JP2004151339A - Optical processing equipment and optical amplification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical attenuator which has extremely small polarization mode dispersion and polarization dependency loss and can be made small in sized and light in weight. <P>SOLUTION: A polarization beam splitter 10 polarizes and separating an input light signal into light signals of two substantially orthogonal polarized components and outputs the light signal of one polarized component and the light signal of the other polarized component. A Faraday rotator 11 rotates the plane of polarization of the light signal of the one polarized component by a 1st Faraday rotational angle and outputs the light signal, and a reflecting mirror 12 reflects the light signal to put it back to the polarization beam splitter 10 through the Faraday rotator 11. A Faraday rotator 21 rotates the plane of polarization of the light signal of the other polarized component by a 2nd Faraday rotational angle and outputs the light signal and a reflecting mirror 22 reflects the light signal to put it back to the polarization beam splitter 10 through the Faraday rotator 21. The polarization beam splitter 10 puts together and outputs the light signals which are returned, and varies the Faraday rotational angles to vary the attenuation quantity of the composite light signal. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical processing device such as an optical attenuator or a polarization mode dispersion compensator, and an optical amplification system using the same.
[0002]
[Prior art]
The amplification characteristics of an optical amplifier used in an optical communication system fluctuate due to fluctuations in the input intensity of an optical signal. Further, in the wavelength division multiplexing transmission system, the amplification characteristic also changes when the number of wavelengths of the optical signal input to the optical amplifier is changed. Therefore, a variable optical attenuator is used to keep the optical signal intensity of the optical amplifier constant and stabilize the amplification characteristics. The variable optical attenuator is an element that attenuates the intensity of incident light, and can change the amount of attenuation. Optical components used in ultra-high-speed optical communication systems of 40 Gbit / s or more require extremely small polarization mode dispersion (PMD) and polarization-dependent loss, and are compact. It is desirable that
[0003]
Further, in an ultra-high-speed optical communication system, PMD on an optical fiber transmission line becomes a problem. The degeneracy of the fundamental mode is released when the optical fiber deviates from a perfect circle or a stress is applied, and a group delay time difference occurs due to a difference in the propagation speed of light of two orthogonal polarization components. As a result, since the optical pulse signal is spread, the transmission speed and the transmission distance in the optical communication system are limited. Also, the polarization state becomes an arbitrary polarization state. In order to solve such a problem, a compensation method for controlling the polarization state at the receiving end to generate a group delay time difference opposite to that of the optical fiber transmission line is required.
[0004]
For example, an optical attenuator according to the related art disclosed in Patent Literature 1 includes two polarization beam splitters, an electro-optic element for rotating a plane of polarization of light, and two reflection mirrors. ing. In this optical attenuator, by applying a predetermined voltage to the electro-optical element, the rotation angle of the polarization plane can be adjusted, and the output light intensity can be controlled.
[0005]
[Patent Document 1]
JP 2001-272638 A
[0006]
[Problems to be solved by the invention]
However, in the optical attenuator according to the related art disclosed in Patent Literature 1, it is difficult to obtain an optical attenuator having extremely small PMD and polarization-dependent loss that can withstand an ultra-high-speed optical communication system, and is relatively large. Had become a device. Further, the optical attenuator could not compensate for PMD.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to use an optical processing device such as an optical attenuator having an extremely small PMD and a polarization dependent loss as compared with the conventional technology, and which can be reduced in size and weight. An optical amplification system is provided.
[0008]
Another object of the present invention is to solve the above-mentioned problems, and to provide a PMD compensator which can compensate for PMD with extremely small PMD and polarization dependent loss as compared with the prior art, and which can be reduced in size and weight. Another object of the present invention is to provide an optical processing device.
[0009]
[Means for Solving the Problems]
An optical processing device according to the present invention has first, second, third, and fourth ports, and converts an optical signal input through the first port into two polarization components substantially orthogonal to each other. Polarized light that is polarization-separated into an optical signal and outputs an optical signal of one polarization component via a second port, while outputting an optical signal of the other polarization component via a third port Separation and synthesis means;
A first Faraday rotator that rotates the polarization plane of the optical signal of one polarization component output from the second port of the polarization separation / combination means at a predetermined first Faraday rotation angle, and outputs the first Faraday rotator;
A second Faraday rotator that rotates the polarization plane of the optical signal of the other polarization component output from the third port of the polarization separation / combination means at a predetermined second Faraday rotation angle, and outputs the second Faraday rotator;
First reflection means for reflecting an optical signal output from the first Faraday rotator and returning the reflected light signal to a second port of the polarization separation / combination means via the first Faraday rotator;
A second reflection means for reflecting an optical signal output from the second Faraday rotator and returning the reflected light signal to a third port of the polarization separation / combination means via the second Faraday rotator;
The polarization separation / combination unit combines the optical signal returned to the second port and the optical signal returned to the third port, and combines the optical signal from at least one of the fourth port and the first port. The first and second Faraday rotation angles to change the attenuation of the combined optical signal output from at least one of the fourth port and the first port. It is characterized by making it.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals.
[0011]
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of an optical attenuator 101 according to the first embodiment of the present invention, and FIG. 2 is a perspective view showing an operation of the polarization beam splitter 10 of FIG. The optical attenuator 101 according to the first embodiment includes a polarization beam splitter 10 that is a polarization separation / combination element, two Faraday rotators 11 and 21 that are polarization conversion elements, and two reflection mirrors 12 and 22 is provided.
[0012]
1 and 2, the polarizing beam splitter 10 has a first surface and a second surface facing each other, and has a third surface and a fourth surface facing each other. As shown in FIGS. 1 and 2, the optical signal is incident on the first surface S1 of the polarizing beam splitter 10 via the input port P1, and the respective polarization components of the TE wave and the TM wave substantially orthogonal to each other. The TE signal, which has been separated into optical signals and which has been polarization-separated, is transmitted and output from the second surface S2 to the reflection mirror 12 via the Faraday rotator 11, while the polarization-separated TM wave is output. The optical signal is polarized at right angles, and output from the third surface S3 to the reflection mirror 22 via the reflection mirror 20 and the Faraday rotator 21. That is, the polarization-separated TE wave optical signal passes through the Faraday rotator 11, is reflected by the reflection mirror 12, passes through the Faraday rotator 11 again, and returns to the second surface S2 of the polarization beam splitter 10. Incident. On the other hand, the polarization-separated optical signal of the TM wave passes through the Faraday rotator 21, is reflected by the reflection mirror 22, passes through the Faraday rotator 21 again, and returns to the third surface S3 of the polarization beam splitter 10. Incident. Next, the polarization beam splitter 10 combines the two returning optical signals and outputs the combined signal from the fourth surface S4 via the output port P11.
[0013]
Here, when a predetermined magnetic field is applied from the magnetic field applying device 30 controlled by the controller 40 to both the Faraday rotators 11 and 21, the plane of polarization of the transmitted optical signal is rotated. Therefore, a polarization conversion from the TM wave to the TE wave or vice versa occurs, and the polarization-converted optical signal is combined by the polarization beam splitter 10 and output to the output port P11 as described above. The remaining optical signals become return optical signals to the input port P1. That is, by rotating the polarization planes of the Faraday rotators 11 and 21, the intensity of the output light from the first output port P11 can be controlled. FIG. 3 shows the relationship between the Faraday rotation angle [degree] of the polarization plane in each of the Faraday rotators 11 and 21 and the output light intensity. Assuming that the rotation angle when the optical signal passes through the Faraday rotators 11 and 21 once is θ, the rotation angle is 2θ when the optical signal is reflected by the reflection mirrors 12 and 22 and passes through the Faraday rotators 11 and 21 again. It becomes. For example, when θ is set to 45 degrees, as shown in FIG. 1, when the optical signal of the TE wave passes through the Faraday rotator 11 twice, it becomes an optical signal of the TM wave and is transmitted to the polarization beam splitter 10. When the optical signal of the TM wave passes through the Faraday rotator 21 twice, it returns to the polarization beam splitter 10 as an optical signal of the TE wave. In the case of the electro-optical element according to the related art disclosed in Patent Literature 1, when the optical signal reciprocates, the Faraday rotation angle returns to zero degree, so that the optical signal is folded back as in the present embodiment. No configuration can be used.
[0014]
In the above embodiment, in order to extremely reduce the PMD and the polarization dependent loss in the transmitted optical signal, the position and the rotation angle of each of the reflection mirrors 12 and 22 must be fine when the optical attenuator 101 is manufactured. After the adjustment, the reflection mirrors 12 and 22 may be fixed with an adhesive or the like. As shown in FIG. 4A, the positions of the reflection mirrors 12 and 22 in the optical axis direction are finely adjusted by the respective moving and rotating mechanisms 13 and 23 so as to move in the direction 200 parallel to the optical axis. By finely adjusting the group delay time difference of the polarization, the PMD can be compensated to be, for example, zero. Further, as shown in FIG. 4B, if the angle φ of each of the reflection mirrors 12 and 22 with respect to the optical axis is finely adjusted by each of the moving and rotating mechanisms 13 and 23, the reflection angles of the reflection mirrors 12 and 22 change. Thus, the loss of each polarization can be finely adjusted. With such an adjustment method, the PMD and the polarization dependent loss can be controlled independently of each other, so that both the PMD and the polarization dependent loss can be extremely reduced.
[0015]
As described above, according to the present embodiment, since the optical signals that have passed through the Faraday rotators 11 and 21 are folded back by the reflection mirrors 12 and 22, the positions and angles of the reflection mirrors 12 and 22 are finely adjusted. Accordingly, the PMD and the polarization dependent loss can be extremely reduced, and the optical attenuator 101 can be reduced in size and weight.
[0016]
Embodiment 2 FIG.
FIG. 5 is a block diagram showing a configuration of the optical attenuator 102 according to the second embodiment of the present invention. The optical attenuator 102 according to the second embodiment is different from the optical attenuator 101 according to the first embodiment illustrated in FIG. 1 in that each Faraday rotator 11, 21 is replaced with the magnetic field applying device 30. On the other hand, magnetic field applying devices 31 and 32 controlled by a controller 41 are separately provided. Note that a magnetic field shielding plate 50 for shielding the magnetic field is provided between the Faraday rotators 11 and 21. Hereinafter, these differences will be described in detail.
[0017]
In FIG. 5, since the Faraday rotators 11 and 21 are independently controlled by the magnetic field applying devices 31 and 32, the output light intensity of each polarization can be controlled independently. Generally, an optical amplifier used in an optical communication system has polarization dependence, and the amplification factor for a TM wave and the amplification factor for a TE wave are different. Therefore, the amplification factor varies depending on the polarization state of the incident optical signal. In order to prevent this, it is preferable to control the Faraday rotation angles θ of the respective polarizations independently of each other and control the intensity of the respective polarizations independently.
[0018]
Therefore, according to the present embodiment, in addition to the functions and effects according to the first embodiment, by independently controlling the Faraday rotation angles θ of the Faraday rotators 11 and 21, the output light of each polarization can be obtained. This has a unique effect that the intensity can be controlled independently.
[0019]
Embodiment 3 FIG.
FIG. 6 is a block diagram illustrating a configuration of the optical attenuator 103 according to the third embodiment of the present invention. The optical attenuator 103 according to the third embodiment is different from the optical attenuator 101 according to the first embodiment illustrated in FIG. 1 in that one Faraday rotator 11 and 12 are replaced with one Faraday rotator 11. The Faraday rotator 11a is provided. Hereinafter, these differences will be described in detail.
[0020]
In FIG. 6, one Faraday rotator 11a is shared by the optical transmission lines of each polarization. Therefore, the output light intensity of each polarization cannot be controlled independently. However, since one Faraday rotator 11a is used, one magnetic field applying device 30 for applying a predetermined magnetic field thereto can be used. . Therefore, in the present embodiment, in addition to the operation and effect of the first embodiment, the power consumption of the entire optical attenuator 103 can be reduced, and the size and weight of the optical attenuator 103 can be reduced.
[0021]
Embodiment 4 FIG.
FIG. 7 is a block diagram showing a configuration of the optical attenuator 104 according to the fourth embodiment of the present invention. The optical attenuator 104 according to the fourth embodiment is different from the optical attenuator 101 according to the first embodiment shown in FIG. 1 in that the input port P1 and the first surface S1 of the polarization beam splitter 10 are different from each other. An optical circulator 51 is inserted between them. Hereinafter, these differences will be described in detail.
[0022]
In FIG. 7, the optical signal input to the input port P1 enters the first surface S1 of the polarization beam splitter 10 via the first port P21 and the second port P22 of the optical circulator 51. Further, the remaining optical signal output from the third surface of the polarization beam splitter 10 and different from the optical signal output to the output port P11 is transmitted from the first surface S1 of the polarization beam splitter 10 to the optical circulator 51. The signal is output to the output port P22 via the second port P22 and the third port P23.
[0023]
FIG. 8 is a graph showing the output light intensity of the output port P12 with respect to the Faraday rotation angle θ of the Faraday rotators 11 and 21 in the optical attenuator 104 of FIG. As is clear from FIG. 8, the output light intensity of the optical signal output from the output port P12 has a reverse phase relationship with the change in the Faraday rotation angle θ in the output light intensity to the output port P11 in FIG. Change.
[0024]
As described above, according to the present embodiment, in addition to the functions and effects of the first embodiment, the optical circulator 51 is arranged on the input side of the polarization beam splitter 10, so that the polarization beam splitter 10 Unnecessary return light signal to the input side of the second port can be prevented, and by monitoring the output light intensity from the second output port P12, the amount of light attenuation by the optical attenuator 104 can be grasped. Having.
[0025]
The insertion of the optical circulator 51 in the above embodiment can be applied to other embodiments.
[0026]
Embodiment 5 FIG.
FIG. 9 is a block diagram showing a configuration of the optical attenuator 105 according to the fifth embodiment of the present invention. The optical attenuator 104 according to the fourth embodiment is different from the optical attenuator 101 according to the first embodiment shown in FIG. 1 in that the input port P1 and the first surface S1 of the polarization beam splitter 10 are different from each other. It is characterized in that an optical isolator 52 is inserted between them. Hereinafter, these differences will be described in detail.
[0027]
In FIG. 9, the optical signal input to the input port P1 is incident on the first surface S1 of the polarization beam splitter 10 via the optical isolator 52. The remaining optical signal output from the third surface of the polarization beam splitter 10 and different from the optical signal output to the output port P11 is transmitted from the first surface S1 of the polarization beam splitter 10 to the optical isolator 52. Returning, the optical isolator 52 prevents the return optical signal from being output to the input port P1.
[0028]
As described above, according to the present embodiment, in addition to the functions and effects according to the first embodiment, since the optical isolator 52 is arranged on the input side of the polarization beam splitter 10, the input side This has a unique effect that unnecessary return light can be prevented.
[0029]
The insertion of the optical isolator 52 in the above embodiment can be applied to other embodiments.
[0030]
Embodiment 6 FIG.
FIG. 10 is a block diagram showing a configuration of PMD compensator 106 according to the sixth embodiment of the present invention. The PMD compensator 106 according to the sixth embodiment is different from the optical attenuator 102 according to the second embodiment illustrated in FIG. 5 in that the input port P1 and the first surface S1 of the polarization beam splitter 10 are different from each other. It is characterized in that a polarization controller 60 is inserted between them. Hereinafter, these differences will be described in detail.
[0031]
In FIG. 10, the optical signal input to the input port P1 enters the first surface S1 of the polarization beam splitter 10 via the quarter-wave plate 61 and the half-wave plate 62 of the polarization controller 60. . Here, the polarization controller 60 includes a 波長 wavelength plate 61 and a 波長 wavelength plate 62, and a control applied to the ４ wavelength plate 61 from a controller 63 that controls the polarization controller 60. By adjusting the levels of the signal Sc1 and the control signal Sc2 applied to the half-wave plate 62, the polarization state of the optical signal propagating through each of the wave plates 11 and 12 is adjusted, whereby the input port P1 is adjusted. The polarization state of the optical signal is controlled such that the polarization axis of the optical signal input and propagated through the optical axis substantially coincides with the optical axis of the polarization beam splitter 10.
[0032]
The PMD compensator 106 can output only one polarization component from the output port P11 by controlling the Faraday rotation angles θ of the Faraday rotators 11 and 21. Therefore, an extra optical signal having a group delay time difference can be eliminated, and a clear signal without pulse spread can be output from the output port P11. That is, by controlling the Faraday rotation angles θ of the Faraday rotators 11 and 21, the PMD can be compensated so that the PMD becomes substantially zero.
[0033]
As described above, according to the present embodiment, in addition to the function and effect according to the second embodiment, since only one polarization component of the optical signal having PMD can be output from output port P11, the optical transmission There is a specific effect that the PMD of the optical signal propagating in the path can be compensated.
[0034]
Modification of the sixth embodiment.
In the PMD compensator 106 according to the sixth embodiment illustrated in FIG. 10, a first distance d1 from the polarization beam splitter 10 to the reflection mirror 12 and a second distance d2 from the polarization beam splitter 10 to the reflection mirror 22 Is set to be different from the above (hereinafter, referred to as a modification of the sixth embodiment).
[0035]
In this modified example, a configuration is such that a group delay time difference occurs between the polarizations separated by polarization. The polarization state of an optical signal having a PMD and in an arbitrary polarization state is adjusted by the polarization controller 1, and is converted into a linearly polarized wave that matches the optical axis of the polarization beam splitter 10. For example, when the polarization state is adjusted by the polarization controller 1 so that a group delay time difference opposite to the group delay time difference between respective polarizations generated in the optical transmission line is generated, and the polarization state is input to the polarization beam splitter 10, the polarization Since the distances d1 and d2 from the beam splitter 10 to the reflection mirrors 12 and 22 are differently set for each polarization, an opposite group delay time difference is generated, and the polarization controller 1 is controlled by the controller 63. By controlling, PMD can be compensated to be substantially zero.
[0036]
Embodiment 7 FIG.
FIG. 11 is a block diagram illustrating a configuration of a PMD compensator 107 according to the seventh embodiment of the present invention. The optical attenuator 107 according to the seventh embodiment is different from the PMD compensator 106 according to the sixth embodiment illustrated in FIG. 10 in that the controller 42 controls the movement and rotation of the moving and rotating mechanisms 13 and 23. And the Faraday rotation angle θ of each of the Faraday rotators 11 and 21 is fixed at 45 degrees. Hereinafter, these differences will be described in detail.
[0037]
In FIG. 11, the polarization state of the input optical signal is adjusted by the polarization controller 1 to adjust the polarization state of the optical signal propagating through each of the wave plates 11 and 12, so that the input optical signal is input via the input port P1. The polarization state of the optical signal is controlled so that the polarization axis of the propagating optical signal substantially coincides with the optical axis of the polarization beam splitter 10. On the other hand, since the Faraday rotation angles θ of the Faraday rotators 11 and 21 are fixed at 45 degrees, all the optical signals are output from the first output port P11, so that an extra return optical signal is output to the input port P1. The polarization beam splitter 10 operates as an optical circulator. Further, the controller 42 controls the respective moving and rotating mechanisms 13 and 23 to adjust the two distances d1 and d2, thereby adjusting the group delay time difference of the optical signal, compensating for the PMD of the optical signal, and adjusting the first. Output from the output port P11. Here, since the group delay time difference between the optical signals can be adjusted, the PMD can be precisely compensated to be substantially zero.
[0038]
As described above, according to the present embodiment, in addition to the operation and effect of the PMD compensator 106 according to the sixth embodiment, the polarization beam splitter 10 operates as an optical circulator and returns light to the input port P1 side. The signal is made substantially zero, and the positions of the reflection mirrors 12 and 22 in the optical axis direction are changed by the moving and rotating mechanisms 13 and 23 controlled by the controller 42, so that the group between the polarization components of the optical signal is changed. By adjusting the delay time difference, PMD can be precisely compensated to be substantially zero.
[0039]
Embodiment 8 FIG.
FIG. 12 is a block diagram showing a configuration of the PMD compensator 108 according to the eighth embodiment of the present invention. The optical attenuator 108 according to the eighth embodiment includes an optical fiber cable 14 having a grating instead of the reflection mirror 12, as compared with the PMD compensator 106 according to the sixth embodiment illustrated in FIG. And an optical fiber cable 24 having a grating in place of the reflection mirror 22. Hereinafter, this difference will be described in detail.
[0040]
In FIG. 12, an optical fiber cable 14 is formed by irradiating a predetermined ultraviolet ray to an optical fiber cable having no grating to form a grating having a constant refractive index in the longitudinal direction. . The optical fiber cable 5 is also formed to have a grating substantially similar to that of the optical fiber cable 4. Each of the optical fiber cables 14 and 24 thus formed reflects only a predetermined spectral component of the input optical signal and transmits the remaining optical signal. Therefore, the optical fiber cables 14 and 24 have a so-called predetermined reflection filter function.
[0041]
In the present embodiment, the distances d1 and d2 from the polarizing beam splitter 10 to the gratings of the optical fiber cables 14 and 24 having the respective gratings are set to be different from each other, and the group delay time difference between the separated polarized waves is set. Occurs. In this case, the polarization state of the input optical signal is adjusted, whereby the polarization axis of the optical signal input and propagated through the input port P1 substantially coincides with the optical axis on the polarization beam splitter 10 side. The polarization state of the optical signal is controlled so as to match. Here, the controller 63 adjusts the polarization state by the polarization controller 1 so that the input optical signal has a group delay time difference opposite to the group delay time difference between the respective polarization components in the optical transmission line. Then, the optical signal whose polarization state has been adjusted is input to the polarization beam splitter 10.
[0042]
Next, the optical signal of the TE wave polarized and separated by the polarization beam splitter 10 is incident on an optical fiber cable 14 having a grating via a Faraday rotator 11, and is then band-filtered by the grating to obtain a spectrum corresponding to the grating. Only the optical signal of the component is reflected, and the remaining optical signal is transmitted through the optical fiber cable 14 and output. The reflected optical signal returns to the polarization beam splitter 10 via the Faraday rotator 11 and is input again. On the other hand, the optical signal of the TM wave polarized and separated by the polarization beam splitter 10 is incident on an optical fiber cable 24 having a grating via a Faraday rotator 21 and then band-filtered by the grating to obtain a spectrum corresponding to the grating. Only the optical signal of the component is reflected, and the remaining optical signal is transmitted through the optical fiber cable 24 and output. Only the optical signal of the spectral component corresponding to the grating is reflected after being band-filtered by the grating, and the remaining optical signal is transmitted through the optical fiber cable 24 and output. The reflected optical signal returns to the polarization beam splitter 10 via the Faraday rotator 21 and is input again. Further, the polarization beam splitter 10 combines the two input reflected light signals and outputs the combined signal to the output port P11.
[0043]
In the PMD compensator 108 configured as described above, when PMD does not occur in the optical signal on the optical transmission line, the polarization controller 1 controls the polarization of the optical signal so that only the TE wave or the TM wave is obtained. The wave state is adjusted and input to the polarization beam splitter 10. In this case, since no group delay time difference occurs between the TE wave and the TM wave, PMD is output to the output port P11 while being substantially zero. Further, in the present embodiment, since the optical fiber cables 14 and 24 having gratings are used as reflectors, the PMD compensator 108 has a function of a wavelength filter.
[0044]
As described above, according to the present embodiment, in addition to the functions and effects of the PMD compensator 106 according to the sixth embodiment, each of the optical fiber cables 14 and 24 as the respective reflectors from the polarization beam splitter 10. Are set so as to be different from each other, and by adjusting the polarization controller 1, the PMD of the optical signal can be compensated to be substantially zero. Further, since the grating of each of the optical fiber cables 14 and 24 is used as a reflector, the PMD compensator 108 has a specific effect of having a function as a wavelength filter.
[0045]
Modification of the eighth embodiment.
Although each of the optical fiber cables 14 and 24 in FIG. 12 has a grating having a constant grating period, the present invention is not limited to this, and a chirped grating in which the grating period is changed depending on the position may be used. The optical fiber cable having the chirp grating can also compensate for chromatic dispersion generated in the optical transmission line.
[0046]
Embodiment 9 FIG.
FIG. 13 is a block diagram showing a configuration of a PMD compensator 109 according to the ninth embodiment of the present invention. The PMD compensator 109 according to the ninth embodiment differs from the PMD compensator 108 according to the eighth embodiment illustrated in FIG. 12 in that the polarization controller 1 and the polarization beam splitter 10 It is characterized in that an optical circulator 51 is inserted. Hereinafter, this difference will be described in detail.
[0047]
In FIG. 13, the optical signal from the polarization controller 60 enters the polarization beam splitter 10 via the optical circulator 51, and the return optical signal from the polarization beam splitter 10 outputs the second output signal via the optical circulator 51. Output to port P12. Therefore, according to the present embodiment, in addition to the functions and effects according to the eighth embodiment, since the optical circulator 51 is arranged on the input side of the polarization beam splitter 10, unnecessary return to the input side is performed. An optical signal can be prevented, and if the intensity of the output light from the second output port P12 is monitored, the amount of light attenuation by the PMD compensator 109 can be grasped.
[0048]
Embodiment 10 FIG.
FIG. 14 is a block diagram showing a configuration of a PMD compensator 110 according to the tenth embodiment of the present invention. The PMD compensator 109 according to the ninth embodiment differs from the PMD compensator 108 according to the eighth embodiment illustrated in FIG. 12 in that the polarization controller 1 and the polarization beam splitter 10 It is characterized in that an optical isolator 52 is inserted. Hereinafter, this difference will be described in detail.
[0049]
14, the optical signal from the polarization controller 60 enters the polarization beam splitter 10 via the optical isolator 52, and the return optical signal from the polarization beam splitter 10 returns to the input port P1 side by the optical isolator 52. Is prevented. Therefore, according to the present embodiment, in addition to the functions and effects according to the eighth embodiment, since the optical isolator 52 is arranged on the input side of the polarization beam splitter 10, unnecessary light to the input port P1 side is unnecessary. Return light signals can be prevented.
[0050]
Embodiment 11 FIG.
FIG. 15 is a block diagram showing a configuration of an optical attenuator 111 according to Embodiment 11 of the present invention. The optical attenuator 111 according to the eleventh embodiment is different from the optical attenuator 104 according to the fourth embodiment shown in FIG. A reflection mirror for reflecting an optical signal incident at a reflection angle of 45 degrees; and a Faraday rotator, reflection mirrors and, a Faraday rotator and a reflection mirror from a second surface of the polarization beam splitter. An optical loop circuit is formed up to the third surface S3 of the polarization beam splitter 10 via the first and second optical beams. Hereinafter, this difference will be described in detail.
[0051]
In FIG. 15, an optical signal input from the input port P1 via the optical circulator 51 is incident on the first surface S1 of the deflection beam splitter 10, and the incident optical signal is polarized into TE and TM optical signals. Wave separated. Next, the polarization-separated TE wave optical signal is transmitted through the Faraday rotator 11, the reflection mirror 16, the reflection mirror 17, the Faraday rotator 21, and the reflection mirror 20, to the polarization beam splitter 10, 3, the polarization-separated optical signal of the TM wave is transmitted through the reflection mirror 20, the Faraday rotator 21, the reflection mirror 17, the reflection mirror 16, and the Faraday rotator 11. Then, the light is output to the second surface S2 of the polarization beam splitter 10. Next, the polarization beam splitter 10 multiplexes the input optical signals of the two polarization components, outputs the multiplexed optical signal from the fourth surface S4 to the first output port P11, and multiplexes the multiplexed optical signal. The remaining optical signal is output from the first surface S1 to the second output port P12 via the ports P22 and P23 of the optical circulator 51.
[0052]
FIG. 16 is a graph showing the output light intensity of the output port P11 with respect to the Faraday rotation angles θ of the Faraday rotators 11 and 21 in the optical attenuator 111 of FIG. 15, and FIG. It is a graph which shows the output light intensity of the output port P12 with respect to the Faraday rotation angle (theta) in the rotors 11 and 21. As is clear from FIGS. 16 and 17, by changing the Faraday rotation angles θ of the Faraday rotators 11 and 21, the levels of the optical signals output to the first output port P11 and the second output port P12 are changed. They can be varied, and the levels of these two optical signals are in anti-phase relationship.
[0053]
As described above, according to the present embodiment, each polarization component polarized and separated by the polarization beam splitter 10 passes through the same loop-shaped optical transmission path. If the group delay time and the loss received by the optical signal of each polarization component are different, PMD and polarization dependent loss occur. In the present embodiment, however, the PMD and the loss received by each polarization are the same, No polarization dependent loss occurs in principle. Therefore, it is possible to realize an optical attenuator having very small PMD and polarization-dependent loss and capable of changing the amount of optical attenuation without finely adjusting the position of the reflection mirror and the like.
[0054]
The configuration in which the polarization components separated by the polarization beam splitter 10 in the above embodiment are transmitted through the same loop-shaped optical transmission line is applicable to the optical attenuator in other embodiments. Can be.
[0055]
Embodiment 12 FIG.
FIG. 18 is a block diagram illustrating a configuration of an optical attenuator 112 according to a twelfth embodiment of the present invention. The optical attenuator 112 according to the twelfth embodiment is different from the optical attenuator 111 according to the eleventh embodiment shown in FIG. Was used to form an optical loop circuit from the second surface S2 of the polarization beam splitter 10 to the third surface S3 of the polarization beam splitter 10 via the Faraday rotator 11, the Faraday rotator 21, and the reflection mirror 20. It is characterized by:
[0056]
This embodiment shown in FIG. 18 also has the same function and effect as the eleventh embodiment. In this embodiment, the polarization maintaining optical fiber cable 18 is used, but the present invention is not limited to this, and a single mode optical fiber cable can be used.
[0057]
The configuration in which the polarization components separated by the polarization beam splitter 10 in the above embodiment are transmitted through the same loop-shaped optical transmission line is applicable to the optical attenuator in other embodiments. Can be.
[0058]
Embodiment 13 FIG.
FIG. 19 is a block diagram illustrating a configuration of an optical amplification system 113 according to Embodiment 13 of the present invention. An optical amplification system 113 according to this embodiment includes an optical attenuator 101, an optical directional coupler 70, a controller 80, an optical amplifier 81, and an excitation light source 82.
[0059]
In FIG. 19, an input optical signal is output to an optical amplifier 81 via an optical attenuator 101 and an optical directional coupler 70 whose optical attenuation is controlled by a controller 80. The optical signal inputted is amplified and output using the pumping light from. Here, the optical attenuator 101 is, for example, the optical attenuator according to the first embodiment and the optical attenuators 101, 102, 103, 104, 105, 111, and 112 according to the other embodiments. Is also good. The optical directional coupler 70 includes two optical waveguides 71 and 72 optically coupled to each other. The branch is detected and output to the controller 80. In response, the controller 80 controls the amount of light attenuation of the optical attenuator 101 so that the level of the optical signal whose branch is detected is substantially constant.
[0060]
In general, the amplification characteristics of the optical amplifier 81 fluctuate due to the fluctuation of the intensity of the input optical signal. Therefore, it is necessary to keep the intensity of the optical signal input to the optical amplifier 81 constant. In this embodiment, an optical attenuator 101 is inserted at a stage prior to an optical amplifier 81, and a light intensity branched by an optical directional coupler 70 at a subsequent stage is detected so that the light intensity is kept constant. The intensity of the optical signal input to the optical amplifier 81 can be kept constant by controlling the optical attenuation of the optical attenuator 101 by the controller 80.
[0061]
As described above, according to the present embodiment, for example, the intensity of an optical signal input to the optical amplification system 113 in an optical communication system can be kept constant, and the amplification characteristics of the optical amplifier 81 can be stabilized.
[0062]
Embodiment 14 FIG.
FIG. 20 is a block diagram illustrating a configuration of an optical amplification system 114 according to Embodiment 14 of the present invention. The optical amplification system 114 according to this embodiment includes an optical attenuator 101, an optical directional coupler 70, a controller 80, an optical amplifier 81, and an excitation light source 82.
[0063]
In FIG. 20, a pump light source 82 generates a predetermined pump light and outputs it to an optical amplifier 81 via an optical attenuator 101. The optical signal input to the optical amplification system 114 is amplified by the optical amplifier 81 using the pump light, and is output via the optical directional coupler 70. Here, the optical directional coupler 70 includes two optical waveguides 71 and 72 that are optically coupled to each other, as in FIG. 19, and includes one optical signal output from the optical amplification system 114. The branch is detected and output to the controller 80. In response to this, the controller 80 controls the amount of optical attenuation of the optical attenuator 101 based on the detected optical signal so that the optical intensity of the optical signal becomes constant. The optical attenuator 101 is, for example, the optical attenuator according to the first embodiment, and may be the optical attenuators 101, 102, 103, 104, 105, 111, and 112 according to other embodiments. Good.
[0064]
Generally, in a wavelength division multiplexing transmission system, when the number of wavelengths of an optical signal input to the optical amplification system 114 changes, the amplification characteristics of the optical amplifier 81 change and the output light intensity also changes. Therefore, it is necessary to adjust the light intensity of the pump light source 82 in order to keep the output light intensity of the optical amplifier 81 constant. In the embodiment of FIG. 20, the optical attenuator 101 is inserted after the excitation light source 82, and the light intensity split by the optical directional coupler 70 provided after the optical amplifier 81 is detected. By controlling the optical attenuator 101 by the controller 80 so as to keep the light intensity constant, the intensity of the optical signal output from the optical amplifier 81 can be kept constant.
[0065]
As described above, according to the present embodiment, the output light intensity can be kept constant even when the number of wavelengths of the optical signal input to the optical amplification system 114 in the optical communication system changes. The operation of the optical communication system can be stabilized.
[0066]
【The invention's effect】
As described in detail above, according to the optical processing device of the present invention, the optical processing apparatus has the first, second, third, and fourth ports, and optical signals input through the first port are substantially mutually exchanged. Polarized light is separated into two polarization component optical signals orthogonal to the optical signal, and one polarization component optical signal is output through the second port, while the other polarization component optical signal is converted to the third polarization component optical signal. Polarization separation / combination means for outputting via a port,
A first Faraday rotator that rotates the polarization plane of the optical signal of one polarization component output from the second port of the polarization separation / combination means at a predetermined first Faraday rotation angle, and outputs the first Faraday rotator;
A second Faraday rotator that rotates the polarization plane of the optical signal of the other polarization component output from the third port of the polarization separation / combination means at a predetermined second Faraday rotation angle, and outputs the second Faraday rotator;
First reflection means for reflecting an optical signal output from the first Faraday rotator and returning the reflected light signal to a second port of the polarization separation / combination means via the first Faraday rotator;
A second reflection means for reflecting an optical signal output from the second Faraday rotator and returning the reflected light signal to a third port of the polarization separation / combination means via the second Faraday rotator;
The polarization separation / combination unit combines the optical signal returned to the second port and the optical signal returned to the third port, and combines the optical signal from at least one of the fourth port and the first port. The first and second Faraday rotation angles to change the attenuation of the combined optical signal output from at least one of the fourth port and the first port. Let it.
Therefore, since the two optical signals output from the polarization splitting / combining means are folded back, the position and angle of the two reflecting means are finely adjusted to minimize the polarization mode dispersion and the polarization dependent loss. And an optical attenuator that is small and lightweight can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an optical attenuator 101 according to a first embodiment of the present invention.
FIG. 2 is a perspective view showing an operation of the polarization beam splitter 10 of FIG.
FIG. 3 is a graph showing an output light intensity of an output port P11 with respect to a Faraday rotation angle θ of the Faraday rotators 11 and 21 in the optical attenuator 101 of FIG.
4A and 4B are diagrams showing the operation of moving and rotating mechanisms 13 and 23 for moving and rotating the positions of the reflecting mirrors 12 and 22 in FIG. 1, wherein FIG. FIG. 7B is a diagram when the moving and rotating mechanisms 13 and 23 perform a rotating operation.
FIG. 5 is a block diagram showing a configuration of an optical attenuator 102 according to a second embodiment of the present invention.
FIG. 6 is a block diagram illustrating a configuration of an optical attenuator 103 according to a third embodiment of the present invention.
FIG. 7 is a block diagram illustrating a configuration of an optical attenuator 104 according to a fourth embodiment of the present invention.
8 is a graph showing the output light intensity of the output port P12 with respect to the Faraday rotation angle θ of the Faraday rotators 11 and 21 in the optical attenuator 104 of FIG.
FIG. 9 is a block diagram illustrating a configuration of an optical attenuator 105 according to a fifth embodiment of the present invention.
FIG. 10 is a block diagram showing a configuration of a PMD compensator 106 according to a sixth embodiment of the present invention.
FIG. 11 is a block diagram showing a configuration of a PMD compensator 107 according to a seventh embodiment of the present invention.
FIG. 12 is a block diagram showing a configuration of a PMD compensator 108 according to an eighth embodiment of the present invention.
FIG. 13 is a block diagram showing a configuration of a PMD compensator 109 according to a ninth embodiment of the present invention.
FIG. 14 is a block diagram showing a configuration of a PMD compensator 110 according to a tenth embodiment of the present invention.
FIG. 15 is a block diagram showing a configuration of an optical attenuator 111 according to Embodiment 11 of the present invention.
16 is a graph showing the output light intensity of the output port P11 with respect to the Faraday rotation angles θ of the Faraday rotators 11 and 21 in the optical attenuator 111 of FIG.
17 is a graph showing the output light intensity of the output port P12 with respect to the Faraday rotation angles θ of the Faraday rotators 11 and 21 in the optical attenuator 111 of FIG.
FIG. 18 is a block diagram illustrating a configuration of an optical attenuator 112 according to a twelfth embodiment of the present invention.
FIG. 19 is a block diagram showing a configuration of an optical amplification system 113 according to Embodiment 13 of the present invention.
FIG. 20 is a block diagram illustrating a configuration of an optical amplification system 114 according to Embodiment 14 of the present invention.
[Explanation of symbols]
Reference Signs List 10 polarizing beam splitter, 11, 11a, 21 Faraday rotator, 12, 22 reflection mirror, 13, 23 moving rotation mechanism, 14, 24 optical fiber cable having grating, 18 optical fiber cable, 20 reflection mirror, 30, 31, 32 magnetic field applying device, 40, 41, 42 controller, 50 magnetic field shielding plate, 51 optical circulator, 52 optical isolator, 60 polarization controller, 61 1/4 wavelength plate, 62 1/2 wavelength plate, 63 controller, 70 light Directional coupler, 71, 72 optical waveguide, 80 controller, 81 optical amplifier, 82 pumping light source, 101, 102, 103, 104, 105, 111, 112 optical attenuator, 106, 107, 108, 109, 110 PMD compensation , 113,114 Optical amplification system, P1 input port, P11, P12 Output ports, S1 first plane, S2 second plane, S3 third plane, S4 fourth plane, T1, T2, T3, T4 ports.

Claims (18)

It has first, second, third, and fourth ports, and separates the polarization of an optical signal input through the first port into two polarization component optical signals that are substantially orthogonal to each other. A polarization separation / combination unit that outputs an optical signal of one polarization component via a second port, and outputs an optical signal of the other polarization component via a third port;
A first Faraday rotator that rotates the polarization plane of the optical signal of one polarization component output from the second port of the polarization separation / combination means at a predetermined first Faraday rotation angle, and outputs the first Faraday rotator;
A second Faraday rotator that rotates the polarization plane of the optical signal of the other polarization component output from the third port of the polarization separation / combination means at a predetermined second Faraday rotation angle, and outputs the second Faraday rotator;
First reflection means for reflecting an optical signal output from the first Faraday rotator and returning the reflected light signal to a second port of the polarization separation / combination means via the first Faraday rotator;
A second reflection means for reflecting an optical signal output from the second Faraday rotator and returning the reflected light signal to a third port of the polarization separation / combination means via the second Faraday rotator;
The polarization separation / combination unit combines the optical signal returned to the second port and the optical signal returned to the third port, and combines the optical signal from at least one of the fourth port and the first port. The first and second Faraday rotation angles to change the attenuation of the combined optical signal output from at least one of the fourth port and the first port. An optical processing apparatus characterized in that the light processing is performed. It has first, second, third, and fourth ports, and separates the polarization of an optical signal input through the first port into two polarization component optical signals that are substantially orthogonal to each other. A polarization separation / combination unit that outputs an optical signal of one polarization component via a second port, and outputs an optical signal of the other polarization component via a third port;
A first Faraday rotator that rotates the polarization plane of the optical signal of one polarization component output from the second port of the polarization separation / combination means at a predetermined first Faraday rotation angle, and outputs the first Faraday rotator;
A second Faraday rotator that rotates the polarization plane of the optical signal of the other polarization component output from the third port of the polarization separation / combination means at a predetermined second Faraday rotation angle, and outputs the second Faraday rotator;
The optical signal output from the first Faraday rotator is returned to the second port of the polarization splitting / synthesizing means via the second Faraday rotator, and is output from the second Faraday rotator. An optical transmission line means for returning an optical signal to the third port of the polarization splitting / combining means via the first Faraday rotator;
The polarization separation / combination unit combines the optical signal returned to the second port and the optical signal returned to the third port, and combines the optical signal from at least one of the fourth port and the first port. The first and second Faraday rotation angles to change the attenuation of the combined optical signal output from at least one of the fourth port and the first port. An optical processing apparatus characterized in that the light processing is performed. 3. An optical processing apparatus according to claim 2, wherein said optical transmission path means includes a plurality of reflection means. 4. The apparatus according to claim 1, further comprising a first control unit that controls the first Faraday rotator and the second Faraday rotator in a similar manner. 5. Light processing equipment. 4. The apparatus according to claim 1, further comprising a second control unit that independently controls the first Faraday rotator and the second Faraday rotator. 5. Light processing equipment. The optical processing device according to claim 1, wherein the first Faraday rotator and the second Faraday rotator are formed by one Faraday rotator. An input optical signal is provided at a stage prior to the first port of the polarization separation / combination means, and is output to the first port of the polarization separation / combination means, while the first port of the polarization separation / combination means is provided. 7. The optical circulator according to claim 1, further comprising: an optical circulator that outputs an optical signal output from a port different from the port of the input optical signal. Light processing equipment. An optical isolator, which is provided at a stage prior to the first port of the polarization separation / combination means and outputs an input optical signal to the first port of the polarization separation / combination means, is further provided. The optical processing device according to any one of 1 to 7. In an optical amplification system including an optical amplifier that amplifies an optical signal using excitation light from an excitation light source,
An optical amplification system comprising the optical processing device according to any one of claims 1 to 8, which processes the optical signal before the optical amplifier. 10. The light according to claim 9, further comprising control means for controlling the amount of light attenuation of the light processing device so that the light intensity of the optical signal output from the light processing device is substantially constant. Amplification system. In an optical amplification system including an optical amplifier that amplifies an optical signal using excitation light from an excitation light source,
An optical amplification system comprising the optical processing device according to any one of claims 1 to 8, which processes the excitation light between the excitation light source and the optical amplifier. 12. The optical amplifier according to claim 11, further comprising control means for controlling an optical attenuation of the optical processing device so that the optical intensity of the optical signal output from the optical amplifier is substantially constant. system. It is provided before the first port of the polarization separation / combination means, adjusts the polarization state of the input optical signal, and the polarization axis of the optical signal corresponds to the first port of the polarization separation / combination means. Polarization control means for controlling the polarization state of the optical signal so as to substantially coincide with the optical axis,
2. The optical processing apparatus according to claim 1, wherein the polarization mode dispersion is compensated by changing the first and second Faraday rotation angles. Polarization control means provided before the first port of the polarization separation / combination means for adjusting the polarization state of an input optical signal,
The second port of the polarization separation / combination means returns to the second port of the polarization separation / combination means via the first Faraday rotator, the first reflection means, and the first Faraday rotator. A first distance from the third port of the polarization separation / combination means via the second Faraday rotator, the second reflection means, and the second Faraday rotator; The second distance back to the third port is set to be different from each other;
2. The optical processing apparatus according to claim 1, further comprising control means for compensating for polarization mode dispersion by controlling said polarization control means. It is provided before the first port of the polarization separation / combination means, adjusts the polarization state of the input optical signal, and the polarization axis of the optical signal corresponds to the first port of the polarization separation / combination means. Polarization control means for controlling the polarization state of the optical signal so as to substantially coincide with the optical axis,
Control means for compensating for polarization mode dispersion by changing the position of the first reflecting means in the optical axis direction and the position of the second reflecting means in the optical axis direction is further provided. The optical processing device according to claim 1. 15. The optical processing device according to claim 14, wherein the first and second reflection means are optical fiber cables having a grating. The polarization control means is provided between the polarization control means and the first port of the polarization separation / combination means, and outputs an optical signal from the polarization control means to the first port of the polarization separation / combination means; 17. The optical circulator according to claim 16, further comprising an optical circulator for outputting an optical signal output from a first port of the polarization splitting / combining means from a port different from a port of the input optical signal. Light processing equipment. An optical isolator that is provided between the polarization control means and a first port of the polarization separation / combination means and outputs an optical signal from the polarization control means to a first port of the polarization separation / combination means; The optical processing device according to claim 16, further comprising:

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