CN100437771C - Coaxial read-write lens of holographic optical disk storage - Google Patents

Abstract

The present invention relates to a coaxial read-write lens of a holographic optical disc memory, which belongs to the technical field of optical storage. The optical axes of all devices of the laser read-write lens are on an identical axial line. A spatial light modulator (2) is positioned on the front focal plane of a front element Fourier transform lens (3), the back focus of the front element Fourier transform lens (3) is coincident with the front focus of a rear element Fourier transform lens (8), a holographic optical disc (10) is placed near the back focal plane of the front element Fourier transform lens (3), and an area array photocoupling device (9) is positioned on the focal plane of the rear element Fourier transform lens (8). A first annular spherical reflector (5) and second annular spherical reflector (6) form a front focal plane of a lens assembly for placing a random phase plate (4), and a back focal plane is coincident with the back focal plane of the front element Fourier transform lens (3). The present invention can reduce the volume of a holographic optical disc memory, is convenient for developing a single beam read-write system with smaller volume and stronger function, and is conductive to the practicability and the commercialization of a holographic optical disc memory.

Description

Coaxial read-write lens for holographic optical disk storage

technical field

The invention relates to a coaxial reading and writing lens of a holographic optical disc memory, belonging to the technical field of optical storage.

Background technique

As a new type of high-density optical storage system, holographic optical disc memory is being further applied to practical use due to its advantages of large storage capacity, high redundancy, fast data transmission rate and short access time.

In recent years, in addition to photorefractive crystal materials, organic photopolymers have been rapidly developed as volume holographic storage materials, and their physical and chemical properties have been greatly improved compared to before. Because this material is very suitable for Large-area disc material, the cost of mass production is also relatively low, making it more and more likely to develop into a commercial holographic disc similar to traditional CD-ROM and DVD-ROM. With the continuous research of volume holographic storage technology and mechanism by scientific and technological workers in various countries, the coaxial volume holographic storage system using the coaxial object light and reference light has become an important research direction, which can be made into a read-write lens similar to traditional optical discs , reducing the volume of the volume holographic memory is conducive to commercialization.

In order to make the holographic optical disc technology more practical, it is necessary to simplify the reading and writing system and make it compatible with the current optical disc drive. In the common holographic optical disc storage system, the off-axis system of the object light and the reference light needs to divide a beam of light into two beams of light in the optical path structure, each of which takes a different path, and requires an independent lens system, so the structure is relatively complicated and very difficult. Difficult to shrink in size. Therefore, it is necessary to share the same optical path with the signal beam of the object beam and the reference beam (readout beam), and the development of a simple and compact coaxial optical system is an important development direction. At present, even if the system adopts the coaxial system of the object light and the reference light, the object light and the reference light share a pair of Fourier transform lenses. However, according to the theory of volume holographic storage, when the object light and reference light use the same coaxial system of Fourier transform lenses, the angle between the object beam and the reference beam is very small, so the angle selectivity of holographic multiplexing is very poor, which is not conducive to Improve the storage density of holographic discs. Especially for holographic discs made of organic photopolymer materials, it is difficult to make very thick media, so the angle selectivity is even worse. Therefore, it is necessary to design a coaxial laser reading and writing lens that can realize the coaxiality of the object light and the reference light, and it is also necessary to solve the problem that the angle between the two beams is too small, so as to improve the storage density of the holographic disc and move toward practical use. .

Contents of the invention

The purpose of the present invention is to solve the problem that the volume of the off-axis optical system of the object light and the reference light of the holographic disc storage proposed above is too large and the angle selectivity of the object light and the reference light sharing a pair of Fourier transform lenses is too small to affect the angle selectivity The problem is to propose a coaxial holographic disc laser reading and writing lens using a circular spherical mirror, which can not only effectively reduce the size of the optical system of the holographic disc storage, but also increase the angle between the object light and the reference light, and effectively improve the holographic Storage angle selectivity improves storage density.

The invention adopts the technology of phase encoding on the reference light, which can further improve the selectivity and suppress the crosstalk noise in storage multiplexing.

The specific structure of the coaxial reading and writing lens of the holographic optical disc memory designed by the present invention is shown in FIG. 1 . The laser reading and writing lens 11 of the present invention consists of a spatial light modulator 2, a front group Fourier transform lens 3, a random phase plate 4, a first annular spherical reflector 5, a second annular spherical reflector 6, a stray light stop 7, a rear It consists of a group of Fourier transform lens 8 and an area array photoelectric coupling device 9, and the optical axes of all devices are on the same axis. Wherein the spatial light modulator 2 is located on the front focal plane of the front group Fourier transform lens 3, the rear focus of the front group Fourier transform lens 3 coincides with the front focus of the rear group Fourier transform lens 8, and the holographic disc 10 is placed on the front group Fourier transform lens 8. Near the back focal plane of the lens 3 , the area array photocoupler 9 is located on the back focal plane of the rear Fourier transform lens 8 . The first annular spherical reflector 5 and the second annular spherical reflector 6 form the front focal plane of the lens group to place a random phase plate 4, and the rear focal plane coincides with the rear focal plane of the front group Fourier transform lens 3.

When recording a hologram, the center of a collimated laser beam 1 that has been expanded and collimated is used as the object beam and irradiated on the spatial light modulator 2 to load the image information to be stored, and then pass through the front group of Fourier transform lenses After 3, make the object beam 20 form a spectral surface on the back focal plane of the front group of Fourier transform lenses 3. The central outer annular part of the collimated laser beam 1 is used as a reference light, and after passing through the random phase plate 4, a random phase coded reference light 19 is formed. The reflection mirror 5 is reflected to the surface of the second annular spherical reflection mirror 6 and converged to the focus position of the Fourier transform lens 3 of the front group. This beam of reference light forms an interference hologram with the zero-order spectrum of the object beam on the back focal plane of the front group Fourier transform lens 3, and the holographic disc 10 is placed near the back focal plane of the front group Fourier transform lens 3, and the interference hologram Record it and realize coaxial holographic storage.

When data is written and read out in the coaxial holographic storage, the reference light shutter 13 and the object beam shutter 17 correspond to the effective apertures of the reference beam and the object beam respectively to control the opening and closing of the object beam and the reference beam. When writing, both the reference light shutter 13 and the object beam shutter 17 are open, and when reading, the object beam shutter 17 is closed, and the reference light shutter 13 is open. Irradiate the interference hologram recorded on the holographic disc 10 with reference light, after passing through the rear group Fourier transform lens 8, and make the holographic disc be positioned at the front focal plane of the rear group Fourier transform lens 8, and at the rear focal plane of the rear group Fourier transform lens 8 The area array photocoupler 9 is placed on the position, and the recorded image data information can be reproduced on the surface of the area array photocoupler 9 to realize data readout. The stray light diaphragm 7 is an annular diaphragm composed of a ring-shaped light-absorbing material, which is used to block the reference light passing through the holographic disc 10, that is, to remove the stray light interference formed by the light, and to meet the requirements for reproducing light information. pass.

Wherein, for the collimated laser beam 1 irradiated to the laser read/write lens 11 of the coaxial holographic disc storage, the beam energy or spot area allocated by the object beam and the reference beam each account for half of the collimated laser beam 1 . The image-side numerical aperture difference between the image-side numerical aperture of the lens group composed of the first annular spherical reflector 5 and the second annular spherical reflector 6 and the image-side numerical aperture of the front group Fourier transform lens 3 is between 0.4～0.7, so that after the second The included angle between the converging light beam reflected by an annular spherical mirror 5 and the object beam 20 is between 30°-60°, which can effectively increase the angle between the object light and the reference light, and improve the angle selectivity of holographic multiplexing storage. After the reference light is coded by a random phase plate, the selectivity can be further improved, and the crosstalk noise in storage multiplexing can be suppressed. The random phase plate 4 is located at the front focal plane position of the lens group formed by the first annular spherical reflector 5 and the second annular spherical reflector 6, and the lens group formed by the first annular spherical reflector 5 and the second annular spherical reflector 6 The back focal plane of the front group coincides with the back focal plane position of the Fourier transform lens 3 of the front group.

The holographic disc 10 is located within the front defocus range of 1-5mm on the rear focal plane of the front group of Fourier transform lenses 3, and the material of the holographic disc may be photorefractive crystal or photopolymer.

When the reference beam 19 passes through the first annular spherical reflector 5 and the second annular spherical reflector 6, the two reflectors can completely reflect the annular reference beam without light blocking phenomenon, as shown in FIG. 1 .

The present invention can realize the recording and reading of holograms in the holographic optical disk memory by using the same light beam, effectively utilizes the energy of the same light beam laser, simplifies the traditional off-axis holographic storage optical path, can reduce the volume of the holographic optical disk memory, and is convenient for development A single-beam reading and writing system with smaller volume and stronger functions will help to make the holographic optical disc memory practical and commercial.

Description of drawings

Figure 1, a schematic diagram of a laser read-write lens for a coaxial holographic disc memory;

1. Collimated laser beam 2. Spatial light modulator 3. Front group Fourier transform lens (FTL1) 4. Annular random phase plate 5. First annular spherical mirror 6. Second annular spherical mirror 7. Stray light stop 8. Rear Fourier Transform Lens (FTL2) 9. Area Array Photocoupler 10. Holographic Disc 11. Laser Reading and Writing Lens for Coaxial Holographic Disc Memory 19. Reference Beam 20. Object Beam

Fig. 2, a schematic diagram of the optical system of the coaxial holographic optical disc storage;

12. Laser 13. Reference light shutter 14. Beam expansion filter collimation system 15. Gaussian beam homogenizer 16. First plane mirror 17. Object beam shutter 18. Second plane mirror.

Detailed ways

Preferred embodiments of the present invention are illustrated below in conjunction with the accompanying drawings.

Example:

See Fig. 2, the vertical linearly polarized Gaussian beam coming out from the laser 12 passes through the reference light shutter 13, and then after the beam expansion and filter collimation are realized by the beam expansion filter collimation system 14, the beam is transformed into a Gaussian beam through a Gaussian beam homogenizer 15 Form a light spot with uniform illumination, then pass through the first plane reflector 16, the beam is deflected by 90° and then reaches the second plane reflector 18, wherein the central part of the beam passes through the shutter 17, and then is reflected by the plane reflector 18 to form a collimated laser beam 1. The spot diameter of the collimated laser beam 1 is 55mm. When recording a hologram, the center of the collimated laser beam 1 is used as the object beam, and the spot diameter is 27mm, which is irradiated on the spatial light modulator 2, and the spatial light modulator 2 is located on the front focal plane of the front group Fourier transform lens 3 (front The working focal length is 88.433mm), and the image information to be stored is loaded, and then after passing through the front group Fourier transform lens 3, the object beam 20 forms a spectrum on the back focal plane of the front group Fourier transform lens 3 (back working focal length 41.698mm) noodle. The annular part of the collimated laser beam 1 is used as a reference light, and the diameter of the annular spot is 36mm (inner ring) and 55mm (outer ring). After passing through the random phase plate 4, a random phase coded reference light 19 is formed. The surface of spherical reflector 5, the curvature of this reflector is-72mm, can reflect all reference light to the surface of the second annular spherical reflector 6, by the curvature surface of-258mm of the second annular spherical reflector 6, the reference light Converge to the focus position of the front group Fourier transform lens 3. The converged reference light forms an interference hologram with the zero-order spectrum of the object beam on the back focal plane of the Fourier transform lens 3 of the front group, and the holographic disc 10 is placed near the back focal plane of the Fourier transform lens 3 of the front group to make the interference The hologram is recorded to realize coaxial holographic storage.

When data is written and read out in the coaxial holographic storage, the reference light shutter 13 and the object beam shutter 17 correspond to the effective apertures of the reference beam and the object beam respectively to control the opening and closing of the object beam and the reference beam. When writing, both the reference light shutter 13 and the object beam shutter 17 are open, and when reading, the object beam shutter 17 is closed, and the reference light shutter 13 is open. Irradiate the interference hologram recorded on the holographic disc 10 with reference light, after passing through the rear group Fourier transform lens 8, and make the holographic disc be positioned at the front focal plane (the front working focal length 27.310mm) of the rear group Fourier transform lens 8, in the rear group Fourier transform lens 8 Place an area array photocoupler 9 on the back focal plane position of the conversion lens 8 (the back working focal length is 39.996 mm), and the recorded image data information can be reproduced on the surface of the area array photocoupler 9 to realize data readout.

Attached table is the design parameter of this coaxial lens 11 in the embodiment

Table 1 Basic Design Parameters of Front Group Fourier Transform Lens 3 (mm)

Table 2 Basic design parameters of the front group Fourier transform lens 8 (mm)

Table 3 Design parameters of annular reflector (mm)

Claims (4)

1. The coaxial reading and writing lens of the holographic disc memory, including the spatial light modulator (2), the front group Fourier transform lens (3), the random phase plate (4), the rear group Fourier transform lens (8), and the area array photoelectric coupling Device (9); the spatial light modulator (2) is located on the front focal plane of the front group Fourier transform lens (3), the back focus of the front group Fourier transform lens (3) and the front focus of the rear group Fourier transform lens (8) coincide, the back focal plane of the front group of Fourier transform lenses (3) is located near the holographic disc (10), and the area array photocoupler (9) is located on the back focal plane of the rear group of Fourier transform lenses (8), characterized in that: Including the first annular spherical reflector (5), the second annular spherical reflector (6); wherein, the optical axes of all devices are on the same axis, the first annular spherical reflector (5) and the second annular spherical reflector ( 6) A random phase plate (4) is placed on the front focal plane of the lens group, and the back focal plane coincides with the back focal plane of the front group Fourier transform lens (3). 2. The coaxial reading and writing lens for holographic disc memory according to claim 1, characterized in that it also includes a stray light stop (7) for blocking the reference light passing through the holographic disc (10), located on the holographic disc (10). Between the rear group Fourier transform lens (8). 3. The coaxial reading and writing lens for holographic disc storage according to claim 1 or 2, characterized in that: the rear focal plane of the front group of Fourier transform lenses (3) is located within the range of 1-5 mm in front of the holographic disc (10). 4. The coaxial reading and writing lens for holographic optical disc memory according to any one of claims 1 or 2, characterized in that: it is composed of a first annular spherical reflector (5) and a second annular spherical reflector (6). The difference between the image-side numerical aperture of the lens group and the image-side numerical aperture of the front group of Fourier transform lenses (3) is between 0.4 and 0.7.

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