CDs celebrate 25 yr of service

Working with Philips and PolyGram, BMS developed CD technology based on a specially tailored PC that still serves as the material for many optical recording media including DVD, HD-DVDs, and Blu-ray discs that provide 80 times the capacity of a CD. And even better materials and technologies are permitting the use of increasingly larger data volumes. The future, contends BMS, belongs to holographic media, with the storage of several hundreds of gigabytes.

BMS modified the Makrolon PC for the special manufacturing process needed in the music industry: Getting the highest possible optical quality and transparency possible in the substrate so that a laser head could read the digital code of a CD without errors. Dieter Freitag was among the early pioneers. The former head of Central Materials Research at Bayer AG had already developed PCs with an extraordinary level of flowability. This is vital for the production of CDs, because the plastic has to spread quickly and evenly within the mold. "What I didn't know, however, was that, with this product, we would be able to split a Beethoven symphony into four billion pits and then press them onto a disc with a diameter of 12 cm," said Freitag.

Data Printing: Increasing density, increasing speed Optical data storage has been developing at a steady pace over the last 25 yr. One collaborator with BMS has been Sony. The first CD-ROM was launched in 1992, with a storage volume of more than 450 floppy discs. Two years later computer users could simply "burn" and archive their documents to recordable or rewritable CDs (CD-Rs or CD-RWs). Next came DVDs that hold several times as much data as a CD (4.7 gigabytes).

Even greater data densities can be achieved on discs through the use of blue lasers, which have shorter wavelengths than red or green ones and can, therefore, be focused more precisely. The new optical engineering technique is used in HD-DVDs and Blu-ray discs with storage capacities of 15 to 100 gigabytes, making these the only discs that can fully satisfy the digital data requirements of high-definition TV. The storage volume of a Blu-ray Disc today is nearly 80 times that of a Compact Disc (650 megabytes). This achievement was made possible by shortening the wavelength of the laser beam used to read and write the data, from infrared (CD), to red (DVD) and then to blue light (Blu-ray Disc, HD-DVD). As a result, data can be written and read on a considerably narrower area.

Even the size of the pits - the indentations containing information - has decreased over the years. The smallest possible structure on Blu-ray Discs is just one-fifth the size of a pit on CDs. In addition, the distance between individual data tracks has been reduced by some 80%.

Researchers at BMS are working with companies such as InPhase Technologies of Colo. on holographic storage media (manufacturing partner: Maxell) that are set to continue the revolution in digital data discs. The new disc type - called Tapestry- has a capacity of 300 gigabytes and is currently in its test phase. Unlike a conventional CD or DVD, data is no longer written and read bit-by-bit, but stored in the form of holograms, i.e., in entire data blocks all at once. This means that the read/write process can be accelerated many times over.