JPH0425804A - Optical connecting structure - Google Patents

Abstract

PURPOSE:To improve a packaging density and to facilitate a connecting operation by inserting short-sized graded index type optical fibers to the incident and exit ends of respective single mode optical fibers and having a capillary to hold the end faces opposite to each other. CONSTITUTION:The assembly is executed by first connecting the long-sized graded index type optical fibers (GIF) 4a, 4b by welding or an adhesive matched in refractive index to the end faces of the single mode optical fibers 3a, 3b to assemble a module, then resistering the fibers by a microscope with a fine adjustment micrometr to the length of odd times the 1/4 of the pitch length determined by the refractive index distribution of the core and cutting the fibers with sufficiently high accuracy of about <=+ or -5mum. The cut GIFs 4a, 4b are inserted into the glass capillary 5 packed with an optical adhesive 5 from both sides and are fixed by adhering. The allowance for the optical axis misalignment at the connection point is increased in this way by using the GIFs and the connecting operation is facilitated.

Description

[Detailed Description of the Invention] <3 Industrial Applications> The present invention relates to an optical connection structure, and is useful when optically connecting optical components using single mode optical fibers as input/output terminals. .

<Conventional technology> Conventionally, optical connections between optical components have been realized as follows.

^) Attach an optical connector to the optical input/output terminal and connect via the connector adapter.

B) Realized by directly fusing optical fibers together.

C) Connect the optical fibers by inserting them into a high-precision capillary.

<Problem that the invention seeks to solve> The prior art as described above has the following problems.

In the case of a) above, the optical connector itself is large in size, so the mounting density of the optical components is reduced.

b) In the case of B) above, an extra connection length of several tens of anns is usually required at the time of connection, so even if the connection point itself is small, it is possible to improve the packaging density due to the space to accommodate the extra length fiber. Can not.

C] The optical fiber is a single mode optical fiber (9 lower SM
(referred to as F), the allowable amount of axis misalignment between the SMFs is ±1 to
Since the thickness is 2 μm (loss increase; at 0.5 dB), it is difficult to actually connect with low loss.

SUMMARY OF THE INVENTION In view of the problems of the prior art described above, it is an object of the present invention to provide an optical connection structure in which the connection portion is small and the packaging density is improved.

<Means for Solving the Problems> The configuration of the present invention that achieves the above object includes: a single-mode optical fiber connected to optical components on the output side and the input side; and an output end and an input end of each single-mode optical fiber. and a capillary that holds the graded index optical fibers inserted from both ends thereof with their end faces facing each other. do.

According to the present invention having the above configuration, the light propagated through the SMF on the output side enters the graded index optical fiber (hereinafter referred to as GIF) on the output side at the output end, and is transmitted by this GIF. The light is diffused, then narrowed down by the GIF on the incident side, and enters the incident end of the SMF on the incident side. Therefore, the beam spot size at the input/output end, that is, at the connection point can be enlarged compared to the case where the connection point is formed between SMFs, so the tolerance for axis misalignment between the fibers can be increased.

<Example> Embodiments of the present invention will now be described in detail based on the drawings.

<First Embodiment> As shown in FIG. 1, SMFs 3a and 3b are installed in the optical component module 2a on the output side and the optical component module 2b on the input side, which are respectively arranged on the printed circuit board 1 for mounting optical components. They are connected to each other. Short GIFs 4a and 4b are connected to the output ends and input ends of these SMFs 3a and 3b by fusion bonding or an adhesive whose refractive index is matched. At this time, the lengths of GIFs 4a and 4b are set to be an odd multiple of 1/4 of the pitch length determined by the refractive index distribution of the core. Also,
The GIFs 4a and 4b are inserted through openings at both ends of the glass capillary 5, with their end surfaces facing each other, and are fixed to the glass capillary 5 with an adhesive.

In the figure, 6 is an air vent hole formed in the glass capillary 5, and 7 is an optical adhesive filling part.

To assemble the structure of this embodiment, first, SMF3a,
A long GIF4a is provided on one end surface of 3b.

4b are connected by fusion bonding or a refractive index-matched adhesive, and then a module is assembled using these as optical input/output terminals. After the module is assembled, the GIFs 4a and 4b are cut into lengths that are an odd multiple of 1/4 of the pitch length determined by the refractive index distribution of the core. This G I F4 m.

The cutting of 4b is done by making a cut on the edge with a cutter and applying stress to tighten it. When making the cut, the GI
The lengths of F4a and 4b can be defined with sufficiently high accuracy of ±5 μrn or less. Then, the cut GIFs 4a and 4b are inserted from both sides into a glass capillary 5 filled with an optical adhesive (adhesive whose refractive index is matched to the fiber) and fixed by adhesive. Finally, for reinforcement, the glass capillary itself may be fixed to the substrate by adhesive, plate springs, or the like.

Here, the principle of increasing the axis misalignment tolerance using the GIFs 4a and 4b will be explained.

Since the signal light basically propagates within the SMFs 3g and 3b, it can be considered as a single mode Gaussian beam. The propagation of this Gaussian beam is expressed as a ray matrix (for example, YARIV
The following formula is derived from the analysis by the author "Fundamentals of Optoelectronics" etc.).

That is, the core radius as a parameter of GIF4a, 4b:
r, core refraction*: n, refraction wheel difference between core and cladding: Δ
, beam spot size in SMF 3a, 3b: ω. ,
When the signal light wavelength is λ, the pitch length of GIF4a and 4b: P=2π42Δ/r, and the length of GIF4m and 4b for this P: L=P/4 ・(2n-1)(
However, n is the value of a typical communication optical fiber in the above formula, λ = 1.3 μm, when the beam spot in GIF4 a, 4 b is a self-created vision.
, n=1.45. ω. =5μm, r625ump Δ
By substituting =0.01, Ql,,, = 10 μm and ω
. It can be seen that the image is enlarged by 2 times.

On the other hand, when there is an axis deviation of X in the direction perpendicular to the optical axis, the beam spot size: ω Gaussian beam coupling efficiency: ηo
c exp (-x” / ω2)
Saruwatari, Wataya, “Sem1eonduetor La5e
rto single-mode fiber cou
pler”APPLIEDOPT■CS vol,
18. h11. pp, 1847-1856)
. Therefore, 0.5 dB loss increase off-axis: x =
0.8d6 0.34 is derived. That is, the axis misalignment tolerance is proportional to ω.

As mentioned above, ω6.8 when attaching GIF4a and 4b
Baω. It can be seen that the axis misalignment tolerance is also doubled.

Also, ωM, , are parameters of GIF4m and 4b. Since it can be further expanded by changing the core radius + rp refractive index difference: Δ, the axis misalignment tolerance can also be further expanded.

In this way, if the axis misalignment tolerance is expanded, the processing accuracy of the glass cabi lug-5 and the accuracy during assembly will be relaxed, and a low-loss connection can be easily realized.

Note that in this embodiment, the optical module 2a.

When assembling 2b, the long G I F4 a.

4b is used as an optical input/output signal terminal, but if this is inconvenient for assembly, perform the cutting process of GIF4a and 4b first, while cutting a similar GIF to another long SMF 3a and 3b.
It is also possible to assemble the parts 4a and 4b fused together by preparing them and temporarily connecting them with a glass capillary 5 filled with matting oil instead of adhesive.

Second Embodiment> FIG. 2 is a diagram illustrating a second embodiment of the present invention.
7 to 7 are the same as in FIG. 1, 8 is a convex portion obtained by processing the core of GIF 4a into a convex spherical surface, and 9 is a concave portion obtained by processing the core of GIF 4b into a concave spherical surface. These assemblies are based on the first embodiment, but
After cutting the GIFs 4a and 4b, the end faces are processed into convex or concave spherical surfaces by selective etching.

As an etching solution for this purpose, for example, for machining a convex spherical surface, a buffered acid solution (a mixed acid of acid and ammonium fluoride) is used.
, by using fluoric acid solution for machining the concave spherical surface, GIF
The core can be selectively processed into a spherical surface.

According to this embodiment, since the core centers are automatically aligned by fitting the convex and concave portions 8 and 9, more reliable optical axis alignment can be realized.

Third Embodiment> FIG. 3 is a diagram illustrating a third embodiment of the present invention,
1 to 7 are common to Example 1, 10 is GIF4a or 4
This is a dielectric film attached to the end surface of b. This dielectric film 1
0 has an optical wavelength filter effect.

These assemblies are also basically proceeded according to the first embodiment,
After cutting GrF4m and 4b, the G! of the module on one side (the output side in Figure 3). A dielectric film 10 is formed on the end face of F4b by vapor deposition or sputtering. At this time, GIF
Care must be taken to cover the surfaces other than the end surfaces of 4b to prevent excess film from being applied and heat from being applied. Thereafter, the steps of inserting it into the glass capillary 5 and fixing it with an optical adhesive are the same as in the first embodiment.

In this example, the film was directly attached to the end surface of GIF4b, but
Alternatively, the dielectric film 10 may be attached to another glass plate, cut into small pieces, and attached to the end face of the GIF 4b. In this case G.I.
F4a.

Since the dimension between 4b increases by the thickness of the glass plate, loss increases.

From the same paper as the axis misalignment tolerance mentioned above, we derive the formula for the coupling efficiency for the misalignment of the Gaussian beam in the optical axis (Z-axis) direction: where ω is the spot size and λ is the signal wavelength.

2 is the amount of axis deviation From the above equation, it can be seen that as ω is expanded, the Z-axis tolerance is also relaxed. For example, if it is 0213 μm, Z, -1
While the loss increase at 00 μm is only 0.2 dB,
Normal SMF3 a, 3 b ((,1=5 μm
), the loss increases by approximately 2 dB.

On the other hand, it is also possible to actively utilize this increase in loss as an optical attenuator. That is, an optical attenuator can be easily constructed by inserting a quartz rod of an appropriate length between GIFs 4m and 4b. Since the light attenuated by this amount of attenuation becomes a radiation mode, it also has the advantage of less reflected back powder light.

Note that in this case as well, it is advantageous to enlarge the spot size because it is easier to adjust the amount of attenuation.

<Effects of the Invention> As specifically explained in conjunction with the above embodiments, according to the present invention, not only can a connection structure using a capillary with good workability be adopted, but also the optical axis at the connection point can be Since the displacement tolerance can be increased, the packaging density can be improved, and the connection work can also be made easier.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams conceptually showing first to third embodiments of the present invention, respectively. In the drawing, 2m and 2b are optical component modules, 3a and 3b are single mode optical fibers (SMF), and 4
m, 4b are graded index optical fibers (G
IF), 5 is a glass capillary 8 with a convex portion, 9 is a concave portion, and 10 is a dielectric film. Patent applicant: Agent of Nippon Telegraph and Telephone Corporation

Claims (5)

[Claims] (1) A single-mode optical fiber connected to the optical components on the output side and the input side, a short graded-index optical fiber connected to the output end and input end of each single-mode optical fiber, and both ends. 1. An optical connection structure comprising: a capillary that holds graded index optical fibers inserted from the respective portions with their end surfaces facing each other. (2) A convex portion is formed on the opposing end face of one graded index type optical fiber, and a recess into which the convex portion is fitted is provided on the opposite end face of the other graded index type optical fiber; The optical connection structure according to claim 1, wherein the uneven portion has an alignment function. (3) The optical connection structure according to claim 1, characterized in that a dielectric film is formed on a surface of one graded index type optical fiber that faces the other. (4) The optical connection structure according to claims 1 and 3, characterized in that a piece of glass is interposed between the opposing graded index optical fibers. (5) The length of the graded index optical fiber is an odd multiple of 1/4 of the pitch length determined by the structure of the graded index optical fiber and the signal wavelength. Optical connection structure according to items 1 to 4.