Optics: measuring and testing – By alignment in lateral direction
Reexamination Certificate
2000-07-07
2004-01-13
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
C356S400000
Reexamination Certificate
active
06678047
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical axis aligning method for aligning the respective optical axes of an optical component and an optical fiber with speed, accuracy, and ease, in connecting the component and the fiber, and an apparatus therefor.
2. Related Art
In constructing optical devices that include optical elements such as light emitting elements, light receiving elements, optical switches, optical modulators, etc., an optical fiber is connected to another optical fiber or an optical element (hereinafter an optical fiber and an optical element connected to an optical fiber will be collectively referred to as an optical component). In connecting the optical fiber and the optical component, their respective optical axes are aligned with each other, that is, optical axis alignment is carried out.
For example, in connecting the optical fiber with an LD module that includes a laser diode (hereinafter referred to as “LD”) element, for use as a light emitting element, and a lens for converging-light emitted from the LD element, it is necessary to align the point of emission on a connecting end face of the LD module and the center of an incidence end face of the optical fiber and align the direction of emission from the LD module and the longitudinal axis of the optical fiber. In other words, the LD module and the optical fiber must be relatively positioned with respect to the X-, Y-, and Z-axes, if a plane that is parallel to the connecting end face of the LD module and the direction perpendicular to the plane are defined as an XY-plane and the Z-axis direction, respectively. The optical axis alignment requires particularly high accuracy when the optical component and the optical fiber are to be connected fixedly, as in the case of joining an LD module and a ferruled optical fiber by YAG welding.
Conventionally, in the optical axis alignment of this type, the quantity of light emitted from an optical component such as an LD module and incident upon a connecting end face of an optical fiber is measured by means of an optical power meter that is connected to the other end of the fiber, as the optical component and the optical fiber are relatively three-dimensionally moved, to thereby find out a relative position (optimum relative position) for a maximum light quantity.
In order to find out the optimum relative position of the optical component and the optical fiber in an XYZ-space with high accuracy, according to the conventional method described above, light quantity measurement should be made at a large number of relative positions in the XYZ-space, so that the optical axis alignment requires much time and labor. In case the longitudinal axis (optical axis) of the optical fiber is deviated from the Z-axis, in particular, the optimum relative positions in the X- and Y-axis directions shift as the relative position in the Z-axis direction varies, so that the optimum relative position in the XYZ-space cannot be found out with ease. Thus, the optimum relative position in the XYZ-space must be obtained by repeatedly measuring the light quantity while changing the relative positions in the X- and Y-axis directions every time the relative position in the Z-axis direction is changed.
If the number of points of light quantity measurement (relative positioning points involving light quantity measurement) is not good enough, local optimum values alone may be determined in the case where the light quantity distribution of the light emitted from the optical component is not represented by a unimodal function. In this case, the position for the maximum light quantity cannot be found out.
Although the problems on the optical axis alignment between a light emitting element and an optical fiber have been described above, the optical axis alignment between an optical fiber and a light receiving element or between optical fibers involves the same problems.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an optical axis aligning method for an optical component and an apparatus therefor, capable of aligning the respective optical axes of the optical component and an optical fiber with speed, accuracy, and ease.
According to one aspect of the present invention, there is provided an optical axis aligning method for an optical component, in which the quantity of light emitted from an optical component or an optical fiber and incident upon the other is measured as the optical component and the optical fiber are positioned successively in a plurality of relative positions, to thereby obtain an optimum relative position for a maximum light quantity. This method comprises a step (a) of subjecting light quantity distribution on a given plane parallel to a connecting end face of the optical component or the optical fiber to quadric surface approximation in accordance with measured light quantities at a plurality of points on the given plane, thereby obtaining an optimum point on the given plane and a step (b) of subjecting light quantity distribution in the direction of the optical axis of the optical component or the optical fiber or in the direction of a given axis perpendicular to the given plane to quadratic function approximation in accordance with measured light quantities at a plurality of points in the direction of the optical axis or the given axis, thereby obtaining an optimum point in the direction of the optical axis or the given axis.
According to the conventional method, in optical axis alignment prior to the connection between an optical component and an optical fiber, a maximum light quantity point (optimum relative position) is searched for as the optical component and the optical fiber are successively relatively positioned at a large number of points in a three-dimensional space (XYZ-space). In other words, the optical component and the optical fiber are relatively positioned in the X-, Y-, and Z-axis directions at the same time.
In the optical axis aligning method of the present invention, the determination of the optimum point on the given plane (XY-plane) based on the quadric surface approximation of the light quantity distribution on the XY-plane and the determination of the optimum point in the direction of the optical axis or the given axis (Z-axis) based on the quadric function approximation of the light quantity distribution in the optical axis direction or the Z-axis direction are carried out independently of each other, so that, in accordance with the optimum point on the XY-plane and the optimum point in the optical axis direction or the Z-axis direction, the optimum relative position in the XYZ-space can be determined more speedily and easily than in the case of the conventional method. Further, optimum relative positions (optimum points) on the XY-plane and in the Z-axis direction can be accurately obtained by the quadric surface approximation and the quadric function approximation, so that the optimum relative position in the XYZ can be obtained accurately. The optimum relative position on the XY-plane and the optimum relative position in the Z-axis direction are represented by X-, Y-, and Z-coordinate values of a target position of the optical component or the optical fiber, for example. More generally, these positions are represented by two sets of X-, Y-, and Z-coordinate values that are indicative of the respective target relative positions of the optical component and the optical fiber.
Preferably, the step (a) includes a sub-step (a
11
) for subjecting light quantity distribution in the direction of a first axis, defining the given plane, to quadric function approximation in accordance with measured light quantities at a plurality of points in the first axis direction, a sub-step (a
12
) for subjecting light quantity distribution in the direction of a second axis, defining the given plane in conjunction with the first axis, to quadric function approximation in accordance with measured light quantities at a plurality of points in the second axis direction, and a sub-step (a
13
) for
Miyazaki Koichi
Taga Yoshiharu
Font Frank G.
Lauchman Layla
The Furukawa Electric Co. Ltd.
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