Optical Recording Technology

MAE 268

Prof. Frank E. Talke

June 2008 Outline z Introduction z Basics of optical recording z Evolution of optical recording systems z Holographic z Atomic level z Conclusion

2 Storage Pyramide 4 Optical Recording z Data is stored on a reflective surface so it can be read by a beam of light. z David Paul Gregg developed an analog optical disk for recording video and patented it in 1961 and 1969 (U.S. patent 3,430,966). z It encompasses systems such as CD, DVD and Blu-ray Disc

5 Optical Recording z The historical advantage of optical over magnetic technology was the potential recording density – Red laser -- spot size ~0.4μ diameter ~5 Gbits/inch2 z Many high end products - but never gave real competition to magnetic products – performance, cost – niche market for write-once applications z magnetic disk has exceeded optical recording densities z BUT magnetic disks see competition from low-end mass market products: CD-R, DVD-R and DVD-RAM 6 Three types of optical storage z CD (Compact Disk) z DVD (Digital Video Disk or Digital Versatile Disk) z BD (Blu-ray Disk)

7 Evolution of optical recording systems

8 ?

9 How Optical Storage Works

10 Optical Storage Devices zAn optical disk is a high-capacity storage medium. An optical drive uses reflected light to read data. zTo store data, the disk's metal surface is covered with tiny dents (pits) and flat spots (lands), which cause light to be reflected differently. zWhen an optical drive shines light into a pit, the light cannot be reflected back. This represents a bit value of 0 (off). A land reflects light back to its source, representing a bit value of 1 (on).

11 Principle of Traditional Optical Storage

pit land 010010110111011000 track 001101110001001110 101111001011011000 user data

eye-pattern track disc lens spiral

PDIC

Laser Signal Processing

12 Assembly of a CD player

13 Laser head

14 1 0

15 Structure diagram of an optical drive

16 17 18 Solid state laser pulsed and focused on spinning disk surface

Laser produces momentarily raised temperature along a track

Thermally driven reflectivity change

19 20 CD disk layout graphic -graphic SONY

21 22 Compact Disk (CD) z Storage capacity ranges from 650 MB to 700 MB

23 Optical Storage Devices – CD-ROM Speeds and Uses • Early CD-ROM drives were called single speed, and read data at a rate of 150 KBps. (Hard disks transfer data at rates of 5 – 15 MBps).

• CD-ROM drives now can transfer data at speeds of up to 7800 KBps. Data transfer speeds are getting faster.

• CD-ROM is typically used to store software programs. CDs can store audio and video data, as well as text and program instructions.

24 Optical Storage Devices

• A CD-Recordable (CD-R) drive lets you record your own CDs, but data cannot be overwritten once it is recorded to the disk.

• A CD-Rewritable (CD-RW) drive lets you record a CD, then write new data over the already recorded data.

• PhotoCD technology is used to store digital photographs.

25 Digital Video Disk (DVD) z Storage capacity ranges from 4.7 GB to 9.4 GB

26 Optical Storage Devices - DVD-ROM

• A variation of CD-ROM is called Digital Video Disk Read-Only Memory (DVD-ROM), and is being used in place of CD-ROM in many newer PCs.

• Standard DVD disks store up to 4.7 GB of data—enough to store an entire movie. Dual- layer DVD disks can store up to 9.4 GB.

• DVD disks can store so much data because both sides of the disk are used, along with sophisticated data compression technologies.

27 Write Once – DVD-R z Preformed polycarbonate substrate – “wobbled groove” to guide and clock laser

protective layer z Photo/heat sensitive dye layer reflective layer cyanine dye – cyanine substrate z Reflection layer deformation recording laser – gold z Laser spot heats dye, changes its structure which in turn deforms the substrate z Read-out laser is absorbed/scattered by the deformation

28 DVD-R z laser system: – λ = 640 nm; numerical aperture = 0.6; refractive index = 0.8 – spot diameter = 0.4 μ z capacity of side : 4.7GB z 1.3 MB/sec record & read speed

29 Erasable DVD-RAM z phase change recording layer - TeGeSb z heated by laser spot phaphasese change – high power write recording layer fast melt-cool cycle leaves amorphous spot with low reflectivity – lower power erase slower melt-cool cycle leaves crystalline spot with high reflectivity z read-out - low power laser graphic - Balzers Process Systems z land & groove recording

30 Blu-ray Disk (BD) z Storage capacity ranges from 20 GB to 25 GB

31 Generations of Optical Recording

CD DVD BD λ = 650 nm λ = 405 nm NA = 0.6 NA = 0.85 4.7 GBytes 22.5 GBytes

0.65 GByte 4.7 GByte 25 GByte

1.2 mm substrate 0.6 mm substrate 0.1 mm substrate

32 33 34 35 36 holographic storage

37 holographic storage graphic: Byte Magazine

38 Writing holographically

39 Reading holographically

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Summary z Many new technologies are being explored z Optical will stay for CD, DVD, etc. z Holographic is unclear z Atomic level storage is most desirable but not certain whether and how soon

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