JP6875431B2 - Refraction distribution type lenses, optical products, optical instruments, glass compositions for refraction distribution type lenses, and methods for manufacturing refraction distribution type lenses. - Google Patents

Description

The present invention relates to a refractive index distributed lens, an optical product, an optical instrument, a glass composition for a refractive index distributed lens, and a method for manufacturing the refractive index distributed lens.

Conventionally, a device for observing defects on the surface of a subject using a Charge-Coupled Device (CCD) has been known. For example, Patent Document 1 describes a surface defect device including a light source, an irradiation means, a light collecting means, and an observation means. The observation means includes an imaging lens and a CCD.

Patent Document 2 describes an inspection device suitable for visual inspection of a photoconductor drum of an electrophotographic copying machine or a printer. This inspection device includes a camera device for photographing a photoconductor drum with a plurality of one-dimensional CCD cameras arranged in a row.

On the other hand, a close contact image sensor (CIS) is also known as an image sensor. The CIS includes a rod lens array. A refractive index distribution type lens is usually used for the rod lens array.

For example, Patent Documents 3 to 5 describe refractive index distributed lenses. The refractive index distribution type lens or the refractive index distribution type rod lens is a rod-shaped (rod-shaped) lens having a refractive index distribution in which the refractive index is continuously decreased from the center to the outer periphery. In the refractive index distribution type lens described in Patent Document 3, the difference Δn between the refractive index on the peripheral surface of the lens and the refractive index on the central axis is 0.003 or more. According to Patent Document 3, when Δn is smaller than 0.003, the opening angle (2θ) becomes smaller than about 10 °, which is suggested to be undesirable. In other words, it is considered that Patent Document 3 suggests that an opening angle (θ) of less than 5 ° is not desirable.

The aperture angle of the refractive index distribution type lens according to the embodiment in Patent Document 4 is about 10.1 to 12.9 °. The aperture angle of the refractive index distribution type lens according to the embodiment in Patent Document 5 is 10.1 to 12.0 °.

Japanese Unexamined Patent Publication No. 7-27709 Japanese Unexamined Patent Publication No. 2003-75906 Special Publication No. 52-1594 Japanese Unexamined Patent Publication No. 2005-289775 Japanese Unexamined Patent Publication No. 2008-230956

Patent Documents 1 and 2 do not describe the use of a refractive index distribution type lens. The refractive index distribution type lenses described in Patent Documents 3 to 5 have a large aperture angle. This cannot be said to be advantageous from the viewpoint of realizing a large depth of field in the refractive index distribution type lens, and it is considered that the depth of field of the refractive index distribution type lens described in Patent Documents 3 to 5 is small.

In view of such circumstances, the present invention provides a refractive index distribution type lens having a large depth of field. The present invention also provides an optical product provided with such a refractive index distribution type lens and an optical device provided with the optical product. In addition, the present invention provides a glass composition for a refractive index distributed lens, which is advantageous for increasing the depth of field of the refractive index distributed lens. The present invention also provides an advantageous method for manufacturing a refractive index distributed lens having a large depth of field.

The present invention
It has a depth of field of 1.5 to 3.0 mm and has a depth of field of 1.5 to 3.0 mm.
The depth of field is determined by subtracting the minimum value from the maximum value of the working distance.
At the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines / mm is 30% or more.
A refractive index distribution type lens is provided.

The present invention
Provided is an optical product provided with the above-mentioned refractive index distribution type lens.

The present invention
Provided is an optical device equipped with the above optical products.

The present invention
Shown in mol%,
40% ≤ SiO ₂ ≤ 65%
0% ≤ TiO ₂ ≤ 10%
0.1% ≤ MgO ≤ 22%
0.15% ≤ ZnO ≤ 15%
0.5% ≤ Li ₂ O <4%
2% ≤ Na ₂ O ≤ 20%
0% ≤ B ₂ O ₃ ≤ 20%
0% ≤ Al ₂ O ₃ ≤ 10%
0% ≤ K ₂ O ≤ 3%
0% ≤ Cs ₂ O ≤ 3%
0% ≤ Y ₂ O ₃ ≤ 5%
0% ≤ ZrO ₂ ≤ 2%
0% ≤ Nb ₂ O ₅ ≤ 5%
0% ≤ In ₂ O ₃ ≤ 5%
0% ≤ La ₂ O ₃ ≤ 5%
Including 0% ≤ Ta ₂ O ₅ ≤ 5%,
At least two selected from the group consisting of CaO, SrO, and BaO are contained in an amount of 0.1 mol% or more and 15 mol% or less, respectively.
Display in mol%,
2% ≤ MgO + ZnO,
0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93,
The conditions of 2.5% ≤ Li ₂ O + Na ₂ O <24% and 0% ≤ Y ₂ O ₃ + ZrO ₂ + Nb ₂ O ₅ + In ₂ O ₃ + La ₂ O ₃ + Ta ₂ O ₅ ≤ 11% are satisfied.
A glass composition for a refractive index distributed lens is provided.

The present invention
This is a method for manufacturing a refractive index distributed lens.
Forming a glass wire composed of a glass composition containing an oxide of the first alkali metal element,
The glass wire is immersed in a molten salt containing a second alkali metal element different from the first alkali metal element, and the first alkali metal element in the glass wire and the second alkali in the molten salt are immersed. By ion-exchange treatment with a metal element, a refractive index distribution is formed on the glass wire.
The glass composition is shown in mol%.
40% ≤ SiO ₂ ≤ 65%
0% ≤ TiO ₂ ≤ 10%
0.1% ≤ MgO ≤ 22%
0.15% ≤ ZnO ≤ 15%
0.5% ≤ Li ₂ O <4%
2% ≤ Na ₂ O ≤ 20%
0% ≤ B ₂ O ₃ ≤ 20%
0% ≤ Al ₂ O ₃ ≤ 10%
0% ≤ K ₂ O ≤ 3%
0% ≤ Cs ₂ O ≤ 3%
0% ≤ Y ₂ O ₃ ≤ 5%
0% ≤ ZrO ₂ ≤ 2%
0% ≤ Nb ₂ O ₅ ≤ 5%
0% ≤ In ₂ O ₃ ≤ 5%
0% ≤ La ₂ O ₃ ≤ 5%
Including 0% ≤ Ta ₂ O ₅ ≤ 5%,
The glass composition contains at least two selected from the group consisting of CaO, SrO, and BaO, each containing 0.1 mol% or more and 15 mol% or less.
The glass composition is expressed in mol%.
2% ≤ MgO + ZnO,
0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93,
The conditions of 2.5% ≤ Li ₂ O + Na ₂ O <24% and 0% ≤ Y ₂ O ₃ + ZrO ₂ + Nb ₂ O ₅ + In ₂ O ₃ + La ₂ O ₃ + Ta ₂ O ₅ ≤ 11% are satisfied.
Provide a method.

The above-mentioned refractive index distribution type lens has a large depth of field. Further, the above-mentioned glass composition for a refractive index distribution type lens is advantageous for increasing the depth of field of the refractive index distribution type lens.

FIG. 1 is a diagram illustrating a method of determining the depth of field of an example of a refractive index distribution type lens according to the present invention. FIG. 2 is a diagram showing an aperture angle of an example of a refractive index distribution type lens according to the present invention. FIG. 3A is a diagram showing an ion exchange treatment in an example of the method for manufacturing a refractive index distribution type lens according to the present invention. FIG. 3B is a graph conceptually showing the refractive index distribution in the refractive index distribution type lens. FIG. 4 is a perspective view showing an example of an optical product according to the present invention. FIG. 5 is a cross-sectional view showing an example of the optical device according to the present invention. FIG. 6 is a cross-sectional view showing another example of the optical device according to the present invention. FIG. 7 is a diagram showing still another example of the optical device according to the present invention. FIG. 8 is a diagram showing still another example of the optical device according to the present invention. FIG. 9 is a graph showing the relationship between the MTF value and the working distance of the refractive index distribution type lens according to Example 2, Comparative Example 3, and Reference Example 1.

The image data collected in the visual inspection of the subject must have a resolution that can identify defects in the subject. If a camera equipped with a one-dimensional CCD sensor is used to obtain high-resolution image data, the effective width that can be captured by one camera becomes small. Therefore, it may be difficult to capture the entire subject with one camera. For example, when the pixel size corresponding to the required resolution in the image data is 90 μm, the width of the region that can be imaged by a camera equipped with a 4096 pixel one-dimensional CCD sensor is about 370 mm. In this case, in order to inspect the entire subject having a width of 1200 mm, it is necessary to arrange four camera systems equipped with a one-dimensional CCD sensor and a camera lens in the width direction. If a plurality of camera systems equipped with a one-dimensional CCD sensor are mounted, the manufacturing cost of the device increases. In addition, each time the type of subject is changed, the adjustment and maintenance of a plurality of camera systems are required, and the running cost of the examination is increased.

Therefore, it is conceivable to perform an visual inspection of the subject using CIS. The CIS includes a plurality of one-dimensional light receiving elements arranged on a substrate and a rod lens array. In CIS, the rod lens array forms an upright 1x image. Using CIS, a one-dimensional image with a width of 1200 mm can be obtained with one unit. The rod lens array is, for example, an array of a plurality of rod-shaped refractive index distribution type lenses. The refractive index distribution type lens has a refractive index distribution in the radial direction thereof, and the refractive index changes from the central portion to the peripheral portion in the radial direction of the refractive index distribution type lens. CIS equipped with a rod lens array can reduce the distance between the image sensor and the object to be photographed to about one tenth of that of a conventional camera system equipped with a CCD sensor and a lens, and the device is compact. It is advantageous in terms of conversion. On the other hand, in CIS, the depth of field (DOF), which is a characteristic value indicating an allowable range of the distance between the object to be photographed and the lens, is small. This causes a problem that when the thickness of the subject varies, a portion of the subject that is in focus and a portion that is not in focus occur. For this reason, the image of the out-of-focus portion is not clear, and there is a possibility that defects may be overlooked and defects may be misidentified.

As described above, the refractive index distribution type lens described in Patent Documents 3 to 5 has a large aperture angle, which cannot be said to be advantageous from the viewpoint of increasing the DOF of the refractive index distribution type lens. Therefore, the present inventors have drastically reviewed the conditions of the glass composition used for producing the refractive index distribution type lens in order to realize the DOF in a desired range in the refractive index distribution type lens. As a result of a great deal of trial and error, the present inventors have finally found a refractive index distribution type lens capable of achieving a DOF in a desired range. The refractive index distribution type lens according to the present invention can be used not only in the technical field of visual inspection of a subject but also in the technical field of image formation such as an image scanner, a copier, a facsimile, and a printer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description relates to an example of the present invention, and the present invention is not limited to the following embodiments.

The refractive index distribution type lens 1b has a depth of field (DOF) of 1.5 to 3.0 mm. The DOF of the refractive index distribution type lens 1b is determined by subtracting the minimum value from the maximum value of the working distance. In the working distance of the refractive index distribution type lens 1b, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lenses / mm is 30% or more.

As shown in FIG. 1, in the DOF of the refractive index distribution type lens 1b, for example, the lens array 10a, the line pattern 3, and the light receiving element 2 are arranged at predetermined intervals in the optical axis direction, and the lens array 10a and the line pattern 3 are arranged. It can be determined by obtaining the value of MTF while changing the distance from. The lens array 10a is configured by arranging a plurality of refractive index distribution type lenses 1b in a direction perpendicular to the optical axis. The line pattern 3 has a black and white line pair corresponding to a spatial frequency of 6 lines / mm. The light receiving element 2 is, for example, a CCD sensor. For example, the light emitted from the halogen lamp is passed through the color filter and the light diffusing plate, and then the line pattern 3 is irradiated. The color filter may, for example, transmit light in the wavelength range of 500 to 600 nm, or may mainly transmit light having a wavelength of 530 nm. At this time, the MTF value is imaged on the light receiving element 2 by the lens array 10a with respect to the image (input image) of the line pattern 3 having a predetermined spatial frequency consisting of the bright part and the dark part before being incident on the lens array 10a. It can be determined as the recall rate of the image (output image) obtained.

_{The distance (distance between the object point and the imaging point) D max} between the line pattern 3 that maximizes the MTF value and the light receiving element 2 is determined. Then, the line pattern 3 is moved in the positive direction (ΔL> 0) and the negative direction (ΔL <0) of the Z axis parallel to the optical axis, and the MTF value is obtained at each position. Thereby, the maximum value and the minimum value of the working distance can be obtained by setting an acceptable range of a predetermined MTF value. As a result, the DOF of the refractive index distribution type lens 1b can be determined. When ΔL> 0, the distance between the line pattern 3 and the lens array 10a is larger than the working distance corresponding to the _{distance D max.} On the other hand, when ΔL <0, the distance between the line pattern 3 and the lens array 10a is smaller than the working distance corresponding to the _{distance D max.} At ΔL = 0, the distance between the line pattern 3 and the lens array 10a is equal to the working distance corresponding to the _{distance D max.}

Since the DOF of the refractive index distribution type lens 1b is in the above range, it is advantageous to obtain image data suitable for visual inspection of a subject having, for example, uneven thickness, steps, and irregularities. Therefore, the refractive index distribution type lens 1b can contribute to the improvement of the accuracy of the visual inspection of the subject and the sophistication of the inspection standard.

The DOF of the refractive index distribution type lens 1b is preferably 1.5 mm or more, more preferably 1.8 mm or more, and further preferably 2 mm or more. The DOF of the refractive index distribution type lens 1b is preferably 2.8 mm or less, and more preferably 2.5 mm or less.

_{The working distance corresponding to the distance D max} between the object point and the imaging point where the MTF value is maximized is, for example, 15 mm or more, preferably 18 mm or more. _{When the distance D max} between the object point and the imaging point is in these ranges, the DOF is in an appropriate range. By incorporating such a rod lens array including the refractive index distribution type lens 1b into the inspection apparatus, it is possible to inspect an object having a step. In addition, the rod lens array can maintain an appropriate distance from the object, facilitating the assembly of the optical system.

The refractive index distribution type lens 1b has, for example, an aperture angle θ of 3 to 6 °. As a result, the DOF of the refractive index distribution type lens 1b can be easily adjusted to a desired range. The aperture angle θ of the refractive index distribution type lens 1b is defined as shown in FIG. 2, for example. The aperture angle θ is the maximum value of the angle formed by the light ray that can be incident on one end of the optical axis of the refractive index distribution type lens 1b and the optical axis. In FIG. 2, F1 is a subject surface, and F2 is a light receiving surface (imaging surface) in a light receiving element or the like. Z ₀ is the length of the refractive index distribution type lens 1b. L _o is the distance between the object plane F1 and gradient index lens 1b when the value of MTF is maximized, L _i is refracted image plane F2 when the value of MTF is maximized This is the distance from the rate distribution type lens 1b. 2, the lens array 10a constitutes the RyakuTadashiritsu like Baiyui imaging system, the distance L _i is substantially equal to the distance L _o. In FIG. 2, X ₀ is the field radius of the refractive index distribution type lens 1b. The aperture angle θ of the refractive index distribution type lens 1b can be determined, for example, according to the method described in Examples. In the method described in the examples, the aperture angle θ may be determined by using the _{refractive index n 0} at the center of the refractive index distribution type lens 1b instead of the refractive index Nc of the glass wire before ion exchange. .. Nc or n ₀ can be obtained by using the V block method described in Japanese Industrial Standards (JIS) B 7071-2: 2018.

The aperture angle θ of the refractive index distribution type lens 1b may be 3.5 ° or more, or 3.7 ° or more. The aperture angle θ of the refractive index distribution type lens 1b is preferably 5.5 ° or less, and more preferably 5.2 ° or less.

The refractive index distribution type lens 1b may have, for example, a refractive index distribution constant (√A) of ^{0.130 to 0.230 mm -1.} Note that √A means the square root of A. Assuming that the refractive index at the radius r of the refractive index distribution type lens is n (r), n (r) = n ₀ × {1- (A / 2) × r ² } holds in the paraxial region of the lens. When the refractive index distribution constant √A is in such a range, the aperture angle θ of the refractive index distribution type lens 1b is likely to fall within a desired range. As a result, the DOF of the refractive index distribution type lens 1b can be easily adjusted to a desired range.

Refractive index distribution constant gradient index lens 1b may also be 0.140 mm ^-1 or more, may be 0.145 mm ^-1 or more. The refractive index distribution constant of the refractive index distribution type lens 1b is preferably 0.210 mm ^-1 or less, and more preferably 0.205 mm ^-1 or less.

The imaging distance of the erect image in the refractive index distribution type lens 1b is, for example, 45 to 80 mm. This is advantageous from the viewpoint of adjusting the DOF of the refractive index distribution type lens 1b to a desired range.

The imaging distance of the erect image in the refractive index distribution type lens 1b may be 47 mm or more, 50 mm or more, 53 mm or more, or 54 mm or more. The imaging distance of the erect image in the refractive index distribution type lens 1b may be 75 mm or less, 70 mm or less, or 67 mm or less.

The refractive index distribution type lens 1b is typically a rod-shaped or fiber-shaped lens. The refractive index distribution type lens 1b has, for example, a refractive index distribution as shown in FIG. 3B in the radial direction. Here, in FIG. 3B, the refractive index n _{0 at the} origin means the refractive index at the central axis of the refractive index distribution type lens 1b. r represents the position of the refractive index distribution type lens 1b in the radial direction.

The refractive index distribution type lens 1b prevents incident light having an incident angle larger than the aperture angle from being reflected by the side surface of the lens to generate noise light (so-called white noise (stray light)), if necessary. It may have a structure. Such a structure may be, for example, a light absorbing layer or a light scattering layer provided on the side surface of the lens. For example, the refractive index distribution type lens 1b may have a core-clad structure in which a colored layer serving as a light absorbing layer is arranged on the side surface of the lens, or a fine uneven portion serving as a light scattering layer may be provided on the side surface. It may have a formed structure.

The refractive index distribution type lens 1b is typically a glass lens. The glass composition for a refractive index distribution type lens is expressed in mol%, 40% ≤ SiO ₂ ≤ 65%, 0% ≤ TiO ₂ ≤ 10%, 0.1% ≤ MgO ≤ 22%, 0.15% ≤ ZnO ≤ 15%, 0.5% ≤ Li ₂ O <4%, 2% ≤ Na ₂ O ≤ 20%, 0% ≤ B ₂ O ₃ ≤ 20%, 0% ≤ Al ₂ O ₃ ≤ 10%, 0 % ≤ K ₂ O ≤ 3%, 0% ≤ Cs ₂ O ≤ 3%, 0% ≤ Y ₂ O ₃ ≤ 5%, 0% ≤ ZrO ₂ ≤ 2%, 0% ≤ Nb ₂ O ₅ ≤ 5%, Includes 0% ≤ In ₂ O ₃ ≤ 5%, 0% ≤ La ₂ O ₃ ≤ 5%, and 0% ≤ Ta ₂ O ₅ ≤ 5%. In addition, the glass composition for a refractive index distribution type lens contains at least two selected from the group consisting of CaO, SrO, and BaO in an amount of 0.1 mol% or more and 15 mol% or less, respectively. Further, the glass composition for a refractive index distribution type lens is expressed in mol%, 2% ≤ MgO + ZnO, 0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93, 2.5% ≤ Li ₂ O + Na ₂ O < The conditions of 24% and 0% ≤ Y ₂ O ₃ + ZrO ₂ + Nb ₂ O ₅ + In ₂ O ₃ + La ₂ O ₃ + Ta ₂ O ₅ ≤ 11% are satisfied. By using such a glass composition, a refractive index distribution type lens having a desired DOF can be obtained.

The refractive index distribution type lens 1b can be manufactured, for example, by subjecting a glass wire made of the above glass composition to an ion exchange treatment.

(SiO ₂ )
SiO ₂ is an essential component that forms the network structure of glass. When _{the content of SiO 2} is less than 40 mol%, the content of other components required to develop the optical characteristics as a refractive index distribution type lens after ion exchange becomes relatively large, and devitrification is likely to occur. Become. If the content is less than 40 mol%, the chemical durability of the glass composition is significantly reduced. On the other hand, when the content exceeds 65 mol%, the content of other components such as an alkaline component for forming a refractive index distribution, a refractive index increasing component, and a physical property value adjusting component is limited, which is practical. It becomes difficult to obtain a glass composition. Therefore, _{the content of SiO 2} is 40 mol% or more and 65% mol or less.

(TiO ₂ )
TiO ₂ is an essential component having an action of increasing the refractive index of the glass composition. By increasing the refractive index of the base glass composition, the central refractive index of the refractive index distribution type lens obtained from the glass composition can be increased. Further, _{by increasing the content of TiO 2} , the refractive index distribution in the refractive index distribution type lens can be brought closer to an ideal state, and a refractive index distribution type lens having excellent resolution can be manufactured. When _{the content of TiO 2} is 10 mol%, no decrease in the resolution of the image based on the obtained lens is observed, but when the content is less than 1 mol%, the resolution of the image is clearly reduced, which is practical. I can't get a lens. On the other hand, if the content exceeds 10 mol%, the coloring becomes strong and the chromatic aberration becomes large, so that a practical lens cannot be obtained. Therefore, in order to obtain a lens capable of increasing the image resolution and having a small chromatic aberration, _{the content of TiO 2} is 1 mol% or more and 10 mol% or less. The content of TiO ₂ is preferably 2 mol% or more and 8 mol% or less.

(MgO)
MgO is an essential component having the effect of lowering the melting temperature of the glass composition and increasing the difference in refractive index (Δn) between the central portion and the peripheral portion of the lens after ion exchange. When the content of MgO exceeds 22 mol%, devitrification is likely to occur. Further, when the content of MgO exceeds 22 mol%, the content of other components is excessively reduced, and a practical glass composition cannot be obtained. Therefore, the content of MgO is 0.1 mol% or more and 22 mol% or less. From the viewpoint of realizing a sufficient refractive index difference, the content of MgO is preferably 2 mol% or more. When the content of MgO is 2 mol% or more, the content of alkaline earth metal oxides (CaO, SrO, BaO) can be more appropriately controlled for the purpose of further reducing the mobility of alkaline ions. .. That is, the content of MgO is preferably 2 mol% or more and 22 mol% or less, and more preferably 2% or more and 16% or less.

(ZnO, MgO + ZnO, ZnO / (MgO + ZnO))
ZnO has an effect of improving the weather resistance of the glass composition and the refractive index distribution type lens. In the glass composition according to the present invention, ZnO may be added to replace a part of MgO. From the viewpoint of enhancing the weather resistance of the glass composition and the refractive index distribution type lens, the ZnO content is 0.15 mol% or more and 15 mol% or less. At this time, the content of MgO and ZnO is adjusted so that the total content of MgO and ZnO (MgO + ZnO) is 2 mol% or more. In addition, the content of MgO and ZnO so that the ratio of the content of ZnO to the total content of MgO and ZnO (ZnO / (MgO + ZnO) is 0.07 ≦ ZnO / (MgO + ZnO) ≦ 0.93). From the viewpoint of further enhancing the weather resistance of the glass composition and the refractive index distribution type lens, the ZnO content is preferably 3% mol or more and 15 mol% or less. In this case, MgO + ZnO is 6 mol%. The above may be satisfied, and the condition of 0.12 ≦ ZnO / (MgO + ZnO) ≦ 0.93 can be satisfied. From the viewpoint of devitrification resistance, the ZnO content is preferably 8 mol% or less. From the viewpoint of further enhancing the weather resistance of the glass composition and the refractive index distribution type lens, the ZnO content is more preferably 4 mol% or more and 15 mol% or less. In this case, MgO + ZnO is 6 mol% or more. MgO + ZnO may be 6 mol% or more and 22 mol% or less. MgO + ZnO may be 15 mol% or less. Also, ZnO / (MgO + ZnO) is preferably 0.07 or more and 0.9 or less. Yes, more preferably 0.25 or more and 0.85 or less, further preferably 0.25 or more and 0.8 or less, and particularly preferably 0.3 or more and 0.8 or less.

(Li ₂ O)
Li ₂ O is an essential component and is one of the most important components for ion-exchange the glass composition of the present invention to obtain a refractive index distribution type lens. _{Conventionally, if the content of Li 2} O in the glass composition is low, it is considered that a sufficient concentration distribution, that is, a sufficient refractive index distribution cannot be developed by ion exchange, and an appropriate refractive index distribution type lens cannot be obtained. Was being done. However, the present inventors have an appropriate refractive index distribution by performing ion exchange under predetermined conditions even in a glass composition having _{a Li 2 O content of 4 mol% or less.} , It has been newly found that a refractive index distribution type lens having a large DOF can be produced. When _{the content of Li 2} O exceeds 4 mol% or less, the aperture angle of the obtained refractive index distribution type lens tends to be large, and the DOF tends to be small. The content of Li ₂ O is 0.5 mol% or more, preferably 0.7 mol% or more, and more preferably 1 mol% or more. The Li ₂ O content is 4 mol% or less, preferably 3.5 mol% or less, more preferably 3 mol% or less, and further preferably 2 mol% or less.

One of the features of the refractive index distribution type lens 1b is that _{the content of Li 2} O is lower than that of various prior arts. Previously, there was a manufacturing process reason that _{the Li 2 O content could not be reduced.} The present inventors have made new efforts such as limiting the amount of glass wire processed per batch by the ion exchange method and reducing the initial content of Li in the molten salt to reduce curvature of field, etc. It has been newly found that a refractive index distribution type lens having a smaller aperture angle than before and having a practical resolution can be obtained while suppressing the aberration of the lens.

(Na ₂ O)
Na ₂ O assists ion exchange between Li and ion-exchange species ions (ions contained in the molten salt) that replace Li ions by the so-called mixed alkali effect during ion exchange, and is easy to ionize. Keep the motility moderate. By maintaining the ion mobility appropriately, the ion exchange rate can be adjusted appropriately, and the optical characteristics of the refractive index distribution type lens can be adjusted. _{If the content of Na 2} O in the glass composition is less than 2 mol%, the glass becomes hard during glass molding, which makes molding difficult. In addition, the melting temperature of the glass rises significantly, making it difficult to manufacture the lens. In addition, it is difficult to sufficiently obtain the effect of maintaining the mobility of ions appropriately. On the other hand, if the Na ₂ O content exceeds 20%, the chemical durability of the glass is lowered and the glass is not practical. Therefore, the Na ₂ O content is 2 mol% or more, preferably 5 mol% or more, and more preferably 10 mol% or more. The Na ₂ O content is 20 mol% or less, preferably 17 mol% or less.

(Li ₂ O + Na ₂ O)
As described above, the total (Li ₂ O + Na _{2 O) of the Li 2} O content and the Na ₂ O content in the glass composition is 2.5 mol% or more and less than 24 mol%. When Li ₂ O + Na ₂ O is in this range, a good resolution image can be obtained by a refractive index distribution type lens manufactured by using this glass composition. Li ₂ O + Na ₂ O is preferably 6 mol% or more, and more preferably 10 mol% or more.

(Li ₂ O / Na ₂ O)
When Na ₂ O Li ₂ O ratio of content of the relative content of _{(Li 2 O / Na 2 O} ) is large, it is possible to improve resolution of refractive index distribution type lenses produced using the glass composition .. On the other hand, when Li ₂ O / Na ₂ O is excessively large (for example, 1.0 or more), the aperture angle of the refractive index distribution type lens manufactured by using the glass composition tends to be large, and its DOF tends to be small. is there. Therefore, Li ₂ O / Na ₂ O is, for example, 0.2 or less, preferably 0.15 or less, and more preferably 0.1 or less.

The above glass composition may further contain the following components.

(B ₂ O ₃ )
B ₂ O ₃ is an optional component that forms the network structure of glass, and promotes vitrification of the glass composition with almost no change in the resolution and aperture angle θ of the obtained refractive index distributed lens, and its viscosity. Has the effect of adjusting. It also has a slight effect of slowing the ion exchange rate of the glass composition. In B ₂ O ₃ , for example, the content of each of the above-mentioned essential components is within the range of the present invention, but when viewed as a composition, the content of some components becomes relatively large, and as a glass. It may be added when stability is reduced (eg, devitrification is likely to occur). By adding B ₂ O ₃ , it is possible to reduce the relatively large content of some of the above components without changing the ratio of the content of the essential components. _{The content of B 2} O _{3 that} can be added without changing the resolution and aperture angle of the obtained refractive index distributed lens is, for example, 20% by mole or less. Therefore, _{the content of B 2} O ₃ is 0% mol or more and 20 mol% or less. The content is preferably 0 mol% or more and 10 mol% or less, and when the glass composition contains B ₂ O ₃ , the content is preferably 1 mol% or more and 10 mol% or less.

(Al ₂ O ₃ )
The glass composition for a refractive index distribution type lens _{may contain Al 2} O ₃ as an optional component, and the content thereof is 0 mol% or more and 10 mol% or less.

(SiO ₂ + TiO ₂ + B ₂ O ₃ )
In the glass composition for a refractive index distribution type lens, the total content of _{SiO 2} , TiO ₂ and B ₂ O _{3 (SiO 2} + TiO ₂ + B ₂ O ₃ ) is, for example, 41 mol% or more and 70 mol% or less. , Desirably 50 mol% or more and 70 mol% or less.

(Y ₂ O ₃ , ZrO ₂ , Nb ₂ O ₅ , In ₂ O ₃ , La ₂ O ₃ , Ta ₂ O ₅ )
_{The glass composition for a refractive index distribution type lens is Y 2} O ₃ , ZrO ₂ , Nb ₂ O ₅ , In for the purpose of adjusting the refractive index of the refractive index distribution type lens obtained after ion exchange or improving the weather resistance. _It may contain at least one component selected from the group consisting of 2 O ₃ , La ₂ O ₃ , and Ta ₂ O _5. The total content of these components is 0 mol% or more and 11 mol% or less, and when the glass composition for a refractive index distributed lens contains these components, the total content of these components is preferably 0. .2 mol% or more and 6 mol% or less. Further, it is desirable that the total of the content of these components and the content of ZnO is 15 mol% or less.

(Y ₂ O ₃ )
The content of Y ₂ O ₃ is preferably 0 mol% or more and 5 mol% or less.

(ZrO ₂ )
The content of ZrO ₂ is preferably 0 mol% or more and 2 mol% or less, and when the glass composition for a refractive index distribution type lens _{contains ZrO 2} , the content is 0.2 mol% or more and 2 mol% or less. Is.

The contents of Nb ₂ O ₅ , In ₂ O ₃ , La ₂ O ₃ , and Ta ₂ O ₅ are each preferably 0 mol% or more and 5 mol% or less.

(K ₂ O, Cs ₂ O)
K ₂ O and Cs ₂ O are optional components having an action of reducing the mobility of alkaline ions by the mixed alkali effect, like MgO, CaO, SrO, and BaO. The contents of K ₂ O and Cs ₂ O are, for example, 0 mol% or more and 3 mol% or less, respectively. From the viewpoint of increasing the water resistance of the glass composition for a refractive index distribution type lens, _{the content of Cs 2} O is preferably less than 2 mol%, more preferably 0 mol% or more and 1 mol% or less, and more preferably. Is 0.5 mol% or less. From the viewpoint of increasing the water resistance of the glass composition for a refractive index distribution type lens, it is desirable that the _{glass composition for a refractive index distribution type lens substantially does not contain Cs 2 O.} As used herein, "substantially free" means that the content of the component is less than 0.1 mol%.

(Other ingredients)
_{GeO 2} may be contained as another component in the glass composition for a refractive index distribution type lens. The content of GeO ₂ can be 0 mol% or more and 10 mol% or less. Further, the glass composition for a refractive index distribution type lens may contain at least one selected from the group consisting of _{SnO 2} , As ₂ O ₃ , and Sb ₂ O _{3 as an additive.} The contents of SnO ₂ , As ₂ O ₃ , and Sb ₂ O ₃ can each be 0 mol% or more and 1 mol% or less. The glass composition for a refractive index distributed lens may substantially consist of the above components. In this case, the content of each component contained in the glass composition and the relationship (total and content ratio) between the contents of each component satisfy the above-mentioned conditions. As used herein, "substantially consisting of" means that impurities having a content of less than 0.1 mol% are allowed.

(PbO)
The glass composition for a refractive index distributed lens is substantially free of lead (typically PbO). Further, the refractive index distribution type lens 1b also contains substantially no lead.

In the glass composition for a refractive index distribution type lens, for example, the water resistance determined in accordance with the Japan Optical Glass Industry Association Standard (JOGIS) 06-2009 is first grade. In this case, the glass composition for a refractive index distribution type lens has high water resistance, and the refractive index distribution type lens manufactured by using the glass composition for a refractive index distribution type lens also tends to have high water resistance. Even in the glass forming the refractive index distribution type lens, the water resistance determined in accordance with JOBIS 06-2009 may be first grade.

The glass composition for a refractive index distribution type lens contains an oxide of a primary alkali metal element. The refractive index distribution type lens 1b can be manufactured, for example, by a method including the following steps (I) and (II).
(I) A glass wire 1a made of the above glass composition for a refractive index distribution type lens is formed.
(II) A glass wire 1a is immersed in a molten salt S containing a second alkali metal element R different from the first alkali metal element Q contained in the glass composition for a refractive index distribution type lens, and the glass wire 1a is contained. By ion-exchange treatment of the first alkali metal element Q and the second alkali metal element R in the molten salt, a refractive index distribution is formed on the glass wire 1a.

In the step (II), for example, as shown in FIG. 3A, the glass wire 1a is put into the molten salt S inside the container V, and the glass wire 1a is immersed in the molten salt S for a predetermined time. In the molten salt S, for example, at least one of potassium nitrate and sodium nitrate is melted. When the glass wire 1a is immersed in the molten salt S, for example, the cations of the first alkali metal element Q such as Li (lithium) contained in the glass wire 1a are dissolved in the molten salt S. On the other hand, cations of the second alkali metal element R such as K (potassium) in the molten salt S invade the glass wire 1a. By adjusting the temperature of the molten salt S and the immersion time of the glass wire 1a in the molten salt S, the ion exchange between the cations of the first alkali metal element Q and the cations of the second alkali metal element R can be appropriately performed. Can be controlled. A specific monovalent cation concentration distribution is generated inside the glass wire 1a, and a refractive index distribution as shown in FIG. 3B is formed on the glass wire 1a according to this concentration distribution. As a result, the refractive index distribution type lens 1b can be manufactured from the glass wire 1a.

The optical product according to the present invention is not limited to a specific product as long as it includes the refractive index distribution type lens 1b. A predetermined lens array can be provided, for example, by using the refractive index distribution type lens 1b. In this case, the lens array may have a 0-dimensional array, a 1-dimensional array, or a 2-dimensional array with respect to the arrangement of the refractive index distribution type lens 1b. The zero-dimensional array is, for example, a configuration in which a single refractive index distribution type lens 1b is arranged, and an optical product composed of a single refractive index distribution type lens 1b is expected to have a desired effect. The one-dimensional arrangement is a configuration in which a plurality of refractive index distribution type lenses 1b are arranged in a row in a specific direction. The specific direction is called the main scanning direction, and the direction perpendicular to the main scanning direction and perpendicular to the optical axis is called the sub-scanning direction. The plurality of refractive index distributed lenses 1b are arranged so that their optical axes are substantially parallel to each other. The two-dimensional array is a configuration in which a plurality of lenses are arranged in a direction different from the one-dimensional array. For example, a configuration in which a plurality of refractive index distribution type lenses 1b are arranged in two or more rows along the main scanning direction may correspond to a two-dimensional arrangement. According to the lens array 10b, a wide range of upright equal magnification images can be obtained even if the diameter of each refractive index distributed lens is small.

For example, the lens array 10b shown in FIG. 4 can be provided by using the refractive index distribution type lens 1b. In the lens array 10b, a plurality of refractive index distributed lenses 1b are arranged so that their optical axes are substantially parallel to each other. In the lens array 10b, the plurality of refractive index distributed lenses 1b are arranged in two rows so as to form a two-dimensional array. In the lens array 10b, the plurality of refractive index distributed lenses 1b are arranged, for example, between a pair of fiber reinforced plastic (FRP) substrates 5. Among the pair of FRP substrates 5, the space between the plurality of refractive index distributed lenses 1b and the space between the FRP substrate 5 and the refractive index distributed lenses 1b are filled with the black resin 7. As a result, a plurality of refractive index distribution type lenses 1b are integrated between the pair of FRP substrates 5. Such a lens array 10b can be manufactured, for example, as follows. First, a plurality of refractive index distribution type lenses 1b are arranged substantially in parallel on the surface of one FRP substrate 5, and the lenses are sandwiched by the other FRP substrate 5. After that, the space between the pair of FRP substrates 5 is filled with the black resin 7 to integrate the whole. Further, if necessary, the end face of the refractive index distribution type lens 1b is polished.

The lens array 10b can be changed from various viewpoints, and a material known in the production of the lens array may be used as the material of each part constituting the lens array. Further, the arrangement of the plurality of refractive index distribution type lenses 1b is not limited to two rows. The plurality of refractive index distribution type lenses 1b may be arranged in one row, or may be arranged in three or more rows. By arranging the refractive index distribution type lenses 1b in a large number of rows, it is possible to provide a lens array that can handle a large area.

The refractive index distribution type lens 1b may be a plastic rod lens having the above optical performance. The plastic rod lens can be manufactured by a method such as a copolymerization method, a sol-gel method, or a mutual diffusion method. In particular, in the mutual diffusion method, resins whose refractive index gradually decreases from the center to the outer circumference are laminated concentrically, and then the materials between the layers are mutually diffused so that the refractive index becomes continuous. After performing such a treatment, further heating and stretching is performed to obtain a rod-shaped rod lens. Due to the characteristics of the material of the plastic rod lens, it is easy to handle and generally inexpensive, and in some cases, it has an advantage.

A lens array provided with a refractive index distribution type lens 1b has a large DOF and, in some cases, has excellent weather resistance, and can be widely used in optical instruments such as scanners, copiers, facsimiles, printers, CIS, and line cameras. it can. Furthermore, since the lens array equipped with the refractive index distribution type lens 1b is particularly excellent in water resistance (moisture resistance), it is not only used for general air conditioning in offices, but also for factories, storage warehouses or transportation exposed to high temperature and humidity conditions. It can be applied to the above-mentioned optical equipment even in various environments including distribution such as trucks.

Using the lens array 10b, for example, the CIS scanner 100 shown in FIG. 5 can be provided. The CIS scanner 100 includes, for example, a lens array 10b, a housing 11, a line-shaped light receiving element 12, a line-shaped lighting device 13, and a document base 14. The line-shaped light receiving element 12 extends in the main scanning direction of the lens array 10b. In FIG. 5, the direction parallel to the X-axis is the main scanning direction, and the direction parallel to the Y-axis is the sub-scanning direction. The line-shaped illumination device 13 extends in the main scanning direction of the lens array 10b. The platen 14 is formed of a glass plate. The glass plate forming the platen 14 is arranged so as to cover the opening of the housing 11. The lens array 10b, the line-shaped light receiving element 12, and the line-shaped lighting device 13 are arranged inside the housing 11. Illumination light is linearly irradiated from the line-shaped illumination device 13 to the document P placed on the platen 14. The lens array 10b is arranged so that the light reflected on the surface of the document P is incident on the line-shaped light receiving element 12. A two-dimensional image of the document P by scanning the scanner mechanism including the lens array 10b and the line-shaped light receiving element 12 in the sub-scanning direction or by transporting the document P placed on the platen 14 in the sub-scanning direction. You can get the data.

Since the lens array 10b includes a refractive index distribution type lens 1b having a large DOF, the quality of the read image can be improved even in a portion where a part of the document P is floated due to, for example, a wrinkle or a spread portion. It tends to be good.

Using the lens array 10b, for example, the scanner 300 shown in FIG. 6 can be provided. The scanner 300 includes a housing 31, a line-shaped light receiving element 32, a line-shaped lighting device 33, a first spacer 34a, a second spacer 34b, and a substrate 35. In the scanner 300, the line-shaped lighting device 33 is arranged outside the housing 31. For example, in the scanner 300, in order to appropriately adjust the optical arrangement of the portion of the document P to be read and the line-shaped light receiving element 32, the lens array 10b is housing with the first spacer 34a and the second spacer 34b. It is positioned and fixed with respect to 31. The scanner 300 may be applied to an apparatus for inspecting the appearance of a subject, or may be used to obtain an image from a subject (inspection object) instead of the manuscript P. In this case, the light beam emitted from the line-shaped illumination device 33 irradiates the subject, and the light reflected on the surface of the subject is imaged on the line-shaped light receiving element 32 by the imaging action of the lens array 10b. The line-shaped light receiving element 32 can sequentially convert one-dimensional image information on the surface of the subject into an electric signal and output it.

Using the lens array 10b, for example, the printer 500 shown in FIG. 7 can be provided. The printer 500 includes a writing head 51, a photosensitive drum 52, a charger 53, a developing device 54, a transfer device 55, a fixing device 56, an erasing lamp 57, a cleaning device 58, and a paper feed cassette 59. I have. The lens array 10b is arranged inside the writing head 51. The printer 500 is an electrophotographic printer. The writing head 51 includes a lens array 10b and a light emitting element array (not shown). The lens array 10b constitutes an imaging optical system that exposes the light emitted from the light emitting element array onto the photosensitive drum 52. Specifically, the focal point of the lens array 10b is located on the surface of the photosensitive drum 52, which constitutes an upright 1x optical system. A photosensitive layer made of a photoconducting material (photoreceptor) such as amorphous Si is formed on the surface of the photosensitive drum 52. First, the surface of the rotating photosensitive drum 52 is uniformly charged by the charger 53. Next, the writing head 51 irradiates the photosensitive layer of the photosensitive drum 52 with the light of the dot image corresponding to the image to be formed, neutralizes the charge in the light-irradiated region in the photosensitive layer, and lurks in the photosensitive layer. An image is formed. Next, when the toner is attached to the photosensitive layer by the developing device 54, the toner adheres to the portion of the photosensitive layer where the latent image is formed according to the charged state of the photosensitive layer. Next, the adhered toner is transferred to the paper sent from the cassette by the transfer device 55, and then the paper is heated by the fixing device 56, so that the toner is fixed to the paper and an image is formed. On the other hand, the charge of the photosensitive drum 52 for which the transfer has been completed is neutralized over the entire region by the erasing lamp 57, and then the toner remaining on the photosensitive layer is removed by the cleaner 58.

Using the lens array 10b, for example, the inspection device 700 shown in FIG. 8 can be provided. The inspection device 700 includes a CIS scanner 71, a line-shaped lighting device 72, a controller 73, an output device 74, a transfer device 75, and a transfer control device 76. A lens array 10b is arranged inside the CIS scanner 71. The transport device 75 is, for example, a belt conveyor. The transport device 75 transports a subject T such as a printed circuit board, textile, and paper. The transfer control device 76 is a digital computer for controlling the transfer device 75, and outputs a control signal for adjusting the transfer speed of the transfer device 75 toward the transfer device 75. The CIS scanner 71 and the line-shaped lighting device 72 are arranged above the transport device 75, for example, and the subject T passes directly under the CIS scanner 71 by the transport device 75. The CIS scanner 71 and the line-shaped illumination device 72 are arranged so that clear image data of the subject T can be obtained. The controller 73 is a digital computer for forming image data of the subject T. When the subject T passes directly under the CIS scanner 71, the controller 73 continuously acquires one-dimensional image information from the CIS scanner 71. In addition, the controller 73 acquires the transport position information of the subject T from the transport control device 76. The controller 73 performs a calculation process based on the one-dimensional image information acquired from the CIS scanner 71 and the transfer position information acquired from the transfer control device 76 to form two-dimensional image information. The formed two-dimensional image information is compared with the information characterizing defects such as foreign matter, cracks, and pinholes stored in advance in the controller 73. As a result, the controller 73 identifies the presence / absence of defects, the number of defects, and the position of defects in the subject T. The controller 73 may determine the quality of the subject T based on the comparison result. The output device 74 is, for example, a monitor and displays two-dimensional image information formed by the controller 73.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples.

(Preparation of glass composition and fabrication of refractive index distributed lens)
The glass raw materials were mixed so as to have the compositions shown in Table 1, and the mixture was melted to obtain molten glass (glass composition) according to Examples 1 to 4, Comparative Examples 1 to 3, and Reference Example 1. The numerical values in Table 1 indicate mol%. Table 2 shows the relationship between the content of a predetermined component in each glass composition based on the mol%. Each molten glass was spun and formed into a fiber shape, the obtained glass fiber was cut to a predetermined length, and the cut surface was polished. As a result, the glass strands according to each Example, each Comparative Example, and Reference Example 1 were obtained. The diameter (wire diameter) of each glass wire was 560 μm. Next, each glass wire was immersed in a molten sodium nitrate heated near the glass transition temperature of the glass composition constituting each glass wire, and ion exchange treatment was performed. As a result, a refractive index distribution was formed on each glass wire. Then, the glass wire after the ion exchange treatment was cut to a length of one cycle, and the cut end face was polished to obtain a refractive index distribution type lens according to each Example, each Comparative Example, and Reference Example 1.

(Characteristic evaluation)
The cut surface of the sample obtained by cutting the refractive index distribution type lens produced as described above to an appropriate length was mirror-polished. Next, a sheet on which a grid pattern is described is brought into contact with one end face of this sample, an erect image of the pattern is observed from the other end face of the sample, and the period length P of each refractive index distribution type lens is determined. Decided. Next, the refractive index distribution coefficient √A of each refractive index distribution type lens was determined based on the relationship of √A = 2π / P. Next, based on the relationship between the refractive index distribution coefficient √A, the radius r ₀ of the refractive index distribution type lens, and the refractive index Nc of the glass wire before the ion exchange treatment, and the relationship shown in the following equation (1). The aperture angle θ of each refractive index distribution type lens was determined. The results are shown in Table 3. The refractive index Nc was 1.60, which could be regarded as the refractive index in the optical axis of each refractive index distribution type lens.
θ = sin ^-1 {√A ・ Nc ・ r ₀ } Equation (1)

The refractive index Nc was determined by evaluating the refractive index of the glass composition according to each Example, each Comparative Example, and Reference Example 1. A rectangular parallelepiped sample having a cross-sectional area of 15 mm square was prepared by cutting out a base glass made of a glass composition, and the refractive index Nc was evaluated according to the V block method described in JIS B 7071-2: 2018. In this method, a sample is placed on a V-block prism, and the declination of the light rays bent by the sample when passed through the dispersed light rays is measured. This method is a method of relatively calculating the refractive index of a sample from the value of this declination and the refractive index of a known V-block prism. KPR-3000 manufactured by Shimadzu Corporation was used for the evaluation.

(Water resistance evaluation)
The water resistance of each glass composition was evaluated according to JOBIS 06-2009. A sample prepared from each glass composition was placed in boiling water for 1 hour to measure the weight loss rate, and the water resistance of each glass composition was evaluated according to the weight loss rate. The water resistance of JOBIS 06-2009 is classified into grades 1 to 6, and it can be said that glass having a water resistance of grade 1 has weather resistance, particularly excellent durability against moisture.

(Measurement of DOF)
Each refractive index distributed lens was subjected to a predetermined treatment (concavo-convex formation treatment) on its side surface for the purpose of removing noise light. After that, a plurality of each refractive index distribution type lens was arranged two-dimensionally to prepare a lens array in which a plurality of refractive index distribution type lenses as shown in FIG. 4 were arranged in two rows. In this way, the lens arrays according to each Example, each Comparative Example, and Reference Example 1 were obtained. A line pattern having 6 pairs of black and white lines at 1 mm intervals was prepared. That is, this line pattern had a spatial frequency of 6 lines / mm. The light emitted from the halogen lamp was passed through a color filter (transmission center wavelength: 530 nm, full width at half maximum 15 nm) to irradiate the line pattern. As shown in FIG. 1, the line pattern, each lens array, and the light receiving element were arranged at the position where the MTF value became maximum. Was determined imaging position distance L _o - in this case, the distance between the lens array and the light receiving element lens. The results are shown in Table 3. Then, while moving the line pattern in the optical axis direction, the MTF value was obtained at each position, and the range of the working distance at which the MTF value was 30% or more was specified from the relationship between ΔL and the MTF value. Then, the depth of field (DOF) of each refractive index distributed lens was determined by subtracting the minimum value from the maximum value of the working distance. The results are shown in Table 3. Further, FIG. 9 shows the relationship between the MTF value and ΔL in the lens array according to Example 2, Comparative Example 3, and Reference Example 1.

As shown in Table 1, the DOF in the lens array provided with the refractive index distribution type lens according to each embodiment is in the range of 1.5 to 3.0 mm, and the refractive index distribution type lens according to each embodiment is desired. It was suggested to have a DOF. In addition, the water resistance of the glass composition according to each example was first grade. On the other hand, the DOF in the lens array provided with the refractive index distribution type lens according to each comparative example was small. The DOF in the lens array provided with the refractive index distribution type lens according to Reference Example 1 was 2.4 mm. However, the water resistance of the glass composition according to Reference Example 1 is grade 4, suggesting that the glass composition according to Reference Example 1 is inferior in water resistance to the glass composition according to each example. Was done.

1a Glass wire 1b Refractive coefficient distribution type lens 2 Light receiving element 3 Line pattern 10a, 10b Lens array 100 CIS scanner 300 Scanner 500 Printer 700 Inspection device

Claims (7)

A refractive index distributed lens having a depth of field of 1.5 to 3.0 mm.
The depth of field is determined by subtracting the minimum value from the maximum value of the working distance while keeping the distance between the refractive index distribution type lens and the imaging position constant.
At the working distance, the value of the modulation transfer function (MTF) at a spatial frequency of 6 lines / mm is 30% or more, and the maximum value of the modulation transfer function is 73.1 to 76.7%.
The refractive index n (r) at the radius r of the refractive index distribution type lens and the refractive index n _{0 at the center of the refractive index distribution type lens are n (r) = n 0} × [1- (A /) in the near axis region. 2) Satisfy the relationship of ^{× r 2]}
The refractive index distribution constant, which is the square root of A in the above relationship, is 0.130 to 0.230 mm ^-1 .
Imaging distance erect is Ri 47~80mm der,
A refractive index distribution type lens having the following composition in the center.
Shown in mol%,
40% ≤ SiO ₂ ≤ 65%
1% ≤ TiO ₂ ≤ 10%
0.1% ≤ MgO ≤ 22%
0.15% ≤ ZnO ≤ 15%
0.5% ≤ Li ₂ O <4%
2% ≤ Na ₂ O ≤ 20%
0% ≤ B ₂ O ₃ ≤ 20%
0% ≤ Al ₂ O ₃ ≤ 10%
0% ≤ K ₂ O ≤ 3%
0% ≤ Cs ₂ O ≤ 3%
0% ≤ Y ₂ O ₃ ≤ 5%
0% ≤ ZrO ₂ ≤ 2%
0% ≤ Nb ₂ O ₅ ≤ 5%
0% ≤ In ₂ O ₃ ≤ 5%
0% ≤ La ₂ O ₃ ≤ 5%
Including 0% ≤ Ta ₂ O ₅ ≤ 5%,
At least two selected from the group consisting of CaO, SrO, and BaO are contained in an amount of 0.1 mol% or more and 15 mol% or less, respectively.
Display in mol%,
2% ≤ MgO + ZnO,
0.07 ≤ ZnO / (MgO + ZnO) ≤ 0.93,
2.5% ≤ Li ₂ O + Na ₂ O <24%, and
Satisfy 0% ≤ Y ₂ O ₃ + ZrO ₂ + Nb ₂ O ₅ + In ₂ O ₃ + La ₂ O ₃ + Ta ₂ O ₅ ≤ 11%. The refractive index distribution type lens according to claim 1, wherein the depth of field is 1.8 to 2.8 mm. The refractive index distribution type lens according to claim 1 or 2, wherein the refractive index distribution constant is 0.140 to 0.210 mm ^-1. The refractive index distribution type lens according to any one of claims 1 to 3, which has an aperture angle of 3 to 6 °. The refractive index distribution type lens according to claim 4, wherein the aperture angle is 3.5 to 5.5 °. An optical product comprising the refractive index distribution type lens according to any one of claims 1 to 5. An optical device comprising the optical product according to claim 6.

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