Optical fiber connector

Details Optical fiber connector Optical fiber connector

2000-01-18

2001-08-28

Sanghavi, Hemang (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Structure surrounding optical fiber-to-fiber connection

C385S031000, C385S033000, C385S035000, C385S093000

Reexamination Certificate

active

06282347

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a connection structure of optical fibers, specifically to a connection device that connects optical fibers having different core diameters and made of different materials, such as a plastic fiber and a glass fiber.
2. Description of the Related Art
In connecting optical fibers, the most important technical task is to achieve a low transmission loss of light as far as possible.
As an example, in connecting two optical fibers having the core diameter of 60 &mgr;m and the specific refractive index difference of 0.7% with their end faces confronted with each other, it is generally conceived that an adequate transmission of light is difficult to be realized, unless, assuming that there is no crimp in the connecting area, the optical axis displacement is made within 0.2 &mgr;m and the connection loss is made within 0.2 dB.
FIG. 17
illustrates a first conventional optical fiber connector
50
that has implemented such a low transmission loss. As illustrated, the first conventional optical fiber connector
50
includes a first optical fiber
51
, a second optical fiber
52
, a cylindrical connecting part
53
that connects the first and second optical fibers
51
,
52
, and a lens
54
contained in this connecting part
53
, in which a light beam emitted from an end face
51
a
of the first optical fiber
51
falls on an end face of the second optical fiber
52
through the lens
54
. Thus, the two optical fibers are optically connected.
FIG. 18
illustrates a second conventional optical fiber connector
60
, which includes a first cylindrical connecting part
65
with a flange
65
a
and a second cylindrical connecting part
66
with a flange
66
a,
and further a first lens
63
contained in the first connecting part
65
and a second lens
64
contained in the second connecting part
66
.
First and second fixing parts
67
,
68
having holes on the centers thereof, are mounted on the ends of the opposite sides to the flanges
65
a
,
66
a
of the first and second connecting parts
65
,
66
. Opposing ends of the first optical fiber
61
and the second optical fiber
62
are guided in the center holes of the fixing parts
67
,
68
.
The first and second lenses
63
,
64
are fixed inside the first and second connecting parts
65
,
66
, respectively, so that the optical axes coincide with each other; and thereafter, the first and second connecting parts
65
,
66
are attached so that the flanges
65
a
,
66
a
are engaged with each other. The first and second fixing parts
67
,
68
are fastened to the first and second connecting parts
65
,
66
with screws, etc. The first and second optical fibers
61
,
62
are stripped of the sheathing parts from the front ends thereof, and the stripped ends each are engaged in the center holes of the fixing parts
67
,
68
.
Thus, the first and second optical fibers
61
,
62
are configured so as to form the focuses on the end faces thereof, for example, a light beam emitted from the end face of the first optical fiber
61
is emitted as a parallel beam from the first lens
63
, and the parallel beam falls on the second lens
64
, which transforms the beam into a convergent beam. Thus, the two optical fibers are optically connected.
FIG. 19
illustrates a third conventional optical fiber connector
70
, which includes a first optical fiber
71
, a second optical fiber
72
, two glass spheres
75
in contact with each other. The two glass spheres
75
are disposed between both front ends of the first and second optical fibers
71
,
72
. The connector
70
also includes, liquid substances
78
having a refractive index of approximately 1, which are inserted between the first optical fiber
71
and one glass sphere
75
and between the second optical fiber
72
and the other glass sphere
75
, and a molded resin
80
that sheathes an area including both the front ends of the first and second optical fibers
71
,
72
, the liquid substances
78
, and the two glass spheres
75
thus disposed.
A parallel beam emitted from the first optical fiber
71
falls on the one glass sphere
75
and converges at a point
76
where the two glass spheres come into contact. The convergent beam is transformed into a parallel beam through the other sphere
75
, which falls on the second optical fiber
72
. Thus, the two optical fibers are optically connected with a symmetrical optical path.
However, in such optical fiber connectors
50
,
60
,
70
, a high positioning accuracy in the connection of the two optical fibers is required in order to transmit a stable light beam through the optical fibers connected. Further, it is necessary to enhance the efficiency of optical connection through the optical elements such as the lenses, so that a lower transmission loss of light than that obtained by the optical fibers being directly connected can be achieved.
Furthermore, in the connection of the two optical fibers having different diameters, for example, in the connection of a plastic optical fiber (POF) and a fused quartz fiber (PCF) having different core diameters, a higher positioning accuracy is required than the connection of optical fibers having the same diameter, and a low transmission loss of light has been difficult to be realized.
SUMMARY OF THE INVENTION
The present invention has been made in view of these problems, and it is an object of the invention to provide an optical fiber connector that enhances the efficiency of optical connection and thereby achieves a low transmission loss of light in the connection of optical fibers with different diameters.
As a first means to solve at least one of the foregoing problems, the optical fiber connector of the invention includes a first optical fiber, a first lens that converges light emitted from the first optical fiber, a second lens that converges light emitted from the first lens, and a second optical fiber that receives convergent light from the second lens. In the optical fiber connector thus configured, provided that the core diameter of the first optical fiber is given by E
1
, the numerical aperture thereof by NA
1
, the core diameter of the second optical fiber by E
2
, the numerical aperture thereof by NA
2
, the focal length of the first lens by f
1
, the focal length of the second lens by f
2
, and (E
1
/E
2
)/(f
1
/f
2
)=x is introduced, the connection efficiency &eegr; of the first and the second optical fibers satisfies the following inequality:
(
E
1
/
E
2
)
2
<&eegr;≦NA
2
/sin(tan
−1
E
1
/
E
2
·NA
1
/
x
),
in
0
<x
≦1;
(
E
1
/
E
2
)
2
<&eegr;≦(1
/x
)
2
·NA
2
/sin(tan
−1
E
1
/
E
2
·
NA
1
/
x
),
in
1<
x<E
1
/
E
2
·NA
1
/sin(tan
−1
NA
2
)
or
(
E
1
/
E
2
)
2
<&eegr;≦(1/
x
)
2
,
in
E
1
/
E
2
·
NA
1
/sin(tan
−1
NA
2
)≦
x.
As a second means, provided that the effective aperture of the first lens is given by D
1
and the effective aperture of the second lens is given by D
2
, the connection efficiency &eegr;
1
by only the influence of the D
1
is expressed by the equation:
&eegr;
1
=D
1
/(
E
1
+2
×f
1
×tan(sin
−1
NA
1
))
2
,
and the connection efficiency &eegr;
2
by only the influence of the D
2
is expressed by the equation:
&eegr;
2
=(
D
1
/(
D
1
×
f
2
/
f
1
))
2
,
the optical fiber connector has a connection efficiency that is the foregoing &eegr; multiplied by &eegr;
1
and/or &eegr;
2
.
Further, as a third means, the optical fiber connector is comprised of the first lens made by forming the end face of the first optical fiber into a spherical face, and the second lens made by forming the end face of the second optical fiber into a spherical face.
Further, as a fourth means, the optical fiber connector is comprised of either one of the first and the second lenses made by forming the end face of the first or the second optical fiber into a spherical face.


REFERENCES:
patent: 5026206 (1991-06-01), Gache
patent: 5638471 (1997-06-01), Semo et al.
patent: 5699464 (1997-12-01), Marcuse et al.
patent: 594056

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