Abstract:
An optical transmission apparatus includes a first transmitter configured to transmit a first optical signal in a first wavelength band and a second optical signal in a second wavelength band located next to the first wavelength band; a second transmitter configured to transmit a third optical signal in a third wavelength band located next to the second wavelength band and a fourth optical signal in a fourth wavelength band located next to the third wavelength band; and a processor coupled to the first transmitter and the second transmitter and configured to select the third wavelength band among the first wavelength band, the second wavelength band, the third wavelength band and the fourth wavelength band, and control the first wavelength band, the second wavelength band, and the fourth wavelength band based on the third wavelength band.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-124832, filed on Jun. 23, 2016, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to an optical transmission apparatus and a wavelength control method. 
       BACKGROUND 
       [0003]    For example, there is provided a super channel that performs wavelength multiplexing on a plurality of sub-channels at high density using a wavelength division multiplexing (WDM) technique so as to output signals as if one signal. The super channel is a technique that transmits a signal, for example, at a data rate of 400 Gbps, 1 Tbps, or the like for each channel. The super channel includes a plurality of units, and a plurality of sub-carriers (SCs) are included for each unit. An optical node is capable of performing Add/Drop on a super channel entirely as a single wavelength channel using a wavelength selective switch (WSS), or the like. 
         [0004]    A plurality of SCs are mountable in a unit in the super channel. However, if it is assumed that the absolute value of the wavelength of an SC has a tolerance of about ±2 GHz with respect to a set wavelength, the SC interval becomes a maximum of 4 GHz. As a result, when the SC interval in a unit becomes large, the frequency usage efficiency deteriorates. Thus, a method of controlling the wavelength of the SC in a unit is demanded so as to reduce the SC interval in the unit in order to increase the frequency usage efficiency. As the related art, for example, Japanese Laid-open Patent Publication No. 2014-217053, Japanese Laid-open Patent Publication No. 2014-217054, and Japanese Laid-open Patent Publication No. 2014-103600, and the like are disclosed. 
         [0005]    However, if the SC interval in a unit is reduced, SCs in the unit overlap each other, and for example, a crosstalk arises between the SCs. Further, a pass band narrowing (PBN) penalty occurs at a WSS filter that transmits SCs in the unit. As a result, the transmission quality of the super channel deteriorates. In view of the above, it is desirable to reduce deterioration of the transmission quality of a super channel. 
       SUMMARY 
       [0006]    According to an aspect of the Invention, an optical transmission apparatus includes a first transmitter configured to transmit a first optical signal in a first wavelength band and a second optical signal in a second wavelength band located next to the first wavelength band; a second transmitter configured to transmit a third optical signal in a third wavelength band located next to the second wavelength band and a fourth optical signal in a fourth wavelength band located next to the third wavelength band, the third optical signal being different from the first optical signal and the fourth optical signal being different from the second optical signal; and a processor coupled to the first transmitter and the second transmitter and configured to: select the third wavelength band among the first wavelength band, the second wavelength band, the third wavelength band and the fourth wavelength band, and control the first wavelength band, the second wavelength band, and the fourth wavelength band based on the third wavelength band. 
         [0007]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0008]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is an explanatory diagram illustrating an example of an optical transmission system according to a first embodiment; 
           [0010]      FIG. 2  is an explanatory diagram illustrating an example of arrangement of a first SC to a fourth SC in a super channel according to the first embodiment; 
           [0011]      FIG. 3  is an explanatory diagram illustrating an example of wavelength control of the first SC and the second SC according to the first embodiment when the first SC and the second SC in a first unit in the super channel are shifted by 2 GHz in the shortest wavelength direction; 
           [0012]      FIG. 4  is an explanatory diagram illustrating an example of arrangement of a first SC to an eighth SC in a super channel according to a second embodiment; and 
           [0013]      FIG. 5  is an explanatory diagram illustrating an example of wavelength control of the first SC and the second SC according to the second embodiment when a first unit in the super channel is shifted by 2 GHz in the shortest wavelength direction. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0014]    In the following, detailed descriptions will be given of an optical transmission apparatus and a wavelength control method according to embodiments of the present disclosure with reference to the drawings. In this regard, the disclosed technique is not limited by the embodiments. Also, the embodiments described below may be suitably combined within a range that does not cause a contradiction. 
       First Embodiment 
       [0015]      FIG. 1  is an explanatory diagram illustrating an example of an optical transmission system  1  according to a first embodiment. The optical transmission system  1  illustrated in  FIG. 1  includes an optical transmission apparatus  2 , an optical transmission apparatus  3  on the opposite side, and an optical transmission path  4 . The optical transmission apparatus  2  includes a plurality of transmitter units  11 , a multiplexing unit  12 , a first WSS  13 , a setting unit  14 , and a control unit  15 . Each of the transmitter units  11  transmits an optical signal of an SC having a light wavelength. The transmitter unit  11  includes a first transmission unit  16 A and a second transmission unit  16 B. The other of the transmitter units  11  includes a third transmission unit  16 C and a fourth transmission unit  16 D. The first transmission unit  16 A transmits an optical signal of an SC having a first wavelength. The second transmission unit  16 B transmits an optical signal of an SC having a second wavelength next to the first wavelength. The third transmission unit  16 C transmits an optical signal of an SC having a third wavelength next to the second wavelength. The fourth transmission unit  16 D transmits an optical signal of an SC having a fourth wavelength next to the third wavelength. The multiplexing unit  12  multiplexes the optical signal of the SC from each of the transmitter units  11 . The first WSS  13  performs filter processing such that the optical wavelength division multiplexed signal including a plurality of SCs that have been multiplexed by the multiplexing unit  12  remains in the signal band of a super channel. The first WSS  13  then outputs the super channel having been subjected to the filter processing to the optical transmission path  4 . 
         [0016]    The setting unit  14  sets a reference SC and a control target SC from the SCs in each of the transmitter units  11 . The reference SC is an SC that becomes a reference of wavelength control of the SCs in a unit. The control target SC is an SC that becomes a target of wavelength control with reference to the reference SC. The setting unit  14  sets, among a plurality of SCs in a unit in the super channel, the SC having a wavelength on the side next to the other units in the same super channel, for example, the SC having a wavelength on the side of the center wavelength λ 0  of the super channel to the reference SC. Further, the setting unit  14  sets the SCs other than the reference SC in the same unit to the control target SCs. The control unit  15  controls the wavelength of the other control target SCs in the unit with reference to the reference SC for each of the transmitter units  11 . 
         [0017]    The optical transmission apparatus  3  on the opposite side includes a second WSS  21 , a demultiplexing unit  22 , and a plurality of receiver units  23 . The second WSS  21  outputs the super channel received via the optical transmission path  4  to the demultiplexing unit  22 . The demultiplexing unit  22  demultiplexes the super channel into optical signals of each SC. Each receiver unit  23  receives an optical signal corresponding to the SC that is demultiplexed by the demultiplexing unit  22 . 
         [0018]    The optical transmission apparatus  2  transmits the super channel including a plurality of SCs to the optical transmission apparatus  3  on the opposite side via the optical transmission path  4 .  FIG. 2  is an explanatory diagram illustrating an example of arrangement of a first SC  33 A to a fourth SC  33 D in a super channel  30  according to the first embodiment. In the super channel  30  illustrated in  FIG. 2 , a first unit  31  and a second unit  32  are arranged with the center wavelength λ 0  of the super channel  30  as center. The center wavelength λ 0  of the super channel  30  corresponding to the center wavelength of the filter band of the first WSS  13 . The first unit  31  includes the first SC  33 A and the second SC  33 B. The first SC  33 A is an SC that was transmitted by the first transmission unit  16 A. The second SC  33 B is an SC that was transmitted by the second transmission unit  16 B. The second unit  32  includes the third SC  33 C and the fourth SC  33 D. The third SC  33 C is an SC that was transmitted by the third transmission unit  16 C. The fourth SC  33 D is an SC that was transmitted by the fourth transmission unit  16 D. 
         [0019]    The setting unit  14  sets the SC  33  having a wavelength closer to the center wavelength λ 0  of the first WSS  13  among each SC  33  in the same unit  31  ( 32 ) in the super channel  30  to the reference SC. Further, the setting unit  14  sets the SC  33  other than the reference SC to the control target SC. In the first unit  31  illustrated in  FIG. 2 , the setting unit  14  sets the second SC  33 B, which is closer to the center wavelength λ 0 , to the reference SC, and sets the first SC  33 A to the control target SC. In the second unit  32 , the setting unit  14  sets the third SC  33 C, which is closer to the center wavelength λ 0 , to the reference SC, and sets the fourth SC  33 D to the control target SC. The tolerance of the reference SC to the setting value is ±2 GHz. The control error of the wavelength control with respect to the setting value of the control target SC is 0 to 1 GHz. 
         [0020]    The control unit  15  sets the second SC  33 B, which is the reference SC in the first unit  31 , to the reference in consideration of the tolerance and the control error. As illustrated in  FIG. 2 , the control unit  15  then controls the wavelength of the first SC  33 A, which is the control target SC in the first unit  31 . The control unit  15  sets the third SC  33 C, which is the reference SC in the second unit  32 , to the reference in consideration of the tolerance and the control error. As illustrated in  FIG. 2 , the control unit  15  then controls the wavelength of the wavelength of the fourth SC  33 D, which is the control target SC in the second unit  32 . 
         [0021]    The maximum wavelength of the second SC  33 B in the first unit  31  becomes a wavelength having an equivalent tolerance of 2 GHz from the center wavelength λ 0  in the shortest wavelength direction. Further, the minimum wavelength of the first SC  33 A becomes a wavelength having an equivalent tolerance of 2×SC band+2 GHz+0 to 1 GHz from the center wavelength λ 0  in the shortest wavelength direction. 
         [0022]    Next, a description will be given of operation of the optical transmission apparatus  2  according to the first embodiment.  FIG. 3  is an explanatory diagram illustrating an example of wavelength control of the first SC  33 A and the second SC  33 B according to the first embodiment when the first SC and the second SC in the first unit  31  in the super channel  30  are shifted by 2 GHz in the shortest wavelength direction. 
         [0023]    The control unit  15  controls the wavelength of the first SC  33 A, which is the control target SC, with reference to the second SC  33 B, which is the reference SC in the first unit  31  in consideration of the tolerance and the control error. The first SC  33 A and the second SC  33 B in the first unit  31  are shifted by 2 GHz in the shortest wavelength direction. 
         [0024]    The maximum wavelength of the second SC  33 B in the first unit  31  in the super channel  30  becomes an equivalent wavelength of 4 GHz from the center wavelength λ 0  in the shortest wavelength direction. Even if the maximum wavelength of the first SC  33 A in the first unit  31  has been shifted by 2 GHz in the shortest wavelength direction, the maximum wavelength of the first SC  33 A in the first unit  31  becomes an equivalent wavelength of 2×the SC band+5 GHz from the center wavelength λ 0 , because the control error is 1 GHz. 
         [0025]    Accordingly, the optical transmission apparatus  2  controlled the wavelength of the first SC  33 A with reference to the second SC  33 B in the case of using the second SC  33 B in the first unit  31  as the reference SC, and using the first SC  33 A as the control target SC. The wavelength of the first SC  33 A is controlled with reference to the second SC  33 B, and thus even if a shift of 2 GHz occurs in the shortest wavelength direction, the second SC  33 B in the first unit  31  and the first SC  33 A do not overlap. As a result, it is possible to reduce crosstalk between the first SC  33 A and the second SC  33 B and the PBN of the first WSS  13 . It is then possible to reduce deterioration of the transmission quality of the super channel  30 . 
         [0026]    For the second unit  32 , the optical transmission apparatus  2  controlled the wavelength of the fourth SC  33 D with reference to the third SC  33 C in the case of using the third SC  33 C in the second unit  32  as the reference SC and using the fourth SC  33 D as the control target SC. The wavelength of the fourth SC  33 D is controlled with reference to the third SC  33 C, and thus even if a shift of 2 GHz occurs in the maximum wavelength, the third SC  33 C in the second unit  32  and the fourth SC  33 D do not overlap. As a result, it is possible to reduce crosstalk between the third SC  33 C and the fourth SC  33 D and the PBN of the first WSS  13 . It is then possible to reduce deterioration of the transmission quality of the super channel  30 . 
         [0027]    The super channel  30  according to the first embodiment includes two units, the first unit  31  and the second unit  32 . However, the present disclosure is not limited to this configuration. For example, the super channel  30  may include four units, and it is possible to suitably change the number of units. Thus, a description will be given below of the case where the super channel including four units is applied as a second embodiment. The same symbol is given to the same component as that in the optical transmission system  1  illustrated in  FIG. 1 , and the description of will be omitted of the duplicated configuration and operation. 
       Second Embodiment 
       [0028]      FIG. 4  is an explanatory diagram illustrating an example of arrangement of a first SC  45 A to an eighth SC  45 H in a super channel  40  according to the second embodiment. The super channel  40  includes a first unit  41  and a second unit  42  on one side, and a third unit  43  and a fourth unit  44  on the other side with a center wavelength λ 0  as center. The first unit  41  includes a first SC  45 A and a second SC 45 B. The second unit  42  includes a third SC  45 C and a fourth SC 45 D. Further, the third unit  43  includes a fifth SC  45 E and a sixth SC  45 F. The fourth unit  44  includes a seventh SC  45 G and an eighth SC  45 H. In the super channel  40 , the tolerance between the SCs  45  is ±2 GHz, and the control error is 0 to 1 GHz. 
         [0029]    The setting unit  14  sets the second SC  45 B having a wavelength closer to the center wavelength λ 0  in the first unit  41  to the reference SC, and sets the first SC  45 A to the control target SC. The setting unit  14  sets the fourth SC  45 D having a wavelength closer to the center wavelength λ 0  in the second unit  42  to the reference SC, and sets the third SC  45 C to the control target SC. The setting unit  14  sets the fifth SC  45 E having a wavelength closer to the center wavelength λ 0  in the third unit  43  to the reference SC, and sets the sixth SC  45 F to the control target SC. The setting unit  14  sets the seventh SC  45 G having a wavelength closer to the center wavelength λ 0  in the fourth unit  44  to the reference SC, and sets the eighth SC  45 H to the control target SC. 
         [0030]    The control unit  15  controls the wavelength of the first SC  45 A with reference to the second SC  45 B in the first unit  41 . Further, the control unit  15  controls the wavelength of the third SC  45 C with reference to the fourth SC  45 D in the second unit  42 . As a result, the minimum wavelength of the fourth SC  45 D in the second unit  42  becomes an equivalent wavelength having a tolerance of 2 GHz in the shortest wavelength direction from the center wavelength λ 0 . The interval between the fourth SC  45 D and the third SC  45 C is 1 GHz. The minimum wavelength of the third SC  45 C becomes the SC band×2+a tolerance of 2 GHz+a control error of 1 GHz, that is to say, an equivalent wavelength of the SC band×2+5 GHz from the center wavelength λ 0  in the shortest wavelength direction. Further, the maximum wavelength of the second SC  45 B in the first unit  41  becomes an equivalent wavelength of 2×SC band+3 GHz+a tolerance of 2 GHz+a tolerance of 2 GHz from the center wavelength λ 0  in the shortest wavelength direction. The Interval between the first SC  45 A and the second SC  45 B is from 0 to 1 GHz. The minimum wavelength of the first SC  45 A becomes an equivalent wavelength of 4×SC band+7 GHz+a control error of 0 to 1 GHz from the center wavelength λ 0  in the shortest wavelength direction. 
         [0031]    Next, a description will be given of operation of the optical transmission apparatus  2  according to the second embodiment.  FIG. 5  is an explanatory diagram illustrating an example of wavelength control of the first SC  45 A and the second SC  45 B according to the second embodiment when the first SC  45 A and the second SC  45 B in the first unit  41  in the super channel  40  are shifted by 2 GHz in the shortest wavelength direction. The control unit  15  controls the wavelength of the first SC  45 A, which is the control target SC with reference to the second SC  45 B, which is the reference SC in the first unit  41 , in consideration of the tolerance and the control error. The first SC  45 A and the second SC  45 B are shifted by 2 GHz in the shortest wavelength direction. 
         [0032]    The maximum wavelength of the second SC  45 B in the first unit  41  in the super channel  40  becomes an equivalent wavelength of 2×SC band+5 GHz+a tolerance of 2 GHz+the amount of shift, 2 GHz, that is to say, 2×SC band+9 GHz from the center wavelength λ0. Even if a shift of 2 GHz in the shortest wavelength direction occurs, the maximum wavelength of the first SC  45 A in the first unit  41  becomes an equivalent wavelength of 4×SC band+10 GHz from the center wavelength λ 0  because the control error is 1 GHz. 
         [0033]    Accordingly, the optical transmission apparatus  2  controlled the wavelength of the first SC  45 A with reference to the second SC  45 B in the case of using the second SC  45 B in the first unit  41  as the reference SC, and using the first SC  45 A as the control target SC. The wavelength of the first SC  45 A is controlled with reference to the second SC  45 B, and thus even if a shift of 2 GHz occurs in the shortest wavelength direction, the second SC  45 B in the first unit  41  and the first SC  45 A do not overlap. As a result, it is possible to reduce the crosstalk between the first SC  45 A and the second SC  45 B and the PBN. It is then possible to reduce deterioration of the transmission quality of the super channel  40 . 
         [0034]    For the second unit  42 , the optical transmission apparatus  2  controlled the wavelength of the fourth SC  45 D with reference to the third SC  45 C in the case of using the fourth SC  45 D in the second unit  42  as the reference SC, and using the third SC  45 C as the control target SC. The wavelength of the fourth SC  45 D is controlled with reference to the third SC  45 C, and thus even if a shift of 2 GHz occurs in the shortest wavelength direction, the third SC  45 C in the second unit  42  and the fourth SC  45 D do not overlap. As a result, it is possible to reduce the crosstalk between the third SC  45 C and the fourth SC  45 D and the PBN. It is then possible to reduce deterioration of the transmission quality of the super channel  40 . 
         [0035]    For the third unit  43 , the optical transmission apparatus  2  controlled the wavelength of the sixth SC  45 F with reference to the fifth SC  45 E in the case of using the fifth SC  45 E in the third unit  43  as the reference SC, and using the sixth SC  45 F as the control target SC. The wavelength of the sixth SC  45 F is controlled with reference to the fifth SC  45 E, and thus even if a shift of 2 GHz occurs in the maximum wavelength, the fifth SC  45 E in the third unit  43  and the sixth SC  45 F do not overlap. As a result, it is possible to reduce the crosstalk between the fifth SC  45 E in the third unit  43  and the sixth SC  45 F and the PBN. It is then possible to reduce deterioration of the transmission quality of the super channel  40 . 
         [0036]    Further, for the fourth unit  44 , the optical transmission apparatus  2  controlled the wavelength of the eighth SC  45 H with reference to the seventh SC  45 G in the case of using the seventh SC  45 G in the fourth unit  44  as the reference SC, and using the eighth SC  45 H as the control target SC. The wavelength of the eighth SC  45 H is controlled with reference to the seventh SC  45 G, and thus even if a shift of 2 GHz occurs in the maximum wavelength, the seventh SC  45 G in the fourth unit  44  and the eighth SC  45 H do not overlap. As a result, it is possible to reduce the crosstalk between the seventh SC  45 G in the fourth unit  44  and the eighth SC  45 H and the PBN. It is then possible to reduce deterioration of the transmission quality of the super channel  40 . 
         [0037]    In the first embodiment and the second embodiment, the examples of the case in which one unit includes two SCs are illustrated. However, three or more SCs may be included in one unit. In this case, among a plurality of SCs in the unit, the SC having a wavelength closer to the center wavelength λ 0  is set to the reference SC, and the other SCs are set to the control target SCs. In the first embodiment and the second embodiment, among a plurality of SCs in the unit, the SC having the wavelength closest to the center wavelength λ 0  of the super channel is set to the reference SC. However, the present disclosure is not limited to this, and it is possible to set an SC having the wavelength other than the farthest from the center wavelength λ 0  to the reference SC among a plurality of SCs in the unit. 
         [0038]    In the first embodiment and the second embodiment, among a plurality of SCs in a unit in the super channel, the SC having a wavelength closest to the center wavelength λ 0  of the super channel is set to the reference SC, and the SCs other than the reference SC is set to the control target SCs. As a result, the reference SC and the control target SCs do not overlap, and thus it is possible to reduce the crosstalk between the SCs in the unit and the occurrence of the PBN. It is then possible to reduce deterioration of the transmission quality of the super channel. 
         [0039]    In the above-described embodiments, the first transmission unit  16 A and the second transmission unit  16 B are included in one of the transmitter units  11 , and the third transmission unit  16 C and the fourth transmission unit  16 D are included in the other of the transmitter units  11 . However, the present disclosure is not limited to these, and it is possible to suitably change the configuration. For example, each transmitter unit  11  may include one transmission unit or three or more transmission units. 
         [0040]    All of or any one of the various processing functions performed by each apparatus may be executed on a central processing unit (CPU) (or a microcomputer, such as a micro processing unit (MPU), a micro controller unit (MCU), or the like). All of or any one of the various processing functions may be performed by a program that is analyzed and executed by the CPU (or the microcomputer, such as the MPU, the MCU, or the like), or by hardware based on wired logic as a matter of course. 
         [0041]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and Inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.