MultiLevel encoding has been demonstrated to significantly increase the linear densities achieved with standard methods of binary encoding in optical data storage systems. An overview of the channel is provided from write encoder and pre-compensation, to readout with a matched adaptive equalizer and Viterbi decoder. Our multilevel channel has been implemented in silicon and designed to operate in parallel with the standard binary channel, thus maintaining full backward functionality of the underlying drive. We have developed an efficient research, development, prototyping, and integration process that allows us to accomplish final system implementation with minimal impact to the host system. We discuss our "helper" servo and firmware functions that ease integration of the multilevel LSI into existing circuit-board architecture, firmware, and software bases. The focus of this paper is on our fully-functional 2GB enhanced CD-R/RW external drive, but we also discuss briefly how multilevel technology has been shown to add to ROM, DVD, and advanced blue-laser, high-NA optic systems.
KEYWORDS: Reflectivity, Optical discs, Modulation, Data storage, Laser marking, Computer programming, Digital video recorders, Analog electronics, Optical storage, Laser optics
MultiLevel recording for high-density, blue-laser systems has achieved approximately 5 X 10-5 BER before ECC using growth-dominant phase-change materials on a 0.6mm cover-layer, 405nm-wavelength, 0.65-NA system.
KEYWORDS: Modulation, Modulation transfer functions, Compact discs, Digital video discs, Head, Reflectivity, Convolution, Optical discs, Photoresist materials, Signal to noise ratio
The technique of pit-depth modulation is applied to optical data storage. Pits of M possible depths are written end-to- end to form a groove encoding log2(M) bits in each mark. Data was encoded onto discs with CD dimensions using standard photoresist mastering and replication methods. Methods for removing inter-symbol interference are demonstrated on pits as short as 0.6 micrometers . A 6-level pattern of 0.6 micrometers pits was read by an optical head from a 6X CD-ROM drive and the original levels were recovered with a standard deviation of approximately 6% of the dynamic range. A system prototype read data encoded as 4-level 0.8 micrometers pits with a raw bit error rate of 3 X 10-4.
Optical laser-feedback microscopy (LFM), a scanning confocal interference microscopy, furnishes nanometer axial and 200 nm lateral resolution of surface topology when examining well-defined reflective hard surfaces such as semiconductors, metals, or other materials. Biological samples (e.g., cells or tissues under physiological conditions) are important objects for examination by LFM as the improved resolution available with this new method of optical microscopy can furnish biological structural information on a scale previously only attainable with electron microscopy but without the necessity for sample fixation or staining or the effect of ionization-produced radiation damage. Although the small refractive-index changes that occur at biological-membrane/water interfaces produce sufficient signal to be useful in LFM- imaging, being able to obtain `optical-sectioning' at a scale of nanometers and derive 3D information at that resolution would allow intracellular biological structures (e.g., organelles, chromosomes) and their functional changes to be determined on physiological-viable samples. By incorporating information from two simultaneously-acquired LFM images (optical phase and amplitude reflectivity), information has been obtained on a variety of biological cells; two examples will be presented, images of a green algae (Chlamydomonas reinhardtii) and of a human erythrocyte.
In mammalian hearing, the frequency-dependent spatial pattern of movement in the basilar membrane (BM) forms the basis of frequency discrimination (tuning). This is not necessarily the case in lower vertebrates; the turtle, for example, has an electrical resonance mechanism in its auditory receptor cells that varies in best frequency from cell-to-cell along the underlying BM. But how much, if any, of the frequency separation by this reptile is done mechanically by its BM? In other animals, vibrational analyses were indirect in that they required the placement of nonphysiological objects on the BM (e.g., the radioactive source of the Mossbaurer technique or the mirror of traditional laser interferometry). Our attempt to find an alternative approach led to the rediscovery of laser-feedback interferometry (LFI), here applied for the first time to vibration analysis in a biological system. LFI is an ideal method to directly measure the nanometer motion (amplitude and phase) of diffuse scattering surfaces such as the BM because of its simple geometry, ease of alignment, and its ability to respond to surfaces with a broad range of reflectances (10-6 to 1). Preliminary LFI investigations of BM motion in the turtle reveal that its BM is broadly tuned and mainly reflects middle ear filter characteristics. No evidence for frequency-selective spatial BM mechanical tuning was found.
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