Abstract: The composite optical grating for optical disk data storage systems uses a first optical grating to generate three light beams disposed approximately on a straight line. A second optical grating in the composite optical grating is juxtaposed with the first optical grating and divides the three light beams into two images, each consisting of a three spot array. The first of these images is focused on a first data storage track while the second image of three spots is focused on a second adjacent data storage track. The three spot array formed on the first track is used in conventional fashion to read data from this data storage track. The center spot is used to read the data from the data storage track while the two outer linearly oriented spots are used for tracking purposes. The second image formed by the second optical grating is focused on a second adjacent data storage track and only the center spot of the three spot array is used to read data from the second data storage track.

Abstract: Many of the data read errors encountered in an optical disk system are due to reading off track. These errors are the result of bit shift, which is the shifting of the data transition relative to the center of the detection timing window. This bit shift is the result of the rounded edges of the data marks on the recording medium. A normal data signal is read off the recording medium while the read apparatus is centeed on the data storage track of the recording medium. If the read beam of the read apparatus moves off track radially to either side of the center of the data storage track, the detected data transitions move toward each other due to the rounded edges of the recorded data on the data storage track. This makes the data mark appear shorter and results in bit shift and increased error rate. The off-track bit shift compensation apparatus compensates for this misalignment and the resultant bit shift by dynamically adjusting the analog detection threshold of the read apparatus.

Abstract: A method and apparatus for measuring the absolute thickness of dust defocus layers upon spinning optical disks utilizes a collimated, expanded beam of light from a helium-neon laser which is focused into a converging beam and directed towards the layer at a predetermined angle of incidence defined by an angular spread centered about the angle of incidence. A pair of divergent beams reflecting from the upper and lower surfaces of the layer are received by a collecting mirror and are recollimated by a collimating lens to be incident upon a self-scanning photodiode array. The divergent beams form a monotonic interference pattern having a fringe density which is proportional to the distance between the upper and lower surfaces, and which is determined by the photodiode array.

Abstract: Apparatus and methods are disclosed for writing data on a track in an optical disk data storage device wherein the track is divided into two parts and binary one bits are written into one part of the data track while binary zero bits are written into the second part of the data track. Detection of data written in this manner is performed using two read coherent radiation beams each positioned over one of the parts of the data track. A binary one is detected if the signal from the beam over the first part of the data track is greater than the signal from the beam over the second part of the data track, and a binary zero is indicated if the signal from the beam over the second part of the data track is greater than the signal of the beam over the first part of the data track. In order to detect the data from the two read beams, they must be aligned accurately over the two halves of the data track. To aid this alignment, a third larger beam is used to measure the total energy from the data track.

Abstract: An optical disk servo system includes a coarse access and tracking system for optical head control and a fine access and tracking system for read/write beam control. Enlarged servo tracks are pre-recorded on the optical disk between bands of data track locations. The coarse system illuminates a relatively large area of the disk surface encompassing at least one of the servo tracks and detects light from the enlarged illuminated area. Suitable means including a photo-detector array identifies and controls the optical head position by means of the light returned from the illuminated servo track. Such photo-detection means are insensitive to light reflected from the data tracks. The fine access and tracking system uses a conventional, three spot tracking and read system, two spots for data track following and one spot for data track reading. The fine access and tracking system controls a galvanometer mirror or other suitable means steering the read spot beams.

Abstract: An optical disk drive system with which data may be permanently and correctly stored on removable media. The system includes a drive into which the media, a disk housed in a cartridge, may be removably inserted. The drive interfaces with a host CPU through a storage control unit, which storage control unit may also have other peripheral devices, such as magnetic disk drives, coupled therethrough to the host CPU. A special data format is used for data stored on the disk in order to provide efficient use of and access to the available storage space. The disk is divided into data bands, each data band having a prescribed number of concentric data tracks therein. Each data track is divided into equal length sectors. The data is organized into data blocks, each block being made up of a selected sequence of prescribed data sections. Many of the data sections commence with synchronization bits followed by the data to be stored. The data of each data section is adapted to fit within each data sector on the disk.

Abstract: An optical disk storage unit has an access and tracking system with a microprocessor which stores a runout signal representing the eccentricity of the tracks and bands as a function of the rotation of the disk surface. The runout signal is summed with the output of the access and tracking system to compensate for eccentricity as the disk rotates.

Abstract: An optical system for writing and reading data from a rotating optical storage disk, comprising a first, second and third coherent light source, providing coarse seek, reading, and writing functions, the three writing sources sharing a plurality of optical elements in common, all cooperating to provide for the coarse seek, fine seek, focus and tracking functions of the device. The read and the write optical beams are optically coupled together to ensure proper spacing of a newly written track with regard to the previously written track.

Abstract: A system for aligning data with corresponding sector marks in an optical disk storage system. In an optical disk storage system, data is written into a number of concentric bands, each of which contains a servo track and a number of data tracks. Each band is divided circumferentially into a series of sectors which are defined by marks in the servo track. The beginning of a sector is detected by identifying one of the marks in the servo track, and the beginning of a data record must coincide with the beginning of a sector. Recorded during the manufacture of the storage disk of the present invention, are pairs of special tracks wherein the first sector mark on a track is identified by an index mark, and the adjacent data track has a beginning of data mark recorded at a fixed location relative to the index mark. The disk read/write head is moved over one of these pairs and the difference in time between the occurrence of the index and occurrence of the beginning of data mark is measured.

Abstract: A general purpose register including two input ports and two output ports, each port being addressed by an independent addressing circuit. The general purpose register includes a number of internal registers, and the provision of four independent addresses enables data to be written into two internal registers while data is being read out of two internal registers. The general purpose register also includes circuitry for transferring data from the input ports directly to the output ports without entering the data into the internal registers. Interchanging of bytes of data input words is also accomplished by the general purpose register. The internal registers, the four independent addressing circuits, the data transferring circuitry and additional undedicated circuitry are integrated into a single chip.

Abstract: A self contained, replaceable diode laser module for providing a fully collimated, de-astigmatized, and circular cross-sectioned beam. In the preferred embodiment a first compound spherical lens partially collimates the beam. An in-line combined cross-section modifier system then de-astigmatizes and modifies the cross-section of the beam. The beam modifier system is comprised of first and second triangular prisms oriented at non-normal angles to the path of the beam. This allows both the cross-section and the astigmatism of the beam to be corrected. A planar mirror between the first and second prisms directs the beam from the first prism to the second prism, so that the beam can exit the second prism co-axial with the incident beam path. The beam then enters the second collimating subsystem.

Abstract: Apparatus and methods are disclosed for writing data on a track in an optical disk data storage device wherein the track is divided into two parts and binary one bits are written into one part of the data track while binary zero bits are written into the second part of the data track. Detection of data written in this manner is performed using two read coherent radiation beams each positioned over one of the parts of the data track. A binary one is detected if the signal from the beam over the first part of the data track is greater than the signal from the beam over the second part of the data track, and a binary zero is indicated if the signal from the beam over the second part of the data track is greater than the signal of the beam over the first part of the data track. In order to detect the data from the two read beams, they must be aligned accurately over the two halves of the data track. To aid this alignment, a third larger beam is used to measure the total energy from the data track.

Abstract: Disclosed is a data detection system and method for accurately detecting data transition marks recorded on a recording surface. A data transition pulse, generated by a data head as recorded data transition marks pass thereby, is presented to consecutive delay circuits in order to generate first and second delay pulses. The second delay pulse and the data transition pulse are subtracted from the first delay pulse, thereby creating a narrow output pulse that indicates the occurrence of a data transition. This narrow output pulse is used to toggle a flip-flop or equivalent logic circuit, the flip-flop output thereby representing a recreation of the data as recorded on the recording surface. The system is best suited for use with an optical storage system wherein data transitions are recorded on an optical disk as spots of substantially uniform size, although the detection system does not require that the spots be uniform size.

Abstract: A subaperture optical system for preventing interference between light inadvertently reflected from the protective overcoat of an optical recording disk from disruptively interfering with light reflected from the active layer of the optical recording disk, thereby causing coarse servo tracking errors as the coarse servo actuator carriage translates over the coarse servo tracks on the disk service. The optical system is comprised of a laser light source, a collimating lens system, an astigmatizing lens system, a subaperture mirror, a carriage actuator, a beam relaying telescope, an objective lens, an objective lens focus actuator, a reflected coarse servo beam focusing lens, and a coarse servo detector. The laser issues a beam which follows a first subaperture path that is parallel to, but off center from, the optical axis of an objective lens of the optical system. The beam is formed into a line focused spot which is focused on the disk surface at a non normal angle.

Abstract: Apparatus and methods are disclosed for acquiring and maintaining focus of a coherent light source used to read and write data in an optical disk data storage device. The system uses a conventional astigmatic focus system in conjunction with a signal processor to detect proximity of focus. After proximity of focus is detected, the signal processor enables a fine focus servo system to maintain focus of the coherent light on the disk surface.

Abstract: A combined collimating, cross-section correcting and de-astigmatizing lens system for providing laser beams which, are fully collimated, de-astigmatized, and have a circular cross-section of the proper diameter. In the preferred embodiment a first compound spherical lens system partially collimates the beam so that the in-line combined cross-section corrector/de-astigmatizer system can properly de-astigmatize the beam. The beam cross-section corrector/de-astigmatizer is comprised of first and second triangular prisms oriented at non-normal angles to the path of the beam. This allows both the cross-section and the astigmatism of the beam to be corrected. A planar mirror between the first and second prisms directs the beam from the first prism to the second prism, so that the beam can exit the second prism co-axial with the incident beam path.

Abstract: In extended for a digital information storage device comprised of a host having the capability of placing Key identifiers in the header of user data blocks to be recorded, a recording device having a random access memory said memory having an Index register, a plurality of Pointer Table registers, a Target register, a Key Start register, a Key Length register and a Pointer Table Select register, and a micro-processor able to perform an indirect binary search between a selected Pointer Table the contents of the Pointer Table being the address from the Index (the address being the band location, and the register contents of the Index being the Identifier Keys selected by the host, said Keys being the lowest Key entry on any given band).

Abstract: A generic key, for allowing a data use to efficiently search a set of user data recorded in blocks in an efficient method using a multiplicity of user keys. As user data blocks are built up for recording, the unique identifiers are placed in the header of the data block, recorded on the disk surface with the contents stored on the device and the platter index. The user can then sort and search the index based upon which of the multiplicity of user keys he selects.

Abstract: A self-checking shared encoder/decoder circuit for use with a Reed-Solomon coding scheme of an optical disk storage system. The optical disk system includes a drive adapted to permanently store data on a removable platter. Prior to recording a data byte on the platter, the data is encoded with a Reed-Solomon code. When the data is read from the disk, it is decoded and error correction syndromes are generated. A plurality of syndrome buffer registers are provided in order to allow several of the error correction functions to be carried out in parallel. Syndromes that are detected to comprise all zeros are used to simplify the error correction processes beyond the normal processes used. The same circuitry is shared for performing the encoding and decoding functions. This circuitry includes independent sets of a RAM, coupled to one input of an exclusive OR (modulo two sum) adding circuit. The output of the adding circuit is fed back to an input of the RAM.

Abstract: An optical disk storage unit has an improved access and tracking system in which a low speed velocity signal is derived from a differentiated position error signal. The output of the differentiator is applied to a blanking circuit which disconnects the steep slope portion of the position error signal from a sample and hold circuit. A medium speed velocity signal is derived from the integral of motor current and a high speed velocity signal is derived by digitally counting the band crossings in the position error signal.