JP6094294B2 - Optical node - Google Patents

Description

  The present invention relates to an optical node, and more particularly to noise reduction of an optical amplifier provided in an input / output unit of the optical node.

  In recent years, communication demand has been rapidly increasing due to the spread of the Internet and the like. Correspondingly, a high-speed and large-capacity optical communication network using an optical fiber or the like is being developed. As a technique used in such an optical communication network, wavelength division multiplexing (WDM) that multiplexes carriers having different optical wavelengths has attracted attention. By using WDM, a plurality of carrier waves can be propagated in parallel on one optical transmission line. For this reason, a large-capacity optical communication network can be constructed at low cost.

  An optical communication network using WDM includes a plurality of optical nodes and an optical transmission line that connects these optical nodes. In this optical communication network, a ROADM node including a reconfigurable optical add / drop multiplexer (ROADM) is used as each optical node (see, for example, Non-Patent Document 1). The ROADM node has a function of inserting a carrier wave of another wavelength into a wavelength-multiplexed carrier wave or branching a carrier wave of a specific wavelength from the wavelength-multiplexed carrier wave.

Atsushi Takada, Tetsuo Takahashi, Ippei Soya "Photonic Node Technology" NTT Technology Journal, pp. 26-29, October 2007

  Here, in a conventional ROADM node such as the ROADM node disclosed in Non-Patent Document 1 described above, an optical signal received from another optical node is amplified by a reception optical amplifier and then transmitted to a ROADM optical switch unit. It is done. An optical signal addressed to another optical node is sent from the ROADM optical switch unit to the transmission optical amplifier, amplified by the transmission optical amplifier, and then transmitted. As these optical amplifiers, amplifiers using an optical fiber in which erbium ions are doped in the core (EDFA: Erbium Doped Fiber Amplifier) are used.

  However, when an EDFA is used as the reception optical amplifier and the transmission optical amplifier, noise (ASE noise) due to light generated by spontaneous emission (spontaneous emission light) cannot be reduced below the quantum limit.

  In view of the above-described problems, the inventors of the present application have studied and found that a PIA (Phase Insensitive Amplifier) is provided before the ROADM optical switch unit, and a PSA is provided after the ROADM optical switch unit. It has been found that by providing (Phase Sensitive Amplifier), the influence of noise can be reduced as compared with a conventional ROADM node using EDFA.

  Accordingly, an object of the present invention is to provide an optical node capable of reducing the noise figure as compared with the conventional configuration by providing PIA and PSA in series before and after the optical processing unit such as the ROADM optical switch unit.

  In order to achieve the above-described object, an optical node provided in the optical communication network of the present invention includes a first optical amplifying unit, a filter unit, an optical processing unit, and a second optical amplifying unit. .

The first optical amplification unit generates idler light based on the input pump light and signal light, and outputs first amplified light including the pump light, signal light, and idler light. A filter part outputs the to-be-processed light containing signal light and idler light among the input 1st amplified lights. The light processing unit performs predetermined processing on the input signal light, and outputs processing light including signal light and idler light that attenuates the light to be processed. The second optical amplification unit includes a processing light and the pump light are input to amplify the signal light included in the inputted processed light, pump light, A Idora light, and a second amplifying light comprising the amplified signal light Is output. The first optical amplification unit functions as a PIA, and the second optical amplification unit functions as a PSA.

  According to the optical node of the present invention, the first optical amplification functioning as a PIA is a constituent element necessary for performing predetermined processing in the optical node, and preceding the optical processing unit that applies predetermined attenuation to the signal light. And a second optical amplification unit functioning as a PSA downstream of the optical processing unit. In the configuration including the optical processing unit that attenuates the signal light between the PIA-PSA in the PIA-PSA cascade structure, the noise figure is improved by about 6 dB compared to the case of using the EDFA in which the noise figure is improved to the quantum limit. To do.

It is a schematic diagram for demonstrating the outline of a structure and operation | movement of an optical node. It is a schematic block diagram for demonstrating a 1st optical node. It is a figure which shows an example of the spectrum in a 1st optical node. It is a schematic block diagram for demonstrating a 2nd optical node.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(Outline of optical node)
The outline of the optical node of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram for explaining the outline of the configuration and operation of an optical node.

  The optical node 10 is used in, for example, an optical communication network that transmits and receives wavelength division multiplexing (WDM) signals. The optical node 10 includes a first optical amplifying unit 40, a filter unit 34, an optical processing unit 50, a second optical amplifying unit 90, and an output side component. A wave unit 82 and an interface unit 36 are provided.

  The optical node 10 branches the signal light addressed to its own optical node 10 out of the signal light S <b> 1 received from another optical node, and sends it to the client device 100. Further, among the signal lights received from other optical nodes, the signal light including the optical signal other than the one addressed to its own optical node 10 and the optical signal addressed to the other optical node received from the client apparatus 100 is sent to the other optical node. Send.

  When the optical node 10 and the client device 100 exchange electric signals, the interface unit 36 of each optical node 10 has an optical / electrical (O / E) conversion function and an electric / optical (E / O). ) Provide conversion function.

  The first optical amplifying unit 40 is used as a PIA, generates idler light based on the input pump light and signal light S33, and outputs first amplified light S41 including pump light, signal light, and idler light.

  The filter unit 34 outputs the processed light S35 including the signal light and the idler light in the first amplified light S41 that is input. Here, the configuration example in which the filter unit 34 blocks the pump light is shown, but the pump light may be branched from the signal light and the idler light and sent to the second optical amplification unit 90.

  The light processing unit 50 performs a predetermined process on the input processed light S35 to generate processed light. For example, as a predetermined process, the optical processing unit 50 divides the signal light addressed to its own optical node and sends it to the interface unit 36, and the signal light addressed to the other optical node received from the interface unit 36 is transmitted to a predetermined channel. Insert it. The optical processing unit 50 passes the received signal light other than the one addressed to its own optical node.

  Here, the signal light passing through the light processing unit 50 is attenuated by components such as a multiplexer / demultiplexer provided in the light processing unit 50. The idler light is also attenuated to the same extent as the signal light. Thus, the signal light and idler light that have been attenuated by the light processing unit 50 and further subjected to predetermined processing are output from the light processing unit 50 as processed light.

  The second optical amplification unit 90 is used as a PSA, amplifies the signal light included in the input pump light and processing light, and outputs the second amplified light S39 including the pump light, the signal light, and the idler light.

  The second amplified light output from the second optical amplification unit 90 is demultiplexed by the output-side demultiplexing unit 82, and only the signal light S83a is output from the optical node 10. Accordingly, the pump light and idler light are not added to the signal light output from the optical node 10. As a result, for example, in an optical communication network, it is possible to prevent problems such as a decrease in frequency utilization efficiency or a fiber fuse caused by excessive increase in light intensity, which occurs when pump light or idler light is output together with signal light.

  The second optical amplification unit 90 operates as a PSA for the signal light passing through the optical processing unit 50. Here, the noise input to the second optical amplifying unit 90 includes the correlation noise generated in the first optical amplifying unit 40 and the first optical amplifying unit in the band of the signal light of the channel passing through the optical processing unit 50. 40 and uncorrelated noise added due to attenuation between the second optical amplification unit 90 and the second optical amplification unit 90. Here, the correlation means that there is a correlation between noise existing in the band of signal light and noise existing in the band of idler light generated from the signal light. Further, uncorrelated means that there is no correlation between noise existing in the band of signal light and noise existing in the band of idler light generated from the signal light. In the following description, the noise in such a state is referred to as correlated noise and uncorrelated noise, respectively. Since the correlation noise generated in the first optical amplification unit 40 is attenuated between the first optical amplification unit 40 and the second optical amplification unit 90, the noise input to the second optical amplification unit 90 is an uncorrelated noise. Become dominant. The correlation noise is amplified with the same gain as that of the signal light in order to satisfy the operation condition as the PSA. On the other hand, uncorrelated noise does not satisfy the operating condition as PSA, and is thus amplified with a gain 3 dB lower than the signal light. For example, when the gain at the PSA operation is 10 dB and the attenuation of 10 dB is given between the first optical amplifying unit 40 and the second optical amplifying unit 90, the noise figure of the second optical amplifying unit 90 is about -2.6 dB. (Z. Tong et al., Optics Express., Vol. 18, no. 15, p. 15426, 2010).

  According to this optical node 10, the first light functioning as a PIA is a component necessary for performing a predetermined process in the optical node 10 and in front of the optical processing unit 50 that gives a predetermined attenuation to the signal light. Amplifying unit 40 is provided, and a second optical amplifying unit 90 that functions as a PSA is provided downstream of optical processing unit 50. In the configuration including the optical processing unit 50 that attenuates the signal light between the PIA and PSA, the noise figure is improved by about 6 dB compared to the optical node using the EDFA whose noise figure is improved to the quantum limit.

(First embodiment)
With reference to FIG.2 and FIG.3, the optical node (henceforth a 1st optical node) of 1st Embodiment of this invention is demonstrated. FIG. 2 is a schematic configuration diagram for explaining the first optical node. In FIG. 2, each component is connected with a line, which schematically shows a transmission path through which a signal propagates. Each component may be connected by, for example, an optical fiber or an optical waveguide, or may be connected by so-called spatial coupling.

FIG. 3 is a diagram illustrating an example of a spectrum in the first optical node. In FIG. 3, the horizontal axis indicates the wavelength, and the vertical axis indicates the signal intensity in arbitrary units. The signal light is a WDM signal having n WDM channels. Here, the carrier wavelength of the k-th channel (k is an integer from 1 to n) is λ _sk , the carrier wavelength of idler light generated from the signal light of the k-th channel is λ _ik , and the wavelength of the pump light is λ _p . Then, 1 / λ _ik = 2 / λ _p −1 / λ _sk .

  In the following description, the signal light of the second channel (ch2) is branched and sent to the client device, the signal light received from the client device is inserted into the third channel (ch3), and the signal light of the other channels is An example of passing one optical node 12 will be described.

  The signal light of each channel is a signal in which one or both of the phase and intensity of the carrier wave are modulated according to the data signal.

  Further, here, a configuration example in a state where the polarization of the signal light is temporally stable is shown. In addition, the polarization diversity configuration is adopted for the polarization dependent components such as the nonlinear optical devices constituting the first optical amplification unit and the second optical amplification unit, or the polarization stabilization device is introduced. By doing so, polarization independence can be achieved.

  The first optical node 12 includes a pump light source 20, a pump light demultiplexing unit 30, a first multiplexing unit 32, a first optical amplification unit 40, an optical processing unit 50, a second multiplexing unit 38, and a second optical amplification unit 90. , An output side branching unit 82, an optical phase shifter control device 84, a phase shifter 70, and a dispersion compensator 80.

  The signal light S <b> 1 input from the input port to the first optical node 12 is first sent to the first multiplexing unit 32. The first multiplexing unit 32 multiplexes the signal light S1 and the pump light S31a. As the first multiplexing unit 32, for example, a WDM multiplexer / demultiplexer (WDM coupler / divider) can be used.

  The pump light S31a is generated by the pump light source 20.

  The pump light source 20 includes, for example, an external resonator light source 22, an optical amplifier 24, and a band pass filter 26. The phase noise of the pump light is added to the signal light. For this reason, it is desirable to use the external resonator light source 22 having a sufficiently narrow frequency spectrum line width as the pump light source 20. For example, as the external resonator light source 22, a laser diode that generates laser diode output light whose polarization plane matches that of the signal light S1 is used.

  In addition, in the nonlinear optical device that constitutes the first optical amplification unit and the second optical amplification unit, it may be necessary to increase the line width of the frequency spectrum, such as when the effect of stimulated Brillouin scattering becomes a problem. In this case, phase modulation may be performed using an optical phase modulator driven by one or more sine waves of about 100 MHz to 2 GHz.

  The wavelength of the pump light must be set outside the wavelength band of the signal light. For example, when the wavelength band of the signal light is the C band (1530 to 1565 nm), the wavelength of the pump light may be set to a wavelength that can be separated from the C band, for example, 1525 nm or 1570 nm.

  Note that the first light amplification unit 40 and the second light amplification unit 90 need at least pump light intensity that causes parametric amplification. For this reason, the intensity of the laser diode output light is amplified by the optical amplifier 24. As the optical amplifier 24, for example, an EDFA is used.

  The laser diode output light amplified by the optical amplifier 24 is sent to the band pass filter 26. In the band pass filter 26, the transmission wavelength is set to a wavelength band that matches the wavelength band of the pump light S21. Then, after the ASE noise existing outside the wavelength band of the pump light is sufficiently reduced in the band pass filter 26, the laser diode output light is output from the pump light source 20 as the pump light S21.

  The pump light S <b> 21 is sent to the pump light demultiplexing unit 30 provided in the preceding stage of the first multiplexing unit 32. The pump light demultiplexing unit 30 divides the pump light S21 into two, sends one to the first multiplexing unit 32 (S31a), and sends the other to the optical phase shifter 70 (S31b). The pump light S31a input to the first multiplexing unit 32 serves as a power source for the first optical amplification unit 40 that operates as a PIA. The pump light S31b input to the optical phase shifter 70 serves as a power source for the second optical amplification unit 90 that operates as a PSA.

  The first multiplexing unit 32 combines the signal light S1 and the pump light S31a, and outputs the first combined light S33 including the signal light and the pump light (FIG. 3A). The first combined light S33 is input to the first optical amplification unit 40.

The first light amplifying unit 40 is used as a PIA, amplifies the signal light, and generates idler light as the wavelength converted light of the signal light included in the first combined light S33 (FIG. 3B). The phase of the idler light is determined by the phase of the input signal light and the pump light, and the signal light and the idler light are in a correlated state. Here, the third channel (ch3) is an empty channel. For this reason, the components of the wavelengths λ _s3 and λ _i3 of the signal light and idler light are not included.

  The first optical amplifying unit 40 needs to obtain a sufficient gain and bandwidth with an allowable pump light intensity. As a device that satisfies this requirement, a highly nonlinear fiber or a PPLN (Periodically Poled Lithium Niobate) waveguide can be used. The first optical amplifying unit 40 is not limited to a configuration using a highly nonlinear fiber or a PPLN waveguide. If a sufficient gain and bandwidth can be obtained, a silicon fine wire waveguide or the like may be used. A specific configuration example of the first optical amplification unit will be described later.

  The first amplified light S41 output from the first optical amplification unit 40 is sent to the filter unit 34. The filter part 34 outputs the to-be-processed light containing signal light and idler light among the input 1st amplified lights. The light to be processed is sent to the light processing unit 50. In the first optical node 12, the filter unit 34 blocks the pump light.

  The optical processing unit 50 includes, for example, an idler optical attenuator 52, an idler optical filter unit 54, and a known ROADM optical switch unit 60. Of the light to be processed, the signal light is sent to the ROADM optical switch unit 60 which is an optical path switching unit. On the other hand, idler light in the light to be processed is sent to the idler light attenuator 52.

  The ROADM optical switch unit 60 performs a process of branching the signal light addressed to the optical node and sending it to the client apparatus, and a process of inserting the signal light received from the client apparatus and addressed to another optical node into a predetermined channel. .

  The ROADM optical switch unit 60 includes, for example, a duplexer 62, a drop switch 64, an add switch 66, and a multiplexer 68.

  The drop switch 64 and the add switch 66 are provided in the same number as the channel number n. The wavelength multiplexed signal is n-branched for each channel by the duplexer 62. The k-th channel signal is sent to the k-th drop switch 64-k.

  The k-th drop switch 64-k switches the destination of the k-th channel signal received from the duplexer 62 to either the k-th add switch 66-k or the interface unit 36. The kth add switch 66-k switches the source of the kth channel signal to be sent to the multiplexer 68 to either the kth drop switch or the interface unit 36. The first to n-channel optical signals output from the first to n-th add switches 66-1 to 66 -n are multiplexed by a multiplexer 68 to become signal light.

  In this way, by switching the n drop switches 64-1 to n and the n add switches 66-1 to 66-n, the optical signal addressed to the optical node is branched from the signal light and sent to the client device. Processing and processing for inserting an optical signal addressed to another optical node received from the client device into the signal light are realized.

  The signal light is attenuated while passing through the duplexer 62, the drop switches 64-1 to n, the add switches 66-1 to 66-n, and the multiplexer 68.

  On the other hand, the idler light included in the light to be processed is output as processed light through the idler light attenuator 52 and the idler light filter unit 54. The idler light attenuator 52 is set so that the attenuation amount of the idler light passing through the idler light attenuator 52 and the idler light filter unit 54 is the same level as the attenuation amount of the signal light passing through the ROADM optical switch unit 60. The As a result, the signal light and idler light of the processed light are attenuated to the same extent in the light processing unit 50.

  The idler optical filter unit 54 blocks signal light addressed to the optical node included in the light to be processed, that is, idler light having a wavelength component corresponding to the signal light branched by the ROADM optical switch unit 60.

  Here, an example in which the optical processing unit 50 includes the ROADM optical switch unit 60, the idler optical attenuator 52, and the idler optical filter unit 54 has been described. However, the present invention is not limited to this example, and only the ROADM optical switch unit is configured. And an idler light attenuator and an idler light filter unit may be provided. In this case, the idler light is also sent to the ROADM optical switch unit, like the signal light, and the drop switch can be used as the idler optical filter unit. If the idler light component corresponding to the signal light addressed to the optical node is sent to the interface unit 36 by controlling the drop switch, the idler light component can be removed from the idler light. The idler light passing through the ROADM optical switch unit is attenuated in the same manner as the signal light passing through the ROADM optical switch unit.

  Each switch of the ROADM optical switch unit 60 and the transmission band of the idler optical filter unit 54 are set by an instruction from a control unit (not shown) included in the first optical node 12. The control means is configured using, for example, an FPGA (Field Programmable Gate Array).

Here, the signal light addressed to the optical node is branched by the optical processing unit 50. For this reason, when the idler light generated corresponding to the signal light addressed to the optical node is input to the second optical amplification unit 90, the second optical amplification unit 90 functions as a PIA for the idler light, There is a risk of generating unnecessary signals in the signal light. In order to prevent this, in the first optical node 12, the idler optical filter unit 54 blocks idler light of the corresponding wavelength. In this example, the signal light of the second channel is branched. Accordingly, the idler light filter unit 54 blocks idler light having a wavelength λ _i2 (= 2 / λ _p −1 / λ _s2 ).

Of the signal light channels received from the client device, the channel addressed to the other optical node from the optical node is an empty channel and is not included in the processed light. That is, the processing light has no corresponding idler light. In this example, the signal light of the third channel is an empty channel in the processed light and is inserted in the first optical node 12. Therefore, idler light having a wavelength λ _i3 (= 2 / λ _p −1 / λ _s3 ) corresponding to the signal light of the third channel is not included in the processing light. Therefore, when this processed light is input to the second optical amplifying unit 90, the second optical amplifying unit 90 functions as a PIA for the signal light of the third channel. For this reason, the gain of the signal light of the third channel in the second optical amplifying unit 90 is 6 dB lower than the gain of the signal light passing therethrough.

  Therefore, the optical signal to be inserted is preferably adjusted to a signal intensity higher by, for example, about 6 dB than other wavelength components in the interface unit 36 (FIG. 3C).

  The processed light generated by the light processing unit 50 is sent to the second multiplexing unit 38. Here, in order to obtain good characteristics of PSA in the second optical amplifying unit 90, the propagation time of the signal light and the idler light is made equal between the filter unit 34 and the second multiplexing unit 38. It is good to be configured.

  Further, pump light is also input to the second multiplexing unit 38 from the light source 20 via the pump light demultiplexing unit 30 and the optical phase shifter 70.

  The optical phase shifter 70 adjusts the phase of the pump light so that the relative phases of the signal light, the pump light, and the idler light given by 2φp−φs−φi are constant. Note that φp, φs, and φi indicate the phases of pump light, signal light, and idler light, respectively. The relative phase may fluctuate due to mechanical vibrations of peripheral devices, environmental temperature changes, and the like. Therefore, the relative phase is made constant by adjusting the phase of the pump light S31b in the optical phase shifter 70. Here, based on a control signal S85 sent from an optical phase shifter control device 84 described later, the second optical amplification unit 90 adjusts the relative phase so that the amplification gain of the signal light is maximized. As the optical phase shifter 70, for example, an optical phase shifter such as a fiber stretcher using a piezoelectric element can be used.

  The pump light whose phase is adjusted by the optical phase shifter 70 is sent to the second multiplexing unit 38.

  The second multiplexing unit 38 combines the signal light and idler light included in the processing light and the pump light to generate the second combined light S39. The second combined light S39 is output from the second combining unit 38 and sent to the dispersion compensator 80.

  The dispersion compensator 80 compensates the chromatic dispersion of the second combined light S39. The dispersion compensation light whose chromatic dispersion is compensated by the dispersion compensator 80 is input to the second optical amplification unit 90.

  The second optical amplification unit 90 described later amplifies the signal light with an amplification gain based on the relative phases of the signal light, the pump light, and the idler light included in the second combined light S39. As described above, by adjusting the phase of the pump light by the optical phase shifter 70, the relative phase is adjusted in the second optical amplification unit 90 so that the amplification gain of the signal light is maximized. However, when chromatic dispersion occurs in the light processing unit 50, the relative phases of the signal light, the pump light, and the idler light included in the second combined light S39 are values that depend on the wavelength of the signal light. As a result, the amplification gain of the signal light in the second optical amplification unit 90 depends on the wavelength of the signal light, and a flat gain characteristic cannot be obtained. Therefore, by using the dispersion compensator 80 to compensate for the chromatic dispersion of the second combined light S39, the relative phase can be kept constant. Then, the amplification gain of the signal light in the second optical amplification unit 90 is stabilized (FIG. 3D).

  Note that the dispersion compensator may not be provided as long as the wavelength dependency of gain does not become a problem.

  The second optical amplification unit 90 is used as a PSA, amplifies the signal light included in the second combined light S39, and outputs the second amplified light S91 including pump light, signal light, and idler light. The second optical amplification unit 90 can be configured in the same manner as the first optical amplification unit 40. A configuration example of the second optical amplification unit 90 will be described later.

  The second amplified light S91 output from the second optical amplifying unit 90 is sent to the output side demultiplexing unit 82.

  The output side demultiplexing unit 82 demultiplexes the signal light, the pump light, and the idler light included in the second amplified light S91. As the output side branching unit 82, for example, a WDM multiplexer / demultiplexer can be used.

  The demultiplexed signal light S83a is output from the first optical node 12. The idler light S83b is sent to the optical phase shifter controller 84.

  Since pump light is unnecessary after being output from the second optical amplifying unit 90, for example, it may be blocked by the output side demultiplexing unit 82 or may be blocked from the output side demultiplexing unit 82. It may be sent to the route and released.

  The optical phase shifter control device 84 includes, for example, intensity detection means and control signal generation means (not shown).

  The optical phase shifter controller 84 detects the intensity of the input idler light S83b in the intensity detector. As already described, the idler light is amplified by the second optical amplification unit 90 with an amplification gain corresponding to the amplification gain of the signal light. Accordingly, when the amplification gain of the idler light is maximized, the amplification gain of the signal light is also maximized. Therefore, the optical phase shifter is controlled so that the intensity of the idler light is maximized. Since the control of the optical phase shifter is conventionally known, the description thereof is omitted here. The optical phase shifter control device 84 determines the relative phase of the second amplified light S91 when the intensity of the idler light is maximized by detecting the intensity of the idler light S83b in the intensity detection means. Then, the control signal generating means generates a control signal S85 for notifying the relative phase at which the intensity of idler light is maximized, and sends it to the optical phase shifter 70 described above.

  Here, the configuration in which the PIA and the PSA are provided before and after the ROADM optical switch unit has been described, but the present invention is not limited to this. If the signal light that passes through the optical node does not go through the optical-electrical-optical conversion, an optical node is provided with PIA and PSA before and after the optical processing unit 50, so that the conventional optical signal is similar to the ROADM optical switch. The SN ratio is improved as compared with the configuration using the EDFA.

  In addition, the optical node used in one-way optical fiber transmission, each having one input port and one output port, has been described. However, as shown in FIG. It is also possible to expand to N paths in which at least one of the output ports is plural.

  Here, the configuration example including the first optical amplifying unit 46 that functions as the PIA and the second optical amplifying unit 90 that functions as the PSA has been described. However, for example, two or more first optical amplifying units 46, A configuration in which the two optical amplifying units 90 are provided in parallel may be employed (not shown). Since the power of the pump light input to the nonlinear optical device is limited by the properties of the material, a sufficient gain may not be achieved for the signal light. A parallel configuration is a solution to this.

(Optical amplifier)
The first optical amplifying unit 46 and the second optical amplifying unit 90 are non-linear optical devices and operate as optical parametric amplifiers. As described above, for example, a highly nonlinear fiber or a PPLN waveguide is used. Four-wave mixing is used for highly nonlinear fibers, and SHG / DFG (second-order high- and long-wave light generation / difference frequency light generation) cascade wavelength conversion is the operating principle of a parametric amplifier.

  When signal light and pump light are input as input light, the optical parametric amplifier functions as a PIA. On the other hand, when the signal light, idler light, and pump light are input as input light, and the relative phases of the signal light, pump light, and idler light are controlled and maintained constant, the optical parametric amplifier functions as a PSA. .

For example, in the case of using a highly nonlinear fiber, the nonlinear constant is, for example, 10 W ⁻¹ km ⁻¹ or more, the length is about 100 m to 1000 m, the zero dispersion wavelength exists in the vicinity of the wavelength of the pump light, and A small dispersion slope and sufficient gain and bandwidth can be obtained. It is also desirable to have polarization maintaining characteristics.

(Second Embodiment)
With reference to FIG. 4, an optical node (hereinafter referred to as a second optical node) according to a second embodiment of the present invention will be described. FIG. 4 is a schematic configuration diagram for explaining the second optical node.

  The second optical node 14 differs from the first optical node in that the pump light S21 generated by the pump light source 20 is not branched and is sent to the first multiplexing unit 32. For this reason, the filter unit 34 branches the pump light from the first amplified light S41 and sends it to the optical phase shifter 70. The pump light is attenuated before being sent to the optical phase shifter 70. For this reason, the pump light is amplified using, for example, EDFA as the optical amplifying unit 74, and further, ASE noise is removed using the band pass filter 76, and then sent to the second multiplexing unit 38. In this configuration, the same effect as that of the first optical node can be obtained.

  The other configuration is the same as that of the first optical node, and a duplicate description is omitted.

10, 12, 14: Optical node 20: Pump light source 22: Laser diode 24: Optical amplifier 26, 76: Band pass filter 30: Pump light demultiplexing unit 32: First multiplexing unit 34: Filter unit 36: Interface unit 38 : Second multiplexing unit 40: first optical amplification unit 74: optical amplification unit 50: optical processing unit 52: idler optical attenuator 54: idler optical filter unit 60: ROADM optical switch unit 62: demultiplexer 64: for drop Switch 66: Add switch 68: Multiplexer 70: Optical phase shifter (phase adjustment unit)
80: dispersion compensator 82: output side demultiplexing unit 84: optical phase shifter control device 90: second optical amplification unit 100: client device

Claims (11)

An optical node provided in an optical communication network,
A first light amplifying unit that generates idler light based on the input pump light and signal light and outputs first amplified light including the pump light, signal light, and idler light;
A filter unit that outputs light to be processed including signal light and idler light among the first amplified light input; and
A light processing unit that performs predetermined processing on the input signal light and attenuates the light to be processed , and outputs processing light including signal light and idler light ;
Wherein the processing light and the pump light are input to amplify the signal light included in the processing light input, the pump light, the second for outputting a second amplified light including A Idora light, and the amplified signal light An optical amplification unit ,
The optical node, wherein the first optical amplification unit functions as a PIA, and the second optical amplification unit functions as a PSA . The optical processing unit branches an optical signal addressed to the optical node from the signal light and inserts an optical signal addressed to another optical node from the optical node into the signal light. Optical node. The said optical processing part removes the idler light produced | generated based on the wavelength component of the optical signal addressed to the said optical node contained in the said to-be-processed light in the said 1st optical amplification part. 2. The optical node according to 2. The light processing unit is
An optical path switching unit for branching an optical signal addressed to the optical node from the signal light, and inserting an optical signal addressed to another optical node from the optical node into the signal light;
An attenuator that attenuates idler light;
The optical node according to claim 3, further comprising an idler optical filter unit that removes idler light generated based on a wavelength component of an optical signal addressed to the optical node included in the processed light. The light processing unit is
The optical signal addressed to the optical node is branched from the signal light, the wavelength component of the idler light generated based on the wavelength component of the optical signal addressed to the optical node included in the processed light is branched from the idler light, The optical node according to claim 3, further comprising an optical path switching unit that inserts an optical signal addressed to another optical node from the optical node into the signal light. The optical communication network is a network for transmitting wavelength division multiplexed signals,
The optical processing unit, after amplifying an optical signal addressed to another optical node from the optical node with respect to other wavelength components of the signal light, inserts the optical signal into the signal light. The optical node according to any one of the above. The output side demultiplexing part provided in the back | latter stage of the said 2nd optical amplification part, and outputting the signal light contained in the said 2nd amplified light to the exterior of the said optical node, The any one of Claims 1-6 An optical node according to claim 1. In response to a control signal generated by the optical phase control unit, a phase adjustment unit that changes the phase of the pump light input to the second optical amplification unit,
The optical node according to claim 7, wherein the output side demultiplexing unit sends idler light to the optical phase control unit. A first multiplexing unit provided in a preceding stage of the first optical amplification unit, which combines the pump light and the signal light and sends the first combined light including the pump light and the signal light to the first optical amplification unit When,
The pump light and the processing light provided between the light processing unit and the second optical amplification unit are combined to amplify the second combined light including the pump light, the signal light, and the idler light. The optical node according to any one of claims 1 to 8, further comprising a second multiplexing unit to be sent to the unit. A first multiplexing unit provided in a preceding stage of the first optical amplification unit, which combines the pump light and the signal light and sends the first combined light including the pump light and the signal light to the first optical amplification unit When,
The pump light and the processing light provided between the light processing unit and the second optical amplification unit are combined to amplify the second combined light including the pump light, the signal light, and the idler light. A second combining section to be sent to the section;
Provided before the first multiplexing section, the pump light and second branch, one sent to the first multiplexing unit, further comprising a <br/> a demultiplexing unit for sending to said phase adjustment portion other The optical node according to claim 8 . A first multiplexing unit provided in a preceding stage of the first optical amplification unit, which combines the pump light and the signal light and sends the first combined light including the pump light and the signal light to the first optical amplification unit When,
The pump light and the processing light provided between the light processing unit and the second optical amplification unit are combined to amplify the second combined light including the pump light, the signal light, and the idler light. The second combining section to send to the section
With
The optical node according to claim 8 , wherein the filter unit sends pump light included in the first amplified light to the phase adjustment unit.

Images