DE3328368A1 - OPTICAL DATA RECOVERY SYSTEM FOR REFLECTIVE DATA STORAGE MEDIA WITH SEVERAL CHARACTERISTICS - Google Patents

Description

The invention relates to data recovery from a storage medium, and in particular, recovery of data from an optical storage medium, with different optical characteristics for prerecorded ones and user-related recorded data.

Materials for laser recording and data storage with different optical characteristics are known. For example, U.S. Patent 4,284,716 discloses a reflective broadband laser recording and recording device Data storage medium known for direct reading after writing. It is made from the conversion of a photosensitive silver halide emulsion formed into a reflective, stable, silver gelatin coated substrate with the silver gelatin coating through the impact of a laser beam is easily provided with pits.

The chemical conversion of the raw material from silver halide emulsion into the laser recording material, as described in the aforementioned US patent, requires four steps. First, unsaturated actinic radiation is used to define areas for recording user data. Normal photographic processing is used to produce a neutral gray density medium. The surface of the remaining silver halide is obscured in a water- or alcohol-based solution to create a very thin layer of silver precipitating nuclei on the surface. Finally, a one-step negative silver diffusion transfer process is used to ibsen the unexposed and undeveloped silver halide, forming silver ion complexes. These complexes are transported by diffusion transfer to the sites of the silver precipitating nuclei and the filamentary silver. The resulting reflective coating has a high concentration of non-filamentary silver particles on the surface of a colloid matrix with a low melting temperature. This matrix forms a sub-layer which is partially light-absorbing. The reflective surface layer and the absorbent sub-layer have a composite reflectance in the range between 50 % and 30 %, a transmittance in the range from 10% to 0.1% of the light actually entering the medium surface, and an absorbance within

of the range from 90 % to 99.9 % of the light actually entering the medium surface.

The writing of data to the medium is done by creating posts achieved with low reflectance in a reflective field. This is done either by laser writing or by melting holes in the reflective medium, or by pre-photographic recording by exposure and development to black.

Holes or are used for laser writing on this recording medium Pits melted into the reflective surface with a low power laser. A laser beam or focused light beam is used to Used to read the recorded data. The beam hits the recorded one Pits with greatly reduced mirror reflection, thanks to scattering and absorption by the pitted underlayer. The reductions the reflectance are measured with a detector and converted into data corresponding to electrical impulses.

One of the advantages of this medium is that it is also pre-written photographically can be. In the first unsaturated exposure step a pattern can be formed with exposure through a mask or through a scanner light source, which after the machining process has two different patterns Surface reflectance results. This pattern is found in both the reflective layer and the underlayer, below the reflective surface layer or in laterally adjacent areas.

One of the problems encountered when reading reflected light from the in pits located in the medium occurs, is that it is not possible to between a pit or hole with a low reflectance due to light scattering and absorption and black pre-recorded silver distinguish which also has a low surface reflectance or a high light absorption. It's also difficult to choose between distinguish between these two types of data and certain types of material defects, including foreign matter particles and material inhomogeneities, which create spots of low reflectance either by light scattering or absorption.

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US Pat. No. 4,145,758 describes a data reading system in which digital Data can be written on a transparent medium, for example a photographic disk, with a modulated laser whose beam is detected by a first photodetector device which measures the laser output signal directed onto the recording medium. One second photodetector means measures the light scattered by the medium, while a third photodetector measures the light scattered by the recording layer light transmitted through the medium surface is detected and measured in order to reduce the Confirm data recording. The amount of light transmitted or scattered by the medium during the recording process is determined by the Laser output light correlated to expected light values to avoid errors in of the recording immediately after the time of the recording. This error detection system is intended for translucent media and should not be used to read reflective media. The defects are detectable by the device before laser recordings are themselves dotektiorbar.

An object of the invention is when reading the data between with laser recorded pits or holes and photographically prerecorded data in the form of areas of blackened silver in a field with to distinguish reflective silver. Another object of the invention is to switch between laser-recorded data on reflective to distinguish optical data storage media of the metal film type or organometallic compounds and light-absorbing foreign particles in the recording media. Another task is to choose between light-absorbing, photographic prerecorded data and light absorbing To distinguish foreign articles in the recording areas.

The above tasks are achieved with a laser system that is described in is capable of storing optical data on optical disks, optical cards or optical tapes of the multi-distinctive type To distinguish characteristics which are interpreted by simultaneous measurements of the specular reflectance and the optical transmittance. The different optical characteristics are associated with different types of prerecorded data in different lateral parts of the medium. Different

optical characteristics are also assigned to foreign particles in the medium, Unlike those that represent recorded data.

In reflective recording media based on silver from the In the manner described in U.S. Patents 4,278,756 and 4,284,716, data in certain areas are photographically prerecorded before Laser recorded data in other areas with reflective silver will. Data prerecorded photographically may be black be or have a matt-silvery appearance, with a higher optical Density for transmission of infrared than the unwritten reflective surface and a lower mirror reflectance for infrared and visible light. Laser recorded data coming from a highly reflective Field or surface layer penetrating pits have a reduced optical density for transmission than that unwritten reflective surface, as the pits partially penetrate the medium, and a lower mirror reflectance, which is due in part to the fact that the pits scatter light. Foreign matter particles in the surface reduce both the composite surface reflectance and the light transmittance of the Medium, since photographically prerecorded data indicate the degree of light transmission of the medium for infrared considerably and the laser-recorded holes can increase the light transmission factor for infrared the presence of foreign matter particles through the intervening Transmittance can be identified. At the same time results in a foreign matter particle higher reflectance as both photographically prerecorded data and laser recorded user data, but not as much as the reflective field in which laser recorded User data are available. By measuring the light reflection at the same time. at a point and the light transmittance through the Medium at this point can take photographic prerecorded data, laser-recorded user data and foreign matter particles from each other differentiated and thus identified.

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BRIEF DESCRIPTION OF THE DRAWINGS

1 is a top plan view of a laser recording medium according to FIG the invention;

Fig. 2 shows a section of an optical information recording medium for use with the system of the invention;

Figure 3 shows a section through an alternative optical information drawing media for use with the system of the invention;

FIG. 4 is a detailed plan view of the recording medium of FIG Fig. 1;

Fig. 5 shows an optical disk reading system according to the invention;

6 shows a diagram of a scheme for correlating reflected and transmitted beam components;

FIG. 7 shows a reading system for optical data cards according to FIG Invention.

In Fig. 1, an optical recording medium is used as a disk 10 with a central opening 12 and an outer edge 14.

The medium does not have to be a disk, but can also be a card. The description of a plate is only intended as an example. Data is recorded on circular tracks 16, partially shown as an enlarged detail. Both user data and prerecorded data are stored on the disk in different lateral directions Areas stored as will be discussed with reference to FIG. 4.

Referring to Fig. 2, an optical recording medium is preferred a laser-writable medium of the type described in U.S. Patent 4,284,716. The two-layer mecdum described in the patent becomes short said made as follows:

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The surface of a light-sensitive medium with a fine-grain silver halide emulsion, for example a Lippman emulsion, is briefly exposed to low to medium level actinic radiation. A mask is used to create a pre-recorded pattern, for example a servo track pattern, in areas that can be laterally differentiated from the user data areas. This exposed silver halide is developed to have an optical density of 0.05 to 2.0 as measured in the red light of a photography densitometer. This gelatin layer containing thread-like silver particles has an optical density of typically 0.05 to 0.8 for a 3 μ thick emulsion and 0.1 to 1.5 for a 6 μ thick emulsion. After this initial processing step, the emulsion layer appears gray, but a large amount of silver halide in the emulsion remains unchanged. A very thin layer of the unexposed silver halide on the surface of this partially developed emulsion layer is then chemically fogged to form a very dense layer of silver precipitating nuclei on that surface. The fogged medium is finally subjected to a negative silver diffusion transfer step in which the silver halide in the emulsion is solvated to form soluble silver complexes. These silver complexes are precipitated on the silver-precipitating cores, so that a reflective layer is formed which consists of non-filamentary Si overparticles η which aggregate with the filamentary silver. The degree of reflection of the surface can be adjusted over a range of values that depends on the proportions of the two types of silver, but should be around 40 % . The same mechanism also precipitates some of the silver ion complexes on the filamentary silver in the absorbing sublayer so that the red light optical density of this already developed sublayer is increased, usually an increase of at least a factor of two for light absorption.

The ultimate result of these two exposure development sequences is a superior reflective laser recording medium made up of a very thin layer of reflective, but non-electrical conductive, reduced, non-filamentary silver and a lot consists of a smaller amount of thread-like silver, under which a highly absorbent, mainly of thread-like silver in a gelatin

matrix existing layer lies. This absorbent backsheet typically has a final red light optical density of between 0.2 and 3.0. The original silver halide emulsion photosensitive medium which ultimately results in the laser reflective recording medium described above is usually coated on either a plastic or glass substrate. The reflective surface has a red light reflectance of 40 % for a typical pattern.

Laser recording on this reflective surface can be very efficient be performed. The absorbent, thread-like silver particles in the reflective layer can be increased to the acceptable minimum degree of reflection has been reached. This thread-like Particles are ultraviolet over a very wide spectral range absorbing to the near infrared, making the use of a wide variety of lasers allowed for recording. Also, the light energy that is not absorbed by the reflective layer becomes substantial absorbed by the underlayer, causing a rise in temperature at the boundary between the reflective layer and the underlayer and thereby facilitates the melting of the reflective layer. A record is made by using a laser beam to melt the gelatin at one point in the reflective layer reached, and thus the mirror reflection level is reduced at this point. The reflective layer reflects before recording reflective; In other words, incident light perpendicular to the surface is reflected back to its origin in a parallel line. After the recording, perpendicular incident light is diffusely reflected, because the light returning to the source will be scattered instead of parallel. This latter effect and the increased degree of absorption on the Place lead to a reduced degree of mirror reflection. The absorbent backsheet should only be slightly through the absorption process to be penetrated. No silver is melted in either layer during the recording process.

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Such a medium can be seen in FIG. A glass or plastic substrate 11 carries a very thin Lippman emulsion 13 which, as abert briefly and more fully described in US Pat. No. 4,284,716, has been processed. This emulsion has an upper layer 15 which is ffoch reflective and a lower layer 17 which is highly absorbent. In FIG. 2, the two layers are separated by a border line 1 $, but this is only for illustrative purposes. In practice there is a smooth transition between the highly reflective upper layer 15 and the highly absorbent lower layer 17 without a discontinuous boundary between them. The upper layer 15 consists mainly of non-thread-like silver particles which are approximately spherical in shape, while the lower layer 17 consists of thread-like silver particles which have an elongated shape. In both layers the particles are in suspension in gelatin. Usually, the volume concentration of the silver particles in the reflective layer 15 is at least 20 % and at most 50 %.

If you want to increase the optical density of the material, you can an arrangement according to FIG. 3 can be used. Substrate 21, a glass or plastic plate, has an emulsion 23 identical to emulsion 13 underneath a reflective layer 25. An additional feature of the recording medium of Figure 3 is that it has been developed to black Emulsion, preferably a Lippman emulsion 29, on the opposite side of the substrate 21 to the emulsion. The backing layer 29 is chemically developed in such a way that the silver in it is primarily thread-like, black silver with an optical density between perhaps 0.2 and 3.0 is after development. A pattern can be added to this layer for security purposes, e.g. a repeating line pattern. Such a pattern could be taken into account by the detection system and serve to deter attempts at forgery, since a medium coated on both sides is usually not available from stock, but would have to be specially made.

In Fig. 4, a pair of data tracks 31 and 32 are laterally spaced between prerecorded guide tracks 32, 34 and 36 are shown. These

Guide tracks can be photographically prerecorded black silver with edges 38 with a wave character which can serve to modulate a light beam with a characteristic frequency. The servo tracks define the data tracks as lanes or tracks laterally between servo tracks. Dark spots 41 can be seen within track 31. These dark marks represent prerecorded data such as control information, database data or the like. The oval marks 43 represent pits on the reflective surface layer of the disk, which are made by pitting the surface layer by laser energy pulses. The broken line 45 represents the size of a laser beam for reading either the prerecorded or the user data. The beam is smaller than the width of a track and of the same order of magnitude as the size of a data bit. Preferably, a semiconductor laser with an infrared beam is used. Infrared is because of its ability dirt particles to penetrate _s better.

Referring to Figure 5, there is shown a data recovery system in accordance with the invention. An optical source, e.g., a laser 61, 'has a beam 63 aimed at a Recording medium 65 is directed according to the in connection with Fig. 2 explained medium construction is constructed. Such a medium can be adapted for rotation on a spindle or a be stationary data card that is read with an optical scanning system. The light beam 63 is directed onto the medium 65, and two optical signals are derived after the beam hits the medium. Specularly reflected light is partially transparent Mirror 69 deflected to the detector 71, the amplitude of the reflected Beam component 73 is detected. The beam component that has passed through 75 is applied to a further detector 77, so that the amplitude of the transmitted component can be converted into a proportional electrical signal, in a similar way to detector 71 the reflected Beam component 73 is converted into a proportional electrical signal. The table below shows the way in which the surface reflectance and the optical density for separating prerecorded and user data and for isolating the presence of Particles can be used so that only unique user or

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pre-recorded data is read by the system,

Tabel

Typical surface reflection level

(Red or infrared light normal to the surface)

Typical optical density for transmitted light (red or infrared light normal to the surface)

Surface condition

Surface treated as described -Recording field

A. recorded data pit, in the field

B. Foreign matter particles in the field

C. by pre-recording blackened silver, by emulsion (Fig. 2)

D. blackened silver, on the back of the normal surface or field (Fig. 3)

E. Inhomogeneity in metal / organic reflective compound (Surface)

40 %

8 %

5-15 %

8 %

40 %

20-30 %

1.5 0 ₅ 7 2.0

3 _s 0 4.5 I ₅ O

The prerecorded data can be distinguished from pits in the reflective surface indicating user data, since in transmission the typical optical density difference is 3.0 compared to 0 _s 7, although the surface reflectivities are similar. Particles of fabric or dirt can be detected because, although those of

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Reflection caused by particles can be similar to prerecorded data, a dirt particle has an optical density of 2.0, compared with 0.7 for data and 3.0 for a pre-recorded black spot. In a medium that was treated according to FIG. 3, the optical Densities can be made even larger for further separation of user and pre-recorded data on the one hand and Particles on the other hand.

Referring to FIG. 5, a third detector 72 checks the output of the laser source by receiving a component 74 of the incident beam from mirror 69. The detector 72 converts the optical signal into a proportional electrical signal. It is important to check the strength of the incident beam in order to convert the electrical signals from detectors 71 and 77 into ratios for percentages of incident light. Since the incident ray must be equal to the amount of light transmitted plus the amount of light reflected minus the amount of light absorbed by the medium, percentages can easily be calculated with a computer or manually if necessary. Since the amount of light absorbed by the medium can be determined experimentally during the calibration procedures, the task of converting the signals received in detectors 71 and 77 to percentages is straightforward as long as the source remains constant. By detecting the source component 74, the strength of the incident beam can be monitored for deviations from the calibration values. Let the intensity of the laser beam be In. What is reflected is Inr, where r is the total reflectance (specular reflection plus scattering). What enters the surface is In (lr) and what is transmitted through the medium is I _B (lr) t, where t is the transmittance. The laser beam energy that is absorbed in the medium is In (lr) (lt).

6, the two detectors 71 and 77 each have electrical ones Outputs 81 and 83. These outputs are electrically via analog / digital converters (not shown) to a computer 85, which is interrupted by an Line is indicated, connected. In the computer is a program which the signals from the detectors 71 and 77 detected

Converts Siqtialintensities into quotient or percentage values.

The computer 85 contains internal programs for comparing the digital signals derived from the detectors 71 and 77. Comparisons are made to determine at block 91 whether the surface reflectance level exceeds 18%. A second determination, illustrated schematically at block 93, relates to whether the optical density exceeds 1.7. A third determination, illustrated schematically by block 95, relates to whether the optical density exceeds 2.5. These determinations are necessary in order to determine which of the states in the table applies to the detected signals. State A in the table, detection of a recorded pit, is present when the three tests indicated by blocks 93 and 95 are all negative. State B in the table, detection of a foreign particle, is present when blocks 91 and 95 are negative and block 93 is positive. Condition C in the table, detection of blackened silver by pre-recording, is present when block 91 is negative and blocks 93 and 95 are positive. Condition D in the table, detection of blackened silver on the back of the normal surface, is when blocks 91, 93 and 95 are all positive. These determinations are made immediately by logic circuits that respond to incoming data at the data rate. State E in the table, detection of an inhomogeneity in the reflective surface with metal / organic compound, is present when blocks and 95 are negative and 91 is positive.

In the implementation according to FIG. 7, a data card 101 has a reflective layer 103 on the underside of the card, not visible in the figure. The layer and the sub-layer carrying it have a composite reflectance in the range between 50 % and 30 % and a transmittance in the range from 10 % to 0.1 % for the light actually entering the surface of the medium. The degree of absorption of the material is in the range of 90 % to 99.9 % for the light actually entering the surface of the medium. The cross section of the material can vary according to the recording medium

Fig. 2 or 3 be similar. A laser such as a semiconductor laser 105, directs a beam 107 along an optical path that includes a focusing lens 109, a beam splitter 111, a mirror 113, a quarter-wave plate 115 and focusing optics 117, to a point of impact 119 on the medium. A first portion of the beam 121 passes through the card and to the first detector 123 where the optical signal is converted into a proportional electrical signal will. A second portion 125 of the beam is from location 119 reflected. The broken line indicates part of the reflected beam. This second beam part is parallel to the incident beam 107 between the reflective layer 103 and the beam splitter 111, there Spieqelreflexion occurs at the point of impact 119. The beam part 125 runs through the beam splitter 111 to a prism 127 and then to the second detector 129, where the reflected light beam is partially converted into a proportional electrical signal.

Correlation measurements are performed prior to reading data, where the system in FIG. 7 for receiving first and second detector signals for pits created by laser inscription in the card, thin Points in the reflective surface layer and weakly reflective points caused by material particles at the point of impact of the beam are used. These states lead to surface states similar to those described in the table, The electrical signals from the detectors become correlation registers sent as they are in Fiq. 6 illustrates and related thereto are described. A decision can be made with this correlation device can be made in real time about which of the states shown in the table for the detectors 123 and 129 received signals is applicable.

As can be seen, in order to read the medium 101, the card in the direction indicated by arrow A direction indicated or the incident beam be deflected by a beam scanner mechanism, not shown.

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By comparing the reflected and transmitted beam components, errors in data reading can be reduced considerably. The effect of dirt particles and the like, as well as defects in the medium, can be reduced considerably ₅ and the signal-to-noise ratio of optical data recording media is increased or, equivalently, the error rate is reduced.

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Claims (8)

Claims Laser system for reading data on an optical data storage medium with different optical characteristics, consisting from a data medium with data and imperfections, which for an incident laser beam with reflected and transmitted Beam components have different characteristics for the specular reflectance and having the optical transmission wheel, first and second detecting means for detecting simultaneously the specularly reflected and the optically transmitted beam component and for generating a first and a second electrical component Signal corresponding to a size of the received light, and a correlation device connected to the detector device is to compare the electrical signal level with stored oozoooo Reference levels representing various data and imperfection states of the medium. 2. Laser system according to claim 1, characterized in that a laser comprises a beam directed onto the medium via a first optical path, a first portion of the beam through the medium is allowed through and impinges on the first detector device, a second part of the beam is specularly reflected from the medium via a second optical path, part of which with the first optical path is common, but diverges at a beam splitter, and the beam splitter is arranged for forwarding the specularly reflected beam to the second detector device. 3. Laser system according to claim 1 or 2, characterized in that the The size of the received light is the light amplitude. 4. Laser system according to claim 1, 2 or 3, characterized by a Infrared laser that generates the incident laser beam. 5. Laser system according to one of claims 1 to 4, characterized in that that the medium consists of a substrate, a partially permeable, partially reflective layer over the substrate and a silver shark emulsion, processed to black, on the back of the Substrates consists. 6. Laser system according to claim 5, characterized in that the to Black processed emulsion contains a line pattern on the back of the substrate. 7. Laser system according to claim 5, characterized in that the reflective Layer is derived from a silver halide emulsion and pre-recorded data areas developed to black and to data areas processed in a partially reflective state Having laser recording. 8. Procedure for distinguishing between data and foreign matter or Imperfections on a partially reflective, partially permeable optical data medium, with the following steps! - Provision of a partially specularly reflective, partially transparent optical data medium with different reflectance and transmittance characteristics for data and imperfections for an incident laser beam, - simultaneous detection of the reflected and transmitted Beam components resulting from the incident laser beam, and - Correlating the specularly reflected and the transmitted Beam component with stored reference levels to different Display data and imperfection states of the medium.