JPH07250025A - Signal transmitting method for optical communication system - Google Patents

Abstract

PURPOSE:To provide the signal transmitting method for enabling high-reliability optical communication even while passing light from any optical fiber at an optical communication system provided with a connecting part for the different mode fibers of a multi-mode optical fiber and a single-mode optical fiber. CONSTITUTION:A Fabry-Perot laser 4 being a light source provided with plural light emitting spectrums is connected with one terminal side 14 of a multi-mode optical fiber 1, one terminal side 16 of a single-mode optical fiber 2 being a mode fiber different from the optical fiber 1 is connected to another terminal side 15 of the optical fiber 1, and a photodiode 12 is connected to another terminal side 17 of the optical fiber 2. A beam coupling means 5 constituted by expanding the core diameter of the connected terminal side 16 of the single-mode optical fiber 2 is installed in the connecting area of the multi-mode optical fiber 1 and the single-mode optical fiber 2, and the light irradiated from the laser 4 is transmitted from the side of the multi-mode optical fiber 1 to the side of the single-mode optical fiber and made incident to a photodiode 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission method of an optical communication system having a splicing portion of different mode fibers of a multimode optical fiber and a single mode optical fiber.

[0002]

2. Description of the Related Art In the field of optical communication, optical communication has heretofore been widely carried out using optical communication cables of multimode optical fibers laid nationwide as optical communication networks. Recently, a single mode optical fiber is being used as an optical fiber in the field of optical communication, and it is necessary to connect the newly installed single mode optical fiber to the already installed multimode optical fiber to perform optical communication. The nature is increasing.

[0003]

However, as is well known, the light propagating in the multi-mode optical fiber has a different delay time for each mode, so that the light in each mode interferes with each other and the multi-mode optical fiber is caused. The intensity of light is not uniform at the end face of, and locally strong and weak portions appear, the difference in intensity is large, and the light intensity becomes a speckled pattern. The speckle pattern caused by this optical interference is very subtle because it changes easily when the human hand touches the optical fiber.Therefore, a multimode optical fiber with a large core diameter and a single mode light with a small core diameter are used. When connecting a fiber and guiding an optical signal from a multimode optical fiber to a single mode optical fiber, especially when disturbance noise or the like is added, a large intensity change occurs in the optical signal incident on the single mode optical fiber. Due to this, there is a problem that a bit error occurs when processing an optical signal and the optical communication property is impaired.It is difficult to perform optical communication through the light from the multimode optical fiber side to the single mode optical fiber side. Was considered.

Therefore, when an optical communication system is constructed by connecting different mode fibers of a multimode optical fiber and a single mode optical fiber, an optical signal is exclusively transmitted from the single mode optical fiber side to the multimode optical fiber side. Is effective, and vice versa,
Optical signal transmission from the multimode optical fiber side to the single mode optical fiber side is expected to be difficult, and it was necessary to clear this restriction when designing an optical communication system.

The present invention has been made to solve the above problems, and an object thereof is to provide an optical communication system having a connection portion of multimode optical fibers and heteromode optical fibers having different core diameters from each other. It is another object of the present invention to provide a signal transmission method for an optical communication system capable of performing highly reliable optical communication through light from any one of a multimode optical fiber and a single mode optical fiber.

[0006]

In order to achieve the above object, the present invention is constructed as follows. That is, the present invention is a signal transmission method of an optical communication system having a connection part of different mode fibers of a multi-mode optical fiber and a single mode optical fiber, in which an emission spectrum incoherent with a light source having a plurality of emission spectra is provided. It is characterized in that light is emitted from any one of the light sources that it has and that light is transmitted from one side of the multimode optical fiber to the other side.

Further, in the connection of the different mode fibers of the multimode optical fiber and the single mode optical fiber, the core diameter or the mode field diameter of the optical fiber on the emitting side and the core diameter or the mode of the optical fiber on the incident side are connected in the connection region. It is also a characteristic configuration of the present invention to make the field diameters substantially the same.

Further, the light source to be used may be any one of a Fabry-Perot type laser, a light emitting diode, and a super luminescent diode having intermediate characteristics between the Fabry-Perot type laser and the light emitting diode. It is a characteristic configuration of the invention.

[0009]

In the present invention having the above-mentioned structure, from any one of the light source having a plurality of light emission spectra and the light source having an incoherent light emission spectrum (a light emission spectrum having a width in which the phases are temporally and spatially not aligned) Since a plurality of emission spectra of emitted light interfere with each other from the beginning, when the light of such a light source is passed through the multimode optical fiber, the interference of light is caused at the end face of the multimode optical fiber. They cancel each other out and are softened, and variations in the power distribution of the light intensity at the end face of the multimode optical fiber are suppressed.

In addition, when connecting different-mode fibers such as a multimode optical fiber and a single-mode optical fiber, in the connection area, the core diameter or mode field diameter of the optical fiber on the exit side and the core diameter of the optical fiber on the entrance side are connected. Or, if the mode field diameters are approximately matched, for example,
When the optical signal propagating in the multimode optical fiber enters the single mode optical fiber side, the core diameter or the mode field diameter of the optical signal emitted from the multimode optical fiber is almost equal to the mode field diameter of the single mode optical fiber. The beam diameters are adjusted so that they coincide with each other, variation in the power distribution of light intensity is suppressed, and the light enters the single-mode optical fiber. Therefore, the occurrence of bit errors due to the variation in the power distribution of the light intensity is suppressed, light leakage does not occur even when light is incident from the single-mode optical fiber to the multi-mode optical fiber, and reliability is improved. High optical communication becomes possible.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an optical communication system for transmitting an optical signal by the signal transmission method of the optical communication system according to the present invention. In the figure, one end side 14 of the multimode optical fiber 1 is connected to the Fabry-Perot type laser 4 which is a light source, and one end side 16 of the single mode optical fiber 2 is connected to the other end side 15 of the multimode optical fiber 1. Is connected, and the other end side 17 of the single mode optical fiber 2 is connected.
A photodiode 12, which is a light receiving device, is connected to.

A beam combining means 5 is provided in the connection area between the multimode optical fiber 1 and the single mode optical fiber 2. As shown in FIG. The mode field diameter of the optical signal propagating in the core 1a (hereinafter, the mode field diameter of the multimode optical fiber 1) and the mode field diameter of the optical signal propagating in the core 2a of the single mode optical fiber 2 (hereinafter, single mode light In order to make the mode field diameter of the fiber 2 substantially equal, the diameter of the core 2a on the connection end side 16 of the single mode optical fiber 2 is expanded. The diameter of the core 2a of the single mode optical fiber 2 is increased by the single mode optical fiber 2
This is done by heating the connection end side of the with a flame of a micro torch or the like. The mode field diameter is
The diameter of the region where the light intensity is attenuated to 1 / e ² with respect to the central axis of the core.

That is, when the connection end side of the single mode optical fiber 2 is heated, the core dopant is thermally diffused, and the core 2 at the connection end of the single mode optical fiber 2 is heated.
When the diffusion of the diameter of a is promoted and the mode field diameter of the single mode optical fiber 2 becomes substantially equal to the mode field diameter of the multimode optical fiber 1 due to this thermal diffusion, the heating is stopped to The mode field diameters at the connection end faces of the mode optical fiber 1 and the single mode optical fiber 2 become substantially equal. The diffusion heating of the core diameter of the single mode optical fiber 2 may be performed by using the fusion heating means or the like at the time of fusion splicing of the multimode optical fiber 1 and the single mode optical fiber 2, and before the fusion splicing. Alternatively, after the fusion of the multimode optical fiber 1 and the single mode optical fiber 2 is performed, only the connection end side of the single mode optical fiber 2 may be heated to perform thermal diffusion.

Further, FIG. 3 shows the result of examining the emission spectrum of the Fabry-Perot type laser 4 of FIG. 1, and the light output with respect to the wavelength is detected. As shown in the figure, it can be seen that the laser 4 is a light source having a plurality of spectra between wavelengths of 1.2900 μm to 1.3400 μm centered around the wavelength of 1.3150 μm.

As described above, since the light from the light source having a plurality of emission spectra interferes with each other from the beginning, when the light from such a light source is passed through the multi-mode optical fiber 1, In the mode optical fiber 1, the interference effects of light cancel each other out and are reduced.
Compared to the case of passing light from a light source that irradiates a sharp emission spectrum of a book, the difference in intensity between a strong light portion and a weak light portion generated on the end face 18 of the multimode optical fiber 1 becomes small, and the light intensity distribution varies. Is reduced, and it becomes difficult to form a spot pattern due to the light intensity distribution. Further, since the optical interference effect in the multimode optical fiber 1 is softened, even when disturbance noise or the like is added to the multimode optical fiber 1, when light is transmitted from a light source that emits one sharp emission spectrum. In comparison, variations in the light intensity distribution on the end face 18 of the multimode optical fiber 1 are reduced.

The present embodiment is configured as described above,
Next, the operation will be described. First, when light (optical signal) is emitted from the Fabry-Perot type laser 4, the light enters the core of the multimode optical fiber 1 from the one end side 14 of the multimode optical fiber 1, passes through the multimode optical fiber 1, and End face of the other end 15 of the mode optical fiber 1
The light enters from one end 16 of the single mode optical fiber 2 from 18, but the optical communication system of this embodiment uses a Fabry-Perot type laser 4 having a plurality of emission spectra as a light source, and the light from this laser 4 is , The lights of the respective modes interfere with each other from the beginning, and when the lights pass through the multimode optical fiber 1, the interference effects of the lights cancel each other out and are softened, and the light intensity at the end face 18 of the multimode optical fiber 1 Variation is suppressed.

Then, in the connection area between the multimode optical fiber 1 and the single mode optical fiber 2, the light is
Since the light is incident on the core of the single mode optical fiber 2 that is substantially the same as the core diameter 1a of the multimode optical fiber 1,
The optical signal propagating from the multimode optical fiber 1 is incident on the single mode optical fiber 2 side with almost no leakage in a state in which the fluctuation of the power distribution of the light intensity is suppressed.

The light is a single mode optical fiber 2
Exits from the other end 17 of the single mode optical fiber 2 and enters the photodiode 12 to enter the photodiode.
The signal is converted into an electric signal at 12 and signal processing is performed by a signal processing circuit provided in the photodiode 12.

As described above, according to this embodiment, the Fabry-Perot type laser 4 having a plurality of emission spectra is used, and the lights of the respective modes interfere with each other from the beginning. When passing through the mode optical fiber 1, the interference effect of light is softened in the multimode optical fiber 1, and the end face of the multimode optical fiber 1 is compared with the case where light from a light source that emits a single sharp emission spectrum is passed.
The variation of the power distribution of the light intensity in 18 is suppressed,
Further, the beam combining means 5 makes the core diameters or the mode field diameters of the connection end faces of the multimode optical fiber 1 and the single mode optical fiber 2 substantially equal to each other, so that the beam spot diameter of the emission end of the multimode optical fiber 1 becomes smaller. Since the core diameter (or mode field diameter) of the single-mode optical fiber 2 is substantially the same, the optical signal propagating from the multi-mode optical fiber 1 is singled in a state in which the fluctuation of the power distribution of the optical intensity is suppressed. It is possible to make the light incident on the mode optical fiber 2 side, reduce fluctuations in connection loss due to fluctuations in power distribution, and reduce bit errors that may occur in the signal processing stage of optical signals. And thereby, the reliability of an optical communication system can be improved.

FIG. 4 shows the connection state of the multimode fiber 1 and the single mode fiber 2 in the second embodiment of the optical communication system for transmitting an optical signal by the transmission method of the optical communication system of the present invention. There is. The second embodiment is also the first
In the same manner as in the above example, one end side of the multimode optical fiber 1
14 is connected to the Fabry-Perot type laser 4, and the other end 17 of the single mode optical fiber 2 is a photodiode.
Connected to 12.

In the second embodiment, the connection end of the multimode optical fiber 1 is heated by a flame of a microtorch or the like, melted and stretched to form the beam coupling means 5, and the exit end of the multimode optical fiber 1 is formed. Single mode optical fiber with core diameter 2
The multimode optical fiber 1
Therefore, only the LP01 mode (all optical signals in modes other than the LP01 mode are emitted) is made incident on the single mode optical fiber 2. The diameter reduction of the core by the heating and stretching of the multimode optical fiber 1 is performed before the connection with the single mode optical fiber 2 and then,
The multimode optical fiber 1 and the single mode optical fiber 2 may be connected by fusion or the like, or after the multimode optical fiber 1 and the single mode optical fiber 2 are fused and connected, the multimode optical fiber 1 side Alternatively, the diameter of the core 1a of the multimode optical fiber 1 may be reduced by heating and melting and stretching only the connection end portion thereof.

FIG. 5 shows an apparatus for producing the beam combining means 5 by melt drawing. A micro torch 7 as a heating means is mounted on a base 6 so as to be movable in the left and right directions. Stages 8 and 9 are arranged on the left and right sides of the torch 7 so as to be movable in the left and right directions, and a clamp 1 for gripping an optical fiber is provided on the upper side of each stage 8 and 9.
0 and 11 are provided. The lateral movements of the micro torch 7 and the stages 8 and 9 are controlled by a control device such as a personal computer (not shown).

After the multi-mode optical fiber 1 and the single-mode optical fiber 2 are fusion-spliced, the spliced optical fibers are hung on the stages 8 and 9 and clamped by the clamps 10 and 11, and the micro-torch 7 is used for fusion-splicing. Among them, the part on the side of the multimode optical fiber 1 is heated and melted, and the stage on the side of the clamp holding the multimode optical fiber 1 is moved in the tension applying direction, whereby the melt drawing of the multimode optical fiber is performed. And multimode optical fiber 1
The diameter of the core 1a is reduced. As a result, the diameter of the core 1a of the multimode optical fiber 1 is substantially equal to the diameter of the core 1a of the single mode optical fiber 1, and a good beam combining means 5 is formed.

In the second embodiment as well, the optical signal emitted from the Fabry-Perot laser 4 is transmitted from the multimode optical fiber 1 side to the single mode optical fiber 2 side by the same operation as in the first embodiment, and the photodiode is Incident on 12. Further, also in the second embodiment, since the light source is the Fabry-Perot type laser 4 having a plurality of emission spectra, light interference on the end face 18 side of the multimode optical fiber 1 is softened and the power distribution of the light intensity is reduced. Is suppressed, and the core diameters of the connection end faces of the multimode optical fiber 1 and the single mode optical fiber 2 are substantially the same,
An optical signal in which the fluctuation of the power distribution is suppressed can be made incident on the single mode optical fiber 2 from the multimode optical fiber 1, and signal processing with few bit errors can be performed as in the first embodiment.

FIG. 6 shows a third optical communication system for transmitting an optical signal according to the signal transmission method of the optical communication system of the present invention.
The connection state of the multi-mode optical fiber 1 and the single-mode optical fiber 2 of the embodiment of FIG. Similarly to the first and second embodiments, the third embodiment is also connected to the Fabry-Perot laser 4 and the photodiode 12. In the third embodiment, the multimode optical fiber 1 and the single mode optical fiber are connected. 2 and 2 are opposed to each other with a space therebetween, and a lens 3 as a beam coupling means is interposed between the connection end faces of the multimode optical fiber 1 and the single mode optical fiber 2. The lens 3 has a refraction structure in which the beam spot of the emission pattern of the multimode optical fiber 1 is focused into a spot size of the diameter of the core 2 a of the single mode optical fiber 2 and is incident on the single mode optical fiber 2.

The third embodiment also operates similarly to the first and second embodiments, and the optical signal emitted from the Fabry-Perot type laser 4 is transmitted from the multimode optical fiber 1 side to the single mode optical fiber 2 side. It is transmitted and enters the photodiode 12. Also in the case of this embodiment, as in the first and second embodiments, the light interference at the end face 18 of the multimode optical fiber 1 is softened, and the optical signal in which the fluctuation of the power distribution is suppressed is converted into the multimode light. The light can be made incident on the single mode optical fiber 2 from the fiber 1, whereby signal processing with few bit errors can be performed.

FIG. 7 shows a fourth optical communication system for transmitting an optical signal by the signal transmission method of the optical communication system according to the present invention.
The connection state of the multi-mode optical fiber 1 and the single-mode optical fiber 2 of the embodiment of FIG. Also in the fourth embodiment, as in the above embodiments, the Fabry-Perot type laser 4 is used.
And is connected to the photodiode 12. In this embodiment, the connection end of the multimode optical fiber 1 and the single mode optical fiber 2 is melted and stretched by heating the connection end of the single mode optical fiber 2 by heating the flame of a microtorch, and the like. The mode field diameter is expanded to form the beam coupling means 5, and the mode field diameter of the connection end face of the single mode optical fiber 2 is made substantially equal to the mode field diameter of the multimode optical fiber 1.

By melting and extending the connecting end of the single mode optical fiber 2, the diameter of the core 2a of the single mode optical fiber 2 is reduced, and the diameter of the core 2a on the connecting end face side becomes very small like a needle. . Core 2a
If the diameter of the core becomes smaller, the optical signal cannot be confined inside this small core space, and the optical signal has the property of diffusing out from the needle-shaped core 2a, and the mode field diameter becomes expanded. By the melt drawing of the single mode optical fiber 2, the single mode optical fiber 2
The mode field diameter of 1 can be substantially matched with the mode field diameter of the multimode optical fiber 1.

The fusion drawing of the single mode optical fiber 2 may be performed at the time of fusion splicing the multimode optical fiber 1 and the single mode optical fiber 2, or after the fusion splicing, or the multimode optical fiber. It may be performed at a stage before fusion-splicing 1. When the single-mode optical fiber 2 is melt-stretched after fusion-splicing, the multi-mode optical fiber 1 and the single-mode optical fiber 2 are fusion-spliced, and then the fusion-splicing optical fiber is connected to the stage of the apparatus shown in FIG. Clamps between 8 and 9
Grasping with 10 and 11, heating and melting the connection end side of the single mode optical fiber 2 in the fusion splicing region, in this state,
By moving the stage on the clamp side holding the single mode optical fiber 2 in the tension applying direction, the core 2a of the single mode optical fiber 2 is stretched, and the mode field diameter of the multimode optical fiber 1 and the single mode optical fiber 2 are increased. The mode field diameters of can be made substantially the same.

In the fourth embodiment, the same operation as in the above-mentioned respective embodiments is performed, and the optical signal emitted from the Fabry-Perot type laser 4 is transmitted from the malt mode optical fiber 1 side to the single mode optical fiber 2 side and photo It is incident on the diode 12. Also, in the fourth embodiment, it is possible to obtain the same effect as that of the above-mentioned embodiment and reduce the occurrence of bit errors at the optical signal processing stage.

FIG. 8 shows a fifth optical communication system for transmitting an optical signal according to the signal transmission method of the optical communication system of the present invention.
The connection region of the multi-mode optical fiber 1 and the single-mode optical fiber 2 of the embodiment of the above is shown. After the multi-mode optical fiber 1 and the single-mode optical fiber 2 are fusion-spliced as shown in FIG. , The fusion-spliced region is heated and melted, and the multimode optical fiber 1 and the single mode optical fiber 2 are drawn together to form the multimode optical fiber 1.
After making the core diameter (mode field diameter) and the mode field diameter of the single-mode optical fiber 2 substantially coincide with each other, one end side 14 of the multi-mode optical fiber 1 is attached to the Fabry-Perot type laser 4 as in the above embodiments. And the other end 17 of the single mode optical fiber 2 is connected to the photodiode 12.

In FIG. 8, first, as shown in FIG. 8A, the multimode optical fiber 1 and the single mode optical fiber 2 are connected by fusion. In the case of this embodiment, the core diameter of the multimode optical fiber 1 is 50 μm,
The outer diameter of the fiber is 125 μm, the core diameter of the single mode optical fiber 2 is 10 μm, and the outer diameter of the optical fiber is
125 μm. This fusion spliced optical fiber is shown in FIG.
The multimode optical fiber 1 side is clamped by, for example, the clamp 10, and the single mode optical fiber 2 side is clamped by the clamp 11. In this gripped state, the fusion splicing portion is arranged to face the micro torch 7.

In this state, the flame of the micro torch 7 is applied to the fusion splicing portion to heat it, and the stages 8 and 9 are applied with tension 3.
Then, melt drawing is carried out as shown in FIG.
In this embodiment, the melt drawing is performed so that the outer diameter of the substantially central portion (connection portion) is
It is carried out until it becomes 70 μm or less (more preferably 60 μm or less). As a result, the multimode optical fiber 1
The core diameter of the connection end portion of is reduced to 24 μm or less.

In the single mode optical fiber 2 in this example, when the outer diameter is reduced to 70 μm or less, the electric power (optical signal) inside the fiber cannot be completely confined in the core 2a, and conversely, Wider field diameter. Therefore, when the outer diameter of the single mode optical fiber 2 is reduced to 70 μm or less, the mode field diameter is expanded to 20 μm or more, and as a result, the core diameter (mode field diameter) of the multimode optical fiber 1 is increased. The mode field diameter of the single-mode optical fiber 2 substantially coincides with each other, and the optical coupling in which the fluctuation of the power distribution of the light intensity is suppressed is achieved. After the melt drawing, the fusion spliced region is reinforced by a reinforcing member (not shown) (the reinforcing member is also reinforced in the first, second, and fourth embodiments).

The fifth embodiment also performs the same operation as each of the above embodiments, has the same effect, and can reduce the occurrence of bit errors at the optical signal processing stage.

The present invention is not limited to the above-mentioned embodiments, and various embodiments can be adopted. For example, in each of the above-described embodiments, the case where the optical signal is propagated from the multimode optical fiber 1 to the single mode optical fiber 2 has been described, but conversely, the optical signal is propagated from the single mode optical fiber 1 to the multimode optical fiber 2. This is also applied to the case of propagation, and as shown in FIG. 9, the multimode optical fiber 1 and the single mode optical fiber 2 are used.
The light emitted by the Fabry-Perot laser 4 may be passed through the multimode optical fiber 1 and the single mode optical fiber 2 and received by the photodiode 12 by designing an optical communication system in which the two are alternately connected. Absent.

By thus transmitting light by the signal transmission method of the optical communication system of the present invention, various optical communication systems can be designed appropriately, and either a multimode optical fiber or a single mode optical fiber can be designed. It is possible to perform highly reliable optical communication even through light from the optical fiber.

In each of the first, second and fourth embodiments,
Only the core diameter (mode field diameter) of the optical fiber on one side of the multimode optical fiber 1 and the single mode optical fiber 2 is expanded or reduced so as to match the core diameter (mode field diameter) of the optical fiber on the other side. However, even in these examples, the core diameter (mode field diameter) of the connection end of the optical fiber on one side to be connected is expanded,
The core diameter (mode field diameter) of the optical fiber on the other side is reduced so that the core diameter of the optical fiber on one side (mode field diameter) and the core diameter of the optical fiber on the other side (mode field diameter) are approximately equal. You may make it match.

Further, in the first, second, fourth and fifth embodiments, the fusion splicing area is heated by the flame of the micro torch, but it may be heated by other heating means such as arc discharge. Good.

Further, in the case where the fusion drawing is performed by heating the fusion splicing region, light is incident from one side of the fusion spliced optical fiber, and the power of the optical signal is monitored at the other end side. If done, disconnection and the like can be easily seen, which is very convenient for work.

Further, when the light from the light source is passed through the multimode optical fiber 1 and the single mode optical fiber 2 for optical communication, the transmission speed of the light is slow and the light is transmitted through the multimode optical fiber 1. When the distance is short, for example, about 50 m, the variation of the light intensity distribution on the end face 18 of the multimode optical fiber 1 due to the interference effect of light passing through the multimode optical fiber 1 does not become so large as to cause a bit error. In the connection region between the multimode optical fiber 1 and the single mode optical fiber 2, the core diameter or the mode field diameter of the multimode optical fiber 1 and the single mode optical fiber 2 do not necessarily need to be substantially the same as in the above embodiment. I do not care.

Further, in the above embodiment, the Fabry-Perot type laser 4 was used as the light source, but the light source used is not limited to the Fabry-Perot type laser 4 and may be, for example, a light emitting diode, and the Fabry-Perot type laser 4. A super luminescent diode or the like having a high power, which has an intermediate property with respect to the light emitting diode, may be used.

Further, in the above embodiment, the Fabry-Perot type laser 4 as the light source had a plurality of emission spectra as shown in FIG. 3, but the wavelength and intensity distribution of the light emitted from the light source, etc. Is not particularly limited, for example, the light of the emission spectrum as shown in FIG. 10, may be used, the optical communication system, a plurality of emission spectra, or by irradiating the light of the incoherent emission spectrum from the light source. Any system may be used as long as it transmits the light from one side of the multimode optical fiber 1 and the single mode optical fiber 2 to the other side.

Further, although the photodiode 12 is used as the light receiving device in the above embodiment, the light receiving device is not limited to the photodiode 12 and may be another light receiving device.

[0045]

According to the present invention, light is emitted from any one of a light source having a plurality of emission spectra and a light source having an incoherent emission spectrum such as a Fabry-Perot type laser, a light emitting diode or a super luminescent diode. However, since the light emitted from these light sources has a plurality of emission spectra that interfere with each other from the beginning,
When the light is passed through the multimode optical fiber, the interference effects of the light cancel each other out, and the light from the light source that emits one sharp emission spectrum is compared to the case where the light is passed through the multimode optical fiber. It is possible to reduce the variation in the light intensity distribution on the end face of the. Also,
By reducing the optical interference effect in this way, even when disturbance noise is added to the multimode optical fiber,
The variation in the light intensity distribution can be reduced as compared with the case of using a light source that emits a sharp emission spectrum of a book.

Then, in the connection region of different mode fibers of the multimode optical fiber and the single mode optical fiber, the core diameter or mode field diameter of the optical fiber on the output side and the core diameter or mode field diameter of the optical fiber on the input side are set. By making them substantially coincident with each other, it is possible to suppress the fluctuation of the power distribution of the light intensity of the optical signal incident on the single mode optical fiber from the multimode optical fiber.
Of course, even when light enters from a single-mode optical fiber to a multi-mode optical fiber, the light does not leak, so it does not cause any bit error in the optical signal processing stage, even if light is passed from any optical fiber of the optical communication system. It is possible to reduce the occurrence of noise, and it is possible to significantly improve the reliability of optical communication.

Further, the means for making the core diameters or mode fields of both fibers in the connecting region of the different mode fibers of the multimode optical fiber and the single mode optical fiber substantially coincide with each other is fusion of the multimode optical fiber and the single mode optical fiber. By heating the connection area,
Alternatively, since it can be formed by an extremely simple method in which at least one optical fiber fusion-spliced while being heated is melt-stretched, its utility value is very large.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical communication system for transmitting an optical signal by a signal transmission method for an optical communication system according to the present invention.

FIG. 2 is a cross-sectional explanatory view showing a connection state of a multimode optical fiber 1 and a single mode optical fiber 2 of FIG.

FIG. 3 is a graph showing an emission spectrum of the Fabry-Perot laser of FIG.

FIG. 4 is an explanatory sectional view showing a connection state of a multimode optical fiber 1 and a single mode optical fiber 2 of a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an example of an apparatus for melt-drawing an optical fiber.

FIG. 6 is a cross-sectional explanatory view showing a connection state of a multimode optical fiber 1 and a single mode optical fiber 2 of a third embodiment of the present invention.

FIG. 7 is an explanatory cross-sectional view showing a connection state of a multimode optical fiber 1 and a single mode optical fiber 2 according to a fourth embodiment of the present invention.

FIG. 8 is a view showing a fifth embodiment of the present invention in which a connection area between a multimode optical fiber 1 and a single mode optical fiber 2 is melt-stretched together so that the mode field diameters of the connection areas of both optical fibers 1 and 2 are substantially the same. It is explanatory drawing which shows a process.

FIG. 9 is an explanatory diagram showing another embodiment of the optical communication system for transmitting an optical signal by the signal transmission method of the optical communication system of the present invention.

FIG. 10 is an explanatory diagram showing an example of an emission spectrum of a light source used in the signal transmission method of the optical communication system of the present invention.

[Explanation of symbols]

 1 multimode optical fiber 2 single mode optical fiber 1a, 2a core 3 lens 4 Fabry-Perot type laser 5 beam combining means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location G02B 6/24 (72) Inventor Shintaro Izumi vs. 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Industry Co., Ltd. (72) Inventor Kazutaka Kinoshita 1-3-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Inc. (72) Inventor Takeo Numanoi 1-3-3 Uchiyuki-cho, Chiyoda-ku, Tokyo Tokyu Electric Power Within the corporation

Claims (3)

[Claims] 1. A signal transmission method of an optical communication system having a splicing part of hetero-mode fibers of a multi-mode optical fiber and a single-mode optical fiber, which has an emission spectrum incoherent with a light source having a plurality of emission spectra. A signal transmission method for an optical communication system, characterized in that light is emitted from any one of the light sources and the light is transmitted from one side of the multimode optical fiber to the other side of the single mode optical fiber. 2. A multi-mode optical fiber and a single-mode optical fiber are connected to each other by different-mode fibers such that a core diameter or a mode field diameter of an emission-side optical fiber and a core diameter or a mode of an incident-side optical fiber are formed in the connection region. 2. The signal transmission method for an optical communication system according to claim 1, wherein the field diameters are substantially matched. 3. The light source used is any one of a Fabry-Perot type laser, a light emitting diode, and a super luminescent diode having intermediate characteristics between the Fabry-Perot type laser and the light emitting diode. The signal transmission method of the optical communication system according to claim 1 or 2.