JP2009175271A - Optical fiber end part shape, and optical fiber end part treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber end part shape and an optical fiber end part treating method, sealing holes by controlling a sealing distance from a fiber tip to a hole located part, to a fixed length, facilitating positioning to a ferrule and fixation thereto, and giving a long period reliability, by using an optical fiber itself, without requiring other substance such as glass powder and a curable substance. <P>SOLUTION: This optical fiber end part shape is formed by fusing with heat an optical fiber end part locally, and by sealing thereby the holes in the optical fiber end part, in the optical fiber 301 having the plurality of holes extended along a major axis direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an end shape of an optical fiber having a plurality of holes extending in the major axis direction and an optical fiber end processing method.

  A photonic crystal fiber (PCF), which is a type of optical fiber having a structure in which holes arranged periodically and defects that break the periodicity extend in the major axis direction, and whether there is periodicity Regardless, an optical fiber having holes, such as a microstructured fiber that includes holes and is guided by total reflection, is called a holey fiber (HF). HF has the property of strongly confining optical power due to the presence of holes. Therefore, it has attracted attention as a new transmission medium because it has many advantages such as a wide transmission band and superior bending loss characteristics compared to conventional optical fibers. However, on the other hand, foreign substances such as liquids such as moisture and oil and dust may enter from the holes at the tip of the HF, which may cause deterioration in transmission characteristics, long-term reliability, connection characteristics, mechanical characteristics, and the like.

  In order to prevent the problem of foreign matter entering the HF holes, it is necessary to perform a process such as closing or filling the holes at the HF end. In Patent Document 1, (1) a method of heating and softening a fiber tip to crush holes, (2) a method of inserting a curable substance into the holes, and (3) a method of attaching a lid to the holes. Are listed. Patent Document 2 describes (4) a method of sealing a hole by putting glass powder in the hole and dissolving the glass powder. Further, Patent Document 3 describes (5) a method of sealing holes by fusing HF and a single mode fiber (SMF). Patent Document 4 describes (6) a sealing method with a highly reliable curable substance. Patent Document 5 describes (7) a method of sealing vacancies by heating HF after protruding from a connector ferrule.

JP 2002-323625 A Japanese Patent Laid-Open No. 2005-24842 Japanese Patent Laid-Open No. 2005-24847 JP 2006-126720 A JP 2007-25531 A

  However, since the sealing distance cannot be controlled by the method (1), the distance that the holes are crushed becomes long. For this reason, transmission characteristics are deteriorated, such as disturbance of the mode field. Moreover, in the example of the said patent document, since pressure reduction apparatuses, such as a vacuum pump, are required for sealing, complicated processing is required. In addition, since the control of the sealing length of the hole is very difficult, the distance varies, and it is difficult to align the ferrule and the fiber at the time of creating the connector.

  The methods (2) and (6) have a drawback that it is difficult to control the curable substance sealed in the pores to a certain distance. In general, since the hardness of the clad part (glass) and the curable material is different, more curable material is polished or remains on the contrary when the connector end surface is polished, and the polished surface can be configured smoothly. Therefore, there is a drawback that it cannot be used for optical fiber connection. In addition, volume shrinkage occurs when the curable material is cured, and the glass interface of the inner wall of the fiber hole peels off from the curable material, creating a minute gap, and liquid or the like may enter from this minute gap. . Furthermore, bubbles may be generated due to volume shrinkage when the curable substance is cured, and voids may remain in the fiber holes.

In the method (3), since the substance to be covered may affect the light guide, the connection loss, the return loss, etc. are increased, so that the optimum waveguide cannot be obtained.
In the method (4), it is necessary to separately prepare minute glass powder having a size that can enter the pores, and it is very difficult to control the amount of glass powder and the sealing distance. In addition, the glass powder may enter the depths of the heated portion and remain without being dissolved. Further, the remaining glass powder may cause scratches on the inner wall of the pores, and the mechanical characteristics may be deteriorated. Further, when glass powder of another component such as a low melting point glass is used, distortion occurs due to the difference in temperature coefficient of the glass, which may cause a problem in terms of long-term reliability.

In the method (5), since the SMF and the HF are fused, the number of connection points increases by one, and the connection loss increases. In addition, since the mode field diameter is generally different, there is an example in which the loss increases depending on the direction of incident light.
In the method (7), there is a restriction that a glass ferrule is used.

  In the present invention, in order to solve the above-mentioned problem, the sealing distance from the fiber tip to the holed portion is controlled to a certain length to seal the hole, and it is easy to align and fix with the ferrule. An object of the present invention is to provide an optical fiber end shape and an optical fiber end processing method characterized by having long-term reliability using an optical fiber itself without using other materials such as glass powder and a curable material. And

  In order to solve the above-mentioned problems, an optical fiber end shape and an optical fiber end processing method according to the present invention are optical fibers having a plurality of holes extending in the major axis direction, and the optical fiber end is locally disposed. It is characterized by heating and melting and sealing and forming holes at the end of the optical fiber.

  Further, according to the optical fiber end shape and the optical fiber end processing method of the present invention, when the optical fiber end is locally heated and melted, the shape of the optical fiber end is made hemispherical to seal the holes. You may stop.

  Further, according to the optical fiber end shape and the optical fiber end processing method of the present invention, after the optical fiber end is locally heated and melted to seal the hole, the hole is again formed at the optical fiber end. The end of the optical fiber may be polished so as not to open.

  Further, according to the optical fiber end shape and the optical fiber end processing method of the present invention, the optical fiber end is locally heated and melted to seal the holes, and then the optical fiber end is attached to the optical ferrule. Then, the end of the optical fiber may be polished together with the optical ferrule so that the holes do not open again.

  The optical fiber end shape and the optical fiber end processing method according to the present invention are such that the end of the optical fiber is locally heated and melted to seal the holes, and then directly connected to another optical fiber. Also good.

  Further, the optical fiber end shape and the optical fiber end processing method of the present invention may use a laser when locally melting and melting the optical fiber end.

  According to the optical fiber end shape and the optical fiber end processing method of the present invention, in the optical fiber end shape, the optical fiber connecting method, and the optical connector, the HF holes are sealed with the glass constituting the optical fiber. Therefore, it is possible to prevent polishing dust, foreign matter, and refractive index matching agent from entering the pores and preventing optical waveguide and mechanical characteristics from deteriorating, and to have the same performance as before. Can do. For this reason, improvement in long-term reliability and variation in connection loss can be prevented.

  In order to prevent foreign matter and the like from entering the inside of a hole from the end of a holey holey fiber (HF: Holey Fiber), the present invention heats the hole end to melt the optical fiber and polish it. A highly reliable optical connection and optical connector can be realized by attaching a connector. Embodiments of an optical fiber end shape and an optical fiber end processing method according to the present invention having such characteristics will be described below in detail with reference to the drawings.

  1 and 2 show typical structure examples of HF to which the present invention is applied. FIG. 1 is a cross-sectional view with respect to the longitudinal direction of the optical fiber, and FIG. 2 is an example of a cross-sectional view when the optical fiber is viewed from the side, with one end portion being cut vertically. . In addition, although demonstrated using HF as an example here, this invention can be implemented also with the fiber of another shape which has a void | hole.

  As shown in FIGS. 1 and 2, the HF 100 is formed by a cladding portion 101, a core portion 102 that propagates light, and a plurality of holes 103 that extend in the optical fiber axial direction so as to surround the core portion 102. It has a structured.

  Next, a sealing method for realizing the optical fiber end sealing structure will be described. First, the HF 100 is cut with a fiber cutter or the like to form an end face substantially perpendicular to the axial direction. Thereafter, the fiber tip is heated to be processed into the shape shown in FIG. FIG. 3 shows a cross-sectional view from the side of the optical fiber end shape 200 after processing by heating HF. Any method such as electric discharge heating or laser irradiation heating can be used as the processing method. However, when heating and melting the optical fiber end, the end of the optical fiber is easily formed by the surface tension generated in the heated portion. In order to deform into a spherical shape, it is necessary to precisely control the heating conditions. Control using gas flame heating, heating using a heater, and discharge heating was very difficult.

  As an example of an embodiment of the present invention, a method for heating an optical fiber end by irradiation with carbon dioxide laser light while controlling the shape of the optical fiber end will be described in detail. The reason why the carbon dioxide laser beam is used is that the carbon dioxide laser can be irradiated with light having a wavelength of about 10 μm which is easily absorbed by glass and easily generates heat.

  A specific method for controlling the shape of the optical fiber end will be described. As shown in FIG. 4, the carbon dioxide laser light irradiated from the carbon dioxide laser light irradiation device 302 installed on the extension in the axial direction is focused by a lens 304 using zinc selenide, and the fiber is focused. Irradiates the tip of the optical fiber 301 fixed by the fixing jig 303. When the carbon dioxide laser light is irradiated, an optical fiber end shape 200 shown in FIG. 3 is formed at the tip of the optical fiber. The optical fiber end shape 200 has a clad part 201 and a core part 202. The clad part 201 melted by the laser forms a hemispherical hole sealing part 204 and seals the hole 203. can do.

  The tip can be formed in any shape, and by adjusting the heating intensity, the heating time, the focal length of the zinc selenide lens, etc., as shown in FIGS. It is possible to adjust the part shape to various shapes. This control is very difficult to realize when other heating methods such as gas flame heating are used. In addition, the heating temperature differs in the optical fiber end shape 210 shown in FIG. 5, the optical fiber end shape 220 shown in FIG. 6, and the optical fiber end shape 230 shown in FIG. The optical fiber end shape 210 is heated at the highest temperature, the optical fiber end shape 220 is the next highest, and the optical fiber end shape 230 is heated at the lowest temperature.

  If the end shape is not controlled, the tip of the optical fiber becomes spherical and the outer diameter becomes thick, so that the tip of the optical fiber cannot be inserted into the optical connector ferrule. On the other hand, when the distance from the fiber tip to the hole is shortened as in the optical fiber end shape 230 shown in FIG. 7, mechanical splices and FA (Field Assembly) connectors are used. Thus, there is an advantage not found in other methods that optical fibers can be directly connected to each other.

  Next, an embodiment in which an optical ferrule is attached will be described using FIG. FIG. 8 shows a cross-sectional view from the side of the optical fiber end shape 400 when the HF tip is sealed by heating and polished with an optical ferrule. The optical fiber end shape 400 includes an optical fiber clad portion 401, an optical fiber core portion 402, a hole 403, and an optical ferrule 405. The optical fiber end shape 400 is obtained by attaching and fixing the optical fiber end shapes 200, 210, 220, and 230 shown in FIGS. 3 and 5 to 7 to the optical ferrule 405 and polishing together with the optical ferrule 405. Created as an optical connector. The position adjustment between the optical ferrule 405 and the shape of the optical fiber end is performed using a dedicated jig.

  Further, only the end face of the optical fiber may be directly polished using a dedicated jig. FIG. 9 shows a cross-sectional view from the side of the optical fiber end shape 500 when only the end face of the optical fiber is directly polished. The optical fiber end shape 500 includes an optical fiber clad portion 501, an optical fiber core portion 502, and a hole 503. The optical fiber end shape 500 is processed so that the hole sealing distance 506 is shortened by directly polishing the end face of the optical fiber. FIG. 10 shows an optical fiber end shape 600 as an actual example in which only the optical fiber end face is directly polished. The optical fiber end shape 600 is processed so that the hole sealing distance 606 is 18 μm.

  Since the hole sealing distances 506 and 606 are very short, the optical fiber end shape and the optical connector produced in this way do not greatly affect the original light guiding. Even if a general optical fiber is connected by a mechanical splice or the like, the refractive index matching agent does not enter the hole due to the hole sealing portion described above, so that it can be connected as usual. Moreover, although the SC type connector using the present invention was attached and detached 500 times, there was no reduction in connection loss or physical deterioration of the connector.

  Using the optical connector according to the present invention, connection loss and return loss at a wavelength of 1310 nm were measured. The measurement was performed by connecting a master SC connector using SMF and an SC connector having an optical fiber end shape 400 shown in FIG. 8 of the present invention using a 6-hole HF core wire. The distribution of connection loss is shown in FIG. 11, and the distribution of return loss is shown in FIG. As is apparent from FIGS. 11 and 12, the characteristics are the same connection loss and return loss as those of the conventional SMF optical connectors, and are sufficiently small with respect to the design standard.

  Moreover, the heat cycle test was done using the optical connector by this invention. The conditions of the heat cycle test were as follows: temperature + 70 ° C. to −40 ° C., 1 cycle 6 hours, 10 cycles, and measurement light wavelength 1550 nm. The measurement sample is composed of four connections (sample Nos. 1 to 4) of HF core SC connectors having the optical fiber end shape 400 shown in FIG. Two connections (sample Nos. 5 to 6) of the HF core SC connector having the optical fiber end shape 400 shown in FIG. 8 of the invention were used.

  The measurement results are shown in FIGS. FIG. 13 shows the optical loss fluctuation in each cycle of connection between the HF core SC type connectors to which the present invention is applied, and FIG. 14 shows the SMF core SC type connector and the HF core SC type to which the present invention is applied. The optical loss variation in each cycle of connector connection is shown. As is apparent from FIGS. 13 and 14, the characteristics are the same as those of the conventional SC connector, the loss is sufficiently small with respect to the design standard, and it has been confirmed that the characteristics are stable.

  From the above results, according to the present invention, the terminal shape and the optical connector have the same performance as in the past and have high reliability against changes in the external environment, etc., with no foreign matter entering the HF core hole. I was able to confirm that

  The present invention is not limited to the above-described embodiment, and in this embodiment, an optical fiber having six holes is used, but the number of holes and the hole arrangement are not limited thereto, PCF or other perforated fiber may be used.

It is sectional drawing from the major axis direction of HF with which this invention is applied. It is sectional drawing from the side surface of HF to which this invention is applied. It is sectional drawing from the side surface after heating and processing HF as an example of the optical fiber end part shape by one Embodiment of this invention. It is explanatory drawing explaining an example of the method of producing the optical fiber edge part shape by one Embodiment of this invention. It is a figure which shows the microscope picture which heated HF as an example of the optical fiber edge part shape by one Embodiment of this invention, and sealed the hole front-end | tip. It is a figure which shows the microscope picture which heated HF weakly rather than FIG. 5 as another example of the optical fiber end shape by one Embodiment of this invention, and sealed the hole front-end | tip. It is a figure which shows the microscope picture which heated HF weakly rather than FIG. 6 as another example of the optical fiber end shape by one Embodiment of this invention, and sealed the hole front-end | tip. It is sectional drawing from the side surface at the time of sealing an HF front-end | tip part by heating as an example of the optical fiber end part shape by another embodiment of this invention, and grind | polishing with an optical ferrule. It is sectional drawing from the side surface at the time of sealing an HF front-end | tip part by heating as an example of the optical fiber end part shape by another embodiment of this invention, and grind | polishing a sealing location directly. It is a figure which shows the microscope picture at the time of sealing an HF front-end | tip part by heating as an example of the optical fiber end part shape by another embodiment of this invention, and grind | polishing the sealing location directly. It is a figure which shows the histogram of the connection loss (wavelength 1310nm) of a SMF master SC type | mold connector and the 6 hole HF connector which has the optical fiber edge part shape by one Embodiment of this invention. It is a figure which shows the histogram of the return loss (wavelength 1310nm) of the SMF master SC type | mold connector and the 6 hole HF connector which has the optical fiber edge part shape by one Embodiment of this invention. It is a figure which shows the heat cycle test graph in the connection of HF core line SC type | mold connectors which have the optical fiber edge part shape by one Embodiment of this invention. It is a figure which shows the heat cycle test graph in the connection of the SMF core wire SC type | mold connector and the HF core wire SC type | mold connector which has the optical fiber edge part shape by one Embodiment of this invention.

Explanation of symbols

100 HF
101, 201, 401, 501 Optical fiber cladding part 102, 202, 402, 502 Optical fiber core part 103, 203, 403, 503 Hole part 200, 210, 220, 230, 400, 500, 600 Optical fiber end shape 204 Hole Sealing Unit 300 Device for Generating Optical Fiber End Shape 301 Optical Fiber 302 Carbon Dioxide Laser Irradiation Device 303 Optical Fiber Fixing Tool 304 Zinc Selenide Lens 405 Optical Ferrule 506, 606 Hole Sealing Distance

Claims (12)

An optical fiber having a plurality of holes extending in the longitudinal direction,
The optical fiber end shape is formed by locally heating and melting the optical fiber end portion and sealing the holes in the optical fiber end portion.   2. The optical fiber end according to claim 1, wherein when the end portion of the optical fiber is locally heated and melted, the shape of the end portion of the optical fiber is made hemispherical to seal the hole. Part shape. After sealing the hole by locally heating and melting the optical fiber end,
The optical fiber end shape according to claim 1 or 2, wherein the optical fiber end portion is formed by polishing so that the holes do not open again at the optical fiber end portion. After sealing the hole by locally heating and melting the optical fiber end,
4. The light according to claim 1, wherein the optical fiber end is attached to an optical ferrule, and the optical fiber end is polished together with the optical ferrule so that the hole does not open again. 5. Fiber end shape. After sealing the hole by locally heating and melting the optical fiber end,
The optical fiber end shape according to any one of claims 1 to 4, wherein the optical fiber end shape is directly connected to another optical fiber.   6. The optical fiber end shape according to claim 1, wherein a laser is used when the optical fiber end portion is locally heated and melted. An optical fiber having a plurality of holes extending in the longitudinal direction,
A method of treating an end portion of an optical fiber, wherein the end portion of the optical fiber is locally heated and melted to seal the hole in the end portion of the optical fiber.   8. The optical fiber end according to claim 7, wherein when the end of the optical fiber is locally heated and melted, the shape of the end of the optical fiber is made hemispherical to seal the hole. Part processing method. After sealing the hole by locally heating and melting the optical fiber end,
The optical fiber end processing method according to claim 7 or 8, wherein the end of the optical fiber is polished so that the holes do not open again at the end of the optical fiber. After sealing the hole by locally heating and melting the optical fiber end,
10. The light according to claim 7, wherein the optical fiber end is attached to an optical ferrule, and the optical fiber end is polished together with the optical ferrule so that the hole does not open again. Fiber end treatment method. After sealing the hole by locally heating and melting the optical fiber end,
The optical fiber end processing method according to claim 7, wherein the optical fiber end processing method is directly connected to another optical fiber.   12. The optical fiber end processing method according to claim 7, wherein a laser is used when the end of the optical fiber is locally heated and melted.