JPH0250065B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a method for forming an antireflection film on the end face of an optical fiber accommodated in an optical connector.

(b) Background of the technology Optical communication uses optical fiber as a transmission path and uses laser light, etc. to communicate. Optical fibers include quartz fibers whose main component is high-purity silicon dioxide (SiO ₂ ), multicomponent fibers made from multicomponent glasses, and plastic fibers made from synthetic resins. However, optical fibers used for optical communications must have low loss, and from this point of view, silica fibers are mainly used, and currently 0.5 μm in the wavelength range of 1.2 to 1.3 μm.
Loss as low as [dB/Km] has been realized.

Now, optical connectors are used to connect optical fibers in optical communication paths, but since the optical fibers and air have different refractive indexes, reflection at the interface is unavoidable, resulting in loss.

(c) Prior Art and Problems Figure 1 shows the cross-sectional structure of an optical connector, in which A shows the state after installation and B shows the appearance of the optical fiber.

In the case of an optical fiber, in order to confine light within the fiber, the refractive index of the central core portion through which the laser beam propagates is made larger than that of the surrounding cladding portion. For example, in the case of a silica-based optical fiber, the refractive index of the core portion is 1.46 and the refractive index of the cladding portion is approximately 1.45, and in the case of a fiber with a wire diameter of 1 mm, the diameter of the core portion is approximately 50 μm, and the refractive index of the cladding portion is approximately 1.45. The diameter is approximately 125 μm, and the fiber cable is constructed by covering and protecting this with a synthetic resin such as nylon.

To connect the optical fibers, see Figure 1B.
As shown in the figure, a pair of optical cables 3 and 3' with the plastic coating 1 partially removed to expose the optical fiber 2 are each fixed to a ferrule, and a polisher is used to polish the end face of the ferrule and the end face of the optical fiber 2. Polish so that they are on the same surface. After polishing, the optical fiber is attached to ferrule 4, as shown in Figure 1A.
The optical fibers 2, 2' are connected by fitting them into the adapter 5 using coupling nuts 6, 6' after housing them in the adapter 5 while being fixed to the optical fibers 4'. However, in this case, the connection between the optical fibers 2 and 2' is not perfect, and the existence of a gap of several tens of micrometers is unavoidable, and since the optical fibers and air have different refractive indexes, reflection occurs, resulting in a gap of approximately 10 μm at each location. A reflection loss of 4% occurs. Further, if reflected light exists, it returns to the laser light source, resulting in instability of laser oscillation. It was known that a way to prevent this would be to provide an anti-reflection coating on the end face of the optical fiber, but since the length of the optical fiber cable is long enough, there was a method to effectively apply an anti-reflection film only on this end face. I couldn't find any.

(d) Object of the Invention An object of the present invention is to provide a method for forming an oxide-based multilayer antireflection coating on the end face of an optical fiber cable.

(e) Structure of the Invention The object of the present invention is to attach a plurality of optical fiber cables with polished end faces to a sputtering device while sandwiching them between vertically split rubber elastic cylindrical fiber holders. An antireflection film in which an antireflection coating consisting of a multilayer film is provided on the tip of an optical fiber by sputtering the tip of the optical fiber so that it protrudes from a plurality of fiber holes previously provided in an anode substrate. This is achieved by a forming method.

(f) Embodiments of the Invention The present invention prevents reflection in the used wavelength range by forming a layered oxide-based thin film, and the material of the thin film is SiO ₂ (refractive index
1.45), titanium dioxide TiO ₂ (refractive index 2.3), aluminum oxide Al ₂ O ₃ (refractive index 1.65), etc., and these are formed into a layer to form an antireflection film.

An example of this combination is SiO ₂ −
A combination consisting of Al ₂ O ₃ −TiO ₂ −SiO ₂ or
A combination of Al ₂ O ₃ −TiO ₂ −SiO ₂ is preferable.

In the present invention, these oxides are formed by a sputtering method, and in this case, the appropriate film thickness is given by the following equation.

λ/4・1/n……(1) here λ……Wavelength of laser light n...Refractive index of oxide The thin film forming method will be explained below.

FIG. 2 is a block diagram of a sputtering apparatus according to the present invention, and FIG. 3 is a block diagram showing the structure of an anode for setting an optical fiber.

The sputtering apparatus shown in FIG. 2 is the same as a conventional sputtering apparatus except for the anode 7 and the fiber holder mounting opening 8. That is, a target 9 made of an oxide to be sputtered is set on a negative electrode 10, is water-cooled on the inside, and is connected to the negative electrode side of a high-voltage power source 11, and the anode 7 is connected to the positive electrode side of the power source 11. ing. Further, the exhaust bell 12, which is insulated from the power supply, is exhausted from the exhaust port 13 by an exhaust system (not shown), and is also supplied with argon (Ar) or oxygen (O ₂ ) through the needle valve 14.
etc., and sputtering is now performed under a certain degree of vacuum. Note that a bias coil 15 is provided to enhance the sputter effect.

In the above-described sputtering device, the plurality of optical cables 3 are inserted into the device through the attachment port 8 of the fiber holder of the exhaust bell, with the tips removed and the plastic coating 1 removed, as shown in FIG. 1B. Then, the anode plate 16 is guided and inserted into a number of cable set holes 17 provided in the anode plate 16. Here, the cable set hole 17 is made in a size that allows the optical cable 3 to fit therein. Here, the fiber hole 18 at the tip of the cable set hole 17 provided in the anode plate 16 is provided with a step according to the diameter of the optical fiber 2, so that the optical fiber 2 protrudes slightly from the bottom surface of the anode 16. It is maintained in the state that it is. The inside of the anode plate 16 is water-cooled to prevent the plastic sheath 1 of the cable from softening and welding due to heat generated during sputtering.

Now, after the required number of optical cables 3 have been inserted into the anode plate 16, the optical cables 3 are clamped in a fiber holder made of a cylindrical rubber elastic material such as silicone resin, which is divided into two vertically. Airtightness can be maintained by attaching it to the

By putting only a part of the optical cable 3 into the device in this way and then performing normal sputtering,
An antireflection film can be made by depositing oxides such as SiO ₂ , TiO ₂ , Al ₂ O ₃ on the cross section of the optical fiber 2 .

(g) Effects of the Invention By carrying out the present invention, it has become possible to form an antireflection film on the end face of an optical fiber, thereby making it possible to eliminate reflection loss in optical connector connection.

[Brief explanation of drawings]

FIG. 1A is a cross-sectional view of the optical connector, FIG. is a front view, and B is a cross-sectional view. In the figure, 1 is a plastic coating, 2, 2'
is the optical fiber 3, 3' is the optical cable, 7 is the anode,
8 is the fiber holder insertion port, 16 is the anode plate, 1
7 is a cable set hole, and 18 is a fiber hole.

Claims (1)

[Claims] 1. A plurality of optical fiber cables with polished end faces are sandwiched between vertically split cylindrical fiber holders with rubber elasticity and attached to a sputtering device.
Next, an anti-reflection coating made of a multilayer film is applied to the tip of the optical fiber by sputtering the tip of the optical fiber so that it protrudes from a plurality of fiber holes previously provided in the anode substrate. A method for forming an anti-reflection film on an end face of an optical fiber, characterized in that: