JPH03187937A - Miniature electric furnace for processing optical fiber - Google Patents

Abstract

PURPOSE:To improve the reproducibility of temperature distribution and that of the processed form of an optical fiber by using a furnace core tube and closely attaching a metal foil to the surface of the core tube or forming a metal thin film on the surface and heating the metal foil, etc., by passing electric current to heat the furnace core tube. CONSTITUTION:A metal foil 3 (e.g. platinum foil) is used as a heating material and closely attached to the surface of a furnace core tube 1 (e.g. alumina insulation tube) having both opened ends or a metal thin film 7 (e.g. platinum film) is formed on the surface to obtain a miniature electric furnace for processing an optical fiber. Electric current is passed through the metal foil 3 or the metal thin film 7 to heat the furnace core tube 1 by the generated heat. An optical fiber 4 is introduced into the furnace core tube 1 to perform the thermal processing such as drawing or welding of the optical fiber 4. The use of the furnace core tube 1 is effective in reducing the size of the apparatus and preventing the influence of wind pressure to cause the bending of the optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a small electric furnace for heating and processing one or more optical fibers.

[Prior Art] Conventionally, small gas burners and discharge heating have been used to heat optical fibers for drawing and fusing.

Small gas burners have the following problems.

■Flame is a chemical reaction, and the temperature of the flame varies depending on the type of gas; even if the same gas contains more oxygen, the temperature will be higher.

The temperature of the flame has nothing to do with the size of the flame. The temperature of the outer flame part of the Bunsen burner, which has the highest temperature, is 1560°C when the oxygen supply is insufficient, and 1 when the oxygen supply is sufficient.
The temperature is 800°C, and the temperature of the outer flame part can only be adjusted within this temperature range.

On the other hand, the drawing temperature of quartz optical fiber is around 1350℃,
The fusion temperature is around 1500°C. Since the outer flame temperature does not match the respective working temperatures, the temperature is adjusted by separating the optical fiber from the outer flame. However, fluctuations in the mixture ratio of gas and oxygen do not stabilize the temperature of the outer flame section itself. Further, fluctuations in gas pressure and flow rate fluctuate the size of the flame, and atmospheric flow causes the flame to fluctuate, making the position of the outer flame part unstable. Therefore, it has been extremely difficult to obtain stability and accuracy in heating temperature.

■While the isothermal curve of a flame is in the shape of a flame, the optical fiber to be heated is placed in a straight line, so the isothermal area on the optical fiber is very narrow, and the stretching and fusion of the optical fiber is also short (long). The only thing I could do was Therefore, a method of swinging the burner parallel to the optical fiber was devised, but instead the flame became unstable and the heating temperature became uneven. Another possible method is to make the burner ports elongated or to arrange small burner ports in a straight line, but in reality it is difficult to design a burner to obtain a uniform temperature distribution, and the control mechanism becomes complicated.

■Creates wind pressure toward the tip of the flame to cause gas to flow out of the burner mouth. The heated and softened optical fiber is pushed and bent by this wind pressure, causing a problem of increasing optical transmission loss.

FIG. 8 shows the measurement results of the horizontal temperature distribution at a position 51111 from the tip of the outer flame of a small gas burner, measured using a thermocouple with a diameter of 0.2mm. FIG. 9 shows the stretched outer shape when a quartz single mode optical fiber with an outer diameter of 0.125 μl is placed at the position where the thermocouple is removed, heated, and the optical fiber is pulled 5 mm on both sides. The vertical axis is the optical fiber outer diameter,
The horizontal axis is the axial position of the optical fiber (IDIV indicates the length of one box; the same applies hereafter). The increase in transmission loss due to stretching (measured at a wavelength of 1.55 μm) was 1 dll. The temperature distribution measurement results show that the temperature is unstable, and the outer diameter measurement results show that smooth stretching is difficult. All results had poor reproducibility.

Furthermore, discharge heating has the following problems.

(2) The center of the discharge has a very high temperature (more than 2000°C), the humid area is extremely narrow, and the temperature distribution is abrupt, so the optimal area where the quartz optical fiber's working temperature is reached is too narrow.

■Characteristics of discharge F Stability was lacking, and it was difficult to precisely adjust the temperature of the optical fiber.

■If you discharge continuously, the electrode itself will melt due to the heat of the discharge, so you have to wait for the electrode to cool down before discharging intermittently, which causes the temperature of the optical fiber to rise and fall in a short time while processing the optical fiber. Therefore, it was not suitable for processing smooth optical fibers.

Furthermore, conventionally, heater-type electric furnaces or electric furnaces in which a heater wire is wrapped around a furnace core tube have not been used for heating optical fiber processing, but it is necessary to heat the optical fiber to the working temperature by several degrees Celsius above that temperature. This is because the temperature of the heater itself must be increased, and it has been considered difficult to realize a heater that can be used at such a high temperature. In addition, since the thickness of optical fiber is less than several hundred microns and the heating length is several tens of am or more, a small, thin and short heater is required, and a heater of this size has too low electrical resistance. This is because designing the power supply becomes difficult. Furthermore, when a support such as a core tube is not used for the heater, there is a problem that the heater deforms at high temperatures.

[Problems to be Solved by the Invention] The objects of the present invention are to be able to avoid wind pressure that causes bending in optical fibers, have a wide heating temperature range, have a stable and smooth temperature distribution, and have temperature control and structure. The object of the present invention is to provide a small electric furnace for simple optical fiber processing.

[Means for solving , iwB] The small electric furnace for processing optical fibers of the present invention includes a furnace core tube with both ends open, and a metal foil as a heating element or the furnace core tube that is closely attached to the surface of the furnace core tube. and a metal thin film as a heating element formed on the surface of the heating element.

[Function] The present invention heats the furnace tube by passing a current through the metal foil or thin metal film from both ends thereof and using the metal foil or thin metal film as a heating element.

Since a furnace core tube is used, the device can be made smaller and can avoid wind pressure that causes bending of the optical fiber. Furthermore, by combining the furnace core tube and metal foil or thin metal film, the optical fiber heating isothermal range can be set freely and widely, resulting in a stable and smooth temperature distribution. Controlling the temperature is also easy, as all you have to do is change the current flowing through the heating element.

[Example] Next, an example of the present invention will be described with reference to the drawings.

Fig. 1 is a perspective view of a small electric furnace for processing optical fibers according to the first embodiment of the present invention, and Fig. 2 shows the measurement results of temperature distribution characteristics of the small electric furnace for processing optical fibers shown in Fig. 1. Graph, 3rd
The figure is a graph showing the measurement results of the outer diameters of the optical fibers and r-bars when the optical fiber shown in FIG.

The small electric furnace for processing optical fibers of this embodiment has an alumina insulating tube 1 with an outer diameter of 3 nun, an inner diameter of 2 mm, and a length of 30 mm, which is open at both ends, has a split 2 in the axial direction, and accommodates an optical fiber 4. (furnace core tube), Jl, l height 0.01mm,
It consists of platinum foils 3 with a length of 15 mm and a width of 15 mm, connected in a comb shape and fixed with heat-resistant cement so as not to cover the split 2. Electric current is passed through the platinum foil 3 from both ends to turn the platinum foil 3 into a heating element. The alumina insulating tube 1 is heated as follows.

The alumina insulating tube 1 shields the wind pressure and convection of the outside air, and at the same time serves as a support that uniformizes the heat generation of the platinum foil 3 by the function of heat diffusion and prevents the platinum foil 3 from being deformed. The temperature increase and temperature can be adjusted by electric current, and it is suitable for use only in certain parts.

As can be seen from FIGS. 2 and 3, the temperature distribution characteristics in this example and the outer diameter of the stretched optical fiber are different from those of the conventional ones (see FIGS. 8 and 3).
It can be seen that this is improved compared to Fig. 9). In addition, the increase in optical transmission loss due to stretching at this time is 1.55 μl at the wavelength.
It was OdB.

As described above, the small electric furnace for adding soil to optical fibers of this embodiment is small and can avoid the wind pressure that causes bending of optical fibers, can freely set the optical fiber heating isothermal range, and can produce stable and smooth heating. It has a temperature distribution. Furthermore, it is possible to freely insert or remove optical fibers or thermocouples from the split 2 to the alumina insulating tube 1. Furthermore, the electrical resistance and temperature distribution can be freely designed by cutting out the platinum 'A3.

In this example, platinum foil 3 was used as the metal foil, but platinum, rhodium or its alloys, kanthal, nichrome, iron chromium, etc., which have good thermal efficiency and can reduce the difference between the heat generation temperature and the temperature of the optical fiber, may also be used. can.

FIG. 4 is a perspective view of a small electric furnace for processing optical fibers according to a second embodiment of the present invention, and FIG. 5 is a graph showing measurement results of temperature distribution characteristics of the small electric furnace for processing optical fibers of FIG. 4. 6th
The figure is a graph showing the measurement results of the outer diameter of the optical fiber when the quartz single mode optical fiber was stretched to 40 mm using the small electric furnace shown in FIG.

A small electric furnace for adding soil using optical fibers, as an example of Kino hb, is open at both ends, has a split 6 in the axial direction, and has an outer diameter of 3ITII11, an inner diameter of 2 mm, and a length of 100 m to accommodate the optical fiber 8.
m alumina insulating tube 5 (furnace core tube) with a thickness of 0.0 m.
A platinum film 7 with a thickness of 0.2 mm is formed so as not to cover the split 6, and a current is passed through the platinum film 7 from both ends to heat the alumina insulating tube 5 using the platinum film 7 as a heating element.

Here, the platinum film 7 serving as the heating element was prepared by rotating the alumina insulating tube 5, uniformly sputtering platinum onto the surface of a length of 50 mm, attaching terminals to both ends, and making slits with a cutter.

The adhesion between the heating element and the alumina insulating tube 5 was improved, and the thermal efficiency was further improved than in the first embodiment.

The temperature distribution characteristics of this example have a wide isothermal range, as shown in FIG. In FIG. 5, the temperature at both ends is elevated because of heat dissipation from the terminals.

Furthermore, the stretched shape of the optical fiber according to this example is smooth and long, as shown in FIG. The increase in optical transmission loss at this time was 0d11.

FIG. 7 is a cross-sectional view showing a state in which two quartz optical fibers are placed in parallel and fused together. It achieves temperatures of over 1500°C. Furthermore, no increase in optical transmission loss was observed during fusion.

As described above, the small electric furnace for processing optical fibers of this embodiment has a high heating temperature, a wide heating isothermal range, and a stable and smooth temperature distribution. This allows the electrical resistance and temperature distribution to be designed freely.

Note that, in addition to platinum, rhodium, tungsten, molybdenum, carbon, etc. can be used for the metal thin film, and the metal thin film may be formed of plating or a group 7 layer.

0 In the first and second embodiments, the alumina insulating tube 1.5
Both are provided with a split 2.6, but the split 2.6 is provided to facilitate the insertion and removal of the optical fiber 4.8 and thermocouple into and out of the alumina insulated tubes 1 and 5, and may be omitted. .

[Effects of the Invention] As described in 1-1 above, the present invention involves closely adhering a metal foil or forming a metal thin film to the surface of a furnace core tube, and passing an electric current through the metal foil or metal thin film to generate heat and heat the furnace core tube. This structure provides the above-mentioned effects in heating processing such as drawing and fusing of optical fibers.

■Excellent reproducibility of temperature distribution and excellent reproducibility of optical fiber processing shapes.

■Since the heating isothermal range is wide, stable and smooth temperature distribution can be realized, and the optical fiber can be stretched in an extremely smooth shape, the increase in transmission loss due to stretching can be stably minimized.

■Since the optical fiber does not bulge due to flame wind pressure or convection, the fusion required for manufacturing optical fiber couplers, etc. can be performed stably with low loss.

■A convenient slot can be inserted for putting in and taking out the optical fiber.

■It is possible to stably process multiple optical fibers or optical fiber couplers at the same time, and the characteristics are also stable.

■The structure of the furnace is simple, and the shape and length of the furnace can be designed freely.

■Temperature control is easy, and the driving device is simple, requiring only a power supply.

■The structure has good thermal efficiency, so the difference between the heating element temperature and the heating temperature can be reduced, and heater materials such as platinum, kanthal, and nichrome, which have low melting points, can be used as the heating element.

■Since there is no self-generated gas, it is possible to create a vacuum and keep the furnace air composition constant, and carbon, tungsten, tantalum, etc. used in an inert atmosphere can also be used as heating elements.

[Phase] Even if the heating element evaporates, it does not adhere to the optical fiber.

2

[Brief explanation of drawings]

FIG. 1 is a perspective view of a small electric furnace for processing optical fibers according to the first embodiment of the present invention, FIG. 2 is a graph showing the measurement results of the temperature distribution characteristics of the electric furnace according to the first embodiment, and FIG. 4 is a graph showing the outer diameter measurement results of the optical fiber drawn in the electric furnace of the first embodiment, FIG. 4 is a perspective view of the small electric furnace for processing optical fibers of the second embodiment of the present invention, and FIG. is a graph showing the measurement results of the temperature distribution characteristics of the electric furnace in Fig. 4, Fig. 6 is a graph showing the measurement results of the outer diameter of the optical fiber drawn in the electric furnace of the second embodiment, and Fig. 7 is a graph showing the measurement results of the temperature distribution characteristics of the electric furnace of the second embodiment. Figure 8 is a graph showing the measurement results of the temperature distribution characteristics of a conventional small gas burner, and Figure 9 shows the results of measuring the outer diameter of a quartz optical fiber drawn with a small gas burner. This is a graph showing. 1.5... Alumina insulating tube, 2.6... Split, 3... Platinum foil, 4.8-... Optical fiber, 7... Platinum film. ! I! l (company) ■! ! 1 Example pH (Company) ■ ■

Claims (1)

[Scope of Claims] 1. A furnace core tube with both ends open, and a metal foil as a heating element closely adhered to the surface of the furnace core tube or a metal thin film as a heating element formed on the surface of the furnace core tube. A small electric furnace for processing optical fibers. 2. The small electric furnace for processing optical fibers according to claim 1, wherein the furnace core tube has a split in its axial direction, and the metal foil or metal thin film is closely attached or formed so as not to cover the split. .