JP2001166108A - Optical device, optical system, optical pickup device and molding die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device and an optical system in which scattering of light in a short wavelength region can be decreased, and to provide an optical pickup device in which scattering of light can be decreased even when a light source in a shorter wavelength than a conventional one is used and which can prevent errors for reading and writing. SOLUTION: In the optical element 1, scattering of light in a short wavelength region, particularly <=500 nm, can be decreased by forming optical faces 1a, 1b having <=5 nm center line surface average roughness on the both surfaces. The optical system contains the aforementioned optical element, and the optical pickup device contains the optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element having an optical surface with a defined surface roughness, an optical system including the optical element, an optical pickup device, and a molding die capable of obtaining the optical element. is there.

[0002]

2. Description of the Related Art In recent years, various types of D which are being put into practical use
For high-density recording or reproduction using high-density optical information recording media of the order of gigabytes, such as VD or large-capacity MO, the pickup optical system requires much higher precision and higher functionality than conventional CD optical systems. Is done. In particular, the aspherical objective lens, which is a key part of such a lens, has conventionally been compatible with high NA for high-density recording or reproduction, and improving the precision of the optical surface shape by shortening the wavelength of light from the light source. Have been demanded and improvements have been made.

[0003] The present inventors have conducted intensive studies and have found that sufficient optical performance cannot be obtained only by responding to the conventional high NA and increasing the precision of the optical surface shape. It has been found out that the surface roughness of an optical element such as an objective lens, which has not been conventionally considered, affects its optical performance. In particular, it has been found that when the wavelength of the light source is 500 nm or less, the influence of the surface roughness of the optical element becomes very large, and the influence on the recording and reproduction performance of the optical information recording medium becomes large. Have arrived at the present invention based on these findings. Some considerations in the course of the invention will now be described. In particular, Rayleigh scattering generated by fine particles of the same order of magnitude as the wavelength of light has a large amount of scattered light in the case of coherent light such as laser light, and increases in inverse proportion to the fourth power of the wavelength of the light source used. When the length is shortened, a large amount of light is lost due to minute irregularities or dust on the optical surface. This causes serious malfunctions such as a decrease in contrast of a focal spot due to scattered stray light and an error due to insufficient light quantity when recording or reproducing on an optical information recording medium. As a countermeasure, it is conceivable to use a semiconductor laser with a higher output for the light source.However, a semiconductor laser with a large output is very expensive and has low reliability. Is not a good way. Then, the inventors examined the scattered light intensity at the same surface roughness of the optical surface of the objective lens for Rayleigh scattering. Assuming that 780 nm, which is the wavelength of the light source used for the CD, is 1, 650 nm which is the wavelength of the light source used for the DVD and 50 of the next generation optical disk
The scattered light intensity at the used light source wavelength of 0 nm or 400 nm is shown in Table 1 below.

Table 1 Wavelength (nm) of light source used (nm) 780 650 500 400 Rayleigh scattering (1 time) 2.1 times 5.9 times 14.5 times From Table 1, when the wavelength of the light source used becomes less than around 500 nm, it becomes sharper. It can be seen that Rayleigh scattering increases.
As described above, when the wavelength of the light source is 500 nm or less,
It has been found that the influence of the surface roughness of the optical element becomes very large, and that the influence on the recording and reproducing performance of the optical information recording medium also becomes large.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce scattered light even when an optical element and an optical system capable of reducing scattered light with respect to light having a short wavelength and a light source having a shorter wavelength than conventional light sources are used. An object of the present invention is to provide an optical pickup device capable of preventing a read / write error and a molding die capable of obtaining the optical element.

[0006]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies and as a result, have sufficiently reduced the surface roughness of the optical surface of an optical element such as a collimator or an objective lens used in a pickup optical system. It has been found that it is necessary to reduce the average surface roughness (Ra) of the optical surface for light having a short wavelength of 500 nm or less, particularly 5 nm or less. It has been reached.

That is, the optical element of the present invention is characterized by having an optical surface having a center line surface average roughness Ra of 5 nm or less. In the optical element of the present invention, the center line surface average roughness Ra of at least one optical surface is 5 nm or less (preferably 3 nm or less). Ra is more preferably 5 nm or less (preferably 3 nm or less).

According to this optical element, its optical surface (preferably, both surfaces of the optical surface) has a center line surface average roughness Ra of 5n.
When it is at most m, the scattered light can be reduced particularly with respect to light having a short wavelength of 500 nm or less, so that it is suitable for application to light having a short wavelength of 500 nm or less. Further, the center line surface average roughness Ra of the optical surface is preferably 0.5 nm or more from the viewpoint of manufacturing, and is preferably in the range of 0.5 to 5.0 nm.

Here, the center line surface average roughness Ra will be described. According to JIS B0601-1994, R
a is defined as follows. In a roughness curve measured in the scanning direction and height coordinates of the surface by a stylus, etc., with a straight line or a curve having the geometric shape of the measured surface,
A line set so that the sum of squares of the deviation from the line to the roughness curve is minimized is referred to as an average line of the roughness curve.
Normally, the average line is displayed as a straight line, and the roughness curve is displayed in orthogonal coordinates with respect to the height direction. The lower straight line is referred to as the center line. Note that the center line surface average roughness is synonymous with the arithmetic average roughness specified in JIS.

The center line average surface roughness Ra is obtained by extracting a portion having a measured length 1 from the roughness curve in the direction of the center line, setting the center line of the extracted portion as the X axis, and the direction of the vertical magnification (height direction). When the roughness curve is represented by y = f (x) on the Y axis, the value obtained by the following equation (1) is represented by micrometers.

Ra = (1 / l) ∫ | f (x) | dx (however, the integration range is from 0 to l) (1) Also, since at least one of the optical surfaces is an aspheric surface, The following additional effects can be obtained. That is, most of the methods for forming the optical surface of the molding die of the optical element into an aspherical shape conventionally rely on diamond cutting. According to the conventional diamond cutting, traces of the cutting performed while feeding a diamond tool called a dent remain on the optical surface of the mold, where light scattering occurs. The folds also function as a diffraction grating because they are arranged at equal intervals, so that not only scattering but also diffraction occurred. Therefore, when a strong light was applied to the aspherical optical surface of the conventional molding die and observed, it appeared to be rainbow-colored.
Since the surface roughness of the optical surface of the molding die is almost directly transferred to the optical element injection-molded or injection-compressed by such a molding die, stray light is generated, which is a factor of deteriorating the quality of the optical surface. Was. However, this optical element has a satisfactory level of optical performance that has conventionally been required for the optical element. As a method for improving this, there is a method of polishing a conventional mold optical surface after diamond cutting. However, while maintaining the accuracy of the aspherical shape of the optical surface, the center line surface average roughness Ra is further improved. Is very difficult to be 5 nm or less.

Therefore, the center line surface average roughness Ra of the optical surface of the optical element is clearly defined as 5 nm, and the aspherical mold optical surface is machined to the center line surface average roughness Ra less than this. Is particularly effective in producing an optical element having an aspherical optical surface used for an optical system for a short wavelength light source.

Also, the center line surface average roughness Ra of the optical element
When the optical surface of which is equal to or less than 5 nm is an aspheric surface, the effect of the present invention is remarkable, which is preferable. Further, when both surfaces of the optical surface of the optical element have a center line surface average roughness Ra of 5 nm or less, it is preferable that both surfaces of the optical surface are aspherical.

The optical element of the present invention may be made of a resin material or a glass material. When the optical element is made of a resin material, the optical surface of the molding die is
90% or more of them are formed by diamond cutting. Therefore, the above-mentioned folds are likely to be generated on the optical surface of the mold by cutting, which may cause scattering and diffraction, but by forming the optical surface mold quantitatively managing the surface roughness described above, An optical element made of a resin material having an optical surface with a center line surface average roughness Ra of 5 nm or less can be obtained.

In this case, the resin material is preferably a thermoplastic resin, a thermosetting resin or a photo-curable resin. Examples of a molding method using these resin materials include, but are not limited to, injection molding, injection compression molding, heat cycle molding, cast molding, and the like. In particular, when molded by injection molding, it is preferable in that it can be easily manufactured and the production cost can be reduced, and when molded by injection compression molding, the molding surface of the mold is higher than the optical surface of the optical element. This is preferable because it can be transferred and molded with high precision.
Further, according to the heat cycle molding, it is possible to transfer and mold with higher precision by changing the temperature of the molding die.

Here, the thermoplastic resin has a property of softening upon heating to exhibit plasticity, and solidifying upon cooling,
It is a resin material that accounts for the majority of optical elements made of conventional resin materials, for example, polystyrene, acrylonitrile styrene, polymethyl methacrylate, polycarbonate,
Examples include, but are not limited to, polyolefins, amorphous polyolefins, norbornene-based resins, and the like.

The thermosetting resin has the property of forming a network structure by heating, becoming three-dimensional and becoming an insoluble and infusible resin, and having the property of not being softened again by heating once cured.
Examples include, but are not limited to, epoxy resins, acrylate resins, methacrylate resins, styrene resins, urethane resins, and the like. Conventionally, glass has been used as a material for optical surface molding dies for thermosetting resins, and glasses have been used for eyeglasses, etc., and soft metals such as aluminum base metal and copper similar to thermoplastic resins and electroless Nickel plating was used. In the former glass mold, an aspherical shape is formed by grinding. In the case of the latter mold,
The optical surface is formed by the diamond cutting described above. In particular, in applications having a short wavelength such as a light source wavelength of 500 nm or less, specific examples of preferable thermosetting resins include UV1000, UV2000, and UV300 manufactured by Mitsubishi Chemical Corporation.
0, RAV-7 manufactured by Mitsui Chemicals, Inc., and Desolite manufactured by JSR, Inc.

The photocurable resin is a resin having a property of starting curing by irradiating ultraviolet rays, and generally the curing speed is accelerated by applying heat. Therefore, even with the same monomer resin, a thermosetting resin and a photocurable resin can be separately formed by selecting a polymerization initiator. Conventionally, an optical element is not made only of a photocurable resin.
It was generally used as a so-called hybrid aspherical lens that forms an aspherical shape with a thickness of about 200 μm. The glass spherical lens that will be the working blank is made by conventional polishing. The aspherical surface shape is made of the above-described mold material or a material that transmits ultraviolet light such as quartz or glass. The method of forming the aspherical optical surface is based on the method described above. Therefore, conventionally, in forming an optical surface of a mold, the surface has not been formed by quantitatively managing the surface roughness independently of the shape accuracy. Specific examples of the photocurable resin material include UV1000, UV2000, and UV3000 manufactured by Mitsubishi Chemical Corporation.
And Kayarad manufactured by Nippon Kayaku Co., Ltd., MR-6 and MR-7 manufactured by Mitsui Chemicals, Inc., and can be cured in about 2 to 3 minutes by optimizing the intensity of ultraviolet irradiation.

In the case where the optical element is made of a glass material, the method of manufacturing the optical element using the glass material is as follows.
There are press molding, grinding, polishing, glass molding, and the like. In particular, when molding by glass molding, the following effects are obtained.

That is, when the optical element is made of a glass material and is manufactured by glass molding, a high heat resistance is required for the mold material, and therefore, difficult-to-process materials such as ceramics and ultra-hard materials are generally selected. It is. In order to make the optical surface roughness of the optical element formed by the glass mold good without scattering, the center line average surface roughness Ra of the optical surface of the mold must also be controlled to 5 nm or less. All of these conventional general mold materials are obtained by sintering powder into a compact, but in the case of ceramic materials in particular, since each particle is crystallized and sintered in a polycrystalline state as a whole, the particles of The structural independence is strong, and even if the optical surface of the conventional mold is polished, grain boundary gaps and dropouts are observed, and small holes called pits are observed on the surface. Of course, the glass lens formed by such a mold has a rough surface on the optical surface, which causes scattering of light used. In particular, when the used light source has a short wavelength of 500 nm or less, the optical surface scattering becomes remarkable, and a light amount loss of several% and stray light occur. Therefore, it is relatively difficult to control the center line surface average roughness Ra of the conventional general ceramic material to 5 nm or less, so that a super hard material having low independence of the grain boundary is employed or the surface is formed by CVD. It is preferable to coat a material having a coefficient of linear expansion close to that of the material and to mold the material, thereby efficiently manufacturing the optical element having the above-described optical surface.

In addition, whether the optical element is made of a resin material or a glass material, at least one of the optical surfaces is not more than 5% of light having a wavelength of at least 400 nm. With such a reflectance, scattered light can be effectively reduced with respect to light having a short wavelength of at least 400 nm. Further, it is preferable that at least one optical surface has a transmittance of 90% or more (more preferably 95% or more) with respect to light having a wavelength of 400 nm.

When at least one of the optical surfaces has a reflectance of 3% or less with respect to light having a wavelength of 300 to 500 nm, scattering of light having a short wavelength such as light having a wavelength of 300 to 500 nm occurs. Light can be effectively reduced. In this specification, the term "reflectance" refers to a reflectance including surface reflection (determined by a difference in refractive index on an optical surface), reflection by scattering, and reflection by diffraction. Further, it is preferable that at least one optical surface has a transmittance of 97% or more for light having a wavelength of 300 nm to 500 nm.

The optical surface of the optical element having a center line average surface roughness Ra of 5 nm or less may be polished, but is preferably not polished. In particular, when the optical element is made of a resin material, it is preferable that polishing is not performed. In addition, when the optical surface of the optical element has an aspherical shape, the shape is easily changed by polishing and the optical performance is easily affected. Therefore, both the optical element made of a resin material and the optical element made of a glass material are polished. It is preferable not to do so. Polishing is usually performed manually, depending on the sensuality of the technician. Polishing as post-processing of cutting and grinding cannot reduce the surface roughness sufficiently, and the working time is very inefficient because it takes almost one hour even for a mold optical surface with a diameter of about 10 mm. is there. In the present invention, “not polished” means that the above-mentioned polishing has not been performed.

The optical element of the present invention is preferably a lens. Further, as the optical element of the present invention, it is also applicable to a diffractive lens or a lens having a step on the optical surface,
In particular, a diffractive lens is preferable because it leads to an improvement in diffraction efficiency. In addition, the following effects can be obtained by using the above-described optical element in the optical system of the optical pickup. The optical element of the optical pickup optical system is required to have a very high precision of the optical surface shape (the shape error of the actual shape with respect to the design shape is 50 nm or less). If the roughness is slightly worse,
A large amount of scattered light is generated, the amount of light for reading and writing pits on an optical information recording medium such as an optical disk to be read / written is reduced, and stray light S
Although the N ratio is deteriorated, in the optical pickup optical system using the above-described optical element of the present invention, the scattered light is reduced and the stray light is reduced. Improve the reading ratio
Write errors can be effectively prevented.

In this case, if the optical element is a collimator lens in the above-described optical pickup optical system, the following effects can be obtained. The collimator lens is disposed relatively close to the light source, and the amount of light loss due to scattering or diffraction is large compared to other optical elements, and the influence on the entire pickup optical system is large. Scattered light and diffracted light on the optical surface of the lens are reduced, so that the condensing intensity on the optical disk can be increased, and for example, the input intensity of the light receiving sensor in the optical pickup device can be increased.

In the above-mentioned optical pickup optical system, if the optical element is an objective lens, scattered light and diffracted light on the optical surface can be reduced, and the SN ratio of the converging point on the optical disk can be improved. At the same time, since the information signal can be clearly picked up from the optical disk, the jitter in the eye pattern or the like is small, the occurrence of a detection error or the like is small, and the pickup performance and its reliability can be improved.

In the above-mentioned optical pickup optical system, when the optical element is an optical element for a sensor, the S / N ratio of a detection signal from the sensor can be kept high, and servo characteristics such as auto focus and tracking are improved.

The optical element as described above has a center wavelength of 500.
When used in an optical pickup device having a light source of nm or less, scattered light can be reduced and read / write errors can be prevented. In this case, the same effect as described above can be obtained by using the optical element for the collimator lens, the objective lens, and / or the optical element for the sensor in the optical pickup optical system of the optical pickup device.

Further, the optical system of the present invention has at least one optical element having at least one optical surface having a center line surface average roughness Ra of 5 nm or less, preferably both surfaces.

According to this optical system, since it has the optical element according to the present invention, it is possible to realize an optical system which can reduce scattered light, particularly for short-wavelength light, to reduce the light amount loss.

In this case, in the above-described optical system, the optical element can be a collimator lens, an objective lens, or an optical element for a sensor.

When the above-described optical system is used for an optical pickup optical system, the same effects as described above can be obtained.

Further, since all the optical elements included in the above-mentioned optical system are optical elements having an optical surface having a center line average surface roughness Ra of 5 nm or less on both surfaces, light of short wavelength can be more effectively obtained. Scattered light can be reduced.

Then, the above-mentioned optical system has a center wavelength of 500.
By using the optical pickup device having a light source having a wavelength of not more than 500 nm, the scattered light is reduced especially for light having a central wavelength of not more than 500 nm, and the S / N ratio of the focal point on the optical disk to be read / written is reduced. It can improve and prevent read / write errors.

According to the optical system having at least one optical element described above, it is possible to realize an optical system capable of reducing scattered light with respect to light having a short wavelength.

Further, the optical pickup device of the present invention has a light source having a center wavelength of 500 nm or less,
It has at least one optical element having at least one optical surface having a center line average roughness Ra of 5 nm or less, preferably on both surfaces. More specifically, an optical pickup device of the present invention for recording and / or reproducing information on an optical information recording medium includes a light source that emits a light beam having a center wavelength of 500 nm or less, and a light beam emitted from the light source. A condensing optical system that condenses light on the information recording surface of the information recording medium (when the optical information recording medium has a transparent substrate, condenses the light on the information recording surface via the transparent substrate), A light detector that detects a light beam reflected by the optical information recording medium or a light beam transmitted through the optical information recording medium. And the condensing optical system or the photodetector has at least one optical element;
The optical element has at least one optical surface having a center line surface average roughness Ra of 5 nm or less. The details of the optical element are the same as described above. Optical information recording media include various conventional CDs, DVDs,
The present invention can be applied to MD and MO, and also to future optical information recording media. In particular, it is applied to optical information recording media using a light beam having a wavelength of 500 nm or less for recording and / or reproducing information. Is preferred. Also, the optical information recording medium may or may not have a transparent substrate on the information recording surface. In addition, a general light receiving sensor can be applied as the photodetector.
D, CCD, CMOS or the like can be used, but is not limited thereto.

According to this pickup device, in particular, scattered light is reduced with respect to light having a short wavelength whose center wavelength is 500 nm or less, and the S / N ratio of a converging point on an optical information recording medium such as an optical disk to be read or written is reduced. It can improve and prevent read / write errors.

In this case, the optical element of the pickup device can be the above-mentioned optical element.

The optical pickup device can be configured to have the above-described optical system. Further, this optical pickup device records and / or records information on an optical information recording medium such as various drivers and players having a spindle motor for rotating a disk-shaped optical information recording medium, an actuator for moving the optical pickup device, and the like. Alternatively, it can be mounted on a playback device.

One molding die of the present invention has a molding surface having a center line average surface roughness Ra of 5 nm or less.
According to this molding die, a molded product having extremely small surface roughness can be obtained.

One molding die of the present invention has an optical surface molding surface having a center line average surface roughness Ra of 5 nm or less. Also, one molding die of the present invention has a first optical surface molding surface having a center line surface average roughness Ra of 5 nm or less;
A second optical surface molding surface is provided so as to face the first optical surface molding surface and has a center line surface average roughness Ra of 5 nm or less. The optical element according to the present invention can be obtained from these molding dies.

The above-mentioned center line surface average roughness Ra is 5
The molding surface having a diameter of not more than nm can be made aspherical. In this case, a molded article having an aspheric surface can be obtained.

The above-mentioned center line surface average roughness Ra is 5
nm or less by making the optical surface molding surface an aspheric surface, or by making at least one of the first optical surface molding surface and the second optical surface molding surface an aspheric surface, An optical element of the present invention having an aspherical surface can be obtained.

Further, the first optical surface molding surface and the second optical surface
By forming both of the optical surface molding surfaces as aspherical surfaces, the optical element of the present invention having both aspherical surfaces can be obtained.

[0045]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a lens molding die according to an embodiment of the present invention, and FIG. 2 is a sectional view of an objective lens having an aspheric surface molded by the molding die of FIG. .

As shown in FIG. 1, the upper mold 11
And a lower mold 12. The molding surface 11a of the upper mold 11 and the lower mold 1 are provided.
The second molding surface 12a corresponds to the shape of the optical surface of the lens 1 to be molded. The lens 1 is formed by pressing the upper mold 11 against the lower mold 12 with, for example, a molten thermoplastic resin between the upper mold 11 and the lower mold 12, cooling, opening the mold, and taking out the lens 1. Can be manufactured.

Lens 1 molded by the molding die of FIG.
As shown in FIG. 2, the optical surface 1a is formed on the molding surface 11 of the upper mold 11.
a, and the optical surface 1 b is formed on the molding surface 12 of the lower mold 12.
a. The optical surfaces 1a and 1b of the lens 1
The molding surface 11a of the upper mold 11 and the molding surface 1 of the lower mold 12 respectively.
2a are formed corresponding to the surface shape and surface roughness, respectively. That is, the surface states of the molding surfaces 11a and 12a are almost directly transferred to the optical surfaces 1a and 1b, respectively.

The lens 1 shown in FIG. 2 includes a first optical disk 5 (which reads information with light from a light source having a wavelength of 500 nm) indicated by broken lines and a second optical disk 6 (a light source having a wavelength of 400 nm) which is thinner than the first optical disk 5. To read information from each optical disk, and to read information from each optical disk.
6 is configured as a common objective lens. Therefore, as shown in FIG. 2, the optical surface 1a of the lens 1 is formed as an aspheric surface as a whole, the shared area 2 is formed near the center of the optical axis, and the dedicated area 3 of the optical disc 6 is It is formed around the boundary region 4. Further, the optical surface 1b of the lens 1 is also formed as an aspheric surface as a whole, though it is gentler than the optical surface 1a.

The two optical surfaces 1a and 1b of the objective lens 1 shown in FIG.
Is molded by a molding die as shown in FIG. 1, and the optical surfaces 1a and 1b of the molded lens 1 are not subjected to post-processing such as polishing, and the center line surface average of the optical surfaces 1a and 1b is obtained. The roughness Ra is 5 nm or less. For this reason, the objective lens 1 can reduce the scattered light on both surfaces with respect to light, particularly to a short wavelength of 500 nm or less.

Next, another lens is shown as a modified example with reference to FIG. This lens 40 is a double optimal substrate thickness lens, and has a first objective lens portion 41 formed at the center.
And an annular phase shifter 42 formed in a groove shape around the
And a second objective lens unit 43 formed on the outer periphery thereof
, And can be shared by optical disks having different substrate thicknesses. Each optical surface 4 of this lens 40
0a, 41a, 42a, and 43a are each formed such that the center line surface average roughness Ra is 5 nm or less. Therefore, the lens 40 can reduce scattered light with respect to light, particularly to short wavelengths of 500 nm or less. .

Optical elements suitable for short-wavelength light such as the lenses 1 and 40 described above are generally molded by injection molding when a thermoplastic resin is used as a molding resin material. Alternatively, a portion may be transferred and molded with high precision by applying a compressive force to the cavity between the upper mold and the lower mold by injection compression molding. Furthermore, a molding method combining a heat cycle of transferring and molding with high accuracy by changing the temperature of the molding die after filling the thermoplastic resin may be adopted. The optical element according to the present invention is an optical element having a surface roughness Ra ≦ 5 nm, particularly 0.5 ≦ Ra ≦ 5 nm, regardless of the molding method. Further, the material of the optical element may be a thermosetting resin or a photocurable resin, which is not limited to the thermoplastic resin, or may be an optical glass. In the case of a thermosetting resin, a molding resin having an optical surface (molding surface) processed in the same manner as the thermoplastic resin is filled with a liquid resin at room temperature.
The optical element can be molded by curing the resin in a molding die heated to about 50 ° C. or kept at a constant temperature.

In the case of a photocurable resin, a part of a molding die is made of a material such as glass that transmits ultraviolet light, and after filling a liquid resin at room temperature into the molding die, it is irradiated with ultraviolet light. And cure to form an optical element.

As described above, even if the type of the resin material is different, the optical element according to the present invention can be obtained by molding without similarly performing post-processing such as polishing.

The optical element according to the present invention can also be obtained without post-processing such as polishing by a glass molding method in which the optical glass is heated and melted and the optical element is molded by pressing.

Next, the center line table of 5 nm or less as described above is used.
Two examples of an optical pickup optical system and an optical pickup device including an optical element having an optical surface with a surface average roughness Ra will be described with reference to FIGS.

An optical pickup device 20 shown in FIG. 8 comprises an optical pickup optical system 21 and a light source 22 composed of a laser diode that emits light having a center wavelength of 400 nm.
And a light receiving sensor 23 composed of a photodiode, and is configured to read information from the optical disk 6 by light having a short wavelength of 400 nm. The optical pickup device 20 is provided with an auto-focus servo mechanism (not shown) so as to move the optical disc 6 in the horizontal direction in FIG. 8 to perform automatic focusing, and to automatically move in the vertical direction in FIG. An auto-tracking servo mechanism (not shown) is provided so as to move to.

The optical pickup optical system 21 includes a diffraction grating 24 for diffracting a laser beam from a light source 22 and a diffraction grating 24.
Splitter 25 that reflects light from the optical disk 6 toward the optical disk 6 and transmits light from the optical disk 6 toward the light receiving sensor 23, a collimator lens 26 that converts the light reflected by the beam splitter 25 into parallel light, and a collimator lens And an objective lens 27 for converging the parallel light from the optical disc 26 onto the optical disc 6.

Of the optical elements 24 to 27 constituting this optical pickup optical system 21, both optical surfaces 26a and 26b of the collimator lens 26 and both optical surfaces 2 of the objective lens 27
The center line surface average roughness Ra of each of 7a and 27b is formed to 5 nm or less.

According to the optical pickup device 20 shown in FIG.
Laser light from the light source 22 is diffracted by the diffraction grating 24, reflected by the beam splitter 25, converted into parallel light by the collimator lens 26, and then focused on the rotating optical disc 6 by the objective lens 27 and collected. The condensed light is reflected from the optical disk 6, and the reflected light follows the reverse path to the above, passes through the beam splitter 25, and
By receiving light at 3 and converting the intensity of the light into an electric signal, information on the optical disk 6 can be read.

In this case, the collimator lens 26 is
2 are relatively close to each other, and the degree of light amount loss due to scattering or diffraction is large as compared with other optical elements, and the influence on the entire pickup optical system is large. Since the center line surface average roughness Ra of 26b is set to 5 nm or less, the generation of scattered light and diffracted light on the optical surfaces 26a and 26b is reduced. The input intensity to the light receiving sensor 23 is also high, and a reading error hardly occurs.

The objective lens 27 has two optical surfaces 27.
a, 27b are formed to have a surface roughness Ra of 5 nm or less, and the generation of scattered light and diffracted light is reduced and stray light is reduced, so that the light condensing intensity on the optical disk 6 is increased and the S / N ratio is improved. Since the information can be clearly read from the device, jitter due to an eye pattern or the like can be reduced, correction of a detection error or the like can be reduced, and pickup performance and its reliability can be improved.

The diffraction grating 24 and beam splitter 25 of other optical elements in the optical pickup optical system 21
Each optical surface may be formed so that Ra exceeds 5 nm. However, if Ra is formed so as to be 5 nm or less, the effect of the present invention can be further obtained.

Next, another optical pickup device will be described with reference to FIG. The optical pickup device 30 is configured as a shared type that can read two different types of optical discs with one device.
A first light source 33 composed of a laser diode emitting light having a center wavelength of 500 nm, a second light source 32 composed of a laser diode emitting light having a center wavelength of 400 nm, and a light receiving sensor comprising a photodiode 34.

When the first optical disk 5 is set, the optical pickup device 30 outputs the wavelength 5 from the first light source 33.
The information is read by light having a short wavelength of
When the optical disk 6 is set, the information can be read by light of a short wavelength of 400 nm in the center wavelength from the second light source 32. The optical pickup device 30 includes an auto-focus servo mechanism (not shown) and an auto-tracking servo mechanism (not shown), as in FIG.

The optical pickup optical system 31 includes a diffraction grating 35 for diffracting the laser light from the first light source 32, and reflects the light from the diffraction grating 35 toward the optical disk 5 or 6 while also reflecting the light from the optical disk 5 or 6. First beam splitter 37 that transmits light toward light receiving sensor 34
A second beam splitter 38 that reflects the laser light from the second light source 33 toward the optical disk 5 or 6 and transmits the light from the optical disk 5 or 6 toward the light receiving sensor 34; A collimator lens 39 for converting the light reflected by the second beam splitter 37 or 38 into parallel light; an objective lens 40 for condensing the parallel light from the collimator lens 39 on the optical disk 5 or 6; A lens 36.
The objective lens 40 can be composed of the one shown in FIG.

Of the optical elements 35 to 40 constituting the optical pickup optical system 31, both optical surfaces 39a and 39b of the collimator lens 39 and both optical surfaces 40 of the objective lens 40
a, 40b and both optical surfaces 36a, 3a of the sensor lens 36;
Each of the center line surfaces 6b has an average roughness Ra of 5 nm or less.

According to the optical pickup device 30 shown in FIG.
When the first optical disk 5 is set in the apparatus, the laser light from the first light source 33 passes through the diffraction grating 35, the first beam splitter 37, the second beam splitter 38, the collimator 39, and the objective lens 40. The light is focused and focused on the rotating first optical disk 5, the collected light is reflected from the first optical disk 5, and the reflected light follows the reverse path to the above, and is reflected by the sensor lens 36. The information on the first optical disk 5 can be read by collecting the light, receiving the light by the light receiving sensor 34, and converting the intensity of the light into an electric signal.

When the second optical disk 6 is set in the apparatus, the laser light from the second light source 32 is rotated via the second beam splitter 38, the collimator 39, and the objective lens 40 to the second rotating optical disk. The light is focused and focused on the optical disk 6, and the collected light is reflected from the second optical disk 6, and the reflected light follows a reverse path to that described above, and is collected by the sensor lens 36 to receive the light. By receiving the light at 34 and converting the intensity of the light into an electric signal, the information on the second optical disc 6 can be read.

In this case, the collimator lens 39 and the objective lens 40 are provided with the respective optical surfaces 39a, 39b, 40a, 40
Since the center line surface average roughness Ra of b is formed to be 5 nm or less, it is possible to obtain the same effect as that of FIG. 8 such that the occurrence of scattered light and diffracted light on each optical surface is reduced and a reading error can be prevented. it can.

The optical surfaces 3 on both outer surfaces of the sensor lens
Since the center line surface average roughness Ra of 6a and 36b is formed to be 5 nm or less, the generation of scattered light and diffracted light in the sensor lens 36 is reduced, the S / N ratio of the detection signal can be maintained high, and autofocusing and tracking can be performed. Servo characteristics such as are improved.

Incidentally, the diffraction grating 34 and the beam splitter 37, which are other optical elements of the optical pickup optical system 31,
Each of the optical surfaces 38 may be formed so that Ra exceeds 5 nm. However, when formed so that Ra is 5 nm or less,
Further, the effects of the present invention can be obtained.

Next, a method for molding an optical element according to the present invention will be described. In FIGS. 1, 2 and 13, the surface states of the molding surfaces 11a and 12a of the molding die are almost directly transferred to the optical surfaces 1a, 1b and 40a to 43a of each lens. Surfaces 1a, 1b, 40a-
The surface roughness of 43a is determined by the molding surfaces 11a and 12a of the molding die.
Depends on the surface roughness. Therefore, first, the problems of the molding die in the conventional molding method will be described in detail below.

In a conventional method for molding the optical surface of an optical element used in a pickup optical system, in a plastic molded lens, an optical surface transfer surface of a molding die manufactured by electroless nickel plating or the like is applied to an ultra-precision lathe. And a diamond tool. In this case, the machined surface roughness is largely governed by four factors: the motion accuracy of the ultraprecision lathe used, the diamond tool accuracy, the cutting conditions, and the mold material.

Next, problems of a method of forming an optical surface (molding surface) of a molding die for molding and transferring an optical surface of a conventional molding optical element will be described.

1. Mold material: Electroless nickel plating (E
NP) Conventionally, the most common optical surface (molding surface) molding die material is an electroless nickel plating (hereinafter referred to as “ENP”) formed on a steel material to a thickness of about 100 μm. It is. The plated layer was turned using a two-axis precision lathe with an R diamond tool having a circular rake face to obtain an optical surface (molding surface) of a molding die. FIG. 10 shows the result of observing the diamond cut surface of ENP with an atomic force microscope (AFM).
m. It can be seen that irregularities and irregularities of several nm are generated on the cutting surface, and the processing on the order of nm is not so completely performed. FIG. 11 shows the state of the cutting edge of the R diamond tool at this time. The left side of FIG. 11 is a flank, and the right side is a rake face. It can be seen that the cutting edge, which would have been sharp in the initial state, has been worn due to much chipping and the cutting edge forming the cutting surface has receded to the center of the tool by about 100 nm. If the R diamond tool is used unmanaged in such a state that the cutting edge retreats unevenly, a high-quality optical surface of the molding die having a small surface roughness corresponding to the initial accuracy cannot be obtained. You can see that. In addition, the tool edge of the R diamond tool is made to be sharp in the initial state, and the mold optical surface (molding surface) having a center line surface average roughness stable over a long period of time is adopted by adopting a mold material having relatively little wear. It can be seen that it can be obtained.

2. R-Round Diamond Roundness of Rake Tool In the above-mentioned R-diamond tool, the roundness of this rake surface is directly transferred by turning as machining optical surface accuracy. It is important to get an optical surface. Generally, in order to improve the tool roundness, the rake face and flank face of the R diamond tool are precisely polished, and a sharp edge without fine chipping on the edge of the cutting edge provides a mold optical surface with good surface roughness. This is a preferable condition. FIG. 12 shows the roundness of the cutting edge of the conventional R diamond tool described above. The abscissa indicates the left and right angles from the center of the rake face circle with the tool center at 0 °. It can be seen that large irregularities are seen in several places, and the cutting edges are irregular. In addition, the roundness of the conventional R diamond tool is at most about 50 nm, but from the viewpoint of forming the optical surface of the optical element into a highly accurate shape, the objective lens for next-generation high-density optical recording. For example, a tool roundness of 30 nm or less is preferable in consideration of other error factors.

3. Machine Tool (Precision Lathe) For the reasons described above, machine tools are required to have a motion accuracy capable of forming a sufficiently small surface roughness. In addition, high machining reproducibility is particularly important for high-precision diamond turning to be significant as a mass production die machining technology. That is,
Machine tools are required to maintain the relative positional relationship between the molding die and the tool with high accuracy without being affected by disturbance factors such as temperature and air pressure, and to be able to achieve ultra-precise motion accuracy with good reproducibility. ing.

In the case where the electroless nickel plating, which is a mold material, is cut by a conventional precision lathe to form the optical surface of the mold, the center line surface average roughness is Ra = 10 to 15
nm. Therefore, the optical surface of the optical element which is molded and transferred by the molding die also has a surface roughness of about this level.
It has not been possible to obtain an optical element having a low amount of scattered light in an optical disk pickup optical system having a next-generation short-wavelength light source such as 0 nm or 400 nm. Further, conventional post-polishing processing, which is mainly performed by hand after cutting, has problems in efficiency and quality in manufacturing a mold while maintaining a constant optical surface accuracy.

As described above, in the conventional molding die machining of an optical element by diamond cutting, an optical element of a pickup optical system using a short-wavelength light source is obtained with an optical surface with little scattering while maintaining high optical surface shape accuracy. It was very difficult.

As described above, according to the study of the present inventor, when the wavelength of the light source used is 400 nm, the amount of scattered light is increased by about one digit as compared with the conventional CD level. It has been found that the surface roughness must satisfy at least Ra (center line surface average roughness) ≦ 5 nm (preferably 3 nm or less). The surface roughness of the optical surface (molding surface) is considered to be mainly due to the above-mentioned four factors being interconnected. Therefore, high-precision molding die optical surface processing to obtain an optical surface with less scattering is realized. In
It is preferred that improvements be made concurrently across all of these factors.

As a result of studying the problems of the prior art as described above, the present inventors have made the following ingenuities in parallel so that lenses and the like as shown in FIGS. The center line surface average roughness Ra is 5 nm for molding.
By far exceeding the following, an extremely smooth optical surface (molding surface) such as an aspheric surface of a molding die, which was Ra ≦ 1 nm, was obtained.

1. As a mold material, a conventional steel material which has been subjected to electroless nickel plating with a thickness of about 100 μm on a conventional steel material is used. As shown in FIG. In the state where the cutting is not performed, the ultra-precision diamond tool in which the roundness of the tool rake face is small and the die machining using the ultra-precision lathe are used. An extremely smooth cutting surface was realized, and high-precision mold processing was realized.

2. About ultra-precision diamond tools 5
As a result of accurately grasping and improving the initial rake face roundness using a tool roundness measuring device with a nm resolution, as shown in FIG. 5, an ultra-precision R having a tool rake face roundness of 30 nm or less was obtained.
Diamond tools can now be selected.

3. For ultra-precision lathes, shaft resolution 1n
m, Ra = 0.8 n when the aluminum alloy S3M was cut in a plane with a slide table rigidity of 1000 N / μm.
An ultra-precision lathe capable of obtaining m, Rtm = 4.9 nm was prepared. In addition, a basic design was performed so that the drift of the tool position due to environmental changes was minimized, and as shown in the interferometer photographs of the spherical cutting surface after machining in FIGS. 6 and 7, an R3 mm concave spherical surface (normal angle 48 °) ) Could be processed for 6 hours, and a high processing reproducibility of a processing shape change of 50 nm or less was realized at a room temperature change of 0.5 ° C. By the various measures described above, the center line surface average roughness Ra of the molding die can be reduced, and an optical element having a small center line surface average roughness Ra can be obtained.

[0085]

Next, Examples 1 and 2 in which an optical element according to the present invention was manufactured will be described.

<Example 1> As Example 1, a molding die of a collimator lens for an optical disk corresponding to a light source having a center wavelength of 400 nm was manufactured by the above-described technique. The surface of the optical surface (molding surface) of the molding die was manufactured. The roughness is Rtm = 5.8n
m, the center line average surface roughness Ra was 1.4 nm. The surface roughness of a collimator lens injection-molded with a thermoplastic resin using this molding die on one side is Ra = 1.4 nm, similar to the optical surface (molding surface) of the molding die. The transmittance when the surface antireflection coating was applied was 94% with respect to light having a wavelength of 400 nm. There was no practical problem, and scattering on both optical surfaces was hardly observed.
The surface roughness was measured in the lateral direction of FIG. 3 (the direction perpendicular to the cutting direction).

Example 2 Next, as Example 2, an objective lens for a short-wavelength light source made of a glass material was manufactured by glass molding. First, an optical surface (molding surface) is formed on a molding die having a cemented carbide material as a base material by grinding, and the conventional polishing is performed. Then, a number of fine diamond abrasive grains having a particle size of 1 to 2 μm are formed. Surface roughness by polishing for
tm = 10.0 nm, center line surface average roughness Ra = 3.0
nm. Further, as a protective coat, P
Coating by t / Ir sputtering is performed.
It was formed on the optical surface (molding surface) of the molding die with a thickness of 5 μm. The objective lens molded by this molding die has Ra =
3.1 nm. When the objective lens was coated with a surface anti-reflection coating and the transmittance of light having a wavelength of 400 nm was measured, the transmittance was 95% or more, and there was almost no scattering on the optical surface of the objective lens. did it.

A molding die used for the above-mentioned glass mold is usually made of an extremely hard heat-resistant material such as ceramics or a super hard material, and its optical surface (molding surface) is provided with a protective coating. There are many. The protective coat of the molding die prevents the optical surface of the molding die from being heated to about 600 ° C., thereby oxidizing the base material and deteriorating, or preventing the molded glass from sticking during mold pressing and becoming unusable. It is for. However, since the thickness of the protective coat is usually as thin as about 1 μm, the optical surface shape and surface roughness to be formed and transferred are largely influenced by the processing result of the base material, such as ceramic or super hard material. For this reason, the optical surface (molding surface) of the molding die is formed by grinding, but since the surface roughness is large only by grinding, polishing is performed as post-processing. The finish surface roughness of general polishing at this time is
In conventional applications, the light source wavelength is longer than 500 nm, so that Rtm ≒ 30 nm and Ra ≒ 10 nm. For this reason, a sufficient surface roughness could not be obtained as an optical element for short wavelength which is out of the conventional specification, but in this embodiment, Ra is 5n as described above.
An objective lens having an optical surface of m or less was obtained by glass molding.

Next, a method of measuring the center line surface average roughness Ra will be described. There are two types of surface roughness measurement methods: non-contact type and stylus type. In the non-contact type, besides using visible light, a method using an electron beam SEM (scanning electron microscope), and a contact type In addition to the method of mechanically tracing the surface of the test object, there is a method using a probe scanning microscope such as AFM. Alternatively, Ra may be measured using an interferometer.

The center line surface average roughness Ra is defined by the above-mentioned equation (1). However, when the same test object is measured, regardless of the above-mentioned measurement methods such as the contact type and the non-contact type, The feature is that it is relatively well matched, and is hardly affected by error factors not related to the original surface roughness, such as dust, dust, and local scratches. Therefore, the Ra value is an optimal surface roughness value in order to obtain a correlation with the overall physical phenomenon of the optical surface called scattering.

As described above, the present invention has been described with reference to the embodiment and the examples. However, the present invention is not limited to these, and various modifications can be made within the technical idea of the present invention. . For example, the type of the optical element is not particularly limited, and it goes without saying that an optical element other than a lens such as a mirror may be used, and its manufacturing method is not limited to injection molding, injection compression molding, and other molding methods described above. . In addition, the optical surface of the optical element is not necessarily required to be an aspherical surface, but may have another shape such as a spherical surface or a flat surface.

The optical system including the optical element according to the present invention comprises:
An optical system other than the optical pickup optical system may be used, and is particularly suitable for an optical system using light having a wavelength of 500 nm or less. Further, the optical pickup device including such an optical system may be a device for writing information on an optical disk.

[0093]

According to the present invention, it is possible to provide an optical element and an optical system which can reduce scattered light, particularly for light having a short wavelength of 500 nm or less.

Further, it is possible to provide an optical pickup device capable of reducing scattered light and preventing reading / writing errors even when a light source having a short wavelength of 500 nm or less is used.

In addition, it is possible to provide a molding die from which the above-mentioned optical element can be obtained. In addition, light loss is small,
An optical element, an optical system, and an optical pickup device with high light use efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a molding die according to an embodiment of the present invention.

FIG. 2 is an optical element according to an embodiment of the present invention,
FIG. 2 is a cross-sectional view of an objective lens formed by a molding die of FIG. 1 and having both optical surfaces formed as aspheric surfaces and having a center line average surface roughness Ra of 5 nm or less.

FIG. 3 is a diagram showing a state of a cutting plane of an optical surface (molding surface) of a molding die according to an embodiment of the present invention.

FIG. 4 is a diagram showing a state of a tip portion of a new ultra-precision R-cut diamond tool used for forming a cutting plane of an optical surface (molding surface) of the molding die of FIG. 3;

5 is a view showing a measurement of the roundness of the rake face of the cutting edge of the ultra-precision R-cut diamond tool of FIG. 4;

FIG. 6 is a view showing a photograph of an interferometer after a spherical cutting surface of a molding die is first processed by cutting in the embodiment of the present invention.

FIG. 7 is a view showing an interferometer photograph of a spherical cutting surface of a molding die after the cutting of FIG. 6 is continued for 6 hours.

FIG. 8 is a diagram schematically illustrating an optical pickup optical system according to an embodiment of the present invention and an optical pickup device including the optical system.

9 is a diagram schematically illustrating an optical pickup optical system different from that of FIG. 8 and an optical pickup device including the optical system.

FIG. 10 is a view showing a state of a cutting plane of an ENP optical surface (molding surface) of a molding die by a conventional cutting method.

11 is a diagram showing a state of a tip portion of a cutting diamond tool used for forming a cutting plane of an ENP optical surface (molding surface) of the conventional molding die shown in FIG.

12 is a view showing a measurement of the roundness of the rake face of the cutting edge of the conventional cutting diamond tool of FIG.

FIG. 13 is a sectional view of another optical element according to the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Objective lens (optical element) 1a, 1b Optical surface 5 First optical disk 6 Second optical disk 11 Upper die 11a Upper die forming surface (optical surface) 12 Lower die 12a Lower die forming surface (optical surface) 20, Reference Signs List 30 optical pickup device 21, 31 optical pickup optical system 22, 32, 33 light source 23, 34 light receiving sensor (optical element) 26, 39 collimator lens (optical element) 27, 40 objective lens (optical element) 36 sensor lens (for sensor) Optical element)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G11B 7/135 G11B 7/135 A // B29K 101: 10 B29K 101: 10 101: 12 101: 12 B29L 11 : 00 B29L 11:00

Claims (38)

[Claims] 1. An optical element having at least one optical surface having a center line average surface roughness Ra of 5 nm or less. 2. The optical element according to claim 1, wherein both surfaces have an optical surface having the center line average roughness Ra of 5 nm or less. 3. The optical element according to claim 1, wherein the optical surface having the center line average roughness Ra of 5 nm or less is an aspheric surface. 4. The optical element according to claim 1, wherein the optical element is made of a resin material. 5. The optical element according to claim 4, wherein said resin material is a thermoplastic resin. 6. The optical element according to claim 4, wherein said resin material is a thermosetting resin. 7. The optical element according to claim 4, wherein said resin material is a photocurable resin. 8. The optical element according to claim 4, wherein the optical element is formed by injection molding. 9. The optical element according to claim 1, wherein the optical element is made of a glass material. 10. The optical element according to claim 9, wherein the optical element is formed by glass molding. 11. At least one of the optical surfaces is
The optical element according to any one of claims 1 to 10, wherein the optical element has a reflectance of 5% or less for light having a wavelength of at least 400 nm. 12. At least one of the optical surfaces is:
11. The light emitting device according to claim 1, which has a reflectance of 3% or less for light having a wavelength of 300 to 500 nm.
An optical element according to the item. 13. The optical element according to claim 1, wherein the optical element is not polished. 14. The optical element according to claim 1, wherein the optical element is used for an optical system of an optical pickup. 15. The optical element according to claim 14, wherein the optical element is a collimator lens. 16. The optical element according to claim 14, wherein the optical element is an objective lens. 17. The optical element according to claim 14, wherein the optical element is a sensor optical element. 18. The optical element according to claim 1, which is used for an optical pickup device having a light source having a center wavelength of 500 nm or less. 19. An optical system comprising at least one optical element having at least one optical surface having a center line average surface roughness Ra of 5 nm or less. 20. The optical system according to claim 19, wherein the optical element has an optical surface having the center line surface average roughness Ra of 5 nm or less on both surfaces. 21. The optical system according to claim 19, wherein the optical element is a collimator lens. 22. The optical system according to claim 19, wherein the optical element is an objective lens. 23. The optical system according to claim 19, wherein the optical element is a sensor optical element. 24. The optical system according to claim 19, which is used for an optical pickup. 25. An optical system according to claim 19, wherein all the optical elements have a center line average surface roughness Ra.
Is an optical element having an optical surface of 5 nm or less on both surfaces. 26. The optical system according to claim 19, wherein the optical system is used in an optical pickup device having a light source having a center wavelength of 500 nm or less. 27. An optical system comprising at least one optical element according to claim 2. Description: 28. A light source having a light source having a center wavelength of 500 nm or less and at least one optical element having at least one optical surface having a center line average surface roughness Ra of 5 nm or less. Optical pickup device. 29. The optical pickup device according to claim 28, wherein the optical element has an optical surface having the center line surface average roughness Ra of 5 nm or less on both surfaces. 30. The optical pickup device according to claim 28, wherein the optical element is the optical element according to any one of claims 2 to 18. 31. An optical pickup device comprising a light source having a center wavelength of 500 nm or less and an optical system according to any one of claims 19 to 27. 32. A molding die having a molding surface having a center line average surface roughness Ra of 5 nm or less. 33. A molding die having an optical surface molding surface having a center line average surface roughness Ra of 5 nm or less. 34. A first optical surface molding surface having a center line average surface roughness Ra of 5 nm or less, and a center line surface average roughness Ra of 5 nm is provided so as to face the first optical surface molding surface. A molding die having the following second optical surface molding surface. 35. The molding die according to claim 32, wherein the molding surface is an aspheric surface. 36. The molding die according to claim 33, wherein the optical surface molding surface is an aspherical surface. 37. The first optical surface forming surface and the second optical surface forming surface.
35. The molding die according to claim 34, wherein at least one of the optical surface molding surfaces is aspheric. 38. The first optical surface forming surface and the second optical surface forming surface.
35. The molding die according to claim 34, wherein both of the optical surface molding surfaces are aspherical surfaces.