FR2476338A1 - Optical information recording system - produces record of sum of projected image and interference raster of laser beam splits - Google Patents

Abstract

The recording system of an optical information consists of projecting the image of an object, carrying the optical information, on a photosensitive thermoplastic carrier. At the same time, a raster grid with interfering beams is applied and the picture produced is fixed. The interfering beams are controlled in such a way that the recorded picture represents the sum of the projected image and of the superimposed raster grid. This creates a method of recording on a photosensitive thermoplastic carrier colour pictures or holograms of objects which are illuminated by non-coherent radiation.

Description

Information recording process
optics and device for its realization.

 The invention relates to the means for recording optical information, and more precisely, to the methods for recording optical information and to the devices for carrying out these methods.

 The present invention can be applied to record holograms of objects, illuminating them with non-coherent light, for example, to record holograms of a moving object, as well as to record color and black images and white on photosensitive materials, such as photothermoplastic information carriers.

 This invention also finds application in pattern recognition systems, for example, such as computer information input and output devices, in devices for reproducing volume and color images capable of transmitting. quickly information through broadcast channels and store recorded information for an extended period.

 A method of recording optical information is known which consists in: electrically charging a photothermoplastic support with a thermoplastic layer; to project an image onto this support; and screening this image simultaneously by projection onto the support of an interference image formed by two convergent coherent beams. Based on this method, it is easy to develop a device for recording optical information comprising: a system for projecting the image of an object on a photothermoplastic support; loading means; a means of developing the tothermoplastic pho support; and a laser associated with a system of light separators and mirrors intended to produce the fluxes of interference radiation.

 However, such solutions do not make it possible to reproduce, from the optical information recorded, the color images on a photoplastic moplastic support, or to obtain the holograms of the moving objects by illuminating them with non-coherent light.

 There is also known a method of recording holograms in which the image of an object, an image which transfers optical information, is projected in monochromatic light separated from the integral light on a recording medium. A stream of light scattered on the object is divided using a diffraction grating into two streams of coherent interference in space which form a hologram.

 The intensity of the interference radiation fluxes ensured by this known process is insufficient and depends on that of illumination of the object and on the efficiency of the diffraction grating. For a more complicated configuration of the object and for moving objects, this known method does not make it possible to have an interference image. In addition, this method involves more severe exiaences to the fitting of the mounting elements.

 There is also known a method of reproducing color images in which the spatial modulation is obtained by projection onto a photosensitive material of a punctual frame in permanent rotation at a constant angular speed. To avoid blurring of the frame, the projection of an image through it is done by a pulse exposure at intervals corresponding to the rotation of the frame of 300. On the path of the light beam, an opaque disc is introduced having holes of different sizes serving as diaphragms. The disc is rotated in a regular manner and in synchronism with the frame, so that at the time of the pulse exposure, an orifice whose size corresponds to the intensity of the light flux necessary for the exposure in given color is on the beam propagation path. In the same way and simultaneously with the disc and the frame, we put on the beam path a necessary color filter. The regular rotation of the punctual screen during the pulse exposure makes it possible to reduce the time interval between the change of color filters.

But to avoid blurring of the rotating frame, the exposure is to be carried out for a very short time interval, which causes a degradation of the sensitivity of the recording system and requiring higher radiation energies for the exposure. In addition, this method does not allow to reach a high resolution.

 The invention aims to develop a method for recording optical information with a control of the light beams and a device for implementing this method which would make it possible to reproduce on a photothermoplastic support the color images or the holograms of the objects, illuminating them with non-coherent (integral) light.

 According to the invention, the method for recording optical information consists in: projecting the image of an object, an image which transfers the optical information, in full light, onto a photothermoplastic support while simultaneously forming the frame of the image at using interference flow; and to fix the resulting image, and it is characterized in that, first, the interference flows are controlled by obtaining a summary image of the projected image and of the superimposed frame, and then, the image obtained.

 It is advantageous, in order to control the interference flows during the recording of color images, to vary the relative orientation thereof, by adopting the number of orientations equal to that of the color components to be separated from the image to project.

 It is also advantageous, in order to control the quality of the summary image obtained from the projected image and the superimposed frame, to visualize for the purpose of observation this summary image in the plane of the image to be projected, in illuminating it by one of the interference flows.

 To control the interference flows during the recording of the holograms, it is possible to see from the plane of the image the other interference flow, serving as reference flow, using the image displayed by the first interference flow as that of the object, and then record a hologram formed from the interference of the two flows.

 It is then advantageous to vary the intensity ratio of the interference flows.

 According to the invention, the device for implementing the method for recording optical information comprises: a system for projecting the image of an object on a photothermoplastic support; electrical charging means; a means of developing the photothermoplastic support; and a laser with its system of light separators and mirrors intended to form the interference fluxes, and it is characterized in that it additionally comprises a means for controlling the orientation and / or the intensity of the interference flow, in connection with the system of separators and mirrors, and in optical connection with the photothermoplastic support via the development means.

 The essence of the invention also resides in that the device for implementing the method for recording optical information comprises: a system for projecting the image of an object on a photothermoplastic support; means of electric charge and development of the photothermoplastic support; a laser associated with a system of light separators and mirrors to form the interference fluxes; and a means for controlling the orientation and / or the intensity of the interference fluxes, in connection with the system of light separators and mirrors, and in optical connection with the photothermoplastic support via the means of development of this support.

 It is advantageous to provide the orientation control means: with a modulator representing an opaque disc with circular slits offset with respect to each other by an angle of = and a distance of Rn according to the radius, where R is the radius of the disc, n is the number of color components to be separated from the image to be projected from "n" light separators arranged between the photothermoplastic support and the opaque disc; and "n-1" separators arranged between the laser and the opaque disc.

 I1 is possible to place in the plane of the image of the object a second phatothermoçlastic support with its means of electrical charge and development, and to provide in the means for controlling the orientation and / or the intensity of the interference flow a light separator and a mirror arranged so as to be able to separate, from the main laser beam, its fraction having the intensity required, on the one hand, to send it to the second photothermoplastic support, and, on the other hand, to use it as a reference interference flow when recording holograms.

 Such a method of recording optical information and such a device for implementing it make it possible to record with high resolution on a photothermoplastic support the color images or the holograms of the objects by illuminating them with non-coherent light. This method and the device for its implementation make it possible to control the interference flows by adjusting their orientation and / or their intensity.

The intensity control ensures the required ratio between the reference flux and the flux coming from the object when recording holograms, as well as when recording interference bands.

 It should be noted that, for recording the color images in the device in question, high frequencies are used for the space carriers independently of the resolution of the optical elements. Thanks to a regular and synchronous rotation of the discs eliminating in practice an interval of time between the changes of color filters and the change of frame, and ensuring a permanent and not impulse illumination (by cutting), such a device presents a sensitivity of higher enrollment.

The essentials of the invention will be explained in the detailed description which follows of its implementation, with reference to the drawings, where:
- Figure 1 shows a device for carrying out the method of recording optical information, established according to the invention
- Figure 2 shows a modulator established according to the invention.

 The method of recording optical information consists in projecting the image of an object, which transfers the optical information, in full light, onto a photothermal plastic support. Simultaneously with the projection, the frame of 1 image is formed using interference streams, by controlling these to obtain a summary image from the projected image and the superimposed frame and then recording this summary image. .

 To control the interference flows during the recording of color images, the relative orientation of the interference flows is varied, the number of orientations adopted being equivalent to that of the color components to be separated from the image. to project.

 To be able to control the quality of the summary image obtained by superimposing the projected image and the frame, it is displayed in the image plane, illuminating it by one of the interference flows.

 To control the interference flows during the recording of holograms, the second interference flow constituting the reference flow is sent to the plane of the image, using the image displayed by the first interference flow as than that of object.

Then we record the hologram created by the interference of the two streams.

 The intensity ratio of the interference flows is then varied.

EXAMPLE 1
The color images are recorded on a photothermoplastic support composed of a photosensitive layer and a thermoplastic memory layer. We alternately project the image of an object through the blue, yellow and red filters. The projected image of the object is diaphragmed as a function of the value of the luminous flux through each colored filter in order to have the same luminous efficiency of the semiconductor layer in the chosen domains of the spectrum.

 Simultaneously, an interference screen is projected onto the support, the orientation of which varies from 1200 with the change of color filter.

The laser beam is divided into three components for a decrease in intensity to 10- 2 w and cha
cm2 each of the components is directed towards the support by a channel ensuring an orientation corresponding to the given color.

 The repeated change of color filters leading to a variation of the appropriate orientation of the screens during a single exposure makes it possible to record a summary table of the image of the object and its color components determined by the screens .

EXAMPLE 2
A color image is recorded using a recording medium and the order of operations in accordance with example 1. In order to control the quality of the recorded color components of the image of an object reproduced on the support, this image is illuminated using an integral laser beam without decreasing the intensity of the latter. By placing a screen in the domain of the first maximum of the diffraction for each frame, the quality of the reproduced image is evaluated.

EXAMPLE 3
We record a holographic image of an object.

The object illuminated by a non-coherent light is projected on a support. At the same time, a frame is projected onto the support at a spatial frequency close to that which is optimal for the thickness used of the thermoplastic layer. The frame is created by convergence of two components of the laser beam at an angle which corresponds to the spatial frequency adopted. The image is
By increasing the intensity of one of the components of the laser beam, it is used to reproduce the image of the object in the first diffraction maximum. At the same time, the second component of the laser beam having an intensity reduced to that of the luminous flux forming the milk in the first diffraction maximum is sent to the hologram formation plane as a reference beam. the object is obtained as a result of the interference between the component which had reproduced the raster image in the first diffraction maximum and the second component, which is that of reference, the intensities being equal in the recording plane.

 The device for carrying out the method of recording optical information comprises a system (FIG. 1) for projecting the image of an object on a photothermoplastic support 3 as well as a means 4 of electric charge and a means 5 of development of the support 3. The device also comprises a laser 6 associated with a system of separators and mirrors intended to create the interference flows.

 The beam emitted by the laser 6 is divided using separators 7 and 8 into a flow equal in number to that of color components to be separated from the image (FIG. 2 represents three flows). Each of these flows in turn passes through a modulator 9. The modulator 9 (FIG. 2) is an opaque disc 9, with circular slots 92 offset R one relative to the other by n at an angle and by at a radius, where R is the radius of the disc, and n is the number of color components of the image to be projected. The system 1 (FIG. 1) comprises "n" separators and mirrors between the support 3 and the modulator 9, and "n-l" separators between the laser 6 and the modulator 9.

 The modulator 9 is rotated by an electric motor 10 via a kinematic chain 11 (Figure 1). The flows are reflected by mirrors 12, 13, 14 and 15 and directed towards separating elements 16, 17 and 18. The latter divide each of the three flows into two equal flows in intensity. The elements 16, 17 and 18 and mirrors 19, 20 and 21 are then located so that the pairs of fluxes formed are in the planes oriented at an angle of 1200 relative to each other.

 The above-mentioned flux pairs are projected onto the support 3 on the side of the device 5.

 The device 5 comprises an adjustable voltage source 22 and a heating element 23.

 The heating element 23 is made transparent.

Such an embodiment of the heating element 23 in the device 5 allows simultaneously with the projection of interference band systems offset by 1200 one with respect to another, to project the image of the object onto the support 3 2 illuminated by integral light using the system 1 equipped with an objective 24 at the focus of which is placed a disc 25 with colored filters and a disc 26 with diaphragms made in the form of orifices. The system 1 also includes an objective 27 intended to project the object 2 onto the support 3 through the means 4.

 The means 4 comprises a high voltage source 28 having its positive output connected to a glow discharge wire and its negative output to the support 3.

The discs 25 (FIG. 1) and 26 rotate in synchronism with the modulator 9, so that each orientation of the interference bands corresponds to the projection of an image of the object 2 via the appropriate color filter.
The means for controlling the orientation of the interference flows comprises the modulator 9, the separators 7, 8, 16, 17 and 18, the mirrors 12, 13, 14, 15, 19, 20, 21, three separators 16, 17, 18 being mounted between the support 3 and the modulator 9, and two others 7, 8 between the laser 6 and the modulator 9.

 The simultaneous electric charge and development of the support 3 during the projection of the interference band system in combination with the synchronous change of color filters allows the recording on the support 3 of color images of the object 2 illuminated by a light. integral.

 The device also makes it possible to record the holograms of this object. For this purpose, the separator 7 is mounted in the device proposed between the laser 6 and the modulator 9 capable of moving relative to the laser beam and of being entirely removed from the latter during the recording of the holograms. The modulator 9 is in turn fixed in a position ensuring the passage of the laser beam.

 In addition, the device comprises a separator 34 and a mirror 35 which allow the control of the intensity and the orientation of the interference flows.

 An enclosure 30 is mounted so as to be able to separate from the main laser beam its fraction having the intensity necessary to send it using a mirror 31 to a second photothermoplastic support 32 and to use it as an interference flux of reference when recording holograms. The other fraction of the laser beam reached after passing through the separator 30 the mirror 15 and, reflecting thereon, is used to form, using the separator 16 and the mirror 19, the interference fluxes. These interference flows create interference bands in the plane of the support 3.

 Simultaneously with the formation of the interference bands, the image of the object 2 is projected on the support 3 using the system 1 in full light.

 The fixed position of the disc 26, the disc 25 being removed, ensures the passage of the integral light towards the support 3.

 In the case of a moving object, the disc 26 rotates, ensuring a pulsed transmission of light from the object 2 to the support 3. The modulator 9 then remains stationary, not preventing the passage of the laser beam.

 The image projected with the superimposed frame interference bands) is recorded on the support 3. At the same time, one of the interference flows reflected on the separator 16 reads the recorded summary image. As the heating element 23 is transparent, the reproduced image of the object is observed in the first maximums of the diffracted radiation. This makes it possible to control the quality of the summary image constituted by the image to be projected and the frame superimposed during the recording.

a reproduced image is used as an object beam when recording a hologram on the support 32.

 When it is necessary to record the color images on the photothermoplastic support 3, the device operates in the manner described below: the image of the object 2 illuminated by an integral light is projected using the system 1 onto the photothermoplastic support 3 on the side of the thermoplastic layer through the discs 25 and 26 rotated in synchronism from the electric motor 10. In order to be able to vary the time interval between the change of filters and diaphragms and for rotation discs 25 and 26, these are arranged in the focal plane of the objective 24 of the projection system 1. The objective 27 of the projection system 1 forms an image of the object 2 in the plane of the support 3 after the modulation of light by rotating discs 25 and 26.

 The frame is formed for the image of 11 object 2 to be projected on the support 3 using the interference frames (or using three interference band systems) rotated one relative to the 'other of 1200 in the plane of the support (2n, n = 3) and to be projected onto the support 3 through the heating element 23 which is transparent. The system of interference bands serving as frames is formed by virtue of the presence in the device of the laser 6 and of the control of the orientation of the interference flows.

The laser beam 6 is then broken down in the separators 7, 8 into three beams. The beams created by the separators 7, 8 and the beam reflected on the mirror 12 pass successively over time through the modulator 9 rotating in synchronism with the discs 25 and 26.

 After passing through the modulator 9, the coherent light fluxes successively incident over time to the mirrors 13, 14, 15. By reflecting on these, each of the fluxes is broken down in the separators 16, 17, 18 into two fluxes of identical intensity. The pairs of light fluxes created successively over time are sent by the separators 16, 17, 18 and the mirrors 19, 20, 21 to the support 3 through the transparent heating element 23 of the device 5. The separators 16, 17 , 18 and the mirrors 19, 20, 21 are located in space so that the pairs of coherent light flows created are in the planes offset by 1200, with respect to each other (D.

 Each pair of interference flows forms in the plane of the support 3 successively over time the interference band systems rotated by 1200 relative to each other. The frequency of the interference bands is a function of the angle between the interference flows and can be easily varied over a wide range by varying the distance between the separators 16, 17, 18 and the mirrors 19, 20, 21 Each orientation of the interference bands to be projected onto the support 3 through the heating element 23 corresponds to the simultaneous projection onto the support 3 of the image of the object through a determined color filter and a diaphragm on the side of the thermoplastic layer. Synchronous change over time of the orientation of the interference bands and of the colored filters and possible thanks to a synchronous rotation of the disks 25 and 26 and of the modulator 9. The summary image formed on the support 3 by the bands d interference and by the image of the object after it has passed through the colored filters and the diaphragms is recorded on the support in the form of phase relief simultaneously with the projection of the image and of the interference bands, the charge of the support 3 from the glow discharge wire 29 and the thermal development using the heating element 23. The summary image recorded on the support 3 represents the interference bands rotated by 1200, one with respect to Each of these bands is modulated in depth and in density of deformation by the intensity of the image of the object, which had been transferred by the color filters and the diaphragm corresponding to the determined orientation of this band. .

 The restoration of the color image thus recorded on the support 3 then becomes possible using known methods and devices (for example, by the method described in patent No. 1,272,031, Great Britain).

 The application in the device as frames of the interference band systems and the change of the orientation of these in synchronism with the change of color filters thanks to the presence of the control of the appropriate orientation allows 'recording the summary image without interruption in time, this offering a gain in sensitivity compared to known devices. The application in the device of the orientation control means significantly higher its resolving power compared to known devices.

 The proposed device allows visual control of the recording quality of an image during the recording process, as well as the recording of holograms of moving objects. For this purpose, the separator 7 is arranged between the laser 6 and the modulator 9 and can move relative to the laser beam.

 During the recording of a hologram, the separator 7 is located beyond the laser beam, and as it propagates, the latter incides at a separator 34; this is carried out such that in the appropriate position, it separates from the main laser beam its fraction having the required intensity. This fraction of the laser beam is sent by the mirror 31 to the second support 32, its autonomous charging and development means. The disc 25 is removed to allow the integral light of the object 2 to pass.

 The electric motor 10 stops in a position allowing passage through the diaphragm disc 26 of the image of the object 2 projected by the system 1, and through the circular slot 92 of the modulator 9 of the main laser beam.

 The recording of the hologramine of the object is done as described below.

 On the support 3 on the side of the thermoplastic layer is projected using the system 1 the image of the object 2 in full light. At the same time on the side of the heating element 23 is projected onto the support 3 a frame in the form of interference bands. The interference bands are formed as follows. The beam emitted by the laser 6 passes through the separator 30, reaches the mirror 15, is reflected there and is broken down in the separator 16 into two coherent beams to be sent by the separator 16 and the mirror 19 to the photothermoplastic support 3. These flows create interference bands in the plane of the support by interference. Simultaneous projection of the interference bands and the image of the object 2 on the support 3, of the charge of the support 3 to the using glow discharge wire 29 and thermal development ensures the recording on the support 3 of a summary image of the radiation in the form of phase relief. The summary image of the radiation recorded on the support re-presents a diffraction grating modulated in depth and in density of deformation by the intensity of the image of the object.

 To restore and visualize in order to observe the image of the object during its recording, one of the interference fluxes is used, for example, that reflected on the separator 16. This flux, diffracting on the phase diffraction grating modulated by the integral image of the object, forms a coherent image of the object 2 in the first maximums of the diffraction. To record the hologram of the object, one of the diffracted fluxes in the first maximums of the diffraction serves as an object brush, and it is sent to the second photothermoplastic support 32. This is the fraction of the laser beam reflected on the separator 34 which is directed as a reference brush, which had already been explained above, towards the support 36. The recording of the hologram of the object on the support 32 is done during the loading and the development of the latter. below after the start of the formation of the raster image on the support 3.

 Such an embodiment of the optical information recording device makes it possible to reproduce an image of the object 2 in monochromatic light after it has passed through the support 3, this making the resolution of the device higher, as well as ensuring the stability in space of 1 image restored and, therefore, making less stringent the requirements to be imposed on the orientation of the reference beam.

 The method for recording optical information and the device for implementing it make it possible to obtain holograms and color images of objects lit by non-coherent light. as well as controlling the quality of the image when it is saved. it is also possible to record holograms of moving objects. The proposed device has a high resolution and sensitivity.

 As goes without saying, and as it already follows from the foregoing, the invention is in no way limited to those of its embodiments and of application which have been more especially envisaged; on the contrary, it embraces all its variants.

Claims (8)

 1. A method of recording optical information consisting in projecting the image of an object carrying the optical information, in full light, on a photothermoplastic support, simultaneously screening the image using fluxes of interference, and to fix the image obtained, characterized in that, first, we coirniande the interference flows to obtain a summary representation of the projected image and of the superimposed frame, then, we record the summary image obtained.  2. Method according to claim 1, characterized in that during the recording of the color images, the control of the interference fluxes is done by variation of their relative orientation, the number of orientations adopted equivalent to that of color components to separate from the projected image.  3. Method according to claim 1, characterized in that the control of the quality of summary representation of the projected image and of the superimposed frame, is carried out by restoring said summary image to visualize it in the plane of the image to project, illuminating it by one of the interference flows.  4. Method according to claim 3, characterized in that the control of the interference flows during the recording of the holograms is carried out by sending in the plane of the image to be projected the other interference flow, serving as a reference flux, while the image restored by the first interference flux is used as that of the object, and a hologram resulting from the two radiation fluxes is then recorded.  5. Method according to one of claims 3 or 4, characterized in that the intensity ratio of the interference flows is varied.  6. Device for carrying out the method according to claim 1, comprising: a system for projecting the image of an object on a photothermoplastic support, a charging means; a means of developing the photothermoplastic support; and a laser associated with a system of separators and mirrors intended to form the interference fluxes, characterized in that it further comprises a means for controlling the orientation and / or the intensity of the fluxes interference, in connection with the system of separators and mirrors, and in optical connection with the photothermoplastic support via the development means.  7. Device according to claim 6, characterized in that the orientation control means comprises a modulator in the form of an opaque disc with circular slots offset from one another by - in R in radius, where R is the radius of the n angle and of n disc, and n is the number of color components to separate from the image to be projected; "n" separators between the photothermoplastic support and the opaque disc; and "n-l" separators between the laser and the opaque disc.  8. Device according to claim 6, characterized in that, in the plane of the image, there is a second photothermoplastic support associated with its charging and developing means, while the means for controlling the orientation and / or of the intensity of the interference flows comprises a separator and a mirror, arranged so as to be able to separate from the main laser beam the fraction thereof having the intensity required, on the one hand, to send it to the second photothermoplastic support, and on the other hand, to use it as a reference interference flux, when recording holograms.