Abstract:
There are provided an optical fiber processing apparatus, a processing method, and an optical fiber capable of monitoring a process of an optical fiber by gas containing at least deuterium and simultaneously detecting the termination of the process. The apparatus for processing an optical fiber in a gas atmosphere includes a door of a treatment container that puts the optical fiber in and out, a gas introducing port, a gas exhausting port, and a sampling fiber taking-out port. Further, the apparatus includes a light source that is connected to the optical fiber drawn from the sampling fiber taking-out port, and a light power meter that measures an absorption loss. In order to judge the termination of the gas process, it is preferable to include mechanism that monitors a value of the light power meter and judges the termination from the change of the value.

Description:
CROSS REFERENCE TO THE RELATED APPLICATION  
       [0001]     The present application is a continuation application of PCT/JP2004/015704 filed on Oct. 22, 2004, which claims priority from a Japanese Patent application No. 2003-367587 filed on Oct. 28, 2003, the entire contents of which are incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a gas process of an optical fiber, and more particularly relates to an optical fiber processing apparatus, a process method, and an optical fiber that are used for a gas process of an optical fiber performed by gas including at least deuterium.  
         [0004]     2. Description of Related Art  
         [0005]     What is most used for a transmission channel making use of an optical fiber is a single mode optical fiber having a zero dispersion wavelength in the neighborhood of 1310 nm. Conventionally, the optical fiber has been used for transmission of signal light of 1310 nm. However, the optical fiber is recently being utilized for transmission of signal light with another wavelength according to the advance of a dispersion compensation technique.  
         [0006]     In recent years, a CWDM (Coarse Wavelength Division Multiplexing) technique has been developed in order to cope with the increase of a required transmission capacity at low cost. Since the transmission technology uses a wide wavelength interval of about 20 nm, interference does not occur between signal wavelengths even if a cheap light source is used. In order to transmit much signal light by means of an optical fiber in this technique, it is desirable that a usable wavelength region is wide. However, a conventional single mode optical fiber has an absorption loss peak caused by an OH radical in the neighborhood of 1383 nm, and thus this wavelength region cannot be utilized. In order to be able to use this wavelength region, a low moisture optical fiber is developed, and is prescribed as International Standard even in ITU-TG652 table C, D.  
         [0007]     In such an optical fiber, it is required to have small absorption loss peak even after ageing by hydrogen in addition to an early small absorption loss peak. For this reason, there is a method for processing an optical fiber in deuterium as one method improving resistance to hydrogen of an optical fiber. This method is a method using a characteristic that an OD radical formed by a reaction is different from an OH radical and does not form an absorption loss peak in a wavelength area to be used as signal light, even if deuterium D reacts on defect in the optical fiber in the same way as that of hydrogen H. See, for example, Japanese Patent Application Publication Nos. 1985-90852, 1995-277770, 2000-148450, and 2003-137580.  
         [0008]     A process of an optical fiber by such deuterium is to put an optical fiber in a container capable of being sealed and leave the optical fiber for predetermined time in an atmosphere containing deuterium. Since deuterium is a combustible gas similarly to hydrogen, it is necessary to substitute an atmosphere within the container for an inert gas such as nitrogen to a risk-free extent before filling the container with an atmosphere containing deuterium.  
         [0009]     In this manner, since the process of an optical fiber by deuterium is performed in a sealed container, the termination of deuterium treatment cannot simultaneously be detected. For that purpose, the termination of treatment has conventionally been confirmed by the confirmation of the improvement of resistance to hydrogen of the optical fiber taken and sampled from a processing apparatus after exposing the fiber to an atmosphere containing deuterium for empirically required time, or the confirmation of the annihilation of an absorption loss peak caused by defect in the vicinity of 630 nm after measuring a loss spectrum before or after the deuterium treatment. See, for example, Japanese Patent Application Publication No. 2003-75293.  
         [0010]     As described above, since the termination of deuterium treatment has been confirmed by the measurement of resistance to hydrogen and the measurement of loss spectrum after the deuterium treatment, there has been a problem that excessive time is required for a deuterium treatment or a re-treatment is required when the treatment is insufficient and further an optical fiber used for sampling is wasted.  
       SUMMARY OF THE INVENTION  
       [0011]     In view of the situation above, an object of the present invention is to monitor a process of an optical fiber by gas containing at least deuterium and provide an optical fiber processing apparatus, a processing method, and an optical fiber capable of simultaneously detecting the termination of process.  
         [0012]     To achieve this object, according to the first aspect of the present invention, there is provided an apparatus for processing an optical fiber in a gas atmosphere. The apparatus includes a door of a treatment container that puts the optical fiber in and out, a gas introducing port, a gas exhausting port, and a sampling fiber taking-out port. Further, the apparatus may include a light source that is connected to the optical fiber drawn from the sampling fiber taking-out port, and a light power meter that measures an absorption loss. In order to judge the termination of the gas process, it is preferable to include mechanism that monitors a value of the light power meter and judges the termination from the change of the value.  
         [0013]     The light source may emit light in a wavelength area in which an absorption loss of the optical fiber is changed by the gas process, and further the wavelength may be an absorption loss peak wavelength of the optical fiber or a wavelength around the peak wavelength. The gas used for the process may be deuterium or gas containing deuterium, and a wavelength of light emitted from the light source may be around 630 nm.  
         [0014]     According to the second aspect of the invention, there is provided a method for processing an optical fiber in a gas atmosphere. The method includes the steps of: putting the optical fiber in a treatment container; filling the container with treatment gas; drawing the optical fiber from a sampling fiber taking-out port provided in the container to connect the fiber to a light source and a light power meter; monitoring an absorption loss of the optical fiber during the gas process; and simultaneously judging the termination of the gas process from the change of the absorption loss. Moreover, the termination of the gas process may be judged when an amount of light in a predetermined wavelength arrives at a set amount of light.  
         [0015]     According to the third aspect of the invention, there is provided an optical fiber processing apparatus that processes an optical fiber in a gas atmosphere. The apparatus includes: a container main body that has an opening for putting the optical fiber in and out; a door that opens and closes the opening and forms airtight space between the door and the container main body by closing the opening; a gas introducing port that introduces gas into the space formed by the container main body and the door; a gas exhausting port that exhausts gas from the space formed by the container main body and the door; and an inside-outside connecting section that optically connects an outside of the space formed by the container main body and the door and both ends of the optical fiber accommodated in the space.  
         [0016]     In the optical fiber processing apparatus, the inside-outside connecting section may draw and hold both ends of the optical fiber accommodated in the space to the outside of the space. Further, the inside-outside connecting section may be arranged in the container main body. Moreover, the inside-outside connecting section may be detachable from the container main body.  
         [0017]     The optical fiber processing apparatus may further include: a light source that is arranged outside the space and introduces light into one side of the both ends of the optical fiber accommodated in the space; and a light power meter that is arranged outside the space and measures an amount of light coming out from the other side of the both ends of the optical fiber accommodated in the space.  
         [0018]     In the optical fiber processing apparatus, the light source may emit light in a wavelength area in which an absorption loss of the optical fiber is changed by the gas process. Particularly, the light source may emit light with a wavelength around 630 nm.  
         [0019]     The optical fiber processing apparatus may further include a termination judging section that judges that the gas process has been terminated when the amount of light measured by the light power meter has exceeded a threshold value.  
         [0020]     The optical fiber processing apparatus may further include a termination judging section that judges that the gas process has been terminated when a ratio of the amount of light measured by the light power meter to an amount of light from the light source has exceeded a threshold value. Moreover, the optical fiber processing apparatus may further include a termination judging section that judges that the gas process has been terminated when a rate of change of the amount of light measured by the light power meter has exceeded a threshold value. Moreover, the optical fiber processing apparatus may further include a termination judging section that judges that the gas process has been terminated when a change rate of a ratio of the amount of light measured by the light power meter to an amount of light from the light source has exceeded a threshold value.  
         [0021]     The optical fiber processing apparatus may further include a gas controlling section that stops the introduction of gas and the exhaustion of gas to the space when the termination judging section judges that the gas process has been terminated.  
         [0022]     The optical fiber processing apparatus may further include a door-opening controlling section that permits the door to be opened when the termination judging section judges that the gas process has been terminated.  
         [0023]     The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above.  
         [0024]     According to the present invention, since resistance to hydrogen of an optical fiber is improved and an absorption loss peak caused by an OH radical in the vicinity of 1383 nm is significantly reduced or disappears, it is possible to obtain an extremely superior single mode optical fiber. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a view schematically showing an optical fiber processing apparatus of Embodiment 1 of the present invention.  
         [0026]      FIG. 2  is a graph showing a state of a change of processing time and an amount of transmitted light during processing gas.  
         [0027]      FIG. 3  is a view schematically showing an optical fiber processing apparatus of Embodiment 2 of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     The invention will now be described based on the preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention.  
         [0029]     As a result of superimposed keen examinations, the present inventor found that a deuterium treatment for an optical fiber has the following special feature.  
         [0030]     For example, when mixed gas under normal pressure of deuterium 1% and nitrogen 99% is used as a treatment gas, a process is terminated in around three and a half days. In the meantime, the process is slowly not performed in proportion to time. For three days, an absorption loss does not have a change at all. Then, the process is terminated after the sudden advance for several hours. This change can be confirmed by annihilation of an absorption loss peak of NBOHC (a non-bridging oxygen hole center) having a peak at 630 nm.  
         [0031]     Thus, a port for taking out an optical fiber is provided in a container of a processing apparatus, both ends of the optical fiber to be processed are drawn, light in a wavelength area in which an absorption loss of the optical fiber is changed by a gas process is introduced from the one end, and the intensity of light transmitted through the other end is monitored during processing gas. In this way, the termination of gas process can simultaneously be grasped.  
         [0032]     In addition, the termination of gas process is judged when an amount of light in a predetermined wavelength reaches a set amount of light. For example, gas containing deuterium is used as treatment gas, and a device emitting light of a wavelength around 630 nm is used as a light source. In this way, the change of transmitted light amount (an absorption loss) is monitored.  
       Embodiment 1  
       [0033]      FIG. 1  shows a gas processing apparatus according to Embodiment 1 of the present invention.  
         [0034]     This processing apparatus includes a container capable of being sealed, which has volume capable of accommodating a bobbin of an optical fiber to be processed with gas. The container is further provided with a gas introducing port, a gas exhausting port, and an optical fiber taking-out port, in addition to a door for putting a bobbin in and out.  
         [0035]     Since the optical fiber taking-out port can be exchanged, after drawing an optical fiber, the port is blocked up with epoxy resin to ensure seal up of the container. A valve is respectively provided in the gas introducing port and the gas exhausting port. When the container is filled with an enough atmosphere, the valves are closed to seal the container.  
         [0036]     A nitrogen line and a treatment gas line are further provided in the gas introducing port. Purging the container and introducing treatment gas can be performed from the same gas introducing port.  
         [0037]     The processing apparatus further includes a light source that introduces monitor light into the optical fiber and a light power meter. Gas including deuterium is used as treatment gas and an LED with a wavelength of 625 nm is used as the light source. An output from the light power meter is input into a computer and the value is always monitored. The computer includes a system that informs a user or the like of the termination of the gas process in a state that the change is settled after a speed of the change of this value exceeds a threshold value set beforehand. Moreover, the system may be a system that informs a user or the like of the termination of the gas process in a state that the change is settled when a change rate of an output value from the light power meter becomes large once and then becomes small.  
         [0038]      FIG. 2  is a graph showing a result of a gas process using this processing apparatus. Here, a horizontal axis shows processing time and a vertical axis shows the change of an amount of transmitted light (light power). An amount of transmitted light suddenly increases at the instant of the passage of a certain time, and the termination of the gas process is shown at an arrow B. This state is monitored by the computer.  
         [0039]     After detecting the termination of the gas process, a hydrogen test has been performed for the taken-out optical fiber at a place of an arrow B. As a result, an absorption loss peak has not been increased and thus the system has functioned as intended.  
         [0040]     In addition, in a hydrogen test for the optical fiber taken out at a place of an arrow A, an absorption loss peak has been increased.  
       Embodiment 2  
       [0041]      FIG. 3  shows a gas processing apparatus  10  according to Embodiment 2 of the present invention. The optical fiber processing apparatus  10  includes a container  100  having a container main body  110  that has an opening for putting an optical fiber  50  in and out and a door  120  that opens and closes the opening and forms airtight space between the door and the container main body by closing the opening. The optical fiber processing apparatus  10  further includes a lock  122  for locking the door  120  to the container main body  110  when closing the door  120 , a gas introducing pipe  130  and a gas exhausting pipe  140  connected to the container  100 , an inside-outside connecting section  150  arranged in the container  100 , and an LED  20 , a light power meter  30 , and a PC  40  that are arranged outside the container  100 .  
         [0042]     The gas introducing pipe  130  introduces gas into space formed by the container main body  110  and the door  120  through a gas introducing port  132  provided in the container  100 . Moreover, the gas exhausting pipe  140  exhausts gas from the space formed by the container main body  110  and the door  120  via a gas exhausting port  142  provided in the container  100 . Valves  60  and  62  are respectively provided in the gas introducing pipe  130  and the gas exhausting pipe  140 . These valves  60  and  62  control flow volume of gas of the gas introducing pipe  130  and the gas exhausting pipe  140 . Here, the gas introducing port  132  and the gas exhausting port  142  are arranged in the container main body  110  in the container  100 . In this way, when opening and closing the door  120 , the gas introducing pipe  130  and the gas exhausting pipe  140  do not obstruct opening and closing.  
         [0043]     The inside-outside connecting section  150  optically connects an outside of the space formed by the container main body  110  and the door  120  and both ends of the optical fiber  50  accommodated in the space. In the embodiment shown in  FIG. 3 , the inside-outside connecting section  150  is arranged in the container main body  110 , draws and holds one end  52  and the other end  54  of the optical fiber  50  accommodated in the space in the container  100  to the outside of the space. The inside-outside connecting section  150  has a taking-out port penetrating through the container main body  110 . Seal up of the space in the container  100  is ensured by blocking the taking-out port with epoxy resin after drawing one end  52  and the other end  54  of the optical fiber  50 . Since the inside-outside connecting section  150  is arranged in the container main body  110 , when opening and closing the door  120 , it is possible to easily open and close the gas introducing pipe  130  without expanding and contracting one end  52  and the other end  54 . Moreover, the inside-outside connecting section  150  may be detached from the container main body  110 .  
         [0044]     The LED  20  is optically connected to one end  52  of the optical fiber  50  accommodated in the space in the container  100 , and introduces light into the one end  52 . The LED  20  emits light in a wavelength area in which an absorption loss of the optical fiber  50  is changed by a gas process. For example, the LED  20  emits light with a wavelength around 630 nm. Moreover, the light power meter  30  is optically connected to the other end  54  of the optical fiber  50  accommodated in the space of the container  100 , and measures an amount of light coming out from the other end  54 .  
         [0045]     The PC  40  has a termination judging section  200  for controlling the LED  20  and the PC  40 , a gas controlling section  210  for controlling the valve  60  and the valve  62 , and a door-opening controlling section  220  for controlling the lock  122 .  
         [0046]     Similarly to Embodiment 1 shown in  FIGS. 1 and 2 , the termination judging section  200  judges that the gas process has been terminated when the amount of light measured by the light power meter  30  has exceeded a threshold value. In addition, the termination judging section  200  may judge whether a ratio of the amount of light measured by the light power meter  30  to an amount of light introduced into one end  52  from the LED  20  exceeds a threshold value, in place of the amount of light. As further another example, the termination judging section  200  may judge whether a change rate of the amount of light measured by the light power meter  30  or a change ratio of the ratio of the amount of light measured by the light power meter  30  to the amount of light introduced into one end  52  from the LED  20  exceeds a threshold value.  
         [0047]     When the termination judging section  200  judges that the gas process has been terminated, the gas controlling section  210  stops introducing gas and exhausting gas to the space in the container  100  by restricting flow volume of the valves  60  and  62 . In this way, introduction or exhaustion of unnecessary gas can be prevented even after the gas process was terminated. Moreover, when the termination judging section  200  judges that the gas process has been terminated, the door-opening controlling section  220  releases the lock  122  to permit opening of the door  120 . In this way, malfunction by opening of the door  120  can be prevented during processing gas.  
         [0048]     As above, according to the embodiment shown in  FIG. 3 , it is possible to judge whether the gas process has been terminated in a state that the optical fiber  50  is accommodated in the container  100 . In this way, compared with the judgment of the termination of the gas process after taking out the optical fiber  50  from the container  100 , it is possible to reduce an amount of optical fiber used for sampling and early terminate a gas process of the optical fiber  50 .  
         [0049]     Although the present invention has been described by way of an exemplary embodiment, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and the scope of the present invention. It is obvious from the definition of the appended claims that embodiments with such modifications also belong to the scope of the present invention.  
         [0050]     It is possible to simultaneously detect the termination of a gas process and utilize it for various gas processes of an optical fiber.