Light sources using lasers for display applications, such as laser TV’s and pocket laser projectors, are expected to have superior properties in terms of size, weight and power consumption. For this reason, R&D activities aimed at commercialization of these devices have expanded rapidly over the past several years. Up to now, only red and blue laser diodes were commercially available, while green lasers were obtained by frequency conversion of infrared lasers. Gallium nitride (GaN) semiconductors, commercially available for blue LEDs, are also expected to be the key material for light-emitting devices in the green region. However, the material has been plagued with a phenomenon where the luminance efficiency shows a rapid decline with increasing wavelength.
At Sumitomo Electric, they have overcome this problem by developing a GaN crystal which inhibits the efficiency drop, resulting in room temperature pulse operation of a laser diode emitting in the pure-green region at 531nm. It is the first green laser diode in the world.
Some of the features of our green laser diode are as follows.
High quality crystal emitting in the green region
The luminous efficiency of GaN light-emitting devices is known to show a sharp decline with increasing wavelength. This is a combined result of the internal field effects as well as the deterioration of the crystal quality of the active layer. Several organizations are studying to alleviate this problem by changing the crystal orientation.
At Sumitomo Electric, we have developed a crystal which weakens the internal field effects and also improves the quality of the active layer. This has lead to the successful development of the world’s first green laser diode.
Tunability of the wavelength in the green region
With a proper design of the active layer, we have succeeded in covering the entire range of the lasing spectrum in the green region. While the lasing wavelengths of the conventional frequency-converted lasers are locked at a specific wavelength, our device can be tuned to any wavelength in the green region. Furthermore, the lasing spectrum remains virtually unshifted even in the high current range, and therefore, we believe our device has advantages in high power applications.
Another advantage of our green laser diode is that the dependence of wavelength at ambient temperature is minimal.