In the 1990s, laser-diode development mainly targeted high-dollar-volume telecom applications. Much of this technology is now available to cost-sensitive industrial applications. Sophisticated industrial systems unable to afford significant downtime need diode reliability at an acceptable price point. The strict quality control and large production capacity of telecom laser-diode manufacturers promise to fulfill these needs for wavelengths ranging from 800 to 1000 nm and high output powers, particularly in aluminum gallium indium arsenide (AlGaInAs) diodes.
Diode lasers can exhibit both sudden (infant or random failure regimes) and gradual degradation (wearout regime). Infant failures arise from an intrinsic semiconductor defect or damage/imperfections introduced during device fabrication. A rigorous burn-in (high drive current, high temperature) screens out infant failures. The high stress of this early screening process, however, requires robust laser technology so as not to introduce new failure mechanisms. beijing homibeauty
where Tj is the diode junction temperature, I is the diode drive current, and kB is the Boltzmann constant. The Arrhenius factor (EA), exponential current acceleration (m), and proportionality constant are fitted by measuring device failure rates under various temperature and current accelerations. Random failure rates are commonly quoted as failures in time (FIT). One FIT corresponds to a single device failure per 109 hours of deployment. One thousand FIT is a useful yardstick, equating to approximately 1% of the device population failing annually. The more-intuitive mean time before failure (MTBF) can be easily calculated from FIT rates.
In the wear-out regime, AlGaInAs-based lasers show negligible degradation except during extremely accelerated high-current and/or high-temperature operation. Since infant failure and wear-out do not occur in AlGaInAs diodes, the overall failure rate follows Equation 1. Generally, AlGaInAs laser-diode technologies tend to have EA = 0.45 eV, or in other words, a failure rate roughly tripling each 20°C. On the other hand, the current acceleration (m) and proportionality factor vary widely depending on manufacturing processes, emission wavelength, and device geometry.
Single-mode laser diodes operating at center wavelength bands of 810, 830, and 850 nm are widely used for printing, metrology, inspection, and beam transmission (such as range-finding, illumination, targeting, and free-space communications) applications. High-performance AlGaAs or GaAs active-emitting-region diodes are considerably more challenging to fabricate than InGaAs QW lasers. Because the active region is unstrained, threshold-current density in AlGaAs or GaAs emitters is higher. The higher photon energy is more likely to spontaneously create semiconductor lattice defects, while the larger bandgap of AlGaAs raises device series resistance. Despite these handicaps, reliable single-mode AlGaAs emitter laser diodes operating at more than 200 mW are feasible.
An extensive reliability test involved a total of 120 lasers run at constant current (averaging 150 mW output power) and 60°C heatsink temperature for 1500 h. Zero failures and no noticeable wearout were observed. Applying the EA = 0.45-eV rule of thumb, each device hour at 60°C equates to approximately 6 h at 25°C. Analysis of these data yields predicts reliability at 150 mW and 25°C of 810 FIT (60% confidence) or, equivalently, an MTBF of at least 1.2 × 106 h. If an application were to require higher reliability or different operating conditions, a more extensive multicell test could improve these statistically limited values.
The 808-nm pump wavelength has long been used for Nd:YAG diode-pumped solid-state (DPSS) lasers. Like their InGaAs cousins, broad-area AlGaAs-based 808-nm pumps are also increasingly used for medical and materials processing applications. An MTBF of more than 10,000 h is preferred for DPSS lasers; more when several diodes are used. Because of the requirements of short wavelength, high power, and high brightness, many 808-nm vendors fall short.
Reliability testing of one laser-diode variety used in low-cost, high-brightness industrial pigtailed products demonstrated zero failures and negligible degradation for standard 1.4 W, 25°C diode operation (see Fig. 3). A version of the standard package passed numerous telecom-inspired robustness tests including vibration, 100 × -40°C to 70°C temperature cycling, 80°C/110-day high-temperature storage, damp heat 40°C/95% relative humidity/56-day storage, and 106-times on/off power-cycling testing. Tens of thousands of devices already deployed for multiple years strongly corroborate the individual results of diode reliability and package robustness established by the in-house testing. A similar 920-nm 100-µm fiber-coupled product rated for 2.5-W operation is scheduled for upgrade to at least 5-W 920-nm fiber-coupled output power in 2003.
The authors thank their colleagues Jim Darchuk and Alex Schoenfelder for their contributions to this article.
laser para remover Toby Strite is European business development manager, and Victor Rossin, Erik Zucker, and Matthew Peters are chip development managers at JDS Uniphase, 90 Rose Orchard Way, San Jose, CA 95134 Toby Strite can be reached at [email protected] .