KR200222421Y1 - Erbium doped fiber amplifier for long wavelength - Google Patents

Abstract

The present invention is to provide a long wavelength erbium-added fiber amplifier, the present invention is a first isolator to block the reflected light to the input signal light and to pass the transmitted light; A first pumping light source for increasing the power of the input signal to cause density inversion in the amplifying medium; A first optical coupling unit coupling an output of the first isolator and the first pumping light source; An amplifying medium for amplifying a signal input from the first optical coupling unit; A second pumping light source for generating pumping light; A second optical coupling unit coupling the amplification medium and the output of the second pumping light source; A filter configured to receive and filter the output of the second optical coupling unit; By including a second isolator to block the reflected light receives the output of the filter and passes the transmitted light, by using a short wavelength reflection filter at the rear end of the optical amplifier to improve the gain and noise figure of the optical amplifier It will be able to amplify the input optical signal in the 1560nm ~ 1610nm band.

Description

Erbium doped fiber amplifier for long wavelength

The present invention relates to a long wavelength Erbium-doped fiber amplifier used in an optical transmission system, and in particular, by using a short wavelength reflection filter at the rear end of the optical amplifier, the gain and noise figure of the optical amplifier are improved and the 1560 nm to 1610 nm band is used. The present invention relates to a long-wavelength Erbium-doped fiber amplifier suitable for amplifying an input optical signal.

In general, an optical amplifier is used in an optical communication system to compensate for signal loss. The optical amplifier is an apparatus for amplifying an optical signal to compensate for the attenuation of the optical signal due to long distance optical communication.

Such optical amplifiers are expected to be widely used in future communication systems. In particular, Erbium Doped Fiber Amplifiers (EDFAs) attenuate optical signals that follow long-distance transmissions when large amounts of data are transmitted over a single strand of fiber, over long distances, without artificial regeneration through external devices. It is used to amplify the optical signal on its own and periodically to prevent it. Therefore, since the erbium-added optical amplifier amplifies the transmitted optical signal itself, it is excellent in amplification efficiency and can suppress noise generation.

However, problems such as dispersion during periodic amplification of optical signals due to such long distance transmission occur. Wavelength Division Multiplexing (WDM) solves some of the problems of dispersion, and transmits a large amount of data in multiple carriers having different wavelengths, thereby increasing transmission speed and capacity.

Assuming that one optical carrier represents one channel, the optical power representing the signal strength may develop differently if the channels are different. This power difference can be greatly increased when the signal is attenuated or repeatedly reamplified in an optical amplification system, or when the signal travels to another path in the optical network.

This power difference can occur for the following reasons.

First, different channels can have different gains. If the gain level of a homogeneously broadened optical amplifier, such as EDFA, is changed, the magnitude of the gain level will vary as the wavelength changes. Moreover, since the gain level changes over time, it is difficult to know at which gain level the optical amplifier operates and in some cases may not be possible. Including EDFAs whose gain is flattened or uniformed independently of the operating conditions, there are uniform EDFAs whose gains are flattened regardless of the wavelength and the gains are the same even if the channels are different. But the gain is not perfectly flattened or equalized. In systems with multiple optical amplifiers connected and installed, even small gain differences between channels can cause loss of the system and can lead to significant power differences.

Second, signal attenuation due to losses between amplifiers may vary depending on the channel. This too causes a significant power difference. With respect to amplification, the attenuation can also change over time, and the change in the attenuation over time can be different for different channels or wavelengths in unpredictable ways.

Under these different operating conditions, it is very difficult to simultaneously match gain and attenuation at several different wavelengths. This is because the attenuation between amplifiers varies with wavelength due to splice degradation, coupling of power splitters or other optical devices on the transmission path, coupling of distributed compensation fibers, and increased micro-bending losses. It is because it appears. And the loss of signal power depends on the wavelength, making it difficult to predict the signal power. Given this uncertainty, it is virtually impossible to ensure gain flattening with a uniformly extended amplifier, such as EDFA, if the losses between the amplifiers change.

Although gain and loss are always balanced for all channels, i.e., the sum of gain and loss for all channels is 0 dB, this does not guarantee that the power is the same on all channels.

The power is not the same for the following reasons.

(1) The signal power applied to the system can be different if the wavelength is different.

(2) When routing in a complex network, different channels go through different paths. Thus, unless the power control is in some form for each channel, the power of the channels is mostly different when the channels are recombined.

(3) Using a tunable optical tap selectively attenuates the power of the channels in an unpredictable manner.

In many applications, it is better to perform an Automatic Power Equalizer (APE) that equals power rather than equalizing the gain between different channels in an optical amplifier. At least the power difference must be kept within a certain range. This requires that the gain of one channel with low input power out of range be higher than the channels with power in range. This effect is called Multichannel Automatic Power Control (MAPC). If the MAPC is obtained in a transmission system that is periodically amplified, the gain means eliminating losses for each and every channel for proper channel power, which is Multichannel Automatic Gain Control (MAGC). Thus, even if the balanced signal power changes, the system is stable against loss variations between amplifiers.

It is well known that MAPC can be achieved in an inhomogeneously broadened amplifier. However, commercially available EDFAs are homogeneously broadened amplifiers at room temperature. As a result, the gain at one wavelength becomes about the same with respect to the gain at all other wavelengths, so that the gain is dependent on the wavelength of the channel.

For a nonuniformly extended amplifier, the gain at one wavelength is partially independent of the gain at another wavelength. In long-range WDM, assuming that the signal power gain at other wavelengths is not affected at least to some extent, the signal gain at that wavelength will be reduced if the signal power increases at any one wavelength. This is called gain compression or gain saturation.

If there is a strong signal that compresses the gain at another wavelength instead of the above-mentioned wavelength, the gain remains the high gain at the first wavelength.

In general, the following methods are used to obtain MAPC or multi-channel automatic gain control (MAGC) in EDFA.

(1) The cooling medium, ie Erbium Doped Fiber (EDF), is cooled to very low temperatures. This can achieve good MAPC or MAGC, but the drawback is that the additional equipment required for cooling is complex.

(2) Use twin-core EDFA. This allows the gain medium as a whole to be effectively unevenly expanded by spatially separating the path through which other wavelengths pass, even if each or all points of the gain medium are dominantly uniformly extended. However, dual core EDFAs have the disadvantage of generating more noise, undesired polarization dependencies, and a significant loss of power than single core EDFAs. Double core optical fibers are also difficult to manufacture.

(3) Multiple wavelengths are divided in a Wavelength Selective Coupler (WSC) and amplified by another Erbium-doped fiber (EDF). Thus, the gains of the channels can be separated from each other, which is a non-uniform extension. However, this also has the drawback that the amplifier is much more complicated and the pump power is not used efficiently.

On the other hand, in WDM networks, the number of channels changes due to network configuration changes, component failures, and frequent add / drop of channels. As a result, a change in the input signal strength causes a transient phenomenon to occur in the optical output of the remaining channel, and a transmission error is instantaneously increased due to a change in gain. Therefore, in the WDM network, the gain change due to the change of the magnitude of the input signal should be minimized.

1 is a block diagram of a conventional long wavelength Erbium-doped fiber amplifier.

As shown therein, a first isolator 11 for blocking the reflected light with respect to the input signal light and allowing the transmitted light to pass therethrough; A first pumping laser light source (LD) 12 for increasing the power of the input signal to cause density inversion in the amplification medium (EDF) 14; A first optical coupling part (WDM) 13 coupling the output of the first isolator 11 and the first pumping light source 12; An amplifying medium (14) for amplifying a signal input from the first optical coupling unit (13); A second pumping light source 15 for generating pumping light; A second optical coupling unit 16 coupling the amplification medium 14 and the output of the second pumping light source 15; The second isolator 17 receives the output of the second optical coupling unit 16 and blocks the reflected light and passes the transmitted light.

Thus, the first and second isolators 11 and 17 block the reflected light with respect to the input signal light and pass the transmitted light. Therefore, ASE (Amplified Spontaneous Emission) emitted from the amplified medium 14, which is an erbium-doped fiber, is reflected at the input or output terminal of the optical signal and enters the amplified medium (EDF) 14 to decrease the amplification efficiency. Prevent.

The first and second pumping light sources 12 generate pumping light to increase the power of the input signal so that density inversion in the amplification medium (EDF) 14 occurs.

The first and second optical coupling units 13 and 16 send the pumping light and the signal light to the amplifying medium 14 which is an erbium-doped optical fiber.

In addition, spontaneous emission light is generated in the erbium-doped fiber irrespective of the signal light, and the difference between the natural emission light and the signal light is called an optical noise index.

The pumping light produced by the pumping light sources 12 and 15 through the optical coupler 13 and 16 excites the erbium ions in an excited state while passing through the amplifying medium 14, which is an erbium-doped optical fiber. At this time, when the weakened signal light is sent to the amplification medium 14, which is an erbium-doped optical fiber, through the input terminal, the light signal is amplified by Stimulated Emission as the erbium ion is lowered from the excited state to the ground state. Is output while passing through the second isolator 17 at the output stage.

Since the Erbium-doped optical fiber has a large gain in the 1550 nm band and a small gain in the 1590 Band, it is used to amplify an optical signal in a long wavelength band, that is, in the 1560 nm to 1610 nm band by lengthening the Erbium-doped optical fiber.

However, in addition to the amplification of signal light by induced emission, erbium-doped optical fiber also has natural emission light (ASE).

FIG. 2 shows the natural emission light of such a conventional erbium-doped fiber amplifier, showing the relationship between the output power versus the long wavelength of the natural emission light.

2, it can be seen that the noise figure is high due to the natural emission light. In addition, the gain of signal light is reduced due to the high ASE power of 1530nm band and 1550nm, and the noise figure is high.

Therefore, the conventional long-wavelength optical fiber amplifier can amplify the optical signal of the long-wavelength band, but because the emission band of the erbium-added fiber amplifier is wide, the ASE is emitted in the short-wavelength band, and thus the conventional optical amplifier has low gain and low noise. The index had a bad problem.

Therefore, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to improve the gain and the noise index of the optical amplifier by using a short wavelength reflection filter at the rear end of the optical amplifier, and the 1560 nm to 1610 nm band. To provide a long-wavelength Erbium-doped fiber amplifier that can amplify the input optical signal of the.

Long wavelength Erbium-added optical fiber amplifier according to an embodiment of the present invention in order to achieve the above object,

A first isolator for blocking the reflected light with respect to the input signal light and passing the transmitted light; A first pumping light source for increasing the power of the input signal to cause density inversion in the amplifying medium; A first optical coupling unit coupling an output of the first isolator and the first pumping light source; An amplifying medium for amplifying a signal input from the first optical coupling unit; A second pumping light source for generating pumping light; A second optical coupling unit coupling the amplification medium and the output of the second pumping light source; A filter configured to receive and filter the output of the second optical coupling unit; The technical configuration is characterized in that it comprises a second isolator for receiving the output of the filter to block the reflected light and pass the transmitted light.

1 is a block diagram of a conventional long-wave Erbium-doped fiber amplifier,

2 is a graph of output power versus long wavelength of natural emission light of a conventional erbium-doped fiber amplifier;

3 is a block diagram of a long wavelength erbium-doped fiber amplifier according to the present invention.

Explanation of symbols on the main parts of the drawings

21, 28: isolator 22, 25: pumping light source

23, 26: optical coupling unit 24: amplification medium

27: filter

Hereinafter, an embodiment according to the inventive concept of the present invention and the long wavelength erbium-doped fiber amplifier will be described with reference to the accompanying drawings.

3 is a block diagram of a long wavelength erbium-doped fiber amplifier according to the present invention.

As shown therein, a first isolator 21 for blocking the reflected light with respect to the input signal light and allowing the transmitted light to pass therethrough; A first pumping light source 22 which increases the power of the input signal to cause density inversion in the amplification medium (EDF) 24; A first optical coupling part 23 coupling the output of the first isolator 21 and the first pumping light source 22; An amplifying medium 24 for amplifying a signal input from the first optical coupling unit 23; A second pumping light source 25 for generating pumping light; A second optical coupling part 26 coupling the output of the amplifying medium 24 and the second pumping light source 25; A filter 27 for receiving and filtering the output of the second optical coupling unit 26; It includes a second isolator 28 that receives the output of the filter 27 and blocks the reflected light and passes the transmitted light.

The filter 27 receives the output of the second optical coupler 26 and reflects the short wavelength band to send the natural emission light of the short wavelength band generated by the amplifying medium 24 back to the amplifying medium 24. We configure with filter.

The operation of the long wavelength Erbium-doped fiber amplifier according to the present invention configured as described above will be described in detail with reference to the accompanying drawings.

First, the first and second isolators 21 and 28 block the reflected light with respect to the input signal light and pass the transmitted light. Therefore, ASE (Amplified Spontaneous Emission) emitted from the amplified medium 24, which is an erbium-doped fiber, is reflected at the input or output terminal of the optical signal and enters the amplified medium (EDF) 24 to decrease the amplification efficiency. Prevent.

The first and second pumping light sources 22 and 25 generate pumping light to increase the power of the input signal so that density inversion in the amplification medium (EDF) 24 is generated.

The first and second optical coupling units 23 and 26 send the pumping light and the signal light to the amplifying medium 24 which is an erbium-doped optical fiber.

The pumping light generated by the pumping light sources 22 and 25 through the optical couplers 23 and 26 excites the erbium ions in an excited state while passing through the amplifying medium 24, which is an erbium-doped optical fiber. At this time, when the weakened signal light is sent to the amplification medium 24, which is an erbium-doped optical fiber, through the input terminal, the light signal is amplified by Stimulated Emission as the erbium ion is lowered from the excited state to the ground state. Is output while passing through the second isolator 28 at the output.

At this time, the filter 27, which is a short wavelength band reflection filter, receives the output of the second optical coupler 26 and sends natural emission light of the short wavelength band generated by the amplifying medium 24 to the amplifying medium 24 again.

The operation of the present invention will be described in more detail.

LD used as a pump light source generates pump light of 980 nm or 1480 nm, and the pump light is input to the amplifying medium 24, which is an erbium-doped optical fiber, such as signal light through the optical coupling units 23 and 26.

The input pump light causes the erbium ions to be excited, and when the signal light is input, the signal light is amplified by the induced emission phenomenon.

Irrespective of the signal light, high natural emission light in the 1530 nm band and the 1550 nm band generated when the erbium ions of the erbium-doped optical fiber descends to the ground state is incident on the amplification medium 24, which is an erbium-doped optical fiber, by the optical fiber grating, thereby causing signal light in the long wavelength band By amplifying the maximizing amplification efficiency of the amplification medium 24, which is an erbium-doped fiber.

That is, by entering the erbium-doped optical fiber again without removing the ASE of 1530nm and 1550nm to contribute to the amplification of the signal light.

As such, the present invention improves the gain and noise figure of the optical amplifier by using the short wavelength reflection filter and amplifies the input optical signal of the long wavelength band.

While the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments. Therefore, the above description does not limit the scope of the present invention as defined by the limitations of the following claims.

As described above, the long wavelength erbium-doped fiber amplifier according to the present invention uses a short wavelength reflection filter at the rear end of the optical amplification part to inject ASE of short wavelength, that is, 1530 nm band and 1550 nm band, into the erbium-doped optical fiber again. By using in the amplification of signal light of long wavelength band, it is possible to improve the gain, amplification efficiency and noise figure of the optical amplifier.

Claims (2)

A first isolator for blocking the reflected light with respect to the input signal light and passing the transmitted light; A first pumping light source for increasing the power of the input signal to cause density inversion in the amplifying medium; A first optical coupling unit coupling an output of the first isolator and the first pumping light source; An amplifying medium for amplifying a signal input from the first optical coupling unit; A second pumping light source for generating pumping light; A second optical coupling unit coupling the amplification medium and the output of the second pumping light source; A filter configured to receive and filter the output of the second optical coupling unit; And a second isolator configured to include the second isolator which blocks the reflected light while passing the output of the filter and passes the transmitted light. The method of claim 1, wherein the filter, The short wavelength band erbium-doped fiber amplifier of claim 2, wherein the output of the second optical coupler is configured as a short wavelength band reflection filter for transmitting the natural emission light of the short wavelength band generated from the amplification medium to the amplification medium.