Quantum well intermixing (QWI) can bring considerable benefits to the reliability and performance of high power laser diodes by intermixing the facet regions of the device to increase the band-gap and hence eliminate absorption, avoiding catastrophic optical damage (COD). The non-absorbing mirror (NAM) regions of the laser cavity can be up to ~20% of the cavity length, giving an additional benefit on cleave tolerances, to fabricate very large element arrays of high power, individually addressable, single mode lasers. As a consequence, large arrays of single mode lasers can bring additional benefits for packaging in terms of hybrization and integration into an optics system. Our QWI techniques have been applied to a range of material systems, including GaAs/AlGaAs, (Al)GaAsP/AlGaAs and InGaAs/GaAs.

Single-frequency grating outcoupled surface emitting (GSE) semiconductor lasers emitting at 1550 nm with output powers exceeding 1.6 mW into a multi-mode fiber, threshold currents below 25 mA and with > 30 dB side-mode suppression ratios are reported. These lasers consist of a 500 μm long horizontal cavity, and a 10 μm long second-order outcoupler grating sandwiched between 250 μm long first-order distributed Bragg reflector (DBRs) gratings. Higher output powers can be achieved with longer outcoupler gratings. These GSE lasers operate at 2.5 Gbps and have a full-width at half-maximum (FWHM) beam divergence of 5 x 9 degrees.

A very wide tuning range of dual-wavelength semiconductor lasers with properly designed nonidentical InGaAsP quantum wells is reported. By well aligning the external cavity, the dual-wavelength operation can be achieved with a record wavelength separation about 191 nm (27.4 THz) at 22.7°C. The wide separation of two wavelengths is possible due to a proper modification of the external-cavity configuration and reduced gain competition of laser modes.

The explosive growth of Internet/intranet traffic has created a strong demand for cost-effective high-speed light-sources to be used in local access networks and data links. The frequency of relaxation oscillation (fr) is a major factor that restricts the high-speed operation of laser diodes. To achieve a high fr, the material of an active layer should have a large differential gain. By using GaInNAs, very deep quantum wells, especially in the conduction band can be formed. Deep quantum wells bring a large differential gain. In this paper, we show how GaInNAs lasers can be applied in this application

Before processing the InGaAsN/GaAs edge emitting lasers, post-growth rapid thermal annealing (RTA) was applied on the wafer. Different RTA results in different threshold current density (J_th). RTA at 720°C reduces the J_th significantly but keeps the linear fit slope of J_th vs 1/L (L is the cavity length). It indicates that RTA at 720°C can decrease the absorption losses. High temperature RTA at 890°C can dramatically decrease the linear fit slope, which indicates that the carrier conductivity is improved dramatically even the RTA time is only one second.

Universal self-organisation on surfaces of semiconductors upon deposition of a few non-lattice-matched monolayers using MOCVD or MBE lead to the formation of quantum dots. Their electronic and optical properties are closer to those of atoms than of solids. We have demonstrated for QD-lasers a record low transparency current density of 6A/cm² per dot layer at 1.16 μm, high-power of 12W, an internal quantum efficiency of 98%, and an internal loss below 1.5 cm-1. Relaxation oscillations indicate the potential for cut-off frequencies larger than 10 GHz. GaAs-based QD-lasers emitting at 1.3 μm exhibit output power of 5 W and single transverse mode operation up to 300 mW. At 1.5 μm again an output power of 5 W has been obtained for first devices showing a transparency current of 700 A/cm². Single mode lasers at 1.16 and 1.3 μm show no beam filamentation, reduced M², sensitivity to optical feedback by 30 db and α-parameter as compared to quantum well lasers. Passive mode locking of 1.3 μm lasers up to 20 GHz is obtained. Thus GaAs-lasers can now replace InP-based ones at least in the range up to 1.3 µm, probably up to 1.55 μm.

Er or Er/Yb doped fibre amplifiers are key components for high bit rate, WDM, networks. Reliable, high power laser diodes at 980nm are the essential devices for pumping these amplifiers. Applications where a high fibre coupling efficiency is required, demand lasers with high spatial beam quality, a property not inherent to broad area multimode lasers. Tapered lasers are today one of the most interesting solution in terms of high brightness (high power with high spatial beam quality). Furthermore, a reduced temperature shift of the emission wavelength is important for high power optical pump applications because this implies a less stringent temperature control for wavelength adjustment. New GaInAs/(Al)GaAs quantum dot materials exhibit a high wavelength stability vs. current and temperature. Combining these quantum dots as active region and tapered waveguide, we have developed tapered laser diodes with standard AR/HR coatings. This devices showed high optical powers at 980nm with low M² factors in the slow axis. Furthermore, we have measured very low wavelength variations at 20°C with current and with temperature, which is weaker than typical wavelength variations of quantum well lasers.

Nanoengineering approach was used to develop an efficient active medium based on self-assembled InAs/GaAs quantum dots (QDs) for laser diodes operating at elevated temperatures. Photoluminescence (PL), transmission electron microscopy, and electroluminescence were used to study the influence of an overgrowth procedure on the properties of multiple-layer QDs. Optical properties of QDs were optimized by the adjustment of a GaAs overlayer thickness prior to a heating step, responsible for the truncation of the pyramid-shaped QDs. Triple-layer QD edge-emitting lasers with 1220 nm emitting wavelength exhibited a maximum saturated modal gain of 16 cm^-1. To use truncated QD active medium for vertical cavity surface emitting lasers, seven layers of QDs with 20 nm of short period superlattice barriers between layers was developed. A wavelength of 1190 nm edge-emitting lasers with 120 nm total thickness 7xQDs active medium showed almost two times higher maximum saturated gain, 31 cm^-1. Unfortunately, these lasers with closer distance between QD layers in active medium demonstrated stronger temperature dependence (with To = 110 K) of threshold current density and lasing wavelength. A record high characteristic temperature for lasing threshold, To = 380 K up to 55 C, was measured for edge-emitting laser diodes, which contained triple-layer truncated QD active medium. We believe that AlAs capping in combination with truncation procedure result in significant suppression of carrier transport between QDs within the layer as well as between QD layers.

This paper provides current status and prospects of quantum-dot semiconductor optical amplifiers, based on our pioneering work covering the proposal of their promising features, the quantum-dot optical device theory, experimental demonstrations, and the design and assembly of all-optical switching modules.

We examine the mechanisms that lead to a low value of saturated modal gain in both 1μm emitting InGaAs based and ≈ 700nm emitting InP/GaInP quantum dot laser systems. We explain the observation that the value of the saturated modal gain increases as the temperature decreases using a simple model of the filling of the available dot and wetting layer states according to a Fermi-Dirac distribution. We show that it is the relatively large number of available wetting layer valence states and their proximity in energy to the dot states that limits the modal gain. We measure the population inversion factor for samples containing different numbers of layers of dots and for samples where the dots are grown in a quantum well (DWELL) and for dots grown in bulk layers of either GaAs or Al_0.15Ga_0.85As (non-DWELL). Comparison of this data with that calculated for a Fermi-Dirac distribution of carriers in the available states demonstrates that for most of the samples the carriers in the ground states of the quantum dots are not in thermal equilibrium with those in higher lying energy states - the excited states or wetting layer.

A full evaluation of the performance of InGaAs quantum dots as saturable absorbers in multi-contact lasers emitting at a wavelength of 1μm has been carried out. The light-current curves of the two-section quantum dot laser have been measured at 300K with varying levels of reverse bias applied to the absorber section and are compared with a quantum well control sample. This measurement indicates that the quantum confined stark effect (QCSE) is very different for the quantum dots, and this is confirmed by measurements of differential loss spectra as a function of reverse bias. Up to voltages of - 6V there is no shift in the absorption edge of the quantum dots showing that the QCSE is weak for this 0D system. Dynamic measurements show that self-pulsation in these lasers is highly temperature dependent, and completely ceases below 150K. We have also measured the absorber recovery time, which is found to increase from 40ps at 300K to 600ps at 50K, demonstrating that a high loss condition cannot be achieved quickly enough at low temperature for self-pulsation to occur.

In this work we present a detailed study of picosecond optical pulse generation using high-repetition rate mode-locked quantum dot lasers. MOCVD-grown quantum dot lasers emitting at 1.1μm and MBE-grown quantum dot lasers emitting at 1.3μm are investigated. Passive mode-locking at 10GHz, 18GHz and 36GHz with pulse widths in the 6-12ps range are reported. Hybrid mode-locking is demonstrated at 10GHz, showing a significant improvement in the RF spectral characteristics when compared with passive mode-locking. A timing jitter of 600fs (2.5MHz to 50MHz) is measured in the 18GHz passively mode-locked laser. Autocorrelation techniques are used to characterise the high repetition rate mode-locked lasers as well as the time-bandwidth product of the optical pulses. Fourier-transform limited pulses are obtained from passively mode-locked QD lasers.

Self-organized quantum dots have been used with great success in quantum dot infrared photodetectors (QDIPs), wherein intersublevel transitions between confined electron states are utilized. Many attributes make self-organized quantum dots attractive for the realization of intersublevel infrared light sources for the mid- to far-infrared wavelength range. Intersublevel electroluminescence has been demonstrated from both bipolar and quantum cascade unipolar structures, with coherent emission observed in the bipolar case. Coherent mid-infrared emission from bipolar selforganized quantum dot devices has been observed at room temperature, centered at 13μm. The cavity is designed to support both intersublevel and interband light, so that interband lasing can quickly depopulate the ground state of the quantum dots. Devices show a distinct turn-on at 1.1kA/cm² but suffer from broad linewidth. Unipolar quantum dot cascade structures are being designed with a strain-compensating GaAs_1-xN_x / GaAs injector region. Using this material system, structures with as many as 30 cascade periods have been successfully grown by molecular beam epitaxy (MBE). TE polarized electroluminescence at 22μm has been observed from such structures at cryogenic temperatures.

This paper is a review of the recently introduced slab-coupled-optical-waveguide laser, a high-power, high-brightness semiconductor laser source that emits light in a single-spatial, lowest-order mode that is nearly circular in cross section and has a modal diameter of several micrometers. Such lasers have been demonstrated in InGaAs-InP materials, emitting near 1.3-μm wavelength, and in AlGaAs-InGaAs-GaAs materials, emitting at several wavelengths in the range between 915 and 980 nm. CW output power over 1 W has been obtained in diffraction limited beams with over 80% coupling efficiency to single-mode optical fibers. This coupling is achieved by simple butt coupling of the fiber directly to the laser without the use of optical lenses.

A new type of laser diodes with good beam quality is introduced. The far-field divergence angle can be close to diffraction-limited value. In the new design, the direction of the waveguide on a broad area Fabry-Perot laser diode is tilted at an angle from the facet normal. This design is called “angled broad area laser diode”. In this tilted waveguide device, filamentation is not observed. The far-field divergence angle is generally within 5 times the diffraction-limited value. This tilted broad area laser is advantageous over the angled grating DFB laser because the difficulty of matching the grating period with peak gain wavelength is avoided.

We present a single-mode, 808 nm, AlInGaAs/AlGaAs/GaAs, strained, quantum-well laser with a record low, vertical divergence-angle of 12 degrees and high slope-efficiency of 1.0 W/A. Epitaxial-up mounted devices have operated with no measurable degradation at 150 mW, 50°C for 3500 hours.

A kink mechanism of a red (658nm) laser diode (LD) has been investigated in order to achieve a higher power operation of over 200mW. The experimental results indicate that a main origin of the kink generation is due to the deviation of the refractive index step caused by the local heat generation at the stripe region. To reduce the heat generation at the stripe region, an extension of a cavity length of the LD is applied. The LD with the cavity length of 1500μm realizes a kink-free 200mW operation even at 80°C. Also, this LD shows a reliable pulsed operation of 230mW at 75°C and 250mW at 70°C for over 1700 hours. This is the highest power operation among narrow stripe 658nm LDs.

Laser diodes at 980 nm have important applications in medicine (surgery, dentistry) and Telecoms for WDM, high bit rate networks (Er or Er/Yb doped fibre amplifiers). These applications need a high coupling efficiency of the source into a fibre. High brightness mini-bars with an emissive length of 2.7 mm have been recently developed. These devices consist of an array of aluminium free active region index guided tapered laser diodes with standard AR/HR coatings. We have improved the performances as a result of a new epitaxial layer and a new mini-bar design. We measure an optical output power of 25W at 40A under CW operation at 15°C. At 25°C and 33A, we obtain 20W CW and the far field along the slow axis has a Gaussian shape, with a low FWHM value of 3.5°. Along the fast axis, the far-field also has a Gaussian shape and a FWHM of 31,5°. To couple this tapered diode laser mini-bar into a 100μm diameter fibre (0.26 numerical aperture), we use a patented collective beam shaping technique for optical coupling. We obtain a coupled power of 11.2W under CW operation at 971 nm, 21°C with an emitted power from the mini-bar of 21.7W, resulting in a coupling efficiency of 52%. The conductively cooled mini-bar, all the optics and the optical fibre connector are assembled into a 82x62x23mm package. To our knowledge this is the highest reported power coupled into 100μm optical fibre from a single laser diode chip using a collective coupling scheme without any array of micro-optics.

We report on the use of etched curved facets to form semiconductor lasers based on unstable resonators with a real internal focus. The lasers which have a cleaved output facet operate to > 1W continuous wave power with a diffraction limited central lobe when corrected for spherical phase. The astigmatism is found to be equal to the geometric calculation and is stable throughout the operating range. Beam degradation is associated with temperature gradients. We have fabricated devices at 1200nm, 980nm and 800nm based on reactive ion etching of GaAs structures demonstrating that the technique can be considered as a platform technology. We discuss the formation of near (facet) fields from the laser and the definition of beam quality for these lasers. The technology has also been used to etch both facets of the resonator to obtain a collimated output beam. In summary, these lasers act both as a high brightness source with reduced power density on the facet as well as a versatile source for designed output and can be scaled into array format.

We present pulsed operation of index-coupled distributed feedback quantum cascade lasers based on the GaInAs/AlInAs/InP materials system emitting at a wavelength around 5.4 μm. The emission is single mode in the entire investigated temperature range between 240K and 350K with a side mode suppression ratio larger than 27 dB. These devices are employed in a fast gas detection experiment for the quantitative detection of nitric oxide. With the present measurement system minimum noise equivalent concentrations between 16.7 ppbv and 23.3 ppbv are obtained, corresponding to minimum detectable optical densities between 4.7•10^-5 and 6.5•^10-5.

Monte Carlo simulation of carrier dynamics and far-infrared absorption in a selectively-doped p-type multi-layer Ge structure with vertical transport was performed to test a novel terahertz laser concept. The design exploits the known mechanism of THz amplification on intersubband transitions in p-Ge, but with spatial separation of light hole accumulation regions from doped regions, which allows remarkable enhancement of the gain. The structure consists of doped layers separated by 300-500 nm gaps of pure-Ge. Vertical electric field (~ 1-2 kV/cm) and perpendicular magnetic field (~ 1T) provide inversion population on direct intersubband light- to heavy-hole transitions. Heavy holes are found to transit the undoped layers quickly and to congregate mainly around the doped layers. Light holes, due to tighter magnetic confinement, are preferably accumulated within the undoped layers. There the relatively small ionized impurity and electron-electron scattering rates allow higher total carrier concentrations, and therefore higher gain, than in bulk crystal p-Ge lasers. In contrast to GaAs-based THz quantum cascade lasers (QCL), the robust design and large structure period suggest that the proposed Ge structures might be grown by the technologically-advantageous chemical vapor deposition (CVD) method. The ability of CVD to grow relatively thick structures will simplify the electrodynamic cavity design and reduce electrodynamic losses in future THz lasers based on the presented scheme.

The recent extension of quantum cascade lasers (QCLs) from the mid-infrared to the terahertz frequency range (1-10 THz) promises to help address the relative lack of compact, coherent radiation sources in this spectral regime. We report our recent development of terahertz QCLs based on a resonant phonon depopulation scheme coupled with high-confinement, low-loss, metal-metal waveguides for mode confinement. A 3.2 THz laser (λ≈ 93.4 μm) is presented that operates in continuous wave mode up to a temperature of 93 K and up to 133 K in pulsed mode. Also presented is a 2.1 THz laser (λ ≈ 141 μm) that lases up to 40 K in continuous wave mode and 72 K in pulsed mode.

The physical processes of quantum-cascade structures (QCSs) and the lasing properties of quantum-cascade lasers (QCLs) have been investigated by current-voltage characteristics, interband photoluminescence (PL) spectroscopy, and intraband infrared spectroscopy. Undoped QCSs with 20 periods as well as complete QCLs with 30 periods based on GaAs/Al_0.33Ga_0.67As have been fabricated by molecular-beam epitaxy. The population of both the lower and upper laser level can be directly observed by interband PL above a critical field strength in undoped QCSs, which are photo-excited only in the GaAs contact layers. This occupation of the laser levels is correlated with a negative differential conductance in the dark I-V characteristic at this critical field strength. The PL line of the upper laser level is split into two lines, originating from the resonant coupling of the upper laser level with the injector level. The lasing properties of a set of complete QCLs have been investigated as a function of the injector doping density between 3.5 and 10×10¹¹ cm^-2. The intermediately doped QCLs with a doping density of about 6×10¹¹ cm-2 exhibit a maximum in the lasing energy, maximum operating temperature, and characteristic temperature parameter, while the threshold current density becomes minimal. For all other QCLs, the threshold current density increases, which is correlated with a decrease in the lasing energy. The frequency dependence of the absorption of free carriers mainly in the waveguides essentially determines the increase of the threshold current density with decreasing lasing energy.

Type-II interband cascade lasers are promising in becoming efficient and compact mid-infrared (3-5 microns) light sources for many applications. Significant progress toward such a goal has recently been made in terms of lowering their threshold current densities (e.g. ~9 A/cm² at 80 K) and raising operation temperature (e.g. 325 K in pulsed and 200 K in cw modes). Also, continuous wave operation of single-mode distributed feedback interband cascade lasers has been demonstrated. We review the recent progress of the Sb-based mid-IR interband cascade lasers and present some latest results.

We describe the realization of Quantum Cascade photonic-crystal microlasers. Photonic and electronic bandstructure engineering are combined to create a novel Quantum Cascade microcavity laser source. A high-index contrast two-dimensional photonic crystal forms a micro-resonator that provides feedback for laser action and diffracts light vertically from the surface of the semiconductor chip. A top metallic contact is used to form both a conductive path for current injection as well as to provide vertical optical confinement to the active region through a bound surface plasmon state at the metal-semiconductor interface. The device is miniaturized compared to standard Quantum Cascade technology, and the emission properties can in principle be engineered by design of the photonic crystal lattice. The combination of size reduction, vertical emission, and lithographic tailorability of the emission properties enabled by the use of a high-index contrast photonic crystal resonant cavity makes possible a number of active sensing applications in the mid- and far-infrared. In addition, the use of electrical pumping in these devices opens up another dimension of control for fundamental studies of photonic crystal and surface plasmon structures in linear, non-linear, and near-field optics.

We have fabricated and characterized 2.7- and 2.8-μm wavelength In(Al)GaAsSb/GaSb two-quantum-well diode lasers. The material was grown using molecular-beam epitaxy. All lasers have 2-mm cavity lengths and 100 μm apertures. Continuous wave operation up to 500 mW was recorded at 16 °C from 2.7-μm lasers, while 160 mW was obtained from 2.8-μm lasers. Threshold current densities as low as 350 A/cm² were recorded from 2.7-μm lasers with external quantum efficiencies of 0.26 photon/electrons. The maximum wall-plug efficiency was 9.2 % at a current of 2.4 A. A peak power of 2.5 W was recorded in the pulsed-current mode operation at 20 °C at 2.7 μm and 2 W at 2.8 μm. Characteristic temperatures of T0 = 71 K and T1 = 86 K were measured from the 2.7-μm devices. T0 = 59 K and T1 = 72 K for the 2.8-μm lasers. The devices have differential series resistances of about 0.18 Ω with estimated thermal resistances of about 5 K/W. Measurements of gain, losses, threshold current, device efficiency and spontaneous emission of the lasers show that it is the hole leakage from QWs into the waveguide, and not Auger recombination that limits CW room temperature output power of long wavelength GaSb-based type-I QW lasers at least up to wavelengths of 2.8 μm. A design approach to extend the operating wavelength of high power In(Al)GaAsSb/GaSb lasers to more than 3 μm is discussed.

Mid-infrared “W” quantum-well diode lasers with reduced turn-on voltages are reported. Devices with coated facets operated in continuous-wave mode up to 195 K, where the emission wavelength was 3.56 microns. At 78 K the threshold current density was 67 A/cm², the maximum output power was 198 mW, and the maximum slope efficiency was 106 mW/A. One of these lasers was used to detect methane, by exploiting the absorption band in the vicinity of 3.3 microns. Preliminary measurements demonstrated detection of methane at partial pressures down to 7 x 10^-7 atm. in a nitrogen atmosphere.

We study effects of modulation doping in a type-II quantum well by performing a self-consistent band structure calculation using the 8-band k • p theory. We show that modulation doping can convert a type-II quantum well structures into type-I. The associated band bending and charge redistribution lead to strong interband transition in such type-II structures comparable to that of a type-I quantum well. The results are shown for InAs/AlSb quantum well, where TM mode optical gain can be as high as 4000cm^-1. We also studied effects of doping on differential gain.

The realization of group III--nitride laser diodes with a vertical current path on a n-conducting SiC substrate is described. The vertical current path and the possibility of cleaved laser facets result in a simpler process technology. Gain spectra measured by the Hakki-Paoli method show a modulation of the modal gain due to parasitic modes in the SiC substrate. As up to now no defect reduction technique was successfully transfered to GaN on SiC, degradation is the major issue. We discuss the impact of degradation on the gain spectra, facet degradation, and rule out formation of cracks during degradation. We show that the high heat conductivity of SiC may give an advantage with respect to degradation as it results in a only moderate temperature rise of the active region.

Design and performance characteristics of InGaN, AlGaN and InAlGaN multiple quantum well (MQW) laser diodes emitting in the ultraviolet spectral region are reported. The nitride laser diodes were grown on quasi-bulk GaN and c-plane sapphire substrates by metalorganic chemical vapor deposition. By reducing the indium content in the InGaN MQW, we have realized laser diodes on GaN substrates emitting at wavelength as short as 366.9 nm with pulsed threshold current densities around 8kA/cm². Improved performance characteristic with differential quantum efficiencies of 7.7% and light output powers of close to 400mW were obtained. We also demonstrate room-temperature pulsed operation of AlGaN and InAlGaN MQW laser diodes grown on sapphire substrates emitting at a record short wavelength of 357.9nm. Light output powers greater than 80mW under pulsed current-injection conditions and differential quantum efficiencies of 4.2% have been achieved.

We have successfully fabricated blue-violet laser diodes, consisting of nitride-based semiconductors, with both high-power and low-noise characteristics on GaN substrates. These laser diodes have a ridge waveguide structure with a dielectric current blocking layer. By improving the crystal quality of the grown materials and optimizing the optical confinement in the device, a kink level as high as 250 mW has been achieved. Optimized optical confinement is also assumed to result in far field patterns without any additional peaks. In addition to this, since the threading dislocation density at the active layer below the ridge portion is reduced to less than 10⁵cm^-2, these laser diodes have been operating reliably for more than 1000 h with a light output power of 100 mW at 60°C under pulsed operation. We have also confirmed that these laser diodes have a noise level as low as -130 dB/Hz, which meets the requirement for practical use, for a light output power of 5 mW. These laser diodes are expected to enable dual layer recording in nextgeneration, large-capacity optical disc systems using blue-violet laser diodes.

High-power laser diodes emitting in the violet - UV region are needed for many applications related to data storage, full color laser projectors, pollution screening etc. This type of device is difficult to fabricate by using the presently available technology of epitaxial growth which employs the lateral overgrowth scheme to reduce the dislocation density in the active layer of the device. This paper presents a new generation of wide stripe laser diodes, which structures were coherently grown on bulk, nearly defect free GaN substrates. Thanks to a low and homogeneously distributed dislocation density (3×10⁵cm^-3), these devices are able to emit a very large optical power in excess of 2.5 W with a slope efficiency per facet of around 0.3 W/A and threshold current densities of 5-10 kA/cm². The use of wide 15 μm stripe lowers the optical power density on the mirrors, and helps avoiding their optical damage. We believe that these devices clearly show the potential of homoepitaxy for high-power lasers applications.

400-nm-band GaN-based blue-violet laser diodes (LDs) operating with a high output power of over 100 mW have been successfully fabricated. A new ridge structure, in which the outside of the ridge was covered with a stacked layer of Si on SiO₂ and the ridge width was as narrow as 1.4 μm, was applied to realize the stable lateral-mode operation. A layer structure around the active layer was carefully designed so as to ensure a high COD level. The lasers have been operated stably for more than 500 h under 130-mW pulsed operation at 60°C. From ambient temperature dependence of the device lifetime, the empirical activation energy was estimated as 0.32 eV. These results indicate that this LD is suitable for next-generation Blu-ray Disc system.