JPS5830716A - Terminal part of optical fiber - Google Patents

Abstract

PURPOSE:To eliminate the reflection in the terminal part of an optical fiber without degrading characteristics of the optical fiber, by connecting optical glass, which has a refractive index approximately equal to that of the optical fiber core, to the obliquely formed end face of the optical fiber. CONSTITUTION:An optical fiber 1 and a glass block 2 are connected on a junction face 3 formed obliquely to the axis of the optical fiber. The other face 4 of the glass block 2 is so coated that a used light wavelength is not reflected, and refractive indexes of the glass block 2 and the optical fiber core are set to the same value. Consequently, even if a luminous flux 11 incident to the optical fiber 1 is reflected partially by discontinuity of refractive index, a reflected luminous flux 12 is much deviated from the fiber optical axis and is easily eliminated because a boundary face 3 is formed obliquely to the fiver optical axis, and as the result, the reflection in the terminal part of the optical fiber is eliminated effectively to obtain a stable optical circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a terminal portion of an optical fiber used in an optical circuit component for an optical fiber transmission line.

Optical fiber terminals used in optical circuit components for optical fiber transmission are often simply cut and polished at right angles to the central axis of the optical fiber. Fresnel reflection at the fiber end face may affect the characteristics of optical circuit components and optical fiber transmission systems. For example, in a semiconductor laser coupler that couples a semiconductor laser and an optical fiber with a lens, a stable semiconductor laser coupler cannot be obtained because the Fresnel reflection component at the end face of the optical fiber returns to the semiconductor laser and changes the characteristics of the semiconductor laser. . In order to eliminate such problems,
The conventional method is to apply an AR coating to the end face of the optical fiber or to polish the end face diagonally with respect to the central axis of the optical fiber. , or to prevent it from entering the optical fiber again. However, applying an AR coating to the end face of an optical fiber is undesirable from the viewpoint of strength of the optical fiber, as the optical fiber is exposed to high temperatures during the AR coating process. The outgoing beam is deflected by refraction at this end face.

As a result, the central axis of the optical fiber and the optical axis of the beam emitted from the optical fiber do not match, resulting in a disadvantage that the optical circuit configuration becomes complicated.

This invention aims to solve these drawbacks.

An optical glass having a refractive index approximately equal to that of the core of the optical fiber is bonded to an obliquely formed end face of the optical fiber, and will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment according to the present invention, in which (1) is an optical fiber and (2) is a glass block. The optical fiber (1) and the glass block (2) are joined at a joining surface (3) formed obliquely to the central axis of the optical fiber. Also, the end face (4) of the glass block (2)
) is coated with anti-reflection coating for the wavelength of light used. The refractive index of the glass block (2) is set approximately equal to the refractive index of the core of the optical fiber. Because it is configured like this.

As shown in FIG.
Even if it is partially reflected due to the discontinuity in the refractive index.

Since the boundary surface (3) is formed obliquely to the optical axis of the fiber, the reflected light beam υ deviates from the optical axis of the fiber, so it can be easily removed and does not affect other optical circuit components. Further, the end face (4) of the glass block (2) is coated with a non-reflection coating, so that no reflection occurs. By the way, such anti-reflection coating on the end face of the glass block (2) can be done at the stage of the glass block alone, before the process of joining the optical fiber +11 and the glass block (2).
If a non-reflection coating can be applied without affecting the characteristics of the optical fiber, all the drawbacks of conventional anti-reflection coating on the end face of the optical fiber at the end of the optical fiber can be eliminated.

Now, on the other hand, as shown in Figure 2(b), the optical fiber (1)
Strictly speaking, the light rays propagating along the optical axis of the glass block (2) and the optical fiber core (1G) cause refraction at the interface (3) formed diagonally due to the difference in refractive index. However, the glass block (2) emits the light at a negative angle to the optical axis of the optical fiber.

Since the refractive index difference between the glass block (2) and the optical fiber core αα can be made sufficiently small very easily, this angle becomes extremely small. For example, if a glass material of BK7, which is a very common optical material, is used for an optical fiber with a core of quartz glass, the difference in refractive index will be approximately 1.4.
6 and 1.52.

On the other hand, the inclination angle σ of the boundary surface (3) shown in Fig. 2(b) is slightly larger than the maximum acceptance angle of the optical fiber, since it is sufficient that the light reflected by this boundary surface can be sufficiently separated from the light emitted from the optical fiber. Just do it.

In a normal optical fiber, this angle is approximately 10 degrees, so α
Suppose that the angle is set to 15 degrees. If calculation is performed using Snell's law of refraction from the above settings, - will be 0.9 degrees, which is sufficiently small compared to the light receiving incident angle of the optical fiber, and the deflection of the optical axis due to the provision of such an end portion can be ignored. On the other hand, if the glass block (2) is not present as in the conventional terminal section, if calculated from the above settings, 0 will be 17 degrees, which is extremely large. From this, it will be understood that the present invention greatly improves the drawbacks of the conventional terminal in which the fiber terminal is formed obliquely.

As described above, according to the present invention, unlike the conventional reflection-eliminating terminal, the optical axis of the output beam of the optical fiber is made to coincide with the central axis of the optical fiber, and the optical fiber is coated with a non-reflective coating on the end face of the optical fiber. This has the advantage that reflection at the optical fiber terminal can be effectively removed without deteriorating the characteristics, and a stable optical circuit can be constructed.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of an optical fiber terminal according to the present invention, and FIGS. 2(a) and 2(b) are sectional views for explaining the operation of the optical fiber terminal. In the figure, (1) is an optical fiber, (2) is an optically transparent block, (3) is a joining surface of the optical fiber and block, and (4) is an end face of the block. Also in Figure 1. Identical or equivalent parts are indicated by the same reference numerals. Agent Shin Kuzuno −

Claims (1)

[Claims] An optically transparent block having a refractive index approximately equal to the refractive index of the core of the optical fiber is spliced to the end face of the optical fiber, and the spliced surface is formed obliquely with respect to the central axis of the optical fiber. It has been done. and an end portion of an optical fiber, wherein the end face of the block opposite to the splicing face is formed to be substantially perpendicular to the central axis of the optical fiber.