JP5088151B2 - Variable dispersion compensation device and variable dispersion compensation method - Google Patents

Description

  The present invention relates to a tunable dispersion compensator and a tunable dispersion compensation method, and more particularly to a tunable dispersion compensator and a tunable dispersion compensation that automatically perform dispersion compensation when chromatic dispersion deteriorates when performing high-speed and large-capacity long-distance optical transmission. Regarding the method.

  When high-speed and large-capacity long-distance optical transmission is performed using an optical fiber, chromatic dispersion occurs due to the optical fiber, and it is necessary to compensate for the chromatic dispersion using a dispersion compensator.

  FIG. 5 shows a block diagram of an example of the above dispersion compensator. The dispersion compensation device 40 constitutes an optical interface package, and includes an optical amplifier / dispersion compensation unit 50 and an optical interface transmission / reception unit 60. The optical amplifier and dispersion compensation unit 40 includes an optical amplifier 51, a fixed DCF (Dispersion Compensating Fiber) 52, and an optical amplifier 53. The optical interface transmission / reception unit 60 includes an optical reception unit 61, a frame synchronization unit 62, a bit error monitoring unit 63, an alarm collection unit 64, and an optical transmission unit 65.

  Next, the operation of this dispersion compensation apparatus will be described. An optical signal transmitted from an opposing device (not shown), transmitted through an optical fiber, and input to the optical amplifier and dispersion compensation unit 50 is amplified by the optical amplifier 51 and then input to the fixed DCF 52. The fixed DCF 52 compensates the chromatic dispersion by canceling the chromatic dispersion deterioration by adding the chromatic dispersion characteristic in the fixed negative direction to the chromatic dispersion in the positive direction received during transmission of the optical signal through the optical fiber. The optical signal output from the fixed DCF 52 is amplified by the optical amplifier 53 and then output to the optical reception unit 61 in the optical interface transmission / reception unit 60.

  The optical receiver 61 generates an electrical signal by photoelectrically converting (O / E converting) the input optical signal, and supplies the electrical signal to the frame synchronization unit 62 to achieve frame synchronization. The bit error monitoring unit 63 monitors a bit error in the transmission path based on the signal input from the frame synchronization unit 62. The alarm collection unit 64 collects frame synchronization information from the frame synchronization unit 62 and bit error information from the bit error monitoring unit 63. In addition, the optical transmitter 65 transmits an optical main signal from the inside of the apparatus toward the opposite apparatus.

  However, this chromatic dispersion compensator compensates for chromatic dispersion during long-distance transmission by canceling out the chromatic dispersion in the positive direction caused by the optical fiber in the actual transmission path by the fixed DCF 52 having fixed chromatic dispersion characteristics in the negative direction. Since it is a configuration to compensate, prepare a dispersion compensation fiber with multiple types of fixed dispersion according to the amount of chromatic dispersion that occurs in the actual transmission line, and select the dispersion compensation fiber with the length that makes the optimum dispersion compensation amount. Need to be used.

  Therefore, instead of a dispersion compensation fiber having a fixed dispersion amount, a method for manually performing optimum chromatic dispersion compensation by using a dispersion compensation fiber composed of a plurality of dispersion compensation amounts prepared in advance by switching with an optical switch. Is known (see, for example, Patent Document 1).

  Also, based on the code error information obtained by the monitor circuit, the dispersion compensation amount of the variable dispersion compensator that compensates the wavelength dispersion of the optical signal whose waveform is degraded in accordance with the wavelength dispersion characteristic of the optical fiber is minimized. A dispersion compensation control device for controlling is also known (see, for example, Patent Document 2). Further, the dispersion compensation control device calculates a code error rate by sweeping a variable range of the dispersion compensation amount of the tunable dispersion compensator, and the position of the minimum value of the code error rate that is equal to or less than a preset threshold value or the code The dispersion compensation amount at the center position in the range of the minimum value of the error rate is set as an initial setting value.

JP 2003-037561 A Japanese Patent Laid-Open No. 2004-236097

  However, in the chromatic dispersion compensation method described in Patent Document 1 in which the dispersion compensation fiber composed of a plurality of dispersion compensation amounts is used by switching with an optical switch, the chromatic dispersion value of the actual transmission path is measured in advance, Alternatively, it is necessary to search for the optimum value while manually changing the chromatic dispersion value little by little.

  Also, when searching for the optimum value while switching the dispersion compensation value automatically using an optical switch or the like for the above chromatic dispersion compensation, the chromatic dispersion value is changed little by little to monitor the bit error on the receiving side. If the method is adopted, there is a problem that it takes time to search the entire range.

  Further, in the chromatic dispersion control device described in Patent Document 2, the variable dispersion compensation range is swept only once and skipped when synchronization is not established, and the center value in the range where the code error rate is equal to or less than the threshold is set as the dispersion compensation amount. Therefore, there is a problem that the accuracy of the set dispersion compensation amount is relatively low.

  The present invention has been made in view of the above points, and provides a tunable dispersion compensation apparatus and a tunable dispersion compensation method capable of setting an optimum value of a chromatic dispersion compensation value set in a DCF with higher accuracy and in a shorter time. The purpose is to do.

In order to achieve the above object, a tunable dispersion compensator according to the present invention includes a tunable dispersion compensator that compensates for chromatic dispersion in a transmission path of an optical signal input through the transmission path by a tunable dispersion compensation characteristic, and a tunable dispersion compensator. Frame synchronization means that performs frame synchronization with respect to the optical signal output from the compensation means, and bits depending on whether the code error rate is equal to or less than a threshold value with respect to the optical signal output from the variable dispersion compensation means a bit error monitoring means for detecting an error, based on the frame synchronization information from the frame synchronization means, variable dispersion compensator all while varying the dispersion compensation value of the dispersion compensation range frame synchronization establishment to have dispersed against A first search means for searching a compensation range to obtain a search result of a range in which frame synchronization is established; bit error information from the bit error monitoring means; The code error rate is below the threshold value while changing the dispersion compensation value of the variable dispersion compensation means within the range in which frame synchronization is established based on the search result of the range in which frame synchronization is established obtained by the means. The dispersion compensation value in the second search means for searching the error-free range and the variable dispersion compensation means corresponding to the center value in the error-free range obtained by the search by the second search means is set as the optimum dispersion compensation value. And a setting means.

In order to achieve the above object, the variable dispersion compensation method of the present invention includes a first step of compensating for chromatic dispersion caused by a transmission path of an optical signal input through the transmission path, using a variable dispersion compensation means, The second step of obtaining frame synchronization with respect to the optical signal output from the tunable dispersion compensating means, and whether the code error rate is equal to or less than the threshold value with respect to the optical signal output from the tunable dispersion compensating means. Based on the frame synchronization information obtained in the second step and the third step for detecting a bit error, the frame synchronization is performed for all dispersion compensation possible ranges while changing the dispersion compensation value of the variable dispersion compensation means. a fourth step of obtaining a search result within the ranges established frame synchronization by searching a dispersion compensation range has been established, to obtain a bit error information obtained in the third step and the fourth step off Search the error-free range where the code error rate is below the threshold while changing the dispersion compensation value of the variable dispersion compensation means within the frame synchronization established range based on the search results of the range established by And a sixth step of setting the dispersion compensation value in the variable dispersion compensation means corresponding to the center value within the error-free range obtained by the search in the fifth step as the optimum dispersion compensation value. It is characterized by including.

  According to the present invention, when searching for the optimum value of the variable DCF, after narrowing down to the range in which frame synchronization is established, the search for the bit error-free range that takes time is performed, thereby optimizing the chromatic dispersion compensation value. The time for setting the value to the variable DCF can be shortened and the optimum value can be set with high accuracy.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a block diagram of an embodiment of a variable dispersion compensator according to the present invention. The tunable dispersion compensator 10 of this embodiment constitutes an optical interface package, and includes an optical amplifier and dispersion compensator 20 and an optical interface transceiver 30.

The optical amplifier and dispersion compensation unit 20 includes an optical amplifier 21, a variable DCF (Dispersion Compensating Fiber) 22, a variable DCF control unit 23, and an optical amplifier 24. The optical interface transmission / reception unit 30 includes an optical reception unit 31, a frame synchronization unit 32, a bit error monitoring unit 33, an alarm collection unit 34, a variable DCF search control unit 35, and an optical transmission unit 36.

  The optical amplifier 21 amplifies an optical signal transmitted from an opposing device (not shown) and transmitted through an optical fiber. The variable DCF 22 is a fiber that compensates for chromatic dispersion by canceling chromatic dispersion degradation by adding chromatic dispersion characteristics in the negative direction to the chromatic dispersion in the positive direction received during transmission of the optical signal through the optical fiber. The wavelength dispersion characteristic is varied by a control signal from the variable DCF control unit 23.

FIG. 2 shows a configuration diagram of an embodiment of the variable DCF 22. As shown in the figure, the variable DCF 22 includes n (n is a natural number of 2 or more) two-input two-output type optical switches 221 _{1 to} 221 _n and two adjacent ones of the optical switches 221 _{1 to} 221 _n . A total of n−1 chromatic dispersion compensating fibers 222 _{1 to} 222 _n−1 are provided between the optical switches.

Here, the chromatic dispersion compensating fibers 222 _{1 to} 222 _n-1 are located between the first output terminal of the input-side optical switch and the first input terminal of the output-side optical switch among the two adjacent optical switches. The second output terminal of the input side optical switch and the second input terminal of the output side optical switch are directly connected without a chromatic dispersion compensating fiber. For example, the chromatic dispersion compensating fiber 222 ₁ includes the first output terminal of the input-side optical switch 221 ₁ and the first input terminal of the output-side optical switch 221 ₂ among the two adjacent optical switches 221 ₁ and 221 _2. Connected between and. The second output terminal of the input-side optical switch 221 ₁ and the second input terminal of the output-side optical switch 221 ₂ are directly connected without a chromatic dispersion compensating fiber.

The optical switches 221 _{1 to} 221 _n output an optical signal from one of the first output terminal and the second output terminal according to a control signal from the variable DCF control unit 23, and the first input Whether or not to pass through the _n-1 wavelength dispersion compensating fibers 222 _{1 to} 222 _n-1 is controlled individually by controlling the optical signals to be input from one of the terminal and the second input terminal. It can be selected. As a result, the variable DCF 22 causes the optical signal to pass through an arbitrary number of chromatic dispersion compensating fibers among the chromatic dispersion compensating fibers 222 _{1 to} 222 _n−1 , and from the optical switch 221 _{n at the} final stage as a whole in an arbitrary negative direction. The optical signal to which the chromatic dispersion characteristic is added is output.

  Returning again to FIG. The optical amplifier 24 amplifies the optical signal output from the variable DCF 22 and outputs the amplified optical signal to the optical receiving unit 31 in the optical interface transmitting / receiving unit 30. The optical receiver 31 performs photoelectric conversion (O / E conversion) on the optical signal input from the optical amplifier and dispersion compensation unit 20 to generate an electrical signal, and supplies the electrical signal to the frame synchronization unit 32. The frame synchronization unit 32 performs frame synchronization of the input signal. The bit error monitoring unit 33 monitors a bit error in the transmission path based on the signal input from the frame synchronization unit 32.

  The alarm collection unit 34 collects the frame synchronization information from the frame synchronization unit 32 and the bit error information from the bit error monitoring unit 33. The variable DCF search control unit 35 performs a frame synchronization establishment range search, an error free range search, and the like based on the frame synchronization information and the bit error information collected by the alarm collection unit 34, and the search results are sent to the variable DCF control unit 23. Output to. In addition, the optical transmission unit 36 transmits an optical main signal from the inside of the apparatus toward the opposite apparatus.

  Here, the optical receiver 31, the frame synchronizer 32, the bit error monitor 33, and the optical transmitter 36 are well known to those skilled in the art and are not directly related to the present invention. The configuration is omitted.

  Next, the chromatic dispersion compensation operation of this embodiment will be described in detail with reference to the flowchart of FIG.

First, the variable DCF search control unit 35 and the variable DCF control unit 23 are initialized (step S1). By this initialization, the dispersion compensation amount of the variable DCF 22 is set to 0 ps / nm by aligning the directions of the optical switches 221 _{1 to} 221 _{n in} the variable DCF 22.

  Subsequently, a search is performed for a range where frame synchronization is established (step S2). In this step S2, the variable DCF search control unit 35 controls the variable DCF 22 by the variable DCF control unit 23, and sets the dispersion compensation value that has established frame synchronization for all dispersion compensation possible ranges while increasing the dispersion compensation amount. Search.

Subsequently, the variable DCF search control unit 35 observes a bit error while searching for a range that is error-free while changing the dispersion compensation amount of the variable DCF 22 within a range in which the establishment of frame synchronization is confirmed (step S100). S3). Here, the bit rate of the transmission path, e la Reto is determined from the observed time of the bit error. In step S3, the bit error monitoring unit 33 observes a bit error for a time required for measurement of a predefined error rate (for example, 10 ^-12 ), and confirms that there is no error.

  At this time, if there is no error free range of 3 points or more, the process ends abnormally. When an optical fiber conforming to the specification is used with a transmission distance guaranteed by design, the design has an error-free range of 3 points or more. Therefore, if there is no error free point of 3 points or more, it can be determined that there is no margin due to some abnormality, so if there is no error free range of 3 points or more, the process ends abnormally.

  Next, the variable DCF search control unit 35 determines the set value of the variable DCF 22 corresponding to the center value of the error free range as the optimum dispersion compensation value (step S4). This is because the center value of the error free range is the dispersion compensation value with the most margin.

  Then, the variable DCF control unit 23 sets the optimum dispersion compensation value determined by the variable DCF search control unit 35 in the variable DCF 22 (step S5). Thereby, DCF configuration (configuration) is complete | finished.

  FIG. 4 shows the relationship between the dispersion compensation value (dispersion set value) and the bit error rate (BER). If the dispersion compensation value (dispersion set value) deviates, the BER deteriorates. Therefore, it is necessary to match the dispersion compensation value to the optimum value.

  As described above, in this embodiment, the frame synchronization establishment range is searched first (by the first search) and the frame synchronization establishment range is not established, and the second search becomes bit error free from the frame synchronization establishment range. Since the center value of the range (that is, the range where the code error rate is equal to or less than the threshold value) is set as the optimum dispersion compensation value, the monitoring time of the time-consuming bit error-free range can be greatly reduced. The time for setting the dispersion compensation value of the variable DCF 22 to the optimum value can be shortened.

  That is, in order to observe a bit error and determine whether it is error free or not, even when the transmission line speed is 40 Gb / s, about 30 seconds are required to guarantee a 10E-12 bit error rate. Take it. If the entire variable range of the dispersion compensation value of the variable DCF 22 is searched, it takes time as many times as the variable DCF 22 can be changed. However, in the present embodiment, the search range in the range where the bit error is free is narrowed down to the range in which synchronization is established, so the search time in the range where the bit error is free can be shortened.

  Note that there are cases where it is necessary to quickly recalculate the chromatic dispersion value and restore the main signal, not only at the time of initial opening, but also when the transmission distance is changed due to a troubled transfer of the transmission path. In this embodiment, the search for the optimum value of the chromatic dispersion value can be speeded up, so that a highly reliable high-speed long-distance optical transmission system with excellent maintainability can be constructed.

  Further, according to the present embodiment, the dispersion compensation value of the variable DCF 22 is automatically controlled to the optimum value, so that a plurality of fixed length dispersion compensation fibers are prepared in advance and replaced with the optimum length fiber. Compared to the dispersion compensation method, labor is not required.

  Further, according to the present embodiment, since only the synchronization establishment range is searched in the first sweep, each point is determined immediately, and only the synchronization establishment range is free of bit errors in the second sweep. Since the range is searched, it is possible to search by setting the threshold value for determining that the bit error is free to a deep place, so that the dispersion compensation value of the variable DCF 22 can be set to an optimum value with higher accuracy. .

It is a block diagram of one embodiment of a tunable dispersion compensator of the present invention. It is a block diagram of one Embodiment of variable DCF in FIG. It is a flowchart for operation | movement description of this invention. It is a figure which shows an example of the relationship between a dispersion compensation value (dispersion setting value) and BER. It is a block diagram of an example of a general variable dispersion compensator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Variable dispersion compensation apparatus 20 Optical amplifier and dispersion compensation part 21, 24 Optical amplifier 22 Variable DCF
23 Variable DCF control unit 30 Optical interface transmission / reception unit 31 Optical reception unit 32 Frame synchronization unit 33 Bit error monitoring unit 34 Alarm collection unit 35 Variable DCF search control unit 36 Optical transmission unit

Claims (4)

Tunable dispersion compensation means for compensating chromatic dispersion of the optical signal input through the transmission line by the variable dispersion compensation characteristic;
Frame synchronization means for performing frame synchronization with respect to the optical signal output from the variable dispersion compensation means;
Bit error monitoring means for detecting a bit error depending on whether a code error rate is a threshold value or less with respect to the optical signal output from the variable dispersion compensation means;
Based on frame synchronization information from the frame synchronization means, frame dispersion is established by searching for a dispersion compensation range in which frame synchronization is established for all dispersion compensation possible ranges while changing the dispersion compensation value of the variable dispersion compensation means. First search means for obtaining a search result in an established range;
Based on the bit error information from the bit error monitoring means and the search result of the frame synchronization established range obtained by the first search means , the dispersion compensation value of the variable dispersion compensation means is established in frame synchronization. Second search means for searching for an error-free range in which the code error rate is less than or equal to the threshold while changing within a certain range;
Setting means for setting, as the optimum dispersion compensation value, the dispersion compensation value in the variable dispersion compensation means corresponding to the center value within the error-free range obtained by searching by the second search means. A characteristic variable dispersion compensator. The variable dispersion compensation means includes
A plurality of optical switches;
A chromatic dispersion compensating fiber provided between two adjacent optical switches among the plurality of optical switches;
The plurality of optical switches are controlled by an external control signal, and an optical signal that has passed through an optical switch on the input side of the two adjacent optical switches is output on the output side via the chromatic dispersion compensation fiber. or supplied to the optical switch, according to claim 1 Symbol placement variable dispersion compensation, characterized in that it is configured to select individual or supplied to the optical switch of the output side without passing through the chromatic dispersion compensating fiber apparatus. A first step of compensating the chromatic dispersion of the optical signal input via the transmission path by the variable dispersion compensation means;
A second step of performing frame synchronization with respect to the optical signal output from the variable dispersion compensation unit;
A third step of detecting a bit error based on whether or not a code error rate is equal to or less than a threshold value with respect to the optical signal output from the variable dispersion compensation unit;
Based on the frame synchronization information obtained in the second step, search for a dispersion compensation range in which frame synchronization is established for all dispersion compensation possible ranges while changing the dispersion compensation value of the variable dispersion compensation means. A fourth step of obtaining a search result of a range in which frame synchronization is established ;
The range in which the dispersion compensation value of the variable dispersion compensation means is established in frame synchronization based on the bit error information obtained in the third step and the search result of the frame synchronization established range obtained in the fourth step. A fifth step of searching for an error-free range in which the code error rate is less than or equal to the threshold while changing within
And a sixth step of setting, as an optimum dispersion compensation value, a dispersion compensation value in the variable dispersion compensation means corresponding to the center value in the error-free range obtained by searching in the fifth step. A variable dispersion compensation method. The variable dispersion compensation means includes
A plurality of optical switches;
A chromatic dispersion compensating fiber provided between two adjacent optical switches among the plurality of optical switches;
The plurality of optical switches are controlled by an external control signal, and an optical signal that has passed through an optical switch on the input side of the two adjacent optical switches is output on the output side via the chromatic dispersion compensation fiber. or supplied to the optical switch, according to claim 3 Symbol placement variable dispersion compensation, characterized in that it is configured to select individual or supplied to the optical switch of the output side without passing through the chromatic dispersion compensating fiber Method.

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