Showing papers on "Semiconductor optical gain published in 1996"

Synchronization of chaotic semiconductor lasers: application to encoded communications

Abstract: We numerically show that the synchronization of two chaotic semiconductor lasers is possible when a small amount of output intensity from one Is injected into the other. We also show that a message can be encoded in the chaotic carrier, transmitted by an optical fiber and decoded by a receiver with a very good quality.

Semiconductor amplifiers and lasers with tapered gain regions

Abstract: Semiconductor amplifiers and lasers with tapered gain regions provide the highest-brightness all-semiconductor sources of near infrared continuous wave (CW) power and have many useful applications. Simple models of these devices are described. Their applications, device performance and brightness limitations are reviewed1.

Optical gain of strained wurtzite GaN quantum-well lasers

Abstract: A theory for the electronic band structure and the free-carrier optical gain of wurtzite-strained quantum-well lasers is presented. We take into account the strain-induced band-edge shifts and the realistic band structures of the GaN wurtzite crystals. The effective-mass Hamiltonian, the basis functions, the valence band structures, the interband momentum matrix elements, and the optical gain are presented with analytical expressions and numerical results for GaN-AlGaN strained quantum-well lasers. This theoretical model provides a foundation for investigating the electronic and optical properties of wurtzite-strained quantum-well lasers.

Lasers and Electro-optics: Fundamentals and Engineering

Abstract: 1. Spontaneous and stimulated transitions 2. Optical frequency amplifiers 3. Introduction to two practical laser systems 4. Passive optical resonators 5. Optical resonators containing amplifying media 6. Laser radiation 7. Control of laser oscillators 8. Optically pumped solid state lasers 9. Gas lasers 10. Molecular gas lasers I 11. Molecular gas lasers II 12. Tunable lasers 13. Semiconductor lasers 14. Analysis of optical systems I 15. Analysis of optical systems II 16. Optics of Gaussian beams 17. Optical fibers and waveguides 18. Optics of anisotropic media 19. The electro-optic and acousto-optic effects and modulation of light beams 20. Introduction to non-linear processes 21. Wave propagation in non-linear media 22. Detection of optical radiation 23. Coherence theory 24. Laser applications Appendices Index.

Theory of the ultrafast optical response of active semiconductor waveguides

Abstract: Analytical expressions for the optical response of active semiconductor waveguides are derived, taking into account the effects of propagation, gain, and index dispersion as well as pulse chirp. The dynamics of the gain and the index that are due to carrier density changes, carrier heating, and spectral holeburning are derived from semiclassical density-matrix equations, and instantaneous two-photon and Kerr effects are included phenomenologically. It is shown that dispersion of the gain strongly affects short-pulse pump-and-probe measurements, since it induces a coupling between the phase and the intensity of the probe pulses. Good agreement with published experimental data is obtained.

Theory and optimization of lens ducts

Abstract: Lens ducts are simple optical devices that have found application in the coupling of pump radiation from extended two-dimensional semiconductor laser diode arrays into solid-state laser gain media. The operation of these devices relies on the combined effects of lensing at their curved input surface and channeling by total internal reflection off their canted planar sides, to contain and couple semiconductor diode laser light efficiently to the input face of a solid-state laser crystal or glass. The lens duct provides a robust method for amplifying the irradiance of laser diode array pump sources and has made possible a scalable diode end-pumping architecture that offers the opportunity to expand significantly the number of ions and transitions that can be practically engaged in diode-pumped solid-state laser systems. An analytic model that describes the transfer efficiency of lens ducts and aids in the optimization of their design is presented.

Prevention of gain saturation by multi-layer quantum dot lasers

Abstract: The authors compare the threshold current density jt/sub h/ against the laser length of a single layer quantum dot (SLQD) laser with a sixfold multilayer quantum dot (MLQD) laser. Gain saturation is not observed in the MLQD laser. They calculate j/sub th/ against the number of dot layers including gain saturation. The strong impact of thermal coupling of carriers on j/sub th/ is demonstrated.

Single-port laser-amplifier modulators for local access

Abstract: We describe a single-port, reflective, waveguide modulator based on semiconductor laser amplifier technology. The single-port geometry reduces the high packaging cost associated with two-port waveguide modulators, while the internal gain of the amplifier compensates for splitting and coupling losses. A modulator with a bulk active layer showed a reflection-mode chip gain of 17 dB at /spl lambda/=1.56 /spl mu/m. When driven with pseudorandom digital data at 100 Mb/s, extinction ratios of >12 dB were observed over the broad wavelength range (20 nm) needed for wavelength division multiplexed systems. Bit-error-rate tests confirmed that there was no distortion penalty, compared to a LiNbO/sub 3/ reference modulator.

Optical gain in gainn/gan heterostructures

Abstract: By optical gain spectroscopy we have studied the fundamental laser properties of GaInN/GaN heterostructures grown on sapphire. Utilizing the stripe excitation method we have measured optical gain spectra at room temperature. Due to the low symmetry of the wurtzite structure and the resulting splitting of the uppermost valence bands, we find optical gain only for the TE mode. Our analysis shows that the optical gain is due to direct band‐to‐band transitions in an electron‐hole plasma. For gain amplitudes typically found in lasers, we find carrier densities up to 3×1019 cm−3, which are likely to lead to rather large threshold current densities.

Theory for passive mode-locking in semiconductor laser structures including the effects of self-phase modulation, dispersion, and pulse collisions

Abstract: We present a theory for passive mode-locking in semiconductor laser structures using a semiconductor laser amplifier and absorber. The mode-locking system is described in terms of the different elements in the semiconductor laser structure. We derive mode-locking conditions and show how other mode-locking parameters, like pulse width and pulse energy, are determined by the mode-locking system. System parameters, like bandwidth, dispersion, and self-phase modulation are shown to play an important role in mode-locking conditions and results. We also discuss the effects of pulse collisions and positions of the mode-locking elements inside the cavity on mode-locking stability and show that these effects can be easily included in the presented model. Finally, we give a number of design rules and recommendations for fabricating passively mode-locked lasers.

Miniature self-pumped monolithically integrated solid state laser

Abstract: The present invention is an integrated, diode laser-pumped, solid state lr which can be fabricated entirely with semiconductor fabrication techniques. The laser includes a substrate, a semiconductor light source grown over the substrate to provide pump light and a solid state laser grown over the substrate. The semiconductor light source produces pump light at a wavelength useful for pumping the solid state laser. The solid state laser includes a pump mirror transparent to the pump light, an output mirror, and a doped semiconductor layer deposited between the pump and output mirrors, the semiconductor, dielectric or polymer layer being doped with active metal ions. The pump light from the semiconductor light source is closely coupled to the solid state laser and passes through the pump mirror to pump the active metal ions.

Semiconductor optical device and method for fabricating the same

Abstract: A semiconductor optical device fabricating method for easily fabricating on a single substrate a plurality of distributed feedback lasers or distributed Bragg reflector lasers with uniform static and dynamic properties and individually different oscillation wavelengths. A plurality of pairs of stripe type insulating thin film masks are formed over that region of the semiconductor substrate which has optical waveguides formed therein for the lasers. Each pair of stripe type masks has a constant gap therebetween. With the masks in place, optical waveguide layers for the lasers are grown in crystallized fashion through metal organic vapor epitaxy. The stripe type masks in pairs differ dimensionally from one another. The semiconductor optical device thus fabricated comprises on one semiconductor substrate a plurality of distributed feedback lasers or distributed Bragg reflector lasers whose optical waveguide layers differ in both film thickness and composition and whose oscillation wavelengths also differ from one another.

8-mV threshold Er/sup 3+/-doped planar waveguide amplifier

Abstract: We report on the gain characteristics of a low threshold (8 mW) Er/sup 3+/-doped planar optical waveguide amplifier. Net fiber to fiber gain of 4.5 dB is achieved at a signal wavelength of 1536 nm with 80 mW of 980-nm pump power. This device represents significant progress toward a planar amplifier module pumped by a single laser diode.

Semiconductor Lasers: Past, Present, and Future

Abstract: Contents: 1 Quantum-Well Semiconductor Lasers 2 Distributed Feedback Semiconductor Lasers 3 Narrow-Linewidth Semiconductor Lasers 4 Ultrashort Pulse Generation 5 Surface-Emitting Semiconductor Lasers 6 High-Power Semiconductor Lasers 7 Visible Semiconductor Lasers 8 Semiconductor Lasers with II-VI Materials 9 Semiconductor Laser Amplifiers 10 Applications of Semiconductor Lasers

Synchronous mode-locking in passively mode-locked semiconductor laser diodes using optical short pulses repeated at subharmonics of the cavity round-trip frequency

Abstract: Synchronous mode-locking was achieved in passively mode-locked semiconductor lasers using optical pulses with repetition rates at subharmonics of the cavity round-trip frequency Stable and continuous mode-locked pulses at 85 GHz were generated when the repetition rate of the control optical pulses was 425 GHz (2nd subharmonic) The timing jitter of the mode-locked pulses was reduced to 1 ps The relationship between repetition rates of the control pulses and the realization of stable and continuous mode-locking was examined

Fundamentals of laser diode amplifiers

Abstract: Basic Principles of Optical Amplifiers Optical Amplification in Semiconductor Laser Diodes Analysis of Transverse Modal Field in Semiconductor Laser Amplifiers Analysis and Modelling of Semiconductor Laser Amplifiers: Gain and Saturation Characteristics Analysis and Modelling of Semiconductor Laser Amplifiers: Noise Characteristics Experimental Studies on Semiconductor Laser Amplifiers.

Small-signal theory of wavelength converters based on cross-gain modulation in semiconductor optical amplifiers

Abstract: We give the exact closed form solution of the coupled-mode equations describing frequency converters based on cross-gain modulation in semiconductor optical amplifiers. We show that the frequency response of the converter is strongly affected by the waveguide internal loss.

Gain dynamics and associated nonlinearities in semiconductor optical amplifiers

Abstract: A rich variety of dynamical processes underlie the operation of active semiconductor light-emitting devices, such as semiconductor optical amplifiers. These processes include interband and intraband carrier dynamics. Interband processes comprise spontaneous recombination, both radiative and Auger, stimulated radiative recombination, and carrier transport. Intraband processes comprise carrier heating and cooling and spectral hole-burning, among others. The dynamical processes affect both the gain and refractive index of the semiconductor optical amplifier. In this article, these dynamic processes and their physical origins are reviewed. Under conditions of large, time-varying changes in carrier density or intraband carrier distribution, nonlinear gain and refraction becomes significant. For applications requiring linear amplification, such nonlinearities are deleterious. However, for many applications such nonlinearities can be the basis for useful device functions. In particular, the nonlinearities of cross-gain modulation, cross-phase modulation, and four-wave mixing in semiconductor optical amplifiers have been applied for the functions of wavelength conversion, optical time-demultiplexing, clock recovery, and trans-multiplexing. Such nonlinear devices based on semiconductor optical amplifiers and their effects on propagating optical signals are also reviewed.

Spectrally resolved near-field mode imaging of vertical cavity semiconductor lasers

Abstract: The transversal mode properties of vertical cavity surface emitting lasers (VCSELs) are studied by spectrally resolved scanning near‐field optical microscopy. In contrast to classical optical microscopy techniques, our method is able to simultaneously decompose lasing transversal modes by their wavelength with lateral superresolution. As the tip‐sample distance is controlled by the well‐established shear‐force detection, additional topographical information showing the surface structure of the laser is provided. Therefore, near‐field spectroscopy allows the detailed analysis of the spatial light distribution emitted by the laser with respect to the current injection contact, making it a promising tool for the characterization and optimization of VCSELs.

Optical gain of a quantum-well laser with non-Markovian relaxation and many-body effects

Abstract: In this article, a theoretical description of the optical gain of a quantum-well laser is developed taking into account non-Markovian relaxation and many-body effects. Single-particle energies are calculated using the multiband effective mass theory, and the valence-band mixing including the spin-orbit (SO) split-off band coupling is considered in the formulation. The Coulomb enhancement and the band-gap renormalization are also considered within the Hartree-Fock approximation. The gain spectra calculated with the Lorentzian line shape function show two anomalous phenomena: unnatural absorption region below the band-gap energy and mismatch of the transparency point in the gain spectra with the Fermi-level separation, the latter suggesting that the carriers and the photons are not in thermal (or quasi-) equilibrium. It is shown that the non-Markovian gain model with many-body effects removes the two anomalies associated with the Lorentzian line shape function. It is also found that the optical gain spectra depend strongly on the correlation time of the system which can be determined by the intraband frequency fluctuations.

Theory of mode-locked semiconductor lasers

Abstract: We present a theoretical study of semiconductor mode-locked lasers at a phenomenological level. We use the slow absorber model of New and Haus, but extend the analysis by taking into account the shift in the gain maximum due to the changing number of carriers. In our analysis of the resulting equation, we show that due to stability requirements the shortest attainable pulse duration is limited. The use of self-phase modulation due to a slow medium can at most lead to a shortening of the pulse by a factor of 2. We show that the shifting of the gain maximum due to the changing number of carriers in the laser is a crucial aspect in the operation of mode-locked semiconductor lasers. We further find that the end mirrors must be reflecting more than about half of the light intensity to prevent a self-pulsation type instability similar to the relaxation oscillation.

Gain dynamics of a saturated semiconductor laser amplifier with 1.47-μm LD pumping

Abstract: The dynamic characteristics of a gain saturated semiconductor laser amplifier with 1.47-/spl mu/m pump light are described. In addition to improving the saturation output power, the pump light injection shortens the gain response time. Bit-error-rate measurements show that signal degradation, induced for a high-bit-rate signal amplified under the gain saturated condition, becomes less with the pump light injection.

Performance characteristics of vertical-cavity semiconductor laser amplifiers

Abstract: The static and dynamic amplification of an external beam in a vertical-cavity surface emitting laser structure is demonstrated experimentally. A high gain of 20 dB and a fast response of 60 ps, as well as a narrow amplification bandwidth, make the device very interesting for active optical filtering and switching.

Improved method for gain/index measurements of semiconductor lasers

Abstract: An improved experimental method for measuring gain and refractive index in semiconductor lasers from below-threshold amplified spontaneous emission spectra is presented. Broad-area, as opposed to narrow-stripe width, diode lasers and a far-field spatial filtering technique are employed to eliminate uncertainties associated with lateral waveguiding and carrier confinement.

Transverse-mode selection in external-cavity vertical-cavity surface-emitting laser diodes

Abstract: A theoretical study is performed of the multimode dynamics and steady-state transverse-mode selection in vertical-cavity surface-emitting lasers subject to weak optical feedback in an external-cavity configuration. Attention is focused on the competition between the two lowest-order modes (LP01 and LP11 degenerate modes) appropriate to the chosen circularly symmetric vertical-cavity surface-emitting laser structure. It is shown that preferential excitation of either mode can be effected by appropriate choice of optical feedback delay. Opportunities for enhancing modal discrimination by adjusting the strength of optical feedback are also presented.

Gain dispersion and saturation effects in four-wave mixing in semiconductor laser amplifiers

Abstract: This paper addresses four-wave mixing (FWM) in semiconductor laser amplifiers from the point of view of a propagation problem. The gain dispersion effect, i.e., the difference of the gain factors for the pump, probe and signal waves is shown to be significant in the case of large detunings >1 THz. It is given an analytical solution of the FWM problem including gain dispersion and saturation effects. Considering the saturation behaviour, it is shown that the linear gain factors for the different waves and the nonlinear susceptibilities associated with the different nonlinear effects must be characterized by different carrier densities at transparency. A comparison of our theory with a numerical model, with previous approaches and with experimental data is given.

Multiwavelength light source with precise frequency spacing using mode-locked semiconductor laser and arrayed waveguide grating filter

Abstract: We report here a multiwavelength light source using semiconductor mode-locked lasers with the optical frequency spacing of 100 GHz. In this light source, a mode-locked semiconductor laser was used for the original light source, which gave multimodes with constant frequency spacings. The output from the mode-locked laser was fed into silica-based arrayed waveguide grating filter (AWG) with the free spectral range of 100 GHz and 16 channels of input/output ports.

Turn-on jitter in zero-biased single-mode semiconductor lasers

Abstract: An analytical expression for the turn-on delay probability density function (pdf) of single-mode lasers biased below threshold is derived, which is in good agreement with results based on computer simulations and measurements. It is shown, that the pdf obtained only depends on the on-state yielding simple requirements for the transmitter in order to achieve a given BER. The results are of particular interest for designing optical interconnects, where zero-biased lasers are used.

Green’s functions theory for semiconductor-quantum-well laser spectra

Abstract: A microscopic approach for the computation of semiconductor quantum well laser power spectra is presented. The theory is based on nonequilibrium Green’s function techniques that allow for a consistent description of the coupled photon and carrier system fully quantum mechanically. Many-body effects are included through vertex corrections beyond the random-phase approximation. Band structure engineering is incorporated in the theory as dictated by the coupled band solutions of the Luttinger Hamiltonian. The influence of the detailed cavity-mode structure is accounted for by the photon Green’s function. The theory describes the interplay among the various many-body, quantum-confinement, and band structure effects in the gain medium and its action as a laser cavity. Numerical results for the recombination rates, optical response, and laser output power spectra are presented for strained-layer and lattice-matched III-V systems at quasiequilibrium with variable design and material parameters and under different excitation conditions. Active optical switching is demonstrated in specially designed structures.

Semiconductor laser apparatus requiring no external modulator, method of driving semiconductor laser device, and optical communication system using the semiconductor laser apparatus

Abstract: In a semiconductor laser apparatus, a waveguide has a buried heterostructure. The confinement effect of light to the waveguide having the buried heterostructure is controlled to control laser oscillation itself. Upon execution of intensity modulation, an oscillation/non-oscillation state is selected by controlling the confinement effect of light, and upon execution of polarized wave modulation, TE or TM mode oscillation is selected by controlling the confinement effect of light.