JP5644043B2 - Wavelength calibration device - Google Patents

Description

  The present invention relates to a wavelength calibration apparatus that performs wavelength calibration of an optical spectrum analyzer equipped with a spectrometer having a diffraction grating.

  In general, an optical spectrum analyzer is equipped with a spectrometer equipped with a diffraction grating. The output wavelength of the spectrometer is determined by the rotation angle of the diffraction grating, and the rotation angle of the diffraction grating is controlled by the controller of the optical spectrum analyzer. The Then, the control unit controls the rotation angle of the diffraction grating based on a table in which the set wavelength that is a desired output wavelength and the rotation angle of the diffraction grating are associated with each other.

By the way, in the optical spectrum analyzer, the groove spacing of the diffraction grating, the sandwich angle between the incident light and the outgoing light of the diffraction grating, and the mounting angle of the diffraction grating may slightly change due to a change in installation environment or an impact during movement. Yes, these changes cause measurement errors.
For this reason, wavelength calibration of an optical spectrum analyzer is performed when a certain period of time has elapsed or when an environmental change has occurred. Specifically, the wavelength calibration of the optical spectrum analyzer is performed by setting the rotation angle of the diffraction grating again with respect to the set wavelength.

A wavelength calibration method for a conventional optical spectrum analyzer will be described below.
First, the wavelength of the emitted light from the spectroscope mounted on the optical spectrum analyzer is given by the following equation (1).
In the following formula (1), m is the diffraction order, λ is the wavelength of the outgoing light (output wavelength of the spectrometer), d is the groove spacing of the diffraction grating, θa is the angle between the incident light and the outgoing light, and θ is The angle formed between the normal line of the diffraction grating and the bisector of the incident light and the outgoing light (that is, the rotation angle of the diffraction grating) is shown.

The groove interval d of the diffraction grating may change due to thermal expansion and contraction of the diffraction grating, for example. Further, the sandwiching angle θa may change when, for example, the position of the entrance slit, exit slit, or other optical component is shifted. Further, the rotation angle θ of the diffraction grating may change, for example, when the mounting angle with respect to the rotation axis of the diffraction grating is shifted. These changes cause measurement errors.
That is, in the above equation (1), the groove interval d of the diffraction grating, the sandwiching angle θa, and the rotation angle θ may include error factors.
The rotation angle θi of the diffraction grating for outputting the set wavelength λi from the spectrometer is expressed as the following equation (2) based on the above equation (1).

Here, considering the above error factors, the above equation (2) becomes the following equation (3).
In the following equation (3), θei represents a rotation angle error caused by the error factor, θofs is a change amount of the rotation angle θ of the diffraction grating, Δd is a change amount of the groove interval d of the diffraction grating, and Δθa is a sandwich angle. The amount of change of θa is shown.

  In the wavelength calibration of the conventional optical spectrum analyzer, the reference light is incident on the spectroscope from a physically stable reference wavelength light source, and the diffraction grating when the wavelength λ of the emitted light becomes the calibration wavelength λref included in the reference light The rotation angle θ of is acquired.

In the spectroscope, when the change amount θofs of the rotation angle θ of the diffraction grating, the change amount Δd of the groove interval d of the diffraction grating, and the change amount Δθa of the sandwiching angle θa are zero, that is, when no error factor is included. The rotation angle θ of the diffraction grating when the wavelength λ of the emitted light is the calibration wavelength λref included in the reference light is the rotation angle θref stored in the table in advance.
However, when an error factor is included, the rotation angle θ of the diffraction grating when the wavelength of the emitted light is the calibration wavelength λref is not the rotation angle θref but a different value θm.

  Then, as shown in the following equation (4), the rotation angle error θcal can be calculated from the rotation angle θm and the rotation angle θref.

  In the wavelength calibration of the conventional optical spectrum analyzer, the table is calibrated using the rotation angle error θcal calculated as described above as a calibration value.

Since wavelength calibration of such a conventional optical spectrum analyzer is performed based on a physically stable reference wavelength light source, highly accurate wavelength calibration can be realized.
JP 2001-208607 A

By the way, the above-mentioned rotation angle θm is the rotation angle (θi + θei) of the diffraction grating including the rotation angle error caused by all error factors, and corresponds to the right side of the above equation (3). As can be seen from Equation (3), the term including the change amount Δd of the groove interval d of the diffraction grating and the change amount Δθa of the sandwiching angle θa is a function of the set wavelength λi. That is, the rotation angle θm changes depending on the set wavelength λi.
Therefore, in the wavelength calibration method of the conventional optical spectrum analyzer, when the set wavelength λi is the calibration wavelength, or when the change amount Δd of the groove interval d of the diffraction grating and the change amount Δθa of the sandwiching angle θa are zero, the wavelength is accurate. Calibration can be performed, but accurate wavelength calibration cannot be performed when the set wavelength λi is not the calibration wavelength but there is a variation Δd of the groove interval d of the diffraction grating or a variation Δθa of the sandwiching angle θa.

Accurate wavelength calibration at all set wavelengths λi is performed by a method of accurately measuring the change Δd of the groove interval d of the diffraction grating or the change Δθa of the sandwiching angle θa, or the wavelength measurement range of the optical spectrum analyzer (that is, the set wavelength range). ) Can be realized by adopting a method using reference wavelength light sources of different wavelengths so as to cover all of the above.
However, either method is difficult to adopt in an actual use site and is not realistic.

  The present invention has been made in view of the above-described problems, and an object thereof is to accurately perform wavelength calibration for all set wavelengths of an optical spectrum analyzer with a single wavelength reference light source.

The present invention adopts the following configuration as means for solving the above-described problems.
A first invention is a wavelength calibration device that performs wavelength calibration of an optical spectrum analyzer equipped with a spectrometer including a diffraction grating, and a reference wavelength light source that makes reference light including a calibration wavelength λref incident on the spectrometer; A design for storing a design value including a rotation angle of the diffraction grating and an output wavelength at the rotation angle at which an incident angle of the reference light with respect to the diffraction grating is equal to an emission angle of light emitted from the spectrometer with respect to the diffraction grating Based on a value storage means, a table in which a plurality of set wavelengths and rotation angles of the diffraction grating with respect to each set wavelength are associated, an actual measurement value obtained by making the reference light incident on the spectrometer, and the design value Calculating means for calculating a calibration value, and calibration means for calibrating the table based on the calibration value. And the rotation angle of the diffraction grating when the calibration value is Shitaei, measured wavelength matches with the output wavelength rotation angle of the diffraction grating in the case of matching the calibration wavelengths λref is to .theta.m, the measured wavelength is included in the design value against The rotation angle error that is the difference from the rotation angle of the diffraction grating included in the design value is θcal0, the setting wavelength that is the calculation target of the calibration value is λi, and the rotation angle of the diffraction grating that is associated with the setting wavelength λi. Is employed, and a calibration value for each of the set wavelengths is calculated using the following equation (5) where θi is the diffraction order and m is the diffraction order .

A second invention is a wavelength calibration device that performs wavelength calibration of an optical spectrum analyzer equipped with a spectrometer including a diffraction grating, and a reference wavelength light source that makes reference light including a calibration wavelength λref incident on the spectrometer; A design for storing a design value including a rotation angle of the diffraction grating and an output wavelength at the rotation angle at which an incident angle of the reference light with respect to the diffraction grating is equal to an emission angle of light emitted from the spectrometer with respect to the diffraction grating Based on a value storage means, a table in which a plurality of set wavelengths and rotation angles of the diffraction grating with respect to each set wavelength are associated, an actual measurement value obtained by making the reference light incident on the spectrometer, and the design value Calculating means for calculating a calibration value, and calibration means for calibrating the table based on the calibration value. When the difference between the rotation angle of the diffraction grating when it matches the output wavelength included in the measured value and the rotation angle of the diffraction grating included in the design value is zero, the calibration value for each of the set wavelengths is θei. When the measured wavelength coincides with the calibration wavelength λref , the rotation angle of the diffraction grating is θm, the set wavelength to be calculated for the calibration value is λi, and the rotation angle of the diffraction grating associated with the set wavelength λi Is employed, and a calibration value for each of the above set wavelengths is calculated using the following equation (6) where θi is the diffraction order and m is the diffraction order .

  According to the present invention, by using the rotation angle of the diffraction grating in which the incident angle of the reference light with respect to the diffraction grating and the emission angle of the emitted light with respect to the diffraction grating are equal and the output wavelength of the spectrometer at the rotation angle, Calibration values for all set wavelengths can be calculated only with values that can be measured using one wavelength reference light source. Therefore, it is possible to accurately perform wavelength calibration for all set wavelengths of the optical spectrum analyzer with a single wavelength reference light source.

First, the concept of wavelength calibration of the optical spectrum analyzer in the wavelength calibration apparatus according to the present invention will be described.
FIG. 1 is a schematic diagram showing the configuration of the spectrometer 1. As shown in this figure, the spectroscope 1 includes a diffraction grating 1a that diffracts and emits incident light, an entrance slit 1b that defines the incident direction of the incident light La, and an exit slit that defines the exit direction of the emitted light Lb. 1c.
In the following description, the angle formed by the normal H of the diffraction grating 1a and the bisector N of the incident light La and the outgoing light Lb (that is, the rotation angle of the diffraction grating) is defined as the rotation angle θ, and the incident light. An angle between La and the emitted light Lb is defined as an angle θa.
The incident angle is an angle formed by the normal H of the diffraction grating 1a and the incident light La. The exit angle is an angle formed by the normal H of the diffraction grating 1a and the exit light Lb.

  As shown in FIG. 2, when the diffraction grating 1a is set to a rotation angle θref0 in which the incident angle θLa of the incident light La with respect to the diffraction grating 1a and the emission angle θLb of the emitted light Lb with respect to the diffraction grating 1a are equal. The emitted light Lb becomes 0th order diffracted light. The 0th-order diffracted light is a case where the diffraction order m in the above equation (1) is zero and is not a spectral spectrum. The wavelength of the 0th-order diffracted light is a value uniquely determined depending on the wavelength of the incident light La, and is used as one of the calibration wavelengths in the present invention. Therefore, in the following description, the wavelength of the 0th-order diffracted light is assumed to be the 0th-order calibration wavelength λref0.

In such a spectroscope 1, when the above-mentioned change amount θofs of the diffraction grating θ, the change amount Δd of the groove interval d of the diffraction grating, and the change amount Δθa of the sandwiching angle θa are zero, that is, an error factor. If the wavelength of the emitted light Lb is zero-order calibration wavelength λref0, the rotation angle θ of the diffraction grating 1a is zero. That is, the rotation angle θref0 is zero.
However, when an error factor is included, the rotation angle θ of the diffraction grating 1a does not become zero when the wavelength of the emitted light Lb is the 0th-order calibration wavelength λref0.
As described above, when the rotation angle θ of the diffraction grating 1a does not become zero but becomes θm0 when the wavelength of the emitted light Lb is the 0th-order calibration wavelength λref0, all the error factors are calculated using the rotation angle θm0. The included rotation angle error θcal0 can be calculated by the following equation (7).

  Further, when the wavelength of the emitted light Lb is the 0th-order calibration wavelength λref0, the rotation angle (θref0 + θref0_e) of the diffraction grating 1a including the rotation angle error θref0_e caused by all error factors is expressed by the above equation (3). And can be calculated by the following equation (8).

  Here, since the diffraction order m and the rotation angle θref0 included in the equation (8) are zero, the equation (8) becomes the following equation (9).

  Note that the rotation angle error θcal0 calculated by the equation (7) is equal to the rotation angle error θref0_e. For this reason, the following formula (10) holds.

  On the other hand, when the reference light including the calibration wavelength λref is incident on the spectroscope 1 as the incident light La and the wavelength of the outgoing light Lb is the calibration wavelength λref, the diffraction including the rotation angle error θref_e caused by all error factors. The rotation angle (θref + θref_e) of the grating 1a can be calculated by the following equation (11) using the above equation (3). The rotation angle θref is the rotation angle of the diffraction grating 1a where the wavelength of the emitted light Lb is the calibration wavelength λref when no error factor is included.

  Therefore, the following equation (12) is obtained by substituting the above equation (10) into the above equation (11).

  Since the left side in the above equation (12) is a constant, it is set to K. The rotation angle (θref + θref_e) is the same as the rotation angle θm of the diffraction grating 1a when the wavelength of the emitted light Lb is the calibration wavelength λref. For this reason, the above equation (12) becomes the following equation (13).

Since the rotation angle θm, the rotation angle error θcal0, the diffraction order m, and the calibration wavelength λref included in the above equation (13) are known or obtained by measurement, the groove interval d of the diffraction grating is obtained by using the above equation (13). The first term on the right side of the above equation (3) can be obtained without requiring the change amount Δd and the change amount Δθa of the sandwiching angle θa. Further, the second term on the right side of the above equation (3) can be obtained from the above equation (10) as a rotation angle error θcal0 by measurement.
Therefore, based on the above equation (3), the above equation (10), and the above equation (13), the rotation angle error θei at each set wavelength λi can be calculated from a known value or a value obtained by measurement.
Therefore, by using the rotation angle error θei as a calibration value for each set wavelength λi, the rotation angle θi of the diffraction grating 1a for all the set wavelengths λi can be accurately revalued.
The rotation angle θm, the rotation angle error θcal0, the diffraction order m, and the calibration wavelength λref can be acquired using the reference light as the incident light La. For this reason, it becomes possible to accurately revalue the rotation angle θi of the diffraction grating 1a with respect to all the set wavelengths λi using only a single reference light.
When the above formula (3), the above formula (10), and the above formula (13) are put together, the above formula (5) for calculating the rotation angle error θei at each set wavelength λi is obtained.

  If the rotation angle error θcal0 (that is, the difference between the rotation angle θm0 of the diffraction grating 1a and the rotation angle θref0 when the wavelength of the emitted light Lb coincides with the zeroth-order calibration wavelength λref0) is zero, Expression (5) can be changed to the above expression (6).

  Therefore, when the rotation angle error θcal0 is zero, the rotation angle error θei at each set wavelength λi can be calculated using the above equation (6).

Next, an embodiment of a wavelength calibration apparatus according to the present invention will be described.
FIG. 3 is a functional block diagram showing the optical spectrum analyzer 10 and the wavelength calibration device 20 of the present embodiment.
As shown in this figure, the optical spectrum analyzer 10 includes a spectrometer 11, a table storage unit 12, a motor control unit 13, and a wavelength measurement unit 14.
Further, the wavelength calibration device 20 of the present embodiment includes a wavelength reference light source 21, a design value storage unit 22 (design value storage unit), a calculation data storage unit 23, a program storage unit 24, and a calculation unit 25 (calculation unit). ) And a wavelength calibration control unit 26 (calibration means).
In FIG. 3, the optical spectrum analyzer 10 and the wavelength calibration device 20 are illustrated as separate bodies, but actually, the table storage unit 12, the design value storage unit 22, the calculation data storage unit 23, and the program storage The unit 24 is embodied by a storage device as hardware included in the optical spectrum analyzer 10 such as a hard disk drive, RAM, and ROM. Further, the motor control unit 13, the calculation unit 25, and the wavelength calibration control unit 26 are embodied by an arithmetic processing device as hardware included in the optical spectrum analyzer 10 such as a CPU.

  Similar to the spectrometer 1 shown in FIG. 1, the spectrometer 11 includes a diffraction grating 11a, an entrance slit (not shown in FIG. 3), and an exit slit (not shown in FIG. 3). In addition to the above configuration, the spectroscope 11 includes a motor 11b for rotating the diffraction grating 11a. For example, a stepping motor can be used as the motor 11b.

The table storage unit 12 stores a table in which a plurality of set wavelengths λi and rotation angles θi of the diffraction grating 11a at the set wavelengths λi are associated with each other.
The table stored in the table storage unit 12 can be rewritten by the wavelength calibration control unit 26 of the wavelength calibration device 20.

The motor control unit 13 controls the rotation angle of the diffraction grating 11a connected to the motor 11b by controlling the motor 11b.
The motor control unit 13 refers to the table stored in the table storage unit 12 so that the set wavelength instructed from an input device (not shown) becomes the output wavelength of the spectroscope 11, and the rotation angle of the diffraction grating 11a. To control.
Further, the motor control unit 13 controls the rotation angle of the diffraction grating 11 a based on an instruction from the wavelength calibration control unit 26 of the wavelength calibration device 20.

The wavelength measuring unit 14 measures the wavelength (output wavelength) of the emitted light emitted from the spectroscope 11, and includes a photodetector, an amplifier, an A / D converter, and the like.
The wavelength measurement unit 14 inputs the measurement result to the wavelength calibration control unit 26 of the wavelength calibration device 20. The wavelength measuring unit 14 inputs the measurement result to a display unit (not shown) that visualizes the received signal.

The wavelength reference light source 21 emits the reference light L including the calibration wavelength λref and enters the spectroscope 11 of the optical spectrum analyzer 10.
As the wavelength reference light source 21, for example, a laser light source in which acetylene gas having an absorption wavelength band at 1.53 μm which is physically stable is sealed can be used.

The design value storage unit 22 includes the rotation angle θref0 of the diffraction grating 11a at which the incident angle of the reference light L incident on the diffraction grating 11a and the emitted light from the spectroscope 11 are equal, and the rotation angle θref0 without including an error factor. The wavelength λref0 (output wavelength) of the emitted light when the reference light L is incident on the diffraction grating 11a is stored as a design value.
When the diffraction grating 11a is set to the rotation angle θref0, the emitted light from the spectroscope 11 becomes the 0th-order diffracted light of the reference light L. That is, the wavelength λref0 of the emitted light is the wavelength of the 0th-order diffracted light of the reference light L. The design value storage unit 22 stores the wavelength λref0 as the zero-order calibration wavelength λref0.
Further, the design value storage unit 22 stores the calibration wavelength λref included in the reference light L and the rotation angle θref of the diffraction grating 11a at which the calibration wavelength λref is the wavelength of the emitted light without including an error factor.

The arithmetic data storage unit 23 stores various arithmetic expressions and various parameters used for calculating a calibration value for calibrating the table stored in the table storage unit 12.
The calculation data storage unit 23 stores the above formula (5) and the above formula (6) as the above calculation formula.
In the wavelength calibration device 20 of the present embodiment, in the above equation (5), θei is a calibration value for each set wavelength λi, θm is the rotation angle of the diffraction grating 11a when the measured wavelength and the calibration wavelength λref match, A rotation angle error, θi, which is a difference between the rotation angle θm0 of the diffraction grating and the rotation angle θref0 of the diffraction grating 11a when θcal0 matches the actual measurement wavelength measured by the wavelength measuring unit 14 with the 0th-order calibration wavelength λref0 is set. The rotation angle of the diffraction grating 11a associated with the wavelength λi is shown.
In the wavelength calibration device 20 of the present embodiment, in the above equation (6), θei is a calibration value for each set wavelength λi, θm is the rotation angle of the diffraction grating 11a when the actually measured wavelength and the calibration wavelength λref match, θi represents the rotation angle of the diffraction grating 11a associated with the set wavelength λi.
In addition, the calculation data storage unit 23 measures the diffraction order m of the set wavelength λi (7) for calculating the rotation angle error θcal0 (usually, the wavelength measurement unit 14 measures the first-order diffracted light having the strongest light output). Therefore, the diffraction order m is 1).

  The program storage unit 24 stores a program indicating the operation procedure of the calculation unit 25 and the wavelength calibration control unit 26 and is accessible from the calculation unit 25 and the wavelength calibration control unit 26.

The calculation unit 25 stores the table, the actual measurement value obtained by making the reference light L incident on the spectrometer 11, and the design value (the rotation angle θref0 and the 0th-order calibration wavelength λref0), and the calculation data storage unit 23. The calibration value θei for each set wavelength λi is calculated based on the arithmetic expression and parameters.
As will be described in detail later in the description of the wavelength calibration method, in the wavelength calibration device 20 of this embodiment, the calculation unit 25 uses the rotation angle of the diffraction grating 11a when the measured wavelength coincides with the calibration wavelength λref as the measured value. θm and the rotation angle θm0 of the diffraction grating 11a when the actually measured wavelength coincides with the 0th-order calibration wavelength λref0 are used.

  Based on the program stored in the program storage unit 24, the wavelength calibration control unit 26 acquires the measurement result of the wavelength measurement unit 14, inputs a command to the motor control unit 13, and calibrates the table stored in the table storage unit 12. And various data necessary for calculation are input to the calculation unit 25.

  Next, the operation of the wavelength calibration apparatus 20 of the present embodiment configured as described above, that is, the wavelength calibration method of the optical spectrum analyzer 10 will be described with reference to the flowchart of FIG.

First, the reference light L is incident on the spectroscope 11 from the wavelength reference light source 21 (step S1).
Subsequently, the wavelength calibration control unit 26 matches the measurement result (that is, the actually measured wavelength) of the wavelength measurement unit 14 with the calibration wavelength λref stored in the design value storage unit 22 (step S2).
Specifically, the wavelength calibration control unit 26 constantly monitors the measurement result of the wavelength measurement unit 14 and drives the motor 11b until the diffraction grating 11a is driven until the measurement result of the wavelength measurement unit 14 reaches the calibration wavelength λref. A command is sent to the motor control unit 13 to rotate.

Subsequently, the wavelength calibration control unit 26 acquires the rotation angle θm of the diffraction grating 11a in a state where the measurement result of the wavelength measurement unit 14 becomes the calibration wavelength λref in step S2 (step S3).
Specifically, the wavelength calibration control unit 26 acquires the control value of the motor 11b from the motor control unit 13 in a state where the measurement result of the wavelength measurement unit 14 becomes the calibration wavelength λref in step S2, and sets the control value to the control value. Based on this, the rotation angle θm is acquired as an actual measurement value.

Subsequently, the wavelength calibration control unit 26 adjusts the measurement result (that is, the actually measured wavelength) of the wavelength measurement unit 14 to the 0th-order calibration wavelength λref0 stored as the design value in the design value storage unit 22 (step S4).
Specifically, the wavelength calibration control unit 26 constantly monitors the measurement result of the wavelength measurement unit 14 and drives the motor 11b until the measurement result of the wavelength measurement unit 14 reaches the 0th-order calibration wavelength λref0 to drive the diffraction grating. A command is sent to the motor controller 13 so that 11a rotates.

Subsequently, the wavelength calibration control unit 26 acquires the rotation angle θm0 of the diffraction grating 11a in the state where the measurement result of the wavelength measurement unit 14 becomes the 0th-order calibration wavelength λref0 in step S4 (step S5).
Specifically, the wavelength calibration control unit 26 acquires the control value of the motor 11b from the motor control unit 13 in a state where the measurement result of the wavelength measurement unit 14 becomes the 0th-order calibration wavelength λref0 in step S4, and the control The rotation angle θm0 is acquired as an actual measurement value based on the value.

Subsequently, the wavelength calibration control unit 26 calculates the rotation angle error θcal0 by the calculation unit 25 (step S6).
Specifically, under the control of the wavelength calibration control unit 26, the calculation unit 25 adds the rotation angle θm0 acquired in step S5 and the design value storage to the above equation (7) stored in the calculation data storage unit 23. The rotation angle error θcal0 is calculated by substituting the rotation angle θref0 stored as the design value in the unit 22.

Subsequently, the wavelength calibration control unit 26 stores the rotation angle θm0 acquired in step S5 (the rotation angle of the diffraction grating 11a when the measured wavelength coincides with the 0th-order calibration wavelength λref0 included in the design value) and the design value. It is determined whether the difference from the rotation angle θref0 is zero (step S7).
Specifically, the wavelength calibration control unit 26 performs the above determination based on whether or not the calculation result in step S6 is zero.

When the difference in step S7 is not zero, the wavelength calibration control unit 26 calculates the calibration values θei of all the set wavelengths λi using the above equation (5) by the calculation unit 25 (step S8).
Specifically, under the control of the wavelength calibration control unit 26, the calculation unit 25 sets the set wavelength λi that is a calculation target of the calibration value θei and the set wavelength λi from the table stored in the table storage unit 12. The associated rotation angle θi is acquired and substituted into the above equation (5). Further, the calculation unit 25 controls the rotation angle θm acquired in step S3, the rotation angle θcal0 calculated in step S6, and the calibration wavelength stored in the design value storage unit 22 under the control of the wavelength calibration control unit 26. Substituting λref and the diffraction order m into the above equation (5). Subsequently, the calculation unit 25 calculates the calibration value θei by solving the above equation (5) for the calibration value θei under the control of the wavelength calibration control unit 26. Then, the calculation unit 25 calculates the calibration values θei for all the set wavelengths λi under the control of the wavelength calibration control unit 6.

Wavelength calibration controller 26 if the difference in step S7 was zero, by the calculating unit 25 calculates the calibration value θei of all the set wavelength λi using the above equation (6) (step S9).
Specifically, under the control of the wavelength calibration control unit 26, the calculation unit 25 sets the set wavelength λi that is a calculation target of the calibration value θei and the set wavelength λi from the table stored in the table storage unit 12. The associated rotation angle θi is acquired and substituted into the above equation (6) . In addition, the calculation unit 25 calculates the rotation angle θm acquired in step S3, the calibration wavelength λref and the diffraction order m stored in the design value storage unit 22 under the control of the wavelength calibration control unit 26, using the above equation (6). Assign to. Subsequently, the calculation unit 25 calculates the calibration value θei by solving the above equation (6) for the calibration value θei under the control of the wavelength calibration control unit 26. Then, the calculation unit 25 calculates the calibration values θei for all the set wavelengths λi under the control of the wavelength calibration control unit 6.

Subsequently, the wavelength calibration control unit 26 calibrates the table stored in the table storage unit 12 using the calibration value θei calculated in step S8 or the calibration value θei calculated in step S9 (step S10). .
Specifically, the wavelength calibration control unit 26 calibrates the table by adding or subtracting the calibration value θei to the rotation angle θi associated with each set wavelength λi in the table to revalue the rotation angle θi. I do.

According to the wavelength calibration device 20 of the present embodiment as described above, the rotation angle of the diffraction grating 11a from which the 0th-order calibration wavelength λref0 stored as a design value and the 0th-order calibration wavelength λref0 can be obtained when no error factor is included. Similarly, by using the rotation angle θref0 stored as a design value, it is possible to calculate calibration values θei for all set wavelengths λi using only a value that can be measured using a known or single wavelength reference light source. it can.
Therefore, according to the wavelength calibration device 20 of the present embodiment, it is possible to accurately perform wavelength calibration for all set wavelengths of the optical spectrum analyzer with a single wavelength reference light source.

In the wavelength calibration device 20 of the present embodiment, in step S7, the rotation angle θm0 of the diffraction grating 11a when the actually measured wavelength coincides with the 0th-order calibration wavelength λref0 included in the design value, and the rotation stored as the design value. When the difference from the angle θref0 is zero, the calibration value θei is calculated using the above equation (6) obtained by removing θcal0 as a parameter from the above equation (5).
Therefore, the calculation load of the calculation unit 25 when the difference in step S7 is zero can be reduced, and the calculation load in the entire wavelength calibration apparatus 20 of the present embodiment can be reduced.

Next, an example of the wavelength calibration device 20 of the present embodiment will be described with reference to FIGS.
In this example, the result of performing wavelength calibration of the optical spectrum analyzer by the above-described conventional wavelength calibration method and the result of performing wavelength calibration of the optical spectrum analyzer using the wavelength calibration device 20 of the present embodiment. Compared.
FIG. 5 is a graph (solid line) showing the result of wavelength calibration of the optical spectrum analyzer using the conventional wavelength calibration method, and FIG. 6 is a wavelength calibration of the optical spectrum analyzer using the wavelength calibration device 20 of the present embodiment. The result of having been shown by a graph (solid line). In addition, the graph shown with a broken line in FIG.5 and FIG.6 shows the state before calibration.

In order to obtain the result of this example, the groove interval d of the diffraction grating is 0.00111111 mm, the sandwiching angle θa is 20 °, the change Δd of the groove interval d of the diffraction grating is 6.1 × 10 ⁻⁸ mm, The change amount Δθa of the sandwiching angle θa was set to 0.2 °, the change amount θofs of the rotation angle θ was set to 0.005 °, the set wavelength λi was set to 600 nm to 1800 nm, the calibration wavelength was set to 1400 nm, and the diffraction order m was set to 1. At this time, the rotation angle θm was 39.78826 ° and θcal0 was 0.005 °.

When the wavelength calibration of the optical spectrum analyzer is performed by the conventional wavelength calibration method as shown in FIG. 5, the rotation angle error becomes zero only at the calibration wavelength of 1400 nm, and this embodiment is performed as shown in FIG. When the wavelength calibration of the optical spectrum analyzer using the embodiment of the wavelength calibration device 20 was performed, the rotation angle error became zero at all set wavelengths.
Thus, according to the wavelength calibration device 20 of the present embodiment, wavelength calibration can be performed accurately at all set wavelengths.

  The preferred embodiments of the wavelength calibration apparatus according to the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to the above embodiments. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

For example, in the above embodiment, the rotation angle θm of the diffraction grating 11a when the measured wavelength matches the calibration wavelength λref and the rotation angle θm0 of the diffraction grating 11a when the measured wavelength matches the zeroth-order calibration wavelength λref0. The calibration value θei was used to calculate the calibration value.
However, the present invention is not limited to this. Instead of the rotation angle θm and the rotation angle θm0, the wavelength when the rotation angle of the diffraction grating 11a coincides with the rotation angle θref, and the rotation angle of the diffraction grating 11a. It is also possible to calculate the calibration value θei by using the wavelength when is coincident with the rotation angle θre0.

In the above embodiment, the configuration has been described on the assumption that the calibration wavelength λref and the set wavelength λi are first-order diffracted light in the wavelength measurement unit 14.
However, the present invention is not limited to this, and the calibration wavelength λref and the set wavelength λi may be higher-order diffracted light.

In the above embodiment, the design value storage unit 22 stores the calibration wavelength λref and the rotation angle θref associated with the calibration wavelength, and the calculation unit 25 stores the calibration wavelength λref and rotation stored in the design value storage unit 22. A configuration in which the calibration value θei is calculated using the angle θref is adopted.
However, the present invention is not limited to this. The calibration wavelength λref and the rotation angle θref are acquired from the table stored in the table storage unit 12, and the calculation unit uses the acquired calibration wavelength λref and the rotation angle θref. 25 may calculate the calibration value θei.

It is a schematic diagram of the spectrometer for demonstrating rotation angle (theta) and sandwiching angle (theta) a. It is a schematic diagram of the spectrometer for showing a mode that the incident angle of the incident light in a diffraction grating and the output angle of the emitted light become equal. It is a functional block diagram which shows the wavelength calibration apparatus and optical spectrum analyzer which are one Embodiment of this invention. It is a flowchart for demonstrating the wavelength calibration method using the wavelength calibration apparatus which is one Embodiment of this invention. It is a figure which shows the result of having performed wavelength calibration of the optical spectrum analyzer by the conventional wavelength calibration method in a graph. It is a figure which shows the result of having performed wavelength calibration of the optical spectrum analyzer using the wavelength calibration apparatus which is one Embodiment of this invention with a graph.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical spectrum analyzer, 11 ... Spectroscope, 11a ... Diffraction grating, 20 ... Wavelength calibration apparatus, 21 ... Wavelength reference light source, 22 ... Design value memory | storage part (design value memory | storage means), 25 ... Calculation unit (calculation unit), 26 ....... Wavelength calibration control unit (calibration unit)

Claims (2)

A wavelength calibration device for performing wavelength calibration of an optical spectrum analyzer equipped with a spectrometer equipped with a diffraction grating,
A reference wavelength light source for inputting a reference light including a calibration wavelength λref to the spectroscope;
A design for storing a design value including a rotation angle of the diffraction grating and an output wavelength at the rotation angle at which an incident angle of the reference light with respect to the diffraction grating is equal to an emission angle of light emitted from the spectrometer with respect to the diffraction grating. Value storage means;
A calibration value is calculated based on a table in which a plurality of set wavelengths and rotation angles of the diffraction grating with respect to each set wavelength are associated, an actual measurement value obtained by making the reference light incident on the spectrometer, and the design value Calculating means for
Calibration means for calibrating the table based on the calibration value;
With
The calculation means has a calibration value for each set wavelength of θei, a rotation angle of the diffraction grating when the measured wavelength matches the calibration wavelength λref , and the measured wavelength matches the output wavelength included in the design value. In this case, the rotation angle error that is the difference between the rotation angle of the diffraction grating and the rotation angle of the diffraction grating included in the design value is θcal0, the set wavelength that is the calculation target of the calibration value is λi, and the set wavelength λi. A wavelength calibration apparatus, wherein a calibration value for each set wavelength is calculated using the following equation (1) in which the rotation angle of the associated diffraction grating is θi and the diffraction order is m .

A wavelength calibration device for performing wavelength calibration of an optical spectrum analyzer equipped with a spectrometer equipped with a diffraction grating,
A reference wavelength light source for inputting a reference light including a calibration wavelength λref to the spectroscope;
A design for storing a design value including a rotation angle of the diffraction grating and an output wavelength at the rotation angle at which an incident angle of the reference light with respect to the diffraction grating is equal to an emission angle of light emitted from the spectrometer with respect to the diffraction grating. Value storage means;
A calibration value is calculated based on a table in which a plurality of set wavelengths and rotation angles of the diffraction grating with respect to each set wavelength are associated, an actual measurement value obtained by making the reference light incident on the spectrometer, and the design value Calculating means for
Calibration means for calibrating the table based on the calibration value;
With
When the difference between the rotation angle of the diffraction grating when the actually measured wavelength matches the output wavelength included in the design value and the rotation angle of the diffraction grating included in the design value is zero, When the calibration value for each set wavelength is θei, the rotation angle of the diffraction grating when the measured wavelength is coincident with the calibration wavelength λref is θm, the set wavelength for which the calibration value is calculated is λi, and the set wavelength λi. 3. The wavelength calibration apparatus according to claim 2, wherein a calibration value for each set wavelength is calculated using the following equation (2) in which the rotation angle of the associated diffraction grating is θi and the diffraction order is m . .

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