Catastrophic Optical Damage Research Articles

High temperature laser diode based on a single sheet of quantum dots

A single sheet of high-density InGaAs quantum dots (QDs) is used as a gain medium of InGaAs–GaAs–AlGaAs lasers. The devices operate at high power in the continuous mode beyond 160 °C with an emission wavelength up to ∼1.27 μm. At short cavity lengths a strong broadening (>300 nm) of the electroluminescence spectrum is observed at high current densities, permitting light sources for broadly wavelength tuneable and multi-wavelength infrared lasers based on a single gain chip, and related frequency conversion devices for the whole visible spectrum range. High power cw operation (>2 W) limited by catastrophic optical mirror damage is realized.

Investigations on electro-optical and thermal performances degradation of high power density GaAs-based laser diode in vacuum environment

Pump laser diodes emitting at 980nm are typically used in distribution network transmission systems and are now implemented in space missions for intra-satellite communication links and calibration systems. Nevertheless, since the pump source is potentially a critical point for such systems, there is a huge need to assess their reliability in space environment, especially in terms of operation under vacuum conditions. We have then studied the electro-optical behavior of several 980nm laser diodes and shown that they may degrade more rapidly when submitted to a vacuum environment. Then, spatially resolved temperature variations have been measured by thermoreflectance on the laser diode front facet and have shown a temperature variation increase under vacuum conditions, in particular near the emission region, where a catastrophic optical damage is most likely to occur. This temperature variation increase could then be one of the causes for the more rapid laser diode degradation.

Suppression of sublinearity of light–current curve in 850 nm quantum well laser with asymmetric barrier layers

An AlGaAs/GaAs quantum well (QW) laser is fabricated with GaInP and AlGaInAs asymmetric barrier layers (ABLs) and its light–current characteristic (LCC) is compared with that of a reference conventional QW laser without ABLs. It was found that the use of the ABLs suppresses the sublinearity of the LCC at high current densities. As a result, the maximum lasing power of 9.2 W, being limited by catastrophic optical mirror damage, is achieved at a considerably lower operating current in the laser with ABLs as compared to the reference laser (12.5 against 20.2 A). The ABL effect is associated with the suppression of the parasitic recombination in the optical confinement layer, as confirmed by a decrease of the intensity of the spontaneous emission from the layer.

Kinetics of catastrophic optical damage in GaN-based diode lasers

Catastrophic optical damage (COD) in 450 nm emitting InGaN/GaN diode lasers is artificially provoked by applying single sub-microsecond current pulses of increasing amplitude. Studying a batch of devices in which COD does not represent the main degradation mode, we find that COD is a ‘hot’ process. It becomes re-ignited in subsequent pulses. During the process, the spatial filamentation changes abruptly and the outer appearance of the damage pattern is predominantly created within the initial pulse. The process can cause material ejection out of the front facet as shown by thermography.

Precise Facet Temperature Distribution of High- Power Laser Diodes: Unpumped Window Effect

A thermoreflectance technique is used to evaluate the temperature variations at the output facet of high-power GaAs-based laser diodes emitting at 980 nm. Two kinds of diodes with different unpumped windows (UPWs) are studied to determine the influence of UPW length on the temperature variation. We show that in the vicinity of the active region, where a catastrophic optical damage is most susceptible to occur, the short UPW diode heats much more (up to 40%) than the long UPW one.

Short-wavelength infrared defect emission as a probe of degradation processes in 980 nm single-mode diode lasers

Infrared emission from 980-nm single-mode high power diode lasers is recorded and analyzed in the wavelength range from 0.8 to 8.0 μm. A pronounced short-wavelength infrared (SWIR) emission band with a maximum at 1.3 μm originates from defect states located in the waveguide of the devices. The SWIR intensity is a measure of the non-equilibrium carrier concentration in the waveguide, allowing for a non-destructive waveguide mapping in spatially resolved detection schemes. The potential of this approach is demonstrated by measuring spatially resolved profiles of SWIR emission and correlating them with mid-wavelength infrared (MWIR) thermal emission along the cavity of devices undergoing repeated catastrophic optical damage. The enhancement of SWIR emission in the damaged parts of the cavity is due to a locally enhanced carrier density in the waveguide and allows for an analysis of the spatial damage patterns. The figure shows a side view of a diode laser during catastrophic degradation as recorded by a thermocamera within 5 successive current pulses. The geometry of the device is given in grayscale. The position of the laser chip is indicated by the dotted line. The thermal signatures of the internal degradation of the diode laser are overlaid in color. The bi-directional spread of the damage along the laser cavity is clearly visible.

Watt-class high-power, high-beam-quality photonic-crystal lasers

The applications of surface-emitting lasers, in particular vertical-cavity surface-emitting lasers (VCSELs), are currently being extended to various low-power fields including communications and interconnections. However, the fundamental difficulties in increasing their output power by more than several milliwatts while maintaining single-mode operation prevent their application in high-power fields such as material processing, laser medicine and nonlinear optics, despite their advantageous properties of circular beams, the absence of catastrophic optical damage, and their suitability for two-dimensional integration. Here, we demonstrate watt-class high-power, single-mode operation by a two-dimensional photonic-crystal surface-emitting laser under room-temperature, continuous-wave conditions. The two-dimensional band-edge resonant effect of a photonic crystal formed by metal–organic chemical vapour deposition enables a 1,000 times broader coherent-oscillation area, which results in a high beam quality of M2 ≤ 1.1, narrowing the focus spot by two orders of magnitude compared to VCSELs. Our demonstration promises to realize innovative high-power applications for surface-emitting lasers. Researchers demonstrate a watt-class high-power, single-mode photonic-crystal laser operating continuously at room temperature. A beam quality of M2 ≤ 1.1 is achieved.

大功率半导体激光器腔面膜的场强分布优化

In order to improve the damage threshold of semiconductor laser facet film and increase the laser output power, the causes of the catastrophic optical mirror damage in the laser are discussed. The highest field intensity in the high-reflective (HR) film is moved out of the interface in view of the damage principle. The reflectance and electric field distribution are simulated with film thickness changing continuously by using optical transmission matrix to get the optimized high reflective film, and the film damage is reduced at the interface by the optimized film. LaB6 with improved higher plasma density is adopted as in situ plasma source, and the cleaning parameter of ion source is optimized. In the earlier period of preparing film, facet deoxidation is made with ion pre-cleaning in vacuum environment, and the film is fabricated with ion-assisted electron beam evaporation, and the stability of the film is tested under high temperature and high humidity environment. The laser output power is raised from 4.5 W to 7.02 W, operating current is raised from 5 A to 8 A in the case of the quasi-continuous operation with the optimized film and cleaning method.

13.4 W single emitter 940 nm semiconductor laser diode with asymmetric large optical cavity

An asymmetric large optical cavity (LOC) waveguide is designed to raise the output power of the 940 nm laser diode. By optimizing the metal organic chemical vapor deposition growth condition and combining with the electrode fabrication and facet coating, single emitter semiconductor laser diodes of 95 mm strip width and 4 mm cavity length are fabricated. Without any active cooling process, an output power of 13.4 W is reached at 15 A injection current without catastrophic optical mirror damage at room temperature. By introducing the asymmetric LOC waveguide, the far-field test shows that only the transverse fundamental mode is lased with a vertical far-field angle full width of half magnitude of 22o.

The Facet Passivation Characteristic of 940nm Semiconductor Laser

A novel facet coating technology is presented by studying catastrophic optical mirror damage mechanism of semiconductor laser. In this technology, semiconductor laser are cleaved in the air, and the surface oxide layer is removed with a low energy ion source, immediately flowed by coating the facet with 20nm of thin ZnSe passivation layer. The function of the passivation layer is to protect semiconductor laser facet, and prevent impurity particles diffusing to the facet. Finally the facet is coated with oxidative optical film. The test results of semiconductor laser output power show that output power with the coated ZnSe passivation layer method is 12% higher than coated Si passivation layer, and 36% higher than that coated oxidative optical film. The device coated oxidative optical film is failed when current is 4.1A, and the device coated with Si passivation layer is failed when current is 4.8A, the final failed of the device is coated ZnSe passivation layer. In conclusion, the method of coated ZnSe passivation layer on the semiconductor laser facet can effectively prevent the catastrophic optical mirror damage, and increase the output power of semiconductor lasers.

Transient thermal characteristics related to catastrophic optical damage in high power AlGaAs/GaAs laser diodes

The transient thermal characteristics related to catastrophic optical damage (COD) in high power AlGaAs/GaAs laser diodes (LDs) are studied experimentally by means of thermal infrared imaging, laser scanning confocal microscopy, and transient thermal technique. The transient thermal technique is based on the diode forward voltage method in which the structure function theory is applied to determine the component thermal resistance and temperature rise of the LDs. We have recorded the dynamics of COD process using thermal infrared camera. Two melting spots are observed in the output facet after COD which location exactly matches the position of the thermal flash from the thermal imaging and even the temperature of COD seed has a sudden increase of 32 K when the COD event occurs. Furthermore, we find that the thermal resistance from chip to In solder increases remarkably after COD, meanwhile the thermal resistance of solder and package does not change apparently. The results are attributed to the heat power dissipation increase originating from the enhancement of nonradiative recombination after COD under constant input electrical power.

InGaAs/GaAsP/GaInP quantum well lasers with window structure fabricated by impurity free vacancy disordering

In order to fabricate 940nm InGaAs/GaAsP/GaInP semiconductor lasers with non-absorbing window (NAW), the induced quantum well intermixing (QWI) is investigated using impurity free vacancy disordering (IFVD) method. Successful intermixing is obtained with 24nm bandgap blue shift between the window and gain regions. Under destructive testing conditions, the catastrophic optical damage (COD) power for the NAM LD is about 116% higher than the conventional LD.

Microscopic Origins of Catastrophic Optical Damage in Diode Lasers

Extremely early phases of the catastrophic optical damage (COD) process in 808-nm emitting GaAs/Al0.35Ga0.65 As high-power diode lasers are prepared by the application of short single current pulses. Typical energy entries during these pulses are on the order of 100 nJ within several 100 ns. The resulting defect pattern is investigated by high-resolution microscopy. The root of the COD is found to be located at the waveguide of the laser structure. Analysis of material composition modifications as a result of early COD phase points to melting being involved in the process. During recrystallization, an Al-rich pattern is formed that encloses a volume of a few cube micron of severely damaged material.

Stable high optical power in quantum well lasers with profiled reflection and tapered structures

A comprehensive model is presented to study quantum well tapered lasers and quantum well stripe lasers with profiled reflectivity output facets and to obtain lateral stability in high power semiconductor laser. Simulation of semiconductor lasers is performed by numerically solving space-dependent coupled partial differential equations for the complex optical forward and backward waves, carrier density distribution and temperature distribution. The coupled equations are solved by finite difference beam propagation method. The effect of nonlinear parameters like Kerr and linewidth enhancement factors, and precise dependence of linewidth enhancement factor and gain factor on the carrier density and temperature are considered in this paper. We use modal reflector in stripe lasers to confine the lateral mode to the stripe centre and provide the stable operation. We also use unpumped window to reduce the facet temperature and improve the catastrophic optical mirror damage level of tapered lasers.

Influence of Package Structure on the Performance of the Single Emitter Diode Laser

The package structure critically influences the major characteristics of semiconductor lasers, such as thermal behavior, output power, wavelength, and far-field distribution. In this paper, a new single emitter package structure called F-mount is designed and compared with the conventional package structure C-mount. The influence of package structure on their performances is characterized and analyzed. The thermal resistances of lasers with different package structures are calculated through simulation, and are contrasted with experimental results. Some devices are also tested for the maximum output power level. Under the continuous wave (CW) condition, the maximum power of F-mount reaches 12.6 W at 808 nm while the output power only reaches 10.9 W for C-mount. Under the condition of 0.5% duty cycle (100 μs, 50 Hz), the catastrophic optical mirror damage level reaches 58.7 W at 74 A for F-mount, and 54.8 W at 57 A for C-mount are reported for the first time. It is experimentally found that there is an obvious wavelength difference between the two type structure lasers: about 1.37 nm in CW mode and 2.89 nm in quasi CW mode. Theoretical analysis shows that red-shift and blue-shift is a result of external strain in the package process of F-mount and C-mount, respectively. It is also found that the package structure has an effect on the divergence angle of slow axis far fields, but little impact on that of fast axis far fields. The analysis shows that package structure has a strong influence on the performance of the laser; therefore, the package should be optimized to achieve better performance for some special applications.

A tunnel regenerated coupled multi-active-region large optical cavity laser with a high quality beam

A novel coupled multi-active-region large optical cavity structure cascaded by a tunnel junction is proposed to solve the problems of facet catastrophic optical damage (COD) and the large vertical divergence caused by the thin emitting area in conventional laser diodes. For a laser with three active regions, a slope efficiency as high as 1.49 W/A, a vertical divergence angle of 17.4°, and a threshold current density of 271 A/cm2 are achieved. By optimizing the structural parameters, the beam quality is greatly improved, and the level of the COD power increases by more than two times compared with that of the conventional laser.

Catastrophic optical bulk damage in InP 7xx emitting quantum dot diode lasers

Catastrophic optical bulk damage occurs in broad-area MOCVD-grown InP/(Al)GaInP 7xx emitting quantum dot diode lasers operated at high power with single, high-current pulses of 5–20 A, in contrast with quantum well devices, which undergo catastrophic optical mirror damage at similar power densities at the facet. After damage the quantum dot devices show a reduction in the nearfield emission intensity across the width of the facet. Panchromatic cathodoluminescence of the active region shows a decrease in intensity and reveals dark, non-radiative spots which enlarge as pulse length increases. The areal density of the spots, also present in unprocessed material from similar structures, is of the order of 106 cm−2, five orders of magnitude lower than the dot populations at 1011 cm−2. Increasing pump current pulse length to 500 ns and beyond did not increase the dark spot size, which depended on the duration of the lasing action, but decreased the cathodoluminescence intensity of both the spots and background regions inside the emitter stripe, while reference regions outside the stripe remained unchanged. These features can be used to characterize improvements in structures and growth in order to improve the performance of InP based quantum dot structures at high powers.

Kinetics of Defect Propagation during the Catastrophic Optical Damage (COD) in Broad-Area Diode Lasers

The initial phase of defect propagation in broad area diode lasers, which are affected by the catastrophic optical damage (COD) effect, is studied. The decay of laser power within the first several 100 ns is found to be determined by defect propagation. When analyzing different device designs, a correlation is found between defect propagation velocities and thermal resistances of the materials vicinal to the quantum well, being the main heat source. The findings are confirmed by direct inspection of the defect pattern in opened devices.

Defect Propagation in Broad-Area Diode Lasers

A simple model is presented for the propagation of macroscopic defects within the quantum well (QW) plane of broad-area high power diode lasers. The catastrophic optical damage (COD) effect is considered the mechanism for creating an initial damage site and further development of defect pattern. The relations between the parameters used in the model and the actual physical properties of the semiconductor materials are discussed. Experimentally observed damage patterns are well described.

The Principle Experiment of AlN Used as a Non-Absorbing Window Material of LDs

In order to reduce the catastrophic optical damage ( COD ) in the cavity surface of the traditional GaAs-LDs, this paper proposed the use of AlN film prepared as a non-absorbing window near the cavity surface of GaAs-LDs. In order to validate its feasibility, first of all, we prepared AIN film with different thickness on GaAs chips by reactive magnetron sputtering technology, and then, the PL spectroscopy of AlN / GaAs surface was acquired, the residual stress of the structure was calculated in accordance with the wavelength drift of GaAs intrinsic peak with the change in testing temperature.The experimental results show that the compression stress on GaAs chip is obvious when the thickness of AlN film is above 0.8 um. After the GaAs chip is subjected to compressive stress, the band gap will be widened,so the Eg of the active region near window area of GaAs-LDs will be wider than one of the active region inner the cavity, so that when the photons pass through this area, the absorption will be reduced, thereby forming non-absorbing window,therefore, the experimental validated that the AlN film used as the non-absorbing window of GaAs-LDs is feasibility.