Xingsheng Liu

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...

Thermal management strategies for high power semiconductor pump lasers

Semiconductor pump lasers are an important component in Erbium-doped fiber amplifiers and Raman amplifiers. Thermal management has become one of the major obstacles of pump laser development. Understanding of the thermal behavior of high power laser packages is crucial to the thermal design and optimization of pump lasers. In this paper, we report on the thermal characteristics of a high power pump laser and discuss the issues associated with heat dissipation. The thermal management of high power pump laser modules mainly consists of three aspects. One is the thermal resistance reduction which reduces bulk temperature rise in the laser diode chip. The second is facet temperature control and the third is the thermoelectric cooler (TEC) coefficient of performance improvement. In this paper, the approaches to reduce thermal resistance and facet temperature at the chip level and package level will be reviewed and the thermal design and optimization of the package assembly to improve the TEC coefficient of performance will be discussed.

Comparison between epi-down and epi-up bonded high-power single-mode 980-nm semiconductor lasers

Epi-down and epi-up bonded high-power single-mode 980-nm lasers have been studied in terms of bonding process, thermal behavior, optical performances, and long-term laser reliability. We demonstrated that epi-down bonding can offer lower thermal resistance and improved optical performance without degrading the long-term laser reliability. An optical power of 630 mW was obtained for the first time from an epi-down bonded 980-nm pump module. Our studies have shown that epi-down bonding of single-mode 980-nm lasers can reduce junction temperature and thermal resistance by up to 30%. Experimental measurements showed over 20% in thermal rollover power improvement and over 25% reduction in wavelength shift versus current in epi-down mounted lasers compared to epi-up mounted lasers. Lifetime test over 14 000 h at 500 mA and 80/spl deg/C of the epi-down bonded lasers is reported for the first time.

107-mW low-noise green-light emission by frequency doubling of a reliable 1060-nm DFB semiconductor laser diode

We have generated 107-mW green-light emission by frequency doubling of a reliable 1060-nm distributed feedback (DFB) laser diode using a periodically poled MgO-doped lithium niobate waveguide in the most compact single-pass configuration. The green power variation is lower than 1% at frequencies below 82 kHz. The relative intensity noise of -150 dB/Hz has been measured at 100 MHz. We also report 5000-h life-test results of 1060-nm DFB lasers at 80/spl deg/C.

High-power high-Modulation-speed 1060-nm DBR lasers for Green-light emission

We report on the static and dynamic performance of high-power and high-modulation-speed 1060-nm distributed Bragg reflector (DBR) lasers for green-light emission by second-harmonic generation. Single-wavelength power of 387 mW at 1060-nm wavelength and green power as high as 99.5 mW were achieved. A thermally induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. Measured rise-fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the lasers suitable for >50-MHz green-light modulation applications

Study of the mechanisms of spectral broadening in high power semiconductor laser arrays

High power semiconductor laser arrays have found increased applications in pumping of solid state laser systems for industrial, military and medical applications as well as direct material processing applications such as welding, cutting, and surface treatment. Semiconductor laser array products are required to have narrow spectral width for applications. Increasing the spectral accuracy by reducing the spectral width of the pump diode enables the laser system designer to improve the laser system compactness, efficiency, power, and beam quality while at the same time reducing thermal management cost in the system. Spectral width is one of the key specifications of laser array products and it is very important to improve the spectral performance to improve production yield, reduce cost and gain competitiveness. In this paper, we study the mechanisms of spectral broadening in high power semiconductor laser arrays.

Technology trend and challenges in high power semiconductor laser packaging

High power semiconductor lasers have found increased applications in pumping of solid state laser systems for industrial, military and medical applications as well as direct material processing applications such as welding, cutting, and surface treatment. Driven by low cost, longer lifetime and new applications, the requirements of high power semiconductor lasers have been changed and the demand for new products has been accelerated in recent years. As a result, the packaging technologies of high power semiconductor lasers have been highly developed and have become more sophisticated. In this paper, we review and discuss the technology development trend of high power semiconductor lasers, including single emitters, bars, horizontal bar arrays and vertical bar stacks. However, the packaging technology is still one of the bottlenecks of the advancement of high power semiconductor lasers. We will discuss the challenges and issues in high power laser packaging and some approaches and strategies in addressing the challenges and issues will be presented.

Study of the mechanism of “smile” in high power diode laser arrays and strategies in improving near-field linearity

High power diode lasers have found increased applications in pumping of solid state or fiber laser systems for industrial, military and medical applications as well as direct material processing applications. The non-linearity of the near-field of emitters (or the so called “smile” effect) in a laser diode array poses significant challenges in optical coupling and beam shaping and has become one of the major roadblocks in broader applications of laser arrays. Increasing the near-field linearity of a pumping laser diode array enables the laser system manufacturer to improve the laser system compactness, optical coupling efficiency, power, and beam quality while at the same time reducing manufacture cost in the laser system. Therefore, the near-field linearity of a laser bar is one of the key specifications of laser array products and improving the near field performance is especially important in order to increase production yield, reduce cost and gain competitiveness. In this paper, we will study the mechanism of “smile” in high power diode laser arrays and discuss the strategies and ways to achieve low “smile”.

Design and implementation of metallization structures for epi-down bonded 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 of epi-down bonded lasers has significant impact on the thermal performance and reliability of the high power semiconductor lasers. In this paper, the influence of the epitaxial-side metal (p-metal) on the thermal behavior of a GaAs-based high power single-mode laser, mounted epi-side down, is studied using finite element analysis. Metallization structures having different diffusion barriers for eutectic AuSn solder are designed and implemented, and the metallurgical stability of the four metal systems, Ti/Pt/thick Au (2-3 /spl mu/m thick), Ti/Pt/thick Au/Ti/Pt/Au, Ti/Pt/thick Au/Ti/Ni/Au, and Ti/Pt/thick Au/Ti/Cr/Au, are reported.

Transient and static thermal behavior of high-power single-mode semiconductor lasers

Transient and static thermal response of high power single-mode laser module has been simulated using finite element method (FEM). FEM modeling revealed the time constants of heat propagation in lateral direction and in vertical direction. The time constants calculated by FEM modeling in the microsecond scale and the sub-millisecond to millisecond scale were experimentally verified by a time-resolved far-field optical measurement and a transient forward-voltage measurement respectively. It is shown that the active region, semiconductor substrate and the solder-submount each contributes about 35%, 50% and 15% to the total static thermal resistance of the laser package.