A polychromatic versatile dynamic testbed for the evaluation of optical disks is presented. The system can be used for all wavelengths from 400 to 690(780) nm, allowing any laser source in this range -- especially the new blue laser diodes -- to be utilized for read-write-erase experiments. In addition, the system allows testing of disk with substrate thicknesses ranging from 0 to 1.7 mm. The polarization of the system can easily be changed from linear to circular at the disk surface, so the use of both magneto-optical (MO) and phase-change disks (PD) is possible, in addition to read-only disks (CD, DVD). A variable leaky polarizing beam splitter has been specially designed for this tester. This device allows to continuously adjust the ratio between the s- an p- polarized components for the reflected beam reaching the detectors, enabling the optimization of the signal-to-noise ratio while adjusting the relative amounts of the two components of polarization at the detectors. The astigmatic method is used for focus control and the push-pull method is used for track control (other focusing and tracking schemes like DPD are under preparation). In an optional setup, the RF data signal and the focus and track servo signals can be derived from the same high speed quad detectors, allowing the use of the full optical power returning of the disk for all these purposes. So the astigmatic FES, the push-pull TES, the differential magneto- optical readout signal and the conventional sum signal for phase-change readout as well as the differential edge-signal for mark-edge detection are obtained. In this paper, we are presenting the basic functions of VERSATEST-I as well as future enhancements for latest optical data storage technology. Additionally typical test results on magneto- optical disks and phase-change disks (DVD-RAM 5.2GB) are reported.

A modified optical microscope consisting of an oil immersion objective, index-matching fluid, transducer material, laser diode source, and photomultiplier tube is used to perform static testing of phase-change optical disks designed for use with nearfield optics. A 780-nm wavelength laser beam is coupled to the microscope optical path for read, write, and erase pulsing of the media. The oil immersion objective has a numerical aperture of 1.25. The transducer serves two purposes. The oil is kept off the surface of the disk, and an air gap is formed between the transducer and the surface of the disk. Rewritable phase-change disks with a first surface sensitive layer of GeSbTe were tested with the oil immersion microscope. The relative change in reflectivity due to writing and erasing of amorphous marks between 200 nm and 500 nm in diameter is detected. This technique provides a simple method of investigating the performance of nearfield optical recording media.

The measurement of bump heights and pit depth on compact discs (CD) with atomic force microscopes (AFMs) is quite different from the measurement of step heights on step height calibration standards. Both the bumps and the pits show much larger transition regimes and more structural irregularities. The irregularities disqualify the effective use of profile based algorithms, which minimize the influence of any remaining motion deviations of the scan apparatus, to determine the height. Therefore a histogram height algorithm has to be used. The results of the bump height and pit depth measurements varied about 20 nm over the different sample regions. The remaining approximately 30 nm difference between the average of the bump height and pit depth is believed to result from the sample preparation procedure. By itself, the large sample variation observed will result in rather large measurement uncertainties for the measurement of the average height and depth of these features, if the averaging does not include a large amount of data taken at many different sample positions.

Data archivists expect information storage media to have a lifetime greater than ten years. Furthermore they desire the ability to predict when the media will fail in order to plan for its replacement. Archival lifetime predictions are based on accelerated aging studies, where the media are subjected to conditions of high temperature and high humidity. The rate of failure is measured and the data extrapolated to obtain rates of failure under ambient conditions. This extrapolation is reasonable provided the degradation process is activated and the Arrhenius relationship holds. However this may not be the case for the complicated materials packages in optical data storage media. A primary concern for the polymeric materials is any phase transition, such a glass transition or a beta relaxation, that may occur at temperatures between ambient and the accelerated aging conditions. It is not clear how one extrapolates through those transitions. These phase transitions can give rise to large changes in the rates of diffusion for water, oxygen and other agents of degradation. Furthermore, for polymers, such as polycarbonate, the mode of failure is often hydrolysis and the degradation products can catalyze further hydrolysis, an autocatalytic degradation. The polymer degradation will change the phase transition temperatures. The degradation products may also plasticize the polymer, causing further changes in diffusion rates. We provide here a simple analysis of accelerated aging techniques and discuss other factors that may be involved.

An intercomparison of optical disc birefringence measurements using commercial instrumentation found in manufacturing settings showed significant measurement variation. We discuss possible sources of variation in these measurements, including changes in disc properties and coherence effects. We describe specific measurement errors related to deviations from circular input polarization in one class of polarimetric instruments. Efforts to mitigate measurement errors, such as the development of calibration artifacts, are discussed.

New azo dye-doped polymer thin films have been made by spin- coating method on single-crystal silicon substrates. The complex dielectric function and optical parameters of the films have been measured with a fixed angle of incidence automatic spectroscopic ellipsometer. The electronic structure of the films has been explained.

At the National Institute of Standards and Technology, we are building a metrology instrument called the Molecular Measuring Machine (M³) with the goal of performing nanometer- accuracy two-dimensional feature placement measurements over a 50 mm by 50 mm area. The instrument uses a scanning tunneling microscope to probe the surface and an interferometer system to measure the lateral probe movement, both having sub-nanometer resolution. The continuous vertical measurement range is 5 micrometer, and up to 2 mm can be covered by stitching overlapping ranges. The instrument includes temperature control with millikelvin stability, an ultra-high vacuum environment with a base pressure below 10^-5 Pa, and seismic and acoustic vibration isolation. Pitch measurements were performed on gratings made by holographic exposure of photoresist and on gratings made by laser-focused atomic deposition of Cr. The line pitch for these gratings ranged from 200 nm to 400 nm with an estimated standard uncertainty of the average pitch of 25 X 10^-6. This fractional uncertainty is derived from an analysis of the sources of uncertainty for a 1 mm point-to- point measurement, including the effects of alignment, Abbe offset, motion cross-coupling, and temperature variations. These grating pitch measurements are uniquely accomplished on M³ because of the combination of probe resolution and long-range interferometer-controlled stage. This instrument could uniquely address certain dimensional metrology needs in the data storage industry.

The paper introduces characters of Near Field Optical Disc (NFOD) Recording Technique. The paper presents electrical and optical waveguide process problems in corn-shaped optical head of NFOD. It also put forward to the three grades approximate model of ultra-small-size laser firstly and simulate calculations in first-grade approximation of corn-shaped optical head of NFOD. The result give the relation between laser's input current and output power and the near field output light intensity pattern, and it is an important basis for the NFOD optical head design with ultra thin active layer and ultra small spot laser.

In optical design verification and interferometric lens testing, wavefront aberrations are expanded in orthogonal Zernike circle polynomials. Due to the continuity of these polynomials, they are less suitable for expanding discontinuous wavefronts. Examples of lenses that contain phase discontinuities are DVD objective lenses that are CD compatible. One of such compatibility solutions is a lens comprising a central pupil zone with one or more concentric annular pupil zones, separated by phase or intensity discontinuities. We have derived an expression that relates the Strehl intensity of the diffraction focus of such discontinuous pupil to the coefficients of the Zernike circle polynomial expansion in the central pupil zone and the Zernike annular polynomial expansion in the concentric annular pupil zones. Furthermore, we have developed a formalism to optimize the Strehl intensity by subtracting piston, tilt and defocus from the wavefront by correcting the coefficients of the Zernike circle and annular polynomials. Numerical calculations have shown that the approximation for the Strehl intensity of discontinuous wavefronts results in deviations from the actual intensity at the diffraction focus, that are comparable to the classical approximation for continuous wavefronts.

The method to measure the apparent reflectivity with gloss meter is applied to the phase-change optical disks before and after initialization process. The apparent reflectivity measurements for relative large area and the reflectivity measured by optical pick-up are compared. The apparent reflectivity measurements are proven to enough for the characterization of recording layer. The measurement with gloss meter has several advantages of speed, simple structure, low price and etc.

Characterization methods of AgInSbTe based phase change optical disc are developed. Reflectivity change of as deposited multilayer structure with changing thickness is measured. The active layer thickness influence on reflectivity is compared with calculated results. We show that Rutherford Back Scattering (RBS) spectroscopy can be used to analyze the composition of the active layer. The X-ray diffraction pattern of CD-RW discs is presented, for both as deposited and initialized case. The TEM image reveals the particular crystal growth mechanism of AgInSbTe quaternary system. Written discs write power window is shown at 2X and 4X write speed.

Several commercial CD-R and CD-RW optical recording disks are exposed to intense white light sources (Halogen Tungsten and High-Intensity Discharge) at different exposure times under three minutes. Main analog playback parameters for CD-R and CD-RW optical recording disks are identified and characterized. The contents of a test disk is recorded onto each CD-R and CD-RW disk using a commercial rewritable/recordable disk drive. For each disk, written marks are imaged under a Nomarsky/Bright field optical microscope before and after exposure. Using a dynamic tester carrier-to- noise ratio and timing jitter are determined before and after exposure. AZO-dye CD-R disks, cyanine-dye CD-R disks, and CD- RW disks show considerable reduction in written mark contrast after exposure. Pthalocyanine-dye CD-R disks do not show significant changes in the mark contrast after exposure. Dynamic tester results confirm the mark contrast results and give insight into playback behavior of exposed disks.

Optical technology for data storage offers media removability with unsurpassed reliability. As the media are removable, data interchange between the media and drives from different sources is a major concern. The optical recording community realized, at the inception of this new storage technology development, that international standards for all optical recording disk/cartridge must be established to insure the healthy growth of this industry and for the benefit of the users. Many standards organizations took up the challenge and numerous international standards were established which are now being used world-wide. This paper provides a brief summary of the current status of the international optical disk standards.

This paper presents techniques developed at the Information Technology Laboratory of the U.S. National Institute of Standards and Technology (NIST/ITL) for enabling microscopic image analysis of optical data storage media such as optical disks. These non-destructive techniques allow investigators to easily locate on the media a pre-existing series of media defects. These techniques can be applied to any type of optical disks including CDs and DVDs. The paper describes the experimental setup and the techniques utilized to achieve localization and registration of media defects. These techniques include data acquisition, computer control, auto focus, image processing, and remote control and observation. An extension of this setup utilizing available graphical programming environments can allow investigators at different locations to share and discuss the information on media defects by use of the Internet.

A method for rapid characterization of DVD multilayer depositions is presented. With a single optical measurement the devised method allows to determine the values of the refractive index (n) and of the extinction coefficient (k) for the wavelength comprised between 400 and 900 nm, and the film thickness. The analysis of these optical and physical properties provides a mean for tracking back possible process deviations in the multilayer sputtering of the DVD-RAM disks.

Literally hundreds of parameters have been specified for measuring Compact Disc (CD) and Digital Video Disc (DVD) characteristics but virtually none for drive performance. For the hundreds of optical disc characteristics, there are many differing methods for measuring each one. After having chosen the 'best' methods for measuring the disc characteristics and conducting the measurements, conformance to the industry specifications (de-facto standards) must be judged. The practical relevance of the relationships between disc parameters, measurement methods, and drive performance must be understood and managed such that the value experienced by the customer is preserved.

A brief history of the evolution of the compact disc is presented. The central focus is on the development role played by the Red Book and its offspring, the Yellow Book and the Orange Book. Following the development of the disc itself came longevity claims made by manufacturers and counter claims in commercial literature. Finally, the construction of technically and statistically sound media testing methodology is traced from the early works of individuals to the refined standards representing the combined input from manufacturers, archivists and industry experts. A suggestion for further independent testing is also made.

Communication to application developers and data users of CD-R characteristics such as data integrity, media reliability and life expectancy should be considered as engineers create optical storage media that can store more data. Though the point of view of this paper is primarily based on the views of a few experienced CD-R end-users, optical engineers should consider implementation of the following design recommendations explained in this paper. The author's extensive experience in using CD-R technology and their substantial interaction with other CD-R users provides a rare perspective on CD-R characteristic information. Although this paper is directed to optical engineers, it is written with the expectation that a broader readership will also benefit from the information presented. The paper presents to the engineering community potential methods of communicating CD-R characteristics with an emphasis on the types of information that would be useful to CD-R users.

In DOW type of phase change optical memories the focus has been mainly on gestate based systems due to their good overwriting capability and very high order cyclability. To avoid the material deterioration problems such as material flow, high melting point, high viscosity or high-density components such as CrTe, (which have the same refractive index) can be added to the active layer. This has led to an improved performance of overwrite cycles from 10⁵ to 10⁶. Material flow occurs due to void formation. Voids and sinks are formed due to porosity of the active layer because the active layer has a density lower than that of the bulk material. One of the reasons for the formation and coalescence of voids is the way in which the film is deposited viz. Sputtering which makes Ar atoms accumulate in the films during deposition. Also the mechanical strength of the protective layer effects the repeatability of the active layer. All the above mentioned processes occur during melting and re- solidification of the nano-sized spots which are laser irradiated. Since the structure of the protective layers is very important in controlling the void formation, it is very important to study the thermal modeling of the full layer structure.

The optical parameters of GeTe and Ge₂Sb₂Te₅ semiconductor films by thermal treatment have been measured carefully by using a new method. A compared study by means of using a spectrum ellipsometer is presented. The optical parameters of the sample films are precisely obtained through the processes of data simulation and correction of the old calculation model. In the meantime, the data calculations of the same samples measured by a spectrum ellipsometer are given, and the complex refractive index curves of them in the spectrum range from 250 nm to 830 nm are obtained.

The conventional inspection methods for the write-once optical disk are consist of visual method with non-destructive and recording/playback of the sampled disks with destructive. So the quality can not be assured when arrived at the customer due to lack of quality inspection. We find the new method consist of recording/playback for each disk manufactured. The recording/playback is performed at the edge area of the disk where tracks are extended. This area is not conflict with the standard and the disk can be used as a virgin disk at the customer. From the experiment, we find that the ratio of bad disks can be reduced to 0.5% from 7% with proposed method.