Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2001-04-27
2003-02-11
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
C385S147000, C385S901000, C362S558000, C362S559000
Reexamination Certificate
active
06519401
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a light fiber (optical fiber) and, more particularly, to a so-called “side light extraction” type light fiber for emitting incident light from at least one end in a longitudinal direction of core through a cladding arranged around the core (i.e. side surface). The present invention also relates to a method of producing such a side light extraction type light fiber.
2. Prior Art
As is well known, a discharge tube such as fluorescent lamp emits visible light in a specific wavelength range, and is normally used for the purpose of illuminating. In case that the discharge tube is a neon tubing, it is also used in the form of a so-called neon sign for the purpose of displaying an advertisement, decoration or the like.
The discharge tube is capable of emitting light by applying a voltage. At this time, the discharge tube generally generates heat. Accordingly, it is necessary to use the discharge tube taking leak and heat generation into consideration. Therefore, it substantially becomes impossible to use the discharge tube, for example, for the purpose of illuminating in water or displaying.
Recently an intense has been shown towards a light emitting device wherein a light source is arranged at a long distance from a place where illumination or display is performed (hereinafter also referred to as an “illuminating place”, or a “displaying place”, in order to realize the above-described illumination or display. Such a light emitting device comprises a light fiber arranged at a distance from the light source, and is capable of performing desired illumination in the vicinity of the illuminating place, or displaying in the same manner. Generally, the light fiber comprises a so-called core capable of transferring incident light from one end of the fiber to the other end in a center portion, and a cladding having a refractive index smaller than that of the core in an peripheral portion.
Among light fibers, there is known a side light extraction type light fiber which makes it possible to extract light from the side portion. Describing such a light fiber with reference to
FIG. 4
, a light fiber
20
comprises a core
21
made, for example, of an acrylate resin and a cladding
22
made, for example, of Teflon™ and has flexibility, as disclosed in U.S. Pat. No. 4,422,719. This cladding
22
uniformly contains a light scattering material
25
made of metal oxide particles such as titanium dioxide particles in the amount of 2 to 10% by weight. Japanese Unexamined Patent Publication (Kokai) No. 10-148725 discloses a light fiber formed by co-extrusion of a molten fluoropolymer containing 50-4000 ppm of at least one light scattering additive and a crosslinkable core mixture. Furthermore, International Publication WO 98/08024 discloses a light fiber wherein a semitransparent cladding containing a pigment of a white color or the other color is provided around a core by melt casting.
In the light fibers constructed as described above, a portion of light can be uniformly extracted out through the cladding when incident light from one end or both ends of the fiber. To make it possible to uniformly extract out from the side portion, a plastic light fiber having a diameter of not less than 1 mm coated with a semitransparent resin is also disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-341125.
Furthermore, Japanese Unexamined Patent Publication (Kokai) No. 10-142428 discloses a light illuminating rod which has made it possible to extract light from the side portion in a specific direction. This light illuminating rod generally comprises a flexible rod member as a core in a center portion, and a transparent cladding layer having a refractive index smaller than that of the core, which is attached to a peripheral portion of this flexible rod member. A light diffusive reflective film made of a light transmitting polymer containing light diffusive reflective particles dispersed therein is partially present between the core and the cladding layer in a longitudinal direction. In case of such a light illuminating rod, when incident light from one end is transmitted to the other end, a portion of light is diffused and reflected by the light diffusive reflective film, thereby to extract from the peripheral portion of the rod member located opposite to the bond surface of the light diffusive reflective film and the core.
Problems to be Solved by the Invention
Among light fibers of the prior art the cladding disclosed in U.S. Pat. No. 4,422,719 or Japanese Unexamined Patent Publication (Kokai) No. 10-148725 contains a predetermined amount of a light scattering material or a light scattering additive, but its thickness is not controlled. In case of the cladding disclosed in WO 98/08024, neither amount of the pigment nor thickness are controlled.
Furthermore, since the light fiber disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-341125 has not a structure wherein the semitransparent resin is directly contacted with the core for transmitting light, light can not be efficiently extracted out from the side portion.
In contrast with these light fibers the light illuminating rod disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-142428 can efficiently extract out light from the side portion. However, an extraction direction of light is limited to only a specific direction as described above. Accordingly, this light illuminating rod can be extracted at a large viewing angle like a neon tubing.
Thus, an object of the present invention is to provide a side light extraction type light fiber capable of extracting light having high rightness at a large viewing angle, and a method of producing a light fiber, capable of simply producing the same.
Means for Solving the Problem
According to the present invention, as the means to solve the above problems, there is provided a light fiber comprising:
a core in the center portion, and
a cladding arranged around said core, characterized in that said cladding comprises:
a light diffusive layer comprising a light diffusive portion made of a light diffusive material containing, as a binder, a polymer having a refractive index smaller than that of said core, which is provided in closely contact with said core in a wall thickness of 1 to 300 &mgr;m in a circumferential direction, and
a protective layer made of a light transmitting resin material, which is formed to integrate with said light diffusive layer and covers said light diffusive layer. In this light fiber, the light diffusive material preferably contains a light scattering material in an amount of 0.01 to 10% by weight.
According to the present invention, there is also provided a method of producing a light fiber comprising a core in the center portion and a cladding arranged around said core, characterized in that said cladding is formed by co-extrusion of a light diffusive material containing, as a binder, a polymer having a refractive index smaller than that of said core and a light transmitting resin material so that the resulting cladding comprises:
a light diffusive layer comprising a light diffusive portion made of said light diffusive material containing, which is provided in closely contact with said core in a wall thickness of 1 to 300 &mgr;m in a circumferential direction, and
a protective layer made of said light transmitting resin material which is integrated with said light diffusive layer and covers said light diffusive layer. In this method, it is preferred that a light scattering material is contained in an amount of 0.01 to 10% by weight in the light diffusive material.
Mode for Carrying Out the Invention
The present invention will be described in accordance with its typical embodiments. In the drawings used as a reference for the description, identical or corresponding portions are identified with the same reference numerals.
In the perspective view of
FIG. 1
, a light fiber
10
as one embodiment of the present invention is shown. This light fiber basically
Imamura Kengo
Irie Shin-ichi
Matsumoto Kenji
Udagawa Atsushi
3M Innovative Properties Company
Buckingham Stephen W.
Sanghavi Hemang
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