JP4652941B2 - Lens and manufacturing method thereof - Google Patents

Description

  The present invention relates to a lens made of a Cu-containing fluorophosphate glass and a manufacturing method thereof, and relates to an imaging lens having a near-infrared absorption filter function suitable for color correction of a semiconductor imaging device such as CCD or CMOS. .

  In general, a semiconductor image sensor such as a CCD or CMOS has a spectral sensitivity extending from the visible region to the near infrared region. Therefore, means for cutting the near-infrared region with a filter, approximating the spectral sensitivity to human visual sensitivity and improving color reproduction is used. On the other hand, if the absorption in the ultraviolet region of the filter reaches the visible region, the image will become darker. Therefore, this type of filter is required to have a light transmittance of 400 to 520 nm as high as possible and to absorb near infrared rays.

As such a filter material, a near-infrared absorption filter glass disclosed in Patent Document 1 is known.
Japanese Patent Laid-Open No. 10-194777

  By the way, in recent years, as typified by camera-equipped mobile phones, the spread of mobile devices having an imaging function equipped with a semiconductor imaging element has been increasing. There is a demand for such an apparatus to configure the imaging optical system as compactly as possible. A conventional imaging optical system is configured by a group of components including a lens system that forms a subject image on a light receiving surface of an imaging element and a color sensitivity correction filter of the imaging element, and in some cases, an optical low-pass filter. Here, if one lens of the lens system is formed of near infrared light absorbing glass, a color sensitivity correction function can be added to this lens, and a color sensitivity correction filter is used separately from the lens system. There is an advantage that it is not necessary. As a result, the number of components can be reduced and the space occupied by the imaging optical system can be reduced, which is advantageous as an imaging apparatus mounted on a mobile device or the like.

  Accordingly, the present invention provides a lens having an optical function as a lens suitable for a small-sized image pickup device equipped with a semiconductor image pickup device and capable of correcting color sensitivity, and a method for manufacturing the same. The purpose is to provide.

The present invention for solving the above problems is as follows.
[1] A lens formed by precision press-molding a fluorophosphate glass containing Cu ²⁺ , wherein the thickness at the central axis portion is t ₀ [mm], and the content of Cu ^{2+ in} the glass is M _Cu [ A lens having a meniscus shape having a thickness t ₀ of 0.8 mm or more and M _Cu × t _{0 in} a range of 0.9 to 1.4 cationic% · mm .
[ 2 ] The lens according to [1] , wherein the glass is a fluorophosphate glass having a glass transition temperature (Tg) of 400 ° C. or lower.
[ 3 ] The lens according to [1] or [2] , which has a convex meniscus shape.
[ 4 ] The glass is expressed in cationic%.
P ⁵⁺ 11 to 43%,
Al ³⁺ 1-29%,
14 to 50% in total of Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ and Zn ²⁺ ,
Li ⁺ , Na ⁺ and K ⁺ in total from 0 to 43%,
La ³⁺ , Y ³⁺ , Gd ³⁺ , Si ⁴⁺ , B ³⁺ , Zr ⁴⁺ and Ta ⁵⁺ in total 0 to 12%,
Cu ²⁺ 0.5% or more,
Sb ³⁺ 0-0.1%,
In addition, in anionic% display,
F ^- 10-80%
The lens according to any one of [1] to [ 3 ], which is a fluorophosphate glass containing
[ 5 ] The method for producing a lens according to any one of [1] to [ 4 ], comprising precision press-molding a glass preform made of a fluorophosphate glass containing Cu ²⁺ .

  According to the present invention, it is possible to provide a lens that is suitable for a small-sized image pickup apparatus equipped with a semiconductor image pickup device and enables color sensitivity correction of the image pickup device, and a manufacturing method thereof. Furthermore, according to the present invention, there is provided a lens formed by precision press molding that combines good imaging performance and the color sensitivity correction function by utilizing the fact that fluorophosphate glass exhibits a low transition temperature. Can do.

In particular, according to the present invention of the above aspect [2], the content of Cu ²⁺ is reduced so that the thickness of the lens is equal to or greater than a predetermined thickness. Therefore, from the optical path length in the lens along the central axis and the optical axis Even a lens having a difference in the optical path length in the lens at a distant portion can reduce a difference in light transmission amount of light passing through each optical path, and can provide a lens with less unevenness in color sensitivity correction. .

  In addition, according to the present invention of the above aspect [3], the lens thickness can be secured at a predetermined value or more even when glass having a low temperature softening property and a narrow glass heating temperature range at the time of precision press molding is used. Thus, it is possible to provide a lens that is difficult to break and can satisfactorily correct the color sensitivity of the semiconductor imaging device.

Furthermore, according to the present invention of the above aspect [6], the lens is formed with a glass composition having excellent weather resistance even when the content of Cu ²⁺ and the thickness of the lens are within the above ranges. An excellent lens can be provided.

  Further, according to the present invention of the above aspect [7], it is possible to provide a method for manufacturing a lens that enables mass production of each lens by precision press molding.

The lens of the present invention is a lens formed by precision press-molding a fluorophosphate glass containing Cu ²⁺ . Since Cu ²⁺ absorbs near-infrared light, it can correct the color sensitivity of a semiconductor image sensor such as a CCD or CMOS. Further, since the base composition containing Cu ²⁺ is a fluorophosphate-based composition, it is possible to provide a lens having excellent weather resistance while realizing a transmittance characteristic suitable for color sensitivity correction. The precision press molding will be described later.

This onset Ming, t ₀ [mm] thick at the center axis portion, the content of Cu ²⁺ of the glass when the M _Cu [cationic%], M _Cu × t ₀ 0.9 cationic%・ Mm〜1. It is a lens in the range of 4 cationic% · mm.

The in-lens optical path length of the light ray incident on the center of the lens varies depending on the direction of the light incident on the lens, but the lens is symmetric with respect to the central axis. The in-lens optical path length of the incident light beam is represented by the in-lens optical path length of the light beam traveling along the lens central axis. Therefore, if a lens is formed using glass containing Cu ²⁺ with a content M _Cu suitable for the color sensitivity correction function for this typical optical path length, better color sensitivity correction can be performed. From such a viewpoint, the preferable range of M _Cu × t ₀ is 1.0 to 1. 4 cationic% · mm, more preferable range is 1 . 05 to 1.4 cationic% · mm.

In a further preferred aspect of the present invention, the lens of the above aspect [M _Cu × t ₀ is 0.9 cation% · mm to 1. A lens in the range of 4 cationic% · mm], which is made of a fluorophosphate glass having a glass transition temperature (Tg) of 400 ° C. or less, and a thickness t _{0 at the} optical axis portion is 0.00. It is a lens that is 8 mm or more.

The 400 ° C. or less and low glass glass transition temperature (Tg), Cu ² glass temperature generally decreases indicating a predetermined viscosity, since the melting temperature of the glass is also low, deteriorating the transmittance properties of the glass ^The change in valence from ⁺ to Cu ⁺ can be suppressed. However, if the glass transition temperature is as low as 400 ° C. or lower as described above, the appropriate glass heating temperature range during precision press molding is narrowed. That is, if the heating temperature is too high, the glass will foam and a homogeneous lens cannot be obtained. On the other hand, if the heating temperature is too low, the glass with high viscosity will be forced to be pressed, and the glass will be easily broken. I can't get a stable lens. When trying to mold a thin lens by precision press molding, the glass preform for precision press molding, that is, the preform must be pressed into a thin shape, and the glass is less than when molding a thick lens. It becomes easy to break. Therefore, in this embodiment, a fluorophosphate glass having a glass transition temperature (Tg) of 400 ° C. or lower is used as the glass, and the thickness t ₀ at the optical axis portion (center axis) of the lens is 0.6 mm or more during precision press molding. Reduce lens damage at A fluorophosphate glass having a glass transition temperature (Tg) of 400 ° C. or lower can be obtained by adjusting the composition of the fluorophosphate glass as follows. That is, P ⁵⁺ , alkaline earth metal ions as essential cation components, Al ³⁺ , Zn ²⁺ , alkali metal ions, etc. are introduced as optional cation components, and F ⁻ and O ²⁻ are included as anion components, By introducing an appropriate amount of Cu ²⁺ into this composition, a fluorophosphate glass having a glass transition temperature (Tg) of 400 ° C. or lower can be prepared. Moreover, there is no restriction | limiting in particular in the minimum of the glass transition temperature (Tg) of the said fluorophosphate glass, However, the preferable range of the glass transition temperature (Tg) of a fluorophosphate glass is 300-400 degreeC on the basis of 300 degreeC. It is a range.

Also, t _{0 is set} to 0. By setting the _thickness to 8 mm or more, appropriate M _Cu can be reduced. As a result, even if there is a difference between the in-lens optical path length in the optical axis portion and the in-lens optical path length in the portion away from the optical axis, the amount of light transmitted through each optical path is smaller than that of the thin lens. Since the difference can be reduced, better color correction can be performed over the entire lens surface. Moreover, the following effects can also be _acquired by reducing appropriate _MCu .

When attention is paid to the transmittance of the glass constituting the lens, the spectral transmittance characteristic at a thickness at which the transmittance is 50% at a wavelength of 615 nm directly affects the color sensitivity correction. When the amount of M _Cu is large, the transmittance at a wavelength of 350 nm to 400 nm at the thickness is reduced, and near infrared light can be cut. However, since the transmittance of blue light is lowered, the color balance of the image may be deteriorated. On the other hand, t _{0 is set} to 0. By setting the thickness to 8 mm or more, infrared light absorptivity that can cut infrared light well even when M _Cu is relatively small can be imparted, and transmittance at a wavelength of 350 nm to 400 nm at the thickness on the optical axis. Can be kept high. As a result, a lens having a better color sensitivity correction performance as a whole can be obtained. From this point of view, t _{0 is set} to 0 . It shall be the more than 8mm. 0 . It is still more preferable to set it as 9 mm or more.

If there is no problem in precision press molding, the upper limit of the thickness is not particularly limited, but for the purpose of providing a color sensitivity correction filter function and a lens function to one optical element to make the imaging optical system compact, t It is preferable to set ₀ to 5 mm or less.

This onset Ming is a lens having a meniscus shape. The meniscus lens has a smaller difference between the thickness of the central axis portion and the thickness of the portion away from the central axis than the biconvex lens, the biconcave lens, the plano-convex lens, and the plano-concave lens. Therefore, in a lens made of glass having a constant composition as in the present invention, the difference between the in-lens optical path length of the light beam passing through the portion near the central axis and the in-lens optical path length of the light beam passing through the portion away from the central axis is reduced. It is possible to reduce the difference in light transmission between the two light beams. Then, by making the thickness at the central axis portion in the above range, it is possible to satisfactorily perform color correction necessary for color sensitivity correction of the semiconductor image pickup device over the entire lens surface. A more preferable aspect of this aspect is a convex meniscus lens (also referred to as a positive meniscus lens). Furthermore, as will be described later, the lens of the present invention can have two hook-shaped flat portions in addition to the two lens surfaces.

  The lens of the present invention is made of a fluorophosphate glass, and the refractive index (nd) of the fluorophosphate glass is generally in the range of 1.45 to 1.58. The lens made of glass having a refractive index (nd) in the above range is advantageously disposed on the image pickup element side of the image pickup optical system. Therefore, a convex meniscus lens having a positive power constitutes the image pickup optical system. Is preferable.

Next, glass suitable as a material for the lens of the present invention will be described. First, if it contains Cu ²⁺ content M _Cu, it is desired that a base glass showing excellent weather resistance, resistance to devitrification. Furthermore, in order to prevent the color sensitivity correction function from being impaired by changing the valence from Cu ²⁺ to Cu ⁺ during melting, a glass that can be melted at a low temperature is desired.

As a glass that satisfies such a demand, for example, in the cationic% display,
P ⁵⁺ 11 to 43%,
Al ³⁺ 1-29%,
14 to 50% in total of Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ and Zn ²⁺ ,
Li ⁺ , Na ⁺ and K ⁺ in total from 0 to 43%,
La ³⁺ , Y ³⁺ , Gd ³⁺ , Si ⁴⁺ , B ³⁺ , Zr ⁴⁺ and Ta ⁵⁺ in total 0 to 12%,
Cu ²⁺ 0.5% or more,
Sb ³⁺ 0-0.1%,
In addition, in anionic% display,
F ^- 10-80%
Fluorophosphate glass containing

  As glass containing Cu, there are generally phosphate glass and fluorophosphate glass. Phosphate glass has poor weather resistance, whereas fluorophosphate glass has excellent weather resistance. Among the fluorophosphate glasses, weather resistance improves when the aluminum content increases. However, when the amount of aluminum becomes excessive, the meltability is lowered. However, in the case of a glass having a lowered meltability, if the melting temperature is raised so that there is no unmelted raw material, the Cu ions are reduced and the color sensitivity correction function deteriorates. The transmittance in the vicinity of the wavelength of 400 nm is lowered, and the amount of light in the wavelength region desired to be transmitted is lowered. The glass composition used in the present invention is a composition that takes into account the balance of the weather resistance, meltability, and color sensitivity correction function of the glass.

This Cu ²⁺ -containing fluorophosphate glass is based on P ⁵⁺ as a component that forms a glass skeleton, and on top of that, Al maintains devitrification resistance sufficient for mass production and improves weather resistance. ³⁺ and a divalent cation (at least one cation of Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ , and Zn ²⁺ ) are contained as essential components. Furthermore, this glass affects the transmittance characteristics of alkali metal ions (at least one cation of Li ⁺ , Na ⁺ , K ⁺ ) for reducing the viscosity of the glass during melting and enabling melting at low temperatures. Cation (La ³⁺ , Y ³⁺ , Gd ³⁺ , Si ⁴⁺ , B ³⁺ , Zr ⁴⁺ , Ta ⁵⁺ cation) is an optional component for improving wear resistance without any problems. Can be included. In addition, in this glass, Sb ³⁺ can be optionally added to this composition for adjusting the valence of Cu.

The weather resistance and transmittance characteristics of the glass do not change greatly even if the kind and content of the divalent cation component in the fluorophosphate glass are changed, and a part of the divalent cation component is alkali metal ion or La ³⁺ , Y ³⁺ , Gd ³⁺ , Si ⁴⁺ , B ³⁺ , Zr ⁴⁺ , Ta ⁵⁺ , or a part of F ⁻ is replaced with O ²⁻ , the above characteristics change significantly. There is nothing. Therefore, it is possible to change the kind and content of the divalent cation component within a certain range, or to substitute part of the divalent cation component and part of F ⁻ with O ²⁻ . This point will be described later.

  Hereinafter, unless otherwise specified, the cation content is expressed in cationic% and the anion content in anionic%.

P ⁵⁺ is a component that forms a glass skeleton as described above. However, vitrification becomes difficult if P ⁵⁺ is less than 11%, and weather resistance is lowered if it exceeds 43%. Accordingly, the amount of P ⁵⁺ is suitably 11 to 43%. The amount of P ⁵⁺ is preferably in the range of 20-40%, more preferably 23-35%.

Al ³⁺ is an effective component that improves weather resistance. However, if Al ³⁺ is less than 1%, the effect is difficult to obtain, and if it exceeds 29%, the meltability of the glass decreases. Accordingly, the amount of Al ³⁺ is suitably in the range of 1 to 29%. The amount of Al ³⁺ is preferably in the range of 5-20%, more preferably 8-18%.

Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ , and Zn ²⁺ are effective components for improving the weather resistance of glass. However, when the total amount of Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ , and Zn ²⁺ is less than 14%, it becomes difficult to vitrify, and when it exceeds 50%, devitrification tends to occur. Accordingly, the total amount is suitably in the range of 14 to 50%. The total amount is preferably in the range of 18-40%, more preferably 20-35%.

Li ⁺ , Na ⁺ and K ⁺ are optional components. When the total amount of Li ⁺ , Na ⁺ and K ⁺ exceeds 43%, the weather resistance of the glass tends to decrease. Therefore, the total amount of Li ⁺ , Na ⁺ and K ⁺ is suitably in the range of 0 to 43%. This total amount is preferably in the range of 5-38%, more preferably 15-35%.

La ³⁺ , Y ³⁺ , Gd ³⁺ , Si ⁴⁺ , B ³⁺ , Zr ⁴⁺ and Ta ⁵⁺ are also optional components. These components serve to improve the abrasion resistance without impairing the transmittance characteristics, but when the total amount exceeds 12%, the stability of the glass tends to be lowered. Therefore, it is appropriate that the total amount of La ³⁺ , Y ³⁺ , Gd ³⁺ , Si ⁴⁺ , B ³⁺ , Zr ⁴⁺ and Ta ⁵⁺ is 0 to 12%. The total amount is preferably 0 to 10%, more preferably 0 to 5%, and still more preferably 0 to 2%.

Cu ²⁺ is an essential cation for absorption in the near-infrared region. If it is less than 0.5%, its absorption becomes insufficient, and it is difficult to introduce it uniformly into glass. Therefore, the amount is suitably 0.5% or more. The upper limit of the Cu ²⁺ content is determined by the relationship with the lower limit of the lens thickness t ₀ , but if the upper limit of the glass stability is taken into account without considering the thickness t ₀ , It is suitably 8% or less, preferably 5% or less, and more preferably 4% or less.

Sb ³⁺ is an optional component. By containing Sb ³⁺ in the range of 0 to 0.1%, it works to improve the transmittance around a wavelength of 400 nm.

F ^- is an essential component that lowers the glass transition temperature and contributes to improving weather resistance. When the amount of F ⁻ is less than 10%, the weather resistance tends to decrease, and when it exceeds 80%, Cu ions tend to become Cu ⁺ and the transmittance near a wavelength of 400 nm tends to decrease. Therefore, the amount of F ⁻ is suitably in the range of 10 to 80%. The amount of F ⁻ is preferably in the range of 17-80%, more preferably 25-60%, still more preferably 25-50%.

Since the glass is a fluorophosphate glass, the total remaining amount of anions is preferably O ^{2− in} order to obtain desired transmittance characteristics.

Next, each amount of Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ , and Zn ^{2+ in} the above composition will be described.

From the viewpoint of improving devitrification resistance, the content of Ba ²⁺ is preferably 0 to 8%, more preferably 1 to 8%, and more preferably 2 to 8% within the above composition range. Is more preferable.

The composition range of Sr ²⁺ , Ca ²⁺ , Mg ²⁺ , and Zn ²⁺ is preferably set to the following range in order to improve devitrification resistance. That is, the content of Sr ²⁺ is preferably 0 to 15%, more preferably 1 to 15%, and further preferably 2 to 14%.

About content of Ca ^<2+ >, the range of 0-15% is preferable, The range of 3-15% is more preferable, The range of 3-13% is further more preferable.

About content of Mg ^<2+> , the range of 0-10% is preferable, The range of 1-10% is more preferable, The range of 1-6% is further more preferable.

About content of Zn ^<2+ >, the range of 0 to 6% is preferable, and the range of 0 to 5% is more preferable.

Next, the amounts of Li ⁺ , Na ⁺ and K ⁺ in the above composition will be described.
From the viewpoint of improving devitrification resistance and not deteriorating durability, the amount of Li ⁺ is preferably 0 to 40%, more preferably 5 to 40%, and more preferably 10 to 35%. The range of is more preferable.

The following composition ranges of Na ⁺ and K ⁺ are also preferably set to the following ranges in order to improve devitrification resistance and not deteriorate durability. That is, the Na ⁺ content is preferably in the range of 0 to 13%, more preferably in the range of 0 to 10%, and still more preferably in the range of 0 to 9%.

The K ⁺ content is preferably in the range of 0 to 5%, more preferably in the range of 0 to 4%, and still more preferably in the range of 0 to 3%.

Among the above compositions, from the viewpoint of improving the above-mentioned properties and improving mass productivity, as for cations, P ⁵⁺ , Al ³⁺ , Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ , Zn ^{2+ are used.} , Li ⁺ , Na ⁺ , Cu ²⁺ and Sb ³⁺ are preferably 99% or more, and more preferably 100%.

Note that the glass can also contain SiO ₂ . Patent Document 1 describes that SiO ₂ has an effect of stabilizing glass. However, the glass containing SiO ₂ has a low meltability, and if the meltability is lowered, the melting temperature must be increased. As a result, the Cu ion is reduced and the color sensitivity correction function may be lowered. Therefore, in consideration of such points, the glass can contain SiO ₂ , but it is preferable not to contain it. As described above, for cations, P ⁵⁺ , Al ³⁺ , Ba ²⁺ , More preferably, the total amount of Sr ²⁺ , Ca ²⁺ , Mg ²⁺ , Zn ²⁺ , Li ⁺ , Na ⁺ , Cu ²⁺ and Sb ³⁺ is 100%.

Next, a method for manufacturing a lens will be described.
The lens of the present invention is a lens obtained by precision press-molding a glass preform, and the production method of the lens including the precision press-molding of the glass preform is also included in the present invention.

  First, in the method for manufacturing a lens, a glass preform made of a fluorophosphate glass constituting the lens is prepared. In order to make a glass preform, glass raw materials such as fluoride, oxide, phosphate, hydroxide, carbonate are prepared, mixed well, introduced into a melting vessel, heated with a lid, 800 Melt at ~ 900 ° C, then clarify and homogenize.

  Homogeneous molten glass flows out of the pipe, is cast into a mold, and is formed into a thick plate-like glass molded body. This molded body is annealed to remove strain, and cut, ground, and polished to produce a spherical preform having a smooth surface. Alternatively, a glass melt is dropped at a trumpet-shaped recess having a gas outlet for receiving a glass droplet obtained by dropping a homogeneous molten glass from a pipe and receiving the obtained glass droplet with a molding die, and jetting gas upward at the bottom of the molding die. May be formed into a spherical preform by rotating in a random direction. The preform thus produced is press-molded with a press mold composed of mold parts including an upper mold, a lower mold, and a sleeve mold to obtain a lens.

  For the processing of the mold material of the press mold and the material of the mold material, the mold release film formed on the molding surface of the upper mold and the lower mold, the method of forming the mold release film, the kind of atmosphere for performing the precision press molding, etc., apply known techniques That's fine.

For example, first, a spherical preform is placed in the center of a concave lower molding surface inserted into a through hole of a sleeve mold, and the upper mold is placed so that the molding surface faces the lower molding surface. Insert inside. In this state, when the preform and the press mold are heated together and the temperature of the glass constituting the preform rises to a temperature showing a viscosity of 10 ⁶ dPa · s, for example, the upper mold and the lower mold Pressurize the preform with. The pressurized preform is spread out in a space (called a cavity) surrounded by the upper mold, the lower mold, and the sleeve mold. In this way, the glass preform is pressed to fill the glass in the sealed space formed with the press mold closed.

  The relative positions of the molding surfaces of the upper mold, the lower mold, and the sleeve mold in the mold closed state, and the angle formed by the surface normal are precisely formed. If the above molding is performed using such a press mold, the optical function surface and the positioning reference surface can be formed with a highly accurate positional relationship and angle.

  The central portion of the upper mold forming surface is a surface on which a lens surface, which is an optical functional surface of the lens, is transferred and molded, and the peripheral portion is a ring-shaped flat surface on which a hook-shaped flat portion is transferred. Similarly, for the lower mold forming surface, the center portion is a surface on which the lens surface is transfer-molded, and the peripheral portion is the plane on the annular zone on which the bowl-shaped flat portion is transfer-molded. Until the press molding is completed, the upper and lower molds are accurately maintained so that the directions of the upper and lower molds face each other and the central axes of the upper and lower molds coincide.

  By filling glass in a sealed space formed with the press mold closed, the inner surface of the sleeve mold through-hole is transferred to the glass. By accurately forming the angle between the central axis of the sleeve-type through hole and the inner surface of the through-hole, and maintaining the central axis of the through-hole and the upper and lower mold central axes precisely until the end of press molding, 2 It is possible to accurately form the two lens surfaces, the two hook-shaped flat portions, the relative position of the edge of the lens on which the inner surface of the sleeve mold is transferred, and the angle formed by the surfaces. Then, one of the two hook-shaped flat portions and the edge are used as a positioning reference surface, and one of the hook-shaped flat portions is used as a reference surface for accurately positioning the distance between the lenses, and the edge is used as the light between the lenses. It can be used as a reference plane for precisely matching the axes.

  In addition, it is desirable to form the ridge where the edge and the bowl-shaped flat portion intersect on the free surface. If the edge and the bowl-shaped flat part are formed, there is no risk of hindering the positioning function, and if the ridge is sharp, the ridge will be chipped or snapped into the holder, It will cause dust generation. When dust adheres to the light-receiving surface of the image sensor, the image quality is greatly reduced. Therefore, in order to prevent such trouble, it is desirable to mold a precision press-molded product having a ridge composed of a free surface.

  An optical multilayer film such as an antireflection film or a near-infrared light reflection film may be formed on the lens thus produced as necessary.

Next, examples of the present invention will be described.
Table 1 shows the composition and characteristics of the glass forming the preform and lens of this example.
First, in order to obtain a glass having the composition shown in Table 1, phosphates, fluorides, oxides, and hydroxides containing each cation component are weighed, prepared, and sufficiently mixed. The glass raw material thus obtained is introduced into a melting vessel, covered, melted at 800 to 900 ° C., stirred, clarified, stirred and homogenized, and then discharged from the pipe at a constant flow rate. And cast into a mold to form a thick plate-like glass molded body. Simultaneously with the molding, the molded body is pulled out in the horizontal direction, and annealed in a continuous annealing furnace. The annealed glass molded body was cut, ground and polished to produce a spherical preform with a smooth and homogeneous surface.

  The preform thus obtained is precision press-molded using a press mold having an upper mold, a lower mold, and a sleeve mold. The center part of each molding surface of the upper mold and the lower mold is a part for transferring the lens surface, and the periphery of the part for transferring the lens surface is a flat surface for transferring the bowl-shaped flat part.

The through holes of the upper and lower molds and the sleeve type for inserting the preform are cylindrical, and the clearance with the upper and lower molds is made as small as possible within a range that does not hinder sliding.
When the preform is pressed with the upper and lower molds by heating and softening, the glass is spread into the cavity in the press mold and filled in the entire cavity.
In this way, the lens including the lens surfaces 11 and 12 to which the upper and lower mold forming surfaces are transferred, the flange-shaped flat portions 13a and 13b, and the edge portion 14 to which the inner surface of the sleeve-type through hole is transferred is precision press-molded. .

The overall cross-sectional shape of the obtained lens is shown in FIG. 1, and the lens type, t ₀ , M _Cu × t ₀ value, and edge thickness are shown in Table 1. 1A is a convex meniscus lens, FIG. 1B is a concave meniscus lens, FIG. 1C is a biconvex lens, and FIG. 1D is a plano-convex lens, and each lens has a bowl-shaped flat portion. .

  In this manner, lenses corresponding to Examples 1 to 39 are molded by precision press molding as shown in Table 1 from combinations of glass composition, shape, and dimensions.

  An imaging optical system is configured by combining one lens made of each near-infrared light absorbing glass obtained above and a lens made of optical glass that does not contain copper and does not have a filter function. When the image of the subject was formed on the surface and the images were viewed, all of the images were corrected for color sensitivity over the entire screen.

In addition, if necessary, a diffraction grating may be formed on the lens surface by the precision press molding to form a lens with an optical low-pass filter function.
Further, an optical multilayer film such as an antireflection film or an infrared light reflection film may be coated on the lens surface.
In this way, various lenses having an aspheric lens shape or a spherical lens shape can be produced.

The cross-sectional shape of the lens prepared in the Example is shown.

Claims (5)

A lens formed by precision press-molding a fluorophosphate glass containing Cu ²⁺ ,
When the thickness at the central axis portion is t ₀ [mm] and the content of Cu ^{2+ in} the glass is M _Cu [cationic%], the thickness t ₀ is 0.8 mm or more, and M _Cu × t A lens having a meniscus shape in which ₀ is in a range of 0.9 to 1.4 cationic% · mm . The lens according to claim 1 glass glass transition temperature (Tg) of 400 ° C. or less of the fluorophosphate glass. The lens according to claim 1 , wherein the lens has a convex meniscus shape. The glass is in% of cationic
P ⁵⁺ 11 to 43%,
Al ³⁺ 1-29%,
14 to 50% in total of Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Mg ²⁺ and Zn ²⁺ ,
Li ⁺ , Na ⁺ and K ⁺ in total from 0 to 43%,
La ³⁺ , Y ³⁺ , Gd ³⁺ , Si ⁴⁺ , B ³⁺ , Zr ⁴⁺ and Ta ⁵⁺ in total 0 to 12%,
Cu ²⁺ 0.5% or more,
Sb ³⁺ 0-0.1%,
In addition, in anionic% display,
F ^- 10-80%
Lens according to any one of claims 1 to 3, which is a fluorophosphate glass containing. Comprising precision press molding a glass preform consisting of fluorophosphate glass containing Cu ^2+, method for producing a lens according to any one of claims 1-4.

Images