1. Optical Disc Technology
CD, DVD, BD and Beyond
A short overview with a focus on
1. Life Expectancy
2. Data Degradation
3. Technology Migration
I have been involved in Optical Disc Technology since its introduction here in the US in I worked as a manufacturing engineer for MKE and built the 2nd manufacturing facility here in the US in 1984 while a grad student at the University of Texas at Dallas.
I worked primarily as a manufacturing expert during the 80’s and designed and built disc manufacturing facilities. Trained other manufacturing technologists and design QC equipment until the CD sales slump in 1990.
I worked on the first recordable technologies in the 1990s with a focus on manufacturing and QC. I worked with H density DVD project in 1994as a member of the MMCD camp. I specialized in disc analysis systems from 1987 to present.
I am active in many technolog standards groups such as the OSTA, Philips labs, ODMA
I’ve spent most of the last decade as a technology consultant for a number of different optical disc lab groups. I’ve spent the last 7 years working on the use of the optical disc drive as a physical measurement tool.
I’ve made a career out of ODT, I’m certain that by the time I retire it will be replaced primarily by solid state technologies.
- 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

2. A little History
- Technology first hit the market as Analog Video discs in First Pressed CD Technology in the US in 1982.
- The market was Primarily CD Audio disc until 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!

3. Optical Disc Features - the sub-micron world CD:
Smallest Feature - 0.8um
Track Length Miles
Features ~ 3 Billion
DVD:
Smallest Feature - 0.4um
Track Length Miles
Features ~ 17.5 Billion
BD: ~ 150 nm, 31 Miles, ~ 64 Billion
- In the early 80’s CD manufacturing rivaled the Semi conductor industry with feature sizes in the sub micron area.
- by applying a derivation on the Spiral of Archimedes equation we can calculated the distance of the spiral if we know the track pitch and starting and ending radius. We can divide the average feature size into that distance to obtain the feature count.
- An optical disc is litterally scanning millions of features a secondand distiguishing the characteristics of 9-10 different feature sizes, real time, to recover digital information.
- This is truly an amazing piece of technology that has been enormously successful because of its enormous economy of Scale.
- Today you can build an optical disc drive that does for about $15 USD. Without this fantastic economy of scale and instrument like this would easily cost > 250K.
M. Worthington LDS 03/17/ Optical Disc 2005

4. We have come along way since the days of CD audio!
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.
There are some very creatives OD Designer out there and many hybrid technologies.
In the 80’s we had the CD standard and not much else. Of course we went from Red Book Audio, to Yellow book Rom and Green Book Interactive, but it wasn’t until the manufacturing slump in 1990 that things really became interesting.
Recordable and Rewritable technologies came out, CD Rom shot up from %3 of the disc market to over %30 in one year. We started spinning discs at higher rates to increase our data transfer rates to the computer and the Video disc was born. Hybrid audio/rom formats came along - Blue Book. Bootable disc came along. DVD discs - wow- what a story that was.
Kodak started manufacturing a CD PROM - combi - recordable and pressed media. A mulitlayer DVD/CD disc was designed that would play back in CD and DVD drives - led to the firs t Combi drives in 1998.
The drive market exploaded and we left disc standardization behind. Standardization was unable to keep up with creativity!
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!

5. Pressed or Molded Optical Discs
If we look at discs today we have basically three types that most combination reader/writers will work with
1. Pressed Media - Pits
2. Recordable one-off media - Amp. -/+ R
3. Rewritable Media - PD type RW and RAM
We store information on a compact disc using pit that act as optical gratings that change light. We know light will do 4 things when it reaches a surface.
- transmission, reflection, refraction, absorption
Optical Media takes advantages of these 4 properties to store digital (1/0’s, off/on) info…
We also use other properties of light - Polarization, phase shifting, coherency, fabry perot apps. To store data in some of the lesser known formats.
1/4 wave depths provide a 180 shift between light reflecting off the land and the light reflecting off the bottom of the pits - results in small signal.
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

6. 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

7. Recordable Optical Discs
- Use Groove tracking for “Writing” function. Pit like Gratings for the “Reading” function.
Recordable discs work much differently than pressed media
we have no information on the disc so we use a wobbling groove to provide a tracking signal for the drive - more later.
Instead of pressing the pits in a manufacturing process we encode and burn the information real time in a writer.
The marks that we create are somewhat different from the pits. Instead of creating pits that are 1/4 wave in depth we create dark areas in the dye and burn marks on the reflective layer that absorb and refract light instead of reflect light. Instead of phase cancellation we create amplitude cancellation effect.
Light at one energy level absorbs (cyanine molecules vibrate very quickly and bonds in the material break) very quick in the dye. At lower energy levels the dye apears transparant and the reflective layer is there.
The disc appears as a normal pressed disc to the drive after recording although the reflectivity is lower. The added layer reduces the reflect from 75% to about 60-65%.
The more layers you go through the more light is lost - unless your design a 1/4 enahanced stack - I.e.- a mirror ---- Snells Law.
- Works primarily through the use of cyanine dyes that absorb energy and create a pit like structures that act as Amplitude Gratings.

8. 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)
Rewritable discs that we use today are primarily phase change discs.
Magneto Optical effect technology is considered very good but it is difficult to make cost effective in the drive designs so it doesn’t bode well with the other formats.
Phase change materials absorb energy during the write process and the material actually changes phasewhen expose to a specific energy level and becomes non reflective (non- crystaline - amorphous state). When we expose the material to a higher energy level it changes back to a crystalline state and becomes reflective again.
This process happens at a very high temp. Without di-electric layers the energy absorbed would burn a hole in the disc- certainly melt the plastic.
Tremendous amount of work goes into the optical design of the stack that is used to get the disc to work correctly. The QC necessary to control th e manufacturing process is very interesting.
The stack has many layers and the Reflectivity can be as low as %14. AGC circuitry is necessary in the drive to read these discs.

9. 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?
Drives are amazing.
There are about 130 drive manufacturers in the World and about 70% of these guys manufacture in Taiwan or Southern China. The component and design of these drive s are driven by the controller that are used. Economies of scale and part designs drive the market.
To be successful as a drive manufacturer today you must provide at least three new designs a year - to the market- in order to compete with the advancing integration. These engineering teams are astounding and they work very hard. I work very closely with a few of them.
Drives have gone from 20 or more chips to about 4 with one major controller.
There are currently 3 major controller in the market. MediaTek, Sanyo and BenQ/Philips.
There are three major OPU designs being used- Sanyo, SONY and Panasonic.
Philips is making a play for the coming BD OPU market.
Multi-layer HD and BD read, write and rewrite will be added to the mix by the first quarter of 2006!

10. 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
When you close your drive the tray mechanism sends a pulse to the laser head which look for a reflection or a signal bump to signify that a disc is there!
The drive will then spin at an adjustable rate referencing only it internal clock pulse
The laser will simultaeously apply a signal to the focusing coil in the OPU sending the head to the top and bottom of its working distance until it finds a focal point and a servo lock.
The OPU will then look for a signal pattern to cross its focal path and provide a tracking reference that can lock the tracking servo loop.
The drive decoder will then look for a synchronization pulse that can be pulled out of the High Frequency or quad sum signal focused on the PD for a sync pulse that can be Phase Locked with the Drive Clock.
This is the way every Optical drive I’ve ever worked with has worked.

11. The Optical Disc OPU
Light is collimated and phase corrected out of the laser. Noise is removed by the grating.
Coherent- Inphase, colimated light travles through a PBS and through a QWP where is is circularly polarized in one direction.
The light is focused by an objective assembly which is design to focus the beam through a specific material to a focal point with minimal spherical abberations.
Objective Design is very interesting.
The returning light is polarized in the opposite direction and when it travel to the PBS it is reflected onto the PD through a cylindrical lens that intriduces an astigmatism used to find a focal point.
The signals gathered at this PD provide all the data and operational function for reading in the drive. For writing there is a signal in the back of the diode that is used to control write laser power - monitor signal….

12. Her e is a real life light path profile showing the voice coil circuit that controls the focal position of the objective.
Today we have OPUs with mult lasers and mult laser paths in the same OPU.
BD OPU’s will three lasers to support Recordable technologies that are wavelength dependent.

13. CD OPU Design Tracking Signal Focus Signal SYNC
Here we show the the operational signals are generated from the reflected information coming back to the PD.
There are 100’s of tracking and focusing method filed in the patent office.
The 3 beam outrigger tracking, astigmatic focusing design above has been the most popular method for CD operation for years.
For recording and wobble detection we use a single spot method that differentiate by subtracting the left part of the PD from the Right.

14. DVD Objective Assembly
DVD focusing is similar to CD focusing. However we use a Differential Phase Detection Method for Tracking.

15. DVD Differential Phase Detection Tracking System.

16. DVD Tracking DPD Signal DVD Sync HF Signal
To make a measurement of disc quality and to characterize the discs we watch these operational signals .
A good Optical Disc Scientist can tell quite a bit from looking at the HF signal on an Oscilloscope. In analyzer we used sampling circuits to measure magnitude and filters to measure quality…
But there is so much we cannot see with an analyzer that we can see with an oscilloscope.
For example. ----dirty pits -botttom of the signal. Dirty land - top of the signal ….Pit burms - roll over on signal bottom.
Envelope dropouts - physical flaws or once arounds.
Poor pit edge- jittering signal….You are looking at the slicer quality right in the middle of ths signal where the 1 and 0’s are determined.
The 3t, 4t pits are smaller in length than the beam so they have a smaller amplitude….so this signal in the middle appears smalller. h
DVD Sync
HF Signal

17. Optical Disc Analysis and Measurement
- Digital Error $
- Analog Signal Error and Magnitude
$$$
- Optical Quality
$$$$
- Physical Error $$
- Logical Error $
HF offset - discuss asymmetry,
Digital Error - small pits- smaller than things we are breathing out of the air right now! We need a robust error correction system to recover info. - we do this through redundant data. About 30% of the data on a CD is redundant and used for recovery. So if you have 700 MB you really have a Gig on the surface. We can measure the activity of redundant use and correction in the drive decode. It is the best over all indicator of disc quality that we know of for
CD. We aren’t sure if this is th ecase for DVD yet.
Analog Error - basically measuring the quality of the operation al signals discussed before. Expensive - but necessary in disc manufacturing for discs that are designed to work in non- AGC drives. Jitter is a great indicator of all of these signals. ECMA standards are excellent at covering all of the signals. Publically available info. - free on the internet.
Optical Quality also important in manufacturing - not the end user- Measure Birefriingence, localized optical flaws, diffraction angles. BIG FOR DVD.
Physical Error - BIG DEAL FOR DVD. Bigger DEAL FOR BD and smaller.
Tilt, flatness, Eccentricity , Unbalance….spin a disc will an offset label in a drive at 6000 RPM - lets see what happens.
Logical - tremendous issue with early DVD - How info. Is org on a disc.
Digital and Logical Error Measurements are very cost effective and have proven to be a good indicator of disc quality and performance.

18. Technology Migration
Finish analyzer discussion with “what makes a good analyzer in a manf. Environment”
Accuracy first in the lab, Repeatability first in Manf. Or Dup.
14. As density of pits increase and things get smaller- we have problems. We can only add redundant data and encoding for so long. We can only make the laser wavelength so small. At DVD we are 1000 times above molecular. At HD we are 500. At HG we are As we get smaller we worry more about chemistry and energy and their impact on our product.
BD has a 3T pit size of 150nm - only a factor of 10 away from Molecular level- very close to chemical interact with the material that is making up the disc………Not good for Archival…..Not good at all………
Small physical things are much more problematic and will not last as long as big physical things……very important consideration.

19. - Handling failure on DVD is of greater concern.
Technology Migration
Smaller Size bad for Disc Archival
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.

20. 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.

22. 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

23. - 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.

24. - 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.

25. - 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

26. - 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

27. CONCLUSIONS
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.
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

28. The End of 2D Disc Design *

29. Blu-Ray, BD, Holographic and Beyond.

30. 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.

31. - 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.

32. Very interesting feature of the BD disc - can store information on the land area and the groove area - basically double the physical density!

33. What is a Hologram?