JPH01202706A - Optical fiber polarization beam splitter - Google Patents

Abstract

PURPOSE:To miniaturize the beam splitter by allowing the polishing surfaces of an optical fiber which is polished up to an adjacent part of a core to be opposed to each other, and interposing a dielectric layer whose refractive index is different from a refractive index of a clad of the optical fiber between these polished surfaces. CONSTITUTION:By using two polished substrates 15 on which a polished optical fiber 12 obtained by polishing and eliminating a part of the optical fiber up to the vicinity of a core 2 is buried and fixed into a groove of a grooved substrate 13, and each polished surface 16, 16 of these polished substrates 15, 15 is opposed and superposed. Between the polished surfaces 16, 16, a dielectric layer 17 whose material is a dielectric having a refractive index being different from a refractive index of a clad 4 of the polished optical fiber 12 is interposed. Accordingly, by reflecting an incident light beam leaking from the polished surface 14 of the substrate 15 by the dielectric layer 17, and also, allowing said light beam to transmit through, the incident light beam can be separated into each polarized wave. In such a way, the optical coupling part can be shortened, and the beam splitter can be miniaturized.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention is applicable to OT D R (Optical Time
Do mainn e lectometry)
The present invention relates to an optical fiber polarization beam splitter that splits or merges light while maintaining the polarization direction of the light in various optical fiber sensors and the like.

“Prior Art” Conventionally, optical fiber polarization beam splitters (hereinafter referred to as beam splitters) used for such purposes consist of two stress-applied polarization-maintaining optical fibers (hereinafter referred to as optical fibers). A structure is known in which a part of the fiber (hereinafter omitted) is heat-fused and further stretched to form a fused part, and optical power is coupled at this fused part.

FIGS. 8 and 9 show an example of such a conventional beam splitter, and the reference numeral 1 indicates the beam splitter. (Fiber-type polarized beam splitter announced at IEICE Quantum Electronics Study Group 0QE85-15 in May 1985) As shown in Figure 1O, this beam splitter consists of a central core 2 and a core 2. It is made using an optical fiber 5 having stress applying parts 3.3 provided on both sides of the fiber and a cladding 4 surrounding them. That is, as shown in FIGS. 11 and 12, two optical fibers 5 are superimposed so that their respective polarization axes X are parallel, and then,
This overlapping portion is melted using heat purification such as an oxyhydrogen flame and further stretched to form a melt-stretched portion 6. The optical fiber 5 of this melt-stretched portion 6
The thickness of the core 2 is reduced to about 1/10 of that before stretching. Therefore, light energy leaks near the core 2 of the melt-stretched portion 6. Light energy is exchanged between the two cores 2 through this light energy leakage portion, and light is coupled.

Incidentally, the equiphasic refractive indexes in the two polarization axes X and Y directions existing in the optical fiber 5 as shown in FIG. 10 are different, and are generally larger on the X direction side. Therefore, the phase constants of the two corresponding modes HE, , (hereinafter referred to as X polarization) and HE, , (hereinafter referred to as Y polarization) are different. Therefore, the coupling coefficient between each core 2.2 differs for each of these modes.

Next, the reason why this beam splitter 1 functions as a polarizing beam splitter will be explained based on FIG. 13. As shown in this figure, one optical fiber 5a has an X polarization component and an
Suppose that 5+1 (polarized light) that contains equal polarization components is incident.
When reaching , due to the optical coupling action of the melt-stretched portion 6,
A part of it is input to the other optical fiber 5b side, and as a result,
The incident light is split at a predetermined splitting ratio and connected to one optical fiber 5.
the output side 5c of a and the branch output side 5 of the other optical fiber 5b
(Emitted from 1.

What is important here is that the degree of light coupling is different between the X polarized light and the Y polarized light. That is, in FIG. 13, more of the X-polarized component in the incident light is emitted toward the branch output side 5d of the other optical fiber 5b than the output side 5c of one optical fiber 5a. On the other hand, a large amount of the X-polarized component of the incident light is output to the output side 5c of one optical fiber 5a. This allows each polarization component of the incident light to be separated.

"Problem to be Solved by the Invention" However, in order to improve the degree of πE of each polarized wave component, it is necessary to make the melt-stretched portion 6 very long, approximately 20 to 30 mm. There was a problem in that the mechanical strength of the splitter l became weak.

Further, since the long melt-stretched portion 6 is required, the size of the beam splitter 1 body also needs to be 60 mm or more, resulting in a problem that the beam splitter 1 becomes large.

In addition, since the melt-stretched portion 6 is formed by melt-stretching two optical fibers 5, errors tend to occur in the circumferential direction of each optical fiber 5. Therefore, a high-performance beam splitter with good optical coupling characteristics is required. The problem was that it was difficult to create. Incidentally, an example of the characteristics of the beam splitter produced as described above was that the extinction ratio was about 20 d13 and the coupling loss was about 2 dB.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a high-performance beam splitter that has high mechanical strength, is small in size, and has good optical coupling characteristics.

"Means for Solving the Problems" The optical fiber polarizing beam splitter according to the present invention uses two polished optical fibers in which a portion of a stress-applied polarization-maintaining optical fiber is polished to the vicinity of the core, and each polished optical fiber is An optical fiber polarizing beam splitter having polished surfaces facing each other, wherein a dielectric material having a refractive index different from the refractive index of the cladding of the polished optical fiber is provided between each polished surface of the polished optical fiber. It was constructed by intervening layers, and was used as a means to solve the two-legged problem.

Embodiment FIGS. 1 and 2 are diagrams showing an embodiment of a beam splitter of the present invention, and reference numeral 11 indicates a beam splitter.

This beam splitter II consists of a polished substrate in which a polished optical fiber 12, which is obtained by polishing a part of the optical fiber 5 shown in FIG. 15 are used, and the polished surfaces 16.16 of these polished substrates 15.15 are placed one on top of the other, and the cladding 4 of the polished optical fiber 12 is placed between each polished surface 16.16. A dielectric layer 17 made of a dielectric material having a refractive index different from the refractive index is interposed therebetween.

As the polished optical fiber 12, for example, the core 2 has a G
e using Ot-doped Sin, and 5i on the cladding 4.
5 using O7 and adding 8203 to the stress applying part 3.3
A quartz-based optical fiber using iOz is preferably used.

The material of the grooved substrate 13 is not particularly limited, but when embedding and fixing the optical fiber 5 in the groove 14, the positional relationship between the X-axis and the Y-axis of the optical fiber 5 may be visually observed and the position finely adjusted. A transparent hard material such as quartz glass is preferably used.

Further, reference numeral 18 in the figure is a transparent adhesive for embedding and fixing the optical fiber 5 in the groove 14.

As the material of the dielectric layer 17, an inorganic material that is transparent or has a refractive index different from that of the cladding 4 is used. For example, the material of the cladding 4 is 810. In this case, examples of particularly suitable materials include epoxy resins, acrylic acid ester resins, methacrylic resins, polyester resins such as polyethylene terephthalate, synthetic resin materials such as polycarbonate, multi-component glass, B,
03 and P.

The material is an inorganic material such as 5iOt whose refractive index is adjusted by doping with 05 or the like. These materials are formed into a thin plate shape and are interposed between each polished surface 16, and the thickness thereof is determined as appropriate depending on the amount of light leakage from the polished surface 16 of the polished optical fiber 12, the refractive index of the dielectric material used, etc. Set. Further, the surface of this dielectric layer 17 is formed to be smooth so that light leaking from each polished surface 16 is not diffusely reflected.

Next, the optical coupling effect of this beam splitter +1 will be explained. Generally, as shown in FIG. 3, when light enters from a certain area A to another area B at a predetermined angle of incidence,
Part of the incident light Pi is reflected at point P (Pr), and part of it is transmitted (PL). What is important here is that the incident light P
The amount of reflected light and the amount of transmitted light differ depending on the polarization plane of i. That is, when the polarization direction of the incident light is parallel to the plane of incidence, the transmittance Tm is T m = 2 cos (71-sinot/sin θ1-
cosθi+sinθ and cosθt.

Furthermore, when the polarization direction of the incident light Pi is perpendicular to the plane of incidence, its transmittance Tt is T L = 2cos(91-sinθ/5in(θ1+
θt).

In this way, the amount of transmitted light varies depending on the polarization direction of the incident light Pi. Since the present invention applies the above principle,
The principle of optical coupling in the beam splitter 11 of this embodiment will be explained based on FIG. 4.

As shown by the solid arrow in the figure, one polished optical fiber 12
The light propagating inside the core 2a of a is exposed near the core 2a (7) and the thin polished surface of the cladding 4! At 6, it is transmitted to the outside. At the boundary with the dielectric layer 17, a portion of this transmitted light is reflected and enters the core 2a, as shown by the dotted arrow in the figure, and a portion of the transmitted light passes through the dielectric layer 17 and is polished by the other side. The light is branched so that it enters the core 2b of the optical fiber +2b, and the light is coupled. In the part where this light is coupled, the amount of light that enters the core 2a of one polished optical fiber I2a and the core 2b of the other polished optical fiber +2b differs due to the difference in the polarization direction of the incident light as described above. , it has a function as a polarizing beam splitter. The polarization characteristics of the beam splitter II configured as shown in FIG. 1 are as shown in FIG.
The X polarized wave is on the output side 12c of a, and the other polished optical fiber +
The X polarized wave is mainly separated to the branch output side +2d of 2b.

The beam splitter 11 configured as described above is produced as follows. First, as shown in FIG. 6, the optical fiber 5 is inserted into the groove 14 of the grooved substrate 13, and then a transparent adhesive 18 is injected into the groove 14 to fix the optical fiber 5 in the groove 14. do.

At this time, the direction of the optical fiber 5 is adjusted so that the X sleeve is along the depth direction of the groove. Next, l^ of the grooved board 13!
! The core 4 of the optical fiber 5 is polished to expose the vicinity of the core 2 of the optical fiber 5. This polishing type is appropriately set depending on the extinction ratio of the beam splitter 11. Through this polishing operation,
A polished substrate I5 shown in FIG. 7 is created. Next, the two polished substrates I5 prepared as described above are placed on each polished surface 16.
Each polishing substrate 15 is fixed so that the two polishing substrates 15 are stacked so as to face each other, and a dielectric layer I7 is interposed between each polishing surface 16. The method for forming the dielectric layer 7 between each polished surface 16 includes a method in which a thin plate-like dielectric material is sandwiched between each polished surface 16 and the dielectric material and the polished surface 16 are bonded using an adhesive. , two polishing substrates 15 are placed facing each other with a predetermined gap therebetween, and a dielectric material is injected into the gap by injecting a melt of a synthetic resin material such as Evokin resin or a mixture of a polymerization compound and a polymerization initiator. A method of forming the body layer 17, etc. may be used. By each of the above operations, the beam splitter 11 having the configuration shown in FIG. 1 is created.

This beam splitter 11 polishes and removes a part of the optical fiber 5 to the vicinity of the core 2, and then attaches the polished optical fiber 12 to the grooved substrate I3. 414 Embedded and fixed in the polishing section 1 (Plate 15
When two polished surfaces 16 and 16 are placed one on top of the other, and the polished surfaces 16 and 16 are stacked one on top of the other, a dielectric layer having a refractive index different from the refractive index of the crat 4 of the polished optical fiber 12 is placed between the polished surfaces 16 and 16. The body is made of a material with a dielectric layer 17 interposed between the polished surface 16 of the polished optical fiber 12 and the dielectric layer I7.
At the boundary, the incident light transmitted through the core 2 of one polished optical fiber 12 and leaking from the polished surface 14 is reflected by the dielectric layer 17 U-1 and transmitted, thereby converting the incident light into each polarized wave. Since the beam splitter can be separated into two parts, the optical coupling part can be shortened compared to a conventional beam splitter that requires a long melt-stretched part, and the beam splitter 11 can be made smaller.

In addition, since two polished substrates I5 with polished optical fibers 12 fixed to a grooved substrate 13 were superimposed and their respective polished surfaces 16 faced each other to form an optical coupling portion, it was compared to a beam splitter having a melt-stretched portion. , mechanical strength can be improved.

Also, this beam splitter 11 connects the optical fiber 5 to d
The surface of the grooved substrate 13 on the groove 14 side is polished to the vicinity of the core 2 of the optical fiber 5 to form a polished substrate I5.
The polarization direction of the optical fiber 5 and the amount of light leakage are improved compared to the case where the two polished substrates 15 are stacked with the dielectric layer 17 interposed between them, and the two optical fibers 5 are melted and drawn. The beam splitter 11 can be manufactured with extremely accurate adjustment, and a high performance beam splitter 11 with good optical coupling properties can be easily manufactured.

Hereinafter, experimental examples of the beam splitter according to the present invention will be described to clarify the effects of the present invention.

"Experimental Example" A beam splitter having the same structure as the previous example was created using two optical fibers having the same structure as the optical fiber shown in FIG. 1θ. The optical fiber used was a silica-based polarization-maintaining optical fiber having a core diameter of 8 μm, a cladding outer diameter of 125 mm, and a stress impression diameter of 30 μm. The loss of this optical fiber was 0.6 dB/km.

This optical fiber was fixed in a groove of a quartz LJR substrate having the shape shown in FIG. 6, with its Y axis directed along the depth direction of the groove. The dimensions of this grooved board are 5mm x 5mm
X: 20 mm, M: depth: 0.2 mm at the center and 2 mm at both ends. Furthermore, an Epoquin adhesive was used as the adhesive for fixing the optical fiber.

Next, the 114 side of the L-sided substrate was polished to form a polished surface, thereby producing a polished substrate having the same structure as that shown in FIG. 7. The polished substrate was polished so that the distance from the center of the core of the polished optical fiber to the polished surface was 6 μm at the center thereof. Next, a mixture of an Epoquine resin material consisting of a mixture of hisphenol A and epichlorohydrin and a curing agent was applied to the polished surface of the polished substrate created in this way, and the polished W plates created in the same manner as above were each polished. The Evokin resin was solidified and a dielectric layer with a thickness of 2 μm was formed between each polished surface, and each polished substrate was fixed by adhesive. By the above 6 operations, the first
A beam splitter having the same configuration as that shown in the figure and FIG. 2 was obtained.

As a result of measuring the optical coupling characteristics of the obtained beam splitter, the loss was 0.3 dB and the extinction ratio was about 10 d13, indicating good polarization separation performance and excellent mechanical strength.

``Effects of the Invention'' As explained in 2 below, the beam splitter of the present invention has two polished optical fibers in which a part of the stress-applied polarization-maintaining optical fiber has been polished to the vicinity of the core, and the To,
They are arranged facing each other with a dielectric layer made of a dielectric material having a refractive index different from that of the cladding,
At the boundary between the polished surface of the polished optical fiber and the dielectric layer, the incident light transmitted through the core of one polished optical fiber and leaking from the polished fiber is reflected by the dielectric layer and transmitted. Since each polarized wave can be separated, the optical coupling part can be made shorter than the conventional beam splitter which uses a long melt-stretched part, and the beam splitter can be made smaller.

In addition, this beam splitter has a polished optical fiber fixed to a grooved substrate to form a polished substrate, and the two polished substrates are stacked on top of each other so that the polished fibers of each polished optical fiber face each other.
The mechanical strength of the beam splitter can be improved compared to a beam splitter that has a melt-stretched portion.

In addition, in this beam distributor, a stress-applied polarization-maintaining optical fiber is fixed to a d4 substrate, the 11q side surface of the grooved substrate is polished to the vicinity of the core, and the two polished substrates are Since it can be created by overlapping a dielectric layer with a Uo filter, the polarization direction of the optical fiber and the amount of light leakage can be adjusted extremely accurately compared to the method of melting and drawing two optical fibers. can be created,
A high-performance beam splitter with good optical coupling properties can be easily created.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an embodiment of the present invention, in which FIG. 1 is a cross-sectional view of a beam splitter, FIG. 2 is a longitudinal cross-sectional view of the beam splitter, and FIG. 3 is a cross-sectional view of the beam splitter. Figures 4 and 5 are diagrams for explaining the relationship between reflection and transmission of light.
6 and 7 are diagrams for explaining an example of the manufacturing process of the beam splitter according to the present invention, and FIGS. 8 and 9 are diagrams for explaining the optical coupling characteristics of the beam splitter shown in the figure. FIG. 8 is a side view of the beam splitter, FIG. 9 is an enlarged sectional view taken along the line CC in FIG. 8, and FIG. 10 is a diagram showing a stress-applied polarization-maintaining optical fiber. FIG. 11 is a cross-sectional view showing an example, and FIG.
The figure is a sectional view taken along the line DD in FIG. 11, and FIG. 13 is a diagram for explaining the optical coupling characteristics of the beam splitter in FIG. 8. 2... Core, 4... Clad, 5... Optical fiber, II... Beam splitter, 12... Polished optical fiber, 16... Polished material, II... Dielectric layer.

Claims (1)

[Claims] An optical fiber polarizing beam splitter using two polished optical fibers in which a part of stress-applied polarization-maintaining optical fiber is polished to the vicinity of the core, with the polished surfaces of each polished optical fiber facing each other. An optical fiber characterized in that a dielectric layer made of a dielectric material having a refractive index different from the refractive index of the cladding of the polished optical fiber is interposed between each polished surface of the polished optical fiber. Polarizing beam splitter.