JPH05249353A - Metal coated optical fiber and its production - Google Patents

Abstract

PURPOSE:To facilitates fixing of the carbon coated optical fiber at the time of a terminal treatment and to enable the application of the fiber to a temp. sensor and image guide to be used in a high temp. atmosphere by electrolytic plating the surface of the optical fiber and providing the metallic coated layer. CONSTITUTION:An annular anode 15 is provided in a plating liquid and is connected via a power source 18 and a metallic roller 17 to serve as one cathode of rollers 16, 17 which press the optical fiber 11 to be driven so as to face the fiber and pass the fiber in a plating cell 14. The effect as the cathode is applied via the metallic roller 17 to the carbon coat layer. And the anode workes to the carbon coat layer as the cathode via the metallic roller 17 at the time of metallic coating. This roller and the anode 15 in the plating liquid 14a are energized to each other, by which a target metal is precipitated and deposited on the optical fiber surface. Namely, the surface of the carbon coat layer is first coated with the metallic layer of the thin layer by using strike plating. The electroplating treatment given the sufficient current density is executed atop the strike plating layer.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention can be easily fixed at the time of terminal processing such as axis alignment and can be applied to a temperature sensor or an image guide which can be used in a high temperature atmosphere. The present invention relates to a metal-coated optical fiber having the same and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, to fix an end of an optical fiber,
Organic adhesives, particularly epoxy adhesives, are widely used because they have little volume shrinkage after polymerization. Also, as an optical fiber that can be used under high temperature, an aluminum-coated optical fiber manufactured by using a known dip foam method is well known, and it is used in an optical fiber coated with an ultraviolet curable resin such as a temperature sensor. It is used in environments that cannot. Furthermore, in an environment where moisture intrusion is expected,
It is known that a hermetically coated fiber in which carbon is coated on the surface of the fiber is effective, and this carbon layer acts as a protective film against the atmosphere and exhibits durability particularly at a place where water may be mixed.

[0003]

However, the above-mentioned epoxy-based adhesive has the advantage that it has a relatively low shrinkage ratio after curing and is easy to handle, but it has a long mixing time and curing time, and time constraints are imposed. There is an inconvenience to receive.

Further, the dip foam method is limited in that the melting point of the metal used is a low melting point metal in the range that does not cause compositional deformation of the glass. For example, in the atmosphere of aluminum, the melting point is 660 ° C. or higher. Can not be expected to use in. Also, the difference in the coefficient of thermal expansion between metal and glass is large,
Occurrence of thermal strain at the interface is unavoidable. Further, in the above-mentioned dip foam method, the uniformity of the film thickness is extremely low, and particularly when the film is formed into a thin film, uncoated portions often occur. For this reason, it was necessary to coat the metal with a large thickness as a whole, the loss increase due to thermal strain was large, and a long sensor could not be used. In particular, since the metal coating by the dip foam method relies on the wettability of the surface, pinholes are likely to be formed, which serve as breaking points, which often lower the strength.

As a metal coating method other than the dip foam, a sputtering method, a plating method and the like are known.

[0006] The sputtering method is indispensable for processing under reduced pressure in a vacuum, and is suitable for short-length processing of substrates. However, when performing long processing or continuous processing, a stepwise pressure-reducing system provided with a large number of air chambers. However, it is difficult to implement because there are many problems in terms of operability, stability, and cost because the device becomes large in scale.

Further, there are electrolytic plating method and electroless plating method as the plating method. To deposit metal on the glass surface of the optical fiber, only the electroless plating is applied because the optical fiber is a non-conductor. I can't.

However, since the electroless plating physically maintains the vapor deposition strength at the interface between the metal and the object, it is a condition for stable coating that the surface is appropriately roughened. This is a major cause of strength deterioration in materials such as glass whose fracture probability increases due to surface scratches.

Further, it is known that the metal initially deposited by electroless plating has a self-shrinking property, and therefore has a hardness twice or more that of the metal deposited by electrolytic plating. For example, Ni metal deposited by electroless plating has a Vickers hardness of about 500, and N having a Vickers hardness of about 200 deposited by electrolytic plating.
It has about 2.5 times the hardness of i-metal. Electroless Ni
Although the layer has high hardness, it exhibits relatively brittle characteristics when it is present alone.

The self-shrinking metal layer can be relaxed by heat treatment, but since it is a high temperature treatment of 600 ° C. or higher, its influence on the fiber layer cannot be ignored. In fact, in a sample obtained by subjecting a fiber having a smooth surface to electroless plating, the metal layer exhibits a pod-like cracking manner with a crack in the fiber axis direction during cutting, and the stability between fiber coat layers may be low. It has been confirmed.

As a result of various studies to solve the above problems, the present inventors have found that the known carbon-coated optical fiber has excellent environmental properties, but the carbon layer itself is relatively weak against external damage and is a resin for protection. Coating is essential and not suitable for use at high temperatures. It was found that the carbon coating layer on the surface of the optical fiber formed by this conventional method usually has a thickness of about 500Å and does not have sufficient conductivity, but electrolytic plating can be performed by using this as a conductive layer. ..

The present invention has been made based on the above findings, and can be applied to a temperature sensor or an image guide which can be easily fixed at the time of terminal processing and can be used in a high temperature atmosphere.
An object of the present invention is to provide a metal-coated optical fiber having high environment resistance and a method for producing the same.

[0013]

In the metal-coated optical fiber according to the present invention, the metal-coated layer is provided on the surface of the carbon-coated optical fiber by electrolytic plating to solve the problem.

The metal coat layer may be a plurality of layers, and an Au layer may be provided on the outermost surface. Further thickness 1-5
It is preferable to have an electrolytically plated Ni layer having a thickness of μm and an Au layer having a thickness of 0.1 to 1 μm provided on the outermost surface.

In the method for producing a metal-coated optical fiber, the carbon coat on the outer surface of the carbon-coated optical fiber is used as a conductor to apply a first metal coat layer by strike electrolytic plating, and then this metal coat is used as a conductor.
Having a step of forming the second metal coat layer by electrolytic plating was taken as a means for solving the problem.

[0016]

In the metal coated optical fiber according to the present invention, the carbon coated optical fiber is electrolytically plated. At that time, the conductivity of the carbon layer is low, and the deposition rate of the metal is low, but a stable metal film is obtained. Since this metal film acts as a conductor, in the subsequent steps, a multilayer film having a desired thickness is obtained. The metal coating of the membrane is possible.

[0017]

[Embodiment] An ordinary carbon-coated fiber in which a raw material gas is pyrolyzed and a carbon coating is applied to the surface of the optical fiber is used, and electrolytic plating is performed using the carbon-coat layer as a conductor, but sufficient conductivity is not maintained. Therefore, a multi-stage electrolytic plating method is adopted.

FIG. 1 is a cross-sectional view of a metal-coated optical fiber according to the present invention, in which a carbon layer 3 is formed on the outer surface of a clad 2 having a core 1 in the center, and a metal layer deposited by electrolytic plating is present on the outside thereof. .. The outline of the dimensions of the above parts is as follows: core: about 10 μm, clad: about 125 μm,
The carbon coat layer has a thickness of about 0.5 μm, and the metal layer has a thickness of about 5 μm. FIG. 2 is a schematic diagram showing an example of a metal-coated optical fiber according to the present invention and an electrolytic plating apparatus used in the method for producing the same. Reference numeral 11 in the drawing is passed between a take-up drum 12 and a delivery drum 13. It is a carbon coated optical fiber. The optical fiber 11 delivered from the delivery drum 13 passes through the plating solution 14a in the plating tank 14 and is wound up on the take-up drum 12. An annular anode 15 is provided in the plating solution, and a metal roller 17 that serves as one cathode of rollers 16 and 17 that presses the driven optical fiber 11 in opposition to allow it to pass through the plating tank 14 and a power supply 18. Connected. The roller 16 is insulated.

In order to perform metal coating using this apparatus, a function as a cathode is given to the carbon coating layer through the metal roller 17 and an electric current is applied between the carbon coating layer and the anode 15 in the plating solution 14a to make the surface of the optical fiber. The target metal is deposited and deposited on.

That is, as a first step, a thin metal layer is coated on the carbon coat layer surface by using strike plating. Strike plating is a method of cleaning and activating the surface with hydrogen gas generated in a liquid. Although the deposition rate is low, a stable metal film can be obtained even when the surface has low conductivity. The metal film coated by strike plating is a thin film of about 0.1 to 1 μm, and the presence of this primary metal layer gives the surface sufficient conductivity.

Next, as a second step, electrolytic plating treatment with a sufficient current density is performed on the upper surface of the strike plating layer. The coating film thickness is determined by the current density and the processing time, that is, the linear velocity of the fiber passing through the processing layer. Since the surface resistance is uniquely determined by the material to be coated, it is necessary to slow the linear velocity or lengthen the processing time in order to obtain the film thickness. The former leads to deterioration in productivity, so the processing time was adjusted.
For this reason, a continuous treatment method is used in which the plating treatment layers are arranged in tandem in the axial direction.

By adopting electrolytic plating, the types of applicable metals are widened, and among these, high melting point, high melting point materials as heat-resistant optical fiber parts and versatile materials for solderable optical fiber parts. In addition, Ni and Cu having excellent solderability were selected. The solderability was determined based on the determination of the solder wettability of the surface and the solder erosion property associated with soldering.

The soldering corresponds to an alloy reaction between the solder and the target metal, and when the alloy formation region reaches the metal-coated interface, delamination is likely to occur. For solder erosion, it was determined whether or not peeling would occur with soldering. As a result of the determination, it was found that the plating coat thickness that does not cause peeling by soldering is 2 μm or more for Ni, and Cu has a slightly larger amount of solder erosion than Ni, and a coat thickness of 7 μm or more is required.

It is desirable that the metal-coated fiber used for the sensor has excellent loss characteristics at room temperature and that the loss increase due to temperature change is suppressed as low as possible. Also, when considering it as a terminal component, it is preferable that the loss of the component is kept as low as possible when used in an optical communication system.

Further, a metal exhibiting excellent characteristics as a heat-resistant material has a coefficient of thermal expansion significantly different from that of silica-based glass constituting the fiber. Therefore, the strain generated by the difference in the coefficient of thermal expansion may increase the loss. Since the absolute amount of stress strain is a function of the cross-sectional area of each region, it is necessary to reduce the absolute cross-sectional area of the metal layer in order to keep the loss increase due to temperature rise low.

Ni was used as a coating material in order to set the coating layer thin without impairing the solderability. Three
By coating Ni with a thickness of μm, it provides sufficient solderability and, after including loss increase due to metal coating, 0.6 dB /
A low loss fiber of less than km was obtained. In addition, since the thickness was reduced to about 3 μm, the existing fiber cutter could be used at the time of cutting, and the handleability did not deteriorate.

It has been found that Ni has a good solderability immediately after coating, whereas it is easily oxidized by oxygen in the atmosphere, and the oxidized Ni deteriorates the solderability extremely. Further, in the case of Cu, it is known that the oxide layer can be removed by using the flux even after it has been oxidized, and there is no problem. However, it is known that Ni oxide is very difficult to remove by the flux. To solve this problem, Au is preferably provided as an overcoat layer in order to apply the Ni-coated fiber as a terminal component for soldering in particular.

Au is used for both electrolytic plating and electroless plating.
It is a material that is easy to apply, and the method is properly used depending on the case. Electroless plating is suitable for processing short objects, and electrolytic plating is suitable for online long processing. Au exhibits excellent stability in the atmosphere and is a very excellent material in a corrosive atmosphere. Furthermore, the solder wettability is also very excellent. However, since solder erosion is very high, when used alone, almost all becomes an alloy layer with the solder, so in practice 1
A coat thickness of 00 μm or more is required. By using this as an overcoat layer in combination with Ni, it became possible to give excellent surface wettability and slight solder erosion. The Au layer overcoated is
If it is 0.1 μm or more, it is possible to sufficiently provide the desired corrosion resistance and oxidation resistance. It was also possible to combine this with Cu, and it was also possible to give corrosion resistance.

In the application of the present invention, it suffices that a carbon coat, which is a conductive layer, be present on the surface, and the identity of the base fiber is not relevant. Fibers often used for sensor applications include single-mode fibers, dispersion-shifted fibers, and pure silica core fibers, but they could be applied to any fiber. Further, regarding the fiber bundle used for the image guide, it is possible to produce the heat resistant image guide coated with the heat resistant metal by applying the carbon coating on the surface. As an application example, by controlling the thickness of the Cu layer coated on the surface, it becomes possible to manufacture an optical fiber capable of conducting electricity to the surface layer.

Experimental Examples 1 to 4 Cu and Ni were used as target metals in order to provide good solderability to the fiber as an optical component. Regarding the solderability of the sample, the wettability of the surface was evaluated using the global method, and the stability was evaluated by performing a peeling test after soldering. Table 1 shows the characteristics of each sample in which the coat thickness was changed.

[0031]

[Table 1]

It is known that the soldering is an alloy forming reaction between the coating material and the solder, and when the alloy layer of the target metal and the solder generated by the solder reaches the carbon layer, peeling easily occurs. In the case of Cu, since the alloy formation rate is high, it is necessary to set the coating layer thick in order to prevent peeling, and it is found that the increase in transmission loss due to the heat shrinkage strain between the metal coating layer and the glass layer cannot be ignored. did. N
In the case of i, it was confirmed that by providing a coating layer having a thickness of about 3 μm, stable soldering characteristics without peeling were obtained. However, Ni was susceptible to surface oxidation, and it was observed that the wettability of the surface was significantly deteriorated with the oxidation.
We applied 0.2 μm A by electroless plating on the Ni surface.
It was confirmed that by overcoating u, deterioration of wettability due to aging can be prevented.

[0033]

As described above, the metal-coated optical fiber according to the present invention is capable of metal coating of 10 μm or less without uneven thickness or coating unevenness not only in the circumferential direction but also in the length direction. The metal can be selected from a wide range according to. Further, since the metal film formed by strike electroplating is provided on the primary layer, it is possible to obtain a stable metal layer having stable characteristics, little change over time, excellent handleability, and no peeling at the glass-metal interface.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a metal-coated optical fiber according to the present invention.

FIG. 2 is a schematic view showing an example of an electrolytic plating apparatus used for producing the metal-coated optical fiber of the present invention.

[Explanation of symbols]

1 ... Core, 2 ... Clad, 3 ... Carbon coat layer, 4 ...
Metal layer, 11 ... Carbon coated optical fiber (optical fiber), 12 ... Take-up drum, 13 ... Delivery drum, 1
4 ... Plating tank, 14a ... Plating liquid, 15 ... Anode, 1
6 ... Roller, 17 ... Metal roller (cathode), 18 ... Power supply

Claims (5)

[Claims] 1. A metal-coated optical fiber comprising a metal-coated layer formed by electrolytic plating on the surface of the carbon-coated optical fiber. 2. The metal-coated optical fiber according to claim 1, wherein the metal-coated layer is a multilayer. 3. The metal-coated optical fiber according to claim 1, wherein an Au layer is provided on the outermost surface of the electroplated metal-coated layer. 4. Electroplated Ni having a thickness of 1 to 5 μm
The metal-coated optical fiber according to claim 1, which has a layer and an Au layer having a thickness of 0.1 to 1 μm provided on the outermost surface. 5. A first metal coating layer is formed on the outer surface of the carbon coated optical fiber by strike electrolytic plating,
Next, a method for producing a metal-coated optical fiber, which comprises a step of forming a second metal-coated layer by electrolytic plating.