JP2000158484A - Mold and method for molding optical element, and optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of optical capacity caused by the deformation of an optical element at the time of mold release. SOLUTION: A mold for molding a long optical element having a diffraction grating formed thereto at a non-uniform pitch in a longitudinal direction thereof consists of a fixed mold 4 and a movable mold 3. In this case, the gate 6 communication with the cavity 8 formed to the mold in such a state that the molds 3, 4 are clamped is provided in the vicinity of a part where the pitch of the diffraction grating is long as compared with other part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold and method for molding an optical element, and an optical element.

[0002]

2. Description of the Related Art Conventionally, plastic optical elements have been used for scanning optical systems such as copying machines and reading optical systems such as scanners.
A plastic-molded diffractive optical element (formed by injection molding, injection compression molding, or compression molding) with a complex fine diffraction grating pattern formed on the surface, designed based on diffractive optics for the purpose of compactness and cost reduction, is used. (For example, see Japanese Patent Publication No. 9-505245 and Japanese Utility Model Publication No. 4-55282).

The diffraction grating of the above-mentioned diffractive optical element has a thickness of 0.1 to 10 μm on one or both sides of the two optical function surfaces.
how many grids with a height of m are provided in parallel
It is common that an elliptical grid is provided in multiple layers,
Each of the lattice shapes has various shapes, such as a shape in which a plane is provided in a stepped shape or a saw-tooth shape. Also, in many diffraction gratings, the spacing between the gratings changes in the longitudinal direction.

In recent years, the optical system has been required to be more compact and the scanning accuracy has been further improved, and the shape accuracy required for the diffractive optical element has become stricter.

[0005] In addition, the diffractive optical element is required to have not only a diffraction grating formed on a flat plate but also a thick shape having a distribution of thickness like a normal optical lens. I have.

[0006]

However, in the case of molding a long diffractive optical element, the holding pressure is set high in order to obtain good transferability from the mold even on the optical function surface apart from the gate. Therefore, especially, the holding pressure is too high in the vicinity of the gate, and the holding pressure is set high also in the entire diffractive optical element. As described above, when the holding pressure of the gate portion of the diffractive optical element is too high, the gate portion is overpacked and has a large internal stress at the time of removal from the mold, so that the releasability is deteriorated. Deformation of the diffraction grating occurs.

For example, a diffractive optical element (fθ) of a scanning optical system
When the distance between the diffraction gratings at the longitudinal end of the diffractive optical element is smaller than that at the center in the longitudinal direction of the diffractive optical element, the compression amount due to the overpack is large near the gate, and the moment when the mold is ejected from the mold Since the diffractive optical element is released while deforming, the optical function surface is released while sliding with respect to the mold, and the shape of the diffraction grating is deformed as shown in FIG. And the optical performance is degraded.

When the holding pressure is too high in the entire diffractive optical element, the entire optical element is compressed by a large amount due to the overpack, and the diffractive optical element is deformed mainly in the longitudinal direction at the moment of ejection from the mold. In order to release the mold, the optical function surface is released while sliding with respect to the mold, and the shape of the diffraction grating is deformed as shown in FIG.
The shape accuracy of the diffractive optical function surface is deteriorated, and the optical performance is reduced.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a mold and a method for molding an optical element and a method for molding the optical element, which can prevent deterioration of optical performance due to deformation of the optical element at the time of release. It is.

[0010]

In order to solve the above-mentioned problems and to achieve the object, a mold for an optical element according to the present invention has a long shape in which a grating is formed at an uneven pitch in the longitudinal direction of the optical element. In the molding die for molding the optical element, the molding die is composed of a fixed die and a movable die, and a cavity is formed inside the mold in a clamped state, and the lattice pitch of the gate communicated with the cavity is compared with that of another part. And provided near the long part.

Further, the optical element of the present invention is a long optical element having a lattice formed at an uneven pitch in the longitudinal direction of the optical element, comprising a fixed type and a movable type. The pitch of the lattice near the gate communicated with the cavity was longer than that of the other mold.

The method of molding an optical element according to the present invention comprises a fixed mold and a movable mold, wherein a molten optical material is injected from a gate communicating with the cavity into a molding mold having a cavity formed therein in a clamped state. By doing so, in a method of molding a long optical element that forms a grating at a non-uniform pitch in the longitudinal direction, a transfer surface on which the shape of the grating is transferred is preferentially separated from the other surface.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. [First Embodiment] FIG. 1 shows a mold used for injection-molding the diffractive optical element of the first embodiment, as viewed from the gate 6 side for injecting a plastic resin. FIG. 2 is a front view of a diffractive optical element injection-molded by the mold of FIG. 1 as viewed from a diffractive optical function surface.

As shown in FIGS. 1 and 2, a runner 7 and a gate for injecting a plastic resin material at the time of injection molding are provided on a parting line 5 provided for taking out a diffractive optical element from a mold. 6 are formed. (In FIG. 1, a dotted line indicates a diffractive optical element). The mold 3 has a diffractive transfer surface 1 mirror-finished to a desired shape to transfer the diffractive optical function surface of the diffractive optical element.

On the other side of the parting line 5, a mold 4, which forms a plane transfer surface 2 mirror-finished into a shape for transferring a plane optical function surface of the diffractive optical element, and a book In the case of the embodiment, as shown in FIG.
The shape of the diffractive optical function surface provided in the diffractive optical element has a long diffraction grating interval of 2000 μm in the center of the
The distance between the diffraction gratings becomes shorter toward the end in the longitudinal direction, and the distance becomes 100
μm. Further, the diffraction grating has a substantially linear shape in the lateral direction of the diffractive optical element.

The mold 3 on the diffractive optical function side and the mold 4 on the plane side are combined with the parting line 5 as a boundary to form a cavity 8 for molding the diffractive optical element, and the gate 6 is used as the diffractive optical element of the diffractive optical element. The space is provided at the long center in the longitudinal direction.

The injection molding process using the above-configured mold will be described. A mold clamping force is applied to the molds 3 and 4 to fill the cavity 8 with the molten plastic resin material through the gate 6 and apply pressure to the plastic resin material. The plastic resin material in the cavity is cooled by heat radiation to the mold and contracts. At this time, even if shrinkage of the plastic resin material occurs, the optical function surface of the diffractive optical element, in particular, the portion of the diffractive optical function surface is transferred to a highly accurate mirror surface close to the shape of the mold 3, which is sufficient for the plastic resin material. Pressure needs to be applied.

When the temperature of the plastic resin material becomes sufficiently lower than the glass transition point of the plastic resin material due to heat radiation, the mold is opened to take out the diffractive optical element. At this time, the diffractive optical element in the cavity is overpacked and high. Since the internal stress remains and the compression amount is particularly large near the gate 6 (the center in the longitudinal direction) of the diffractive optical element, the molds 3 and 4 open with the parting line 5 as a boundary, and the diffractive optical element is closer to the mold 3 side. The shape accuracy is deteriorated as shown in FIG. 15 at the moment when the surface including the optical functional surface is released from the mold. However, since the diffraction grating interval near the gate of the diffractive optical element of this embodiment is as long as 200 μm, as shown in FIG. When evaluated in terms of a decrease in the diffraction efficiency b / a, the diffraction grating interval a is as short as 2000 μm, and the deformed portion b is 50 μm, so that an optical element which can sufficiently satisfy the optical performance can be obtained. It is. [Conventional Example] FIG. 3 is a view of a mold used for injection molding a conventional diffractive optical element, as viewed from the parting line 105 side. FIG. 4 is a front view of a conventional diffractive optical element viewed from a diffractive optical function surface.

As shown in FIGS. 3 and 4, the mold is mirror-finished to a desired shape on the mold 103, and then onto the mold 103 to transfer the diffractive optical function surface of the diffractive optical element to the mold. The diffraction transfer surface 101 is formed.

On the other side of the parting line 105, there is formed a mold 104 constituting the plane transfer surface 2 mirror-finished to a shape for transferring the plane optical function surface of the diffractive optical element. I have.

In the conventional example, the shape of the diffractive optical function surface provided on the mold 103 is such that the interval between the diffraction gratings is long at 2000 μm at the center of the diffractive optical element, and the interval between the diffraction gratings becomes shorter at 100 μm toward the end in the longitudinal direction. I have. The diffraction grating has a substantially linear shape in the lateral direction of the diffractive optical element.
The mold 103 on the diffractive optical function surface side and the flat mold 104 are combined with the parting line 105 as a boundary to form a cavity 108 for molding the diffractive optical element. It is provided on the side in the hand direction.

In the injection molding process using the mold having the above-described structure, a mold clamping force is applied to the molds 103 and 104 to fill the cavity 108 with the molten plastic resin material through the gate 106 and apply pressure to the plastic resin material. The plastic resin material in the cavity is cooled by heat radiation to the mold and contracts. At this time, even if the plastic resin material shrinks, the optical functional surface of the diffractive optical element, particularly, the portion of the diffractive optical functional surface is transferred to a highly accurate mirror surface close to the shape of the mold 103, which is sufficient for the plastic resin material. Pressure needs to be applied.

When the temperature of the plastic resin material becomes sufficiently lower than the glass transition point of the plastic resin material due to heat radiation, the mold is opened to take out the diffractive optical element. At this time, the diffractive optical element in the cavity is overpacked and high. Since the internal stress remains and the compression amount is particularly large near the gate of the diffractive optical element (the end in the longitudinal direction = short side surface), the molds 103 and 104 are opened to open the mold 103 of the diffractive optical element.
The shape accuracy deteriorates as shown in FIG. 15 at the moment when the surface including the optical function surface on the side is released. The diffraction grating spacing near the gate of the conventional diffractive optical element is as short as 100 μm, and the diffraction efficiency is reduced. A = 100 μm, b = 5
An optical element having a sufficient optical performance of 0 μm cannot be obtained, causing a problem in optical performance. [Second Embodiment] FIG. 5 is a sectional view of a mold used when injection-molding a diffractive optical element according to a second embodiment. FIG. 6 is a front view of a diffractive optical element injection-molded by the mold of FIG. 5 as viewed from a diffractive optical function surface.

In the following, in order to clarify the difference from the first embodiment, a new number is assigned only to a different part,
Others will be described with the same reference numerals.

As shown in FIGS. 5 and 6, a gate 6 for injecting a resin is provided across a parting line 5 provided in the mold, and the mold 3 has a diffractive optical function surface of the diffractive optical element. A diffraction transfer surface 31 is mirror-finished to a desired shape for transfer.

On the other side of the parting line 5, there is arranged a mold 4 constituting a mirror-finished plane transfer surface 2 having a shape for transferring the planar optical function surface of the diffractive optical element. ing.

In the case of the present embodiment, the shape of the diffractive optical function surface provided on the mold 3 is such that the diffraction grating interval is long at 1800 μm at both ends of the diffractive optical element, and becomes shorter at 50 μm toward the center in the longitudinal direction. ing. The grating has a substantially straight shape in the short direction of the diffractive optical element. The mold 3 on the diffractive optical function side and the flat mold 4 are combined with the parting line 5 as a boundary to form a cavity 8 for molding the diffractive optical element. It is provided on the side of the hand.

In the injection molding process using the mold having the above-described configuration, a mold clamping force is applied to the molds 3 and 4 to fill the cavity 8 with the molten plastic resin material through the gate 6 and apply pressure to the plastic resin material. The plastic resin material in the cavity is cooled by heat radiation to the mold and contracts. At this time, even if shrinkage of the plastic resin material occurs, the optical function surface of the diffractive optical element, in particular, the portion of the diffractive optical function surface is transferred to a highly accurate mirror surface close to the shape of the mold 3, which is sufficient for the plastic resin material. Pressure needs to be applied.

When the temperature of the plastic resin material becomes sufficiently lower than the glass transition point of the plastic resin material due to heat radiation, the mold is opened to take out the diffractive optical element. At this time, the diffractive optical element in the cavity is overpacked and high. Since the internal stress remains and the compression amount is particularly large near the gate (center in the longitudinal direction) of the diffractive optical element, the mold 3,
At the moment when the mold 4 is opened and the surface including the optical function surface on the mold 3 side of the diffractive optical element is released, the shape accuracy is deteriorated as shown in FIG.
Since the diffraction grating interval near the gate of the diffractive optical element of the present embodiment is long, an optical element that can sufficiently satisfy optical performance can be obtained when evaluated in terms of reduction in diffraction efficiency. [Third Embodiment] FIGS. 7 to 10 are cross-sectional views of a mold used when molding the optical element of the third embodiment, and are diagrams showing from molding to mold opening. FIG. 11 is a view as seen from the movable mold when the mold of FIG. 7 is opened at the parting line 10.

As shown in FIG. 7 and FIG. 11, one of the parting lines 10 provided on the mold has a fixed mold plate 13 constituting a fixed mold, and is inserted and mounted on the fixed mold plate 13. The fixed-side type piece 11 is arranged. A shape for transferring the shape of the present optical element is formed on the fixed-side mold plate 13 and the fixed-side mold piece 11, and especially on the surface of the fixed-side mold piece 11, it is desirable to transfer the optical functional surface of the optical element. A plane transfer surface 11a having a mirror-finished shape is formed.

The other part of the parting line 10 includes a movable mold plate 14 constituting a movable mold, a movable mold piece 12 inserted and mounted on the movable mold plate 14, and a movable mold piece 12. A sliding device 21 for moving the movable member 12 relative to the movable mold plate 14 and an ejector pin 18 are provided. A concave portion for transferring the shape of the present optical element is formed in the movable mold plate 14 and the movable mold piece 12, and the diffractive optical function surface of the optical element is transferred to the surface of the movable mold piece 12 in particular. A mirror-finished diffraction transfer surface 12a is formed in a desired shape. Further, a spool 24 for injecting a plastic resin material, a runner 23, and a gate 22 are formed on the movable mold plate 14 as shown in FIG.

In the case of this embodiment, the parting line 1
Combining the fixed mold and the movable mold with 0 as the boundary,
A cavity 25 for molding the optical element is formed, and the movable mold 12 can be moved with respect to the movable mold plate 14 by the sliding device 21.

The injection molding process using the mold having the above configuration will be described.

As shown in FIGS. 7 to 10, a mold clamping force is applied to the fixed mold and the movable mold so that the molten plastic resin material is filled into the cavity 25 through the spool 24, the runner 23, and the gate 22, and the plastic is filled. Apply pressure to the resin material. The plastic resin material in the cavity is cooled by heat radiation to the mold and contracts. At this time, even if the plastic resin material shrinks, the optical function surface of the optical element, in particular, the portion where the lattice spacing of the diffractive optical function surface is small is transferred as a highly accurate mirror surface close to the shape of the movable mold piece 12. It is necessary to apply sufficient pressure to the resin material.

When the temperature of the plastic resin material becomes sufficiently lower than the glass transition point of the plastic resin material due to heat radiation, the mold is opened and the optical element is taken out. At this time, since the optical element in the cavity is overpacked, Since the stress remains, and particularly the amount of compression in the longitudinal direction of the optical element is large, as shown in FIG. 8, before the mold is opened and the surface including the optical function surface on the fixed mold side of the optical element is released, The movable mold 12 slides with respect to the movable mold 14 by the sliding device 21, and the surface of the optical element is constrained by the fixed mold 11 and the fixed mold 13. Release the mold. This makes it possible to prevent the deformation of the optical element during the release process, so that the deformation of the diffractive optical function surface during the release as shown in FIG. 16 can be suppressed.

As described above, deformation of the diffraction grating is minimized because no slippage occurs with respect to the mold, and the deformed portion b is about 1 μm, and the minimum grating interval a is about 100 μm. Is obtained.

Subsequently, as shown in FIG. 9, the mold is opened with the parting line 10 as a boundary, the ejector rod of the injection molding machine pushes the ejector plates 19 and 20, and the ejector pins 18 connected thereto move the optical element. The end surface excluding the optical function surface on the side mold side is released, and the optical element is released from the mold as shown in FIG.

Thus, a diffractive optical element satisfying the diffractive optical performance can be formed without causing a shape defect of the diffractive optical function surface at the time of releasing the mold. Fourth Embodiment FIGS. 13 and 14 are cross-sectional views of a mold used when molding an optical element according to a fourth embodiment.
It is a figure showing from molding to mold opening. FIG.
FIG. 5 is a view of the mold on the movable side when the mold is opened at the parting line.

As shown in FIGS. 13 and 14, one of the parting lines 10 provided on the mold is provided with a fixed mold plate 13 constituting a fixed mold and inserted and mounted on the fixed mold plate 13. The fixed-side type piece 11 is arranged. A transfer surface for transferring the outer shape of the optical element is formed on the fixed mold plate 13 and the fixed mold piece 11, and the diffractive optical function surface of the optical element is transferred onto the fixed mold piece 11 in particular. Transfer surface 11a, which is mirror-finished to a desired shape, is formed.

On the other side of the parting line 10, a movable mold plate 14 constituting a movable mold and a movable mold piece 12 inserted and mounted on the movable mold plate 14 are arranged. A transfer surface for transferring the outer shape of the optical element is formed on the movable mold plate 14 and the movable mold piece 12, and in particular, on the surface of the movable mold piece 12, for transferring the optical functional surface of the optical element. A plane transfer surface 12a mirror-finished to a desired shape is formed. A spool 2 for injecting a plastic resin material into the movable mold plate 14 as shown in FIG.
4, a runner 23 and a gate 22 are formed.

In the case of this embodiment, the parting line 1
Combining the fixed mold and the movable mold with 0 as the boundary,
The cavity 25 for molding the optical element is formed, and the diffractive optical function surface of the optical element can be preferentially released with the mold opening operation of the injection molding machine.

A mold clamping force is applied to the fixed mold and the movable mold, and the molten plastic resin material is filled into the cavity 25 through the sprue 24, the runner 23 and the gate 22, and pressure is applied to the plastic resin material. Is cooled and becomes sufficiently lower than the glass transition point, the mold is opened and the optical element is taken out, as shown in FIG.
The fixed mold is released while the outer shape of the entire optical element other than the diffraction transfer surface 11a is restrained by the movable mold piece 12 and the movable mold plate 14 by the operation of opening the mold. As a result, as shown in FIG. 16, it is possible to suppress the deformation of the optical element during the release process and the deformation of the diffractive optical function surface during the release, so that the deformed portion b is about 10 μm and the minimum lattice spacing a
Is about 100 μm, and a molded product having no problem in diffraction efficiency can be obtained.

At this time, it is necessary to perform the mold opening operation of the movable mold plate and the fixed mold plate without precision displacement, and depending on the mold opening accuracy of the injection molding machine, the movable mold plate and the fixed mold plate may be fixed to each other. Guide pins may be required to precisely position the side template.

Accordingly, a diffractive optical element satisfying the diffractive optical performance can be formed without causing a shape defect of the diffractive optical function surface at the time of releasing the mold.

According to each of the embodiments described above, deterioration of optical performance due to deformation of the diffractive optical function surface at the time of mold release can be prevented by providing a gate in a portion where the diffraction grating interval of the optical function surface is coarse.

The deformation of the diffraction grating at the time of release from the mold largely occurs in a portion where the pressure is locally high. On the other hand, in the case of a scanning optical system such as a laser beam, although the diameter of the laser beam passing through the diffractive optical function surface of the long optical element is substantially the same at each point in the longitudinal direction, the distance between the diffraction gratings is large. Is often different. That is, the number of diffraction gratings existing within the beam diameter when one beam passes through the optical element differs depending on the position in the longitudinal direction.

In this embodiment, focusing on the fact that the amount of deformation of the diffraction grating near the gate is large, the gate is provided at a portion where the diffraction grating interval is coarse and the number of diffraction gratings per beam diameter is small. The deterioration of the optical performance of the optical element due to deformation near the gate can be prevented.

In the molding of the optical element of this embodiment,
When the optical element is taken out of the mold, the optical function surface having the diffraction grating is released from the other optical function surfaces or constituent surfaces in preference to the optical function surface. Deterioration can be prevented.

Since the pressure of the diffraction grating upon release from the mold is generally 0.5 mm to 1.
May extend about 0mm. In the present embodiment, in order to minimize the expansion of the optical element at the time of mold release, in the step of releasing the optical element from the mold and taking it out, the mold release of the diffractive optical function surface has priority over the other surface. By doing so, the other surface (particularly, the optical function surface opposite to the diffractive optical function surface) is constrained by the mold, and separation of the diffractive optical function surface is performed in a state where the overall deformation (elongation) of the optical element is suppressed. The molding can be performed to prevent a decrease in the optical performance of the optical element due to the deformation.

The present invention can be applied to a modified or modified embodiment without departing from the spirit of the invention.

[0051]

According to the present invention, the gate for injecting the resin of the diffractive optical element is provided in a portion where the distance between the diffraction gratings is long,
By releasing the diffractive optical function surface more preferentially than the other surfaces, deformation of the diffractive optical function surface of the diffractive element at the time of release can be suppressed.

[0052]

[Brief description of the drawings]

FIG. 1 is a view showing a mold used when injection-molding a diffractive optical element according to a first embodiment, as viewed from a gate 6 side for injecting a resin.

FIG. 2 is a front view of a diffractive optical element injection-molded by the mold of FIG. 1 as viewed from a diffractive optical function surface.

FIG. 3 is a view of a mold used when injection molding a conventional diffractive optical element, viewed from a parting line 105 side.

FIG. 4 is a front view of a conventional diffractive optical element viewed from a diffractive optical function surface.

FIG. 5 is a sectional view of a mold used when injection-molding the diffractive optical element according to the second embodiment.

FIG. 6 is a front view of a diffractive optical element injection-molded by the mold of FIG. 5 as viewed from a diffractive optical function surface.

FIG. 7 is a cross-sectional view of a mold used when molding the optical element according to the third embodiment, illustrating a process from molding to mold opening.

FIG. 8 is a cross-sectional view of a mold used when molding the optical element according to the third embodiment, illustrating a process from molding to mold opening.

FIG. 9 is a cross section of a mold used when molding the optical element of the third embodiment, and is a diagram showing from molding to mold opening.

FIG. 10 is a cross-sectional view of a mold used when molding the optical element according to the third embodiment, illustrating a process from molding to mold opening.

11 is a view of the mold of FIG. 7 as viewed from the movable mold when the mold is opened at the parting line 10. FIG.

12 is a view of the mold of FIG. 13 as viewed from the movable mold when the mold is opened at the parting line 10. FIG.

FIG. 13 is a cross-sectional view of a mold used when molding the optical element according to the fourth embodiment, illustrating a process from molding to mold opening.

FIG. 14 is a cross-sectional view of a mold used when molding the optical element according to the fourth embodiment, illustrating a process from molding to mold opening.

FIG. 15 is a diagram illustrating a deformed state of a diffraction grating having a problem in diffraction efficiency.

FIG. 16 is a diagram showing a deformed state of the diffraction grating such that diffraction efficiency does not matter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diffractive optical function surface 2 Optical function surface 3 type (diffractive optical function surface) 4 type (optical function surface) 5 Parting line 6 Gate 7 Runner 8 Cavity 10 Parting line 11 Fixed mold piece 12 Movable mold piece 13 Fixed Side mold plate 14 Movable mold plate 15 Fixed-side mounting plate 16 Movable-side receiving plate 17 Movable-side mounting plate 18 Ejector pin 19 Ejector plate 20 Ejector plate 21 Sliding mechanism 25 Cavity

Claims (9)

[Claims] 1. A mold for molding a long optical element having a lattice formed at an uneven pitch in a longitudinal direction of the optical element, wherein the mold comprises a fixed mold and a movable mold, and is in a clamped state. Wherein a cavity is formed inside the mold, and a gate communicated with the cavity is provided near a portion where the lattice pitch is longer than in other places. 2. The mold according to claim 1, wherein the optical element is a lens of a scanning optical system on which a diffraction grating is formed at an uneven pitch. 3. A long optical element in which a grating is formed at an uneven pitch in the longitudinal direction of the optical element, comprising a fixed mold and a movable mold, wherein the mold has a cavity formed therein in a mold-clamped state. An optical element, wherein the pitch of the lattice near the gate communicated with the cavity is longer than that of the other part. 4. The optical element according to claim 3, wherein the optical element is a lens of a scanning optical system on which a diffraction grating is formed at a non-uniform pitch. 5. A molding method comprising a fixed mold and a movable mold, wherein a molten optical material is injected from a gate communicating with the cavity into a molding mold having a cavity formed therein in a mold-clamped state. A molding method for molding a long optical element that forms a grating at a pitch, wherein a mold transfer surface for transferring the shape of the grating is preferentially released to another surface. 6. The method according to claim 5, wherein the optical element is a lens of a scanning optical system on which a diffraction grating is formed at an uneven pitch. 7. The molding method according to claim 5, wherein the gate of the molding die is provided in the vicinity of a portion where the pitch of the lattice is longer than that of other parts. 8. The method according to claim 5, wherein after releasing only the transfer surface for transferring the shape of the lattice, the other surface is released.
The molding method according to any one of claims 1 to 7. 9. An optical element obtained by the molding method according to claim 5. Description: