Kaai pushes nitride lasers on to 525 nm
Kaai, a US start-up that is pioneering the development of non-polar and semi-polar nitride lasers, has broken its own record for the longest wavelength, CW green laser.
The company’s director of engineering, James Raring, told CompoundSemiconductor.net that it demonstrated a 525 nm, CW laser last week. That effort beats Kaai’s previous record of 523 nm, which it announced at this year’s Consumer Electronics Show.
The 525 nm laser produces a 6 mW, single-mode output at room temperature, and has a threshold current of 150 mA. This output is higher than its 523 nm laser, which produced 2-3 mW, but less than a 521 nm variant that can deliver nearly 10 mW.
These results were realized with a base temperature of 20 degrees Celsius, and a standard thermoelectric cooler in a standard package.
“We didn’t really play any tricks with this device to get the heat out. It was singulated, so it was a narrow chip, and it was mounted in a standard package,” explained Raring.
Efforts will now be directed at improving the efficiency of the device, so that its output can be increased to 40-50 mW.
If the Goleta-based start up can meet this goal, it will then be able to target commercial success in micro displays, high power pointers and some industrial and defence applications.
Kaai has spent several months improving the performance of its green lasers. Raring revealed that the company had fabricated 520-522 nm lasers last September, which required operating voltages of around 20 V. Since then this has fallen to 8.5V, and efforts are now being directed at reducing this to below 6.0 V.
“Not only does this [lower voltage] effect the wall plug efficiency – lower voltage means lower heating, and better slope efficiency,” explained Raring.
The green lasers that have been fabricated to date have not been optimized, and lower voltages should be realized by implementing standard modifications, such as the introduction of coatings of both of the laser’s facets.
Raring believes that it will be possible to make further progress and reach 532 nm, a wavelength produced by many commercial green lasers, which combine a 1064 nm source with some form of frequency doubling.
However, Kaai’s focus will be on optimizing the efficiency of its 525 nm lasers. Potential customers are telling Kaai that 525nm is “green enough”. They say that they would rather start to receive product at that wavelength, than wait for a 532 nm source to be developed.
Kaai’s engineers are still to determine the reliability of their green lasers. However, blue equivalents have shown lifetimes of 4,000 or 5,000 hours, and Raring believes that this can be extended to 10,000 hours. And according to him, there is no reason why Kaai’s green lasers cannot deliver similar lifetimes.
Raring believes that these lifetimes are suitable for many commercial markets, and in some cases a lower figure is even acceptable.
