JPH0484110A - Light control element built-in type member for optical transmission - Google Patents

Abstract

PURPOSE:To obtain the optical transmission member which is excellent in productivity while the member is of an integral type and is low in excess loss by forming a part in contact with the notched part of an optical fiber as a part expanded in core diameter without changing the outside diameter. CONSTITUTION:The core 11 in the prescribed section of the optical fiber 10 is heated by a flame 81 of a microtorch 8 to the extent that the optical fiber 10 is not melted and deformed to expand and dopant contained in the core 11. The part 14 where the diameter of the core is expanded is then formed substantially in the core 11 and the V value is changed as well. The free and easy expansion of the mode field diameter DI of the part 14 where the diameter of the core is expanded to, for example, about 40mum is possible. The optical transmission member which is of the integral type and is low in the excess loss is obtd. with the high productivity in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical transmission member with a built-in optical control element used for optical fiber transmission lines, optical fiber connectors, and the like.

<Background Art> With the progress of light wave technology, optical fiber transmission systems for optical signals and optical energy are being used in various fields. Especially in systems that transmit optical signals,
So-called optical control elements, which have the function of selecting and transmitting an optical signal of a specific wavelength from among many optical signals of different wavelengths or attenuating the amplitude of an optical signal, have come to be used in various places. ing.

As a light control element, for example, one in which metal or the like is deposited in a thin film on the surface of a plate-shaped transparent material (glass or the like) is often used. By changing the material and thickness of the deposited metal, as well as the number of thin films, it is possible to function as a filter that selects and transmits an optical signal with a specific wavelength from among many types of optical signals, or to change the function of an optical signal. It can function as an optical fixed attenuator that attenuates the amplitude.

In order to improve workability, optical control elements are usually installed in some kind of component in an optical fiber transmission line, or in an optical connector that connects optical fibers. . As a conventional example of such a device, as described in Japanese Patent Application No. 63-252000 (hereinafter referred to as a reference), a ferrule containing an optical fiber is provided with a notch deep enough to cut the optical fiber, and the notch is There is a "light transmission member characterized by inserting a light control element".

Since the ferrule of such a transmission member is required to have a shape accuracy of sub-μm, a highly hard material such as zirconia or alumina is used. Therefore, the notch is processed using a thin-walled precision rotating saw coated with diamond abrasive grains. In this case, in order to ensure manufacturability, it is desirable that the width of the notch is equal to or larger than IM.

<Problems to be Solved by the Invention> By the way, in the conventional technology, especially when used in a system using a single mode fiber, the width of the notch must be made extremely narrow in order to reduce excessive loss, which will be described later. There was a problem.

Hereinafter, the relationship between the gap of the notch and the excess loss will be explained using the schematic diagram of FIG. 8 and the graph of FIG. 9.

In FIG. 8, 10 is an optical fiber fitted into a ferrule 2o, and a notch 30 is formed in the center of the figure. That is, this is equivalent to optical fibers 10 and 10' having the same Mole field diameter facing each other with a gap t. The Mohrfield diameter is the diameter of light propagating in the core 11 of the optical fiber 10, and is obtained by the formula described later, but its value is determined by the diameter d of the core 11 and the path distance - Therefore, in the figure, the Mohrfield diameter and the core diameter d are shown as being the same.

The light that has been guided within the core 11 is transferred to one optical fiber 10.
After exiting from the end face 13 with an aperture angle (referred to as NA, approximately represented by the refractive index difference Δ between the core 11 and the cladding 12), it travels inside the notch 30 while expanding, and the end face 13" and enters the other optical fiber 10'. At this time, the light is spreading, so a part of it enters the core 11".
The other light beams are incident on the cladding 12'. The light incident on the core 11' is transmitted, but the light incident on the cladding 12' is scattered to the outside from the optical fiber 11' and is not transmitted.

Therefore, the light incident on the cladding 12° has an excess loss (
Transmission loss due to gap) is L.

FIG. 9 shows the relationship between the gap t and excess loss when the wavelength of light is 1.3 μm and the refractive index of the cladding 12 is 1.46 (for example, D, t4ARCUSS: r
Loss Analysis of Single-
Mode Fiber 5price”, BSTJ, p.
p, 703-718, vo156, No, 5.197
7 (according to 221, (23), etc.).

In a normal single mode optical fiber, the mode field diameter is about 10 μm, and in FIG. 9, the relationship between the gap t and the excess loss is represented by a line a.

As the gap t increases, the excess loss naturally increases, and the gap t
is 0.5M, the excess loss is about 10dB. When designing a light control element such as a wavelength filter, it is required that the excess loss is, for example, 1 dB or less, and the gap t
must be approximately 0.1M or less.

Therefore, in order to realize an optical transmission member with a built-in light control element having such dimensions and shape, it is essential that the processing width of the notch is approximately 0.1M, and the above-mentioned reference also states that The width of the notch is, for example, 0-15 mm. In this way, the width of the notch is set to about 0.1, and the depth is set to about 0.1, for example, about the radius of the ferrule.
It is very difficult to process a groove as narrow as 15 wun using conventional techniques, which has the drawback of increasing the manufacturing cost of the member.

On the other hand, as described in the reference, there is a method in which the above-mentioned optical transmission member is manufactured by sandwiching a light control element between two independent ferrules, rather than by providing a notch in the ferrule. However, in this case, in order to prevent transmission loss due to misalignment of the center axes of both ferrules, in addition to the shape accuracy of each ferrule, the holding accuracy of the optical fiber within the ferrule and the alignment accuracy between both ferrules must be sub-optimal. μm, which has the disadvantage of being expensive and making it difficult to guarantee reliability. In addition, this method required a member (alignment sleeve) to align the two ferrules, and the length of the optical transmission member was twice the length of a single ferrule, resulting in a long length. .

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical transmission member with a built-in light control element that is integrated, has low excess loss, and has excellent productivity.

<Means for Solving the Problem> Therefore, in order to solve this problem, the present invention provides a cylindrical ferrule with an optical fiber arranged in the center, and a ferrule formed on the side surface of the ferrule to cut the optical fiber. In an optical transmission member with a built-in light control element having a deep notch and a plate-shaped light control element inserted and fixed into the notch, a portion of the optical fiber that comes into contact with the notch The present invention proposes an optical transmission member with a built-in optical control element, characterized in that the core diameter is expanded without changing the outer diameter.

Effect> Since the core diameter is enlarged, the mode field diameter also increases, making it possible to reduce excess loss even if the gap is increased.

<Example> An embodiment of the present invention will be specifically described based on the drawings.

1 to 5 relate to a first embodiment of the present invention, in which FIG. 1 shows a method of increasing the mode field diameter without changing the outer diameter of the optical fiber, and FIGS. 4 shows a cross-sectional view of the embodiment, FIG. 4 shows a perspective view, and FIG. 5 shows an enlarged view of the vicinity of the enlarged core diameter portion.

Figure 1 ((support) shows the optical fiber 10 before the core 11 is expanded. - the characteristic constant of the optical fiber determined from the wavelength, etc.), and is determined by the following formula (the above, D, MARC
USS: Loss Ana, 1ysis of Si
ngle-Mode Fiber Sp! 1c-eJ. ).

D= (0,65+1.62・V-””+2.88・■
-6)・d In a normal single mode optical fiber, the core diameter is about 9μI'n, the value of V is about 2.4, and D is 10μ
It is about m. FIG. 1(f) schematically shows the principle of a method for enlarging the core 11 of the optical fiber 10. is heated to such an extent that it does not melt and deform, and the dopant (additive for increasing the refractive index of the core) contained in the core 11 is diffused.As a result, a core diameter enlarged portion 14 is substantially formed in the core 11. The V value also changes, and the mode field diameter D1 of the core diameter enlarged portion 14 can be freely and easily enlarged to, for example, about 40 μm.

The optical fiber 10 with the enlarged core diameter portion 14 formed in this manner is attached to the ferrule 20 as shown in FIG. 2(a). In the ferrule 20, a through hole 25 having the outer diameter and the diameter of the optical fiber 10 is precisely formed in the center of the ferrule 20, and the optical fiber 10 is passed through the through hole 25, as shown in FIG. As shown in FIG. 2 (→ middle, enlarged view of part A), the core diameter enlarged portion 14 of the optical fiber
is attached to the ferrule 20 so that it is at a predetermined position (the position of the narrow diameter part 23 in FIG. 2(a)), and
The ferrule 2o is fixed by a polishing or the like, and the end surface 21 of the ferrule 2o is subjected to an end treatment such as polishing.

After the optical fiber 10 is inserted and fixed into the ferrule 20, a notch 30 is formed at a position corresponding to the enlarged core diameter portion 14, as shown in FIG.

In the figure, 24 is a collar formed at the end of the ferrule 20, and is used for locking in a plug or the like. In this embodiment, the mode field diameter D1 of the core diameter enlarged portion 14 is set to 40 μm so that the width of the notch 30, that is, the gap tJ, is determined from FIG. Therefore, the relationship between the gap t and excess loss is represented by a line in FIG. Therefore, for example, when setting the excess loss to 1 dB or less, the conventional
The gap t, which was about m, could be increased by more than 10 times to about 1 mm or more. Therefore, it has become possible to process the notch 3o using a device with good processability, such as a so-called diamond saw, which could not be used due to its poor productivity for processing a gap t of about 0.1 mm.

After processing the notch 30, the light control element 40 is mounted and fixed in the notch 30, as shown in FIG. Light control element 4
The thickness of 0 is slightly smaller than the gap t so that it can be inserted into the notch 30.

In the light control element 40, a light control surface 42 is formed on one or both sides of a main body 41, such as a thin film formed by vapor-depositing metal or the like. The light control surface 42 controls the material to be deposited, the number of deposited layers,
Depending on the vapor deposition method, etc., various functions can be realized, such as attenuating the transmitted light or transmitting only a specific wavelength.

FIG. 5(a) is a schematic diagram for explaining the state in which the light control element 40 is attached to the notch 3° in this embodiment. 14 is a schematic diagram showing a state in which a conventional optical fiber 10 without a fiber 14 is used.

In either case, the light control element 4o is arranged in the notch 30 so that the light control surface 42 is between the end faces 13.degree. 13' of the optical fiber 10.10'. The gap between the notch 30 and the light control element 40 is air in this example, but if it is necessary to reduce light reflection at the light control element 40 or the end surfaces 1B and 13', the refractive index may be changed to the core 11. Fill with refractive index matching agent or adhesive set the same as .

In this embodiment, as shown in FIG. 5, the light that has passed through the core 11 of the optical fiber 10 is
The mode field diameter D1 is expanded and the light is emitted from the end face 13, passes through the light control surface 42 of the light control element 40, and the light is attenuated or a specific wavelength is selected. After that, main body 4
1, enters the enlarged core diameter portion 14' of the optical fiber 10' from the end face 13°, and is transmitted to the core 11'. The optical fibers 10°10'' are originally the same optical fiber and are placed in the same through holes 25 and 25', so there is no misalignment or angular bending in the central axes of the optical fibers 10, 10'. In addition, the divergence angle (NA) emitted from the end face 13 is different from that of the core 14 due to dopant diffusion.
Due to the reduction in the refractive index difference between the cladding 12 and the cladding 12, the refractive index difference is smaller than that of a normal one. Due to these and the large mode field diameter D1 of the core diameter enlarged portion 14, the end face 13'
Most of the incident light passes through the core diameter enlarged portion 14', is focused on the core 11', and is transmitted. In other words, transmission is performed with significantly less loss than in the conventional system in which the core 11 shown in FIG. 5 is not enlarged.

The ferrule 20 of this embodiment is used by being incorporated into a plug 60 of an optical connector, as shown in FIG. 6 (quoted from the proceedings of the 1986 National Conference of the Institute of Electronics, Information and Communication Engineers).

In the figure, 50 is an adapter, and 51 is an alignment sleeve.

FIG. 7 relates to a second embodiment of the present invention, in which FIG. 7(a) shows the structure of an individual ferrule 70 in partial cross section, and FIG. be.

As shown in FIG. 7 (to), in this embodiment, the optical fiber 10 having the enlarged core diameter portion 14 is fixed to an individual ferrule 70.The individual ferrule corresponding to the enlarged core diameter portion 14 of the optical fiber 10 A notch 30 is formed at a portion 70, and a light control element 40 is mounted in the notch 30.

Both ends 26,26' of the individual ferrules 70 are polished. The light control element 40 is formed with a light control surface 42 corresponding to the required function, similar to that described above.

In this embodiment, after this individual ferrule 70 incorporating the light control element 40 is placed in the alignment sleeve 51 in the adapter 50, the plugs 60, 60' are inserted from both sides thereof. As a result, when light is transmitted from the ferrule 61 in the plug 60 via the individual ferrule 70 to the ferrule 61° in the plug 60°, the light control element 40 controls the light. With this configuration, the light control function can be easily changed by appropriately replacing the individual ferrules 70 arranged in the adapter 50 with ones having the desired light control element 40. .

<Effects of the Invention> As described above in detail based on the embodiments, according to the present invention, an integrated optical transmission member with a built-in optical control element having low excess loss can be manufactured with high productivity. Therefore, it becomes possible to realize various types of light control that will become increasingly necessary in the future at a low cost. In addition, since the ferrule is integrated, for example, when you want to block only the monitor light in a device that uses two wavelengths, 0TDR signal light and monitor light, you can use the ferrule to which the present invention is applied to the optical connector plug at the tip of the device. By incorporating it, it is possible to perform this without requiring a complicated configuration.

On the other hand, in systems that require various types of light control,
By adopting the configuration as shown in the embodiment, it is possible to easily and flexibly change the light control function by replacing the individual ferrules.

[Brief explanation of the drawing]

1 to 5 relate to the first embodiment of the present invention, and FIG. 1 is an explanatory diagram showing a method of increasing the mode field diameter without changing the outer diameter of the optical fiber, and FIG. FIG. 3 is a sectional view of the embodiment, FIG. 4 is a perspective view, and FIG. 5 is an enlarged view of the vicinity of the enlarged core diameter portion. FIG. 6 is a perspective view of an optical fiber connector, FIG. 7 is a second embodiment of the present invention, and FIG. 7(a) is a partial sectional view showing the structure of an individual ferrule. Figure 7 is a schematic diagram showing how to use it. Figure 8 is a schematic diagram of light propagation when there is a gap t between fibers with the mode field diameter, and Figure 9 is a diagram showing the mode field diameter. This is a graph showing the relationship between the gap t and excess loss when the diameter is taken as a constant. In the drawing, 10 is the core of the optical fiber 11, 12 is the cladding, 14 is the core diameter enlarged part, O is the ferrule, and 5 is the core. Through hole, O is notch, 0 is light control element, O is adapter, 0 is plug, 0 is individual ferrule.

Claims (1)

[Claims] A cylindrical ferrule with an optical fiber placed in the center,
An optical transmission member with a built-in optical control element, comprising a notch formed on the side surface of the ferrule and having a depth to cut the optical fiber, and a plate-shaped light control element inserted and fixed into the notch. An optical transmission member with a built-in light control element, characterized in that the core diameter of the portion of the optical fiber that comes into contact with the notch portion is expanded without changing the outer diameter.