We present a study of high-power quantum-cascade lasers (QCL) for 8 μm spectral range with active regions of latticematched to InP substrate and strain-balanced designs. The use of the strained quantum well/barrier pairs made it possible to increase the energy barrier between the upper laser level and continuum by ~ 200 meV. Our experiments show that utilization of the strain-balanced design of the active region makes it possible to more than double the characteristic temperature T0 to 253 K from 125 K for the lattice-matched design. In pulsed mode, QCLs with strain-balanced active region demonstrated high efficiency of 12% and high output optical power of 21 W (over 10 W per facet). This is the highest value of the optical power demonstrated to date in 8 μm spectral region to the best of our knowledge.
We present a study of quantum cascade laser dynamical properties accounting for the Joule heating released in the active region. In particular, we study the QCL emitting at 8 μm in the pulsed pumping mode and present experimental measurements, as well as a theoretical description of the QCL build-up time, showing the features appearing due to the Joule heating released inside the active region.
The effect of the number and position of AlInAs energy barrier layers on the output characteristics of high-power multimode AlGaInAs / InP lasers, spectral range 1400–1600 nm, has been studied. It was shown that the use of energy barriers allows increasing the laser maximum output power 1.5-2 times. It was found that the barrier layer should be installed at the waveguide-cladding heterojunction from the p-side in order to localize electrons in the waveguide layer.
The study was supported by the Russian Science Foundation, project No. 19-79-30072
The results of research and development of a pulse laser module are presented. The aim was to create and a compact pulse laser source with a peak power of more than 10 W for optical pulses of 10 ns - 10 μs duration, emitting in spectral range 900-1600 nm. Pulsed modules were based on MOCVD-grown edge-emitting multimode semiconductor lasers integrated with a pulse pumping board. It was shown that the laser output characteristics can be optimized via a series resistance in the laser pump circuit. The 1550 nm wavelength modules with free-space outputs showed power levels of 15 and 25 W, for 1 μs and 100 ns pulses respectively, at 25° C temperature with a regular pulse shape.
The design of the AlGaAs/InGaAs/GaAs laser heterostructure with an ultra-narrow waveguide was developed and studies on the generation of high-power laser pulses with high beam quality were carried out. The heterostructure design included a 100-nm-thick waveguide and an InGaAs quantum well for a lasing at 1060 nm. For the studies the mesa-stripe geometry single-mode lasers with a 5.1-μm-width contact were fabricated. The mesa-stripe geometry parameters were optimized using a 2D-simulation of waveguide properties, taking into account the spatial distribution of temperature and gain. As a result, the divergence was of 18.5 and 5 degrees in the growth direction and parallel to the heterostructure layers, respectively. Studies of the light-current characteristics in the range of pulse durations of 5–1000 ns showed that the peak power of 1.75 W was limited by the catastrophic optical damage. The dynamics is associated with modes of high-quality factor that approach their threshold conditions at high pumping level. A spectral line of these modes is redshifted relative to a fundamental one.
Vertical stacks based on high-power semiconductor lasers and low-voltage high-current AlGaAs/GaAs and InGaAs/AlGaAs/GaAs thyristors have been developed and studied for generating current pulse in low-impedance load circuits based on semiconductor lasers. Pump current pulses with an amplitude up to 200 A for AlGaAs/GaAs thyristors and up to 70 A for InGaAs/AlGaAs/GaAs thyristors were realized in broad area diode lasers and 3-stripe diode laser mini bars, with optical pulse duration of 40-600 ns and a total peak power of about 78 W. The feasibility of generating current pulses with an amplitude of 16 A and a duration of 2.5 ns is shown, which makes it possible to obtain laser pulses with a peak power of 8 W and a duration of 2 ns. It is shown that the parallel joint of single thyristors allows one to multiply the increase in the current pulse amplitude, while maintaining efficiency and duration.
The temperature behavior of operating characteristics in semiconductor lasers with a quantum-confined active region is studied with a proper account for (i) non-instantaneous capture of charge carriers from the waveguide region into the active region and (ii) internal optical loss that depends on the carrier densities. Because of (i), the carrier densities are not pinned in the lasing mode, i.e., they are functions of the injection current. In view of (ii) and as a result of pump-currentdependence of the carrier densities, so becomes the internal loss coefficient. This in turn leads to the roll-over of the light-current characteristic at high currents (i.e., decreasing optical power with increasing injection current) and, under certain conditions, appearance of the second branch in it. The laser characteristics are shown to transform qualitatively with varying temperature: they are conventional, i.e., consist of one branch, at low temperatures but they have two branches, i.e., are of a binary nature, at high temperatures. The two branches merge together at the maximum operating current beyond which the lasing quenches. In contrast to the first (conventional) lasing threshold, the threshold for emerging the second branch decreases with increasing temperature. The pump-current-dependence of the carrier densities and internal loss coefficient is also fascinating: these quantities decrease with increasing current in their second branches.
The results of designing, manufacturing and investigating characteristics of AlGaAs/InGaAs/GaAs lasers with ultranarrow waveguides are presented. Low threshold current density near 40 A/cm2 has been observed for the lasers with quantum wells. We have demonstrated the possibility of obtaining up to 5 W of output power in continuous mode and up to 40 W in pulsed mode, with a beam convergence (FWHM) of 17.8° It is demonstrated that such lasers can exhibit main characteristics similar to conventional laser heterostructures and allow a potential for further improvement and optimization.
Studies of multimode and single-mode semiconductor lasers with a surface distributed Bragg reflector (S-DBR) were carried out. S-DBR with a period of 2 μm was formed in the upper cladding layer by contact photolithography. The spectrum width for all laser designs did not exceed 0.3 nm both at continuous wave (CW) and pulse of 100 ns pump. Temperature stability of emission wavelength increase from a value of 0.35 nm/°С for a Fabry-Perot laser to a value of 0.075 nm/°С for a S-DBR laser was demonstrated. The relatively low output optical power of high-order S-DBR lasers is associated with the presence of diffraction modes emitting from the surface of the DBR.
This communication presents a dynamic model of a multi-junction heterostructure that combines the functions of a fast current switch and a high-efficiency laser emitter. Approaches to designing a multi-junction heterostructure with faster switching (rise and decay times of about 1 ns) and higher peak current (>10 A) are considered. It is shown that an important role is played in the dynamics of the injection drive currents of the laser part by the modulation by excess carriers in the lightly doped base and collector regions of the N-p-N transistor part. As a result, a field domain is formed, which serves as a virtual emitter of electrons and holes via impact ionization.
Sergey Slipchenko, Aleksandr Podoskin, Olga Soboleva, Maxim Zakharov, Kirill Bakhvalov, Dmitrii Romanovich, Nikita Pikhtin, Il`ya Tarasov, Timur Bagaev, Maxim Ladugin, Aleksandr Marmalyuk, Vladimir Simakov
We present a new approach based on the integration of the functions of a high-efficiency current switch and a laser emitter into a single heterostructure as elements of time-of-flight (TOF) systems. The approach being developed employs the effect of an electrical bistability, which occurs in the general case in thyristor structures. We report recent results obtained in a study of the dynamic electrical and optical characteristics of the pulsed sources we developed. An effective generation of 2- to 100-ns laser pulses at a wavelength of 905 nm is demonstrated. The possibility of generating laser pulses shorter than 1 ns is considered. The maximum peak power reached values of 7 and 50 W for 10- and 100-ns pulses, respectively.
The model of a new type of high-power laser light generators, based on epitaxially and functionally integrated fast highpower current switch and laser heterostructure, the so-called laser-thyristor, has been developed. In this model, the functional characteristics of the laser-thyristor were analyzed by considering the epitaxially integrated structure as an optoelectronic pair constituted by a heterophototransistor and a laser diode. It was demonstrated that the turn-on of lasing fundamentally affects the injection efficiency of the laser-thyristor. The dynamic characteristics of the laser-thyristor were examined by using analytical relations for the optical feedback. It is shown that the impact ionization can substantially raise the build-up rate of the through current across the laser-thyristor structure and, as a result, make shorter the leading edge of a laser pulse. It is demonstrated that the developed dynamic model is in good agreement with experimental results at the maximum blocking voltages.
A new approach to generation of high optical peak power by epitaxially and functionally integrated high-speed highpower current switch and laser heterostructure (so-called laser-thyristor) has been developed. This approach makes it possible to reduce the loss in external electrical connections, which is particularly important for the short-pulse highamplitude current pumping. In addition, it considerably simplifies the fabrication technology of pulsed laser sources as a commercial product and allows stacking of multiple-element systems. The epitaxially integrated AlGaAs/GaAs heterostructure of low-voltage laser-thyristor has been studied and optimized for generation of high-power pulses at a 900-nm wavelength. It is shown that the incomplete switch-on of the laserthyristor in the initial stage and the nonlinear dynamics of the emitted laser power are due to the insufficient efficiency of the vertical optical feedback in the epitaxially integrated heterostructure. Optimization of the composition and the interband absorption spectra of transistor base layers makes it possible to substantially raise the efficiency of control signals due to the rise in the photogeneration speed. Experimental laser-thyristor samples with a 200-μm aperture have been fabricated and studied. The maximum static blocking voltage does not exceed 20 V. It is shown that the generated laser pulses have a perfect bell-like shape without any indications of a nonlinear dynamics. This confirms that the changes introduced into the heterostructure design provide a sufficient efficiency of photogeneration of the control signal. As a result, the maximum optical peak power reaches 40 and 8 W at FWHM pulse durations of 95 and 13 ns, respectively. An analysis of the potential dynamics has shown that the heterostructure provides pumping of the active layer with up to 90-A pulses.
Dynamics of change of the laser heterostructure spectral characteristics under alternating strain caused by
surface acoustic wave is investigated. The study of spectral distribution of the laser radiation intensity has been also
fulfilled to reveal the interaction mechanisms in the studied structures. The interaction models are offered and the
theoretical analysis of the obtained experimental data has been carried out. Is shown, that mainly acousto-electron
interaction determines surface acoustic wave effect on spectral parameters of InGaAsP/InP laser radiation.
Power and spectral characteristics of Fabry-Perot semiconductor lasers based on at high excitation levels in
pulsed lasing mode (200 A, 100 ns, 10 kHz) are investigated and double-band lasing is reached.
Investigations of stimulated recombination processes and reasons of output optical power saturation at superhigh
pump levels (up to 0.1 MA/cm2) of semiconductor lasers based on wide variety of quantum well heterostructures (&lgr;=980-
1900 nm) are presented for the first time.
Two-photon absorption of 1.55 μm light in quantum well InGaAsP/InP laser heterostructures has been measured. Nonlinear response as high as 0.78 nA/mW2 has been found. Minimal detectable peak power 60 μW allows using this kind of semiconductor waveguide as a detector in optical autocorrelator to investigate low-power signal.
Auger coefficients have been measured in five light emitting diodes (LEDs) with strained quantum wells in active region covered a wide range of wavelength. LED were fabricated from identical high efficient laser heterostructures. The obtained Auger coefficients increase from 3 x 10-30 to 1.8 x 10-28 cm6/c as wavelength changes from 0.78 to 1.8 μm.
Development of submonolayer deposition technique can offer significant flexibility in creation of strained heterostructures of different types and material systems. It was found that under certain growth conditions the deposition of InAs insertions of less than 1 monolayer (ML) thickness in GaAs matrix forms so-called sub-monolayer quantum dots (SML QDs). The energy spectrum of these QDs can be varied over a wide range by tuning the InAs coverage and the thickness of GaAs spacers. Stranski-Krastanow (In,Ga)As QDs (SK QDs), which have been investigated in more details, have proved theoretically predicted lower threshold current density of 26 A/cm2 in compare with QW lasers. However, strong size variation of SK QDs in combination with the relatively low sheet density leads to low peak gain achievable in the ground state. This problem is the reason of typically low efficiency of SK QD-based lasers. Due to higher gain, SML QDs have proved their potential for high power laser application. In this presentation we report on further progress in the technology of SML QD lasers demonstrating high output power (6W) from 100-μm-wide laser diode emitting at 0.94 μm. High power QW-based lasers of the state-of-the-art performance are also presented for comparison.
A set of high power single mode InGaAsP/InP ridge waveguide laser diodes emitting in 1440 - 1500 nm range on peak wavelengths used for optical fiber pumping were developed and fabricated. Room temperature continuous wave output power of 300 mW was reached. Stable operation on fundamental optical mode with only 1° increase of lateral far-field pattern FWHM was confirmed up to 180 mW output power.
InGaAsP/InP SC DHS lasers with different waveguide design were fabricated and studied. Extremely high values of internal quantum efficiency of stimulated emission ηist about 97% was demonstrated experimentally in structures with step-like waveguide design which is related to lowest leakage currents above threshold and reduced threshold carriers concentration. Theoretically was shown, that it is possible to create lasers emitting at λ = 1.5 μm, with an internal quantum efficiency of stimulated emission close to 100%. ηist for structure with different waveguide design was calculated and prove to be in good agreement with experimental data.
The concept of resonant carrier many body interaction during radiative recombination was applied to explain spectra of quantum well electroluminescence at 77 K. Extremely good agreement of the calculated and experimental spectra in the entire range of emission has been achieved. Estimations give a sub-picosecond characteristic time of such radiation process.
The results of photon flux noise measurements in a quantum well semiconductor laser with 1.3 micrometer wavelength and antireflection coating on the front surface are presented. The results are compared with the theory based on quantum mechanical Langevin-Heisenberg equations.
We report the improved LPE regrowth prooess o InGaAsP/InP BR
lasers.This method is based on the efeot o laP layers growth
seleotivity. The proposed etched mesa proi1e provides the
localization o! blocking p-n-junction on the mesa sidewall in the
close vicinity o active layer. The mechanism responsible ror the
increase of threshold current density(Jth) and the decrease o
differential quantum eicienoy (ηd) in narrow (W<1Oμm) BR lasers
was revealed in the set or special experiments. The modification
of the rerowth process allowed to improve the lasing
characteristics and to achieve 160 mW single-lobe output.
The development of SCH InGaAsP/InP structures with low internal optical losses made it possible to achieve 1.2 W cw output for (lambda) equals 1.3 micrometers diodes with 100 micrometers aperture. The diode-to-fiber coupling arrangement enables one to reach a 700 mW power level in a 200 micrometers fiber.
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