JP2005043786A - Optical coupling structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical coupling structure, wherein an optical axis is easily aligned, a deterioration in performance is hardly caused by a change in temperature, and coupling loss is reduced. <P>SOLUTION: The optical coupling structure includes a first and a second optical fiber 6, 7 whose end face is machined at a 45° angle relative to the optical axis of the optical fibers, and a first and a second optical film formation 12, 13 in which an optical reflection film or an optical filter is formed on the end face of the two optical fibers. The mutual positional relation between the first and the second optical fiber 6, 7 is adjusted in such a manner that at least a part of the light wave (light 16) propagated in the first optical fiber and reflected on the first optical film formation crosses the second optical film formation and that at least a part of the light wave (light 15) propagated in the second optical fiber and reflected on the second optical film formation crosses the first optical film formation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical coupling structure, and more particularly to an optical coupling structure with reduced coupling loss.

FIG. 7 shows the configuration of the optical module of Conventional Example 1 (see Patent Document 1).
The optical module includes a prism 41 whose cross-sectional shape in the width direction is a right-angled isosceles triangle, a triangular prism-shaped prism 42 whose cross-sectional shape in the width direction is a right-angled isosceles triangle, and a distributed refractive index type glass rod 49 having a lens effect. , 50 and two optical fibers 47, 48 concentrically connected to each other, the side surface (surface A) facing the edge forming the right angle of the prism 41 and the end faces of the gradient index glass rods 49, 50 are It is in contact with the refractive index matching agent, and the length of the bottom side (surface B) of the end surface of the prism 41 is matched with the length of the oblique side (surface C) of the end surface of the prism 42 so that both end surfaces are in contact.
Further, on the surface B of the prism 41, a reflection film (wavelength selective filter: short wavelength path filter 51) that provides a predetermined reflectance with respect to a predetermined wavelength is formed.
Further, a spherical lens 43 and a light source 44 are disposed on the extension line of the central axis of the optical fiber 48 via the prisms 41 and 42.
The 1.3 μm light from the light source 44 and the spherical lens 43 is incident on the surface E, passes through the wavelength selective filter 51 and the surface A, and is coupled to the optical fiber 48, while 1.55 μm from the optical fiber 48. The received light enters the surface A, is reflected by the wavelength selective filter 51 and the surface D, passes through the surface A, and is coupled to the optical fiber 47.

FIG. 8 shows the configuration of the optical coupling structure of Conventional Example 2 (see Patent Document 2).
The optical coupling structure includes an optical fiber 80 and optical waveguide substrates 60 and 70, and the optical fiber 80 is fixed to the optical waveguide substrate 70 with an adhesive 91. The optical fiber 80 has a core 81 disposed at the center thereof and a clad layer 83 surrounding the core 81. The optical waveguide substrate 60 (70) includes an optical waveguide 61 (71) having a rectangular cross section provided on the upper portion thereof, a cladding layer 62 (72) surrounding the optical waveguide, and a buffer layer 63 (73). The end portion of the optical waveguide substrate 60 (70) is cut obliquely to form a cut surface 65 (75). Similarly, the end face of the optical fiber 80 is cut obliquely to form a cut surface 85.
The cut surface 65 is cut at an angle (180 degrees−α) with respect to the optical axis direction of the optical waveguide 61, and here, α = 45 ° is set. A semi-transmissive reflective film 90 is provided on the cut surface 65 or the cut surface 75 by sputtering or the like. The semi-transmissive reflective film 90 is a multilayer film of metal or dielectric, and has a characteristic of partially transmitting / reflecting light waves. The cut surface 65 is bonded to the cut surface 75 with an adhesive via the semi-transmissive reflective film 90 so that the optical waveguide 71 and the optical waveguide 61 are linearly arranged.

Next, propagation of light waves will be described.
The light wave L <b> 1 that has propagated through the optical waveguide 71 is incident on a semi-transmissive reflective film 90 provided between the cut surface 75 and the cut surface 65. Next, the light wave L1 is branched by the semi-transmissive reflective film 90. In other words, the light wave L1 is split into a light wave L2 that is transmitted through the semi-transmissive reflective film 90 and propagates to the optical waveguide 61, and a light wave L3 that is reflected by the semi-transmissive reflective film 90. The reflected light wave L3 passes through the clad layer 72 and the adhesive 91 having the same refractive index as the clad layer and the clad layer 83, and enters the cut surface 85. Thereafter, the light wave L3 is incident on the cut surface 85 of the core 81. The light is reflected and propagates through the optical fiber 80. Therefore, the light wave L1 is branched into the light wave L2 propagating to the optical waveguide 61 and the light wave L3 propagating to the optical fiber 80 by the transflective reflection film 90.

Further, a wavelength separation filter may be installed instead of the semi-transmissive reflective film 90. This wavelength separation filter is provided by laminating high / low refractive index dielectric films. Here, a wavelength-selective transmission film that allows only the light wave having the wavelength λ1 to pass is installed as a wavelength separation filter. Thus, as described above, when the light wave L1 is incident on the optical waveguide 71, the light wave L2 becomes a light wave of only the wavelength λ1, and the light waves of other wavelengths are totally reflected by the wavelength separation filter and split into the light wave L3. . That is, only the wavelength λ 1 is propagated through the optical waveguide 61, and the light wave L 3 other than the wavelength λ 1 is propagated through the optical fiber 80.
Further, instead of the optical waveguide substrate 60, an optical fiber or a light receiving element can be used.
Japanese Patent Laid-Open No. 9-26525 (FIG. 1, claims) JP 2002-23004 (FIG. 12, paragraphs 0091-0098)

In the optical module of Conventional Example 1, (1) The size reduction of the prism cannot be reduced due to the stress caused by the film formation of the wavelength selective filter, and is generally about 1 mm □ with a small size. Further, (2) the two optical fibers, the light source, and the prism are separated from each other, and at least three active optical axis alignments are necessary, resulting in high costs. First, the optical axes of the light source, the spherical lens, and the prism are determined, and then the XY direction and tilt alignment of the light source and the optical fiber 48 are required. Next, the XY direction and tilt alignment of the optical fiber 48 and the optical fiber 47 are required. ,
In the optical coupling structure of Conventional Example 2, (1) In general, the optical fiber and the optical waveguide substrate are different in material structure, and the difference in thermal expansion is a significant cause of deterioration in optical coupling characteristics. Further, (2) the loss due to the emission to the outside is reduced by propagating the light wave through the adhesive having the same refractive index as that of the cladding layer, but the loss due to the diffusion of the light wave is not considered.

In order to solve the above problems, the present invention
A structure for optically coupling two optical fibers,
Two optical fibers whose end faces are processed at 45 degrees with respect to the optical axis of the optical fiber;
A first reflecting surface and a second reflecting surface on which optical reflecting films or optical filters are formed on the end faces of the two optical fibers;
The mutual positional relationship between the first optical fiber and the second optical fiber is:
At least a portion of the light wave propagating through the first optical fiber and reflected by the first reflecting surface intersects the second reflecting surface;
And the positional relationship is adjusted such that at least a part of the light wave propagating through the second optical fiber and reflected by the second reflecting surface intersects the first reflecting surface. And

  In the present invention, when the coating diameter of the optical fiber is 250 μm, the interval is 250 μm. For example, when there are 32 channels, the width from end to end of the fiber is 8 mm. On the other hand, in the conventional example 1, if the length of the prism is 1 mm, the total width is 32 mm, and the size becomes four times larger. Further, in the present invention, as shown in FIG. 1, the 45 ° inclined surface on which the optical fiber and the wavelength selective filter are formed has an integral structure and the positional relationship is fixed with high accuracy. The alignment of the first oblique polishing optical fiber Assy 9 and the second oblique polishing optical fiber Assy 10 uses an accurate V-groove (± 1 μm), so that the optical axes are aligned in the XY directions with a slight stroke. That's okay. Therefore, the tilting direction that requires alignment time is not necessary due to the accuracy of the V-groove. The second oblique polishing optical fiber Assy10 and the third oblique polishing optical fiber Assy11 need only be aligned with a precise V-groove, so no alignment is required and the optical axis alignment cost can be greatly reduced. .

In addition, the present invention can provide a lens effect with a structure in which two optical fibers whose end surfaces are obliquely polished are combined back to back, thereby preventing light diffusion and reducing loss.
That is, in the present invention, the light wave reflected by the reflecting surface processed at 45 degrees with respect to the optical axis of the core of one optical fiber is once emitted in the air from the circular outer surface of the cladding layer, and then the other The light wave that has passed through the outer circular surface of the cladding layer of the optical fiber and reflected by the reflecting surface processed at 45 degrees with respect to the optical axis of the core propagates through the core. Therefore, the light emitted into the air is bent (converged) by the lens effect due to the outer surface of the clad layer and the refractive index difference between the clad layer and air, so that it can be prevented from diffusing. The efficiency can be improved and the loss can be reduced.
Since the optical fiber and the waveguide of Conventional Example 2 are generally different in material configuration, the difference in thermal expansion due to temperature change is a significant cause of performance degradation. However, the present invention is a coupling between optical fibers and is affected by thermal expansion. Performance degradation can be prevented without being received. Furthermore, it has a structure that can be easily arrayed and can be reduced in size.

FIG. 1 shows a configuration example of the optical coupling structure of the present invention. FIG. 2 is a perspective view of the optical coupling structure of FIG.
As shown in FIG. 1A, the optical fiber 1 is fixed to the V-groove substrate 4, and the end of the optical fiber 1 and the side surface of the V-groove substrate 4 are polished to 45 degrees (θ). As shown in FIGS. 1B and 2, the obliquely polished optical fiber Assy produced in this way is composed of a first obliquely polished optical fiber Assy9 and a second obliquely polished optical fiber Assy10. Are attached so as to face each other in an orthogonal direction, and the oblique polishing surface of the third oblique polishing optical fiber Assy11 is attached so as to be in contact with the oblique polishing surface of the second oblique polishing optical fiber Assy10.
The optical fiber and the V-groove substrate are usually fixed with an adhesive.
In FIG. 1 (b), the cores of the second optical fiber 7 and the third optical fiber 8 are shown to coincide with each other, but strictly speaking, as shown in FIG. The optical axis passing through the second optical film 13 is refracted. Therefore, by shifting the positions of the cores of the second optical fiber 7 and the third optical fiber 8 by the amount of positional deviation due to refraction, low-loss optical coupling is made possible. Since the refractive index of the second optical film 13 is generally higher than the refractive index of the optical fiber, θ1 (= θ3)> θ2 is obtained from Snell's law, and the light 32 is shifted downward from the light 31 by h.

FIG. 3 shows an example of the use of a wavelength division multiplexer (WDM) in a B-PON (Broadband-Passive Optical Network) system that will become the mainstream in the future in optical communication systems.
In the communication center on the station side, the video signal placed on the light having the wavelength of 1.55 μm and the light placed on the wavelength of 1.49 μm from the media converter (MC) are combined by the wavelength multi-wavelength multiplexer (WDM) 31. Sent. On the other hand, the light having a wavelength of 1.31 μm transmitted from the home side is separated by the WDM 31 and sent to the MC 33 where it is converted into an electric signal.
The light transmitted from the station side to the home side is separated by the home-side WDM 26 into light having a wavelength of 1.55 μm and light having a wavelength of 1.49 μm, and the light having a wavelength of 1.55 μm is transmitted to the video device 27 and also to a wavelength of 1.49 μm. Are sent to the MC 28 for treatment. On the other hand, light having a wavelength of 1.31 μm from the MC 28 on which data is loaded is multiplexed by the WDM 26 and transmitted to the station side.

  Here, for example, in order to achieve the WDM 26 and WDM 31 shown in FIG. 3, an optical film is formed on the 45 ° oblique polished surface of the optical fiber as shown in FIG. Type 1 shown in (a) assumes a WDM on the home side. The first optical film 12 is formed with a reflective film, and the second optical film 13 is formed with a wavelength selection filter (WDM filter). ) Is formed. This wavelength selective filter is characterized to transmit 1.55 μm and reflect short wavelength bands below 1.49 μm. Light 15 indicates received light transmitted from the station side, and is demultiplexed into transmitted light 18 and reflected light (light 17) by the second optical film formation 13. The reflected light becomes light 17 that is reflected by the first optical film 12 and propagates through the first optical fiber 6. On the other hand, the light 16 from the first optical fiber 6 is reflected by the first optical film 12, reflected by the second optical film 13, and transmitted light that propagates through the second optical fiber 7. In the embodiment of the WDM 26 shown in FIG. 3, the wavelength λ1 corresponds to 1.49 μm, the wavelength λ2 corresponds to 1.55 μm, and λ3 corresponds to 1.31 μm. Since the end face of the first optical fiber 6 is obliquely polished at 45 degrees, a reflection surface that totally reflects even without a reflection film is formed. Type 2 shown in (b) assumes a WDM on the local side. The first optical film 12 is formed with a reflective film, and the second optical film 13 is formed with a wavelength selection filter (WDM filter). ) Is formed. This wavelength selective filter has the same characteristics as the WDM on the home side. The light 20 from the second optical fiber 7 indicates the received light transmitted from the home side, is reflected by the second optical film 13, and then reflected by the first optical film 12. The optical fiber 6 is propagated.

On the other hand, the light 21 from the first optical fiber 1 is reflected by the first optical film 12, reflected by the second optical film 13, and transmitted light 22 inserted from the third optical fiber 8. The combined light is transmitted light 19 that propagates through the second optical fiber 7. Here, the wavelengths λ1 to λ3 are the same as those on the home side.
Here, in order to increase the isolation between the wavelengths λ1 and λ2 of type 1, the first optical film 12 is a wavelength selective filter for further removing the λ2 component (in the embodiment, λ2 = 1.55 μm) from the simple reflection film. May be used. In type 1 and type 2 WDM, a wavelength selective filter may be applied to the oblique polished surface of the third optical fiber in order to increase the isolation of the second optical film 13.
FIG. 4C shows the light reflected by the first (second) optical film 12 (13) formed on the obliquely polished surface of the first (second) optical fiber 6 (7). Shows a state of entering the second (first) optical fiber 7 (6). Since the light emitted from the first optical fiber 6 once exits into the air while spreading, and then enters the second optical fiber 7, the circular shape of the cross section of the optical fiber, the refractive index nc of the optical fiber, and the air The light is bent inward (converged) by the lens effect due to the difference in refractive index na (nc> na), thereby increasing the coupling efficiency and reducing the loss.
FIG. 5 shows a multi-channel optical coupling structure in which optical coupling structures are arranged and can be used on the station side.
By arranging the optical coupling structures of the present invention in this way, it is possible to achieve an array and miniaturization.

  FIG. 6 shows a columnar lens for efficiently coupling the reflected light from the obliquely polished surface of the first obliquely polished optical fiber Assy9 or the second obliquely polished optical fiber Assy10 to the core of the opposite obliquely polished optical fiber Assy. Alternatively, a refractive index distribution type optical fiber is sandwiched. The first slant polishing optical fiber Assy9 and the second slant polishing optical fiber Assy10 are cut to make it easy to sandwich the gradient index optical fiber, and the first slant polishing optical fiber Assy9 and the second slant polishing optical fiber Assy9. The optical path between the polishing optical fibers Assy10 is made shorter to reduce the coupling loss. The decision to not cut is a relationship between loss and cost.

The figure which shows the structural example of the optical coupling structure of this invention. The perspective view of the optical coupling structure of FIG. The figure explaining the usage example of the optical coupling structure of this invention. The figure explaining the optical path of the optical coupling structure of this invention. The figure which shows the structural example of the multichannel optical coupling structure of this invention. The figure which shows the structural example of the other optical coupling structure of this invention. The figure which shows the structure of the optical module of the prior art example 1. FIG. The figure which shows the structure of the optical coupling structure of the prior art example 2. FIG.

Explanation of symbols

6 ... 1st optical fiber, 7 ... 2nd optical fiber, 8 ... 3rd optical fiber, 9 ... 1st slant polishing optical fiber Assy, 10 ... 2nd Diagonal polishing optical fiber Assy, 11... Third oblique polishing optical fiber Assy, 12... First optical film formation, 13.

Claims (3)

A structure for optically coupling two optical fibers,
Two optical fibers whose end faces are processed at 45 degrees with respect to the optical axis of the optical fiber;
A first reflecting surface and a second reflecting surface on which optical reflecting films or optical filters are formed on the end faces of the two optical fibers;
The mutual positional relationship between the first optical fiber and the second optical fiber is:
At least a portion of the light wave propagating through the first optical fiber and reflected by the first reflecting surface intersects the second reflecting surface;
And the positional relationship is adjusted such that at least a part of the light wave propagating through the second optical fiber and reflected by the second reflecting surface intersects the first reflecting surface. And optical coupling structure. The optical coupling structure according to claim 1,
The second optical fiber is bonded to a third optical fiber;
The mutual positional relationship between the second optical fiber and the third optical fiber is:
The light coupling structure, wherein light transmitted through the second reflecting surface is optically coupled to a third optical fiber. The optical coupling structure according to claim 1 or 2,
An optical coupling structure, wherein the optical reflection film formed on the end face of the first optical fiber is a reflection surface without forming an optical filter.

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