Optical waveguides – Optical fiber waveguide with cladding – With graded index core or cladding
Reexamination Certificate
1999-10-26
2002-02-19
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
With graded index core or cladding
C385S122000, C385S127000
Reexamination Certificate
active
06349162
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a field distribution converting optical fiber, and a laser diode module using the field distribution converting optical fiber, which are used when connecting optical components having different field distributions to each other in a case where, for example, in an optical transmission and sensor field, an optical component having a circular cross section to an optical component having an elliptical cross section exists.
BACKGROUND ARTS
Optical fibers have been used for optical transmission, and the cores of optical fibers are covered with cladding. The cross sectional shape of the core of an optical fiber generally is circular (that is, the section where an optical fiber is cut off in a plane XY where it is assumed that the optical axis of the optical fiber is Z, and three axes orthogonal to each other are X, Y and Z). In addition, the light intensity distribution, on the plane XY, of light propagating in the core is also circular. On the other hand, as for a semiconductor laser and a planar optical waveguide, generally, the light intensity distribution on the plane XY is elliptical. Therefore, when connecting an optical component of a semiconductor laser and a planar optical waveguide, etc., to the above optical fiber, an optical connection loss occurs due to a difference between the field distribution (electric field distribution) at the connection end faces of these optical components and the field distribution of the optical fiber. Moreover, an optical connection loss resulting from such a difference between the field distributions is called a mode non-matching loss.
For example,
FIG. 13
shows a result of an investigation of an optical connection loss between an optical component having an elliptical field distribution and an optical component having a circular field distribution, changing the aspect ratio (ratio of the major axis to the minor axis) of an elliptical shape in the optical component having an elliptical field distribution. As has been made clear in this drawing, if an optical component having elliptical field distribution exists, the aspect ratio of which is 3 or more, to an optical component having circular field distribution, it can be understood that an optical connection loss of 2dB or more occurs. In addition, in
FIG. 13
, the spot diameter of either the X or Y direction of the above elliptical field distribution is made coincident with the spot diameter of the above circular field distribution.
Therefore, for example, the following optical fiber is disclosed in Laid-open patent application No. 33706 of 1988 filed and laid open in Japan. That is, the optical fiber has an elliptical core
2
such as that shown in
FIG. 14
, wherein one end side of a single mode optical fiber, in which the refractive index distribution of the core
2
is uniform, is heated to cause a dopant to be diffused, which is contained in the core
2
or cladding
3
, whereby the cross-sectional shape of the core
2
at one end side of the optical fiber is made roughly circular. Then, the core profile becomes an elliptical shape at the end side
11
of an optical fiber, and the core profile at the end side
12
(where the above heating is carried out) becomes a circular shape. In such an optical fiber, the field distribution of optical waves propagating in the optical fiber becomes elliptical at the end side
11
of the optical fiber, and becomes circular at the end side
12
of the optical fiber, wherein mutual conversion of an ellipse and a circle in the field distribution is performed, and such an optical fiber can be used as a field distribution converting optical fiber.
However, in a field distribution converting optical fiber formed by utilizing dopant diffusion like an optical fiber shown in
FIG. 14
, there were the following shortcomings and problems.
(1) In the optical fiber shown in
FIG. 14
, the normalizing frequency viewed in the greater diameter direction of an elliptical core before diffusion of a dopant is different from that view in the minor diameter direction, and the aspect ratio of the field distribution does not become greater than the aspect ratio of the core
2
. Therefore, the aspect ratio of the field distribution of the end part
11
of an optical fiber is smaller than the aspect ratio of the core
2
, for example, the aspect ratio of the field distribution is
2
at the most, wherein such an elliptical optical fiber will have a field distribution very similar to that of a circular optical fiber. Therefore, if such an optical fiber as shown in
FIG. 14
is used, mutual conversion is impossible between an ellipse and a circle as regards the field distribution.
(2) If the above dopant diffusion is utilized, the elliptical field distribution may be shaped to be circular in only the direction of expanding the field distribution. Therefore, there was such a problem by which a large elliptical profile could not be converted to a small circular profile.
(3) Since it takes a long time to obtain a dopant diffusion, productivity is not satisfactory. Moreover, unless the portion at which a part of an. optical fiber is partially heated is accurately taken out, it is impossible to utilize the optical fiber as a field distribution converting optical fiber. Therefore, after being partially heated, the optical fiber must be accurately cut off one by one, whereby working efficiency worsens, and it is difficult to mass produce the field distribution converting optical fibers.
It is therefore an object of the invention to provide a field distribution converting optical fiber which can solve such shortcomings and problems, and a laser diode module using the field distribution converting optical fiber.
That is, it is an object of the invention to provide a field distribution converting optical fiber, which can be mass produced, capable of universally carrying out mutual conversion between field distribution of an elliptical profile and field distribution of a circular profile in either direction of reduction, equal magnification (mutual conversion between a circle having a diameter which is the same as the major or minor axis of an ellipse, and an ellipse), or enlargement as, for example, in conversion between the field distribution of a laser diode and the field distribution of an optical fiber, and a laser diode module using the field distribution converting optical fiber.
DISCLOSURE OF THE INVENTION
A field distribution converting optical fiber according to the first aspect of the invention is an optical fiber having cladding covered around its core, which is composed so that the optical axis is assumed to be Z, either of the refractive index profiles of the above core in the X and Y directions of the orthogonal three axes X, Y and Z orthogonal to each other is made into a square-law distribution profile, a slope of the refractive index distribution in the corresponding X direction is made different from a slope of the refractive index distribution in the Y direction, and the optical fiber length is made almost coincident with the length of the common multiple between a one-fourth cycle length of a field distribution change cycle of a light beam propagating in the XZ plane in the Z direction and a one-fourth cycle length of a field distribution change cycle of a light beam propagating in the YZ plane in the Z direction.
A field distribution converting optical fiber according to the second aspect of the invention is an optical fiber having cladding covered around its core, which is composed so that the optical axis is assumed to be Z, either of the refractive index profiles of the above core in the X and Y directions of the orthogonal three axes X, Y and Z orthogonal to each other is made into a square-law distribution profile, a slope of the refractive index distribution in the corresponding X direction is made different from a slope of the refractive index distribution in the Y direction, either field distribution in the X direction or Y direction satisfies conditions for which light does not change while
Oishi Isamu
Shiraishi Kazuo
Knauss Scott
Lacasse & Associates
Sanghavi Hemang
The Furukawa Electric Co. Ltd.
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