Lingling Xiong

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.

Packaging of high power semiconductor lasers

This book introduces high power semiconductor laser packaging design. The challenges of the design and various packaging and testing techniques are detailed by the authors. New technologies and current applications are described in detail.

Double-cutting beam shaping technique for high-power diode laser area light source

Abstract. A new beam-shaping technique is proposed to improve the beam quality of a high-power diode laser area light source. It consists of two staggered prism arrays and a reflector array, which can cut the slow axis beam twice and rearrange the divided beams in fast axis to make the beam quality of both axes approximately equal. Furthermore, the beam transformation and compression can be carried out simultaneously, and the assembly error of this technique induced by the machining accuracy of prism’s dimensions also can be greatly decreased. By this technique, a fiber-coupled system for one three-bar laser diode stack is designed and characterized. The experimental results demonstrate that the laser beams could be transformed into the required distribution with ∼93.4% reshaped efficiency and coupled into a 400  μm/0.22  NA fiber, which are consistent with the theory.

Thermal modeling and analysis of high power semiconductor laser arrays

With the continuous increase of the output power of semiconductor laser array, the heat generation in the active region also increases continuously, which influences the performances and lifetime of semiconductor laser array seriously. In order to improve the performances and lifetime, understanding of the thermal behavior of high power semiconductor laser array packages and optimizing the thermal performance are crucial. By means of numerical analysis, a three-dimensional thermal model has been established, and the static and transient thermal characteristics in continuous-wave (CW) and quasi-continuous-wave (QCW) modes also have been studied systematically for a hard solder, conduction-cooled-packaged 808nm semiconductor laser array. Based on the thermal modeling and analysis, the approaches to reduce thermal resistance have been proposed. The results show that: compared with copper-tungsten (CuW), adopting the copper-diamond composite material as the submount can decrease the thermal crosstalk behavior between emitters, and reduce the thermal resistance by about 30%. In addition, a novel thermal design for the packaging structure of the mounting heat-sink is demonstrated, which has the ability of reducing the thermal resistance of the devices significantly.

A high power light emitting diode module for projection display application

Light emitting diode (LED) has numerous advantages such as long lifetime, large color gamut, small size and the absence of mercury vapor. In recent years, there has been recognition that LED could be an alternative light source for projection display application. In this work, dielectric compound parabolic concentrators (CPCs) were designed and optimized for multiple-LED array packaging structure for projection display application. The performance of rectangular CPC was studied and compared to theoretical simulations. Rectangular CPC was fabricated as the collector and collimator. A high power green LED module combined with rectangular CPC was fabricated and its performance was characterized. More than 90% light emitted by multiple-LED array can be collected by the CPC and transmit within the designed angle. A high power of 2.09W and a high luminous flux of 800 lm were obtained.

High-power semiconductor laser array packaged on microchannel cooler using gold-tin soldering technology

High power semiconductor laser arrays have found increased applications in many fields. In this work, a hard soldering microchannel cooler (HSMCC) technology was developed for packaging high power diode laser array. Numerical simulations of the thermal behavior characteristics of hard solder and indium solder MCC-packaged diode lasers were conducted and analyzed. Based on the simulated results, a series of high power HSMCC packaged diode laser arrays were fabricated and characterized. The test and statistical results indicated that under the same output power the HSMCC packaged laser bar has lower smile and high reliability in comparison with the conventional copper MCC packaged laser bar using indium soldering technology.

RGB High Brightness LED Modules for Projection Display Application

Light-emitting diodes (LEDs) have numerous advantages, such as long lifetime, large color gamut, small size, and absence of mercury vapor. In recent years, there has been recognition that high brightness LED could be an alternative light source for projection display application. In this work, dielectric compound parabolic concentrators (CPCs) were designed and optimized for multiple-LED array package for projection display application. The performance of rectangular CPC was studied and compared to theoretical simulations. More than 85% light, emitted by multiple-LED arrays, can be collected by the CPC and transmitted within the designed angle. A rectangular CPC was fabricated as the collector and collimator. The CPC was integrated with multiple-LED array package, and RGB high brightness LED modules with rectangular CPCs were fabricated and their performances were characterized.

Development of diode lasers for pumping high power ultrashort pulse lasers

Ultrashort pulse lasers have found increased applications in material processing with particular emphasis on laser-based micromachining applications, biomedical areas such as hard tissues ablating, and military fields. A new era of ultrashort pulse lasers was started when diode laser pumping gradually became more and more feasible, especially after the “high-power diode lasers” became available. In recent years, more and more wavelengths were covered by high-power diode lasers so that a large variety of solid-state laser and fiber laser materials could be diode-pumped or became good candidates for direct diode pumping. Diode lasers are playing a key role in the technology advancement and wide spread application of high power ultrashort pulse lasers. On the other hand, high power ultrashort pulse solid state lasers and fiber lasers demand higher performance and more reliable diode lasers to be developed. To achieve high pumping efficiency and reduce the thermal load of a high power ultrashort pulse laser, the spectrum of the pumping diode laser should be narrow enough to be mostly within the absorption region of the gain medium and more importantly the wavelength of should be kept near the absorption peak of the gain medium over the operation temperature and condition. Also the beam uniformity and brightness of the pumping source significantly affects the beam quality of a high power ultrashort pulse laser. Furthermore, for different applications, the requirements of the pumping diode lasers are different. In this paper, the development of diode lasers for pumping high power ultrashort pulse solid state lasers and fiber lasers is reviewed and discussed. We review the technology development trend of high power semiconductor lasers, including single emitters, bars, horizontal bar arrays and vertical bar stacks. We will discuss the strategies and approaches to achieve high output power, high brightness, narrow spectrum, low “smile” and long lifetime. Different diodes pumped ultrashort lasers and amplifiers are demonstrated to illustrate the effect of the pumping diode lasers. For example, the shortest pulse with 150fs are generated in Yb fiber laser with ring cavity and intracavity dispersion control using the single mode(SM) diodes with stable narrow linewidth by fiber grating. After two-stage dispersion compensation, the clean shortest pulses less than 30fs are generated. In high average power fiber amplifier, the largest pulse energy of 150uJ are generated at 30kHz with pulse width of 525fs after bulk grating compressor using high power multimode diodes by large size pigtailed fiber.

A new package structure for high power single emitter semiconductor lasers

High power semiconductor lasers have found increased applications in pumping solid state or fiber laser systems for industrial, military and medical applications as well as direct material processing applications. The reliability requirement for high power semiconductor lasers has been increased in recent years and it has been proven that indium-free packaging is one of the most effective ways in improving lifetime. The performance including reliability of high power semiconductor lasers is highly depended on the package structure. We have designed a new package structure for high power single emitter semiconductor lasers which is called F-mount. In contrast to traditional single emitter package structures, the F-mount offers indium-free packaging while improving or at least not sacrificing the thermal management. The heat sink of this new structure is insulated and easy for system integration. Finite element numerical analysis was used to compare the thermal resistance between F-mount structure and traditional structure. It was found that F-mount has high power and high electrical-to-output efficiency than the traditional structure. Lifetime testing was conducted on the F-mount devices and it was found that there was no obvious degradation in power over 7000 hours.

Packaging of high power semiconductor laser arrays using a novel macro-channel cooler

High power semiconductor laser arrays have been widely used in many fields, such as pumping solid state laser aerospace, industry, medicine and display. For many applications, high power semiconductor lasers operating quasi-continuous wave (QCW) mode are demanded. For QCW laser, the output peak power is higher and average power is low. Therefore, the transient thermal density is very high. The most common method of removing the large amounts of waste heat in a semiconductor laser package is by using commercially-available copper micro-channel coolers (MCC). However, due to the coefficient of thermal expansion (CTE) mismatching between copper and laser chip, hard-solder cannot be directly used. On the other hand, indium solder has the problem of electro-thermal migration when the temperature grads were high in QCW mode. Furthermore, copper material is susceptible to erosion and corrosion. To overcome these hurdles in many applications, a novel macro channel cooler (MaCC) was presented in this work. The thermal behavior of MaCC-packaged high power semiconductor laser arrays in QCW mode was studied using finite element analysis (FEA). A high power of >250W QCW semiconductor laser array/bar using hard solder was fabricated. The performances of laser arrays, including output power, slope efficiency, threshold, conversion efficiency, spectral width, near field, lifetime etc. were characterized. The measured results indicated that the output power of a MaCC- packaged high power semiconductor laser array was very close to that of copper micro-channel cooler. Based on MaCC-packaged single laser array/bar, multiple-bar stack and two dimension area array lasers with output powers of several kilowatts and several tens of kilowatts were fabricated.