JPS583B2 - Introduction structure of optical fiber to repeater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure for introducing an optical fiber of an optical transmission cable into a repeater thereof, and particularly to a repeater of an optical transmission cable housed in a pressure-resistant container and laid in the deep sea. This is a suitable structure for use.

Pressure-resistant containers that house and protect repeaters of information transmission cables laid on the ocean floor, etc. generally must be made of materials and structures that can withstand use for 20 years or more, and in particular When cables are installed on the seabed at a depth of 1,000 meters, pressure resistance and airtightness are extremely important at the point where the cable is introduced to the repeater inside the pressure vessel.

By the way, optical fibers are attracting attention as an information transmission medium that can replace conventional copper wires due to their broadband properties and economic efficiency. Because it is thin, when connecting it to the repeater body housed in a pressure-resistant container, it is necessary to ensure that the external force acting on this optical fiber is applied uniformly to the entire outer circumference and that there is a water permeation path along the outer circumference of this optical fiber. A structure is required to block the damage, but there has been no structure that satisfies these conditions.

In view of the above points, the present invention has been developed so that when an optical fiber is introduced into a repeater main body housed in a pressure-resistant container, an external force acting on the optical fiber is uniformly applied to the entire outer periphery of the optical fiber, and the outer periphery of the optical fiber is An object of the present invention is to provide a structure for introducing an optical fiber into a repeater that can reliably block a water permeation path along a repeater.

The structure for introducing an optical fiber into a repeater according to the present invention that achieves this object is to tightly join an introduction tube to a pressure-resistant container in which a repeater main body is housed, and to tightly fit a connecting fitting into this introduction tube. the other end surface of the introduction optical fiber whose one end is connected to the repeater main body is brought into close contact with the condenser lens, and the signal light from the transmission optical fiber is condensed and guided to the introduction optical fiber. A condensing lens is tightly attached within the introducing tube, and the coupling fitting is configured such that one end surface of the transmission optical fiber faces the other end surface of the introducing optical fiber, sandwiching the condensing lens within the introducing tube. One end of the transmission optical fiber is passed through the introduction tube into the introduction tube, and the introduction tube is filled with a filling liquid. Furthermore, a hole communicating with the outside is formed in the connecting fitting, and this external pressure and the introduction tube are A movable plug is slidably attached to the hole so that the pressure of the filling liquid in the hole becomes equal to the pressure of the filling liquid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a structure for introducing optical fibers into a repeater according to the present invention will be described in detail below with reference to drawings showing a cross-sectional structure thereof.

A repeater main body 11 consisting of a large number of electrical circuits (not shown) is housed in a pressure-resistant container 12 that protects it airtight.
An introduction tube 15 is tightly joined to a conical opening 14 formed in an end plate 13 that constitutes a part of the pressure vessel 12 .

This introduction tube 15 is firmly fixed to the end plate 13 by an annular fixing nut 16 screwed into the end plate 13, and in this embodiment, it is tightly fitted and tightly held to keep the inside of the pressure vessel 12 airtight. The end plate 13 is designed to prevent seawater from entering the conical opening 14 of the end plate 13 and the conical portion of the introducing tube 15 having a corresponding shape and corroding these portions.
An O-ring 17 is interposed between the introduction tube 15 and the introduction tube 15.

Additionally, a connecting fitting 1 that tightly fits into this introduction tube 15 is provided.
8 is securely fixed to the introduction tube 15 by a set screw 19 screwed into the introduction tube 15, and this coupling fitting 18 has one end of a transmission optical fiber 20 whose one end surface is located inside the introduction tube 15. The part is penetrated.

An adhesive 21 such as an epoxy adhesive is filled between the coupling fittings 18 and the transmission optical fiber 20 to bond them together, so that the transmission optical fiber 20 is fixed to the coupling fitting 18. ing.

On the other hand, a condensing lens 22 that condenses the signal light from the transmission optical fiber 20 is tightly attached inside the introduction tube 15. The other end surface of the introduction optical fiber 23 which is connected and transmits the signal light from the transmission optical fiber 20 to this repeater main body 11 passes through the opening 14 of the end plate 13 and sandwiches the condensing lens 22 for transmission. It is in close contact with one end surface of the optical fiber 20 so as to face it.

A filling liquid 25 is sealed in the introduction tube 15 between one end surface of the transmission optical fiber 20 and the condensing lens 22, and is injected from an injection hole 24 formed in the introduction tube 15. 24 is hermetically sealed by a watertight plug 26 that is screwed here.

In order to prevent this filling liquid 25 from leaking from between the introduction cylinder 15 and the connecting fitting 18, an O-ring 27 is interposed between them, and so that the filling liquid 25 is always equal to the external pressure. A movable stopper 28, one end of which is located on the filling liquid 25 side and the other end located outside, is slidably fitted into a hole 29 formed in the connecting fitting 18.

In addition, in the present invention, since the optical fiber is divided into the transmission optical fiber 20 and the introduction optical fiber 23, transmission loss of the signal light cannot be avoided. In addition to using the filling liquid 25 with a refractive index that takes into account reflection on surfaces, the material and shape of the condenser lens 22 and the shape of the other end surface of the introduction optical fiber 23 that is in close contact with the condenser lens 22 are designed to reduce scattering. By,
This loss can be reduced to a level that poses no problem in practice.

The signal light from the transmission optical fiber 20 passes through the filling liquid 25, is focused by the condenser lens 22, and is transmitted from the introduction optical fiber 20 into the repeater main body 11.

On the other hand, the filling liquid 25 becomes equal to the pressure of the seawater, etc. due to the action of the movable stopper 28, making it difficult for external seawater, water vapor, etc. to penetrate into the introduction tube 15 along the outer periphery of the transmission optical fiber 20. Moreover, even if it permeates and mixes into the filling liquid 25, the condenser lens 22 and the introduction tube 15 come into close surface contact, and at the same time the condenser lens 22 is pressed toward the introduction tube 15 by the pressure of the filling liquid 25. Therefore, there is no risk of it entering the pressure vessel 12.

Furthermore, since no uneven force is applied to the optical fiber, deformation and stress occurring in the optical fiber are reduced, making it possible to obtain stable transmission characteristics over a long period of time.

As described above, according to the structure for introducing an optical fiber into a repeater of the present invention, the optical fiber is divided into two fibers, one for transmission and one for introduction, and a filling liquid having a pressure equal to the external pressure is interposed between them. Since the curved surface of the condensing lens is used to create an airtight seal between the filling liquid and the pressure-resistant container, the water permeation path along the outer periphery of the optical fiber is reliably blocked.

In addition, a movable stopper is attached to the connecting fitting so that the introduction tube is filled with a filling liquid and the pressure of this filling liquid is equal to the external pressure, so an equal external force is applied to the outer periphery of the optical fiber, causing pressure inside the optical fiber. Since it becomes possible to uniformly disperse the generated stress, the life and characteristics of the optical fiber can be maintained constant for a long period of time.

[Brief explanation of the drawing]

The drawing is a sectional view showing the structure of an embodiment of the structure for introducing optical fibers into a repeater according to the present invention. In the drawing, 11 is a repeater body, 12 is a pressure container, 15 is an introduction tube, 18 is a connecting fitting, 20 is a transmission optical fiber, 21
22 is an adhesive, 22 is a condensing lens, 23 is an optical fiber for introduction, 25 is a filling liquid, 28 is a movable stopper, and 29 is a hole.

Claims (1)

[Claims] 1. An introduction tube is tightly joined to a pressure-resistant container in which a repeater main body is housed, and a connecting fitting is tightly fitted and fixed to this introduction tube, and the other end surface of an introduction optical fiber whose one end is connected to the repeater main body. The condenser lens is closely attached to the condenser lens, and the condenser lens is tightly attached in the introduction tube to condense the signal light from the transmission optical fiber and guide it to the introduction optical fiber,
One end of the transmission optical fiber is inserted into the introduction tube from the connecting fitting so that one end surface of the transmission optical fiber sandwiches the condenser lens within the introduction tube and faces the other end surface of the introduction optical fiber. and filling the inside of the introduction cylinder with the filling liquid, and further forming a hole communicating with the outside in the connecting fitting so that the external pressure and the pressure of the filling liquid in the introduction cylinder are equal. A structure for introducing an optical fiber into a repeater, characterized in that a movable stopper is slidably attached to the hole.