JPH01239508A - Processing system for connection between single-mode optical fiber and multi-mode optical fiber - Google Patents

Abstract

PURPOSE:To prevent transmission quality from deteriorating by interposing an optical fiber for connection which has a low-refractive index part having a lower refractive index than a core part in the center part of the core part between a single-mode optical fiber and a multi-mode optical fiber, and entering light which is projected from the single-mode optical fiber into the low-refractive-index part. CONSTITUTION:When the single-mode optical fiber 1 and multi-mode optical fiber 2 are connected to each other, the optical fiber 5 for connection which has the low- refractive-index part having the lower refractive index than the core part 3 is interposed in the center part of the core part 3 between both fibers. Then the light which is projected by the single-mode optical fiber 1 is entered into the low-refractive-index part 4 is entered into the low-refractive-index part 4. The projection light of the single- mode optical fiber 1 which is entered the low-refractive-index part 4 is transmitted through the lwo-refractive-index part 4 and entered into the multi-mode optical fiber 2 directly or after being converted into various modes through a high-refractive-index part. Consequently, even if the state of abutting between the fibers at the connection part changes, variation in waveform shape on a reception side is prevented.

Description

[Detailed description of the invention] 4!1 Regarding the connection processing method of single mode optical fiber and multimode optical fiber on the transmitting side of optical fiber transmission, for the purpose of preventing deterioration of transmission quality, single mode optical fiber and multimode optical fiber are connected. When connecting optical fibers, a connecting optical fiber having a low refractive index portion having a refractive index lower than the refractive index of the core portion is interposed in the center of the core portion between them, and from the single mode optical fiber. The structure is such that the emitted light is made to enter the low refractive index section.

INDUSTRIAL APPLICATION FIELD The present invention relates to a connection processing method between a single mode optical fiber and a multimode optical fiber on the transmission side of optical fiber transmission.

On the transmission side of optical fiber transmission, a semiconductor laser (hereinafter also referred to as LD) is generally intensity-modulated with a time-series electrical signal, and this modulated light is introduced into the optical fiber via a lens system. .

The LD, lens system, and optical fiber for connection are usually
It is used in an integrated configuration as a module, and the transmission side is configured by connecting the above-mentioned connection optical fiber and the optical fiber of the optical transmission line using, for example, an optical connector. By the way, as is well known, optical fibers are broadly classified into single mode optical fiber and multimode optical fiber.
These are used depending on transmission capacity, transmission distance, etc. Therefore, when connecting the optical fibers on the transmitting side, it is required that they have good consistency.

BACKGROUND OF THE INVENTION FIG. 5 is a diagram for explaining a conventional connection between multimode optical fibers on the transmitting side.

In the configuration of the transmitting side shown in FIG. 3(a), 31 is L
A module main body 32 that is a D module and has a built-in LD and lens system (not shown);
It is composed of a multimode optical fiber 33 led out in a pigtail shape from a fiber, and an optical connector 34 attached to the end of the multimode optical fiber 33. A multimode optical fiber 35 serves as an optical transmission line, and optical connectors 36 and 37 are attached to both ends of the fiber.

Optical connectors 34, 36 are interconnected and optical connector 37
is connected to a receiving module (not shown).

FIG. 2B shows the waveform of an optical signal near the optical connector 36 of the multimode optical fiber 35. Various modes 38-1.2, 3. ... are superimposed at almost the same timing.

FIG. 2C shows the waveform of an optical signal in the vicinity of the optical connector 37 of the multimode optical fiber 35. Each mode component is affected by its own unique mode dispersion, resulting in a uniform mountain-shaped waveform 39.

The reason why the waveforms of the optical signals differ at both ends of the multimode optical fiber 35 is that the optical transmission path is sufficiently long compared to the pigtail portion of the module, and the influence of mode dispersion becomes noticeable. Note that if the waveform is noticeably rounded, as shown in Figure (C), problems will occur such as code errors when the transmission speed increases, but the shape of the waveform itself is due to the connection between optical fibers. It does not change depending on the condition of the optical fiber or the bending of the optical fiber.

Problems to be Solved by the Invention FIG. 6 shows a case where a single mode optical fiber and a multimode optical fiber are connected on the transmitting side. In the same figure (a), 41 is the module main body 42
and a single mode optical fiber 43
The single mode optical fiber 43 is a module, and the single mode optical fiber 43 is
It is connected to a multimode optical fiber 45 as an optical transmission line via optical connectors 44 and 46. 47 is an optical connector for connecting the multimode optical fiber 45 to a receiving module (not shown). Although such connection between different optical fibers has not been actively carried out in the past, the need has arisen for the following reasons. In other words, in recent years, as the price of single-mode optical fibers and light source LDs suitable for them have decreased, modules with single-mode optical fibers as pigtails have become more versatile, and these can be used for single-mode and multi-mode optical fibers. This is because they are trying to share it.

FIG. 4B shows the waveform of the optical signal near the optical connector 4G of the multimode optical fiber 45. Since the respective optical axes at the connecting portions are substantially parallel, a waveform 48-1.2 of a low-order mode (usually about two modes) is generated.

FIG. 2C shows the waveform of an optical signal in the vicinity of the optical connector 47 of the multimode optical fiber 45. A propagation delay time difference Δt occurs between each mode component, resulting in an unstable waveform 49. The shape of this waveform 49 is
The distribution ratio is determined according to the distribution ratio of each mode component shown in FIG. Therefore, the shape of the waveform observed on the receiving side becomes extremely unstable. When the waveform shape becomes unstable, transmission quality such as bit error rate deteriorates, causing a practical problem.

The present invention was made to solve these technical problems, and its purpose is to prevent deterioration in transmission quality when a single mode optical fiber and a multimode optical fiber are connected on the transmitting side.

Means for Solving the Problems FIG. 2 is an auxiliary diagram for explaining the principle of the present invention, and shows geometrically the state when the multimode optical fiber 2 is excited by the output light of the single mode optical fiber 1. There is. The light emitted from the single-mode optical fiber 1 can be considered as light from a point light source with a small numerical aperture, and the end face of the fiber can be considered to be polished perpendicular to the optical axis, so it is not a multi-mode light. In the fiber 2, only about two modes M 1 and M 2 on the lower order side are excited, and the above-mentioned problem occurs. Considering these circumstances, if multimode light is excited in the multimode optical fiber 2, a stable waveform can be obtained.

FIG. 1 is a diagram showing the principle of the present invention.

When connecting a single mode optical fiber 1 and a multimode optical fiber 2, a low refractive index section 4 having a refractive index lower than the refractive index of the core section 3 is provided in the center of the core section 3 between them. An optical fiber 5 is interposed therebetween.

The light emitted from the single mode optical fiber 1 is made to enter the low refractive index section 4.

Function: The reason why the multimode optical fiber 2 is configured as described above is to excite the multimode optical fiber 2 in multiple modes. That is, the light emitted from the single mode optical fiber 1 that is incident on the low refractive index section 4 is converted into various modes either directly after passing through the low refractive index section 4 or via the high refractive index section to form multimode light. Since the light is input to the fiber 2, even if the butting state of the fibers at the connection portion changes, the waveform shape on the receiving side is prevented from changing.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 3 is a diagram for explaining the cross-sectional configuration and refractive index distribution of a connecting optical fiber that can be used in implementing the present invention.

The connecting optical fiber 10 is composed of a core portion including a low refractive index portion 11 and a high refractive index portion 12, and a cladding portion 13. The refractive index 11n of the low refractive index portion 11 is approximately equal to the refractive index 13n of the cladding portion 13, and the refractive index 11n of the low refractive index portion 11
The refractive index 12n is set larger than the refractive indexes 11n and 13n. Such a connection optical fiber 10
To manufacture, for example, first, a part that will become a cladding layer is formed on the inner surface of a pure quartz tube using an inner material CVD method,
Next, a portion to be a high refractive index portion is formed on the inner surface, and finally a portion to be a low refractive index portion is formed, and a line may be drawn using a usual method. To change the refractive index of each part, F, GeO2, Px
The doping amount of Os or the like may be different.

FIG. 4 is a diagram showing an example of use of the above-mentioned connecting optical fiber 10. Reference numeral 21 denotes an LD module, which includes a module body 22 in which an LD chip and a lens system are housed, a single mode optical fiber 23 led out in a pigtail shape from the module body 22, and a module body 23 attached to the end of the single mode optical fiber 23. It is composed of an optical connector 24. Optical connectors 25 are installed at both ends of the connecting optical fiber lO.
26, of which the optical connector 25 is connected to the optical connector 24. A multimode optical fiber 27 serves as an optical transmission line, and optical connectors 28 and 29 are attached to both ends of the fiber. The optical connector 28 is connected to the optical connector 26, and the optical connector 29 can be connected to a receiving module (not shown). The length of the connecting optical fiber 10 can be several tens of cm to several meters, and as the multimode optical fiber 27, either a graded index type or a step index type can be used.

In this way, when connecting a single mode optical fiber on the output side to a multimode optical fiber as an optical transmission path, by using a connecting optical fiber with a special refractive index distribution as a mode scrambler, it is possible to connect a multimode optical fiber to a multimode optical fiber. Various modes of light are excited, and the waveform of the optical signal on the receiving side becomes stable.

In this embodiment, optical connectors 25 and 26 are attached to both ends of the connecting optical fiber 10 to connect each optical fiber, but the connecting optical fiber is permanently connected to the LD by means such as fusion. It may be integrated with the module side.

Effects of the Invention As detailed above, according to the present invention, since the multimode optical fiber is excited in multiple modes, the transmission quality deteriorates when connecting the single mode optical fiber and the multimode optical fiber. This has the effect of preventing this.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is an auxiliary diagram for explaining the principle of the present invention, Figs. 3 and 4 are illustrations of embodiments of the present invention, and Figs. 5 and 6 are
The figure is a diagram of a conventional example. 1.23.43...Single mode optical fiber, 2.
27, 33, 35.45... Multimode optical fiber, 5.10... Optical fiber for connection. Figure 1 Principle of the Tsukimori 4 Figure 2 50 Fig. 4 Damaged rice (A row) Fig. 5 4 rows A (A row Fig. 6)

Claims (1)

[Claims] When connecting the single mode optical fiber (1) and the multimode optical fiber (2), a low refractive index lower than that of the core portion (3) is placed between them in the center of the core portion (3). A connecting optical fiber (5) having a refractive index portion (4)
), and the light emitted from the single mode optical fiber (1) is made to enter the low refractive index section (4). .