased differential efficiency

Abstract: Semiconductor lasers emitting at 1.55 μm with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. This is accomplished by epitaxially stacking a number of p–i–n multiquantum well active regions with intermediate n++–p++ back diodes, which enable the entire terminal current to flow through each active region stages in series. Such lasers should also improve the impedance match as well as provide for low-noise, high-efficiency microwave links.

The modulation response of a semiconductor laser amplifier

Abstract: We present a theoretical analysis of the modulation response of a semiconductor laser amplifier. We find a resonance behavior similar to the well-known relaxation oscillation resonance found in semiconductor lasers, but of a different physical origin. The role of the waveguide (scattering) loss is investigated in detail and is shown to influence the qualitative behavior of the response. In particular, it is found that a certain amount of waveguide loss may be beneficial in some cases. Finally, the role of the microwave propagation of the modulation signals is investigated and different feeding schemes are analyzed. The nonlinear transparent waveguide, i.e., an amplifier saturated to the point where the stimulated emission balances the internal losses, is shown to be analytically solvable and is a convenient vehicle for gaining qualitative understanding of the dynamics of modulated semiconductor optical amplifiers.

Time-domain modeling of semiconductor optical amplifiers for OTDM applications

Abstract: An advanced time-domain dynamical model for the investigation of semiconductor optical amplifiers (SOA) is presented. The model accounts for the ultrafast gain dynamics, the gain saturation and the gain spectral profile. It is also suitable for analyzing the amplifier in a system environment. As an example the model is used to investigate the gain dynamics of an SOA as well as the characteristics of an interferometer switch semiconductor laser amplifier in a loop mirror (SLALOM). Good agreement between modeling and experiment is shown. The model can be applied to the investigation of other optically time-division multiplexed (OTDM) applications, too.

Image display and light-emitting device

Abstract: A liquid crystal projector having a simple optical system and operating at a high efficiency of use of light, comprises a light-emitting device (50), a parallel transforming optical system (60), an optical switch (70), and a display optical system (80). The light-emitting device (50) includes LD arrays (51, 52, 53) where semiconductor lasers (54) are arranged two-dimensionally. The output beams from the semiconductor lasers (54) are transformed into parallel beams by means of the lens arrays (61, 62, 63). Since the output beams from the semiconductor lasers (54) are linearly P- or S-polarized, no polarization transforming optical system is needed. By adequately combining semiconductor lasers (54), the shapes of the LD arrays (51, 52, 53) can be the same as those for light utilization of a red-light transmission liquid crystal panel (71), a green-light transmission liquid crystal panel (72), and a blue-light transmission liquid crystal panel (73).

Measurement of semiconductor laser gain and dispersion curves utilizing Fourier transforms of the emission spectra

Abstract: A new technique for the measurement of semiconductor laser gain and dispersion spectra is presented. The technique is based on an analysis of the subthreshold emission spectrum by Fourier transforms. Applications of this method to AlGaInP-based interband laser diodes and mid-infrared intersubband quantum cascade lasers are discussed. A good agreement between the measured dispersion of the refractive index and tabulated values in the literature was found.

Frequency-doubled vertical-external-cavity surface-emitting laser

Abstract: A frequency-doubled semiconductor vertical-external-cavity surface-emitting laser (VECSEL) is disclosed for generating light at a wavelength in the range of 300-550 nanometers. The VECSEL includes a semiconductor multi-quantum-well active region that is electrically or optically pumped to generate lasing at a fundamental wavelength in the range of 600-1100 nanometers. An intracavity nonlinear frequency-doubling crystal then converts the fundamental lasing into a second-harmonic output beam. With optical pumping with 330 milliWatts from a semiconductor diode pump laser, about 5 milliWatts or more of blue light can be generated at 490 nm. The device has applications for high-density optical data storage and retrieval, laser printing, optical image projection, chemical-sensing, materials processing and optical metrology.

Low-frequency fluctuations in vertical-cavity surface-emitting semiconductor lasers with optical feedback

Abstract: We study the dynamics of a vertical-cavity surface-emitting laser operating near threshold and with isotropic optical feedback, using a model developed by San Miguel, Feng, and Moloney [Phys. Rev. A 52, 1728 (1995)]. The model couples the polarization state of the electric field to the semiconductor medium by including the magnetic sublevels of the conduction and valence bands in the quantum wells. The laser dynamics depend significantly on the value of the relaxation rate, ${\ensuremath{\gamma}}_{s},$ of the material magnetization. For low relaxation rates the time-averaged intensity abruptly drops to zero and then recovers, a phenomenon revealed to be a sequence of picosecond pulses. The dropouts are similar to those occurring in conventional semiconductor lasers, but underlying the dropouts there is an antiphase competition between the time-averaged orthogonal linearly polarized components of the electric field. For large values of the relaxation rate, the dropouts tend to disappear and the time-averaged intensity is nearly constant.

High-sensitivity intracavity laser absorption spectroscopy with vertical-external-cavity surface-emitting semiconductor lasers

Abstract: We report the demonstration of high-sensitivity intracavity laser absorption spectroscopy with multiple-quantum-well vertical-external-cavity surface-emitting semiconductor lasers (VECSEL's). A detection limit of 3 x 10(-10) cm (-1) has been achieved. The spectrotemporal dynamics of a VECSEL in the 1030-nm wavelength region has been studied. The laser was operating cw at room temperature, with a baseline signal-to-noise ratio as high as 400. The laser was optically pumped with a threshold as low as 80 mW and was broadly tunable over a spectral range of approximately 75 nm .

Influence of amplitude-phase coupling on the dynamics of semiconductor lasers subject to optical feedback

Abstract: We present extensive experimental investigations of the dynamics of semiconductor lasers subject to optical feedback in dependence on the linewidth enhancement factor \ensuremath{\alpha} which accounts for the amplitude phase coupling of the optical field. A reduction of \ensuremath{\alpha} leads to conspicuous changes of the dynamics of the system which are characterized and classified in the phase space of feedback strength versus injection current, thus demonstrating the importance of \ensuremath{\alpha} as the system's main nonlinearity. In particular, we demonstrate a drastic extension of the regime of coexistence between coherence collapsed dynamics and stable emission, and an increased stability of this stable emission state. We show that a theoretical analysis of the Lang-Kobayashi rate equation model provides a qualitative understanding of the physical mechanisms underlying the observed dynamical behavior and its dependence on \ensuremath{\alpha}. Finally, being able to control the nonlinearity of the system, we open up new perspectives for the stabilization of semiconductor lasers subject to moderate to strong optical feedback.

Far-field characteristics of random lasers

Abstract: We report on experimental observation of the far-field intensity and mode distributions of random lasers. Laser emission from highly disordered semiconductor polycrystalline thin films could be observed in all directions. The angle dependence of the laser output from the edge of the film is different from that of the laser emission scattered out of the surface of the film. More lasing modes are observed from the surface of the film than from the edge of the film. A qualitative explanation of the experimental results are presented based on the laser cavities formed by optical scattering being located in the plane of the films.

Picosecond intensity statistics of semiconductor lasers operating in the low-frequency fluctuation regime

Abstract: We present detailed statistical investigations of the irregular fast pulsing behavior present in the dynamics of semiconductor lasers with delayed optical feedback operating in the low-frequency fluctuation and coherence collapse regimes. We demonstrate that the probability density distributions of the laser intensity on a picosecond time scale are essentially independent of the number of optical modes involved in the laser emission, using two complementary high-resolution experimental measurement systems: a high-bandwidth sampling digitizer and a single-shot streak camera. The experimental results are supported by numerical studies using the singlemode Lang-Kobayashi equations, as well as a multimode extension of the model. Furthermore, we also demonstrate that gain saturation and coexisting attractors can cause substantial qualitative changes of the probability density distribution. @S1050-2947 ~99!09507-4#

Switching between polarized modes of a vertical-cavity surface-emitting laser by isotropic optical feedback

Abstract: Experiments are described that show that polarization of light in a vertical-cavity surface-emitting laser subjected to isotropic optical feedback can jump regularly back and forth between two orthogonal states when the injection current is increased. The polarization-resolved light-current characteristic curves are thus channeled. This effect occurs when the dichroism of the laser is weak enough to allow the effective (isotropic) reflectance to impose the polarization. A comparison of a model introduced by San Miguel [Phys. Rev. A52, 1728 (1995)] and the standard equations indicates that the best description is given when no spin relaxation is included.

Quantum maxwell-bloch equations for spatially inhomogeneous semiconductor lasers

Abstract: We present quantum Maxwell-Bloch equations (QMBE) for spatially inhomogeneous semiconductor laser devices. The QMBE are derived from fully quantum mechanical operator dynamics describing the interaction of the light field with the quantum states of the electrons and the holes near the band gap. By taking into account field-field correlations and field-dipole correlations, the QMBE include quantum noise effects, which cause spontaneous emission and amplified spontaneous emission. In particular, the source of spontaneous emission is obtained by factorizing the dipole-dipole correlations into a product of electron and hole densities. The QMBE are formulated for general devices, for edge emitting lasers and for vertical cavity surface emitting lasers, providing a starting point for the detailed analysis of spatial coherence in the near-field and far-field patterns of such laser diodes. Analytical expressions are given for the spectra of gain and spontaneous emission described by the QMBE. These results are applied to the case of a broad area laser, for which the frequency and carrier density dependent spontaneous emission factor $\ensuremath{\beta}$ and the evolution of the far-field pattern near threshold are derived.

Quasiperiodic synchronization for two delay-coupled semiconductor lasers

Abstract: The dynamical behavior of two mutually coupled semiconductor lasers is studied experimentally, numerically, and analytically for weak coupling. The lasers have dissimilar relaxation oscillation frequencies and intensities, and their mutual coupling strength may be asymmetric. We find experimentally that the lasers preferentially entrain to the relaxation oscillation frequency of either one of the lasers. But quasiperiodic synchronization, where both relaxation oscillation frequencies appear, is possible. We show that there exist two distinct mechanisms leading to these regimes corresponding to either a bifurcation to a mixed-mode solution or a bifurcation induced by the delay of the mutually injected signal. However, only the second transition can be observed experimentally if the injection strength is continuously increased from zero.

Suppression of low-frequency fluctuations and stabilization of a semiconductor laser subjected to optical feedback from a double cavity: theoretical results.

Abstract: We demonstrate numerically that low-frequency fluctuations (LFF's) observed in a laser diode subjected to a first optical feedback with a short delay are suppressed by means of an adequate second optical feedback. The general idea of this technique is based on the observation that second feedback can suppress the antimodes that are responsible for the crises in the LFF regime. Furthermore, we observe that the second optical feedback can steer an unstable laser that is biased near threshold into a stable regime.

High-performance small vertical-cavity lasers: a comparison of measured improvements in optical and current confinement in devices using tapered apertures

Abstract: We analyze the scaling characteristics of the optical and current confinement for three different vertical-cavity surface-emitting laser (VCSEL) structures with tapered apertures. The improvements in scaling have allowed devices with apertures <3 /spl mu/m to have wall-plug efficiencies over 20% at output powers as low as 150 /spl mu/W. The combination of low threshold (<200 /spl mu/A), single modedness, and good wall-plug efficiency even at low output powers makes these devices excellent candidates for short distance (<1 m) interconnects within computers.

Dynamics of a semiconductor laser with optical feedback

Abstract: We investigate both experimentally and theoretically the dynamics of a semiconductor laser with optical feedback in the low-frequency fluctuation regime. First we demonstrate that low-frequency fluctuations can be observed for both single and multimode operation of a semiconductor laser with optical feedback. The analysis of the fast dynamics associated with this low-frequency instability is well described by single-mode rate equations. In the multimode regime, fast pulsation is observed in every laser mode. In this case the fluctuations in total intensity are much smaller than those in the intensity of each individual mode. This indicates the presence of anticorrelations dynamics at high frequency between the different laser modes.

Integrated optically pumped vertical cavity surface emitting laser

Abstract: An integrated optically pumped vertical cavity surface emitting laser (VCSEL) is formed by integrating an electrically pumped in-plane semiconductor laser and a vertical cavity surface emitting laser together with a beam steering element formed with the in-plane semiconductor laser. The in-plane semiconductor laser can be a number of different types of in-plane lasers including an edge emitting laser, an in-plane surface emitting laser, or a folded cavity surface emitting laser. The in-plane semiconductor laser optically pumps the VCSEL to cause it to lase. The in-plane semiconductor laser is designed to emit photons of relatively short wavelengths while the VCSEL is designed to emit photons of relatively long wavelengths. The in-plane semiconductor laser and the VCSEL can be coupled together in a number of ways including atomic bonding, wafer bonding, metal bonding, epoxy glue or other well know semiconductor bonding techniques. The beam steering element can be an optical grating or a mirrored surface.

Theory and Experiment of In Ga As P and In Ga Al As Long-Wavelength Strained Quantum-Well Lasers

Abstract: We present a comprehensive model for the calcu- lation of the bandedge profile of both the In Ga As P and In Ga Al As quantum-well systems with an arbitrary composition. Using a many-body optical gain model, we compare the measured net modal gain for both material systems with calculations from the realistic band structure including valence band mixing effects. Calibrated measurements of the side light spontaneous emission spectrum based on its fundamental relation to the optical gain spectrum give values for the radiative current density. These measurements allow us to extract the relationship between total current density and carrier density. A fit of this relation yields values for the Auger coefficient for each material system. In this paper, we present a comprehensive model for the calculation of the band structure of samples made of either of these systems with an arbitrary composition. Then, using a many-body model for the optical gain and spontaneous emission, we compare the model to experimental data for each material system. Also, from simultaneous measurements of both the spontaneous emission spectrum from the side of the lasers and the gain spectrum from the facet emission, we are able to compare the relative contributions of the different recombination mechanisms in each laser system. In Section II, we present our model for the calculation of the bandedge of each material system and the quantum-well (QW) band edge discontinuities, followed by the model for the optical gain and spontaneous emission. In Section III, we describe the structure of the lasers as well as our experimental measurements. Section IV describes the comparison of the optical gain data with calculations using our model, and the extraction of the relative contributions of the recombination mechanisms in each system. Finally, a brief conclusion is given in Section V.

Semiconductor laser array and its manufacturing method, optical integrated unit and optical pickup

Abstract: A semiconductor laser array including a plurality of index-guided semiconductor lasers different in oscillation wavelength is made by collectively controlling their double transverse modes and collectively processing them to form their current-blocking structures and buried layers. Thus, a semiconductor laser having a flat element surface and excellent in heat radiation can be made in a reduced number of manufacturing steps. When the laser array of this multi-wavelength type and a detector PD are mounted with a predetermined positional relationship, return light from an optical disk can be converted into a single point to enable detection thereof at PD on one chip. Therefore, an optical disk driving apparatus remarkably reduced in size and weight and having a high reliability can be realized.

Electrical polarization control of vertical-cavity surface-emitting lasers using polarized feedback and a liquid crystal

Abstract: We report electrical control of the polarization state of a vertical-cavity surface-emitting laser (VCSEL), The VCSEL is subject to strong external optical feedback (up to 6% of emission), with polarization controlled by a liquid-crystal (LC) element, It is found that the contrast ratio of the complete system can be enhanced compared to the contrast ratio of the LC element alone.