Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-03-30
2003-12-30
Patel, Tulsidas (Department: 2839)
Optical waveguides
With optical coupler
Input/output coupler
Reexamination Certificate
active
06671432
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plastic optical fiber with a lens portion having a function of controlling light rays, such as a light-condensing function, in which a concave recess such as a spherical recess is formed on an end face of the plastic optical fiber, and a refractive index adjusting material or filler (including air or the like) with a refractive index different from (typically larger than) that of the plastic optical fiber being filled in the concave recess. The present invention also relates to an optical fiber connector using the plastic optical fiber, a connecting structure or method using the plastic optical fiber, a light-emitting/receiving apparatus (this term means a light-emitting or light-receiving apparatus in this specification) in which a light-emitting/receiving device (this term means a light-emitting or light-receiving device in this specification) is combined with the plastic optical fiber with a lens portion, and the like.
2. Related Background Art
In recent years, in order to enhance the coupling efficiency between plastic optical fibers, or a plastic optical fiber and a light-emitting device/receiving device, there have been proposed some methods of forming a convex lens at the end face of the plastic optical fiber. For example, Japanese Patent Application Laid-Open No. 10(1998)-239538 discloses a method of forming a spherical contour on the end face of a plastic optical fiber by using a solvent, Japanese Patent Application Laid-Open No. 11(1999)326689 discloses a method of forming a spherical contour on the end face of a plastic optical fiber by immersing the end thereof in an organic solvent containing an optical fiber material and drying the end face after the optical fiber is lifted from the solvent, Japanese Patent Application Laid-Open No. 5(1993)-107427 discloses a method of forming a spherical contour on the end face of an optical fiber by immersing the end thereof in a photosensitive resin and hardening the end face after the optical fiber is lifted from the resin, Japanese Patent Application Laid-Open No. 8(1996)-75935 discloses a method of forming a lens shape on the end face of an optical fiber by pressing the end face thereof against a heated lens-forming mold, and Japanese Patent Publication No. 62(1988)-57001 discloses a method of forming a spherical surface on the end face of an optical fiber by heating and softening the end thereof, using its surface tension.
Further, there have been proposed, for fabricating a concave contour on the end face of a plastic optical fiber with a refractive index distribution, a method of molding the end face of an optical fiber by a heated metal mold, and a method of solving the end face of an optical fiber by a solvent (see Japanese Patent Application Laid-Open No. 11(1999)-242129).
However, end faces of those optical fibers all have convex contours, and hence, alignment between such an optical fiber and a light-emitting/receiving device is hard to achieve, compared to the case of an optical fiber with a flat end face. Further, when the end face of the optical fiber is caused to abut on an optical device, a high pressure is likely to be applied to a portion of the device, and therefore, there is a considerable possibility of damaging the device.
Moreover, the transmission efficiency in long-distance optical transmissions using optical fibers is greatly influenced by coupling losses at connecting portions between optical fibers and between an optical fiber and a light-emitting/receiving device. The coupling loss is due to deviation of the optical axis, light scattering on the end face of the optical fiber, and the like. A variety of connecting methods using light-condensing lenses have been conventionally proposed to reduce such coupling loss.
On the other hand, a large-diameter plastic optical fiber that can be readily fabricated at a relatively low cost has been recently developed, and is used in medium and short distance networks. Where those local networks are connected to a trunk-line network, there is a need of performing connection between transmission light from devices with different core diameters or numerical apertures, such as between large-diameter optical fiber and crystal or silica-contained optical fiber. The numerical aperture is determined by refractive indices of the medium around the optical fiber, its core and its cladding, while the core diameter is a physical size of the core of the optical fiber. Therefore, those terms have different categories. Problem occurs in the connection between optical fibers of which at least one of the numerical aperture and the core diameter is different.
As a method of obtaining a high coupling efficiency in such a connecting portion, there have been conventionally proposed structures as illustrated in
FIGS. 1 and 2
. In
FIG. 1
, there is illustrated a numerical-aperture converting structure using a light-condensing lens
403
such as a ball lens and a rod lens (see Japanese Patent Application Laid-Open Nos. 60(1985)-61707 and 5(1993)-34545). In
FIG. 2
, there is shown a numerical-aperture converting structure using a lensed optical fiber
414
whose end face is shaped into a spherical convex contour. Representative optical rays are indicated in
FIGS. 1 and 2
. Conversely, there has also been proposed a method in which a concave lens or the like is attached to the end face of an optical fiber with a smaller numerical aperture.
In the structure of
FIG. 1
having three elements or more, however, there is the problem of deviation and inclination between optical axes of optical fibers
402
and lens
403
. Particularly, alignment of a distance between end faces of the optical fibers
402
, and fixation of the lens
403
are difficult, and resistance of fixture thereof to external shocks is small. In
FIG. 2
, the possibility of deviation in the optical system is lowered since a light-condensing lens is integrated with the lensed optical fiber
414
and the number of optical devices (
402
and
414
) is hence reduced to two. However, it is difficult to cause the end face of the optical fiber
414
to abut on a spacer and fix the optical fiber
414
since its end face is spherical.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a plastic optical fiber with a lens portion having a function of controlling light rays, such as a light-condensing function, in which a concave recess such as a spherical recess is formed on an end face of the plastic optical fiber, and a refractive index adjusting material or filler with a refractive index different from (and typically larger than) that of the plastic optical fiber is filled in the concave recess, an optical fiber connector using the plastic optical fiber, a connecting structure or method using the plastic optical fiber, a light-emitting/receiving apparatus in which a light-emitting/receiving device is combined with the plastic optical fiber with a lens portion, and the like.
In this specification, the plastic optical fiber means an optical fiber whose core and cladding are made of a polymer, or an optical fiber whose core is made of a polymer. In such a plastic optical fiber, the cladding may be covered with a protective layer, or a polymer jacket. Further, the plastic optical fiber may be a step-index (SI) type wherein a refractive index along its radial direction is uniform throughout but exhibits an abrupt step at its core-cladding interface, a graded-index (GI) type wherein a refractive index varies in some continuous fashion as a function of radial distance, or the like.
According to one aspect of the present invention, there is provided a plastic optical fiber with a lens portion which includes a plastic optical fiber with a concave portion formed on its end face, and a lens portion having a function of controlling light rays. The lens portion is formed of a refractive index adjusting material filled in the concave portion and having a refractive index different from a refractive index of the plastic optical fi
Imada Aya
Sakata Hajima
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