The new blue-violet diode laser element.

They claimed that the development of the new diode laser is a giant step toward multilayer recording on an optical disc made by using a single material and the realization of a low-cost optical disc with a capacity of more than 1 Tbyte.

"This time, we have just verified the principles," Sony said. "We cannot tell when we can realize the large-capacity disc, but we have solved a major problem."

Writing data on transparent material
The new diode laser emits blue-violet laser light in pulsed operation. The time-averaged output of the laser is 300 to 400mW, which is not high. But the peak output of the pulse is as high as 100W.

When such a high output is concentrated by using a lens, a nonlinear phenomenon called "multiphoton absorption" occurs at the focal point, making that point on a transparent optical disc non-transparent. Because more than one photon is gathered in one point, a bandgap energy that cannot be exceeded with a single photon can be exceeded.

As a result of the phenomenon, the material of the optical disc absorbs light and goes through a chemical change. A hole of 280 x 350nm size opens on the disc, and data is recorded. Because the depth of a layer used to record data can be changed just by controlling the lens, it may become possible to record data on several tens to 100 layers of an optical disc made by using a single material.

Sony has been developing the large-capacity optical disc by using multiphoton absorption for some time. For example, at ISOM 2009, an international conference on optical recording technologies that took place in the fall of 2009, the company announced that it successfully formed 34 layers on an optical disc made by using a single material, recorded data of 204 Gbytes (6 Gbytes on each layer) and read it out.