JP3735039B2 - Wavelength multiplexed excitation Raman amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength-division-pumped Raman amplifying apparatus that is an optical fiber amplifier for performing optical amplification, and can be used as either a centralized or distributed wavelength-division-pumped Raman amplifying apparatus.
[0002]
[Prior art]
An example of using a wavelength-division-pumped Raman amplifying apparatus as an optical fiber amplifier for amplification of an optical signal has been known. There are a concentrated type and a distributed type of wavelength multiplexing excitation Raman amplifying apparatus. As shown in FIG. 3, the concentrated type is one in which an optical fiber A used as an optical amplification medium is housed in a module housing B together with an excitation light unit C, a WDM coupler D, etc., and the distributed type is used as an optical amplification medium. The optical fiber is laid outside the module housing. In any wavelength multiplexing pumping Raman amplifying apparatus, pump light is incident on an optical fiber which is a signal propagation medium and used as an optical amplifying medium, and performs optical amplification.
[0003]
[Problems to be solved by the invention]
In the conventional concentrated wavelength-division-multiplexed Raman amplifying device, the fiber length of the optical fiber used as the optical amplifying medium was selected so that the Raman gain was maximized, so the amplification efficiency was good, but it was more than a certain length However, since noise is amplified together with the signal, the S / N deteriorates as a result.
[0004]
In a conventional distributed wavelength-division-multiplexed pump Raman amplifier, the fiber length of an optical fiber used as an optical amplifying medium depends on the installation environment. Therefore, it is not always necessary to select the fiber length so that the gain is maximized. was difficult. For this reason, the desired amplification efficiency could not be obtained.
[0005]
[Means for Solving the Problems]
An object of the present invention is to provide a wavelength multiplexing pump Raman amplifying apparatus with good amplification efficiency and less optical signal degradation due to noise.
[0006]
A first wavelength multiplexing pump Raman amplifying apparatus according to the present invention is a wavelength multiplexing pump Raman amplifying apparatus using an optical fiber for optical amplification, wherein the fiber length of an optical fiber used as an optical amplifying medium is determined by differentiating the fiber length and the Raman gain. By setting the length near the intersection between the Raman gain characteristic indicating the relationship with the value and the fiber loss characteristic indicating the fiber loss per unit length, the S / N is set to a length that is the best or the vicinity thereof. is there.
[0007]
According to a second wavelength-division-pumped Raman amplifying apparatus of the present invention, in the wavelength-division-pumped Raman amplifying apparatus according to claim 1, an optical fiber used as an optical amplifying medium is housed in a module housing together with a pumping light source, WDM, and the like. A centralized type or a distributed type installed outside the casing of the module.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the wavelength division multiplexing Raman amplifying device of the present invention will be described below with reference to FIGS. The relationship between the fiber length of the optical fiber used as the optical amplification medium and the Raman gain differs depending on the type (line type) of the optical fiber. For example, the Raman gain characteristic showing the relationship between the fiber length of a typical DCF (Dispersion Compensating Fiber), the differential value of the Raman gain, and the fiber loss per unit length is as shown in FIG. The fiber loss characteristic indicating the relationship between the fiber length and gain differential value of the dispersion shifted fiber and the fiber loss per unit length is as shown in FIG. Here, both a line in FIGS. 1 and 2 represent the slope of Raman gain of each fiber, and both b lines in FIGS. 1 and 2 represent fiber loss per unit length. From these, it can be seen that the Raman gain increases gently as the fiber length increases, reaches a maximum at a certain fiber length, and then decreases. On the other hand, since the fiber loss per unit length is always constant, the fiber loss increases as the fiber length increases. Here, in any fiber, it is known that the rate of increase in fiber loss (a line in FIGS. 1 and 2) with respect to a certain length of fiber length is the same as the rate of increase in noise. In the compensation fiber, the point where the a line and the b line in FIG. 1 intersect becomes the point where the difference between the Raman gain and the noise is the largest, that is, the best S / N point. Here, the corresponding fiber length is approximately 4 km. Similarly, in the non-zero dispersion shifted fiber, the point where the a line and the b line in FIG. 2 intersect is the point where the difference between the Raman gain and the noise is the largest, that is, the best S / N point, and the corresponding fiber length is optimum. Become long. The relationship between the fiber length, the differential value of Raman gain, and the fiber loss per unit length varies depending on the line type as shown in FIGS. 1 and 2, but the intersection of both lines is the best S / N point. Absent. That is, the present invention is not limited to the fiber types already shown, but for all fiber types such as SMF (single mold fiber), RDF (inverted dispersion fiber), DSF (dispersion shifted fiber), and HNLF (highly nonlinear fiber). Is equally applicable.
[0009]
The wavelength multiplexed pump Raman amplifying apparatus of the present invention in which the fiber length is set as described above can be employed for both concentrated and distributed types. In the case of the distributed type, depending on the fiber installation environment, the length of the intersection of the a line and the b line is not necessarily set, so the length is slightly shifted to the left and right. be able to. The allowable range is about + -0.5L when the optimum fiber length is L. When the upper limit of the allowable range is exceeded, the noise increases and the S / N deteriorates. Sufficient Raman gain efficiency cannot be obtained and it cannot be put into practical use.
[0010]
In the above description, the S / N best point of the optical fiber amplifier or the fiber length in the vicinity (optimum fiber length) is obtained from the relationship between the fiber length, the differential value of Raman gain, and the fiber loss per unit length. Of course, the optimum fiber length can also be obtained from the relationship between the fiber length, gain characteristics, and noise. In that case, the optimum fiber length is determined at a location where the difference between the Raman gain and the noise is maximum, that is, the S / N best point.
[0011]
【The invention's effect】
In the wavelength multiplexing pump Raman amplifying apparatus of the present invention, since the fiber length of the optical fiber used as the optical amplifying medium is set to the length at which the S / N of the optical fiber amplifier is the best or the vicinity thereof, the following effects are obtained. There is.
1. By supplying the pumping light after setting the fiber length of the optical fiber used as the optical amplifying medium so that the S / N is the best, it is possible to obtain good optical amplification with good Raman gain efficiency and low noise. It becomes possible. In this case, any of forward excitation, backward excitation, and bidirectional excitation can be performed.
2. The present invention can be employed in both concentrated and distributed wavelength multiplexing pump Raman amplifying apparatuses.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of fiber length setting when DCF is used for a fiber of an optical fiber amplifier.
FIG. 2 is an explanatory diagram of fiber length setting when a non-zero dispersion shifted fiber is used as a fiber of an optical fiber amplifier.
FIG. 3 is an explanatory diagram of a concentrated wavelength division multiplexing Raman amplifying apparatus.

Claims (2)

In a wavelength-division-pumped Raman amplifying apparatus used for optical amplification, the fiber length of an optical fiber used as an optical amplifying medium, the Raman gain characteristic indicating the relationship between the fiber length and the differential value of Raman gain, and the unit length A wavelength-division-pumped Raman amplifying apparatus characterized in that the S / N of the optical fiber amplifier is set to the best or near length by setting the length in the vicinity of the intersection with the fiber loss characteristic indicating the per-fiber loss. .   2. The wavelength division multiplexing Raman amplifying apparatus according to claim 1, wherein an optical fiber as an optical fiber amplifier is used as a centralized type in which a pumping light source, WDM, etc. are housed in a module housing, or as an optical amplification medium outside the module housing. A wavelength-division-pumped Raman amplifying apparatus characterized in that the optical fiber to be distributed is a distributed type.

Images