JP3537169B2 - Manufacturing method of cylindrical index distribution type optical transmission body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source of any wavelength when used as a lens array having a high resolution, a small distortion at the periphery of a transmission image, and a large number of such light transmission bodies arranged in parallel. The present invention relates to a method of manufacturing a columnar refractive index distribution type optical transmission body which does not cause a reduction in the resolution of a read image due to noise caused by crosstalk between lenses.

[0002]

2. Description of the Related Art Glass-index and plastic-type refractive index distribution type optical transmission bodies have been developed and are usefully used as image reading sensors for copying machines, facsimile machines, LED printer heads and the like. I have. Although these refractive index distribution type optical transmitters have a difference in their manufacturing methods, usually, with respect to the radius r of the optical transmitter,
The range of 0.2r to 0.70r has a refractive index distribution approximately similar to the quadratic curve represented by [Equation 2], and the image transmission characteristics on the center side within 0.70r are good, but the outer part of Image side

(Equation 2) The image quality of the portion is insufficient, and a grid image of 4 line pairs / mm is formed on the CCD line sensor through the light transmitting body, and the maximum value i _max and the minimum value i _min of the measured light amount are measured. ,
The MTF value calculated by [Equation 3] is as low as less than 60%.

[Equation 3] In addition, when a large number of such refractive index distribution type optical transmission bodies are arranged in parallel and used as a rod lens array, the wavelength of the light source used, particularly when a long wavelength light source mainly composed of red light such as an LED is used, Crosstalk occurs between the parallel-arranged refractive index distribution type optical transmission bodies, and a blurred portion due to flare light occurs in a transmission image, and the resolution of the rod lens array cannot be increased.

[0003] As a method of preventing the deterioration of the resolution due to the flare light of the graded index type glass optical transmission body, the side surface of the graded index type optical transmission body is chemically etched to be roughened.
Japanese Patent Application Laid-Open No. 58-38901 discloses an invention relating to an optical transmission body in which the generation of flare light is reduced by providing an acrylic resin layer containing carbon particles on the roughened surface.

[0004]

Problems to be Solved by the Invention JP-A-58-3890
The side surface of the glass refractive index distribution type optical transmission body according to the invention disclosed in Japanese Patent Publication No. 1 has a sharp uneven surface, and has a disadvantage that it is easily broken by stress concentration,
Its resolution is not always high.

[0005] The refractive index distribution in the cross section of the refractive index distribution type optical transmission member produced by the usual method is represented by
The range of 0.2r to 0.70r has a refractive index distribution curve approximately similar to an ideal quadratic curve, and the image transmission characteristics of the internal portion within 0.70r are good. However, since the outer portion exceeding 0.70r has a refractive index distribution greatly deviating from the ideal quadratic curve, the image forming property of the outer portion is extremely poor.

Therefore, conventionally, a method has been adopted in which the outer peripheral portion of the graded index optical transmission body is subjected to chemical etching treatment to transmit light that does not contribute to image formation as scattered light, which is transmitted through the outer layer of the optical transmission body. It is difficult to etch the refractive index distribution of the above-mentioned refractive index distribution type optical transmission body to an area where the refractive index distribution deviates from the ideal quadratic curve by a chemical etching method. Even if a black coating layer of carbon black is provided on the outer periphery,
The improvement of the MTF of the optical transmitter is not so much improved, and the improvement of the blur of the transmitted image by the flare light has not yet been sufficiently improved, and the MTF value at which these points have been improved is high. There is a demand for the development of a gradient index optical transmission body that does not cause crosstalk.

[0007]

Means for Solving the Problems Accordingly, the present inventors have
As a result of studying to obtain a gradient index optical transmission body satisfying the above-mentioned demands, the present invention has been completed. The gist of the invention is as follows: (1) a columnar refractive index distribution type optical transmission body; Swollen part on outer periphery
Is formed and the swelling portion is removed.
How to make a covered columnar graded index optical transmitter
Law, (2) before the formation of the swelling portion cylindrical GRIN optical transmission
The feeder (radius L) decreases from the central axis toward the outer peripheral surface.
Both quadratic songs whose range from 0.25 L to 0.85 L is specified by [ Equation 1]
It has a refractive index distribution that is approximately similar to the line,

N (L) = n ₀ {1- (g / 2) L ² } (where n ₀ is the refractive index of the central portion of the optical transmission body, and n (L) is
The refractive index at a position L from the central axis of the optical transmitter, g is the optical transmitter
, L is the distance from the center of the optical transmitter,
Is shown. ) And satisfying 1.40 ≦ n ₀ ≦ 1.60 0.4 mm ≦ L ≦ 0.55 mm 0.15 mm ⁻¹ ≦ g ≦ 0.7 mm ⁻¹ .
Manufacturing method .

[0008] The refractive index distribution type optical transmitter according to the present invention, having a refractive index distribution in at least the range of 0.2 L to 0.85 L having a distribution approximately similar to the quadratic curve defined by [Equation 4], is as follows. It is preferable to make. First, there is a refractive index distribution type optical transmitter precursor having a circular cross section having a radius of r, and at least 0.25r to 0 from the central axis of the optical transmitter precursor toward the outer periphery.
The refractive index distribution in the range of 70r has a refractive index distribution approximately similar to the quadratic curve defined by [Equation 5], and

(Equation 5) 1.40 ≦ n ₀ ≦ 1.60 0.4mm ≦ L ≦ 0.55mm 0.15mm ⁻¹ ≦ g ≦ 0.7mm ^-1 Cut the outer periphery of the gradient index optical transmitter precursor having the characteristic of at least 0.25r to 0.85r. It is preferable that the refractive index distribution in the range has a refractive index distribution approximately similar to the curve shown in [Equation 4] and the outer peripheral portion is covered with a mesh-like crack layer.

[0009] The refractive index distribution type optical transmitter precursor used in practicing the present invention can be produced by various methods. In particular, when the precursor is made of plastic, it is produced as follows. Is good. That is,
N uncured liquid substances having a viscosity of 10 ³ to 10 ⁸ poise, and the cured product obtained by curing the substance has a refractive index of n ₁ > n ₂ >
n ₃ ...> n _N (where N ≧ 2) uncured liquid materials are concentrically arranged in such a manner that the refractive index gradually decreases from the center toward the outer periphery from the composite spinning nozzle. By extruding and shaping the fiber into a strand fiber shape, and performing the interdiffusion treatment of the material between the layers of the strand fiber, or after performing the interdiffusion treatment, the curing treatment of the uncured strand fiber is carried out. To obtain a refractive index distribution type optical transmitter precursor used in (1).

FIG. 1 shows the results of measuring the refractive index distribution of the optical transmitter precursor having a radius of 0.58 mm obtained as described above. In FIG. 1, b is a refractive index distribution curve of the optical transmitter precursor formed as described above, and a is an ideal quadratic curve of the refractive index distribution. In this precursor, the refractive index distribution curve having a radius in the range of at least 0.1r to 0.7r has almost the same distribution as its ideal distribution curve, and the image transmission characteristics of the precursor in this range are extremely good. The refractive index distribution on the outer side of the curve deviates significantly from the ideal curve, and causes flare light.

In the present invention, first, the outer periphery of the optical transmission body precursor as described above is shaved, and the outer periphery, which is the point c in FIG. 1, is cut to 4.3 mm (L) to obtain a refractive index distribution type light. When a transmission body is made, its refractive index distribution curve can take a distribution approximate to the quadratic curve shown in [Equation 4] in the range of 0.25 L to 0.95 L as shown by b in FIG. Therefore, it is possible to provide an extremely good image transmission characteristic without generating flare light or the like. Further, by doing so, a light absorbing layer or a light scattering layer can be formed on the outer peripheral portion.

As a method for grinding the outer peripheral portion of the optical transmitter precursor used in practicing the present invention, for example , a melting grinding method using a solvent or the like can be used. In particular, the hydrated optical transmitter precursor is immersed in an organic solvent having an affinity for water to form a swelling layer on its outer periphery, and this swelling layer is placed in an elastic material such as silicon rubber. By cutting and removing through a drilled hole and drying, a light absorbing layer can be formed on the outer surface of the hole, and a light transmission body in which flare light hardly occurs can be obtained.

Solvents used for solvent grinding include organic chlorine solvents such as methylene chloride, chloroform and carbon tetrachloride, and lower ketones such as acetone and methyl ethyl ketone.
Lower esters of organic acids such as ethyl acetate can be used. Non-solvent optical transmission body after solvent grinding, for example,
It is also a good method to perform a washing treatment with water, alcohol, or the like.

The refractive index distribution type optical transmitter obtained as described above has a very small generation of flare light and has good image transmission characteristics. When used in an array, it is necessary to prevent crosstalk between the optical transmitters. In order to prevent the image characteristics of the optical transmission body from deteriorating due to the crosstalk, the side surfaces of the refractive index distribution type optical transmission body prepared as described above are treated with a carbon black-containing light shielding agent to form a light shielding film. Is the most effective method.

As the coating material used for forming the light-shielding film, various coating materials containing carbon black soluble in water or a solvent can be used.
Alkyd resins, polyester resins, acrylic-modified polyester resins, and the like can be given as specific examples.

Hereinafter, the present invention will be described in more detail with reference to examples. The MTF was measured using the following method. [Measurement of MTF] MTF was measured using the apparatus shown in FIG. The continuous light obtained from the light source is made monochromatic by transmitting through a filter and a diffusion plate, and the spatial frequency n
An original image is obtained using a grid having (line pairs / mm) (FIG. 4). By forming an image of this original image using a single light transmitting body or an optical transmitting body array in which a plurality of light transmitting bodies are arranged, and reading the image using a CCD line sensor provided on the image forming surface (FIG. 5), [Equation 3] is obtained. , The MTF of the optical transmitter alone or the optical transmitter array was measured.

[0017]

Reference Example 1 First, a method of manufacturing a refractive index distribution type optical transmission body preform used for manufacturing the optical transmission body of the present invention and a method of grinding the outer peripheral portion thereof will be described. Polymethyl methacrylate ([η] = 0.56, methyl ethyl ketone (ME
K) Measured at 25 ° C) 46 parts by weight, 44 parts by weight of benzyl methacrylate, 10 parts by weight of methyl methacrylate, 0.2 parts by weight of 1-hydroxycyclohexylphenyl ketone and 0.1 parts by weight of hydroquinone are heated and kneaded at 70 ° C to form the first layer. (Center part) It was used as a stock solution for formation. Also, 50 parts by weight of polymethyl methacrylate ([η] = 0.41, measured at 25 ° C. in MEK), 50 parts by weight of methyl methacrylate, 0.2 parts by weight of 1-hydroxycyclohexyl phenyl ketone and 0.1 part by weight of hydroquinone are heated and kneaded at 70 ° C. To give a stock solution for forming a second layer, and further, polymethyl methacrylate ([η] =
0.34, measured at 25 ° C in MEK) 45 parts by weight, 2,2,3,3,4,4,
5,5-octafluoropentyl methacrylate 35 parts by weight,
20 parts by weight of methyl methacrylate, 0.2 part by weight of 1-hydroxycyclohexyl phenyl ketone and hydroquinone
A solution prepared by heating and kneading 0.1 part by weight at 70 ° C. was used as a stock solution for forming a third layer (outer layer).

Using a molding apparatus equipped with a true conjugate type composite spinning nozzle, the above three types of stock solutions are arranged in order from the center to the outside so that the refractive index of the uncured material becomes lower, and simultaneously extruded. Strand fiber was used. The viscosity of the first layer was 4,5 × 10 ⁴ poise,
The layer is 2.0 × 10 ⁴ poise, and the undiluted solution of the third layer is 2.2 × 10 4
⁴ poise. The temperature of the composite spinning nozzle is 55 ° C.
And

Next, the light was passed through a 90 cm-long inter-diffusion processing section of each layer, and thereafter, 12 fluorescent lamps having a length of 120 cm and 40 W were passed through a strand fiber centered on circularly arranged light irradiation sections. At a speed of 50 cm / min, radius (r ₀ ) 0.50 mm
Was taken by a nip roller.
The discharge amount ratio was set as first layer: second layer: third layer = 1: 1: 1. The refractive index distribution is 1.512 at the center (N ₀ ) and 1. at the periphery.
470, the refractive index distribution constant (g) is 0.52, and 0.25r ₀ from the center toward the outer surface as shown in [II] in FIG.
The refractive index distribution in the range of about 0.75r ₀ almost coincided with the quadratic curve [II] satisfying [Equation 1].

The end faces of the optical transmission body preform were polished to a lens length of 7.2 mm, and the MTF measured using a grid of 4 line pairs / mm was 57%.
15.4 mm. The image of the obtained lattice was a clear image with little distortion, but some distortion was recognized in the peripheral portion. A plurality of polished objects on both end surfaces of this optical transmission body preform are arranged in parallel, bonded and sandwiched between two substrates, and both end surfaces are polished and finished, and an optical transmission array having a lens length of 7.1 mm and a conjugate length of 15 mm. The MTF of this optical transmitter array measured using a grating of 4 line pairs / mm was 49%.

The preform was immersed in chloroform maintained at 10 ° C. for 45 seconds, passed through a small hole formed in a 1 mm thick silicon rubber sheet, and swollen with chloroform (FIG. 2). Cut off part F), radius 0.48
mm optical transmission body was obtained. The refractive index distribution of this optical transmitter is shown in FIG.
As shown in the middle [II], the center (n ₀ ) is 1.512 and the periphery is
1.474 and the refractive index distribution constant (g) is 0.52.
As shown in [II], 0.24L from the center to the outer surface
The range of 0.83 L had a refractive index distribution approximately matching the quadratic curve [I]. When the outer peripheral surface of the obtained optical transmission body was observed with a microscope, it was confirmed that a mesh-like scattering layer was formed.

Both ends of the lens cut from the optical transmission body were polished to a lens length of 7.2 mm, and the MTF measured using a grating of 4 line pairs / mm was 65%, and the conjugate length at that time was 15.4. mm. Also, the image of the obtained grating is compared with the optical transmitter preform before the surface is scraped,
It was a clear image with very little distortion.

A plurality of the light transmitting members are arranged in parallel to form an optical transmitting member array having a lens length of 7.1 mm, and the MTF is measured using a grating of 4 line pairs / mm.
Was 61% at its conjugate length of 15.4 mm. An image scanner was assembled with this light transmitter array by combining an LED as a light source and a CCD as a light receiving element. This image scanner had a high resolution and was able to transmit clear images. However, blurring of the image has occurred due to the crosstalk of the flare light.

As described above, the refractive index distribution type optical transmission body which has been subjected to the outer periphery grinding of the optical transmission body is subjected to a blackening tank (25 ° C., length: 25 ° C.) filled with an emulsion paint containing carbon black.
50 cm), and then lifted and passed through a 70 ° C. drying cylinder (length 2.5 m) at a take-up speed of 70 cm. On the surface of the obtained refractive index distribution type optical transmission body, a black light blocking layer was formed with a thickness of 2.5 μm. The MTF as a single lens and the image formation state of the grating did not change from before processing. However, a plurality of the optical transmitters are sandwiched between two substrates in a parallel arrangement, and both end surfaces are polished and assembled into an optical transmitter array having a lens length of 7.1 mm. The MTF measured using a grating of / mm was 65% at its conjugate length of 15.4 mm. This optical transmitter array uses LED as a light source and CC
An image scanner having D as a light receiving element was assembled. This image scanner did not show any image bleeding due to flare light crosstalk, and was able to transmit a very clear image.

[0025]

[Reference Example 2] Carbon black 3 parts by weight blackening bath, 100 parts by weight of polymethyl methacrylate, with a blackening solvent consisting of methyl ethyl ketone 5000 parts by weight, an optical transmission member that cutting the outer peripheral portion used in Reference Example 1 Reference The same operation as in Example 1 was performed to form a black coating layer. A black light blocking layer was formed on the surface of the light transmitting body with a thickness of 3.0 μm. Using this optical transmitter, an optical transmitter array having a lens length of 7.1 mm was assembled in the same manner as in Reference Example 1, and the MTF of this optical transmitter array measured using a grid of 4 line pairs / mm was the conjugate length of the MTF.
It was 66% at 15.4 mm. This optical transmitter array has LEDs
An image scanner was assembled in which the light source was used as a light source and a CCD was used as a light receiving element. This image scanner does not show image bleeding due to crosstalk of flare light,
A very clear image could be transmitted.

[0026]

Example 1 After immersing the refractive index distribution type optical transmitter precursor produced in Reference Example 1 in water for 60 minutes, it was immersed in an ethyl acetate / methanol (2: 3) mixed solution at 30 ° C. for 90 seconds to form an outer periphery. A swollen portion was formed in the portion, and then the swollen portion was removed through a pore provided in the silicone rubber. Observation of the side surface of the obtained refractive index distribution type optical transmission body with a microscope revealed that a light scattering layer was formed on the surface. The outer diameter of this optical transmission body is 0.
90mm, the effective diameter of this lens is 0.80mm
And the range of 0.2 L to 0.88 L had a refractive index distribution almost similar to a quadratic curve. The conjugate length of this refractive index distribution type lens was 15.4 mm, and the MTF measured using a grating of 4 line pairs / mm was 68%. A coating layer of carbon black was provided on the outer periphery of the optical transmission body in the same manner as in Reference Example 2 to form a lens having a lens length of 7.1 mm, and a large number of these lenses were arranged in parallel to assemble a lens array. The lens array was set to have a lens length of 7.1 mm and a conjugate length of 15.4 mm, and the MTF measured using a grating of 4 line pairs / mm was 63%. When an image scanner was assembled with this light transmitter using an LED as a light source and a CCD as a light receiving element, no crosstalk between lens elements due to flare light was observed, and no image bleeding was observed. Could be transmitted.

[Brief description of the drawings]

FIG. 1 is an example of a refractive index distribution curve of a gradient index optical transmission body used in the present invention.

FIG. 2 is a diagram showing another example of the refractive index distribution curve of the gradient index optical transmission body used in the present invention.

FIG. 3 is a perspective view schematically showing an MTF measuring device for a lens element.

FIG. 4 is a measurement diagram of light amount levels I _max and I _min when a grating is read by an MTF measurement device.

FIG. 5 is a measurement diagram of light amount levels i _max and i _min when a grating is read through a lens element by an MTF measurement device.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-152332 (JP, A) JP-A-3-196451 (JP, A) JP-A-3-213806 (JP, A) JP-A-3-213 174105 (JP, A) JP-A-58-38901 (JP, A) JP-A-53-127294 (JP, A) JP-A-58-155947 (JP, A) WO 92/015901 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 3/00 G02B 5/02

Claims (2)

(57) [Claims] 1. An outer peripheral portion of a columnar refractive index distribution type optical transmission body.
The swelling part is formed and the swelling part is removed.
Of a cylindrical graded-index optical transmission medium covered with a turbostratic
Production method. 2. A columnar refractive index component before forming a swollen portion.
The cloth-type optical transmission body (radius L) moves from the central axis to the outer peripheral surface.
The range of at least 0.25 L to 0.85 L is defined by [ Equation 1].
Substantially has a refractive index distribution of the approximation, Equation 1] _{n (L) = n 0 {} 1- (g / 2) L 2} ( where, _{n 0} is the center of the optical transmission member to the secondary curve that The refractive index of the part, n (L) is
The refractive index at a position L from the central axis of the optical transmitter, g is the optical transmitter
, L is the distance from the center of the optical transmitter,
Is shown. 2. The columnar refractive index distribution type optical transmission body according to claim ^1, which satisfies 1.40 ≦ n ₀ ≦ 1.60 0.4 mm ≦ L ≦ 0.55 mm 0.15 mm ⁻¹ ≦ g ≦ 0.7 mm ^−1.
Manufacturing method.