JP2009049728A - Dispersion amount judgment method, dispersion amount judgment program, optical reception method, and optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly judge a dispersion amount even when fluctuation of duty ratios occurs in a transmission signal. <P>SOLUTION: A received optical signal coming from an optical fiber is photoelectrically converted, a received electric signal amplified to fixed amplitude is judged by a plurality of different thresholds, the respective obtained judgment results are separately integrated, magnitude of inclination of connection connected by plotting the respective obtained integrated values in order of high threshold or in order of low threshold is detected, when the distribution amount by the optical fiber is judged from the magnitude of inclination, the duty ratio of the transmission signal is judged from magnitude of the integrated value corresponding to a specific threshold among the plurality of thresholds, and the distribution amount is judged based on the judged duty ratio and the magnitude of the inclination. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dispersion amount determination method for determining a dispersion amount of an optical fiber based on deterioration due to dispersion of a high-speed optical signal in the optical fiber, a dispersion amount determination program, an optical reception method for performing dispersion compensation, and The present invention relates to an optical receiver.

  At present, with the spread of the Internet, in access networks, it is required to economically realize further speedup by introducing an optical communication system. In an optical communication system, the transmission rate per user can be increased by increasing the transmission rate of an optical transceiver that inputs and outputs optical signals.

  However, when the transmission speed of an optical signal is increased, the problem that the optical signal after being transmitted through the optical fiber is deteriorated due to the dispersion of the optical fiber (wavelength dispersion or polarization mode dispersion) is common in Non-Patent Document 1 and the like. Known to. Therefore, many optical receivers using an electrical dispersion compensation (EDC) technique have been studied in order to economically restore the waveform of the received electrical signal deteriorated due to dispersion to the original waveform. An electrical dispersion compensation circuit and an eye monitor circuit are added to the optical receiver using the electrical dispersion compensation technique. In order to perform economical dispersion compensation, it is common to change the dispersion compensation amount of the electrical dispersion compensation circuit according to the dispersion amount judged by the eye monitor circuit. This is a very important function for dispersion compensation.

  FIG. 6 shows the configuration of a conventional feedback-type electric dispersion compensator that forms part of the optical receiver. This electrical dispersion compensator includes an automatic gain control type amplifier (GCA) 10 that amplifies a received electrical signal subjected to photoelectric conversion so that the amplitude is constant, an electrical dispersion compensation circuit 20 that performs dispersion compensation of the received electrical signal, and electrical dispersion. It comprises an electrical dispersion compensation circuit control unit 30 that sends a dispersion compensation control signal to the compensation circuit 20 and an eye monitor circuit 40 that determines the amount of dispersion. The eye monitor circuit 40 includes three determination circuits 41, 24, and 43 having different threshold values H, M, and L, three integrators 44, 45, and 46 that integrate the determination results, and a dispersion amount determination. The device 47 is configured.

  In this configuration, the eye monitor circuit 40 operates as follows. Each of the determination circuits 41, 42, and 43 outputs a high-level determination result when the input signal exceeds the thresholds H, M, and L, and outputs a low-level determination result when the input signal is below the thresholds H, M, and L. Output. The determination result signals output from the determination circuits 41, 42, 43 are input to the integrators 44, 45, 46. Each integrator 44, 45, 46 integrates the input signal and outputs a DC voltage. The dispersion amount determiner 47 determines the amount of dispersion based on the output voltage values of these three integrators 44, 45, and 46 and transmits the result to the electrical dispersion compensation circuit control unit 30. The electrical dispersion compensation circuit control unit 30 sets the compensation amount based on the determined dispersion amount so that the dispersion compensation in the electrical dispersion compensation circuit 20 is optimized.

  FIG. 7 shows the output voltage characteristics of the integrators 44, 45, and 46 when a received electric signal that is not deteriorated due to dispersion and a received electric signal that is deteriorated due to dispersion are input. Here, the threshold value is H> M> L. Characteristic A (dotted line) is a characteristic at the time of input of a received electric signal without deterioration, and characteristic B (solid line) is a characteristic at the time of input of a received electric signal deteriorated by dispersion. When the received electrical signal without deterioration (characteristic A) is input, if the output voltages of the integrators 44, 45, and 46 corresponding to the low threshold (L) from the high threshold (H) are sequentially plotted, each plot is slightly to the right. It can be seen that they are lined up in a straight line. On the other hand, when the received electrical signal deteriorated due to the dispersion (characteristic B) is found, the upward slope becomes larger than that of the characteristic A. This is because the received electrical signal spreads in time and the duty ratio decreases due to dispersion.

Therefore, if the amount of dispersion is large, the phenomenon that the tail of the received electrical signal spreads remarkably appears. Therefore, the greater the slope of the connection obtained by plotting the output voltage of each integrator 44, 45, 46, the greater the influence of dispersion. It can be estimated that they are receiving a lot. Therefore, the dispersion amount determination unit 47 can determine the dispersion amount by calculating the inclination of this connection.
Govind P. Agrawal, “Fiber-optic communication systems”, John Wiley & Sons INS 1997

  However, the method of judging the amount of dispersion only from the slope of the connection made by plotting the output voltages of the integrators 44, 45, and 46 of the eye monitor circuit 40 converts the deterioration of the received electric signal waveform into a change in the duty ratio. Therefore, when the duty ratio of the transmission signal fluctuates, the dispersion amount cannot be determined correctly. Therefore, if the determined dispersion amount is used, the electrical dispersion compensation circuit 20 cannot normally perform dispersion compensation of the received electrical signal.

  In view of the above points, an object of the present invention is to make it possible to correctly determine the amount of dispersion even when the duty ratio of a transmission signal fluctuates, and to receive data that has deteriorated based on the result of determination of the amount of dispersion. The purpose is to normally perform dispersion compensation of electrical signals.

In order to achieve the above object, a dispersion amount determination method according to a first aspect of the present invention is to determine a received electrical signal obtained by photoelectrically converting a received optical signal arriving from an optical fiber and amplifying the received optical signal with a plurality of different threshold values. Integrating each obtained judgment result individually, and plotting at least two of the obtained integral values in order of increasing or decreasing threshold value to detect the magnitude of the slope of the connection. In the method of determining the amount of dispersion by the optical fiber from the magnitude of the inclination, the duty ratio of the transmission signal is determined from the magnitude of the integral value corresponding to a specific threshold value among the plurality of threshold values, and the determination The amount of dispersion is determined based on the duty ratio and the magnitude of the slope.
The invention according to claim 2 is characterized in that, in the dispersion amount determination method according to claim 1, a threshold value that minimizes the amount of fluctuation of the integral value is used as the specific threshold value. According to a third aspect of the present invention, there is provided a dispersion amount determination program including a first step of determining a received electrical signal obtained by photoelectrically converting a received optical signal arriving from an optical fiber and amplifying the received optical signal to a predetermined amplitude with a plurality of different threshold values, A second step of individually integrating each determination result obtained in the step to obtain an integral value; and a duty ratio of the transmission signal from the magnitude of the integral value corresponding to a specific threshold value among the plurality of threshold values. A third step of determining, and a fourth step of detecting the magnitude of the slope of the connection obtained by plotting and connecting each of the integral values corresponding to at least two of the plurality of threshold values in order of increasing or decreasing threshold value And a fifth step of determining the amount of dispersion based on the determined duty ratio and the magnitude of the inclination.
According to a fourth aspect of the present invention, there is provided an optical receiving method for performing dispersion compensation on a received electric signal obtained by photoelectrically converting a received optical signal arriving from an optical fiber and amplifying the received optical signal to a constant amplitude. On the other hand, the dispersion compensation is performed according to the dispersion amount determined by the dispersion amount determination method according to claim 1.
According to a fifth aspect of the present invention, there is provided an optical receiver comprising: an amplifier that amplifies a signal obtained by photoelectrically converting a received optical signal arriving from an optical fiber to a received optical signal having a constant amplitude; and a received electrical signal output from the amplifier. An electrical dispersion compensation circuit that compensates for dispersion caused by the optical fiber, and a received electrical signal output from the electrical dispersion compensation circuit or the amplifier is input and determined by a plurality of different thresholds, and the determined results are integrated individually, Plotting at least two of the obtained integral values in order of increasing or decreasing threshold value and detecting the magnitude of the slope of the connection, and determining the amount of dispersion by the optical fiber from the magnitude of the slope An optical receiver comprising: an eye monitor circuit that generates a dispersion compensation control signal in the electrical dispersion compensation circuit according to a dispersion amount determined by the eye monitor circuit The eye monitor circuit determines a duty ratio of the transmission signal from the magnitude of the integral value corresponding to a specific threshold value among the plurality of threshold values, and determines the determined duty ratio and the magnitude of the slope. The amount of dispersion is determined based on this.
According to a sixth aspect of the present invention, in the optical receiver according to the fifth aspect of the present invention, as the specific threshold value, a threshold value that minimizes the amount of fluctuation of the integral value is used. According to a seventh aspect of the present invention, in the optical receiver according to the fifth or sixth aspect, the eye monitor circuit includes a plurality of determination circuits in which different threshold values are set, and an integrated value of determination results of the plurality of determination circuits. And determining a duty ratio of a transmission signal from the magnitude of an integral value obtained by a specific integrator among the plurality of integrators, and determining the determined duty ratio and the magnitude of the slope. The amount of dispersion is determined based on the above.
According to an eighth aspect of the present invention, in the optical receiver according to the fifth or sixth aspect, the eye monitor circuit includes one determination circuit whose threshold value is switched to a plurality of different values, and a determination based on each threshold value of the determination circuit. One integrator that obtains an integral value for each threshold for the result, and determines a duty ratio of the transmission signal from the magnitude of the integral value corresponding to a specific threshold among the plurality of thresholds, and the determined duty The amount of dispersion is determined based on the ratio and the magnitude of the slope.

  According to the present invention, even when the duty ratio fluctuates in the transmission signal, it is possible to correctly determine the dispersion amount of the optical fiber, and the received electric signal deteriorated based on the dispersion amount determination result can be obtained. It becomes possible to compensate for dispersion normally.

<Example 1>
FIG. 1 is an explanatory diagram of a dispersion amount determination method according to an embodiment of the present invention. In the present embodiment, the output voltages of the three integrators 44, 45, 46 corresponding to the three determination circuits 41, 42, 43 of the eye monitor circuit 40 in the configuration of the feedback type electric dispersion compensation device shown in FIG. Based on the above, the dispersion amount determination program for determining the duty ratio and the dispersion amount performs processing in the dispersion amount determination unit 47.

  In FIG. 1, characteristics A1, A2, and A3 (dotted lines) indicate integrators 44 corresponding to a high threshold (H) to a low threshold (L) when a received electrical signal that is not deteriorated by dispersion is input to the eye monitor circuit 40. , 45 and 46 are plotted in order from left to right, and the plots are connected. Characteristics B1, B2, and B3 (solid lines) are similar characteristics when the received electrical signal deteriorated due to dispersion is input to the eye monitor circuit 40. ○ (A2, B2) is the characteristic when the duty ratio is 50%, Δ mark (A1, B1) is the characteristic when the duty ratio exceeds 50%, and □ (A3, B3) is the characteristic when the duty ratio is less than 50% Is a characteristic. The threshold value M of the determination circuit 42 is set to a value that minimizes the amount of fluctuation in the output voltage of the integrator 45 when dispersion is given. Further, the threshold values H, M, and L of the determination circuits 41, 42, and 43 are set so that mark level> H> M> L> space level.

  FIG. 2 shows a difference in signal waveform when a received optical signal deteriorated due to dispersion is converted into a received electrical signal when the duty ratio of the transmitted optical signal is less than 50%, 50%, or more than 50%. When the duty ratio is 50%, when dispersion is given, the upper and lower sides of the received electrical signal spread evenly, and the slope of the connection plotting the output voltages from the integrators 44, 45, and 46 increases. On the other hand, when the duty ratio is less than 50%, if the dispersion is given, the received electrical signal spreads downward, so that the output voltage from the integrators 44, 45, and 46 is reduced overall, but their outputs are reduced. The slope of the connection in which the voltage is plotted is larger than that at 50%. Further, when the duty ratio exceeds 50%, if the dispersion is given, the received electric signal spreads upward, so that the output voltage from the integrators 44, 45, 46 increases as a whole. The slope of the connection in which the voltage is plotted is larger than that at 50%.

  In such a case, in this embodiment, the amount of dispersion is detected as follows. First, it is determined whether the duty ratio of the transmission signal is less than 50%, 50%, or more than 50% based on the output voltage of the integrator 45, and then the determined duty ratio and the integrators 44 and 46 are used. The corresponding amount of dispersion is determined from the slope of the connection in which the output voltage is plotted.

  Specifically, in determining the duty ratio, a first correspondence table (conversion table) indicating the relationship between the output voltage of the integrator 45 and the duty ratio is created in advance by experiments or the like and stored in the dispersion amount determiner 47. This is done with reference to the first correspondence table according to the actual output voltage of the integrator 45. For example, when the output voltage of the integrator 45 belongs to the high level range, the duty ratio exceeds 50%. When the output voltage belongs to the middle level range, the duty ratio is 50%. When the output voltage belongs to the low level range, the duty ratio is less than 50%. Determined.

  Also, the determination of the dispersion amount is made in advance by a second correspondence table (conversion table) showing the relationship between the slope of the connection plotting the output voltages of the integrators 44 and 46 at each duty ratio and the dispersion amount by experiments or the like. Is stored in the dispersion amount determination unit 47, and the temporary dispersion amount is obtained by referring to the second correspondence table according to the slope of the connection in which the actual output voltages of the integrators 44 and 46 are plotted. The temporary dispersion amount obtained in step 1 is corrected by the duty ratio described above. For example, when the duty ratio exceeds 50%, the amount of dispersion is determined to be smaller than the actual amount. Therefore, it is corrected with a coefficient set in advance so as to increase. When the duty ratio is less than 50%, the amount of dispersion is larger than the actual amount. Is obtained with a larger value, so that it is corrected with a preset coefficient so as to be smaller. No correction is made when the duty ratio is 50%. In this way, the final dispersion amount is determined.

  In the above description, the procedure of determining the duty ratio → determining the temporary dispersion amount from the slope → finally determining the dispersion amount based on the duty ratio is not limited to this procedure. The dispersion amount can also be obtained by the procedure of final determination of the dispersion amount from the relationship between the duty ratio and the slope (a table created in advance). That is, a procedure for determining the dispersion amount after fixing the duty ratio first may be used.

  FIG. 3 shows a flowchart of a dispersion amount determination program processed by the dispersion amount determination unit 47. In step S1, the received electrical signal obtained by photoelectrically converting the received optical signal coming from the optical fiber and amplifying it to a constant amplitude is determined by the threshold values H, M, and L of the determination circuits 41, 42, and 43. In step S2, the three determination results obtained in step S1 are integrated by integrators 44, 45, and 46 to obtain an output voltage. In step S3, the duty ratio of the transmission signal is determined as described above from the magnitude of the output voltage of the integrator 45 corresponding to the determination circuit 42. In step S4, the magnitude of the slope of the connection obtained by plotting the output voltages of the integrators 44 and 46 is detected. In step S5, the amount of dispersion is determined as described above based on the duty ratio obtained in step S3 and the magnitude of the slope obtained in step S4.

  Then, the electrical dispersion compensation circuit control unit 30 performs optimum dispersion compensation based on, for example, a third correspondence table (conversion table) indicating the relationship between the dispersion amount and the compensation control set value created in advance through experiments or the like. Create a control signal. The electrical dispersion compensation circuit 20 receives this control signal and performs dispersion compensation on the received electrical signal. As a result, even when the duty ratio fluctuates in the transmission signal, it is possible to correctly determine the amount of dispersion and normally compensate for the dispersion of the deteriorated received electrical signal.

<Example 2>
FIG. 4 shows the configuration of a feedforward type electric dispersion compensator according to the second embodiment of the present invention. The photoelectrically converted received electrical signal is amplified to a voltage having a constant amplitude by the automatic gain control type amplifier 10, branched into two, and input to the electrical dispersion compensation circuit 20 and the eye monitor circuit 40.

  The dispersion amount determination unit 47 of the eye monitor circuit 40 performs dispersion according to the dispersion caused by the optical fiber from the duty ratio of the transmission signal and the slope of the connection in which the integrated output voltage is plotted by the same processing as in the first embodiment. Determine the amount. The electrical dispersion compensation circuit control unit 30 creates a control signal for performing optimum dispersion compensation based on the third correspondence table. The electrical dispersion compensation circuit 20 receives this control signal and compensates for dispersion of the received electrical signal. As a result, even when the duty ratio fluctuates in the transmission signal, it is possible to correctly determine the amount of dispersion and normally compensate for the dispersion of the deteriorated received electrical signal.

<Example 3>
FIG. 5 shows the configuration of a feedforward type electric dispersion compensator according to Embodiment 3 of the present invention. The difference between the present embodiment and the second embodiment is that the eye monitor circuit 50 includes one determination circuit 51, one integrator 52, and one dispersion amount determination unit 53. The received optical signal is photoelectrically converted, amplified to a voltage having a constant amplitude by the automatic gain control amplifier 10, branched into two, and input to the electric dispersion compensation circuit 20 and the eye monitor circuit 50.

  In the eye monitor circuit 50, the threshold value of the determination circuit 51 is sequentially switched to H, M, and L every predetermined time, and the output voltage of the integrator 52 for each switching is divided for each of the threshold values H, M, and L and the dispersion amount. It is stored in the determination unit 53. Then, the duty ratio of the transmission signal is determined by referring to the first correspondence table according to the output voltage of the integrator 52 corresponding to the stored threshold value M. Further, the slope of the connection in which the output voltage of the integrator 52 corresponding to the stored threshold values H and L is plotted is obtained. Then, the temporary dispersion amount is determined by referring to the second correspondence table described above, and the final dispersion amount is determined by correcting the temporary dispersion amount according to the determined duty ratio.

  The electrical dispersion compensation circuit control unit 30 creates a control signal for performing optimum dispersion compensation by referring to the third correspondence table according to the determined dispersion amount. The electrical dispersion compensation circuit 20 receives this control signal and compensates for dispersion of the received electrical signal. As a result, even when the duty ratio fluctuates in the transmission signal, it is possible to correctly determine the amount of dispersion and normally compensate for the dispersion of the deteriorated received electrical signal.

<Other examples>
In the above embodiment, three threshold values H, M, and L are used. However, if four or more threshold values are used, four or more integrated output voltages can be obtained, and the accuracy of dispersion determination is further improved.

It is explanatory drawing of the dispersion amount determination method which shows Example 1 of this invention. It is a characteristic view which shows the mode of the waveform degradation by the dispersion | distribution for every duty ratio of a transmission signal, and a threshold value. It is a flowchart of a dispersion amount determination program. It is a block diagram which shows the structure of the electrical dispersion compensation apparatus of Example 2 to which the dispersion amount determination method of Example 1 of this invention is applied. It is a block diagram which shows the structure of the electrical dispersion compensation apparatus of Example 3 to which the dispersion amount determination method of Example 1 of this invention is applied. It is a block diagram which shows the structure of the conventional electrical dispersion compensation apparatus. It is explanatory drawing of the conventional dispersion amount determination method.

Explanation of symbols

10: Automatic gain control type amplifier (GCA)
20: Electric dispersion compensation circuit 30: Electric dispersion compensation circuit controller 40: Eye monitor circuit, 41-43: Determination circuit, 44-46: Integrator, 47: Dispersion amount determination device 50: Eye monitor circuit, 51: Determination circuit 52: Integrator, 53: Dispersion determination unit

Claims (8)

A received electrical signal obtained by photoelectrically converting a received optical signal arriving from an optical fiber and amplified to a constant amplitude is judged with a plurality of different thresholds, and each obtained judgment result is integrated individually, and each obtained integrated value is obtained. In the method of detecting the magnitude of the inclination of the connection obtained by plotting and connecting at least two of the threshold values in order from the highest or lowest threshold, and determining the amount of dispersion by the optical fiber from the magnitude of the inclination,
Determining a duty ratio of a transmission signal from the magnitude of the integral value corresponding to a specific threshold value among the plurality of threshold values, and determining the amount of dispersion based on the determined duty ratio and the magnitude of the slope. A characteristic method for determining the amount of dispersion. The dispersion amount determination method according to claim 1,
As the specific threshold value, a threshold value that minimizes the amount of variation in the magnitude of the integral value is used. A first step of determining a received electrical signal obtained by photoelectrically converting a received optical signal arriving from an optical fiber and amplifying the received optical signal at a predetermined amplitude with a plurality of different threshold values;
A second step of individually integrating each determination result obtained in the first step to obtain an integral value;
A third step of determining a duty ratio of the transmission signal from the magnitude of the integral value corresponding to a specific threshold value among the plurality of threshold values;
A fourth step of detecting the magnitude of the slope of the connection obtained by plotting each integrated value corresponding to at least two of the plurality of threshold values in order of increasing or decreasing threshold value; and
A fifth step of determining the amount of dispersion based on the determined duty ratio and the magnitude of the slope;
A dispersion amount determination program comprising: In an optical reception method for performing dispersion compensation on a received electrical signal obtained by photoelectrically converting a received optical signal coming from an optical fiber and amplifying the received optical signal to a constant amplitude,
An optical reception method, wherein the dispersion compensation is performed on the received electrical signal according to the dispersion amount determined by the dispersion amount determination method according to claim 1. An amplifier that amplifies a signal obtained by photoelectrically converting a received optical signal arriving from an optical fiber into a received optical signal having a constant amplitude, and an electric dispersion compensation circuit that receives the received electrical signal output from the amplifier and compensates for dispersion caused by the optical fiber And receiving electric signals output from the electric dispersion compensation circuit or the amplifier, determining with a plurality of different threshold values, integrating the determined results individually, and at least two of the obtained integration values. Are detected in order of increasing or decreasing threshold value, the magnitude of the inclination of the connection is detected, and the amount of dispersion by the optical fiber is determined from the magnitude of the inclination, and the eye monitor circuit determines In an optical receiver comprising: an electrical dispersion compensation circuit control unit that generates a control signal for dispersion compensation in the electrical dispersion compensation circuit according to the dispersion amount
The eye monitor circuit determines a duty ratio of a transmission signal from a magnitude of the integral value corresponding to a specific threshold value among the plurality of threshold values, and the variance is based on the determined duty ratio and the magnitude of the slope. An optical receiver characterized by determining the quantity. The optical receiver according to claim 5.
As the specific threshold value, a threshold value that minimizes the amount of variation in the magnitude of the integral value is used. The optical receiver according to claim 5 or 6,
The eye monitor circuit includes a plurality of determination circuits in which different threshold values are set, and a plurality of integrators for obtaining integrated values of determination results of the plurality of determination circuits, and a specific integration among the plurality of integrators An optical receiver characterized in that a duty ratio of a transmission signal is determined from a magnitude of an integral value obtained by a receiver, and the amount of dispersion is determined based on the determined duty ratio and the magnitude of the slope. The optical receiver according to claim 5 or 6,
The eye monitor circuit includes one determination circuit in which a threshold value is switched to a plurality of different values, and one integrator that obtains an integrated value for each threshold value for a determination result based on each threshold value of the determination circuit. A light characterized in that a duty ratio of a transmission signal is determined from the magnitude of an integral value corresponding to a specific threshold value among the threshold values, and the amount of dispersion is determined based on the determined duty ratio and the magnitude of the inclination. Receiver.

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