JPH01500225A - lens device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] lens device Technical field The present invention relates to lenses. More specifically, the present invention provides an apparatus for optically retrieving information. For example, for the small diameter lenses used in compact disc players. related, but not limited to.

Background technology The light from the laser diode is focused on a specific spot on the disk and its reflection Passing the light through the optics and back to the detector means that the compact disc player It is well known for its products such as rollers and similar products. Information contained on the disc The amount is large compared to the size of the disk, and thus other points on the disk The beam of the laser beam should be The beam must be focused very precisely on a specific spot. This is conventionally was done with a somewhat complex series of lenses. These lenses cover the entire surface of the disc. It was difficult to move it so that it looked at the surface. In another aspect, the laser having a single lens that focuses the light from the iode directly onto this point on the disc there was. However, this condition requires that the spacing between the diode and the disk information is correct. The disadvantage is that it must be known with certainty.b The aim of the invention is to provide a lens arrangement that overcomes the above-mentioned drawbacks. Len Another purpose of this is to use one surface, e.g. It is to correct surface aberration and use the other surface to correct coma aberration. (very Since small off-axis angles are used, curvature aberrations are less important. ) present invention Another purpose is to manufacture plastic lenses for use in such lens devices. The objective is to provide a manufacturing method.

Disclosure of invention According to a first feature of the invention, a lens for use in reading optical data is provided. A lens device is provided, which includes a pickup having a finite or infinite conjugate. This pickup lens has a plane lens as one component, and this pickup lens has an ekiben spherical surface. The surface has a basic curve that is spherical, parabolic, or entirely conical, If necessary, it has a maximum of 30 higher order correction terms.

According to a second feature of the invention, a pair of relatively soft metals, such as brass, are provided. The blank is machined with a diamond into the required shape and then machined with a hard material, e.g. nickel. A negative copy is made by electroforming the material, and a pair is made from the negative copy. Replicate one or more dies in a hard material, such as nickel, and replace it with a plastic material. a lens made of plastic material, consisting of using said pair of dies to mold A method of manufacturing is provided.

According to a third feature of the invention, a pair of blanks made of a hard material, for example tool steel, is provided. Materials that can be processed more easily by relatively rough machining with an accuracy of ±1 μm, e.g. electroplating the blank with nickel, and then electroplating the electroplated layer with diamond. Machined to form die faces, a pair of such dies are used to form plastic materials. Another method of manufacturing lenses made of plastic material consists of molding the plastic material. provided.

Preferably, the layer of metal such as electroplated nickel has a thickness of the order of 3 μm. Ru.

According to a fourth feature of the invention, the third feature uses a die made of hardened steel; Made from diamond-processed silicon or ceramics such as sapphire. A ceramic die is inserted and the ceramic die is paired to form the plastic material. Another method of manufacturing lenses made of plastic material consists of using be done.

1st. Second. Third. and the fourth characteristic, the preferred plastic material The material is polymethyl methacrylate.

In environmental conditions where humidity may have a detrimental effect on lens performance, Acrylic acid resin with low water absorption, polycarbonate, polystyrene derivatives, and It is further advantageous to make them from polyolefins such as TPX and their derivatives.

Embodiments of the invention will be described in more detail below by way of example with reference to the accompanying drawings, in which: FIG.

Brief description of the drawing FIG. 1 is a schematic diagram of a prior art lens with two hyperbolic aspheric surfaces; FIG. 2 is a schematic diagram of a lens whose first surface is an ellipse and whose second surface is a hyperboloid, Figure 3 shows another lens that is more elliptic and less hyperbolic than the lens in Figure 2. 5 is a ray diagram of the lens of FIG. 4, and FIG. 6 is a ray diagram of the lens of FIG. The figure is a schematic diagram of a lens based on the finite conjugate principle, and the M7 diagram takes into account higher-order terms. FIG. 8 is a diagram of a lens shown in FIGS. 4 and 5 using an interferometer. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Referring to Figures 2, 3 and 4, plastic material, preferably poly Lenses made of methyl methacrylate or other materials with low hygroscopicity are shown. . This lens has two different aspherical surfaces and can be flattened from a finite or infinite conjugate. The beam is focused precisely and without distortion onto a point.

Figure 4 shows a lens holder that is integrally molded with the abutment body to protect the lens surface. A lens adapted to cooperate with the da is shown. As you can see in Figure 4, the right A locating surface is provided on the side to position the lens from the disc. It can be maintained at a distance of, for example, 2w++i.

Lenses can be formed from dies made in one of a number of ways. Wear. The simplest method is to use a diamond cutter with a nominal accuracy of 0.025 μm. This involves machining twin brass blanks. These are continuations (plastic resin It can be used as a die for molding lenses. However, brass is relatively soft. Due to the high quality, the life of the die is short.

The characteristics of the above-mentioned method are that the brass blank is machined as described above, and then the duplicate and From this blank, a known nickel electroformed replica was made. after that , this copy was used to produce nickel reproductions known as falsifications, This can be used as a die for the molding process. This method uses a large number of die has the advantage that it can be manufactured from a single brass blank.

A variant is to grind a hard tool steel blank relatively roughly, for example with a nominal accuracy of 1 μm, The process involves machining to the approximate contour of the desired surface. Afterwards, this tool steel Electroplating is carried out to a depth of approximately 3 μm using a metal plate. This nickel layer is then replaced with diamond It can be precisely machined into the desired shape with a cutter as described above. This is made It can be used directly as a molding die.

Another variant is made from a ceramic of some kind, for example silicon or sapphire. The process involves machining a hard tool steel around which an inserted insert is mounted. child These are machined directly from diamond and are used as manufacturing guides.

It is preferred for manufacturing that the mold is made to produce multiple lenses.

A lens according to Figure 4 is adapted to focus parallel rays of light onto a point within the material of the disk. ing. Therefore, if disc material is not available, quality control is required for such lenses. It is impossible to test for

The lens shown in Figure 3 has an intermediate infinite conjugate design so that the interferometer can be used as a container in the laboratory. It has become. This is because this lens focuses on the real meaning in space. be.

Pass parallel rays through the lens and position it so that the center of curvature coincides with the focal point of the lens. The test is performed by reflecting from a defined conventional spherical reflector. reflection The light forms fringes at the interferometer's beam splitter and doubles at the lens. road performance.

The lens in Figure 6 is a finite conjugate lens, and the test for this lens is to must have the same taper angle as the light actually used Other than that, the test was the same as the test conducted on the lens shown in FIG.

The lenses in Figures 4 and 5 can be directly added to D+ using the lens method shown in Figure 3. It is not possible. This is because the real focus of the ray is contained within the body of the disk at the rear surface. This is because it is

Therefore, we conducted a simulation experiment with a disk and volume space made of similar materials, and It is necessary to provide a reflective sphere as the back surface of the space. This test plate is shown in Figure 8. Shown below. It is manufactured very precisely in BK7 glass. finite or infinite common Manufacturing lenses in role form are tested directly in this manner.

A preferred light source is a laser diode with a peak wavelength of 780ns. child The refractive index of polymethyl methacrylate for light with a wavelength of is 1.4848.

In an infinite conjugate lens device, the lens is separated from the collimator lens and reaches the pickup lens. The light arriving consists of parallel rays, so the separation of these two lenses is relatively is not important. The pickup lens is a plus that stores data. is maintained at a predetermined distance from the disc made of tick material. This disc is light enough So you can move it to the container.

In order to accurately focus the lens on the data stored on the disk, It is important to note that the focal point of the configuration to be detected has a small spot diameter and that It is important that the wavelength aberration of the spot to be placed is sufficiently low. This way In order to do this, the surface geometry is calculated as follows.

The formula for a conic section is y-2rx+px2-0.

The equation for general aspheric surfaces is: where y is the curve height, X is the radial distance from the axis; p is the eccentricity; r is a tie; A4, A6, A8, AIO, etc. are correction coefficients.

The first term is used in three forms.

a) p-1, which attributes the basic curve of a sphere to the surface, and the higher-order terms attribute the surface to an aspherical surface. Determine the starting point from the ball.

The above equation becomes:

b) p-0, which attributes a parabolic fundamental curve to the surface, and higher-order terms make the surface non-linear. Determine the starting point from the paraboloid to make it spherical.

The above equation becomes:

This can also be expressed as follows.

y = A2 x2 + A4 x' +・----A30x30c) p=n, n is Any value.

This is the most common formula used for the lenses shown in FIGS. 1-4. The value of P changes can move. This formula has a problem in calculation time. That's because P allows me to This is because fluctuations in the curve change the basic curve. In the case of a) and b) where P is a constant, It is the most economical in terms of calculation time.

In Table 2, the rear surface parifocal distance of the embodiment shown in Fig. 4 is calculated assuming that there is no disk. has been done. The spot diameters shown in the table are calculated geometrically and are The results are not taken into account.

Other drawings will be obvious to those skilled in the art.

These drawings for the lens in Figure 4 show that the data is 1.3 behind the front of the disk. It is based on the assumption that the distance will be 1 m, and the refractive index of the material is 1.55.

Obviously, if the disc materials have different refractive indices or thicknesses, the lens The exact parameters may need to be slightly modified.

As an example, the coefficients for various lenses are shown in the table below.

Table 2 Figure 1 Tie point radius R1 (Dragon) 4.42897 Point radius R2 (Dragon) 4.42897 Eccentricity Pi -1,3961 Eccentricity P2 -1.3961 Front diameter (mm) 5 Rear diameter (dragon) 5 Center thickness (1 piece) 3 Edge thickness (+am) 1. 77242 Focal Length FVFL (+11m) lX l0-” Focal length BVFL (am) 3.99996 Cap height 1 (Dragon) 0.61379 Cap height 2 (MM) 0. 61379 focal numerical aperture 2 ．． 5X10' Rear numerical aperture 0.44407 Axial working distance (related) − Perimeter diameter (+am) 9 Wavefront aberration wavelength 5.5364X10" Average spot diameter (μm) - Maximum spot diameter (μm) - Refractive index N at 780 nm - Front coefficient A4 - Front coefficient A6 - Front coefficient A8 - Front coefficient AIO- Rear coefficient 84 - Rear coefficient 86 - Rear coefficient 88 - Rear coefficient BIO- Table 2 (continued) Figure 2 Tie radius R1 (dragon) 4.5 Tie point radius R2 (m) 4.28147 Eccentricity Pi 0.43618 Eccentricity P2 -5.91061 Focal diameter (mm) 5 Rear diameter (mm) 5 Center thickness (section) 3 Edge thickness (m) 1.49612 tA focal length HF V F L (mm) IX 109 Focal length BVFL (m m) 3.98505 key + knob height 1 (mm) 0.72016 cap height 2 (MM) 0.78371 focal numerical aperture 2.5X10” Rear numerical aperture 0.43043 Axial working distance (related) − Perimeter diameter (+n) 9 Wavefront aberration wavelength 0 Average spot diameter (μm) 8.24482X10' Maximum spot diameter (μm) Refractive index N at 0.41457780 ns 1.4848 Front coefficient A4 1 ．． 35043X10-5 front coefficient A6 1.21182X10' front coefficient A8 1.61490X10' Front coefficient AIO-4,72817xlO' Rear coefficient B4 0.1096 Rear coefficient 86 -1.93513X10-3 Rear coefficient B8 3.876 09X10-4 rear coefficient BIO-3, 11299xlO' Table 2 (continued) 3rd figure Tie radius R1 (related) 4 Tie point radius R2 3.62377 Eccentricity Pi 0.43906 Eccentricity P2 -4.73852 Front diameter (angle) 4.67 Rear diameter (related) 3.91441 Center thickness (section) 3 Edge thickness (m+s) 1. 90417 Focal Length FVFL (+sm) 1x 109 Focal length MB V F L (m+s) 3. 39803 cap height 1 (Dragon) 0.70939 Cap height 2 (MM) 0. 50071 Front opening B! 2.335xlO″″9 Rear numerical aperture 0.45938 Axial working distance (mm) - Perimeter diameter (m+w) 9 Back surface aberration wavelength 6.48003X10' Average spot diameter (μm) 6.967 82xlO-3 Maximum spot diameter (μm) Refraction at 0.02384780 nm Rate N 1.4848 Front f) Coefficient A4 2.02566X10-5D surface (7) Coefficient A6 -1.562g2X10'Ft surface (1) Coefficient A8 -7.21 319xlO-6 front 11ij fi AIO-3, 66427xlO-9 rear (7) Coefficient 84 -2.91488X10' rear coefficient R63,37156 xlO-' Rear surface m number 88 - 3.03817xlO-5 rear i? 1j (7) Section f i BIO1,44043X10' Table 2 (continued) Figure 4 Tie point radius R1 (mm) 3. 5 Point radius R2 (ms) 4.17071 Eccentricity Pi 0.43782 Eccentricity P2 -6.02993 Front diameter (■+s) 4.67 Rear diameter (dragon) 3.81635 Center thickness (1m) 3 Edge thickness (section) 1.85678 Focal length MF VF L (am) IX 109 Focal length BVFL (related) 3.32996 Cap height 1 (m) 0.82167 Cap height 2 (M M) 0.32153 Front numerical aperture 2.335xlO' Rear numerical aperture 0.44648 Axial working distance li! (1m) 2.46642 Average spot diameter (μm) 5 ．． 55085X10-3 Maximum spot diameter (μm) 0.026111 Rear surface engagement Number 84 -2.94112X10' Rear coefficient R63,35664xlO' Rear coefficient 88 -2.96989xlO' Rear coefficient BIO1,3954 9xlO’Table 2 (continued) Tie radius R1 (gap) 3.5 Tie point radius R2 (+n) 1.34174694 Eccentricity PI -1,7089 737 Eccentricity P2 -1.95289956 Front diameter (mm) 3. 2 Rear diameter (mm) 2.77357138 Center thickness (m) 3 Edge thickness (related) 2.13276926 Front distance 11i1FVFL (+m) 21. 11 Focal length jtIBVFL (+o+s) 2. 11403851. ”/-9,87201929E-09 Cap height 1 (s+s) 0.367 715424 Cap height 2 (MM) 0.499515317 Front opening number 0.0742899633 Rear numerical aperture 0.468716913 Axial working distance (ms) - Perimeter diameter (■11)9 Wavefront aberration wavelength 0.0114945761 Average spot diameter Cam) 7.74 456871E-03 Maximum spot diameter (μm) 0.06579658757 Refractive index at 80 nm N 1.4848 Front coefficient A4 5.26050195 E-03 Front face coefficient A6 -3.27078542E-04 Front face (7) coefficient A8 2.29074906E-05n surface (1) coefficient AIO-9,47253 292E-07 rear coefficient 84 -8.69752098E-03 rear coefficient Number R62, 43576402E-03 Rear coefficient 88 -5.096786 03E-04 Rear coefficient BIO5, 30418995E-05 One other lens The lens has a first surface that is a modified paraboloid and a second surface that is a sphere.

The coefficients of this lens are as follows.

R1-4,00004423 Pi-0,0 A4 -4.97077925E-03A6 --6.44283909E-0 4A8 -4.63956166E-05AIO--1,98201830E- 06A12-1.38707138E-06A14-1.01685400E- 08A16-1.26126874E-09A18--1.80280027E -011A20-7.51358007E-011A22-1.9787016 2E-011A24-2.89682560E-012A26--2.0033 1516E-013R2-3,6237 P2-1.0 CT-3,0 0D San 4.40 n=1.4848 BVF-3, 39803 Ftc, ihG, 2 Country a style incense cake announcement Enter NNEX τ0 τ5Σ INτ3RNAτrONAL SEA only CHR3P OR Ding ON

Claims (9)

[Claims] 1. Pickup lens with finite or infinite conjugate as one component , and this pickup lens is biaspherical, so these surfaces are It has a basic curve that is spherical, parabolic, or entirely conical, and if necessary, the maximum Used for reading optical data, characterized by having a high-order correction term of 30 terms. lens device used. 2. further comprising a collimator lens disposed near the light source, the pickup lens Claim 1, wherein the lenses are positioned adjacent to the data. The lens device described. 3. The pickup lens has an ellipsoidal first surface facing the collimator lens and , and a second surface forming a hyperboloid facing the data. 2. The lens device according to item 2. 4. A pair of blanks made of relatively soft metal, such as brass, are dabbed into the desired shape. By machining from diamonds and electroforming from hard materials, e.g. nickel. make a negative copy, and from the negative copy, one or more of the paired dies are made of a hard material. The pair of dies is used to replicate materials such as nickel and mold plastic materials. A method of manufacturing a lens made of plastic material, comprising using. 5. Compare a pair of blanks made of hard materials, such as tool steel, with an accuracy of ±1 μm Roughly machined and added a layer of more easily machined material to the blank, The recording layer is machined to form the die face, and a pair of such dies is used to form the plastic. A method of manufacturing lenses made of plastic material, consisting of molding a plastic material. . 6. According to claim 1, wherein said layer is an electroplated metal, for example nickel. The method described in scope item 5. 7. Claims characterized in that the electroplated metal layer has a thickness of about 3 μm. The method described in scope item 5. 8. Additional layers may be made of diamond machined silicon or sapphire. Claim 5, characterized in that the die is made of ceramics. the method of. 9. Claims characterized in that the plastic material is polymethyl methacrylate The method according to any one of the ranges 4 to 8.