JP2000221548A - Phase conjugate light generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to output a phase conjugate light separating from signal light with respect to any signal light wavelength without using a variable optical filter, and also efficiently generate the phase conjugate light without depending on signal optical polarization. SOLUTION: Signal light is inputted from an input port (1) of a nonlinear loop mirror containing an optical nonlinear medium in the loop, and linear- polarized pumping light 1, 2 which have a same optical frequency and a same power clockwise and counterclockwise and are mutually orthogonal to each other are inputted to the loop. A nonlinear loop mirror has such a configuration as signal light propagating from an output port (2) to an output port (3) and signal light propagating from the output port (3) to the output port (2) experience the same propagation phase, and are inputted to the output ports (2) and (3) respectively in the same polarization state. The signal light inputted from the input port (1) is outputted from the input port (1), and phase conjugate light, which are generated clockwise and counterclockwise through the optical nonlinear medium and mutually orthogonally polarized, are outputted to the input ports (1), (4) in equal power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a four-wave mixing phenomenon caused by a third-order optical parametric effect induced in an optical nonlinear medium to convert phase conjugate light having a phase (spectrum) inverted with respect to signal light. The present invention relates to a device for generating phase conjugate light.

[0002]

2. Description of the Related Art In optical fiber transmission, chromatic dispersion and optical nonlinearity of an optical fiber are factors that limit the propagation distance and the number of multiplexes in a wavelength division multiplexing system. As a method for overcoming these, a method using phase conjugate light is known.

[0003] Phase conjugate light is light obtained by inverting the phase of the original signal light. At the middle point of the optical fiber transmission line, a phase conjugate light of the signal light whose waveform has been deteriorated due to the chromatic dispersion and optical nonlinearity of the first half transmission line is generated and propagated in the second half transmission line. The waveform of the phase conjugate light changes following the reverse process of the first half, and returns to the original waveform at the final point. By utilizing this property, it is possible to overcome the transmission limitation due to chromatic dispersion and optical nonlinearity.

Normally, four-wave mixing is used to generate phase conjugate light. Four-wave mixing means that the optical frequency is f ₁ ,
When three light waves f ₂ and f ₃ are input to the optical nonlinear medium, f ₁ + f ₂ −f ₃ =
new frequency light that f ₄ is a phenomenon that occurs. The amplitude E ₄ of the generated light having the optical frequency f ₄ is expressed as E ₄ = kE ₁ E ₂ E ₃ ^* , where the input light amplitudes are E ₁ , E ₂ , and E ₃ , respectively. k represents a proportional constant representing the generation efficiency, and * represents a complex conjugate.

[0005] Accordingly, if the light of the optical frequencies f ₁ and f ₂ is the stationary light and the light of the optical frequency f ₃ is the signal light, the generated four-wave mixed light of the optical frequency f ₄ becomes the phase conjugate light of the signal light. . Note that the stationary light having the optical frequencies f ₁ and f ₂ used to generate the phase conjugate light is called pump light. Usually, for simplicity, one pump light and one signal light are input to an optical nonlinear medium with f ₁ = f _2, and phase conjugate light is generated at an optical frequency position of 2f ₁ −f ₃ = f ₄ .

[0006]

As an optical nonlinear medium for generating phase conjugate light, an optical fiber or a semiconductor optical amplifier is used. This is because high-density optical power is confined over a certain length by the waveguide structure, so that nonlinearity can be strengthened, and as a result, phase conjugate light can be generated efficiently.

In the case of using an optical fiber or a semiconductor optical amplifier, when signal light and pump light are input from the same direction for efficient interaction, the generated phase conjugate light is output together with the signal light and pump light. Therefore, when it is desired to output only the phase conjugate light, it is necessary to provide an optical filter at the output stage for blocking the signal light wavelength and the pump light wavelength. In order to output only the phase conjugate light for an arbitrary signal light wavelength, a wavelength-variable optical filter is required, and a device such as a tuning mechanism of the optical filter becomes complicated.

The characteristic that both the signal light and the phase conjugate light are output is a factor that limits the signal wavelength band when the phase conjugate light is generated from the wavelength multiplexed signal light at a time. FIG. 14 shows this state. Here, the phase conjugate light of the wavelength-multiplexed signal light of four channels is illustrated. The subscript s of the optical frequency indicates signal light, p indicates pump light, c indicates phase conjugate light, and the numbers indicate the corresponding signal light and phase conjugate light, respectively. (a) shows the input light of the optical nonlinear medium, and (b) shows the output light of the optical nonlinear medium.

When the four-channel signal light shown in FIG. 14A is input to the optical nonlinear medium together with the pump light, the four-channel signal light and the pump light shown in FIG. Conjugate light appears. Therefore, in order to extract only the phase conjugate light using the optical filter, the signal light and the phase conjugate light need to have different wavelength bands. That is,
As shown in FIG. 14, it is necessary to arrange all of the wavelength multiplexed signal light in an optical frequency band higher (or lower) than the pump light.

In general, the generation efficiency of phase conjugate light tends to decrease when the pump light frequency and the signal light frequency are separated. For example, an optical frequency difference that can be generated with high efficiency is Δf. In this case, in the optical nonlinear medium, it is possible to generate the phase conjugate light for the signal light in the range of f _P −Δf <f _S <f _P + Δf, but it is necessary to separate the signal light and the phase conjugate light. From the characteristics, the signal light frequency range that can be actually applied is f _P <f _S <f _P + Δf (or f _P −Δf <f _S <f
_P ). That is, in principle, it is possible to generate collective phase conjugate light over an optical frequency range of 2Δf, but the signal light band that can be actually applied is limited to Δf.

Further, the conventional configuration using an optical nonlinear medium has a problem that the generation efficiency of the phase conjugate light depends on the polarization of the signal light. That is, the four-wave mixing efficiency in the optical nonlinear medium depends on the polarization state of the input light. In an optical fiber or a semiconductor optical amplifier, the efficiency is highest when the signal light and the pump light are the same polarization, and when the signal light and the pump light are orthogonal. No four-wave mixing light is generated. Therefore, in order to generate phase conjugate light with respect to signal light in an arbitrary polarization state, it is necessary to provide some kind of polarization control means before the optical nonlinear medium. But,
Such a configuration becomes an obstacle particularly when collectively generating phase conjugate light from wavelength multiplexed signal light.

According to the present invention, the phase conjugate light for an arbitrary signal light wavelength can be separated and output from the signal light without using a variable optical filter, whereby the optical frequency range determined by the performance limit of the optical nonlinear medium can be reduced. It is an object of the present invention to provide a phase conjugate light generator that can output only phase conjugate light collectively from wavelength multiplexed signal light and can efficiently generate phase conjugate light without depending on signal light polarization. Aim.

[0013]

According to a first aspect of the present invention, there is provided a phase conjugate light generator, wherein a signal light is input from an input port of a nonlinear loop mirror including an optical nonlinear medium in a loop;
Into the loop, pump lights 1 and 2 of linearly polarized waves which are orthogonal to each other at the same optical frequency and the same power in the clockwise and counterclockwise directions are input. The nonlinear loop mirror has a configuration in which signal light propagating from an output port to an output port and signal light propagating from an output port to an output port experience the same propagation phase, and are input to the output port in the same polarization state. is there. As a result, the signal light input from the input port is output from the input port, and the phase conjugate light of mutually orthogonal polarized waves generated clockwise and counterclockwise in the optical nonlinear medium is output with equal power to the input port. Is done. Therefore, the phase conjugate light output from the input port can be extracted independently of the signal light without depending on the polarization of the signal light.

According to a third aspect of the present invention, there is provided a phase conjugate light generating device comprising a non-linear loop mirror using an MZ demultiplexer.
Pump lights 1 and 2 of linearly polarized waves having the same optical frequency and the same power and orthogonal to each other are input from an input port, propagate in the loop clockwise and counterclockwise, and output from the input port. The configuration in which the signal light is input from the input port and the phase conjugate light output from the output port is extracted is the same as that of the phase conjugate light generating device according to the first and second aspects. However, means for separating and outputting only the phase conjugate light from the pump light 2 input to the output port and the pump light 1 and the phase conjugate light output is used.

According to a sixth aspect of the present invention, there is provided a phase conjugate light generator.
In the phase conjugate light generator according to the first and third aspects, the optical fiber and the optical nonlinear medium constituting the loop of the nonlinear loop mirror are polarization maintaining optical fibers.

According to a seventh aspect of the present invention, there is provided a phase conjugate light generator.
The optical fiber and the optical nonlinear medium constituting the loop of the nonlinear loop mirror are a polarization maintaining optical fiber and a semiconductor optical amplifier having a polarization independent gain.

According to another aspect of the present invention, there is provided a phase conjugate light generating apparatus comprising: an optical fiber for connecting an output port of a polarization beam splitter while maintaining the polarization of propagation light; and an optical nonlinear medium; The signal light and the pump light 1 are input to the input port and the pump light 2 is input to the input port.
The pump lights 1 and 2 are in a polarization state outputted to the output ports at the same power, and have the same optical frequency and the same power. The signal light and the pump light 1 are output from the input port, and the pump light 2 is output from the input port.

In the optical nonlinear medium, the first polarization component of the signal light, the first polarization component of the pump light 1, and the second polarization component of the pump light 2 are used to determine the phase conjugate light of the first polarization. The phase conjugate light of the second polarization is generated. The first polarization phase conjugate light is output from the input port of the polarization beam splitter, and the second polarization phase conjugate light is output from the input port of the polarization beam splitter. Accordingly, by extracting the phase conjugate light of the second polarization at the input port, it is possible to output the light separated from the signal light output from the input port.

According to another aspect of the present invention, there is provided a phase conjugate light generator comprising an optical fiber and an optical nonlinear medium for connecting an output port of a polarization beam splitter with the polarization of propagation light being rotated by 90 degrees. The signal light and the pump light 1 are input to the input port, and the pump light 2 is input to the input port. The pump lights 1 and 2 are in a polarization state outputted to the output ports at the same power, and have the same optical frequency and the same power. The signal light and the pump light 1 are output from the input port, and the pump light 2 is output from the input port.

In the optical nonlinear medium, similarly, phase conjugate light of the first polarization and phase conjugate light of the second polarization are generated. The first polarization phase conjugate light is output from the input port of the polarization beam splitter, and the second polarization phase conjugate light is output from the input port of the polarization beam splitter. Accordingly, by extracting the phase conjugate light of the second polarization at the input port, it is possible to output the light separated from the signal light output from the input port.

Note that a similar configuration is disclosed in
No. 415, FIG. 10 and FIG. 35, which generate phase conjugate light of the first polarization from the first polarization component of the signal light and the first polarization component of the pump light 1, and as a whole, The signal light and the phase conjugate light are output from the same output port. Therefore, it does not solve the above-mentioned conventional problems. On the other hand, the phase conjugate light generation device of the present invention extracts phase conjugate light from an output port different from the signal light, and realizes polarization independence of the input signal light.

According to a fourteenth aspect of the present invention, there is provided a phase conjugate light generating device in which the optical fiber of the phase conjugate light generating device according to the first to thirteenth aspects comprises a planar optical waveguide.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows a first embodiment of a phase conjugate light generating device according to the present invention. In the figure, a signal light is input to a port of a 2 × 2 3 dB coupler 11. The port of the 3 dB coupler 11 is
They are connected in a loop via polarization maintaining WDM couplers 12 and 13 and polarization maintaining optical fibers 14 and 15. The WDM coupler 12 is arranged at a position near the port, and the WDM coupler 13 is arranged at a position near the port.

The polarization-maintaining optical fibers 14 and 15 are birefringent fibers and have two orthogonal refractive index axes. Here, one refractive index axis is defined as a P axis, and is indicated by an arrow in the figure. The P axis is horizontal at the connection point between the polarization maintaining optical fiber 14 connected to the port of the 3 dB coupler 11 and the WDM coupler 12, and P at the connection point between the polarization maintaining optical fiber 15 and the WDM coupler 13 connected to the port. Connected so that the axis is vertical. Further, the polarization maintaining optical fiber 1
At the intermediate position of the loop where the loops 4 and 15 are connected to each other, the loops are connected so that the P axes are orthogonal to each other. Hereinafter, the horizontal direction is defined as the x-axis and the vertical direction is defined as the y-axis on the paper.

The pump light 2 is linearly polarized in the x-axis direction or y-axis direction, the same optical frequency and the same power P _p. Here, assuming that the amplitude (x-axis component) of the pump light 1 is E _p1 and the amplitude (y-axis component) of the pump light 2 is E _p2 , | E _p1 | ² = | E _p2 | ² = P _p . Pump light 1
Is input clockwise to the polarization maintaining optical fiber 14 via the WDM coupler 12, and the pump light 2 is input counterclockwise to the polarization maintaining optical fiber 15 via the WDM coupler 13. The two WDM couplers 12 and 13 pass light other than the pump light wavelength through. Pump lights 1 and 2 that have propagated in the loop in the opposite directions, respectively, are WDM
The signals are output from the couplers 13 and 12 to the outside.

The power of the signal light input to the port of the 3 dB coupler 11 is P _s , and the polarization state is arbitrary. Here, the signal light of the amplitude of the x-axis component E _sx, when the y-axis component and E _sy, | a ^{_{2 = P s | E sx |}} 2 + | E sy. This signal light is branched into two ports by the 3 dB coupler 11, propagates through the polarization maintaining optical fibers 14 and 15 clockwise and counterclockwise, respectively, and is multiplexed again by the 3 dB coupler 11. The x-axis component of the amplitude of the signal light propagating in both directions is E _sx / √2, and the y-axis component is E _sy / √2. This configuration is known as a non-linear loop mirror, and the multiplexed signal light is always output from the port as a result of interference. For that purpose, when the signal lights branched by the 3 dB coupler 11 are multiplexed, it is necessary that (a) the same polarization and (b) the same propagation phase be experienced clockwise / counterclockwise. It is. The reason why the polarization maintaining optical fibers 14 and 15 are used is to satisfy the former condition (A), and the axes of the refractive indexes of the polarization maintaining optical fibers 14 and 15 are connected orthogonally at the midpoint of the loop. Is to satisfy the latter condition (a).

In such a configuration, the polarization maintaining optical fibers 14 and 15 act as an optical nonlinear medium, and generate phase conjugate light with respect to the signal light. The phase conjugate light is generated for a component in which the polarizations of the signal light and the pump light match. Here, the pump light 1 in the x-axis direction propagates clockwise,
Pump light 2 in the y-axis direction propagates counterclockwise.
Therefore, the clockwise, and the phase conjugate light is generated in the x-axis direction of the amplitude ^{_{E cx = kE p1 2 (E}} sx / √2) * ... (1), the counter-clockwise, the y-axis direction amplitude There ^{_{E cy = kE p2 2 (E}} sy / √2) * ... phase conjugate light is generated (2).

Each of the generated phase conjugate lights passes through WDM couplers 12 and 13 as shown in FIG.
And are multiplexed. Here, since the phase conjugate lights generated in both directions are in the orthogonal polarization state, they are branched to the ports and output without interfering with each other. Power of the phase conjugate light output to a ^{_{port, | E cx / √2 | 2}} + | E cy / √2 | 2 = (k 2/4) {| E p1 | 4 | E sx | 2 + | E _p2 | ⁴ | _Esy | ² ｝ (3) Here, as described above, | E _p1 | ² = | E _{p2
^{| 2 = P p, | E}} sx | 2 + | E sy | because it is ² = P _s, formula
^{_{(3), | E cx / √2 | 2}} + | E cy / √2 | 2 = (k 2/4) P p 2 {| E sx | 2 + | E sy | 2} = (k 2 / 4) P _p ² P _s (4)

The same applies to the phase conjugate light output to the port of the 3 dB coupler 11, but the signal light is also output to the port at the same time, so this phase conjugate light is not used.
Similarly, it can be considered that the pump light 1 is linearly polarized in the y-axis direction and the pump light 2 is linearly polarized in the x-axis direction.

[0030] Looking equation (4), from the port of the 3dB coupler 11, without depending on the polarization state of the input signal light, a phase conjugate light depends only on the signal light power P _s and the pump light power P _p is It turns out that it is output. Further, as described above, the input signal light is output from the port and does not appear at the port. Therefore, it is possible to obtain a phase conjugate light generator that outputs only the phase conjugate light regardless of the wavelength and the polarization state of the signal light. For example, the polarization maintaining optical fibers 14 and 15
In the above, when the phase conjugate light can be generated with high efficiency with respect to the signal light in the range of f _P −Δf <f _S <f _P + Δf, the signal light and the phase conjugate light are mixed as shown in FIG. Even when mixed on the frequency axis, only phase conjugate light can be output. That is, only the phase conjugate light can be output collectively from the wavelength multiplexed signal light within the optical frequency range determined by the performance limit of the polarization maintaining optical fiber.

In this embodiment, the polarization maintaining optical fiber is used as the optical nonlinear medium. However, for example, a semiconductor optical amplifier having a polarization independent gain may be used as the optical nonlinear medium.

(Second Embodiment) FIG. 4 shows a second embodiment of the phase conjugate light generator of the present invention. The feature of this embodiment is that a 2 × 2 MZ duplexer 21 is used instead of the 3 dB coupler 11 in the first embodiment, and the WDM coupler 1
Instead of inputting the pump lights 1 and 2 into the loop via the ports 2 and 13, the signal light and the pump light 1 are input from the ports and the pump light 2 is input from the ports.
The MZ demultiplexer 21 is a polarization maintaining type. The polarization-maintaining optical fibers 14 and 15 that connect the ports of the MZ demultiplexer 21 in a loop shape are coupled so that the P-axes are orthogonal to each other at an intermediate position of the loop as in the first embodiment.

The MZ splitter 21 has a periodic transmission characteristic as shown in FIG. That is, the transmission characteristics (solid line) of the through port (and the) and the cross port (
, And) have a complementary relationship (broken line). In this transmission characteristic, the optical frequency of the signal light is set so as to be the intersection of the two complementary transmission characteristics, that is, the optical frequency position where the signal light input to the port is output to the port with equal power. On the other hand, the optical frequencies of the pump lights 1 and 2 are the peak positions of the transmission characteristics indicated by the solid lines, that is, the optical frequencies at which the pump light 1 input to the port is output to the port and the pump light 2 input to the port is output to the port. Set to position.

By setting such an optical frequency arrangement, M
The Z splitter 21 acts on the signal light in the same manner as the 3 dB coupler 11. Therefore, similarly to the first embodiment,
The signal light propagated in the loop is output from the port of the MZ demultiplexer 21. On the other hand, as shown in FIG. 6 (a), the pump light 1 passes through the ports of the MZ duplexer 21 and propagates through the loop clockwise.
Is output from port to port. Also, as shown in FIG. 6 (b), the pump light 2 is transmitted from the port of the MZ duplexer 21 to the port, propagates through the loop counterclockwise, and is output from the port of the MZ duplexer 21 to the port. Is done. That is, in the loop, the pump light 1 of the x-axis polarization propagates clockwise, and the pump light 2 of the y-axis polarization propagates counterclockwise.

The optical frequency may be such that the pump lights 1 and 2 are output to the cross port of the MZ demultiplexer 21. The pump light 1 is linearly polarized in the y-axis direction, and the pump light 2 is
The linearly polarized wave in the axial direction may be used.

The situation in the loop of this embodiment is the same as that of the first embodiment. When the optical frequencies of the signal light and the pump lights 1 and 2 are set as shown in FIG. 5, the optical frequency of the phase conjugate light is inevitably set at the intersection of the two transmission characteristics of the MZ duplexer 21,
That is, the optical frequency position where the MZ demultiplexer 21 operates as the 3 dB coupler 11 is set. Therefore, phase conjugate light is generated similarly to the first embodiment, and is output from the port of the MZ demultiplexer 21 with the power represented by the equation (4).

Here, the signal light does not appear at the port of the MZ demultiplexer 21, but the pump light 1 is output from the port together with the phase conjugate light. Therefore, in order to separate from the pump light 2 input to the port of the MZ demultiplexer 21 and to output only the phase conjugate light separately from the pump light 1, the optical circulator 22 and the optical filter 2 for blocking the pump light 1
3 is used.

In place of the optical circulator 22 and the optical filter 23, a WDM coupler 24 that passes through the pump lights 1 and 2 and reflects the phase conjugate light may be used as shown in FIG.

Since the MZ demultiplexer 21 has a periodic transmission characteristic as shown in FIG. 5, the MZ demultiplexer 21 collectively performs phase conjugation on signal light wavelength-multiplexed at a periodic optical frequency position. Light can be generated and only its phase conjugate light can be output.

In this embodiment, the polarization maintaining optical fiber is used as the optical nonlinear medium. However, as in the first embodiment, for example, a semiconductor optical amplifier having a polarization independent gain is used as the optical nonlinear medium. Is also good.

(Third Embodiment) FIG. 8 shows a third embodiment of the phase conjugate light generator according to the present invention. In the figure,
The signal light and the pump light 1 are input to a port of a 2 × 2 polarization beam splitter 32 via an optical circulator 31, and the pump light 2 is input to a port of the polarization beam splitter 32. The port of the polarization beam splitter 32 is connected in a loop via a polarization maintaining optical fiber 33 and a semiconductor optical amplifier 34 having a polarization independent gain.

The polarization beam splitter 32 outputs the polarization component in the x-axis direction to the through port, and outputs the polarization component in the y-axis direction to the reflection port. The polarization maintaining optical fiber 33 is
When the light output from the polarization beam splitter 32 circulates around the loop and is input to the polarization beam splitter 32 again, they are connected so as to be in the same polarization state. Accordingly, the signal light input from the port of the polarization beam splitter 32 has its x-axis component output from the port, propagates counterclockwise and enters the port, and the y-axis component is output from the port and rotates clockwise. And input to the port, and both are output from the port. Similarly, the pump light 1 input from the port is output from the port, and the pump light 2 input from the port is output from the port. The above situation is shown in FIG.

The power of the signal light is P _s , and the polarization state is arbitrary. Here, the signal light of the amplitude of the x-axis component E _sx, when the y-axis component and E _sy, | a ^{_{2 = P s | E sx |}} 2 + | E sy. The pump lights 1 and 2 have the same optical frequency and the same power, and the polarization components in the x-axis direction and the y-axis direction have the same power _Ppp . Here, if the x-axis component of the amplitude of the pump light 1 is E _p1x , the y-axis component is E _p1y , the x-axis component of the amplitude of the pump light 2 is E _p2x , and the y-axis component is E _p2y ,
_p1x = _Ep1y , _Ep2x = _Ep2y , | _Ep1x | ² = | _Ep1y
| ² = | a ^{_{2 = P pp | E p2x |}} 2 = | E p2y.

As shown in FIG. 8, the port of the polarization beam splitter 32, the y-axis component E _sy of the signal light, and a y-axis component E _p1y of the pumping light 1, x-axis component of the pump light 2 E _p2x
Is output and input to the semiconductor optical amplifier 34 clockwise via the polarization maintaining optical fiber 33. The port includes an x-axis component E _sx of the signal light and an x-axis component E _s of the pump light 1.
and _p1x, y-axis component E _P2Y of the pump light 2 is output and input via the polarization-maintaining optical fiber 33 to the semiconductor optical amplifier 34 in the counterclockwise direction. These lights generate phase conjugate light in the semiconductor optical amplifier 34. Unlike the first and second embodiments, the pump light input in the same direction is composed of two orthogonal components.

Of the phase conjugate light generated in such a case, the x-axis component E _cyx and the y-axis component E _cyy of the clockwise phase conjugate light are: E _cyx = kE _p2x E _p1y E _sy ^* (5a) E _cyy = kE _p1y ² E _sy ^* (5b), and the x-axis component E _cxx and the y-axis component E _cxy of the phase conjugate light in the counterclockwise direction are E _cxx = kE _p2x ² E _sx ^* ... (6a) E _{cxy = kE p1x E p2y E sx} * ... the (6b). Equations (5b) and (6a) are the phase conjugate lights generated by the interaction between the same polarizations as in the first and second embodiments, and are further expressed by the equations (5) by the interaction with the orthogonal pump light.
Components of the phase conjugate light represented by (a) and (6b) are generated.

The generated phase conjugate light propagates through the polarization maintaining optical fiber 33, is input to the port of the polarization beam splitter 32, and is output to the port. Here, due to the operation of the polarization beam splitter 32, as shown in FIG. 10, the x-axis component E _cyx of the clockwise phase conjugate light and the y-axis component E _cyx of the counterclockwise phase conjugate light are applied to the port.
_{cx y} is output. The phase conjugate light output to the port is not used because it is output together with the signal light.

The phase conjugate light of the power which is output to a port of the polarization beam splitter ^{_{32, | E cyx | 2 + |}} E cxy | 2 = k 2 (| E p2x | 2 | E p1y | 2 | E sy | _{^{2 + | E p1x | 2 |}} E p2y | 2 | E sx | 2) ... a (7). Here, the signal light and the pumping lights 1 and 2 has the above relationship, Equation (7) ^{_{is, | E cyx | 2 + |}} E cxy | 2 = k 2 P pp 2 (| E sy | _{^{2 + | E sx | 2)}} = k 2 P pp 2 P s ... is (8). Looking at equation (8), from the port of the polarization beam splitter 32, without depending on the polarization state of the input signal light, the signal light power P _s and power P _pp in each axis direction of the pump light
It can be seen that phase conjugate light depending only on the phase is output.

However, as shown in FIG. 9, since the pump light 2 is output to the port together with the phase conjugate light, it is separated from the signal light and the pump light 1 input to the port by the optical circulator 31 and furthermore, the optical filter 35 By blocking the pump light 2, the phase conjugate light alone can be output. Instead of the optical circulator 31 and the optical filter 35, a WDM coupler for separating the pump light 1 and the pump light 2 from the signal light and the phase conjugate light may be used. Also, the input signal light is output from the port,
Since it does not appear at the port, a phase conjugate light generator that outputs only phase conjugate light can be obtained regardless of the wavelength and the polarization state of the signal light.

In this embodiment, the semiconductor optical amplifier 3
4 is used as an optical nonlinear medium, but other media,
For example, similar effects can be obtained by using an optical fiber. However, in the case of an optical fiber, since the polarization state of propagating light is generally not maintained, the light output from the polarization beam splitter into the loop circulates around the loop and remains in the same polarization state. It is necessary to provide a polarization control unit on the loop path in order to satisfy the condition of “input to the loop”. Although the polarization state of the propagating light is maintained by using the polarization maintaining optical fiber, the phase matching cannot be achieved due to the influence of the polarization dispersion, and the interaction between the orthogonal propagating lights does not occur. Cannot be used as an optical non-linear medium.

(Fourth Embodiment) FIG. 11 shows a fourth embodiment of the phase conjugate light generator of the present invention. In the figure, a signal light and a pump light 1 are input to a port of a 2 × 2 polarization beam splitter 41, and a pump light 2 is a WD.
The signal is input to the port of the polarization beam splitter 41 via the M coupler 42. The port of the polarization beam splitter 41 is connected in a loop via a polarization maintaining optical fiber 43, a semiconductor optical amplifier 44 having a polarization independent gain, and a λ / 2 wavelength plate 45. Here, the λ / 2 wavelength plate 4
5 is connected to the port side of the polarization beam splitter 41. It is assumed that the WDM coupler 42 transmits light other than the pump light wavelength through.

The feature of this embodiment is that the λ / 2 wavelength plate 45 is arranged on the loop path in the configuration of the third embodiment. Thereby, the polarization beam splitter 4
When the light output from 1 is input around the loop, the polarization is rotated by 90 degrees. Therefore, the signal light and the pump light 1 input from the port of the polarization beam splitter 41 are output from the port, and the pump light 2 input from the port is output from the port. The above situation is shown in FIG.

The condition of the signal light and the pump lights 1 and 2 is the third.
It is the same as the embodiment. The input state to the semiconductor optical amplifier 44 is the same as that of the third embodiment in the clockwise direction, but in the counterclockwise direction, the polarization is rotated by 90 degrees for both the signal light and the pump light as shown in FIG. I have. Therefore, the x-axis component E _cyx and the y-axis component E _cyy of the phase conjugate light generated clockwise are the same as in the equations (5a) and (5b),
X-axis component E _cxx and y-axis component E _cxy phase conjugate light generated in the _{counter-clockwise, E cxx = kE p1x E p2y} E sx * ... (9a) E cxy = kE p1x 2 E sx * ... (9b) Becomes

The generated phase conjugate light is input to the port of the polarization beam splitter 41, but due to the action of the λ / 2 wave plate 45, the clockwise phase conjugate light is polarized as shown in FIG. Input by rotating 90 degrees. Therefore, the port, y-axis component E _Cyx and x-axis component E _cxx counterclockwise of the phase conjugate light clockwise phase conjugate light is output. The phase conjugate light output to the port is not used because it is output together with the signal light.

[0054] Power of the phase conjugate light output port of the polarization beam splitter ^{_{41, | E cyx | 2 + |}} E cxx | 2 = k 2 (| E p2x | 2 | E p1y | 2 | E sy | _{^{2 + | E p1x | 2 |}} E p2y | 2 | E sx | 2) = k 2 P pp 2 (| E sy | 2 + | E sx | 2) = k 2 P pp 2 P s ... (10) Become. Looking at equation (10), from the port of the polarization beam splitter 41, without depending on the polarization state of the input signal light, the signal light power P _s and power P _pp in each axis direction of the pump light
It can be seen that phase conjugate light depending only on the phase is output.

However, as shown in FIG. 12, the pump light 2 is output to the port together with the phase conjugate light. However, since the pump light 2 is reflected by the WDM coupler 42, the pump light 2 is phase conjugate to the through port of the WDM coupler 42. Only light can be output. Further, since the input signal light is output from the port and does not appear at the port, it is possible to obtain a phase conjugate light generator that outputs only the phase conjugate light regardless of the wavelength and the polarization state of the signal light.

In the configuration of FIG. 11, the λ / 2 wavelength plate 4
5 is connected to the port side of the polarization beam splitter 41, but it is the same when connected to the port side. Also, λ
Instead of using the half-wave plate 45 to rotate the polarized light by 90 degrees, the same applies if the polarization maintaining optical fiber 43 is simply twisted 90 degrees around the axis and connected to the polarization beam splitter 41. Instead of the WDM coupler 42, a combination of an optical circulator and an optical filter for blocking the pump light 2 as in the third embodiment may be used.

In this embodiment, the semiconductor optical amplifier 4
4 is used as an optical nonlinear medium, but other media,
For example, similar effects can be obtained by using an optical fiber. When an optical fiber is used, it is the same as the third embodiment that a polarization control unit needs to be provided on the loop path.

[0058]

As described above, according to the present invention, only the phase conjugate light can be separated from the input signal light and the pump light and output without using a variable optical filter, and the polarization of the input signal light can be improved. A phase conjugate light generator that does not depend on waves can be realized. Thus, when collectively generating the phase conjugate light with respect to the wavelength multiplexed signal light, there is no problem even if each signal light and the phase conjugate light are close on the optical frequency axis, and it is determined by the performance limit of the optical nonlinear medium. Operation for wavelength multiplexed signal light in the optical frequency range becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a phase conjugate light generation device according to the present invention.

FIG. 2 is a diagram illustrating a flow of phase conjugate light according to the first embodiment.

FIG. 3 is a diagram illustrating a relationship between signal light and phase conjugate light according to the first embodiment.

FIG. 4 is a diagram showing a second embodiment of the phase conjugate light generating device of the present invention.

FIG. 5 is a diagram showing transmission characteristics and optical frequency arrangement of an MZ duplexer.

FIG. 6 is a diagram showing a flow of pump lights 1 and 2 in the second embodiment.

FIG. 7 is a diagram illustrating a configuration example using a WDM coupler according to a second embodiment.

FIG. 8 is a diagram showing a third embodiment of the phase conjugate light generator according to the present invention.

FIG. 9 is a diagram showing flows of signal light and pump light in the third embodiment.

FIG. 10 is a diagram showing a flow of phase conjugate light according to the third embodiment.

FIG. 11 is a diagram showing a fourth embodiment of the phase conjugate light generation device of the present invention.

FIG. 12 is a diagram showing flows of signal light and pump light according to the fourth embodiment.

FIG. 13 is a diagram illustrating a flow of phase conjugate light according to the fourth embodiment.

FIG. 14 is a diagram showing an optical frequency arrangement of conventional wavelength multiplexed signal light and phase conjugate light.

[Explanation of symbols]

Reference Signs List 11 3 dB coupler 12, 13 WDM coupler 14, 15 Polarization maintaining optical fiber 21 Mach-Zehnder interferometer type optical multiplexer / demultiplexer (MZ demultiplexer) 22 Optical circulator 23 Optical filter 31 Optical circulator 32 Polarization beam splitter 33 Polarization maintaining light Fiber 34 semiconductor optical amplifier 35 optical filter 41 polarization beam splitter 42 WDM coupler 43 polarization maintaining optical fiber 44 semiconductor optical amplifier 45 λ / 2 wavelength plate

Claims (14)

[Claims] 1. A 3 dB coupler that has a 2 × 2 input / output port, inputs a signal light to an input port, and outputs an equal power to an output port and an output port of the 3 dB coupler. An optical fiber and an optical signal to be input to the output port of the 3 dB coupler in a state where the signal light propagating from the port to the output port and the signal light propagating from the output port to the output port experience the same propagation phase and are respectively in the same polarization state. A non-linear medium; first multiplexing means for multiplexing first linearly polarized first pump light with signal light propagating from the output port of the 3 dB coupler to the output port; output port of the 3 dB coupler To the signal light propagating from the second pump light to the output port, the second pump light having a polarization state orthogonal to the first pump light and having the same optical frequency and the same power. And means, the phase conjugate light generator, characterized in that the input port of the 3dB coupler is configured to output a phase conjugate light generated in the optical nonlinear medium within. 2. The phase conjugate light generator according to claim 1, wherein said first multiplexing means is a polarization maintaining type wavelength inserted into said optical fiber at a position near an output port of said 3 dB coupler. Wherein the second multiplexing means is a polarization-maintaining wavelength multiplex coupler inserted into the optical fiber at a position near an output port of the 3 dB coupler. apparatus. 3. A polarization-maintaining Mach-Zehnder interferometer type multiplexer / demultiplexer having 2 × 2 input / output ports and having periodic transmission characteristics between the input / output ports (hereinafter referred to as “MZ demultiplexer”). ) And the output port of the MZ demultiplexer, wherein light propagating from the output port to the output port and light propagating from the output port to the output port experience the same propagation phase;
An optical fiber and an optical non-linear medium input to the output port of the MZ demultiplexer in the same polarization state, and a phase conjugate generated in the optical non-linear medium from input / output light of the input port of the MZ demultiplexer. Phase conjugate light separating means for separating light and outputting the same. The signal light is an optical frequency that is input from an input port of the MZ demultiplexer and output to an output port with equal power. The pump light has an optical frequency and a predetermined linear polarization that is input from the input port of the MZ demultiplexer and transmitted to any one of the output ports, and the second pump light is an input of the MZ demultiplexer. A phase conjugate light generating device, which is inputted from a port, has the same optical frequency and the same power as the first pump light, and is in a polarization state orthogonal to the first pump light. 4. The phase conjugate light generation device according to claim 3, wherein the phase conjugate light separation means is output from an input port and a second pump light input to an input port of the MZ demultiplexer. An optical circulator for separating the first pump light and the phase conjugate light, and a light for blocking the first pump light from the first pump light and the phase conjugate light separated by the optical circulator and outputting only the phase conjugate light A phase conjugate light generating device comprising a filter and a filter. 5. The phase conjugate light generation device according to claim 3, wherein the phase conjugate light separation means is configured to input and output a second pump light and a first pump light to and from an input port of the MZ demultiplexer. And a wavelength multiplexing coupler for separating the phase conjugate light output from the input port. 6. The phase conjugate light generating device according to claim 1, wherein the optical fiber connecting the 3 dB coupler or the output port of the MZ demultiplexer and the optical nonlinear medium are polarization maintaining light. A phase conjugate light generator characterized by being a fiber. 7. The phase conjugate light generator according to claim 1, wherein the optical fiber connecting the 3 dB coupler or the output port of the MZ demultiplexer and the optical nonlinear medium are polarization maintaining light. A phase conjugate light generator, comprising a semiconductor optical amplifier having a fiber and a polarization independent gain. 8. A polarization beam splitter having a 2 × 2 input / output port, separating polarization of a signal light input from an input port and outputting the signal light to an output port, and an output port of the polarization beam splitter. , An optical fiber and an optical non-linear medium connecting the polarization beam splitter while maintaining the polarization of the propagating light, and separating phase conjugate light generated in the optical non-linear medium from input / output light at an input port of the polarization beam splitter. The first pump light is input from an input port of the polarization beam splitter and is output to the output port with equal power, and the second pump light is in a polarization state. The pump light is in a polarization state that is input from the input port of the polarization beam splitter and is output to the output port at the same power, and has the same optical frequency and the same power as the first pump light. A phase conjugate light generator characterized by the above-mentioned. 9. The phase conjugate light generation device according to claim 8, wherein the phase conjugate light separation means receives the signal light input to the input port of the polarization beam splitter, the first pump light, and the input port. An optical circulator for separating the output second pump light and the phase conjugate light, and an optical circulator for blocking the second pump light from the second pump light and the phase conjugate light separated by the optical circulator so as to output only the phase conjugate light. A phase conjugate light generating device, comprising: an optical filter for outputting. 10. The phase conjugate light generating device according to claim 8, wherein the phase conjugate light separating means is configured to input and output a first pump light and a second pump light to and from an input port of the polarization beam splitter. And a wavelength multiplexing coupler for separating signal light and phase conjugate light input / output to / from an input port. 11. A polarization beam splitter having a 2 × 2 input / output port, separating polarization of a signal light input from an input port and outputting the signal light to an output port, and an output port of the polarization beam splitter. , An optical fiber and an optical nonlinear medium that connect the polarization of the propagating light while rotating the polarization by 90 degrees, and a phase conjugate light generated in the optical nonlinear medium from input / output light of an input port of the polarization beam splitter. Phase conjugate light separating means for separating and outputting the first pump light, wherein the first pump light is input from an input port of the polarization beam splitter and is output to the output port at an equal power, and is in a polarization state. The second pump light is in a polarization state in which it is input from the input port of the polarization beam splitter and is output to the output port at the same power, and has the same optical frequency and the same power as the first pump light. Phase conjugate light generator, characterized in that there. 12. The phase conjugate light generation device according to claim 11, wherein the phase conjugate light separation means outputs the second pump light input to an input port of the polarization beam splitter and the input pump light. An optical circulator for separating the second pump light and the phase conjugate light, and a light for blocking the second pump light from the second pump light and the phase conjugate light separated by the optical circulator and outputting only the phase conjugate light A phase conjugate light generating device comprising a filter and a filter. 13. The phase conjugate light generation device according to claim 11, wherein the phase conjugate light separation means outputs a second pump light input / output to / from an input port of the polarization beam splitter and an output from an input port. A phase conjugate light generator, which is a wavelength multiplexing coupler for separating the phase conjugate light from the light. 14. The phase conjugate light generator according to claim 1, wherein the optical fiber is constituted by a planar optical waveguide.