JPH0792308A - Distributed refractive index type rod lens array - Google Patents

Abstract

PURPOSE:To prevent stray light and to obtain a good contrast and brightness without reducing the effective diameters of rod lenses by directly coating rod lenses with a resin having a specific refractive index to the refractive index of the outermost peripheral parts of these rod lenses. CONSTITUTION:The sides 3 of the rod lenses 1 constituting the distributed index type lens array (SLA) are coated with the resin adjusted to a refractive index within a range from -0.01 to +0.035 of the refractive index of the outermost peripheral parts of the rod lenses without roughening the flanks 3 thereof. The incident light of an angle larger than the opening angle of the rod lenses 1, therefore, eventually passes through to the resin side from the sides 3 of the rod lens side without making total reflection at the boundary of the sides 3 of the rod lenses and the coated resin when the incident light arrives at the sides 3 of the rod lenses. Then, the incident light does not turn to stray light. A good result is obtd. if the range of the refractive index of the resin is confined to -0.007 to +0.02 of the refractive index in the outermost peripheral parts of the rod lenses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradient index rod lens array used in a lens of a unity magnification coupling optical system of an optical device such as a facsimile, a copying machine, a printer, etc. The present invention relates to a gradient index rod lens array.

[0002]

2. Description of the Related Art A gradient index lens having a refractive index distribution in a radial direction is provided between two black substrates as an equal magnification coupling optical system inside an optical device such as a facsimile machine, a copying machine and a printer. A composite lens in which one or more rows are lined up and both end surfaces are optically polished is used. This compound lens is generally a gradient index lens array (hereinafter referred to as S
It is called LA (registered trademark)), and has a function of combining a band-shaped image on an image sensor or a photosensitive drum.

At present, the wire diameter of each rod lens that constitutes a commercially available SLA is about 1 mm. For example, product numbers SLA-12A and SLA of Nippon Sheet Glass Co., Ltd.
-12B or the like. In recent years, along with the miniaturization of optical equipment, the wire diameter of each rod lens is about 0.6 mm.
LA has come to be manufactured. For example, product numbers SLA-12D, SLA-20D, and SLA of Nippon Sheet Glass Co., Ltd.
-4D etc.

The rod lens constituting this SLA is mainly manufactured by an ion exchange method. In the rod lens that has been ion-exchanged, of the incident light on the end face, the incident light having an angle larger than the aperture angle of the rod lens reaches the side face of the rod lens and causes total reflection on the side face.

This totally reflected light becomes light that does not participate in image formation, so-called stray light, and lowers the contrast of the rod lens. Further, since the SLA is composed of a large number of rod lenses, stray light inside each rod lens is SLA.
It causes a decrease in the overall contrast.

In order to remove the stray light, in the current SLA manufacturing process, the rod lens constituting the SLA is immersed in a mixed solution of hydrofluoric acid, ammonium fluoride and water (hereinafter referred to as a treatment solution) for several minutes. The lens side surface is chemically roughened (hereinafter referred to as flare cut), and then a black coating is applied to the side surface (hereinafter referred to as black coat). For example, JP-A-58-58
See 38901. By performing the above two processes, stray light in the rod lens can be removed to the extent that the contrast of image formation is not deteriorated. See FIG.

The reason for this is as follows. In other words, since the side surface of the rod lens is rough, total reflection at that portion is suppressed and becomes scattered light. Moreover, since the scattered light is absorbed by the black paint applied to the side surface of the rod lens, stray light can be effectively prevented.

Since optical devices tend to be further miniaturized, it is required that the SLA constituting the optical system be further miniaturized. For that purpose, the wire diameter of each rod lens that constitutes the SLA is
It is required to be thinner.

[0009]

In order to effectively carry out the above-mentioned flare cutting treatment, the thickness of the side surface layer of the rod lens to be cut by the treatment is a certain thickness (regardless of the wire diameter of the rod lens). Normally, it should be several tens of μm) or more.

Therefore, in a rod lens having a large wire diameter, the thickness cut by the flare cutting process is a small proportion of the entire effective diameter of the rod lens,
As the wire diameter becomes smaller, the ratio gradually increases and the effective diameter of the lens decreases.

Particularly, in the case of a rod lens having a wire diameter of 0.5 mm or less, when the above flare cut treatment is performed, it is about 1
Since the effective diameter is reduced by more than 40% (this results in an effective area reduction of about 20%), the brightness of the SLA is extremely reduced.

Further, since the above-mentioned flare cutting treatment is a chemical reaction, the temperature of the treatment liquid varies depending on the season,
There is also a problem that it is difficult to always obtain the same surface condition because the roughness of the side surface of the rod lens fluctuates greatly due to the difference in the treatment amount (treatment area) of the rod-shaped glass with respect to the unit treatment liquid amount. there were.

Furthermore, since the lens characteristics (aperture angle) of the rod lens are mainly determined by the monovalent cations (Li, Tl, Cs ions), the lenses having different lens characteristics naturally have different glass compositions. It will be. In the flare cutting process described above, it is necessary to prepare a treatment liquid according to the glass composition of various rod lenses, and a treatment liquid tank must be provided for each treatment liquid, which is extremely economically inefficient. Become.

On the other hand, it is conceivable that the side surface of the rod lens is mechanically roughened and flare cut processing is performed, but even in this case, the effective lens diameter is inevitably reduced. Moreover, the mechanical roughening causes cracks in the rod lens element wire, which reduces the tensile strength thereof. Especially in a rod lens having a small wire diameter, the influence is great. Furthermore, this makes continuous production of rod lens element wires difficult, which in turn leads to high costs.

As described above, in the case of a rod lens having a small wire diameter, the flare cut processing of the above two examples causes a reduction in the lens effective diameter, and as a result, the brightness of the SLA using the lens is reduced. Therefore, there is a problem that it is difficult to construct a practical SLA using a rod lens having a small wire diameter.

[0016]

Therefore, the present invention provides a gradient index rod lens array in which a large number of rod lenses having a gradient index distribution in the radial direction are arranged in a row or in a plurality of rows to form a rod lens array. A gradient index rod lens array in which a resin having a refractive index within the range of −0.01 to +0.035 with respect to the refractive index of the outer peripheral portion is directly coated without roughening the side surface of the rod lens. Constitute.

Further, the range of the refractive index of the resin is from -0.007 to + with respect to the refractive index of the outermost peripheral portion of the rod lens.
A value of 0.02 is suitable.

[0018]

As described above, with respect to the refractive index of the outermost peripheral portion of the rod lens constituting the SLA, it is -0.01 to +0.
By coating the resin adjusted to have a refractive index within the range of 035 on the side surface of the rod lens, incident light having an angle larger than the opening angle of the rod lens is coated on the side surface of the rod lens when reaching the side surface of the rod lens. It will escape from the side surface of the rod lens to the resin side without causing total reflection at the interface of the resin. Therefore, the incident light does not become stray light.

By the above-mentioned operation, stray light of the rod lens constituting the SLA can be prevented, and the S
The contrast of LA can be improved.

[0020]

EXAMPLES First, a preliminary experiment was conducted to investigate the relationship between the refractive index of the outermost peripheral portion of the rod lens and the refractive index of the resin to be coated as follows.

The side surface (side surface) of the rod lens that has not been subjected to flare cutting or black coating is filled with an organic solvent instead of the resin to be coated, and a lattice pattern of 6 (lp / mm) is formed on one end surface of the rod lens. Then, the image formed on the other end surface of the rod lens was observed with an optical microscope at a magnification of 100 times. The reason for using the organic solvent instead of the resin as described above is that the organic solvent can evaluate only the effect of the difference in refractive index without being influenced by the coating state unlike the resin. is there.

At that time, the organic solvent is selected from the following five kinds (xylene, bromobenzene, aniline, phenylhydrazine, 1-chloronaphthalene) to gradually change the refractive index from about 1.50 to 1.63. Change to
The contrast of the lattice pattern image was examined. Regarding the evaluation, a lens with the same contrast as the conventional flare-cut and black-coated lens is marked with ○, a lens with the same degree as the untreated lens is marked with ×, and an intermediate one is marked with △.
It was evaluated in three stages.

At this time, the temperature of the organic solvent was about 22 ° C. (room temperature), but in the case of phenylhydrazine having a refractive index closest to the refractive index (1.6010) of the outermost peripheral portion of the rod lens, , The temperature of the organic solvent is changed from about 22 to about 45 ° C., and its refractive index is 1.593 to 1.60 with the refractive index of the outermost peripheral portion of the rod lens sandwiched therebetween.
The contrast was examined by continuously changing it to 6.

The aperture angle of the rod lens is about 9 degrees, and the refractive index of the outermost periphery thereof is about 1.601 (wavelength λ
= 570 nm). Furthermore, its size is 1.
It has a length of 1 mm and a length of 35.20 mm, and both end faces thereof are optically polished.

The results are shown in Table 1. In this case, in order to obtain the same contrast as that of the rod lens that has been subjected to flare cut and black coating, which is a conventional method for preventing stray light, the refractive index of the organic solvent should be set to a range in the vicinity of the refractive index of the outermost peripheral portion of the rod lens. I understand that it is good. That is,
Similarly, when a resin is used, the refractive index of the resin may be set in the range near the refractive index of the outermost peripheral portion of the rod lens.

[0026]

[Table 1]

Carbon black was not added to the organic solvent used in this preliminary experiment. This is because only the contrast of one rod lens is evaluated, so that the light emitted from a certain rod lens, which occurs in the case of being composed of a large number of rod lenses like SLA, is This is because there was no phenomenon of re-entering into the rod lens adjacent to it and becoming stray light.

(Example) A rod lens which is ion-exchanged in advance and has a refractive index distribution in the radial direction is prepared. The side surface of the rod lens is coated with a transparent resin to match the refractive index. As the transparent resin,
For example, an ultraviolet curable resin, an electron beam curable resin or a thermosetting resin can be used. A resin for adjusting the refractive index (for example, 9-vinylcarbazole, polycarbonate, etc.) is added to this resin, and the refractive index of the resin is adjusted in the vicinity of the refractive index of the outermost peripheral portion of the rod lens. This is directly coated on the side surface of the rod lens. After that, the resin is cured by irradiating or heating with an ultraviolet ray or an electron beam.

As described above, by coating the resin having a matching refractive index in the vicinity of the refractive index of the outermost peripheral portion of the rod lens, it is possible to obtain a rod lens in which the effective diameter of the lens is not reduced. .

A plurality of rod lenses manufactured by the above method are arranged in a line between two FRP plates, and the gap is filled with black silicone resin. After that, both end surfaces are optically polished so as to have a predetermined lens length, and an SLA is manufactured.

Next, the SL produced by the above-mentioned method
MTF (Modulation Transfer Function) of A is measured. In this MTF, the image of the rectangular wave grating pattern formed by SLA is received by the CCD image sensor, and the response function MTF of SLA is calculated by the following equation from the light amount level.

MTF (W) = {i (w) max-i (w) min} / {i (w) max + i (w) min} × 100 (%) (1) where i (w) max and i (w) min are the maximum value and the minimum value of the rectangular wave response at the spatial frequency w (lp / mm). That is, the closer the MTF is to 100%, the more faithfully the original image is formed. The measurement here is performed using monochromatic light in which halogen light is passed through an optical filter having a wavelength of 570 nm, and the spatial frequency of the test chart is 6 (lp / mm).

The MTF, which is one of the indexes of the optical performance of the SLA described above, generally reflects the contrast of the image formed by the individual rod lenses constituting the SLA, and a high MTF value indicates that SLA. It indicates that the individual rod lenses constituting the lens have good contrast (that is, there is little stray light), and conversely, a low MTF value shows that the contrast is poor (the amount of stray light is large).

The reason for this is that in the above equation (1), when the stray light is small, the minimum value i (w) min of the rectangular wave response becomes small, and therefore the ratio of the numerator to the denominator in the above equation, that is, the MTF value is Because it will grow. For example, if there is no stray light and i (w) min is very close to zero,
The numerator and denominator are as close to the same i (w) max as possible,
The MTF value will approach 100%.

That is, since the stray light that causes the reduction in the contrast of the rod lens does not relate to the image formation, it uniformly passes through the rod lens and pushes up i (w) min to raise the background. However, the MTF of the SLA is reduced for the above reason.

Therefore, in the following specific examples, the effect of preventing stray light of the rod lens will be determined by the MTF value of the SLA manufactured using the rod lens.

(Specific Example 1) An ultraviolet curable resin (Desolite (registered trademark) 950Y132: manufactured by Nippon Synthetic Rubber Co., Ltd.) was used as a resin for adjusting the refractive index on the side surface of the rod lens having the characteristics shown in Table 2. 9-Vinylcarbazole was added and the refractive index thereof was changed to form a coating having a thickness of about 30 μm. In this case, the refractive index of the ultraviolet curable resin was changed from 1.517 to 1.567. The 9-vinylcarbazole is provided in the form of powder or granules, is soluble in the desolite resin in a wide mixing range, and is suitable for increasing the refractive index of the desolite resin.

[0038]

[Table 2]

Further, as a black pigment in the resin, about 3
Carbon black of weight% was added to give a black color. In this way, by making the resin black, it is possible to absorb the light that has escaped from the side surface of a certain rod lens and prevent the light from reentering the rod lens adjacent thereto and becoming stray light.

Then, the rod lens coated with the above resin was irradiated with ultraviolet rays for about 10 minutes by using a 120 W ultraviolet lamp to cure the resin to prepare a rod lens which becomes an SLA element wire.

A large number of rod lenses produced by the above-mentioned method were arranged in a line between two FRP plates in a range of about 15 mm, and the gap was filled with black silicone resin.
After that, both end faces were optically polished so as to have a lens length of about 1.48 mm, and an SLA was produced.

In Table 3, the amount of 9-vinylcarbazole added and the refractive index of the coating resin (wavelength λ = 570 nm)
And MT of SLA produced using the rod lens
The F value is shown.

[0043]

[Table 3]

FIG. 3 shows the refractive index of the coating resin and SLA.
The relationship of the MTF value of is shown. As is clear from this figure,
It can be seen that the MTF value has a peak when the refractive index of the coating resin is about the same as that of the outermost peripheral portion of the rod lens.

In this case, the MTF value from the peak MTF value
However, for example, the range of the refractive index when it is decreased by 5% is 1.519 to 1.547, that is, -0.01 to +0.018 with respect to the refractive index of the outermost peripheral portion of the rod lens.
Met. The range of the refractive index when the refractive index is further reduced by 2% is -0.0 with respect to the refractive index of the outermost peripheral portion of the rod lens.
It was from 07 to +0.009.

(Specific Example 2) An ultraviolet curable resin ((product code) 2 was formed on the side surface of the rod lens having the characteristics shown in Table 2.
310C: manufactured by Nippon Loctite Co., Ltd.) was coated with 9-vinylcarbazole as a transparent resin for adjusting the refractive index to change its refractive index to a thickness of about 30 μm. In this case, the refractive index of the resin is 1.55
Varyed from 8 to 1.661. The 9-vinylcarbazole is soluble in the 2310C resin in a wide mixing range and is suitable for increasing the refractive index of the 2310C resin.

When the amount of 9-vinylcarbazole added was 40% or more, the resin could not be completely dissolved in the 2310C resin. Therefore, the resin temperature was raised to 40 to 50 ° C. to dissolve the 9-vinylcarbazole.

Further, in the same manner as in Example 1, about 3% of the above resin was added.
Carbon black was added by weight% to make it black so as to absorb the light emitted from the side surface of the rod lens. Other than that, the SLA was manufactured by the same method as in the specific example 1.

In Table 4, the amount of 9-vinylcarbazole added and the refractive index of the coating resin (wavelength λ = 570 nm)
And MT of SLA produced using the rod lens
The F value is shown. Here, the length of the rod lens of this SLA was processed to about 2.99 mm.

[0050]

[Table 4]

FIG. 4 shows the refractive index of the coating resin and SLA.
The relationship of the MTF value of is shown. As is clear from this figure,
It can be seen that the MTF value has a peak when the refractive index of the coating resin is about the same as that of the outermost peripheral portion of the rod lens.

In this case, the MTF value is calculated from the peak MTF value.
However, for example, the range of the refractive index when it is decreased by 5% is 1.567 to 1.612, that is, -0.01 to +0.035 with respect to the refractive index of the outermost peripheral portion of the rod lens.
Met. The range of the refractive index when the refractive index is further reduced by 2% is -0.0 with respect to the refractive index of the outermost peripheral portion of the rod lens.
It was from +07 to +0.02.

Here, in specific examples 1 and 2, the MTF of the refractive index of the resin relative to the refractive index of the outermost peripheral portion of the rod lens.
Let us consider the effect on the value.

When the refractive index of the resin is smaller than the refractive index of the outermost peripheral portion of the rod lens, that is, the change of the MTF value on the negative side is the same as that of the first and second embodiments, the MTF value increases as the difference in the refractive index increases. The value drops sharply.

On the other hand, when the refractive index of the resin is larger than the refractive index of the outermost peripheral portion of the rod lens, that is, the change in the MTF value on the plus side shows different tendencies in the first and second examples. . That is, in the specific example 1, the MTF value suddenly decreases as the difference in the refractive index increases, but in the specific example 2, the MTF value gradually decreases.

The cause of this is desolite, which is the resin used in Example 1, and 23, which is the resin used in Example 2.
A difference in ease of application of 10C to the rod lens is considered. Desolite cannot be applied well to the surface of rod lenses as compared to 2310C. Moreover, as the amount of 9-vinylcarbazole added increases, this tendency becomes particularly strong. So in Desolite,
It is conceivable that the matching of the refractive index is not successful at the interface with the rod lens, as compared with the case of 2310C. In particular, it is considered that the tendency becomes stronger as the amount of 9-vinylcarbazole added increases.

As a result, in the case of using 2310C,
It can be seen that when the refractive index of the resin is larger than the refractive index of the outermost peripheral portion of the rod lens, the tolerance of the refractive index matching between the resin and the outermost peripheral portion of the rod lens is large.

As described above, by coating the side surface of the rod lens with a resin having a refractive index that matches the refractive index of the outermost peripheral portion of the rod lens, stray light can be prevented without reducing the effective diameter of the rod lens. Can be prevented.

Further, the SLA produced by using this rod lens is the SL using the rod lens which has been subjected to flare cut and black coat which are the conventional stray light preventing methods.
It is possible to obtain an MTF equivalent to A.

Further, the effect of the addition amount of carbon black was also investigated. Increasing the amount of carbon black added can effectively absorb the scattered light on the side surface of the rod lens.

However, if the addition amount exceeds 5% by weight, the transmittance of ultraviolet rays into the resin is lowered by the carbon black, and the curing speed of the resin is extremely slowed.
It becomes impractical. On the contrary, when the addition amount is small, the effect of absorbing scattered light becomes low. For this reason, it is preferable that the amount of carbon black added is as large as possible within the practical range of the curing speed of the resin. Specifically, about 3-5
A weight% range is preferred.

As described above, the SLA having the strand diameter of 0.2 mm prepared this time can be sufficiently used for the application in which the conventional SLA is used, and the miniaturization of the optical device which the conventional SLA cannot deal with. Can be fully supported.

[0063]

According to the present invention as described above, for example, in an SLA using a rod lens having a wire diameter of 0.5 mm or less, stray light can be prevented without reducing the effective diameter of the rod lens, and good contrast and Have brightness,
It is possible to obtain a gradient index rod lens array that can respond to the miniaturization of the optical system.

In order to examine the effect of the present invention, a comparison was made between the conventional flare cut and black coat treatments.

The SLA of Sample 4, which has the highest MTF value in the second embodiment of the present invention, and the same lens as the rod lens used in the second embodiment, are rod lenses obtained by subjecting them to conventional flare cut and black coat treatment. SL made in
The brightness of each of A was compared. When the brightness of the sample 4 of the specific example 2 is 100, the SLA of the conventional process is set.
The brightness was 67. The brightness here is obtained from the light amount level of a fixed amount of light source light that has passed through the SLA and is received by the CCD image sensor.

From the above results, even if the SLA is manufactured using the same rod lens, there is a significant difference in brightness between the case where the stray light prevention treatment of the present invention is performed and the case where the conventional stray light prevention treatment is performed. It turned out to occur.

[Brief description of drawings]

FIG. 1 is a perspective view of a gradient index rod lens array according to the present invention.

FIG. 2 is a diagram showing a sectional structure of a rod lens element wire in the SLA of the present invention.

FIG. 3 is a diagram showing the relationship between the refractive index of resin and MTF in Concrete Example 1.

FIG. 4 is a diagram showing the relationship between the refractive index of resin and MTF in Example 2.

FIG. 5 is a diagram showing a cross-sectional structure of a rod lens element wire in a conventional SLA.

[Explanation of symbols]

 1 rod lens 2 coated resin (including black pigment) 3 side plate of SLA 4 black paint 5 roughened rod lens side surface

Claims (3)

[Claims] 1. A gradient index rod lens array in which a large number of rod lenses having a gradient refractive index distribution in the radial direction are arranged in one or a plurality of rows to form an array, and the refractive index of the outermost peripheral portion of the rod lens is −0. From 0.01 to +0.03
A gradient index rod lens array characterized in that a resin having a refractive index within the range of 5 is directly coated without roughening the side surfaces of the rod lens. 2. The gradient index rod lens array according to claim 1, which is coated with a resin having a refractive index within the range of −0.007 to +0.02. 3. The gradient index rod lens array according to claim 1, wherein the rod lens has a wire diameter of 0.5 mm or less.