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New design transforms diode arrays

08 Jul 2004

US start-up reveals a surface-emitting prototype that promises cheaper, more powerful laser-diode arrays.

Compact laser diode arrays that emit more than 1 kW and are far easier and cheaper to package than current modules could result from a new technology being pioneered by a US start-up. Quintessence Photonics Corporation (QPC) in California claims to have developed 2D surface-emitting diode arrays that are made from a single piece of semiconductor.

The Los Angeles-based firm, which was founded in November 2000, has just demonstrated a monolithic semiconductor chip that contains a 3x25 array of laser diodes and emits more than 100 W CW. And the firm says that the technology is scalable to produce arrays that emit more than 1000 W.

In contrast, high-power diode arrays on the market today emit a few hundred watts and are made from a stack of edge-emitting discrete bars (a strip of semiconductor wafer containing up to 25 individual laser diodes) which are soldered together in series. The drawback of this approach is that the bars each have to be cleaved and are tricky to connect together, package and cool.

As a result the stacks tend to be expensive and are hard to scale to higher powers. They are also prone to unpredictable failure at high powers often due to catastrophic optical damage (COD) of the diodes' light emitting facets.

QPC seems to have come up with an ingenious solution to problem. When making its wafer of edge-emitting laser diodes it etches a series of 45 deg mirrors next to the diodes to reflect their light out of the surface of the wafer. As a result, 2D arrays of laser diodes can be made from a single piece of semiconductor without the need for cleaving the wafer into a series of discrete bars.

One company that's certainly impressed is Pro-Lite Technology, the distributor of QPC's products in the UK and Ireland. It believes that the development could pave the way for much cheaper diode-arrays that are compact and easy to cool.

"As the light is now coming out of the surface you can cool through the bottom of the wafer, which is far easier," explained Peter Blyth from Pro-Lite. "The other fantastic benefit is that because the diodes are not cleaved their facets are never exposed to the environment. This removes the risk of any potential problems due to contamination or oxidation."

QPC says that it plans to demonstrate direct diode welding before the end of the year with its new devices. However, it is not clear when they will be commercially available.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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