V M Ustinov

The time-resolved spectroscopy of InGaAs/AlGaAs heterostructures with asymmetric funnel-shape quantum wells for near- and mid-IR lasing

The dynamics of interband transitions in InGaAs/AlGaAs heterostructures with funnel-shaped quantum wells, when a narrow and deep well is positioned asymmetrically in wide and shallow ones, has been studied experimentally. These structures have been proposed as a dual-colour laser in mid- and near-IR range simultaneously. The lifetime of electrons in the ground and excited states in the quantum wells has been determined by the time of the photoluminescence intensity decline. The obtained lifetime values allow precise identification of peaks in the photoluminescence spectra and a deep insight into the process of high electron states populating. The experimentally found electron lifetime for the interband transitions corresponds on the order of magnitude with the interband transitions lifetime in GaAs. Analysis of the photoluminescence spectra as well as the time dependence of the photoluminescence intensity decline indicates a possibility of population inversion achievement in these structures under high excitation.

Optical phenomena connected with intraband carrier transitions in quantum dots and quantum wells

Optical phenomena in the mid-infrared range connected with interlevel and intersubband charge-carrier transitions in quantum dot and quantum well (QW) heterostructures under optical and electrical pumping were investigated. Spectra of interband photoluminescence are also presented. The existence of a metastable level in funnel-shaped QWs is experimentally confirmed. The intersubband transition dynamics in asymmetrical pairs of tunnel-coupled QWs was studied by means of pump-and-probe time-resolved spectroscopy. This paper was presented at the 3rd Russian Workshop on Nanophotonics, Nizhnii Novgorod, Russia, 26-29 March 2001.

Investigation of the Modified Structure of a Quantum Cascade Laser

The process of obtaining a modified structure for quantum cascade lasers is studied; this process includes growth using molecular-beam epitaxy, plasma etching, photolithography with the use of liquid etching, and the formation of special contacts for decreasing losses in the waveguide. The use of a special type of structure makes it possible, even without postgrowth overgrowth with a high-resistivity material, to attain parameters satisfying requirements to heterostructures in high-quality quantum cascade lasers at maximal simplification of the entire preparation process.

Quantum dot semiconductor disk laser at 1.3 μm.

We present a semiconductor disk laser (SDL) emitting at the wavelength of 1.3xa0μm. The active region of the SDL comprises InAs quantum dots (QDs) that are embedded into InGaAs quantum wells (QWs). An output power over 200xa0mW is obtained at 15°C, which represents the highest output power reported from QD-based SDLs in this wavelength range. The results demonstrate the feasibility of QD-based gain media for fabricating SDLs emitting at 1.3xa0μm.

Optical absorption and birefringence in GaAs/AlAs MQW structures due to intersubband electron transitions

Optical absorption and birefringence due to intersubband electron transitions were investigated in GaAs/AlAs MQW structures. These structures are intended for creation of a mid-infrared laser of a new type. Experimental results on electron redistribution between size-quantization levels under electron heating were obtained up to an electric field of 3500?V?cm-1.

Optical characterization of mid-infrared range quantum-cascade laser structures grown by MBE

Optical characteristics of quantum-cascade laser structures were studied in this work. Current-voltage characteristics and dependencies of photoresponse signal on current through the structure were measured together with the spontaneous and stimulated emission spectra. The stimulated emission with wavelength close to 9.56 μm with optical power of tens of milliwatt was observed in a pulsed mode.

1.3 μm InAs quantum dot semiconductor disk laser

Vertical-external-cavity surface-emitting lasers (VECSEL), or semiconductor disk lasers (SDL), are attractive laser source for a wide range of applications owing to unique possibility to combine high output power with an excellent beam quality [1]. The intrinsic features of InAs quantum dots (QD) can offer low threshold, broad wavelength tunability, fast carrier dynamics and low temperature sensitivity. Recently, continuous wave (CW) operation of QD-based VECSEL emitting at 1.25 μm with output powers reaching multi-watt levels were achieved at room temperature [2]. However, extending the emission wavelength to 1.3 μm and beyond becomes more challenging. To date, QD-based VECSEL with optical power greater than 0.5 mW at 1305 nm has been demonstrated [3]. Here, we present a record-high power InAs/InGaAs QD-based VECSEL operating at the wavelength of 1.3 μm.

VCSEL polarization control by rhomboidal selectively-oxidized current aperture

Vertical-cavity surface-emitting lasers (VCSELs) are low-cost high-performance light sources for high-speed data communication systems, optical interconnects and different sensors. New VCSEL applications (spectroscopy, compact atomic clock) require single-mode operation with stable linear polarization combined with high temperature stability. While conventional GaAs-based VCSELs with small selectively-oxidized current apertures demonstrate stable fundamental transverse mode operation they have unstable polarization due to cylindrical symmetry and isotropic gain. Currently the most popular method for VCSEL polarization control is based on precise etching of sub-wavelength grating in output distributed Bragg reflector. Drawbacks of this approach are relatively complicated fabrication technology and limited output power. In this work we discuss alternative approach for single-mode polarization-stable VCSELs based on rhomboidal selectively-oxidized current aperture combined with intracavity contacts.

Ultimate modulation bandwidth of 850 nm oxide-confined vertical-cavity surface-emitting lasers

Complex influence of photon lifetime (controlled by the mirror loss) and aperture size on the performance of 850 nm InGaAlAs oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with fully doped AlGaAs-based distributed Bragg reflectors (DBR) was investigated. We find a tradeoff between photon lifetime and gain nonlinearity for maximizing the optical bandwidth, leading to the optimum aperture size close to 4-6 μm. In spite of the reduced photon lifetime (from 4 ps to 1 ps), the excess damping caused by the current-induced self-heating limits the ultimate modulation bandwidth for the given VCSELs design at 24-25 GHz. Further improvement in high frequency characteristics can be facilitated by decrease of the heat generation and improvement of the heat removal from the active region as well as by proper engineering of the scattering loss at the oxide aperture while keeping the low capacitance optimizing design of the oxide aperture.

Intersubband emission and carrier dynamics in GaAs/AlGaAs tunnel‐coupled quantum wells after ultrafast optical pumping

Optical mid‐infrared (MIR) gain in n‐doped tunnel‐coupled semiconductor quantum well structures is studied at a sample temperature of 20 K. The structure is excited via the e1‐e3, intersubband transition by an ultrashort MIR pulse and the gain at the e2‐e3 transition frequency is monitored by a second time‐delayed tunable pulse in the MIR. At high pump intensities, even a narrow MIR emission band is found at the e2‐e3 transition frequency.