JP2004170585A - Device for adjusting optical axis, and method for adjusting optical axis between optical element connection interfaces - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for accurately and speedily adjusting an optical axis for adjusting an angular shift especially between the connection interfaces by active alignment at the time of optical coupling between optical elements, and thereby realizing simplification of the configuration and decrease of a coupling loss. <P>SOLUTION: When coupling a coated optical fiber (11) to a waveguide type optical element (12), a position of a connection interface (12A) is firstly determined by the active alignment as an aligned position when a maximum optical output (I<SB>0</SB>) can be obtained from the wavguide type optical element (12). Next, the connection interface (12A) of the waveguide type optical element (12) is shifted in parallel in the direction of the axis X<SB>0</SB>from the aligned position by +Δx, and an optical output (I<SB>1</SB>) then is defined as the 1st optical power. Further, the connection interface (12A) of the waveguide type optical element (12) is shifted in parallel in the direction of the axis X<SB>0</SB>from the aligned position by -Δx, and an optical output (I<SB>2</SB>) then is defined as the 2nd optical power. An angular shift amount β about the axis Y<SB>0</SB>is obtained based on the ratio of the 1st optical power (I<SB>1</SB>) to the 2nd optical power (I<SB>2</SB>), and then the connection interface (12A) of the waveguide type optical element (12) is turned about the axis Y<SB>0</SB>by the angular shift mount β. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to optical technology including, for example, optical communication or optical measurement, and optical axis adjustment for performing precise alignment (alignment) when an optical element (also referred to as an optical component or an optical device) and an optical module are mutually coupled. The present invention relates to an apparatus and an alignment method thereof. In particular, the present invention relates to a method for adjusting an angle shift between connection surfaces of optical elements to be coupled.
[0002]
[Prior art]
In optical communication, a light source including a semiconductor laser or a light emitting diode, or a combination thereof with an optical modulator functions as a transmitter, an optical fiber functions as a transmission line, and a light receiving element including a photodiode functions as a receiver. .
In addition to these optical elements, various types of optical elements such as optical amplifiers, optical splitters, optical couplers, and optical switches are used. The various optical elements are coupled together and modularized. Further, the optical modules are connected to each other by an optical fiber to form an optical communication network.
[0003]
In optical communication, light loss (propagation loss) during propagation must be suppressed as much as possible. In the coupling between the optical elements, for example, a minute gap between the connection surfaces, a deviation of the optical axis (axis deviation), and a relative inclination (angle deviation) increase the propagation loss. These losses occurring at the coupling portion between the optical elements are called coupling losses.
The angular deviation between the connecting surfaces also causes a so-called one-sided contact of the connecting surfaces. At that time, stress concentrates on a contact portion between the connection surfaces, and deterioration such as breakage or cracking of the optical element may occur. In addition, for example, since the thickness of the adhesive layer between the connection surfaces is non-uniform, a large distortion occurs in the temperature distribution in the optical element, and the temperature characteristics of the optical element may be deteriorated.
To reduce the coupling loss and prevent the optical element from deteriorating, it is necessary to precisely align the connection surface.
[0004]
There are two types of alignment methods, active alignment and passive alignment.
Active alignment refers to a method in which light is actually input to a pair of optical elements to be coupled and the position of the connection surface is adjusted while monitoring the optical output by the pair of optical elements. In active alignment, an optical element pair is fixed at a position where a maximum light output is obtained.
The passive alignment is an alignment that does not use a light output unlike the active alignment. The passive alignment includes, for example, a method of adjusting the position of the connection surface by monitoring the mechanical fit of the connection portion or the displacement of a predetermined mark provided on the connection portion.
Active alignment is advantageous in its high accuracy. On the other hand, passive alignment is advantageous in terms of mass productivity due to a reduction in the number of steps and a reduction in adjustment time.
[0005]
As a conventional alignment incorporating the advantages of both active alignment and passive alignment, for example, the following method is known (see Patent Document 1).
In this method, coarse positioning of a connection surface is first performed by passive alignment, and then highly accurate axis deviation adjustment (also simply referred to as alignment) is performed by active alignment. Thereby, the deviation of the connection surface from the target position, particularly the angular deviation between the connection surfaces, is sufficiently reduced before the active alignment, so that the adjustment time in the active alignment is reduced.
[0006]
FIG. 5 is a schematic diagram for explaining a conventional alignment in which a single-core optical fiber 11 and a waveguide-type optical element 12 are coupled as an example.
The coupling portion of the optical fiber 11 is covered with, for example, a substantially rectangular parallelepiped ferrule 13 and is fixed straight on a fine movement stage (not shown). On the other hand, the waveguide type optical element 12 is fixed on a fixed stage (not shown). At this time, the optical axes of the optical fiber 11 and the waveguide type optical element 12 are horizontal and substantially coincide with each other.
The connection surface 11A of the optical fiber 11 and the connection surface 13A of the ferrule 13 are formed on a common plane. Further, in the example of FIG. 5, the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 are perpendicular to the optical axis of each optical element. Alternatively, each connection surface may be inclined by a common angle with respect to each optical axis.
[0007]
The connection surface 11A of the optical fiber 11 is slightly displaced by the fine movement stage. Here, it is assumed that an XYZ orthogonal coordinate system having an origin at an intersection with the optical axis is provided on the connection surface 11A. In the coordinate system, the Z axis indicates an optical axis direction, the X axis indicates a direction perpendicular and horizontal to the optical axis, and the Y axis indicates a vertical direction.
The minute displacement of the connection surface 11A is caused by three degrees of freedom for translation in each coordinate axis direction of the XYZ coordinate system and two degrees of freedom for rotation around the X axis and the Y axis (see arrows α and β in FIG. 5). ), Including a total of 5 degrees of freedom. Unlike the example of FIG. 5, in the coupling between the connection surfaces inclined with respect to the optical axis or in the coupling of a multi-core optical fiber (optical fiber array), one degree of freedom for rotation around the Z axis is reduced to the above five degrees of freedom. Add more.
[0008]
Utilizing the above five degrees of freedom, the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 are positioned with coarse accuracy through the following image recognition. In particular, the distance between the two connecting surfaces is adjusted to be sufficiently small by utilizing the degree of freedom of translation in the Z-axis direction. Further, the degree of parallelism between the two connection surfaces is adjusted as follows by using the degrees of freedom around the X axis and the Y axis.
As shown in FIG. 5, the vicinity of the joint between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide-type optical element 12 is determined by the first camera 21 from the direction MX parallel to the X axis. From the direction MY parallel to the axis, the second camera 22 observes each.
FIG. 6 is a schematic diagram showing the vicinity of the joint between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide-type optical element 12 observed by each of the first camera 21 and the second camera 22. . FIG. 6A is an image of the second camera 22, that is, a plan view of a combined portion. FIG. 6B is an image of the first camera 21, that is, a side view of the combined portion.
[0009]
As shown in FIG. 6A, when it is recognized from the image of the second camera 22 that the connection surface 13A of the ferrule 13 is inclined by the angle β with respect to the connection surface 12A of the waveguide type optical element 12, The optical axis C1 of the optical fiber 11 is inclined by substantially the same angle β from the optical axis C2 of the waveguide type optical element 12. Therefore, the connection surface 13A of the ferrule 13 is rotated around the Y axis using the degree of freedom of rotation of the fine movement stage around the Y axis. Thereby, on the image of the second camera 22, the position is adjusted to a position parallel to the connection surface 12A of the waveguide type optical element 12.
As shown in FIG. 6B, when it is recognized from the image of the first camera 21 that the connection surface 13A of the ferrule 13 is inclined by the angle α with respect to the connection surface 12A of the waveguide-type optical element 12, The optical axis C1 of the optical fiber 11 is inclined by substantially the same angle α from the optical axis C2 of the waveguide type optical element 12. Therefore, the connection surface 13A of the ferrule 13 is rotated around the X axis by utilizing the degree of freedom of rotation of the fine movement stage around the X axis. Thereby, on the image of the first camera 21, the position is adjusted to a position parallel to the connection surface 12A of the waveguide type optical element 12.
The angle adjustment around each of these X axis and Y axis is alternately repeated. Thereby, the angle shift between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 is reduced.
[0010]
Next, using the two translational degrees of freedom on the XY plane, highly accurate alignment between the optical fiber 11 and the waveguide-type optical element 12 is performed as follows.
First, light enters the optical fiber 11 and exits from the connection surface 11A. The emitted light enters the waveguide type optical element 12 from the connection surface 12A, and is emitted from another output end (not shown). The intensity of the emitted light is measured by, for example, an optical power meter (not shown).
This measurement is repeated while translating the connection surface 11A of the optical fiber 11 on the XY plane. Thereby, the position on the XY plane of the connection surface 11A when the measured value of the optical power meter becomes substantially the maximum is determined. The relative position of the optical fiber 11 with respect to the waveguide type optical element 12 at that time is referred to as the alignment position of the optical fiber 11. When the optical fiber 11 is in the centered position, the loss due to the misalignment is substantially minimal.
[0011]
[Patent Document 1]
JP-A-10-197751
[0012]
[Problems to be solved by the invention]
In the conventional alignment as described above, the adjustment of the angle deviation between the connection surfaces is performed by passive alignment using image recognition. Therefore, to further improve the accuracy of the angle shift adjustment, it is necessary to further improve the accuracy of image recognition, the accuracy of molding the optical elements, and the accuracy of their positioning. However, they were generally difficult.
In the above alignment, in particular, for the optical element to be coupled such as the optical fiber 11 and the waveguide type optical element 12 and the coupling member such as the ferrule 13, the outer shapes thereof are strictly controlled and the predetermined shape is obtained. Deviations, such as distortion and cracks, must be prevented. Further, for example, in the connection of the optical fiber 11 in the ferrule 13 or the connection of the optical fiber in the optical fiber array, the respective positioning must be realized with high precision. It has been difficult to further improve the reliability of the management of those shapes.
[0013]
In the alignment based on the image recognition described above, when the optical element to be coupled includes, for example, a lens and the connection surface has a shape different from a flat surface such as a curved surface, it is generally difficult to adjust the angle deviation between the connection surfaces with high accuracy. .
Moreover, the use of image recognition required a complex arrangement of many components, such as cameras, lighting, and computers for image recognition processing, and their parallel control. Therefore, it has been difficult to simplify the optical axis adjustment device and the adjustment process using the same. As a result, for example, when a plurality of optical elements are connected to each other to form a module, it has been difficult to further reduce the manufacturing cost of the optical module.
[0014]
SUMMARY OF THE INVENTION The present invention provides an optical device that performs high-precision and quick adjustment of an angle shift between connection surfaces, particularly with active alignment, at the time of coupling between optical elements, thereby simultaneously simplifying the configuration and further reducing the coupling loss. An object of the present invention is to provide an axis adjusting device and an optical axis adjusting method thereof.
[0015]
[Means for Solving the Problems]
The optical axis adjusting device according to the present invention includes:
(A) a light source unit for outputting a substantially constant optical power;
(B) a first stage for fixing the first optical element and transmitting light emitted from the light source section from the input end of the first optical element to the connection surface;
(C) a second stage for fixing the second optical element and transmitting light transmitted from the connection surface of the first optical element to the output end from the connection surface of the second optical element;
(D) a photodetector for detecting transmitted light from the output end of the second optical element and measuring the optical power;
(E) a stage driver for finely moving the first stage or the second stage by a predetermined amount; and
(F) (a) With respect to one of the first optical element and the second optical element (hereinafter, referred to as an optical element to be adjusted), substantially with respect to a substantially symmetric plane including an optical axis of a connection surface thereof. Two directions (hereinafter, referred to as a first direction and a second direction) that are symmetric and substantially parallel to the connection surface are selected, and (b) the optical element to be adjusted is moved from the centering position to the first direction. (C) measuring the optical power from the output end of the second optical element as a first optical power and a second optical power, respectively, when the optical element is shifted by a certain distance to each of the second direction; Is rotated around a line of intersection with the plane of symmetry (hereinafter, referred to as the axis of symmetry) by a predetermined rotation angle in a direction to make the first optical power and the second optical power substantially equal, Angle deviation adjustment unit for:
Having.
[0016]
The centering position of the optical element refers to a position at which the coupling loss due to the axial deviation is substantially minimized. Specifically, each optical axis is substantially aligned in the gap between the connection surfaces of the optical elements. (That is, within the range of the measurement error).
The alignment position between the first optical element and the second optical element is preferably determined by the following active alignment.
Light is input from the light source unit to the input end of the first optical element, and while moving either the first optical element or the second optical element in parallel with its connection surface, the output end of the second optical element The optical output (ie, the optical power of the transmitted light) is measured. Thereby, the respective positions of the first optical element and the second optical element when the substantially maximum light output is obtained are determined as the respective centering positions.
[0017]
In general optical element coupling, the connection surfaces of the respective optical elements each have a substantially symmetric plane including the optical axis.
The light emitted from the connection surface of the first optical element has a substantially symmetric intensity distribution with respect to a substantially symmetric plane including the optical axis of the connection surface. On the other hand, the incident light on the connection surface of the second optical element substantially matches the optical axis with the connection surface, and is substantially symmetric with respect to a substantially symmetric plane including the optical axis of the connection surface. When showing an intensity distribution, it is most easily transmitted to the connection surface. Accordingly, when the connection surface of the first optical element and the connection surface of the second optical element substantially align their respective optical axes and planes of symmetry, and thereby align in terms of symmetry, the space between them Coupling loss is suppressed.
[0018]
For example, when the connection surface of the first optical element and the connection surface of the second optical element are both substantially planar and substantially symmetric with respect to the respective optical axes, those optical axes are connected to each other. If the gaps between them substantially coincide and their connecting surfaces are substantially parallel, their connecting surfaces are substantially symmetric with respect to their common optical axis. On the other hand, in the arrangement, since both the axis shift and the angle shift are substantially minimized, the coupling loss due to them is substantially minimized.
[0019]
Matching for symmetry between connection planes reduces coupling loss as described above.
Such matching further enhances, for example, the respective uniformity of the stress distribution between the connecting surfaces and the thickness of the adhesive layer. Therefore, deterioration such as distortion or cracking of the connection surface due to stress concentration or temperature gradient is suppressed.
[0020]
In the above-described optical axis adjusting device, the symmetry matching between the connection surface of the first optical element and the connection surface of the second optical element is realized by the angle shift adjustment unit as follows.
For the connection surface of the optical element to be adjusted, the displacement from the centering position at the time of measuring the first optical power and the displacement at the time of measuring the second optical power are relative to the plane of symmetry at the centering position. Substantially symmetric. Therefore, when the symmetry plane of the connection surface of another optical element is substantially inclined with respect to the symmetry plane, a substantial difference occurs between the first optical power and the second optical power. In particular, the difference corresponds to the inclination between the planes of symmetry.
The angle shift adjusting unit detects a substantial difference between the first optical power and the second optical power, and rotates the connection surface of the optical element to be adjusted around the above-mentioned axis of symmetry so as to reduce the difference. Thereby, the inclination between the above-mentioned symmetry planes is reduced. In this way, the angular displacement between the connecting surfaces around its axis of symmetry is adjusted.
[0021]
Here, for a certain angle shift, the ratio of the substantial difference between the first optical power and the second optical power to the first optical power (that is, the ratio of the second optical power to the first optical power) Is larger than the value of the coupling loss itself due to the angle shift. Furthermore, the above-mentioned fixed distance, that is, the magnitude of displacement from the centering position of the connection surface of the adjustment target optical element can measure the substantial difference between the first optical power and the second optical power with high accuracy. Can be optimized as follows. As a result, the angle deviation adjustment by the above-described optical axis adjustment device has higher sensitivity than the active alignment by the conventional device.
In the above optical axis adjusting device, the first direction and the second direction are particularly preferably opposite to each other. At that time, for a certain angle shift, the substantial difference between the first optical power and the second optical power is maximum. Therefore, the sensitivity to the angle shift is particularly high.
[0022]
In the above-described optical axis adjustment device, the above-described angle shift adjustment may be repeated while the angle shift adjuster adjusts the rotation angle about the symmetry axis with respect to the connection surface of the optical element to be adjusted. For example, the rotation angle may be increased or decreased in accordance with an increase or decrease in a substantial difference between the first optical power and the second optical power. Thereby, the position of the connection surface when the first optical power and the second optical power are substantially equal is quickly determined.
Further, preferably, the distance between the connection surface of the first optical element and the connection surface of the second optical element is L, and the above-mentioned constant distance (that is, the displacement of the connection surface of the adjustment-target optical element from the centering position). Magnitude) is Δx, and the first optical power is I ₁ , The second optical power is I ₂ In this case, the angle shift adjusting unit sets the angle shift amount around the symmetry axis between the connection surfaces of the first optical element and the second optical element to L (I ₁ / I ₂ -1) / (4Δx), and the angle shift amount is determined as the rotation angle. The approximation of the angle shift amount is sufficiently high by adjusting the distance L between the connection surfaces and the magnitude Δx of the displacement of the optical element to be adjusted. Therefore, the angle shift adjustment can be performed quickly.
[0023]
When the connection surface of the optical element has a plurality of the above-mentioned symmetry planes, the above-described optical axis adjustment device may perform the above-described angle shift adjustment on each of the symmetry planes. For example, in the coupling of an optical fiber having an elliptical core, the above-described angle shift adjustment may be performed on a symmetric plane including the major axis and the minor axis of the cross section of the elliptical core. In addition, in the coupling of an optical waveguide having a rectangular cross section, the above-described angle shift adjustment is performed with respect to a symmetric plane which is parallel to each of the long side and the short side of the cross section and passes through the center of the cross section. May be performed.
As in these examples, when the above-described angle shift adjustment is performed on a plurality of symmetry planes, each angle shift adjustment may be alternately repeated. Thereby, an error due to the accuracy of each angle shift adjustment and an error due to the mutual influence of the angle shift adjustment for different symmetry planes (for example, the angle around the other symmetry axis due to the reduction of the angle shift around the other symmetry axis) Increase in displacement) can be reduced. As a result, the stability of the angle shift adjustment is improved.
[0024]
The above-mentioned optical axis adjustment device may further repeat the above-mentioned alignment alternately with the above-mentioned angle shift adjustment. When an angle shift is included between the connection surfaces, the above-described alignment position generally includes an error. Further, when the connection surface of the optical element to be adjusted is rotated by adjusting the angle shift, the axis shift can generally increase due to a positioning error of the rotation axis. Therefore, the axis shift and the angle shift can be further reduced by alternately repeating the alignment and the angle shift adjustment.
[0025]
In the coupling between a core optical fiber or a waveguide type optical element having a circular cross section, particularly when the connection surface is rotationally symmetric around the optical axis, the angle shift adjusting unit is connected to the connection surface of the adjustment target optical device. Three or more parallel directions may be selected. A pair consisting of any two of these directions can be regarded as a pair of the first direction and the second direction. Therefore, for each of these various pairs, the above-mentioned symmetry axis and the amount of angular deviation around it are obtained in the same manner as described above, and from the combination of these symmetry axes and the amount of angular deviation, A rotation angle about a predetermined axis may be determined.
[0026]
In a coupling between an optical fiber having an elliptical core, an optical fiber array, or an optical element having a connection surface inclined with respect to the optical axis, the connection surface is not rotationally symmetric about the optical axis. At that time, the angle shift adjusting unit may rotate the connection surface of the optical element to be adjusted by a predetermined rotation angle around the optical axis in addition to the above-mentioned symmetric axis. Thereby, the coupling loss due to the rotational deviation around the optical axis can be reduced in the same manner as the coupling loss due to the angular deviation described above.
[0027]
The method of adjusting the optical axis between the optical element connection surfaces according to the present invention,
(A) A substantially constant optical power is output by the light source unit, the emitted light is transmitted from the input end of the first optical element fixed to the first stage to the connection surface, and the transmitted light is further transmitted. Transmitting light from the connection surface of the second optical element fixed to the second stage to the output end, and measuring the optical power of the transmitted light;
(B) repeating the step of measuring the optical power each time either the first optical element or the second optical element is moved substantially parallel to its connection surface, and measuring the resulting optical power Determining the positions of the first optical element and the second optical element when measuring the substantially largest value among the values as the respective alignment positions;
(C) One of the first optical element and the second optical element (hereinafter, referred to as an adjustment target optical element) is substantially symmetric with respect to a substantially symmetric plane including the optical axis of the connection surface, and Selecting two directions substantially parallel to the connection surface (hereinafter, referred to as a first direction and a second direction);
(D) shifting the optical element to be adjusted from the centering position in the first direction by a certain distance, and measuring the optical power at that time as the first optical power;
(E) shifting the optical element to be adjusted from the centering position in the second direction by a certain distance, and measuring the optical power at that time as the second optical power;
(F) The connection surface of the optical element to be adjusted is predetermined around a line of intersection with the symmetry plane (hereinafter referred to as a symmetry axis) in a direction in which the first optical power and the second optical power are substantially equal. Rotating by the rotation angle of;
Having.
[0028]
The light emitted from the connection surface of the first optical element has a substantially symmetric intensity distribution with respect to a substantially symmetric plane including the optical axis of the connection surface. On the other hand, the incident light on the connection surface of the second optical element substantially matches the optical axis with the connection surface, and is substantially symmetric with respect to a substantially symmetric plane including the optical axis of the connection surface. When showing an intensity distribution, it is most easily transmitted to the connection surface. Accordingly, when the connection surface of the first optical element and the connection surface of the second optical element substantially align their respective optical axes and planes of symmetry, and thereby align in terms of symmetry, the space between them Coupling loss is suppressed.
The symmetry matching between the connecting surfaces further enhances, for example, the respective uniformity of the stress distribution between the connecting surfaces and the thickness of the adhesive layer. Therefore, deterioration such as distortion or cracking of the connection surface due to stress concentration or temperature gradient is suppressed.
[0029]
In the above optical axis adjustment method, the symmetry matching between the connection surface of the first optical element and the connection surface of the second optical element is realized as follows.
For the connection surface of the optical element to be adjusted, the displacement from the centering position at the time of measuring the first optical power and the displacement at the time of measuring the second optical power are relative to the plane of symmetry at the centering position. Substantially symmetric. Therefore, when the symmetry plane of the connection surface of another optical element is substantially inclined with respect to the symmetry plane, a substantial difference occurs between the first optical power and the second optical power. In particular, the difference corresponds to the inclination between the planes of symmetry.
In the step of rotating the connection surface of the optical element to be adjusted around the axis of symmetry, a substantial difference between the first optical power and the second optical power is detected, and the direction of rotation reduces the difference. Is determined. Thereby, the inclination between the above-mentioned symmetry planes is reduced. In this way, the angular displacement between the connecting surfaces around its axis of symmetry is adjusted.
[0030]
Here, for a certain angle shift, the ratio of the substantial difference between the first optical power and the second optical power to the first optical power (that is, the ratio of the second optical power to the first optical power) Is larger than the value of the coupling loss itself due to the angle shift. Furthermore, the above-mentioned fixed distance, that is, the magnitude of displacement from the centering position of the connection surface of the adjustment target optical element can measure the substantial difference between the first optical power and the second optical power with high accuracy. Can be optimized as follows. As a result, the above-described optical axis adjustment method has higher sensitivity to the angle shift than the conventional method.
In the above optical axis adjustment method, the first direction and the second direction are particularly preferably opposite to each other. At that time, for a certain angle shift, the substantial difference between the first optical power and the second optical power is maximum. Therefore, the sensitivity to the angle shift is particularly high.
[0031]
In the optical axis adjustment method described above, each step may be repeated while adjusting the rotation angle about the symmetry axis with respect to the connection surface of the optical element to be adjusted. For example, the rotation angle may be increased or decreased in accordance with an increase or decrease in a substantial difference between the first optical power and the second optical power. Thereby, the position of the connection surface when the first optical power and the second optical power are substantially equal is quickly determined.
In the above optical axis adjustment method, more preferably, the distance between the connection surface of the first optical element and the connection surface of the second optical element is L, and the above-mentioned fixed distance (that is, the adjustment of the connection surface of the optical element to be adjusted). Δx, and the first optical power is I ₁ , The second optical power is I ₂ In this case, the amount of angular displacement around the axis of symmetry between the connection surfaces of the first optical element and the second optical element is L (I ₁ / I ₂ -1) / (4Δx) and determining the rotation angle. The approximation of the angle shift amount is sufficiently high by adjusting the distance L between the connection surfaces and the magnitude Δx of the displacement of the optical element to be adjusted. Therefore, the angle shift adjustment can be performed quickly.
[0032]
When the connection surface of the optical element has a plurality of the above-mentioned symmetry planes, the above-described optical axis adjustment method may be used for each of the symmetry planes. At that time, the respective angle shift adjustments may be repeated alternately. Thereby, errors due to the accuracy of the respective angle deviation adjustments and errors due to the mutual influence of the angle deviation adjustments for different symmetry planes (for example, the angle deviation about the other symmetry axis due to the reduction of the angle deviation about the other symmetry axis) Increase) can be reduced.
[0033]
In the above-described optical axis adjustment method, in particular, the step relating to the angle deviation adjustment and the step relating to the alignment may be alternately repeated. When an angle shift is included between the connection surfaces, the above-described alignment position generally includes an error. Further, in the step of rotating the connection surface of the optical element to be adjusted, the axis deviation may generally increase due to a positioning error of the rotation axis. Therefore, the axis shift and the angle shift can be further reduced by alternately repeating the alignment and the angle shift adjustment.
[0034]
In the coupling between a core optical fiber or a waveguide type optical element having a circular cross section, particularly when the connection surface is rotationally symmetric about the optical axis, the connection of the optical element to be adjusted is performed by the above optical axis adjustment method. Three or more directions parallel to the plane may be selected. A pair consisting of any two of these directions can be regarded as a pair of the first direction and the second direction. Therefore, for each of these various pairs, the above-mentioned symmetry axis and the amount of angular deviation around it are obtained in the same manner as described above, and from the combination of these symmetry axes and the amount of angular deviation, A rotation angle about a predetermined axis may be determined.
[0035]
In a coupling between an optical fiber having an elliptical core, an optical fiber array, or an optical element having a connection surface inclined with respect to the optical axis, the connection surface is not rotationally symmetric about the optical axis. At this time, the connection surface of the optical element to be adjusted may be rotated around the optical axis by a predetermined rotation angle in addition to the above-mentioned symmetry axis. Thereby, the coupling loss due to the rotational deviation around the optical axis can be reduced in the same manner as the coupling loss due to the angular deviation described above.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings by way of preferred embodiments.
<< Example 1 >>
FIG. 1 is a block diagram showing an optical axis adjusting device according to Embodiment 1 of the present invention. FIG. 1 illustrates the coupling between a single-core optical fiber 11 and a waveguide-type optical element 12.
The laser 1 is preferably a semiconductor laser and stably supplies a constant light output (about 1 mW) at a wavelength of about 1.55 μm or about 1.3 μm. The optical output of the laser 1 enters the input end 11B of the optical fiber 11, is transmitted along the optical fiber 11, and is emitted from the connection surface 11A.
[0037]
The first stage 2 is a fixed stage, and its base is fixed substantially horizontally. On the first stage 2, a coupling portion 11C of the optical fiber 11 is fixed horizontally and straight.
The second stage 3 is a fine movement stage and is set close to the first stage 1. The second stage 3 slightly translates the table surface in, for example, two directions parallel to the table surface and one direction perpendicular to the table surface (accuracy: about 0.05 μm), and rotates the table slightly around each direction. (Accuracy about 0.001 °). On the second stage 3, a waveguide type optical element 12 is fixed with its optical waveguide 12C horizontal. At this time, particularly, the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 face each other.
[0038]
The sub optical fiber 14 couples between the output end 12B of the waveguide type optical element 12 and the photodetector 4, and transmits the optical output of the waveguide type optical element 12 to the photodetector 4.
The photodetector 4 is preferably an optical power meter, and measures the optical output of the waveguide type optical element 12 input from the sub optical fiber 14. The measured value is output to the control unit 5.
The control unit 5 is preferably a personal computer, and functions as an axis deviation adjustment unit 5A and an angle deviation adjustment unit 5B by a predetermined program. The axis deviation adjusting unit 5A controls active alignment relating to alignment between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12. On the other hand, the angle shift adjusting unit 5B executes active alignment related to the angle shift adjustment between the two connection surfaces. The control unit 5 processes the measurement value of the photodetector 4 by each function, and determines a control amount for the second stage 3.
The driver 6 is a driving device for a motor that actually finely moves the second stage 3, and slightly translates or rotates the second stage 3 according to a control amount from the control unit 5.
[0039]
The optical fiber 11 is, for example, a single-core single-mode optical fiber, and includes a core having a circular cross section with a diameter of about 10 μm. The diameter of the entire optical fiber 11 including the clad is about 125 μm. The optical fiber 11 also exhibits substantially the lowest loss for light having a wavelength of about 1.55 μm or about 1.3 μm. Alternatively, the optical fiber 11 may be a multimode optical fiber.
The connection surface 11A of the optical fiber 11 is substantially perpendicular to its optical axis and is substantially planar.
The waveguide type optical element 12 is, for example, a ridge type and includes an optical waveguide (core) 12C having a rectangular cross section of about 10 μm square. The waveguide type optical element 12 may be a buried type. Further, the waveguide type optical element 12 may be an optical fiber.
The connection surface 12A of the waveguide type optical element 12 is substantially perpendicular to the optical axis of the optical waveguide 12C and is substantially planar.
[0040]
FIG. 2 is a perspective view schematically showing the vicinity of a coupling portion between the optical fiber 11 and the waveguide type optical element 12. On the connection surface 11A of the optical fiber 11, three coordinate axes (X axis, Y axis, and Z axis) of a rectangular coordinate system are shown. On the other hand, on the connection surface 12A of the waveguide type optical element 12, three coordinate axes (X ₀ Axis, Y ₀ Axis and Z ₀ Axis) is shown.
The origin of the XYZ coordinate system is an intersection P between the connection surface 11A of the optical fiber 11 and the optical axis C of the core 11C. The XY plane is substantially parallel to the connection surface 11A, the X axis indicates a horizontal direction, and the Y axis indicates a vertical direction. The Z axis indicates the direction of the optical axis C. Here, the connection surface 11A is rotationally symmetric about the Z axis.
On the other hand, X ₀ Y ₀ Z ₀ The coordinate system is composed of a connection surface 12A of the waveguide type optical element 12 and an optical axis C of the optical waveguide 12C. ₀ Intersection P with ₀ Is the origin. X ₀ Y ₀ The plane is substantially parallel to its connecting surface 12A and X ₀ The axis is horizontal, Y ₀ The axes indicate the vertical direction, respectively. Z ₀ The axis is the optical axis C ₀ The direction of is shown. Here, the connection surface 12A is X ₀ Z ₀ Plane and Y ₀ Z ₀ Let each plane be a plane of symmetry.
[0041]
On each of the first stage 2 and the second stage 3, a positioning reference using, for example, a groove or a pin is provided. The optical fiber 11 is fixed on the first stage 2 and the waveguide type optical element 12 is fixed on the second stage 3 according to the positioning standards. Further, when the second stage 3 is set at the initial position, the XYZ coordinate system and X ₀ Y ₀ Z ₀ Corresponding coordinate axes between the coordinate system and the coordinate system are substantially parallel.
[0042]
The second stage 3 slightly displaces the connection surface 12A of the waveguide type optical element 12. The minute displacement is caused by X substantially parallel to the connection surface 12A. ₀ Y ₀ Two degrees of freedom for translation on a plane, the optical axis C of the optical waveguide 12C ₀ Direction (Z ₀ One degree of freedom for translation in the axial direction) and X ₀ Axis and Y ₀ Includes a total of five degrees of freedom, two degrees of freedom (see arrows α and β in FIG. 2) for rotation about each of the axes. In addition, Z ₀ One degree of freedom for rotation about the axis may be further added.
Hereinafter, the position of the connection surface 12A of the waveguide type optical element 12 with respect to the connection surface 11A of the optical fiber 11 is represented by X ₀ Y ₀ Z ₀ Coordinate system origin P ₀ XYZ coordinates.
[0043]
The axis misalignment adjusting unit 5A is configured to control the X ₀ Y ₀ Using the degree of freedom of translation on a plane, active alignment relating to alignment between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 is performed as follows. Here, the distance L between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 is Z ₀ It is set to be sufficiently narrow (for example, about 25 μm) in advance by utilizing the degree of freedom of translation in the axial direction.
First, light enters the input end 11B of the optical fiber 11 from the laser 1 and is emitted from the connection surface 11A. The emitted light R enters the waveguide type optical element 12 from its connection surface 12A, and is transmitted from the output end 12B to the photodetector 4 through the sub optical fiber 14 (see FIG. 1). The photodetector 4 measures the intensity of the emitted light.
X ₀ Y ₀ Z ₀ Coordinate system origin P ₀ Is defined as (x, y, z), the optical power (hereinafter, referred to as received light intensity) I measured by the photodetector 4 is expressed as a function I = I (x, y, z) of the XYZ coordinate. Is represented. In particular, when the inclination between the connection surfaces is sufficiently small, the received light intensity I is approximated with high accuracy by the following equation (1).
[0044]
I (x, y, z) = Aexp ｛− (Bx ² + Cy ² )｝ / Z ² . (1)
[0045]
Here, coefficients A, B, and C are X ₀ Y ₀ Z ₀ Coordinate system origin P ₀ Is a positive constant that does not substantially depend on the XYZ coordinates (x, y, z).
The distance between the connection surfaces is maintained at a constant value L, and the Z axis of the XYZ coordinate system, that is, the optical axis C of the optical fiber 11 is X ₀ Y ₀ Z ₀ Coordinate system origin P ₀ Is substantially pierced, as is apparent from the equation (1), the received light intensity I becomes the maximum value I ₀ = I (0,0, L) = A / L ² Reach
The axis deviation adjusting unit 5A sets the connection surface 12A of the waveguide type optical element 12 to X ₀ Y ₀ The above measurement is repeated while translating on a plane. The translation gives X ₀ Y ₀ Z ₀ Coordinate system origin P ₀ Changes the XYZ coordinates, so that the received light intensity I changes according to equation (1). The axis deviation adjusting unit 5A monitors the change, and when the received light intensity I is substantially the maximum value I ₀ = A / L ² Is determined on the XY plane of the connection surface 12A when the contact surface 12A is reached. Thus, the centering position of the waveguide type optical element 12 with respect to the optical fiber 11 is set.
[0046]
The angle shift adjusting unit 5B is configured to select X out of the five degrees of freedom of the second stage 3. ₀ Axis and Y ₀ Using the degree of freedom of rotation about each of the axes, active alignment relating to the adjustment of the angle deviation between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 is performed as follows.
FIG. 3 is an enlarged plan view schematically showing the vicinity of the core 11C of the connection surface 11A of the optical fiber 11 and the vicinity of the optical waveguide 12C of the connection surface 12A of the waveguide-type optical element 12, that is, when viewed from vertically upward. It is an enlarged view. In FIG. 3, the connection surface 12A of the waveguide type optical element 12 is inclined by a small angle β with respect to the connection surface 11A of the optical fiber 11. That is, Y of the connection surface 12A of the waveguide type optical element 12 with respect to the connection surface 11A of the optical fiber 11 ₀ The angle shift amount around the axis is equal to the minute angle β.
First, the connection surface 12A of the waveguide type optical element 12 is set at the centering position. At this time, the optical axis C of the optical fiber 11 and the optical axis C of the optical waveguide 12C ₀ Is the gap between the connecting surfaces, ie, the point PP ₀ A substantial match between Therefore, the optical axis C of the optical fiber 11 is equal to the connection surface 12A of the waveguide type optical element 12, and the optical axis C of the connection surface 12A and the optical waveguide 12C. ₀ Intersection P with ₀ Can be regarded as substantially intersecting. That is, X ₀ Y ₀ Z ₀ Coordinate system origin P ₀ The XYZ coordinates (x, y, z) of are substantially equal to (0, 0, L): (x, y, z) = (0, 0, L).
[0047]
Next, the connecting surface 12A of the waveguide type optical element 12 is moved X from the centering position. ₀ The translation is made by a substantially constant distance Δx in the positive direction of the axis. Here, the fixed distance Δx is substantially the same as the size of the optical waveguide 12C, and is about 10 μm. At this time, the connection surface 12A of the waveguide type optical element 12 and the optical axis C of the optical waveguide 12C ₁ Intersection (X ₀ Y ₀ Z ₀ Origin of coordinate system) P ₁ XYZ coordinates (x, y, z) of the origin P ₁ Using the translational displacement magnitude Δx and the distance L between the connecting surfaces and the inclination β, the following expression is obtained: (x, y, z) = (Δx · cosβ, 0, L + Δx · sinβ).
In this arrangement, similarly to the alignment performed by the axis deviation adjusting unit 5A, light enters the input end 11B of the optical fiber 11 from the laser 1 and the light output from the output end 12B of the waveguide type optical element 12 is detected by a photodetector. Measure with 4. The measured value (hereinafter referred to as first optical power) I ₁ Is approximated by the following equation (2) by the above equation (1).
[0048]
I ₁ = I (Δx · cosβ, 0, L + Δx · sinβ)
= Aexp ｛-B (Δx · cosβ) ² ｝ / (L + Δx · sinβ) ² . (2)
[0049]
Subsequently, the connecting surface 12A of the waveguide type optical element 12 is moved from the centered position by X. ₀ The translation is performed in the negative direction of the axis by a distance substantially equal to the constant distance Δx. At this time, the connection surface 12A of the waveguide type optical element 12 and the optical axis C of the optical waveguide 12C ₂ Intersection (X ₀ Y ₀ Z ₀ Origin of coordinate system) P ₂ XYZ coordinates (x, y, z) of the origin P ₂ Using the translational displacement magnitude Δx and the distance L between the connecting surfaces and the inclination β, the following expression is obtained: (x, y, z) = (− Δx · cosβ, 0, L−Δx · sinβ) .
In this arrangement, light enters the input end 11B of the optical fiber 11 from the laser 1 and the light output from the output end 12B of the waveguide type optical element 12 is measured by the photodetector 4. The measured value (hereinafter, referred to as second optical power) I ₂ Is approximated by the following equation (3) by the above equation (1).
[0050]
I ₂ = I (−Δx · cosβ, 0, L−Δx · sinβ)
= Aexp ｛-B (Δx · cosβ) ² ｝ / (L-Δx · sinβ) ² . (3)
[0051]
From the equations (2) and (3), the first optical power I ₁ And the second optical power I ₂ Is determined by the following equation (4).
[0052]
I ₁ / I ₂ = (L + Δx · sinβ) ² / (L-Δx · sinβ) ² . (4)
[0053]
When the inclination between the connection surfaces, that is, the angle shift amount β is sufficiently small, the angle shift amount β is obtained from the first optical power I from the equation (4). ₁ And the second optical power I ₂ Ratio I ₁ / I ₂ , The distance L between the connection surfaces, and the magnitude Δx of the translational displacement of the connection surface 12A of the waveguide type optical element 12, and are approximated by the following equation (5).
[0054]
β = L (I ₁ / I ₂ -1) / (4Δx). (5)
[0055]
The angle shift adjusting unit 5B moves the connection surface 12A of the waveguide type optical element 12 by the second stage 3 by the angle shift amount β obtained by Expression (5). ₀ Rotate around an axis. Thus, the inclination (angle shift) β between the connection surfaces when viewed from the vertical direction is reduced, and the X-axis and the X-axis ₀ The parallelism with the axis is improved. Furthermore, the YZ plane and Y ₀ Z ₀ The inclination with respect to the planes is reduced, and the symmetry of the joint with respect to those planes is improved. As a result, the coupling loss due to the angle shift β is reduced.
[0056]
Here, for a fixed angle shift amount β, the first optical power I ₁ Second optical power I for ₂ Difference between the ratio of 1 and 1 (I ₁ / I ₂ -1) is sufficiently larger than the value of the coupling loss itself due to the angle shift amount β. Further, the distance L between the connection surfaces and the fixed distance Δx are the first optical power I ₁ And the second optical power I ₂ Can be optimized so that a substantial difference from the measurement can be measured with high accuracy. As a result, the above-described angle shift adjustment has higher sensitivity than active alignment by a conventional apparatus.
[0057]
The connection surface 12A of the waveguide type optical element 12 is set to X with respect to the connection surface 11A of the optical fiber 11. ₀ When tilted by a small angle α around the axis, ie, X ₀ When the angle shift amount around the axis is equal to the minute angle α, the angle shift adjustment unit 5B performs the angle shift adjustment X ₀ The same process is performed in the axial direction, and the angle shift amount α is reduced in the same manner as the above-described angle shift amount β. Thereby, the Y axis and Y ₀ The parallelism with the axis is improved. XZ plane and X ₀ Z ₀ The inclination with respect to the planes is reduced, and the symmetry of the joint with respect to those planes is improved. As a result, the coupling loss due to the angle shift α is reduced.
[0058]
The angle shift adjusting unit 5B ₀ Adjustment of the angle shift around the axis (that is, reduction of the angle shift amount α) and Y ₀ Adjustment of the angle shift around the axis (that is, reduction of the angle shift amount β) may be alternately repeated. Thereby, an error due to the accuracy of each angle shift adjustment and an error due to mutual influence of the angle shift adjustment for different symmetry planes (for example, X ₀ Y by reducing the amount of angular deviation α around the axis ₀ Increase in the amount of angular deviation β around the axis). As a result, the stability of the angle shift adjustment is improved.
[0059]
The control unit 5 may alternately repeat the alignment by the axis deviation adjustment unit 5A and the angle deviation adjustment by the angle deviation adjustment unit 5B. When an angle shift is included between the connection surfaces, the above-described alignment position generally includes an error. Further, when the connection surface 12A of the waveguide type optical element 12 is rotated by adjusting the angle shift, the rotation axis (Y ₀ Axial misalignment can generally increase due to the positioning error of the axle). Therefore, the axis shift and the angle shift can be further reduced by alternately repeating the alignment and the angle shift adjustment.
[0060]
FIG. 4 is a flowchart of the optical axis adjustment method according to the first embodiment.
<Step S1>
The optical fiber 11 is fixed at a predetermined position on the first stage 2, and the waveguide type optical element 12 is fixed at a predetermined position on the second stage 3, and the second stage 3 is set to an initial position. Then, the XYZ coordinate system and X ₀ Y ₀ Z ₀ Corresponding coordinate axes between the coordinate system and the coordinate system are substantially parallel.
Further, the distance between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 is set to a sufficiently small distance L.
Here, the optical output of the laser 1 is incident on the input end 11B of the optical fiber 11, and the optical output from the output end 12B of the waveguide type optical element 12 is detected by the photodetector 4 to determine whether The initial position of the stage 3 may be adjusted.
[0061]
<Step S2>
The axis deviation adjusting unit 5A performs the above-described alignment, and determines the alignment position.
<Step S3>
The angle shift adjusting unit 5B moves the connection surface 12A of the waveguide type optical element 12 from the centering position by X. ₀ Translated by a fixed distance Δx in the positive direction of the axis, and the measured value (first optical power) I of the photodetector 4 at that time is I ₁ Record
<Step S4>
The angle shift adjusting unit 5B moves the connection surface 12A of the waveguide type optical element 12 from the centering position by X. ₀ Translated by a fixed distance Δx in the negative direction of the axis, and the measured value (second optical power) I of the photodetector 4 at that time I ₂ Record
<Step S5>
When the angle shift adjusting unit 5B has the first optical power I ₁ And the second optical power I ₂ Is calculated, and Y is calculated from Expression (5). ₀ The amount of angular deviation β around the axis is determined.
<Step S6>
The angle shift adjusting unit 5B sets the connection surface 12A of the waveguide type optical element 12 to Y. ₀ It is rotated around the axis by the angle shift amount β.
[0062]
<Step S7>
The angle shift adjusting unit 5B moves the connecting surface 12A of the waveguide type optical element 12 from the centering position by Y. ₀ Translated by a fixed distance Δy in the positive direction of the axis, and the measured value (third optical power) I of the photodetector 4 at that time is I ₃ Record
<Step S8>
The angle shift adjusting unit 5B moves the connecting surface 12A of the waveguide type optical element 12 from the centering position by Y. ₀ Translated by a fixed distance Δy in the negative direction of the axis, and the measured value (fourth optical power) I of the photodetector 4 at that time is I ₄ Record
<Step S9>
The angle shift adjusting unit 5B has the third optical power I ₃ And the fourth optical power I ₄ Is calculated, and X is calculated from the following equation (6). ₀ The amount of angular deviation α around the axis is determined.
[0063]
α = L (I ₃ / I ₄ -1) / (4Δy). (6)
[0064]
<Step S10>
The angle shift adjusting unit 5B moves the connection surface 12A of the waveguide type optical element 12 to X ₀ It is rotated about the axis by the angle shift amount α.
The above steps S2 to S10 are repeated.
Thus, the axial displacement and the angular displacement between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12 are stably reduced, and the coupling loss between the connection surfaces is large and quickly reduced. I do.
[0065]
The connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide-type optical element 12 are bonded together by, for example, an adhesive after the axis shift and the angle shift are sufficiently removed as described above. At this time, the stress distribution and the thickness of the adhesive layer are highly uniform between the two connection surfaces. Therefore, deterioration such as distortion or cracking of the connection surface due to stress concentration or temperature gradient is suppressed. As a result, high reliability for the connection is maintained for a long time.
[0066]
In the optical axis adjusting device according to the first embodiment, the waveguide type optical element 12, that is, the optical element connected to the photodetector 4 is fixed to the fine movement stage and slightly displaced. That is, the optical element on the side of the photodetector 4 is to be adjusted for the axis shift and the angle shift. In addition, the optical element on the side connected to the photodetector 4 may be fixed to the fixed stage, and the optical element on the side connected to the laser 1 may be fixed on the fine movement stage and slightly displaced.
[0067]
The optical axis adjusting device automatically processes the measurement value of the photodetector 4 by the control unit 5 and automatically controls the active alignment. Alternatively, the measured value of the photodetector 4 may be displayed, the user may visually read the measured value, and manually drive the fine movement stage using a micrometer or the like.
[0068]
【The invention's effect】
As described above, the optical axis adjustment device according to the present invention, for the connection surface of the optical element to be adjusted, the displacement from the alignment position at the time of measuring the first optical power and the displacement at the time of measuring the second optical power. Is set substantially symmetric with respect to the symmetry plane at the centering position. Furthermore, the connecting surface of the optical element to be adjusted is rotated around the line of intersection with the plane of symmetry (that is, the axis of symmetry) in such a direction as to reduce the substantial difference between the first optical power and the second optical power. . Thereby, the inclination between the symmetry planes, that is, the angle shift between the connection planes around the symmetry axis is reduced. As a result, the coupling loss due to the angle shift is greatly reduced, and the deterioration due to the stress concentration and the temperature gradient is largely suppressed.
[0069]
This angle shift adjustment can be realized with fewer components than the conventional passive alignment by image processing. Further, since the adjustment is performed by active alignment, the accuracy of the adjustment is high.
In particular, for a certain amount of angular deviation, the difference between the ratio of the second optical power to the first optical power and 1 is sufficiently larger than the value of the coupling loss itself due to the amount of angular deviation. Further, the distance between the connection surfaces and the magnitude of the displacement from the centering position can be optimized so that the substantial difference between the first optical power and the second optical power can be measured with high accuracy. As a result, the above-described angle shift adjustment is achieved more quickly because it has higher sensitivity than active alignment by the conventional apparatus.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an optical axis adjusting device according to a first embodiment of the present invention.
FIG. 2 is a perspective view schematically showing the vicinity of a joint between an optical fiber 11 and a waveguide type optical element 12 in the optical axis adjusting apparatus according to the first embodiment of the present invention.
FIG. 3 schematically shows the optical axis adjusting device according to the first embodiment of the present invention, in the vicinity of the core 11C of the connection surface 11A of the optical fiber 11 and in the vicinity of the optical waveguide 12C of the connection surface 12A of the waveguide type optical element 12. It is an enlarged plan view.
FIG. 4 is a flowchart of an optical axis adjustment method according to the first embodiment of the present invention.
FIG. 5 is a schematic diagram for explaining a conventional optical axis adjustment method, taking as an example the coupling between a single-core optical fiber 11 and a waveguide-type optical element 12.
FIG. 6 shows the connection between the connection surface 11A of the optical fiber 11 and the connection surface 12A of the waveguide type optical element 12, which are observed by the first camera 21 and the second camera 22, respectively, by the conventional optical axis adjustment method. It is a schematic diagram which shows a part vicinity. (A) is an image of the second camera 22, that is, a plan view of a combined portion. (B) is an image of the first camera 21, that is, a side view of the connection portion.
[Explanation of symbols]
11 Optical fiber
11A Connection surface of optical fiber 11
11C Core of optical fiber 11
C Optical axis of optical fiber 11
P Intersection between optical axis C of optical fiber 11 and connection surface 11A
12. Waveguide type optical device
12A Connection surface of waveguide type optical element 12
12C Optical waveguide of waveguide type optical element 12
L Spacing between connection surfaces
β Y between connecting surfaces ₀ Angle shift around axis
Δx X of connection surface 12A of waveguide type optical element 12 ₀ Axial displacement magnitude
C ₀ Optical axis of optical waveguide 12C at the centering position
P ₀ Optical axis C of optical waveguide 12C at the centering position ₀ Point of intersection with the connecting surface 12A
I ₀ Optical power from the waveguide type optical element 12 at the centering position
C ₁ X ₀ Optical axis of optical waveguide 12C at axial displacement + Δx
P ₁ X ₀ Optical axis C of optical waveguide 12C at axial displacement + Δx ₁ Point of intersection with the connecting surface 12A
I ₁ First optical power
C ₂ X ₀ Optical axis of optical waveguide 22C at axial displacement-Δx
P ₂ X ₀ Optical axis C of optical waveguide 22C at axial displacement -Δx ₂ Point of intersection with the connecting surface 22A
I ₂ Second optical power

Claims (6)

(A) a light source unit for outputting a substantially constant optical power;
(B) a first stage for fixing a first optical element and transmitting light emitted from the light source section from an input end of the first optical element to a connection surface;
(C) a second stage for fixing the second optical element and transmitting light transmitted from the connection surface of the first optical element to the output end from the connection surface of the second optical element;
(D) a photodetector for detecting transmitted light from the output end of the second optical element and measuring the light power;
(E) a stage drive unit for finely moving the first stage or the second stage by a predetermined amount; and
(F) (a) With respect to one of the first optical element and the second optical element (hereinafter, referred to as an adjustment target optical element), substantially with respect to a substantially symmetric plane including an optical axis of a connection surface thereof. Two directions (hereafter, referred to as a first direction and a second direction) which are symmetrically and substantially parallel to the connection surface thereof, and (b) move the optical element to be adjusted from the centering position to the second direction. When shifting by a certain distance to each of the one direction and the second direction, the optical power from the output end of the second optical element is measured as a first optical power and a second optical power, respectively, c) A direction in which the first optical power and the second optical power are substantially equal around a line of intersection (hereinafter, referred to as a symmetry axis) of the connection surface of the optical element to be adjusted with the symmetry plane. An angle shift adjustment unit for rotating the camera by a predetermined rotation angle;
An optical axis adjusting device having: The optical axis adjustment device according to claim 1, wherein the first direction and the second direction are opposite to each other. The distance between the connection surface of the first optical element and the connection surface of the second optical element is L, the fixed distance is Δx, the first optical power is I ₁ , and the second optical power is I ₂ In this case, the angle shift adjusting unit sets the angle shift amount around the symmetry axis between the connection surfaces of the first optical element and the second optical element to L (I ₁ / I ₂ −1) / 3. The optical axis adjustment device according to claim 2, wherein the rotation angle is approximated by (4.DELTA.x), and the angle shift amount is determined as the rotation angle. (A) A substantially constant optical power is output by the light source unit, the emitted light is transmitted from the input end of the first optical element fixed to the first stage to the connection surface, and the transmitted light is further transmitted. Transmitting light from the connection surface of the second optical element fixed to the second stage to the output end, and measuring the optical power of the transmitted light;
(B) repeating the step of measuring the optical power each time one of the first optical element or the second optical element is moved substantially parallel to the connection surface thereof, and Determining a position of the first optical element and a position of the second optical element when measuring a substantially largest one of the measured values of optical power as respective alignment positions;
(C) One of the first optical element and the second optical element (hereinafter referred to as an adjustment target optical element) is substantially symmetric with respect to a substantially symmetric plane including an optical axis of a connection surface thereof. Selecting two directions substantially parallel to the connecting surface (hereinafter referred to as a first direction and a second direction);
(D) shifting the optical element to be adjusted from the centering position by a certain distance in the first direction, and measuring the optical power at that time as a first optical power;
(E) displacing the adjustment target optical element from the alignment position in the second direction by the predetermined distance, and measuring the optical power at that time as a second optical power;
(F) The first optical power and the second optical power are made substantially equal around a line of intersection (hereinafter, referred to as a symmetry axis) of the connection surface of the optical element to be adjusted with the symmetry plane. Rotating in a predetermined direction by a predetermined rotation angle;
An optical axis adjustment method between optical element connection surfaces, comprising: The method of adjusting an optical axis between optical element connection surfaces according to claim 4, wherein the first direction and the second direction are opposite to each other. The distance between the connection surface of the first optical element and the connection surface of the second optical element is L, the fixed distance is Δx, the first optical power is I ₁ , and the second optical power is I ₂ In this case, the amount of angular displacement around the symmetry axis between the connecting surfaces of the first optical element and the second optical element is approximated by L (I ₁ / I ₂ -1) / (4Δx), The method of adjusting an optical axis between optical element connection surfaces according to claim 5, further comprising the step of determining the amount of angular deviation as the rotation angle.

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