Patent Publication Number: US-2010111486-A1

Title: Dispersion compensating module

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dispersion compensating module used to compensate for waveform deterioration of signal light in an optical communications system. 
     2. Related Background of the Invention 
     In an optical communications system, single-mode optical fibers, which are commonly used as the optical transmission line for transmitting signal light, have positive chromatic dispersion in the signal light wavelength. During signal light propagates through such an optical fiber, its waveform deteriorates due to cumulative chromatic dispersion. In view of this, a dispersion compensating optical fiber or a dispersion compensating module is used as a constituent element of an optical communications system in order to compensate for the waveform deterioration of signal light caused by cumulative chromatic dispersion. 
     Dispersion compensating optical fibers have a negative chromatic dispersion in the signal light wavelength. When single-mode optical fibers having positive chromatic dispersion and dispersion compensating optical fibers having negative chromatic dispersion are connected at a suitable length ratio, such a configuration lowers the absolute value of the cumulative chromatic dispersion of the overall optical transmission line. This suppresses the waveform deterioration of signal light and makes even faster optical communications possible. 
     Also, dispersion compensating optical fibers are sometimes installed as part of an optical transmission line of a relay section, but they sometimes also form part of a dispersion compensating module by being held in a housing in a state of being wound in a coil. A dispersion compensating module is an optical component that is disposed in the relays of optical communications systems and so forth, and among its advantages is ease of maintenance. 
     Meanwhile, in Document 1 (P. M. Krummrich et al., “Extremely fast (microsecond time scale) polarization changes in high speed long haul WDM transmission systems,” OFC 2004, FI3) and in Document 2 (E. Yamada et al., “Fast polarization change due to mechanical vibration of a spooled optical fiber,” 2007 General Conference of the Electronic Information Communications Society, B-10-49, p. 388), there are reports on the effect when a dispersion compensating module, which is constituted by housing such a dispersion compensating optical fiber into a housing while the dispersion compensating optical fiber wound in a state of coil, is imparted with impact or vibration. In particular, according to Documents 1 and 2, the polarization state of output light that has propagated through a dispersion compensating optical fiber changes at high speed. Also, the rate of change of the polarization state of signal light when a dispersion compensating module is imparted with impact or vibration is known to be dependent on the fiber length (see Document 2). 
     SUMMARY OF THE INVENTION 
     The present inventors have examined the above conventional dispersion compensating modules, and as a result, have discovered the following problems. Namely, polarization mode dispersion compensation is sometimes performed in high-speed optical communications. More specifically, the polarization mode dispersion compensation controls, while monitoring the polarization state of signal light, the polarization state so as to keep it constant. In the case that a polarization state of signal light changes at high speed while this polarization mode dispersion compensation is carried out, the polarization mode dispersion compensation is not performed properly because a polarization mode dispersion compensator cannot follow such high speed fluctuations in the polarization state. 
     Fluctuations in the polarization state of signal light, propagating through an optical transmission line, occurs due to various causes, such as changes in temperature and changes in external force. Of these, high-speed polarization changes in signal light occur when the optical transmission line is imparted with mechanical impact or vibration. Therefore, in the case that a dispersion compensating module, in which a long dispersion compensating optical fiber is housed, is imparted with impact or vibration, high-speed polarization changes will occur, and therefore these will make polarization mode dispersion compensation difficult. 
     The present invention has been developed to eliminate the problems described above. It is an object of the present invention to provide a dispersion compensating module having a configuration for effectively suppressing high-speed fluctuations in the polarization state of light even when being imparted with impact or vibration. 
     A dispersion compensating module according to the present invention comprises a dispersion compensating optical fiber, a holder, a buffer, and a struct. Here, the holder holds the dispersion compensating optical fiber with the dispersion compensating optical fiber fixed in a state of coil. The buffer functions to absorb impact or vibration imparted to the holder. The struct fixes the holder via the buffer. 
     More specifically, the holder has a configuration capable of holding a coiled dispersion compensating optical fiber in a fixed state, and includes, for example, a housing serving as a container for housing this coil in its interior, or a bobbin on which the dispersion compensating optical fiber is wound. The struct is a member that fixes the holder, and includes, for example, an installation bench such as a rack to which the holder is fixed, or a container for housing the holder in its interior. As the buffer, a liquid, a gel, a sponge, rubber, plastic, a spring, an air cushion, an air suspension, or the like can be used favorably. 
     A first configuration that can be applied to the dispersion compensating module according to the present invention can be realized by a bobbin, on which a dispersion compensating optical fiber has been wound in a state of coil, functioning as the holder and a housing, which housing the holder together with the buffer in its interior, functioning as the struct. In this first configuration, the buffer is arranged so as to be in contact with both the holder and the struct. 
     Particularly, in the first configuration, when the holder is imparted with impact or vibration via the buffer, there is the possibility that there will be a relative positional change between the housing corresponding to the struct of the dispersion compensating module and the bobbin corresponding to the holder. Meanwhile, in the first configuration, since jumpers corresponding to the end portions of the dispersion compensating optical fiber wound around the bobbin are taken out, there is a greater probability that disconnection will occur in the jumpers, in the condition that these jumpers are fixed to the housing. In view of this, it is preferable that the dispersion compensating module further comprises a configuration for reducing a tension applied to jumpers that constitute part of the dispersion compensating optical fiber and are taken out from the bobbin to the outside of the housing. Also, it is preferable that a take-out part of the jumpers from the housing is provided to the surface perpendicular to the surface where the housing is installed, out of the surfaces constituting the housing, since this prevents the jumpers from being subjected to unnecessary tension. 
     Furthermore, a second configuration that can be applied to the dispersion compensating module according to the present invention can be realized by a housing, in which a coiled dispersion compensating optical fiber is housed, functioning as the holder and an installation bench, on which the holder is fixed via the buffer, functioning as the struct. In this second configuration, the buffer is arranged so as to be in contact with both the holder and the struct. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a first embodiment (first configuration) of the dispersion compensating module according to the present invention; 
         FIGS. 2A to 2C  are diagrams of modified examples of the jumper take-out configuration in the dispersion compensating module according to the first embodiment; 
         FIG. 3  is a diagram of a second embodiment (first configuration) of the dispersion compensating module according to the present invention; 
         FIG. 4  is a diagram of a third embodiment (first configuration) of the dispersion compensating module according to the present invention; 
         FIG. 5  is a diagram of a fourth embodiment (first configuration) of the dispersion compensating module according to the present invention; 
         FIG. 6  is a diagram of a fifth embodiment (first configuration) of the dispersion compensating module according to the present invention; 
         FIGS. 7A and 7B  are diagrams of a sixth embodiment (second configuration) of the dispersion compensating module according to the present invention; 
         FIG. 8  is a diagram of a seventh embodiment (second configuration) of the dispersion compensating module according to the present invention; 
         FIG. 9  is a diagram of the cross sectional struct of the dispersion compensating module according to the seventh embodiment shown in  FIG. 8 ; 
         FIG. 10  is a diagram of an eighth embodiment (second configuration) of the dispersion compensating module according to the present invention; and 
         FIG. 11  is a diagram of a ninth embodiment (second configuration) of the dispersion compensating module according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments of the dispersion compensating module according to the present invention will now be described in detail through reference to  FIGS. 1 ,  2 A to  2 C,  3  to  6 ,  7 A and  7 B, and  8  to  11 . In the description of the drawings, identical or corresponding components are designated by the same reference numerals, and overlapping description is omitted. 
     The dispersion compensating module according to the present embodiment comprises a dispersion compensating optical fiber, a holder holding the dispersion compensating optical fiber fixed in a state of coil, a buffer absorbing impact or vibration imparted to the holder, and a struct fixing the holder via the buffer. Incidentally, in the dispersion compensating module, various configurations can be realized by the combination of a constituent element serving as the holder and a constituent element serving as the struct. Therefore, in the following description, the first to fifth embodiments will be explained as an embodiment having a first configuration, and sixth to ninth embodiments will be explained as an embodiment having a second configuration. 
       FIG. 1  is a diagram of a first embodiment of the dispersion compensating module according to the present invention. The dispersion compensating module  1  according to the first embodiment comprises a dispersion compensating optical fiber  11 , a bobbin  12  around the barrel of which the dispersion compensating optical fiber  11  is fixed in a state of being wound, a housing  13  in which the entire bobbin  12  is housed, and a buffer  14  filled in the space between the bobbin  12  and the inner walls of the housing  13 . The buffer  14  is a material or configuration that absorbs impact or vibration applied to the bobbin  12 , and functions to fix the bobbin  12  in a specific location in the interior of the housing  13 . 
     In the dispersion compensating module  1  according to this first embodiment, the first configuration is realized by the bobbin  12  functioning as a holder that holds the dispersion compensating optical fiber  11  fixed in a state of coil and the housing  13  functioning as a struct fixing the holder. The first configuration is also employed for the dispersion compensating modules  2  to  5  according to the second to fifth embodiments, which are described below. 
     In the dispersion compensating module  1  according to the first embodiment having the first configuration as discussed above, the buffer  14  is filled in the space between the housing  13  and the bobbin  12  whose barrel is wound with the dispersion compensating optical fiber  11 . Furthermore, in this first embodiment, the buffer  14  is also filled in the space between the two flanges of the bobbin  12  (which together function to sandwich the dispersion compensating optical fiber  11  wound around the barrel). In the dispersion compensating module  1  constituted in this way, even when the housing  13  is imparted with impact or vibration, the action of the buffer  14  will effectively reduce impact or vibration applied to the dispersion compensating optical fiber  11  wound around the barrel of the bobbin  12 . Accordingly, high-speed fluctuations in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be suppressed. 
     In the dispersion compensating module  1  according to this first embodiment, the dispersion compensating optical fiber  11  that is wound around the barrel of the bobbin  12  has an end  11   a  including one light input/output end surface, and an end  11   b  including the other light input/output end surface, with these being called jumpers and constituting part of the dispersion compensating optical fiber  11  that is taken out from the bobbin  12  to the outside of the housing  13 . Also, as shown in  FIG. 1 , the dispersion compensating module  1  may be disposed on an installation surface A 1 , or on an installation surface A 2 . 
     In the first configuration described above, when the bobbin  12  is imparted with impact or vibration via the housing  13 , there is the possibility of a relative positional change occurring between the housing  13  corresponding to the struct and the bobbin  12  corresponding to the holder. On the other hand, in the first configuration, since the jumpers  11   a  and  11   b  corresponding to the end portions of the dispersion compensating optical fiber  11  wound around the barrel of the bobbin  12  are taken out to the outside of the housing  13 , there is a greater probability of disconnection in the jumpers  11   a  and  11   b  in the condition that the jumpers  11   a  and  11   b  are fixed to the housing  13 . In view of this, various modified examples can be applied in an effort to reduce the risk of disconnection in the jumpers  11   a  and  11   b  (part of the dispersion compensating optical fiber  11 ).  FIGS. 2A to 2C  are diagrams of various modified examples of the jumper take-out struct in the dispersion compensating module  1  according to the first embodiment. The various configurations described below ( FIGS. 2A to 2C ) are not limited to the dispersion compensating module  1  according to the first embodiment, and can also be applied to the embodiments discussed below, namely, the dispersion compensating modules  2  to  5  according to the second to fifth embodiments to which the first configuration is applied, as well as to the dispersion compensating modules  6  to  9  according to the sixth to ninth embodiments to which the second configuration is applied. 
     Specifically, in the dispersion compensating module  1  according to the first embodiment, the part of the jumper  11   a  and the part of the jumper  11   b  located inside the housing  13  are fixed by the buffer  14 , while the part of the jumper  11   a  and the part of the jumper  11   b  located outside the housing  13  are not fixed. In this case, there is the risk of disconnection in the jumpers  11   a  and  11   b  at the open ends of the through-holes in the housing  13  through which the jumpers  11   a  and  11   b  pass. Therefore, the jumpers  11   a  and  11   b  are preferably taken out from a surface, out of the surfaces constituting the housing  13 , perpendicular to the installation surface of the dispersion compensating module  1 . For example, in the case that the dispersion compensating module  1  is placed on the installation surface A 1 , as shown in  FIG. 1 , the jumpers  11   a  and  11   b  are preferably taken out from a surface of the housing  13  that is perpendicular to the installation surface A 1 . On the other hand, the dispersion compensating module  1   a  shown in  FIG. 2A  is installed on the installation surface A 2 , and the jumpers  11   a  and  11   b  are taken out from a surface of the housing  13  that is perpendicular to the installation surface A 2 . 
     Also, in the dispersion compensating module  1   b  shown in  FIG. 2B , hollow pipes  110   a  and  110   b  are fixed in a state of passing through the housing  13  so that the jumpers  11   a  and  11   b  do not come into direct contact with the housing  13 . In this case, since the jumpers  11   a  and  11   b  are taken out to the outside of the housing  13  in a state of passing through the hollow pipes  110   a  and  110   b,  the positions of the hollow pipes  110   a  and  110   b  with respect to the housing  13  can be varied freely. Therefore, even when the relative position of the bobbin  12  with respect to the housing  13  should change due to impact or vibration, the jumpers  11   a  and  11   b  can be prevented from being subjected to unnecessary tension. 
     In the dispersion compensating module  1   c  shown in  FIG. 2C , surplus length portions  111   a  and  111   b  are provided to the portions of the jumpers  11   a  and  11   b  located inside the housing  13 . In this case, the surplus length portions  111   a  and  111   b  of the jumpers  11   a  and  11   b  will absorb any change in the relative position of the bobbin  12  with respect to the housing  13  caused by impact or vibration, so the jumpers  11   a  and  11   b  can be prevented from being subjected to unnecessary tension. Furthermore, the surplus length portions  111   a  and  111   b  of the jumpers  11   a  and  11   b  may be housed in the housing  13  while being brought together in a state of loop shape or infinity sign shape, or being brought together in a spiral manner like a spring. 
       FIG. 3  is a diagram of a second embodiment of the dispersion compensating module according to the present invention, and the dispersion compensating module  2  in the second embodiment also has the first configuration, just as in the first embodiment. The configurations shown in  FIGS. 2A to 2C  can also be applied to this dispersion compensating module  2  according to the second embodiment. 
     Specifically, in the dispersion compensating module  2  according to the second embodiment, the configuration, which is constituted by the bobbin  12  functioning as the holder and the housing  13  functioning as the struct, is the same as in the first embodiment described above. In the dispersion compensating module  2  according to the second embodiment, the buffer  14  is filled in the space between the bobbin  12  and the housing  13 , but is not filled in the space between the two flanges of the bobbin  12 . Again in the dispersion compensating module  2  constituted in this way, when the housing  13  is imparted with impact or vibration, the action of the buffer  14  reduces the impact or vibration that is applied to the dispersion compensating optical fiber  11  wound around the barrel of the bobbin  12 . Therefore, again in the dispersion compensating module  2  according to the second embodiment, high-speed changes in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be effectively suppressed. 
       FIG. 4  is a diagram of a third embodiment of the dispersion compensating module according to the present invention, and the dispersion compensating module  3  according to the third embodiment also has the first configuration, just as in the first embodiment. The configurations shown in  FIGS. 2A to 2C  can also be applied to this dispersion compensating module  3  according to the third embodiment. 
     Specifically, in the dispersion compensating module  3  according to the third embodiment, the configuration, which is constituted by the bobbin  12  functioning as the holder and the housing  13  functioning as the struct, is the same as in the first embodiment described above. In the dispersion compensating module  3  in the third embodiment, the buffer  14  is filled in the space between the flanges of the bobbin  12  and the opposing wall surfaces of the housing  13 , but is not filled in the space between the two flanges of the bobbin  12 , nor is it filled in the space between the bobbin  12  and the side surfaces of the housing  13 . Again in the dispersion compensating module  3  constituted in this way, when the housing  13  is subjected to impact or vibration, the action of the buffer  14  reduces the impact or vibration that is applied to the dispersion compensating optical fiber  11  wound around the barrel of the bobbin  12 . As a result, again in the dispersion compensating module  3  according to the third embodiment, high-speed changes in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be effectively suppressed. 
       FIG. 5  is a diagram of a fourth embodiment of the dispersion compensating module according to the present invention, and the dispersion compensating module  4  according to the fourth embodiment also has the first configuration, just as in the first embodiment. The configurations shown in  FIGS. 2A to 2C  can also be applied to this dispersion compensating module  4  according to the fourth embodiment. 
     Specifically, in the dispersion compensating module  4  according to the fourth embodiment, the configuration, which is constituted by the bobbin  12  functioning as the holder and the housing  13  functioning as the struct, is the same as in the first embodiment described above. In the dispersion compensating module  4  in the fourth embodiment, the buffer  14  is filled in only the space between one flange of the bobbin  12  and the opposing wall surface of the housing  13 . On the other hand, the buffer  14  is not filled in the space between the two flanges of the bobbin  12 , nor is it filled in the space between the other flange of the bobbin  12  and the opposing side surface of the housing  13 , nor is it filled in the space between the bobbin  12  and the side surfaces of the housing  13 . Again in the dispersion compensating module  4  constituted in this way, when the housing  13  is subjected to impact or vibration, the action of the buffer  14  reduces the impact or vibration that is applied to the dispersion compensating optical fiber  11  wound around the barrel of the bobbin  12 . As a result, again in the dispersion compensating module  4  according to the fourth embodiment, high-speed changes in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be effectively suppressed. 
       FIG. 6  is a diagram of a fifth embodiment of the dispersion compensating module according to the present invention, and the dispersion compensating module  5  according to the fifth embodiment also has the first configuration, just as in the first embodiment. The configurations shown in  FIGS. 2A to 2C  can also be applied to this dispersion compensating module  5  according to the fifth embodiment. 
     Specifically, in the dispersion compensating module  5  according to the fifth embodiment, the configuration, which is constituted by the bobbin  12  functioning as the holder and the housing  13  functioning as the struct, is the same as in the first embodiment described above. In the dispersion compensating module  5  in the fifth embodiment, a buffer  15  is a member that connects the flanges of the bobbin  12  to the wall surfaces of the housing  13 , and is constituted by a cord-like member, a spring, or the like that is elastic. The bobbin  12  serving as the holder floats in the internal space of the housing  13  without touching the inner wall surfaces of the housing  13 . In the dispersion compensating module  5  constituted in this way, when the housing  13  is subjected to impact or vibration, the action of the buffer  15  reduces the impact or vibration that is applied to the dispersion compensating optical fiber  11  wound around the barrel of the bobbin  12 . As a result, again in the dispersion compensating module  5  according to the fifth embodiment, high-speed changes in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be effectively suppressed. 
       FIGS. 7A and 7B  are diagrams of a sixth embodiment of the dispersion compensating module according to the present invention, and the dispersion compensating module  6  according to the sixth embodiment has a second configuration, unlike in the first to fifth embodiments. 
     In particular, as shown in  FIG. 7A , the dispersion compensating module  6  according to the sixth embodiment comprises a holder  21  housing an dispersion compensating optical fiber wound in a state of coil, a rack  22 , a fastener  23 , an a buffer  31 . An installation bench to which the holder  21  is fixed is constituted by the rack  22  and the fastener  23 . The internal struct of the holder  21  is as shown in  FIG. 7B , for example, in which a bobbin  12 , around the barrel of which is coiled the dispersion compensating optical fiber  11 , is fixed inside the housing  13 . The internal structure of the buffer  31  shown in  FIG. 7B  differs from the above-mentioned first embodiment in that the housing  13  serving as the container and the bobbin  12  located in the interior thereof are fixed by a suitable member (no buffer is present inside the housing  13 ). 
     In the dispersion compensating module  6  according to the sixth embodiment, the holder  21  is placed on the rack  22 , and is fixed to the rack  22  by the fastener  23  via the buffer  31 , which absorbs impact or vibration, in a state of being entirely covered. The jumpers  11   a  and  11   b,  which constitute part of the dispersion compensating optical fiber housed inside the holder  21 , are taken out to the outside of the module via the rack  22  and the fastener  23 , and the configurations shown in  FIGS. 2A  to  2 C can also be applied as needed to the dispersion compensating module  6  according to the sixth embodiment. 
     In the second configuration applied to the dispersion compensating module  6  according to the sixth embodiment, the holder  21  houses the dispersion compensating optical fiber fixed in a state of coil. The rack  22  and the fastener  23  constituting the installation bench correspond to a struct for fixing the holder. In the dispersion compensating module  6  in the sixth embodiment, the buffer  31  is filled in the space between the rack  22  and the holder  21  holding the dispersion compensating optical fiber, and also is filled in the space between the holder  21  and the fastener  23 . In the dispersion compensating module  6  constituted in this way, when the rack  22  is subjected to impact or vibration, the action of the buffer  31  will reduce the impact or vibration that is applied to the dispersion compensating optical fiber housed in the holder  21 . As a result, high-speed changes in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be effectively suppressed. 
       FIG. 8  is a diagram of a seventh embodiment of the dispersion compensating module according to the present invention, and  FIG. 9  is a diagram illustrating the cross sectional configuration of the dispersion compensating module according to the seventh embodiment shown in  FIG. 8 . The dispersion compensating module  7  according to the seventh embodiment also has the second configuration, just as in the sixth embodiment. 
     Specifically, in the dispersion compensating module  7  according to the seventh embodiment, the holder  21  that houses the coiled dispersion compensating optical fiber is placed on the rack  22 , and is fixed by a fastener  24  via the buffer  31  that absorbs impact or vibration. The holder  21  has a through-hole in its center, and the fastener  24  is fixed with the rack  22  through this through-hole. The second configuration is applied to the dispersion compensating module  7  according to the seventh embodiment, and therefore the holder  21  houses the dispersion compensating optical fiber fixed in a state of coil. The fastener  24  and the rack  22  constituting the installation bench correspond to a struct for fixing the holder. The jumpers  11   a  and  11   b  constituting part of the dispersion compensating optical fiber housed in the holder  21  are taken out to the outside of the module via the housing  13  (see  FIG. 7B ), and again in the dispersion compensating module  7  according to the seventh embodiment, the configurations shown in  FIGS. 2A to 2C  can be applied as needed. 
     In the dispersion compensating module  7  according to the seventh embodiment, the buffer  31  is filled in the space between the rack  22  and the holder  21  housing the dispersion compensating optical fiber, and us filled in the space between the fastener  24  and the holder  21 . In the dispersion compensating module  7  constituted in this way, even when the rack  22  is subjected to impact or vibration, the action of the buffer  31  will reduce the impact or vibration that is applied to the dispersion compensating optical fiber held in the holder  21 . As a result, high-speed changes in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be effectively suppressed. 
       FIG. 10  is a diagram of an eighth embodiment of the dispersion compensating module according to the present invention, and the dispersion compensating module  8  according to the eighth embodiment has the second configuration, just as in the sixth embodiment. 
     Specifically, in the dispersion compensating module  8  according to the eighth embodiment, the dispersion compensating optical fiber  11  is fixed in a state of being wound around the barrel of the bobbin  12 . Also, the bobbin  12 , on the barrel of which is wound the dispersion compensating optical fiber  11 , is housed inside the housing  13 . The bobbin  12  is fixed to the housing  13  by a specific member so that the relative positions of the bobbin  12  and the housing  13  will not change. Also, the housing  13  having such a configuration has substantially the same configuration as in the sixth and seventh embodiments described above (see  FIG. 7B ). The housing  13  is placed on the rack  22 , and is fixed by a fastener  25  via the buffer  31  that absorbs impact or vibration. The fastener  25  is fixed to the bottom surface of the bobbin  12  through the rack  22  from under the rack  22 . The second configuration is applied to the dispersion compensating module  8  of this eighth embodiment, and therefore the bobbin  12  and the housing  13  (corresponding to the holder  21  in the sixth and seventh embodiments above) correspond to a holder that houses the dispersion compensating optical fiber  11  fixed in a state of coil. Also, the fastener  25  and the rack  22  constituting the installation bench correspond to a struct that fixes the holder. The jumpers  11   a  and  11   b  constituting part of the dispersion compensating optical fiber  11  held in the housing  13  are taken out to the outside of the module via the housing  13 , and the configurations shown in  FIGS. 2A to 2C  can be applied as needed to the dispersion compensating module  8  according to this eighth embodiment as well. 
     In the dispersion compensating module  8  according to the eighth embodiment, the buffer  31  is filled in the space between the rack  22  and the housing  13  that houses the dispersion compensating optical fiber  11 , and is also filled in the space between the fastener  25  and the housing  13 . In the dispersion compensating module  8  constituted in this way, even when the rack  22  is subjected to impact or vibration, the action of the buffer  31  will reduce the impact or vibration that is applied to the dispersion compensating optical fiber  11  housed in the housing  13 , so high-speed changes in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be suppressed. 
       FIG. 11  is a diagram of a ninth embodiment of the dispersion compensating module according to the present invention, and the dispersion compensating module  9  according to the ninth embodiment also has the second configuration. 
     Specifically, in the dispersion compensating module  9  according to the ninth embodiment, the dispersion compensating optical fiber  11  is fixed in a state of being wound around the barrel of the bobbin  12 . Also, the bobbin  12 , on the barrel of which is wound the dispersion compensating optical fiber  11 , is housed inside the housing  13  (just as in the eighth embodiment above, the bobbin  12  and the housing  13  are fixed via a specific member). The housing  13  is placed on the rack  22 , and is fixed by a fastener  26  via the buffer  31  that absorbs impact or vibration. The fastener  26  is fixed to the rack  22  through the bottom surface of the bobbin  12  from inside the bobbin  12 . The second configuration is applied to the dispersion compensating module  9  of the ninth embodiment, and therefore the bobbin  12  and the housing  13  correspond to a holder housing the dispersion compensating optical fiber  11  fixed in a state of coil. Also, the fastener  26  and the rack  22  constituting the installation bench correspond to a struct that fixes the holder. The jumpers  11   a  and  11   b  constituting part of the dispersion compensating optical fiber  11  housed in the housing  13  are taken out to the outside of the module via the housing  13 , and the configurations shown in  FIGS. 2A to 2C  can be applied as needed to the dispersion compensating module  9  according to the ninth embodiment as well. 
     In the dispersion compensating module  9  in the ninth embodiment, the buffer  31  is filled in the space between the rack  22  and the housing  13  housing the dispersion compensating optical fiber  11  (wound around the barrel of the bobbin  12 ), and is also filled in the space between the housing  13  and the fastener  26 . In the dispersion compensating module  9  constituted in this way, even when the rack  22  is subjected to impact or vibration, the action of the buffer  31  will effectively reduce impact or vibration applied to the dispersion compensating optical fiber  11  housed in the housing  13 . As a result, high-speed fluctuations in the polarization state of light propagating through the dispersion compensating optical fiber  11  can be suppressed. 
     As described above, in the dispersion compensating module according to the present invention, even when the holding struct for a dispersion compensating optical fiber is subjected to impact or vibration, high-speed fluctuations in the polarization state of light propagating through the dispersion compensating optical fiber can be effectively suppressed.