JPH0529684A - Signal folding device - Google Patents

Abstract

PURPOSE:To efficiently fold an exciting light by increasing a reflection attenuating amount of a signal light. CONSTITUTION:An exciting light/signal light separating filter 13 having characteristics for transmitting an exciting light 15 and reflecting a signal light 3 to an output end of a rare earth element-doped optical fiber 5, is obliquely disposed, and a mirror 14 for reflecting a transmitted exciting light is disposed perpendicularly to the exciting light. The light 15 is transmitted through the filter 13, reflected by the mirror 14, again transmitted through the filter 13, and folded to the fiber 5. The light 3 is reflected to be output by the filter 13. The light 3 is attenuated by 60dB or more by the filter 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal folding device used in an optical fiber communication system or the like, and, for example, to an optical amplifier having an amplifying optical fiber for amplifying incident signal light and emitting the amplified signal light.

[0002]

2. Description of the Related Art FIG. 4 shows, for example, Japanese Patent Application No. 1-29881.
It is a figure explaining the structure of the conventional optical amplifier which used the rare earth dope optical fiber as the optical fiber for amplification shown in No. 5, and is a perspective view which notched and shown one part. In FIG. 4, 1 is an optical amplifier, 2 is a housing of the optical amplifier 1, 3 is signal light incident on the optical amplifier 1, 4 is an input connector provided on the housing 2 for allowing the signal light 3 to enter, Reference numeral 5 is a rare-earth doped optical fiber used as an amplification optical fiber, and 6 is a pumping LD module which is pumping means for pumping pumping light from one end of the rare-earth doped optical fiber 5.
And 7 are LDs for driving the excitation LD module 6.
The drivers and 8 are optical couplers for making the signal light 3 and the pumping light incident on the rare earth doping optical fiber 5, and 9 is the rare earth doping.
In order to take out the signal light 3 amplified in the optical fiber 5, the output connector 10 provided on the housing 2 is the signal light 3
, 11 is excitation light, and 12 is a rare earth doping light which is provided at the exit end of the excitation light of the rare earth doping optical fiber 5 and which transmits the signal light and reflects the excitation light. It is a pumping light returning means for returning the light into the fiber 5.

Further, in this embodiment, the excitation light folding means 12 is an interference filter such as a dielectric multi-layer film filter, which is brought close to the emission end of the rare earth doped optical fiber 5 and is aligned with the optical axis. It is installed vertically. Figure 5
Is an example of a general transmission characteristic of the dielectric multilayer interference filter used for transmitting the signal light 3 and reflecting the excitation light. Here, this transmission characteristic is an example of a case where light having a wavelength of 1480 nm is used as the excitation light and light having a wavelength near 1535 nm or 1552 nm is used as the signal light 3, as described below. From FIG. 4, the transmittance for the signal light 3 is 94 to 99%, and the reflectance for the excitation light is 99.9% or more.

Here, the general operation and properties of the optical amplifier of the above embodiment will be described. In the above embodiment, the wavelength of the pumping light is set shorter than the wavelength of the signal light 3, and the rare-earth doped optical fiber 5 absorbs the pumping light to generate a gain inside. When the signal light 3 having a wavelength corresponding to the gain band is incident on the rare earth doped optical fiber 5 in which the gain is generated as described above, the signal light 3 is amplified. FIG. 6 shows an example of gain wavelength distribution characteristics when an optical fiber doped with an Er element as a rare earth element is pumped with pumping light having a wavelength of 1480 nm. From Figure 5 wavelength 1535nm
It can be seen that there are gain peaks in the vicinity and in the vicinity of 1552 nm.

Therefore, the signal light 3 is usually 1535n
Light having a wavelength near m or 1552 nm is used. In the above, the amplification degree of the signal light 3 has a property that it increases in accordance with the gain generated in the rare earth doped optical fiber. Further, the gain in the rare earth-doped optical fiber has a property that it increases according to the intensity of the pumping light input from the pumping LD module 6 to the rare-earth doped optical fiber.

Next, the operation of the optical amplifier in the above embodiment will be described. In the optical amplifier configured as described above, the pumping light and the signal light 3 emitted from the pumping LD module 6 are combined by the optical coupler 8 and are incident from one end of the rare earth doped optical fiber 5. To do. At this time,
The excitation light propagates while being gradually absorbed by the rare earth in the rare earth doped optical fiber 5 and reaches the emission end. Here, the excitation light returning means 1 transmits the signal light to the emission end, reflects the excitation light, and returns it into the rare-earth doped optical fiber 5.
Two are provided.

Therefore, the amplified signal light 3 is emitted, but the pumping light is reflected and returned to the rare earth doped optical fiber 5 again. The folded excitation light returned to the rare-earth-doped optical fiber 5 again propagates in the opposite direction while being further absorbed in the rare-earth-doped optical fiber 5.

As described above, since the pumping light is used by being returned in the optical amplifier of this structure, the rare-earth doped optical fiber 5 is used.
The intensity of the excitation light inside increases. Therefore, as described above, there is an advantage that the gain is increased, a larger amplification degree is obtained, and the efficiency is high.

On the other hand, in this type of optical amplifier, when there are reflection points on both sides of the rare earth doped optical fiber 5, there is a possibility that laser oscillation will occur at the peak wavelength of the gain by using these reflection points as resonance mirrors. There is. When the laser oscillation occurs, the signal light 3 cannot be amplified, and a strong laser oscillation light enters the pumping LD module 6 to destroy the pumping LD. In particular, the gain peak near 1535 nm is larger than the gain peak near 1552 nm, so that laser oscillation is likely to occur. This laser oscillation is caused by the loss (reflection attenuation) at the reflection point and the rare earth dose.
This occurs when the amplification factors in the optical fiber 5 are balanced. Therefore, in order to obtain a large amplification degree without causing laser oscillation, it is necessary to increase the return loss at the reflection point as much as possible.

On the input side, an input connector-
4, LD module 6 for optical coupler 8 excitation, at the output side,
There is an output connector-9 and excitation light return means 12. Here, the optical coupler 8 is of a general fiber fusion type and can obtain a return loss of 40 dB or more. The LD module 6 for excitation has an isolator inserted inside.
A return loss of dB or more can be obtained. Further, in the input connector-4 and the output connector-9, a return loss of 45 dB or more can be obtained by using a super-PC polishing connector.

However, since the pumping light returning means 12 has a transmittance of 94 to 99% for the signal light 3 as described above, only a return loss of about 13 to 20 dB can be obtained and the reflection at other reflection points. Small compared to the amount of attenuation. Therefore, the amplification degree of the optical amplifier is limited by the return loss of the pumping light folding means 12.

[0012]

In the conventional optical amplifier, as described above, the interference filter as the pumping light folding means is placed close to the emitting end of the rare earth doped optical fiber and is installed perpendicularly to the optical axis. Therefore, the return loss of the signal light is only about 13 to 20 dB, which causes a problem that the amplification degree is limited.

The signal folding device according to the present invention has been made in order to solve such a problem, and efficiently folds back signals such as pumping light and at least the return loss of the signal light to other optical components. Is about the same as 40
It is intended to provide a signal folding device capable of securing at least dB.

[0014]

A signal folding device according to the present invention is an optical filter (signal separation filter) having a characteristic of reflecting signal light (first signal) and transmitting excitation light (second signal). ) Is inclined with respect to the rare earth doped optical fiber (signal transmission medium), and a mirror (reflector) that reflects the excitation light (second signal) transmitted through the optical filter (signal separation filter). Is provided.

[0015]

In the present invention, at the output end of the rare earth doped optical fiber (signal transmission medium), the excitation light (second signal) is transmitted through the optical filter (signal separation filter) and then the mirror (reflector). Is reflected by the optical filter (signal separation filter) and then returned to the rare earth doped optical fiber (signal transmission medium). On the other hand, the signal light is reflected by the optical filter (signal separation filter) and output from the signal folding device.

[0016]

EXAMPLES Example 1. FIG. 1 is a block diagram of an embodiment of an optical amplifier using a signal folding device according to the present invention. In FIG. 1, 13 is a pumping light / signal light separating filter having a characteristic of transmitting pumping light and reflecting signal light, which is obliquely inserted into an output end of a rare earth doped optical fiber, and 14 is pumping light / A mirror having a characteristic of reflecting the excitation light, which is inserted perpendicularly to the excitation light transmitted through the signal light separation filter 13, 15 is the excitation light, and 3, 5,
6, 8 and 11 are the same as those in FIG.

Next, the operation of the above embodiment will be described. Excitation light and signal light 3 emitted from the excitation LD module 6
Are merged by the optical coupler 8 and enter from one end of the rare earth doped optical fiber 5. At this time, the excitation light is rare earth
The optical fiber 5 is propagated while being gradually absorbed by the rare earth element and is emitted from the emission end.
Incident on. Here, since the excitation light / signal light separation filter 13 transmits the excitation light, the excitation light is transmitted and further the mirror 14
Incident on. Here, the pumping light is reflected by the mirror 14 and again enters the pumping light / signal light separation filter 13, passes through the pumping light / signal light separation filter 13, and then re-enters the rare-earth doped optical fiber 5.

As described above, the pumping light is returned to the rare earth-doped optical fiber 5 by the pumping light / signal light separation filter 13 and the mirror 14 and is further absorbed in the rare-earth doped optical fiber 5, while being in the opposite direction. Propagate to. Therefore,
The intensity of the excitation light in the rare earth doped optical fiber 5 increases,
Therefore, the gain is increased and a larger amplification degree is obtained.
On the other hand, the signal light 3 that is merged by the optical coupler 8 and is incident from one end of the rare earth-doped optical fiber 5 is greatly amplified as described above and then is emitted from the rare earth-doped optical fiber 5 to generate the excitation light / It enters the signal light separation filter 13. Here, since the excitation light / signal light separation filter 13 reflects the signal light 3, the signal light 3 is reflected and output.

FIG. 2 shows a pump light / signal light separation filter 13
2 is an example of a transmission characteristic of a general interference filter that can be used as As described above, it is assumed that the pumping light has a wavelength of 1480 nm and the signal light 3 has a wavelength of 1535 nm or 1552 nm. From FIG. 2, the transmittance of the interference filter for the excitation light is 94 to 9
9%, and the reflectance for the signal light is 99.9% or more. Therefore, 99.9% or more of the signal light 3 emitted from the rare earth doped optical fiber 5 and incident on the excitation light / signal light separation filter 13 is reflected and output, and 0.1% is transmitted. 0.1% of the signal light 3 that has passed through this excitation light / signal light separation filter 13 is reflected by the mirror 14, and
It re-enters the signal light separation filter 13, but here it is further 9
9.9% or more of the signal light is attenuated by reflection and re-enters the rare-earth doped optical fiber 5.

Therefore, the signal light 3 is attenuated by 60 dB or more by passing through the pumping light / signal light separating filter 13 twice. On the other hand, the amount of attenuation of the pumping light is about 0.5 dB, and the loss due to passing through the pumping light / signal light separation filter 13 twice is small.

As described above, in this embodiment, the amplification optical fiber that amplifies the incident signal light and emits it, the excitation means that makes the excitation light incident from one end of the amplification optical fiber, and excites the excitation light. In an optical amplifier comprising pumping light return means for returning the pumping light provided at the other end of the amplification optical fiber into the amplification optical fiber, the pumping light return means reflects light in the band of the signal light. An optical amplifier has been described, which is composed of a pumping light / signal light separation filter that transmits light in the band of the pumping light and a mirror that reflects the pumping light that has passed through the optical filter.

As described above, in the optical amplifier according to this embodiment, the pumping light turning-back means at the output end of the rare earth doped optical fiber has a characteristic of transmitting pumping light and reflecting signal light. By using the signal light separation filter and the mirror having the characteristic of reflecting the excitation light, it is possible to secure a reflection attenuation amount of 60 dB or more for the signal light, and to obtain a high amplification degree with stable characteristics.

Example 2. FIG. 3 is a diagram showing another embodiment of the signal folding device according to the present invention, in which signals having three types of bands are transmitted to the rare earth-doped optical fiber 5, two types of signals of which are extracted, and the remaining one type is used. This is a case where the signal of is returned. For example, 3a and 3b are signal lights having different signal bands, and 11 is an arrow indicating the path of pumping light. Further, 13a is a signal separation filter that reflects the signal light 3a, and 13b is a signal separation filter that reflects the signal light 3b. According to the signal folding device according to the present invention as in this embodiment, as shown in FIG. 3, it is possible to separate two or more signals and easily fold one signal.

Example 3. Although the amplification optical fiber is a rare-earth doped optical fiber in the above embodiments, the present invention can be applied to other amplification optical fibers and has the same effect as above. For example, it can be applied to a Raman amplifier or the like.

Example 4. Further, in the above embodiments, the rare earth-doped optical fiber is shown as an example of the signal transmission medium, but the present invention can be applied to other signal transmission media.

Example 5. Further, in the above embodiments, the case of the optical amplifying device is shown, but the signal folding device according to the present invention is not limited to the case of being used for the optical amplifying device, and other optical transmission devices, optical devices, and other signals. It can also be used for processing equipment.

[0027]

As described above, in the signal folding device according to the present invention, when the signal folding at the output end of the signal transmission medium is performed, the signal separation having the characteristic of transmitting the first signal and reflecting the second signal is performed. By constructing the filter and the reflector having the characteristic of reflecting the second signal, it is possible to secure a large amount of return loss for the first signal, and to obtain a high amplification factor with stable characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an optical amplifier using signal folding and a device according to the present invention.

FIG. 2 is a diagram showing an example of transmission characteristics of a general interference filter that can be used as a pumping light / signal light separation filter of pumping light folding means of an optical amplifier using the signal folding and device according to the present invention.

FIG. 3 is a diagram showing another embodiment of the signal folding device according to the present invention.

FIG. 4 is a partially cutaway perspective view illustrating a configuration of a conventional optical amplifier.

FIG. 5 is a diagram showing an example of a general transmission characteristic of an interference filter that is used in a pumping light folding means of a conventional optical amplifier and that transmits signal light and reflects pumping light.

FIG. 6 is an example diagram of a gain wavelength distribution characteristic when an optical fiber doped with Er element as a rare earth element is excited by pumping light having a wavelength of 1480 nm.

[Explanation of symbols]

1 Optical Amplifier 2 Housing 3 Signal Light (Example of First Signal) 4 Input Connector-5 Rare Earth Dope Optical Fiber (Example of Signal Transmission Medium) 6 LD Module for Pumping 7 LD Driver-8 Optical Coupler 9 Output connector-10 Arrow showing the path of signal light 3 11 Arrow showing the path of pumping light 12 Pumping light folding means 13 Pumping light / signal light separation filter (an example of a signal separation filter) 14 Mirror (an example of a reflector) 15 Excitation light (an example of the second signal)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01S 3/105 8934-4M

Claims (1)

Claim: What is claimed is: 1. A signal folding device (a) having the following elements: transmitting a first signal having a predetermined band and a second signal having a band different from the first signal. A signal transmission medium, (b) a signal separation filter which is provided at one end of the signal transmission medium and reflects a first signal and transmits a second signal, and (c) a second signal which has passed through the signal separation filter. A reflector that reflects and returns to the signal transmission medium.