KR20040098975A - Optical signal quality observing apparatus - Google Patents

Abstract

An optical signal performance monitoring apparatus is disclosed. The optical signal performance monitoring apparatus includes an optical signal detector for converting an optical signal received through a transmission line into an electrical signal, a reference voltage generator for generating reference voltages at a predetermined interval including a full range of signal levels of the electrical signal, Comparator for comparing the signal level of the signal and the magnitude of the reference voltages respectively to calculate the difference value according to the comparison result, the average voltage calculation unit for calculating the average voltage value for the difference value in units of a predetermined signal level, accumulate the average voltage value And a processor configured to calculate a distribution function using the accumulated average voltage value stored in the memory.

Description

Optical signal performance monitoring device {OPTICAL SIGNAL QUALITY OBSERVING APPARATUS}

The present invention relates to an optical signal performance monitoring apparatus, and more particularly, to monitor the optical signal performance that can monitor the distortion of the optical signal generated when the optical signal is transmitted and received using a change in the distribution of data according to the change in the reference voltage Relates to a device.

The optical signal transmitted and received in the optical transmission system may cause distortion of the signal due to loss in the optical device used, nonlinear phenomenon due to the characteristics of the optical fiber as a transmission medium, color dispersion, and ASE noise caused by the optical amplifier. Accordingly, there is a need for an optical signal performance monitoring apparatus capable of measuring the performance of a signal according to whether the optical signal is distorted.

Monitoring the performance of optical signals is one of the methods used to determine the transmission channel performance of optical signals at specific points. Using this optical signal performance monitoring method, it is possible to find out the quality or performance of an optical signal at a specific point in the network without prior knowledge of data transmission information or path.

Current optical signal performance monitoring method is to monitor the bit interleaved parity bit (B1) of the SONET frame to determine the bit error rate (BER) and Q value. This method counts " 1 " in each bit from 1 to 8 of every byte to determine even and odd. In this case, the current parity byte and the past byte are compared with each other, and a difference is generated. However, such an optical signal performance monitoring method is not suitable when an even number of bits in which parity is calculated does not affect the overall parity value, and thus an actual bit error rate and difference are affected by the data rate. There is this.

Another method for monitoring optical signal performance is to measure indirectly by measuring variables that affect the bit error rate. This method can also be used to calculate the cause of signal-to-noise ratio (SNR) reduction and the degree of signal distortion by measuring the noise figure or optical fiber dispersion of the optical amplifier. However, next generation networks are becoming more dynamic. In addition, optical signals are subject to various complex paths such as optical fibers, amplifiers, optical branch / coupling multiplexers, and optical cross-connects. Therefore, the wavelength signal in a specific part of the network goes through different transmission processes, and the transmission path and process change dynamically as the wavelength is dynamically branched / combined. Accordingly, the direct measurement of the bit error rate is quite difficult because the data pattern is random and only a part of the power needs to be monitored to prevent degradation of the pass signal.

Accordingly, channel characteristics are monitored through dispersion, crosstalk, extinction ratio, signal-to-noise ratio, channel power, and the like, as a suboptimal measure for optical signal performance monitoring. In addition, the optical signal-to-noise ratio (OSNR), which can be obtained from the signal-to-noise ratio, can predict the performance of the optical signal. However, the measurement of the optical signal-to-noise ratio requires a lot of monitoring points in the middle of the path, and the input signal of several channels is required for the useful optical signal-to-noise ratio data. In addition, since the optical signal-to-noise ratio is a measurement for the average time, there is a problem that the optical signal-to-noise ratio is not sensitive to signal distortion such as nonlinear characteristics or optical fiber dispersion and thus is not reflected in the measurement result. In addition, the optical signal-to-noise ratio has characteristics that are independent of the signal extinction ratio or receiver type, and the decision point for determining "1" and "0" of the bit. For this reason, it is difficult to determine the exact bit error rate through the optical signal-to-noise ratio.

As described above, various methods for predicting the bit error rate or the Q value of the optical signal have been proposed for monitoring the optical signal performance. However, this approach is limited to the scope of histogram analysis of sampled signals as a means for predicting bit errors or Q values of signals. That is, as each of μ _1, μ ₀ and σ _1, σ _0, the mean and standard deviation values of "1" and "0" level of the output voltage, and, Q values to approximate the ASE noise distribution to a Gaussian random variable The bit error rate (BER) can be calculated through Equations 1 and 2 below.

On the other hand, there are asynchronous and synchronous methods for sampling optical signals. The asynchronous sampling method randomly samples the signal level among all bits without a fixed sampling point related to decision time, thereby eliminating the need for clock recovery and ensuring complete transparency in bit rate or signal format. However, the asynchronous sampling scheme affects the accuracy of the results due to the large amount of additional and unwanted samples.

On the other hand, the synchronous sampling method effectively samples the signal level only at the decision level, thereby creating a histogram and analyzing the Q value and the bit error rate of the signal. In general, a value closer to the desired data can be obtained than the data of the asynchronous sampling method, but a receiver having a clock recovery circuit is separately required. Accordingly, in the synchronous sampling method, when using a clock recovery circuit having a fixed bit rate, there is no transparency for the bit rate, and transparency for the data format is guaranteed.

As an example of a direct bit error rate measuring method, a method of measuring a bit error rate by comparing a change of data values "1" and "0" according to a small change of a threshold with a logic element ExOR has been proposed. .

FIG. 1 is a diagram schematically illustrating a method of measuring a bit error rate using a logic device for monitoring optical signal performance. As shown, this scheme recognizes the second bit determined as "0" when the reference voltage value is Vth1 and an error as determined by "1" when the reference voltage value is Vth2. This method can be easily configured with only two decision circuits having a fixed reference voltage and a decision circuit capable of varying the reference voltage. However, since it does not monitor the full range of signal levels, it is quite different from the actual bit error rate.

A representative method of estimating the bit error rate by determining the Q value through a histogram is a "0" level counting method. This method converts an optical signal into an electrical signal and counts a signal level smaller than the reference voltage value (ie, a "0" level) while changing the reference voltage of the signal level. Accordingly, in this method, a value counted at a specific reference voltage is stored in a memory, a histogram is obtained through a distribution obtained for each variable reference voltage, and μ1,0 and σ1,0 are determined to calculate a Q value. Since this method compares the photoelectrically converted electrical signal with the reference voltage and obtains a histogram using the data after determining "0" and "1", it is necessary to subdivide the reference voltage level to obtain an accurate distribution. Do. In addition, when using this method, it is difficult to find a minute change in the signal due to ASE noise.

An object of the present invention for solving the above problems is to solve the disadvantage of the method of indirectly monitoring the degraded performance of the optical signal by measuring the variables affecting the bit error rate, and the method of measuring the bit error rate through the Q value It is to provide an optical signal performance monitoring device that can reduce the error rate.

Another object of the present invention is to provide a device capable of monitoring the quality and performance of a signal that may be crosstalk due to various factors in an optical transmission system, and thus more actual bit error rate than "0" and "1" data determined by reference voltage. It is an object of the present invention to provide an optical signal performance monitoring apparatus capable of obtaining a value close to.

It is still another object of the present invention to provide an optical signal performance monitoring apparatus capable of easily monitoring crosstalk due to minute changes in signal levels.

1 is a view briefly illustrating a method of measuring a bit error rate using a logic device for monitoring optical signal performance;

2 is a block diagram showing a preferred embodiment of the optical signal performance monitoring apparatus according to the present invention;

3 to 5 are views for explaining the operation of the comparator for calculating the average voltage using the difference between the electrical signal and the reference voltage input by FIG.

6 is a graph for explaining a method of calculating a voltage distribution of an input signal level using an average voltage value.

Explanation of symbols on the main parts of the drawings

120: optical signal detector 130: clock generator

140: comparison unit 160: reference voltage generation unit

180: average voltage calculation unit 220: memory

260: Processor

The object as described above, according to the present invention, the optical signal detection unit for converting the optical signal received through the transmission line into an electrical signal, generating a reference voltage for generating a reference voltage of a predetermined interval including the full range of the signal level of the electrical signal A comparison unit for comparing the signal level of the electrical signal and the magnitude of the reference voltages to calculate the difference value according to the comparison result, the average voltage calculation unit for calculating the average voltage value for the difference value in units of a predetermined signal level, average voltage An optical signal performance monitoring apparatus includes a memory for accumulating and storing a value, and a processor for calculating a distribution function using the accumulated average voltage value stored in the memory.

Preferably, when generating the reference voltage, the reference voltage generator detects the minimum and maximum values of the signal level of the electrical signal and generates reference voltages having equal intervals between the minimum and maximum values.

In addition, the comparison unit compares all the signal levels of the electrical signal with the reference voltage generated by the reference voltage generation unit to calculate the absolute value for the difference value according to the comparison result. Accordingly, the average voltage calculator calculates an average value of the absolute values in units of a predetermined signal level.

On the other hand, the average value calculation unit is to calculate the average voltage value for each reference voltage by dividing the absolute value of the difference by the sum of the absolute value of the difference value calculated according to the comparison result of the comparison unit by the total number of signal levels of the electrical signal Do.

Accordingly, the processor calculates a distribution function for the signal level of the electrical signal from the average voltage value calculated by the average voltage calculator and calculates the average value and the standard deviation value of the "0" level and the "1" level of the signal level, respectively. It is preferable to calculate the Q value and the bit error rate which are variables for monitoring the performance of the optical signal.

According to the present invention, an average voltage value is calculated by comparing an input signal level with a reference voltage value, and a distribution function of a signal level is calculated using the average voltage value, and the "0" level and "1" level are calculated from the calculated distribution function. By calculating the average value and the variance, and calculating the Q value and the bit error rate, which are variables for monitoring the optical signal performance using the calculated average value and the variance, the performance of the optical signal can be monitored regardless of the data format. In addition, it is possible to easily measure the deterioration of the optical signal due to various factors such as loss occurring in the optical device, nonlinear phenomenon in the optical fiber, color dispersion, and deterioration of the optical signal to noise ratio.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail. It should be noted that the same elements in the figures are represented by the same numerals wherever possible. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

2 is a block diagram showing a preferred embodiment of the optical signal performance monitoring apparatus according to the present invention. As shown, the optical signal performance monitoring apparatus, the optical signal detector 120, the reference voltage generator 160, the clock generator 130, the comparison unit 140, the average voltage calculation unit 180, the memory ( 220, and a processor 260.

The optical signal detector 120 converts the input optical signal into an electrical signal. The reference voltage generator 160 variably generates the reference voltage. The clock generator 130 detects the reference clock from the electrical signal converted by the optical signal detector 120. The comparator 140 determines and detects a level difference between the reference voltage generated by the reference voltage generator 160 and the electrical signal converted by the optical signal detector 120. The average voltage calculator 180 calculates an average voltage of the comparison result of the specific reference voltage and the electrical signals in the comparator 140. The memory 220 accumulates and stores the average voltage calculated by the average voltage calculator 180. The processor 260 calculates a Q value and a bit error rate by obtaining a distribution of data using an average voltage value stored in the memory 220.

3, 4 and 5 are views for explaining the operation of the comparator 140 for calculating the average voltage using the difference between the electrical signal and the reference voltage input by FIG. Therefore, a comparison method for calculating the average voltage according to the present embodiment will be described with reference to FIG. 2.

The electrical signal converted by the optical signal detector 120 may be represented as shown in FIGS. 3A, 4A, and 5A. Here, the reference voltage generator 160 detects the lowest value a (V _min ) and the highest value d (V _max ) of the signal level (V _i ) of the converted electric signal, and the reference voltage (V _th ) at a predetermined interval (Δ). Occurs. In this embodiment, V _th 1, V _th 2, and V _th 3 are set as the reference voltage V _th . More specifically, V _th 1 is is set between the minimum value of the signal level _{(V i) a (V min} ) and a maximum value of "0" level (b), V _th 2 is "0" level and "1 "it is set between the levels, and, V _th is a 3-level signal (V _i) up to the value d (V _max) and the" is set between the first "minimum value (c) of the level.

Comparator 140 is the difference between the reference voltage (V _th ) generated by the reference voltage generator 160 and the signal level (V _i ) of the electrical signal transmitted from the optical signal generator 120 (V _th- the absolute value of _{V i) (| V th -V} i | a) and outputs the average voltage calculation unit 180.

3B is a graph illustrating a comparison result calculated by the comparator 140 when the reference voltage is V _th 1 adjacent to the "0" level. In other words, the figure is represented a difference between the reference voltage (V _th) is V _th in case of 1, V _th 1 and an input signal level (V _i).

4B is a graph illustrating a comparison result calculated by the comparator 140 when the reference voltage is V _th2 between the level "0" and the level "1". In other words, the figure is represented a difference between the reference voltage (V _th) is V _th 2 when il, V _th 2 and an input signal level (V _i).

5B is a graph illustrating a comparison result calculated by the comparator 140 when the reference voltage is Vth3 adjacent to the "1" level. In other words, the figure is represented a difference between the reference voltage (V _th) is 3 V _th be when, V _th 3 and an input signal level (V _i).

As to above, the comparator 140 outputs a specific reference voltage (V _th) and an input signal level (V _i) comparing the result (FIG. 3B, FIG. 4B, FIG. 5B) to the average voltage calculation unit 180 do. An average voltage calculation unit 180 calculates an average voltage value by dividing the result of the comparison, to the reference voltage (V _th), the total signal level of the comparison result output by each of the respective reference voltage (V _th). At this time, the memory 220 is stored an average value of an input signal level (V _i) to the reference voltage (V _th) calculated from the average voltage calculation unit 180. Preferably, the memory 220 accumulates and stores until the reference voltage V _th , which varies at a predetermined interval Δ compared by the comparator 140, becomes “V _min + α”.

6 is a graph for explaining a method of calculating a voltage distribution of an input signal level using an average voltage value.

FIG. 6A is a graph illustrating the average voltage value stored in the memory 220 divided by the reference voltage V _th . Here, the function of the average voltage value stored in the memory 220 is defined as g (υ _i ), and the range of the reference voltage V _th is largely divided into five parts as a, b, c, d, and e. have.

Mean Time to increase as the first to the scope of the a domain reference voltage (V _th) is from "0" to V _min (a), any input signal level (V _i), so even areas that the reference voltage (V _th) The voltage will decrease linearly.

Second, area b includes the reference voltage V _th 1 in which the "0" level is distributed. The lowest value of the "0" level (a in FIG. 3A) to the highest value of the "0" level (b in FIG. 3A) is included. Say. Eventually, we can find the distribution in this area to find the mean and standard deviation of the "0" level.

Third, the region c is a value between the level "0" and the level "1" including the reference voltage V _th 2, and the graph is changed according to the overall distribution of the level "0" and the level "1". In FIG. 4A, the region c shows the same distribution, and the average value in the region c remains constant.

Fourthly, the d region is a region in which the reference voltage V _th 3 is included and the "1" level is distributed. That is, the d region refers to the lowest value (c in FIG. 3A) to the highest value (d in FIG. 3A) at the " 1 " level. As a result, the distribution in the d region is obtained to obtain the mean and standard deviation of the "1" level.

Finally, in the e region, when the reference voltage is greater than V _max (d in FIG. 3A), the average voltage value increases linearly.

The processor 260 calculates the change amount F (v _i ) of the average voltage by using Equation 3 below using the average voltage value shown in FIG. 6A.

The variation amount F (v _i ) of the average voltage value thus calculated may be represented as shown in FIG. 6B. In addition, the processor 260 calculates the voltage distribution f (υ _i ) of the signal by using Equation 4 below.

The voltage distribution f (υ _i ) of the signal thus calculated may be represented as shown in FIG. 6C. Here, the distribution function f (υ _i ) representing the voltage distribution f (υ _i ) of the signal can be expressed by two Gaussian distributions having average values υ _mi and υ _m0 . At this time, the average values υ _mi and υ _m0 are equivalent to marks / spaces rail in the absence of ASE noise and satisfy the following Equation 5.

,

Accordingly, the voltage distribution f (υ _i ) of the marks / spaces rail may be expressed as Equation 6 below as a general Gaussian distribution.

In addition, the standard deviation values σ ₀ and σ ₁ can be generally expressed by Equation 7 below using the distribution functions f (υ _i ) and the average values υ _mi and υ _m0 .

The processor 260 calculates the Q value and the bit error rate by calculating the signal distribution function f (υ _i ) and the mean values υ _mi and υ _m0 of the signals / spaces rail and the standard deviations σ ₀ and σ ₁ from the above equations. Can be.

The Q value may be calculated by Equation 1. Here, mu ₀ and mu ₁ represent the average values when the input signal levels of the electrical signals to which the optical signals are converted and input are "0" and "1", respectively. σ ₁ and σ ₀ represent the variance for each mean value. Accordingly, the bit error rate may be calculated by Equation 2.

Therefore, the optical signal performance monitoring apparatus of this embodiment calculates the distribution of signal levels by converting the input optical signal into an electrical signal and calculating the average voltage value by comparing the signal level of the converted electrical signal with a reference voltage value. Thus, the optical signal performance monitoring apparatus calculates an average value and a variance of the "0" level and the "1" level from the calculated distribution function, respectively, and uses the calculated average value and the variance of the Q values, which are variables for monitoring the optical signal performance. Calculate the bit error rate. Accordingly, the optical signal performance monitoring apparatus can monitor the performance of the optical signal regardless of the data format, such as loss in the optical device, nonlinear phenomenon in the optical fiber, color dispersion, and degradation of the optical signal-to-noise ratio. The deterioration of the optical signal due to various factors can be easily measured. By measuring the degradation of the optical signal using the optical signal performance monitoring device, it is possible to implement a flexible and stable transmission system using the measurement results.

According to the present invention, an average voltage value is calculated by comparing an input signal level with a reference voltage value, and a distribution function of a signal level is calculated using the average voltage value, and the "0" level and "1" level are calculated from the calculated distribution function. By calculating the average value and the variance, and calculating the Q value and the bit error rate, which are variables for monitoring the optical signal performance using the calculated average value and the variance, the performance of the optical signal can be monitored regardless of the data format. In addition, it is possible to easily measure the deterioration of the optical signal due to various factors such as loss occurring in the optical device, nonlinear phenomenon in the optical fiber, color dispersion, and deterioration of the optical signal to noise ratio.

In the above, specific preferred embodiments of the present invention have been illustrated and described. However, the present invention is not limited to the above-described embodiment, and various modifications can be made by any person having ordinary skill in the art without departing from the gist of the present invention attached to the claims. will be.

Claims (5)

In the optical signal performance monitoring device, An optical signal detector for converting an optical signal received through a transmission line into an electrical signal; A reference voltage generator for generating reference voltages at a predetermined interval including a full range of signal levels of the electrical signal; A comparison unit comparing the signal level of the electrical signal with the magnitudes of the reference voltages and calculating a difference value according to a comparison result; An average voltage calculator configured to calculate an average voltage value of the difference in units of a predetermined signal level; A memory for accumulating and storing the average voltage value; And And a processor for calculating a distribution function using the accumulated average voltage value stored in the memory. The method of claim 1, The reference voltage generation unit generates the reference voltage having an equal interval between the minimum value and the maximum value by detecting the minimum value and the maximum value of the signal level of the electrical signal when generating the reference voltage. Signal performance monitoring device. The method of claim 2, The comparison unit compares all the signal levels of the electrical signal with the reference voltage generated by the reference voltage generation unit to calculate an absolute value for the difference value according to the comparison result, And the average voltage calculator calculates an average value of the absolute value in units of the predetermined signal level. The method of claim 3, wherein The average value calculator calculates an average voltage value for each reference voltage by dividing the absolute value of the difference value by the total number of signal levels of the electrical signal by adding the absolute values of the difference values calculated according to the comparison result of the comparison unit. Optical signal performance monitoring device, characterized in that. The method of claim 4, wherein The processor calculates a distribution function for the signal level of the electrical signal from the average voltage value calculated by the average voltage calculator and calculates an average value and a standard deviation value of "0" level and "1" level of the signal level, respectively. And calculating a Q value and a bit error rate, which are variables for monitoring the performance of the optical signal.