Ion Patterning Yields Distributed Feedback Lasers

A research team from the Universität Würzburg in Germany and the Alcatel Corporate Research Center in Marcoussis, France, announced in the Sept. 13 issue of Applied Physics Letters a simplified technique for the production of InP-based distributed feedback lasers. The team employed ion-beam lithography to define the coupled index and gain gratings on the passive section of the 1550-nm laser diodes, eliminating the need for two growth steps, additional phase shifts and antireflection coatings. The lasers have applications in dense wavelength division multiplexing systems.

The researchers used an electron beam to fabricate 2-µm-wide ridge waveguides in a template. A Ti/Ni mask transferred that ridge pattern to the semiconductor in a combined wet- and dry-etching process, and a 100-keV Ga⁺ focused ion beam inscribed the gratings. A 2-min ultrasonic bath in HF acid at 80 ^°C ensured 100-nm deep, high-contrast lines.

The GaInAsP/InP lasers display single-mode operation with linewidths less than 2 MHz and a yield that is greater than 90 percent over an 88-nm tuning range.