JP2010066428A - Wavelength converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately convert the frequency of signal light without increasing a circuit scale. <P>SOLUTION: The PBS 16 of a wavelength conversion loop circuit 20 outputs a first polarized wave component and a second polarized wave component orthogonal to the first polarized wave component from composite light of the signal light and pump light to two output ports. A wavelength conversion circuit 18 is provided on a wavelength conversion loop which is a transmission line connecting the two output ports in a loop shape, and the wavelength conversion circuit 18 generates the signal light frequency-converted by four-wave-mixing for each of the first polarized wave component and the second polarized wave component. The signal light is propagated through the wavelength conversion loop and multiplexed again in a PBS 16, the composite light output from the input port of the PBS 16 passes through a BPF 19 which makes only the frequency fc of the frequency converted signal light pass through, and the frequency converted signal light is output from the BPF 19. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wavelength converter that converts the wavelength of polarization multiplexed signal light.

  In recent years, in a transmission network using optical signals, signals of a plurality of wavelengths are multiplexed and transmitted through a transmission line by wavelength division multiplexing (WDM). Here, signal collision occurs when the same wavelength is used in different channels. Therefore, in a device (switching device) that is placed in a transmission network and receives signal light from multiple transmission lines and superimposes the signals, the wavelength of the incident signal light is converted to avoid signal collision. Thus, it is necessary to superimpose the wavelength-converted signal lights.

  The wavelength conversion described above is conventionally realized by using electric signal processing. However, it is expected that the problems of electric signal processing can be solved by using optical signal processing from the viewpoint of the limitation of the processing speed of electric signal processing and the increase in power consumption. In optical signal processing, there is a response speed of femtoseconds or more depending on a device such as an optical fiber. Therefore, even if the transmission speed is further increased, a sufficient response speed is expected.

For example, Patent Document 1 and Patent Document 2 propose wavelength conversion using optical signal processing. In particular, in Patent Document 1, wavelength conversion is realized by four-wave mixing (FWM). Four-wave mixing is a phenomenon in which fourth light (frequency f4 = f1 + f2−f3) is generated when three lights having frequencies f1, f2 and f3 are incident on the nonlinear device. When f1 = f2, this is referred to as degenerate four-wave mixing, and the frequency of the fourth light is f4 = 2f1-f3. If the frequency of the pump light is f1, and the frequency of the signal light whose wavelength is converted is f3, the wavelength-converted light of the frequency f4 can be obtained.
JP 2004-109598 A Japanese Patent Laying-Open No. 2007-240780 (FIG. 5)

In addition, research on polarization multiplexing transmission is being carried out in order to realize high frequency utilization efficiency and ultra-high speed and large capacity transmission. In polarization multiplexing transmission, information is placed on two polarizations whose directions are 90 degrees different (for example, horizontal and vertical) in the vertical direction of the traveling direction. As a result, compared to conventional transmission using a single polarization,
Two times the amount of information can be transmitted. That is, when the same amount of information is sent, transmission can be performed at a transmission rate (symbol rate) that is half that of transmission using a conventional single-directional polarization.

  In polarization multiplexing transmission, it is possible to transmit more data by multiplexing signals of a plurality of wavelengths for each polarization. However, even in this case, wavelength conversion of signal light is necessary to prevent signal collision.

  For example, it is impossible to directly apply the wavelength conversion device for polarization in a single direction disclosed in Patent Literature 1 and Patent Literature 2 to a polarization multiplexed signal. In practice, it is necessary to prepare two wavelength converters, separate the polarization multiplexed signal once, pass the respective polarized waves through the wavelength converter, and multiplex them. However, in this case, since it is necessary to provide two wavelength converters, there is a problem that the circuit scale becomes large.

  An object of this invention is to provide the wavelength converter which can convert the wavelength of signal light appropriately, without enlarging a circuit scale.

An object of the present invention is to accept signal light of a polarization orthogonal multiplexed signal in which two optical signals of orthogonal polarization states propagated through a transmission line and are multiplexed by polarization multiplexing transmission, and determine the wavelength of the signal light. A wavelength conversion device that converts and outputs wavelength-converted signal light,
Pump light generating means for generating pump light having a wavelength fp different from the frequency fs of the signal light (where fc = 2fp−fs fc: frequency of the wavelength-converted signal light);
First polarization control means for controlling the polarization state of the signal light;
Multiplexing means for multiplexing the signal light output from the first polarization control means and the pump light;
The combined light from the multiplexing means is received at the input port, and the first polarized wave component and the second polarized wave component orthogonal to the first polarized wave component are output from the combined light into two outputs. A polarization beam splitter that outputs to the port, a wavelength conversion loop that is a transmission path in which the two output ports are connected in a loop, and the first polarization component and the second Wavelength conversion loop means having wavelength conversion means for generating light of frequency fc by four-wave mixing in each of the polarization components of
Propagating through the wavelength conversion loop of the wavelength conversion loop means, and receiving the combined light including the signal light of the frequency fc that is recombined and output from the input port of the polarization beam splitter in the polarization beam splitter. Bandpass filter means for passing light of frequency fc in the combined light;
Each of the ports has at least three ports, and each port is connected to the multiplexing unit, the wavelength conversion loop unit, and the band-pass filter unit, and the combined light from the multiplexing unit is output to the wavelength conversion loop unit And an optical path determination unit that outputs combined light including the signal light having the frequency fc from the wavelength conversion loop unit to the band-pass filter unit.

  In a preferred embodiment, second polarization control means for controlling the polarization state of the pump light is provided.

In a more preferred embodiment, the first polarization control means has a polarization state of the signal light, and the first polarization component of the polarization orthogonal multiplexed signal is the first polarization signal in the polarization beam splitter. Control to be linearly polarized with respect to the axis,
The second polarization control unit is configured to change a polarization state of the pump light with respect to the first axis in the polarization beam splitter when the combined light including the pump light is input to the polarization beam splitter. In order to obtain a linearly polarized light of 45 degrees.

In another preferred embodiment, the first polarization control means has the polarization state of the signal light, and the first polarization component of the polarization orthogonal multiplexed signal is the first polarization component in the polarization beam splitter. The polarization state of the pump light is controlled when the combined light including the pump light is input to the polarization beam splitter. A pump light polarization adjusting means for rotating the pump light by a predetermined angle so as to be linearly polarized light of 45 degrees with respect to the axis;
A transmission path from the pump light generation means to the polarization splitter is configured to maintain its polarization state. In a preferred embodiment, the wavelength conversion loop means includes polarization adjustment means that is disposed on the wavelength conversion loop and adjusts the polarization states of the first polarization component and the second polarization component. .

In a more preferred embodiment, the polarization beam splitter maintains the polarization state of the input combined light, and the first polarization component and the second polarization component are transmitted from the two output ports. Configured to output,
The jumper cable constituting the wavelength conversion loop, and the wavelength conversion means are configured to maintain the polarization state; and
The polarization adjusting unit is configured to rotate the polarization states of the received first polarization component and second polarization component by 90 °.

In another preferred embodiment, the first polarization component is output from the first output port of the polarization beam splitter and propagates on the wavelength conversion loop, so that the second port of the polarization beam splitter. Is again input to the polarization beam splitter, the second polarization component is output from the second output port, propagates on the wavelength conversion loop, and is again input to the polarization beam at the first port of the polarization beam splitter. Input to the splitter,
The polarization adjusting means is
When the first polarization component is input to the polarization beam splitter again at the second port, the second polarization component when the polarization state is output from the second port And the same polarization state, and
When the second polarization component is input to the polarization beam splitter again at the first port, the first polarization component when the polarization state is output from the first port The polarization states of the first polarization component and the second polarization component are controlled so as to be the same as the polarization state.

Further, in a preferred embodiment, the polarization beam splitter is configured to rotate and output only the polarization state of any one of the polarization components, and
The jumper cable that constitutes the wavelength conversion loop and the wavelength conversion means are configured to maintain polarization.

In a preferred embodiment, signal light polarization control means for generating a first control signal for the first polarization control means,
First demultiplexing means disposed between the first polarization control means and the multiplexing means;
A first polarization state observation unit that receives the signal light demultiplexed by the first demultiplexing unit and calculates an index value based on a polarization state of the signal light; and the first polarization state observation Signal light control signal generating means for generating a first control signal for controlling the first polarization control means based on the index value calculated by the means so as to optimize the index value. With signal light polarization control means,
From the output port of the first polarization control means to the input port of the polarization beam splitter of the wavelength conversion loop means through the first demultiplexing means, the multiplexing means, and the optical path determination means Are configured to maintain their polarizations.

In a preferred embodiment, the signal light polarization control means generates a first control signal for the first polarization control means,
In the wavelength conversion loop means, a first demultiplexing means arranged on a wavelength conversion loop from one output port of the polarization beam splitter;
A first polarization state observation unit that receives the signal light demultiplexed by the first demultiplexing unit and calculates an index value based on a polarization state of the signal light; and the first polarization state observation Signal light control signal generating means for generating a first control signal for controlling the first polarization control means based on the index value calculated by the means so as to optimize the index value. Signal light polarization control means is provided.

In another preferred embodiment, pump light polarization control means for generating a second control signal for the second polarization control means,
Second demultiplexing means disposed on the optical transmission line from the output port of the bandpass filter means;
A polarization acquisition unit that receives the wavelength-converted signal light demultiplexed by the second demultiplexing unit and acquires each polarization component of the wavelength-converted signal light; and the polarization acquisition unit The second polarization state observation means for calculating the index value based on the light intensity of each of the polarization components acquired by the step, and the index value calculated by the second polarization state observation means is optimized. A pump light polarization control means having a pump light control signal generation means for generating a second control signal for controlling the second polarization control means,
An optical path from the input port of the polarization beam splitter of the wavelength conversion loop means to the polarization acquisition means via the optical path determination means, the band pass filter means, and the second demultiplexing means Is configured to retain its polarization.

Further, in a preferred embodiment, the pump light polarization control means for generating a second control signal for the second polarization control means,
A second demultiplexing unit and a third demultiplexing unit respectively disposed on the wavelength conversion loop from the two output ports of the polarization beam splitter in the wavelength conversion loop unit;
Second polarization state observing means for calculating an index value based on the light intensity of each polarization component demultiplexed by the second demultiplexing means and the third demultiplexing means; and the second polarization A pump light control signal generating means for generating a second control signal for controlling the second polarization control means so that the index value calculated by the wave state observing means is optimized. Wave control means is provided.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the wavelength converter which can convert the wavelength of signal light appropriately, without enlarging a circuit scale.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of the wavelength converter according to the first embodiment of the present invention. The wavelength conversion device 10 is disposed in the transmission line of the polarization multiplexing transmission system, particularly adjacent to the input / output end of PXC (Photonic Cross-Connect), and converts the wavelength of the incident signal light and outputs it. In the wavelength converter, for convenience of explanation, the wavelength which is the reciprocal is often used instead of handling the wavelength. Therefore, also in the present embodiment, the frequency of the signal light is represented as fs, and the frequency of the signal light subjected to frequency conversion (wavelength conversion) is represented as fc.

  As shown in FIG. 1, a wavelength converter 10 according to this embodiment includes a polarization controller 11 that controls the polarization state of signal light input from a transmission line, and pump light that generates pump light of a predetermined wavelength. Receiving the combined light from the generation circuit 12, the polarization controller 13 for controlling the polarization state of the pump light output from the pump light generation circuit 12, the optical coupler 14 for combining the signal light and the pump light, and the optical coupler 14. The combined light is output to a wavelength conversion loop circuit 20 described later, and an optical signal from the wavelength conversion loop circuit is received, and the received optical signal is sent to a band pass filter (BPF) 19 disposed on the output side. And an optical circulator 15 for outputting. Further, the wavelength conversion device 10 according to the present embodiment has a wavelength conversion loop circuit 20 that receives the combined light from the optical circulator 15 and converts the frequency of the signal light included in the combined light.

  The wavelength conversion loop circuit 20 includes a polarization beam splitter (PBS) 16, a polarization adjustment circuit 17, and a wavelength conversion circuit 18.

  Schematically, the wavelength conversion device 10 according to the present embodiment operates as follows. In the present embodiment, a polarization orthogonal multiplexed signal obtained by multiplexing two optical signals having orthogonal polarization states in the transmission line is propagated as signal light and accepted by the wavelength conversion device 10.

  The polarization state (SOP: State of Polarization) of the signal light is a straight line on the same axis as the X axis of the PBS 16 in which either the X polarization or Y polarization, which is a component of the polarization orthogonal multiplexed signal, is the same. The polarization controller 11 adjusts the polarization so as to be polarized.

  The polarization controller 11 includes, for example, one or more λ / 2 plates and one or more λ / 4 plates. The λ / 2 plate and the λ / 4 plate can be rotated around the optical axis by the control signal, respectively, and the polarization directions of the X-polarization component and the Y-polarization component of the polarization orthogonal multiplexed signal can be adjusted simultaneously. . The same applies to the polarization controller 13. The control of the polarization state using the polarization controllers 11 and 13 will be described in detail later.

  The pump light generation circuit 12 generates pump light that is continuous light (CW light) having a frequency fp different from the frequency fs of the signal light. The polarization controller 13 adjusts the polarization state (SOP) of the pump light so that the light intensity from each of the output ports of the PBS 16 becomes equal. Ideally, the pump light is 45-degree linearly polarized light with respect to the X axis of the PBS 16. The signal light output from the polarization controller 11 and the pump light output from the polarization controller 13 are combined by the optical coupler 14.

  The optical circulator 15 outputs light received from each port from one adjacent port. The optical circulator 15 shown in FIG. 1 outputs input light from a port adjacent in the clockwise direction in FIG. For example, the combined light output from the optical coupler 14 passes through the optical circulator 15 and enters the PBS 16. Further, the light output from the PBS 16 is incident on the BPF 19 through the optical circulator 15.

In the combined light incident on the PBS 16 of the wavelength conversion loop circuit 20, the signal light S (fs) is demultiplexed into an X polarization component S ₁ (fs) and a Y polarization component S ₂ (fs). Further, since the pump light S (fp) is ideally linearly polarized at 45 degrees with respect to the X axis of the PBS 16, signals having the same light intensity are output from the two output ports of the PBS 16. . At the output port of the PBS 16, the polarization states of the X-polarized light and the Y-polarized signal light and the pump light are linearly polarized light in the same direction. 2A is a diagram illustrating an example of the frequency fs of the signal light and the frequency fp of the pump light, and FIG. 2B is a diagram illustrating the polarization state of the signal light and the pump light at the input port 101 of the PBS 16. FIGS. 2C and 2D are diagrams showing the polarization states of the signal light and the pump light at the output ports 102 and 103 of the PBS 16, respectively.

As shown in FIG. 2B, at the input port 101 of the PBS 16, the X polarization component S ₁ (fs) and the Y polarization component S ₂ (fs) of the signal light and the axis of the PBS 16 are 45. The pump light S (fp) that is linearly polarized light appears. At the output port 103 after passing through the PBS 16, the Y polarization component S ₂ (fs) of the signal light and the Y polarization component S ₂ (fp) of the pump light appear. On the other hand, at the output port 102, the X polarization component S ₁ (fs) of the signal light and the X polarization component S ₁ (fp) of the pump light appear. The signal passing through the PBS 16 will be described in more detail with reference to FIG.

  In the wavelength conversion loop circuit 20, the light (see FIG. 2C) output from the PBS 16 to the port 102 is propagated clockwise through the transmission path (wavelength conversion loop) on the loop and output from the PBS 16 to the port 103. The light (see FIG. 2D) is propagated through the wavelength conversion loop counterclockwise. The light that has propagated through the clockwise wavelength conversion loop and the counterclockwise wavelength conversion loop is subjected to wavelength conversion by the wavelength conversion circuit 18. In the present embodiment, wavelength conversion using four-wave mixing is performed.

  Four-wave mixing will be described below. Four-wave mixing is a phenomenon in which fourth light (frequency f4 = f1 + f2−f3) is generated when three lights having frequencies f1, f2 and f3 are incident on the nonlinear device. When f1 = f2, this is referred to as degenerate four-wave mixing, and the frequency of the fourth light is f4 = 2f1-f3. In order to cause four-wave mixing, a certain phase matching condition must be satisfied.

  In the present embodiment, wavelength conversion using degenerate four-wave mixing is realized. As shown in FIG. 2A, in the present embodiment, the wavelength-converted signal light (with the frequency f1 as the pump light (frequency fp) and the light with the frequency f3 as the signal light (frequency fs)) ( Frequency fc = 2fp−fs). In the present embodiment, a high nonlinear fiber (HNLF: High Non-Linear Fiber) is used as the wavelength conversion circuit 18 in order to realize the wavelength conversion using the four-wave mixing.

  The wavelength-converted X-polarized light and Y-polarized light are combined again in the PBS 16. In the present embodiment, the polarization adjustment circuit 17 is disposed on the wavelength conversion loop of the wavelength conversion loop circuit 20, and the light transmitted through the clockwise wavelength conversion loop and the counterclockwise wavelength conversion loop is transmitted. The polarization state is adjusted. The function of the polarization adjustment circuit 17 will also be described later.

  The light combined in the PBS 16 enters the BPF 19 through the optical circulator 15. The BPF 19 is configured to pass light having the frequency fc of the signal light subjected to wavelength conversion. Therefore, only the signal light wavelength-converted by the BPF 19 passes, and finally the wavelength-converted signal light is output. The wavelength-converted signal light output from the BPF 19 is sent to the transmission path.

  Hereinafter, the wavelength conversion loop circuit 20 according to the present embodiment will be described. At each port of the PBS 16, the direction of polarization of the input / output signal is defined. For this reason, the input signal needs to be incident in the prescribed polarization direction, and the output signal is output in the prescribed polarization direction.

For example, the following two modes are conceivable as the polarization state of the output port of the 1-port input 2-port PBS.
(1) 0 ° (horizontal) and 90 ° (vertical) of the input signal of the polarization orthogonal multiplexed signal are output as polarization states of 0 ° and 90 ° at the two output ports.
(2) 0 ° and 90 ° of the input / output signal of the polarization orthogonal multiplexed signal are output as a polarization state in which both of the two output ports are 0 ° or 90 °. That is, one component is rotated by 90 ° and output.

  In the present embodiment, the PBS 16 of the aspect (1) is used. In FIG. 3, at the input port, the signal light includes 0 ° polarization (X polarization) indicated by a solid line and 90 ° polarization (Y polarization) indicated by a broken line (see reference numeral 300), and passes through PBS 16. 90 ° polarization (Y polarization) propagating through the wavelength conversion loop counterclockwise (see reference numerals 301 and 302) and 0 ° polarization (X polarization) propagating through the wavelength conversion loop clockwise (Refer to reference numerals 303 and 304).

  When the polarization state of propagating light (X-polarized light and Y-polarized light) is maintained in the jumper cable constituting the wavelength conversion loop of the wavelength conversion loop circuit 20 and in the wavelength conversion circuit 18 think of. For example, this is a case where the jumper cable and the highly nonlinear fiber (HNLF) constituting the wavelength conversion circuit 18 are configured by polarization maintaining fibers (PMF).

  The polarization adjustment circuit 17 causes the polarization adjustment circuit 17 to rotate the polarization state of the light propagating through the wavelength conversion loop clockwise and the light propagating through the wavelength conversion loop counterclockwise by 90 °. Thus, each can be input again to the PBS 16 and combined. That is, in this case, the polarization adjustment circuit 17 may rotate the polarization state of each light by 90 °. A λ / 2 plate can be used as the polarization adjustment circuit 17. Alternatively, a polarization controller provided with at least one λ / 2 plate and λ / 4 plate may be applied as the polarization adjustment circuit 17.

  Alternatively, by using an adapter as the polarization adjustment circuit 17 instead of the wave plate, and adjusting the key of the adapter so that the fiber axis rotates 90 ° at the connection point of the adapter, the offset of 0 ° and 90 ° is obtained. It is also possible to switch the wave state.

  The polarization adjustment circuit 17 rotates the light in the polarization state of 0 ° (see reference numeral 303) clockwise through the wavelength conversion loop by 90 ° (see reference numeral 305), and rotates the wavelength conversion loop counterclockwise. The propagating light in the 90 ° polarization state (see reference numeral 301) is also rotated by 90 ° (see reference numeral 306).

  In addition, when the jumper cable and the wavelength conversion circuit 18 constituting the wavelength conversion loop are not configured by PMF, as shown in FIG. 4, the polarization state of 0 ° propagating clockwise through the wavelength conversion loop is shown. Both the light (see reference numeral 303) and the 90-degree polarization state light (see reference numeral 301) propagating counter-clockwise are in an arbitrary polarization state (see reference numerals 402 and 401). Therefore, in this case, a polarization controller provided with at least one λ / 2 plate and one λ / 4 plate is applied as the polarization adjustment circuit 17 so that the λ / 2 plate and the λ / 4 plate are predetermined. The polarization state is appropriately controlled by rotating the angle. That is, the polarization adjustment circuit 17 adjusts the polarization so that the polarization direction at the port of the PBS 16 is appropriate in consideration of the change in polarization in the jumper cable or the like.

  Next, the generation of the control signal for the polarization controller 11 and the polarization controller 11 for controlling the polarization state of the signal light according to the present embodiment will be described. Regarding the signal light, in order to appropriately perform polarization separation of the polarization orthogonal multiplexed signal in the PBS 16 of the wavelength conversion loop circuit 20, the X polarization component of the polarization orthogonal multiplexed signal is linear with respect to the X axis of the PBS 16. It is necessary to control the polarization state so as to be polarized. Similarly, it is necessary to make the Y polarization component linearly polarized with respect to the Y axis of the PBS 16. In particular, for signal light that has propagated through the transmission line, the state of the transmission line always changes, and the polarization state of the incident polarization orthogonal multiplexed signal changes, so the polarization state must always be controlled. .

  FIG. 5 is a block diagram including a signal light polarization control unit that generates a control signal to the polarization controller 11 of the signal light according to the present embodiment. As shown in FIG. 5, the signal light polarization control unit 30 according to the present embodiment is output from the optical coupler 31 disposed on the transmission path between the polarization controller 11 and the optical coupler 14 and the optical coupler. And a polarization state observation unit 33 and a control signal generation unit 34.

  In the present embodiment, in order to control the polarization of the signal light incident on the PBS 16, an optical coupler 31 is provided in front (upstream side) of the optical coupler 14 for multiplexing with the pump light. The light is monitored. Therefore, the polarization state of the signal light needs to be constant from the output port of the polarization controller 11 to the input port of the PBS 16 of the wavelength conversion loop circuit 20 in the downstream direction (see reference numeral 500). Therefore, in the present embodiment, the transmission path 500 from the output port of the polarization controller 11 to the input port of the PBS 16 of the wavelength conversion loop circuit 20 is configured with a polarization maintaining fiber (PMF).

  The operation of the signal light polarization controller 30 shown in FIG. 5 will be described below. The signal light is branched by the optical coupler 31 and input to the polarizer 32. PBS may be used instead of the polarizer 32. The axis of the polarizer 32 (the axis of PBS when PBS is used) is the same as the axis of PBS 16 of the wavelength conversion loop circuit 20. Therefore, if the polarization state is appropriately controlled in the polarizer 32, an appropriate polarization state can be obtained also in the input port of the PBS 16 of the wavelength conversion loop circuit 20.

  The output of the polarizer 32 is sent to the polarization state observation unit 33, and a control signal for the polarization controller 11 is generated and output by the polarization state observation unit 33 and the control signal generation unit 34. For example, the polarization state observation unit 33 and the control signal generation unit 34 operate as follows.

  If the X polarization component and the Y polarization component of the orthogonal polarization signal to be separated by the PBS 16 are not properly separated by the PBS 16, the X polarization component and the Y polarization component are simultaneously output to one port. The A beat signal is observed when light including the X polarization component and the Y polarization component as described above is received by the optical receiver. When the beat signal is generated, the electric signal power is increased as compared with the case where the beat signal is not generated. Therefore, the polarization control state observation unit 33 includes an optical receiver and a power observation unit, and outputs a signal indicating the power state to the control signal generation unit 34. The control signal generation unit 34 receives a signal indicating the power state and outputs a control signal to the polarization controller 11 so that the power decreases (interference detection method). The polarization controller 11 rotates the angles of the λ / 2 plate and the λ / 4 plate according to the control signal.

  Alternatively, the polarization state observation unit 33 and the control signal generation unit 34 may have the following configuration. For example, in the transmitter, low-frequency intensity modulation is performed on one of the X-polarized wave and the Y-polarized wave of the polarization orthogonal signal that is a transmission signal, or low-frequency signals having different frequencies are applied to both the X-polarized wave and the Y-polarized wave. The intensity modulation is performed, and the polarization state observation unit 33 monitors the low frequency modulation component.

  More specifically, the polarization state observation unit 33 uses an optical receiver to convert an X-polarized wave or a Y-polarized wave as an electric signal and a center frequency as a low-frequency modulation frequency. And only the low frequency modulation component is extracted. Next, the electric power is observed using an electric power meter or the like. The control signal generation unit 34 outputs a control signal to the polarization controller 11 so that the power is optimal (maximum or minimum).

  Next, generation of a control signal for the polarization controller 13 and the polarization controller 13 for controlling the polarization state of the pump light according to the present embodiment will be described.

  The polarization state of the pump light combined with the signal light in the optical coupler 14 and incident on the PBS 16 needs to be dynamically controlled according to the fluctuation state of the polarization. For the pump light, the polarization controller 13 adjusts the polarization state so that two signals having the same light intensity are output from the two output ports of the PBS 16. The pump light is ideally linearly polarized light that is 45 degrees with respect to the axis of the PBS 16 when incident on the PBS 16.

  As for the pump light, in the situation where the physical distance between the pump light generation circuit 12 and the PBS 16 is short, the jumper cable between them is fixed, and the polarization state of the pump light input to the PBS 16 hardly changes. Therefore, it is sufficient to adjust the polarization state once, and dynamic control is not necessary. However, in an environment where the jumper cable length is long and the polarization state of the pump light input to the PBS 16 changes, dynamic control is required. In this embodiment, the polarization state is dynamically controlled.

  FIG. 6 is a block diagram including a pump light polarization controller that generates a control signal to the polarization controller 13 of the signal light according to the present embodiment. As shown in FIG. 6, the pump light polarization control unit 40 according to the present embodiment outputs an optical coupler 41 that demultiplexes the output of the BPF 19 that outputs the wavelength-converted signal light, and is output from the optical coupler 41. A PBS 42 that separates light, a polarization state observation unit 43, and a control signal generation unit 44 are provided. In FIG. 5 described above, only the signal light polarization controller 30 that generates the control signal to the polarization controller 11 is described. In FIG. 6, the pump that generates the control signal to the polarization controller 13 is described. Only the optical polarization controller 40 is described. Actually, the wavelength conversion device 10 includes both the signal light polarization controller 30 and the pump light polarization controller 40. 5 and 6 illustrate one of them for convenience of explanation.

  The pump light polarization controller 40 observes the light intensity of each of the X polarization component and the Y polarization component of the polarization-converted polarization multiplexed signal. In the present embodiment, both the X polarization component and the Y polarization component are wavelength-converted by wavelength conversion. When pump light is not output with the same light intensity to the two output ports of the PBS 16, this wavelength conversion is not performed equally for the X polarization and the Y polarization. Therefore, in the optical coupler 41 which is a monitor location, the light intensity of the X polarization component and the Y polarization component is different.

  Therefore, the pump light polarization control unit 40 generates a control signal so that the light intensities of the X polarization component and the Y polarization component of the polarization orthogonal multiplexed signal subjected to wavelength conversion become the same, and the polarization controller 13 is output. That is, in this embodiment, the polarization state observation unit 43 calculates a difference value between the light intensity of the X polarization component and the light intensity of the Y polarization component output from the PBS 42. Based on the difference value from the polarization state observation unit 43, the control signal generation unit 44 generates and outputs a control signal for the polarization controller 13 so that the difference value is set to “0” which is a target value.

  When the wavelength-converted signal light (output light of BPF 19) is monitored as in the present embodiment, between the PBS 16 of the wavelength conversion loop circuit 20 and the optical circulator 15, and from the optical circulator to the BPF 19, light The transmission path (see reference numeral 600) through the coupler 41 to the PBS 42 must be configured with a polarization maintaining fiber (PMF). This is because the polarization multiplexed signal of the frequency-converted signal light is again polarization-separated at the monitor location to observe the light intensity of the X polarization component and the Y polarization component. This is because the axis of the PBS 16 of the wavelength conversion loop circuit 20 needs to be the same.

  Next, modifications of the components in the optical repeater according to the present embodiment will be described. First, another configuration example for realizing the function of the optical circulator will be described. The optical circulator 15 used in the first embodiment outputs light received from each port from one predetermined adjacent port. The function of the optical circulator 15 can also be realized by using an optical isolator and an optical coupler.

  FIG. 7 is a block diagram showing the configuration of the wavelength converter according to the second embodiment of the present invention. In FIG. 7, the same components as those of the wavelength conversion device according to the first embodiment and the second embodiment are denoted by the same reference numerals.

  As shown in FIG. 7, the wavelength conversion device 70 according to the second embodiment receives light output from the optical coupler 14, outputs it in a predetermined direction, and returns from the wavelength conversion loop circuit 20. An optical path determination unit 71 that outputs light in another predetermined direction is provided. The optical path determination unit 71 includes an optical isolator 72 and an optical coupler 73. The optical isolator 73 is disposed between the optical coupler 14 and the optical coupler 73, and is configured to output only light in one direction, that is, light output from the optical coupler 14 to the optical isolator 73. On the other hand, the light from the optical coupler 73 is blocked and is not output to the optical coupler 14 side.

  For example, when the optical intensity of an optical signal incident on two input ports is a and b, the 2-input 2-output optical 3 dB coupler has (a + b) / 2 and (a + b) / 2 on the two output ports, respectively. And has the property of outputting light intensity. By using this, the optical isolator 73 according to the present embodiment uses the optical coupler 73 as described above as one input and two outputs, and enters the light from the optical isolator 72 into one input port. Output to the wavelength conversion loop circuit 20. On the other hand, when the light output from the wavelength conversion loop circuit 20 is applied to the optical coupler 73, 1/2 of the light is output to the BPF 19, and the remaining 1/2 is output to the optical isolator 72 side. In the optical isolator 72, the light from the optical coupler 73 is blocked. On the other hand, as for the light output to the BPF 19, only the signal of the frequency fc is extracted and output from the BPF.

  Next, another example of the PBS in the wavelength conversion loop circuit will be described. As shown in FIG. 3, in the first embodiment and the second embodiment, in the PBS 16, the polarization signals of 0 ° (horizontal) and 90 ° (vertical) of the input signal of the polarization orthogonal multiplexed signal are polarized. The state is output as 0 ° and 90 ° polarization states at the two output ports. On the other hand, as described above, in PBS, the polarization state of 0 ° or 90 ° of the input / output signal of the polarization orthogonal multiplexed signal is the polarization state in which both of the two output ports are 0 ° or 90 °. Some are output.

  As described above, the case where the PBS in which one component is output by being rotated by 90 ° will be described. As shown in FIG. 8, in the wavelength conversion loop 120, at the input port of the PBS 116, the signal light has a 0 ° polarization (X polarization) indicated by a solid line and a 90 ° polarization (Y polarization) indicated by a broken line. (See reference numeral 300). The PBS 116 outputs light that propagates through the wavelength conversion loop counterclockwise, which corresponds to the Y polarization component at the input port (see reference numeral 801). As indicated by reference numeral 801, the polarization state of this light is rotated 90 ° by the PBS 116. Further, the PBS 116 outputs light that propagates through the wavelength conversion loop in a clockwise direction corresponding to the X polarization component at the input port (see reference numeral 802). This light is output as it is without being rotated.

  When the polarization state of propagating light (X-polarized light and Y-polarized light) is maintained in the jumper cable constituting the wavelength conversion loop of the wavelength conversion loop circuit 120 and in the wavelength conversion circuit 18 think of. For example, this is a case where the jumper cable and the highly nonlinear fiber (HNLF) constituting the wavelength conversion circuit 18 are configured by polarization maintaining fibers (PMF). In this case, the polarization input at 0 ° (90 °) propagates with 0 ° (90 °). Since the polarization directions of the two output ports of the PBS 116 are the same, the signal output from one side of the PBS 116 can be directly input to the other port as it is. That is, polarization adjustment in the wavelength conversion loop is unnecessary.

  On the other hand, when the jumper cable and the wavelength conversion circuit 18 that constitute the wavelength conversion loop are not configured by PMF, the light that propagates the wavelength conversion loop counterclockwise and the light that propagates the wavelength conversion loop clockwise Are in an arbitrary polarization state. Therefore, in this case, as described with reference to FIG. 4, the polarization adjustment circuit 121 is disposed in the wavelength conversion loop. The polarization adjustment circuit 121 includes, for example, one or more λ / 2 plates and λ / 4 plates, and appropriately sets the polarization state by setting the λ / 2 plates and λ / 4 plates to a predetermined angle. Control.

  Next, another configuration example of the signal light polarization control unit will be described. FIG. 9 is a block diagram including another configuration example of the signal light polarization controller that generates a control signal to the polarization controller 11 of the signal light according to the present embodiment. As shown in FIG. 9, the signal light polarization control unit 80 includes an optical coupler 81 disposed between the PBS 16 and the polarization control circuit 17 in the wavelength conversion loop of the wavelength conversion loop circuit 20, and an optical coupler 81. A band-pass filter (BPF) 82 that extracts light of frequency fs from the demultiplexed light, a polarization state observation unit 83, and a control signal generation unit 84 are provided.

  In the signal light polarization controller 80 shown in FIG. 9, light from the output port of the PBS 16 (see arrow 901) is incident on the BPF 82 via the optical coupler 81. In the BPF 82, the signal light having the frequency fs is extracted, and the extracted signal light having the frequency fs is supplied to the polarization state control unit 83.

  The polarization state control unit 83 and the control signal generation unit 84 operate in the same manner as the polarization state control unit 33 and the control signal generation unit 34 illustrated in FIG. That is, the polarization control state observation unit 83 includes an optical receiver and a power observation unit, and outputs a signal indicating the power state to the control signal generation unit 84. The control signal generator 84 receives a signal indicating the power state and outputs a control signal to the polarization controller 11 so that the power decreases. The polarization controller 11 rotates the angles of the λ / 2 plate and the λ / 4 plate according to the control signal.

  In the wavelength conversion device provided with the signal light polarization control unit 80 shown in FIG. 9, the monitor position of the signal light is between the PBS 16 and the polarization control circuit 17 in the wavelength conversion loop. Therefore, it is not necessary to configure a jumper cable or the like extending between the polarization controller 11 and the optical coupler 81 of the wavelength conversion loop circuit 20 with a polarization maintaining fiber (PMF).

  Next, another configuration example of the pump light polarization control unit will be described. FIG. 10 is a block diagram including another configuration example of the pump light polarization controller that generates a control signal to the polarization controller 13 of the signal light according to the present embodiment. As shown in FIG. 10, the pump light polarization control unit 90 includes an optical coupler 91 disposed between the PBS 16 and the polarization control circuit 17 in the wavelength conversion loop of the wavelength conversion loop circuit 20, and an optical coupler 91. A band-pass filter (BPF) 92 for extracting light of frequency fp from the demultiplexed light, an optical coupler 93 disposed between the PBS 16 and the wavelength conversion circuit 18 in the wavelength conversion loop, and an optical coupler 93 are used. A band-pass filter (BPF) 94 that extracts light having a frequency fp from the waved light, a polarization state observation unit 95, and a control signal generation unit 96 are provided.

  In the pump light polarization controller 90 configured as described above, the light intensity of light output from the two output ports of the PBS 16 is observed, and the polarization controller 13 is controlled so that the light intensity of both is equal. The polarization state observation unit 95 measures the light intensity of the optical signals from the BPF 92 and the BPF 94 and calculates the difference value. Based on the difference value from the polarization state observation unit 95, the control signal generation unit 96 generates and outputs a control signal for the polarization controller 13 so that the difference value is set to the target value “0”.

  In the wavelength conversion device provided with the pump light polarization control unit 90 shown in FIG. 10, the monitor location of the pump light is in the wavelength conversion loop. Therefore, it is not necessary to configure a jumper cable or the like between the polarization controller 13 and the optical couplers 91 and 93 of the wavelength conversion loop circuit 20 with a polarization maintaining fiber.

  FIG. 11 is a block diagram showing an example in which the wavelength converter according to the present embodiment is applied in a polarization multiplexing transmission system. The switching apparatus 11 shown in FIG. 11 is generally arranged in a ring network. When optical add / drop is performed in a transmission network, a collision occurs when the wavelength of a signal to be added and the wavelength of a transmitted signal are the same. In order to avoid this, the wavelength conversion device converts the frequency of the input signal to an unused wavelength on the line side to be added. Thereby, it becomes possible to prevent the collision at the time of adding a signal. In the example of FIG. 11, a wavelength division multiplexing (WDM) signal is propagated in the transmission network (ring network).

  In FIG. 11, the switching apparatus 1100 includes a photonic cross connect (PXC) 1101 and optical multiplexers (MUX) 1103 to 1104. In addition, the wavelength conversion device 10 according to the present embodiment is arranged on a transmission path for each wavelength between the optical MUX 1104 and the PXC 1101. In the transmission path of the ring network (see reference numerals 1111 and 1112), the signal incident on the switching apparatus 1100 is separated for each wavelength by the optical MUX 1102 and is incident on the PXC 1101. In the PXC 1101, a predetermined signal among the incident signals is changed in the path, is incident on the optical MUX 1105, is wavelength-multiplexed, and is transmitted to the transmission path 1113.

  The light incident on the light MUX 1104 via the transmission line 1114 is added to the light incident via the transmission line 1111 in the PXC 1101. Here, in order to avoid collision of signals with the same wavelength, the wavelength conversion apparatus 10 performs wavelength conversion on the signal.

  In a full-mesh type optical network as well as a ring network that performs only optical add / drop, an exchange apparatus needs to have a wavelength conversion function in order to avoid wavelength collision. FIG. 12 is a block diagram showing another example in which the wavelength conversion device according to the present embodiment is applied in a polarization multiplexing transmission system. 12 includes a PXC 1201 and a plurality of optical MUXs (for example, reference numeral 1202). Each of the plurality of optical MUXs is connected to a transmission path that forms a full mesh transmission network.

  The wavelength conversion device 10 according to the present embodiment is disposed on a transmission path for each wavelength between the optical MUX (for example, the optical MUX 1202) and the PXC 1201. For example, light that has entered the light MUX 1202 through the transmission line is subjected to wavelength conversion in the wavelength conversion device 10 and is incident on the PXC 1201 in order to avoid collision of signals of the same wavelength.

  As shown in FIGS. 11 and 12, when the wavelength converter according to the present embodiment is provided in an exchange device arranged in a transmission network, the wavelength (frequency) of the signal light subjected to wavelength conversion in the wavelength converter. , The frequency fp of the pump light generated by the pump light generation circuit 12 is determined, and the center frequency of the BPF 19 needs to coincide with the frequency fc of the signal light subjected to wavelength conversion.

  The frequency fp of the pump light and the frequency fc of the wavelength-converted signal may be determined independently in the exchange devices 1100 and 1200. In this case, the switching apparatuses 1100 and 1200 detect the wavelength of the currently received signal light, assign a wavelength (frequency) that does not match the wavelength to the new signal light, and generate a new signal light. Is converted to the assigned wavelength. Alternatively, the switching apparatus 1100 receives information on the wavelength of the signal light from another switching apparatus arranged on the transmission network via the transmission network or other network, and switches the switching apparatus according to the received wavelength information. The wavelength (frequency) that can be used by the 1100 itself may be determined to convert the wavelength of the signal light.

  In addition, a control system that manages the wavelength (frequency) of signal light transmitted through the transmission network is provided separately from the switching device, and the control system provides signals to each of the switching devices arranged in the transmission network. You may comprise so that the frequency allocated to light may be notified.

  When the switching apparatus obtains the frequency of the signal light to be wavelength-converted and the frequency of the signal light subjected to wavelength conversion, the frequency of the pump light for wavelength conversion is set to fc = 2fp-fs (fc: signal subjected to wavelength conversion). Calculation is based on the frequency of light, fs: frequency of signal light to be wavelength-converted, fp = frequency of pump light. In a predetermined wavelength conversion device provided in the exchange device, the pump light generation circuit 12 is controlled so as to generate pump light having a frequency fp. Further, the center frequency of the BPF 19 is controlled so that the BPF 19 outputs signal light having the frequency fc.

  The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

  In the above-described embodiment of the present invention, the polarization controller 13 controls the polarization of the pump light so that the pump light output from the pump light generation circuit 12 is 45 linearly polarized light with respect to the X axis of the PBS 16. The state is controlled. The polarization controller 13 is controlled by, for example, a control signal generated by a pump light polarization control unit 40 having an optical coupler 41, a PBS 42, a polarization state observation unit 43, and a control signal generation unit 44 shown in FIG. Realized. However, it is not limited to the said structure. FIG. 13 is a block diagram showing the configuration of the wavelength converter according to the third embodiment of the present invention.

  As shown in FIG. 13, the wavelength conversion device 100 according to the third embodiment receives the pump light generated by the pump light generation circuit 12 and sends the pump light to a straight line of 45 degrees with respect to the X axis of the PBS 16. A polarization adjustment circuit 113 that adjusts the polarization state of the pump light so as to be polarized light is provided. The light output from the polarization adjustment circuit 113 enters the optical coupler 14 and is output from the polarization controller 11. The signal light is combined. In the present embodiment, pump light is output from the pump light generation circuit 12 with 0 degree linearly polarized light. Therefore, the polarization adjustment circuit 113 rotates the incident light by 45 degrees.

  For example, a polarization controller provided with one or more λ / 2 plates and λ / 4 plates may be applied as the polarization adjustment circuit 113. Alternatively, an adapter may be used. When an adapter is used, the pump light is adjusted so that the linear polarization of 45 degrees with respect to the X axis of the PBS 16 is obtained by adjusting the adapter key so that the fiber axis rotates 45 ° at the connection point of the adapter. The polarization state can be adjusted. Alternatively, the polarization state of the pump light can be adjusted by fusion-bonding the PMF fibers at both ends of the polarization adjustment circuit 113 so as to rotate by 45 °.

  In this embodiment, between the pump light generation circuit 12 and the polarization adjustment circuit 113, between the polarization adjustment circuit 13 and the optical coupler 14, and between the optical coupler 14 and the PBS 16, that is, A transmission line (1300) from the pump light generation circuit 12 to the PBS 16 is constituted by a polarization maintaining fiber (PMF). As a result, the pump light can be incident on the PBS 16 while maintaining a state of linear polarization of 45 degrees with respect to the X axis of the PBS.

  In the third embodiment, pump light that is linearly polarized light of 45 degrees with respect to the X axis of the PBS 16 is output by the polarization adjustment circuit. Further, the transmission path (1300) from the pump light generation circuit 12 to the PBS 16 is configured by a polarization maintaining fiber (PMF), and the polarization state of the pump light is maintained. Therefore, as in the first embodiment and the second embodiment, the polarization controller 13 for controlling the polarization state of the pump light and the configuration for generating a control signal in the polarization controller 13 ( For example, the pump light polarization controller 40) shown in FIG. 6 is not necessary.

  The wavelength conversion device according to the present invention can be applied to both the phase modulation signal and the intensity modulation signal.

  Two types of polarization multiplexed signals are known: an interleave type and a non-interleave type. The wavelength converter according to the present invention is applicable to any type of polarization multiplexed signal. For the non-interleaved type, the positions of the X polarization and Y polarization bits coincide. On the other hand, the interleave type is a method in which the positions of the X-polarized wave and Y-polarized bit do not match and are shifted by half a bit. In this case, the interference detection method cannot be used for polarization state observation and control signal generation. Therefore, in the case of non-interleave, it is possible to control by monitoring the power of the clock component of the electric signal.

  In the above embodiment, the pump light generation circuit 12 generates pump light that is continuous light (CW light) having a frequency fp different from the frequency fs of the signal light. However, the present invention is not limited to this. . For example, the pump light generation circuit may receive the signal light and generate the pump light that is clock light synchronized with the data modulation of the signal light.

  Furthermore, in the above embodiment, an optical amplifier that amplifies the pump light and the signal light may be provided. FIG. 14 is a block diagram showing the configuration of the wavelength converter according to the fourth embodiment of the present invention. In the wavelength converter shown in FIG. 14, the same components as those of the first embodiment shown in FIG. As shown in FIG. 14, the wavelength converter 140 according to the fourth embodiment includes an optical amplifier 141 that amplifies signal light output from the polarization controller 11 and pump light output from the polarization controller 13. An optical amplifier 142 for amplification is provided. In the fourth embodiment, the output light of the optical amplifier 141 and the output light of the optical amplifier 142 are incident on the optical coupler 14.

  In the fourth embodiment, by providing the optical amplifiers 141 and 142 on the output side of the polarization controllers 11 and 13, respectively, it becomes possible to make a higher-power optical signal enter the optical loop. Also, compared to the case where an optical amplifier is provided on the input side of the polarization controller and the output from the optical amplifier is incident on the polarization controller, the fourth embodiment is not affected by the loss of the polarization controller. Accordingly, the gain in the optical amplifiers 141 and 142 can be suppressed by that amount.

  Also in the second and third embodiments, an optical amplifier may be added as in the fourth embodiment. In the second embodiment, an amplifier that amplifies the signal light from the polarization controller 11 of FIG. 9 and enters the optical coupler 14, and amplifies the pump light from the polarization controller 13 and enters the optical coupler 14. And an amplifier to be used. In the third embodiment, the signal light from the polarization controller 11 is amplified and incident on the optical coupler 14, and the pump light from the polarization adjustment circuit 113 is amplified and incident on the optical coupler 14. And an amplifier to be used.

FIG. 1 is a block diagram showing the configuration of the wavelength converter according to the first embodiment of the present invention. 2A is a diagram illustrating an example of the frequency fs of the signal light and the frequency fp of the pump light, and FIG. 2B is a diagram illustrating the polarization state of the signal light and the pump light at the input port 101 of the PBS 16. FIGS. 2C and 2D are diagrams showing the polarization states of the signal light and the pump light at the output ports 102 and 103 of the PBS 16, respectively. FIG. 3 is a diagram illustrating an example of a polarization state of light in the present embodiment. FIG. 4 is a diagram illustrating another example of the polarization state of light in the present embodiment. FIG. 5 is a block diagram including a signal light polarization control unit that generates a control signal to the polarization controller 11 of the signal light according to the present embodiment. FIG. 6 is a block diagram including a pump light polarization controller that generates a control signal to the polarization controller 13 of the signal light according to the present embodiment. FIG. 7 is a block diagram showing the configuration of the wavelength converter according to the second embodiment of the present invention. FIG. 8 is a diagram illustrating still another example of the polarization state of light in the present embodiment. FIG. 9 is a block diagram including another configuration example of the signal light polarization controller that generates a control signal to the polarization controller 11 of the signal light according to the present embodiment. FIG. 10 is a block diagram including another configuration example of the pump light polarization controller that generates a control signal to the polarization controller 13 of the signal light according to the present embodiment. FIG. 11 is a block diagram showing an example in which the wavelength conversion system according to the present embodiment is applied to a polarization multiplexing transmission system. FIG. 12 is a block diagram showing another example in which the wavelength conversion system according to the present embodiment is applied to the polarization multiplexing transmission system. FIG. 13 is a block diagram showing the configuration of the wavelength converter according to the third embodiment of the present invention. FIG. 14 is a block diagram showing the configuration of the wavelength converter according to the fourth embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Wavelength converter 11 Polarization controller 12 Pump light generation circuit 13 Polarization controller 14 Optical coupler 15 Optical circulator 16 PBS
17 Polarization adjustment circuit 18 Wavelength conversion circuit 19 BPF
20 Wavelength conversion loop circuit

Claims (12)

Wavelength conversion is performed by receiving the signal light of the polarization orthogonal multiplexed signal in which two optical signals in the orthogonal polarization state propagated through the transmission path and multiplexed by polarization multiplexed transmission are converted, and the wavelength of the signal light is converted. A wavelength converter for outputting the transmitted signal light,
Pump light generating means for generating pump light having a wavelength fp different from the frequency fs of the signal light (where fc = 2fp−fs fc: frequency of the wavelength-converted signal light);
First polarization control means for controlling the polarization state of the signal light;
A multiplexing unit that combines the signal light output from the first polarization control unit and the pump light;
The combined light from the multiplexing means is received at the input port, and the first polarized wave component and the second polarized wave component orthogonal to the first polarized wave component are output from the combined light into two outputs. A polarization beam splitter that outputs to the port, a wavelength conversion loop that is a transmission path in which the two output ports are connected in a loop, and the first polarization component and the second Wavelength conversion loop means having wavelength conversion means for generating light of frequency fc by four-wave mixing in each of the polarization components of
Propagating through the wavelength conversion loop of the wavelength conversion loop means, and receiving the combined light including the signal light of the frequency fc that is recombined and output from the input port of the polarization beam splitter in the polarization beam splitter. Bandpass filter means for passing light of frequency fc in the combined light;
Each of the ports has at least three ports, and each port is connected to the multiplexing unit, the wavelength conversion loop unit, and the band-pass filter unit, and the combined light from the multiplexing unit is output to the wavelength conversion loop unit And an optical path determining unit that outputs combined light including the signal light having the frequency fc from the wavelength conversion loop unit to the band-pass filter unit.   The wavelength converter according to claim 1, further comprising second polarization control means for controlling a polarization state of the pump light. The first polarization control means indicates the polarization state of the signal light, and the first polarization component of the polarization orthogonal multiplexed signal is linearly polarized with respect to a first axis of the polarization beam splitter. As well as controlling
The second polarization control unit is configured to change a polarization state of the pump light with respect to the first axis in the polarization beam splitter when the combined light including the pump light is input to the polarization beam splitter. The wavelength conversion device according to claim 2, wherein the wavelength conversion device is controlled so as to be 45 ° linearly polarized light. The first polarization control means indicates the polarization state of the signal light, and the first polarization component of the polarization orthogonal multiplexed signal is linearly polarized with respect to a first axis of the polarization beam splitter. The polarization state of the pump light is controlled so that when the combined light including the pump light is input to the polarization beam splitter, a straight line of 45 degrees with respect to the first axis in the polarization beam splitter. The pump light polarization adjusting means for rotating the pump light by a predetermined angle so as to be polarized,
The wavelength conversion device according to claim 1, wherein a transmission path from the pump light generation unit to the polarization splitter is configured to maintain a polarization state thereof.   2. The wavelength conversion loop means includes polarization adjustment means that is disposed on the wavelength conversion loop and adjusts the polarization states of the first polarization component and the second polarization component. Thru | or 4. The wavelength converter as described in any one of 4. The polarization beam splitter is configured such that the polarization state of the input combined light is maintained and the first polarization component and the second polarization component are output from the two output ports. ,
The jumper cable constituting the wavelength conversion loop, and the wavelength conversion means are configured to maintain the polarization state; and
6. The wavelength according to claim 5, wherein the polarization adjusting unit is configured to rotate each polarization state of the received first polarization component and second polarization component by 90 degrees. Conversion device. The first polarization component is output from the first output port of the polarization beam splitter, propagates on the wavelength conversion loop, and is input again to the polarization beam splitter at the second port of the polarization beam splitter. The second polarization component is output from the second output port, propagates on the wavelength conversion loop, and is input to the polarization beam splitter again at the first port of the polarization beam splitter;
The polarization adjusting means is
When the first polarization component is input to the polarization beam splitter again at the second port, the second polarization component when the polarization state is output from the second port And the same polarization state, and
When the second polarization component is input to the polarization beam splitter again at the first port, the first polarization component when the polarization state is output from the first port The wavelength conversion device according to claim 5, wherein the polarization states of the first polarization component and the second polarization component are controlled to be the same as the polarization state of the first polarization component. The polarization beam splitter is configured to rotate and output only the polarization state of any one of the polarization components, and
5. The wavelength conversion device according to claim 1, wherein the jumper cable constituting the wavelength conversion loop and the wavelength conversion unit are configured to maintain polarization. 6. Signal light polarization control means for generating a first control signal for the first polarization control means,
First demultiplexing means disposed between the first polarization control means and the multiplexing means;
A first polarization state observation unit that receives the signal light demultiplexed by the first demultiplexing unit and calculates an index value based on a polarization state of the signal light; and the first polarization state observation Signal light control signal generating means for generating a first control signal for controlling the first polarization control means based on the index value calculated by the means so as to optimize the index value. With signal light polarization control means,
From the output port of the first polarization control means to the input port of the polarization beam splitter of the wavelength conversion loop means through the first demultiplexing means, the multiplexing means, and the optical path determination means The wavelength conversion apparatus according to claim 1, wherein the optical path is configured to maintain the polarization. Signal light polarization control means for generating a first control signal for the first polarization control means,
In the wavelength conversion loop means, a first demultiplexing means arranged on a wavelength conversion loop from one output port of the polarization beam splitter;
A first polarization state observation unit that receives the signal light demultiplexed by the first demultiplexing unit and calculates an index value based on a polarization state of the signal light; and the first polarization state observation Signal light control signal generating means for generating a first control signal for controlling the first polarization control means based on the index value calculated by the means so as to optimize the index value. 9. The wavelength converter according to claim 1, further comprising a signal light polarization control unit. Pump light polarization control means for generating a second control signal for the second polarization control means,
Second demultiplexing means disposed on the optical transmission line from the output port of the bandpass filter means;
A polarization acquisition unit that receives the wavelength-converted signal light demultiplexed by the second demultiplexing unit and acquires each polarization component of the wavelength-converted signal light; and the polarization acquisition unit The second polarization state observation means for calculating the index value based on the light intensity of each of the polarization components acquired by the step, and the index value calculated by the second polarization state observation means is optimized. A pump light polarization control means having a pump light control signal generation means for generating a second control signal for controlling the second polarization control means,
An optical path from the input port of the polarization beam splitter of the wavelength conversion loop means to the polarization acquisition means via the optical path determination means, the band pass filter means, and the second demultiplexing means 4. The wavelength converter according to claim 2, wherein the wavelength converter is configured to maintain the polarization. Pump light polarization control means for generating a second control signal for the second polarization control means,
A second demultiplexing unit and a third demultiplexing unit respectively disposed on the wavelength conversion loop from the two output ports of the polarization beam splitter in the wavelength conversion loop unit;
Second polarization state observing means for calculating an index value based on the light intensity of each polarization component demultiplexed by the second demultiplexing means and the third demultiplexing means; and the second polarization A pump light control signal generating means for generating a second control signal for controlling the second polarization control means so that the index value calculated by the wave state observing means is optimized. 4. The wavelength converter according to claim 2, further comprising a wave control unit.

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