In this letter, we report about mode characteristics of microcavity lasers with red-emitting InP quantum dots. The mode spectra and the quality factor of devices with different oxide aperture sizes are analyzed. The lateral mode confinement in the electrical devices is defined via oxide apertures. We found a good agreement between a simple analytical modeling of the mode structure and measurements, which allows to adjust the design of future devices. The quality factors show an analogous behavior as etched micropillars. The enhanced intensity of the higher order modes compared to the fundamental mode can be explained with the current density distribution within the device favoring higher order modes.

We report on in-lab free space quantum key distribution (QKD) experiments over 40 cm distance using highly efficient electrically driven quantum dot single-photon sources emitting in the red as well as near-infrared spectral range. In the case of infrared emitting devices, we achieve sifted key rates of 27.2 kbit s−1 (35.4 kbit s−1) at a quantum bit error rate (QBER) of 3.9% (3.8%) and a g(2)(0) value of 0.35 (0.49) at moderate (high) excitation. The red emitting diodes generate sifted keys at a rate of 95.0 kbit s−1 at a QBER of 4.1% and a g(2)(0) value of 0.49. This first successful proof of principle QKD experiment based on electrically operated semiconductor single-photon sources can be considered as a major step toward practical and efficient quantum cryptography scenarios.

In the current work, we show a detailed analysis of the transverse beam profile and polarization characteristics of devices with one and three oxide apertures. A Gaussian transverse beam profile is achieved with an oxide aperture diameter of less than 6 μm. The laser light is linearly polarized with a high degree of polarization (> 97 %) in the complete current range. The stable polarization direction can be attributed to ordering effects ocurring during epitaxial growth of the GaInP material system and a reduction in crystal symmetry. Different oxide aperture diameters can be implemented in one device due to high oxidation selectivity of the AlxGa1-xAs layer depending on aluminum content. These deep oxidation layers lead to a reduction of the parasitic capacitance, while beam profile and polarization characteristics are not affected.

The wide range of applications in biophotonics, television or projectors, spectroscopy and lithography made the vertical external cavity surface-emitting lasers an important category of power scalable lasers. The possibility of bandgap engineering, inserting frequency selective and converting elements into the external laser cavity and laser emission in the fundamental Gaussian mode leads to ongoing growth of the area of applications for tunable laser sources. We present an intra cavity frequency-doubled VECSEL with emission wavelength around 330 nm and a maximum tuning range of more than 7 nm with output powers exeeding 100 mW. Frequency doubling is realized with an anti-reflection coated beta barium borate crystal, while a birefringent filter, placed inside the laser cavity under Brewster's angle, is used for frequency tuning. The fundamental laser, pumped by a 532nm Nd:YAG laser under an angle of 50 degrees normal to the surface, is realized by a multi quantum well structure consisting of 20 compressively strained GaInP quantum wells in an AlxGa1-xInP separate confinement heterostructure and it emits around 660 nm. The VECSEL-chip with its n-lambda cavity is completed by a 55 lambda/4 pairs Al0.50Ga0.50As/AlAs distributed Bragg reflector. Next to the optical properties of the device, we show results of different arrangements of the quantum wells, namely five times four and ten times two packages.

For a single quantum dot under excitation with short electrical pulses the dependence of the photon anti-bunching on pulse width and excitation strength is studied in a theory-experiment collaboration.

We present excitation-pulse-width- and pump-power-dependent microelectroluminescence and photon statistics measurements on electrically driven single-photon devices based on InP/AlGaInP quantum dots (QDs). For an excitation regime far below QD saturation, the results show a characteristic decrease of the purity of the single-photon emission [${g}^{(2)}(0)$ value] with increasing excitation pulse width. For stronger excitation pulses close to QD saturation, strong antibunching is maintained for a much larger pulse width. In this case the ground-state exciton emission, which is used for the single-photon source, is inhibited during the pump pulse due to the presence of higher excited states. This prevents multiple-ground-state emission and reexcitation during long pump pulses and delays the single-photon emission to the end of the pulse, as predicted by theory and confirmed experimentally.

We present experimental investigations of the transverse beam profile and polarization characteristics of GaInP-based oxide-confined vertical-cavity surface-emitting lasers in dependence on the oxide aperture size, mesa size, current, and temperature. We demonstrate that these lasers with aperture diameters of less than 6 mu m are required for stable fundamental-mode operation. The influence of operation current and external temperature on the mode shape is investigated. We experimentally present a highly stable linearly polarized GaInP-based microcavity laser emitting at around 655 nm, where the polarization characteristics originate from intrinsic material properties.

This paper presents a vertical external cavity surface emitting lasers (VECSEL) system based on 20 compressively-strained GalnP quantum wells (QWs) for an operation wavelength of around 660 nm. In the active region, five QW packages are placed in (Al0.55Ga0.45)0.51In0.49P cladding layers in a resonant periodic gain (RPG) design. With simulations based on the transfer matrix method, the QW packages are placed in the antinodes of the standing wave of the electric field intensity in the active region. The 3-λ cavity is fabricated on a 55λ/4 pairs Al0.50Ga0.50As/AlAs distributed Bragg reflector.

In our work pulsed electrical excitation was used to excite single InP/Ga 0.51 In 0.49 P quantum dots which were embedded into the intrinsic region of a p-i-n mesa structure. To enhance collection efficiency the active region is surrounded by two Bragg reflectors forming a low-Q cavity. The samples are excited using a pulse pattern generator together with a fast amplifier. We obtain triggered single-photon emission in the red spectral range (~ 650 nm) at an excitation repetition rate of up to 200 MHz.

We present a detailed analysis of the transverse beam profile and the polarization characteristics of red-emitting oxide-confined vertical-cavity surface- emitting lasers (VCSELs). We demonstrate that oxide aperture sizes smaller than 6 mu m are required for emission in fundamental mode. We further show first steps towards integrating beam shaping optics directly into the top mirror of the VCSEL.

We demonstrate electrical pumping of self-assembled InP/Ga(0.51)In(0.49)P quantum dots embedded in a p-i-n resonant-cavity-diode structure with emission in the red spectral region. A high aluminum containing Al(0.98)Ga(0.02)As layer allows wet thermal oxidation and implementation of a current restricting oxide aperture above the active region. The intended use of these InP-quantum dots in such a resonant-cavity-LED structure as a pulsed electrically driven single-photon emitter was confirmed by measuring the second order intensity correlation function g((2))(tau) with a Hanbury-Brown and Twiss type setup. The correlation measurements performed on a single quantum dot (approximate to 40K) show a clear antibunching behavior (g((2))(0) <0.24) up to 200 MHz as expected for a single-photon emitter. (C) 2010 Elsevier B.V. All rights reserved.

We present a non-resonantly pumped red-emitting vertical external cavity surface-emitting laser system based on a multi-quantum-well structure with 20 compressively-strained GaInP quantum wells for an operation wavelength between 645-675 nm. Five quantum well packages with four quantum wells are placed in a separate confinement heterostructure in a resonant periodic gain design in quaternary AlGaInP barriers and cladding layers, respectively. The 3 lambda cavity is fabricated on a 55 lambda/4 pairs Al0.50Ga0.50As/AlAs distributed Bragg reflector. By bonding an intra-cavity diamond heatspreader to the chip, continuous-wave operation exceeding 700 mW output power at a wavelength of 662 nm with a low threshold power of 0.8 W was achieved. A thermal resistance value of R-1 = 5 K/W and R-2 = 7 K/W could be determined for our setup at operation heatsink temperatures of T-hs = -28 degrees C and T-hs = 16 degrees C, respectively. Measurements of the slope efficiency within a v-type cavity with different outcoupling mirror reflectivities lead to a cavity round-trip transmission factor of T-loss = 98.6% and an absorption efficiency of eta(abs) = 17.6%. Using a birefringent filter in a folded cavity, a maximum tuning range of 22 nm at a center wavelength of 667 nm could be shown. With this method wavelengths below 650 nm were observed. Utilizing a non-linear crystal for intra-cavity frequency doubling in this cavity geometry, coherent emission down to 322 nm could be detected. In the UV spectral range, a maximum tuning range of 10 nm could be measured at a center wavelength of 330 nm, so we could match the HeCd laser line at 325 nm.

Vertical-cavity surface-emitting laser (VCSEL) emitting at 650 nm are promising candidates as transmitter in optical data communication systems based on polymer optical fibres (POF) because of a narrow minimum in transmission loss of POF at this wavelength. So far, small-signal resonance frequencies fr have been reported for 670 nm devices of 7 GHz and for 656 nm VCSEL of 3.75 GHz, respectively. In this paper the authors discuss theoretically and experimentally the influence of heat dissipation on the modulation behaviour of red 650 nm VCSEL.

In this letter, we report on laser light emission, in the red spectral range, of electrically pumped self-assembled InP quantum dots which were embedded in a microcavity structure realized by monolithically grown highly reflective AlGaAs distributed Bragg reflectors. Common semiconductor laser processing steps were used to fabricate stand-alone index-guided vertical-cavity surface-emitting lasers with oxide apertures for optical transverse mode confinement and electrical current constriction. Ultra-low threshold current densities of around 10 A/cm2 and room temperature lasing were achieved.

We used sub‐nanosecond electrical pulses to excite single InP/GaInP quantum dots to realize triggered single‐photon emission in the red spectral range. The electroluminescence of different quantum dots was investigated and the successful injection of short voltage pulses was verified by time—resolved and autocorrelation measurements.

We present a vertical external cavity surface-emitting laser system based on a multi-quantum-well structure with 20 compressively strained GaInP quantum wells for an operation wavelength of around 665 nm with a monolithic integrated distributed Bragg reflector. With the help of an intra-cavity diamond heatspreader the laser operates in continuous-wave mode. Operation with a TEM00 Gaussian beam profile and a beam propagation factor of M 2≤1.05 is shown as well as a high resolution spectrum of the laser line, which shows the etalon effect of the diamond. The laser can be operated at a maximum output power exceeding 1.2 W with a slope efficiency of η diff=18%. At maximum output power the wavelength of the laser resonance is at 670 nm, which is shortest reported until now at powers exceeding 1 W. By rotating a birefringent filter in an extended folded cavity arrangement a wavelength tuning of 21 nm was attained.

We demonstrate an optically pumped vertical external-cavity surface-emitting laser in a compact v-shaped cavity configuration for frequency doubling to the ultraviolet (UV) spectral range at ∼330 nm. The fundamental red laser emission is realized with a metal-organic vapor-phase epitaxy grown (GaxIn1−x)0.5P0.5/[(AlxGa1−x)yIn1−y]0.5P0.5 multi-quantum-well structure. Second harmonic generation is accomplished by using a beta barium borate non-linear crystal to generate maximum UV output powers exceeding 100 mW. By using a birefringent filter, we are able to tune the fundamental laser resonance to realize a maximum tuning range of 7.5 nm of the second harmonic.