Catastrophic Optical Degradation Research Articles

P‐4.6: High‐efficiency and high‐power 660 nm laser diode

A highly reliable and high-power laser diode with 110 um stripe width is designed and fabricated. At 25 °C, the lasing wavelength is 660.2 nm at 1.5 A and low threshold current of 506.4 mA can be obtained. At the output power of 2.5 W, the wall-plug efficiency (WPE) can achieve 48.7%. In addition, it can produce as high as 5.1 W at 25 °C and the maximum power can still reach over 4.2 W at 40 °C under CW. Attributed to the non-absorbing mirror, the catastrophic optical degradation (COD) power of this device can reach 6.5 W at 20°C. Till now, the laser diodes have stably operated for 510 hours at the operation current of 2.0 A and heatsink temperature of 40 °C.

Optimization of technology of diode laser mirror processing to maximize the threshold of catastrophic optical degradation

In this paper, optimization works on the technology of passivation and optical coatings of laser diode facets are described. The main goal is to increase the optical power at which the catastrophic optical mirror damage occurs. The coatings and passivation processes have been done in an ion source-aided electron-beam evaporator. The essence of passivation was to remove native oxides and produce a native thin nitride layer with simultaneous saturation of the dangling atomic bonds. The procedure has been realized with the help of nitrogen or forming gas (N2 + H2) beam. As a result, we present sets of technological parameters allowing to increase the catastrophic optical mirror damage threshold of diode lasers.

Инжекционные лазеры InGaAlP/GaAs оранжевого оптического диапазона (~600 нм)

Lasing in orange spectral range(599−605 nm)in(AlxGa1−x)0.5In0.5P−GaAs laser diodes grown by MOVPE on GaAs substrates(211) and (322) was demonstrated. The active region consisted of 4 layers of InxGa1−xP vertically coupled quantum dots. Carrier leakage from the active area was suppressed by using barriers formed with 4 quantum-sized layers of InGaAlP with high Ga content. The maximum optical power in the pulsed regime was limited by catastrophic optical mirror degradation and reached 800 mW. Lower threshold current density, higher differential efficiency, and lower internal losses were demonstrated by lasers processed from epitaxial structures grown on(322)A substrates in comparison to those grown on(211)A. This fact is due to the higher energy barrier for electrons in the first case.

Highly efficient red single transverse mode superluminescent diodes

Optimisation of the epitaxial growth of AlGaInP/GaInPAs nanoheterostructures and improvement of the technologies of active channel formation and p-contact deposition made it possible to considerably increase the external differential quantum efficiency (up to 0.5 mW mA−1), the catastrophic optical degradation threshold (up to 40 mW), and the spectral width (to FWHM exceeding 15 nm) of single transverse mode superluminescent diodes with the centre wavelength of about 675 nm. Lifetime tests demonstrated high reliability of these diodes at a cw output optical power up to 30 mW.

Catastrophic optical damage of high power InGaAs/AlGaAs laser diodes

The defects generated by the catastrophic optical degradation (COD) of high power laser diodes have been examined using cathodoluminescence (CL). Discontinuous dark lines that correspond to different levels of damage have been observed along the ridge. Finite element methods have been applied to solve a physical model for the degradation of the diodes that explicitly considers the thermal and mechanical properties of the laser structure. According to this model, the COD is triggered by a local temperature enhancement that gives rise to thermal stresses leading to the generation of dislocations. Damage is initially localized in the QW, and when it propagates to the waveguide layers the laser ends its life.

Reliability study on high-power 638nm broad stripe laser diode

High-power laser diodes (LDs) are strongly demanded as a light source of display applications. In this work, the reliability of a high-power 638 nm broad stripe (BS) LD was studied from the viewpoint of not only gradual degradation but also catastrophic optical degradation (COD) at a front facet. Long term acceleration aging tests for the 638 nm BS-LD with the window-mirror structure by using Zn diffusion were performed. It was confirmed that COD only occurs at a high output power and this mode was dominant compared with gradual degradation. The result also revealed that the mean time to failure due to COD was proportional to optical density to the power of −3:2. It is clarified that maintaining a low optical output power density is essential to develop high-power and highly reliable red BS-LDs.

Catastrophic optical degradation of the output facet of high-power single-transverse-mode diode lasers. 2. Calculation of the spatial temperature distribution and threshold of the catastrophic optical degradation

The temperature distribution and the power threshold during the catastrophic optical degradation arecalculated within the framework of the developed model of the COD of the output facet in high-power single-transverse-mode diode lasers. Comparison of the calculation results and the experiment show the model adequacy. The contribution of different physical mechanisms into the heating of the laseroutput facet is analysed. It is shown that the model under study can help to develop the method for predicting the laser lifetime by the accelerated ageing tests.

Catastrophic optical degradation of the output facet of high-power single-transverse-mode diode lasers. 1. Physical model

The physical model of catastrophic optical degradation (COD) of the output facet of high-power single-transverse-mode diode lasers is developed. The model excels other models both in completeness of the physical analysis of the processes leading to COD and in allowance for design feature of lasers used to increase the COD threshold — protective coating of the output facet and current limitationsnear it.

High-power lasers (γ = 808 nm) based on the AlGaAs/GaAs heterostructures of separate confinement

Laser diodes with a wavelength of 808 nm obtained by the MOC-hydride epitaxy in a system of the AlGaAs alloys have been studied. Parameters of the laser diodes with symmetric narrow and asymmetric wide waveguides are compared. It is shown that the maximum optical power in these laser diodes is limited by the catastrophic optical degradation of the SiO2/Si mirrors. In laser diodes with a symmetric narrow waveguide, the maximum power was 3 W, and with an asymmetric wide waveguide, it was 6 W. It is shown that it is possible to increase the maximum optical power by using the barrier Si3N4 layer introduced between the cleavage of the laser diode and SiO2/Si insulator coatings. The power of a laser diode with the barrier Si3N4 layer and with the asymmetric wide waveguide was 8.5 W.

Direct real-time observation of catastrophic optical degradation in operating semiconductor lasers using scanning tunneling microscopy

Cross-sectional scanning tunneling microscopy is performed on operating semiconductor quantum well laser devices to reveal real time changes in device structure. Low and nominally doped capping regions adjacent to the quantum well active region are found to heat under normal operating conditions. The increase in anion-vacancy defect formation and the generation of surface states pins the Fermi level at the surface and begins the process of catastrophic optical degradation which eventually destroys the device. The technique has implications for the study of defect generation and in-operation changes in all nanostructures.

Thermal Rollover around 460 mW Observation in Single-Lateral Mode 780 nm Laser Diodes with Window-Mirror Structure

Narrow stripe 780 nm window-mirror structure laser diodes (LDs) with and without a leakage current blocking structure in the window-mirror region were studied in terms of catastrophic optical degradation (COD) at facets. It was experimentally proved that a non-leakage-current-injection structure using proton implantation was effective in improving the COD level even in LDs with a window-mirror made by multi quantum well disordering. The thermal rollover phenomenon at around 460 mW at room temperature was observed in this LD. This is the highest output power recorded among narrow stripe LDs with a wavelength of 780 nm. Stable lateral mode operation up to 350 mW was also realized. This LD is suitable for the next generation of high speed (48 ×-) CD-R/RW drives necessitating 250 mW class LDs.

MOCVD-grown InGaAs/GaAs/AlGaAs laser structures with a broad-area contact

A metal-organic chemical vapor deposition (MOCVD) technique is developed for a diode laser heterostructure in a system of InGaAs/GaAs/AlGaAs solid solutions; the optimal sizes and the doping profile of the structure are determined to minimize the internal optical losses. Mesa-strip diode lasers with a threshold density of current Jth=150–200 A/cm2, internal optical loss factor αi=1.6–1.9 cm−1, and an internal quantum yield ηi=85–95% were fabricated. In the continuous lasing mode of a diode laser with a 100-µm-wide aperture and a wavelength of 0.98 µm, the optical power output was as high as 6.5 W and was limited by the catastrophic optical degradation of mirrors. The radiation divergence in the plane normal to the p-n junction amounts to θ⊥. The use of wide-gap waveguide layers, which deepens the potential electron well in the active region, is shown to reduce the temperature sensitivity of the InGaAs/GaAs/AlGaAs laser heterostructures in the temperature range from 0 to 70°C.

Operation and Catastrophic Optical Degradation of II–VI Laser Diodes at Output Powers larger than 1 W

Operation and Catastrophic Optical Degradation of II–VI Laser Diodes at Output Powers larger than 1 W

Operation and Catastrophic Optical Degradation of II-VI Laser Diodes at Output Powers larger than 1 W

An output power of 1.55 W, the highest ever reported, at 20 °C has been achieved for a ZnCdSSe/ZnSSe/ZnMgSSe separate-confinement heterostructure laser diode under short-pulsed operation. A differential quantum efficiency of 28% and a maximum conversion efficiency of 1.5% were obtained. The output power was limited by catastrophic optical damage (COD) of the facets, as proved by atomic force microscopy (AFM).

Analysis of 6-nm AlGaAs SQW low-confinement laser structures for very high-power operation

This paper reports experimental results on single quantum-well separate confinement heterostructures (SQW SCH) with low-confinement factor, designed for very high-power operation. The maximum power output for AR/HR coated 3-mm-long devices, measured in very short pulsed conditions (100 ns/1 kHz), from 10-/spl mu/m-wide stripes was as high as 6.4 W before catastrophic optical degradation. If scaled to continuous-wave (CW) conditions, this value would be 800-1100 MW, which would mean a factor of 22.7 times more than reported for the best devices with normal design for threshold minimization. The absorption coefficient for the symmetrical structure is as low as 1.1 cm/sup -1/, in spite of the low trapping efficiency of carriers in the quantum well (QW). The maximum differential efficiency is 40% (both faces, uncoated devices) for symmetrical structure and 33% for the asymmetrical one (all measurements in pulsed conditions). Threshold current densities were 800 A/cm/sup 2/ for 5-mm-long devices in the symmetrical case and 2200 A/cm/sup 2/ in the asymmetrical one. The effects of inefficient carrier trapping in the QW on the threshold current densities and differential efficiency are discussed.

Nonplanar quantum well heterostructure window laser

Data are presented on a nonplanar graded barrier quantum well heterostructure window laser formed by a single metalorganic chemical vapor deposition (MOCVD) growth. By utilizing a selectively etched substrate, a transparent window region is formed in the vicinity of the facets thereby relaxing the maximum power limit imposed by catastrophic optical degradation. The ultimate output power available from such devices is approximately 50% higher than from devices with the same structure but grown on unetched substrates. The processing required for device fabrication is minimized by taking advantage of the properties of MOCVD growth on nonplanar substrates.