JP6092745B2 - Optical transmission equipment - Google Patents

Description

  The present invention relates to an optical transmission apparatus capable of performing at least one of insertion and separation of a specific mode in order to realize mode multiplexing transmission of signal light.

  In recent years, in optical fiber communication, spatial multiplexing (mode multiplexing) transmission technology has attracted attention in addition to wavelength multiplexing and polarization multiplexing as a technology for increasing the transmission capacity compared to the prior art. An existing optical network using a single mode fiber (SMF) is constructed by providing an optical wavelength insertion / separation device at each network base. The optical wavelength inserting / separating device separates an optical signal having a specific wavelength from a wavelength multiplexed optical signal transmitted by the SMF, and inserts (multiplexes) an optical signal having a specific wavelength into the wavelength multiplexed optical signal. Used for.

  In the future, when the mode multiplexing transmission technology is applied to the optical network, the optical signal of a specific mode is separated from the mode multiplexed optical signal at each network base as well as the wavelength optical signal. Therefore, it is required that an optical signal of a specific mode can be inserted. As described above, conventionally, there are techniques as described in Non-Patent Documents 1 to 3 as techniques for separating or inserting optical signals of respective modes in mode multiplexing transmission. Non-Patent Document 1 describes a technique for inserting an optical signal of a specific mode using a computer-generated hologram. Non-Patent Document 2 describes a technique for inserting an optical signal of a specific mode by arbitrarily switching interference fringes using a spatial light modulator (SLM). Non-Patent Document 3 describes a technique for separating an optical signal of a specific mode using a volume hologram.

F. Dubois, Ph. Emplit, and O. Hugon, “Selective Mode Excitation in Grated-Index Multimode Fiber by a Computer -Generated Optical Mask”, Optics Letters, Vol. 19, Issue 7, pp. 433-435 (1994) . A. Okamoto, K. Aoki, Y. Wakayama, D. Soma, and T. Oda, “Multi-Excitation of Spatial Modes using Single Spatial Light Modulator for Mode Division Multiplexing,” in National Fiber Optic Engineers Conference, OSA Technical Digest ( Optical Society of America, 2012), paper JW2A.38. A. Okamoto, K. Morita, Y. Wakayama, J. Tanaka, K. Sato, “Mode division multiplex communication technique based on dynamic volume hologram and phase conjugation,” Photonics in Europe 2010, proc. Vol.7716, (2010) . Junichi Sakai, “Phase Conjugation Optics”, Asakura Shoten, November 1990

  However, the conventional techniques as described above have the following problems. For example, when a signal light of a specific mode is separated from a mode multiplexed optical signal by displaying a pattern capable of diffracting the signal light of a specific mode on the SLM, the signal light of a mode other than the specific mode is transmitted to the SLM. As it passes, its phase distribution changes.

  Here, as shown in FIG. 2, it is assumed that the LP01, LP11, and LP21 mode signal light propagating in the optical fiber is incident on the SLM on which the pattern for diffracting the LP11 mode signal light is generated and displayed. To do. In this case, the LP11 mode signal light is diffracted by the pattern displayed on the SLM, whereby the LP11 mode signal light can be separated from the other mode signal lights. The mode of the separated signal light is converted to LP01 instead of LP11, and LP01 and LP21 mode signal lights other than LP11 are transmitted (passed) through the SLM as they are. However, since the phase distribution of the LP11 and LP21 mode signal light that has passed through the SLM changes due to the action of the SLM, there is a problem that the signal quality is extremely deteriorated.

  The present invention has been made in view of the above-described problems. The present invention provides a technique for performing insertion and separation of a specific mode of signal light using a spatial light modulator without degrading the quality of the signal light of another mode in mode multiplexed transmission of signal light. It is an object.

  The present invention can be realized as an optical transmission device, for example. An optical transmission device according to an aspect of the present invention includes an optical output unit that outputs one or more modes of signal light that has propagated through an optical fiber, and a position at which the signal light output from the optical output unit is incident A spatial light modulator that displays a diffraction pattern that diffracts signal light of a specific mode and transmits signal light of a mode other than the specific mode, and that is incident on the diffraction pattern When the signal light of the specific mode is included in the signal light of the specific mode, the spatial light is separated from the signal light of the other mode by diffracting the signal light of the specific mode by the diffraction pattern When the signal light transmitted through the diffraction pattern is incident on the modulator and the spatial light modulator in the propagation direction of the signal light output from the light output unit, the propagation of the incident signal light A phase conjugate mirror that generates phase conjugate light propagating in a direction opposite to the direction, and the phase conjugate light transmits the diffraction pattern displayed on the spatial light modulator in the opposite direction, The signal light in the other mode is input from the light output unit into the optical fiber.

  According to the present invention, in mode multiplexing transmission of signal light, there is provided a technique for inserting and separating a specific mode of signal light using a spatial light modulator without degrading the quality of the signal light of other modes. it can.

The figure which shows the structural example of an optical transmission apparatus. The figure which shows an example of isolation | separation of the signal light of a specific mode using SLM. Explanatory drawing for demonstrating the mechanism which compensates the change of the phase distribution in an optical transmission apparatus. The figure which shows the example which inserts the signal light of a specific mode in an optical transmission apparatus. The figure which shows the structural example of the optical transmission apparatus provided with the optical circulator. The figure which shows the structural example of the optical transmission apparatus provided with the some optical circulator. The figure which shows the example which isolate | separates the signal light of a some specific mode in an optical transmission apparatus. The figure which shows the example which isolate | separates and inserts the signal light of a several specific mode in an optical transmission apparatus. The figure which shows the structural example of the optical transmission apparatus provided with the optical circulator.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

  FIG. 1 is a diagram illustrating a configuration example of an optical transmission apparatus 100 according to an embodiment of the present invention, and particularly illustrates a configuration example of a portion that performs separation (dropping) on signal light in a specific mode. As shown in FIG. 1, the optical transmission device 100 includes an optical output unit 120 that outputs signal light in one or more modes that have propagated through the optical fiber 110, a spatial light modulator (SLM) 130, a phase A conjugate mirror 140. The SLM 130 is provided at a position where the signal light output from the light output unit 120 is incident. The phase conjugate mirror 140 is provided at the subsequent stage of the SLM 130 in the propagation direction of the signal light output from the light output unit 120. In the present embodiment, the optical fiber 110 is configured by a multimode fiber (MMF) that is an optical fiber capable of propagating a plurality of spatial mode signal lights. In addition to the SLM 130, a half-wave plate (HWP: Half Wave Plate), a polarizer P, and an analyzer A are also provided on the optical path from the light output unit 120 to the phase conjugate mirror 140. The polarization state of is adjusted.

  The SLM 130 can display a diffraction pattern that diffracts signal light of a specific mode and transmits signal light of a mode other than the specific mode. The SLM 130 can generate an arbitrary diffraction pattern in accordance with control from the outside, and can display the generated diffraction pattern. When the signal light of one or more modes output from the light output unit 120 is incident on the diffraction pattern displayed on the SLM 130, the signal light of the mode that can be diffracted by the diffraction pattern displayed on the SLM 130 is predetermined. Diffracted at a diffraction angle. In addition, signal light in other modes passes through the diffraction pattern displayed on the SLM 130 and propagates to the subsequent stage of the SLM 130. In this way, signal light in a specific mode can be separated from signal light in other modes.

  In FIG. 1, the LP01, LP11, and LP21 mode signal lights that have propagated through the optical fiber 110 are output from the light output unit 120 and enter the SLM 130. The SLM 130 displays a diffraction pattern capable of diffracting LP11 mode signal light. For this reason, the SLM 130 diffracts only the LP11 mode signal light among the LP01, LP11, and LP21 mode signal lights incident on the diffraction pattern and separates them from the other mode signal lights.

  On the other hand, LP01 and LP21 mode signal lights other than LP11 are transmitted through the SLM 130. In the signal light transmitted through the diffraction pattern of the SLM 130, a phase distribution change occurs (that is, the phase distribution is lost) as shown in FIG. For this reason, the signal light of the remaining mode light after the signal light of a specific mode is separated by the SLM 130 is in a state where signal quality is extremely deteriorated.

  In the present embodiment, a phase conjugate mirror 140 is used as shown in FIG. 1 in order to compensate for the change in the phase distribution as described above. FIG. 3 is an explanatory diagram for explaining a mechanism for compensating for the change in phase distribution as described above using the phase conjugate mirror 140. The phase conjugate mirror 140 inverts the wavefront of the light incident on the reflecting surface to generate phase conjugate light (see, for example, Non-Patent Document 4).

  As shown in FIG. 3, when the signal light transmitted through the SLM 130 enters the phase conjugate mirror 140, the phase conjugate mirror 140 propagates in the opposite direction (arrow 320) to the propagation direction of the signal light (arrow 310). Phase conjugate light is generated. The phase conjugate light generated by the phase conjugate mirror 140 transmits the diffraction pattern displayed on the SLM 130 again in the direction of the arrow 320. As a result, the phase change caused in the signal light by the first transmission from the optical output unit 120 side to the phase conjugate mirror 140 side is changed to the second transmission from the phase conjugate mirror 140 side to the optical output unit 120 side. Is compensated by The signal light transmitted again through the SLM 130 is restored to the signal light of the original mode pattern, that is, the signal light of the remaining modes other than the specific mode separated by the SLM 130 is again transmitted from the optical output unit 120 to the optical fiber 110. It is input in.

  Specifically, in FIG. 1, the signal light in the LP01 and LP21 modes other than the LP11 mode separated by the SLM 130 is restored to the signal light of the original mode pattern in which the change in the phase distribution is compensated. The light is input from the light output unit 120 into the optical fiber 110. As described above, according to the present embodiment, it is possible to separate the signal light of a specific mode by the SLM 130 without causing signal quality degradation in the signal light of other modes.

  Although not shown in FIG. 1, the optical transmission device 100 includes an optical output unit for outputting signal light in a mode other than a specific mode, separated by diffraction in the diffraction pattern displayed on the SLM 130. The signal light may be provided in the direction in which it is diffracted.

  In the optical transmission apparatus 100 according to the present embodiment, not only the separation of the signal light in the specific mode as described above, but also the insertion (add) of the signal light in the specific mode is performed using the configuration shown in FIG. ) Is also possible. FIG. 4 is a diagram illustrating an example in which signal light of a specific mode is inserted in the optical transmission device 100. In the drawing, an example in which LP11 mode signal light is inserted (multiplexed) in the optical transmission apparatus 100 with respect to LP01 and LP21 mode signal light propagating through the optical fiber 110 is shown as an example.

  In this case, the SLM 130 may be provided with an interference pattern that can generate the LP11 mode. That is, the SLM 130 may display a diffraction pattern that diffracts the LP11 mode signal light. In this state, when the signal light is irradiated to the diffraction pattern from the direction opposite to the diffraction direction of the signal light by the diffraction pattern of the SLM 130 (the direction of the arrow 410), LP11 mode signal light corresponding to the diffraction pattern is emitted. Occurs in the direction of the light output unit 120. The LP11 mode signal light generated in this way is input into the optical fiber 110 from the optical output unit 120 in a state multiplexed with the signal light of other modes (LP01, LP21).

  At this time, for the LP01 and LP21 mode signal lights, the phase distribution change by the SLM 130 is compensated by the action of the phase conjugate mirror 140 as in the case of the separation shown in FIG. Therefore, according to the present embodiment, it becomes possible to insert (multiplex) signal light of a specific mode by the SLM 130 without causing signal quality degradation in signal light of other modes.

  In the optical transmission apparatus 100 according to the present embodiment, it is possible to simultaneously perform the separation and insertion of signal light in a specific mode using the SLM 130 shown in FIGS. 1 and 4. In this case, as shown in FIG. 1, the SLM 130 separates the first signal light in the specific mode (LP11) output from the light output unit 120, and as shown in FIG. Multiplexing for the second signal light in the mode (LP11) is performed.

  Further, the optical transmission device 100 according to the present embodiment can be arranged on the optical transmission line by using an optical circulator. FIG. 5 is a diagram illustrating a configuration example of the optical transmission device 100 including the optical circulator 150. In the figure, LP01, LP11, LP21 three-mode signal light is input to the optical transmission apparatus 100, the optical transmission apparatus 100 separates the LP01 mode signal light, and the remaining LP11, LP21 mode signal light. The example which outputs is shown.

  As shown in FIG. 5, the optical transmission device 100 includes an optical circulator 150. The optical circulator 150 is an element that outputs signal light input from the first port to the second port and outputs signal light input from the second port to the third port. In the present embodiment, the second port of the optical circulator 150 is connected to the optical output unit 120 via the optical fiber 110, and the first port and the third port are the input port of the optical transmission device 100 and Each functions as an output port.

  In the optical transmission device 100 shown in FIG. 5, when signal light of one or more modes (LP01, LP11, LP21) is input from the first port of the optical circulator 150, the signal light is output to the optical output unit. 120. As a result, the LP01 mode signal light is separated by the SLM 130 as shown in FIG. Further, the remaining signal light in the LP11 and LP21 modes is returned into the optical fiber 110 via the optical output unit 120 in a state where the change in phase distribution by the SLM 130 is compensated. As a result, the LP01, LP11, and LP21 mode signal light input from the first port of the optical circulator 150 is output from the third port of the optical circulator 150 in a state where the LP01 mode signal light is separated. Is done.

  In the optical transmission device 100 shown in FIG. 5, it is also possible to insert signal light of a specific mode by the SLM 130 as shown in FIG. That is, the LP01, LP11, and LP21 mode signal lights input from the first port of the optical circulator 150 are subjected to at least one of separation and insertion of the LP01 mode signal light. It can be output from the third port.

  Further, by changing the configuration shown in FIG. 5 to the configuration shown in FIG. 6, in the optical transmission apparatus 100, it is possible to simultaneously perform separation and insertion of a plurality of specific mode signal lights. FIG. 6 is a diagram illustrating an example of separating or inserting a plurality (N) of signal light in a specific mode in the optical transmission device 100 including a plurality (N) of optical circulators 150-1 to 150-N. is there. In the figure, three modes of signal light LP01, LP11, and LP21 are input to the optical transmission apparatus 100, and the optical transmission apparatus 100 is subjected to signal light separation and insertion by the SLMs 130-1 to 130-N. In this example, signal light in the LP01 ′, LP11 ′, and LP21 ′ modes is output.

  As shown in FIG. 6, the optical transmission apparatus 100 includes N optical circulators 150-1 to 150-N connected in cascade (N is an integer of 2 or more) and N optical circulators corresponding to the optical circulators. Optical output units 120-1 to 120-N, N SLMs 130-1 to 130-N, and phase conjugate mirrors 140-1 to 140-N. The third ports of the optical circulators 150-1 to 150- (N-1) are connected to the first port of the next-stage optical circulator. The first port of the optical circulator 150-1 functions as an input port of the optical transmission device 100, and the third port of the optical circulator 150-N functions as an output port of the optical transmission device 100.

  The optical output units 120-1 to 120-N are connected to the second ports of the corresponding optical circulators 150-1 to 150-N via optical fibers. In addition, the SLMs 130-1 to 130-N display diffraction patterns corresponding to different specific modes in accordance with external control.

  In the optical transmission device 100 shown in FIG. 6, signal light of one or more modes (LP01, LP11, LP21) is input from the first port of the optical circulator 150-1. These signal lights are subjected to at least one of separation and insertion (multiplexing) with respect to each specific mode of signal light corresponding to each diffraction pattern displayed by the SLMs 130-1 to 130-N. The resulting signal light in the LP01 ′, LP11 ′, and LP21 ′ modes is output from the third port of the optical circulator 150-N. Similar to the embodiment shown in FIG. 5 described above, the signal light in the LP01 ′, LP11 ′, and LP21 ′ modes is output in a state where changes in the phase distribution by the SLMs 130-1 to 130-N are compensated.

  According to the embodiment shown in FIG. 6, it is possible to selectively execute insertion and separation of signal light in a plurality of modes by controlling the diffraction patterns displayed on each of the SLMs 130-1 to 130-N. It is.

  As described below, the above-described embodiment can be implemented with various modifications. Hereinafter, an example in which a single SLM 130 performs separation and insertion (multiplexing) on signal light in a plurality of specific modes will be described with reference to FIGS.

  FIG. 7 is a diagram illustrating an example in which signal light in a plurality of specific modes is separated in the optical transmission device 100. As shown in the figure, the SLM 130 displays a combined pattern obtained by combining a plurality of diffraction patterns that diffract signal lights of different specific modes as a diffraction pattern, thereby simultaneously separating the signal lights of a plurality of modes. Is possible.

  In FIG. 7, the SLM 130 generates and displays a combined pattern obtained by combining patterns that can diffract LP11 and LP21 mode signal lights. The LP01, LP11, and LP21 mode signal lights propagating through the optical fiber 110 are output from the optical output unit 120 and enter the SLM 130. The SLM 130 separates the signal light in the other modes (LP01) by diffracting the signal light in the LP11 and LP21 modes corresponding to the composite pattern among the signal lights incident on the composite pattern.

  On the other hand, the remaining LP01 mode signal light is input from the light output unit 120 into the optical fiber 110 in a state where the signal light has been restored to the original mode pattern signal light in which the change in the phase distribution is compensated. As described above, according to the embodiment shown in FIG. 7, it is possible to separate the signal light in a plurality of specific modes by the SLM 130 without causing signal quality degradation in the signal light in other modes. .

  Note that the SLM 130 may display a combined pattern in which interference fringes of a plurality of diffraction patterns are set at different pitches. In this case, the SLM 130 diffracts a plurality of specific modes of signal light corresponding to the combined pattern at different diffraction angles. As a result, it is possible to individually extract the separated signal lights in a plurality of modes.

  In addition, in the optical transmission device 100 shown in FIG. 7, not only the signal light of a plurality of specific modes but also the insertion can be performed at the same time. FIG. 8 is a diagram illustrating an example in which signal light of a plurality of specific modes is separated and inserted in the optical transmission device 100. In FIG. 8, the SLM 130 separates the signal light of a specific mode (LP11) output from the optical output 120 and simultaneously inserts the signal light of another specific mode (LP21). In this manner, the SLM 130 displays a composite pattern corresponding to a plurality of specific modes, thereby performing at least one of separation and insertion for each specific mode of signal light corresponding to the composite pattern.

  FIG. 9 is a diagram illustrating a configuration example of the optical transmission device 100 including the optical circulator 150, as in FIG. However, FIG. 9 shows an example in which a combined pattern obtained by combining a plurality of diffraction patterns that diffract signal light in different specific modes is displayed on the SLM 130 as a diffraction pattern, as in FIGS. 7 and 8. With such a configuration, the signal light input from the first port of the optical circulator 150 is subjected to at least one of separation and insertion with respect to each specific mode of signal light corresponding to the combined pattern displayed on the SLM 130. In this state, the light is output from the third port of the optical circulator 150.

  According to the embodiment shown in FIG. 9, it is possible to separate and insert a plurality of modes of signal light by using one SLM 130. That is, as shown in FIG. 6, it is not necessary to provide a plurality of SLMs and phase conjugate mirrors, and a simpler device configuration can be realized.

  According to the various embodiments described above, in mode multiplexing transmission of signal light, insertion and separation of signal light in a specific mode using the SLM can be performed without degrading the quality of signal light in other modes. It becomes possible. Thus, it is possible to separate and insert a required number of modes of signal light at each site in the optical network. Therefore, mode separation and insertion can be performed in mode multiplexing transmission, as in the case of wavelength separation and insertion in the conventional wavelength division multiplexing technique.

Claims (10)

An optical output unit for outputting one or more modes of signal light propagating in the optical fiber;
Spatial light that is provided at a position where the signal light output from the light output unit is incident, diffracts the signal light of a specific mode, and displays a diffraction pattern that transmits signal light of a mode other than the specific mode When the signal light of the specific mode is included in the one or more modes of signal light incident on the diffraction pattern, the modulator diffracts the signal light of the specific mode with the diffraction pattern. Separating the spatial light modulator from the signal light of the other mode;
In the propagation direction of the signal light output from the light output unit, when the signal light that has been transmitted through the diffraction pattern is incident on the propagation direction of the incident signal light with respect to the propagation direction A phase conjugate mirror that generates phase conjugate light propagating in the opposite direction;
The phase conjugate light passes through the diffraction pattern displayed on the spatial light modulator in the reverse direction, and is input as signal light of the other mode from the light output unit into the optical fiber. A characteristic optical transmission device. The spatial light modulator is configured to propagate the signal in the specific mode propagating in the opposite direction to the propagation direction when the signal light is irradiated from the opposite direction to the diffraction direction of the signal light by the diffraction pattern. The signal light is generated, and the signal light of the specific mode is input from the light output unit into the optical fiber in a state of being multiplexed with the signal light of the other mode. An optical transmission device according to 1.   The spatial light modulator performs the separation on the first signal light in the specific mode output from the light output unit and the multiplexing on the second signal light in the specific mode. The optical transmission device according to claim 2. An optical circulator that outputs the signal light input from the first port to the second port and outputs the signal light input from the second port to the third port;
A second port of the optical circulator is connected to the optical output unit via the optical fiber;
The signal light of the one or more modes is input from the first port of the optical circulator, and the signal light of the specific mode is separated from the third port of the optical circulator. The optical transmission device according to claim 1, wherein the optical transmission device is output. An optical circulator that outputs the signal light input from the first port to the second port and outputs the signal light input from the second port to the third port;
A second port of the optical circulator is connected to the optical output unit via the optical fiber;
The signal light in the one or more modes is input from a first port of the optical circulator, and the light in the state in which at least one of the separation and multiplexing is performed on the signal light in the specific mode The optical transmission device according to claim 2, wherein the optical transmission device is output from a third port of the circulator. The optical transmission device is:
N optical cascades (N is an integer of 2 or more) connected in cascade;
N optical output units individually provided for the N optical circulators, each connected to a second port of a different optical circulator via an optical fiber;
N spatial light modulators provided individually for the N light output units, each displaying the diffraction pattern corresponding to a different specific mode;
N phase conjugate mirrors individually provided for the N spatial light modulators,
Of the N optical circulators, the third port of each optical circulator excluding the Nth optical circulator is connected to the first port of the next-stage optical circulator,
The signal light of the one or more modes is input from a first port of the first optical circulator among the N optical circulators, and corresponds to each diffraction pattern displayed by the N spatial light modulators. 6. The signal output from the third port of the Nth optical circulator in a state where at least one of the separation and the multiplexing for the signal light in each specific mode is performed. The optical transmission device described. The spatial light modulator is
A combined pattern obtained by combining a plurality of diffraction patterns that diffract signal light in different specific modes is displayed as the diffraction pattern,
Of the one or more modes of signal light output from the light output unit, the plurality of specific modes are diffracted by the composite pattern in a plurality of specific modes corresponding to the composite pattern. The optical transmission apparatus according to claim 1, wherein the signal light is simultaneously separated from the signal light of the other mode.   The spatial light modulator displays, as the diffraction pattern, a combined pattern obtained by combining a plurality of diffraction patterns that diffract signal light of different specific modes, and the signal light of each specific mode corresponding to the combined pattern. 4. The optical transmission device according to claim 2, wherein at least one of the separation and the multiplexing is performed. An optical circulator that outputs the signal light input from the first port to the second port and outputs the signal light input from the second port to the third port;
A second port of the optical circulator is connected to the optical output unit via the optical fiber;
The signal light of the one or more modes is input from the first port of the optical circulator, and at least one of the separation and the multiplexing is performed on the signal light of each specific mode corresponding to the synthesis pattern. 9. The optical transmission device according to claim 8, wherein the optical transmission device is output from the third port of the optical circulator in a state where   The spatial light modulator displays a combined pattern in which the interference fringes of the plurality of diffraction patterns are set at different pitches, and displays a plurality of specific mode signal lights corresponding to the combined pattern. The optical transmission device according to claim 7, wherein the optical transmission device is diffracted at a folding angle.