JP2001255406A - Distributed refractive index type optical element and distributed refractive index type rod lens array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core/cladding distributed refractive index type optical element preventing optical characteristics based on the part where the refractive index is deviated from the normal parabolic distribution from deteriorating, at the same time preventing flare light from invading and having excellent resolution even in the case being used for the optical device influenced by the near infrared ray region and a rod lens array using the same. SOLUTION: In the distributed refractive index type optical element with a core/cladding structure containing a metal oxide coloring component in the cladding glass and manufactured with the ion exchange method, the distributed refractive index type optical element is characterized by comprising the cladding glass which contains 0.5-4.0 wt.% CoO and 2.0-12.0 wt.% total iron oxide (expressed in terms of Fe2O3) as the metal oxide coloring component taking the total amount of the mother glass components excluding the coloring component as 100 wt.% and which contains FeO expressed in terms of Fe2O3 occupying 23-75% of the total iron oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradient index optical element having a core / cladding structure having a refractive index distribution in the radial direction, and more particularly to a gradient index optical element having a colored glass composition cladding.

[0002]

2. Description of the Related Art A refractive index distribution type optical element whose refractive index changes in a parabolic manner from a center to an outer periphery in a cross section, for example, a light converging lens is a spherical lens even if the lens surface is flat. It has the same image forming function as that of, and has the advantage that a lens with a small diameter and a single focal point can be easily manufactured. Therefore, it is widely used in optical heads of optical devices such as copiers, optical printers and facsimile machines. Have been. The gradient index optical element includes a gradient index rod lens, a gradient index fiber, and the like.

[0003] As a method of manufacturing a gradient index optical element, a glass rod is immersed in a molten salt.
An ion exchange method for imparting a refractive index distribution is widely performed industrially. For example, a glass rod containing cations such as Li ⁺ , Tl ⁺ , Cs ⁺ , and Ag ⁺ is immersed in a molten salt such as sodium nitrate or potassium nitrate to exchange cations in the glass with cations in the molten salt. By doing so, a rod lens having a refractive index distribution can be obtained.

Instead of using a molten salt, the core / clad glass rod in which the glass rod is coated with a clad glass layer containing sodium ions or potassium ions is heated during molding or after molding. By exchanging ions with cations in the cladding glass layer, a rod lens having a core / cladding structure having a refractive index distribution can be obtained. The core / clad glass rod can be manufactured by a double crucible method, a pipe rod method, or the like.

In a rod lens manufactured by the above-mentioned ion exchange method, since ion exchange mainly proceeds by a diffusion phenomenon, it often deviates from a parabolic distribution (square distribution) mainly in the vicinity of a side surface thereof. FIG. 1 shows the refractive index distribution of a rod lens having a core / clad structure. The lens has a circular cross section, a core in the center, and a concentric cladding around the core. The refractive index distribution curve is shown below. The horizontal axis r is the radial distance from the core center, and n is the refractive index. At this time, the composition of the core glass and the clad glass before the ion exchange should be selected so that the refractive index continuously changes at the boundary between the core and the clad after the ion exchange, especially in relation to the core diameter. It is preferable when increasing the thickness of the cladding layer.

When transmitting information such as images,
Light rays passing through the portion near the side surface that deviates from the normal parabolic distribution cause distortion and aberration, and deteriorate the optical characteristics of the refractive index distribution type rod lens. Also, light (flare light) entering from the outside through the vicinity of the side surface of the gradient index rod lens also degrades the optical characteristics of the gradient index rod lens.

In order to prevent the deterioration of the optical characteristics of the lens and the invasion of flare light, Japanese Patent Application Laid-Open No. 63-30190 discloses a method.
No. 1 discloses that a core / clad glass rod containing a cation such as Li ⁺ is immersed in a molten salt such as sodium nitrate for a predetermined time to melt lithium ions in the core / clad glass rod. When producing a gradient index optical element by exchanging with sodium ions in the salt, Mn, Cr, Co, Ni, Fe, Cu, A
A technique is disclosed in which a light absorbing layer of glass containing metal ions such as g, Ti, Pb, Ru, Cd, V, and Mo is formed to prevent flare light from entering. However, the MnO, CoO, or CoO and Mn used in the example were used.
With an O combination colorant, an optical device using monochromatic light as a light source is sufficient, but an optical device using white light has a problem that the resolution is insufficient.

Japanese Patent Application Laid-Open No. Hei 10-139472 discloses a refractive index distribution type optical element formed by a thermal reciprocal diffusion method using a double crucible, in which CoO, MnO, and Cr as coloring agents are used as cladding glass layers. the ₂ O _3, for example, CoO 1.5 wt%, using MnO 1.0 wt%, and Cr ₂ O ₃ 0.4 wt% containing light absorbing glass, prevents the penetration of flare light, and the outer diameter A technique for improving accuracy is disclosed. However, this coloring agent tends to cause devitrification in the core and the clad glass, and there is a problem that the usable glass composition range for the core and the clad glass is narrowed.

As a method for solving these problems, a method using a light-absorbing glass containing CoO and Fe ₂ O ₃ as coloring agents in a cladding glass layer is disclosed in International Publication WO00.
No. 0/04409. According to this method, it is possible to obtain a refractive index type optical element that absorbs the visible region and prevents the intrusion of flare light in the visible region without causing devitrification of the glass during glass melting or ion exchange. However, since the absorption range of the coloring agent used is 380 to 660 nm, the effect of preventing flare light from entering the visible region is sufficient, but light in the near infrared region is hardly absorbed and passes through. As a result, there is a problem that the invasion of flare light in the near infrared region cannot be prevented. For example, when the gradient index optical element is used by being incorporated in an apparatus such as a flatbed scanner or a copying machine, a lid is often used when copying a thick book or the like. At this time, external light directly enters the device, but the external light usually contains a lot of near-infrared light, so depending on the characteristics of the device, it may be greatly affected by the near-infrared light. However, in such a case, there is a problem that the above-mentioned coloring agent cannot cope with the problem and the resolution is reduced.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a decrease in optical characteristics due to a portion where the refractive index deviates from a normal parabolic distribution, to prevent the invasion of flare light, and to reduce the near-infrared region. An object of the present invention is to provide a core / cladding type gradient index optical element having excellent resolution even when used in an optical device affected by the same, and a rod lens array using the same.

[0011]

According to the present invention, there is provided a gradient index optical element having a core / clad structure produced by an ion exchange method, wherein the clad glass contains a metal oxide coloring component. As the metal oxide coloring component, the total of the mother glass components excluding the coloring component is defined as 100% by weight, and expressed as a percentage by weight, CoO 0.5 to 4.0, and total iron oxide (converted to Fe ₂ O ₃₎ 2.0) to 12.0, and FeO in terms of Fe ₂ O ₃ is 23 to 75% of the total iron oxide.

[0012] The content of the metal oxide coloring component in the clad glass was additionally added when the total of the mother glass component (excluding the metal oxide coloring component) of the clad glass was 100% by weight. Defined as

Hereinafter, the metal oxide coloring component (coloring agent) will be described. As the metal oxide used as the colorant, one that is basically unrelated to the ion exchange reaction itself is selected. Generally, properties such as density, viscosity, and thermal expansion of glass change in proportion to the increase in colorant. Further, when the amount of the coloring agent added is large, devitrification tends to occur during the forming of the core / clad glass rod, for example, during the spinning step using a double crucible. Therefore, the addition amount (% by weight) of the coloring agent is preferably as small as possible within a range in which light having a desired wavelength can be absorbed. Further, in order to make the refractive index distribution obtained by the ion exchange method as close as possible to the parabolic distribution, it is preferable that the amount of the coloring agent is small. From such a viewpoint, CoO is suitable as a coloring agent.

When CoO is contained in the glass, the glass exhibits an absorption capacity for strongly absorbing light in the 520 to 680 nm band due to Co ²⁺ ions. CoO
Since the absorption increases in proportion to the amount of CoO added, the greater the amount of CoO added, the greater the effect of removing light incident on the cladding layer and not contributing to imaging. However, for the reasons described above, the amount of CoO added is 0.5 to 4.0% by weight,
Desirable is 0.5-2.5% by weight, and more desirable is 0.5-2.0% by weight.

When using white light as the light source, it is necessary to consider removal of light having a wavelength of the entire visible light. With only CoO described above, the ability to absorb light having a wavelength of 500 nm or less is insufficient. Fe ions are used as metal ions absorbing short wavelengths of 500 nm or less. Fe ⁺³
The ions strongly absorb light of 380 to 460 nm. Fe
The addition amount of Fe ₂ O ₃ , which is an oxide in the form of ⁺³ ions, is an essential component for absorbing visible light of a relatively short wavelength,
If the amount is too large, the glass tends to be devitrified, so it is desirable not to use the glass excessively.

When the gradient index optical element of the present invention is used in an apparatus or the like affected by the near infrared region, it is necessary to remove flare light in the near infrared region. 660 to 1000n
Fe ⁺² ions are used as metal ions that efficiently absorb the near infrared region near m. Upon melting in a normal air atmosphere, Fe ions are present in the glass almost in the form of Fe ⁺³ . Therefore, in order to make Fe ⁺² ions exist in the glass, it is necessary to produce the glass in a reducing atmosphere. In order to increase absorption in the near infrared region, F
It is sufficient to increase the amount of e ⁺² ions, but in order to increase the concentration of Fe ⁺² ions, it is necessary to melt under a strong reducing atmosphere. The possibility of changing the valence of the element,
Since there are problems such as that the platinum crucible used for melting is affected and that the concentration of Fe ⁺³ becomes too low, the amount of FeO, which is an oxide in the form of Fe ⁺² ions, is Fe ₂ O It is necessary to be 23 to 75% of the total amount of iron oxide added (the amount converted to Fe ₂ O ₃ , hereinafter referred to as “T-Fe ₂ O ₃ ”), expressed as a value converted to ₃ . Desirably, it is 30 to 75%. Fe ₂ O ₃ and T-Fe ₂ O ₃ amount is the sum of the FeO is 2.0 to 12.0 wt%.

[0017] Since near infrared absorption is proportional to the absolute amount of Fe ⁺² ions in the glass, it is also necessary to think about absolute amount of Fe ⁺² ions cladding glass. 0.1m thick
In order to reduce the transmittance at 750 nm to 75% or less for the glass of m m, the absolute amount of FeO converted to Fe ₂ O ₃ is 2
It is desirable that the content be not less than% by weight. Therefore, the absolute amount of FeO contained in the glass (in terms of Fe ₂ O ₃ ) is 2% by weight.
More preferably, it is more preferably 3% by weight.
That is all.

Glass containing much MgO as mother glass
When used, the occurrence of devitrification is remarkable.
Is 100% by weight of the total of the mother glass components.
When the content is 5% by weight or more in terms of% by weight, T-Fe
_TwoO_ThreeIs preferably 2.0 to 6.0% by weight.
New In such a case, the T-Fe contained in the glass _Two
O_ThreeFe in the glass⁺²Increase the amount of ions
T-Fe_TwoO_ThreeThe ratio of FeO to
Need to be Therefore, Fe_TwoO_ThreeOf FeO converted to
The proportion is T-Fe_TwoO_Three50% to 75% of the
And more preferably 55 to 75%, more preferably
It is 55-70%.

When a mother glass having a low MgO concentration is used, devitrification hardly occurs.
Fe ₂ O ₃ can be added. Fe ⁺³ compared to Co ⁺²
Is small, it is desirable to increase the absorption of light of 380 to 460 nm and to increase the amount of Fe ₂ O ₃ as much as possible in order to improve the resolution in this wavelength range.
When the concentration of MgO is less than 5% by weight in terms of% by weight when the total of the mother glass components is 100% by weight, TF
e ₂ O ₃ can be added up to 12.0% by weight. T
-Fe ₂ O ₃ amount is preferably 3.0 to 12.0 wt%, more preferably from 6.0 to 10.0% by weight.

As described above, Co ⁺² ions and Fe ⁺² , F
By coexisting e ⁺³ ions in the cladding glass, light having wavelengths of visible light and near-infrared light can be efficiently removed.

Although NiO is not an essential component, by using it together with CoO and Fe ₂ O ₃ , light (420 to 500 nm) in the band between the visible light absorption region by CoO and the visible light absorption region by Fe ₂ O ₃ is obtained. It is preferred because it absorbs. To increase the absorption in the near infrared region, most of T-Fe ₂ O ₃ is changed to Fe ⁺²
When reduced to ions, the absorption in the visible region due to Fe ⁺³ ions is insufficient, so the addition of NiO can make up for the insufficiency. If the amount of NiO added is too large, the glass tends to be devitrified. The addition amount of NiO is 0.0 to 2.0% by weight, preferably 0.2 to 2.0% by weight, and more preferably 0.2 to 1.0% by weight.

Cr is known as another metal ion that absorbs a short wavelength in the visible light region. Co, F above
In addition to e and Ni added as necessary, Cr can be additionally used as described below. Although Cr ₂ O ₃ is not an essential component, it absorbs light of 380 to 430 nm similarly to Fe ₂ O _3, and its absorption ability is higher than that of Fe ₂ O ₃ . However, Cr ₂ O ₃ is liable to devitrify clad glass, particularly glass containing lithium, so that it can be contained without devitrification at 0.2% by weight or less.

The clad glass containing the above colorant is
As preferred examples of the mother glass before the ion exchange treatment, expressed as% by weight, Li ₂ O 0, Na ₂ O 14 to 28, MgO 2.5 to 15, BaO 2 to 10, PbO 0 to 25, TiO ₂ 2 -10 and SiO ₂ 45-60 (total 100% by weight).

The core glass is a preferred example of the glass before the ion exchange treatment, expressed as% by weight: Li ₂ O 3 to 12, Na ₂ O 0 to 15, MgO 2.5 to 15, BaO 2 to 10 , PbO 0 to 25, TiO _{2 2 to} 10, and SiO ₂ 45 to 60 (total 100% by weight).

The clad glass and the core glass are:
The combination is used such that the refractive index of the core glass is 0.005 to 0.1 higher than the refractive index of the clad glass.

The composition of both the clad glass and the core glass is not uniform but distributed in the radial direction (particularly, Li ₂ O and Na ₂ O components) as a result of the ion exchange treatment. gradient index optical element has as its cladding glass, preferable examples of the mother glass, on average, expressed in terms of _{weight%, Li 2 O 0.5~12, Na} 2 O 14~28, MgO 2.5 -15, BaO 2-10, PbO 0-25, TiO ₂ 2-10, SiO ₂ 45-60 (total 100% by weight).
On average, expressed as% by weight, Li ₂ O 2-9, Na ₂ O 0.5-25, MgO 2.5-15, BaO 2-10, PbO 0-25, TiO ₂ 2-10, SiO ₂ 45-60, containing the composition of the (total 100 wt%), the content of Na ₂ O of the cladding glass is greater than the content of Na ₂ O in the core glass and Li ₂ O in the core glass The content has a composition that is greater than the Li ₂ O content in the cladding glass. Here, the “average” means that the composition distribution is a value calculated as being homogenized in the clad glass and the core glass, respectively.

The gradient index optical element of the present invention preferably comprises a core glass having a diameter of 100 to 1000 μm and
A cladding glass layer having a thickness of 0 to 100 μm (the thickness of the cladding glass layer is 1 to 25% of the core glass diameter), and a refractive index constant g of 0.1 to 4 (mm ⁻² , in the radial direction of the optical element) Is expressed in mm), and the glass of the clad glass layer has a thickness of 38 μm when the thickness is 100 μm.
It has a transmittance of 75% or less for light of all wavelengths in the range of 0 nm to 1000 nm.

Further, in the gradient index rod lens array of the present invention, the above gradient index optical element may have a refractive index of 50 to 1000.
The adhesive is arranged in one or more rows, for example, 2 to 4 rows in a zigzag pattern so that the optical axes of the books are parallel to each other, and both end faces of each optical element form the same plane. It is manufactured by fixing to each other using

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

Example 1 A double glass rod was obtained as follows by spinning using a double crucible using the core and clad glass compositions shown in Table 1. As shown in FIG. 2, the double crucible 1 is composed of an inner crucible 2 and an outer crucible 3, and a glass cullet for core glass and a glass cullet for clad glass are put into the inner crucible 2 and the outer crucible 3, respectively. 1 is heated and melted, and the core glass 4 is supplied from the inner crucible 2, and the clad glass 5 containing a colorant is supplied from the outer crucible 3 to the lower nozzle 6.
The double glass rod is drawn out and spun by a tension roller (not shown), and the two are fused and integrated to obtain a double glass rod. The concentration of Fe ^{+2 in} the clad glass was adjusted by changing the amount of a carbon-based reducing agent (such as graphite) added when producing a glass cullet for the clad glass. Clad glass (CoO 1.0, Fe ₂
O total iron oxide in terms of _{3 (T-Fe 2 O 3} ) 3.0 Each wt%, total iron oxide is added "T-Fe ₂ O _3" amount (Fe ₂ O ₃
Ratio of FeO converted to Fe ₂ O ₃ with respect to (converted to)
FIG. 3 shows a transmittance spectral characteristic (converted to a glass thickness of 0.1 mm) of 69%).

The glass rod was cut into a length of about 1 m, immersed in a bath of a molten salt of sodium nitrate maintained at about 445 ° C. for about 24 hours, and the lithium ions in the glass rod and the After the ion exchange with sodium ion, it was pulled up. This rod was cut, and both end surfaces were polished flat to obtain a rod lens having a length of 4.13 mm and a refractive index distribution. Outer diameter of this rod lens (m
m), length (mm), refractive index on the central axis (n ₀ ), refractive index constant g (mm ⁻² ), and TC (inter-object image distance at which an equal-size erect real image is formed, mm) Is as shown in Table 3. Note that the refractive index constant g (mm ⁻² ) is obtained by calculating the distribution of the refractive index (n) at a distance r (mm) in the radial direction, where n ₀ is the refractive index on the central axis, and n = n ₀ (1-gr). ² ) This is a constant when approximated by. Then, the refractive index continuously changed at the boundary between the core and the clad. In the glass compositions shown in Tables 1 and 2, the amount of the coloring component (% by weight) is calculated by adding the total amount of components other than the coloring component to 100%.
It is a value in terms of% by weight.

[0032]

[Table 1] Example 1 2 3 4 5 core / cladding core / clad core / clad core / dark head core / clad ---------------------------------- Li ₂ O 4.2 /0.0 4.2 / 0.0 4.2 / 0.0 4.2 / 0.0 4.2 / 0.0 Na ₂ O 8.3 / 16.4 8.3 / 16.4 8.3 / 16.6 8.3 / 16.6 8.3 / 16.4 MgO 8.4 / 8.1 8.4 / 8.1 8.4 / 4.5 8.4 / 4.5 8.4 / 8.1 PbO 20.0 /19.1 20.0 / 19.1 20.0 / 19.1 20.0 / 19.1 20.0 / 19.1 BaO 4.6 / 4.4 4.6 / 4.4 4.6 / 4.3 4.6 / 4.3 4.6 / 4.4 TiO ₂ 4.2 / 4.0 4.2 / 4.0 4.2 / 3.7 4.2 / 3.7 4.2 / 4.0 SiO ₂ 50.3 /40.8 50.3 / 40.8 50.3 / 51.8 50.3 / 51.8 50.3 / 40.8 T-Fe ₂ O ₃ 0 / 3.0 0 / 5.0 0 / 8.0 0 / 10.0 0 / 3.0 FeO 0 / 2.1 0 / 3.1 0 / 3.9 0 / 2.5 0 / 1.9 FeO / T-Fe ₂ O ₃ (%) 0/69 0/62 0/49 0/25 0/53 CoO 0 / 1.0 0 / 2.0 0 / 1.0 0 / 1.0 0 / 1.0 NiO 0/0 0/0 0/0 0/0 0 / 1.75 ─────────────────── ──────────────

[0033]

[Table 2] ────────────────────────── ―――― Comparative Example 1 2 3 Core / cladding Core / cladding Core / cladding --- −−−−−−−−−−−−−−−−−−−−−−−−−−−−− Li ₂ O 4.2 / 0.0 4.2 / 0.0 4.2 / 0.0 Na ₂ O 8.3 / 16.4 8.3 / 16.6 8.3 /16.6 MgO 8.4 / 8.1 8.4 / 4.5 8.4 / 4.5 PbO 20.0 / 19.1 20.0 / 19.1 20.0 / 19.1 BaO 4.6 / 4.4 4.6 / 4.3 4.6 / 4.3 TiO ₂ 4.2 / 4.0 4.2 / 3.7 4.2 / 3.7 SiO ₂ 50.3 / 40.8 50.3 / 51.8 50.3 / 51.8 T-Fe ₂ O ₃ 0 / 3.0 0 / 6.0 0 / 10.0 FeO 0 / 0.5 0 / 0.6 0 / 1.6 FeO / T-Fe ₂ O ₃ (%)-/ 14-/ 10-/ 13 CoO 0 / 1.0 0 / 2.0 0 / 1.0 NiO 0/0 0/0 0/0 ────────────────────────── ――――

[0034]

[Table 3] ────────────────────────────────── Example Comparative example ──────── ─────── １ 1 2 3 4 5 1 2 3 −−−−−−−−−−−−−−−−−−−−−−−−−−−− -------- outer diameter (mm) 0.30 Same as at left Same as at left Same as at left Same as at left Same as at left Same as at left Same as left length (mm) 4.13 Same as at left Same as at left Same as at left Same as at left Same as at left Same as at left Same as left n0 1.612 Same as at left Same as at left Same as at left Same as at left Same as at left Same as at left Same as at left g (mm ^-2) 0.891 Same as left Same as left Same as left Same as left Same as left Same as left TC (mm) 9.20 Same as left Same as left Same as left Same as left Same as left 73.1 72.6 71.3 53.4 54.3 65.7 ─────────────────────────── ──────

Approximately 200 refractive index distribution type rod lenses were arranged in two rows in a staggered manner so that their optical axes were parallel to each other, and were fixed to each other using an adhesive to produce a rod lens array. For this rod lens array, the spatial frequency of the grid pattern was set to 12 Lp / mm, and white light was used as the measurement light.
MTF (Modula) at wavelengths of 0 nm and 740 nm
Table 3 shows the values of Option Transfer Function. Note that M
TF represents the contrast ratio between the object and the image as a function of the spatial frequency. The closer the MTF is to 100%, the more faithful the original image is formed, and the higher the resolving power is maintained. FIG. 3 is a graph showing the transmittance spectral characteristics (glass thickness 0.1 mm conversion) of this clad glass.
Shown in

[Examples 2 to 5] Double glass rods were produced by spinning using a double crucible in exactly the same manner as in Example 1, using the core and clad glass compositions shown in Table 1. . This glass rod was subjected to ion exchange treatment in exactly the same manner as in Example 1 to produce a rod lens and a rod lens array having a refractive index distribution. Table 3 shows various dimensions and refractive index constants of the rod lens, and optical characteristics of the rod lens array. Then, the clad glass used in Example 2 (CoO 2.0, T-Fe ₂ O ₃ 5.0% by weight, the total amount of iron oxide added (Fe ₂ O ₃ equivalent, T-
(Fe ₂ O ₃ ) ratio of FeO converted to Fe ₂ O ₃ : 62%)
FIG. 4 is a graph showing the relationship between the cladding glass used in Example 3 (CoO 1.0, T-Fe ₂ O ₃ 8.0 wt% each, T-Fe ₂ O ₃ , and Fe ₂ O ₃₎ . FeO converted
%: 49%) transmittance spectral characteristics (glass thickness 0.1)
FIG. 5 is a graph showing the relationship between the clad glass (CoO 1.0, T-Fe ₂ O ₃ 10.0% by weight, T-Fe ₂ O ₃ , and Fe ₂ O ₃₎ . Fe converted
O: 25%) transmittance spectral characteristic (glass thickness: 0. 0%).
FIG. 6 shows a graph (converted to 1 mm) of the clad glass (CoO 1.0, T-Fe ₂ O ₃ 3.0) used in Example 5.
Each weight%, F converted to Fe ₂ O ₃ with respect to T-Fe ₂ O ₃
FIG. 7 shows a graph of transmittance spectral characteristics (converted to a glass thickness of 0.1 mm) at an eO ratio of 53%.

[Comparative Examples 1 to 3]
A rod lens and a rod lens array having a refractive index distribution were produced in exactly the same manner as in Example 1 except that the composition of the cladding glass shown in Table 2 was used. Table 3 shows various dimensions and refractive index constants of the rod lens, and optical characteristics of the rod lens array. Then, the clad glass (CoO 1.0, T-Fe ₂ O ₃₎ used in Comparative Example 1 was used.
3.0 Each wt%, the percentage of FeO which in terms of Fe ₂ O ₃ against T-Fe ₂ O _3: transmittance spectral characteristics of 14%) the graph (converted to glass thickness 0.1 mm) in FIG. 8, compare cladding glass used in example _{2 (CoO2.0, T-Fe 2} O 3
6.0 Each wt%, the percentage of FeO which in terms of Fe ₂ O ₃ against T-Fe ₂ O _3: transmittance spectral characteristics of 10%) the graph (converted to glass thickness 0.1 mm) in Fig. 9, compare The cladding glass used in Example 3 (CoO 1.0, T-Fe ₂ O ₃
Respectively transmittance spectral characteristics of 13%) the graph (converted to glass thickness 0.1 mm) in Figure 10: 10.0 each weight percent, the ratio of FeO which in terms of Fe ₂ O ₃ against T-Fe ₂ O ₃ .

Examples 1 to 5 and Comparative Examples 1 to 3 are compared.
Examples 1 to 5 are all 470, 530, 660,
At each wavelength of 740 nm, a high MTF value is obtained. On the other hand, Comparative Examples 1 to 3 show that the MTF value at 740 nm is low, and the resolution is reduced when used in an apparatus that is easily affected by the near infrared region.

[0039]

As described above, according to the present invention, at least the coloring components of CoO, Fe ₂ O ₃ and FeO are contained, and FeO converted to Fe ₂ O ₃ with respect to the total iron oxide content is contained. Exchange of the core / clad double glass rod having a clad glass having a diameter of 23 to 75%, the outer diameter accuracy is extremely good, and the influence of light passing through a portion where the refractive index distribution is disordered in the outer peripheral portion is reduced. And
Even when used in an optical device that prevents flare light from entering and is easily affected by the near-infrared region, a gradient index rod lens and rod lens array having excellent resolution can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a refractive index distribution curve of a gradient index rod lens.

FIG. 2 is a side sectional view showing a spinning furnace for a double glass rod for a gradient index rod lens of the present invention.

FIG. 3 is a diagram showing transmission spectral characteristics of the clad glass of Example 1.

FIG. 4 is a view showing transmission spectral characteristics of the clad glass of Example 2.

FIG. 5 is a diagram showing transmission spectral characteristics of the clad glass of Example 3.

FIG. 6 is a diagram showing transmission spectral characteristics of the clad glass of Example 4.

FIG. 7 is a diagram showing transmission spectral characteristics of the clad glass of Example 5.

FIG. 8 is a diagram showing transmission spectral characteristics of the clad glass of Comparative Example 1.

FIG. 9 is a view showing transmission spectral characteristics of the clad glass of Comparative Example 2.

FIG. 10 is a diagram showing transmission spectral characteristics of the clad glass of Comparative Example 3.

[Explanation of symbols]

1. Double crucible, 2. Internal crucible, 3. External crucible,
4. Core glass, 5 Clad glass, 6 Lower nozzle

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G02B 6/04 G02B 6/04 A 6/18 6/18 F term (Reference) 2H046 AA06 AZ02 AZ11 2H050 AB03Z AC07 AC76 4G059 AA11 AA18 AC09 HB03 HB13 HB15 4G062 AA04 AA06 BB01 CC04 DA05 DA06 DB01 DC01 DD01 DE01 DF01 DF02 DF03 DF04 EA01 EA03 EA04 EB01 EB02 EB03 EB04 EC01 ED03 ED04 EE01 EF01 FG01 F01 FG01 F01 FG01 HH01 HH03 HH05 HH07 HH09 HH11 HH12 HH13 HH15 HH17 JJ01 JJ03 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK07 KK10 MM02 MM04 NN01 NN05 NN40

Claims (7)

[Claims] 1. A gradient index optical element having a core / cladding structure produced by an ion exchange method and containing a metal oxide coloring component in the cladding glass, wherein the cladding glass is used as the metal oxide coloring component. CoO 0.5 to 4.0, and the total iron oxide (converted to Fe ₂ O ₃ ) 2.0 to 12.0, expressed as% by weight, with the total of the mother glass components excluding the coloring component as 100% by weight. , And wherein the FeO in terms of Fe ₂ O ₃ is 23 to 75% of the total iron oxide. 2. The clad glass according to claim 1, wherein the total amount of the mother glass component excluding the coloring component is 100% by weight as the metal oxide coloring component. iron oxide (converted to Fe ₂ O ₃₎ 2.0~6.0, contain, and refractive index distribution according to claim 1 FeO which in terms of Fe ₂ O ₃ is 50% or more of the total iron oxide Type optical element. 3. The clad glass according to claim 1, wherein the total amount of the mother glass component excluding the coloring component is 100% by weight as the metal oxide coloring component. (converted to Fe ₂ O ₃₎ 3.0 to 12.0 containing, and refractive index distribution type optical element according to claim 1 FeO which in terms of Fe ₂ O ₃ is 2% by weight or more. 4. The clad glass according to claim 1, wherein the total amount of the mother glass component excluding the coloring component is 100% by weight as the metal oxide coloring component. iron oxide (converted to Fe ₂ O ₃₎ 6.0 to 10.0, containing, and refractive index distribution type optical element according to claim 3 FeO which in terms of Fe ₂ O ₃ is 3 wt% or more . 5. The clad glass further comprises: NiO 0.2 to 2.0, expressed as a percentage by weight, with the total of the base glass components excluding the coloring component as 100% by weight as the metal oxide coloring component. The refractive index distribution type optical element according to any one of claims 1 to 4. 6. The clad glass layer has a thickness of 1 to 100 μm.
Wherein the glass has a transmittance of 75% or less for light of all wavelengths in the range of 380 to 1000 nm when the thickness is 100 μm.
6. The gradient index optical element according to any one of the above items 5. 7. A gradient index rod lens, wherein a plurality of the gradient index optical elements according to claim 1 are arranged such that their optical axes are parallel to each other and are fixed to each other. array.