JPH04147116A - Method for optical branch transmission and device for optical branch amplification - Google Patents

Abstract

PURPOSE:To cope speedily with an increase in the number of repeater stations by branching signal light into plural components by the optical branch amplification device and inputting a least one of branch outputs of this optical branch amplification device to another optical branch amplification device. CONSTITUTION:The respective repeater stations 2a - 2c are easy equipped with an optical branch amplification device, which branches the signal light into two components and sends one to another repeater station and branches and sends the other to plural users 3. Consequently, when the repeater stations increase in number, the repeater stations are only linked by an optical fiber 10 without varying the number of signal light branches at a transmission station 1. Consequently, the increase in the number of the repeater stations can be coped with speedily.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical branching transmission method and an optical branching amplification device for relaying signal light from a source station to a relay station or from a relay station to another relay station. In particular, the present invention relates to an optical branching transmission method and an optical branching amplification device suitable for transmitting images in CATV (cable television) and the like.

[Conventional technology] FIG. 4 is a schematic diagram showing a conventional signal light transmission method.

Conventionally, in 0ATV and the like, signals are transmitted from a transmitting station 11 to a plurality of relay stations 12 in a star pattern.

That is, the transmitting station 11 and the plurality of relay stations 12 are connected to the optical fiber 2.
Connected by 0. Then, from transmitting station 11,
Signal light is transmitted toward each relay station 12 . Each relay station 1
2 receives this signal light, distributes and amplifies the signal, and sends the signal to a plurality of users 13.

Therefore, conventionally, optical fibers 20 are directly installed between the transmitting station 11 and each relay station 12. In this case, the number of relay stations 12 must be determined in advance, and the number of relay stations 12 must be determined in advance.
In this case, it is necessary to branch the signal light in advance by the number of relay stations 12.

[Problems to be Solved by the Invention] However, conventionally, in the transmitting station 11, the relay station 1
2, the number of signal lights to be distributed from the transmitting station 11 to the relay stations 12 can be greatly increased.
When making changes such as distributing signal light from the relay station 12 to a plurality of other relay stations 12, there is a problem in that it is not possible to respond quickly.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide an optical branching transmission method and an optical branching amplification device that can quickly respond to changes in the number of signal light distributions.

[Means for Solving the Problems] An optical branching transmission method according to the present invention branches a signal light into a plurality of parts using an optical branching and amplifying device, and transmits at least one of the branched outputs of the optical branching and amplifying device to another. It is characterized by being input to an optical branching and amplifying device.

An optical branching and amplifying device according to the present invention includes an optical fiber coupler having a pair of input ends and a pair of output ends, and an optical fiber amplifier connected to one output end of the optical fiber coupler, The optical fiber coupler outputs a combined signal obtained by combining a signal light input from one input end and a signal light input from the other input end to the one output end,
A signal obtained by branching the signal light is output to the other output end.

[Operation] In the optical branching and transmission method according to the present invention, a signal light is branched into a plurality of optical branches by an optical branching and amplifying device, and at least one branched output of this optical branching and amplifying device is inputted to another optical branching and amplifying device. That is, in the present invention, each relay station is equipped with an optical branching and amplifying device. By connecting these optical branch amplifiers in series, the increase in the number of relay stations can be handled by connecting the optical branch amplifiers installed at each relay station without increasing the number of signal branches at the transmitting station. be able to.

In the optical branching and amplifying device according to the present invention, pump light input to one input end of an optical fiber coupler is multiplexed with signal light input from the other input end. The multiplexed signal is input to an optical fiber amplifier, amplified by the optical fiber amplifier, and then output from the optical branching amplifier. As a result, signal light is sent out from one output end of the optical fiber coupler with relatively high output. Therefore, even if a plurality of optical branching amplifiers are connected in series, signal deterioration can be suppressed. Further, a signal obtained by branching the signal light is output from the other output end of this optical fiber coupler. This signal can be branched into multiple branches depending on the number of users.

The branching ratio of the optical fiber coupler to the excitation light is preferably 95% or more. If the branching ratio of the optical fiber coupler to the pumping light is less than 95%, the coupling of the pumping light to the optical fiber coupler is small, so the input to the fiber amplifier is reduced, and a large amplification factor cannot be achieved.

Therefore, it is preferable that the branching ratio of the optical fiber coupler to the excitation light is 95% or more.

Also, the branching ratio of the optical fiber coupler for the signal light is 1
Preferably, it is 0 to 50%. If the branching ratio of the optical fiber coupler to the signal light is less than 10%, S/
Since the N ratio deteriorates, the quality when reproducing the signal is not sufficient. Furthermore, if the branching ratio of the optical fiber coupler to the signal light exceeds 50%, the amplification degree in the excitation fiber will be saturated because the input of the signal light is large. Furthermore, in the case of a single point branch, the input to the photoelectric converter is saturated. Therefore, the branching ratio of the optical fiber coupler for the signal light is lO to 50
% is preferable.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing an example method of the present invention.

The signal light sent out from the transmitting station 1 is inputted via the optical fiber 10 to an optical branching and amplifying device provided at the first relay station 2a. This optical branching amplifier device splits the input signal light into two
The signal light is branched, and one signal light is amplified and sent to the second relay station 2b via the optical fiber 10. Then, the other signal light is branched into a plurality of lights by a branching device and sent out to a plurality of users 3a.

The second relay station 2b branches the signal light from the first relay station 2a into two by an optical branching and amplification device, amplifies one of the signal lights, and sends it to the third relay station 2c via the optical fiber 10. do. Then, like the first relay station 2a, the other signal light is branched into a plurality of signals, and these signals are sent out to a plurality of users 3b.

The third relay station 2c branches the signal from the second relay station 2b into two using an optical branching and amplifying device. Then, one signal light is branched into a plurality of signals, and these signals are sent out to a plurality of users. Furthermore, the other signal light can be sent to another relay station as needed.

In this embodiment, each of the relay stations 2a, 2b, and 2C is equipped with an optical branching and amplifying device, and after branching the signal light into two, the optical branching and amplifying device sends the signal light to the other relay station. The other part is branched into multiple parts and sent to multiple users. Therefore, when the number of relay stations increases, it is sufficient to connect the relay stations with optical fibers without changing the number of signal light branches at the originating station. This makes it possible to quickly respond to an increase in the number of relay stations.

FIG. 2 is a schematic diagram showing an optical branching and amplifying device according to an embodiment of the present invention.

This optical branching and amplification device includes a pumping semiconductor laser 5, an optical fiber coupler (wavelength multiplexing coupler) 6, an optical amplification fiber (optical fiber amplifier) 7, an optical isolator 8, and filters 9a and 9b.

The excitation semiconductor laser 5 generates excitation light in the 1.48 μm band, for example. This excitation light is input to the optical fiber coupler 6. On the other hand, the optical fiber coupler 6 receives, for example, a signal light in the 1.55 μm band. The excitation light is
This coupler 6 combines the signal light with the signal light. Further, the signal light is split into two at this coupler 6.

The optical amplification fiber 7 is composed of a fiber doped with erbium (Er). When the excitation light enters the optical amplification fiber 7, a population inversion is formed. The signal light is amplified by making the signal light incident on the portion where this population inversion is formed. This amplified signal light is sent out through an isolator 8 for preventing laser oscillation due to reflected light and a filter 9a for removing light other than the signal light, and is used as a signal to be input to another optical branching amplifier. used.

Further, the other signal light branched by the coupler 6 is sent out to the outside via the filter 9b, and is branched according to the number of users.

Optical fiber coupler is 100% attached to the pump light amplification fiber.
Preferably, they are combined. Usually, the branching ratio of an optical fiber coupler is 95 to 100% for the excitation light, but
For signal light, it is 10 to 50%.

Figure 3 shows the wavelength on the horizontal axis and the degree of coupling on the vertical axis.
FIG. 2 is a graph diagram showing the degree of coupling between the optical fiber coupler used in this example and a conventional optical fiber coupler.

As is clear from this figure, the optical fiber coupler used in this example has a branching ratio of about 95 to 100% for light with a wavelength of 1.48 μm, similar to the conventional one, but for light with a wavelength of 1.48 μm. In the case of light in the vicinity of 55 μm, any signal strength can be obtained at that wavelength by appropriately controlling the branching ratio. Therefore, the signal can be efficiently amplified and the signal light can be branched as appropriate.

Such fiber couplers are achieved by controlling the coupling ratio of the fibers.

Next, the results of investigating the signal loss when the optical branching amplifier according to this embodiment was actually manufactured and transmitting a signal will be explained.

A 200m optical amplifier (amplification fiber) made of erbium-doped optical fiber is used, and this optical amplifier has the following characteristics:
Excitation light in the 1.48 μm band emitted from a semiconductor laser for excitation was input. The output of this excitation light is 100 mW. This optical amplifier amplifies the input signal light by 25 dB.

The signal light in the 1.55 μm band that is incident on the optical fiber coupler that combines the signal light and the excitation light is split into two in this coupler, and two signal lights with an output level of 115 dBm are obtained. One of the signal lights branched by the coupler is output to the outside through a filter. This signal light was branched into 10 branches by an external branching device and distributed to each usage site. In this case, even if connector loss was added, a receiving sensitivity of -28 dBm or more could be obtained at each used site.

On the other hand, the other signal light branched by the coupler is attenuated by about 5 dB before being input to the other branch amplifier.
Since it is amplified by 25 dB by the optical amplifier, it is effectively 5 dB.
The Bm signal light is input to the next optical branching amplifier.

[Effects of the Invention] As explained above, according to the method of the present invention, a signal light is branched into a plurality of optical branches by an optical branching amplifier, and at least one output of this optical branching and amplifier is inputted to another optical branching and amplifier. Therefore, without changing the number of signal light branches at the source station,
It is possible to quickly respond to the increase in the number of relay stations.

Moreover, the optical branching amplifier according to the present invention has an optical fiber coupler and an optical fiber amplifier, and since one of the signal lights branched into two is amplified and outputted by the optical fiber coupler, it is possible to use a plurality of optical branching amplifiers. Even when connected in series, signal deterioration can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment method of the present invention, FIG. 2 is a schematic diagram showing an optical branching and amplifying device according to an embodiment of the present invention, and FIG.
The figure is a graph showing the degree of coupling between the optical fiber coupler used in the example and the conventional optical fiber coupler.
The figure is a schematic diagram showing a conventional signal light transmission method. 1.11; Originating station, 2a+ 2b+ 2c, 12; Relay station, 3a, 3b+ 3c+ 13; User, 5;
Excitation semiconductor laser, 6; optical fiber coupler 7; amplification fiber, 8; optical isolator, 9a.

Claims (3)

[Claims] (1) An optical branching transmission method characterized in that a signal light is branched into a plurality of parts by an optical branching amplifier, and at least one output of the branched outputs of the optical branching amplifier is inputted to another optical branching amplifier. . (2) An optical fiber coupler having a pair of input ends and a pair of output ends, and an optical fiber amplifier connected to one output end of the optical fiber coupler, wherein the optical fiber coupler has one of the output ends. A combined signal obtained by combining the signal light input from the input end and the signal light input from the other input end is output to the one output end, and the signal light is branched to the other output end. An optical branching amplifier characterized by outputting a signal. (3) The optical branching and amplifying device according to claim 2, wherein the branching ratio of the optical fiber coupler is 95% or more with respect to the pumping light and 10 to 50% with respect to the signal light. .