JP2025016816A - Optical element manufacturing method and optical element - Google Patents

Abstract

The present invention provides a method for manufacturing an optical element which is more suitable in terms of reducing material loss and molding.
A method for manufacturing an optical element includes: performing a mirror finishing process to mirror-finish the entire surface of a columnar material by heating to form a mirror-finished material from the columnar material; and then subjecting the mirror-finished material to mold press molding.
[Selected figure] Figure 2

Description

The present disclosure relates to a method for manufacturing an optical element and the optical element. More specifically, the present disclosure relates to a method for manufacturing an optical element that at least contributes to light transmission, and also to an optical element obtained thereby.

Optical elements made of resin or glass materials have been used for various purposes. For example, optical elements are used as lenses, prisms, mirrors, optical fibers, etc.

In recent years, optical elements have also been used in the field of optical sensing, such as optical sensors for monitoring systems for disaster prevention and/or crime prevention, or in-vehicle sensor modules for driving assistance systems.

JP 2013-14455 A International Publication No. 2020/071071

The inventors of the present application realized that there were problems to be overcome in the conventional manufacturing of optical elements, and found it necessary to take measures to address these problems. Specifically, they found the following problems:

Optical elements are manufactured through molding or by machining methods such as cutting, grinding and/or polishing. When manufacturing optical elements by grinding and/or polishing, the final shape of the optical element is obtained by cutting it out from the raw material, resulting in a large amount of material loss (Figure 13).

Mold press molding is sometimes used to mold optical elements. In this manufacturing method, a mold is used to apply pressure to the material, so it is difficult to actively use materials made of brittle materials.

This disclosure has been made in light of these problems. In other words, the main objective of this disclosure is to provide a manufacturing method for optical elements that is more suitable in terms of reducing material loss and molding.

The inventors of the present application attempted to solve the above problems by approaching them from a new direction, rather than simply extending the conventional technology. As a result, they arrived at a method for manufacturing optical elements that achieves the above-mentioned main objective.

This disclosure provides a method for manufacturing an optical element, which involves performing a mirror-finishing process to heat a columnar material to make the entire surface of the columnar material into a mirror-finished material, and then subjecting the mirror-finished material to mold press molding.

The present disclosure also provides an optical element obtained by the above manufacturing method. The optical element of the present disclosure has a light-transmitting portion and a flange portion extending outward from the light-transmitting portion, and the light-transmitting portion has different internal strains between a peripheral region and an inner region that is located more inward than the peripheral region.

The manufacturing method disclosed herein allows for more optimal production of optical elements in terms of reducing material loss and molding.

In terms of reducing material loss, the method disclosed herein can manufacture optical elements under conditions that reduce material loss. Because the material used in mold press molding has a columnar shape, there is no need to grind the material to a shape that is relatively close to the shape of the optical element prior to the molding. For example, when manufacturing optical elements such as lenses, there is no need to grind the material to a shape that is similar to a sphere or a flattened lens shape, and material loss in the optical element can be reduced.

In terms of mold forming, the method of the present disclosure can form an optical element without applying excessive pressure to the material. In this regard, in the present disclosure, a mirror finish treatment is performed by heating prior to mold press forming. The mirror finish treatment itself can contribute to the transmittance of the optical element, but in the present disclosure, the mirror finish treatment is performed by heating the entire surface of the columnar material. This mirror finish treatment by heating can make the overall shape of the columnar material closer to the final shape of the optical element compared to the original columnar material, making it possible to reduce the excessive pressure applied to the material during mold press forming. Therefore, even if the material is made of a brittle material, it can be used more actively in mold press forming.

Cross-sectional views showing lenses as optical elements (FIG. 1(A): biconvex lens, FIG. 1(B): biconcave lens, FIG. 1(C): meniscus lens) Schematic cross-sectional view for explaining a part of the manufacturing method of the present disclosure. A cross-sectional view showing a schematic example of the configuration of a die used in mold press molding. 1 is a process cross-sectional view illustrating a mold press molding method according to the present disclosure; FIG. 1 is a cross-sectional view showing a schematic example of a configuration of a non-sleeve type die used in mold press molding. FIG. 1 is a cross-sectional view showing a schematic example of mold press molding in the manufacturing method of the present disclosure (using a non-sleeve type mold); Schematic cross-sectional view for explaining "aspects of mirror finishing treatment using a mold" Schematic cross-sectional view for explaining "aspects of continuous processing using a mold" Cross-sectional views showing lenses as optical elements (FIG. 9(A): biconvex lens, FIG. 9(B): biconcave lens, FIG. 9(C): meniscus lens) 1A and 1B are perspective and plan views illustrating an example embodiment of an optical element according to the present disclosure; FIG. 1 is a schematic diagram showing an example of internal distortion characteristics in a light-transmitting portion of an optical element according to the present disclosure. FIG. 1 is a cross-sectional view showing a schematic embodiment of a meniscus lens formed by press molding according to the present disclosure. FIG. 1 is a schematic diagram for explaining an example embodiment of manufacturing a lens by cutting out a raw material by grinding and polishing (prior art);

Below, a method for manufacturing an optical element according to one embodiment and an optical element obtained by the manufacturing method will be described in more detail. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of matters that are already well known or duplicate explanations of substantially identical configurations may be omitted. This is to avoid unnecessarily lengthy explanations and to facilitate understanding by those skilled in the art.

The applicant provides the attached drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and does not intend for them to limit the subject matter described in the claims. Note that the various elements in the drawings are merely shown as schematic and illustrative examples for understanding the manufacturing method and optical element of the present disclosure, and the appearance and dimensional ratios may differ from the actual ones.

The terms "upward" and "downward" used directly or indirectly in this specification correspond to the upward and downward directions in the drawings, respectively. In a preferred embodiment, the vertical downward direction (i.e., the direction in which gravity acts) corresponds to the "downward direction," and the opposite direction corresponds to the "upward direction."

In this specification, a "cross-sectional view" is based on a virtual cross-section obtained by cutting an optical element along its thickness direction. In other words, a sketch of a cross-section cut along the thickness of an optical element corresponds to a "cross-sectional view." Typically, the "thickness direction of an optical element" may correspond to the light transmission direction in an optical element. In addition, the "plan view" used in this specification is based on a sketch of an object viewed from above or below along the thickness direction.

Various numerical values and ranges mentioned in this specification are intended to include the lower or upper limit numerical value itself, unless a special term such as "less than" or "more than/greater than" is used. In other words, for example, a numerical range such as 1 to 10 can be interpreted as including the lower limit of "1" and the upper limit of "10."

[Manufacturing method of the present disclosure]
The present disclosure relates to a method for manufacturing an optical element, and in particular, to a method for manufacturing an optical element from a material by mold press molding. Mold press molding is a method for pressing a material using a die to form it, and the present disclosure is characterized in matters related to the molding method.

Specifically, a mirror-finished material is formed from the columnar material by performing a mirror-finishing process in which the entire surface of the columnar material is heated to give it a mirror finish, and the material obtained by the mirror-finishing process through heating, i.e., the mirror-finished material, is then subjected to mold press forming.

In this specification, the term "optical element" broadly means a member for transmitting light. Thus, the optical element may be, for example, a lens, a prism, or a mirror. Furthermore, the optical element may be a window product related to light transmission. In the narrow sense, the term "optical element" means a member for converging or diverging light, such as a lens (see FIG. 1). When the optical element 10 is a lens, the "light transmitting portion" of the optical element 10 corresponds to the lens portion (at least the "R surface" portion including the optically effective surface).

In the manufacturing method disclosed herein, the material used in mold press molding is a mirror-finished material obtained from a columnar material by heating the entire surface of the columnar material. In other words, the material used in mold press molding is a material whose entire surface has been mirror-finished by heating.

Figure 2 shows a schematic diagram of an exemplary embodiment of the mirror finish treatment in the present disclosure. As shown in Figure 2, the material to be subjected to mold press molding is a columnar material 20, and the entire surface of the material is heated to obtain a mirror finish material 25. The mirror finish material 25 is then subjected to mold press molding using an appropriate mold.

The columnar material 20, as its name suggests, is a material that has a columnar shape overall. In other words, the material that will be mirror-finished by heating is a material that has a three-dimensional shape in which the cross-sectional shape in a predetermined direction (for example, the cross-sectional shape of an optical element cut along a direction perpendicular to the thickness direction) is substantially constant. Such columnar material 20 may have an overall shape such as a triangular prism, a square prism, a hexagonal prism, or a cylinder.

The columnar material 20 is preferably a single item. Such a material can be obtained from an ingot. When the columnar material is obtained from an ingot, the material loss is small. In other words, the material 20 used in the manufacturing method disclosed herein does not need to be ground or otherwise processed to obtain a shape relatively close to the final optical element shape, and material loss is small. For example, when performing mold press molding, there is no need to obtain a material in a spherical shape or a lens-like shape such as a flattened version of that shape in advance, and therefore material loss is small.

The columnar material may be polygonal or cylindrical. In other words, the material to be subjected to the mirror finish by heating may be a prismatic material or a cylindrical material. Prismatic materials have a relatively simple shape and can be easily obtained from an ingot. In addition, prismatic materials are less likely to create an enclosed space between the die surface and the material during molding. Therefore, compared to materials with large R surfaces, prismatic materials are less likely to create so-called "air pockets" during molding. Prismatic materials may have a quadrilateral or approximately quadrilateral shape in plan view. In this specification, quadrilateral means shapes such as square and rectangular. On the other hand, cylindrical materials may have a circular or approximately circular shape in plan view.

The columnar material may contain, for example, a glass material. In other words, a mirror-finished material may be obtained from a material containing a glass material, and the mirror-finished material may be subjected to mold press molding. Glass materials generally have a large linear expansion coefficient, and the amount of expansion when heated and the amount of contraction when cooled during mold press molding are large, making them difficult to mold. In the manufacturing method disclosed herein, as described below, the "mirror-finishing process by heating" prevents excessive pressure from being applied to the material, and materials containing glass materials can be more actively used.

In the manufacturing method disclosed herein, the heating performed as the mirror finishing process is performed by heating the columnar material from the outside as a whole. In other words, the surface area of the columnar material is heated as a whole, rather than localized heating in which only a portion of the surface area of the columnar material is heated. This type of heating for the mirror finishing process causes overall plastic deformation of the columnar material, making it possible to make the overall shape of the material closer to the shape of the optical element compared to the original columnar material, and to reduce the pressing force applied to the material during mold press forming. Therefore, even if the material is made of a brittle material, it can be used more actively in mold press forming.

The heating performed as a mirror finishing process may be performed from the entire periphery of the columnar material. In other words, the columnar material may be heated from all directions, above, below, and to the sides. This results in the surface of the columnar material being heated overall, rather than locally, making it easier for the entire material to be molded by press molding to resemble the shape of an optical element. Note that the "side direction" referred to here corresponds to the direction perpendicular to the material axis along the upward direction of the columnar material and the opposite downward direction.

In the mirror finishing process, it is preferable to soften the entire surface of the columnar material by heating to mirror the columnar material. This is because it is easier to make the overall shape of the material closer to the shape of the optical element, and the effects of the present disclosure are more likely to be manifested. The heating time for such a mirror finishing process may be relatively short. In other words, it is not necessary to soften the columnar material to the center, and since it is sufficient to soften at least the surface portion, the heating time may be short. Specifically, in the case of a columnar material containing chalcogenide glass (IRG203 made by Xinhuaguang), the heating time for the mirror finishing process may be within 800 seconds, within 700 seconds, or within 650 seconds at a temperature higher than the glass transition temperature (Tg). For example, the columnar material may be heated for the mirror finishing process for 400 to 800 seconds, 500 to 700 seconds, or 550 to 650 seconds.

In the manufacturing method disclosed herein, the mirror-finished material obtained by heat-treating the entire surface of the columnar material preferably has a smooth or glossy surface. In other words, the mirror-finished material may preferably have a smooth or glossy surface as its mirror surface.

Because the mirror-finished material is a mirror surface, its surface roughness is low. For example, the mirror-finished material may have a surface roughness of Ra 50 nm or less, preferably Ra 20 nm or less, by mirror-finishing. In other words, the "mirror surface" of "mirror-finished treatment"/"mirror-finished material" in this disclosure essentially refers to a mirror surface having a surface roughness of Ra 50 nm or less, preferably Ra 20 nm or less. There is no particular limit to the lower limit of the surface roughness Ra, and it may be, for example, Ra 0 nm (excluding 0). In this disclosure, "Ra" is the so-called arithmetic mean roughness, and its value is measured using a scanning white light interferometer (Zygo NewView) for at least one surface that constitutes the outer surface of the mirror-finished material.

In the mirror finish treatment by heating, the columnar material may be heated to a temperature higher than its glass transition temperature Tg. In other words, the entire surface of the columnar material may be heated under heating conditions higher than the glass transition temperature Tg of the material of the columnar material. For example, as a mirror finish treatment, the columnar material is heated and softened under heating conditions 50 to 200°C higher than the glass transition temperature Tg of the columnar material, more preferably 100 to 190°C higher. Such heating conditions tend to soften the entire surface of the columnar material more effectively, and the effects of the present disclosure tend to be more evident. For example, if the heating temperature is lower than the lower limit of the above temperature range, it becomes difficult to obtain a sufficient mirror finish, and the mirror finish of the material is likely to be defective, while if the temperature is higher than the upper limit of the above temperature range, phenomena such as material cracking are likely to occur during mold press molding. Here, the "glass transition temperature Tg" in this disclosure is a value obtained from a thermal expansion curve showing the relationship between temperature and sample elongation. As an example of the material of the columnar material, the glass transition temperature Tg of chalcogenide (IRG203 manufactured by Xinhuaguang) is, for example, about 266°C, and the glass transition temperature Tg of chalcohalide is, for example, about 375°C.

In the manufacturing method disclosed herein, the entire surface of the mirror-finished material is heat-treated, and the resulting material is then subjected to mold press molding. This allows the mirror-finished material to be molded into an optical element through pressure deformation. In other words, the light-transmitting portion and flange portion of the optical element can be integrally molded from a single mirror-finished material through mold press molding.

3 shows a mold used in mold press molding. As shown in the figure, the mold 50 used in the manufacturing method of the present disclosure is composed of, for example, a pair of upper and lower dies 51 and 52, which are the main parts of the mold, and a mold sleeve 53. The upper and lower dies 51 and 52 can be driven to move relatively closer or farther apart, and a mold cavity 56 is formed between them. The mirrored material is pressed and deformed between the pair of upper and lower dies 51 and 52, thereby forming at least the light transmitting part of the optical element. When the optical element is a lens, the mirrored material is deformed by the pressing force received from the upper and lower dies 51 and 52, and the shape of the lens part, which is the "main part" of the optical element, is obtained. On the other hand, the mold sleeve 53 has a "cylindrical shape" as can be seen from its name, and is provided on the outer circumferential surface of the main part of the mold. The mold sleeve 53 is a mold member that contributes to the formation of the mold cavity together with the upper die side 51 and the lower die 52, and preferably acts to bound the outer edge of the mold cavity.

As can be seen from this explanation, the "main mold part" in this specification refers to the main mold part that contributes to the formation of most of the mold cavity. On the other hand, the "mold sleeve" in this specification refers to a mold part that performs a secondary function and is provided on the outer circumferential surface of the main mold part so as to form at least a part of the body of the mold. When the mold cavity is formed by the space surrounded by the upper and lower mold parts and the mold sleeve of the main mold part, the mold sleeve is a cylindrical mold part that bounds the outer edge of the mold cavity.

For example, the mold cavity has a circular or approximately circular shape in plan view. That is, the inner peripheral surface of the mold sleeve that bounds the outer edge of the mold cavity may have a circular or approximately circular shape in plan view. Specifically, for example, the outer peripheral surface of the main mold part may have a cylindrical outer surface, to which a cylindrical mold sleeve may be provided, resulting in a mold cavity that is circular or approximately circular in plan view.

Mold press molding using such a mold may be performed under temperature conditions specific to the mirror-finished material. For example, mold press molding may be performed under temperature conditions lower than the heating temperature of the mirror-finished treatment. This is because the pressure deformation of the mirror-finished material becomes more favorable, making it easier to obtain an optical element in which the light-transmitting portion and the flange portion are more favorably molded integrally. For example, mold press molding may be performed under temperature conditions that are preferably 20°C to 130°C lower than the heating temperature conditions of the mirror-finished treatment, for example, 40°C to 90°C lower. From another perspective, the heating of the mirror-finished treatment may be performed under temperature conditions that are preferably 20°C to 130°C higher than the heating conditions during mold press molding, for example, 40°C to 90°C higher. Such heating for the mirror-finished treatment tends to soften the surface of the columnar material overall in a favorable manner, making the effects of the present disclosure more likely to be manifested.

In terms of the glass transition temperature of the columnar material, mold press molding may be performed at a temperature higher than the glass transition temperature of the columnar material. For example, mold press molding may be performed under temperature conditions that are preferably 40°C to 150°C higher than the glass transition temperature of the columnar material, for example 60°C to 100°C higher. This is because the mirror-finished material obtained by the mirror-finishing process based on heating can be plastically deformed more suitably.

In the manufacturing method of the present disclosure, mold press molding may be performed in an inert atmosphere. For example, a nitrogen atmosphere may be used as the atmospheric condition for mold press molding. For example, the nitrogen atmosphere may have an oxygen concentration of 10 ppm or less.

Next, mold press molding will be explained over time with reference to Figure 4. In the mold press molding shown in Figure 4, the end face of the flange portion of the optical element molded in the mold cavity formed between the upper and lower molds is subjected to mold transfer.

First, as shown in FIG. 4(A), the mirror-finished material 25 is placed in the mold 50. That is, as shown in the figure, the mirror-finished material 25 is placed in the mold cavity 56 surrounded by, for example, the upper mold 51, the lower mold 52, and the mold sleeve 53.

The mirrored material 25 may be a single piece of material. Such mirrored material 25 preferably has a mirror surface on its outer surface that is obtained without using mechanical tools such as grinding or polishing and/or liquid treatment (particularly a process in which a chemical liquid is brought into contact with the material to obtain a mirror surface, such as a chemical treatment using a chemical polishing liquid with an adjusted pH, such as an acidic range). In relation to such a mirror surface, the overall shape of the mirrored material 25 may have a shape that is closer to the final shape of the optical element than the original columnar material.

The mirrored material 25 put into the die 50 is subjected to deformation by the pressing force from the heated die 50 during mold press molding. That is, the mirrored material 25 is heated by the heat of the die 50 and deformed by the pressing force from the die 50 as shown in Fig. 4 (B) and Fig. 4 (C) to be formed into the desired shape. More specifically, the pressing force from the die 50 plastically deforms the single mirrored material 25, and the inner shape of the die 50 (particularly the upper die 51 and the lower die 52) is transferred to the mirrored material 25, so that the light transmitting portion and the flange portion are integrally obtained from the material 25. Note that when the columnar material corresponds to a prismatic material and a biconvex lens is formed from the mirrored material obtained by heating the entire surface of the material, the mirrored material 25 in the die is likely to have the advantage of being less likely to cause undesirable "air pockets" on its upper or lower surface.

The mirrored material 25 undergoes plastic deformation during mold pressing, deforming so as to spread outward, and then comes into contact with the mold sleeve 53 (see FIG. 4(D)). In other words, the material 25 comes into contact with the inner circumferential surface 58 of the mold sleeve 53, which has a circular or nearly circular shape in a plan view. In mold press molding, mold transfer is performed on the entire periphery of the end face of the mirrored material in this manner. Mold transfer of the entire periphery of the end face makes it easier to shape the flange shape of the optical element, i.e., the peripheral contour of the optical element, into the desired shape.

During mold pressing, the deformation of the mirrored material is brought about by the pressing force received from the mold. In the manufacturing method disclosed herein, the pressing force that can be applied to the material can be set to a pressure that is not excessively excessive. This is because the mirrored material has an overall shape that is preferably closer to the final optical element than the original columnar material due to the above-mentioned "heating of the entire surface". Therefore, even if the material is made of a brittle material, it can be used more actively in mold press molding. For example, glass materials such as chalcogenide materials and/or chalcohalide materials are lens materials with excellent optical properties, but are brittle to pressing forces and are generally considered unsuitable for mold press molding. In the manufacturing method disclosed herein, even such glass materials can be used. In addition, the fact that the load applied to the mirrored material during mold press molding is not excessive means that it is not necessary to prepare the material in advance into a shape relatively close to the shape of the optical element (for example, a lens-like shape) by grinding the material prior to mold press molding. In other words, the material loss of the material is reduced as a result, and from this perspective, glass materials such as chalcogenide materials and/or chalcohalide materials are easily adopted in this disclosure.

The pressure applied to the mold press molding of a mirror-finished material containing a glass material (e.g., a chalcogenide material and/or a chalcohalide material) can be reduced by, for example, at least 5% compared to the case of a material obtained by a mechanical mirror-finishing process. In one embodiment, the mold press molding pressure applied to the mirror-finished material obtained by a heat treatment can be reduced by 5% to 50% or 10% to 40% compared to the case of a material obtained by a mechanical mirror-finishing process.

The mirrored material 25 that has been transferred to the mold as desired is demolded in the final stage of mold pressing. In other words, the mirrored material that has been plastically deformed by mold pressing is finally removed from the mold after being unloaded and cooled, and is used as the desired optical element 10 (see FIG. 4(E)).

The manufacturing method disclosed herein can be embodied in a variety of ways.

(Non-edge aspect)
In this embodiment, mold press molding is performed without using a mold sleeve. That is, in mold press molding, the end face of the flange part of the optical element molded in the mold cavity formed between the upper mold and the lower mold is not subjected to mold transfer. As the mold, for example, a non-sleeve type mold 50 as shown in FIG. 5 may be used. As shown in the figure, the non-sleeve type mold 50 is mainly composed of an upper mold 51 and a lower mold 52, and does not include a sleeve member (for example, the mold sleeve 53 shown in FIG. 3).

In this embodiment, when the mirror-finished material is inserted between the upper and lower dies, the outer periphery of the material that is not in contact with the upper and lower dies is not subjected to mold transfer. For example, as shown in the schematic process diagram of Figure 6, mold press molding is performed without transferring to the die sleeve. This means that mold press molding is performed in the same way as in the embodiment described in Figure 4, but the entire periphery of the end face of the mirror-finished material is not subjected to mold transfer.

Specifically, the mirrored material 25 (see FIG. 6(A)) put into the mold 50 is heated by the heat of the mold 50 and deformed by the pressing force from the mold 50 (see FIG. 6(B) and FIG. 6(C)). In particular, the mirrored material 25 receiving the pressing force from the upper mold 51 and the lower mold 52 of the mold 50 is plastically deformed so as to spread outward. The mirrored material 25 (FIG. 6(D)) that is transferred to the mold as desired through such plastic deformation is released at the final stage of mold press molding and is taken out as the optical element 10 (see FIG. 6(E)). In this embodiment, the mirrored material 25 that is plastically deformed during mold press molding is not pressed against the mold sleeve 53 (see FIG. 4(D)), and therefore the entire circumference of the end surface of the mirrored material is not transferred to the mold. Therefore, the outermost end surface (particularly the end surface of the flange portion) of the obtained optical element 10 may have, for example, a rounded shape (see FIG. 6(E)).

In the manufacturing method disclosed herein, the mirrored material that is molded by press molding has an overall shape that is closer to the final optical element compared to the original columnar material due to the mirroring process. Therefore, plastic deformation of the mirrored material that deforms toward the outer periphery that is not in contact with the upper and lower dies during mold press molding is easily uniform, and the material can be pressurized and deformed into the desired lens shape by mold press molding without using a die sleeve.

In addition, when a mold sleeve is not used, close contact between the mold sleeve and the lens edge surface during molding is essentially avoided. In other words, if there is close contact between the mold sleeve and the lens edge surface, there may be some concern that cracks may occur due to differences in shrinkage caused by differences in the linear expansion coefficient during the cooling process after molding, but this is reduced when a mold sleeve is not used.

(Aspects of mirror finishing treatment using a mold)
In this embodiment, the entire surface of the columnar material is heated and mirror-finished by utilizing a die used in mold press molding. For example, the mirror-finishing treatment may be performed by utilizing a die cavity of a lower die used in mold press molding. More specifically, as shown in FIG. 7, the heat of a lower die 52 may be utilized to perform the mirror-finishing treatment of the columnar material 20. This means that the columnar material may be mirror-finished by the molding means prior to mold press molding.

In this embodiment, the columnar material 20 is heated while being placed in the lower die 52, thereby subjecting the columnar material 20 to a mirror finish (see FIG. 7). For example, the columnar material may be placed in a lower die that has been heated to the heating temperature conditions for the mirror finish treatment, or in a lower die that is in the process of being heated to the heating temperature, and the columnar material may be heated using the heat from the lower die. Alternatively, the columnar material may be placed in the lower die, and then the lower die may be heated to the heating temperature conditions, and the columnar material may be heated using the heat from the lower die. When the die cavity of the lower die is used for the mirror finish treatment in this manner, the lower die may be in contact with only a portion of the bottom surface of the columnar material. The columnar material is supported by the lower die at the contact point, and is heated by the lower die that supports it. Note that if the bottom surface of the columnar material is in full contact with the lower die, the heating of the bottom surface of the columnar material may become too strong, but if only a portion of the bottom surface of the columnar material is in contact with the lower die, the entire surface is more likely to be heated evenly due to thermal radiation. The lower mold may be, for example, a mold that forms a convex or concave shape of the optical surface of the optical element. In other words, the cavity forming surface of the lower mold may have a shape that is complementary to the convex or concave shape of such an optical surface.

When mirror finishing is performed by heating using the mold cavity, the mirror-finished material can be subjected to mold press molding more smoothly. In other words, since the same mold is used for both mirror finishing and mold press molding, the transition from mirror finishing to mold press molding is relatively smooth.

There are no particular limitations on the method of heating the mold. For example, the mold may be heated using a heating coil built into the mold and/or a heat medium flowing through the heat medium pipe of the mold. The mold may be heated using a heating means provided separately from the mold. For example, as shown in FIG. 7, the lower mold 52 may be heated using a heating means 60 provided on the outside of the lower mold 52 to perform the mirror finish treatment of the columnar material. Furthermore, a heating means 65 may be used that is provided in place of the upper mold at the position where the upper mold is placed when the mold is in use (see FIG. 7), and the columnar material may be heated to perform the mirror finish treatment.

(Aspects of continuous processing using a mold)
In this embodiment, the columnar material is subjected to a mirror-finishing process and the mirror-finished material obtained thereby is cooled continuously using a mold. For example, as shown in FIG. 8, by using a mold press molding mold 50, the entire surface of the columnar material is heated to perform a mirror-finishing process to obtain a mirror-finished material, and then the mirror-finished material can be cooled using the same mold 50. Since the mirror-finished material is obtained using a mold used for mold press molding and the mirror-finished material can be mold-press molded using the mold, smoother production of optical elements can be achieved. In such a continuous process, for example, the time required for mold press molding may be shorter than the time required for the mirror-finishing process.

(Lens Product Aspects)
In this embodiment, a lens is manufactured as the optical element 10. That is, a lens for converging or diverging light is manufactured. The type of lens is not particularly limited, and may be a convex lens or a concave lens. The convex lens may be a biconvex lens (FIG. 1(A)) or a plano-convex lens, and the concave lens may be a biconcave lens (FIG. 1(B)) or a plano-concave lens. Furthermore, the lens may be a meniscus lens as shown in FIG. 1(C). Note that the optical element obtained according to the above-mentioned "non-edge embodiment" may have a unique shape since the entire circumference of the end face of the mirror-finished material is not molded and transferred. Specifically, the outermost edge surface of the optical element 10 may have a rounded shape as a whole. For example, in the case of the lens shown in FIG. 9, the outline of the outermost edge surface may be curved as a whole in a cross-sectional view of a biconvex lens (FIG. 9(A)), a biconcave lens (FIG. 9(B)), a meniscus lens (FIG. 9(C)), etc.

As described above, in the manufacturing method of the present disclosure, the entire surface is heated and the resulting mirror-finished material is subjected to mold press molding, so excessive pressure is unlikely to be applied to the material during mold press molding, and brittle materials can be actively used. Therefore, in the manufacturing method of the present disclosure, chalcogenide materials and/or chalcohalide materials can be more actively used. Chalcogenide materials have suitable transmission characteristics for the infrared region, and chalcohalide materials can have suitable transmission characteristics not only for the infrared region but also for the visible light region, so the manufacturing method of the present disclosure can suitably manufacture lenses for at least the infrared region as optical elements.

[Optical element of the present disclosure]
The optical element of the present disclosure is obtained by the above-mentioned manufacturing method and corresponds to the optical element obtained from the material through the above-mentioned mold press molding. In other words, the optical element of the present disclosure is an optical element obtained by mold press molding of a columnar material that has been subjected to a mirror finish treatment by heating the entire surface.

The optical element of the present disclosure preferably comprises a light-transmitting portion and a flange portion extending outward from the light-transmitting portion. When the optical element is a lens, the optical element of the present disclosure comprises a light-transmitting portion corresponding to the lens portion and a flange portion extending outward from the light-transmitting portion. The flange portion corresponds to the outermost edge of the optical element that does not contribute to light transmission when the optical element is in use, and is a portion of the optical element that may have, for example, a substantially constant thickness.

Figure 10 shows a schematic diagram of the optical element 10 being a lens. Although this is merely one example of an optical element, Figure 10 shows a perspective view and a plan view of the appearance of a biconvex lens as the optical element 10.

In the optical element 10 according to the present disclosure, the light-transmitting portion 11 has different internal strains between the peripheral region (for example, the "region including the outermost peripheral portion" in the light-transmitting portion) and the inner region inside the peripheral region. That is, as shown in the schematic diagram of FIG. 11, the amount of internal strain may be different between the inner region 11A corresponding to the substantial light-transmitting portion of the light-transmitting portion 11 and the peripheral region 11B. The lower diagram of FIG. 11 illustrates the relative magnitude relationship of the internal strain. In the lower diagram of FIG. 11, the relatively dark parts indicate relatively large internal strain, and the relatively light parts indicate relatively small or no internal strain. The characteristics of the internal strain in FIG. 11 are preferably related to the manufacturing method described above. In particular, the internal strain associated with mold press molding, which is performed with little material loss, may be brought about in the optical element. The internal distortion shown in FIG. 11 is an example of internal distortion that is characteristic of optical elements obtained by mold press molding a material without obtaining a lens-approximate shape by grinding or other means prior to mold press molding (preferably by mold press molding a material that has been heat-treated as a mirror finish).

In the present disclosure, the "peripheral region" may correspond to a region including the outermost periphery of the light-transmitting portion 11 in a planar view. For example, if the diameter of the circle of the light-transmitting portion 11 in a planar view is D (see FIG. 11), the light-transmitting region outside the concentric region having a diameter of at least 0.5D may be considered to be the "peripheral region".

The planar shape of the inner region may be a polygon such as a square with each side curved toward the center or periphery. For example, if the light-transmitting portion of the optical element is virtually divided into an inner region with each side of a square curved toward the center in a planar view and an outer peripheral region, the amount of internal distortion between them may be different.

In a preferred embodiment, the outer shape of the inner region corresponds to the outer shape of the columnar material before mold press molding to form the optical element. The distortion-free region of the polygonal columnar material, such as a square, may be processed by mold press molding into a shape in which each side of the polygon, such as a square, is curved toward the center or periphery. In such a case, the internal distortion may be different between the region corresponding to the outer shape of the columnar material (hereinafter also referred to as the "material-equivalent region") and other regions in the light-transmitting portion. In other words, as shown in FIG. 11 (particularly an exemplary plan view in which the optical element shown below is a lens), the amount of internal distortion is different between the lens surface of the area portion corresponding to the dimensions of the material-equivalent region and the lens surface of the other area portion in the light-transmitting portion 11.

In the present disclosure, the internal strain in the light-transmitting portion can be ascertained, for example, by measuring the retardation (phase difference). A commercially available measuring device may be used to measure such retardation (phase difference), and the internal strain in the light-transmitting portion (i.e., the distribution of internal strain as shown in the lower diagram of FIG. 11) can be ascertained by using a measuring device (manufactured by Photonic Lattice Co., Ltd., model PA-300-MT-NIR850).

If the columnar material that has been subjected to the mirror finish treatment has a prismatic shape, the area corresponding to the material of the light-transmitting portion in plan view may be a quadrilateral such as a square. In such a case, for example, the amount of internal strain may be different between the area corresponding to the dimensions of the square-shaped material-corresponding area in plan view and the area corresponding to the other light-transmitting portion (i.e., the surrounding area). While this is merely an example, the internal strain in the square area corresponding to the dimensions of the prismatic shape may be about 8 to 12 nm, while the internal strain in the other area (i.e., the surrounding area) may be a maximum of about 30 nm.

In this way, in the optical element of the present disclosure, the amount of internal distortion may differ between the inner region of the light-transmitting portion and the surrounding region of its periphery, but the distortion in the inner region including the central portion of the light-transmitting portion is small or substantially nonexistent. Due to such distortion characteristics, the optical element of the present disclosure may have desired optical characteristics as a whole. For example, the optical element of the present disclosure may have optical characteristics that are substantially comparable to those of an optical element manufactured through mechanical processing such as cutting, grinding, and/or polishing (see FIG. 13) (e.g., light transmission characteristics that are substantially equivalent to those of an optical element manufactured through such mechanical processing).

In a preferred embodiment, the optical element has a stress distribution according to the planar shape of the columnar material. In other words, when the optical element is made of a glass material, the above manufacturing method may result in a stress distribution according to the glass material shape being brought about in the optical element after molding. In addition, in the optical element of the present disclosure, if it is desired to change the average value of the internal strain within the optically effective diameter, this can be achieved by changing the dimensions of the columnar material. In other words, when changing the average value of the internal strain within the optically effective diameter, the dimensions of the columnar material to be mirror-finished can be changed as desired. In addition, the material is not limited to a prismatic material (i.e., the planar shape of the material-equivalent region of the light-transmitting portion is not limited to a quadrangle such as a square), but may be a polygonal shape such as a triangular prism or hexagonal prism, or a cylindrical shape. In other words, the planar shape of the material-equivalent region of the light-transmitting portion may be a triangle, hexagon, or circle. In such a case, a stress distribution according to the triangular prism, hexagonal prism, or cylinder of such a material can be obtained in the light-transmitting portion of the optical element.

The optical element 10 of the present disclosure is preferably obtained by mold press molding from a single material 20, and therefore has a unique configuration. Specifically, the optical element 10 of the present disclosure preferably has a light-transmitting portion 11 and a flange portion 12 made of the same material and integrated with each other. In the embodiment shown in FIG. 10, the light-transmitting portion 11 corresponding to the lens portion and the flange portion 12 on the outside thereof are made of the same material and integrated with each other. When integrated with the same material in this way, the homogeneity is increased compared to when the light-transmitting portion 11 and the flange portion 12 are integrated with different materials, and the structural strength of the optical element 10 can be improved.

The optical element 10 of the present disclosure is obtained under conditions in which the mirror-finished material is not subjected to excessive load during mold press molding. Thus, the optical element 10 can be suitably obtained from chalcogenide materials and/or chalcohalide materials through mold press molding. In other words, a preferred embodiment of the optical element 10 includes a chalcogenide material and/or a chalcohalide material. It can also be said that the optical element 10 can include so-called chalcogenide-based and/or chalcohalide-based glass. In the simplest terms, it can be said that the optical element 10 is preferably made of chalcogenide glass or chalcohalide glass.

In the present specification, the term "chalcogenide material" broadly means a material having at least one chalcogen element selected from the group consisting of S (sulfur), Se (selenium) and Te (tellurium) of group VIb of the periodic table as one of its main components. For example, the chalcogenide material may be a material having a composition in which at least one chalcogen element selected from the group consisting of S (sulfur), Se (selenium) and Te (tellurium) is combined with at least one element selected from the group consisting of Ge (germanium), As (arsenic), Sb (antimony), P (phosphorus), Ga (gallium), In (indium) and Si (silicon). In the present specification, the term "chalcohalide material" means a material having a composition in which a halogen element (at least one element selected from the group consisting of fluorine, chlorine, bromine and iodine) or a compound thereof is introduced into such a chalcogenide material. Such chalcogenide materials and/or chalcohalide materials may have suitable transmission characteristics for the infrared region or for both the infrared region and the visible light region. Therefore, the optical element 10 of the present disclosure may be suitably used as a lens for transmitting light rays in at least the infrared region.

The above describes the embodiments, but they are merely typical examples. Therefore, those skilled in the art will easily understand that the manufacturing method and optical element disclosed herein are not limited to these, and that various embodiments are possible.

For example, in the above description, a preferred manufacturing method for an optical element is described with reference to the drawings, but this is for convenience of explanation only. The manufacturing method of the present disclosure may be one in which the overall process is based on actual manufacturing. For example, the manufacturing method of the present disclosure may be one based on continuous processing as a whole, or on batch processing.

In the above description with reference to FIG. 7, the columnar material is heated with heat from the lower die to perform the mirror finish treatment, but the present disclosure is not limited thereto. For example, the columnar material may be heated and mirror finished using the upper die of the die in addition to or instead of the upper die. In such a case, the upper die may be heated using a heating coil built into the upper die and/or a heat medium flowing through the heat medium pipe of the upper die to perform the mirror finish treatment of the columnar material. Also, a heating means provided separately from the upper die may be used, and for example, the upper die may be heated using a heating means arranged outside the upper die to perform the mirror finish treatment.

Furthermore, the above description has focused on the case where a biconcave lens or a biconvex lens is mold-press molded as a lens, but the present disclosure is not limited to this. For example, as shown in FIG. 12, the present disclosure can be similarly applied to the case where an optical element 10 that is a meniscus lens is mold-press molded.

The optical element according to the present disclosure can be used as various lenses. In particular, the optical element according to the present disclosure can be made of a chalcogenide material and/or a chalcohalide material in a preferred embodiment, and can be used as an infrared lens (which is merely one example, but is a lens intended for at least far-infrared light), a visible light lens, or a broadband transmission lens that transmits light in both the infrared and visible light regions.

REFERENCE SIGNS LIST 10 Optical element 11 Light transmitting portion 11A Inner region of light transmitting portion 11B Peripheral region of light transmitting portion 12 Flange portion 20 Columnar material 25 Mirror-finished material 50 Mold 51 Upper mold 52 Lower mold 53 Mold sleeve 56 Mold cavity 58 Inner peripheral surface of mold sleeve 60 Heating means 65 Heating means

Claims (17)

A method for manufacturing an optical element, comprising the steps of:
A method for manufacturing an optical element, comprising: subjecting a columnar material to a mirror-finishing treatment in which the entire surface of the columnar material is mirror-finished by heating to form a mirror-finished material from the columnar material; and subjecting the mirror-finished material to mold press molding. The method for manufacturing an optical element according to claim 1, wherein the mirror finishing process involves heating and softening the columnar material under heating conditions that are 50°C to 200°C higher than the glass transition temperature of the columnar material. The method for manufacturing an optical element according to claim 1 or 2, wherein the heating is performed by heating the columnar material from above, below, and to the sides. The method for manufacturing an optical element according to any one of claims 1 to 3, wherein the mold press molding is performed at a temperature 20°C to 130°C lower than that of the mirror finishing treatment. The method for manufacturing an optical element according to any one of claims 1 to 4, wherein the mold press molding is performed under a temperature condition that is 40°C to 150°C higher than the glass transition temperature of the columnar material. The method for manufacturing an optical element according to any one of claims 1 to 5, wherein the mirror finishing process is carried out using a mold cavity of a lower mold used in the mold press molding. The method for manufacturing an optical element according to claim 6, wherein the lower die contacts only a portion of the bottom surface of the columnar material. The method for manufacturing an optical element according to claim 6 or 7, wherein the lower mold forms a convex or concave shape of the optical surface of the optical element. The method for manufacturing an optical element according to any one of claims 1 to 8, wherein the surface roughness of the mirror-finished material is set to Ra 50 nm or less by the mirror-finishing treatment. The method for manufacturing an optical element according to any one of claims 1 to 9, wherein the columnar material is in the shape of a polygonal column or a cylinder. The method for manufacturing an optical element according to any one of claims 1 to 10, wherein the columnar material includes a chalcogenide material and/or a chalcohalide material. The method for manufacturing an optical element according to any one of claims 1 to 11, wherein in the mold press molding, the end face of the flange portion of the optical element molded in a mold cavity formed between an upper mold and a lower mold is subjected to mold transfer. The method for manufacturing an optical element according to any one of claims 1 to 11, wherein in the mold press molding, the end face of the flange portion of the optical element molded in a mold cavity formed between an upper mold and a lower mold is not subjected to mold transfer. An optical element,
a light transmitting portion and a flange portion extending outwardly from the light transmitting portion;
An optical element, wherein the light transmitting portion has a different internal strain between a peripheral region and an inner region located more inward than the peripheral region. The optical element according to claim 14, wherein the planar shape of the inner region is a polygon with each side curved toward the center or periphery. The optical element according to claim 14 or 15, wherein the outer shape of the inner region corresponds to the outer shape of the columnar material before mold press molding to form the optical element. The optical element according to any one of claims 14 to 16, wherein the optical element comprises a chalcogenide material and/or a chalcohalide material.

Images