David Y. Lou

Bit oriented optical storage with thin tellurium films

We discuss here some of the basic issues involved in the development of an optical storage medium based on the laser micromachining of thin tellurium films. Results are presented in the areas of recording sensitivity, materials resolution, error statistics, and archival stability. It is shown that a medium using 20–30 nm of tellurium deposited on polymethyl methacrylate substrates is an extremely attractive choice.

Characterization of optical disks

One key element of an optical storage system is the recording medium. An important part of the successful development of media technology are the various techniques for characterization of the media. In this paper, several techniques are described with spatial resolutions ranging from millimeters to microns. It is shown that useful information concerning the performance of the media can be derived without actual recording and playback. These techniques are obviously of extreme importance when the recording technology is based on a nonerasable write-once read-only type of media.

Surface profile measurement with a dual-beam optical system

A system for the noncontact measurement of surface profiles is reported. Instead of measuring the absolute displacement profile, we measure its derivative, the velocity profile. This is done by measuring the difference in the focus errors between two laser spots. Data processing is then used to recover the displacement information. The system has demonstrated sensitivities of the order of nanometers on soft plastic surfaces. It also permits the real-time measurement of surface profiles in dynamic conditions. Thus it has special applicability to magnetic and optical disks. Results of measurements on several substrates are described.

Digital Optical Recorders At 5 Mbit/S Data Rate

Five optical disk recorder/readers were developed, each having an on-line user storage capacity of 101° user bits per disk side. The advantages of optical recording, as compared to magnetic-tape recording, are improved archival life, low cost media, and rapid random access capabilities. Recording at a 5 Mbit/s user data rate is done by laser machining of micron-sized holes in a thin tellurium alloy film allowing direct-read-after-write recording of information. Coding and error correction reduce the user error rate to 10-1°. The recorders have been interfaced to DEC PDP-11 minicomputers and for test purposes to a SEL 32/77 computer.

Defect measurements in digital optical disks

A method of characterizing defects on an unrecorded optical disk is described. Information on the density of defects is obtained by analyzing the statistical distribution of the widths of the pulses obtained when playing back an unrecorded disk. It was shown that disk quality, as measured by bit error rates on actual recording, can be correlated with defect densities measured in this manner. The same method can also be used to characterize defects on uncoated substrates. It was demonstrated that defects on tellurium coated disks are largely the result of defects on the uncoated substrates.

An Optical Disc Data Recorder

We discuss the development of an optical disc recorder with an on-line storage capacity of 1010 bits. Recording is done by laser machining of micro-sized pits in a thin tellurium film allowing direct-read-after-writing (DRAW) of the information. The recording format maps each bit of information to a recorded pit. The tellurium is deposited on a clear plastic disc configured to be self-protecting and easily handled. A major program objective was to demonstrate the feasibility of an inexpensive recorder and disc.

Characterization Of Optical Disks

One of the key elements of an optical storage system is the recording medium. An important part to the successful development of media technology are the various techniques for characterization of the media. In this paper, several of the techniques are described. It is shown that useful information concerning the performance of the media can be derived without actual recording and playback. These techniques are obviously important when the recording technology is based on a non-erasable, write-once, read-only type of media.

A prototype optical disk recorder

(3) small excitation current requiring a small heat sink, (4) transverse mode stability, (5 ) low noise level, and (6) easy adjustment and maintenance. These requirements can be met quite satisfactorily in buried-heterostructure (BH) diode lasers.’ They have the lowest-order transverse (TE,,) mode, which can be focused to a spotsize of diameter less than 2 pm on the disk. Moreover, this mode is quite stable against he changes of the operating current. Since the operating currents are quite low in these lasers (10 mA) and their thermal characteristics are very good, very small heat sinks are sufficient to obtain continuous operation at room temperature. The noise level can be lowered if the BH lasers are operated well above threshold ( I > 1.2 It,,), a condition which is compatible with the requirement of high laser output power (> 0.6 mW). Good quality NTSC color pictures have been sucessfully obtained from reflective video disks using BH laser optical pickups.’ The semiconductor laser can be used as detectors as well as light sources. The SCOOP (Self-coupled Optical Pickup) method to detect the reflected light from the disk by the laser itself has been p r ~ p o s e d . ~ The laser beam reflected from the mirror has been shown to reduce the light output and to increase the terminal voltage of the diode.