Distributed graded index type optical transmission plastic article and method of manufacturing same

• US 5,390,274 A
• Filed: 07/30/1992
• Issued: 02/14/1995
• Est. Priority Date: 09/29/1989
• Status: Expired due to Term

• Current Assignee: Mitsubishi Rayon Company Limited (Mitsubishi Chemical Holdings Corporation)
• Original Assignee: Mitsubishi Rayon Company Limited (Mitsubishi Chemical Holdings Corporation)
• Inventors: Oda, Masaaki, Murata, Ryuji, Mishina, Yoshihiko, Toyoda, Nobuhiko, Uozu, Yoshihiro, Ishimaru, Teruta
• Primary Examiner(s): Lee, John D.
• Application Number:
  US07/908,603
• Time in Patent Office: 929 Days
• Field of Search: 385/115, 385/116, 385/120, 385/121, 385/123, 385/124, 359/652, 359/653, 359/654, 359/900
• US Class Current: 385/124
• CPC Class Codes: G02B 6/02038 with core or cladding having graded refractive index
• CPC Class Codes: G02B 6/06 the relative position of the fibres being the same at both ends, e.g. for transporting images
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A distributed refractive index type optical transmission plastic article has a circular cross section of a radius r₀ which is in a range of 0.4 to 0.6 mm. A refractive index distribution of the optical transmission article substantially approximates a predetermined ideal refractive index distribution curve at least in a range of 0.25r₀ to 0.70r₀ extending from a center axis toward a peripheral surface of the article. A refractive index n₀ at a central part of the article is in a range of 1.4 to 1.6. The article has a refractive index distribution constant of larger than 0.15 mm^-1 and smaller than 0.3 mm^-1, and a modulation transfer function of at least 55%. This optical transmission article is made from uncured liquid substances each having a viscosity of between 10³ and 10⁸ poises. N (N≧2) uncured liquid substances having refractive indexes n of n₁ >n₂ >n₃ . . . n_N when cured are arranged in such a way that the refractive indexes n are successively reduced from a central portion toward a peripheral portion, and concentrically laminated one upon the other to form an uncured strand fiber. The substances between adjacent layers of the fiber are mutually diffused. During the diffusion or thereafter, the uncured strand fiber is cured, thereby completing the production of the optical transmission article.

Claims

1. A distributed refractive index type optical transmission plastic article having a circular cross section of a radius r₀ and a refractive index distribution which substantially approximates a refractive index distribution curve defined by the following equation (1) at least in a range of 0.25r₀ to 0.70r₀ extending from a center axis toward a peripheral surface of the optical transmission article:

space="preserve" listing-type="equation">n(r)=n.sub.0 {1-(g.sup.2 /2)r.sup.2 } (1)

where n₀ is a refractive index at the center axis of the optical transmission article;

n(r) is a refractive index at a position of radius r away from the center axis of the optical transmission article;

g is a refractive index distribution constant (mm^-1) of the optical transmission article;

r is a distance (mm) from the center axis toward the peripheral surface of the optical transmission article; and

1.4≦

n₀ ≦

1.6

0.4≦

r₀ (mm)≦

0.6

0.15≦

g (mm^-1)<

0.3

wherein when a grid image of 4 line-pairs/mm is formed through the optical transmission article on a CCD line sensor and a maximum value i_max and a minimum value i_min of light quantities of the image are measured, a modulation transfer function (MTF) calculated according to the following equation (2);

space="preserve" listing-type="equation">MTF={(i.sub.max -i.sub.min)/(i.sub.max +i.sub.min)}×

100 (2)

is at least 55%.

2. A distributed refractive index type optical transmission plastic article as set forth in claim 1, wherein the refractive index distribution of the optical transmission article substantially approximates the refractive index distribution curve defined by the equation (1) at least in a range of 0.20r₀ to 0.75r₀ extending from the center axis toward the peripheral surface of the optical transmission article.

3. A method of manufacturing a distributed refractive index type optical transmission plastic article comprising the steps of preparing N (N≧

2) uncured liquid substances having a viscosity between 10³ and 10⁸ poises each and refractive indexes n of n₁ >

n₂ >

n₃ . . . n_N when cured, concentrically laminating the substances in such a way that the refractive indexes are successively reduced from the center toward the periphery of the laminated substances to form an uncured strand fiber, mutually diffusing the substances between adjacent layers in such a way that the refractive indexes are continuously distributed between the layers, and thereafter, curing the uncured strand fiber.

4. An optical transmission article array comprising an assembly of a plurality of distributed refractive index type plastic optical transmission articles arranged in a single line or a plurality of lines, said distributed refractive index type optical transmission plastic articles each having a circular cross section of a radius r₀ and a refractive index distribution which substantially approximates a refractive index distribution curve defined by the following equation (1) at least in a range of 0.25r₀ to 0.70r₀ extending from a center axis toward a peripheral surface of the optical transmission article:

space="preserve" listing-type="equation">n(r)=n.sub.0 {1-(g.sup.2 /2)r.sup.2 } (1)

where n₀ is a refractive index at the center axis of the optical transmission article;

n(r) is a refractive index at a position of radius r away from the center axis of the optical transmission article;

g is a refractive index distribution constant (mm^-1) of the optical transmission article;

r is a distance (mm) from the center axis toward the peripheral face of the optical transmission article; and

1.4≦

n₀ ≦

1.6

0.4≦

r₀ (mm)≦

0.6

0.15≦

g (mm^-1)<

0.3

wherein when a grid image of 4 line-pairs/mm is formed through the optical transmission article on a CCD line sensor and a maximum value i_max and a minimum value i_min of light quantities of the image are measured, a modulation transfer function (MTF) calculated according to the following equation (2);

space="preserve" listing-type="equation">MTF(%)={(i.sub.max -i.sub.min)/(i.sub.max +i.sub.min)}×

100(2)

is at least 55%.