Optical Recording Technology MAE 268 Prof. Frank E. Talke June 2008
Outline � Introduction � Basics of optical recording � Evolution of optical recording systems � Holographic � Atomic level � Conclusion 2
Storage Pyramide
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Optical Recording � Data is stored on a reflective surface so it can be read by a beam of laser light. � David Paul Gregg developed an analog optical disk for recording video and patented it in 1961 and 1969 (U.S. patent 3,430,966). � It encompasses systems such as CD, DVD and Blu-ray Disc 5
Optical Recording � The historical advantage of optical over magnetic technology was the potential recording density – Red laser -- spot size ~0.4 μ diameter ~5 Gbits/inch 2 � Many high end products - but never gave real competition to magnetic products – performance, cost – niche market for write-once applications � magnetic disk has exceeded optical recording densities � BUT magnetic disks see competition from low-end mass market products: CD-R, DVD-R and DVD-RAM 6
Three types of optical storage � CD (Compact Disk) � DVD (Digital Video Disk or Digital Versatile Disk) � BD (Blu-ray Disk) 7
Evolution of optical recording systems 8
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How Optical Storage Works 10
Optical Storage Devices � An optical disk is a high-capacity storage medium. An optical drive uses reflected light to read data. � To store data, the disk's metal surface is covered with tiny dents (pits) and flat spots (lands), which cause light to be reflected differently. � When 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 disc track lens spiral PDI C Laser Signal Processing 12
Assembly of a CD player 13
Laser head 14
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Structure diagram of an optical drive 16
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Solid state laser pulsed and focused on spinning disk surface Laser produces momentarily raised temperature along a track Thermally driven reflectivity change 19
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graphic - SONY CD disk layout 21
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Compact Disk (CD) � 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) � 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 � Preformed polycarbonate substrate – “wobbled groove” to guide and clock laser � Photo/heat sensitive dye layer protective layer reflective layer cyanine dye – cyanine substrate deformation � Reflection layer recording laser – gold � Laser spot heats dye, changes its structure which in turn deforms the substrate � Read-out laser is absorbed/scattered by the deformation 28
DVD-R � laser system: – λ = 640 nm; numerical aperture = 0.6; refractive index = 0.8 – spot diameter = 0.4 μ � capacity of side : 4.7GB � 1.3 MB/sec record & read speed 29
Erasable DVD-RAM � phase change recording layer - TeGeSb � heated by laser spot phase change phase change – high power write recording layer recording layer graphic - Balzers Process System s fast melt-cool cycle leaves amorphous spot with low reflectivity – lower power erase slower melt-cool cycle leaves crystalline spot with high reflectivity � read-out - low power laser � land & groove recording 30
Blu-ray Disk (BD) � Storage capacity ranges from 20 GB to 25 GB 31
Generations of Optical Recording CD DVD BD λ λ = 650 nm = 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
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holographic storage 37
graphic: Byte Magazine holographic storage 38
Writing holographically 39
Reading holographically 40
Summary � Many new technologies are being explored � Optical will stay for CD, DVD, etc. � Holographic is unclear � Atomic level storage is most desirable but not certain whether and how soon 45
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