We report a realization of single-frequency quantum-cascade lasers in continuous-wave mode on thermo-electrical cooler at frequencies ~ 1830 cm^-1 (~ 5.46 μm) and ~ 1900 cm^-1 (~ 5.26 μm). The active region of the lasers is based on the broad gain bound-to-continuum concept. We report a 1.5 mm-long, 18 μm-wide quantum-cascade laser exhibiting single-mode emission over the entire investigated temperature and current ranges with a side-mode suppression ratio > 25 dB. Output powers up to 54 mW at -30°C and 1.2 mW at +27°C are demonstrated. A tuning range of 12.8 cm^-1 (0.7%) can be obtained between 1823.1 cm^-1 and 1835.9 cm^-1. A different device, 1.5 mm-long, 12 μm-wide, is reported in the range 1892.8 cm^-1 to 1905.5 cm^-1, exhibiting output power of 59 mW at -30°C and 0.8 mW at +20°C. The objective of this development is to obtain a room-temperature continuous-wave quantum-cascade laser at 1900cm^-1, important for NO (nitric oxide) measurements. We demonstrate also Fabry-Pérot continuous-wave operation of quantum-cascade lasers grown by metal organic vapour phase epitaxy up to -5°C without the need of buried heterostructure processing.

Quantum Cascade Lasers (QCL), emitting between 5 and 9 μm, have been realised with a view to achieving QCLs fabrication on a production scale. The growth of the structures was carried out in a multi-wafer RIBER 49 system (13 x 2" platen), and the processing sequence involved an Inductively Coupled Plasma (ICP) step for homogeneity and reproducibility purposes. To validate the approach used, a first batch of lasers, emitting around 9μm, based on a design already published [1], has been realised. State of the art performance on these devices (J_th = 4.2 kA cm^-2, η = 304 mW A^-1, P_max = 690 mW) has been achieved. A second set of strained balanced structures, emitting around 5.4μm, has been demonstrated, working in pulsed operation at room temperature(J_th = 3.9 kA cm^-2, η = 362 mW A^-1, P_max = 420 mW).

Since the first demonstration of a pulsed InGaN laser diodes (LDs) grown on sapphire substrate in 1995, we have been developing longer lifetime and higher optical output power LDs in the 400 - 410 nm wavelength range. Moreover, we have already succeeded in the expansion of the lasing wavelength range from ultraviolet (UV) to blue-green. In this paper, we reported the recent progress of high-power and wide wavelength range GaN-based LDs with an optical output power of 20 mW single mode (375nm), 160 mW single mode (405nm), 200 mW multi mode (405nm), 50 mW single mode (445nm), 300 mW multi mode (445nm), and 20 mW single mode (473nm).

We report on various kinds of structural defects frequently observed in nitride-based laser diodes (LDs). First, we discuss threading dislocations in the nitride-based LDs. By investigating structural analysis of epitaxial lateral overgrown (ELO) GaN layers, comparison study between short-lived LDs and long-lived LDs, and degradation analysis, we show that although threading dislocations do not multiple during the device operation, reduction of threading dislocations is primarily important for improving device reliability. Secondly, we investigate the Mg-related structural defects. The other important aspect for extending the device lifetime is optimization of Mg doping. During the course of our study of LDs, inverse pyramidal defects were often found in Mg-doped layers. We analyze the relationship between the pyramidal defects and the atomic concentration of Mg [Mg] and discuss device degradation mechanism in terms of degradation rate and Mg doping. Thirdly, we describe structural defects observed in GaInN multiple quantum wells (MQWs). Apart from previously reported structural defects such as In-rich precipitates and clusters, we found a new type of structural defects in GaInN MQWs with higher In concentrations. These defects consist of planar defects and associated dislocations. These multiple defects can be formed merely by one monolayer In-In bond.

The I-V characteristics, lasing thresholds, and wallplug efficiencies of type-II "W" mid-IR diode lasers from 16 different wafers were studied in order to determine the influence of various device parameters. At T = 90 K, the wallplug efficiency for a 1-mm-long gain-guided device was > 10% and the slope efficiency was 142 mW/A (38% external quantum efficiency). When a 22-μm-wide ridge was lithographically defined on a 5-period "W" laser with a p-GaSb etch stop layer, the maximum cw operating temperature increased to 230 K. We also investigated 5-stage and 10-stage interband cascade lasers containing "W" active quantum wells. For 10-stage devices, the low-temperature threshold current densities were somewhat higher than in the "W" diodes while at higher temperatures they were slightly lower. The threshold voltage was only ≈ 0.1 V larger than the photon energy multiplied by the number of stages, corresponding to a voltage efficiency of > 96%, while the differential series resistance-area product above threshold was as low as 0.21 mΩ^.cm² at 100 K. At T = 78 K, the cw slope efficiency was 0.48 mW/A (126% external quantum efficiency), and a maximum cw power of 514 mW was produced by an epi-side-up-mounted 2-mm-long 10-stage laser cavity with uncoated facets. A 5-stage 2-mm-long interband cascade laser produced ≈ 700 mW of output power at 80 K, with a maximum wallplug efficiency of 20% per facet.

This paper describes an application-centric development of broadly tunable and multi-spectral mid/long-wave IR semi-conductor lasers. Examples of various external-cavity lasers capable of broad, continuous wavelength tuning with type-I and type-II quantum cascade lasers are discussed. Laser configurations studied include conventional Littman-Metcalf, Littrow, multi-segment and Bragg-grating-coupled surface-emitting. All were capable of single-mode continuous tuning with high side-mode-suppression ratio. The lasers were evaluated with spectroscopic applications, which include wave-length-modulation spectroscopic imaging and multi-wavelength decomposition of a gas mixture. The results showed that these lasers were capable of maintaining wavelength accuracy and stability over the entire tuning range. Multi-spectral imaging with discrete wavelengths over a wide spectral range was also studied. The results with a modest 4-wavelength system demonstrated the potential application for target discrimination, detection, and identification. These results suggest potential value for broadly tunable, wide-band M/LWIR laser technology.

Diode lasers with a high very conversion efficiency can be obtained when carefully taken into account several partly opposed requirements for the design of the layer structure. Results are given for 940nm laser structures based on the well established InGaAs/AlGaAs material with a relatively low vertical divergence of about 45° including 95% of optical power. Laser bars were processed and mounted on passively cooled heat sinks. 73% conversion efficiency was achieved at 70W output power. 150μm stripe lasers with only 1500μm resonator length mounted on usual C-mounts have a thermal rollover of about 18W, which is a record high value for a resonator length below 2mm. Reliability tests show an excellent stability at 75W in CW and 95W in long pulse operation mode over about 10000h test time.

Photonic integration of large arrays of high power, single mode lasers using quantum well intermixing technology in a small form-factor package is described. Lifetime analysis reveals excellent reliability of large element laser arrays packaged into small form-factor optical systems.

In this paper, results for 650 nm high-power broad area lasers and bars will be presented. The optimized layer structure consists of GaInP quantum wells embedded in AlGaInP waveguide layers. The n-cladding layer consists of AlInP, the p-cladding layer of AlGaAs. The vertical far field of this structure has a width below 32° (FWHM). Devices were fabricated and mounted p-side down on CuW heat spreader using AuSn solder. Broad area lasers reach a maximum output power of 0.94 W at 15°C limited only by thermal rollover. Up to now reliable operation at 500 mW over 6300 h was achieved. The spectral width of the emission is below 1 nm (FWHM). Bars consisting of 19 emitters with 30 μm x 750 μm reached a maximum output power of 9.6 W and a wall-plug efficiency of 30%. Reliable operation from a 5 mm bar at 5 W and 15°C over 1500 h was shown.

We have developed high power and high brightness tapered lasers based on an Al-free active region at 915 nm. The material structure, which was grown by MOCVD (Metallorganic Chemical Vapor Deposition), has very low internal losses of 0.5 cm^-1, a very low transparency current density of 86 A/cm², a high internal quantum efficiency of 86%, and a high characteristic temperature T₀ of 171 K. Based on these good results, we have realised index-guided tapered lasers (IG1) with a narrow output width of a few tens of microns, a narrow taper angle of less than 1^o, which deliver 1 W CW, together with an M² beam quality parameter of 3.0, and a divergence angle in the slow axis of 6^o FWHM and 10.2^o at 1/e². We have also realised a small array of six IG1 lasers, which delivers 4 W CW, together with a divergence angle of 5.6^o FWHM and 10.2^o at 1/e². Clarinet lasers were also fabricated. These devices were recently proposed to achieve high brightness together with a very narrow divergence angle, which is stable with current. These index-guided tapered lasers have also a narrow output width, but a larger taper angle of 2^o. The Clarinet lasers at 915 nm deliver 0.65 W CW, together with an M² beam quality factor of less than 1.5 at 1/e², and a very narrow divergence angle of 2.6^o FWHM, and 4.8^o at 1/e².

Experimental investigations on high-power broad area (BA) distributed-feedback (DFB) lasers emitting in the wavelength range around 808 nm are presented. An output power of 4.7 W at 20 °C with a differential quantum efficiency of 1.06 W/A is achieved with BA-DFB lasers having a stripe width of 100 μm and a cavity length of 3000 μm. The measured lateral far field angle is about 10° at a power of 3 W. The vertical far field angle is near 29°. The emission has a narrow spectral width of 0.06 nm (FWHM) at 3 W and 0.10 nm at 4 W. From mappings of the optical spectra a wavelength variation with output power of Δλ/ΔP = 0.44 nm/W and with injection current of 0.4 pm/mA can be deduced. At a temperature of 50°C a maximum output power of 2 W is measured. From the measurements a temperature coefficient of Δλ/ΔT = 0.075 nm/K is determined.

In this paper we report on carrier lifetime measurements performed on 1.3 μm p-doped InAs quantum-dot lasers. The carrier lifetimes were determined by fitting the measured sub-threshold optical modulation response to a single pole response function, and then correcting this time constant for the diode junction capacitance to obtain the carrier lifetime. The sub-threshold frequency response curves did indeed show a single pole behavior at all the bias currents and, as expected, the extracted carrier lifetimes monotonically decrease with increasing bias currents. The differential carrier lifetime versus bias current data was then fitted, using a simple single carrier level rate equation analysis, to determine the recombination coefficients. Using this simplified analysis, the values of the recombination coefficients are found to be: A = 1.0 x 10⁷ /s, B = 2.5 x 10^-11 cm³/s, and C = 1.1 x 10^-29 cm⁶/s at room temperature. Since, the carriers are distributed among the dots in a complicated manner that depends on bias, the lifetimes and recombination coefficients extracted using the single carrier level analysis are the effective or average values. Thus we have also built a multi-level rate equation model including the capture and escape times between various QD and wetting layer states. The multi-level rate equation model yields intrinsic recombination coefficients of A_QD = 5.5 x 10⁷ /s, B_QD = 6.5 x 10^-11 cm³/s, C_QD = 5.6 x 10^-29 cm⁶/s. Regardless of the model used the dominant contribution to the threshold current is found to be Auger recombination which accounts for approximately 80 % of the threshold current in our 1.3 μm p-doped QD lasers.

The presence of laser phase noise (or frequency jitter) limits the resolution of a variety of interferometric sensors ranging from fiber optic acoustic sensors to gravitational wave detectors. At low frequencies, 0 to 100 kHz, the laser phase noise in semiconductor and diode pumped solid-state lasers is dominated by 1/f noise, the source of which is not well understood. We report on phase noise measurements for external cavity semiconductor lasers (ECSLs) utilizing a fiber Bragg grating in a compact butterfly package design produced by K2 Optronics. The results show that the phase noise is dominated by 1/f noise for low frequencies (10 to 100 kHz) transitioning to a white noise due to spontaneous emission for f > 100 kHz. We observed a factor of 40 improvement in the magnitude of the 1/f phase noise as compared to previously published results for a Hitachi HLP 1400 830 nm diode laser. The magnitude of the low frequency phase noise ranges from 100 to 10 microradians per meter per root Hz for frequencies ranging from 10 Hz to 2 kHz. These results are within a factor of 10 for phase noise measurements of the more expensive Lightwave Electronics Nd:YAG laser and a variety of Er-doped fiber lasers in this frequency range. For nominally similar ECSLs, experimental results indicate that the phase noise increases for lasers with larger leakage currents. Linewidth measurement results showed a Schawlow-Townes inverse power dependence for output powers up to 33 mWatts with the observed onset of a linewidth floor of 30 kHz. The RIN of the ECSLs varied from -120 to -155 dB Vrms per root Hz for frequencies ranging from 10 to 500 kHz. These RIN results are roughly equal to those observed for the Nd:YAG laser for frequencies less that 100 kHz. In summary, such low phase noise and RIN results make such ECSLs suitable for all but the most sensitive fiber optic sensing applications where the frequency range of interest is below 1 MHz.

We compare the electrical power dependence of the lattice temperature and the electronic temperature of THz quantum cascade lasers (QCLs) operating in the range 2.5- 3.8 THz and based on a resonant-phonon and bound-to-continnum quantum design. This analysis is performed by means of microprobe band-to-band photoluminescence experiments carried out on operating THz QCLs both below and above the lasing threshold. Thermalized non-equilibrium hot-electron distributions are found in both classes of QCLs. While in the case of bound-to-continuum devices a unique value of the electronic temperature is found in the active region minibands, in the case of resonant-phonon devices we found that the upper radiative state, in the lasing range, heats up to ~ 200 K, more than 100 K with respect to the ground state levels. From the measured thermal resistance and the power dependence of the ground state electronic temperature we obtain in the case of resonant-phonon structures a value of the electron-lattice energy relaxation rate comparable with that typical of mid-infrared QCLs, in the case of resonant-phonon structures and a value ~ 50 times higher in bound-to-continuum devices.

High power and high efficiency AlInGaN-based laser diodes with 405 nm were fabricated for the post-DVD applications. Magnesium doped AlGaN/GaN multiple quantum barrier (MQB) layers were introduced into the laser diode structure, which resulted in considerable improvement in lasing performances such as threshold current and slope efficiency. Asymmetric waveguide structure was used in order to improve the characteristics of laser diodes. Aluminum content in the n-cladding layer was varied in connection with the vertical beam divergence angle and COD level. By decreasing Al content in the n-cladding layer, the vertical divergence angle was reduced to 17 degree and the COD level was enhanced to over 300mW. The maximum output power reached as high as 470 mW, the highest value ever reported for the narrow-stripe GaN LDs. In addition, the fundamental transverse-mode operation was clearly demonstrated up to 500 mW-pulsed output power.

In this paper we report on progress in the development of nitride laser diodes by molecular beam epitaxy (MBE). We review the steps taken to achieve continuous wave (CW) operation of 405nm lasers grown by MBE and evaluate the performance of such devices. The future potential of the growth method for lasers depends on the demonstration of long lived lasers with good operating characteristics such as high power output and low threshold current. We assess the challenges to achieving such performance in MBE-grown lasers and the progress in evaluating the key laser parameters in our devices.

Properties of the quantum noise and the optical feedback noise in blue-violet InGaN semiconductor lasers were measured in detail. We confirmed that the quantum noise in the blue-violet laser becomes higher than that in the near-infrared laser. This property is an intrinsic property basing on principle of the quantum mechanics, and is severe subject to apply the laser for optical disc with the small consuming power. The feedback noise was classified into two types of "low frequency type" and "flat type" basing on frequency spectrum of the noise. This classification was the same as that in the near infra-red lasers. Theoretical discussions on the feedback noise were also added in this paper.

We demonstrate the operation of wide-stripe InGaN laser diodes grown on bulk gallium nitride substrates obtained by high-pressure synthesis. The use of almost dislocation-free substrates resulted in very low defect densities of obtained laser structures - typically in the range of 10⁵cm^-2. We tested 3 types of devices of the dimensions: 20μmx500μm, 20μmx1000μm and 50μmx500μm. All three types of lasers showed good properties during pulse current experiments, exhibiting threshold currents of 400, 850 and 950 mA, respectively. The lasing wavelength varied between 405 and 420 nm, depending on the particular device. After p-down mounting on diamond heatspreaders, the first two types of lasers showed CW operation with a total output power reaching 200 mW. These devices, after optimization, offer good prognostics for reaching an optical power in the 1 W range needed for the applications in large area displays.

We have performed a systematic study of structural and optical properties of Quantum dot (QDs) lasers based on InAs/InGaAs quantum dots grown on GaAs substrates emitting in the 1.3 - 1.5 μm range. 1.3 μm range QD lasers are grown using GaAs as matrix material. It is shown that the lasers, grown with large number of QD stacks are metamorphic, with plastic relaxation occurring through the formation of misfit dislocations. Thus, 1.3 μm QD lasers with large number of stacks grown without strain compensation are metamorphic. Another type of defects is related to local dislocated clusters, which are the most dangerous. When proper optimization of the growth conditions is carried out, including a selective thermal etching off of statistically formed dislocated clusters through the defect-reduction technique (DRT), no significant impact of misfit dislocations on the degradation robustness is observed. In uncoated devices a high cw single mode power of ~700 mW is realized limited by thermal roll-over, which is not affected by 500 h ageing at room temperature. At elevated temperatures the main degradation mechanism revealed is catastrophic optical mirror damage (COMD). When the facet are passivated, the devices show the extrapolated operation lifetime in excess of 10⁶ h at 40°C at ~100 mW cw single mode output power. Longer wavelength (1.4 - 1.5 μm) devices are grown on metamorphic (In,Ga,Al)As layers deposited on GaAs substrates. In this case, the plastic relaxation occurs through formation of both misfit and threading dislocations. The latter kill the device performance. Using DRT in this case enables blocking of threading dislocation with growth of QDs in defect-free upper layers. DRT is realized by selective capping of the defect-free areas and high-temperature etching of nano-holes at the non-capped regions near the dislocation. The procedure results in etching of holes and is followed by fast lateral overgrowth with merger of the growth fronts. If the defect does not propagate into the upper layer when the hole is capped, the upper layers become defect-free. Lasers based on this approach exhibited emission wavelength in the 1.4 -1.5 μm range with a differential quantum efficiency of about ~50%. The narrow-stripe lasers operate in a single transverse mode and withstand continuous current density above 20 kA cm^-2 without degradation. A maximum continuous-wave output power of 220 mW limited by thermal roll-over is obtained. No beam filamentation was observed up to the highest pumping levels. Narrow stripe devices with as-cleaved facets are tested for 60°C (800 h) and 70°C (200 h) on-chip temperature. No noticeable degradation has been observed at 50 mW cw single mode output power. This shows the possibility of degradation-robust devices on foreign substrates. The technology opens a way for integration of various III-V materials and may target degradation-free lasers on silicon for further convergence of computing and communications.

Self-assembled In(Ga)As quantum dot (QD) lasers incorporating p-type modulation doping have generated much interest recently due to reports of a temperature insensitive threshold current and increased modulation bandwidth. The mechanism by which p-type doping improves the performance of QD lasers is thought to be similar to that envisaged for quantum well lasers, where increased gain is expected for a given quasi-Fermi level separation due to a shift in both quasi-Fermi levels towards the valence states. However, the benefits may be much more pronounced in quantum dot structures since the population of the smaller number of dot states can be dramatically affected using relatively low doping levels, which may incur less penalty with regard to increased non-radiative recombination and internal optical mode loss. We present results of direct measurements of the modal gain measured as a function of the quasi-Fermi level separation for samples with different degrees of doping, which demonstrate unambiguously the increased gain that can be obtained at a fixed quasi-Fermi level separation. In addition, we have measured the internal optical mode loss and radiative and non-radiative recombination currents for samples containing 0, 15 and 50 dopant atoms per dot and show that, although the internal optical mode loss is similar for all three samples, the non-radiative recombination current increases for samples containing p-doping. We show that our experimental results are consistent with a simple computer simulation of the operation of our structures.

We have investigated the molecular beam epitaxial growth and characteristics of self-organized In(Ga)As quantum dot lasers grown on GaAs and silicon. Utilizing the techniques of tunnel injection and acceptor-doping of quantum dots, we have achieved high performance 1.3 μm InAs quantum dot lasers on GaAs, which exhibit J_th=180 A/cm², T₀=∞, dg/dn≈1×10^-14 cm², f_-3dB=11 GHz, chirp of 0.1 Å and zero α-parameter. Utilizing thin (⩽ 2 μm) GaAs buffer layers and quantum dots as dislocation filters, we have demonstrated room-temperature operational In_0.5Ga_0.5As quantum dot lasers grown directly on silicon, which are characterized by relatively low threshold current (J_th ~ 900 A/cm²), high output power (> 150 mW), large characteristic temperature (T₀ = 244 K) and constant output slope efficiency (⩾ 0.3 W/A) in the temperature range of 5 to 95 °C.

We report a novel laser architecture, the silicon evanescent laser (SEL), that utilizes a silicon waveguide and offset AlGaInAs quantum wells. The silicon waveguide is fabricated on a Silicon-On-Insulator (SOI) wafer using a CMOS-compatible process, and is bonded with the AlGaInAs quantum well structure using low temperature O2 plasma-assisted wafer bonding. The optical mode in the SEL is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain. This approach combines the advantages of high gain III-V materials and the integration capability of silicon technology. Moreover, the difficulty of coupling an external laser source is overcome as the hybrid waveguide can be self-aligned to silicon-based passive optical devices. The SEL lases continuous wave (CW) at 1568 nm with a threshold of 23 mW. The maximum single-sided fiber-coupled CW output power is 4.5 mW. The SEL characteristics are dependent on the silicon waveguide dimensions resulting in different confinement factors in the III-V gain region.

We discuss practical benefits of the nonlinear active quantum-cascade structures that support both laser action and, at the same time, nonlinear self-conversion of laser light into coherent radiation at different frequencies. We show that the proposed approach can greatly enhance the performance of quantum cascade lasers and provide new functionalities. Examples considered include extreme frequency up- or down-conversion, fast and wide-range electric tuning, and multi-frequency generation.

A simple, novel self-aligned deep etch plus wet thermal oxidization process is demonstrated which enables high-index-contrast (HIC) ridge waveguide (RWG) lasers fabricated in a high-efficiency, high-power AlGaAs/InAlGaAs/GaAs graded-index separate confinement heterostructure to operate with a curved half-ring resonator geometry having a bend radius as low as 10 μm. A wet thermal oxidation process modified through addition of <1% O₂ to the N₂ carrier gas is shown to smooth the sidewall roughness of etched AlGaAs ridge structures 10-100 fold as the oxidation front progresses inward. The reduction of propagation scattering loss due to the reduced sidewall roughness is examined. The thermal oxide grown on the deeply-etched RWG sidewalls and base also provides electrical isolation from the contact metallization, resulting in a simplified, self-aligned process, and yields a RWG structure which effectively prevents current spreading. The thermal oxide appears to be of sufficiently high quality to passivate the etched active region surface based on a comparative analysis of straight RWG lasers of varying stripe widths (w=5 to 150 μm) passivated with native-oxide vs. PECVD-deposited SiO₂. For example, at w<15 μm, the SiO₂-insulated devices have ~2X higher threshold current densities than the native-oxide devices for comparable bar lengths. The resulting high lateral optical confinement factor at the semiconductor/oxide interface (Δn=1.69) significantly enhances the laser gain and efficiency. A native-oxide-defined straight laser (w=7 μm, L= 452 μm) operates cw (300 K, unbonded, p-side up) with a threshold current of I_th=21.5 mA (J_th=679.5 A/cm²) and slope efficiency of 1.19 A/W (differential quantum efficiency = 78%) at a wavelength of ~813 nm.

The properties of a 1.3μm GaInNAs Double Quantum Well (QW) ridge waveguide (RWG) laser have been systematically studied for GaAs based uncooled long wavelength lasers. The threshold current, transparency current, optical gain, internal loss and quantum efficiency characteristics were assessed by light-current (L-I) measurement using devices with different geometries. Measurements of gain spectra versus injection current and temperature were taken and used to analyze GaInNAs as an active material in terms of gain, loss and transparency. The experimental observations are discussed. The results are compared with those obtained from lasers made by other conventional materials. The high characteristic temperature (T₀=155K from 20°C to 75°C) and comparable stimulated emission to InP based lasers offer the promise of application as a light source for low cost data communication systems.

GaSb based diode laser arrays emitting at wavelengths around 2 μm have a significant potential for a variety of applications including material processing, such as welding of transparent plastic materials, and optical pumping of mid-infrared solid state lasers. Even though high output power broad area single emitters and laser arrays have already been demonstrated, they all suffer from a large fast axis beam divergence of typically 67° FWHM due to the broadened waveguide design employed. Here we will present results on (AlGaIn) (AsSb) quantum-well diode laser single emitters and linear arrays consisting of 19 emitters on a 1 cm long bar emitting at around 1.9 μm. To improve on the poor fast axis beam divergence we abandoned the broadened waveguide concept and changed over to a novel waveguide design which features a rather narrow waveguide core. This results in a remarkable reduction in fast axis beam divergence to 44° FWHM for the new waveguide design. For single emitters a cw output power of more than 1.9 W have been observed. 16.9 W in continuous-wave mode at a heat sink temperature of 20 °C have been achieved for arrays. The maximum wall-plug efficiency amounts to 26% both for the single emitters and the laser arrays. These efficiencies are among the highest values reported so far for GaSb based diode lasers, and allow us to use passively cooled and thus less expensive heat sinking technologies.

Narrow-linewidth (<100 kHz) 850 nm distributed Bragg reflector (DBR) three-section tunable laser diodes are reported. An asymmetric cladding ridge-waveguide structure was used for transverse and lateral mode control. Single longitudinal mode performance was achieved via first-order DBR surface-etched gratings fabricated using inductively-coupled plasma reactive ion etching (ICP-RIE). Epitaxial material with spontaneous emission peak values at 835 nm and 850 nm were used for device fabrication. Stable single-mode powers of up to 30-mW were achieved at 100 mA with spectral side-mode suppression ratio (SMSR) values in excess of 35 dB. Laser tuning by DBR current injection in excess of 7 nm was measured. Narrow spectral linewidths were observed on both sets of devices, with linewidths below 40 kHz for devices with the 835 nm spontaneous emission peak. This is due to the reduced spontaneous emission contribution to the device linewidth. These results demonstrate that extremely narrow linewidths can be achieved using onestep epitaxial growth in an unstrained material system with surface etched first-order gratings on asymmetric cladding ridge-waveguide lasers.

Atomic clocks will be used in the future European positioning system Galileo. Among them, the optically pumped clocks provide a more accurate alternative. For these systems, diode lasers emitting at 852nm are strategic components. The laser in a conventional bench for atomic clocks presents disadvantages for spatial applications. A better approach would be to realise a system based on a distributed-feedback laser. Thus we have developed laser structures emitting at λ=852nm, using an aluminium free active region. The device is a separate confinement heterostructure with a GaInP large optical cavity and a single compressive-strained GaInAsP quantum well. The broad-area laser diodes are characterised by low internal losses (<3 cm^-1), a high internal efficiency (94%) and a low transparency current density (100A/cm²). For an AR/HR coated 2mm long around 4μm wide ridge diode, we obtain a low threshold current (40mA) and a high slope efficiency (0.90W/A). We obtain 852nm wavelength at 145mW (I=200mA, 15°C). We measure an optical power of 230mW (I=280mA) in a single spatial mode with the beam quality parameter M²=1.3. From our first attempt for a DFB laser, we obtained a threshold at 20°C of 45mA and a slope efficiency about 0.45W/A with an uncoated 2mm long around 4μm wide device. At 40mW (I=140mA,), both near and far fields in the slow axis are gaussian-shaped with respective full widths at 1/e² of 7μm and 10.4°, corresponding to a single spatial mode emission with the beam quality parameter M²=1.2. At this power, the laser wavelength is 853.8nm with a side-modesuppression ratio over 30dB.

The combination of high power, small linewidth and fast tunability is essential for many fields in high resolution spectroscopy. External cavity laser diode systems are limited in tuning speed to several kHz by the resonance frequency of the mechanical assembly together with the actuator. We report on the application of a directly modulated DFB laser as master laser within a master laser power amplifier (MOPA) configuration. This DFB MOPA system combines fast frequency tuning up to more then 100kHz tuning speed, a tuning amplitude of more than 10GHz, a narrow linewidth below 5MHz with high output power of 1500mW and an almost Gaussian shaped beam quality (M²<1.2). The coupling efficiency to optical waveguides as well as single mode fibers exceeds 60%. This concept can be realized within the wavelength regime between 730 and 1060nm. We approved this light source for high resolution spectroscopy by frequency locking to the saturated Rubidium absorption at 780nm. Applying two DFB lasers as master lasers of the MOPA configuration opens the choice to high frequency modulated THz radiation.