High-power Semiconductor Lasers Research Articles

Integrated electroplated heat spreaders for high power semiconductor lasers

Thermal management of high power semiconductor lasers is challenging due to the low thermal conductivity of the laser substrate and the active device layers. In this work, we demonstrate the use of a microfabricated laser test device to study the thermal management of edge emitting semiconductor lasers. In this device, metallic heat spreaders of high thermal conductivity are directly electroplated on structures that mimic edge-emitting semiconductor lasers. The effects of various structural parameters of the heat spreader on the reduction of the thermal resistance of the laser test device are demonstrated both experimentally and theoretically. Without resolving to computational costive simulations, we developed two independent analytical models to verify the experimental data and further utilized them to identify the dominant thermal resistance under different laser mounting configurations. We believe our approach here of using microfabricated devices to mimic thermal characteristics of lasers as well as the developed analytical models for calculating the laser thermal resistance under different mounting configurations can potentially become valuable tools for thermal management of high power semiconductor lasers.

High-power external-cavity AlGaAs/GaAs/InGaAs quantum-dimensional heterolasers (λ = 1.06 μm)

Use of an external cavity with a grating ensures effective narrowing of the linewidth (∼0.35 nm) of a high-power multimode semiconductor laser with a broad (100 μm) stripe contact. An output power of up to 550 mW has been reached with experimental external-grating-cavity laser diodes. It is demonstrated that a 3-mm-long multimode laser diode based on a quantum-dimensional AlGaAs/GaAs/InGaAs heterostructure (λ = 1.06 μm) can be used with a directly pumped PPLN crystal waveguide to obtain second-harmonic radiation with λ = 0.532 μm.

Passively Mode-Locked High-Power (210 mW) Semiconductor Lasers at 1.55-$\mu$m Wavelength

We report on the generation of stable passively mode-locked pulses at 1.55-mum wavelength from high-power electrically pumped, large transverse mode semiconductor diode lasers. Optical pulses as short as 5.8 ps were measured directly from the laser. This is the shortest pulsewidth reported (without external compression) from a monolithic mode-locked slab coupled optical waveguide laser. The highest average power measured in mode-locked operation was 212 mW albeit the pulsewidths were larger. It was also found that length of the laser changes the power-current efficiency with the largest recorded efficiency of 165 mW/A.

High-Power Low-Beam Divergence Edge-Emitting Semiconductor Lasers with 1- and 2-D Photonic Bandgap Crystal Waveguide

We report on edge-emitting lasers based on the 1- and 2-D longitudinal photonic bandgap crystal concept. The longitudinal photonic bandgap crystal (PBC) design allows a robust and controllable extension of the fundamental mode over a thick multilayer waveguide to obtain a very large vertical mode spot size and a narrow vertical beam divergence.

High-Power Hybrid Mode-Locked External Cavity Semiconductor Laser Using Tapered Amplifier with Large Tunability

We report on hybrid mode-locked laser operation of a tapered semiconductor amplifier in an external ring cavity, generating pulses as short as 0.5 ps at 88.1 MHz with an average power of 60 mW. The mode locking is achieved through a combination of a multiple quantum well saturable absorber (>10% modulation depth) and an RF current modulation. This designed laser has 20 nm tuning bandwidth in continuous wave and 10 nm tuning bandwidth in mode locking around 786 nm center wavelength at constant temperature.

Radiation Hardness in Red and Infrared High Power Semiconductor Lasers

Radiation Hardness in Red and Infrared High Power Semiconductor Lasers

高功率半导体激光器电压饱和特性与器件质量

高功率半导体激光器电压饱和特性与器件质量

Three-dimensional failure analysis of high power semiconductor laser diodes operated in vacuum

The damaged region of a semiconductor laser diode that failed in a vacuum environment was analyzed using focused ion beam (FIB) serial sectioning, time-of-flight secondary ion mass spectrometry (ToF-SIMS), high resolution transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), energy dispersive x-ray spectroscopy (EDS), and nanodiffraction. The FIB nanotomography models and the TEM cross sections show a damage structure extending deep into the core and originating at the diode/antireflective (AR) coating interface. Nanocrystalline gold was detected at this interface using both TEM diffraction and EDS, and the localization of gold along the core at the diode/AR interface was corroborated using 3D ToF-SIMS. A thinning of the AR coating above the failure site was observed by TEM with a corresponding increase in carbon content on the AR surface detected with EELS. It is suggested that failure proceeded by pyrolysis of adsorbed hydrocarbons on the AR coating, which, in the presence of a high optical flux, contributed to carbothermal reduction of the AR coating. As the optical flux increased, thermal gradients facilitate metal migration, leading to larger gold clusters. These clusters are sites for deep level traps and may promote catalytic reactions.

Characteristics of a high-power broad-area laser operating in a passively stabilized external cavity

We narrowed the spectral bandwidth of our 2 W broad-area laser to 8+/-1 GHz with a coarse tunability of 12 nm centered near 790 nm in an external cavity. Our passively stabilized external cavity was designed for use with high-power semiconductor lasers. The cavity length and mount are modular with a fixed pivot point so that the optical elements can be changed to access a broad frequency spectrum and enable multiple applications. The bandwidth was observed to be dependent on the multimode transverse structure of the laser.

Stability of steady-state high-power semiconductor laser models

Fox-Li iteration-based algorithms form the core of steady-state design tools for high-power semiconductor lasers. The theoretical formalism is developed for Fox-Li iteration-based algorithms as applied to high-power lasers. This allows us to study their numerical properties, explain their behavior, and show the nature of the calculated approximate cavity modes. Lower-dimensional models are used to identify and explain the source of numerical instabilities and to find ways of improving the convergence rate of Fox-Li iteration algorithms. Finally, the results of the lower-dimensional analysis are verified by performing simulations of high-power tapered laser diodes in two dimensions using the finite-difference beam-propagation method.

Single-mode output power enhancement of an extended cavity broad-area laser diode by an intracavity photorefractive crystal

Brightness improvement of high-power semiconductor lasers can be achieved by placing a broad-area laser diode, used as a pure optical amplifier, in an extended cavity. We report the modal behavior of an extended cavity which contains a photorefractive crystal. The dynamic holographic medium that plays the role of a spatial and spectral filter acts on the transverse and axial structure of the extended cavity modes and improves the single-mode operating range of the laser. An enhancement of the brightness in single-mode operation by a factor of seven has been experimentally observed thanks to the intracavity photorefractive crystal.

Compact beam-shaping system for high-power semiconductor laser bars

The strong asymmetry in the emission of the fast and slow axes of semiconductor power lasers requires a significant optical beam transformation system to reach the parameters needed for micromachining, laser end-pumping and advanced applications. In this paper, a simple solution to this problem is proposed based on an array of cylindrical mirrors. Three examples of practical interest are considered, in which the compactness and effectiveness of the solution are demonstrated.

Optical transmission of ceramic shielding blocks made from Al2O3

We have studied the transmission of bulk Al2O3 ceramic used as heat shields for the working chamber of a turbine. We have established that radiation scattered from such an object has a pronounced speckle structure, while the scattering indicatrix is the same as the indicatrix for an ideal scatterer. We show that existing highpower semiconductor laser sources make it possible to penetrate sufficiently deeply into such materials, and the small transmission coefficient is not the limiting factor for development of optical methods for inspecting the quality of ceramic shielding blocks.

A novel high-power semiconductor laser diode with large cavity for high efficiency coupling with the optical fibers

A novel high-power semiconductor laser diode (LD) with very large cavity using multi-active -layer cascaded by tunnel-junction was developed. The window size of the LD was enlarged extremely and less than 20 degree of the lasing beam divergency was obtained，which benefits the coupling between the LD and the optical fiber. Many types of lensed fibers were used to test with the LD and the coupling efficiencies were increased over 30% compared with the conventional LD.

1240nm high-power GaInNAs laser diodes

We have fabricated 1240nm GaInNAs high-power semi-conductor laser diodes. In pulsed operation 1000 mum x 100 mum laser diodes show record low threshold current densities of 174 Acm(-2). Continuous wave output powers exceeding 4.6 Watts at room temperature and 6.2 Watts at a heatsink temperature of -5 degrees C are obtained from 1300 mum x 200 mum devices. The maximum wallplug efficiency of the device exceeds 40 % and the internal quantum efficiency reaches 0.89. Preliminary lifetime tests were performed for about 1000 h and show stable high-power operation.

New laser crystals for the generation of ultrashort pulses

Since the beginning of the 1990s, titanium sapphire has become the crystal of choice for the development of ultrashort laser systems producing very short and powerful pulses using the Chirped Pulse Amplification technique. In parallel to these developments leading to commercial products, new laser crystals have been studied in order to reach directly other wavelength ranges and to overcome the need to develop cw or pulsed green laser to pump the titanium sapphire crystal. In order to be able to directly pump the crystals with a very efficient and high-power semiconductor laser, new crystals doped with chromium or ytterbium ions have been developed. This article will review the latest development in this research field with the best performances obtained in terms of pulse duration. To cite this article: F. Druon et al., C. R. Physique 8 (2007).

A Metallization Scheme for Junction-Down Bonding of High-Power Semiconductor Lasers

High-power semiconductor lasers have found increasing applications in industrial, military, commercial, and consumer products. The thermal management of high-power lasers is critical since the junction temperature rise resulting from large heat fluxes strongly affects the device characteristics, such as wavelength, kink power, threshold current and efficiency, and reliability. The epitaxial-side metallization structure has significant impact on the thermal performance of a junction-down bonded high-power semiconductor laser. In this paper, the influence of the epitaxial-side metal (p-metal) on the thermal behavior of a junction-down mounted GaAs-based high-power single-mode laser is studied using finite-element analysis. It is shown that a metallization structure with thick Au layer can significantly reduce the thermal resistance by distributing the heat flow to wider area laterally, and the thermal resistance of a junction-down bonded laser with thick Au metallization is much less sensitive to the voiding in the die attachment solder interface than a laser with thin Au metallization. A metallization structure of Ti-Pt-thick Au-Ti-Cr-Au is designed and implemented, and the metallurgical stability of this metallization scheme is reported. It was found that, without a diffusion barrier, the thick Au layer in the epi-side metallization would be mostly consumed and form intermetallics with the Sn from the AuSn solder during soldering and thermal aging. The Ti-Pt-thick Au-Ti-Cr-Au metallization scheme prevents the diffusion of Sn into the thick Au layer and preserves the integrity of the metallization system. It is a promising candidate for junction-down bonding of high-power semiconductor lasers for improved thermal management and reliability

Studying the characteristics of pulse-pumped semiconductor 1060-nm lasers based on asymmetric heterostructures with ultrathick waveguides

High-power semiconductor lasers based on asymmetric quantum-dimensional separate confinement InGaAs/GaAs heterostructures with ultrathick waveguides were fabricated by means of metalorganic hydride vapor phase epitaxy technology. The laser characteristics were studied in a pulsed pumping regime, in which the emission was excited by current pulses of 100 ns duration at a repetition frequency of 10 kHz and an amplitude of up to 200 A. The passage to a pulsed lasing regime allowed the active region heating to be reduced and the output power to be increased to 145 W for a laser diode with a 100-μm exit aperture. The results obtained for the pulsed lasing regime show that saturation of the output power-current characteristic observed in the continuous-wave regime is fully determined by overheating of the active region of a semiconductor laser.

A study on the reliability of indium solder die bonding of high power semiconductor lasers

High power semiconductor lasers have found increased applications. Indium solder is one of the most widely used solders in high power laser die bonding. Indium solder has some advantages in laser die bonding. It also has some concerns, however, especially in terms of reliability. In this paper, the reliability of indium solder die bonding of high power broad area semiconductor lasers was studied. It was found that indium solder bonded lasers have much shorter lifetime than AuSn solder bonded devices. Catastrophic degradation was observed in indium solder bonded lasers. Nondestructive optical and acoustic microscopy was conducted during the lifetime testing to monitor the failure process and destructive failure analysis was performed after the lasers failed. It was found that the sudden failure was caused by electromigration of indium solder at the high testing current of up to 7A. It was shown that voids were created and gradually enlarged by indium solder electromigration, which caused local heating near the facets of the laser. The local heating induced catastrophic optical mirror damage (COMD) of the lasers. It was discussed that current crowding, localized high temperature, and large temperature gradient contributed to the fast indium solder electromigration. It was observed that some bright pattern structures appeared on the front facet of the indium solder bonded lasers after the devices failed and the bright patterns grew and spread upon further testing. Failure analysis showed that the bright pattern structure apparent on the front facet was due to crystallization of the TiOx material of the front facet coating as a result of overheating during lifetime testing. It was concluded that indium solder is not suitable for high power laser applications due to electromigration at high current densities and high temperatures.

High-power laser diodes (λ = 808–850 nm) based on asymmetric separate-confinement heterostructures

Symmetric and asymmetric separate-confinement AlGaAs/GaAs heterostructures have been grown by MOCVD in accordance with the concept of design of high-power semiconductor lasers. High-power laser diodes with a 100-µm aperture, emitting in the 808–850-nm range, were fabricated from these structures. The internal optical loss in asymmetric separate-confinement heterostructures with broadened waveguide is reduced to 0.5 cm−1. In the lasers with 1.7-µm-thick waveguide, the output optical power of 7.5 W in CW mode was achieved owing to reduction of the optical emission density at the cavity mirror to 4 mW/cm2.