Inexpensive packaging techniques of fiber pigtailed laser diodes

Commercial single heterojunction GaAs laser diode chips have been fiber pigtailed with a 100/140 micrometers fiber. These lasers, producing 5 ... 10 W peak pulse power, are used in time-of-flight distance measurement instruments. The laser chips were purchased mounted on a coaxial TO-5 base. Two different types of packaging constructions were tested: a sleeve construction and a butt construction. In the sleeve construction the fiber was aligned with the laser chip using a loose sleeve and a fiber ferrule. In the butt construction the fiber ferrule was butt coupled to the laser submount. The fiber ferrule was actively aligned with the laser and fixed with an adhesive or with an adhesive and laser welding. Silicone gel potting was tested to improve the module stability in outdoor applications. The pigtailed laser modules and commercial laser modules were temperature cycled and results were compared. The measurements show that the properties of the adhesive are crucial to the temperature stability of the module. The tests show that optical output variation of the module was 6 dB in the temperature range of -20 ... 55 degree(s)C when the peak power was 3.7 W at room temperature. The stability of poor adhesive joints can be improved utilizing laser welding. However, the drawback is the high investment cost of equipment required. The results show that simple and inexpensive fiber pigtailed modules can be made using properly selected adhesives.