DE1918031A1 - Process for the optical recording and storage of information - Google Patents

Description

IBM Germany Internationale Büro-Maschinen Geteilschaft mbH

Boeblingen, April 8, 1969 pr -hn

Applicant:

International Business Machines Corporation, Armonk, N.Y. 10 504

Official file number:

New registration

Applicant's file number: Docket PO 9-67-093

Process for the optical recording and storage of information

The invention relates to a method for recording and storing Information by means of the superposition of the object and reference beam i len formed interference patterns.

Well-known methods for the formation of interference patterns are the Lippmann method, holography or Lippmann holography. In a storage system based on the Lippmann process, the back of the food is more of a medium reflective. The interference pattern consists of blackening (or clouding) and lightening at the antinodes of the Standing waves arising from the interference of

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falling ray and reflected ray of monochromatic light. With holography / the interference pattern in the storage medium formed by the interference of the wave modulated with information, e.g. the light diffracted from the illuminated object, with the plane, i.e. unmodulated wavefront of the reference radiation. Both coherent Radiations enter the storage medium from the same side. In Lippmann holography, the interference pattern is formed by superimposing the signal-carrying wavefronts with the reference radiation, the radiations being directed opposite one another by different pages fall into the storage medium.

A disadvantage of the above methods is that in the Recording a large part of the energy of the reference beam and when reading out a large part of the energy of the query beam is lost. This disadvantage is particularly troublesome in such cases where as for recording as well as for playback or for reading out coherent Beams with very high energy density are used.

These disadvantages are accentuated according to the invention by a method of recording and storage of information by avoiding interference patterns formed by the superposition of object and reference beams, which is characterized in that after a first interference / nit the ob-

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Jektstrahl remaining part of the reference beam at least one more Times is returned to the same area and again with the Object beam is brought to interference.

A particularly advantageous development of the method according to the invention i is characterized in that when recording in the storage medium at least one additional interference pattern by interference of an information-carrying radiation with a reference radiation in the the same memory area is formed, the reference radiation for the formation of the interference pattern following the first from the non-diffracted Part of the reference radiation is obtained as a beam The zeroth order penetrates the storage medium and is again directed to the same storage area by optical means in order to be able to use the same information-carrying radiation to interfere, and that when reading the information from the storage medium, the non-diffracted Part of the interrogation beam is deflected by optical means and directed at least one more time onto the storage area, wherein each time the diffracted portion of the interfering radiation contributes to the reconstruction of an image of the optical memory content.

The method according to the invention achieves a significantly better utilization of the reference beam and the interrogation beam. Furthermore with a suitable arrangement of the optical means causing the multiple use of the reference beam, a significant

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improvement in the quality of the image achieved, mainly due to a Blurring is due to the structure of the laser beam.

The invention is explained in more detail below with reference to the figures. Show it:

Fig. 1 is a schematic representation of an arrangement for optical

Storage of information,

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Fig. 2 schematically shows an arrangement for reading out the

corresponding to the setup shown in Fig. 1 information stored in the drawing process,

3 and 4 separately schematically two types of generation virtual and real images according to the in <Fig. 2 readout procedure shown,

Fig. 5 shows another arrangement for the optical

Storage of information and

6 schematically shows a further arrangement for the optical

Storage of information.

According to the illustration in FIG. 1, the from an object 11 diffracted radiation as a wavefront 10 on a suitable Recording medium such as photographic layer 12, steered. At the same time, the reference radiation. 13 of one Light source 14 also directed onto this layer 12. In each. Case can be the beams 10 and 13 from a suitable

a 9 ^ -6 «^ 0: 93"

Source of coherent electromagnetic radiation supplied
will. For this description it is assumed that; the rays through light sources, · like ζ. Β. Laser, delivered
. will.

The coherent rays 10 and. 13 interfere on the same side of layer 12, and the interference pattern produced by this interference is recorded in layer 12. That
Patterns formed in this way consist of light and dark areas which represent the stored information. This acts
it is initially still a matter of the conventional method for
holographic recording in a photographic
Emulsion.

The light impinging on the layer 12 in the reference beam 13 interferes with the information-modulated light in the wavefront 10. However, not all of the light in the emulsion is absorbed and a substantial part of the light penetrates the photographic layer as beam 15 uttd; Amplitude of the beam 13 mi £ Eb / zs ». M denotes wectiten ,. sioi üsit.

according to studies the intensity and amplitude of the Beam 15 is approximately 0.5 I or 0.7 A. With conventional holographic methods, this light is lost in the system.

Now we also have a mirror 16 with respect to layer 12 arranged on the side facing away from the radiation source 14 so that it is in the path of the beam passing through the layer 12 15 lies in the axis of the incident beam 13. The ray 15 is reflected by the mirror 16 in such a way that it is deflected back onto the photographic layer 12 in the direction of the arrows 17, in order to move with the information-carrying beams 10 from the object 11 interfere. In the layer 12, a second interference pattern, now nar! I based on the recording principle of Lippmann holography. The object 11 is thus in the layer. 12 a. recorded second time.

However, the first interference image recorded in the photographic layer 12 does not necessarily need to be in the holographic one Technology and the second not necessarily in technology

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the Lippmann holography, but the order of these images can also be reversed. to For this purpose, the reference source 14 can take the place of the mirror 16 and the mirror 16 can take the place of the source 14 be set. This would reverse the process so

that first the Lippmann hologram in layer 12 and that an ordinary hologram in the second interference pattern is formed in the emulsion of the photographic layer 12. Similarly, the otherwise lost light in the beam 15 can also be directed by suitable optical elements so that it enters the layer from the same side each time occurs. .

For the readout process shown in Fig. 2, the photographic layer 12 was developed and processed in conventional photographic technology in order to form a hologram 28 which, for reading out the stored information pattern, is placed in the same position where the photographic layer is also located for recording. A source 20 for an interrogation beam 21 directs the latter onto the hologram 28 along

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the same axis that the reference beam 13 in Fig. 1
recording method shown. The ray 21
falls on the hologram 28 and the light rays 22 are diffracted and form a virtual holographic image. The virtual image appears to be three-dimensional to an observer 27
behind the hologram from the he-.
drawn area to emerge.

A substantial part of the incident on the hologram 28 Beam 21 is not diffracted by the hologram, but passes through it as beam 24 of the zeroth order. The ray 24

contains no information, but it is attenuated when the hologram 28 is passed. If the intensity and amplitude of the interrogating beam 21 are designated with I or A, the intensity of the beam 24 is approximately 0.25 I and its Amplitude 0.5 A.

The mirror 25 is placed in the same place as that at
the recording according to FIG. 1 used mirror 16. The otherwise lost light of the zero order beam is

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directed back onto the hologram 28 by the mirror 25 in the direction of the arrows 26. As before the rays 22 the light is bent again, now in the form of a virtual image according to the Lippmann holography. The observer this image appears again in the space designated by 23 as being located behind the hologram 28. It is true corresponds in size to the virtual holographic image and also has the same spatial position as the virtual one Hologram. . ■.

When reading out the stored information arises on In this way, in the area 23, a significantly enhanced image. The efficiency in reconstructing the in interference patterns Stored information is significantly increased. The virtual images appearing at 23 could be displayed on a screen at the position of an observer 27 when the diffracted light rays 22 are first passed through a lens.

3 and 4 separately show two aspects of the in

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Fig. 2 shown readout method. The virtual hologram is created in FIG. 3 when the interrogating beam 21 hits the Hologram 28 falls. The diffracted light 22 provides this virtual image. The non-diffracted light passes through the hologram 28 as a zero-order beam 24.

In FIG. 4, the mirror 25 reflects the beam 24 in the direction of the arrows 26 onto the hologram 28. The diffracted light supplies at 23 the virtual image according to the Lippmann holography. Both reconstructed from the interfering wave fronts Pictures are the same in size, have the same spatial position and are superimposed. The resulting The efficiency of the output image is therefore greater than either only the holographic technique or only the Lippmann holography scored. This method of information storage and retrieval increases the efficiency of the image reconstruction by at least 50%.

According to the illustration in FIGS. 3 and 4 arise in the query, besides the virtual images, also real ones

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Pictures. In FIG. 3, in addition to the virtual hologram, a real image corresponding to the Lippmann holography is obtained. Because the light 30 is reflected by the hologram 28 and generates this real image according to the Lippmann- ' Holography at 23. Similarly in Fig. -4 causes the generation of the virtual image according to the Lippmann holography through the diffracted light 22 also the formation of a real holographic image at 23 by diffraction of light 31. In contrast to the formation of real images at the The process of conventional holography and Lippmann holography is used here, with the reconstruction the hologram in the same position and orientation as the Recording. The resulting images are created in the same location as the original object was created in the. Record according to FIG. 1 was located. In the normal formation of a real image, the HoIo-

grarara by 180 from the position of the layer during the recording be moved. The image forms on the side of the hologram that faces away from the original object lies. Now that the resulting real image is at the location of the

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original. Object is created, it can be done with the The originals are compared and any mismatches used to indicate any lateral misregistration. For registration or precise alignment, the plate can then be moved sideways until the image and the object to coincide.

Such an alignment method can be used in an interference pattern storage system are applied and form an essential part of the storage device. If the information starts with This technique is used to reconstruct the wavefronts from any block of information in one Storage medium with several blocks "as an indicator for the exact alignment. Such a technique can also be used for the precise alignment of optical display devices, devices for the manufacture of printed or integrated circuits and for monolithic semiconductor circuits are used.

The storage and readout procedure is also used to display the precise alignment because of the two procedures used

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which is the reconstruction of the images from the interfering Wavefronts takes place. Although the intensity changes, it moves or shifts according to the holography does not reconstruct the image when the hologram is rotated about any axis in the plane of the film. That accordingly the image reconstructed by Lippmann holography, which is formed by the reflection of the zero-order beam, however, moves when the hologram is rotated ". By adjusting the hologram until the collapse of the The exact angular alignment of the hologram takes place in both reconstructed images.

The real images formed by the light 30 (FIG. 3) and 31 (FIG. 4) can also be used in interference pattern storage systems be used. Since the hologram does not need to be reversed, the readjustment of the hologram. simplified. The formation of a real image according to conventional holography requires the inversion of the. Curvature of the illuminating or interrogating radiation compared to the curvature of the original reference radiation during the incident

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/ fs.

drawing. According to the procedure described that is no longer necessary. The readout device can also be at the location of the original information area lie. '"■ ·

According to the above description for Figs. 1-4 belongs to the Recording process the formation of a first interference pattern by holographic processes and the subsequent Formation of a second interference pattern according to Lippmann holography or in reverse order. In each case follows that used for the formation of the second interference pattern Reference beam on the same axis as the original one incident beam to form the first interference pattern. Sine Modification of this technique is also possible. .

Referring to Fig. 5, there is shown an apparatus for directing the reference beam when recording to the rear of the photographic layer around to re-expose the same areas of the layer from the front in a direction only slightly different from the original direction Angle. Every time the reference ray hits the layer again

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hits, it penetrates the same surface or side of the layer to interact with the same signal beam and thus creates a different interference pattern in the same volume of the
photographic layer with the same optical

Information. .

■. · ■. ·. - · ■ ··
The layer 40 lies between the spherical mirrors 41

and 42. The mirror 42 is provided with an opening 43, through which a reference beam 44 falls from a source 45. At the same time, the diffracted light 46 emanates from the object 47. The light 46 is the information-carrying beam which falls on the photographic layer 40. The beam 44 interferes with beam 46 and forms a first interference pattern. The unabsorbed light of the reference ray occurs through the layer 40 as a beam 48, is reflected by the mirrors 41, 42 and strikes again as a beam 49 to the interference with the beam 46. on the layer 40. Not that absorbed light of the beam 49 passes through the layer 40 as a beam 50 passing through the mirror. 41, 42 is reflected and again interferes with beam 46 as beam 51.

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This process continues, with the reference beam around the Layer 40 is redirected around to back into layer 40 to form a new interference pattern with the signal beam 46 to enter. Every time the reference ray enters the photographic layer occurs, this is done by the same Page. The angle of incidence of the reference ray changes at each pass through the layer a little. How often this The process can be repeated depends on the angular resolution of the emulsion, the coherence length of the radiation and the complexity of the mirror system required.

After processing the photographic layer, the hologram thus formed is in the optical system at the same place set where the shift was during the recording »A query beamed from the same place where the source 45 is sent through the developed hologram in the same way as the reference beam in the Record covered. The light that is not diffracted during each passage through the hologram is reflected by the mirror arrangement reflected on the new passage through the hologram.

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Since only ordinary holograms were stored in the photographic emulsion, at point 47 of the
original object with virtual holographic images

• -

of the same optical information. Each virtual image is overlaid by the following virtual images, which results in a significantly greater efficiency of the
Image reconstruction "results in., '. \ ·'

When the signal beam 46. from the other side into the photographic Layer 40 is incident or the reference source is placed on the other side of layer 40 during recording ., all virtual images are generated at the location of the original object according to the Lippmann holography when reading out. When the holographic plate is able to be reversed or the directions of the interrogation beam after recording, accordingly of the description for the system in FIG. 5 are reversed, instead of the original object 47 only real holographic images are generated.

Another modification of the process described

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and des Gerät8 provides a combination of these techniques for a multitude of ordinary holograms to be formed with a multitude of Lippmann holograms, in Fig. 6 the object to be imaged is at 55. Diffracted light from the object 55 forms the information-carrying radiation 56 and is directed onto a photographic layer 57 ... Pie Reference radiation 58 comes from a source 59. Lenses

60 and 61 are with plane mirrors or roof prisms 62

or 63 combined and guide the part of the reference radiation that passed through the layer from the same side from which it emerged, again, back on the shift. The mirrors or prisms and 63k are axially parallel from the optical axis of the system Shifted, as indicated by the digits 65 and 66, rays to an axial shift for the purpose of separating the feedback to reach. ,

During the recording, the beam 56 in the layer 57 interferes with the reference beam 58 which passes through the lens.

61 is focused on the layer 57, and forms a hologram. That part of the reference ray 58 which passes through the layer 57

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passes through, runs as beam 67 through lens 60 and forms the second reference beam 68 with the signal beam 56 a Lippmann hologram. The portion of the beam 68 that. passes through layer 57 becomes beam 69. which re-enters through the mirror surface 63 and the lens 61 as beam 70 and with the signal beam 56 in of the photographic layer 57 forms a second ordinary hologram.

As described in connection with Figure 5, this process can be repeated a number of times being, this number being dependent on the angular resolution of the Emulsion, the coherence length of the radiation and the complexity of the optical system depends. After processing the The photographic layer 57 becomes the hologram thus formed for reading at the same location as the photographic layer before Shift brought. The interrogation beam initially comes from the same location as reference beam 59. Multiple Overlapping virtual images arise at the location of the object 55. These virtual images represent a combination

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the holographic virtual images and the virtual images according to the Lippmann holography.

With the method described, the efficiency when reading out recorded interference patterns because of the multiple use of the interrogation beam or reference beam significantly increased and thereby a larger area of application of recording techniques for interference patterns opened up. The photographic layers used in the embodiment can, for. B. as plates from Type 649-F available from Eastman Kodak. Such emulsions have a high resolution on recording of interference patterns.

Although in the description of the exemplary embodiment Licutwellen of the visible spectrum were used, the invention is by no means restricted to it, but can interference patterns with wavefronts of electromagnetic energy outside this part of the spectrum are also used when these are transverse waves.

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The increase in efficiency through the process,

is best shown by the following numbers. Both ■ |

in the conventional as well as in the Lippmann-HoIo-

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The efficiency is around 4%. If *

Although both methods are used, but this application is not carried out at the same time, the efficiency of the method is even only 3 "Jo. If two holograms or Lippmann holograms are formed by the method described, the efficiency increases to about 6.5% with one possible achievable limit of 16%.

Claims (12)

PATENT CLAIMS 1. Procedure for recording and storing information by means of formed by the superposition of object and reference rays Interference pattern, characterized in that after a first interference occurring in the area of the recording medium, the the part of the reference beam remaining to the object beam at least once again returned to the same area and again brought into interference with the object beam. 2. Procedure for recording and storing information according to Claim 1, characterized in that during the recording in the storage medium (12, 40, 57) at least one additional interference pattern by interference of an information-carrying radiation (10, 46, 56) with a reference radiation (IS, 44, 58) in the same memory area is formed, the reference radiation for the formation which is obtained from the non-diffracted portion of the reference radiation after the first following interference pattern, which is the beam The zeroth order (15, 48, 50, 67, 60) penetrates the storage medium and appears again through optical means (16, 41, 42, 60 ... 63) the same memory area is directed to interfere with the same information-carrying radiation, and that at 9098 ^ 3/1 5OA PO 9-67-09 3 Reading out the information from the storage medium (28, 40, 57) the non-deflected portion (24, 26, 48, ... 51, 67, 69) of the interrogation beam (21, 44, 58) by optical means (25, 41, 42, 60, ... 63) is deflected and directed at least one more time to the memory area, each time the deflected portion the interfering radiation. (22, 30, 31) contributes to the reconstruction of an image (23) of the optical memory contents. 3. Process according to claims 1 and 2, characterized in that during the recording, at least one additional interference pattern is formed in that the non-diffracted portion (15) of the reference beam (13) is reflected in itself and the original direction of incidence is opposite from the rear side as a new reference beam (17) in the storage medium (12). 4. Process according to claims 1 to 3, characterized in that during the recording at least one additional interference pattern is formed in that the non-deflected portion (48) of the reference beam (44) is incident on the storage medium (40) as a new reference beam (49) at an angle that differs from the original direction of incidence. 5. Process according to claims 1 to 4, characterized in that 90 9 8 A3 / 1 5 PO 9-67-093 a series of additional interference patterns during recording is formed in that after each pass of the reference radiation "The portion of the reference radiation not diffracted by the storage medium is directed again at the storage medium. 6. The method according to claim ß, characterized in that the deflected components of the reference radiation each time incident from the same side in the storage medium. 7. The method according to claim 6, characterized in that the deflected Portions of the reference radiation each time from the front, based on the original direction of incidence, into the storage medium and form a plurality of holograms by interference with the information-carrying radiation. 8. The method according to claim 6, characterized in that the deflected Portions of the reference radiation each time from the rear based on the original direction of incidence into the storage medium and form a plurality of Lippmann holograms by interference with the information-carrying radiation. 9. The method according to claim 5, characterized in that the deflected components of the reference radiation alternately from the rear 9098 A3 / 1 504 PO 9-67-093 and from the front, based on the original direction of incidence, fall into the storage medium and by interference with of the information-carrying radiation form a plurality of conventional holograms and Lippmann holograms. 10. A method for reading out the recorded information according to claim 1, characterized in that the part of the interrogation beam remaining after leaving the part of the recording medium to be read out is returned to the same area at least one more time. 11. The method according to claim 1 and 10, characterized in that at reading out the information, the non-diffracted portion of the interrogation beam covers the same path as when the corresponding portion of the reference beam was recorded. 12. The method according to claims 1, 10 and 11, characterized in that that each time the deflected interrogation beam passes through the storage medium, an image of the optical storage content is reconstructed where all these images are superimposed on each other. 909843/1504 PO 9-67-093