JP2002176216A - Gain equalizer for polarized plane retaining optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gain equalizer that can equalize transmission loss dependency on wavelength for each polarization when equalizing the gain of amplified light that is amplified by a polarized plane retaining optical amplifier. SOLUTION: The amplified light containing X and Y polarized waves is divided into X and Y polarized waves by a polarization beam splitter 2, the gain of X and Y polarized waves is equalized, and a polarization beam combiner 5 is used for recombining the X and Y polarized waves, thus equalizing the transmission loss dependency on wavelength for each polarization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gain equalizer for an optical amplifier used in the field of optical information communication, and more particularly to a gain equalizer for a polarization maintaining optical amplifier used for a polarization maintaining optical amplifier. Is provided.

[0002]

2. Description of the Related Art As the density of wavelength division multiplexing optical communication increases, polarization-maintaining optical amplifiers that perform polarization amplification while maintaining a polarization plane have been developed. When this polarization-maintaining optical amplifier is used for wavelength-division multiplexed optical communication, it is necessary that the amplification wavelength band is wide, but not only the amplification wavelength band is wide but also for a plurality of optical signals having different wavelengths. It is required that the gain be as constant as possible. For this reason, the gain is smoothed using a gain equalizer for the purpose of canceling the amplification wavelength dependence of the optical amplifier itself.

[0003] Such a gain equalizer is roughly divided into:
A non-polarization-maintaining gain equalizer and a polarization-maintaining gain equalizer have been developed. Among these, non-polarization-maintaining gain equalizers include bulk-type gain equalizers such as etalons and dielectric multilayers, and fiber-type gain equalizers such as forming gratings on non-polarization-maintaining fibers. One of the polarization-maintaining gain equalizers is a fiber-type gain equalizer in which a grating is formed on a polarization-maintaining fiber.

[0004]

However, all of these gain equalizers perform gain equalization of unpolarized amplified light or gain of only X-polarized light or only Y-polarized light in amplified light. As a polarization-maintaining gain equalizer, it has not been possible to equalize the gain of both the X-polarization and the Y-polarization with good characteristics.

When the amplified light amplified by the polarization-maintaining optical amplifier is subjected to gain equalization using a non-polarization-maintaining gain equalizer, a polarization-maintaining fiber and a non-polarization-maintaining gain are obtained. Degradation of polarization crosstalk occurs at the connection point with the equalizer, and it has been difficult to realize good polarization crosstalk.

On the other hand, when a gain equalizer is formed by using a polarization-maintaining fiber, the X-polarized light and the Y-polarized light have different center wavelengths that receive loss during gain equalization. Y
The transmission loss wavelength dependence with respect to the polarization cannot be equalized. This is because, in a fiber having a sufficient polarization plane preserving performance, the birefringence is usually about 10 ^-4 , whereby the center wavelengths receiving loss are different between X-polarized light and Y-polarized light. . The deviation of the center wavelength of the loss due to the polarization is about 0.3 to 0.4 nm in the case of the short-period type fiber grating and about 50 to 200 nm in the case of the long-period type fiber grating. It has been difficult to realize a gain equalizer having a loss wavelength dependence equivalent to polarization. The present invention has been made in view of such circumstances, and in performing gain equalization of the amplified light amplified by the polarization-maintaining optical amplifier,
It is an object of the present invention to provide a gain equalizer that can make the transmission loss wavelength dependence for each polarization equal.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 performs gain equalization while holding the polarization plane of the signal light amplified by the polarization-maintaining optical amplifier. Means for polarization-separating signal light, means for equalizing gain for each polarization-separated signal light, and signal for polarization-separated signal after gain equalization in a gain equalizer for a polarization-maintaining optical amplifier A gain equalizer for a polarization-maintaining optical amplifier, comprising: means for recombining light.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The present invention separates amplified light including X-polarized light and Y-polarized light into X-polarized light and Y-polarized light using a polarizing beam splitter, and after equalizing each of X-polarized light and Y-polarized light, By recombining the X polarization and the Y polarization using a polarization beam combiner, a gain equalizer that can equalize the transmission loss wavelength dependence for each polarization is realized.

FIG. 1 shows a first example of a gain equalizer for a polarization-maintaining optical amplifier according to the present invention. In FIG. 1, reference numeral 1 denotes an optical transmission line for transmitting the signal light amplified by the polarization-maintaining optical amplifier. This optical transmission line 1 is connected to an input port of a polarization beam splitter 2. One output port of the polarization beam splitter 2 is connected to a first gain equalizer 3 for performing gain equalization of X-polarization of signal light, and the other output port of the polarization beam splitter 2 is connected to a first output port.
A second gain equalizer 4 for performing gain equalization of the Y polarization of the signal light is connected.

A first gain equalizer 3 for gain equalization of X polarization is connected to one input port of the polarization beam combiner 5, and a second gain equalizer for gain equalization of Y polarization. Vessel 4
Is connected to the other input port of the polarization beam combiner 5. The output port of the polarization beam combiner 5 is
It is connected to the optical transmission line 1.

Here, as the polarization beam splitter 2 and the polarization beam combiner 5, an optical fiber coupler composed of a PANDA fiber, which is one of polarization maintaining fibers, a birefringent prism or the like is used. In addition, as the first gain equalizer 3 and the second gain equalizer 4, a polarization maintaining fiber, for example, a long-period fiber grating formed on a PANDA fiber is used, and a polarization plane is maintained. The etalon, the dielectric multilayer filter, and the short-period fiber grating are used on condition that this is the case. Further, even if a short-period fiber grating is formed on a polarization-maintaining fiber such as a PANDA fiber, the polarization plane is retained, so that it can be used.

Next, the operation of the gain equalizer for a polarization-maintaining optical amplifier of this embodiment will be described. The signal light amplified by the polarization-maintaining optical amplifier is transmitted by the optical transmission line 1 and separated into an X polarization and a Y polarization by the polarization beam splitter 2. The X polarization is sent to a first gain equalizer 3 for gain equalization, and the Y polarization is sent to a second gain equalizer 4 for gain equalization. The X-polarized light and the Y-polarized light after the gain equalization are sent to the polarization beam combiner 5, respectively, recombined and transmitted on the optical transmission line 1.

In the gain equalizer for a polarization-maintaining optical amplifier according to the first embodiment, after separating the X polarization and the Y polarization, gain equalization is performed for each polarization. Therefore, the wavelength shift of the transmission loss due to the polarization does not occur, and the transmission loss wavelength dependence for each polarization can be equalized.

FIG. 2 shows a second example of a gain equalizer for a polarization-maintaining optical amplifier according to the present invention. In this example, in a polarization-maintaining optical amplifier, the amplification factor of an amplification medium depends on polarization (hereinafter referred to as “amplification characteristic polarization dependence”).
It is related to the case with. Reference numeral 1 denotes an optical transmission line for transmitting signal light amplified by a polarization-maintaining optical amplifier having amplification characteristic polarization dependence. The connection of the optical transmission line 1, the polarization beam splitter 2, the first gain equalizer 3, the second gain equalizer 4, and the polarization beam combiner 5 is the same as in the first example.

Here, for example, a semiconductor amplifier or the like is used as a polarization-maintaining optical amplifier having amplification characteristics and polarization dependence. As the polarization beam splitter 2 and the polarization beam combiner 5, one of the polarization maintaining fibers P
The use of an optical fiber coupler composed of an ANDA fiber, a birefringent prism, or the like is the same as in the first embodiment. Further, as the first gain equalizer 3 and the second gain equalizer 4, a polarization maintaining fiber such as PA
In addition to using a long-period fiber grating formed on an NDA fiber, an etalon, a dielectric multilayer filter, and a short-period fiber grating may be used provided that the polarization plane is maintained. This is the same as the embodiment. Further, even when a short-period fiber grating is formed on a polarization-maintaining fiber such as a PANDA fiber, the polarization plane is retained, so that it can be used as in the first embodiment.

Next, the operation of the gain equalizer for a polarization-maintaining optical amplifier of this embodiment will be described. Amplification characteristics The signal light amplified by the polarization-maintaining optical amplifier having polarization dependence has a gain difference between the X polarization and the Y polarization because the amplification factor of the amplification medium has polarization dependence. I have. As described above, the amplified lights having different gains depending on the polarization are transmitted through the optical transmission line 1,
The polarization beam splitter 2 separates the light into X-polarized light and Y-polarized light. The X polarization is sent to a first gain equalizer 3 for gain equalization, and the Y polarization is sent to a second gain equalizer 4 for gain equalization. As described above, since the X polarization and the Y polarization are gain-equalized by the separate gain equalizers, the amplification factor polarization generated at the time of optical amplification by the polarization-maintaining optical amplifier having the amplification characteristic polarization dependency is obtained. Wave dependence is eliminated. The X-polarized light and the Y-polarized light after gain equalization are sent to the polarization beam combiner 5, respectively, recombined and transmitted on the optical transmission line 1.

In the gain equalizer for a polarization-maintaining optical amplifier according to the second embodiment, gain separation is performed on each polarization after separating the X polarization and the Y polarization. Therefore, the polarization dependence of the amplification factor, which is generated at the time of optical amplification by the polarization-maintaining optical amplifier having the amplification characteristic polarization dependence, is eliminated, and the gain for each polarization can be equalized.

[0018]

As described above, according to the present invention,
After the X polarization and the Y polarization are separated, gain amplification is performed for each polarization, so that there is no wavelength shift in transmission loss due to polarization, and the transmission loss wavelength dependence for each polarization is equal. A realizable gain equalizer is possible.

According to the present invention, even when the polarization-maintaining optical amplifier has amplification characteristic polarization dependency, gain equalization is performed for each polarization after separating the X polarization and the Y polarization. Therefore, it is possible to provide a gain equalizer that can equalize the gain for each polarization.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a gain equalizer for a polarization-maintaining optical amplifier according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a gain equalizer for a polarization-maintaining optical amplifier according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical transmission line, 2 ... Polarization beam splitter, 3 ... 1st gain equalizer, 4 ... 2nd gain equalizer, 5 ... Polarization beam combiner

Claims (1)

[Claims] 1. A gain equalizer for a polarization-maintaining optical amplifier that performs gain equalization while retaining the polarization plane of signal light amplified by a polarization-maintaining optical amplifier, wherein the signal light is polarization-separated. Means for gain equalization for each polarization-separated signal light, and means for recombining the polarization-separated signal light after gain equalization, polarization-maintaining light. Gain equalizer for amplifier.