JP3095511B2 - Polarization-maintaining optical fiber coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization maintaining optical fiber coupler for splitting or coupling light while maintaining the polarization direction of light in an optical communication system or various optical fiber sensors.

[0002]

2. Description of the Related Art Conventionally, as one of optical fiber couplers used for such a purpose, a part of a stress imparting type polarization maintaining optical fiber (hereinafter referred to as PM optical fiber) is polished to a portion near a core. 2. Description of the Related Art A PM optical fiber coupler that uses two optical fibers and forms a contact portion by bringing the respective polished portions into contact with each other and couples or branches optical power at the contact portion is known. FIGS. 3 and 4 are views showing an example of such a conventional PM optical fiber coupler, wherein reference numeral 1 denotes a PM optical fiber coupler, and reference numerals 2a and 2b denote polished PM optical fibers.

[0003] This PM optical fiber coupler 1 has a polishing PM
Two rectangular prism-shaped glass blocks 3a, 3b in which a part of the optical fibers 2a, 2b are buried and fixed in a groove are adhered, and the polished portions of the polished PM optical fibers 2a, 2b are brought into contact. I have. This glass block 3a, 3
b, a groove 4 in which the polished PM optical fiber is buried is formed along the longitudinal direction thereof.
The M optical fiber is formed in an arc shape such that the central portion in the longitudinal direction swells when the M optical fiber is embedded.

[0004] At a contact portion 6 (optical coupling portion) where the respective polished portions 5 of the two PM polished optical fibers 2a and 2b come into contact, the cores 7 of the polished PM optical fibers 2a and 2b approach each other, and one of the PM polished optical fibers 2a and 2b approaches one. The optical power propagating in the core 7 of the polished PM optical fiber 2a leaks and the other polished PM optical fiber 2b
Of the optical power transferred into the core 7 and the polishing PM of both
The optical power of the optical fibers 2a and 2b is coupled.

The PM optical fiber coupler 1 is manufactured by the steps shown in FIGS. First, as shown in FIG. 5, the PM optical fiber 1 is inserted into the groove 4 of the glass block 3.
Insert 1. This PM optical fiber 11 is composed of a core 7 at a central portion, stress applying portions 12 provided on both sides thereof, and a cladding 13 surrounding these. Next, the adhesive 14 is injected into the groove 4 and solidified, and the PM optical fiber 11 is fixed to the glass block 3 (FIG. 6). Next, the surface of the glass block 3 on the groove 4 side is polished. This polishing is performed so that the polished surface 15 reaches the vicinity of the core of the PM optical fiber 11, and the optical power propagating in the core 7 leaks from the polished surface 15 to some extent (FIG. 7). The amount of optical power leakage is determined by the amount of polishing on the polished surface, and various types of glass blocks 3a and 3b having different amounts of polishing depending on the usage of the coupler are manufactured. Next, the two polished glass blocks 3a and 3b polished as described above are superimposed on each polished surface 15 via a matching liquid 16. Then, as shown in FIG. 8, the mutual position of the two glass blocks 3a, 3b is moved while monitoring the optical power from the light source 17 with the optical power meter 18 connected to the output side of both the polished PM optical fibers 2a, 2b. , Are adjusted so that a predetermined output branch ratio can be accurately obtained. Next, each of the glass blocks 3a and 3b is fixed with an adhesive or the like to obtain a PM optical fiber coupler 1.

[0006]

As a method of polishing a fiber for producing such a PM optical fiber coupler, a physical polishing method, that is, a method using a polishing machine or a polishing liquid is generally used. . In the case of a PM optical fiber, a part of the stress applying part 12 is removed to polish to the vicinity of the core, and after polishing is finished, the cross section of the stress applying part 12 is shown in FIGS. 9 (a) and 9 (b). As shown in the figure, the surface is exposed on the polished surface. In a state where a part of the stress applying part is removed in this way, the stress applying part 12 is easily cracked by partial release of stress. Further, the stress applying section 12
It is considered that, by directly exposing to the water or the polishing liquid during the polishing step, cracks and cracks are liable to occur in the stress applying portion 12. Such cracks in the stress applying portion not only cause deterioration of crosstalk and loss of optical power, but also extend to cracks extending over the entire optical fiber, and may greatly deteriorate the characteristics of the optical fiber coupler.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a manufacturing method capable of manufacturing a PM optical fiber coupler without causing the above-described problem when polishing a stress applying section.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a polished optical fiber having a polished surface in which a portion near the core is exposed by removing the cladding of a part of the optical fiber. The polished optical fiber is buried in the groove, and the polished substrate is fixed so that the polished surface thereof faces upward. The two polished substrates are fixed such that the polished surfaces of the polished substrates are in contact with each other. Joining to form a contact,
In the optical fiber coupler that branches and couples optical power at the contact portion, a single mode fiber is interposed as a part of the polarization maintaining optical fiber as the optical fiber, and both of the optical fibers are opposed to each other via the single mode fiber. A polarization maintaining optical fiber coupler characterized by using a composite optical fiber in which the principal axes of the polarization maintaining optical fibers are made to coincide with each other, and wherein the polished surface is formed on a single mode fiber portion of the composite optical fiber.

[0009]

In the polarization maintaining optical fiber coupler of the present invention, a single mode fiber is interposed in a part of the polarization maintaining optical fiber, and the main axes of both the polarization maintaining optical fibers opposed to each other via the single mode fiber. Since the polished surface is formed on the single mode fiber portion of the composite optical fiber using the matched composite optical fiber, without deteriorating the polarization maintaining characteristics of the polarization maintaining optical fiber, Problems such as cracks generated during polishing can be prevented.

[0010]

FIG. 1 shows an embodiment of a polarization maintaining optical fiber coupler according to the present invention. This polarization maintaining optical fiber coupler (hereinafter, referred to as a coupler) 21 has a stress applying portion removing portion formed by fusion-splicing polarization maintaining optical fibers 23 and 24 at both ends of a short single mode fiber 22. The composite optical fiber 25 is connected to the glass block 2
6, the single-mode fiber 22 is disposed at the center of the groove and fixed, and the groove-side surface is polished to polish the single-mode fiber 22 to the vicinity of the core. 28b are bonded, and the polished surfaces formed on the respective composite optical fibers 25 are brought into contact with each other to form a contact portion (optical coupling portion) 29.

The polarization maintaining optical fibers 23 and 24 used in the composite optical fiber 25 are composed of a core 30 at a central portion, stress applying portions 31 arranged on both sides thereof, and a cladding 32 surrounding them. ing. Usually the core 30 is S
GeO ₂ is added to iO _2, and is made of a material having a higher refractive index than the cladding 32 made of SiO ₂ . The stress applying section 31 is formed of a material obtained by adding B ₂ O ₃ or the like to SiO ₂ , has a lower refractive index than the cladding 32, and when the polarization maintaining optical fibers 23 and 24 are observed from the side, the refractive index of the material is increased. , The stress applying section 31 can be identified as dark. The single mode fiber 22 is composed of a core 30 and a clad 32 surrounding the core, and those usually used in the optical communication field can be used. The polarization maintaining optical fibers 23 and 24, the clad outer diameter and Those having the same core diameter are preferably used.

The polarization maintaining optical fibers 23 and 24 facing each other via the single mode fiber 22 are connected so that the two polarization axes (x-axis and y-axis) exactly coincide with each other. As a result, the composite optical fiber 25 includes the single mode fiber 22 without the stress applying section 31 without deteriorating the polarization maintaining characteristics of the polarization maintaining optical fiber. This optical fiber 25 can be used if no bending or pressure is applied to the single mode fiber 22 portion.
The polarization characteristics of the polarization maintaining optical fibers 23 and 24 are maintained.

To manufacture the composite optical fiber 25,
A single mode fiber 22 is fusion-spliced to one end of the polarization maintaining optical fiber 23, and the single mode fiber 22
Is cut while leaving a length of about 5 to 30 mm, and another polarization maintaining optical fiber 24 is fusion-spliced to the cut surface. In order to match the positional relationship between the stress applying portions of the two polarization maintaining optical fibers 23 and 24 (that is, to match the polarization axes), another polarization maintaining When the optical fiber 24 is fused, it is preferable to rotate the fiber 24 while monitoring the relationship between the incident light angle and the outgoing light angle of the polarization maintaining optical fiber 24 to perform both polarization axes alignment. Further, the polarization axes of the two polarization-maintaining optical fibers 23 and 24 may be deliberately connected by being shifted by 90 degrees to change the propagation axis of light.

The composite optical fiber 25 uses the coupler 2
In order to manufacture the glass block 2 as shown in FIG.
6, the composite optical fiber 25 is inserted so that the single mode fiber 22 is located at the center in the longitudinal direction of the groove. Reference numerals 31 and 32 in the drawing denote fusion spliced portions between the polarization maintaining optical fibers 23 and 24 and the single mode fiber 22. Next, an adhesive is injected into the groove 27 and solidified, and the composite optical fiber 25 is fixed to the glass block 26. The groove 27 of the glass block 26 is formed in an arc shape so that the center in the longitudinal direction swells.
7 and is fixed in a swelling state.

Next, the surface of the glass block 26 on the groove side is polished, and a part of the single mode fiber 22 is
Forming a polishing surface exposing the vicinity, and polishing block 2
8a and 28b. This polishing can be performed by a physical polishing method using a polishing machine or the like. The amount of polishing is set according to the desired branching ratio of the coupler 21. In this polishing, since the single mode fiber 22 having no stress applying portion in the composite optical fiber 25 is polished, it is possible to prevent the stress applying portion 31 from being broken when the polishing is performed. Next, the two polishing blocks 28a and 28b are overlapped so that their respective polishing surfaces are in contact with each other, a matching liquid is injected between the two, and light is incident from one end of one of the composite optical fibers 25 to mix the two. The position of both polishing blocks 28a and 28b is finely adjusted while monitoring the intensity of the optical power emitted from the optical fiber 25, and then both polishing blocks 2a and 2b are bonded using an adhesive or the like.
8a and 28b are joined to produce the coupler 21 shown in FIG.

The coupler 21 has a polarization maintaining optical fiber 23, 24 fusion-spliced to both ends of a single mode fiber 22, and a pair of polarization maintaining optical fibers 23, 24 facing each other via the single mode fiber 22. A composite optical fiber 25 having the same principal axis is used, a polishing surface is formed on the single mode fiber 22 of the optical fiber 25, and two polishing blocks 28a and 28b to which the composite optical fiber 25 is fixed are joined. Since the polished surfaces of the two composite optical fibers 25 are brought into contact with each other to form the contact portion 29, cracks or the like generated during polishing of the stress applying portion 31 without deteriorating the polarization maintaining characteristics of the polarization maintaining optical fiber. Can be prevented, the production yield of the coupler 21 can be improved, and the reliability of the coupler 21 can be improved. It can be.

(Production Example) A coupler 21 shown in FIG. 1 was produced. Cladding outer diameter 125 μm, core diameter 10 μm,
Relative refractive index difference Δ = 0.3%, cutoff wavelength 1.3 μm, stress imparting type polarization maintaining optical fiber 23 (PANDA fiber)
A single mode fiber 22 having the same clad outer diameter and the same core diameter was fusion-spliced to one end, and this single mode fiber was cut so as to have a length of about 10 mm. Another PANDA fiber 24 having the same characteristics as the previous one was fusion-spliced to the cut surface so that the polarization axes thereof were matched to produce a composite optical fiber 25. At the time of the fusion splicing, the linearly polarized light having a wavelength of
While monitoring the output light of another PANDA fiber 24 using an analyzer, the connected PANDA fiber is rotated, and both PANDA fibers are rotated.
The axes were aligned such that the polarization axes of the fibers coincided. The composite optical fiber 25 thus obtained had a splice loss at two fusion spliced portions of 0.1 dB or less and a crosstalk of -35 dB or less.

This composite optical fiber 25 is 5 mm × 25 mm
The single mode fiber 22 was inserted into the groove 27 of the glass block 26 having a size of 2.5 mm and formed with a groove for embedding the fiber along the longitudinal direction, with the center being the center, and an adhesive was injected and solidified. The groove 27 is gently curved so that the central portion is shallow and both sides are deep, and the composite optical fiber 25 is bent along this curvature. Composite optical fiber 2
5 is subjected to the bending along the groove and the stress caused by the solidification and contraction of the adhesive, but the influence on the polarization maintaining characteristics of the optical fiber 25 by these does not substantially matter. The axis alignment operation when fixing the composite optical fiber 25 to the glass block is performed by first monitoring the central part of the stress applying part 31 of one of the PANDA fibers 23 from above the groove with a microscope, The fiber 23 is rotated so as to overlap with each other, and positioning is performed, and the same positioning is performed for another PANDA fiber 24. After this state, an adhesive is injected into the groove and solidified. The adhesive may be injected before the adjustment of the optical fiber 25 in the axial direction.

Next, the side surfaces of the grooves of the glass block 26 were precision polished with a polishing machine. In this polishing, since only the portion of the single mode fiber 22 of the composite optical fiber 25 was polished, unlike the case where the stress applying portion was polished, the polishing could be performed without any trouble such as cracking. Next, the two polished blocks 28a and 28b having been polished are overlapped with each other via a matching liquid, and the positions of both blocks are finely adjusted and adhered while monitoring the intensity of the emitted light to produce the coupler shown in FIG. . The obtained coupler had characteristics comparable to non-defective polarization-maintaining optical fiber couplers manufactured by a conventional method.

[0020]

As described above, according to the polarization maintaining optical fiber coupler of the present invention, it is possible to prevent cracks or the like generated during polishing of the stress applying portion without deteriorating the polarization maintaining characteristics of the polarization maintaining optical fiber. It is possible to prevent problems, improve the production yield of the polarization maintaining optical fiber coupler, and improve the reliability of the polarization maintaining optical fiber coupler.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing one embodiment of a polarization maintaining optical fiber coupler of the present invention.

FIG. 2 is a perspective view for explaining a method of manufacturing the coupler of FIG.

FIG. 3 is a side sectional view of a conventional polarization maintaining optical fiber coupler.

FIG. 4 is a sectional view taken along line BB of the coupler of FIG. 4;

FIG. 5 is a perspective view showing a process of manufacturing the coupler of FIG. 4, showing a state where a fiber is inserted into a glass block.

FIG. 6 is a cross-sectional view showing a fixed state of the fiber.

FIG. 7 is a sectional view showing a polishing step in the same manner.

FIG. 8 is a configuration diagram showing a mutual position adjustment process of two blocks.

FIG. 9 is a schematic diagram showing a state of a polished surface of a polished fiber.

[Explanation of symbols]

21: polarization maintaining optical fiber coupler, 22: single mode fiber, 23, 24: polarization maintaining optical fiber, 25 ...
Composite optical fiber, 26: glass block, 27: groove, 2
8a, 28b: polishing block, 29: contact portion, 30: core, 31: stress applying portion, 32: clad, 33, 34 ...
Fusing stretch section.

Continuation of the front page (56) References JP-A-2-259706 (JP, A) JP-A-1-202706 (JP, A) JP-A-63-249809 (JP, A) JP-A-63-234209 (JP, A) , A) JP-A-63-136009 (JP, A) JP-A-60-203904 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/28-6/293

Claims (1)

(57) [Claims] An optical fiber in which a clad portion is removed by polishing a part of an optical fiber to form a polished surface exposing a portion near a core, and the polished optical fiber is embedded in a groove.
And a polished substrate fixed with its polished surface facing upward, and two polished substrates joined together such that the polished surfaces of the polished substrates are in contact with each other to form a contact portion. In an optical fiber coupler that branches and couples optical power at a contact portion, a single mode fiber is interposed as a part of the polarization maintaining optical fiber as the optical fiber, and both of the polarization modes opposing each other via the single mode fiber. Using a composite optical fiber in which the main axes of the wave holding optical fiber are matched,
A polarization maintaining optical fiber coupler, wherein the polished surface is formed on a single mode fiber portion of the composite optical fiber.