Sony has developed a large output blue-purple semiconductor laser diode with a small laser beam aspect ratio of 2.3.
The company announced it at the "2001 Autumn Japan Society of Applied Physics (JSAP)" annual meeting held Sept. 11-14 at Aichi Institute of Technology.
If the laser beam aspect ratio is lowered within the range of 2 and 2.5, it becomes easier to assemble a semiconductor laser into an optical pickup for an optical-disk apparatus. Based on the judgment of its blue-purple LED's life and reliability characteristics being reached to the commercialization level of volume production, Sony is setting the next development target "to realize the blue-purple LEDs with prominent characteristics, which will be easy to use for the optical disk apparatus manufactures," such as to lower the laser beam aspect ratio.
In order to realize the reduction of laser beam aspect ratio, it is necessary to expand the far field pattern of the laser beam to the direction of the horizontal plane along the activated layer of the element, and to shrink to a vertical direction.
The far field pattern of the light emission spot at the plane of the diode element edge is reversed against the beam spot figure along the activated layer plane. Therefore, in the development of this LED, Sony tried to process the figure of the light emission spot, which spreads out within the activated layer plane of the element, as 1) to shrink the beam spot to a direction of the horizontal plane along the activated layer, and 2) to expand to the vertical direction of the activated layer.
As for the LED elements with a large aspect ratio of 3.2, Sony said it already has realized the characteristics of volume production level. The major LED characteristics of its announcement are as follows: 1) the threshold current of 34.3mA and threshold voltage of 4.1V, 2) the operation current of 56mA and operation voltage of 4.6V at its continuous oscillation with a light output power of 30mW, and 3) the mean time to failure of the LED at an operating temperature of 60 degrees Celsius, and at its continuous oscillation with a light output power of 30mW is estimated to be around 15,000 hours from the experimental life test slope of the characteristics. This MTTF and other characteristics shows the LED devices of this development are well within the level of commercialization.