Showing papers on "Semiconductor optical gain published in 2007"

Photonics : optical electronics in modern communications

Abstract: 1. Electromagnetic Fields and Waves 2. Rays and Optical Beams 3. Dielectric Waveguides and Optical Fibers 4. Optical Resonators 5. Interaction of Radiation and Atomic Systems 6. Theory of Laser Oscillation and Some Specific Laser Systems 7. Chromatic Dispersion and Polarization Mode Dispersion in Fibers 8. Nonlinear Optics 9. Electro-Optics and AO modulators 10. Noise in Optical Detection and Generation 11. Detection of Optical Radiation 12. Periodic Structures 13. Waveguide Coupling 14. Nonlinear Optical Effects in Fibers 15. Semiconductor Lasers 16. Advanced Semiconductor Lasers 17. Optical Amplifiers 18. Classical Treatment of Quantum Optics, Quantum Noise, and Squeezing A. WAVE EQUATION IN CYLINDRICAL COORDINATES AND BESSEL FUNCTIONS B. EXACT SOLUTIONS OF THE STEP-INDEX CIRCULAR WAVEGUIDE C. KRAMERS-KRONIG RELATIONS D. TRANSFORMATION OF A COHERENT ELECTROMAGNETIC FIELD BY A THIN LENS E. FERMI LEVEL AND ITS TEMPERATURE DEPENDENCE F. ELECTRO-OPTIC EFFECT IN CUBIC 43M CRYSTALS G. CONVERSION FOR POWER UNITS AND ATTENUATION UNITS

Single-exciton optical gain in semiconductor nanocrystals

Abstract: Nanocrystal quantum dots have favourable light-emitting properties. They show photoluminescence with high quantum yields, and their emission colours depend on the nanocrystal size—owing to the quantum-confinement effect—and are therefore tunable. However, nanocrystals are difficult to use in optical amplification and lasing. Because of an almost exact balance between absorption and stimulated emission in nanoparticles excited with single electron–hole pairs (excitons), optical gain can only occur in nanocrystals that contain at least two excitons. A complication associated with this multiexcitonic nature of light amplification is fast optical-gain decay induced by non-radiative Auger recombination, a process in which one exciton recombines by transferring its energy to another. Here we demonstrate a practical approach for obtaining optical gain in the single-exciton regime that eliminates the problem of Auger decay. Specifically, we develop core/shell hetero-nanocrystals engineered in such a way as to spatially separate electrons and holes between the core and the shell (type-II heterostructures). The resulting imbalance between negative and positive charges produces a strong local electric field, which induces a giant (∼100 meV or greater) transient Stark shift of the absorption spectrum with respect to the luminescence line of singly excited nanocrystals. This effect breaks the exact balance between absorption and stimulated emission, and allows us to demonstrate optical amplification due to single excitons. Semiconductor nanocrystals have very good light-emitting properties, so have potential as optical amplification media that can be easily processed with solution-based techniques: possible applications include optical interconnects in microelectronics, lab-on-a-chip technologies and quantum information processing. The problem with these structures is that at least two excitons (bound electron–hole pairs) need to be present in a nanocrystal before optical gain can be achieved, and this limits performance. In effect, the excitons annihilate each other before optical amplification can occur. This obstacle has now been overcome using nanocrystals with cores and shells made from different semiconductor materials, constructed in such a way that electrons and holes are separated from each other. This makes optical gain based on single excitons possible, significantly enhancing their promise as a practical optical material for laser applications. Semiconductor nanocrystals seem good candidates for 'soft' optical gain media, but optical gain and lasing is hard to achieve owing to a fundamental optical effect, which involves the problem that at least two excitons need to be present in a nanocrystal to achieve gain, and this limits performance. Here the problem is circumvented by designing nanocrystals with cores and shells made from different semiconductor materials, and in such a way that electrons and holes are separated from each other: this makes possible optical gain based on single excitons, thereby significantly enhancing the promise of semiconductor nanocrystals as practical optical materials for a wide range of lasing applications.

Photon statistics of semiconductor microcavity lasers.

Abstract: We present measurements of first- and second-order coherence of quantum-dot micropillar lasers together with a semiconductor laser theory. Our results show a broad threshold region for the observed high-beta microcavities. The intensity jump is accompanied by both pronounced photon intensity fluctuations and strong coherence length changes. The investigations clearly visualize a smooth transition from spontaneous to predominantly stimulated emission which becomes harder to determine for high beta. In our theory, a microscopic approach is used to incorporate the semiconductor nature of quantum dots. The results are in agreement with the experimental intensity traces and the photon statistics measurements.

Excitability in a quantum dot semiconductor laser with optical injection.

Abstract: We experimentally analyze the dynamics of a quantum dot semiconductor laser operating under optical injection. We observe the appearance of single- and double-pulse excitability at one boundary of the locking region. Theoretical considerations show that these pulses are related to a saddle-node bifurcation on a limit cycle as in the Adler equation. The double pulses are related to a period-doubling bifurcation and occur on the same homoclinic curve as the single pulses.

Phase-resolved measurements of stimulated emission in a laser.

Abstract: Laser radiation is usually measured with detectors that determine frequency and intensity, but gather no information about the phase of the radiation. By measuring the phase it would become possible to gain insights in the dynamic processes of optical amplification and attenuation underlying laser operation. Kroll et al. have now developed a way of measuring amplitude as well as phase of laser radiation from so-called quantum cascade lasers, which operate in the terahertz regime. The technique, which could be extended to other types of lasers, can be used to study effects leading to optical losses — useful information to improve the laser performance. Laser radiation is usually measured with intensity detectors that determine frequency and intensity, but throw away information about the phase of the radiation. But a scheme has been developed to measure amplitude as well as phase of laser radiation from so-called quantum cascade lasers, which operate in the terahertz regime. Lasers are usually described by their output frequency and intensity. However, laser operation is an inherently nonlinear process. Knowledge about the dynamic behaviour of lasers is thus of great importance for detailed understanding of laser operation and for improvement in performance for applications. Of particular interest is the time domain within the coherence time of the optical transition. This time is determined by the oscillation period of the laser radiation and thus is very short. Rigorous quantum mechanical models1,2 predict interesting effects like quantum beats, lasing without inversion, and photon echo processes. As these models are based on quantum coherence and interference, knowledge of the phase within the optical cycle is of particular interest. Laser radiation has so far been measured using intensity detectors, which are sensitive to the square of the electric field. Therefore information about the sign and phase of the laser radiation is lost. Here we use an electro-optic detection scheme to measure the amplitude and phase of stimulated radiation, and correlate this radiation directly with an input probing pulse. We have applied this technique to semiconductor quantum cascade lasers, which are coherent sources operating at frequencies between the optical (>100 THz) and electronic (<0.5 THz) ranges3. In addition to the phase information, we can also determine the spectral gain, the bias dependence of this gain, and obtain an insight into the evolution of the laser field.

Bloch gain in quantum cascade lasers

Abstract: Esaki and Tsu’s superlattice1, made by alternating two different semiconductor materials, was the first one-dimensional artificial crystal that demonstrated the ability to tailor semiconductor properties. One motivation of this work was the realization of the Bloch oscillator2,3 and the use of its particular dispersive optical gain4,5 to achieve a tuneable source of electromagnetic radiation. However, these superlattices were electrically unstable in the steady state6. Fortunately, because it is based on scattering-assisted transitions, this particular gain does not arise only in superlattices, but also more generally in semiconductor heterostructures7,8 such as quantum cascade lasers9 (QCLs), where the electrical stability can be controlled10. Here, we show the unambiguous spectral signature of Bloch gain in a special QCL designed to enhance the latter by exhibiting laser action in the condition of weak to vanishing population inversion.

Semiconductor lasers in optical phase-locked loops

Abstract: This invention relates to opto-electronic systems using semiconductor lasers driven by feedback control circuits that control the laser's optical phase and frequency. Feedback control provides a means for coherent phased laser array operation and reduced phase noise. Systems and methods to coherently combine a multiplicity of lasers driven to provide high power coherent outputs with tailored spectral and wavefront characteristics are disclosed. Systems of improving the phase noise characteristics of one or more semiconductor lasers are further disclosed.

Slow Light in a Semiconductor Waveguide for True-Time Delay Applications in Microwave Photonics

Abstract: We have investigated the slow and fast light properties of a semiconductor waveguide device employing concatenated gain and absorber sections. This letter presents the experimental results as well as theoretical modeling. A large phase shift of 110deg and a true-time delay of more than 150 ps are demonstrated. The combination of amplitude and phase control of the modulated signal shows great promise for applications within microwave photonics.

DFB semiconductor lasers based on reconstruction-equivalent-chirp technology

Abstract: A distributed feedback (DFB) semiconductor laser with equivalent phase shifts and chirps is proposed for the first time to our knowledge and is investigated numerically. As an example, it is shown that the desired λ/4 phase shift in a phase-shifted laser can be obtained equivalently by a specially designed sampling structure instead of an actual phase shift, while the external characteristics are unchanged. This novel DFB structure is advantageous in that it can be fabricated by standard holographic technology. Hence, the proposed scheme is expected to provide a low-cost method for fabricating a high-performance DFB semiconductor laser with complex structures.

Bistability and all-optical switching in semiconductor ring lasers

Abstract: Semiconductor ring lasers display a variety of dynamical regimes originating from the nonlinear competition between the clockwise and counter-clockwise propagating modes. In particular, for large pumping the system has a bistable regime in which two stationary quasi-unidirectional counter-propagating modes coexist. Bistability is induced by cross-gain saturation of the two counter-propagating modes being stronger than the self-saturation and can be used for data storage when the semiconductor ring laser is addressed with an optical pulse. In this work we study the response time when an optical pulse is injected in order to make the system switch from one mode to the counter-propagating one. We also determine the optimal pulse energy to induce switching.

Small optical volume terahertz emitting microdisk quantum cascade lasers

Abstract: The authors fabricate and characterize a series of quantum cascade laser micropillars emitting at ≈3.5THz. The optical confinement by double plasmon guiding in the vertical direction creates a large impedance mismatch between the confined optical modes and free space. Thus, unlike standard dielectric structures, large quality (Q) factors are maintained for small radius to wavelength ratios. The narrow bandwidth of the optical mode results in low threshold current (8mA) single-mode lasers. Cavity pulling enables a fine dynamic tuning of the emission wavelength. Comparison of the frequency shift due to cavity pulling and the Stark effect provides an experimental measure of the gain (36cm−1).

Common-chaotic-signal induced synchronization in semiconductor lasers.

Abstract: We experimentally and numerically observe synchronization of two semiconductor lasers commonly driven by a chaotic semiconductor laser subject to optical feedback. Under condition that the relaxation oscillation frequency is matched between the two response lasers, but mismatched between the drive and the two response lasers, we show that it is possible to observe strongly correlated synchronization between the two response lasers even when the correlation between the drive and response lasers is low. We also show that the cross correlation between the two responses is larger than that between drive and responses over a wide parameter region.

Slow-to-fast light using absorption to gain switching in quantum-well semiconductor optical amplifier

Abstract: Room temperature quantum-well semiconductor optical amplifier with large input power is utilized in both the absorption and gain regime as an optical group delay and advance (slow and fast light), respectively. Material resonance created by coherent population oscillation and four wave mixing is tuned by electrical injection current, which in turn controls the speed of light. The four-wave mixing and population oscillation model explains the slow-to-fast light switching. Experimentally, the scheme achieves 200 degrees phase shift at 1 GHz, which corresponds to 0.56 delay-bandwidth product. The device presents a feasible building block of a multi-bit optical buffer system.

Long-wavelength instability in broad-area semiconductor lasers

Abstract: We introduce a set of effective Maxwell-Bloch equations for broad area semiconductor lasers, and study the long-wavelength instability of the homogeneous solution. Unlike in two-level lasers, the presence of the semiconductor $\ensuremath{\alpha}$ factor allows us to observe this pattern forming instability even in the frequency domain where the homogeneous solution emission has the lower threshold.

Electrically pumped semiconductor evanescent laser

Abstract: An apparatus and method electrically pumping a hybrid evanescent laser. For one example, an apparatus includes an optical waveguide disposed in silicon. An active semiconductor material is disposed over the optical waveguide defining an evanescent coupling interface between the optical waveguide and the active semiconductor material such that an optical mode to be guided by the optical waveguide overlaps both the optical waveguide and the active semiconductor material. A current injection path is defined through the active semiconductor material and at least partially overlapping the optical mode such that light is generated in response to electrical pumping of the active semiconductor material in response to current injection along the current injection path at least partially overlapping the optical mode.

2.7 W tunable orange-red GaInNAs semiconductor disk laser.

Abstract: We report on a GaInNAs/GaAs semiconductor disk laser frequency-doubled to produce orange-red radiation. The disk laser operates at a fundamental wavelength of 1224 nm and delivers an output power of 2.68 W in the visible region with an optical-to-optical conversion efficiency of 7.4 %. The frequency-converted signal could be launched into a single-mode optical fiber with 70–78 % coupling efficiency, demonstrating good beam quality for the visible radiation. Using a Fabry-Perot glass etalon the emission wavelength could be tuned over an 8 nm spectral range.

High power frequency doubled GaInNAs semiconductor disk laser emitting at 615 nm.

Abstract: We report on an optically-pumped intracavity frequency doubled GaInNAs/GaAs -based semiconductor disk laser emitting around 615 nm. The laser operates at fundamental wavelength of 1230 nm and incorporates a BBO crystal for light conversion to the red wavelength. Maximum output power of 172 mW at 615 nm was achieved from a single output. Combined power from two outputs was 320 mW. The wavelength of visible emission could be tuned by 4.5 nm using a thin glass etalon inside the cavity.

Multistability in a semiconductor laser with optoelectronic feedback.

Abstract: The multistability in a single-mode distributed feedback semiconductor laser with delayed optoelectronic feedback is observed experimentally. For a given delay time, the observed dynamical state of the laser output is critically dependent on the process of varying the delay time and is limited by the range of variation. Various routes of delay time variation results in multistabilities characterized by states of different time series and power spectra.

Planar lightwave circuit(plc) device, wavelength tunable light source comprising the same device and wavelength division multiplexing-passive optical network(wdm-pon) using the same light source

Abstract: In the manufacture and application of a PLC-ECL type wavelength tunable light source, provided is a wavelength tunable mechanism with improved performance and stability, a light source with improved packaging performance and mass productivity, and a light source applied to a WDM-PON with initialization and stabilization functions. The wavelength tunable light source having a PLC (planar lightwave circuit)-ECL (external cavity laser) structure includes a first housing in which a semiconductor optical gain medium is mounted, a second housing in which a PLC device is mounted, and a third housing in which an optical fiber is mounted. The first, second, and third housings make an optical axis alignment through an optical coupling lens and combined in a laser welding method.

Excitation dependences of gain and carrier-induced refractive index change in quantum-dot lasers

Abstract: The excitation-density dependence of optical gain and refractive index changes in quantum-dot active media is investigated on the basis of a microscopic theory. Carrier-carrier Coulomb interaction and carrier-phonon interaction are treated on the level of a quantum-kinetic description. In the range of small optical gain the authors find small values of the α factor, while in the regime of gain saturation ∣α∣ increases drastically.

The variable stripe-length method revisited: Improved analysis

Abstract: The variable stripe length method described by Shaklee and Leheny, [Appl. Phys. Lett. 18, 475 (1971)] is a straightforward way to determine the steady-state gain spectrum of laser material. Here, common sources of error are identified and several new, robust ways of calculating the gain from the data are presented. The advantages of these methods are underlined by applying them to data obtained from a Ga(AsSb)∕GaAs∕(AlGa)As heterostructure.

Pulsed pumping of semiconductor disk lasers.

Abstract: Efficient operation of semiconductor disk lasers is demonstrated using uncooled and inexpensive 905nm high-power pulsed semiconductor pump lasers. Laser emission, with a peak power of 1.7W, is obtained from a 2.3μm semiconductor disk laser. This is seven times the power achieved under continuous pumping. Analysis of the time-dependent spectral characteristics of the laser demonstrate that significant device heating occurs over the 100-200ns duration of the pumping pulse - finite element modelling of the thermal processes is undertaken in support of these data. Spectral narrowing to below 0.8nm is obtained by using an intra-cavity birefringent filter.

Method for measurement of analyte concentrations and semiconductor laser-pumped, small-cavity fiber lasers for such measurements and other applications

Abstract: A hybrid laser comprising a semiconductor pump laser and small-cavity rare earth fiber laser where laser cavities of both lasers are butt coupled or otherwise optically coupled to form a plurality of laser cavities that produce a plurality of emission wavelengths, one which may be the pump laser emission wavelength at the output of the fiber laser thereby forming a multi-wavelength combined output. The wavelengths in such an output may substantially match distinguishing spectral characteristic features along at least a portion of a characteristic optical spectrum of the analyte under examination providing a method of determining the concentration of an analyte in a specimen undergoing examination.

Role of optical gain broadening in the broadband semiconductor quantum-dot laser

Abstract: The authors present a theoretical model and analysis to gain a further insight of the broadband InGaAs∕GaAs quantum-dot laser characteristics. A detailed analysis of the role of both inhomogeneous and homogeneous optical gain broadenings on the broad lasing emission is incorporated in the theoretical model and compared with the experimental results. The experimental data of broadband laser signature agrees well with theoretical calculation confirming that the broadband stimulated emission from the laser at room temperature is a result of the occurrence of bistate lasing in highly inhomogeneous dots.

Optical gain, loss, and transparency current in high performance mid-infrared interband cascade lasers

Abstract: The net modal gain, optical loss, and transparency current of high-performance, narrow ridge waveguide interband cascade (IC) lasers have been measured using the Hakki–Paoli technique in the temperature range from T=78 to 270 K. In this temperature range, the optical loss of IC lasers increases from αw≈17 cm−1 at T=78 K to αw≈35 at T=270 K, the transparency current density rises from Itr=10 to 330 A∕cm2, and the differential gain decreases from gd≈2.2 cm∕A to gd≈0.06 cm∕A with a characteristic temperature of T0=130 K. The implications of these observed characteristics for IC lasers are discussed.

Bistability and nonlinear gain in 1.55 μm vertical cavity semiconductor optical amplifiers: theory and experiments

Abstract: We report experimental measurements of power and wavelength optical bistability and nonlinear gain in two 1.55μm vertical-cavity semiconductor optical amplifiers operated in reflection. Anticlockwise and clockwise nonlinear switching and bistability, both with high on-off contrast ratio up to 3.5:1, have been observed in the optical power and wavelength domains. Theoretical modeling gives excellent agreement with the experimental measurements.

Optical Gain Analysis of Strain Compensated InGaN-AlGaN Quantum Well Active Regions for Lasers Emitting at 420-500 nm

Abstract: Strain-compensated InGaN quantum wells with tensile AlGaN barriers are analyzed as improved gain media for laser diodes emitting at 420-500 nm The optical gain analysis, taking into account spontaneous and piezoelectric polarizations, exhibits significant improvement in the peak optical gain and differential gain for the strain compensated structures

Dynamics of pulse formation in mode-locked semiconductor disk lasers

Abstract: We report on optically pumped semiconductor disk lasers passively mode locked with a semiconductor saturable absorber mirror. The effect of second- and third-order dispersion and dynamic gain saturation on the pulse formation is studied both experimentally and numerically. Improvement of the pulse quality and duration in the disk laser with resonant periodic gain structure requires accurate control of dispersion by wavelength detuning.

Localized traveling waves in vertical-cavity surface-emitting lasers with frequency-selective optical feedback.

Abstract: Spatially self-localized states have been found in a model of vertical-cavity surface-emitting lasers with frequency-selective optical feedback. The structures obtained differ from most known dissipative solitons in optics in that they are localized traveling waves. The results suggest a route to realization of a cavity soliton laser using standard semiconductor laser designs.