A dual-wavelength holographic optical storage optical head objective lens

Abstract

The present invention relates to the field of optical component technology, and more particularly to an objective lens for a dual-wavelength holographic optical storage optical head. The objective lens comprises an aspherical lens and a spherical lens arranged sequentially from the object plane to the image plane, and is designed for operation at dual wavelengths. The optical axes of the aspherical and spherical lenses coincide. The dual-wavelength holographic optical storage optical head objective lens provided by the present invention not only has an entrance pupil diameter of 8.1 mm, but is also designed specifically for holographic optical disc materials, achieving excellent focusing and resolution at both wavelengths on holographic materials. The objective lens consists of only two lenses, is lightweight and compact, and a servo system can drive the movement of the entire objective lens.

Description

Technical Field

[0001] The present invention relates to the technical field of optical elements, and in particular to a dual-wavelength holographic light storage optical head objective lens. Background Art

[0002] With the advent of the big data era, the ability to cost-effectively preserve large amounts of data for an extended period has become a critical requirement in the network information industry. Existing storage technologies, such as semiconductor and magnetic storage, are no longer able to meet the demand for storage capacity and access speeds. While these storage methods are constantly improving, they are approaching their physical limits. High-density, long-life optical storage will play a crucial role in this endeavor.

[0003] Optical discs have evolved through three generations: CDs, DVDs, and BDs. To expand their storage capacity, Japanese BD manufacturers continue to develop and research BDs, extending the BD's two-dimensional storage space in the thickness direction. Companies like Sony and Panasonic have already launched four- and six-layer products. Traditional multi-layer optical disc technology offers the potential for increased storage capacity, but the increased number of layers also increases the difficulty of servo control during reading and writing. Holographic optical storage, on the other hand, offers a high-density, high-speed storage method.

[0004] Holographic optical storage uses holographic methods to record and reproduce information. One type of holographic optical storage is "dual-beam holographic optical storage". This method uses interference between object light and reference light to record interference fringes in the holographic medium. By changing the incident direction of the reference light, different information can be stored in the same position of the holographic medium, thereby achieving high-density storage.

[0005] The objective lens of a holographic optical storage optical head needs to operate at dual wavelengths of 532nm and 650nm, and the root mean square value of the wavefront aberration of the optical head objective lens must be less than 0.07λ. To fit the optical head module, the optical head objective lens needs to be lighter. Currently, common commercial objective lenses on the market cannot meet the working requirements of holographic optical storage optical heads.

[0006] Therefore, those skilled in the art are committed to developing a dual-wavelength holographic optical storage optical head objective lens suitable for holographic optical storage. Summary of the Invention

[0007] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a light-weight and small-volume dual-wavelength holographic optical storage optical head objective lens suitable for dual-beam holographic optical storage.

[0008] To achieve the above objectives, the present invention provides a dual-wavelength holographic optical storage optical head objective lens, which is arranged in sequence from the object plane to the image plane as an aspherical mirror and a spherical mirror, and is used to work at dual wavelengths, and the optical axes of the aspherical mirror and the spherical mirror coincide.

[0009] In a preferred embodiment of the present invention, the aspheric mirror and the spherical mirror adopt a meniscus structure, with the convex surface facing the object plane.

[0010] Preferably, the entrance pupil diameter of the objective lens is 8.1 mm.

[0011] Preferably, the dual wavelengths are 532 nm and 650 nm.

[0012] Preferably, the focal length of the objective lens is 5.98 mm when the operating wavelength is 532 nm, and is 6.10 mm when the operating wavelength is 650 nm.

[0013] Preferably, the image-side numerical aperture of the objective lens is 0.56 when the operating wavelength is 532 nm, and is 0.55 when the operating wavelength is 650 nm.

[0014] Preferably, the working distance of the objective lens is 2.91 mm when the working wavelength is 532 nm, and is 3.00 mm when the working wavelength is 650 nm.

[0015] Preferably, the left curvature radius of the aspheric mirror is 6.785 mm, and the right curvature radius of the aspheric mirror is 13.474 mm.

[0016] The present invention also provides a holographic optical storage device, which adopts the dual-wavelength holographic optical storage optical head objective lens as described above.

[0017] Preferably, it also includes a holographic material, the thickness of the holographic material is 1.18mm

[0018] The beneficial effects of the present invention are:

[0019] 1. The dual-wavelength holographic optical storage optical head objective lens provided by the present invention not only has an entrance pupil diameter of 8.1 mm, but is also designed specifically for holographic optical disc materials, and has excellent focusing effect and resolution at both wavelengths on holographic materials;

[0020] 2. The dual-wavelength holographic optical storage optical head objective lens provided by the present invention consists of only two lenses, is light in weight and small in size, and the servo system can drive the entire objective lens to move.

[0021] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the objective lens structure of a dual-wavelength holographic optical storage optical head according to a preferred embodiment of the present invention;

[0023] Figure 2 is an MTF curve of a preferred embodiment of the present invention;

[0024] Figure 3 FIG. 4 is an MTF curve of another preferred embodiment of the present invention. DETAILED DESCRIPTION

[0025] The following describes several preferred embodiments of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0026] In the drawings, components with identical structures are denoted by the same reference numerals, and components with similar structures or functions are denoted by similar reference numerals. The size and thickness of each component shown in the drawings are arbitrary and are not limited by the present invention. For clarity, the thickness of components in some places in the drawings is appropriately exaggerated.

[0027] like Figure 1 As shown, in a preferred embodiment of the present invention, a dual-wavelength holographic optical storage optical head objective lens is provided. The objective lens comprises an aspherical mirror L1 and a spherical mirror L2, arranged sequentially from the object plane to the image plane, for operation at dual wavelengths. The optical axes of the aspherical mirror L1 and the spherical mirror L2 coincide or nearly coincide. The aspherical mirror L1 has a meniscus structure, with the convex surface facing the object plane. The spherical mirror L2 has a meniscus structure, with the convex surface facing the object plane.

[0028] Commercially available objective lenses on the market cannot meet the system requirements for the optical head objective lens required for coaxial holographic optical storage materials. Coaxial holographic optical storage uses a 532nm operating wavelength, which is sensitive to holographic materials, as recording and reading light, and a 650nm operating wavelength, which is insensitive to recording materials, as servo light. The two types of light are focused on different focal planes of the recording material. The servo system needs to move the objective lens, and the objective lens needs to be lightweight and small. The light beam passes through some optical elements before passing through the objective lens. When the light beam reaches the objective lens, it is relatively wide, and the objective lens requires a certain size of entrance pupil diameter.

[0029] To meet the requirements of holographic optical storage systems, various performance requirements must be met for both reading and recording. In holographic optical storage systems, a light beam passes through several optical components before reaching the objective lens. When the light beam reaches the objective lens, it is relatively wide, requiring a specific entrance pupil diameter. This invention aims to achieve excellent focusing and resolution for holographic recording materials. This dual-wavelength aspheric objective lens for holographic optical storage, composed of one aspheric lens and one spherical lens, operates at wavelengths of 532nm and 650nm. The objective lens has an entrance pupil diameter of 8.1mm.

[0030] The focal length of the objective lens is 5.98 mm when the working wavelength is 532 nm, and is 6.10 mm when the working wavelength is 650 nm; the image-side numerical aperture of the objective lens is 0.56 when the working wavelength is 532 nm, and is 0.55 when the working wavelength is 650 nm; the working distance of the objective lens is 2.91 mm when the working wavelength is 532 nm, and is 3.00 mm when the working wavelength is 650 nm. The working distance is the distance between the rear surface of the objective lens and the holographic recording material, and the objective lens focuses on the holographic recording material.

[0031] The present invention controls structural parameters such as the radius of curvature, glass thickness, air gap, and aspheric cone coefficient through operands in the Zemax OpticStudio optical design software. Glass is replaced in a specified glass library, and a more suitable glass model is optimized and selected. Zemax OpticStudio optical design software is a mature technology in the prior art, and the present invention will not go into details. The optimization method selected is 3 rings and 6 arms, with the point array diagram as the target and RMS as the reference for optimization. By continuously correcting and balancing aberrations and changing the required performance weights, an objective lens structure is finally obtained in which various performance indicators and structural parameters meet the technical indicators.

[0032] In a preferred embodiment of the present invention, the specific parameters of the holographic optical storage objective lens are as follows:

[0033]

[0034]

[0035] Among them, standard surface 1 is the left side of the aspheric mirror L1, aspheric surface 2 is the right side of the aspheric mirror L1, standard surface 3 is the left side of the spherical mirror L2, standard surface 4 is the right side of the spherical mirror L2, and standard surface 5 is the surface of the holographic recording material. The thickness of the holographic material is 1.18.

[0036] The parameters of the aspheric mirror in this implementation case are as follows:

[0037] 2Aspherical K＝0.16 R＝13.474 E2＝0.000000000000000 E4＝0.000215100000000 E6＝-0.000002625000000 E8＝0.000000440400000 E10＝-0.000000056810000 E12＝0.000000004328000 E14＝-0.000000000172900 E16＝0.000000000002833

[0038] Depend on Figure 2-Figure 3It can be seen from the MTF curve that the MTF value of the optical head objective lens in this embodiment is close to the diffraction limit at the required 0° field of view and 0.1° field of view.

[0039] Depend on Figure 2-Figure 3 It can be seen from the MTF curve that when the spatial rating is 900pl / mm, the MTF values ​​of the two wavelengths are both greater than 0.4 and close to the diffraction limit, that is, the imaging indicators reach the limit value under ideal conditions, indicating that the imaging quality is excellent.

[0040] The preferred embodiments of the present invention have been described in detail above. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible without inventive effort by those skilled in the art. Therefore, any technical solution that can be derived by one skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A dual-wavelength holographic optical storage optical head objective lens, characterized in that: An aspheric lens and a spherical lens are arranged in sequence from the object plane to the image plane, and are used for dual-wavelength operation. The optical axes of the aspheric lens and the spherical lens coincide with each other. The aspheric lens and the spherical lens adopt a meniscus structure, with the convex surface facing the object plane. The entrance pupil diameter of the objective lens is 8.1 mm. The dual wavelengths are 532 nm and 650 nm. The focal length of the objective lens is 5.98 mm when the operating wavelength is 532 nm and 6.10 mm when the operating wavelength is 650 nm. The parameters of the objective lens are as follows: Among them, standard surface 1 is the left side of the aspheric mirror, aspheric surface 2 is the right side of the aspheric mirror, standard surface 3 is the left side of the spherical mirror, standard surface 4 is the right side of the spherical mirror, and standard surface 5 is the surface of the holographic recording material.

2. The dual-wavelength holographic optical storage optical head objective lens according to claim 1, wherein: The image-side numerical aperture of the objective lens is 0.56 when the working wavelength is 532 nm, and is 0.55 when the working wavelength is 650 nm.

3. The dual-wavelength holographic optical storage optical head objective lens according to claim 2, wherein: The working distance of the objective lens is 2.91 mm when the working wavelength is 532 nm, and is 3.00 mm when the working wavelength is 650 nm.

4. A holographic optical storage device, characterized in that: The dual-wavelength holographic optical storage optical head objective lens as described in any one of claims 1 to 3 is used.

5. The holographic optical storage device according to claim 4, wherein: Also included is a holographic material, the holographic material having a thickness of 1.18 mm.

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