2015 July

Light switches on a DVD

Thursday, 30th July 2015Publication highlights

Since the electronic properties of an optical storage material change faster than its structure, it could serve new applications

There could be more to DVDs than has been assumed to date. The material comprised of germanium, antimony and tellurium in which data media store information may also be suitable as an extremely fast light switch for optical communication or data processing. This is what an international team working with researchers at the Fritz Haber Institute of the Max Planck Society in Berlin and the ICFO-Institut de Ciències Fotòniques in Barcelona has succeeded in finding out. The storage mechanism in DVDs is based on the fact that laser pulses rearrange the structure of the material, switching it from a transparent to a non-transparent state. As the scientists have now discovered, the optical properties change much faster than the structure, which could be used in designing new types of photonic components.

Order versus disorder: Electrons are diffracted differently in the crystalline structure of a compound of germanium, antimony and tellurium (GST) than in the amorphous one. It is possible to distinguish clearly between the diffraction image of the crystal (left) and that of the amorphous material (right).

While DVDs are likely to soon become a thing of the past, this may not apply to their storage material. This is because the data media, which have become familiar mainly as media for films, are increasingly being replaced by other storage techniques. The Ge2Sb2Te5 compound, which specialists call GST for short, could find itself taking on new tasks.  The material owes its job to the fact that, in rewritable DVDs, laser pulses can convert it very quickly from a strongly reflective crystalline state into a much less reflective disordered version.. The two states then encode the zeros and ones of digital information. “The work we have done shows that the material can also be used for applications other than data storage,” as Ralph Ernstorfer, Research Group Leader at the Fritz Haber Institute of the Max Planck Society in Berlin states. “GST could be suitable for modulators in optical communication or for components in optical computer technology, for example.” (read more)

Original publication:
Lutz Waldecker, Timothy A. Miller, Miquel Rudé, Roman Bertoni, Johann Osmond, Valerio Pruneri, Robert E. Simpson, Ralph Ernstorfer und Simon Wall
Time-domain separation of optical properties from structural transitions in resonantly bonded materials
Nature Materials, 27. Juli 2015; DOI: 10.1038/NMAT435