Method for aligning laser diode and optical fiber

What is claimed is:

1. An alignment method of a laser diode chip for emitting laser light with an optical fiber for receiving the laser light comprising the steps of:

facing the laser diode chip to a coupling end face of the optical fiber;

aligning a position in a Z direction where the optical fiber is aligned with the laser diode chip at a position in a Z-axis direction of an optical axis of the laser light; and

aligning a position in an XY direction where the optical fiber is aligned with the laser diode chip at a position of an X direction and a Y direction on an XY plane of an X-axis and a Y-axis orthogonal to the Z-axis, wherein

the step of aligning a position in the Z direction has the steps of:

acquiring light power data at a Z position where the coupling end face of the optical fiber is moved relatively with respect to the laser diode chip in the Z-axis direction to measure a light power received by the optical fiber and light power data is acquired at every predetermined reference distance of movement, in a state that the laser diode chip is faced to the coupling end face of the optical fiber; and

determining an alignment position in the Z direction where the alignment position for the optical fiber in the Z-axis direction is determined with respect to the laser diode chip based on the light power data at every predetermined reference distance of movement, and

wherein the reference distance of movement is an amount of integer multiples of (1/2).lambda., wherein a wavelength of laser light is set to .lambda..

2. The alignment method of the laser diode chip with the optical fiber according to claim 1, wherein the step of acquiring light power data at a Z position includes intermittently moving the coupling end face of the optical fiber at every reference movement in the Z-axis direction to acquire a received light power measured at an endpoint of each of the intermittent moves as light power data at every reference movement, wherein

the step of aligning a position in the Z direction includes setting a position at which the coupling end face of the optical fiber is moved where a maximum light power data has been acquired or a neighboring position thereof where a received light power is much greater as an alignment position for the optical fiber in the Z-axis direction, and

wherein the step of aligning a position in the Z direction includes:

confirming a start of downward trend of a value of light power data acquired at every reference movement intermittently moving the coupling end face of the optical fiber at every predetermined reference distance of movement from the confirmed position in an opposite direction in turn at time when confirming the downward trend and finding a start position of the downward trend of the value of light power data on a side of the opposite direction, setting a substantial mid-point between a position, where the downward trend of light power is confirmed on a going side and a position, where the downward trend of light power is confirmed on a returning side as a reference point; intermittently moving the coupling end face of the optical fiber by a reference movement having a value smaller than that of the reference movement in the Z-axis direction within a range of the position where the downward trend of light power is confirmed on the going side of the position where the downward trend of light power is confirmed on the returning side, centering the reference point; and setting a position where a measured light power taken at every intermittent move becomes the maximum or a neighboring position thereof where a received light power is much greater as an alignment position for the optical fiber in the X-axis direction.

3. The alignment method of the laser diode chip with the optical fiber according to claim 1, wherein the step of acquiring the light power data at Z position includes:

measuring a light power received by the optical fiber as the optical fiber is continuously moved in the Z-axis direction; and

acquiring relative data between the received light power measured and a movement of the coupling end face of the optical fiber as classified data at every predetermined reference distance of movement, wherein

the step of aligning a position in the Z direction includes:

determining a central value according to a predetermined method for deciding a central value at every classified data of a reference movement; and

microaligning and setting an alignment position for the optical fiber in the Z-axis direction within a section of a reference movement where a central value becomes the maximum; and

wherein microaligning includes determining a position at which the coupling end face of the optical fiber is moved in the Z-axis direction where a received light power becomes the maximum within a section of a reference movement where a central value becomes the maximum, and setting the determined position as an alignment position in the Z-axis direction.

4. The alignment method of the laser diode chip with the optical fiber according to claim 1, wherein an alignment method of a laser diode chip for emitting laser light with an optical fiber for receiving the laser light comprising the steps of:

facing the laser diode chip to a coupling end face of the optical fiber,

aligning a position in a Z direction where the coupling end face of the optical fiber is aligned with the laser diode chip at a position in a Z-axis direction of an optical axis of the laser light; and

aligning a position in a XY direction where the optical fiber is aligned with the laser diode chip at a position of an X direction and a Y direction on an XY plane of an X-azis and a Y-axis orthogonal to the Z-axis, wherein the step of aligning a position in the XY direction has the steps of:

acquiring light power data at an XY position where a light power received by the optical fiber is measured as the coupling end face of the optical fiber is moved relatively with respect to the laser diode chip following a whirl-shaped trace from a starting point to outward on the XY plane and light power data is acquired, in a state that the laser diode chip is faced to the coupling end face of the optical fiber, and setting an alignment position in the XY direction were an alignment position for the optical fiber in the XY direction is defined with respect to the laser diode chip based on the light power data acquired.

5. The alignment method of the laser diode chip with the optical fiber according to claim 4, wherein the whirl-shaped trace traveled by the coupling end face of the optical fiber is a rectangular whirl-shaped traveling trace where a movement in a long axis direction (Y-axis) is greater than a movement in a short axis direction (X-axis) in an elliptic beam pattern of the laser light emitted from the laser diode chip.

6. The alignment method of the laser diode chip with the optical fiber according to claim 4, wherein the step of setting an alignment position in the XY direction includes setting a moved position where a received light power becomes the maximum as an alignment position in the whirl-shaped traveling trace.

7. The alignment method of the laser diode chip with the optical fiber according to claim 5, wherein the step of acquiring light power data at the XY position includes acquiring a received light power measured at every step movement, according to intermittent step move where an amount of a step moved in a long axis direction is made greater than an amount of a step moved in a short axis direction, and the step of setting an alignment position in the XY direction includes setting a step moved position where a maximum received light power among received light power acquired at every step movement has been acquired or a neighboring position thereof where a received light power is much greater as an alignment position.

8. The alignment method of the laser diode chip with the optical fiber according to claim 7, including:

giving thresholds for received light power at a plurality of stages where a value of the thresholds becomes sequentially greater, alternatively performing operations of the step of acquiring light power data at an XY position and the step of setting an alignment position in the XY direction;

deciding a step moved position where a maximum received light power acquired in the whirl-shaped traveling trace exceeds a threshold at a first stage as a first alignment position;

then step moving the coupling end face of the optical fiber in a whirl shape as the first alignment position is used as a starting position and acquiring a received light power at every step movement;

deciding a step moved position where a maximum received light power among received light power acquired exceeds a threshold at a subsequent stage as a second alignment position;

then repeating operations of acquiring received light power and deciding an alignment position such that the coupling end face of the optical fiber is step moved in a whirl shape as the second alignment position is used as a starting position and a received light power is taken; and

setting a step moved position of the coupling end face of the optical fiber when a value of a maximum received light power acquired exceeds a threshold at a final stage or a neighboring position thereof where a received light power is much greater as an alignment position in the XY direction.

9. The alignment method of a laser diode chip with the optical fiber according to claim 4 further including the step of microaligning a position in the XY direction performed after the step of setting an alignment position in the XY direction, the step of microaligning a position in the XY direction comprising the following steps of: setting an alignment position setting by the operation of the step of aligning a position in the XY direction as a rough alignment position and using the rough alignment position as an origin on the XY plane to set a plurality of point positions around the origin; moving the coupling end face of the optical fiber to the origin and each of the set point positions to measure and acquire a light power received by the optical fiber at each position: approximating a light power distribution in the X-axis direction and a light power distribution in the Y-axis direction to quadratic functions, respectively, based on a value of a received light power acquired at each position; and setting microalignment positions in the X-axis direction and the Y-axis direction based on the respective quadratic functions in the X-axis direction and the Y-axis direction.

10. The alignment method of the laser diode chip with the optical fiber according to claim 9, wherein the point positions set around the origin are to be five-point positions including a point position on a positive side on the X-axis centering the origin, a point position on a negative side on the X-axis, a point position on the positive side on the Y-axis passing through the origin, a point position on a negative side on the Y-side and the origin.

11. The alignment method of the laser diode chip with the optical fiber according to claim 9, wherein point positions on positive and negative sides on the X-axis centering the original are given at positions having an equal distance from the origin, and point positions on positive and negative sides on the Y-axis centering the origin are given at positions having an equal distance from the origin, where distance from the original for a position give on the Y-axis is shorter than distance from the origin for a position given on the X-axis.

12. The alignment method of the laser diode chip with the optical fiber according to claim 9, including: setting a multinational approximate expression expressing a light power distribution on the XY plane by a function of X and Y position coordinates based on values of received light power measured at a plurality of point positions given on the XY plane; and giving an X position coordinate of a maximum received light power in the X-axis direction and a Y position coordinate of a maximum received light power in the Y-axis direction determined by using a quadratic approximate expression as values of X and Y in the multinomial approximate expression and determining a value of light power according to the multinational approximate expression, wherein when a difference between the value of light power determined by the multinomial approximate expression and a value of a maximum received light power in X and Y coordinate positions determined by the quadratic approximate expression on the XY plane reaches within a predetermined allowable range, the X an Y coordinate positions are determined as a microalignment position in the X-axis direction and the Y-axis direction.

13. The alignment method of the laser diode chip with the optical fiber according to claim 4 further including:

the step of microaligning a position in the XY direction performed after the step of aligning a position in the XY direction, the step of microaligning a position in the XY direction is an operation step according to the simplex method.

14. The alignment method of the laser diode chip with the optical fiber according to claim 9, wherein alignment of the coupling end face of the optical fiber has an order of performing aligning a position in the XY direction, then performing aligning a position in the Z-axis direction and further performing aligning a position in the XY direction, wherein at time when aligning a position in the XY direction performed after aligning a position in the Z-axis direction, a step movement in moving the coupling end face of the optical fiber in a whirl shape is set smaller than that at time when aligning a position in the XY direction performed before aligning a position in the Z-axis direction.

15. An alignment apparatus of the laser diode chip for emitting laser light with an optical fiber for receiving the laser light comprising:

a placement part for a laser diode chip for placing the laser diode chip;

a placement part for an optical fiber for placing the optical fiber;

a moving unit capable of relatively moving a side of the laser diode chip and a side of the optical fiber in three orthogonal axis directions of an X-axis, a Y-axis and a Z-axis, setting an optical axis direction of the laser light as the Z-axis direction;

an algorithm storage part for storing algorithm for an alignment method of the laser diode chip with the optical fiber; and

a control part for controlling move of the moving unit in accordance with the algorithm storage part stores algorithm for an alignment method of a laser diode chip with an optical fiber according to claim 1.

16. The laser diode comprising a laser diode chip and an optical fiber, both aligned by the alignment method according to claim 1.

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BACKGROUND OF THE INVENTION

In the field of the optical communications, for example, a laser diode module is used in which a laser diode (LD) chip for outputting light is coupled to an optical fiber for emitting light from the laser diode chip to form a module. In fabricating this type of the laser diode module, a method for accurately and easily aligning the laser diode chip with the optical fiber is desired.

SUMMARY OF THE INVENTION

The present invention is to provide an alignment method of a laser diode chip with an optical fiber, an alignment apparatus adapted to the alignment method and a laser diode module aligned by employing the alignment method.

An alignment method of a laser diode chip with an optical fiber of the invention comprising the steps of:

facing the laser diode chip with a coupling end face of the optical fiber;

aligning a position in the Z direction where the optical fiber is aligned with the laser diode chip at a position in the Z-axis direction of an optical axis of the laser light; and

aligning a position in the XY direction where the optical fiber is aligned with the laser diode chip at a position in the X direction and the Y direction on the XY plane of an X-axis and a Y-axis orthogonal to the Z-axis,

wherein the step of aligning a position in the Z direction has the following steps of:

acquiring light power data at a Z position where the coupling end face of the optical fiber is moved relatively with respect to the laser diode chip in the Z-axis direction to measure a light power received by the optical fiber and light power data is acquired at every predetermined reference movement, in a state that the laser diode chip is faced to the coupling end face of the optical fiber; and

setting an alignment position in the Z-axis direction where the alignment position for the optical fiber in the Z-axis direction is determined with respect to the laser diode chip based on the light power data at every predetermined reference movement.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described in conjunction with drawings in which:

FIG. 1 depicts a configurational diagram illustrating one embodiment of an alignment apparatus employing the alignment method of the laser diode chip with the optical fiber in the invention;

FIGS. 2A and 2B depict illustrations of the alignment operation of the laser diode chip with the optical fiber in the optical axis direction, employing the apparatus of the embodiment;

FIGS. 3A, 3B and 3C depict illustrations of an exemplary traveling trace of the optical fiber in the alignment (rough alignment) operation of the laser diode chip with the optical fiber on the XY plane, employing the apparatus of the embodiment;

FIG. 4 depicts an illustration on the microalignment operation of the laser diode chip with the optical fiber on the XY plane, employing the apparatus of the embodiment;

FIG. 5A depicts a diagram taken by a camera of the apparatus of the embodiment;

FIG. 5B depicts an enlarged side view of the diagram illustrating a state of the laser diode chip being faced to a lensed fiber;

FIG. 6 depicts a flow chart illustrating one example of the alignment (rough alignment) operation of the laser diode chip with the optical fiber on the XY plane, employing the apparatus of the embodiment;

FIG. 7 depicts a flow chart illustrating the alignment operation of the laser diode chip with the optical fiber following FIG. 6;

FIG. 8 depicts a flow chart illustrating one example of the microalignment operation of the laser diode chip with the optical fiber on the XY plane, employing the apparatus of the embodiment;

FIG. 9A depicts results of measuring intensities of laser light incident into the optical fiber from the laser diode chip, changing the positions of the optical fiber in the optical axis direction of the laser light;

FIG. 9B depicts a schematic analysis diagram of the graph shown in FIG. 9A;

FIG. 10 depicts an illustration showing one example of a simplex method adapted as the alignment method of the laser diode chip with the optical fiber of the invention;

FIG. 11 depicts a flow chart illustrating an exemplary alignment operation employing the simplex method; and

FIGS. 12A and 12B depict illustrations showing one example of a laser diode module where the laser diode chip and the optical fiber are aligned and assembled.

DETAILED DESCRIPTION

Laser diode modules are configured variously. FIGS. 12A and 12B depict one example of the laser diode modules. The laser diode module has a metal package, but the package is omitted in the drawing here. The laser diode module shown here is a type of a laser diode module comprised of a laser diode chip directly optically coupled to an optical fiber.

Additionally, FIG. 12A depicts a side configuration of the laser diode module and FIG. 12B depicts a plane configuration of the laser diode module. The structure shown in FIGS. 12A and 12B is housed inside a package, which is not shown here, to configure the laser diode module. As shown in FIGS. 12A and 12B, the laser diode module is provided with a base 1. A laser diode chip 3 is arranged and fixed to a device mounting platform 2 of the base 1 through a carrier 22. The laser diode chip 3 emits laser light in a waveband of 980 nm, for example.

The laser diode chip 3 is faced to the tip end side of a lensed fiber 8. The lensed fiber 8 is an optical fiber formed with a lens (a wedge-shaped lens in the example shown here) 5 on the tip end side thereof. The lens 5 of the lensed fiber 8 is extended forward from an end face 15 of a ferrule 4. The ferrule 4 is fixed to the base 1 through fixing parts 19. Furthermore, as the configuration of the fixing parts 19, alternative configurations are proposed variously other than the form shown in the drawings.

A carrier 40 is placed on the base 1 and a monitor photodiode 11 is fixed to the carrier 40. On the underside of the base 1, a Peltier module 20 for constantly maintaining temperatures of the laser diode chip 3 is disposed. The bottom of the Peltier module 20 is fixed to the top face of the bottom wall of the package, not shown.

In this type of the laser diode module, it is demanded that the laser diode chip 3 is highly accurately aligned with the lensed fiber 8 for optical coupling.

Traditionally, the alignment has been conducted as follows: for example, the lensed fiber 8 is moved in three axial directions, the optical axis direction of the laser light (Z-axis direction), the X-axis direction orthogonal to the Z-axis direction and almost parallel to the bottom surface of the laser diode chip 3 and the Y-axis direction orthogonal to both the X- and Z-axis directions; then, the lensed fiber 8 receives the laser light emitted from the laser diode chip 3 by the lens 5 on the tip end side of the lensed fiber 8 as the lensed fiber 8 is moved; an optical power meter measures light power emitted from the back end side of the lensed fiber 8; and a position where the light power becomes the maximum is determined as an alignment position.

However, the traditional optical axis alignment method needs to measure light power at many positions as the lensed fiber 8 is moved in the three axial directions, X, Y and Z. On this account, a lot of hours and efforts are required for alignment. Then, a method has been demanded that the alignment work of the laser diode chip 3 with an optical fiber such as the lensed fiber 8 can be conducted efficiently and the laser diode chip can be directly optically coupled to the optical fiber. However, such the method has not been established yet.

In one aspect, the invention is to provide an alignment method of a laser diode chip with an optical fiber capable of efficiently conducting the alignment work of the laser diode chip with the optical fiber and directly optically coupling the laser diode chip with the optical fiber and an alignment apparatus therefor.

Generally, when optical components are faced each other and light emitted from one of the optical components is incident into the other of the optical components, one of the optical components is moved in the optical axis direction (Z-axis direction) of light to approach the optical components each other. Then, the light power distribution of light incident into the other of the optical components from one of the optical components forms the light power distribution having a single peak where a certain focal length is the peak.

However, the circumstances are different in the case where the laser diode chip is faced to the coupling end face of the optical fiber and laser light emitted from the laser diode chip is directly incident into the optical fiber to optically couple the laser diode chip to the optical fiber. In the case of optically coupling the optical fiber, it is necessary to consider the reflection influence of light reflected from the coupling end face of the optical fiber. For example, even through an antireflection coating is applied to the coupling end face of the optical fiber, the reflection in the coupling end face of the optical fiber is not suppressed completely. When light is reflected from the coupling end face of the optical fiber, interference phenomena occur between the coupling end face of the optical fiber and the outgoing end face of the laser diode chip. The interference phenomena affect the optical coupling strength in the optical coupling of the laser diode chip to the optical fiber.

Then, this influence disturbs the light power distribution of the laser light. On this account, as shown in FIG. 9A, for example, the optical coupling strength of the laser diode chip to the optical fiber does not form the light power distribution having a single peak as described above.

FIG. 9A depicts results of measuring the light power of laser light directly incident into the optical fiber as the optical fiber is moved in the Z-axis direction on the basis of the reference position in the optical axis direction (Z-axis direction) of the laser light of the laser diode chip.

The lateral axis shown in FIG. 9A illustrates in which setting the reference position in the Z-axis direction as a reference (zero), it is set positive (+) when the optical fiber is moved close to the laser diode chip in the Z-axis direction, whereas it is set negative (-) when the optical fiber is moved away from the laser diode chip. Additionally, a wavelength of the laser light used in the measurement is a wavelength of 980 nm. The light power (intensity) of the laser light is measured at every time when the optical fiber is moved by 0.1 .mu.m.

As shown in FIG. 9A, the light power distribution of optical coupling of the laser diode chip to the optical fiber repeats variations in the light power in which optical power (the light power of the laser light) is increased or decreased with the move of the optical fiber in the Z-axis direction. On this account, the light power distribution is disturbed. It is considered because the light oscillated from the laser diode chip returns from the tip end face of the optical fiber.

Accordingly, in determining the optimum position of the optical fiber in the Z-axis direction, when the optical fiber is not properly moved in the Z-axis direction or measured data is not appropriately selected, it is likely that the optimum position of the optical fiber might not be found because of the hindrance of the light power variations or the coupling end face side of the optical fiber might be damaged because the laser diode chip comes too close to the optical fiber.

In short, the meaning that the optimum position of the optical fiber is not found because of the hindrance of the light power variations is as follows. That is, when the light power distribution of optical coupling of the laser diode chip to the optical fiber is a single peak type, a received light power to be measured is monitored as the optical fiber is moved in the Z-axis direction and the position where the received light power forms the first peak can be found easily as the optimum position (optimum optical coupling position). However, as shown in FIG. 9A, when the light power variations occur, many peak positions are appeared such that the received light power is gradually increased to form a peak and then the received light power is decreased in turn, but it is increased again to reach the next peak. On this account, as similar to the single peak type, when the first peak position where the received light power turns from increase to decrease is set as the optimum position, a problem arises that the position far from the actual optimum position is wrongly set as the optimum position. In order to avoid such the problem, it is also considered that the received light power is minutely measured over the entire length in the Z-axis direction, but the method takes too much time to be practical.

The inventor analyzed the light power variations to form a model as shown in FIG. 9B. Then, the inventor found that the light power distribution is varied at a cycle of a half of a wavelength of the laser light. This phenomenon in which the light power distribution is varied periodically has been first found by the inventor. In one aspect, the invention effectively utilizes the study result by the inventor in which the light power distribution is varied at a cycle of a half of a wavelength of the laser light.

FIG. 1 schematically depicts one embodiment of an alignment apparatus of the laser diode chip with the optical fiber in the invention in a state that a laser diode chip 3 and a lensed fiber 8 are placed.

As shown in FIG. 1, the alignment apparatus of the embodiment has a placement part 9 for the laser diode chip 3, an optical fiber moving stage 11 equipped with a ferrule gripping part (ferrule hand) 10, a camera 25, a camera moving unit 16, and a control unit 30. The control unit 30 has a stage control part 7, an algorithm storage part 6, and a manual operation part 31. The optical fiber moving stage 11 equipped with the ferrule gripping part (ferrule hand) 10 functions as a placement part for an optical fiber.

The placement part 9 is formed in which a package bottom plate 18 of a laser diode module is fixed and placed. On the package bottom plate 18, the laser diode chip 3 is fixed through a Peltier module (it is not shown in FIG. 1, see FIG. 12A) and a base 1.

The ferrule gripping part 10 is formed to grip a ferrule 4 inserted and fixed with the lensed fiber 8. The ferrule 4 is moved as it is gripped by the ferrule gripping part 10, whereby a lens 5 on the tip end side of the lensed fiber 8 inserted and fixed to the ferrule 4 is faced to a light emitting part of the laser diode chip 3 with a space. Additionally, an optical power meter 32 is connected to the back end side of the lensed fiber 8.

The camera 25 is disposed above the placement part 9. The camera 25 is mounted on the camera moving unit 16. An image taken by the camera 25 is added to the manual operation part 31 disposed inside the control unit 30. FIG. 5A depicts one example of the image taken by the camera 25. The control unit 30 is configured in which the manual operation part 31 operates the move and control of the camera moving unit 16.

The optical fiber moving stage 11 functions as a moving unit for moving the ferrule 4 gripped by the ferrule griping part 10. The optical fiber moving stage 11 is formed to allow the optical fiber faced to the laser diode chip 3 to be moved in directions of three orthogonal axes, the X-, Y- and Z-axes. The Z-axis direction is the optical axis direction of laser light emitted from the laser diode chip 3. In the apparatus shown in FIG. 1, a Z stage 14 performs the move in the Z-axis direction. An X stage 12 performs the move in the X-axis direction. A Y stage 13 performs the move in the Y-axis direction. Furthermore, the stage control part (control part) 7 disposed in the control unit 30 is configured to perform these moves.

The stage control part 7 has functions of moving and controlling the optical fiber moving stage 11 in accordance with the operation by the manual operation part 31 and of automatically controlling the move of the optical fiber moving stage 11 based on algorithms stored inside the algorithm storage part 6. Inside the algorithm storage part 6, the following algorithms for an alignment method of the laser diode chip with the optical fiber are stored.

Inside the algorithm storage part 6, an algorism for alignment in the Z-axis direction is stored as a first algorithm. This alignment method in the Z-axis direction determines the optimum position of the optical fiber in the Z-axis direction as follows.

First, as shown in FIGS. 12A and 12B, the laser diode chip 3 is faced to the coupling end face (the end face of the lens 5) of the lensed fiber 8. Then, the lensed fiber 8 takes in the laser light emitted from the laser diode chip 3 as it is moved in the optical axis direction (the Z-axis direction) of the laser light. At every time when the lensed fiber 8 is moved by a predetermined reference movement on the basis of the reference position in the Z-axis direction, the light power of the laser light incident into the lensed fiber 8 is measured and data of measured values of light power is acquired. Then, the position where the measured value of the light power becomes the maximum or a neighboring position thereof is determined as the optimum position of the optical fiber in the Z-axis direction.

The neighboring position is that centering the moved position of the reference movement where the measured value of light power becomes the maximum, for example, light power is measured as the optical fiber is inspected and moved at continuous or minute step intervals over the same section as the reference movement, for instance, and then an inspected and moved position where a light power greater than that measured at the moved position of the reference movement has been measured can be set as the neighboring position for determining the optimum position.

The reference movement is set to an amount of integral multiples of (.lambda./2), where a wavelength of the laser light is set .lambda.; the reference movement is set: (.lambda./2)=(980/2) nm.congruent.0.5 .mu.m in this embodiment.

Accordingly, the optimum position of the optical fiber can be found in the Z-axis direction with no influence of the disturbed light power distribution in the Z-axis direction.

Inside the algorithm storage part 6, an algorithm for rough alignment in the X- and Z-axis directions is stored as a second algorithm. This alignment method determines a rough alignment position for the optical fiber on the XY plane as follows.

First, as similar to that described above, the laser diode chip 3 is faced to the coupling end face of the lensed fiber 8. Then, as shown in FIG. 3A, starting at a predetermined reference position on the XY plane, the coupling end face side of the lensed fiber 8 is moved outside to form a rectangular whirl long in the Y-axis direction on the XY plane. More specifically, the coupling end face side of the lensed fiber 8 is moved relatively with respect to the laser diode chip 3 so that the trace drawn by the coupling end face of the lensed fiber 8 is formed into a rectangular whirl. Subsequently, the lensed fiber 8 takes in the laser light as it is moved.

At this time, the light power of the laser light incident into the lensed fiber 8 is measured. A position where the measured light power becomes the maximum is determined as a first rough alignment position in the whirl alignment of the laser diode chip with the optical fiber. After that, the whirl alignment is again performed, starting at the first rough alignment position. In this manner, the operation of the whirl alignment is performed one time or more, and the optimum position (final rough alignment position) of the optical fiber on the XY plane in the rough alignment is determined.

As described above, the image taken by the camera 25 is to be an image shown in FIG. 5A, for example. This image is an image in the XZ plane. Therefore, it is difficult to adjust positions in the Y-axis direction by the operation of the manual operation part 31. In addition to this, in the lensed fiber 8 for use in optically coupling a laser diode chip of a wavelength of 980 nm having an elliptic light emitting pattern, for example, the form of the lens 5 formed on the tip end side thereof is a wedged shape as shown in FIG. 5B for obtaining a high coupling efficiency. In the case of the wedged lens form, when a misalignment in the Y-axis direction occurs, a degree of dropping the optical coupling efficiency to the laser diode chip 3 is greater as compared with a misalignment in the X-axis direction.

Additionally, as is well known, the laser light emitted from the laser diode chip 3 of a waveband of 980 nm forms an elliptic shape long in the X-axis direction at a position extremely close to the end face (laser light outgoing face) of the laser diode chip 3. However, the beam pattern of the laser light forms an elliptic shape long in the Y-axis direction radii when it separates a little from the end face of the laser diode chip 3.

In consideration of such the phenomena, the coupling end face side of the lensed fiber 8 was moved in alignment so as to follow an approximately rectangular whirl-shaped trace long in the Y-axis direction on the XY plane in this embodiment. Accordingly, the rough alignment in the XY direction has been performed efficiently. As one example, a step width Sx in the X-axis direction shown in FIG. 3A is one-tenth of a step width Sy in the Y-axis direction. Furthermore, in FIG. 3A, a measured range of the light power incident into the lensed fiber 8 was formed to be approximately a rectangular shape, but the whirl shape may be a planform having a long axis in the Y-axis direction such as an approximately elliptic shape (FIG. 3B) and an approximately rhombic shape (FIG. 3C).

Moreover, in this embodiment, the rough alignment by the second algorithm first determines the optimum position (rough alignment position) of the optical fiber on the XY plane. Then, on the basis of the optimum position of the rough alignment, the laser diode chip and the optical fiber are microaligned on the XY plane to finally determine the optimum position of the optical fiber on the XY plane. This algorithm for the microalignment is stored inside the algorism storage part 6 as a third algorithm.

When the optimum position on the XY plane is determined by the third algorithm, first, the reference position on the XY plane in the rough alignment is to be the first reference position. Centering this reference position, the coupling end face of the lensed fiber 8 is moved to a plurality of set positions on the XY plane. Then, the light power of the laser light incident into the lensed fiber 8 at this time is measured at each of the positions. According to the measured results, the light power distribution on the XY plane is approximated to a quadric surface and an operation of detecting a maximum light power position is performed that a maximum light power position where the light power (received light power) becomes the maximum is determined.

Subsequently, the operation of detecting a maximum light power position is performed one time or more such that the operation of detecting a maximum light power position according to the quadric surface approximation is again performed on the basis of the maximum light power position. Then, the maximum light power position finally determined is defined as the optimum position of the optical fiber on the XY plane according to the microalignment.

There are various methods of the quadric surface approximation, but five set points in total are defined in this embodiment as shown in FIG. 4; one point at a predetermined reference position, two points sandwiching this reference position in the X-axis direction and two points sandwiching this reference position in the Y-axis direction. The coupling end face side of the lensed fiber 8 is moved to these set points and the operation of detecting a maximum light power position according to the quadric surface approximation is performed by applying the five-point alignment method.

The stage control part 7 performs an alignment operation in which the first to third algorithms are properly combined according to the specification of the first to third algorithms (specifications of assigning which algorithms to be used and of an operation order for each of the assigned algorithms). Accordingly, the optimum position of the optical fiber (the coupling end face of the optical fiber) in the X-, Y- and Z-axis directions is determined. The lensed fiber 8 is moved to the determined microalignment position to optically couple the lensed fiber 8 to the laser diode chip 3.

Next, the alignment method of the laser diode chip with the optical fiber (the lensed fiber 8 here) employing the alignment apparatus will be described.

First, as shown in FIG. 1, the laser diode chip 3 is fixed to the base 1 on the placement part 9. The ferrule 4 inserted and fixed with the lensed fiber 8 is gripped by the ferrule gripping part 10. At this time, the position of the laser diode chip 3 is preferably adjusted so as to match the optical axis of the laser light emitted from the laser diode chip 3 with the Z-axis on which the lensed fiber 8 is moved. In this state, the operation of the manual operation part 31 allows the stage control part 7 to perform control operations, whereby the move of the optical fiber moving stage 11 is controlled. Then, the laser diode chip 3 is faced to the coupling end face of the lensed fiber 8 to start alignment (step 101 shown in FIG. 6).

In step 101, the ferrule 4 gripped by the ferrule griping part 10 is moved to bring the end face of the ferrule 4 close to the vicinity of the end face of the laser diode chip 3. This operation is performed by operating the manual operation part 31 based on an image taken by the camera 25, for example.

Then, in step 102 shown in FIG. 6, rough alignment on the XY plane is started. This rough alignment is performed by the second algorism.

More specifically, starting at a predetermined reference position on the XY plane, the coupling end face side of the lensed fiber 8 is moved outside in a whirl shape long in the Y-axis direction on the XY plane, as shown in FIG. 3A. Then, the coupling end face (the end face of the lens 5) of the lensed fiber 8 receives the laser light emitted from the laser diode chip 3 as it is moved. Subsequently, the position where the detected value of the received light power becomes the maximum, the value is detected by the optical power meter 32 connected to the lensed fiber 8, is defined as the rough alignment position in the whirl alignment of the laser diode chip 3 to the lensed fiber 8 on the XY plane. After that, the whirl alignment is repeated one time or more up to 20 times such that the rough alignment position on the XY plane is used as a starting point to again perform the whirl alignment, if necessary.

Additionally, in the embodiment, in order to reduce the number of steps of rough alignment, the interval between measurement points in the long axis direction was set greater than that in the short axis direction, where the step width (an interval between measurement points) Sx in the X-axis direction, a short axis in the whirl alignment, is set to a set value within the range of 1 to 10 .mu.m and the step width Sy in the Y-axis direction as a long axis is set to a set value within the range of 10 to 100 .mu.m. Then, in step 103, the value of the detected light power at the rough alignment position reaches equal to or above a set value within the range of 0.1 to 1 mW that has been determined as a threshold of the light power and then proceed to step 104.

In step 104, only the threshold of the light