JP2004191486A - Polarization maintaining optical fiber and optical connector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization maintaining optical fiber and an optical connector that reduce cracking of a stress-imparted part in end surface working of the polarization maintaining optical fiber, make small recess of the stress-imparted part in high-temperature, high-humidity environment, minimize projection of the stress-imparted part on an optical fiber end surface, and never impede PC connection of the optical connector. <P>SOLUTION: The polarization maintaining optical fiber 1 has the stress-imparted part 4, to which B<SB>2</SB>O<SB>3</SB>is added, at a clad part at the outer periphery of a core part 2 across the core part 2, and the quantity of projection of the stress-imparted part 4 from the optical fiber end surface in specified high-temperature, high-humidity environment is ≤0.1 μm. Further, the mean concentration of B<SB>2</SB>O<SB>3</SB>of the stress-imparted part 4 is 14 to 16 wt%. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polarization control component for multiplexing and demultiplexing linearly polarized light emitted from a light source, an optical communication using coherent light, and a stress imparting type polarization maintaining optical fiber and an optical connector used for a sensor and the like.
[0002]
[Prior art]
The polarization maintaining optical fiber causes a propagation constant difference between the two polarization modes, and suppresses coupling from each polarization mode to the other polarization mode. For example, if the polarization axis of the linearly polarized light is incident on the optical fiber according to the polarization mode, the light propagates through the optical fiber while maintaining the polarization state, and only the same polarized light is obtained at the output end. It is an indispensable optical fiber for propagating light while maintaining the polarization state.
[0003]
Generally, a polarization-maintaining optical fiber has equivalent birefringence by giving different stresses from two directions orthogonal to the core. As the polarization maintaining optical fiber 1, for example, as shown in FIG. 1, a stress applying portion 4 is provided on both sides of the core portion 2 so as to sandwich the core portion 2 in a clad portion 3 surrounding the outer periphery of the core portion 2. Known in shape. Representative examples of this shape include a panda-type optical fiber in which the stress applying section 4 is formed in a cylindrical shape as shown in FIG. 1A, and a fan-shaped optical fiber in which the stress applying section 4 is formed as shown in FIG. A bow-tie type optical fiber formed as described above is known.
[0004]
Stress applying unit 4 is typically formed by glass doped with _B 2 _{O 3} in the glass component SiO _2, by adding B 2 _{O 3,} it is possible to increase the thermal expansion coefficient in comparison with the SiO ₂ . When a glass preform on which a stress applying member is arranged so as to sandwich the core is drawn into an optical fiber, in the process of being cooled from the heating and melting, the tensile stress X with respect to the core 2 due to shrinkage of the stress applying section 4. The compressive stress Y remains from the direction orthogonal to this. When a different stress is applied to the core portion 2 depending on the direction, birefringence occurs because the refractive index changes accordingly. The higher the concentration of B ₂ O _3, the greater the difference in stress acting on the core 2 and the greater the birefringence characteristics.
[0005]
However, if the concentration of B ₂ O _{3 in} the stress applying section 4 is increased, bubbles are likely to be generated at the interface with the clad section 3 when the glass base material is heated and stretched. It is said that a crack occurs in the imparting section 4 and as a result, the birefringence characteristic deteriorates (for example, see Patent Document 1). Therefore, in the above Patent Document 1, as well as to increase the concentration of B ₂ O ₃ stress applying portions 4 as the center, the concentration of B ₂ O ₃ of the outer peripheral portion in contact with the cladding portion 3 below 15 wt% and I am trying to become. The average concentration of B ₂ O _{3 in} the stress applying section 4 is set to be about 20 wt%.
[0006]
If the concentration of B ₂ O _{3 at} the center of the stress applying section 4 is high, the stress applying section 4 may be dissolved in a moist heat environment, and the stress applying section 4 may be dented. It is said that if a depression occurs in the stress applying section 4, a constant stress cannot be applied to the core section 2, so that the polarization maintaining dependence characteristic is reduced and polarization crosstalk may occur (for example, Patent Document 2). For this reason, in Patent Document 2, the average concentration of B ₂ O _{3 in} the stress applying section 4 is 17 to 21 wt%, and the maximum concentration of B ₂ O ₃ is 17 to 22 wt%. .
[0007]
[Patent Document 1]
JP-A-8-101323 [Patent Document 2]
JP-A-2002-214465
[Problems to be solved by the invention]
When the concentration of B ₂ O _{3 in} the stress applying section 4 is low, if the polarization maintaining optical fiber 1 is exposed to a high temperature and high humidity environment for a long time, a phenomenon that the stress applying section protrudes from the end face of the optical fiber may occur. is there. When an optical connector is formed using the polarization maintaining optical fiber 1, when the stress applying portion 4 protrudes from the end face of the optical fiber, the contact at the projecting portion of the stress applying portion occurs before the tips of the core portions 2 come into contact with each other. Occurs, and the bonding (Physical Contact: so-called PC bonding) of the core portion 2 is hindered, and connection loss and reflection vary.
[0009]
Further, in Patent Document 2, when the maximum value of the B ₂ O ₃ concentration of the stress applying section 4 exceeds 22 wt%, it is eroded by the deliquescence of B ₂ O _{3 in} a moist heat environment. However, even when the concentration of B ₂ O ₃ is 17 wt%, erosion may occur due to moisture. Further, in Patent Document 2, when the concentration of B ₂ O ₃ is less than 17 wt%, sufficient stress cannot be applied to the core portion, and the polarization plane is not preserved. However, even if the average concentration of B ₂ O _{3 in} the stress applying section 4 is 14 wt%, the polarization maintaining performance can be maintained by reducing the distance between the core section 2 and the stress applying section 4. .
[0010]
The present invention has been made in view of the above-described circumstances, and it is possible to reduce the occurrence of cracks in a stress applying section by processing the end face of a polarization maintaining optical fiber, and to reduce the dent of the stress applying section in a wet heat environment, and to reduce the optical fiber end face. An object of the present invention is to provide a polarization maintaining optical fiber and an optical connector which minimize the protrusion of the stress applying section in the optical fiber and do not hinder the PC joining of the optical connector.
[0011]
[Means for Solving the Problems]
The polarization-maintaining optical fiber according to the present invention is a polarization-maintaining optical fiber in which a stress-applying portion to which B ₂ O ₃ is added is disposed in a clad portion on the outer periphery of the core portion so as to sandwich the core portion. The amount of protrusion of the stress applying portion from the end face of the optical fiber in a wet environment is set to 0.1 μm or less. The average concentration of B ₂ O _{3 in} the stress applying portion is set to 14 wt% to 16 wt%. Further, the optical connector according to the present invention is constructed by using the polarization maintaining optical fiber and polishing the end face together with the ferrule. The predetermined high-temperature and high-humidity environment means a temperature of 85 ° C. and a humidity of 85 RH% for 336 hours.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cross section of a polarization maintaining optical fiber used in the description of the prior art, and FIG. 1A shows a panda type optical fiber, and FIG. 1B shows a bowtie type optical fiber. . In the figure, 1 is a polarization maintaining optical fiber, 2 is a core portion, 3 is a cladding portion, and 4 is a stress applying portion.
[0013]
The polarization-maintaining optical fiber 1 to which the present invention is applied is given birefringence equivalently by applying different stresses from two directions orthogonal to the core portion 2 as described in the related art. Things. As shown in FIG. 1, the polarization-maintaining optical fiber 1 has a shape in which stress applying portions 4 are provided on both sides of the core portion 2 so as to sandwich the core portion 2 in a clad portion 3 surrounding the outer periphery of the core portion 2. Things. As typical examples of this shape, a panda-type optical fiber in which a stress applying portion is formed in a columnar shape as shown in FIG. 1A, and a fan-shaped stress applying portion is formed as shown in FIG. 1B. There is a bow-tie type optical fiber.
[0014]
By adding B ₂ O ₃ to the glass component of SiO ₂ , the stress applying section 4 can increase the coefficient of thermal expansion as compared with the SiO ₂ glass forming the clad section 3. When a glass preform having a stress applying member disposed on both sides of the core portion is drawn into an optical fiber, a tensile stress X is applied to the core portion 2 by shrinkage of the stress applying portion 4 in the process of cooling from heating and melting. , And a compressive stress Y remains in the fiber from a direction orthogonal to this. When different stresses are applied to the core portion 2 in two directions, the X direction and the Y direction, the refractive index changes accordingly and birefringence occurs in the core portion 2.
[0015]
If the above-described polarization maintaining optical fiber 1 is used for a long time in a high-humidity and high-temperature environment, a phenomenon occurs in which the stress applying section 4 protrudes from the end face of the optical fiber. FIG. 2 is a diagram showing an example of observation of the protruding shape of the stress applying portion, which protrudes into a mountain shape whose maximum value reaches 1.5 μm. Such a phenomenon is often observed particularly when the average concentration of B ₂ O ₃ is 13 wt% or less.
[0016]
Investigation and elucidation of this phenomenon revealed that the boron (B) added to the stress applying part 4 had disappeared. Although the reason for the disappearance of boron (B) is not clear, the bond of silicon (Si) after the disappearance of boron (B) is combined with the hydroxyl group (OH) under high temperature and high humidity to form Si-OH having a long bond. It is considered that this causes a change in volume and causes the stress applying portion to protrude.
[0017]
FIG. 3 is a diagram illustrating the relationship between the average concentration of B ₂ O ₃ and the amount of protrusion in the stress applying part after the high temperature and high humidity test. The high-temperature and high-humidity test was performed using a pressure cooker test apparatus at a temperature of 120 ° C., a humidity of 90 RE%, and a pressure of 0.12 MPa for 54 hours. The pressure cooker test condition (temperature 120 ° C., humidity 90 RE%, pressure 0.12 MPa) is an acceleration test corresponding to about 10 times the temperature 85 ° C. and humidity 85% in a normal high temperature and high humidity test. From the results of FIG. 3, the range where the unevenness in the stress applying portion is reduced to around 0.1 μm is the range where the average concentration of B ₂ O ₃ is 14.0 to 14.5 wt%. Was found to protrude, and it was also found that when this range was exceeded, there was a tendency to dent.
[0018]
When the average concentration of B ₂ O ₃ increases, the erosion of boron (B) proceeds due to moisture, and a dent is formed in the stress applying portion at the end face of the optical fiber as disclosed in Patent Document 2 described above. When the average concentration of B ₂ O _{3 in} the stress applying portion becomes small, the reaction with the hydroxyl group (OH) of the bond of silicon (Si) becomes more dominant than the erosion of boron (B) by moisture. Is thought to stick out. A similar test was performed at 100 h using a pressure cooker test apparatus. The results were almost the same as those in FIG. 3 and the range where the unevenness of the stress applying portion was small was that the average concentration of B ₂ O ₃ was 14.0 to 14 It was in the range of 0.5 wt%.
[0019]
FIG. 4 is a view for explaining an example in which an optical connector is connected using the above-mentioned polarization maintaining optical fiber. FIG. 4A is a sectional view of an optical connector, and FIG. 4B is an enlarged view of an end face of an optical fiber. In the figure, 5 is a ferrule, 5a is a ferrule end face, 5b is an optical fiber hole, 5c is a fiber coating insertion hole, 6 is a connection key, 7 is a holder, 7a is a through hole, and 8 is an adhesive. The description of other symbols is omitted by using the same symbols as used in FIG.
[0020]
As shown in FIG. 4A, the optical connector is configured by inserting and fixing the polarization maintaining optical fiber 1 in a ferrule 5 and holding and fixing the ferrule 5 to a holder 7 or the like. The polarization-maintaining optical fiber 1 is positioned by inserting the distal end with the coating removed into the optical fiber hole 5 b formed on the distal end side of the ferrule 5, and into the fiber coating insertion hole 5 c and the through-hole 7 a of the holder 7. The adhesive 8 is filled and fixed. The ferrule 5 or the holder 7 is provided with a connection key 6 and the like for making connections in the same polarization direction.
[0021]
When butt-connecting optical fibers using an optical connector, the optical fiber end face 1a may be polished to a convex surface together with the ferrule end face 5a so as to project from the ferrule end face so that the optical fibers are PC-bonded. As a result, as shown in an enlarged manner in FIG. 4B, the joined state of the optical fibers is such that the ends of the optical fiber end faces 1a polished in an arc shape are in physical contact with the ends of the core portions 2 at the center position. A low-loss connection can be formed.
[0022]
However, when the projecting portion 4a occurs in the stress applying portion 3, contact occurs at the projecting portion before the core portion 2 comes into contact, and the bonding between the core portions 2 is hindered. For this reason, the reflection from the end face of the core portion and the butting interval are widened and are not constant, so that the connection loss increases and varies.
[0023]
According to the above investigation and verification, in the present invention, the stress applying section from the optical fiber end face after exposing the polarization maintaining optical fiber to a predetermined high temperature and high humidity environment (temperature 85 ° C., humidity 85 RH%, 336 h). Is set to 0.1 μm or less. When the protrusion amount Δ is 0.1 μm or less, when the optical fiber end face 1a is polished to a convex face together with the ferrule end face 5a by an optical connector, it does not hinder the joining between the core portions 2 and increases the connection loss and the variation. Occurrence can be reduced.
[0024]
In order to make the protrusion amount of the stress applying portion 0.1 μm or less, it is desirable that the average concentration of B ₂ O _{3 in} the stress applying portion be 14 wt% or more based on the results of FIG. On the other hand, when the average concentration of B ₂ O _{3 in} the stress applying portion is increased, a dent is formed on the end surface of the stress applying portion, but this does not hinder the joining of the optical connector. However, when the concentration of B ₂ O _{3 in} the stress applying portion increases, cracks are likely to occur in the stress applying portion during polishing of the end face of the optical fiber as disclosed in Patent Document 1. Further, as disclosed in Patent Document 2, when subjected to a moist heat environment, the stress applying portion is eroded, and there is a possibility that the polarization crosstalk is deteriorated.
[0025]
However, when the average concentration of B ₂ O _{3 in} the stress applying portion is set to 16 wt% or less, the generation of cracks in the stress applying portion and the degradation of crosstalk due to the increase in the amount of dents substantially hinder the problem. Did not occur. Therefore, by setting the B ₂ O ₃ average concentration of the stress applying section of the polarization maintaining optical fiber to 14 wt% to 16 wt%, the stress applying section of the stress applying section can be used for an optical connector used in a high temperature and high humidity environment. The protrusion can be minimized, the occurrence of cracks due to the end face polishing can be reduced, and the occurrence of dents can be suppressed to substantially no problem.
[0026]
Further, by maintaining the average concentration of B ₂ O _{3 in} the stress applying portion at 14 wt% to 16 wt% and increasing the concentration on the central portion side, the concentration of B ₂ O ₃ on the outer peripheral surface side in contact with the clad is reduced. can do. Therefore, when the glass base material provided with the stress applying member is stretched and heated as disclosed in Patent Document 1, the generation of bubbles at the interface between the cladding portion and the stress applying member is small, and the generation of cracks is further reduced. Can be reduced.
[0027]
A polarization maintaining optical fiber in which the amount of protrusion of the stress applying portion from the end face of the optical fiber after exposure to the above-mentioned predetermined high temperature and high humidity environment (temperature 85 ° C., humidity 85 RH%, 336 h) is 0.1 μm or less; Alternatively, an optical connector as shown in FIG. 4 was prepared using a polarization maintaining optical fiber in which the average concentration of B ₂ O _{3 in} the stress applying section was 14 wt% to 16 wt%. At this time, the connection end surface side was polished together with the end surface of the ferrule to a central convex surface having a radius of curvature of 25 mm or less (for example, 20 mm) so that the end surface of the optical fiber protruded from the ferrule surface.
[0028]
In the optical connector manufactured with the above configuration, no crack was generated in the stress applying portion due to the end surface polishing. Further, the amount of protrusion of the stress applying portion after exposure to the above-mentioned high temperature and high humidity environment was 0.1 μm or less. Further, the connection characteristics due to the attachment / detachment of the optical connector were verified. The variation in the connection loss was ± 0.1 dB or less, the return loss was also 45 dB to 50 dB, and the variation due to the attachment / detachment of the optical connector was small.
[0029]
【The invention's effect】
As described above, according to the present invention, the occurrence of cracks in the stress applying portion by processing the end face of the polarization maintaining optical fiber is reduced, and the use of the dent of the stress applying portion for use in a high-temperature and high-humidity environment. It is possible to suppress the occurrence of the stress applying portion from the end face of the optical fiber to a minimum by suppressing the occurrence thereof to such an extent that the influence is not substantially affected. As a result, even when the polarization maintaining optical fiber is PC-joined by an optical connector, it is possible to reduce the increase and the variation in the connection loss without deteriorating the polarization characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a polarization maintaining optical fiber.
FIG. 2 is a diagram illustrating a state in which a stress applying section of a polarization maintaining optical fiber protrudes.
FIG. 3 is a diagram illustrating the relationship between the average concentration of B ₂ O ₃ and the amount of protrusion in a stress applying section of the polarization maintaining optical fiber.
FIG. 4 is a diagram illustrating a configuration of an optical connector using a polarization maintaining optical fiber.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Polarization maintaining optical fiber, 1a ... Optical fiber end face, 2 ... Core part, 3 ... Clad part, 4 ... Stress giving part, 4a ... Protruding part, 5 ... Ferrule, 5a ... Ferrule end face, 5b ... Optical fiber hole, 5c: Fiber coating insertion hole, 6: Connection key, 7: Holder, 7a: Through hole, 8: Adhesive.

Claims (5)

A polarization-maintaining optical fiber in which a stress applying portion to which B ₂ O ₃ is added is disposed on a cladding portion around a core portion so as to sandwich the core portion, and the stress applying portion is provided under a predetermined high temperature and high humidity environment. Wherein the amount of protrusion from the optical fiber end face is 0.1 μm or less. A polarization maintaining optical fiber in which a stress applying portion to which B ₂ O ₃ is added is disposed on a cladding portion around a core portion so as to sandwich the core portion, and the average concentration of B ₂ O _{3 in} the stress applying portion is A polarization maintaining optical fiber having a content of 14 wt% to 16 wt%. The concentration of B ₂ O ₃ stress applying section, a polarization-maintaining optical fiber according to claim 2, characterized in that it has a concentration distribution which increases as the center. An optical connector, wherein the polarization-maintaining optical fiber according to claim 2 is fixed to a ferrule, and an end face of the ferrule is polished so that the polarization-maintaining optical fiber protrudes. The optical connector according to claim 4, wherein the center of the end surface of the ferrule is a convex surface having a radius of curvature of 25 mm or less.

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