JP2829518B2 - Plastic lens - Google Patents

Description

The present invention relates to a laser for writing and reading optical information on optical information recording media such as compact discs (CDs), optical discs and optical cards. The present invention relates to a small, high-performance plastic lens for an optical information recording medium that focuses light. [Prior art] Conventionally, a holding frame is integrally formed around a lens portion, and various types of plastic lenses having good mountability and handleability to an optical device main body are provided, for example, in Japanese Patent Application Laid-Open No. 61-14617. It has been disclosed. However, in the conventional plastic lens, since an acute angle concave portion is formed at the boundary between the lens portion and the holding frame, the performance of the lens, that is, the high accuracy of the reference point in the measurement of the curvature of the effective lens surface is high. Setting was impossible. Here, it is considered that the lens portion and the holding frame are continuously formed with a smooth curved surface. However, similarly to the above, it is impossible to set the reference point with high accuracy in measuring the curvature of the effective lens surface. . In addition, regarding the moldability, the flow of the injected acrylic resin or the like is disturbed in the acute-angled concave portion at the boundary of the holding frame of the lens portion, causing a phenomenon in which the resin is cooled non-uniformly. Non-uniform density causes local variations in the refractive index, which can have a significant effect on the performance of the lens. The edge may be damaged and there is a problem in durability. Further, since the side surface of the holding frame facing the lens surface is formed as an inclined surface which is expanded outward, both lens surfaces are moved in parallel in the optical axis direction with respect to the holding frame fixed to the optical device body. If it is necessary to perform the molding, the mold must be remade, and the cost tends to be high. [Problems to be Solved by the Invention] In view of the above situation, the present invention is to solve the problems described above, because it is possible to easily set a measurement reference point such as a curvature of an effective lens surface of a molded lens, and A plastic lens with a shape that allows the edges of the effective lens surface to be clearly distinguished so that the laser light incident outside the surface can be reliably cut, and that the resin such as acrylic resin flows well and the refractive index inside the lens unit is uniform. The point is to provide. [Means for Solving the Problems] In order to solve the above-described problems, the present invention provides a method in which a width in a direction orthogonal to the optical axis is provided between a holding frame integrally formed around a lens portion and outer peripheral edges of both effective lens surfaces. A plastic lens for an optical information recording medium comprising a flat portion having a thickness of 0.2 to 0.5 mm and a mounting reference surface provided on the holding frame perpendicular to the optical axis. Further, a cylindrical portion parallel to the optical axis is provided at an inner peripheral end facing the lens surfaces on both sides of the holding frame. [Effect] The plastic lens of the present invention having the above-described contents measures the curvature and minute unevenness of the flat portion formed between the holding frame and the outer peripheral edge of the effective lens surface on both sides when the performance of the effective lens surface is evaluated. Can be used as a reference point. In addition, since the incident light such as laser light applied to the flat portion travels in parallel, it can be completely separated from the focused light applied to the effective lens surface and stray light is completely cut off. Since there is no sharp edge in the mold, the resin flows well and the resin is uniformly injected into the mold. In addition, it is possible to mount the optical pickup device to the optical device main body with high accuracy by using the mounting reference surface provided on the holding frame perpendicular to the optical axis. In the case where a cylindrical portion parallel to the optical axis is provided at the inner peripheral end facing the lens surfaces on both sides of the holding frame, the mold forming the lens surface is moved in parallel in the optical axis direction, and the lens surfaces on both sides are moved. Even if the relative position with respect to the holding frame and the distance between both lens surfaces are changed, no major change occurs in the overall shape. [Examples] Next, the details of the present invention will be further described based on examples shown in the accompanying drawings. FIG. 1 shows a typical embodiment of the present invention, in which A indicates a plastic lens, 1 indicates a lens portion, and 2 indicates a holding frame. In a plastic lens A according to the present invention, a holding frame 2 is integrally formed around a lens portion 1 which is an aspherical lens widely used in the field of microoptics, and an effective lens surface 3 on both sides of the lens portion 1 is formed. An annular flat portion 5 orthogonal to the optical axis 4 is formed between the outer peripheral edge of the holding frame 2 and the holding frame 2, and the light is formed on the inner circumferential end facing the effective lens surfaces 3, 3 on both sides of the holding frame 2. A cylindrical portion 6, 6 parallel to the axis 4 is formed. Here, the width of the flat portion 5 perpendicular to the optical axis 4 is preferably 0.2 to 0.5 mm. The holding frame 2 is formed so as to protrude from the effective lens surface 3 in the direction of the optical axis 4 to form holding rings 7, 7 which also have a protective effect on the effective lens surface 3. A projecting annular mounting ring 8 is formed. In addition, the both flat portions 5,
The interval of 5 is set to be substantially equal to or wider than the width of the mounting ring 8 in the optical axis direction so as to improve the resin flow. Further, a tapered inclined surface 9 which is expanded outward from the outer edge of the flat portion 5 to the cylindrical portion 6 is formed to widen the field of view, and an antireflection film is formed on the inclined surface 9. Thus, it is possible to prevent the incident light irradiated on the inclined surface 9 from being reflected again toward the effective lens surface 3 and becoming stray light. In the plastic lens A of the present invention, as shown in FIG. 2, one holding ring 7 is fitted inside a mounting hole 11 opened in the optical device main body 10, and one side of the mounting ring 8 is provided on a peripheral edge of the mounting hole 11. Or, a mounting reference surface 12 orthogonal to the optical axis 4 formed on both sides.
The laser beam 13 incident from one of the effective lens surfaces 3 is focused on an optical information recording medium 14 such as a compact disk, an optical disk, or an optical card, and the reflected light is again reflected on the effective lens surface. Detected by light detector through 3
It reads optical information. The optical information recording medium
14 laminates a recording film 17 in which pits 16 are formed on tracks by forming fine irregularities or locally changing the light reflectance and the direction of magnetization on a substrate 15 and using it on the upper surface thereof. It has a structure in which a protective film 18 transparent to the wavelength of the laser light to be emitted is laminated. Normally, this type of pickup lens has a very short focal length of several mm, and the spot diameter is set as small as possible for the pit 16 in consideration of the increase in the amount of information, and the spot diameter is adjusted accordingly. Since the light is converged as small as the same, and is set to, for example, 1 μm or less, high accuracy is required for attachment to the optical device main body 10, and further, uniformity of the refractive index in the lens unit 1 is required. For this purpose, the respective optical axes 4 of the both-side effective lens surfaces 3 and 3 are made to coincide with each other, and the thickness d of the lens portion 1 is set with high accuracy. It is required to set the relative position of 3 with high accuracy, and it is necessary to design the shape to be excellent in resin flow, and accordingly, the shape and structure of the mold 19 require special measures. The plastic lens A has been invented so as to satisfy all the above requirements. The mold 19 is a third mold.
As shown in the figure, the divided depth of the divided molds 20 and 21 that can form the outer periphery of the plastic lens A and the cylindrical portion 6 and the insertion depth of the circular holes 22 formed in the divided molds 20 and 21 can be adjusted with high precision. And a concave surface 25 corresponding to the effective lens surface 3 is formed at the tip of the core 23, 24, and an annular plane corresponding to the flat portion 5 is formed around the concave surface 25.
26, a tapered surface 27 corresponding to the inclined surface 9 is formed on the outer periphery, and an outer peripheral surface 28 corresponding to the cylindrical portion 6 has a structure in which the outer peripheral surface of the core 23 coincides with the outer peripheral surface. Also,
An injection path 29 for injecting a resin usable as a lens such as an acrylic resin is formed between the split molds 20 and 21 so as to communicate with a portion of the holding frame 2 located on the side surface of the mounting ring 8. Thus, the respective circular holes 22,
The cores 23, 24 are fitted into the core 22, and one of the cores 23 is attached to a portion of the split mold 20 corresponding to the mounting reference surface 12 of the holding frame 2.
While adjusting the insertion depth of the lens unit 1 and adjusting the distance between the other core 24 and the core 23 to set the thickness d of the lens unit 1.
The focus position with respect to the mounting reference plane 12 of the holding frame 2 can be set with high accuracy. And the core 23,2
Since the depth of insertion into the split molds 20 and 21 can be adjusted, the work of optimally setting the plastic lens A at the trial production stage can be performed in an extremely short time, and the holding frame 2 with respect to the mounting reference plane 12 can be adjusted. A minute change of the focal position can be easily performed. As described above, if the holding frame 2 has a shape in which the cylindrical portion 6 parallel to the optical axis 4 is provided at the inner peripheral end facing the lens surfaces 3 on both sides,
The molds for forming the lens surfaces 3, that is, the cores 23 and 24 are moved in parallel in the optical axis direction to adjust the relative positions of the two lens surfaces 3 with respect to the holding frame 2 and the distance between the two lens surfaces 3 and 3. The focus position for lens 2 and the thickness d of lens unit 1 can be set optimally, and when fine adjustment of the mold is necessary after trial production, a change is made to slightly translate lens surface 3 in the optical axis direction. However, it does not cause a significant change in the overall shape. Furthermore, since the tip of the cores 23 and 24 is inserted into the cavity formed by the split molds 20 and 21, the space between the cores 23 and 24 and the split molds 20 and 21, ie, the cylinder Burrs do not occur on the outer edge of the portion 6. [Effect of the Invention] According to the plastic lens for an optical information recording medium of the present invention as described above, the direction orthogonal to the optical axis is between the holding frame integrally formed around the lens portion and the outer peripheral edges of both effective lens surfaces. Since the flat portion having a width of 0.2 to 0.5 mm, and the mounting reference surface of the holding frame are provided so as to be orthogonal to the optical axis, the flat portion has a curvature and a minute size when the performance of the effective lens surface is evaluated. It is possible to attach the plastic lens to the optical device main body with high accuracy by using a reference point for measuring the unevenness and the attachment reference surface formed on the holding frame. In addition, since the incident light such as laser light applied to the flat portion travels in parallel, it can be completely separated from the focused light applied to the effective lens surface and completely cut off stray light. Can be. And since there is no sharp edge in the mold, the resin flow can be well and uniformly injected into the mold, so that the cooling of the resin is performed uniformly, the sink is small, the density and The refractive index can be made uniform. In addition, since a cylindrical portion parallel to the optical axis is provided at the inner peripheral end facing the lens surfaces on both sides of the holding frame, a mold forming the lens surface is moved in parallel in the optical axis direction to form Adjust the relative position to the holding frame and the distance between both lens surfaces,
The focus position with respect to the holding frame and the thickness of the lens portion can be set optimally, and when fine adjustment of the mold is necessary after trial production, a change is made to slightly translate the lens surface in the optical axis direction. Also do not cause a significant change in the overall shape.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of the plastic lens of the present invention, FIG. 2 is an abbreviated partial cross-sectional view showing a use state, and FIG. is there. A: plastic lens, 1: lens part, 2: holding frame, 3: effective lens surface, 4: optical axis, 5: flat part, 6: cylindrical part, 7: holding ring, 8: mounting ring, 9: inclined surface ,Ten:
Optical device body, 11: mounting hole, 12: mounting reference plane, 13: laser beam, 14: optical information recording medium, 15: substrate, 16: pit, 17: recording film, 18: protective film, 19: mold, 20: split mold, 21: split mold,
22: circular hole, 23: core, 24: core, 25: concave curved surface, 26: annular flat surface, 27: tapered surface, 28: outer peripheral surface, 29: injection path.

Claims (1)

(57) [Claims] The width in the direction perpendicular to the optical axis is between 0.2 and 0.5 between the holding frame integrally molded around the lens part and the outer peripheral edges of both effective lens surfaces.
A plastic lens for an optical information recording medium, wherein a flat portion of mm is provided, and a reference mounting surface is provided on the holding frame at right angles to an optical axis. 2. 2. The plastic lens for an optical information recording medium according to claim 1, wherein a cylindrical portion parallel to the optical axis is provided at an inner peripheral end facing both lens surfaces of the holding frame.