JP4523588B2 - Optical signal quality monitoring device - Google Patents

Abstract

There are provided an interferometer (2) for outputting data of phase difference between adjacent bits of a given optical signal; first and second photoreceptors (3,4) for converting output optical signals from the interferometer (2) to electrical signals; arithmetic means (5) for performing predetermined arithmetic operations of the electrical signals as converted by the first and second photoreceptors (3,4); clock generator means (6) for generating and outputting a clock signal of a predetermined frequency; a discriminator (7) for discriminating outputs from the arithmetic means (5) at the timing of the clock signal; a counter (8) for calculating an integration result obtained by counting discrimination outputs from the discriminator (7) for each of logic levels in a predetermined time period; and a quality information calculating part (9) for calculating, based on the integration result from the counter (8), and outputting a quality information of the given optical signal. The discriminator (7) develops discrimination outputs as discriminated for every two or more different discrimination voltages. The quality information calculating part (9) calculates the quality information based on the integration results as calculated for each of amplitude discrimination voltages.

Description

  The present invention relates to an optical signal quality monitoring apparatus for monitoring the quality of an optical signal.

  Conventionally, in an optical transmission system that connects two points, quality monitoring by monitoring the number of error corrections in FEC (Forward Error Collection) processing at the receiving end, and quality in the signal frame of an SDH (Synchronous Digital Hierarchy) signal Quality monitoring is performed by monitoring the monitoring bit.

  On the other hand, recently, with the progress of networking of optical communication, there is an increasing demand for quality monitoring for optical signals in networked optical communication lines.

  A new technique for monitoring the quality of an optical signal in response to such a request has been disclosed. For example, a method for estimating a histogram of an electric signal waveform in synchronization with a signal transmission rate and estimating an optical signal quality (for example, Patent Document 1 and Non-Patent Document 1), or asynchronous sampling without depending on the signal transmission speed There is a method (for example, Patent Document 2) that estimates optical signal quality by performing histogram analysis at a frequency.

Japanese Patent No. 3212401 JP 2003-90766 A R. Wiesmann, O.M. Beck, H .; Heppner, “Cost effective performance monitoring in WDM systems” OFC 2000, paper,

  However, the methods disclosed in Patent Document 1 and Non-Patent Document 1 described above have a drawback in that there is a certain limitation on the signal transmission speed and the configuration of the apparatus becomes complicated.

  Further, the technique disclosed in Patent Document 2 described above has a drawback that accurate signal quality cannot be obtained.

  In view of such a situation, an object of the present invention is to provide an optical signal quality monitoring device that can output accurate signal quality information with a simple configuration and not depending on a signal transmission rate.

  The optical signal quality monitoring apparatus according to the present invention is an optical signal quality monitoring apparatus that monitors the signal quality of a predetermined optical signal transmitted through a communication line of an optical network system, and is an adjacent bit of the predetermined optical signal. An interferometer that outputs phase difference data between the interferometer, first and second optical receivers that convert the output optical signal output from the interferometer into an electrical signal, and the first and second optical receivers. A means for performing a predetermined operation on the converted electric signal, a clock generating means for generating and outputting a clock signal of a predetermined frequency, and an identification for identifying the output of the operation means at the timing of the clock signal A counter for calculating an integration result within a predetermined time obtained by counting the discrimination output of the discriminator for each logic level, and calculating and outputting quality information of the predetermined optical signal based on the integration result of the counter. A quality information calculation unit that outputs an identification output identified for each of two or more different identification voltages, and the quality information calculation unit calculates an integration result calculated for each amplitude identification voltage. The quality information is calculated based on the above.

  According to this invention, the identification outputs identified for each of two or more different amplitude identification voltages are integrated, and quality information is calculated based on the integration result calculated for each identification voltage.

  Exemplary embodiments of an optical signal quality monitoring apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings. In addition, this invention is not limited by this embodiment.

Embodiment 1 FIG.
First, the configuration of the optical signal quality monitoring apparatus according to the first embodiment of the present invention will be described. FIG. 1 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the first embodiment of the present invention. The optical signal quality monitoring apparatus shown in FIG. 1 includes, for example, an interferometer 2 that outputs phase difference data between adjacent bits of an optical DPSK signal input from the optical fiber 1, and a first that converts the optical signal into an electrical signal. , Optical receivers 3 and 4 which are second receivers, an adder 5 which is an example of a calculation means for performing a predetermined calculation, a clock signal generator 6 for generating a clock signal, a clock signal and a control signal The discriminator 7 for discriminating the logic level (logic “1” or logic “0”) of the input data based on the counter 8, the counter 8 as the counting means for counting the discriminant output of the discriminator 7, A quality information calculation unit 9 that calculates and outputs quality information necessary for the quality monitoring of the optical signal, and a control unit 10 that controls predetermined components of the quality monitoring apparatus are provided.

  Next, the operation of the optical signal quality monitoring apparatus shown in FIG. In the figure, for example, an optical DPSK (Differential Phase Shift Keying) signal is input to the interferometer 2. The interferometer 2 includes a 1-bit delay line (not shown), for example, and outputs an interference output generated based on an optical signal that has passed through the 1-bit delay line and an optical signal that has not passed through. Is done.

  Here, the interferometer 2 has two output ports, which are output to one of the optical receivers 3 and 4 according to the phase difference of the interference result. For example, when the phase difference of the interference result is “0”, it is output to one optical receiver (for example, the optical receiver 3), and when the phase difference of the interference result is “1”, the other optical receiver (for example, the optical receiver) It is output to the light receiver 4). The optical receivers 3 and 4 convert the input optical signal into an electrical signal.

  The electrical signals converted by the optical receivers 3 and 4 are added by the adder 5 and output to the discriminator 7. The discriminator 7 outputs the discrimination result (logic level determination result) identified at the timing of the clock (external clock) generated by the clock signal generation unit 6 to the counter 8 based on the discrimination voltage output from the control unit 10. . The counter 8 counts the identification result for each logic level (logic “1” or logic “0”), and outputs an integration result within a predetermined time to the quality information calculation unit 9. The quality information calculation unit 9 generates and outputs predetermined quality information based on information such as the count value of the identification result and the identification voltage.

  The control unit 10 controls predetermined components of the optical signal quality monitoring apparatus. For example, the interferometer 2 is controlled to be stabilized with respect to the optical signal wavelength. Further, the control of the identification voltage of the classifier 7 and the output control of the quality information calculation unit 9 are also performed based on the control of the control unit 10.

FIG. 2 is a diagram showing an example of a probability density distribution of an input optical signal. In the figure, a waveform K1 is a probability density distribution (noise distribution) corresponding to logic “1”, and a waveform K2 is a probability density distribution (noise distribution) corresponding to logic “0”. Also, σ ₁ indicates the standard deviation in the probability density distribution corresponding to logic “1”, and σ ₀ indicates the standard deviation in the probability density distribution corresponding to logic “0”.

  Next, the operation when the discrimination voltage of the discriminator 7 shown in FIG. 1 is varied will be described with reference to FIG. 2 and FIG. FIG. 3 is a diagram showing the relationship between the electrical waveform of an NRZ (Non Return to Zero) -OOK signal, the identification voltage when the NRZ-OOK signal is input, and the error rate of the identification result.

Returning to FIG. 2, let us consider a case where the identification voltage is V ₁ when the distribution of logic “1” and logic “0” is as shown in FIG. At this time, the data in the area A1 indicated by the horizontal line is determined to be logic “1”. Accordingly, the area A1 has a probability that data of logic “0” is determined to be logic “1”.

Next, consider the case where the identification voltage is V ₂ (V ₁ > V ₂ ). At this time, the data of both areas obtained by adding the portion of area A2 indicated by diagonal lines to the portion of area A1 indicated by horizontal lines is determined to be logic “1”. Therefore, the areas A1 and A2 have a probability that data of logic “0” is determined to be logic “1”.

  Now, the probability that the data of logic “0” is determined to be logic “1” at the predetermined identification voltage, or the probability that the data of logic “1” is determined to be logic “0” is represented by “ It is defined as “mismatch rate”.

  The discrepancy rate defined in this way means the rate at which the logical level of the transmission data when the identification voltage is varied does not match the determined logical level. It can be equated with the data error rate. Therefore, this mismatch rate can be used for monitoring the optical signal quality.

The portions indicated by broken lines K3 and K4 in FIG. 3 are plots of this mismatch rate. Of these, the portion indicated by the broken line K4 indicates that the counter 8 counts the number that the discriminator 7 discriminates as the logic “1” when the discrimination voltage is varied to the logic “0” side. The mismatch rate calculated by the quality information calculation unit 9 based on the plot is plotted. In the figure, if the mismatch rate at the identification voltage V ₁ is P ₁ and the mismatch rate at the identification voltage V ₂ is P ₂ , P ₁ <P ₂ (where V 1 ₁ > V ₂ ). Accordingly, the portion of the broken line K4 is a downward-sloping curve (histogram).

  Similarly, when the identification voltage is set on the distribution side of logic “1”, the result as shown by the broken line K3 is obtained. However, the slope of the curve representing the mismatch rate is an upward curve (histogram), which is symmetrical with the curve shown by the broken line K4.

  By the way, when the distribution of the optical signal is known in advance or when the histogram of the optical signal is obtained, the signal quality can be evaluated using the following well-known expression.

Q = (μ ₁ −μ ₀ ) / (σ ₁ −σ ₀ ) (1)

Here, μ ₁ and μ ₀ are average values of the respective distributions of logic “1” and logic “0”, and σ ₁ and σ ₀ are the respective distributions of logic “1” and logic “0”, respectively. Standard deviation.

At this time, the above μ ₁ , μ ₀ and σ ₁ , σ ₀ can be calculated from the histogram of the mismatch rate as shown in FIG. These values are calculated by the quality information calculation unit 9.

  Up to this point, the processing of the discriminator 7 in the case where the discrimination voltage is varied has been mainly described, but in the following description, the processing of the optical signal quality monitoring apparatus according to the first embodiment will be described.

  4A is a diagram showing signal waveforms of main parts of the optical signal quality monitoring apparatus according to the first embodiment to which an optical DPSK signal is inputted, and FIG. 4B is a diagram showing respective timing charts. FIG. 4C is a diagram showing the distribution of the mismatch rate (error rate) with respect to the identification voltage.

  As shown in FIGS. 4A and 4B, the optical DPSK signal waveform (A) input to the interferometer 2 has binary phase difference information (0, π) with constant intensity. The waveforms (B) and (C) obtained by photoelectrically converting the outputs of the interferometer 2 by the optical receivers 3 and 4 become NRZ signals having opposite polarities (different polarities). Therefore, the sum signal obtained by adding these two signals is a signal that is all logic “1” as shown in FIG. 4B (D) as a signal obtained by adding both of FIGS. 4B (B) and (C). Is obtained.

Incidentally, it is known that the logic “1” and the logic “0” have the same probability density distribution in the optical DPSK signal, and the probability density distribution of the signal obtained by adding both is the same as the logic “1” of the original optical DPSK signal. A probability density distribution of logic “0” is added. In particular, when the probability density distributions of logic “1” and logic “0” follow a Gaussian distribution, the relationship of σ ₁ = σ ₀ (= σ ₁₀ ) is established. Further, it is known that the logic “1” and the logic “0” have the same average value with respect to the zero potential, and the average value of the signal obtained by adding both is the logic “1” and the logic “1” of the original DPSK signal. The average value of 0 ”is averaged. Therefore, the relationship of μ ₁ = −μ ₀ (= μ ₁₀ ) is established.

The discriminator 7 to which such an addition signal is input outputs the discrimination result identified at the timing of the external clock to the counter 8 based on the discrimination voltage output from the control unit 10. The counter 8 counts the identification result and outputs the result to the quality information calculation unit 9. The quality information calculation unit 9 estimates the average value μ ₁ and the standard deviation σ ₁ of the probability density distribution based on the histogram obtained by the above processing, and generates optical signal quality information based on the equation (1). Output.

  The signals processed in this embodiment are all signals having a logic “1” level as shown in FIG. 4B (D), so that an identification voltage is applied to the logic “0” level side as described above. There is no need to change it. That is, only the upper half distribution (histogram) as shown in FIG. 4C is obtained, but it is assumed that the probability density distributions of logic “1” and logic “0” follow a Gaussian distribution. The distribution can be treated as being symmetrical with the upper half of the distribution.

Next, the Q value of the optical signal quality monitoring apparatus of this embodiment is calculated using equation (1). Now, in Equation (1), if μ ₁ = −μ ₀ = μ ₁₀ and σ ₁ = σ ₀ = σ _10, it can be simplified as the following equation.

Q = μ ₁₀ / σ ₁₀ (2)

  As described above, according to the optical signal quality monitoring apparatus of this embodiment, the identification output identified for each of two or more different amplitude identification voltages is integrated with respect to the optical signal of the DPSK modulation method, and the identification voltage is integrated. Since the quality information is calculated based on the integration result calculated every time, it is possible to easily estimate and evaluate the quality of the optical signal without depending on the transmission speed.

  In the above description, the case where the DPSK signal input to the interferometer 2 is an NRZ-DPSK signal has been described. However, the present invention is not limited to the NRZ-DPSK signal, and may be, for example, an RZ-DPSK signal. Absent.

  Further, in the configuration of this embodiment shown in FIG. 1, there is almost no portion depending on the signal transmission speed as in the clock extraction circuit. For example, the configuration of the interferometer 2 can be cited, but the influence of the transmission rate difference due to the error correction redundancy is small. Further, when the transmission rate is N times (N ≧ 2), the interferometer 2 operates as an N-bit interferometer. Therefore, by using an interferometer corresponding to the minimum transmission rate existing on the optical network, a signal can be obtained. An optical signal quality monitoring device that does not depend on the transmission speed can be obtained.

In addition, the average value μ ₁ of the probability density distribution and the standard deviation σ ₁ only need to have a mismatch rate calculated based on at least two different identification voltages. This is because the average value μ ₁ of the Gaussian distribution and the standard deviation σ ₁ can be estimated if there are at least two points of data.

  Further, the number of bits for each discrimination voltage is detected by replacing the discriminator 7 and the counter 8 in FIG. 1 with a soft decision discriminator having M (M ≧ 2) discrimination voltages and a D / A converter. Can be performed in parallel, and the quality of the optical signal with high accuracy can be estimated and evaluated in real time.

Embodiment 2. FIG.
FIG. 5 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the second embodiment of the present invention. The optical signal quality monitoring apparatus shown in FIG. 1 is the same as the optical signal quality monitoring apparatus shown in FIG. 1 except that the polarity of the optical receiver 4 is inverted and the signal photoelectrically converted by each optical receiver is sent to the subtractor 12. The difference signal is generated by inputting. In addition, about another structure, it is the same as that of Embodiment 1, or is equivalent, and attaches | subjects and shows these parts about the same part.

  Next, the operation of the optical signal quality monitoring apparatus shown in FIG. 5 will be described. FIG. 6A is a diagram showing signal waveforms of the main part of the optical signal quality monitoring apparatus according to the second embodiment to which an optical DPSK signal is inputted, and FIG. 6B is a diagram showing respective timing charts. FIG. 6C is a diagram showing the distribution of the mismatch rate (error rate) with respect to the identification voltage.

  As shown in FIGS. 6A and 6B, the optical DPSK signal waveform (A) input to the interferometer 2 has binary phase difference information (0, π) with constant intensity. The waveforms (C) and (B) obtained by photoelectrically converting the outputs of the interferometer 2 by the optical receivers 3 and 4 have the same logic, and the waveform (B) is an NRZ signal having a negative potential. Become. However, the output of the optical receiver 4 shown in FIG. 6A is inverted as compared with the output of FIG. 4A. Therefore, the signals obtained by subtracting the two signals (B) and (C) by the subtracting circuit 12 are all signals having the logic “1” as shown in FIG. 6B (D). Since the subsequent processing is the same as the processing in the first embodiment, description thereof is omitted.

  The number of bits for each identification voltage is detected by replacing the classifier 7 and the counter 8 in FIG. 5 with a soft decision classifier having M (M ≧ 2) identification voltages and a D / A converter. In the same manner as in the first embodiment, the quality of the optical signal can be estimated and evaluated in real time.

  Similarly to the case of the first embodiment, the interferometer 2 is less affected by the transmission rate difference due to error correction redundancy. When the transmission rate is N times (N ≧ 2), the N-bit interferometer Therefore, by using an interferometer corresponding to the minimum transmission rate existing on the optical network, an optical signal quality monitoring device that does not depend on the signal transmission rate can be obtained.

  As described above, according to the optical signal quality monitoring apparatus of this embodiment, the identification output identified for each of two or more different amplitude identification voltages is integrated with respect to the optical signal of the DPSK modulation method, and the identification voltage is integrated. Since the quality information is calculated based on the integration result calculated every time, it is possible to easily estimate and evaluate the quality of the optical signal without depending on the transmission speed.

Embodiment 3 FIG.
FIG. 7 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the third embodiment of the present invention. The optical signal quality monitoring apparatus shown in the figure is configured to replace the interferometer 2 with an optical splitter 28 in the optical signal quality monitoring apparatus shown in FIG. ing. In addition, about another structure, it is the same as that of Embodiment 2, or is equivalent, and attaches | subjects and shows these parts about the same part.

  Next, the operation of the optical signal monitoring apparatus shown in FIG. 7 will be described. FIG. 8A is a diagram illustrating signal waveforms of main parts of the optical signal quality monitoring apparatus according to the third embodiment to which an optical NRZ (NRZ-OOK) signal is input, and FIG. 8B is a timing chart of each. FIG. 8C is a diagram showing a distribution of a mismatch rate (error rate) with respect to an identification voltage.

  As shown in FIGS. 8A and 8B, the optical NRZ signal waveform input to the optical splitter 28 has binary intensity information. Waveforms (c) and (b) obtained by photoelectrically converting the outputs of the optical splitter 28 by the optical receivers 3 and 4 have the same polarity, and the waveform (B) is an NRZ signal having a negative potential. It becomes. Therefore, the signals obtained by subtracting the two signals (B) and (C) by the subtracting circuit 12 are all signals having a logic “1” as shown in FIG. 8B (D).

Since the optical signal processed in this embodiment is an OOK signal, unlike the second embodiment, the probability density distributions of logic “1” and logic “0” are different. The probability density distribution is dominated by the logic “1” probability density distribution of the original optical OOK signal, and the relationship of σ ₁₀ ≈σ ₁ > σ ₀ is established. In addition, although the average values of logic “1” and logic “0” are different, the average value of the signal obtained by adding both is the sum of the average values of logic “1” and logic “0” of the original optical OOK signal. Therefore, the relationship of μ ₁₀ = μ ₁ + μ ₀ is established.

  As a result, the Q value of the present embodiment obtained from the histogram shown in FIG. 8C can be simplified as the following equation.

Q = μ ₁₀ / σ ₁₀ (3)

  In the above description, the case where the OOK signal input to the optical branching unit 28 is an NRZ-OOK signal has been described. However, the present invention is not limited to the NRZ-OOK signal, and may be, for example, an RZ-OOK signal. I do not care.

  Further, since the subsequent processing is the same as that of the second embodiment, description thereof is omitted.

  As described above, according to the optical signal quality device of this embodiment, the identification output identified for each of two or more different amplitude identification voltages is integrated with respect to the optical signal of the OOK modulation method, and each identification voltage is integrated. Since the quality information is calculated based on the calculated integration result, the quality of the optical signal can be estimated and evaluated easily without depending on the transmission speed.

Embodiment 4 FIG.
FIG. 9 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the fourth embodiment of the present invention. The optical signal quality monitoring apparatus shown in FIG. 1 is based on the transmitted optical RZ-DPSK signal (electric signal) applied to the discriminator 7 in the optical signal quality monitoring apparatus shown in FIG. The optical receiver 14 that is a third receiver for generation and a delay adjuster 15 that adjusts the phase (timing) of the clock signal applied to the discriminator 7 are provided. This configuration is the same as or equivalent to that of the first embodiment, and these portions are denoted by the same reference numerals.

  Next, the operation of the optical signal quality monitoring apparatus shown in FIG. 9 will be described. FIG. 10A is a diagram showing signal waveforms of main parts of the optical signal quality monitoring apparatus according to the fourth embodiment to which an optical RZ-DPSK signal is inputted, and FIG. 10B shows respective timing charts. FIG. 10C is a diagram showing the distribution of the mismatch rate (error rate) with respect to the identification voltage.

  As shown in FIGS. 10A and 10B, the optical RZ-DPSK signal waveform (A) input to the interferometer 2 is an optical pulse train whose repetition frequency is the bit rate frequency, and binary phase difference information (0 , Π). The waveforms (B) and (C) obtained by photoelectrically converting the outputs of the interferometer 2 by the optical receivers 3 and 4 are RZ signals having opposite polarities. By adding these two signals, an RZ signal indicating a logic “1” can be obtained.

In the optical RZ-DPSK signal, it is known that the logic “1” and the logic “0” have the same probability density distribution as in the optical NRZ-DPSK signal, and the probability density distribution of the signal obtained by adding the two together. Is the sum of the probability density distributions of logic “1” and logic “0” of the original optical RZ-DPSK signal. In particular, when the probability density distributions of logic “1” and logic “0” follow a Gaussian distribution, the relationship of σ ₁ = σ ₀ (= σ ₁₀ ) is established, as in the first embodiment. is there.

  The subsequent processing is the same as the processing in the first and second embodiments except that the determination of the logic level is performed based on the identification voltage varied based on the clock signal separately reproduced in the discriminator 7. Therefore, explanation is omitted.

  In the configuration shown in FIG. 9, since the repetition frequency of the input optical RZ-DPSK signal is a pulse train having a bit rate frequency, and no special clock extraction circuit is required, the clock extraction circuit itself depends on the transmission speed. It is not the structure to do.

  Similarly to the first and second embodiments, the interferometer 2 has a small influence on the transmission rate difference due to the error correction redundancy, and N bits when the transmission rate is N times (N ≧ 2). Since it can be operated as an interferometer, an optical signal quality monitoring device independent of the signal transmission rate can be obtained by using an interferometer corresponding to the minimum transmission rate existing on the optical network.

  As described above, according to the optical signal quality monitoring apparatus of this embodiment, since the clock signal is generated based on the electrical signal converted by the optical receiver, it is not dependent on the transmission speed and is simple. In addition, the quality of the optical signal can be estimated and evaluated.

Embodiment 5 FIG.
FIG. 11 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the fifth embodiment of the present invention. The optical signal quality monitoring apparatus shown in the figure is the same as the optical signal quality monitoring apparatus of the fourth embodiment shown in FIG. (Electrical signal) is used. In addition, about another structure, it is the same as that of Embodiment 4, or is equivalent, and attaches | subjects and shows these parts about the same part.

  Next, the operation of the optical signal quality monitoring apparatus shown in FIG. 11 will be described. In this figure, when an optical RZ-DPSK signal is input to the interferometer 2, the output signal (electric signal) of the adder 5 itself becomes the clock signal itself whose repetition frequency is the bit rate frequency. Can be used as a clock signal to be applied to the discriminator 7.

  Therefore, even the optical signal quality monitoring apparatus configured as shown in FIG. 11 can retain the same or equivalent function as in the fourth embodiment.

  As described above, according to the optical signal quality monitoring apparatus of this embodiment, since the clock signal is generated based on the addition output of each electric signal converted by the optical receiver, the transmission speed is increased. It is possible to easily estimate and evaluate the quality of the optical signal without depending on it.

Embodiment 6 FIG.
FIG. 12 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the sixth embodiment of the present invention. The optical signal quality monitoring apparatus shown in FIG. 1 includes an optical variable attenuator 16 that adjusts the optical signal power of an optical NRZ-DPSK signal or RZ-DPSK signal input from an optical fiber 1, and adjacent bits of the input optical signal. Interferometer 2 that outputs phase difference data between them, optical receivers 3 and 4 that are first and second optical receivers that convert optical signals into electrical signals, and output of optical receivers 3 and 4, respectively. The clock extractors 17 and 18 that generate the respective clock signals based on the clock signals, the discriminators 19 and 20 that respectively identify the logical levels of the input data based on the clock signals, and the outputs of the discriminators 19 and 20 An exclusive OR circuit 21 that performs an exclusive OR operation, a counter 8 that counts the output of the exclusive OR circuit 21, and the quality required for monitoring the quality of the optical signal based on the output of the counter 8 Quality information calculating unit 9 calculates and outputs the broadcast, and a control unit 10 for controlling the predetermined configuration of the quality monitoring apparatus.

  Next, the operation of the optical signal quality monitoring apparatus shown in FIG. In the figure, for example, an optical NRZ-DPSK signal or an RZ-DPSK signal is input from the optical fiber 1 to the interferometer 2, and the optical signals at the two output ports of the interferometer are respectively received by the optical receivers 3 and 4. Electrically converted. At this time, the optical signal power input to the interferometer 2 is adjusted to a desired value by the optical variable attenuator 16.

  Each electrical signal photoelectrically converted by the light receivers 3 and 4 shows a different logic level (logic “1” or logic “0”) from the logic level of the input optical signal. Each electric signal is branched independently and inputted to the discriminators 19 and 20 and the clock extractors 17 and 18. The clock signals extracted independently by the clock extractors 17 and 18 are input to the discriminators 19 and 20 after phase adjustment. Here, the identification voltage applied to the two discriminators 19 and 20 is given a constant value that minimizes the number of errors.

  The discrimination results discriminated by the discriminators 17 and 18 are respectively input to the exclusive OR circuit 21, and whether the two discrimination results match or do not match is discriminated. It is output to the calculation unit 9. The quality information calculation unit 9 generates and outputs predetermined quality information based on information such as the count value of the identification result.

  The control unit 10 controls predetermined components of the optical signal quality monitoring apparatus. For example, the variable attenuator 16 is controlled so that the level of the input optical signal is optimum, and the interferometer 2 is controlled to be stabilized with respect to the optical signal wavelength. The output control of the quality information calculation unit 9 is also performed based on the control of the control unit 10.

  By the way, since the optical signals output from the two output ports of the interferometer 2 are obtained from different components on the optical frequency axis, the respective probability density distributions have no correlation with each other. Therefore, in the discriminators 19 and 20, when the discrimination voltages are set on the respective distributions of the input signals, the discrimination results discriminated by the discriminators 19 and 20 are erroneous at almost the same rate. , Uncorrelated relationships are maintained.

  FIG. 13 is a diagram showing the relationship between the coincidence rate of the discrimination results and the error rate of the input signal. In view of the above-described relationship, as shown in the figure, the proportion of the two discrimination results discriminated by the discriminators 19 and 20 can be regarded as being proportional to the error rate of the input signal. In this way, by calculating the ratio at which the discrimination results match, the quality of the input optical signal can be estimated and evaluated.

  In this embodiment, since the discrimination voltage of each discriminator is set to a fixed value in advance, there is no need to vary (search) the discrimination voltage, and optical signal quality monitoring excellent in real-time performance is performed. Can do.

  As described above, according to the optical signal quality monitoring apparatus of this embodiment, the quality information is generated based on the ratio at which the two results identified by the clock signal match. It is possible to easily estimate and evaluate the quality of the optical signal without depending on it.

Embodiment 7 FIG.
FIG. 14 is a block diagram showing a configuration of the optical signal quality monitoring apparatus according to the seventh embodiment of the present invention. The seventh embodiment shown in the figure shows an example of the case where the optical signal quality monitoring apparatus shown in the first to fifth embodiments is arranged on the transmission line on which the optical wavelength division multiplexed signal is transmitted. .

  In the figure, an optical wavelength multiplexed signal transmitted through an optical transmission line 22 is connected to an optical cross connect 24 via a branch coupler 23. On the other hand, the output of the branch coupler branched for optical signal quality monitoring extracts a desired optical signal in the variable optical filter 25 and is output to the optical signal quality monitoring device 26. The optical signal quality monitoring device 26 outputs predetermined quality information related to the optical signal shown in the first to fifth embodiments to the control unit 27. The extracted signal extracted by the variable optical filter 25 and the quality information related to the extracted signal output from the optical signal quality monitoring device 26 are notified to the optical cross connect 24 via the control unit 27.

  As described in the first to fifth embodiments, the optical signal quality monitoring device 26 does not depend on the transmission rate for the optical signals of the DPSK modulation method and the OOK modulation method, and the quality of the optical signal. Since the apparatus can be easily evaluated, for example, even if the optical signal transmitted through the transmission line 22 is an optical wavelength multiplexed signal in which optical signals having different transmission speeds are multiplexed, any transmission speed can be obtained. Therefore, it can be applied uniformly to any optical signal, and the signal quality of each optical signal can be easily estimated and evaluated.

  As described above, according to this embodiment, the quality of the optical signal transmitted through the optical network system is not dependent on the transmission speed using the optical signal quality monitoring apparatus shown in the first to fifth embodiments. It is possible to easily estimate and evaluate.

  As described above, the optical signal quality monitoring apparatus according to the present invention is useful for evaluating the signal quality of an optical signal, and is particularly suitable for evaluating the quality of an optical signal in a networked optical communication line. It is.

FIG. 1 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the first embodiment of the present invention. FIG. 2 is a diagram showing an example of a probability density distribution of an input optical signal. FIG. 3 is a diagram showing a relationship between an electrical waveform of an NRZ (Non Return to Zero) -OOK signal, an identification voltage when the NRZ-OOK signal is input, and an error rate of an identification result. FIG. 4A is a diagram illustrating signal waveforms of main parts of the optical signal quality monitoring apparatus according to the first embodiment to which an optical DPSK signal is input. FIG. 4B is a diagram showing respective timing charts. FIG. 4C is a diagram showing the distribution of the mismatch rate (error rate) with respect to the identification voltage. FIG. 5 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the second embodiment of the present invention. FIG. 6A is a diagram illustrating signal waveforms of main parts of the optical signal quality monitoring apparatus according to the second embodiment to which an optical DPSK signal is input. FIG. 6B is a diagram showing respective timing charts. FIG. 6C is a diagram showing the distribution of the mismatch rate (error rate) with respect to the identification voltage. FIG. 7 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the third embodiment of the present invention. FIG. 8A is a diagram illustrating signal waveforms of main parts of the optical signal quality monitoring apparatus according to the third embodiment to which an optical NRZ (NRZ-OOK) signal is input. FIG. 8B is a diagram showing respective timing charts. FIG. 8C is a diagram showing the distribution of the mismatch rate (error rate) with respect to the identification voltage. FIG. 9 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the fourth embodiment of the present invention. FIG. 10A is a diagram illustrating signal waveforms of main parts of the optical signal quality monitoring apparatus according to the fourth embodiment to which an optical RZ-DPSK signal is input. FIG. 10B is a diagram showing respective timing charts. FIG. 10C is a diagram showing the distribution of the mismatch rate (error rate) with respect to the identification voltage. FIG. 11 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the fifth embodiment of the present invention. FIG. 12 is a block diagram showing the configuration of the optical signal quality monitoring apparatus according to the sixth embodiment of the present invention. FIG. 13 is a diagram showing the relationship between the coincidence rate of the discrimination results and the error rate of the input signal. FIG. 14 is a block diagram showing a configuration of the optical signal quality monitoring apparatus according to the seventh embodiment of the present invention.

Claims (14)

An optical signal quality monitoring device for monitoring the signal quality of a predetermined optical signal transmitted through a communication line of an optical network system,
An interferometer that outputs phase difference data between adjacent bits of the predetermined optical signal;
First and second optical receivers that convert the output optical signal output from the interferometer into an electrical signal and output mutually different polarity signals;
Adding means for performing an addition operation between the electric signal converted by the first optical receiver and the electric signal converted by the second optical receiver;
Clock generating means for generating and outputting a clock signal of a predetermined frequency;
A discriminator for identifying the output of the adding means at the timing of the clock signal;
A counter for calculating an integration result within a predetermined time obtained by counting the discrimination output of the discriminator for each logic level;
A quality information calculation unit that calculates and outputs quality information of the predetermined optical signal based on an integration result of the counter;
With
The discriminator outputs an identification output identified for each of two or more different discrimination voltages,
The quality information calculating unit, before the optical signal quality monitoring apparatus characterized by calculating the quality information on the basis of the integration result calculated for each Ki識 by voltage. An optical signal quality monitoring device for monitoring the signal quality of a predetermined optical signal transmitted through a communication line of an optical network system,
An interferometer that outputs phase difference data between adjacent bits of the predetermined optical signal;
First and second optical receivers that convert output optical signals output from the interferometer into electrical signals and output signals of the same polarity to each other;
Subtracting means for performing a subtraction operation between the electric signal converted by the first optical receiver and the electric signal converted by the second optical receiver;
Clock generating means for generating and outputting a clock signal of a predetermined frequency;
An identifier for identifying the output of the subtracting means by the timing of the clock signal;
A counter for calculating an integration result within a predetermined time obtained by counting the discrimination output of the discriminator for each logic level;
A quality information calculation unit that calculates and outputs quality information of the predetermined optical signal based on an integration result of the counter;
With
The discriminator outputs an identification output identified for each of two or more different discrimination voltages,
The quality information calculating unit, before the optical signal quality monitoring apparatus characterized by calculating the quality information on the basis of the integration result calculated for each Ki識 by voltage. It said predetermined optical signal, the optical signal quality monitoring system according to claim 1 or 2, characterized in that the NRZ-DPSK signal. It said predetermined optical signal, the optical signal quality monitoring system according to claim 1 or 2, characterized in that the RZ-DPSK signal. 3. The optical signal quality monitoring apparatus according to claim 1, wherein an external output is used as the clock signal. 3. The optical signal quality monitoring apparatus according to claim 1, wherein the discriminator is a soft decision discriminator. Before SL predetermined optical signal, the optical signal quality monitoring system according to claim 2, characterized in that the NRZ-OOK signals. Before SL predetermined optical signal, the optical signal quality monitoring system according to claim 2, characterized in that the RZ-OOK signals. Optical signal quality monitoring system according to claim 7 or 8, wherein the interferometer optical divider in place is found with. A third optical receiver for converting the predetermined optical signal into an electrical signal;
It said clock signal, the optical signal quality monitoring system according to claim 1 or 2, characterized in that it is generated based on the converted electric signal in the third optical receiver. 11. The optical signal quality monitoring apparatus according to claim 10 , wherein the clock signal is generated based on an addition output of electrical signals converted by the first and second optical receivers. 12. The optical signal quality monitoring apparatus according to claim 10 , wherein the predetermined optical signal is an RZ-DPSK signal. The quality information calculation unit
3. The optical signal quality monitoring apparatus according to claim 1, wherein the quality information is generated based on a ratio at which two results identified by the clock signal match. The predetermined optical signal is a wavelength-multiplexed optical signal;
A branching optical coupler for branching the wavelength multiplexed optical signal;
An optical filter that extracts an optical signal of a predetermined wavelength;
And an optical signal quality monitoring system as claimed in claims 1 to 13,
With
The optical signal quality monitoring device is:
An optical network system for monitoring the quality of an optical signal extracted by the optical filter.

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