Flared Laser Produces 650 mW

Gary Boas

Researchers at the University of Illinois at Urbana-Champaign and Nuvonyx Inc. in Bridgeton, Mo., have developed a flared semiconductor laser in which the strength of the waveguide decreases as the width of the laser increases, resulting in optimal single lateral mode control over the entire length of the device. The group envisions several applications of the laser, which produces up to 650 mW of 1040-nm radiation, including use in fiber amplification pumps, free-space communications and direct diode welding.

Output powers of 650 nW have been produced by a semiconductor laser that features a flared buried ridge design. The waveguide varies in width from 2 to 8 µm.

Semiconductor lasers are increasingly finding a place in telecommunications, materials processing and medicine, but their performance often is limited by loss of fiber coupling efficiency and laser brightness at high output powers. Flared laser structures combine the mode quality of narrow-stripe lasers with the higher output power of wide-stripe lasers to overcome these issues, but until now they have presented additional difficulties.

The researchers produced the laser using a three-step deposition process. They fabricated the GaAs laser ridge structure atop an InGaAs quantum-well region and GaAs barrier using a metallorganic chemical vapor deposition selective area epitaxy process to grow the waveguide in an area that they lithographically etched into a layer of SiO₂.

The waveguide, which they subsequently buried under AlGaAs and GaAs, is 2 mm long and varies in width from 2 µm at one end to 8 µm at the other. "The result is a laser with a width of 8 µm at the output facet that performs with the lateral mode stability of a laser four times narrower, enabling high output power," said Reuel B. Swint, a researcher at the university.

There are other available means with which to attain single lateral mode outputs from diode lasers -- such as distributed feedback and resonant array structures -- but they do not offer the same benefits. "These structures are expensive to fabricate or have a limited range over which they operate in a bright, single lateral mode," Swint said. "Flared amplifiers can create large single-mode powers, but the lack of a real index guide creates astigmatism, which increases the expense of the optics."

The researchers have obtained a patent for their design and hope to bring it to market within 18 months. "We have an Air Force program that is sponsoring some of the effort, and we are working with a commercial company that will be sponsoring the rest," said Mark S. Zediker, CEO at Nuvonyx. "But with the current economic conditions, finding the funding is the real issue."
Nevertheless, Zediker said, fabrication of the laser is straightforward, and the researchers have produced a number of them with good repeatability. "This gives us great confidence in our ability to transition the technology to production."