Operation Of Semiconductor Lasers Research Articles

0.5-W single transverse-mode operation of an 850-nm diode-pumped surface-emitting semiconductor laser

We report the power scaling of a diode-pumped GaAs-based 850-nm vertical external-cavity surface-emitting laser, by use of an intracavity silicon carbide (SiC) heatspreader optically contacted to the semiconductor surface. To our knowledge, this is the first demonstration of bonding of SiC to a III-V semiconductor structure using the technique of liquid capillarity. High output power of >0.5 W in a circularly symmetric, TEM/sub 00/ output beam has been achieved with a spectral shift of only 0.6 nm/W of pump power. No thermal rollover was evident up to the highest pump power available, implying significant further output-power scaling potential using this approach.

Picosecond pulse generation with 1.5 µm passively modelocked surface-emitting semiconductor laser

The authors report the first demonstration of an optically pumped passively modelocked surface-emitting semiconductor laser operating in the 1.5 µm region. The modelocked laser emits pulses of 6.5 ps full width at half maximum duration with an average power of 13.5 mW at a fundamental repetition rate of 1.342 GHz. The peak power was 1.6 W.

External cavity multiwavelength superbroadband diode laser

Multiwavelength semiconductor laser source for dense wavelength division multiplexing (DWDM) applications based on a novel dispersive cavity is described. Multiline lasing on the basis of a single-diode laser chip and multi-stripe diode laser is analyzed theoretically and demonstrated experimentally. Simultaneous lasing across ∼80% of the FWHM of the luminescence bandwidth of the AlGaAs active medium (657–667 nm) in multiline regime with a special pre-assigned spectral composition was realized. For DWDM applications a prototype of this superbroadband semiconductor laser operating in one of the telecommunication wavelength bands around 1.5 μm has been designed on the basis of a multi-stripe diode chip. Simultaneous lasing of four spectral lines in the region 1567–1577 nm has been obtained.

Microscopic theory of gain and spontaneous emission in GaInNAs laser material

A fully microscopic model is used to calculate absorption/gain and spontaneous emission for GaInNAs quantum-well laser gain media. It is demonstrated how this approach can be used to derive the optical properties for the regime of semiconductor laser operation from low density photo luminescence spectra which can be obtained from simple experiments. Numerical results are presented showing that increased well depth leads to strongly increased differential gains and gain amplitudes and pronounced shifts of the gain maximum with increasing density. On the basis of a quantum Blotzmann model for the incoherent carrier dynamics it is shown, that high carrier confinement can lead to unusually long carrier capture times. Furthermore, temperature dependent bandstructure parameters for GaInNAs for the applied 10-band k · p -model are presented that have been derived from comparison to recent experimental data.

Sub-500-fs soliton-like pulse in a passively mode-locked broadband surface-emitting laser with 100 mW average power

We report on femtosecond operation of a broadband diode-pumped external-cavity surface-emitting semiconductor laser, passively mode locked with a fast quantum–well Semiconductor Saturable Absorber Mirror grown at 735 °C. We obtained 477 fs pulses at 1.21 GHz. The average output power is 100 mW at 1040 nm, the pulse peak power 152 W, with ∼1 W of 830 nm pump. The rf spectrum shows a linewidth <50 kHz at the noise level (−65 dB). We believe that the group-delay dispersion is compensated by the negative self-phase modulation in the absorber structure, leading to soliton-like mode locking. This system requires no additional technological step after the growth of the structures.

Side-mode gain in grating-tuned extended-cavity semiconductor lasers: investigation of stable single-mode operation conditions

In semiconductor lasers, nonlinear phenomena inside the active medium change the side-mode gain with respect to the static threshold-gain. For a given side mode, the sign and the magnitude of the change depend on the lasing-mode optical power and on the wavelength detuning from the lasing mode. If the side-mode gain is enhanced, mode-hopping can occur toward a side mode whose loss is higher than the lasing-mode one. Conversely, in the case of side-mode-gain suppression, the side-mode loss can be smaller with no mode-hop. In this paper, effects of carrier-density pulsation, carrier heating, and spectral-hole burning on the conditions of stable single-mode operation in grating-tuned single-mode extended-cavity semiconductor lasers are investigated. Taking into account the external cavity spectral selectivity and mode coupling, we present a theoretical analysis of experimental results. We perform calculations that compare well with the experimental data obtained with a 1.55-/spl mu/m extended-cavity laser.

ZnSe-Based Room Temperature Low-Threshold Electron-Beam Pumped Semiconductor Laser

We report on room temperature operation of blue-green ZnSe-based electron-beam pumped semiconductor lasers grown by molecular beam epitaxy. The lowest ever reported values of threshold current density in transverse excitation geometry (3-3.5 A/cm 2 ), which is independent of the electron beam energy in the 15-35 kV range, have been obtained. Possible ways to improve the electron-beam pumped laser characteristics are discussed.

Continuous wave operation of a mid-infrared semiconductor laser at room temperature.

Continuous wave operation of quantum cascade lasers is reported up to a temperature of 312 kelvin. The devices were fabricated as buried heterostructure lasers with high-reflection coatings on both laser facets, resulting in continuous wave operation with optical output power ranging from 17 milliwatts at 292 kelvin to 3 milliwatts at 312 kelvin, at an emission wavelength of 9.1 micrometers. The results demonstrate the potential of quantum cascade lasers as continuous wave mid-infrared light sources for high-resolution spectroscopy, chemical sensing applications, and free-space optical communication systems.

Time-domain analysis of fiber grating semiconductor laser operation in active mode-locking regime

We analyze in detail the mode-locking characteristics of fiber grating semiconductor lasers using a split-step time-domain approach. The accuracy of the simulations is demonstrated by the capability of the numerical code to describe the fine structure of the resonance peak spectral splitting (RPSS) of the intensity modulation (IM) response near the FSR modulation frequency with a very good agreement with analytical results reported in the literature. The mode-locking (ML) frequency range was found to be closely related to the IM characteristic shapes around the resonance peak. The ML pulse characteristics and frequency range of Gaussian gratings with different apodization and dispersion characteristics have been reported as an example.

Single-mode operation of a broad-area semiconductor laser with an anamorphic external cavity: experimental and numerical results

The emission of high-power broad-area semiconductor lasers inherently contains many lateral modes that increase the beam divergence and reduce the spatial coherence. Elimination of higher-order lateral modes from the output beams of commercially available broad-area lasers will be beneficial in many applications of these lasers. Experimental results obtained with a broad-area laser coupled to an anamorphic external cavity are presented and are compared with the predictions from our numerical model. We have predicted and observed with the anamorphic external cavity a greatly improved discrimination against high-order lateral modes. The measurement of the spectrally resolved near-field intensity patterns provides much more comprehensive information on their longitudinal- and lateral-mode content than do observations of near-field and far-field beam intensity profiles. With a broad-area laser of 100-mW nominal power, it has been possible to extract 40% of the maximal power in a stable single-lateral and single-longitudinal mode regime.

Noise characteristics of single-mode semiconductor lasers under external light injection

Presents a theoretical investigation of the noise behavior of a semiconductor laser operating under relatively strong light injection. Equations have been presented to describe the noise effect through the calculation of the relative intensity noise as well as the carrier-to-noise ratio available at the receiving end. Illustrative examples are given, showing the impact of the master and slave laser bias currents. Also, the injection-locked and free-running operation regimes have been comparatively analyzed. The results show how the noise characteristics are affected by optical injection and, consequently, how the operating conditions must be chosen to reduce this effect. In particular, it is shown, in agreement with previous works, that the master laser emission noise will essentially take the lead. As a result, to improve the noise behavior by injection locking a solitary laser, the use of a low-noise master laser is required. To make it easy to apply the present results to any laser diode under the stable-locking condition, the necessary relations are explicitly given before specifying the parameters of simulation.

Mathematical modelling of thermal hot-spots in semiconductor laser operation

A new mathematical model describing the coupling of electrical, optical and thermal effects in semiconductor lasers is introduced. The underlying (perfect) isothermal system has a transcritical bifurcation as the current varies. The steady-state light intensity is found to exhibit exponential growth as the wave traverses the laser and the steady-state electron concentration satisfies an integral equation, the solution of which specifies the threshold current. The (imperfect) isothermal and thermal problems also have this behaviour at leading order. In the thermal problem, an asymptotic analysis results in the decoupling of the various time-scales and length-scales leading to considerable simplification. Composite asymptotic expansions are constructed on each time-scale and compared with numerical results. These analytical solutions provide valuable insight and predict the role played by the various physical processes. In particular, the temperature rise of the active region is found to exhibit localized hot-spots at both mirrors, in contrast to the temperature rise of the surround where no such hot-spots are observed.

Entraining power-dropout events in an external-cavity semiconductor laser using weak modulation of the injection current

We measure experimentally the effects of injection current modulation on the statistical distribution of time intervals between power-dropout events occuring in an external-cavity semiconductor laser operating in the low-frequency fluctuation regime. These statistical distributions are sensitive indicators of the presence of pump current modulation. Under most circumstances, we find that weak low-frequency (in the vicinity of 19 MHz) modulation of the current causes the dropouts to occur preferentially at intervals that are integral multiples of the modulation period. The dropout events can be entrained by the periodic perturbations when the modulation amplitude is large (peak-to-peak amplitude /spl ges/8% of the dc injection current). We conjecture that modulation induces a dropout when the modulation frequency is equal to the difference in frequency between a mode of the extended cavity laser and its adjacent antimode. We also find that the statistical distribution of the dropout events is unaffected by the periodic perturbations when the modulation frequency is equal to the free spectral range of the external cavity. Numerical simulations of the extended-cavity laser display qualitatively similar behavior. The relationship of these phenomena to stochastic resonance is discussed and a possible use of the modulated laser dynamics for chaos communication is described.

Influence of Nonlinear Gain Saturation on the Time-Bandwidth Product of Optical Pulse from a Gain-Switched Semiconductor Laser

It is found numerically that the time-bandwidth product (TBP) of optical pulse from a gain-switched semiconductor laser operating under a sufficient gain saturation condition increases monotonously with increasing modulation amplitude. This enhancement of the TBP becomes remarkable for longer-wavelength semiconductor lasers (1.3, 1.55 μm) having large value of the gain compression factor e (∼ 10−23 m3), making the pulse chirp estimation using the TBP difficult.

Forcing pulsatile behaviour in semiconductor lasers by periodic control

Abstract In this paper, we apply optimal control theory for the operation of a standard edge-emitter semiconductor laser so as to produce good quality pulsing output signals. This is achieved by using a sinusoidal injection current whose characteristics (frequency and amplitude) are suitably tuned. The performances obtained from this optimal control strategy are compared with those achievable with a novel self-pulsing device recently designed.

Transition to pulsed operation in short external-cavity FM semiconductor lasers

Conditions are established for the occurrence of a transition from FM operation to pulsed output in short external-cavity FM semiconductor lasers. It is shown that there are dual operating points around which FM operation is possible. The position of the modulation frequency in relation to these two FM operating frequencies determines the type of behavior exhibited by the configuration. In particular, pulsed and mixed pulsed-FM behavior is observed when the modulation frequency is between the two possible FM operating frequencies.

Efficiency and intensity distribution in a semiconductor laser operating in the 'leaky' regime

The differential efficiency is calculated for a semi-conductor laser having an optical waveguide with a wave leaking out into the substrate. The differential efficiency is shown to be close to the limit if the optical quality of the substrate (with losses ~1 cm-1 or less) is sufficiently high and the remaining laser parameters have typical and attainable values. Optimisation of the parameters of such a laser makes it possible to increase the output power severalfold compared with the power of a laser generating a conventional waveguide mode without radiation leakage.

Critical Microscopic Processes in Semiconductor Lasers

ABSTRACTThe cascade of microscopic processes relevant to semiconductor laser operation is outlined. An integrated laser simulator which encapsulates these processes is applied to illustrate the connection between an accurate model of the optical gain in the quantum wells and measured characteristics of representative 1.3 μm InGaAsP/InP lasers. These results highlight the impact of carrier transport effects on the observed optical gain and the modulation response of semiconductor lasers.

Apodizing holographic gratings for dual-wavelength operation of broad-area semiconductor lasers

Apodizing holographic gratings are designed to have a Gaussian reflectivity profile in the -1 order and a complementary reflectivity profile in the specular (0) order. They are obtained by the interference of two Gaussian beams on a glass plate covered with a photoresist. These gratings are intended to be used as the coupler of the external cavity of a broad-area semiconductor laser. When the grating is oriented to get the -1 order counterpropagating with respect to the incident beam, single-longitudinal- and single-lateral-mode operation is obtained. We report on the fabrication technique of an apodizing holographic grating designed to allow lasing on two wavelengths simultaneously, with a preselected wavelength separation. The results obtained with a commercial broad-area laser are presented.

Superradiant generation of femtosecond pulses in quantum-well heterostructures

We propose a new type of accessible source of ultra-short pulses based on the phenomenon of collective coherent recombination (superradiance) of electrons and holes in semiconductor heterostructures. We find and analyse a novel regime of ultra-fast operation of quantum-well semiconductor lasers in which a quasiperiodic sequence of femtosecond superradiant pulses is emitted under continuous pumping. According to our calculations for AlGaAs - GaAs heterostructures, the coherent optical pulses of duration 30 fs and peak intensity can be generated in a low-Q cavity of length .