KR19990074010A - Gain Clamp Fiber Amplifier Using Distributed Compensation Fibers - Google Patents

Abstract

The present invention emits induced Brillouin scattering (SBS) light and inputs it back to the EDF when the intensity of the signal output from the amplifying medium is greater than or equal to a set reference value, behind the amplifying medium, and saturates the amplifying medium to output the signal output of the EDF. The present invention relates to a gain clamp optical fiber amplifier using distributed compensation optical fiber having a limited nonlinear mineral, DCF (Dispersion Compensating Fiber). According to the present invention, a gain clamp optical fiber amplifier using a distributed compensation optical fiber has an input signal of nk channels according to the addition / removal of wavelengths or changes to other wavelengths in the wavelength division network. When incident, the saturation of the amplification medium without changing the density inversion level, even if the number of channels changes, it is possible to implement an optical amplifier with a fixed all-channel optical amplification gain that has a constant amplification gain regardless of the number of input signal channels. .

Description

Gain Clamp Fiber Amplifier Using Distributed Compensation Fibers

The present invention relates to a gain clamp optical fiber amplifier using EDF (erbium doped fiber) as an amplifying medium. Specifically, an induction Brillouin is provided when an intensity of a signal output from an amplifying medium and received from an amplifying medium is higher than a set reference value. The present invention relates to a gain clamp optical fiber amplifier using distributed compensation optical fiber having a dispersion compensating fiber (DCF), which is a nonlinear mineral that emits scattered light and re-enters the EDF to saturate an amplifying medium to limit the signal output of the EDF.

Generally, optical amplifiers are used in optical communication systems to compensate for signal loss. However, in an all-optical network with various channels, signal loss varies in accordance with environmental changes due to branching / tapping or fault.

1 is a view showing a schematic configuration of a conventional erbium-doped fiber amplifier. As shown, a conventional erbium-doped fiber amplifier includes an optical isolator 11 for preventing scattering back to the input optical signal side, an erbium-doped optical fiber (EDF) 12 which is an amplifying medium for amplifying and outputting a signal, A WDM coupler 13 for coupling the input optical signal to a wavelength division multiplexing, and a pump connected to the optical coupler 13 to generate density inversion in the EDF 12 which is an amplifying medium. 15) and an optical isolator 14 for preventing scattering from the output stage. In the conventional erbium-doped fiber amplifier configured as described above, when the input signal P _in ^sig / channel, which is n channels, or the input signal P _in1 ^sig / channel, which is nk channels, is input to the EDF 12 via the optical isolator 11, , EDF (12) is to amplify each of the n channels, the input signal P _in1 ^sig / channel, nk channels, the input signal P _in1 ^sig / channel via an optical coupler 13 and optical isolator (14) P _out1 ^sig / Output channel, P _out2 ^sig / channel respectively. At this time, the output signal P _out1 ^sig / channel, which is n channels, is the GP _in1 ^sig / channel multiplied by the gain gain G by the input signal P _in1 ^sig / channel, which is n channels, and the P _out2 ^sig / channel is nk channels. The signal P _in1 ^sig / channel can be expressed as G1P _in1 ^sig / channel multiplied by the gain G1. As such, the amplification gains have different values as G and G1, respectively. This means that the density inversion level of the EDF 12 changes according to the change of the total input signal level according to the change in the number of channels of the input signal.

As described above, in the conventional erbium-doped fiber amplifier, the density inversion level is changed according to the change in the number of channels of the input signal, so that the output of the signal per channel is changed. Therefore, the design of the system is difficult. In addition, in a WDM network, as the network becomes more complicated, a change in the output level for each channel occurs due to a change in the number of input signal channels of the amplifier as the addition / removal of the wavelength or the conversion to another wavelength. . Therefore, there is a demand for a system for automatically and constantly fixing a gain of an amplifier for each channel according to a change in the number of input signal channels. Methods of automatically fixing gain include a method of controlling gain by electrically adjusting a pump level required for an amplification medium, and a method of controlling amplification gain by forming a laser using the gain medium as an amplification medium of a laser. These techniques,

[1] H.Okamura, "Automatic Optical-Loss compensation with Er-Doped Fiber Amplifier", Electron Lett., Vol. 27, no. 23, pp. 2155-2156,1991

[2] E. Delavaque et al., "Gain Control in Erbium-Doped Fiber Amplifiers by Lasing at 1480 nm with Photoinduced Bragg Gratings written on Fiber Ends", Electron Lett., Vol. 29, no. 12, pp. 1112-1114 , 1993

[3] J.F.Massicott et al., "1480 nm Pumped Erbium Doped Fiber Amplifier with All optical Automatic Gain Control," Electron Lett., Vol. 30, no. 12, pp. 962-964, 1994, and the like.

However, since these methods have to set the gain characteristics of the amplifying medium according to the pump level according to the pump level, the characteristics (noise characteristics) are adjusted downward, and when a laser is formed, the relaxation oscillation of the amplifying medium is dependent on the pumping level. there is a problem.

The present invention has been made to solve the above problems, and provides a gain clamp optical fiber amplifier using a distributed compensation optical fiber having a constant gain characteristic over all channels designed regardless of the number of input signals applied to various input channels. There is a purpose.

1 is a view for explaining a schematic configuration of a conventional erbium-doped fiber amplifier and the amplification characteristics according to the change in the number of input channels thereof;

2 is a gain-clamped fiber amplifier using a dispersion compensation optical fiber according to the present invention,

3 is a view for explaining amplification characteristics for n input signal channels in the gain clamp fiber amplifier of FIG.

FIG. 4 is a diagram for describing amplification characteristics of n-k input signal channels in the gain clamp fiber amplifier of FIG. 2; FIG.

FIG. 5 is a graph showing a change in intensity of induced Brillouin scattering (SBS) with respect to input intensity in the distributed compensation optical fiber of the gain clamp fiber amplifier of FIG. 2.

<Description of the symbols for the main parts of the drawings>

1. Isolator 2. EDF

3. Optical coupler 4. DCF

5. Optical isolator 6. Pump

In order to achieve the above object, a gain-clamp optical fiber amplifier using the distributed compensation optical fiber according to the present invention includes: an optical isolator for preventing scattering from being returned to an input optical signal; EDF (erbium doped fiber) which is an amplifying medium for amplifying and outputting a signal; An optical coupler (WDM coupler) for coupling the input optical signal in a wavelength division scheme; A pump connected to the optical coupler for causing density inversion to the amplification medium EDF; And an optical isolator for preventing scattering from the output stage. In the rear of the EDF, which is the amplifying medium, when the intensity of the signal output from the amplifying medium is greater than or equal to a set reference value, an induced Brillouin dispersion (SBS) light is provided. And a non-linear mineral, DCF (Dispersion Compensating Fiber), which limits the signal output of the EDF by saturating the amplifying medium by releasing it back into the EDF.

According to the present invention, in a wavelength division multiplexing network, an input signal of n channels is added to an amplification medium as nk channels according to the addition / removal of wavelengths or a change to another wavelength. When incident, the amplification medium is saturated without changing the density inversion level even if the number of channels changes, so that a constant amplification gain can be obtained regardless of the number of input signal channels.

Hereinafter, a gain clamp optical fiber amplifier using distributed compensation optical fiber according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing a schematic configuration of a gain clamp optical fiber amplifier using distributed compensation optical fiber according to the present invention. As shown, the gain clamp optical fiber amplifier using the distributed compensation optical fiber according to the present invention, an optical isolator (1) for preventing scattering back to the input optical signal, and EDF (2) which is an amplifying medium for amplifying and outputting the signal ), An optical coupler (3) for coupling the input optical signal in a wavelength division scheme, a pump (6) connected to the optical coupler (3) for causing density inversion in the EDF (2), and an amplification medium. Behind the EDF (2), when the intensity of the signal output from the amplifying medium is greater than or equal to the set reference value, the emitted Brillouin scattering (SBS) light is emitted and input again to the EDF (2) to saturate the amplifying medium. Dispersion Compensating Fiber (DCF) 4, which is a non-linear mineral that restricts the signal output of the signal, and an optical isolator 5 for preventing scattering from the output end. In particular, a distributed compensation optical fiber (DCF) is used, which is an optical fiber having a tertiary nonlinearity as a nonlinear mineral and having an SBS threshold for input strength less than that of other optical fibers.

The gain clamp optical fiber amplifier using the distributed compensation optical fiber having such a configuration operates as follows.

3 is a view for explaining the amplification characteristics for the n input signal channels in the gain clamp fiber amplifier according to the present invention, Figure 4 is a view for explaining the amplification characteristics for the nk input signal channels. First, as shown in FIG. 3, when the input signal P _in1 ^sig / channel, which is n channels, is input to the EDF 2 through the optical isolator 1, the EDF 2 inputs the input signal P _in1 which is n channels. Amplify the output of ^sig / channel and output it. At this time, when the signal P _out1 / channel of the n channels output from the EDF (2) is smaller than the intensity of P ^th _GC , the output signal P _out1 ^sig / channel = GP which is finally n channels through the DCF 4. _in1 ^sig / channel is printed. The amplification gain is G. In addition, as shown in FIG. 4, when the input signal P _in1 ^sig / channel of the nk channels is input to the EDF 2 through the optical isolator 1, the EDF 2 inputs the input signal P _in1 which is nk channels. Amplify the output of ^sig / channel and output it. At this time, when the intensity of the output signal P _out2 / channel of the nk channels output from the EDF 2 is greater than the intensity of P ^th _GC , as shown in FIG. 4, the DCF 4 is induced Brillouin. P ^sig _SBS / channel scattered in the reverse direction of the signal by the characteristics of scattering (SBS) is output. Then, the P ^sig _SBS / channel is inputted to the EDF 2 again to saturate the EDF 2.

Therefore, the final output output through the DCF (4) is the output signal P _out2 ^sig / channel = G1P _in1 ^sig / channel which is nk channels. At this time, the amplification gain is G1. As shown in FIG. 3, it can be seen that G1 is equal to the output signal size, that is, the gain G when the number of channels is n. This means that even if the number of channels of the input signal changes, the amplification gain is fixed constantly by the action of the DCF.

Here, the induction Brillouin scattering (SBS) will be described in more detail as follows. When strong intensity light is incident on a tertiary nonlinear mineral such as DCF (5), the photon and the material's phonon interact to generate a scattered Stokes signal in the reverse direction of the signal. This scattering is called induced Brillouin scattering (SBS) and increases proportionally as the intensity of the input optical signal increases. 5 shows the transmitted light intensity and the returned light intensity according to the light intensity applied to the DCF. As the applied light intensity increases, Rayleigh scattering occurs, and the intensity of SBS generation and return rapidly increases for the applied light intensity above a certain threshold point, and thus the transmitted light intensity becomes saturated. Therefore, P ^th _GC represents a critical point at which the SBS generated from the DCF 5 is fed back to the EDF 3 to control the amplification gain to a value to be fixed by saturating the EDF 3. It is proportional to the effective length and inversely proportional to the effective area. It is also proportional to the modulation bandwidth of the input signal.

Therefore, when the line width and modulation bandwidth of the input signal are greater than or equal to the SBS optical line width, a test beam of less than or equal to the SBS optical line width is added, thereby emitting the SBS light using this probe beam to provide full channel light. An optical amplifier with a fixed amplification gain is implemented.

As described above, the gain clamp optical fiber amplifier using the distributed compensation optical fiber according to the present invention has an input signal of nk channels in response to the addition / removal of wavelengths or the change to other wavelengths in the wavelength division network. When the signal is incident on the amplifying medium, even if the number of channels is changed, the saturation of the amplification medium without changing the density inversion level, and thus the optical amplifier with a fixed all-channel optical amplification gain that has a constant amplification gain regardless of the number of input signal channels. Implementation is possible.

Claims (3)

An optical isolator for preventing scattering back to the input optical signal; Erbium-doped optical fiber which is an amplifying medium for amplifying and outputting a signal; An optical coupler for coupling the input optical signal in a wavelength division scheme; A pump connected to the optical coupler for causing density inversion to the amplification medium EDF; An optical isolator for preventing scattering from the output stage; In the optical amplifier provided, Behind the EDF, the amplifying medium, when the intensity of the signal output from the amplifying medium is greater than or equal to a predetermined reference value, the induced brillouin-dispersed light is emitted and input again to the erbium-doped optical fiber to saturate the amplifying medium to thereby signal the erbium-doped optical fiber. Gain-compensated optical fiber amplifier using distributed compensation optical fiber, characterized in that it comprises; distributed compensation optical fiber is a tertiary nonlinear mineral that limits the output. The method of claim 1, In the wavelength division network, when an input signal of n channels is incident on an amplifying medium with an input signal of nk channels in accordance with the addition / removal of wavelengths or a change to another wavelength, the density reversal level is maintained even if the number of channels is changed. A gain-clamp optical fiber amplifier using distributed compensation optical fiber, wherein the amplification medium is saturated without change and a constant amplification gain can be obtained regardless of the number of input signal channels. The method of claim 1, If the line width and the modulation bandwidth of the input signal are greater than the induced Brillouin scattering light width, a test beam having a width less than the induced Brillouin scattering line width is added, and the induced Brillouin scattering light is emitted using this test beam to obtain full channel optical amplification gain. Gain clamp fiber amplifier with fixed distributed compensation fiber.