KR100540700B1 - Objective Lens for Optical-Storage Device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high aperture ratio wafer-based integrated objective lens mounted on a compact optical pickup for recording and reproducing on an optical disk using a semiconductor laser beam.

An objective lens for a wafer-based optical storage device according to the present invention includes a hologram plate having a hologram surface for correcting aberration of an optical system with respect to parallel rays incident from a light source, and a beam passing through the hologram surface of the hologram plate. The upper side hemispherical lens refracted according to the radius, the upper side wafer bonded to the hologram plate to bond and support the upper side hemisphere lens through the hole, and the light irradiated from the hemispherical lens supported on the upper side wafer And a lower side hemispherical lens for refraction to focus on the disk surface, and a lower side wafer bonded along the bottom surface of the upper wafer to bond and support the lower side hemispherical lens through a hole. . Here, the hologram plate, the lens and the structure wafer may be changed in position. In addition, the present invention is a wafer processing step to serve as a spacer to maintain a gap when the wafer is bonded, the step of mounting the ball lens in the hole on the wafer processed from the step, the ball lens seated on the wafer in the step Bonding the ball lens to the wafer using an adhesive means to adhere and fix the wafer to the wafer; and polishing the ball lens to remove unnecessary spherical surfaces of the ball lens seated on the wafer through the bonding step. have. Accordingly, it is possible to provide an ultra-small sized next-generation optical storage device that can be mass-produced with a wafer-based high aperture ratio, high optical characteristics, excellent processability in manufacturing, and the like.

Optical storage device, wafer, objective lens, optical lens, optical pickup

Description

Objective Lens for Optical-Storage Device

1 is a schematic diagram of an optical path of an optical pickup for a general optical storage device;

2 is a view showing the configuration of an objective lens for a conventional ultra-compact optical storage device

Figure 3 shows the configuration of a lens known in the optical communication field

4 is a configuration diagram of the objective lens of the wafer-based form according to the present invention

5 is a configuration diagram of another wafer-based objective lens according to the present invention.

Figure 6 is another wafer-based objective lens configuration in accordance with the present invention

7 is a view for explaining the driving and characteristics of the objective lens for a wafer-based optical storage device according to the present invention

8A to 8D are views for explaining a ball lens wafer manufacturing method in manufacturing a wafer-based objective lens according to the present invention;

* Description of the symbols for the main parts of the drawings *

50: hologram plate 51: holographic surface

52: upper side hemispherical lens 53: hole

54: upper side wafer 55: disk surface

56: lower side hemispherical lens 57: hole

58: lower side wafer 60: adhesive layer

72: space

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high aperture ratio wafer-based integrated objective lens mounted on a compact optical pickup for recording and reproducing on an optical disk using a semiconductor laser beam.

The Blu-ray Disc (BD), which is being developed as a CD, DVD, and next-generation optical storage device, is stored by mounting an NA (Numerical Aperture) 0.85 objective lens and a blue violet laser diode (LD) with a wavelength of 405 nm. As capacity is increasing, and demand for mobile devices such as mobile phones, notebook PCs, and MP3 players is expected to increase, application development as a portable storage device is progressing.

The recently announced 1-inch disk-based 1GB storage class optical storage device has a BD-based standard and presents the visible possibility of ultra-compact optical storage device. However, in order to develop an ultra-small optical storage device, a new pickup assembly capable of securing sufficient performance while being smaller than an existing pickup has to be developed and provided. There was a need.

The conventional technical problems related to the design, structure, and manufacture of an optical lens, which are essential components for implementing such a microscopic optical storage device, will be described with reference to the optical storage device.

The main part of the general optical storage device includes a lens for converting light from LD into parallel light, a beam splitter for spectroscopy of the light passing through the lens, and It consists of an objective lens that focuses the disk surface, and a photodetector lens and a photo detector.

The optical path of the optical pickup for the general optical storage device to which the objective lens is applied is shown in FIG. 1 shows a general optical path of an optical pickup for an optical storage device such as a CD and a DVD. As shown in FIG. 1, the optical path of the optical pickup, that is, the beam 8 from the LD, that is, the laser diode 1, enters the collimating lens 2 and becomes parallel rays. This light beam is transmitted by the beam spectroscopy plate 3 in the advancing direction to focus on the disk surface 7 via the objective lens 4. This light beam is reflected on the disk surface 7 and again in the reverse order through the objective lens 4 and in the beam spectroscopy plate 3 in the reverse order and then again through the objective lens and in the beam splitter plate to reflect the photodetecting lens 5. Through the port detector 6 is converted into a signal.

In the optical storage device as shown in FIG. 1, the beam diameter and the numerical aperture, which are the spot size of the light beam, are described by the following equation.

That is, when λ is the wavelength of the light emitted by LD, n is the refractive index of the disk, and θ is the angle at which the light refracted by the lens is incident on the focal point,

Numerical aperture (NA) = nsinθ

Spot size =

It can be represented as

That is, the spot size can be reduced by increasing NA and decreasing λ, and reducing the spot size can increase the storage capacity by enabling the recording of many recording marks in the same area.

In general, a CD uses an objective lens with an aperture ratio of 0.45 and a wavelength of 780 nm, whereas a DVD uses an objective lens with an aperture ratio of 0.6 and a wavelength of 650 nm, and an objective with an aperture ratio of 0.85 for a next-generation DVD, Blue-lay Disc (BD). A lens and LD wavelength of 405nm are used. Each storage capacity is up to 700MB with a CD on a 12cm single sided disc. DVDs can have more than 4.7GB of storage and BDs up to 27GB.

BD is not only used for desktop and audio video (A / V) such as CDs and DVDs, but also for use in mobile devices such as mobile phones, notebook PCs, and MP3 players that are expected to increase in the future. Application development as a small size and portable optical storage device is in progress.

The ultra-portable optical storage device is a kind of optical storage device that allows recording / playback on a 1-inch-diameter disk using BD's principle of operation and its high storage density to increase portability. In order to develop a new optical pickup that can secure performance while being smaller than conventional pickups, it is necessary to develop an ultra-small objective lens to be mounted on the optical pickup.

At present, such an optical lens for an ultra-small optical storage device has a combination of two aspherical molding lenses and one aspherical molding lens and a spherical molding lens, as shown in FIG. 10) There is a mixed form of one and the etching lens 11 using the MEMS process, in the case of the shape including the molding lens 10, it is not easy to manage the error when manufacturing the aspherical shape, Since the lens must be separately mounted on the mechanical structure 12, a gap may exist between the molding lens 10, the etching lens 11, and the structure 12, which are lens parts, due to deformation due to temperature change in the pickup. It is a cause of deterioration of performance, and in particular, it is difficult to align each lens. As a result, workability depends on the alignment and structure of the lens during actual manufacturing and mass production. Decreases and high quality of the lens produced, so it appears to be produced as a difficult problem.

There is another lens known in the optical communication field. This lens is a wafer-based support structure as shown in FIG. 3, in which the cover glass 20 and the high refractive resin 21 are bonded together, and the lenses L1, L2, and L3 are formed around the high refractive resin 21. It is a lens manufactured by placing a gap 22 for light passing through S1 and S2.

The lens may be regarded as a wafer based lens by combining an etched lens layer for optical communication, but it is difficult to use as a lens of an optical storage device. That is, in the optical storage device, the working distance, which is a distance between the cover glass 29 layer and the lenses L1, L2, L3 and the cover glass 20 layer, is not considered. In this manufacturing method, high curvature (Sag hight; distance from the wafers S1 and S2 substrate to the lens vertex) cannot be obtained, and due to this manufacturing limitation, only the NA 0.7 level is produced.

Accordingly, an object of the present invention is to provide an objective lens that can be applied to a microscopic optical storage device as it is, based on a wafer without mechanical redesign or setting for alignment.

Another object of the present invention is to obtain a suitable optical power and the desired high aperture ratio by using a ball lens and a hologram, while being insensitive to error factors and allowing aberration correction of light diffraction through holograms, which is required in a micro optical storage device. It is to provide an objective lens.

Yet another object of the present invention is to include a spacer function in the wafer to mount the ball lens based on the wafer, thereby eliminating design constraints and reducing the manufacturing process.
An objective lens for an optical storage device according to the present invention for achieving the above object includes a collimating lens for converting light from a light source of a laser diode (LD) into parallel light, and a spectroscopic plate for spectroscopy of light emitted through the lens. And an objective lens for focusing light emitted from the spectroscopic plate onto a disk surface, and a light detecting lens for transmitting light to a photodetector for detecting and converting light incident on the spectroscopic plate into a signal. In the optical pickup for storage devices,

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The objective lens of the optical storage device,

A hologram plate having a hologram surface for correcting aberration of an optical system having parallel light incident from a light source;

An upper side hemispherical lens for refracting a beam passing through the hologram surface of the hologram plate according to a radius of curvature;

An upper wafer adhered to the hologram plate to support the upper hemisphere lens by bonding it through the hole;

A lower hemispherical lens for refocusing the disk surface by refracting light emitted from the hemispherical lens supported on the upper wafer;

And a lower side wafer adhered along a lower surface of the upper side wafer in order to support the lower side hemispherical lens through a hole.
Another objective lens for an optical storage device according to the present invention includes a collimating lens for converting light from a light source of a laser diode (LD) into parallel light, a spectroscopic plate for spectroscopy of light passing through the lens, and the spectroscopy. Light for an optical storage device comprising an objective lens for focusing light from a plate onto a disk surface, and a photodetector lens for transmitting light to a photo detector for detecting and converting light incident on the spectroscopic plate into a signal. In the pickup,

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The objective lens of the optical storage device,                         

An upper hemispherical lens for refracting parallel light incident from a light source according to a radius of curvature thereof;

An upper wafer for bonding and supporting the hemispherical lens through a hole;

A hologram plate having a hologram surface for transmitting a refracted ray through the upper hemispherical lens and correcting aberration of the optical system;

A lower hemispherical lens for refraction of the beam passing through the hologram surface of the hologram plate according to a radius of curvature to focus on the disk surface;

A lower wafer for bonding and supporting the lower hemisphere lens through a hole;

The lower side wafer and the hologram plate are adhered to each other at a constant distance, and an adhesive layer is formed between the hologram plate and the lower side wafer to form an optical path around an optical axis of the upper and lower hemispherical lenses.
Thus, when the hologram and the wafer-based objective lens are configured in the optical storage device, the size can be reduced, and the wafer layers can be assembled at the component level with the alignment error level that can be secured by the lithography process. In mass production, it is more advantageous in terms of mass production than conventional lens processing. In addition, when the lens is manufactured at the wafer-based level, it is possible to overcome the limitation of NA, which has been the mainstream etched lens, by using the ball lens, while satisfying the performance required in the optical storage device, and applying it as the objective lens for the micro optical storage device. This is possible, and can be used as a basic technology to manufacture the module for the optical pickup in the future.

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Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

4 is a wafer-based objective lens according to the present invention. 5 is another wafer-based objective lens configuration according to the present invention, Figure 6 shows another wafer-based objective lens configuration according to an embodiment of the present invention. 7 is a view for explaining the driving and characteristics of a representative wafer-based optical storage device according to the present invention, Figure 8 (a) ~ (d) is a wafer-based objective lens manufacturing in accordance with the present invention Process example of ball lens wafer processing is shown in order.

The objective lens for the optical storage device according to the present invention is combined in a wafer-based form as shown in FIGS. 4 to 6.

That is, a collimating lens that converts light from the light source of the laser diode LD into parallel light, a spectroscopic plate for spectroscopy of the light passing through the lens, and the light emitted through the spectroscopic plate to focus on the disk plane. The present invention relates to a wafer-based optical storage device including an objective lens and a photodetector lens that sends light to a photo detector for detecting and converting light incident on the spectroscopic plate into a signal.

The wafer-based objective lens structure according to the present invention may be composed of one hologram optical element (HOE) plate wafer and a hemispherical ball lens fixed on two wafers as shown in FIG. 4.

Specifically, a hologram plate 50 having a hologram surface 51 for transmitting parallel light incident from a light source and correcting an aberration of the optical system using a diffraction effect, and a hologram surface 51 of the hologram plate 50. The upper side hemispherical lens 52 for refracting the beam passing through the curvature radius, and the upper side wafer bonded to the hologram plate 50 for bonding and supporting the upper side hemispherical lens 52 through the hole 53 ( 54, a lower side hemispherical lens 56 for refracting light emitted from the hemispherical lens 52 supported on the upper side wafer 54 to focus on the disk surface 55, and a lower side hemispherical lens ( In order to bond and support 56 through the hole 57, the lower side wafer 58 adhered along the lower surface of the upper side wafer 54 may be sequentially configured on a wafer basis.

Optionally, the inclination angles of the holes 53 and 57 on the upper and lower wafers 54 and 58 that support the upper and lower hemispherical lenses 52 and 56 are the same inclination angle in the left and right, and the upper and lower sides are the same. The same alignment angle can be set for the hemispherical lenses 52 and 56. Here, the holes 53 and 57 serve as light paths that pass through the lens while supporting the lens. The hole also has a space around the lens, the lower side of which forms a spacer with another neighboring wafer.

In addition, the holes 53 and 57 formed on the upper and lower wafers 54 and 58 are designed to gradually narrow in width toward the lower side, so that the upper and lower hemispherical lenses 52 having different sizes from each other ( 56).

In addition, the size of the upper hemispherical lens 52 and the lower hemispherical lens 52 is larger than that of the lower hemispherical lens 56 under the condition that the shapes of the upper and lower hemispherical lenses 52 and 56 are symmetrical. Can be configured to induce.

Another wafer-based objective lens structure according to the present invention is an objective lens composed of one hologram and two hemispherical ball lenses as shown in FIG. 5, and the hologram is positioned between the two hemispherical ball lenses.

Specifically, the upper side hemispherical lens 52 for refracting parallel light incident from the light source according to its radius of curvature, and the upper side wafer 54 for bonding and supporting the upper side hemispherical lens 52 through the hole 53. ), A hologram plate (50) having a hologram surface (51) for transmitting the refracted light through the upper side hemispherical lens (52) and correcting aberration of the optical system, and a hologram surface (51) of the hologram plate (50). The lower side hemispherical lens 56 for refraction of the beam passing through the curvature radius to focus on the disk surface 55 and the lower side wafer for bonding the lower side hemispherical lens 56 by bonding through the hole 57. 58 and the lower wafer 58 and the hologram plate 50 are bonded at a constant distance to form the optical path 59 around the optical axes of the upper and lower hemispherical lenses 52 and 56. Hologram plate 50 and lower side wafer 58 The wafer-based objective lens may be formed by placing the adhesive layer 60 between the layers.

Here, the shapes of the upper and lower hemispherical lenses 52 and 56 are asymmetric, and the size of the upper hemispherical lens 52 is larger than that of the lower hemispherical lens size 56 to induce the difference in refraction of light. It can be configured to be.

Another wafer-based objective lens structure according to the present invention is the structure of the objective lens consisting of one hologram plate and one hemispherical ball lens as shown in FIG.

Specifically, a hologram plate 50 having a hologram surface 51 for sending parallel light incident from a light source to a lens and correcting aberration of the optical system, and a beam passing through the hologram surface 51 of the hologram plate 50. The hemispherical lens 56 for refraction according to the radius of curvature to focus on the disk surface 55, and the wafer 58 for bonding and supporting the hemispherical lens 56 through the hole 57 to form an optical path. In order, the wafer-based objective lens may be configured.
The characteristics of the objective lens according to the present invention, which are combined in a wafer-based form as shown in FIGS. 4 to 6, are as follows.

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When composed of a hemisphere lens fixed on one hologram plate and two wafers as shown in FIG.

Each layer is bonded to an alignment error level that can be secured by a lithography process, so that the layers can be assembled in the form of an integrated lens, thereby eliminating a separate alignment process.

Compared to the conventional molding lens type processing method, which has to be directly adjusted and assembled for each component in mass production, this structure can be obtained by bonding and cutting in units of wafers. All optical systems for optical pickup can be fabricated on a wafer basis, so that the optical pickup itself can be integrated.

5 is made of one hologram and two hemispherical ball lens, the hologram is a structure located between the two hemispherical ball lens,

Conventional wafer-based lenses for optical communication and optical storage devices are mainly composed of etched lenses using thermal reflow method. The wafer-based lenses manufactured as described above have a NA due to limited curvature as described above. The limit was raised to 0.85.

On the other hand, the wafer-based objective lens as shown in FIG. 5 can achieve NA 0.85 by making optical power required by the radius of curvature of the ball lens by using two spherical hemispherical lenses. In addition, by dispersing the optical power to each of the two ball lenses, it is a structure that is insensitive to the error factors of the light beam.

In addition, in general, the objective lens for the optical storage device must have the required NA, and at the same time, it is essential to correct the aberration of the optical system. In the case of the conventional ultra-small optical storage objective lens, the use of an aspherical lens Although aberration is corrected, in the wafer-based objective according to the present invention as shown in FIG. 5, the hologram plate using the diffraction phenomenon of light plays a role of aberration correction.

In the case of the objective lens structure consisting of one hologram plate and one hemispherical ball lens as shown in FIG.

When manufacturing a hemispherical ball lens wafer, a spacer is required to maintain the distance between the wafers. In the conventional manufacturing method, the bonding material is used to play the role of a spacer, but in such a case, only about 5 μm of space can be secured and the design is limited, and a separate spacer layer is added to overcome this problem. Space is secured. On the contrary, when the objective lens having the structure as shown in FIG. 6 is included, a spacer function can be included in the fused silica wafer on which the lens is to be mounted, which is an advantageous advantage of overcoming the constraints of the design and at the same time reducing the process. Has

Referring to FIG. 7, the driving principle and characteristics of the objective lens for the micro-optical storage device according to the present invention are as follows.

The incident parallel light passes through the hologram plate 50, which is a fused silica wafer, and passes through the optical component hologram surface 51 using the diffraction phenomenon. At this time, the diameter of the incident light bundle is adjusted to a desired size by the metal film aperture. As the light passes through the hologram surface 51, the light beam is designed to correct the aberration of the optical system so as to satisfy the performance required when the final disk surface 55 is focused. The beam passing through the hologram surface 51 passes through the first upper side hemispherical lens 52. At this time, the light beam is refracted according to the radius of curvature of the lens, and the refracted light beam is transmitted again to the lower hemispherical lens 56 and then refracted again, eventually having a thickness of 0.1 mm and having a disk surface 55 made of polycarbonate. Will come into focus. The upper and lower wafers 54 and 58, which are fused silica wafers, serve to fix the upper and lower hemispherical lenses 52 and 56, and serve as spacers to maintain the distance between the wafers and to support the structure. do.

As described above, in the case of the objective lens of FIG. 4 based on three wafers combined, each of the layers may be manufactured in units of wafers, bonded through an alignment process, and then integrally manufactured. The objective lens according to the present invention is divided into a hologram plate portion and a hemispherical lens portion to perform different functions, and the hologram plate serves to correct aberration of the entire lens and is processed by engraving a hologram pattern on a fuse silica wafer. Hemispherical lenses can produce optical power to achieve NA 0.85.

The upper hemispherical lens 52 has a medium BK7 with a refractive index of 1.52 and a radius of 0.85 mm, and a lower hemispherical lens 56 using LaSF015 with a refractive index of 1.90 and a radius of 0.45 mm. The light path medium through which light passes in each layer is selected to minimize light loss of the lens by maintaining a transmittance of more than 95% at a wavelength of 405 nm. Since the hemispherical ball lens 52 and 56 can be mass-produced, they can contribute to lower production costs, and the limitation of design variables generated due to the difficulty in producing aspheric surfaces causes the hologram plate to correct all aberrations of the optical system. Compensation is possible.

When the hologram has optical power, the dependence of diffraction efficiency on the diffraction angle is increased, and thus optical performance is deteriorated. Therefore, the hologram is designed to minimize the optical power to maintain diffraction efficiency of 95% or more.

In addition, it is possible to realize excellent performance of less than 0.06㎛ when the shift amount of focus is changed only 1nm in the LD wavelength 400nm and 415nm range without the compensation device for the chromatic aberration of the lens in question because of the short wavelength laser diode.

8 is a schematic view showing a ball lens wafer manufacturing method in manufacturing a wafer-based objective lens according to the present invention.

As shown in (a) of FIG. 8, the fused silica wafer 70 is first etched to form holes 71 at a predetermined angle in both directions. At this time, the space 72 below the ball lens is provided to serve as a spacer to maintain the gap when the other wafers are bonded. In the case of the manufacturing method according to the present invention, it has the advantage of having a structure that can include a spacer only by the processing process of the fused silica wafer 70. (b) shows the ball lens 73 placed on the hole. At this time, the inclined surface of the ball lens 73 and the fused silica wafer 70 are in contact with each other. Then, the ball lens 73 is tightly fixed to the fused silica wafer 70 using the adhesive 74 as shown in (c). Bond using a bonding material. Finally, as in (d), unnecessary portions are polished 75 to obtain a desired shape.

As described above, the present invention has an effect that the wafer-based structure can easily overcome various problems caused by the assembly adjustment of the lens manufactured by the existing molding due to the miniaturization of the objective lens in the compact optical storage device. have. In addition, each wafer layer has the effect of enabling the assembly of each component to an alignment error level that can be ensured by the lithography process. In addition, the mass-production process is more effective in terms of mass production than conventional lens-type processing, and it is possible to overcome the limitations of the NA of etching lenses that used to be mainstream when manufacturing lenses at the wafer-based level. It can be applied as an objective lens for ultra-small optical storage device by satisfying the performance required in the optical storage device, and it can be used as an advantageous basic technology for manufacturing the optical pickup module in one piece in the future.

Claims (8)

A collimating lens for converting light from the light source into parallel light, a spectroscopic plate for spectroscopy of the light passing through the lens, an objective lens for focusing the light emitted from the spectroscopic plate on the disk surface, In the optical pickup for the optical storage device consisting of a light detection lens for transmitting the light to the photo detector to detect the light incident on the spectroscopic plate and convert it into a signal, The objective lens of the optical storage device, A hologram plate having a hologram surface for transmitting parallel light incident from a light source and correcting aberration of the optical system by using a diffraction effect; An upper side hemispherical lens for refracting a beam passing through the hologram surface of the hologram plate according to a radius of curvature; An upper wafer adhered to the hologram plate to support the upper hemisphere lens by bonding it through the hole; A lower hemispherical lens for refocusing the disk surface by refracting light emitted from the hemispherical lens supported on the upper wafer; And a lower side wafer adhered along a lower surface of the upper side wafer to support the lower side hemispherical lens through a hole. The method of claim 1, A wafer-based optical storage device characterized in that the inclination angles of the holes on the upper and lower wafers supporting the upper and lower hemispherical lenses are the same inclination angles symmetrically to support the upper and lower hemispherical lenses at the same alignment angle. Objective lens. The method of claim 1, And the hole forms a light path that supports the lens and passes through the lens, and the lower part of the hole has a space for forming a spacer with another wafer adjacent thereto. The method of claim 1, The holes formed on the upper and lower wafers are designed to gradually decrease in width toward the lower side to independently support the upper and lower hemispherical lenses having different sizes, respectively. Objective lens. The method of claim 1, Wafer-based optical storage device, characterized in that the upper side hemisphere lens size is larger than the lower side hemisphere lens size to gradually induce the refractive angle of the light in a condition that the shape of the upper, lower hemisphere lens is symmetrical Objectives. A collimating lens for converting light from the light source into parallel light, a spectroscopic plate for spectroscopy of the light passing through the lens, an objective lens for focusing the light emitted from the spectroscopic plate on the disk surface, In the optical pickup for the optical storage device consisting of a light detection lens for transmitting the light to the photo detector to detect the light incident on the spectroscopic plate and convert it into a signal, The objective lens of the optical storage device, An upper hemispherical lens for refracting parallel light incident from a light source according to a radius of curvature thereof; An upper wafer for bonding and supporting the hemispherical lens through a hole; A hologram plate having a hologram surface for transmitting a refracted ray through the upper hemispherical lens and correcting aberration of the optical system; A lower hemispherical lens for refraction of the beam passing through the hologram surface of the hologram plate according to a radius of curvature to focus on the disk surface; A lower wafer for bonding and supporting the lower hemisphere lens through a hole; A wafer comprising a bonding layer formed between the hologram plate and the lower wafer to bond the lower wafer and the hologram plate at a constant distance and form an optical path around an optical axis of the upper and lower hemispherical lenses. Based optical storage objective lens. delete delete

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