JP2011066161A - Optical direct amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical direct amplifier capable of preventing the degradation of transmission characteristics, even when rare earth added fiber is excited by modulated excitation light. <P>SOLUTION: The optical direct amplifier 302 includes an excitation light source unit 32 for output of excitation light whose light intensity is smoothed by multiplexing a plurality of modulated lights, and a rare earth added fiber 13 excited by the excitation light from the excitation light source unit 32. The optical direct amplifier 302 performs an optical direct amplification method of exciting the rare earth added fiber 13 by the excitation light whose light intensity is smoothed by multiplexing the plurality of modulated lights. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical direct amplifier that directly amplifies light.

  In an optical direct amplifier for wavelength division multiplexing (WDM) optical transmission systems, it is necessary to support a wide range of inputs from 1 ch to the maximum ch as the number of multiplexed wavelengths increases, and level changes such as loss in the transmission path Therefore, it is required to operate corresponding to an input dynamic range of 30 dB or more depending on the situation.

  In addition, transmission characteristics of multistage relay have been required due to the introduction of long distance systems and ROADM (Reconfigurable Optical Add / Drop Multiplexer) systems. For this reason, the optical direct amplifier is required to have a low noise figure and high output light stability.

  In order to support a wide input dynamic range, the pump LD (Laser Diode) is required to operate stably from a low output to a high output in order to control the output power of the optical direct amplifier. The output power at the time of output power tends to become unstable. In particular, in the case of an excitation LD in the 980 nm band that is used to reduce the noise figure, an external resonator using a fiber grating is generally adopted because high wavelength accuracy is required. Sometimes it tends to be unstable. In order to solve this, Patent Documents 1 and 2 describe a method of superimposing modulation on an excitation LD.

  In the optical repeater monitoring and control system of Patent Document 1, the optical repeater has a pumping light supply unit that supplies a plurality of pumping lights having different wavelengths to the Raman amplification medium on the optical transmission line, and operates as follows. . The excitation light supply unit modulates excitation light that enables Raman amplification of a long wavelength optical signal included in the wavelength multiplexed signal light among the plurality of excitation lights supplied to the Raman amplification medium. An optical modulator is provided in the optical repeater, and a response signal to the supervisory control command is returned by the modulation component included in the long wavelength side optical signal Raman-amplified by the pump light modulated by the pump light modulator.

  The Raman amplifier of Cited Document 2 includes a transmission medium that propagates a WDM signal, an excitation light source that generates a plurality of excitation lights having different frequencies, a modulation unit that modulates each of the plurality of excitation lights, and a modulation by the modulation unit. Light guide means for guiding the plurality of pumping lights to the transmission medium. The modulation means of the Raman amplifier operates as follows. The modulation means modulates the plurality of pump lights so that energy is not transferred between the pump lights whose frequency difference is substantially the Raman shift frequency.

  On the other hand, in addition to the Raman amplifier described above, there is an optical direct amplifier including a rare earth doped fiber. FIG. 1 is a configuration diagram illustrating a related optical direct amplifier 301. The optical direct amplifier 301 pumps a rare earth-doped fiber with modulated pumping light described in Patent Documents 1 and 2. Specifically, the optical direct amplifier 301 operates as follows. The modulation light source 15 receives a control signal from the control unit 16 that adjusts the output level of the optical direct amplifier and a signal from the modulation unit 17 that superimposes the modulation signal. With this configuration, the excitation light source unit 31 achieves stable operation even when the output power of the modulation light source 15 is low. The optical direct amplifier 301 combines the signal light input to the input port 11 by the multiplexer 12 with the pumping light from the modulation light source 15 and couples it to the rare earth doped fiber 13. The rare earth doped fiber 13 amplifies the signal light and outputs it from the output port 14.

Japanese Patent Laid-Open No. 2003-124889 JP 2004-170533 A

  When the rare earth doped fiber 13 is pumped with the modulated pump light modulated as described above in the configuration as shown in FIG. 1, the pumped state of the rare earth doped fiber 13 changes. Part of the modulation will be superimposed. For example, the amplification characteristic of an optical direct amplifier including a rare earth-doped fiber has a high-frequency cutoff characteristic with respect to modulation of pumping light. % Signal light modulation is superimposed. For this reason, the optical direct amplifier that pumps the rare-earth doped fiber with the modulated pumping light has been a factor of deteriorating transmission characteristics in an optical transmission system in which the optical direct amplifiers are connected in multiple stages.

  That is, the optical direct amplifier that excites the rare earth doped fiber with the modulated pumping light as described above has a problem that it is difficult to perform a stable output operation over a wide input dynamic range.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical direct amplifier that performs stable output operation over a wide input dynamic range, which is the above-described problem.

  In order to achieve the above object, an optical direct amplifier according to the present invention includes a pumping light source unit that outputs pumping light having a smoothed light intensity by combining a plurality of modulated lights, and pumping from the pumping light source unit. A rare earth-doped fiber that is excited by light.

  In order to achieve the above object, an optical transmission system according to the present invention includes the optical direct amplifier and an optical transmission path in which the optical direct amplifiers are arranged at predetermined intervals.

  In order to achieve the above object, the optical direct amplification method according to the present invention pumps a rare earth-doped fiber with pumping light obtained by combining a plurality of modulated lights and smoothing the light intensity.

  In order to achieve the above object, an optical transmission method according to the present invention amplifies signal light for each predetermined optical path length by the optical direct amplification method.

  In order to achieve the above object, the optical direct amplification program according to the present invention executes a direct optical amplification method in which a rare-earth doped fiber is pumped with pumping light obtained by combining a plurality of modulated lights and smoothing the light intensity. Let

  According to the present invention, it is possible to provide an optical direct amplifier that performs a stable output operation over a wide input dynamic range.

It is a block diagram explaining the related optical direct amplifier. It is a block diagram explaining the optical direct amplifier which concerns on this invention. It is a flowchart explaining the optical direct amplification method which concerns on this invention. 1 is a block diagram illustrating an optical transmission system according to the present invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 2 is a configuration diagram illustrating the optical direct amplifier 302 of the present embodiment. The optical direct amplifier 302 includes a pumping light source unit 32 that outputs pumping light whose light intensity is smoothed by combining a plurality of modulated lights, and a rare earth doped fiber 13 that is pumped by pumping light from the pumping light source unit 32. . FIG. 3 is a flowchart for explaining an optical direct amplification method of the optical direct amplifier 302. The direct optical amplifier 302 performs a direct optical amplification method in which the rare earth doped fiber 13 is pumped with pumping light obtained by combining a plurality of modulated lights and smoothing the light intensity. Specifically, the optical direct amplifier 302 pumps the rare-earth doped fiber 13 with the pumping light, the light intensity smoothing step S01 for outputting the pumping light whose light intensity is smoothed by combining the plurality of modulated lights. The fiber excitation step S02 is sequentially performed.

  For example, the optical direct amplification method may be realized by causing a computer (not shown) connected to the excitation light source unit 32 to execute an optical direct amplification program. The direct optical amplification program causes a computer to execute an optical direct amplification method of exciting a rare earth-doped fiber with excitation light obtained by combining a plurality of modulated lights and smoothing the light intensity.

  The rare earth doped fiber 13 is, for example, an erbium doped optical fiber (EDF). The excitation light source unit 32 multiplexes a plurality of modulated lights and outputs the excitation light, and modulates the excitation light to be smoothed when the modulated light is multiplexed by the multiplexer 21. A plurality of modulated light sources (15, 25) that modulate light and output the light to the multiplexer 21. The modulated light source (15, 25) is, for example, a laser diode (LD). The modulated light source (15, 25) can stably oscillate even at a low output by modulating the output light. The multiplexer 21 is, for example, a coupler. The multiplexer 21 combines the output lights of the modulated light sources (15, 25) and outputs them as excitation light to the multiplexer 12. The multiplexer 12 is, for example, a WDM coupler. The multiplexer 12 multiplexes the signal light from the input port 11 and the excitation light from the multiplexer 21 and inputs them to the rare earth-doped fiber 13.

  The optical direct amplifier 302 combines a plurality of modulated lights and outputs a pumping light, and a plurality of such that the pumping light is smoothed when the modulated light is multiplexed in the multiplexing procedure S12. A modulation procedure S11 for modulating the modulated light is performed.

  For example, when the computer connected to the pumping light source unit 32 executes the optical direct amplification program, the computer may cause the multiplexer 21 to perform the multiplexing procedure S12 and cause the modulators (17, 27) to perform the modulation procedure S11. Good. Specifically, the computer causes the control unit 16 to output a control signal to the modulated light source (15, 25) in order to adjust the output level of the optical direct amplifier. The computer controls the modulation control unit 29 as follows.

  In the modulation procedure S11, the modulation control unit 29 inputs the modulation signal to the modulation light source (15, 25) so that the modulated lights output from the modulation light source (15, 25) are in opposite phases. Since the modulated light is out of phase, when the multiplexing unit 21 combines the two modulated lights in the multiplexing procedure S12, the modulation component of the modulated light is canceled, and the light intensity of the excitation light is smoothed to be constant. Become. Therefore, the optical direct amplifier 302 can directly amplify the signal light without superimposing the modulation of the excitation light on the signal light.

  The optical direct amplifier 302 includes a modulated light source (15, 25) that can stably oscillate even at a low output, and further, the light intensity of the pump light combined with the modulated light from the modulated light source (15, 25) is smoothed. Therefore, stable amplification of signal light can be realized over a wide input range. That is, the optical direct amplifier 302 has a wide input dynamic range, can stably control the light intensity of the pumping light from high output to low output, and can obtain signal light output that does not affect the transmission characteristics of the optical transmission line. .

  In FIG. 2, there are two modulated light sources, but there may be three or more. When there are three or more modulation light sources, in the modulation procedure S11, the modulation control unit 29 modulates the modulated light on which the modulation components such that the modulation components of all the modulated light are canceled when combined by the multiplexer 21 are superimposed. The modulation signal is input to each modulation light source.

  For example, the modulation control unit 29 may input the modulation signal to the modulation light source so as to change the duty ratio of the modulation light according to the number of modulation lights to be combined. Specifically, if the number of modulated lights to be combined is 4, the duty ratio of the modulated light is 25%, and if the number of modulated lights to be combined is 5, the duty ratio of the modulated light is 20%. To do. In order to make the light intensity of the excitation light combined with the modulated light constant, the modulation control unit 29 inputs a modulated signal with a shifted light intensity of each modulated light to the modulated light source.

  In the present optical direct amplifier, even when there are three or more modulation light sources, the light intensity of the pumping light can be smoothed to be constant, and stable amplification of signal light can be realized over a wide-band input range.

(Embodiment 2)
FIG. 4 is a configuration diagram illustrating the optical transmission system 402 of the present embodiment. The optical transmission system 402 includes an optical direct amplifier 302 and an optical transmission path 330 on which the optical direct amplifier 302 is arranged at a predetermined interval. The optical transmission system 402 connects the transmitting station 310 and the receiving station 320 to both ends of the optical transmission path.

  In the optical transmission system 402, an optical direct amplifier 302 is inserted for each predetermined length of the optical transmission path 330. The optical transmission system 402 transmits the signal light from the transmission station 310 to the reception station 320 while amplifying the signal light for each predetermined optical path length by the optical direct amplifier 302.

  As described in the first embodiment, since the optical direct amplifier 302 can obtain a signal light output that does not affect the transmission characteristics, the optical transmission system 402 that uses this in multiple stages suppresses deterioration of the transmission characteristics. Can do.

11: input port 12, 21: multiplexer 13: rare earth doped fiber 14: output port 15, 25: modulation light source 16: control unit 17, 27: modulation unit 29: modulation control unit 31, 32: excitation light source unit 301, 302: Optical direct amplifier 310: Transmitting station 320: Receiving station 330: Optical transmission path 402: Optical transmission system

Claims (14)

An excitation light source unit that outputs excitation light in which the light intensity is smoothed by multiplexing a plurality of modulated lights;
A rare earth-doped fiber that is excited by excitation light from the excitation light source unit;
With optical direct amplifier. The excitation light source unit is
A multiplexer that combines the plurality of modulated lights and outputs the excitation light;
A plurality of modulated light sources that modulate the modulated light so that the pumping light is smoothed and output to the multiplexer when the modulated light is multiplexed by the multiplexer;
The optical direct amplifier according to claim 1, comprising: The modulated light source outputs each of the modulated light on which modulation components are superimposed so that the modulation components of all the modulated light are canceled when combined by the multiplexer. Optical direct amplifier as described. 3. The optical direct amplifier according to claim 2, wherein the number of the modulated light sources is two, and the modulated light on which modulated components having opposite phases are superimposed is output. An optical direct amplifier according to any one of claims 1 to 4,
An optical transmission line in which the optical direct amplifiers are arranged at predetermined intervals;
Including optical transmission system. A direct optical amplification method in which a rare earth-doped fiber is pumped with pumping light obtained by combining a plurality of modulated lights and smoothing the light intensity. A multiplexing procedure for multiplexing a plurality of the modulated lights and outputting the excitation light;
A modulation procedure for modulating a plurality of the modulated light so that the excitation light is smoothed when the modulated light is multiplexed in the multiplexing procedure;
The optical direct amplification method according to claim 6, comprising: 8. The modulated light on which the modulation component is superimposed so that the modulation components of all the modulated light are canceled when combined in the multiplexing procedure in the modulation procedure is output. Optical direct amplification method. 8. The optical direct amplification method according to claim 7, wherein the number of the modulated lights is two, and the modulated light on which modulated components having opposite phases are superimposed is output in the modulation procedure. 10. An optical transmission method for amplifying signal light for each predetermined optical path length according to the optical direct amplification method according to claim 6. An optical direct amplification program for causing a computer to execute an optical direct amplification method for exciting a rare earth-doped fiber with excitation light obtained by combining a plurality of modulated lights and smoothing the light intensity. A multiplexing procedure for combining a plurality of modulated lights into a multiplexer and outputting the excitation light;
A modulation procedure for outputting the modulated light such that the excitation light is smoothed when the modulated light is multiplexed by the multiplexing procedure to a plurality of modulated light sources;
The optical direct amplification program according to claim 11, which causes a computer to execute an optical direct amplification method characterized by comprising: In the modulation procedure, each modulated light source is caused to output the modulated light on which a modulation component is superimposed so that the modulation components of all the modulated light are canceled when multiplexed in the multiplexing procedure. 13. The optical direct amplification program according to claim 12, which causes a computer to execute the optical direct amplification method. The computer executes the optical direct amplification method characterized in that the modulated light is two, and the modulated light is output in the modulated procedure by superimposing the modulated light components having opposite phases to each other in the modulated procedure. The optical direct amplification program according to claim 12.

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