JP4493601B2 - Distributed management transmission line - Google Patents

Description

  The present invention relates to dispersion management of a transmission line for large-capacity optical communication.

  In large-capacity optical transmission of 10 Gb (Gbit) / s (sec) / ch (channel) or higher, the signal waveform is distorted due to the chromatic dispersion of the transmission path. Dispersion compensation is performed in the part.

  Since the deterioration due to distortion cannot be compensated when the accumulated dispersion of the transmission line is large, a dispersion management transmission line that performs dispersion compensation is used even at the 1R relay point using the optical amplifier.

  For example, in the technique disclosed in Patent Document 1, when serially connecting optical fibers having a plurality of different lengths and a plurality of different dispersion values, the value of the group velocity dispersion is used to enable soliton communication. The combination of the optical fibers is selected so that the average value according to the distance becomes anomalous dispersion.

  Further, for example, in the technique disclosed in Patent Document 2, in an optical soliton transmission line configured using an optical fiber, the average value of the group velocity dispersion of the optical fiber obtained over the entire transmission distance is anomalous dispersion. In this way, an optical fiber is constituted by a plurality of optical fiber pieces.

  In addition, for example, in the technique disclosed in Patent Document 3, a linear transmission method (average dispersion value is zero) that does not use the nonlinear optical effect is used in the transmission path (transmission optical fiber and dispersion compensator). In addition to the optical fiber, a soliton optical fiber having a dispersion value that generates N = 1 soliton is arranged, and a nonlinear transmission method using a nonlinear optical effect is concentrated on the soliton optical fiber.

  There is also a method of giving pre-dispersion compensation with an opposite sign on the transmission side to reduce the accumulated dispersion after transmission. For example, in the technique disclosed in Patent Document 4, the pre-chirp frequency shift amount in the transmission unit is reduced or increased with respect to the frequency shift amount when self-phase modulation is ignored. Alternatively, the frequency shift direction is reversed and increased or decreased.

JP-A-8-146472 JP-A-8-286219 Japanese Patent Laid-Open No. 2001-160779 JP-A-5-183512 ELECTRONICS LETTERS, 1st April 2004, Vol. 7, p444-445 ELECTRONICS LETTERS, 28th October 2004, Vol. 22, p 1443-1444

  When the cumulative dispersion in the transmission line using the optical fiber exceeds ± 400 ps / nm, a large deterioration occurs only in one subsequent transmission section. Conventionally, it was thought that it would be better if the accumulated dispersion did not increase. However, when numerical analysis was performed by changing the amount of pre-dispersion compensation, for example, as shown in FIG. It became clear that there was an optimal cumulative dispersion range. In other words, it is difficult to configure a transmission line that does not have an optimal cumulative dispersion range only by pre-dispersion compensation. For example, unless pre-dispersion compensation and dispersion management are combined, transmission characteristics deteriorate. It was found that a transmission line with few lines could not be constructed.

  The present invention has been made under such a background, and provides a dispersion management transmission line combining pre-dispersion compensation and dispersion management that can satisfy the intended transmission characteristics. Objective.

  The present invention is an invention for deriving a combination with little deterioration in transmission characteristics from a combination of a pre-dispersion compensation amount and dispersion management.

  The amount of dispersion compensation varies randomly due to dispersion in the dispersion value of the transmission line, dispersion in the dispersion compensation fiber, temperature fluctuation, etc., so in multi-relay transmission, the accumulated dispersion at the transmission end of each relay point is changed to the optimum accumulated dispersion. It is preferable to suppress.

  If the individual dispersion cannot be adjusted in this way in various transmission paths, it is also effective to set only the pre-dispersion compensation amount at the transmitting end as a second best measure.

When the dispersion slope compensation rate is 100%, 100% dispersion compensation can be performed at all wavelengths. Since the dispersion slope of the dispersion-shifted fiber is typically 0.07 ps / km / nm ² , when a transmission path of 85 km is considered, when the dispersion slope compensation rate is 90%, the deviation is ± 15 nm from the center wavelength. The dispersion compensation deviation is ± 9 ps / nm / km at 70 nm and ± 27 ps / nm at 70%. In wavelength division multiplex transmission, it is necessary to take this deviation into consideration and to keep the accumulated dispersion at this value at an arbitrary wavelength.

  That is, the present invention relates to a DQPSK transmission unit, a DQPSK reception unit, a transmission path of 30 km or more by a dispersion-shifted optical fiber provided between the DQPSK transmission unit and the DQPSK reception unit, and transmission of the DQPSK transmission unit A dispersion management transmission line includes a pre-dispersion compensator that receives a signal and a reception-end dispersion compensator that receives a reception signal of the DQPSK receiver.

  Here, the present invention is characterized in that the amount of pre-dispersion compensation of the pre-dispersion compensator is −300 ps / nm to −120 ps / nm or 30 ps / nm to 350 ps / nm.

  Alternatively, in the present invention, a DQPSK transmission unit, a DQPSK reception unit, a transmission line using a dispersion-shifted optical fiber provided between the DQPSK transmission unit and the DQPSK reception unit, and inserted in the middle of the transmission line A linear repeater and dispersion compensator; a pre-dispersion compensator that receives the transmission signal of the DQPSK transmission unit; and a reception-end dispersion compensator that receives the reception signal of the DQPSK reception unit. After the transmission in each transmission section between the dispersion compensator and the linear repeater or between the linear repeaters, an outline of dispersion is compensated by the linear repeater provided in the transmission section, and the reception end dispersion compensator This is a dispersion management transmission line that compensates for residual dispersion.

  Here, the feature of the present invention is that the accumulated dispersion amount at the transmission end of each relay point is -300 ps / nm to -120 ps / nm or 30 ps / nm to 350 ps / nm.

  Alternatively, in the present invention, a DQPSK transmission unit, a DQPSK reception unit, a transmission line using a dispersion-shifted optical fiber provided between the DQPSK transmission unit and the DQPSK reception unit, and inserted in the middle of the transmission line A linear repeater and dispersion compensator; a pre-dispersion compensator that receives the transmission signal of the DQPSK transmission unit; and a reception-end dispersion compensator that receives the reception signal of the DQPSK reception unit. After the transmission in each transmission section between the dispersion compensator and the linear repeater or between the linear repeaters, an outline of dispersion is compensated by the linear repeater provided in the transmission section, and the reception end dispersion compensator This is a dispersion management transmission line that compensates for residual dispersion.

  Here, the present invention is characterized in that the pre-dispersion compensation amount of the pre-dispersion compensator is −270 ps / nm to −120 ps / nm or 80 ps / nm to 300 ps / nm.

  In addition, it is desirable that the restriction on the amount of pre-dispersion compensation be lifted in a section where the distance between the transmission sections is less than about 30 km.

  A plurality of DQPSK transmitters, a wavelength multiplexing device for wavelength-multiplexing transmission signals of the plurality of DQPSK transmitters, a plurality of DQPSK receivers, and a wavelength-multiplexed unit for the plurality of DQPSK receivers. A wavelength demultiplexer that separates the received signal for each wavelength, and the pre-dispersion compensator is provided with one wavelength-multiplexed transmission signal output from the wavelength multiplexer as an input, The edge dispersion compensator may be configured to have a plurality of reception signals for each wavelength output from the wavelength multiplexing / demultiplexing device to the plurality of DQPSK reception units. In this case, for example, the amount of pre-dispersion compensation by the pre-dispersion compensator is −200 ps / nm or +200 ps / nm.

  As a means for providing such pre-dispersion compensation, a dispersion medium having no dispersion slope or a dispersion medium having a dispersion slope of 1/10 or less as compared with a general optical fiber can be used.

  According to the present invention, it is possible to realize a dispersion management transmission line that combines pre-dispersion compensation and dispersion management that can satisfy desired transmission characteristics.

(First Example)
A first embodiment will be described with reference to FIGS. The first embodiment is an example of a DQPSK transmission method (see, for example, Non-Patent Document 1 or 2) and relayless transmission. FIG. 1 shows a schematic diagram of a transmission system used in the description of this embodiment. 1 is a DQPSK transmitter, 2 is a DQPSK receiver, 3 is a pre-dispersion compensator (DCT), 4 is a transmission path (dispersion shifted fiber), 5 is a dispersion compensator, 6 is a linear repeater, and 7 is This is a receiving end dispersion compensator. Since the first embodiment is an embodiment of non-relay transmission, the dispersion compensator 5 and the linear repeater 6 in FIG. 1 are not used.

  Further, the dispersion compensator 5 ′ immediately before the reception end dispersion compensator 7 can be omitted depending on the magnitude of the accumulated dispersion. The DQPSK transmission system is mainly used for large capacity transmission of 40 Gb / s / ch or more.

  FIG. 2 shows a pre-dispersion with a transmission rate of 43 Gb / s / ch, a transmission line distance of 85 km, a group velocity dispersion of 1 ps / km / nm and 4 ps / km / nm, and a signal strength at the input of the transmission line of +1 dBm. The calculation results are obtained by changing the compensation amount (DCT). The horizontal axis represents the pre-dispersion compensation amount (DCT), and the vertical axis represents the deterioration amount (dB). In addition, the graph shown by the black circle (●) in FIG. 2 represents 1 ps / km / nm, and the graph shown by a triangle (Δ) represents 4 ps / km / nm. The DQPSK transmitter 1 and the DQPSK receiver 2 are adjusted to the optimum operating point, and the pre-dispersion compensation amount (DCT) is changed from −500 ps / nm to +500 ps / nm to adjust the receiving end dispersion compensator 7. The transmission characteristics in this case are evaluated by the Q value (a quantity indicating the degree of signal variation), and the deterioration amount of the Q value due to transmission is depicted.

  Here, the range of DCT in which deterioration is within twice that in the case where the amount of pre-dispersion compensation (DCT) is optimum is defined as a range in which good transmission characteristics can be obtained. When the group velocity dispersion is 1 ps / km / nm to 4 ps / km / nm and the amount of pre-dispersion compensation (DCT) is -300 ps / nm to -120 ps / nm or 30 ps / nm to 350 ps / nm, the deterioration is small. It can be seen that good transmission characteristics can be obtained (range shown by ⇔ in FIG. 2).

  The signal intensity exhibits the same characteristics other than this value. In the transmission system, an appropriate value may be set according to the characteristics of the receiving circuit or the loss of the transmission path.

(Second embodiment)
A second embodiment will be described with reference to FIGS. In the second embodiment, multi-relay transmission using the DQPSK transmission system is considered. A schematic diagram of the transmission system is shown in FIG. 1, which is the same as in the first embodiment, but has a plurality of transmission lines 4 between which a dispersion compensator 5 and a linear repeater 6 are used.

  In the case of multi-relay transmission, the accumulated dispersion after passing through the dispersion compensator 5 can be considered as a pre-dispersion amount at the output point of each linear repeater 6. Therefore, as explained in the first embodiment, when the group velocity dispersion is 1 ps / km / nm to 4 ps / km / nm, the amount of pre-dispersion compensation (DCT) is -300 ps / nm to -120 ps / nm or 30 ps / nm. It can be seen that there is little deterioration and good transmission characteristics can be obtained when it is 350 ps / nm.

  From the calculation result of FIG. 2, it can be seen that the absolute value of the cumulative dispersion at the transmission end of each relay point is preferably 50 ps / nm to 350 ps / nm.

(Third embodiment)
A third embodiment will be described with reference to FIGS. The third embodiment is an example in the case of the DQPSK transmission method and multi-relay transmission, and is an example of 5 relays (using 6 sections of the transmission path 4). A schematic diagram of the transmission system is shown in FIG. 1, which is the same as in the first embodiment.

  FIG. 3 shows the signal strength at the input of the transmission line 4 with a transmission speed of 43 Gb / s / ch, a transmission line distance of 85 km, a group velocity dispersion of 1.5 ps / km / nm and 4.5 ps / km / nm. The calculation results are obtained by changing the pre-dispersion compensation amount (DCT) as +1 dBm, and the pre-dispersion compensation amount (DCT) is taken on the horizontal axis and the deterioration amount (dB) is taken on the vertical axis. In addition, the graph shown by the black circle (●) in FIG. 3 represents 1.5 ps / km / nm, and the graph shown by the triangle (Δ) represents 4.5 ps / km / nm.

  As in the first embodiment, it is assumed that the DQPSK transmission unit 1 and the DQPSK reception unit 2 are adjusted to the optimum operating point, and the pre-dispersion compensation amount (DCT) is changed from −500 ps / nm to +500 ps / nm, The transmission characteristics when the receiving end dispersion compensator 7 is adjusted are evaluated by the Q value (a quantity representing the degree of signal variation), and the amount of deterioration of the Q value due to transmission is depicted.

  FIG. 4 shows the same analysis as when FIG. 3 was drawn when the distance of the transmission line 4 was 40 km. It can be seen that good transmission characteristics can be obtained within the same range as in FIG.

  Thus, when the group velocity dispersion is in the range of 1.5 ps / km / nm and 4.5 ps / km / nm, the amount of pre-dispersion compensation (DCT) is -270 ps / nm to -120 ps / nm or 80 ps / nm to 300 ps. It can be seen that there is little deterioration when it is / nm, and good transmission characteristics can be obtained (the range indicated by ⇔ in FIGS. 3 and 4).

  Since the present invention reduces transmission characteristic deterioration due to the nonlinear optical effect, when the transmission distance is about 30 km or more (fiber loss is about 7 dB, light intensity is attenuated to about 1/5), Applicable regardless of distance.

  The signal strength exhibits the same characteristics other than this value. In the transmission system, an appropriate value may be set according to the characteristics of the receiving circuit, the loss of the transmission path, and the like.

(Fourth embodiment)
In the multi-relay transmission, the cumulative dispersion at the input of each transmission path 4 varies around the design value. At this time, even if the degradation in one section is severe, the transmission characteristics as a whole can be maintained in a good state if the degradation in other sections is small.

  That is, even when individual dispersion cannot be adjusted, an effect can be obtained by designing the pre-dispersion compensation amount at the transmitting end. Since the design value is the same as that of the third embodiment, it is reasonable that the allowable range is the same as that of the third embodiment.

(Fifth embodiment)
The fifth embodiment is an embodiment for wavelength division multiplexing transmission, and the parameter used to explain the fifth embodiment is group velocity dispersion (GVD, unit: ps / km / nm), for example, about 0.07 ps / In a normal dispersion shifted optical fiber with a dispersion slope of km / nm ² , a group velocity dispersion of 1 ps / km / nm corresponds to a wavelength difference of about 15 nm (1 / 0.07).

  A schematic configuration in the case of wavelength multiplexing transmission is shown in FIG. Although the case of multi-relay is shown, in the case of non-relay, the dispersion compensator 5 and the linear repeater 6 in the figure are not used. Transmitters having different wavelengths are collected by the wavelength division multiplexer 8 and propagated simultaneously through one optical fiber, and are separated and received by the wavelength division multiplexer 9 for each wavelength.

  In the dispersion compensator 5, when the dispersion slope compensation rate is 100%, dispersion compensation of 100% can be performed at an arbitrary wavelength. Therefore, the conditions described in the first to third embodiments can be realized in the same manner. .

Since the dispersion slope of the dispersion-shifted fiber is typically 0.07 ps / km / nm ² , when a transmission path of 85 km is considered, when the dispersion slope compensation rate is 90%, the deviation is ± 15 nm from the center wavelength. The dispersion compensation deviation is ± 9 ps / nm / km at 70 nm and ± 27 ps / nm at 70%.

  In wavelength division multiplex transmission, it is necessary to take this deviation into consideration and to keep the accumulated dispersion at this value at an arbitrary wavelength. Taking the 85 km repeaterless transmission described in FIGS. 1 and 2 as an example, in the case of wavelength multiplex transmission using a band of 30 nm (± 15 nm from the center) when the dispersion slope compensation rate is 90%, −291 ps / It is sufficient that the thickness is from nm to -129 ps / nm or from 39 ps / nm to 341 ps / nm.

  The same applies to other compensation rates, transmission distances, bandwidths, and multi-relay transmissions. However, even when there is no region satisfying this, the pre-dispersion compensation amount can be set to the approximate central value of −200 ps / nm or +200 ps / nm to suppress the deterioration to the minimum.

  In these examples and other embodiments, when there is a section with a transmission distance of less than 30 km in multi-relay transmission, if the degradation due to the nonlinear optical effect is reduced by reducing the transmission output of the section, The interval can be excluded from the pre-dispersion compensation constraints described above. Similar restrictions are imposed when the transmission output is not reduced.

  In the present invention, the amount of pre-dispersion compensation is preferably equal for each wavelength. For this purpose, the dispersion medium used for pre-dispersion compensation has a small dispersion slope (for example, 1/10 compared with a general optical fiber). Or it is preferable not to have a dispersion slope. It is possible to use a VIPA or a dispersion compensating fiber subjected to dispersion slope compensation.

  According to the present invention, it is possible to realize a dispersion management transmission line that combines pre-dispersion compensation and dispersion management that can satisfy the desired transmission characteristics, so that the degree of freedom in designing an optical transmission line can be increased.

The schematic diagram of the transmission system used by description of a 1st-4th Example. The figure which shows the calculation result which changed the amount of pre-dispersion compensation (DCT). The figure which shows the numerical analysis result of 85kmx5 relay (six sections). The figure which shows the numerical analysis result of 40kmx5 relay (six sections). The schematic diagram of the transmission system using the wavelength division multiplexing transmission used by description of a 5th Example.

Explanation of symbols

1, 1 'DQPSK transmission unit 2, 2' DQPSK reception unit 3 Pre-dispersion compensator (DCT)
4 Transmission path (dispersion shifted optical fiber)
5, 5 ′ dispersion compensator 6 linear repeater 7, 7 ′ receiving end dispersion compensator 8 wavelength multiplexing device 9 wavelength multiplexing demultiplexing device

Claims (6)

Before a DQPSK transmitter, a DQPSK receiver, a transmission path of 30 km or more by a dispersion-shifted optical fiber provided between the DQPSK transmitter and the DQPSK receiver, and a transmission signal of the DQPSK transmitter are input In a dispersion management transmission line comprising a position dispersion compensator and a reception-end dispersion compensator that receives a received signal of the DQPSK receiver,
The dispersion management transmission line, wherein the amount of pre-dispersion compensation of the pre-dispersion compensator is -300 ps / nm to -120 ps / nm or 30 ps / nm to 350 ps / nm. DQPSK transmission unit, DQPSK reception unit, transmission path using dispersion-shifted optical fiber provided between DQPSK transmission unit and DQPSK reception unit, linear repeater and dispersion compensation inserted in the middle of this transmission path A pre-dispersion compensator that receives the transmission signal of the DQPSK transmission unit, and a reception-end dispersion compensator that receives the reception signal of the DQPSK reception unit,
After the transmission of each transmission section between the pre-dispersion compensator and the linear repeater or between the linear repeaters, the linear repeater provided in the transmission section compensates for the outline of dispersion, and the receiving end In a dispersion management transmission line that compensates for residual dispersion with a dispersion compensator,
A dispersion management transmission line characterized in that a cumulative dispersion amount at a transmission end of each relay point is -300 ps / nm to -120 ps / nm or 30 ps / nm to 350 ps / nm. DQPSK transmission unit, DQPSK reception unit, transmission path using dispersion-shifted optical fiber provided between DQPSK transmission unit and DQPSK reception unit, linear repeater and dispersion compensation inserted in the middle of this transmission path A pre-dispersion compensator that receives the transmission signal of the DQPSK transmission unit, and a reception-end dispersion compensator that receives the reception signal of the DQPSK reception unit,
After the transmission of each transmission section between the pre-dispersion compensator and the linear repeater or between the linear repeaters, the linear repeater provided in the transmission section compensates for the outline of dispersion, and the receiving end In a dispersion management transmission line that compensates for residual dispersion with a dispersion compensator,
A dispersion management transmission line, wherein a pre-dispersion compensation amount of the pre-dispersion compensator is −270 ps / nm to −120 ps / nm or 80 ps / nm to 300 ps / nm. A plurality of DQPSK transmitters, a wavelength multiplexing device that wavelength-multiplexes transmission signals of the plurality of DQPSK transmitters, a plurality of DQPSK receivers, and a wavelength-multiplexed reception for the plurality of DQPSK receivers A wavelength demultiplexing device that separates the signal for each wavelength,
The pre-dispersion compensator is provided with one wavelength-multiplexed transmission signal output from the wavelength multiplexing device as input, and the receiving-end dispersion compensator receives a plurality of DQPSK reception signals from the wavelength demultiplexing device. The dispersion management transmission line according to any one of claims 1 to 3 , wherein a plurality of reception signals for each wavelength respectively output to a part are provided as inputs. The dispersion management transmission line according to claim 4, wherein a pre-dispersion compensation amount by the pre-dispersion compensator is −200 ps / nm or +200 ps / nm. Wherein as a pre-dispersion compensator, the dispersion managed transmission according to any one of claims 1 using a dispersion medium dispersing medium or dispersion slope is compared to 1/10 or less as dispersion-shifted fiber does not have a dispersion slope 5 Road.

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