JP4320718B2 - WDM signal monitor - Google Patents

Description

  The present invention relates to a WDM (wavelength division multiplexing) signal monitor using a wavelength dispersion element, and more particularly to a WDM signal monitor capable of improving the accuracy of wavelength measurement without being affected by the use environment. It is.

  The WDM signal monitor emits light to be measured, which is a WDM signal, at different angles for each wavelength by a wavelength dispersive element and separates the light, and the light to be measured dispersed by the wavelength dispersive element is received and detected by a photodetector. The wavelength of the optical signal is measured by the output from the photodetector (see, for example, Patent Document 1).

  FIG. 4 is a block diagram showing a conventional example of such a WDM signal monitor. In FIG. 4, the spectroscope 10 receives measurement light, measures the spectrum of the measurement light, and outputs measurement data that is sampling data. The spectroscope 10 includes an optical fiber 11, a collimating lens 12, a diffraction grating 13, a focusing lens 14, and a photodiode array module 15.

  The optical fiber 11 is a transmission line having an emission port that emits light to be measured. The collimating lens 12 is installed to face the exit of the optical fiber 11 and emits the light to be measured emitted from the optical fiber 11 as parallel light.

  The diffraction grating 13 is a wavelength dispersion element, and is inclined with respect to the collimating lens 12 in order to diffract the emitted light from the collimating lens 12 to a desired angle. Further, the diffraction grating 13 emits the light to be measured at a different angle for each wavelength and separates it. The focusing lens 14 is installed on the optical path of the outgoing light from the diffraction grating 13, and converges the outgoing light to form an image.

  A photodiode array module (hereinafter abbreviated as PDM) 15 is a photodetector having a plurality of photodiodes as light receiving elements, and is installed at a position where the light to be measured converges and forms an image. The PDM 15 samples the optical power of the light to be measured by the light receiving element, and outputs the sampling data as measurement data. The PDM 15 is assigned a wavelength in advance for each light receiving element.

  The memory 20 is a storage unit and stores measurement data from the spectrometer 10. The wavelength calculation unit 30 reads the measurement data in the memory 20 and calculates the wavelength of the optical signal from the wavelength assigned to each light receiving element of the PDM 15.

  The operation of such an apparatus will be described. The light to be measured emitted from the optical fiber 11 becomes parallel light by the collimating lens 12. The light to be measured that has passed through the collimating lens 12 enters the diffraction grating 13. Then, the light to be measured is split by the diffraction grating 13 for each wavelength. In other words, the emission angle from the diffraction grating 13 differs for each wavelength. Then, the light to be measured dispersed by the diffraction grating 13 for each wavelength is converged by the focusing lens 14 at each light receiving element of the PDM 15 to form an image.

  For example, in the light receiving elements located at “FP01”, “FP02”, and “FP03” in FIG. 4, light of different wavelengths is converged and imaged. And each light receiving element of PDM15 outputs the electric current (photocurrent) corresponding to the optical power of each to-be-measured light. In addition, the PDM 15 converts the photocurrent output from each light receiving element into a voltage by a converter (not shown). Further, since the signal converted into the voltage is an analog signal, the conversion unit converts the analog signal into a digital signal and stores it in the memory 20 as measurement data. Thus, the measurement data is sampling data sampled by the light receiving element.

  Then, the wavelength calculation means 30 reads the measurement data of the memory 20, obtains the wavelength of the optical signal from the wavelength assigned to each light receiving element, and outputs these calculation results to an output unit (not shown). For example, the calculation result is displayed on the screen of the display unit or output to an external device (not shown).

Subsequently, the relationship between the incident angle and the outgoing angle of the light to be measured by the diffraction grating 13 will be described. The incident angle and the emission angle of the light to be measured by the diffraction grating 13 sinθ _gi + sinθ _go = λ _/ represented by the following formula (1) (n a · d ) (1)

Here, θ _gi is the incident angle of the light to be measured to the diffraction grating 13. θ _go is the emission angle of the light to be measured from the diffraction grating 13. λ is a wavelength. n _a is the refractive index of the medium of the environment in which the diffraction grating 13 is used (generally air), d is the lattice constant of the diffraction grating 13.

Further, the relationship between the change in wavelength and the change in emission angle is expressed by the following equation (2) from the equation (1).
Δλ / Δθ _go = n _a · d · cos θ _go (2)

  As described above, even when the light to be measured is superimposed with the optical signals having a plurality of wavelengths, the diffraction grating 13 emits at different angles for each wavelength, and the light to be measured is converged at different positions of the light receiving element of the PDM 15. Since the image is formed, the wavelength of each optical signal can be obtained.

JP 2000-304613 A

  However, when obtaining the desired wavelength, it is necessary that the refractive index of the medium (air) is constant, but if the composition of the air, altitude, altitude, atmospheric pressure, temperature, humidity, water vapor pressure, etc. that are used are different, The refractive index of air also varies. For this reason, even if the light to be measured has the same wavelength, the emission angle from the diffraction grating 13 varies.

The change in the emission angle with respect to the change in the refractive index of the medium is expressed by the following formula (3) from the formula (1).
Δθ _go / Δn _a = −λ / (n _a ² · d · cos θ _go ) (3)

For example, in the case of λ = 1.55 [μm], d = 1.111 [μm], n _a = 1.000268, θ _go = 1.248 [rad] (71.5 [deg]), the formula (3 )Than,
Δθ _go / Δn _a ≈−4.42
It becomes.

Thus the refractive index _{n a} of the air, and from 1.000268 to 1.000258, (in terms of the altitude change to 0 [m] to about 300 [m]) slightly 0.00001 change even if the emission angle 0.0442 [mrad] changes. This corresponds to 15.5 [pm] in terms of wavelength from the equation (2). That is, even if the wavelength is the same, if the refractive index of air changes, the imaging position on the PDM 15 also changes. Then, since the wavelength calculation unit 30 calculates the wavelength of the light to be measured from the image formation position on the PDM 15, there is a problem that accuracy is deteriorated.

  Therefore, an object of the present invention is to realize a WDM signal monitor with improved accuracy of wavelength measurement without being affected by the use environment.

The invention described in claim 1
The light to be measured is emitted by the diffraction grating at different angles for each wavelength and dispersed, and the light to be measured dispersed by the diffraction grating is received by the photodetector, and the wavelength calculation means is covered by the output from the photodetector. In the WDM signal monitor for determining the wavelength of the measurement light,
A correction unit that corrects the wavelength obtained by the wavelength calculation unit based on the refractive index of the medium in which the diffraction grating is provided;
The composition of the air provided with the diffraction grating in addition to at least one of altitude or elevation provided with the diffraction grating, pressure, from at least one of humidity or vapor pressure, determine the refractive index of the medium, the refractive index determined the correction A refractive index calculating means for outputting to the unit ;
Environmental measurement means for measuring at least one of the composition of the air, the atmospheric pressure, the humidity or the water vapor pressure in addition to the altitude or the altitude, and outputting the measurement result to the refractive index calculation means; >
The correction unit is
Correction value storage means for storing a wavelength correction value;
Based on the change in the imaging position on the photodetector by the change in the exit angle of the light to be measured emitted from the diffraction grating due to the change in the refractive index of the medium provided with the diffraction grating obtained by the refractive index calculating means A correction value calculating means for obtaining a correction value for correcting the wavelength shift and storing the correction value in the correction value storage means;
And a wavelength correction unit that reads the correction value stored in the correction value storage unit and corrects the wavelength obtained by the wavelength calculation unit.

The invention according to claim 2 is the invention according to claim 1 ,
The environment measuring means for measuring the altitude or the altitude is an altimeter.

The invention according to claim 3 is the invention according to claim 1 ,
The environment measuring means for measuring the altitude or the altitude is GPS.

The invention according to claim 4 is the invention according to any one of claims 1 to 3 ,
The photodetector is a photodiode array module in which a wavelength is assigned in advance for each light receiving element.

The present invention has the following effects.
According to the first to fourth aspects , the correction unit corrects the wavelength obtained by the wavelength calculation unit based on the refractive index of the medium in which the wavelength dispersion element is provided. As a result, the refractive index of the medium changes, the emission angle from the wavelength dispersion element changes, the imaging position of the light to be measured on the photodetector shifts, and an error occurs in the calculation result of the wavelength calculation means. Even the error can be reduced. Therefore, the accuracy of wavelength measurement can be improved without being affected by the use environment.

In addition , since the refractive index calculation means calculates the refractive index of the medium in the usage environment where the wavelength dispersion element is installed and outputs it to the correction unit, maintenance personnel input a refractive index that is generally difficult to determine to the correction unit. There is no need to do. Thereby, the wavelength correction value can be easily obtained.

The environment measuring means measures the use environment near the wavelength dispersion element and outputs it to the refractive index calculation means, so that maintenance personnel are not required, and the use environment is obtained at a desired time. A correction value for correcting the deviation can be obtained. Thereby, cost can be reduced and a correction value can be newly obtained when desired.

Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
FIG. 1 is a block diagram showing a first embodiment of the present invention. Here, the same components as those in FIG. In FIG. 1, a correction unit 40 is newly provided, and corrects the wavelength obtained by the wavelength calculation unit 30 based on the refractive index of air in which the diffraction grating 13 is provided. The correction unit 40 includes a correction value calculation unit 41, a correction value storage unit 42, and a wavelength correction unit 43.

  The correction value calculation means 41 obtains a correction value for correcting the wavelength shift from the refractive index of the air provided with the diffraction grating 13. The correction value storage unit 42 stores the correction value obtained by the correction value calculation unit 41. The wavelength correction unit 43 reads the correction value from the correction value storage unit 42 and corrects the wavelength obtained by the wavelength calculation unit 30.

  The operation of such an apparatus will be described. A maintenance person inputs the refractive index of the air provided with the diffraction grating 13 to the correction value calculation means 41 from an input means (not shown) such as a keyboard or operation buttons.

  Then, the correction value calculating means 41 measures the wavelength correction value at the refractive index input from the input means from the expressions (2) and (3), that is, the light to be measured emitted from the diffraction grating 13 by the change in the refractive index of air. The correction value for correcting the wavelength shift based on the change of the image forming position on the PDM 15 is obtained by the change of the emission angle of and is stored in the correction value storage means 42. Further, the wavelength correction means 43 reads the correction value stored in the correction value storage means 42 and corrects the wavelength obtained by the wavelength calculation means 30 with this correction value. Then, the correction unit 40 outputs these calculation results to an output unit (not shown), and this output unit displays the calculation results on, for example, a screen of the display unit or outputs it to an external device (not shown).

  The correction unit 40 obtains a correction value for correcting the shift of the wavelength from the refractive index of the air in which the diffraction grating 13 is provided, and the operations other than correcting the wavelength obtained by the wavelength calculation means 30 using this correction value are shown in FIG. Since this is the same as the apparatus shown in FIG.

  In this way, the correction value calculation means 41 obtains the wavelength correction value for the refractive index of the air in which the diffraction grating 13 is provided, and the wavelength correction means 43 corrects the wavelength obtained by the wavelength calculation means 30 based on this correction value. To do. Thereby, even if the refractive index of air changes, the imaging position of the light to be measured on the PDM 15 is shifted, and an error occurs in the calculation result of the wavelength calculation means 30, the error can be reduced. Therefore, the accuracy of wavelength measurement can be improved without being affected by the use environment.

[Second Embodiment]
FIG. 2 is a block diagram showing a second embodiment of the present invention. Here, the same components as those in FIG. In FIG. 2, the refractive index calculating means 50 is newly provided, the refractive index of air at the altitude where the diffraction grating 13 is provided is obtained, and the obtained refractive index is output to the correction value calculating means 41 of the correction unit 40.

The operation of such an apparatus will be described.
The altitude at which the spectroscope 10 having the diffraction grating 13 is installed is input to the refractive index calculating means 50 from an input device (not shown) such as a keyboard or a button. Then, the refractive index calculation means 50 calculates the refractive index of air at the input altitude and outputs the calculated refractive index to the correction value calculation means 41 of the correction unit 40. Then, the correction value calculating means 41 obtains the correction value of the wavelength at the refractive index obtained by the refractive index calculating means 50 from the equations (2) and (3), similarly to the apparatus shown in FIG. To store.

  Further, since the refractive index calculation means 40 obtains the refractive index of air at the altitude at which the diffraction grating 13 is provided and outputs it to the correction value calculation means 41 of the correction unit 40, the operation is the same as that of the apparatus shown in FIG. Is omitted.

  In this way, the refractive index calculating means 50 obtains the refractive index of air at the altitude at which the spectroscope 10 having the diffraction grating 13 is installed. For example, in the local area where the spectroscope 10 is installed, air adjustment and temperature adjustment are performed, and the refractive index of air is determined by altitude. Thereby, since a refractive index can be calculated | required only from an altitude, the correction value of a wavelength can be calculated | required easily.

[Third embodiment]
FIG. 3 is a block diagram showing a third embodiment of the present invention. 2 that are the same as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted and illustration is omitted. In FIG. 3, an environment measuring unit 60 is newly provided in the vicinity of the diffraction grating 13 of the spectrometer 10, measures the altitude of the environment measuring unit 60, and outputs the obtained altitude to the refractive index calculating unit 50. The environment measuring means 60 is, for example, an altimeter, GPS (Global Positioning System) or the like.

The operation of such an apparatus will be described.
The environment measuring unit 60 measures the altitude near the diffraction grating 13 and outputs the obtained altitude to the refractive index calculating unit 50. Then, the refractive index calculating means 50 obtains the refractive index from the altitude as in the apparatus shown in FIG.

  Further, since the environment measurement unit 60 measures the altitude near the diffraction grating 13 and outputs the obtained altitude to the refractive index calculation unit 50, the operation is the same as that of the apparatus shown in FIG.

  Thus, since the environment measuring means 60 measures the altitude near the diffraction grating 13 and outputs it to the refractive index calculating means 50, maintenance personnel are not required, and the altitude is obtained when desired, and from this altitude. A correction value for correcting the wavelength shift can be obtained. Thereby, cost can be reduced and a correction value can be newly obtained when desired.

In addition, this invention is not limited to this, The following may be sufficient.
In the apparatus shown in FIG. 1, the correction value calculation means 41 obtains the correction value from the input refractive index and stores it in the correction value storage means 42. However, the altitude or the like where the spectroscope 10 is installed in advance is shown. If the environment is known, the correction value calculation means 41 may not be provided, and a wavelength correction value based on the refractive index of air may be obtained in advance and stored in the correction value storage means 42. The wavelength correction unit 43 may read the correction value from the correction value storage unit 42 and correct the wavelength obtained by the wavelength calculation unit 30.

  Moreover, in the apparatus shown in FIG. 2 and FIG. 3, although the refractive index calculating means 50 showed the structure which calculates | requires a refractive index from the altitude which shows the height on the basis of a fixed sea surface, the ground of the desired position was made into the reference | standard. It is good also as a structure which calculates | requires a refractive index from the height which shows height. Of course, in this case, the environment measuring means 60 outputs altitude instead of altitude.

  Moreover, in the apparatus shown in FIG. 2 and FIG. 3, although the refractive index calculating means 50 showed the structure which calculates | requires a refractive index from the altitude which shows the height on the basis of a fixed sea surface, the local where the spectrometer 10 is installed is shown. Considering the case where local air conditioning and temperature regulation are stopped due to failure, power outage, etc., not only the altitude but also other usage environment air composition (nitrogen, oxygen, argon, carbon dioxide, etc.), altitude, atmospheric pressure, The refractive index may be obtained from humidity, temperature, water vapor pressure, or the like. Further, at least one of the parameters of the usage environment may be used. Similarly, in the apparatus shown in FIG. 3, the environment measuring means 60 measures and outputs the altitude. However, at least one of the parameters of the operating environment is measured, and the measurement result is used as the refractive index calculating means. 50 may be output. Of course, the environment measuring means 60 is appropriately changed for each parameter of the usage environment to be measured. For example, a temperature sensor is used for temperature measurement.

  1 to 3, the polychromator type spectrometer 10 has been described. However, all the spectrometers configured to disperse the light to be measured and sample the dispersed spectrum are included in the present invention.

  In addition, in the apparatus shown in FIGS. 1 to 3, the configuration in which the diffraction grating 13 is used for the wavelength dispersion element that splits the measured light is shown. However, instead of the diffraction grating 13, the measured light is split using a prism or the like. May be.

  Further, in the apparatus shown in FIGS. 1 to 3, the spectroscope 10 is a transmission type optical system using lenses 12 and 14, but may be a reflection type optical system using a parabolic mirror or the like.

It is the block diagram which showed the 1st Example of this invention. It is the block diagram which showed the 2nd Example of this invention. It is the block diagram which showed the 3rd Example of this invention. It is a block diagram of the conventional WDM signal monitor.

Explanation of symbols

13 Diffraction grating 15 Photodiode array module 30 Wavelength calculation means 40 Correction unit 41 Correction value calculation means 42 Correction value storage means 43 Wavelength correction means 50 Refractive index calculation means 60 Environmental measurement means

Claims (4)

The light to be measured is emitted by the diffraction grating at different angles for each wavelength and dispersed, and the light to be measured dispersed by the diffraction grating is received by the photodetector, and the wavelength calculation means is covered by the output from the photodetector. In the WDM signal monitor for determining the wavelength of the measurement light,
A correction unit that corrects the wavelength obtained by the wavelength calculation unit based on the refractive index of the medium in which the diffraction grating is provided;
The composition of the air provided with the diffraction grating in addition to at least one of altitude or elevation provided with the diffraction grating, pressure, from at least one of humidity or vapor pressure, determine the refractive index of the medium, the refractive index determined the correction A refractive index calculating means for outputting to the unit ;
Environmental measurement means for measuring at least one of the composition of the air, the atmospheric pressure, the humidity or the water vapor pressure in addition to the altitude or the altitude, and outputting these measurement results to the refractive index calculation means; >
The correction unit is
Correction value storage means for storing a wavelength correction value;
Based on the change in the imaging position on the photodetector by the change in the exit angle of the light to be measured emitted from the diffraction grating due to the change in the refractive index of the medium provided with the diffraction grating obtained by the refractive index calculating means A correction value calculating means for obtaining a correction value for correcting the wavelength shift and storing the correction value in the correction value storage means;
A WDM signal monitor, comprising: wavelength correction means for reading the correction value stored in the correction value storage means and correcting the wavelength obtained by the wavelength calculation means. The altitude or environment measuring means for measuring the elevation, WDM signal monitor according to claim 1, wherein it is altimeter. The altitude or environment measuring means for measuring the elevation, WDM signal monitor according to claim 1, characterized in that the GPS. Photodetector, WDM signal monitor according to claim 1, characterized in that a photodiode array module assigned in advance wavelength for each light-receiving element.

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