JPS6224440A - Apparatus for recording mark on disc - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for recording indicia on a disc, and more specifically, for recording information on an optical disc as a carrier wave frequency having a time-varying frequency variation. Regarding the device.

Various schemes currently exist for recording signals at video frequencies on disk tape or other media.

It has already been developed. These systems have utilized optical recording on photosensitive media, electron beam recording on thermoplastic surfaces, and other systems that provide replayable recording of video information, among others.

Prior art techniques utilize photographic surfaces, electron beam sensing surfaces, magnetic recording techniques, and techniques in which a beam of radiant energy, similar to that of the present invention, causes irreversible changes to the surface and transfers information thereto. can be roughly classified into methods of "writing".

Photographic systems are disclosed in U.S. Pat. No. 3,361,873, owned by D. R. Johnson, which teaches the photographic recording of video information into images.

U.S. Patent No. 328 owned by Doubliny Sea Fuse Pond
No. 3310 describes the recording of information on thermoplastic film surfaces, which is similar to U.S. Pat.
An electron beam writing device such as that disclosed in No. 91 is utilized.

Ike's method also uses an electron beam to record information on a special storage medium. One such approach is disclosed in US Pat. No. 3,350,503 owned by TB Bullet. Ike's proposal to utilize an electron beam onto a photosensitive medium such as photographic film was published in U.S. Patent No. 344 owned by R.F.
No. 4,317.

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

These methods are described in the magazine ``Electronics (Ele
ctronics) J March 8, 1969 Issue No. 1
It is discussed in detail on page 10. Additionally, the ``laser thermal microimage refuder'' was described in some detail by C. O. Carlson and H. D. Iges at the 1968 WESCON meeting (Western E 1 electronic
hou+and Convention), which was published in a paper distributed at the Wescon
Technical Papers (WESCON Techn.
ical Papers), Volume 12, 1968, Section 16/1, Page 1. This author published the book “Science (5)” on December 23, 1966.
science ) J Vol. 54 No. 3756 No. 1550
~1551 pages, 1966 7 All Joey
Computer Cons 77 Lens (Fall Joi
ngCoIIlputer Conference
)'s Proceedings
), pp. 711-716, and “
Bell Systems Technical Journal (Be1l)
Systems Technical J o
urnal), pages 385 and 405.

These publications disclose recording techniques that utilize very thin metal films on a substrate. This thin metal 74 ilm 1 is heated and melts rapidly, creating small spherules within the recorded spot. A highly focused spot of laser light can impart enough heat in a short enough time that a suitably modulated laser beam impinging onto 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 Eiges article cited above, the size of the recorded spot or hole can be much smaller than the diameter of the imaging laser beam.

By appropriately selecting the metal film material, film thickness, laser divergence and spot power, a suitable scheme for recording video frequencies at high resolution can be achieved.
can be designed.

In accordance with the present invention, the Carlson and Eiges 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.

This invention relates to storing information on optical discs. Conventionally, when storing video information on a disc, a processing method has been used to directly create recorded information on the disc from an information signal whose amplitude changes over time.

The present invention provides an improved apparatus and method for reliably storing information on an optical disk in the form of a carrier frequency having a frequency variation L that varies in time from the carrier frequency. In the present invention, an optical disk is provided with a photoresponsive coating covering the substrate of the disk, and a light source generates a light beam of sufficient intensity to interact with the responsive coating of the optical disk during rotation of the disk.

An optical device defines an optical path between the light source and a responsive coating on the disk and focuses the light beam onto the coating. A light intensity modulator responsive to the information signal is disposed in the optical path to intensity modulate the light beam. A beam optically focused through an intensity modulator onto a responsive coating on the disk forms an information track consisting of indicia representing a frequency modulated information signal.

The information signal as well as the modified coating of the disc contain information in the form of a carrier frequency whose frequency varies as a function of time.

The configuration 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 speed along the radius of the rotating disk. - As can be seen, it is desirable to synchronize or otherwise cooperate the drive of the disk with the translational drive in order to create a helical trajectory of a predetermined pitch. In a preferred embodiment, the spacing between adjacent turns of the spiral is 2μ+n from center to center. If the spot diameter is 1 μm, there is a guard region of 1 μm between spots on adjacent tracks.

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.

A 40X dry microscope objective was found to be satisfactory in focusing the energy of the laser beam and allowing the writing of a 1 μm spot at the disk surface.

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

An argon ion laser is used as the writing beam. A combination of Pockels cells and grannibrism 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 selected such that the read beam illuminates an area on the written track that is approximately 2 μm below the write spot.

This read beam is reflected from the disk surface back through the write head and passes through a dichroic m1rror which has inserted the read beam into the write path.
) and then retraces its optical path.

The read beam is then directed to a beam splinter and then through a Pandopa filter that blocks any write beam that follows 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.

"Write then read" information can also be utilized in error checking schemes, 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 spot and the read spot. 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 can be seen, it is required that the two drives be synchronized or otherwise cooperate so that a helical track of a predetermined pitch can be created. 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 spot diameter is 1 μm, there is a guard region of 1 μm between spots in adjacent tracks.

The novel features believed to be characteristic of the invention, both as to its mechanism and method of operation, together with further objects and advantages thereof, 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. It should be noted, however, that the drawings are for illustration and explanation only and are not intended to limit the scope of the invention.
You have to understand this.

Turning 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.
It is. It has been found that 40X1< lenses are satisfactory. Disc 18 is specially prepared,
This can be constructed according to the teachings of the prior art, in which the substrate is coated with a very thin film of a metal with a very 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 .

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

Translation carriage 28, which is driven through a translation drive element 26S, two uplifts, a lead screw and a transfer nut;
Write head 12 is moved radially relative to rotating disk 18 . The carriage 28 is mounted such that the remainder of the optical and electronic systems necessary for the writing device are permanently mounted.
Equipped with suitable mirrors and lenses.

In an embodiment of the invention, a polarization splitting laser 30, (
The beam (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, Pockels cell 32 responds to an applied signal voltage by rotating the plane of polarization of the light beam. A linear polarizer transmits light only in a given plane of polarization. A polarizer, such as a Glan prism 38 in an embodiment, is placed in the write beam path to provide a modulated write beam 40.

A modulated writing beam 40 emerging from the Pockels cell 32 and Glan prism 38 combination is directed to a first mirror 4 which directs the writing beam 40 onto a translation carriage 28.
Can be applied to 2. This first mirror 42 transmits a portion of the writing beam 40 to a Pockels cell stabilization circuit 44 which maintains the energy level of Bea A 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 5
The beam can then be directed through the lens 14 to change the point of impact of the beam 40 on the surface of the disk 18.

Objective lens 14 and associated air bearing 16
effectively floats on a cushion of air at a substantially constant distance from the surface of disk 18. This distance is
It is determined by the geometry of the bearing 16, the linear speed 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 μm spot is also on the order of 1 μm.

A second relatively low power laser 52 directs the monitor beam 5
Give 4. In an embodiment, readout laser 52 is a helium neon device in which readout beam 54 can be erased from the write beam by wavelength. Polarizing beam splitting cube 56 transmits readout beam 54 to mirror 58 which directs beam 54 through a second diverging lens 60 which spreads readout beam 54 to fill the entrance aperture of objective lens 14. do.

A quarter-wave plate 62 is placed in the optical path in conjunction with the plane polarizing beam splitter 56 to prevent light reflected from the disk 18 from re-entering the laser S2 and perturbing its oscillation mode. To prevent. The quarter-wave plate 62 rotates the polarization plane of the beam by 45 degrees each time it passes;
The reflected beam is then directed to the polarizing beam splitter 56 at a 90° angle.
degree and therefore does not pass through it.

A second mirror 64 in the read beam 54 path directs the beam into a dichroic m1rror 48 such that the read beam "spot" is located downstream from the write beam spot as described 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 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 . The He-Ne read beam 54 returned from the disk surface 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 the first application, the video output is the television monitor 7
6 and Otsushirohisa hoop 78. tv set·
A monitor 76 shows the video fidelity of the recording, and an oscilloscope 78 shows the signal-to-noise ratio of the recording and the quality of the cutting, light or heavy. Although not shown, a suitable feedback loop is provided to ensure that there is sufficient discrimination on the disc between "holes" or "black" and "non-hole" or "white" areas. can be provided.

As an alternative use, the video output of discriminator 74 is applied to comparator 80. The input of comparator 80 is taken from the video input signal, which is directed through delay line 81. The accumulated delay of the writing method and the delay equal to the time that elapses 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 contributed to the human video signal. No.

Ideally, the video output signal of discriminator 74 should be identical in all respects to the video input signal after an appropriate delay. The differences to be seen represent errors caused by defects in the surface of the disk, or by malfunctions of the main or 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 given disk. When the counted error exceeds the standard,
The write operation can be completed. If necessary, you can burn a new disc. Discs with excessive errors can then be reprocessed and serve as "new" discs for subsequent recordings.

Known techniques are available for radially translating write head assembly 12 relative to rotating disk 18. In FIG. 1, a rotational and translational drive 20
．． 22 are shown independently, these drives are synchronized by a common crystal oscillator 20 to drive the disk 18.
The line writing assembly 12 may be translated by a predetermined increment with each rotation of the line writing assembly 12.

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 is coincident with the optical axis of the microscope objective 14. The reading beam 54, in contrast, makes an angle α with the optical axis such that the writing beam 40
It is shifted ``downstream'' from the point of ``cutting'' by a distance X equal to 0 times the focal length of the objective lens. 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 mostly melted, it will not give adequate information to adjust the recording parameters.

This is best illustrated in FIG. 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 media movement, is a readout point B at an angle a 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 diagram 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 of light, and the rotated light is passed through a plane polarizer, such as a Plan prism.

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

Depending on the individual Pockels cell, a voltage change of approximately 100 pol F will cause the cell to rotate the plane of polarization 360 degrees. However, the transfer characteristics of an individual cell can vary arbitrarily in response to voltage changes of ±50 volts, so a feedback loop is desirable to maintain the cell within a useful, reasonably linear operating range. It will be done.

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 is coupled to a differential amplifier 86 to establish the average light level delivered by Pockels cell 32.
can be set.

A pair of output terminals of differential amplifier 86 are then connected to input terminals of Pockels cell 32 of FIG. 1 through resistive elements 94 and 96, respectively. It is noted that Pockels cell driver 34 is AC coupled to Pockels cell 32, while differential amplifier 86 is DC coupled to 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. at first,
The partial pressure meter 90 is adjusted to produce light at a predetermined average level of intensity. A correction voltage is then generated in differential amplifier 86 as the average level of intensity impinging on silicon cell 82 increases or decreases. 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.

An improved video disc recording assembly has thus been demonstrated. A microscope objective mounted on an air bearing "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
It 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 analysis of the information written on the disk.

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 drawings]

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... Rotation driving element, 1
2...Writing head, 20...Translational drive element, 3
0...Polarization splitting laser, 40...Writing beam,
32 Pockels cell, 38...Grand prism, 46...Objective lens, 16...Bearing, 5
0... Seki WJ mirror, 52... Readout laser 6 O 2 Figure

Claims (1)

[Claims] means for rotating a disk having a radiation-sensitive layer on its surface; a laser source for generating a writing beam of intensity causing a reaction in said sensitive layer; and in response to information to be recorded;
beam intensity control means for modulating the writing beam to a value above a predetermined average level at which the beam forms an indicia in the sensitive layer and below a predetermined average level at which the beam does not form an indicia in the sensitive layer; means for focusing the modulated beam to a small spot on the disk surface;
a translation drive means for moving the small spot and the rotating disk relative to each other in the radial direction of the disk; and a beam intensity control means for setting the operation level of the beam intensity control means to the predetermined average level. a voltage source connected and means for monitoring the intensity of said modulated light beam and filtering the measured intensity to obtain a measure of average modulated intensity, regardless of changes in the laser source or said beam intensity control means; means for detecting a difference between the average level of the modulated beam and the predetermined average level and generating a feedback signal for adjusting the voltage from the voltage source to stabilize the average level of the modulated beam; and means for applying a voltage superimposed on a voltage connected to the beam intensity control means.