[show abstract][hide abstract] ABSTRACT: High power (3W) and low divergence (4/spl deg/ at FWHM) are demonstrated at 990 nm using arrays of index guided GaInAs/(Al)GaAs quantum dot tapered lasers. A low temperature shift (0.10 nm/K) of the wavelength is observed.
Annals of Physical and Rehabilitation Medicine. 01/2004;
[show abstract][hide abstract] ABSTRACT: Semiconductor lasers and amplifiers were developed based on self-assembled quantum-dot gain material. This paper gives an overview about the recent work on GaAs- and InP-based quantum-dot devices mainly dedicated for telecom applications. The major advantage of quantum-dot like gain material, i.e. the possibility to tailor the spectral and spatial gain properties of an amplifying material, was used to optimize different device aspects, like low threshold current, broad band amplification or low temperature sensitivity. High performance GaAs-based continuous wave (cw) operating quantum-dot lasers could be fabricated with threshold currents of about 2 mA (L = 400 mum). Single mode emitting devices with emission wavelengths > 1.3 mum were realized by laterally coupled feedback gratings with threshold currents below 5 mA, output powers > 5 mW and cw operation temperatures up to 85 °C. Modulation frequencies of up to 7.5 GHz were obtained for standard device structures. For long wavelength telecom applications quantum-dot like material with dash geometry was developed on InP substrates with basic properties in the transition region between quantum-dot and -wire systems. A very large tuning range of the emission wavelength between 1.2 and 2.0 mum (room temperature) was obtained which allow the realization of material with ultra-wide gain bandwidth. Quantum-dash laser structures reaches threshold current densities < 1 kA/cm2. Ridge waveguide lasers with a cavity length of 1.9 mm show cw threshold currents of about 100 mA and maximum output powers > 40 mW per facet. With 300 mum long facet coated devices cw threshold currents of 23 mA and maximum operation temperatures in pulsed mode of 130 °C were achieved. Semiconductor optical amplifiers were fabricated by using broad band quantum-dash material. For a 1.9 mm long device, up to 22 dB gain was obtained with a three times larger spectral range than in comparable quantum well devices. High speed nearly pattern free signal amplification up to 10 GBit/s could be demonstrated and wavelength conversion experiments were performed.
[show abstract][hide abstract] ABSTRACT: Short-period Super Lattices (SSLs) have been proposed as a method of reducing carrier leakage in semiconductor lasers. SSLs increase the carrier confinement by increasing the effective barrier height due to the carriers being reflected from the SSL. Thermionically driven leakage of electrons from the quantum wells has been suggested as an important non-radiative current path in (Al)GaAs based devices which is exacerbated at high temperatures. Due to the fact that the application of high pressure causes a reduction in the zone centre -X minima splitting, pressure can be used to investigate the extent to which such leakage increase the threshold current. In this study, we compare devices with and without SSL layers and find direct evidence for leakage suppression in devices containing SSLs up to a temperature of 60 °C.
Physica Status Solidi B-basic Solid State Physics - PHYS STATUS SOLIDI B-BASIC SO. 01/2004; 241(14):3405-3409.
[show abstract][hide abstract] ABSTRACT: The monolithic combination of active light sources with photonic crystal (PC) waveguide components is a key building block for future highly integrated photonic circuits. We demonstrate the coupling of light from an InGaAs/AlGaAs ridge waveguide laser to a monolithically integrated 2D PC waveguide. The PC guide is formed by removing three or five rows in a triangular lattice of air rods etched into the semiconductor. A tapered ridge waveguide geometry is demonstrated to improve coupling efficiency, so that maximum output powers of up to 10 mW from the PC waveguide are achieved. The resulting coupled cavity laser shows single mode emission with side mode suppression ratios > 35 dB over a broad range of injection currents.
Optical and Quantum Electronics 10/2002; 34(11):1137-1144. · 0.99 Impact Factor
[show abstract][hide abstract] ABSTRACT: The authors have investigated tunable distributed feedback (DFB) lasers based on InGaAs quantum dots grown by molecular beam epitaxy. Two-section tunable DFB lasers were fabricated by patterning laterally gain coupling binary superimposed gratings perpendicular to the ridge waveguide. Side-mode suppression ratios of up to 40 dB have been achieved. The tuning range covers 30 nm.
[show abstract][hide abstract] ABSTRACT: We have fabricated waveguide based 2D photonic crystal defect microcavities. At moderate excitation powers below saturation it is possible to observe simultaneously both individual quantum dot emission tines and the cavity modes. Using the different temperature shifts of the quantum dot emission lines and the cavity modes, individual dots can be tuned in and out of resonance with the cavity. Thereby it is possible to control the spontaneous emission rate of individual quantum dots.
Quantum Electronics and Laser Science Conference, 2002. QELS '02. Technical Digest. Summaries of Papers Presented at the; 02/2002
[show abstract][hide abstract] ABSTRACT: High quality two-dimensional photonic crystals were fabricated by electron-beam lithography and a combination of reactive ion etching (RIE) and chemically assisted ion beam etching (CAIBE) in GaAs/AlGaAs slab waveguides. With optimized parameters, etch depths of more than 2 μm were achieved. This technique was used to fabricate three-dimensionally confined optical microcavities defined by a slab waveguide and a two-dimensional photonic crystal mirror structure. The optical quality of the deeply etched structures were tested by optical spectroscopy. The Q-factor of the cavity mode is dependent on the structural quality and depth of the holes in the photonic crystals. Due to the large etch depth and smooth surfaces, high quality planar microcavities could be realized with Q-factors of about 1000.
[show abstract][hide abstract] ABSTRACT: The fine structure of excitons is studied by magnetophotoluminescence spectroscopy of single self-assembled In(Ga)As/(Al)GaAs quantum dots. Both strength and orientation of the magnetic field are varied. In a combination with a detailed theoretical analysis, these studies allow us to develop a comprehensive picture of the exciton fine structure. Symmetry of the dot structures as well as its breaking cause characteristic features in the optical spectra, which are determined by the electron-hole exchange and the Zeeman interaction of the carriers. The symmetry breaking is either inherent to the dot due to geometry asymmetries, or it can be obtained by applying a magnetic field with an orientation different from the dot symmetry axis. From data on spin splitting and on polarization of the emission we can identify neutral as well as charged exciton complexes. For dots with weakly broken symmetry, the angular momentum of the neutral exciton is no longer a good quantum number and the exchange interaction lifts degeneracies within the fine-structure manifold. The symmetry can be restored by a magnetic field due to the comparatively strong Zeeman interactions of electron and hole. For dots with a strongly broken symmetry, bright and dark excitons undergo a strong hybridization, as evidenced by pronounced anticrossings when states within the manifold are brought into resonance. The fine structure can no longer be described within the frame developed for structures of higher dimensionality. In particular, the hybridization cannot be broken magnetically. For charged excitons, the exchange interaction vanishes, demonstrating that the exchange splitting of a neutral exciton can be switched off by injecting an additional carrier.
[show abstract][hide abstract] ABSTRACT: InAs/GaInAs-quantum-dot lasers emitting at 1.3 mum have been grown on GaAs substrates by solid source molecular beam epitaxy, and the device performance has been studied. Laser structures with 6 dot layers in the active region yield the best results. They show low transparency current densities and high characteristic temperatures. Ridge waveguide lasers with a cavity length of 400 mum and high reflectivity coatings exhibit threshold currents as low as 4.4 mA and output powers of 12 mW in continuous wave (cw) operation at room temperature. Unmounted devices can be operated in cw mode beyond 80°C. In pulsed mode laser operation above 150°C could be achieved with uncoated 800 mum long devices. By application of lateral chromium gratings, distributed feedback (DFB) lasers were fabricated. 800 mum high reflectivity (HR) coated devices display threshold currents of 20 mA, high side mode suppression ratios well above 40 dB and stable single mode operation.
Japanese Journal of Applied Physics 01/2002; 41:1158-1161. · 1.07 Impact Factor
[show abstract][hide abstract] ABSTRACT: The high frequency properties of InAs/GaInAs quantum dot
distributed feedback (DFB) lasers emitting at 1.3 μm have been
examined. The lasers display a small static linewidth of 1.3 MHz and a
chirp as low as 83 MHz/mA. More than 5 GHz small-signal modulation
bandwidth was observed in the first devices indicating the potential for
high-speed operation of quantum dot lasers
[show abstract][hide abstract] ABSTRACT: High-performance 1.3-/spl mu/m-emitting quantum-dot lasers were fabricated by self-organized growth of InAs dots embedded in GaInAs quantum wells. The influence of the number of quantum-dot layers on the device performance was investigated. Best device results were achieved with six-dot layers. From the length dependence; a maximum ground state gain of 17 cm/sup -1/ for six dot layers could be determined. Ridge waveguide lasers with a cavity length of 400 /spl mu/m and high-reflection coatings show threshold currents of 6 mA and output powers of more than 5 mV. Unmounted devices can be operated in continuous wave mode up to 85/spl deg/C. A maximum operating temperature of 160/spl deg/C was achieved in pulsed operation for an uncoated 2.5-mm-long ridge waveguide laser.
[show abstract][hide abstract] ABSTRACT: Highly reflecting Bragg mirrors in combination with GaInAs/AlGaAs
laser structures with two layers of self-organised GaInAs quantum-dots
are used to realise CW-operating edge-emitting microlasers with cavity
lengths down to 12 μm. Owing to the large spacing of the longitudinal
modes of 8.2 nm for 12 μm long lasers, quasi-singlemode operation is
[show abstract][hide abstract] ABSTRACT: Singlemode operation of 1.3 μm InAs/GaInAs quantum dot lasers
has been achieved using the concept of complex coupled distributed
feedback. Mode selection was realised by laterally patterned metal
gratings. At room temperature the lasers show stable singlemode emission
with sidemode suppression ratios of up to 55 dB, threshold currents as
low as 17 mA and output powers of up to 8 mW under continuous wave
[show abstract][hide abstract] ABSTRACT: We have fabricated and investigated AlGaAs-InGaAs-based ridge waveguide (RWG) lasers with two-dimensional (2-D) triangular photonic crystal (PC) mirrors using a wet-oxidized Al/sub 2/O/sub 3/ mask for the dry etching of the PC at one end of the ridge. The laser structure includes a 60-nm-thick AlAs layer positioned in the upper cladding, which is converted into Al/sub 2/O/sub 3/ after the definition of the PC by electron beam lithography and shallow etching. Etching of the holes is then continued using the Al/sub 2/O/sub 3/ mask, to a final depth of 600 nm. The continuous-wave characteristics of the lasers show a clear dependence on the period of the PC including a significant decrease of the threshold current and an increase of the efficiency for properly adjusted crystal parameters.