Doubled Diode Offers Blue Output

Richard Gaughan

Research on semiconductor lasers in recent years has focused on making them small and making them blue. Compact blue lasers can provide diffraction-limited spots roughly half the size of those generated by red diode lasers, promising increases in optical data storage, but the intensity and expense of available blue diode sources limit their possible applications.

Using aperiodically poled lithium niobate to frequency-double the output of an infrared laser diode, researchers have generated 3.45 mW of 490-nm laser light.

An alternative approach to the direct generation of blue light is to frequency-double the output of tried-and-true infrared laser diodes. Researchers at St. Andrews University and Southampton University in Southampton, UK, have demonstrated blue light from a frequency-doubled laser diode, using commercially available 980-nm InGaAs/GaAs laser diodes from JDS Uniphase Corp.

Aperiodically poled lithium niobate, which they lithographically patterned with eight gratings corresponding to different spectral acceptance bandwidths, served as the nonlinear crystal. A 30x aspheric lens collimated the output of the laser diode, which passed through a half-wave plate and a cylindrical lens to the lithium niobate crystal. At an incident power of 230 mW, the device produced 3.45 mW of 490-nm continuous-wave light.

Commercial interest

"It is always very satisfactory when lots of blue is seen," said David J.L. Birkin, a St. Andrews University researcher. He said that interest within the user community has already encouraged the team to consider commercializing the device. "Compared with other sources, our scheme has the potential to be made extremely compact."

The researchers reported their work in the May 21 issue of Applied Physics Letters.