JPH068566Y2 - Mode conversion adapter - Google Patents

Description

[Detailed Description of the Invention] Overview A mode conversion adapter for converting a propagation mode from a single mode to a multi mode in an optical communication system using an optical fiber as a transmission line, and a single mode having a sufficient 6 dB band improvement effect with a simple configuration. / Mode conversion for connecting a light source side single mode fiber and a light receiving side multimode fiber to an optical connector and connecting both optical connectors to convert a single mode into a multimode The adapter is provided with a first receptacle to which an optical connector of a single mode fiber is coupled and a second receptacle to which an optical connector of a multimode fiber is coupled, and a tapered spacer in which the first and second receptacles are inclined at a predetermined angle. It is fixed by sandwiching it and is integrally fixed. That.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mode conversion adapter for converting a propagation mode from a single mode to a multi mode in an optical communication system using an optical fiber as a transmission line.

Depending on the transmission capacity, there are a single mode fiber (hereinafter referred to as SM fiber) and a multimode fiber (hereinafter referred to as MM fiber) depending on the transmission capacity. The MM fiber is a step index fiber (hereinafter referred to as SI fiber). ) And graded index
Fiber (hereinafter referred to as GI fiber).
In this specification, the MM fiber will be described as a representative of the GI fiber.

There are two types of light source devices, one for SM and one for GI, corresponding to SM fiber and GI fiber. Recently, there is a tendency to unify the light source for SM and to apply the SM light source to the existing GI fiber. It has increased. However, when entering from the SM light source to the GI fiber, the transmission characteristic originally possessed by the GI fiber (baseband characteristic expressed in the 6 dB band) may be apparently deteriorated, and this is improved by a low loss method. Is required to do so.

The 6 dB band will be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic diagram showing the attenuation of the amplitude due to the optical fiber transmission, and the incident light having the amplitude A ₀ incident on the optical fiber 10 is attenuated to the amplitude A and output at the output end of the optical fiber. In optical fiber transmission, mode dispersion, material dispersion,
Due to three causes of waveguide dispersion (structural dispersion), the amplitude A of the modulation waveform appearing on the output side becomes smaller as the modulation frequency becomes higher as shown in FIG. The band of the intensity modulation frequency starting from this direct current is called the base band, and the transmission band of the optical fiber is the frequency at which the output amplitude in the base band becomes smaller than the maximum value A ₀ by 6 dB,
It is called the 6 dB band.

2. Description of the Related Art Since it is the group delay time between the modes propagating in the fiber that limits the baseband characteristics of the GI fiber, conventionally, when the GI fiber is incident on the GI fiber from the SM light source, the GI fiber is in a state of low-order mode excitation. Therefore, it was thought that the baseband characteristics would be apparently better than the original 6 dB band of the GI fiber due to the smaller number of modes. In fact, when the refractive index distribution (hereinafter referred to as profile) of the fiber is ideal as shown in FIG. 7 (A), the 6 dB band is apparently improved. However, the profile is shown in Fig. 7 (B).
In the case of a fiber deviating from the ideal as shown in (4), the 6 dB band apparently deteriorates as described above.

The difference in the refractive index distribution between FIGS. 7 (A) and 7 (B) is mainly due to the manufacturing method. In order to manufacture an optical fiber, it is manufactured by a two-step process in which a preform (base material) is first prepared, and then this preform is heated and softened to be drawn. As a typical method for making a preform, an internal CVD method (MCVD method), an external CVD method,
The VAD method (vapor phase axial attachment method) can be used. Although the VAD method can produce a fiber having a profile as shown in FIG. 7 (A), the internal CVD method and the external C method can be used.
According to the VD method, GeO _{2 is} added in the final “collapse” process.
The molecules escape, and a dip region 11 having a low refractive index is generated in the central portion of the core.

As described above, in the case of a fiber whose profile is not ideal as shown in FIG. 7 (B), conventionally, a step index (SI) fiber having a large core diameter is inserted several meters after the SM light source. Then, the emission pattern of the SM light source is brought closer to the steady mode pattern of the GI fiber,
Alternatively, JP-A-57-158604 and JP-A-62-7
As described in No. 8506, a method has been proposed in which a lens system is inserted after the SM light source to expand the size of the emitted beam.

However, as can be seen from the graph of FIG. 9, an SI fiber is inserted between the SM light source and the GI fiber to bring the light emitted from the SM light source closer to the steady mode pattern of the GI fiber. The method has a certain 6 dB band improvement effect,
It turned out that the increase in light loss was far from complete. Here, the graph of FIG. 9 is measured by arranging the apparatus as shown in FIG.

Further, as is clear from FIG. 9, it was found that there is almost no improvement effect when the lens system is inserted instead of the SI fiber. In particular, as described in JP-A-57-158604 and JP-A-62-78506,
The prior art that attempts to improve the 6 dB band by enlarging the spot size of the incident light on the GI fiber is
It was found that almost no effect was obtained as shown in the graph of FIG. FIG. 11 is a graph showing the relationship between the spot size of the incident light on the GI fiber and the 6 dB band measured by disposing the device as shown in FIG.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a single mode / multimode conversion adapter having a sufficient 6 dB band improvement effect with a simple configuration.

Means for Solving the Problems The present inventor has therefore found that when the SM light source is incident on the GI fiber, the 6 dB band is deteriorated due to the fact that the low-order mode excitation is maintained even after propagating in the GI fiber for 10 km or more. It was considered that the reason for the above is that the group delay time difference between the low-order modes (two or very few modes) becomes large due to the disturbance of the profile and the band is limited. That is, in the case of a GI fiber having a profile as shown in FIG. 7 (B), since the dip region 11 having a low refractive index exists in the center of the core in the optical fiber manufacturing process, the group delay between low order modes is large. It is considered that the time difference becomes large. From this finding, GI is required to improve the 6 dB band.
It is necessary to convert the incident condition on the fiber into a form close to the excitation of a stationary mode including higher-order mode components.

Therefore, the present invention is directed to a mode conversion adapter for connecting a single-mode fiber on the light source side and a multimode fiber on the light-receiving side to optical connectors, and coupling both optical connectors to convert single mode to multimode. A first receptacle to which the connector is coupled and a second receptacle to which the optical connector of the multimode fiber is coupled are provided, and the first and second receptacles are integrally fixed by sandwiching a tapered spacer inclined at a predetermined angle. With this configuration, the above-mentioned problems can be solved.

By configuring the working mode conversion adapter as described above, the optical axis of the multimode fiber is inclined and coupled with respect to the optical axis of the single mode fiber. Therefore, the optical axis of the incident light that enters the multimode fiber is tilted with respect to the optical axis of the multimode fiber, so that a large amount of high-order mode components are generated and the light that enters the multimode fiber is steadily excited from the low-order mode Can be converted to mode excitation. Therefore, the 6 dB band of the multimode fiber can be improved.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention, in which a mode conversion adapter 12 is constructed by integrally fixing a first flanged receptacle 14, a second flanged receptacle 16 and a tapered spacer 18. The flanged first receptacle 14 has a large diameter portion 14a and a small diameter hole 1 at the center thereof.
4b is formed, and the second receptacle 1 with a flange is formed.
6 also has a large-diameter hole 16a and a small-diameter hole 16b formed in the center thereof. The tapered spacer 18 is inclined at a predetermined angle, for example, 6 °, and a through hole 18a is formed in the central portion thereof. 24 is a single mode fiber,
An optical connector 26 is attached to the tip portion thereof. Two
8 is a ferrule. On the other hand, 30 is, for example, a graded index type multimode fiber, and an optical connector 32 is attached to the tip thereof. 34 is a ferrule.

The mode conversion adapter 12 of this embodiment is assembled as follows, for example.

The flanged first receptacle 14 and the tapered spacer 18 are fixed in advance with the screw 20, and the optical connector 26 of the single mode fiber 24 is coupled to the flanged first receptacle 14. Next, the multimode fiber 3
0 optical connector 32 and flanged second receptacle 16
And the second flanged receptacle 16 and the tapered spacer 18 are temporarily fixed with a screw 22. Next, light is incident on the single-mode fiber 24, the screw 22 is loosened, and the positional relationship between the flanged second receptacle 16 and the tapered spacer 18 is adjusted.
When the optical output of 0 becomes maximum, the screw 22 is tightened and finally fixed to complete the assembly. When assembled in this manner, the ferrules 28 and 34 are brought into contact with each other, and the axes of both ferrules are tilted to obtain a desired angular deviation.

In the above-described embodiment, the flanged first and second receptacles 14 and 16 and the tapered spacer 18 are attached to the screws 20 and 2.
However, the fixing method of the present invention is not limited to this, and may be fixed by, for example, fixing with an adhesive or welding.
Since the degree of improvement in the 6 dB band is determined by the degree of angular deviation, the adjustment simply searches for the point where the light output is maximum, and the assembly is greatly simplified. Therefore, at the point where the light output is maximum, there is no problem even if there is some axial misalignment in addition to the angular misalignment in the embodiment.

Next, referring to the graph of FIG. 3, this graph is a graph showing the relationship between the angular deviation and the 6 dB band, and is the data obtained by arranging the measuring device as shown in FIG. From the graph of FIG. 3, it can be seen that when the degree of angular deviation is about 5 ° or more, the original 6 dB band of the multimode fiber is approached. However, if the degree of angular deviation is made too large, optical loss increases, so the upper limit of angular deviation is determined in relation to optical loss.

FIG. 4 shows the relationship between the outgoing light angle of the far-field image of the outgoing light at the end of the multimode fiber and the relative light intensity. (A) shows the case where there is no angular deviation of the fiber when entering the SM light source. The emission pattern, (b) is the SM according to the present invention
FIG. 3C shows an emission pattern when there is an angular deviation of the fiber when the light source is incident, and FIG. 7C shows a normal steady mode pattern of the multimode fiber when the multimode light source is incident. As is clear from this graph, according to the mode conversion adapter of the present invention, the excitation mode in the multimode fiber can be brought close to the steady mode pattern, so that the 6 dB band of the multimode fiber can be improved.

Effect of the Invention Since the present invention is configured as described above in detail, it is excellent in economy and manufacturability, has a relatively low loss and has a sufficient 6 dB band improvement effect, and is lightweight, small in size, and easy to be mounted on a device. It is possible to provide a mode conversion adapter.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a device layout diagram for obtaining fluctuation data in a 6 dB band due to an angular deviation, FIG. 3 is a graph showing a relationship between the angular deviation and a 6 dB band, and FIG. FIG. 7 is a diagram showing a far-field image of outgoing light at the end of a multimode fiber, FIG. 5 is a schematic diagram showing amplitude attenuation by optical fiber transmission, FIG. 6 is a diagram showing optical fiber transmission band, FIG. Is a diagram showing an example of the refractive index distribution of a GI multimode fiber, FIG. 8 is a layout diagram of a conventional 6 dB band measuring device, FIG. 9 is a graph showing a 6 dB band improvement example by the conventional example, and FIG. 10 is a spot size. FIG. 11 is a graph showing the relationship between the spot size and the 6 dB band, and FIG. 11 is a device layout diagram for measuring the relationship between the 6 dB band and 6 dB band. 12 ... Mode conversion adapter, 14 ... First receptacle with flange, 16 ... Second receptacle with flange, 18 ... Tapered spacer, 24 ... Single-mode fiber, 26, 32 ... Optical connector, 28, 34 ... ferrule, 30 ... multimode fiber.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiko Takeda 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) References JP-A-63-71811 (JP, A) JP-A-62-78506 (JP, A)

Claims (1)

[Scope of utility model registration request] 1. A light source side single mode fiber (24) and a light receiving side multimode fiber (30) are respectively connected to an optical connector (2).
6,32), and the optical connectors (26) of the single mode fiber (24) are coupled in a mode conversion adapter that couples the optical connectors (26, 32) to convert single mode to multimode. First receptacle (14) and multimode fiber (30)
A second receptacle (16) to which the optical connector (32) of (1) is coupled, and the first (14) and the second receptacle (16) are sandwiched by a tapered spacer (18) inclined at a predetermined angle. A mode conversion adapter characterized by being fixed integrally.