JP2009025220A - Optical spectrum analyzer and peak detection technique of optical spectrum analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical spectrum analyzer implementing peak detection of each optical signal even if adjacent optical signal are close to each other so that peaks of optical signals are not isolated. <P>SOLUTION: Improvement is added to an optical spectrum analyzer implementing measurement of light to be measured containing a plurality of optical signals. The present device is characterized by preparing a spectrometer outputting measured data sampling the light to be measured with desired wavelength interval, a response feature data containing section containing response feature data to line spectrum of the spectrometer, and an operation section where, after detecting peaks from the measured data of the spectrometer, affected part of optical signal corresponding to the peak are removed from the measured data using the response feature data and the peak is detected again by the measured data removed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical spectrum analyzer (in particular, an optical spectrum analyzer having a polychromator-type spectroscope) that measures light to be measured including a plurality of optical signals, and a peak detection method for the optical spectrum analyzer. The present invention relates to an optical spectrum analyzer that detects the peak of each optical signal even if the optical signal is close and the peaks of the optical signal are not separated, and a peak detection method for the optical spectrum analyzer.

  One type of optical communication system that transmits optical signals using optical fibers is WDM communication. The WDM communication is a communication method for transmitting a plurality of optical signals having different wavelengths through a single optical fiber. A plurality of optical signals having different wavelengths are also called WDM signals. Each optical signal of the WDM signal is often counted as one channel and two channels from the shortwave side, for example.

  In recent years, with the expansion of transmission capacity, high-density multiplexing of WDM signals has progressed, and the optical signal level, peak wavelength, optical SNR, and the like of each channel have become important measurement parameters. Monitoring these parameters is essential for maintaining the quality of the WDM signal.

  The optical spectrum analyzer uses a wavelength dispersive element to split the light to be measured, which is a WDM signal, for each wavelength, and obtains optical power existing in an arbitrary wavelength width. And it is an apparatus which measures parameters, such as an optical signal level of each optical signal, a wavelength, from the calculated | required optical power. Some optical spectrum analyzers are configured using, for example, a small spectroscope so that they can be incorporated into a part of an optical communication system in an in-line format and constantly monitored.

  FIG. 4 is a diagram showing the configuration of an optical spectrum analyzer that measures such a WDM signal. In FIG. 4, a spectroscope 10 receives a WDM signal as light to be measured, measures the spectrum of the WDM signal, and outputs measurement data as sampling data.

  The calculation unit 20 receives the measurement data output from the spectrometer 10. Further, the calculation unit 20 detects the peak of each channel from the measurement data, calculates the optical signal level and peak wavelength of each channel from the measurement data near the peak, and outputs these calculation results.

  FIG. 5 is a configuration diagram showing a specific example of the spectrometer 10. Here, as the method of the spectrometer 10, a polychromator method that is easy to downsize is given. In FIG. 5, the spectroscope 10 includes an optical fiber 11, a collimating lens 12, a diffraction grating 13 that is a wavelength dispersion element, a focusing lens 14, and a photodiode array module (hereinafter abbreviated as PDM) 15.

  The optical fiber 11 is a transmission path through which the measured light 100 enters the spectrometer 10. The collimating lens 12 is installed facing the exit of the optical fiber 11 and emits the measured light 100 emitted from the optical fiber 11 as parallel light.

  The diffraction grating 13 is tilted with respect to the collimating lens 12 in order to diffract the emitted light from the collimating lens 12 at a desired angle. In addition, the diffraction grating 13 divides and emits the light to be measured 100 at different angles for each wavelength. The focusing lens 14 is installed on the optical path of the outgoing light from the diffraction grating 13 and converges the outgoing light.

  The PDM 15 is installed at a position where the measured light 100 converges. The PDM 15 is provided with a PD array in which a plurality of photodiodes (hereinafter abbreviated as PDs) which are strip-shaped or dot-shaped light receiving elements are arranged. This PD generates a current (photocurrent) corresponding to the optical power of the incident measurement light 100. The PDM 15 sequentially outputs the photocurrent of the PD from, for example, the short wavelength side PD.

  Each PD is assigned a wavelength in advance. The wavelength assignment corresponds to the position where the light to be measured 100 is dispersed by wavelength by the diffraction grating 13 and converges in the PD array.

The operation of such a spectrometer 10 will be described.
It is assumed that the measured light 100 is multiplexed with two optical signals (wavelength λA and wavelength λB (wavelength λA is the first channel optical signal, wavelength λB is the second channel optical signal)). The light to be measured 100 emitted from the optical fiber 11 is emitted to the diffraction grating 13 by the collimating lens 12 as parallel light.

  The diffraction grating 13 splits the measured light 100 for each of the wavelengths λA and λB, and the focusing lens 14 converges the split measured light 100A and 100B on the PD array of the PDM 15. Of course, the converged positions are shifted corresponding to the wavelengths λA and λB of the measured light 100A and 100B.

  Then, the PDM 15 sequentially outputs the photocurrent generated in each PD from the short wavelength side PD. Then, a conversion unit (not shown) of the spectroscope 10 converts the photocurrent into a voltage, converts the voltage-converted analog signal into a digital signal, and outputs it as measurement data to the calculation unit 20. Thus, the measurement data is sampling data sampled by the PD.

  Next, an operation in which the calculation unit 20 calculates the optical signal level and peak wavelength of each channel will be described. FIG. 6 is a diagram schematically showing that the light to be measured 100A and 100B is irradiated to a part of the PD array, taking as an example the case where the PD of the PDM 15 shown in FIG.

In FIG. 6, PDs 15 a to 15 j have a strip shape, and are arranged along the direction in which the light to be measured 100 is dispersed by wavelength by the diffraction grating 13. Also each PD15a~15j are the wavelengths of _{λ 1 ~λ 10 (λ 1 <} λ 2 <··· <λ 10) assigned. Photocurrents are sequentially output from one or both sides of the PDs 15a to 15j through signal lines (not shown).

The light to be measured 100A and 100B forms an elliptical or circular light spot whose light power has a Gaussian distribution. Here, it is assumed that the centers of the measured light 100A and 100B are in the vicinity of the PDs 15d and 15j, respectively. When a line spectrum is input, the beam radius ω of the light spot with respect to the arrangement direction of the PDs 15a to 15j depends on the combination of the lenses 12 and 14, but is, for example, about 1 to 1.5 times the width in the arrangement direction of the PDs 15a to 15j. Adjusted to The beam radius ω is a distance until the light power becomes 1 / e ² times the light power of the strongest point in the light spot. Needless to say, a small amount of light power is also present outside the light spot indicated by the beam radius ω.

  FIG. 7 is a graph representing measurement data that is output from the PDs 15a to 15j shown in FIG. In FIG. 7, the horizontal axis represents wavelengths corresponding to the PDs 15a to 15j, and the vertical axis represents measurement data of the PDs 15a to 15j. Measurement data from the PDs 15a to 15j are indicated by black circles. The measurement data is an output (solid line in FIG. 7) obtained by combining the measured light 100A and 100B (these are broken lines in FIG. 7). The vertical axis represents a relative value and is represented by a logarithm.

  Using the measurement data of each of the PDs 15a to 15j as an example, an operation in which the calculation unit 20 obtains the peak wavelength λA and the optical signal level of the measured light 100A will be described. The computing unit 20 detects the measurement data that becomes a peak, that is, the measurement data of the PD 15d, and creates an approximate curve from the measurement data of the PDs 15c to 15e near the detected peak. Then, the peak wavelength λA of the light to be measured 100A is obtained from the peak (x point in FIG. 7) value of the obtained approximate curve.

  And the calculating part 20 adds the measurement data of the detected peak vicinity, for example, three measurement data of PD15c-15e, and calculates | requires an optical signal level. Here, the value obtained by adding the three points may be converted so as to be a desired unit (for example, [mW], [dBm], etc.).

  The operation of the calculation unit 20 for obtaining the optical signal level and peak wavelength λB of the light to be measured 100B, which is an optical signal of another channel, is also the same, and the description thereof is omitted.

JP 2004-56700 A

  The wavelength resolution of the polychromator type spectroscope 10 varies depending on the element width of the PDs 15a to 15j and the beam radius ω of the light spot formed on the surfaces of the PDs 15a to 15j. For example, the beam radius ω is an arrangement of the PDs 15a to 15j. When adjusted to about 1 to 1.5 times the width in the direction, if the peak wavelength difference between adjacent optical signals is at least 3 elements apart, it can be detected as a peak. That is, the wavelength difference of the three elements PD15a to 15j is the wavelength resolution.

  However, in the WDM signal incident on the spectrometer 10, the wavelength interval of the optical signal of each channel is not constant, and the optical signal level is not always constant. In particular, when the optical signal levels of adjacent optical signals are different, there is a problem that even if the peak wavelength is 3 or more elements apart, the peak of the other optical signal is buried in one optical signal having a large optical signal level, so that the peak cannot be detected. .

A case where a WDM signal as shown in FIG. 8 is input will be described.
The case where the optical power of the optical signal of the first channel (measured light 100A) is larger than that of the optical signal of the second channel (measured light 100B) and both optical signals are adjacent to each other is illustrated. As in FIG. 7, the measured light 100A and 100B are indicated by broken lines, and the output of the PDM 15 (that is, the output in which two optical signals are combined) is indicated by a solid line.

  When such an optical signal is input, there is only one peak in the output from the PDM 15, and in fact, even though two optical signals are input, the computing unit 20 is in the first channel. There is a problem that only the peak wavelength and optical signal level of the optical signal are calculated.

  Accordingly, an object of the present invention is to realize an optical spectrum analyzer and an optical spectrum analyzer peak detection method for detecting the peak of each optical signal even when adjacent optical signals are close to each other and the optical signal peaks are not separated. It is in.

The invention described in claim 1
In an optical spectrum analyzer that measures light under test including multiple optical signals,
A spectrometer that outputs measurement data obtained by sampling the light to be measured with a desired wavelength width;
A response characteristic data storage unit for storing response characteristic data for the line spectrum of the spectrometer;
After detecting the peak from the measurement data of the spectrometer, the influence of the optical signal corresponding to this peak is removed from the measurement data by the response characteristic data of the response characteristic data storage unit, and the peak is detected again by the removed measurement data And an arithmetic unit for performing the above.
The invention according to claim 2 is the invention according to claim 1,
The calculation unit
Peak detection means for detecting a peak from the measurement data of the spectrometer;
Peak calculating means for calculating the peak wavelength and peak value of the peak detected by the peak detecting means;
Correction means for correcting the measurement data based on the response characteristic data of the response characteristic data storage unit and the peak wavelength and peak value of the peak calculation means, and the peak detection means is corrected by the correction means. It is characterized in that the peak is detected again from the measurement data.
The invention according to claim 3 is the invention according to claim 1 or 2,
Spectrometer
A diffraction grating that splits the light under measurement;
And a photodiode array module including a plurality of photodiodes that receive light dispersed by the diffraction grating.
The invention according to claim 4 is the invention according to any one of claims 1 to 3,
The plurality of optical signals are WDM signals;
The response characteristic data storage unit stores response characteristic data for the modulated optical signal.
The invention according to claim 5
A spectrometer outputting measurement data obtained by sampling light to be measured including a plurality of optical signals;
A peak detecting means for detecting a peak from the measurement data of the spectrometer;
A step of calculating a peak wavelength and a peak value from the measurement data in the vicinity of the detected peak;
A correcting unit that removes the influence of the optical signal corresponding to the peak from the measurement data and corrects based on the response characteristic data and the peak wavelength and peak value of the calculating unit;
The peak detecting means includes a step of detecting a peak from the measurement data corrected by the correcting means.

The present invention has the following effects.
After the calculation unit detects the peak from the measurement data of the spectrometer, the influence of the optical signal corresponding to this peak is removed from the measurement data by the response characteristic data, and the peak is detected again with the removed measurement data. The other optical signal buried in the other optical signal can be detected. That is, even if adjacent optical signals are close to each other and the optical signal peaks are not separated, the peak detection of each optical signal can be performed. Thereby, the peak wavelength of each optical signal, an optical signal level, etc. can be calculated | required.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. Here, the same components as those in FIGS. 4 to 6 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 1, a calculation unit 30 is provided instead of the calculation unit 20. In addition, a response characteristic data storage unit 40 for storing response characteristic data is newly provided.

  The calculation unit 30 includes a peak detection unit 31, a peak calculation unit 32, and a correction unit 33. The peak detection unit 31 detects the peak of the optical signal from the measurement data of the PDM 15 and the measurement data corrected by the correction unit 33. The peak calculator 32 calculates the peak wavelength, peak value, optical signal level, etc. of the peak detected by the peak detector 31. The correction unit 33 reads the response characteristic data from the response characteristic data storage unit 40, and corrects the measurement data in the vicinity of the peak detected by the peak detection unit 31 with the response characteristic data.

  The response characteristic data storage unit 40 stores response characteristic data of the spectrometer 10 with respect to the line spectrum.

  FIG. 2 is a diagram showing an example of response characteristics of the response characteristic data f (Δλ) stored in the response characteristic data storage unit 40 in FIG. In FIG. 2, when a line spectrum is input to the spectroscope 10, the response characteristic with respect to this input becomes a response spectrum having a spread like a Gaussian distribution in the vicinity of the peak. A response characteristic data f (Δλ) obtained by normalizing the response spectrum is a function f (Δλ) represented by an output value of a wavelength and an optical signal level. Here, Δλ represents a wavelength difference from the peak wavelength, and f (0) when the wavelength difference Δλ = 0 is the maximum value of this function. The response characteristic data f (Δλ) is obtained offline and stored in the response characteristic data storage unit 40.

The operation of such an apparatus will be described.
A WDM signal is input to the spectrometer 10. Then, the spectroscope 10 samples the spectrum of a plurality of optical signals with a wavelength width based on the size of the PD, and outputs measurement data that is optical signal level sampling data. Since the operation of the spectrometer 10 is the same as that of the apparatus shown in FIGS.

  Here, FIG. 3 is a graph representing measurement data and the like which are outputs from the PDs 15 a to 15 j of the spectrometer 10. As in FIG. 8, the case where the optical signals of the first channel and the second channel are close to each other and the optical signal level of the optical signal of the second channel is lower than the optical signal level of the optical signal of the first channel will be described as an example. To do. The horizontal axis represents the wavelengths corresponding to the PDs 15a to 15j, and the vertical axis represents the measurement data of each of the PDs 15a to 15j, correction response characteristic data, corrected measurement data, and the like.

  FIG. 3A is a diagram showing measurement data of actual data output from the spectroscope 10, and measurement data from the PDs 15a to 15j are indicated by black circles. Of course, the measurement data, which is actual data, is an output (solid line in FIG. 3) in which measured light 100A and 100B (these are broken lines in FIG. 3) are combined.

  FIG. 3B is a diagram showing fitting of response characteristic data to the optical signal of the first channel (shown by white circles in FIG. 3), and FIG. 3C is a measurement after correction. FIG. 4 is a diagram showing data (illustrated by white triangle points in FIG. 3).

  Subsequently, the operation of the calculation unit 30 will be described with reference to FIG. 3 as an example. The peak detection means 31 of the calculation unit 30 detects the measurement data that becomes a peak, that is, the measurement data of the PD 15d. Further, the calculation means 32 creates an approximate curve (a Gaussian curve, a quadratic curve, a curve obtained by interpolating between the measurement data, etc.) from the measurement data of the three PDs 15c to 15e in the vicinity of the detected peak. Then, the peak value (maximum value) and peak wavelength λA of the obtained approximate curve are obtained. Further, the calculating means 32 adds the detected measurement data in the vicinity of the peak, for example, the three measurement data of PDs 15c to 15e, and obtains the optical signal level. Here, the value obtained by adding the three points may be converted so as to be a desired unit (for example, [mW], [dBm], etc.) (see FIG. 3A).

  Then, the correction means 33 of the calculation unit 30 reads the response characteristic data from the response characteristic data storage unit 40. Further, the correcting means 33 obtains a relative wavelength difference Δλ to each PD 15a to 15j from the peak wavelength of the first channel optical signal obtained by the computing means 32, and outputs the response characteristic data output value (f (Δλ) from each wavelength difference. )). Further, each output value (f (Δλ)) of the response characteristic data is obtained from the peak value (optical power) of the optical signal of the first channel and the normalized peak value (f (0)) of the response characteristic data. It converts into the optical power of real data (refer FIG.3 (b)).

  Then, the correction means 33 corrects the measurement data by subtracting the measurement data of the actual data by the correction output value obtained from the response characteristic data. As a result, the influence of the optical signal of the first channel (measurement light 100A) is removed from the measurement data, and the measurement light 100B buried in the measurement light 100A becomes obvious (see FIG. 3C).

  Then, the peak detection unit 31 performs peak detection again with the measurement data corrected by the correction unit 33, and detects the measurement data of the PD 15f. Hereinafter, similarly, the calculation means 32 obtains the peak wavelength and the optical signal level of the optical signal of the second channel from the measurement data 15e to 15g near the peak.

  When the calculation based on the measurement data before correction and the calculation based on the measurement data after correction are completed, the calculation unit 30 outputs these calculation results (peak wavelength, optical signal level) to an output unit (not shown). The unit displays the calculation result on, for example, a screen of a display unit (not shown) or outputs it to an external device (not shown).

  In this way, the correction means 33 generates measurement data from which the influence of the optical signal detected with the actual data is removed, and the peak detection means 31 performs peak detection again with the corrected measurement data, so that a large optical signal is obtained. It is possible to detect an optical signal of a small optical signal level buried in the optical signal of a level. Thereby, the peak wavelength of each optical signal, an optical signal level, etc. can be calculated | required.

The present invention is not limited to this, and may be as shown below.
(1) The response characteristic data storage unit 40 is configured to store the response characteristic data of the spectrometer 10 for a single line spectrum. However, the WDM signal is generally modulated. Therefore, response characteristic data of the spectrometer 10 for a plurality of modulated line spectra may be stored. Further, since there are various modulation methods, a plurality of response characteristic data for each modulation method may be stored, and correction may be performed using optimum response characteristic data.

(2) The configuration in which the optical spectrum analyzer performs the measurement on the WDM signal as the light to be measured has been shown, but what is measured as long as the light to be measured has a plurality of optical signals having different wavelengths. May be. For example, an optical signal from an optical fiber sensor (for example, measured light from an optical fiber provided with a plurality of optical fiber gratings) may be measured.

It is the block diagram which showed one Example of this invention. It is the figure which showed an example of the response characteristic data. It is the figure which showed an example of the measurement data etc. of the apparatus shown in FIG. It is the figure which showed the structure of the conventional optical spectrum analyzer. 1 is a diagram illustrating a configuration of a spectroscope 10. FIG. It is a schematic diagram which shows a part of photodiode array. It is a figure which shows an example of measurement data. It is a figure which shows the other example of measurement data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Spectrometer 13 Diffraction grating 15 Photodiode array module 30 Calculation part 31 Peak detection means 32 Peak calculation means 33 Correction means 40 Response characteristic data storage part

Claims (5)

In an optical spectrum analyzer that measures light under test including multiple optical signals,
A spectrometer that outputs measurement data obtained by sampling the light to be measured with a desired wavelength width;
A response characteristic data storage unit for storing response characteristic data for the line spectrum of the spectrometer;
After detecting the peak from the measurement data of the spectrometer, the influence of the optical signal corresponding to this peak is removed from the measurement data by the response characteristic data of the response characteristic data storage unit, and the peak is detected again by the removed measurement data An optical spectrum analyzer characterized by comprising an arithmetic unit for performing the above. The calculation unit
Peak detection means for detecting a peak from the measurement data of the spectrometer;
Peak calculating means for calculating the peak wavelength and peak value of the peak detected by the peak detecting means;
Correction means for correcting the measurement data based on the response characteristic data of the response characteristic data storage unit and the peak wavelength and peak value of the peak calculation means, and the peak detection means is corrected by the correction means. An optical spectrum analyzer characterized by detecting a peak again from measurement data. Spectrometer
A diffraction grating that splits the light under measurement;
3. An optical spectrum analyzer according to claim 1, further comprising: a photodiode array module comprising a plurality of photodiodes that receive light split by the diffraction grating. The plurality of optical signals are WDM signals;
4. The optical spectrum analyzer according to claim 1, wherein the response characteristic data storage unit stores response characteristic data for the modulated optical signal. A spectrometer outputting measurement data obtained by sampling light to be measured including a plurality of optical signals;
A peak detecting means for detecting a peak from the measurement data of the spectrometer;
A step of calculating a peak wavelength and a peak value from the measurement data in the vicinity of the detected peak;
A correcting unit that removes the influence of the optical signal corresponding to the peak from the measurement data and corrects based on the response characteristic data and the peak wavelength and peak value of the calculating unit;
And a step of detecting the peak from the measurement data corrected by the correction means.

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