Optical Disc Technology
CD, DVD, BD and Beyond
A short overview with a focus on
1. Life Expectancy
2. Data Degradation
3. Technology Migration
- The technology of CDs and DVDs
- Advantages and disadvantages of them, problems encountered, longevity, care & handling, quality control, testing, etc
- Perceptions / trends for optical media in the future, Blu-ray, HD, MO, alternative technologies, etc.
- Optical media and the suitability for digital preservation
A little History
- Technology first hit the market as Analog Video discs in 1978. First Pressed CD Technology in the US in 1982.
- The market was Primarily CD Audio disc until 1990. CD Recordable, CD Rewritable and CD-ROM grew very quickly in the early 90’s.
- MMCD and SuperDisc War in 1994 lead to DVD consortium.
- DVD-R introduced by Pioneer in 1997.
- Plextor introduces the 2X CD-ROM drive. The speed race is on!
M. Worthington LDS 03/17/0 Optical Disc Technologies @ 2005
CD:Smallest Feature - 0.8um
Track Length - 3.74 Miles
Features ~ 3 Billion
DVD:Smallest Feature - 0.4um
Track Length - 7.8 Miles
Features ~ 17.5 Billion
BD: ~ 150 nm, 31 Miles, ~ 64 Billion
Optical Disc Features - the sub-micron world
DENSITY AND FUNCTION
Today an Optical Disc can be a CD, DVD, BD or HD Density Disc.
It may be single layer, double layer, Parallel track path, Opposite Track Path, Mixed Density Hybrid, ect………………..
It may be pressed, recordable, rewritable or degradable in Function.
There are over 150 known logical disc formats.
An optical disc today can be quite a mixture of Density, Format and Function.
We have come along way since the days of CD audio!
Pressed or Molded Optical Discs
Reflected information from Pit structures work as Phase Gratings to provide Operational Signals.
CD (e = 1.2mm), DVD (e = 0.6mm), BD and HD (e = 0.1mm)
~h = 1.2mm
Recordable and ReWritable Discs
- Contain Grooves that are using for tracking during the write process
- Information encoded in the wobble signal is used to setup the write process
- Pit are written in and ON (BD) the grooves
Recordable Optical Discs
- Works primarily through the use of cyanine dyes that absorb energy and create a pit like structures that act as Amplitude Gratings.
- Use Groove tracking for “Writing” function. Pit like Gratings for the “Reading” function.
REWRITABLE OPTICAL DISCS
-RW technologies use phase change materials. Active layer (metallic stack) changes states when exposed to pulse low energy level. Returns to reflective state when exposed to higher energy level. (crystal/Amorphous)
Optical Disc Drive Design
Todays drive consumer can expect his drive to be compatible across most Optical disc Densities and Formats.
Todays drive consumer can expect his disc drive to play back over 23 different CD formats at with a data transfer rate approaching 48X. The drive should play back DVDs, Dual Layer DVD’s, DVD Recordables and DVD Rewritables with a data transfer rate approaching 12X. The same drive would be expected to format and write to 2 DVD rewritable formats. The drive would be expected to write to 2 DVD recordable formats at 16X! Dual Layer Anyone?
Multi-layer HD and BD read, write and rewrite will be added to the mix by the first quarter of 2006!
How does a Drive Read (and Write) to a Disc?
- Detect and Spin the Disc
- Focus the Laser on the surface
- Track the Surface
- Synchronize
The Optical Disc OPU
CD OPU Design
Tracking Signal
Focus Signal
SYNC
DVD Objective Assembly
DVD Differential Phase Detection Tracking System.
DVD Sync
HF Signal
DVD Tracking
DPD Signal
Optical Disc Analysis and Measurement
- Digital Error
- Analog Signal Error and Magnitude
- Optical Quality
- Physical Error
- Logical Error
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Digital and Logical Error Measurements are very cost effective and have proven to be a good indicator of disc quality and performance.
Technology Migration
Technology Migration
As features get smaller and laser wavelengths get shorter we develop some limitations in our optical design.
- As Numerical Aperatures get smaller the working distance of the OPU gets smaller.
- Higher Density Formats are more susceptable to Physical Flaws and Optical Anomalies.
- Handling failure on DVD is of greater concern.
Smaller Size bad for Disc Archival
Some Limitations of Recordable Media
- Most are based on Organic Cyanine Dye Materials which can degrade quickly.
- Optical Design is based on Amplitude Grating which is less robust than Phase Grating.
- DVD recordable discs market has had trouble getting the quality level that CD recordable has.
- New Recordable format have very small features. Harder to care for in um environment.
NIST Performs Accelerated tests on a group of CD-R media and a Group of DVD media.
- Exposed Media to specially designed light chamber. Also used extreme humidity and extreme temperatures per incubation cycle shown below
- Discs evaluated using CD-CAT analyzer. BLER and Uncr. Were monitored during CD-R evaluation. PI and POF were monitored during
DVD-R evaluation.
- Jitter was also measured and showed a strong correlation to BLER and PI error during the evaluations
- Results show that Media Samples S2 and S4 performed very well in Accelerated Light Exposure.
- Media Sample S4 performed best in Accelerated Humidity and Temperature exposure testing.
- All Phthalo stabilized cyanine media out performed the other media.
- Jitter increased correlated with BLER across all media.
- Media Samples 2 and 4 also maintained Jitter below 50ns for more than 1400 Hrs of exposure in the light chamber.
- Jitter on the AZO dye samples increased drastically after about 400 Hrs. of exposure.
- Samples S2 and S4 also went more than 1000 Hrs with No Uncrs.
- Dye Technology in DVD samples is still not fully known
- Only three types of media were identified for the test
- Sample D2 out performed the other two samples in the PI Error Testing
- Jitter increases also correlated well with PI Error (8sum) in DVD Testing.
- Sample D2 stands out as the most stable going more than 800 Hours with no substantial increases in Jitter or PO error
Sample size in the Study was small so forecasting statistical failure life was not possible.
It is apparent that light exposure has a significant effect on the life and performance of the media. Some media may fail with only a few weeks of exposure.
CONCLUSIONS
Phthalo stabilized CD-R dyes performed much better than the AZO dyes.
A much larger test with a larger sample size is in the works
The End of 2D Disc Design
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Blu-Ray, BD, Holographic and Beyond.
BLUE RAY - BD and the QUEST for High Density Video
Blue Laser Formats are Available today and in the market place - UDO, Sony Pro Versions.
- NA and Working Distance for 2D Discs at the edge.
- Potential for Optical and Physical error on un-encased disc is extremely high...
- Dual layer BD-W disc is working very well - 50 Gbytes.
Very interesting feature of the BD disc - can store information on the land area and the groove area - basically double the physical density!
What is a Hologram?
