JP2904101B2 - Optical amplifier with noise elimination function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifying device for amplifying an optical signal, and more particularly to an optical amplifying device having a function of removing noise at a stage subsequent to an optical amplifying unit.

[0001]

2. Description of the Related Art In optical fiber transmission, an optical amplifying device that amplifies an optical signal output as it is without converting the output of the optical signal into an electric signal is used in order to increase a transmission distance.

[0002] Optical amplifiers generally include a semiconductor amplifier, a fiber Raman scattering amplifier, a fiber Brillouin amplifier, and a rare earth doped fiber amplifier. In particular, erbium-doped fiber amplifiers, which are one of the rare-earth-doped fiber amplifiers, are widely used because they have no polarization dependence and can be pumped by a semiconductor laser.

[0003] When optical amplification is performed by an erbium-doped fiber amplifier, ASE (Amplified Spontan) is output in addition to the amplified original signal light.
noise light called “eous Emission” light. In particular, when the intensity of the input optical signal is small, the AS signal is relatively smaller than the intensity of the amplified signal light.
Since the intensity of the E light is large, it also causes deterioration of transmission quality.

In order to suppress this deterioration, it is necessary to remove only the ASE light from the output of the erbium-doped fiber amplifier. The ASE light includes the wavelength of the signal light.
Since white noise light exists in a band of about 0 nm, it can be almost removed by limiting the band. Generally, since the light source of an optical signal is a single-wavelength laser diode, the signal light is reduced by inserting an optical band-pass filter whose pass band is adjusted to the wavelength of the signal light into the output section of the erbium-doped fiber. ASE light can be removed without using the ASE light.

[0005] Generally, the range of the wavelength variation of the signal light is wider than the pass band of the optical band-pass filter. Therefore, when an optical band-pass filter is used for an optical amplifier, a variable type that can change the center wavelength of the pass band by external control is used. The tunable optical band-pass filter controls the center wavelength of the pass band so as to match the wavelength of the signal light.

FIG. 4 shows an example of the configuration of a conventional optical amplifier. In the conventional configuration, on the output side of the optical amplifier 4,
An optical bandpass filter 5 that transmits only light near the center wavelength of the optical signal is provided. The optical band pass filter 5 is connected to the control circuit 7, and can change the pass band by an external control signal. As such a variable optical band-pass filter, there is known a variable optical band-pass filter that changes an incident angle by rotating a band-pass interference film filter.

The amplified optical signal output from the optical amplifier 4 is
ASE input to the optical bandpass filter 5 and out of the passband
Light is removed. A part of the amplified optical signal is partly split by the optical splitter 8 and is subjected to optical-electrical conversion by the light receiver 6. Then, the passband of the optical bandpass filter 5 is controlled by the control circuit 7 so that the current converted by the light receiver 6 is maximized.

The optical band-pass filter 5 has signal light and ASE
Both light are input. Therefore, the optical bandpass filter 5
The relationship between the set value of the center wavelength of the pass band and the current flowing through the light receiver 6 at that time is as shown in FIG. FIG.
In the figure, the center wavelength of the optical signal 8 exists in a sharply rising portion on the right side in the drawing. On the other hand, there is a convex portion 9 to the left. This is due to the ASE light 9 which becomes noise. Therefore, when the center wavelength of the pass band of the optical band-pass filter 5 is limited near the center wavelength of the signal light 8, the wavelength of the signal light 8 can be detected by the conventional configuration.

[0009]

However, in the above-described conventional optical amplifying device, if the center wavelength of the pass band of the optical band-pass filter 5 is not restricted, the wavelength apart from the wavelength of the signal light 8 is not limited. ASE input to the receiver 6 at
The intensity of the light 9 may be higher than the intensity of the signal light 8. In such a case, there is a problem that the current flowing through the light receiver 6 at a wavelength other than the original wavelength of the signal light 8 becomes maximum, and the wavelength of the signal light 8 cannot be detected.

An object of the present invention is to provide an optical amplifier having a function of detecting the wavelength of signal light without being affected by ASE light.

[0011]

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks of the conventional optical amplifying device, the optical amplifying device with a noise removing function of the present invention amplifies an optical signal and outputs an amplified optical signal. In an optical amplifying apparatus having a noise removing function including an amplifying means and a noise removing means for removing noise light included in an amplified optical signal, the noise removing means detects a peak wavelength at which a maximum optical output of the optical signal is detected. Means, and first wavelength selective transmission means for selectively transmitting only light having a wavelength component near the peak wavelength in the amplifier optical signal.

The peak wavelength detecting means comprises: an optical splitting means for splitting and extracting a part of the optical signal;
Optical signal wavelength selection means for changing the center wavelength of the band with a predetermined bandwidth and selectively transmitting the same to output a narrowband optical signal; and optical-electrical conversion for converting the narrowband optical signal into an electric signal Means for detecting a maximum value of the electric signal and outputting a control signal . The first wavelength selective transmission means includes an amplified optical signal wavelength selection means for transmitting only light near a transmission center wavelength having a predetermined bandwidth, and a wavelength for making the transmission center wavelength coincide with a peak wavelength by a control signal. Control means. One of the features of the optical amplifying device of the present invention is that the conventional method extracts the center wavelength from the amplified optical signal, but detects the peak wavelength from the optical signal before being input to the optical amplifying device. That's what I did. By adopting such a configuration, the center wavelength of the optical signal can be detected without being affected by the ASE light, and the optical bandpass filter is controlled in accordance with the center wavelength. The noise can be removed appropriately.

As another configuration of the optical amplifying device with a noise removing function according to the present invention, the first wavelength selective transmitting means is disposed at a stage subsequent to the optical amplifying means, and only the vicinity of the center wavelength determined by the control signal among the amplified optical signals is provided. An optical signal wavelength selecting means for transmitting the light of the optical signal, the peak wavelength detecting means is arranged in front of the optical amplifying means, and splits a part of the optical signal to output a split optical signal; A branched optical signal input means for inputting the amplified optical signal wavelength selecting means from the opposite side to the amplified optical signal and outputting a narrowband optical signal, an optical-electrical converting means for converting the narrowband optical signal into an electric signal, A maximum value detecting means for detecting a maximum value of the electric signal and outputting a control signal.

Here, a characteristic is that a variable optical band-pass filter arranged downstream of the optical amplifying unit for noise removal is used as it is for detecting the peak wavelength of the optical signal. That is, before an optical signal is input to the optical amplifier, a part of the optical signal is split by an optical splitter, and the split light is directed backward of the variable optical bandpass filter, that is, in a direction opposite to the direction in which the amplified optical signal travels. The feature is that the input is made from the direction. With such a configuration, the variable optical bandpass filter can be used as it is for peak wavelength detection, so that the configuration can be simplified. Further, unlike the case where another optical band-pass filter is used, it is not necessary to link peak wavelength detection and noise removal.

As an embodiment of each means in the configuration of the optical amplifying apparatus having a noise removing function of the present invention, the optical amplifying means is an erbium-doped optical fiber amplifying apparatus, and the optical signal wavelength selecting means is a dielectric multilayer film. It is characterized by including a filter.

Further, as a more specific configuration of the optical amplifying device with a noise removing function according to the present invention, an optical amplifying section for amplifying an optical signal input from an input port and outputting an amplified optical signal from an output port; An optical band-pass filter disposed at a stage subsequent to the port for removing noise light included in the amplified optical signal. A first optical splitter disposed before the input port for branching a part of the optical signal and outputting a branched optical signal; and a first optical splitter disposed on the output side of the variable optical bandpass filter and amplifying the branched optical signal. An optical coupler input to the variable optical band-pass filter from the opposite side, and a part of the branched optical signal output from the variable band-pass filter disposed between the optical amplifier and the variable optical band-pass filter. A second optical splitter for outputting a wavelength-selective split optical signal and a photodetector for converting the wavelength-selective split optical signal into an electric signal are provided. Such a configuration is characterized in that a wavelength control circuit is provided for controlling the center wavelength of the pass band of the variable optical band pass filter so that the electric signal converted by the light receiver is maximized.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical amplifier with a noise removing function according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a first embodiment of the optical amplifying apparatus with a noise removing function according to the present invention. The optical amplifier 4 has a function of amplifying an optical signal input from the left side of the drawing and outputting the amplified optical signal as an amplified optical signal. As a specific configuration of the optical amplifying unit 4, an erbium-doped fiber amplifier or the like is assumed as described in the section of the related art. Of the present invention.

An optical bandpass filter 5 is disposed downstream of the optical amplifier 4 to remove noise. The optical band pass filter 5 is of a variable type, and the pass band is controlled by the control circuit 7.

An optical splitter 1 for splitting a part of an optical signal is disposed at a stage preceding the optical amplifier 4. A part of the branched optical signal is coupled to the optical band-pass filter 5 by the optical coupler 3 disposed further downstream of the optical band-pass filter 5. At this time, the traveling direction of the signal light is opposite to that of the main signal system which is amplified and output as is clear from the drawing.
Therefore, the optical signal input to the optical bandpass filter 5 is input without being mixed with the amplified optical signal. This optical signal passes through the optical band-pass filter 5 and is
The optical receiver 6 is split by the optical splitter 2 disposed between
Is converted into an electric signal. The current at this time is detected and fed back by the control circuit 7, and the pass band is controlled so that the current becomes maximum.

Next, the operation of the optical amplifier shown in FIG. 1 will be described. Part of the input signal light is split by the optical splitter 1, is coupled to the main signal system from the opposite direction by the optical coupler 3, and passes through the optical bandpass filter 5 in the opposite direction. Thereafter, a part of the light is split by the optical splitter 2, and the light is photoelectrically converted by the light receiver 6. Only the signal light for monitoring passes through the optical bandpass filter 5 in the reverse direction. Accordingly, the relationship between the set value of the center wavelength of the pass band of the optical band-pass filter 5 and the current flowing through the light receiver 6 at that time is only light near the center wavelength, as shown in FIG. The control circuit 7 can detect the wavelength of the signal light 8 because the center wavelength of the pass band of the optical band pass filter 5 is controlled so that the current flowing through the light receiver 6 is maximized.

[0022]

Next, a specific result of an embodiment of the optical amplifying apparatus with a noise removing function of the present invention will be described.

Referring to FIG. 1, the configuration of one embodiment will be described. An erbium-doped fiber amplifier is used for the erbium-doped fiber amplifier 4, and thereby a signal light in the 1550 nm band is amplified. As the optical bandpass filter 5, a filter whose full width at half maximum of the passband is 1 nm and which can control the center wavelength of the passband by rotating the dielectric film is used. The optical splitters 1 and 2 are of an optical fiber fusion type, and their branch ratios are 10 dB and 3 dB, respectively. The same optical coupler 3 is used, and the branching ratio is 3 dB.
The light receiver 6 is a PD using a photodiode (PD).
The module has a light receiving sensitivity of 800 μA / mW.

Next, the operation of the embodiment of the present invention will be described.

When signal light having a wavelength of 1550 nm and power of -20 dBm is input, about 1/10 of the signal light is input from the optical splitter 1 to the optical splitter 3, and the rest is input to the erbium-doped fiber amplifier 4. Input and amplified.

One-tenth of the monitor signal light input to the optical splitter 3 passes through the optical bandpass filter 5 in the reverse direction via the optical splitter 3,
One half is input to the PD module 6 and converted into a current.

When the center wavelength of the pass band of the optical band-pass filter 5 is not 1550 nm, no current flows through the PD module 6, but when it is near 1550 nm, a current of 0.1 μA flows. By monitoring this current value, the center wavelength of the pass band of the optical band-pass filter 5 can be set so as to coincide with 1550 nm which is the wavelength of the signal light.

On the other hand, the erbium-doped fiber amplifier 4
Is optically amplified and output together with the ASE light. The amplified signal light passes through the optical splitter 2 and is input to the optical band-pass filter 5, which has the center wavelength of the pass band set to 1550 nm. Therefore, noise light other than near the center wavelength of the signal light is removed by the optical band-pass filter 5, and only the signal light passes through the optical splitter 3 and is output.

FIG. 3 shows the configuration of another embodiment of the optical amplifying apparatus having a noise removing function according to the present invention. In the above configuration, the signal light as shown in FIG. 1 is input in the opposite direction in order to use the optical band-pass filter 5 for both detecting the center wavelength and removing noise. In FIG. 3, an optical band-pass filter 51 for detecting a center wavelength is arranged at a stage preceding the optical amplifier 4, and an optical band-pass filter 52 is arranged at a stage subsequent to the optical amplifier 4 for noise removal. However, both are interlocked so that the center wavelength detected by the optical bandpass filter 51 and the passband set by the optical bandpass filter 52 always match. With such a configuration, the same effect as described above can be obtained.

[0030]

As described above, in the optical amplifying apparatus with noise elimination function of the present invention, the variable optical band-pass filter for transmitting only the amplified optical signal near the center wavelength is disposed at the subsequent stage of the optical amplifying section. Noise is removed by removing light other than the center wavelength. Here, the center wavelength is detected by an optical signal before being input to the optical amplifier, and the center wavelength of the variable optical bandpass filter is set based on the center wavelength. Also, a part of the optical signal input to the optical amplifier is split by an optical splitter arranged in front of the optical amplifier, and the split optical signal is filtered from the opposite side to the amplified optical signal by a variable optical bandpass filter. To enter. Then, the light is split by an optical splitter disposed between the optical amplifier and the variable optical bandpass filter, and the wavelength that becomes the maximum due to a change in intensity with respect to the wavelength of the split light is detected to set the center wavelength.

By adopting such a configuration, since the center wavelength is not set based on the amplified optical signal, the center wavelength is determined without being affected by the ASE light, and noise to be truly removed is removed. And high quality optical amplification is realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of an optical amplifying apparatus with a noise removing function according to the present invention.

FIG. 2 is a diagram showing a relationship between a set value of a center wavelength of a pass band of an optical band-pass filter and a current flowing to a photodetector at that time in the first embodiment shown in FIG.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the optical amplifying device with a noise removing function according to the present invention.

FIG. 4 is a block diagram illustrating a configuration of a conventional optical amplifier.

5 is a diagram showing a relationship between a set value of a center wavelength of a pass band of an optical band-pass filter and a current flowing to a photodetector at that time in the first embodiment shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first optical splitter 2 second optical splitter 3 optical coupler 4 optical amplifier 5 optical bandpass filter 51 optical bandpass filter 52 optical bandpass filter 6 light receiver 7 control circuit 8 optical signal 9 ASE light 10 Optical splitter

Claims (8)

(57) [Claims] And 1. A light amplifying means for amplifying an optical signal and outputs the amplified optical signal, a noise removal function with optical amplifier including a noise removing means for removing the noise light contained in the amplified optical signal The noise removing means detects a peak wavelength at which the optical signal has a maximum optical output.
Wavelength detection means, and a light amplification means
And is determined by a control signal of the amplified optical signal.
Wavelength selective transmission means for transmitting light only near the center wavelength
With the door, the peak wavelength detection means is disposed in front of said optical amplifying means, a portion of the optical signal
Optical branching means for branching and outputting a branched optical signal; and
Branch to input to long selective transmission means and output narrowband optical signal
Optical signal input means, and an optical-electrical converter for converting the narrowband optical signal into an electric signal.
And detecting a maximum value of the electric signal and outputting the control signal.
Noise removal function with optical amplifier apparatus characterized by and a maximum value detecting means that. 2. The optical amplifying device with a noise removing function according to claim 1 , wherein said optical amplifying means is an erbium-doped optical fiber amplifying device. Wherein the amplified optical signal wavelength selection means according to claim 1, characterized in that it comprises a dielectric multilayer film filter
Or an optical amplifying device with a noise removing function according to claim 2 . 4. An optical amplifying unit for amplifying an optical signal input from an input port and outputting an amplified optical signal from an output port; and an optical amplifier disposed downstream of the output port for reducing noise light included in the amplified optical signal. An optical band-pass filter to be removed, a first optical splitter arranged before the input port, for splitting a part of the optical signal and outputting a split optical signal, and an output side of the optical band-pass filter. Arranged and passes the branch optical signal through the optical band pass from the side opposite to the amplified optical signal.
An optical coupler for input to the filter is disposed between the optical bandpass filter and the optical amplifier unit, the branch to the wavelength selection branch optical signal a portion of the branched optical signal output from the optical bandpass filter a second optical splitter for outputting a passage of the variable optical band pass filter to a photodetector, the electrical signal converted by the photodetector is maximized for converting the wavelength selection branched optical signal into an electric signal An optical amplifier with a noise removing function, comprising: a wavelength control circuit for controlling a center wavelength of a band. (5)Amplify optical signal and output amplified optical signal
Light amplification means; Noise removing means for removing noise light contained in the amplified optical signal
An optical amplifying device with a noise removing function including a step and The noise removing means includes: A peak for detecting a peak wavelength at which the optical signal has a maximum optical output.
Wavelength detection means, The optical amplifier is disposed downstream of the optical amplifying means, and is configured to receive the amplified optical signal.
Pass band near the center wavelength determined by the control signal
First wavelength selective transmission means for transmitting light as an area; Be prepared
e, The peak wavelength detecting means, A part of the optical signal is arranged in front of the optical amplification means.
Optical splitting means for splitting and outputting a split optical signal; It is arranged before the optical branching means and is the same as the pass band.
Second wavelength selective transmission means for transmitting light in a pass band; Optical-electrical conversion means for converting the branched optical signal into an electric signal
When, Detecting a maximum value of the electric signal and outputting the control signal;
Maximum value detection means Noise characterized by having
Optical amplifier with removal function. 6. The optical amplifying means is an erbium-doped optical fiber amplifying device.
The optical amplifying device with a noise removing function according to claim 5 . 7. The apparatus according to claim 5, wherein said amplified optical signal wavelength selecting means includes a dielectric multilayer filter.
7. An optical amplifying device with a noise removing function according to claim 6 . 8. An optical signal input from an input port is amplified.
An optical amplifier for outputting an amplified optical signal from an output port; and an optical amplifier disposed downstream of the output port and included in the amplified optical signal.
A first optical band-pass filter that removes noise light from the input port;
An optical splitter for splitting and outputting a split optical signal; and a first optical band-pass filter disposed before the optical splitter.
A second optical band that transmits light in the same pass band as the filter
A pass filter, a light receiver for converting the branched optical signal into an electric signal, and an electric signal converted by the light receiver being maximized.
The center wavelength of the pass band of the first optical band pass filter.
And a wavelength control circuit for controlling the optical amplifier.