JP6355993B2 - Optical axis adjusting device and optical axis adjusting method - Google Patents

Description

  The present invention relates to an optical axis adjustment device and an optical axis adjustment method for adjusting an optical axis between an optical element module and an optical fiber.

  In recent years, the communication speed of optical communication is increasing, and there is a demand for an optical communication module that has a high communication speed, a smaller size, and lower power consumption. Therefore, a plurality of laser diode elements (hereinafter referred to as LD elements) having different wavelengths are mounted in one optical communication module, light output from these LD elements is multiplexed, and optically coupled to a single optical fiber. Therefore, an integrated optical communication module (hereinafter referred to as an integrated module) having a small size and a high communication speed has been developed.

  Conventionally, one LD element is incorporated in one optical communication module, and the optical axis is adjusted with the optical fiber for this LD element, and optical communication is performed at a position where the light intensity measured through the optical fiber is optimal. The module and optical fiber were fixed.

  However, since a plurality of LD elements having different wavelengths are mounted in the integrated module, the optical axis of the optical fiber is adjusted for each LD element, and the optical axis adjustment coordinates corresponding to each LD element are adjusted. Therefore, it is necessary to determine the optimum position of the optical fiber with respect to the integrated module. Therefore, the number of executions of optical axis adjustment increases by the number of LD elements mounted in the integrated module, and as a result, the time required for optical axis adjustment also increases.

  In the following Patent Document 1, it has been proposed to reduce the time for adjusting the optical axis by shortening the stage moving and stopping time associated with the light intensity measurement of the optical axis adjusting device and further performing the light intensity measurement synchronized with the stage position. ing. Specifically, a drive motor including a rotary encoder is attached to a stage that adjusts the relative position between the optical communication module and the optical fiber, and an output signal of the rotary encoder is supplied to a synchronization signal output circuit. The intensity of light transmitted through the optical fiber is measured by the optical power detector and input to the A / D converter. The A / D converter starts A / D conversion in synchronization with the external synchronization signal from the synchronization signal output circuit, and the converted digital value is stored in the buffer memory. Thereby, the stage stop time for measuring the light intensity is reduced, and the optical axis adjustment time is reduced.

  Here, the output signal of the rotary encoder is input to the A / D converter via the synchronization signal output circuit. Therefore, the output timing between the output signal of the rotary encoder and the synchronization signal input to the A / D converter has a time delay due to the intervention of the synchronization signal output circuit, and the measured light intensity by the time delay. Deviation occurs in synchronization with the.

Further, although not explicitly disclosed in Patent Document 1, a counter that counts the output signal of the rotary encoder and detects the coordinate position and the moving direction of the stage is also required. Therefore, the synchronization between the position data of the stage and the light intensity data is required. The gap will increase even more.
In Patent Document 1, when a plurality of LD elements are mounted in a module like an integrated module, the number of optical axis adjustments increases.

JP 2003-185495 A JP-A-9-311250

  In Patent Document 1, as described above, in the optical axis adjustment between the optical communication module and the optical fiber, the position data of the stage for adjusting the relative position of the two and the light intensity of the LD element measured by the optical fiber are synchronized. In the case of measurement, there is a deviation in synchronization between the stage position and the light intensity. Further, the above-mentioned synchronization deviation becomes more prominent as the stage is driven at a higher speed. Therefore, when the optical axis adjustment is speeded up, the adjustment accuracy is deteriorated.

  In an integrated optical communication module in which a plurality of LD elements having different wavelengths are mounted in one optical communication module, it is necessary to adjust the optical axis with the optical fiber for each of the plurality of LD elements. The number of shaft adjustments increases, and the adjustment and assembly time of the optical fiber becomes longer.

  An object of the present invention is to provide an optical axis adjustment device and an optical axis adjustment method that can suppress a synchronization shift between a position signal and a light intensity signal and can achieve high-precision optical axis adjustment at high speed.

In order to achieve the above object, the present invention provides an optical axis adjusting device for adjusting an optical axis between an optical element module and an optical fiber,
A moving mechanism for controlling a relative position between the optical element module and the optical fiber;
A position sensor that outputs an analog position signal corresponding to the relative position;
A photodetector that outputs an analog light intensity signal corresponding to the intensity of light incident on the optical fiber from the optical element module;
An analog-to-digital converter that converts an analog position signal and an analog light intensity signal into corresponding digital values in synchronization with each other;
A storage unit for storing digital values from the analog-digital converter;
An arithmetic unit that searches for a relative position optimal for optical axis adjustment based on the digital value stored in the storage unit.

The present invention is also an optical axis adjustment method for adjusting the optical axis between the optical element module and the optical fiber,
An analog light intensity signal corresponding to the intensity of light incident on the optical fiber from the optical element module while continuously scanning the relative position between the optical element module and the optical fiber within a predetermined scanning range. And a continuous scanning step of converting analog position signals corresponding to the relative positions into corresponding digital values in synchronization with each other and storing them in a storage unit,
And a search step of searching for an optimum relative position for optical axis adjustment based on the digital value stored in the storage unit.

  According to the present invention, both the analog position signal corresponding to the relative position between the optical element module and the optical fiber and the analog light intensity signal corresponding to the intensity of light incident on the optical fiber are synchronized with each other. By converting to a corresponding digital value, a synchronization shift between the position signal and the light intensity signal can be suppressed, so that highly accurate optical axis adjustment can be achieved at high speed.

It is a block diagram which shows the optical axis adjustment apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows the conventional optical axis adjustment method as a comparative example. It is a flowchart which shows an example of the optical axis adjustment method which concerns on this invention. It is a graph which shows an example of the relationship between a scanning position and light intensity, when several LD element is mounted in LD module. FIG. 5A is an explanatory diagram illustrating an example of a spiral scan, and FIG. 5B is an explanatory diagram illustrating an example of a raster scan.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram illustrating an optical axis adjusting apparatus according to Embodiment 1 of the present invention. The optical axis adjusting device includes an LD module 1, an optical fiber 2, an XY stage 3, a Z stage 4, a position sensor 5, a duplexer 6, a photodetector 7, and an A / D converter 8. And a computer 9. For easy understanding, the direction in which the light from the LD module 1 travels is the Z direction, the direction perpendicular to the Z direction and perpendicular to the paper surface is the Y direction, and the direction perpendicular to the Z direction and parallel to the paper surface is X. The direction.

  The LD module 1 incorporates a single or a plurality of LD elements and lenses, and is mounted on a movable part of the XY stage 3. The LD element is supplied with power at a desired timing from an LD power source (not shown) via a power supply jig (not shown). In the case of wavelength division multiplex communication (WDM), a plurality of LD elements having different emission wavelengths are mounted on the LD module 1, and the optical axes of the LD elements are positioned so as to be substantially coaxial.

  The XY stage 3 includes a fixed portion, a movable portion that is displaced in the X direction and the Y direction with respect to the fixed portion, and an X motor and a Y motor that drive the movable portion. A drive circuit (not shown) that operates according to a command from the computer 9 is connected to each motor. The XY stage 3 is provided with two position sensors 5 that output analog position signals corresponding to the relative positions of the movable part in the X direction and the Y direction.

  The optical fiber 2 has a function of receiving and transmitting light emitted from the LD module 1, and is attached to the movable part of the Z stage 4.

  The Z stage 4 includes a fixed portion, a movable portion that is displaced in the Z direction with respect to the fixed portion, a Z motor that drives the movable portion, and the like. A drive circuit (not shown) that operates according to a command from the computer 9 is connected to the Z motor. The Z stage 4 is provided with one position sensor 5 that outputs an analog position signal corresponding to the relative position of the movable part in the Z direction.

  At the rear end of the optical fiber 2 is provided a photodetector 7 that outputs an analog light intensity signal corresponding to the intensity of light incident on the optical fiber 2 from the LD module 1. In the case of wavelength division multiplex communication (WDM), a demultiplexer 6 for demultiplexing light transmitted through the optical fiber 2 by wavelength is interposed at the rear end of the optical fiber 2. A plurality of photodetectors 7 that output analog light intensity signals of the waved light are provided for each wavelength. The photodetector 7 can be an O / E converter of a type having an analog voltage output as an output interface, a power meter, or the like.

  The A / D converter 8 has a function of synchronizing both the analog position signal from the position sensor 5 and the analog light intensity signal from the photodetector 7 with each other and converting them into corresponding digital values. The A / D converter 8 is preferably equipped with a buffer memory 8a, which temporarily stores digital values to be converted for each preset period, and further stores the storage unit 9b of the computer 9 at a desired timing. Transferred to and saved.

  There are a method of giving a trigger signal from the outside and a method of using the voltage value itself of the input signal as a trigger as the timing at which the A / D converter 8 converts the input analog signal into a digital value. Either trigger method can be used. When using an external trigger signal, it is necessary to provide a trigger signal generator in the apparatus. In addition, any trigger method can be used even when the conversion of the analog signal is stopped.

  The computer 9 includes a calculation unit 9a such as a microprocessor, a storage unit 9b such as a ROM, a RAM, and a magnetic disk device, and a personal computer equipped with various interfaces. Based on the digital value stored in the unit 9b, it has a function of searching for a relative position optimal for optical axis adjustment, for example, a relative position where the maximum light intensity is obtained. Such functions can generally be realized by software.

  In this embodiment, the case where the XY stage 3 is installed on the LD module 1 side and the Z stage 4 is installed on the optical fiber 2 side is illustrated as a moving mechanism for controlling the relative position between the LD module 1 and the optical fiber 2. However, the present invention is not limited to this. For example, the XY stage 3 may be installed on the optical fiber 2 side and the Z stage 4 may be installed on the LD module 1 side. Alternatively, either the LD module 1 or the optical fiber 2 is fixed and the other side is installed. An XYZ stage that is displaced in the XYZ direction may be provided.

  Further, although not shown in FIG. 1, a mechanism for adjusting the surface on either side of the LD module 1 or the optical fiber 2 by adjusting the rotational directions (θx, θy) around the X axis and the Y axis. (For example, a gonio stage or the like) and / or a mechanism (for example, a rotation stage or the like) that adjusts in the rotation direction (θz) around the Z axis may be additionally provided.

  In the present embodiment, the XY stage 3 and the Z stage 4 are provided with position sensors 5 that output analog position signals corresponding to the relative positions in the X direction, the Y direction, and the Z direction. The output of the position sensor 5 preferably changes linearly with respect to the change in the stage position, but a relational expression in which both values are uniquely determined, such as a monotone increase curve or a monotone decrease curve, is sufficient.

  Further, as a motor for driving the XY stage 3 and the Z stage 4, a stepping motor, a servo motor or the like can be used, and a piezo stage having a position sensor 5 built in the stage may be used. Although the piezo stage has a high resolution, its driving range is smaller than that of the above-described stepping motor and servo motor, so it is preferable to use a combination of these.

  Next, an optical axis adjustment method will be described. FIG. 2 is a flowchart showing a conventional optical axis adjustment method as a comparative example. Here, an optical axis adjustment procedure on the XY plane is shown.

  First, the movable portion of the XY stage 3 is moved by a fixed amount in any one axis, for example, the X direction (step a1), and the light intensity is measured using the photodetector 7 in a state where it is stopped (step a1). Step a2). Next, it is determined whether the measured light intensity satisfies the standard (step a3). If the standard is not satisfied, return to step a1, move the movable part of the XY stage 3 in the same direction by a fixed amount, measure the light intensity (step a2), and repeat until the light intensity satisfies the standard To do. On the other hand, when the standard is satisfied in step a3, the stage movement in the X direction is finished, and the optical axis adjustment in the X direction is completed.

  Next, optical axis adjustment is performed for the remaining coordinate axes. The movable part of the XY stage 3 is moved by a fixed amount in the Y direction (step a4), and the light intensity is measured using the photodetector 7 in a temporarily stopped state (step a5). Next, it is determined whether the measured light intensity satisfies the standard (step a6). If the standard is not satisfied, return to step a4, move the movable part of the XY stage 3 in the same direction by a fixed amount, measure the light intensity (step a5), and repeat until the light intensity satisfies the standard To do. On the other hand, when the standard is satisfied in step a6, the stage movement in the Y direction is finished, and the optical axis adjustment in the Y direction is completed. Thus, the optical axis adjustment in the X direction and the Y direction is completed.

  Here, the amount of movement of the XY stage in steps a1 and a4 is determined from the amount of change in light intensity with respect to the relative position change between the LD module 1 and the optical fiber 2. For example, if the movement amount is about 1 μm, and the optical axis adjustment range in the XY directions is 100 μm, data of 10000 (= 100 × 100) points at maximum is acquired. Therefore, since it stops every step movement, the optical axis adjustment time becomes long. Therefore, in general, the movement amount is set to about 10 μm at first, and the optical axis is adjusted (coarse adjustment) so that the light intensity can be obtained to some extent. Finally, the light is adjusted in steps of 1 μm with the adjustment range narrowed. The amount of movement is adjusted in stages, such as adjusting the axis (fine adjustment). Further, as the stage scanning method, a spiral scan, a raster scan, or the like is generally used.

FIG. 3 is a flowchart showing an example of the optical axis adjusting method according to the present invention. Here, a rectangular scanning range surrounded by four coordinates (X _S , Y _S ), (X _E , Y _S ), (X _S , Y _E ), and (X _E , Y _E ) on the XY plane. The optical axis adjustment procedure is shown below. Hereinafter, a case where a spiral scan is performed with this scanning range from the outer periphery toward the inner periphery will be exemplified.

[Step b1]
First, the movable part of the XY stage 3 is continuously scanned at a constant speed in the X direction from the coordinates (X _S , Y _S ) to (X _S , Y _E ) without stopping. That is, data is stored in the buffer memory 8a of the A / D converter 8 while performing analog measurement of light intensity simultaneously with scanning in the X direction. At this time, the position sensor 5 that measures the change in the position of the movable part in the X direction continuously outputs an analog voltage according to the amount of movement of the movable part, and the A / D is synchronized with the light intensity measurement data. It is stored in the buffer memory 8a of the converter 8. Here, in the case of wavelength division multiplexing (WDM), the light transmitted through the optical fiber 2 is demultiplexed for each wavelength by the demultiplexer 6, and the light intensity measurement data for each wavelength is simultaneously stored in the buffer memory 8a. Is done.

FIG. 4 is a graph showing an example of the relationship between the scanning position and the light intensity when a plurality of LD elements are mounted on the LD module 1. Here, an example in which four LD elements are mounted is shown. If the movable portion of an XY stage 3 is scanned from the start position X _S in the X direction to the end position X _E, the light intensity measurement data D1~D4 corresponding to four LD device can be obtained. From these data D1 to D4, it can be seen that the peak positions X1 to X4 and the peak height fluctuate due to fluctuations in the mounting position of the LD element.

[Step b2]
When the movable portion of the XY stage 3 reaches the end position X _E from the starting position X _S, it stops the operation of the XY stage 3.

[Step b3]
This time, the movable portion of the XY stage 3 is continuously scanned at a constant speed in the Y direction from the coordinates (X _E , Y _S ) to (X _E , Y _E ) without stopping. As in step b1, data is stored in the buffer memory 8a of the A / D converter 8 while analog measurement of light intensity is performed simultaneously with scanning in the Y direction. At this time, the position sensor 5 that measures the change in the position of the movable part in the Y direction continuously outputs an analog voltage according to the amount of movement of the movable part, and the A / D is synchronized with the light intensity measurement data. It is stored in the buffer memory 8a of the converter 8. When a plurality of LD elements are mounted on the LD module 1, light intensity measurement data for the number of elements is obtained.

[Step b4]
When the moving part of the XY stage 3 is reached from the start position Y _S in the end position Y _E, it stops the operation of the XY stage 3.

[Step b5]
Steps b1 to b4 are repeated until the XY coordinate position and the corresponding light intensity measurement data can be comprehensively acquired over the above scanning range. Accordingly, in the case of the spiral scan, as shown in FIG. 5A, the coordinates (X _E , Y _E ) → (X _S , Y _E ) → (X _S , Y _{S + 1} ) → (X _E−1) , Y _{S + 1} ) → (X _E−1 , Y _E−1 ) → (X _{S + 1} , Y _E−1 ) → (X _{S + 1} , Y _{S + 2} ) → (X _{S + 2} , Y _{E− 2} ) →. Scan. When a raster scan is performed instead, as shown in FIG. 5B, coordinates (X _S , Y _S ) → (X _E , Y _S ) → (X _E , Y _{S + 1} ) → (X _S , Scanning is performed as follows: Y _{S + 1} ) → (X _S , Y _{S + 2} ) → (X _E , Y _{S + 2} ) → (X _E , Y _{S + 3} ) → (X _S , Y _{S + 3} ) →.

  Here, when a piezo stage is used in the XY stage 3, since the optical axis adjustment range is smaller than the motor stage, a separate motor stage may be provided. If the specified amount of light intensity is not satisfied within the drive range of the piezo stage, the motor stage is driven by the drive range of the piezo stage and the optical axis is adjusted again from step 1a, so that the optical axis is adjusted over a wider range. Is possible.

[Step b6]
When the scanning of the predetermined range is completed, the calculation unit 9a of the computer 9 refers to the XY coordinate position stored in the storage unit 9b and the light intensity measurement data corresponding thereto, for example, the optimal coordinate position for optical axis adjustment, for example, The coordinate position where the maximum light intensity is obtained is searched.

[Step b7]
The movable part of the XY stage 3 is positioned so that the optimum coordinate position obtained in step b6 is obtained.

  Here, in the case of wavelength division multiplex communication (WDM), the light demultiplexed by the demultiplexer 6 is input to the A / D converter 8 as separate channels. Therefore, as shown in FIG. 4, it is possible to obtain the stage positions X1 to X4 at which the light intensity is maximum for each of the light intensity measurement data D1 to D4 corresponding to the four LD elements. Similarly, in the Y-direction scanning, it is possible to obtain the stage positions Y1 to Y4 at which the light intensity is maximum for every four LD elements.

  In this case, as a method for determining the optimum coordinate position for optical axis adjustment, a) an average value of positions X1 to X4 and an average value of positions Y1 to Y4, b) an XY position where the light intensity of each LD element is uniform, And so on.

  In the above description, the optical axis is adjusted in one Z plane (Z = Za), and the XY stage 3 is positioned so that the relative position between the LD module 1 and the optical fiber 2 is optimal.

  Subsequently, the Z stage 4 provided on the optical fiber 2 side is driven, and the optical axis adjustment described above is performed in the XY direction in a state where the Z stage 4 is changed to another Z plane (Z = Zb). The optimal position can be determined.

  Finally, when the optimum relative position between the LD module 1 and the optical fiber 2 is determined with respect to the X coordinate, the Y coordinate, and the Z coordinate, the LD module 1 and the optical fiber 2 are positioned in the optimum relative position. Fix to a common housing (not shown). As the fixing method, YAG laser welding, adhesion or the like is generally used.

  As described above, in the conventional method, since the drive stage is stopped every time the light intensity is measured, the optical axis adjustment time becomes long. On the other hand, in the present invention, the optical axis adjustment time can be greatly shortened by measuring the light intensity signal and the stage position signal in synchronization with each other while scanning without stopping the XY stage 3. .

  Further, the light transmitted through the optical fiber 2 is demultiplexed by the demultiplexer 6 and input to different channels of the A / D converter 8 to mount a plurality of LD elements in one module. Also in the integrated optical communication module, the optimum optical axis adjustment position for all LD elements can be obtained by one optical axis adjustment, and the number of optical axis adjustments can be reduced.

1 LD module, 2 optical fiber, 3 XY stage, 4 Z stage,
5 position sensor, 6 duplexer, 7 photodetector, 8 A / D converter,
8a buffer memory, 9 computer, 9a arithmetic unit, 9b storage unit.

Claims (5)

An optical axis adjusting device for adjusting an optical axis between an optical element module and an optical fiber,
A moving mechanism for controlling a relative position between the optical element module and the optical fiber;
A position sensor that outputs an analog position signal corresponding to the relative position;
A photodetector that outputs an analog light intensity signal corresponding to the intensity of light incident on the optical fiber from the optical element module;
An analog-to-digital converter that converts both the analog position signal and the analog light intensity signal into corresponding digital values in synchronization with each other;
A storage unit for storing digital values from the analog-digital converter;
An optical axis adjustment apparatus comprising: an arithmetic unit that searches for a relative position optimal for optical axis adjustment based on a digital value stored in the storage unit. In the optical element module, a plurality of light emitting elements having different emission wavelengths are mounted,
2. The optical axis adjusting device according to claim 1, further comprising: a demultiplexer that demultiplexes light transmitted through the optical fiber by wavelength and supplies the demultiplexed light to the photodetector provided for each wavelength. An optical axis adjustment method for adjusting an optical axis between an optical element module and an optical fiber,
An analog light intensity signal corresponding to the intensity of light incident on the optical fiber from the optical element module while continuously scanning the relative position between the optical element module and the optical fiber within a predetermined scanning range. And a continuous scanning step of converting both of the analog position signals corresponding to the relative positions into corresponding digital values in synchronization with each other and storing them in a storage unit,
And a search step for searching for the optimum relative position for optical axis adjustment based on the digital value stored in the storage unit. In the optical element module, a plurality of light emitting elements having different emission wavelengths are mounted,
4. The light according to claim 3, wherein, in the searching step, the light transmitted through the optical fiber is demultiplexed by wavelength using a demultiplexer, and the relative position where the maximum light intensity is obtained is searched for by wavelength. Axis adjustment method.   5. The optical axis adjustment according to claim 4, further comprising a step of positioning so that a relative position between the optical element module and the optical fiber becomes an average value of a maximum light intensity position for each wavelength. Method.

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