JPS6235170B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Various schemes have been developed for recording signals at video frequencies on disk tape or other media. These systems have utilized optical recording on photosensitive media, electron beam recording on thermoplastic surfaces, and other systems that provide reproducible recording of debio information, among others.

Conventional technologies include a method using a photographic surface, a method using an electron beam sensing surface, a magnetic recording method,
and in which a beam of radiant energy similar to that in the present invention causes irreversible changes to the surface, thereby "writing" information thereto.

The photographic system was developed by US Patent No. 1, owned by BC Goldmark et al.
No. 3,234,326, or US Pat. No. 3,361,873, owned by D. R. Johnson, which teaches the photographic recording of video information on a rotating disk in a helical path.

U.S. Pat. No. 3,283,310, owned by D.C. Hughes et al., describes the recording of information on a thermoplastic film surface, which can be used with an electron beam writing device such as that disclosed in U.S. Pat. No. 3,120,991. is used.

Note that other systems have also used electron beams to record information on special storage media. One such method is T.B.
No. 3,350,503 owned by Gregg. Another proposal using an electron beam onto a photosensitive medium such as photographic film has been proposed by R.F.
As taught in U.S. Pat. No. 3,444,317 owned by Teyutube et al.

In recent years, other methods for high-density recording have been disclosed, based on removal of material by laser beam bombardment or deposition of material.

These methods are discussed in detail in Electronics, March 8, 1969, page 110. Additionally, the "Laser Thermal Micro Image Recorder" was described in some detail by C.O. Carlson and H.D. Ipes at the 1968 WESCON meeting (Western Electronic Show and
This paper was published in WESCON Technical Papers, Volume 12, 1968, Section 16/1, Page 1. This author was published in Science, Volume 54, No. 3756, December 23, 1966, No. 1550-1551.
Page, 1966 Fall Joining Computer Conference.
Proceedings of the Conference, pp. 711-716, and 3/1968.
Monthly “Bell Systems Technical Journal” issue
It also refers to a paper on page 385,405.

These publications disclose recording techniques that utilize very thin metal films on a substrate. This thin metal film is heated and melts rapidly, creating small spherules within the recorded spot. A highly concentrated spot of laser light can impart enough heat in a short enough time that a suitably modulated laser beam impinging on a moving surface produces a pattern of holes in the metal surface. The recorded information can be played back when "reading back".

As pointed out in the Carlson and Ipes article cited above, the size of the recorded spot or hole can be much smaller than the diameter of the imaging laser beam. By appropriate selection of metal film material, film thickness, laser divergence and spot power, a suitable scheme for recording video frequencies at high resolution can be designed.

In accordance with the present invention, the Carlson and Ipes laser thermal microimage recording system is used in conjunction with prior art disk recording to provide a new and useful arrangement and method for recording video information.

The present invention relates to an apparatus for processing information on a video disc.

The arrangement of the present invention includes a spindle that rotates the disk in a precise circle, and a lead screw that translates the head at a very constant rate along the radius of the rotating disk.

The apparatus of the invention also includes a first light source that provides a light beam of sufficient intensity to interact with the coating of the record carrier as it rotates uniformly. The first optical device includes an objective lens for defining the optical path between the first light source and the coating of the record and focusing the light beam onto the coating. The apparatus of the invention further includes a second light source and a second optical device between the light source and the record carrier for focusing the reading beam onto the photoresponsive coating. The second optical device shares an objective lens with the first optical device.

As can be seen, it is desirable to synchronize or otherwise cooperate the drive of the disk with the translational drive to create a helical trajectory of predetermined bits. In a preferred embodiment, the spacing between adjacent turns of the helix is 2 μm from center to center.

If the diameter of the spot is 1 .mu.m, there is a guard region of 1 .mu.m between the spots of adjacent tracks.

Whatever pattern is used, both the writing beam from the first light source and the reading beam from the second light source are applied to the record carrier by moving a carriage carrying the first optical means and the second optical means. is moved radially with respect to.

The first optical means includes a first optical lens, a first light beam directing means, and an objective lens. A second optical means is provided between the second optical lens, the second light beam directing device, the first light beam, and the objective lens. and a third light beam directing device disposed.

The "write head" in the preferred embodiment is a microscope objective suspended at a constant height above the disk on an air bearing. This constant height is necessary because the depth of focus of the objective lens is shallow. The objective lens of the 40X dry microscope focuses the energy of the laser beam on the disk surface,
It has been found that the method is satisfactory in that it enables writing on m spots.

The write beam portion is sensed by a novel Pockels cell stabilization circuit that helps maintain the average power of the level modulated beam for a given level.

An argon ion laser is used as the writing beam. A Pockels cell and Glan prism combination modulates the laser beam with video information. In accordance with the invention, a "read-after-write" capability is provided to monitor write operations. A second, helium-neon (He-Ne) "readout" laser is provided, which directs a lower power beam into the write beam path, but which is slightly smaller than the write beam as it enters the write head. It's facing at a certain angle. This angle is chosen so that the read beam illuminates an area on the written track that is approximately 2 μm below the write spot.

The read beam is reflected from the disk surface back through the write head and passes through a dichroic mirror that has inserted the read beam into the write path.
retrace its optical path to the mirror).

The read beam is then directed to a beam splinter and further through a bandpass filter that blocks any write beams that follow the same path. The readout beam then impinges on a photodetector to generate a video information signal. The characteristics of this signal are displayed on an oscilloscope or television monitor to indicate peak "record" power, average record power, and whether focus is accurate.

"Read then write" information can also be utilized in an error checking scheme, especially when digital type information is being written. The input video information is delayed by a time equal to the time difference between the write and read spots. The returned information is then compared for "identity" with the delayed input information. If there are too many discrepancies, recheck and realign the device or eliminate the disk.

The configuration of the invention includes a precision lathe that rotates the disk in a perfect circle and translates the recording "head" at a constant speed along the radius of the rotating disk. As is clear, in order to be able to create a helical track of a given pitch,
It is required that the two drives be synchronized or otherwise cooperate. If desired, concentric circles can also be created by alternating translation and writing.

In a preferred embodiment using a spiral, the spacing between adjacent spiral turns is 2 μm center to center. If the diameter of the spot is 1 μm, there is a distance of 1 μm between the spots on adjacent tracks.
There is a guard region of μm.

The novel features believed to be characteristic of the invention, together with further objects and advantages thereof, both as to mechanism and method of operation, are set forth in the accompanying drawings in which a preferred embodiment of the invention is shown by way of example. will be better understood by considering the following description. However, it is specifically to be understood that the drawings are for purposes of illustration and description only and are not intended to limit the scope of the invention.

Referring first to FIG. 1, the writing device includes a writing head 12, which in this embodiment is a dry microscope objective 14 mounted on an air bearing support member 16. A 40X lens has been found to be satisfactory. A disk 18 is specifically provided, which can be constructed according to the teachings of the prior art;
The substrate is coated with a very thin film of metal with a reasonably low melting point and high surface tension.

A crystal oscillator 20 controls the driving elements. The disk 18 is rotated by a first rotary drive element 22, which is connected to a spindle 24.

A second translational drive element 26 controls the position of write head 12.

A translation carriage 28, which is driven by a translation drive element 26 through a lead screw and a transfer nut, moves the write head 12 to the rotating disk 18.
move in its radial direction. Shuttle 28
is equipped with suitable mirrors and lenses so that the remainder of the optical and electronic systems necessary for the writing device are permanently mounted.

In this embodiment of the invention, the beam of a polarization splitting laser 30, which is an argon ion laser, passes through a Pockels cell 32, which is driven by a Pockels cell driver 34. FM modulator 36 receives the video signal to be recorded and provides appropriate control signals to Pockels cell driver 34. As is well known, the Pockels cell 32 responds to an applied signal voltage by rotating the plane of polarization of the light beam. Since a linear polarizer transmits light only in a given plane of polarization, a polarizer, such as a Glan prism 38 in the embodiment, is placed in the writing beam path to provide a modulated writing beam 40.

Pockels Cell 32 and Grand Prism 38
A modulated writing beam 40 emerging from a combination of
is applied to the first mirror 42 which directs the writing beam 40 onto the translation carriage 28 . This first
mirror 42 transmits a portion of the writing beam 40 to a Pockels cell stabilization circuit 44 that maintains the energy level of the beam in response to the average intensity of the writing beam.

A lens 46 is inserted into the path of the writing beam 40 to diverge a substantially parallel beam that fills and diverges the entrance aperture of the objective lens 14 to provide optimal resolution. A dichroic mirror 48 is placed in a passageway oriented to transmit substantially all of the writing beam 40 to a second arthroscope 50 . Mirrors such as those shown in the prior Eliot patent applications may also be used in this invention. This arthroscope 50
can then direct the beam through lens 14 to change the point of impact of beam 40 on the surface of disk 18.

The objective lens 14 and its associated air bearing 16 effectively float above a cushion of air at a substantially constant distance from the surface of the disk 18. This distance depends on the geometry of the bearing 16,
It is determined by the linear velocity of the disk 18 and the force used to load the head against the disk 18. This certain amount of space is required because the focal tolerance of a lens capable of resolving a 1 .mu.m spot is also on the order of 1 .mu.m.

A second relatively low power laser 52 is connected to the monitor and
A beam 54 is provided. In an embodiment, readout laser 52 is a hetium neon device in which readout beam 54 can be wavelength-excluded from the write beam. Polarization beam splitting cube 56
transmits the readout beam 54 to a mirror 58 which directs the beam 54 through a second diverging lens 60;
This lens spreads the readout beam 54 to fill the entrance aperture of the objective lens 14.

A quarter wave plate 62 is placed in the optical path in association with the plane polarizing beam splitter 56 and
This prevents light reflected from 8 from entering laser 52 again and disrupting its oscillation mode. The quarter-wave plate 62 changes the polarization plane of the beam.
It rotates by 45 degrees each time it passes, so that the reflected beam is rotated 90 degrees relative to the polarizing beam splitter 56 and therefore does not pass through it.

A second mirror 64 in the read beam 54 path directs the beam into a dichroic mirror 48 so that the read beam "spot" is downstream from the write beam spot, as explained in more detail below. Limited adjustments can be made so that the paths of the write and read beams are substantially identical, except that they impinge on the disk 18 at .

A filter 66 opaque to the argon ion beam is inserted into the path of the light reflected from beam splitter 56 . returned from the disk surface
The He.Ne readout beam 54 may pass through a filter 66 and a lens 68 onto a photodetector 70.

The output of photodetector 70 is applied to a preamplifier 72 which provides a signal with sufficient amplitude and signal strength for subsequent use. A video discriminator 74 then provides a video output signal, which can be utilized in a variety of ways, two of which are shown by way of example only.

In a first application, video output is applied to a television monitor 76 and an oscilloscope 78. A television monitor 76 shows the video fidelity of the recording, and an oscilloscope 78 shows the signal-to-noise ratio of the recording and the cutting quality, light or heavy. Although not shown, “hole” or “black”
and the “no hole”, or “white” area,
Appropriate feedback loops may be provided to ensure sufficient discrimination on the disk.

As an alternative use, the video output of discriminator 74 is applied to comparator 80. The other input of comparator 80 is taken from the video input signal, which is directed through delay line 81. The accumulated delay of the writing scheme and the delay equal to the time elapsed between the moment of writing the information and the time required for the incremental area of the disk to reach the reading point must be imparted to the input video signal. It won't happen.

Ideally, the video output signal of discriminator 74 would be:
It should be identical in all respects to the video input signal after an appropriate delay. The noticeable differences represent errors caused by defects in the surface of the disk or by adverse effects of the write circuit.

This application is important when writing digital information, but less critical when other information is recorded.

The output of comparator circuit 80 can be quantified and counted so that an acceptable number of errors can be established for any disk. When the counted error exceeds the standard, the write operation can be terminated. If necessary, a new disk can be written. Disks with excess errors can then be reprocessed and serve as "new" disks for subsequent recordings.

Write head assembly 12 rotates disk 18
In contrast, known techniques can be used to translate in the radial direction. Although the rotational and translational drives 20, 22 are shown independently in FIG. 1, they are connected to a common crystal oscillator 20.
can be synchronized to translate write assembly 12 by a predetermined increment for each rotation of disk 18.

Turning now to FIG. 2, the slightly different optical paths of beam 40 from write laser 30 and beam 54 from read laser 52 are shown in somewhat exaggerated form. The writing beam 40 coincides with the optical axis of the microscope objective 14. The read beam 54, in contrast, makes an angle α with the optical axis, where the beam is offset a distance X equal to α times the focal length of the objective lens “downstream” from where the write beam 40 “cuts”. . The resulting delay between reading and writing causes the molten metal to solidify, whereupon the record is read in its final state.

If the metal is read out so quickly that it is still molten, it will not give adequate information to adjust the recording parameters.

This is best illustrated in Figure 3 where two points on the same information channel are shown offset. Point A, which is the point of impact of writing beam 40, is shown to be on the optical axis of objective lens 14. Away from point A, in the direction of the movement of the medium, there is a readout point B at an angle α from the axis of the microscope objective 14, as indicated by the arrow. A distance of 2 μm between points A and B provides satisfactory monitoring of write operations.

Turning finally to FIG. 4, an idealized diaphragm of a Pockels cell stabilization circuit 44 suitable for use in the apparatus of FIG. 1 is shown. As is well known, a Pockels cell rotates the plane of polarization of applied light as a function of applied voltage.

Therefore, a Pockels cell is used to rotate a plane-polarized beam, and the rotated light is
It is passed through a plane polarizer like a prism.

The light emerging from the polarizer is amplitude modulated by the applied voltage.

It depends on the individual Pockels cell, but approximately
A voltage change of 100 volts causes the cell to rotate the plane of polarization 360 degrees. However, the migration characteristics of individual cells are ±50
A feedback loop is desired to maintain the cell within a useful, reasonably linear operating range since it can vary arbitrarily in response to voltage changes in volts.

Stabilization circuit 44 includes a photosensitive silicon diode 82 positioned to receive a portion of write beam 40 reflected from mirror 42 of FIG. This silicon diode 82 acts in much the same manner as a solar cell, providing a source of electrical energy when illuminated by incident light.

One terminal of silicon diode 82 is connected to a common reference potential 84, typically represented by a ground signal, and the other terminal is connected to one input of differential amplifier 86. Silicon cell 82 is shunted by load 88 which enables a linear response mode.

The other input of differential amplifier 86 is connected to common reference 84 through a suitable voltage divider 90. A power supply 92 is coupled to a voltage divider 90, which can set a differential amplifier 86 to establish the average light level delivered by the Pockels cell 32.

Therefore, a pair of output terminals of the differential amplifier 86 are
Each is connected to the input terminal of Pockels cell 32 of FIG. 1 through resistive elements 94 and 96, respectively. The Pockels cell driver 34 is a Pockels cell driver 34.
Note that the differential amplifier 86 is AC coupled to the Pockels cell 32, while the differential amplifier 86 is DC coupled to the Pockels cell 32.

In operation, this scheme is activated. Light from the writing beam impinging on silicon diode 82 generates a differential voltage at the input to differential amplifier 86 . Initially, the partial pressure meter 90 is adjusted to produce light at a predetermined average level of intensity. after that,
As the average level of intensity impinging on silicon cell 82 increases or decreases, a correction voltage is generated by differential amplifier 86. Pockels Cell 3
The correction voltage applied to 2 is of sufficient polarity and magnitude to restore the average level intensity to a predetermined level.

Thus, an improved video disc recording assembly has been shown. A microscope objective mounted on an air bearing is
It "floats" at a predetermined distance from the surface of the metallized disk. The metallized coating is such that the laser beam, under appropriate modulation, can emit sufficient energy to melt localized areas of its surface.

Under surface tension, the molten metal contracts leaving a distinct area approximately 1 micron in diameter.

A second low energy laser utilizing substantially the same optical path is directed through the same microscope objective, but is brought to the surface of the disk a short distance "downstream" from the point of writing.

The read beam is returned through a suitable optical scheme that rejects the reflected energy of the write beam, allowing the information written on the disk to be resolved.

The reproduction information, among other things, controls the intensity of the writing beam to ensure an appropriate "recording level" and determines whether an unacceptable number of errors are occurring in the recording process.

[Brief explanation of the drawing]

FIG. 1 is a schematic drawing of the device of the invention. FIG. 2 is a diagram of the optical path through the objective of FIG. 1; FIG. 3 is a diagram illustrating the relative spacing between the points of impact of the write beam and the read beam. FIG. 4 is a diagram of the novel Pockels cell stabilization circuit. 18...Disc, 22...Rotary drive element, 1
2...Writing head, 20...Translational drive element, 30
...Polarization splitting laser, 40...Writing beam, 32
...Pockels cell, 38...Grand prism, 46...Objective lens, 16...Bearing, 50...
...Arthroscope, 52...Readout laser.

Claims (1)

Claims: 1. A record carrier comprising a substrate having a surface covered with a photoresponsive coating, and a light beam of suitable intensity to act on the coating and modulate the coating so as to leave an information-coherent indicia. a first light source emitting light, means for imparting relative rotation to the light beam on the recording carrier;
a first optical device forming a first optical path between a light source and a record carrier with a coating and focusing a first light beam onto the coating by an objective; said first light source and said record carrier; a light intensity modulator that is disposed in the optical path between and acts to modulate the intensity of the light beam having information to be recorded; a second light source that generates the second light beam; and the second light source. and the recording carrier, and focusing a second beam of light onto the coating at a position spaced apart from the point of incidence of the first beam in the direction of movement of the substrate surface by the objective lens. a second optical device adapted to collect a second beam of light reflected by the substrate surface; and a second optical device adapted to collect a second beam of light reflected by the substrate surface; and a second optical device configured to generate a corresponding electrical signal in response to the reflected light. an information processing apparatus including a sensing means for generating a light beam, and a moving means is provided, whereby the light beam incident on the substrate surface is always moved in a direction transverse to the direction of movement of the substrate surface. In an information processing device adapted to be moved, the first optical means includes a first optical lens 46, a first beam directing device 50, and an objective lens 14; a second optical lens 60 , a second beam directing device 64 , and a third beam direction through which the first beam passes and disposed between the first optical lens 46 and the first beam directing device 50 . a directing device 48 and a first beam directing device 50
and an objective lens 14, a carrier is provided for holding these lenses and a beam directing device, and a drive for displacing the carrier in a radial direction with respect to said rotating recording carrier. an optical path portion located between the first optical lens and the first beam directing device;
The beam path portions located between the third beam directing device are substantially parallel to each other and to the movement caused by the carrier displacement device, and the beam path portions located between the third beam directing device and the objective lens are substantially parallel to each other and to the movement caused by the carrier displacement device. An information processing device characterized in that it is provided so as to substantially cooperate with both light beams.