Optical Power Adjustment System and Optical Power Adjustment Apparatus

Abstract

Embodiments of this application provide an optical power adjustment system and an optical power adjustment apparatus. The system includes a multi-mode light source, a mode demultiplexer, and an optical power adjustment apparatus. The multi-mode light source is configured to output a multi-mode optical signal, where the multi-mode optical signal includes N transverse-mode optical signals, N=2.sup.M, and M is an integer greater than 1. The mode demultiplexer is configured to convert the N transverse-mode optical signals into N fundamental-mode optical signals, and output the N fundamental-mode optical signals. The optical power adjustment apparatus includes M optical power adjustment modules and a control apparatus, each optical power adjustment module includes a plurality of phase shifters, and the control apparatus is electrically connected to the M optical power adjustment modules. A K.sup.th optical power adjustment module includes 2.sup.K1 multi-mode interferometers MMIs.

Claims

1. An optical power adjustment system, comprising: a multi-mode light source, a mode demultiplexer, and an optical power adjustment apparatus, wherein an output port of the multi-mode light source is connected to an input port of the mode demultiplexer, and an output port of the mode demultiplexer is connected to an input port of the optical power adjustment apparatus; the multi-mode light source is configured to output a multi-mode optical signal, wherein the multi-mode optical signal comprises N transverse-mode optical signals, N=2M, and M is an integer greater than 1; the mode demultiplexer is configured to convert the N transverse-mode optical signals into N fundamental-mode optical signals, and output the N fundamental-mode optical signals; the optical power adjustment apparatus comprises M optical power adjustment modules and a control apparatus, each optical power adjustment module comprises a plurality of phase shifters, the control apparatus is electrically connected to the M optical power adjustment modules, the M optical power adjustment modules are sequentially arranged from the input port of the optical power adjustment apparatus to an output port of the optical power adjustment apparatus, and the M optical power adjustment modules are connected together in series; and a K.sup.th optical power adjustment module in the optical power adjustment apparatus comprises 2K1 multi-mode interferometers MMIs, each MMI comprises 2MK+1 input ports and 2MK+1 output ports, 1KM, an I.sup.th input port or a (2MK+1I+1).sup.th input port in the 2MK+1 input ports is connected to one phase shifter, and 1I2MK+1; and the control apparatus is configured to adjust the phase shifters in the K.sup.th optical power adjustment module, to enable a phase difference between an optical signal input from the I.sup.th input port of each MMI in the K.sup.th optical power adjustment module and an optical signal input from the (2MK+1I+1).sup.th input port of the MMI to be 0 or an integer multiple of 2, and enable output optical power of an I.sup.th output port of each MMI in the K.sup.th optical power adjustment module to be the same as output optical power of a (2MK+1I+1).sup.th output port of the MMI.

2. The optical power adjustment system according to claim 1, wherein the optical power adjustment apparatus comprises a first optical power adjustment module and a second optical power adjustment module, the first optical power adjustment module comprises a first MMI, a first phase shifter, and a second phase shifter, and the second optical power adjustment module comprises a second MMI, a third MMI, a third phase shifter, and a fourth phase shifter; and a second input port or a third input port of the first MMI is connected to the first phase shifter, a first input port or a fourth input port of the second MMI is connected to the second phase shifter, the first input port of the second MMI is connected to a first output port of the first MMI, a second input port of the second MMI is connected to a second output port of the first MMI, a first input port of the third MMI is connected to a third output port of the first MMI, and a second input port of the third MMI is connected to a fourth output port of the first MMI; and the third phase shifter is connected between the first input port of the second MMI and the first output port of the first MMI or between the second input port of the second MMI and the second output port of the first MMI, and the fourth phase shifter is connected between the first input port of the third MMI and the third output port of the first MMI or between the second input port of the third MMI and the fourth output port of the first MMI; the control apparatus is configured to adjust the first phase shifter, to enable a phase difference between an optical signal input from the second input port of the first MMI and an optical signal input from the third input port of the first MMI to be 0 or an integer multiple of 2, and enable output optical power of the second output port of the first MMI to be the same as output optical power of the third output port of the first MMI; the control apparatus is configured to adjust the second phase shifter, to enable a phase difference between an optical signal input from a first input port of the first MMI and an optical signal input from a fourth input port of the first MMI to be 0 or an integer multiple of 2, and enable output optical power of the first output port of the first MMI to be the same as output optical power of the fourth output port of the first MMI; the control apparatus is configured to adjust the third phase shifter, to enable a phase difference between an optical signal input from the first input port of the second MMI and an optical signal input from the second input port of the second MMI to be 0 or an integer multiple of 2, and enable output optical power of a first output port of the second MMI to be the same as output optical power of a second output port of the second MMI; and the control apparatus is configured to adjust the fourth phase shifter, to enable a phase difference between an optical signal input from the first input port of the third MMI and an optical signal input from the second input port of the third MMI to be 0 or an integer multiple of 2, and enable output optical power of a first output port of the third MMI to be the same as output optical power of a second output port of the third MMI.

3. The optical power adjustment system according to claim 1, wherein multi-mode interference region lengths of all the MMIs in each optical power adjustment module are all 3L.sub./2, and L.sub. is a beat length of each of two lowest-order modes in an MMI waveguide.

4. The optical power adjustment system according to claim 3, wherein multi-mode interference region lengths of MMIs in different optical power adjustment modules are different.

5. The optical power adjustment system according to a claim 1, wherein the K.sup.th optical power adjustment module further comprises a plurality of beam splitters, the control apparatus comprises M control modules, and 2MK+1 input ports of each MMI in the K.sup.th optical power adjustment module are respectively connected to first output ports of 2MK+1 beam splitters; and second output ports of the 2MK+1 beam splitters are all connected to a K.sup.th control module, and the K.sup.th control module is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; each beam splitter is configured to split an input optical signal, output one of the split optical signals to an MMI corresponding to the beam splitter, and output another of the split optical signals to the K.sup.th control module; and the K.sup.th control module is configured to detect the input optical signal, and adjust each phase shifter in the K.sup.th optical power adjustment module based on a result of the detection.

6. The optical power adjustment system according to claim 5, wherein the K.sup.th control module comprises 2MK couplers, 2MK photodetectors, and 2MK phase control units, the I.sup.th input port is connected to a first output port of an I.sup.th beam splitter, the (2MK+1I+1).sup.th input port is connected to a first output port of a (2MK+1I+1).sup.th beam splitter, and a second output port of the I.sup.th beam splitter and a second output port of the (2MK+1I+1).sup.th beam splitter are connected to an input port of a J.sup.th coupler, 1J2MK, an output port of the J.sup.th coupler is connected to an input port of a J.sup.th optical detector, an output port of the J.sup.th photodetector is electrically connected to an input port of the phase control unit, and an output port of the phase control unit is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; the J.sup.th coupler is configured to couple input optical signals; the J.sup.th photodetector is configured to detect the coupled optical signal; and the phase control unit is configured to adjust an I.sup.th phase shifter in the K.sup.th optical power adjustment module based on a detection result of the J.sup.th photodetector, wherein the I.sup.th phase shifter is connected to the I.sup.th input port or the (2MK+1I+1).sup.th input port.

7. The optical power adjustment system according to claim 1, wherein the K.sup.th optical power adjustment module further comprises a plurality of beam splitters, the control apparatus comprises M control modules, and 2MK+1 output ports of each MMI in the K.sup.th optical power adjustment module are respectively connected to input ports of 2MK+1 beam splitters; and first output ports of the 2MK+1 beam splitters are connected to input ports of 2K MMIs in a (K+1).sup.th optical power adjustment module, second output ports of the 2MK+1 beam splitters are all connected to a K.sup.th control module, and the K.sup.th control module is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; each splitter is configured to split an input optical signal, output one of the split optical signals to an MMI corresponding to the beam splitter in the (K+1).sup.th optical power adjustment module, and output another of the split optical signals to the K.sup.th control module; and the K.sup.th control module is configured to detect the input optical signal, and adjust each phase shifter in the K.sup.th optical power adjustment module based on a result of the detection.

8. The optical power adjustment system according to claim 7, wherein the K.sup.th control module comprises 2MK+1 photodetectors and 2MK phase control units, second output ports of the 2MK+1 beam splitters are connected to input ports of the 2MK+1 photodetectors, output ports of the 2MK+1 photodetectors are all electrically connected to an input port of the phase control unit, and an output port of the phase control unit is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; and an I.sup.th photodetector is configured to detect an input optical signal, wherein an input port of the I.sup.th photodetector is connected to a second output port of an I.sup.th beam splitter; a (2MK+1I+1).sup.th photodetector is configured to detect an input optical signal, wherein an input port of the (2MK+1I+1).sup.th photodetector is connected to a second output port of a (2MK+1I+1).sup.th beam splitter; the phase control unit is configured to adjust an I.sup.th phase shifter in the K.sup.th optical power adjustment module based on detection results of the I.sup.th photodetector and the (2MK+1I+1).sup.th photodetector, wherein the I.sup.th phase shifter is connected to the I.sup.th input port or the (2MK+1I+1).sup.th input port; each photodetector is configured to detect an input optical signal; and the phase control unit is configured to adjust each phase shifter in the K.sup.th optical power adjustment module based on a detection result of each photodetector.

9. The optical power adjustment system according to claim 1, wherein the multi-mode light source is a multi-mode pump light source, and an optical signal output by the optical power adjustment apparatus is for injection to an erbium-doped fiber.

10. The optical power adjustment system according to claim 1, wherein the mode demultiplexer is a photonic lantern, a demultiplexer in a waveguide form, or a demultiplexer in a spatial light form.

11. The optical power adjustment system according to claim 1, wherein the output port of the multi-mode light source is connected to the input port of the mode demultiplexer through a multi-mode fiber, and the output port of the mode demultiplexer is connected to the input port of the optical power adjustment apparatus through N single-mode fibers or N waveguides.

12. An optical power adjustment apparatus, comprising: M optical power adjustment modules and a control apparatus, wherein M is an integer greater than 1, each optical power adjustment module comprises a plurality of phase shifters, the control apparatus is electrically connected to the M optical power adjustment modules, the M optical power adjustment modules are sequentially arranged from an input port of the optical power adjustment apparatus to an output port of the optical power adjustment apparatus, and the M optical power adjustment modules are connected together in series; and a K.sup.th optical power adjustment module in the optical power adjustment apparatus comprises 2K1 multi-mode interferometers MMIs, each MMI comprises 2MK+1 input ports and 2MK+1 output ports, 1KM, an I.sup.th input port or a (2MK+1I+1).sup.th input port in the 2MK+1 input ports is connected to one phase shifter, and 1I2MK+1; and the control apparatus is configured to adjust the phase shifters in the K.sup.th optical power adjustment module, to enable a phase difference between an optical signal input from the I.sup.th input port of each MMI in the K.sup.th optical power adjustment module and an optical signal input from the (2MK+1I+1).sup.th input port of the MMI to be 0 or an integer multiple of 2, and enable output optical power of an I.sup.th output port of each MMI in the K.sup.th optical power adjustment module to be the same as output optical power of a (2MK+1I+1).sup.th output port of the MMI.

13. The optical power adjustment apparatus according to claim 12, wherein the optical power adjustment apparatus comprises a first optical power adjustment module and a second optical power adjustment module, the first optical power adjustment module comprises a first MMI, a first phase shifter, and a second phase shifter, and the second optical power adjustment module comprises a second MMI, a third MMI, a third phase shifter, and a fourth phase shifter; and a second input port or a third input port of the first MMI is connected to the first phase shifter, a first input port or a fourth input port of the second MMI is connected to the second phase shifter, the first input port of the second MMI is connected to a first output port of the first MMI, a second input port of the second MMI is connected to a second output port of the first MMI, a first input port of the third MMI is connected to a third output port of the first MMI, and a second input port of the third MMI is connected to a fourth output port of the first MMI; and the third phase shifter is connected between the first input port of the second MMI and the first output port of the first MMI or between the second input port of the second MMI and the second output port of the first MMI, and the fourth phase shifter is connected between the first input port of the third MMI and the third output port of the first MMI or between the second input port of the third MMI and the fourth output port of the first MMI; the control apparatus is configured to adjust the first phase shifter, to enable a phase difference between an optical signal input from the second input port of the first MMI and an optical signal input from the third input port of the first MMI to be 0 or an integer multiple of 2, and enable output optical power of the second output port of the first MMI to be the same as output optical power of the third output port of the first MMI; the control apparatus is configured to adjust the second phase shifter, to enable a phase difference between an optical signal input from a first input port of the first MMI and an optical signal input from a fourth input port of the first MMI to be 0 or an integer multiple of 2, and enable output optical power of the first output port of the first MMI to be the same as output optical power of the fourth output port of the first MMI; the control apparatus is configured to adjust the third phase shifter, to enable a phase difference between an optical signal input from the first input port of the second MMI and an optical signal input from the second input port of the second MMI to be 0 or an integer multiple of 2, and enable output optical power of a first output port of the second MMI to be the same as output optical power of a second output port of the second MMI; and the control apparatus is configured to adjust the fourth phase shifter, to enable a phase difference between an optical signal input from the first input port of the third MMI and an optical signal input from the second input port of the third MMI to be 0 or an integer multiple of 2, and enable output optical power of a first output port of the third MMI to be the same as output optical power of a second output port of the third MMI.

14. The optical power adjustment apparatus according to claim 12, wherein multi-mode interference region lengths of all the MMIs in each optical power adjustment module are all 3L.sub./2, and L.sub. is a beat length of each of two lowest-order modes in an MMI waveguide.

15. The optical power adjustment apparatus according to claim 14, wherein multi-mode interference region lengths of MMIs in different optical power adjustment modules are different.

16. The optical power adjustment apparatus according to claim 12, wherein the K.sup.th optical power adjustment module further comprises a plurality of beam splitters, the control apparatus comprises M control modules, and 2MK+1 input ports of each MMI in the K.sup.th optical power adjustment module are respectively connected to first output ports of 2MK+1 beam splitters; and second output ports of the 2MK+1 beam splitters are all connected to a K.sup.th control module, and the K.sup.th control module is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; each beam splitter is configured to split an input optical signal, output one of the split optical signals to an MMI corresponding to the beam splitter, and output another of the split optical signals to the K.sup.th control module; and the K.sup.th control module is configured to detect the input optical signal, and adjust each phase shifter in the K.sup.th optical power adjustment module based on a result of the detection.

17. The optical power adjustment apparatus according to claim 16, wherein the K.sup.th control module comprises 2MK couplers, 2MK photodetectors, and 2MK phase control units, the I.sup.th input port is connected to a first output port of an I.sup.th beam splitter, the (2MK+1I+1).sup.th input port is connected to a first output port of a (2MK+1I+1).sup.th beam splitter, and a second output port of the I.sup.th beam splitter and a second output port of the (2MK+1I+1).sup.th beam splitter are connected to an input port of a J.sup.th coupler, 1J2MK, an output port of the J.sup.th coupler is connected to an input port of a J.sup.th optical detector, an output port of the J.sup.th photodetector is electrically connected to an input port of the phase control unit, and an output port of the phase control unit is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; the J.sup.th coupler is configured to couple input optical signals; the J.sup.th photodetector is configured to detect the coupled optical signal; and the phase control unit is configured to adjust an I.sup.th phase shifter in the K.sup.th optical power adjustment module based on a detection result of the J.sup.th photodetector, wherein the I.sup.th phase shifter is connected to the I.sup.th input port or the (2MK+1I+1).sup.th input port.

18. The optical power adjustment apparatus according to claim 12, wherein the K.sup.th optical power adjustment module further comprises a plurality of beam splitters, the control apparatus comprises M control modules, and 2MK+1 output ports of each MMI in the K.sup.th optical power adjustment module are respectively connected to input ports of 2MK+1 beam splitters; and first output ports of the 2MK+1 beam splitters are connected to input ports of 2K MMIs in a (K+1).sup.th optical power adjustment module, second output ports of the 2MK+1 beam splitters are all connected to a K.sup.th control module, and the K.sup.th control module is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; each splitter is configured to split an input optical signal, output one of the split optical signals to an MMI corresponding to the beam splitter in the (K+1).sup.th optical power adjustment module, and output another of the split optical signals to the K.sup.th control module; and the K.sup.th control module is configured to detect the input optical signal, and adjust each phase shifter in the K.sup.th optical power adjustment module based on a result of the detection.

19. The optical power adjustment apparatus according to claim 18, wherein the K.sup.th control module comprises 2MK+1 photodetectors and 2MK phase control units, second output ports of the 2MK+1 beam splitters are connected to input ports of the 2MK+1 photodetectors, output ports of the 2MK+1 photodetectors are all electrically connected to an input port of the phase control unit, and an output port of the phase control unit is electrically connected to each phase shifter in the K.sup.th optical power adjustment module; and an I.sup.th photodetector is configured to detect an input optical signal, wherein an input port of the I.sup.th photodetector is connected to a second output port of an I.sup.th beam splitter; a (2MK+1I+1).sup.th photodetector is configured to detect an input optical signal, wherein an input port of the (2MK+1I+1).sup.th photodetector is connected to a second output port of a (2MK+1I+1).sup.th beam splitter; the phase control unit is configured to adjust an I.sup.th phase shifter in the K.sup.th optical power adjustment module based on detection results of the I.sup.th photodetector and the (2MK+1I+1).sup.th photodetector, wherein the I.sup.th phase shifter is connected to the I.sup.th input port or the (2MK+1I+1).sup.th input port; each photodetector is configured to detect an input optical signal; and the phase control unit is configured to adjust each phase shifter in the K.sup.th optical power adjustment module based on a detection result of each photodetector.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 is a schematic structural diagram of an optical power adjustment system according to an embodiment of this application;

[0029] FIG. 2 is a schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application;

[0030] FIG. 3 is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application;

[0031] FIG. 4(a) is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application;

[0032] FIG. 4(b) is a schematic structural diagram of a control module according to an embodiment of this application;

[0033] FIG. 5(a) is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application;

[0034] FIG. 5(b) is another schematic structural diagram of a control module according to an embodiment of this application; and

[0035] FIG. 6 is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

[0036] Embodiments of this application provide an optical power adjustment system and an optical power adjustment apparatus. A mode demultiplexer may convert N transverse-mode optical signals output by a multi-mode light source into N fundamental-mode optical signals. By using the optical power adjustment apparatus, power of each fundamental-mode optical signal can be the same, power adjustment precision is higher, and applicability is wider.

[0037] It should be noted that in the specification, claims, and accompanying drawings of this application, the terms first, second, third, fourth, and the like are intended to distinguish between similar objects but do not limit a specific order or sequence. It should be understood that the foregoing terms are interchangeable in proper cases, so that embodiments described in this application can be implemented in a sequence other than the content described in this application. In addition, the terms include, have, and any other variant thereof are intended to cover a non-exclusive inclusion. For example, a process, a method, a system, a product, or a device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products, or devices.

[0038] The optical power adjustment system provided in this application is mainly applied to a scenario in which power equalization is performed on a plurality of single-mode optical signals after a multi-mode optical signal is demultiplexed into the plurality of single-mode optical signals. As an example, the optical power adjustment system may be specifically applied to an EDFA). A pump light source is an indispensable part of the EDFA. The magnitude of pump light power affects the gain of the erbium-doped fiber amplifier. Generally, a single-mode pump light source is expensive, while a multi-mode pump light source is cheap. However, because light output by the multi-mode pump light source has a plurality of transverse modes, the light cannot be directly applied to the EDFA. Generally, the light needs to be mode demultiplexed into a plurality of single-mode light before being output. In addition, power equalization needs to be performed on a plurality of single-mode optical signals, to provide a plurality of single-mode optical signals with approximate or same power for a plurality of EDFAs.

[0039] Therefore, this application provides an optical power adjustment system, configured to make power of each fundamental-mode optical signal be the same by adjustment. The following describes the optical power adjustment system provided in this application. It should be noted that in the following accompanying drawings, solid lines represent transmission paths of optical signals, and dashed lines represent transmission paths of electrical signals.

[0040] FIG. 1 is a schematic structural diagram of an optical power adjustment system according to an embodiment of this application. As shown in FIG. 1, the optical power adjustment system includes: a multi-mode light source 10, a mode demultiplexer 20, and an optical power adjustment apparatus 30. An output port of the multi-mode light source 10 is connected to an input port of the mode demultiplexer 20, and an output port of the mode demultiplexer 20 is connected to an input port of the optical power adjustment apparatus 30. The optical power adjustment apparatus includes M optical power adjustment modules and a control apparatus. The M optical power adjustment modules are sequentially arranged from the input port of the optical power adjustment apparatus to an output port of the optical power adjustment apparatus, and the M optical power adjustment modules are connected together in series, where M is an integer greater than 1. The control apparatus is electrically connected to the M optical power adjustment modules. Specifically, the multi-mode light source 10 is configured to output a multi-mode optical signal, where the multi-mode optical signal includes N transverse-mode optical signals, and N=2M. It should be understood that a light field output by the multi-mode light source 10 has both a plurality of transverse modes and a plurality of longitudinal modes, and the plurality of longitudinal modes have little impact on the pumping of an EDFA. However, the EDFA uses a single-mode erbium-doped fiber, which cannot support a high-order transverse mode. The plurality of transverse modes cause a waste of pump optical power. Therefore, the N transverse-mode optical signals need to be converted into N fundamental-mode optical signals by the mode demultiplexer 20, and the N fundamental-mode optical signals need to be output to the optical power adjustment apparatus 30. Further, after power adjustment by the optical power adjustment apparatus 30, power of N optical signals output by the optical power adjustment apparatus 30 is the same. It should be understood that, in an actual application, the power of the N optical signals output by the optical power adjustment apparatus 30 may be considered as the same as long as the power is within an acceptable error range.

[0041] It should be noted that the multi-mode light source 10 may be specifically a multi-mode pump light source, and the multi-mode light source 10 is connected to the mode demultiplexer 20 through a multi-mode fiber. The N optical signals output by the optical power adjustment apparatus 30 are respectively for injection to corresponding erbium-doped fibers. The mode demultiplexer 20 may be a demultiplexer in a fiber form, for example, a photonic lantern. Alternatively, the mode demultiplexer 20 may be a demultiplexer in a waveguide form, for example, a demultiplexer of a planar optical waveguide (PLC) and a silicon optical mode demultiplexer. Alternatively, the mode demultiplexer 20 may be a demultiplexer in a spatial form, for example, a spatial optical mode demultiplexer based on a phase mask template. It should be understood that, if the mode demultiplexer 20 is a demultiplexer in a fiber form, the mode demultiplexer 20 is connected to the optical power adjustment apparatus 30 through N single-mode fibers, and the M optical power adjustment modules in the optical power adjustment apparatus 30 are also connected together in series through the fibers. If the mode demultiplexer 20 is a demultiplexer in a waveguide form, the mode demultiplexer 20 is connected to the optical power adjustment apparatus 30 by N waveguides, and the M optical power adjustment modules in the optical power adjustment apparatus 30 are also connected together in series through the waveguides.

[0042] The following describes a specific power adjustment manner with reference to a structure of the optical power adjustment apparatus 30. FIG. 2 is a schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application. As shown in FIG. 2, each optical power adjustment module includes at least one multi-mode interferometer (MMI) and a plurality of phase shifters. A quantity of MMIs and a quantity of phase shifters in each optical power adjustment module are determined by a sequence of the optical power adjustment modules. An input port of a first optical power adjustment module is an input port of the optical power adjustment apparatus 30, and an output port of an M.sup.th optical power adjustment module is an output port of the optical power adjustment apparatus 30. Specifically, a K.sup.th optical power adjustment module includes 2K1 multi-mode interferometers MMIs, and each MMI includes 2MK+1 input ports and 2MK+1 output ports, where 1KM. An I.sup.th input port or a (2MK+1I+1).sup.th input port in the 2MK+1 input ports is connected to one phase shifter, where 1I2MK+1. A control apparatus adjusts each phase shifter in the K.sup.th optical power adjustment module, to enable a phase difference between an optical signal input from the I.sup.th input port of each MMI in the K.sup.th optical power adjustment module and an optical signal input from the (2MK+1I+1).sup.th input port of the MMI to be 0 or an integer multiple of 2. Further, output optical power of the I.sup.th output port of each MMI in the K.sup.th optical power adjustment module may be the same as output optical power of the (2MK+1I+1).sup.th output port of the MMI. Each optical power adjustment module performs power adjustment in the foregoing manner, so that it can be ensured that optical power of N optical signals output by the M.sup.th optical power adjustment modules is the same.

[0043] It should be noted that multi-mode interference region lengths of all the MMIs in each optical power adjustment module are all 3L.sub./2, and L.sub. is a beat length of each of two lowest-order modes in an MMI waveguide. In addition, multi-mode interference region lengths of MMIs in different optical power adjustment modules are different.

[0044] The following further describes a specific power adjustment manner by taking a minimum structure that can be supported by the optical power adjustment apparatus as an example. FIG. 3 is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application. As shown in FIG. 3, the optical power adjustment apparatus 30 includes an optical power adjustment module 301, an optical power adjustment module 302, and a control apparatus 303. The optical power adjustment module 301 includes a 44 MMI 301a, a phase shifter 301b, and a phase shifter 301c. The optical power adjustment module 302 includes a 22 MMI 302a, a 22 MMI 302b, a phase shifter 301c, and a phase shifter 301d. It should be understood that locations of the phase shifters shown in FIG. 3 are merely an example. Specifically, an input port 1 or an input port 4 of the MMI 301a is configured to be connected to the phase shifter 301c, and an input port 2 or an input port 3 of the MMI 301a is configured to be connected to the phase shifter 301b. An input port 1 or an input port 2 of the MMI 302a is configured to be connected to a phase shifter 302c. An input port 1 or an input port 2 of the MMI 302b is configured to be connected to a phase shifter 302d. The control apparatus 303 adjusts the phase shifter 301b, to enable a phase difference between an optical signal input from the input port 2 of the MMI 301a and an optical signal input from the input port 3 of the MMI to be 0 or an integer multiple of 2, and enable output optical power of an output port 2 of the MMI 301a to be the same as output optical power of an output port 3 of the MMI. The control apparatus 303 adjusts the phase shifter 301c, to enable a phase difference between an optical signal input from the input port 1 of the MMI 301a and an optical signal input from the input port 4 of the MMI to be 0 or an integer multiple of 2, and enable output optical power of an output port 1 of the MMI 301a to be the same as output optical power of an output port 4 of the MMI. The control apparatus 303 adjusts the phase shifter 302c, to enable a phase difference between an optical signal input from the input port 1 of the MMI 302a and an optical signal input from the input port 2 of the MMI to be 0 or an integer multiple of 2, and enable output optical power of an output port 1 of the MMI 302a to be the same as output optical power of an output port 2 of the MMI. The control apparatus 303 adjusts the phase shifter 302d, to enable a phase difference between an optical signal input from the input port 1 of the MMI 302b and an optical signal input from the input port 2 of the MMI to be 0 or an integer multiple of 2, and enable output optical power of an output port 1 of the MMI 302b to be the same as output optical power of an output port 2 of the MMI.

[0045] Based on the foregoing description, four optical signals input from the optical power adjustment module 301 may be divided into two groups. After adjustment, in one group, optical power output by the output port 1 is the same as that output by the output port 4, and in the other group, optical power output by the output port 2 is the same as that output by the output port 3. Then, the optical power adjustment module 302 adjusts the optical power of the two groups of optical signals to be consistent, and finally optical power of four optical signals output by the optical power adjustment module 302 is the same. The following describes a principle of using the foregoing design manner.

[0046] It is assumed that the four signals input from the input port 1 to the input port 4 of the MIMI 301a are respectively: E.sub.1=a, E.sub.2=b exp(j.sub.2), E.sub.3=c exp(j.sub.3), E.sub.4=d exp(j.sub.4), where a, b, c, and d are optical power of the four inputs respectively, j is an imaginary number, .sub.2, .sub.3, and .sub.4 are phase differences between the optical signals of the input port 2, the input port 3, and the input port 4 and the optical signal of the input port 1 respectively. A phase transfer function from an input port x to an output port y is expressed as:

[00001]${}_{\mathrm{xy}}={}_1-\frac{}{2}{\left(-1\right)}^{x+y+N}+\frac{}{4N}\left[x+y-x^2-y^2+{\left(-1\right)}^{x+y+N}\left(2\mathrm{xy}-x-y+\frac{1}{2}\right)\right].Math.{}_1$

is a constant phase. When N=4, a transmission matrix of an input/output port is represented as follows:

[00002]$T_{4C}=\frac{1}{2}\left[\begin{array}{cccc}1& \exp \left(j\frac{3}{4}\right)& \exp \left(-j\frac{1}{4}\right)& 1\\ \exp \left(j\frac{3}{4}\right)& 1& 1& \exp \left(-j\frac{1}{4}\right)\\ \exp \left(-j\frac{1}{4}\right)& 1& 1& \exp \left(j\frac{3}{4}\right)\\ 1& \exp \left(-j\frac{1}{4}\right)& \exp \left(j\frac{3}{4}\right)& 1\end{array}\right]$

[0047] For the 44 MMI 301a, the transmission matrix of the input/output port is represented as follows:

[00003]$T_4=T_{4C}{T}_{4C}=\frac{1}{4}\left[\begin{array}{cccc}2\left[1+\exp \left(-j\frac{1}{4}\right)\right]& 0& 0& 2[1+\exp \left(j\frac{1}{2}\right))]\\ 0& 2\left[1+\exp \left(-j\frac{1}{4}\right)\right]& 2[1+\exp \left(j\frac{1}{2}\right))]& 0\\ 0& 2[1+\exp \left(j\frac{1}{2}\right))]& 2\left[1+\exp \left(-j\frac{1}{4}\right)\right]& 0\\ 2[1+\exp \left(j\frac{1}{2}\right))]& 0& 0& 2\left[1+\exp \left(-j\frac{1}{4}\right)\right]\end{array}\right]$

[0048] Light fields of the four output ports of the MMI 301a are respectively represented as follows:

[00004]$E_{1\mathrm{out}}=\frac{1}{4}\left\{2a\left[1+\exp \left(-j\frac{1}{4}\right)\right]+2d\left[1+\exp \left(j\left({}_4+\frac{1}{2}\right)\right)\right]\right\}$$E_{2\mathrm{out}}=\frac{1}{4}\left\{2b\left[\exp (j\left({}_2\right)+\exp \left(j\left({}_2-\frac{1}{2}\right)\right)\right]+2c\left[\exp (j\left({}_3\right)+\exp (j\left({}_3+\frac{1}{2}\right)\right]\right\}$$E_{3\mathrm{out}}=\frac{1}{4}\left\{2b\left[\exp (j\left({}_2\right)+\exp \left(j\left({}_2+\frac{1}{2}\right)\right)\right]+2c\left[\exp (j\left({}_3\right)+\exp (j\left({}_3-\frac{1}{2}\right)\right]\right\}$$E_{4\mathrm{out}}=\frac{1}{4}\left\{2a\left[1+\exp \left(-j\frac{1}{4}\right)\right]+2d\left[1+\exp \left(j\left({}_4-\frac{1}{2}\right)\right)\right]\right\}$

[0049] When .sub.4=0, .sub.2=.sub.3, that is, the phase difference between the optical signal of the input port 1 and the optical signal of the input port 4 is 0 or an integer multiple of 2, and the phase difference between the optical signal of the input port 2 and the optical signal of the input port 3 is 0 or an integer multiple of 2, the output optical power of the four output ports of the MMI 301a is respectively represented as follows:

[00005]$P_{1\mathrm{out}}={.Math.E_{1\mathrm{out}}.Math.}^2=\frac{a^2+d^2}{2}$$P_{2\mathrm{out}}={.Math.E_{2\mathrm{out}}.Math.}^2=\frac{b^2+c^2}{2}$$P_{3\mathrm{out}}={.Math.E_{3\mathrm{out}}.Math.}^2=\frac{b^2+c^2}{2}$$P_{4\mathrm{out}}={.Math.E_{4\mathrm{out}}.Math.}^2=\frac{a^2+d^2}{2}$

[0050] It can be learned from the foregoing formula that, when phases of the optical signals of the input port 1 and the input port 4 of the MMI 301a are equal, the output port 1 and the output port 4 implement power equalization on the input port 1 and the input port 4. Similarly, when phases of the optical signals of the input port 2 and the input port 3 are equal, the output port 2 and the output port 3 implement power equalization on the input port 2 and the input port 3.

[0051] Next, the output port 1 and the output port 2 of the MMI 301a are respectively connected to the input port 1 and the input port 2 of the MMI 302a, and the phase shifter 302c is adjusted, so that phases of the two optical signals input to the input ports of the MMI 302a are the same. A transmission matrix of the MMI 302a is as follows:

[00006]$T_2=\frac{\sqrt{2}}{2}\left[\begin{array}{cc}1& \exp \left(j\frac{1}{2}\right)\\ \exp \left(j\frac{1}{2}\right)& 1\end{array}\right]$

[0052] It can be obtained through calculation that output optical power of the output port 1 of the MMI 302a and output optical power of the output port 2 of the MMI are both

[00007]$\frac{a^2+d^2+b^2+c^2}{4}.$

Similarly, output optical power of the output port 1 the MMI 302b and output optical power of the output port 2 of the MMI are both

[00008]$\frac{a^2+d^2+b^2+c^2}{4},$

thereby implementing power equalization of the four optical signals.

[0053] It should be noted that, an NN MMI and an NN optical coupler used in this application have the following differences. First, the NN optical coupler can only be used when N input light is non-coherent light. However, in a scenario where a multi-mode optical signal is converted into N single-mode optical signals, the N single-mode optical signals are coherent light. Therefore, the NN optical coupler cannot be directly used to implement optical power equalization. Second, for the NN optical coupler, phases of N input optical signals need to be adjusted to be consistent, so that N output optical power is the same. However, because a quantity of N is usually large, absolute phases of the N input optical signals cannot be detected. Therefore, it cannot be ensured that the phases of the N input optical signals are completely consistent via the NN optical coupler. For the NN MMI provided in this application, a relative phase difference between two optical signals can be detected, and phases of the two input optical signals in this group can be adjusted to be consistent via the phase shifter. Based on this design idea, optical power equalization of N outputs can be implemented via a plurality of cascaded optical power adjustment modules.

[0054] It should be understood that the control apparatus provided in this application may extract a phase difference between two input optical signals, and control the phase shifter to adjust phases of the input optical signals. In other words, the optical power adjustment apparatus provided in this application automatically implements power adjustment without manual control. Specifically, this application provides a plurality of implementations of detecting a phase difference by a control apparatus. The following separately uses the optical power adjustment apparatus shown in FIG. 3 as an example for description.

[0055] First Implementation

[0056] FIG. 4(a) is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application. As shown in FIG. 4(a), the optical power adjustment module 301 and the optical power adjustment module 302 each further include a plurality of beam splitters. The control apparatus 303 includes a control module 1 and a control module 2. The control module 1 is configured to control a phase shifter in the optical power adjustment module 301, and the control module 2 is configured to control a phase shifter in the optical power adjustment module 302. Take the beam splitters in the optical power adjustment module 301 as an example. Each beam splitter is configured to split each optical signal input to the MMI 301a, output one of the split optical signals to the MMI 301a, and output another of the split optical signals to the control module 1. Similarly, the method is also applicable to the beam splitters in the optical power adjustment module 302, and details are not described herein again. It should be noted that a split ratio of each beam splitter is not limited in this application. In an implementation, most split optical signals should be output to a corresponding MIMI, and a few split optical signals should be output to a corresponding control module.

[0057] FIG. 4(b) is a schematic structural diagram of a control module according to an embodiment of this application. As shown in FIG. 4(b), the control module 1 includes a coupler 303a, a photodetector 303b, and a phase control unit 303c. The beam splitter connected to the input port 1 of the MMI 301a is further connected to the coupler 303a, and the beam splitter connected to the input port 4 of the MMI 301a is further connected to the coupler 303a. The coupler 303a is configured to couple an input optical signal. The photodetector 303b is configured to detect the coupled optical signal. The phase control unit 303c is configured to adjust the phase shifter 301c based on a detection result output by the photodetector 303b. Specifically, the phase control unit 303c may gradually adjust a voltage output by the phase control unit, to enable a phase value of the phase shifter 301c to be scanned within a range of 0 to 2. In this process, the photodetector 303b continuously performs power detection on an optical signal output by the coupler 303a. The phase control unit 303c may continuously read a voltage output by the photodetector 303b. It should be understood that, if a phase difference between two optical signals input to the coupler 303a is 0 or an integer multiple of 2, constructive interference occurs on the two optical signals. In this case, output optical power of the coupler 303a is the largest, and an output voltage of the photodetector 303b is also the largest. The phase control unit 303c may maintain a current output voltage, to enable the phase difference between the two optical signals input to the coupler 303a to be 0 or an integer multiple of 2. Therefore, output optical power of the output port 1 and output optical power of the output port 4 of the MMI 301a are the same. It should be noted that FIG. 4(b) shows only a part of the control module 1 corresponding to the phase shifter 301c, and a structure corresponding to the phase shifter 301b is similar to the part shown in FIG. 4(b), and details are not described herein again.

[0058] Second Implementation

[0059] FIG. 5(a) is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application. As shown in FIG. 5(a), the optical power adjustment module 301 and the optical power adjustment module 302 each further include a plurality of beam splitters. The control apparatus 303 includes a control module 1 and a control module 2. The control module 1 is configured to control a phase shifter in the optical power adjustment module 301, and the control module 2 is configured to control a phase shifter in the optical power adjustment module 302. Take the beam splitters in the optical power adjustment module 301 as an example. Each beam splitter is configured to split each optical signal output to the MMI 301a, output one of the split optical signals to the optical power adjustment module 302, and output another of the split optical signals to the control module 1. Similarly, the method is also applicable to the beam splitters in the optical power adjustment module 302, and details are not described herein again. It should be noted that a split ratio of each beam splitter is not limited in this application. In an implementation, most split optical signals should be output to a corresponding MMI, and a few split optical signals should be output to a corresponding control module.

[0060] FIG. 5(b) is another schematic structural diagram of a control module according to an embodiment of this application. As shown in FIG. 5(b), the control module 1 includes a photodetector 303d, a photodetector 303e, and a phase control unit 303c. The beam splitter connected to the output port 1 of the MMI 301a is further connected to the photodetector 303d, and the beam splitter connected to the output port 4 of the MMI 301a is further connected to the photodetector 303e. The photodetector 303d and the photodetector 303e are respectively configured to detect optical signals each input from the photodetector 303d and the photodetector 303e. The phase control unit 303c is configured to adjust the phase shifter 301c based on detection results output by the photodetector 303d and the photodetector 303e. Specifically, the phase control unit 303c may gradually adjust a voltage output by the phase control unit, to enable a phase value of the phase shifter 301c to be scanned within a range of 0 to 2. In this process, the phase control unit 303c may continuously read voltages output by the photodetector 303d and the photodetector 303e, and calculate a difference between two input voltages. It should be understood that, when a voltage difference calculated by the phase control unit 303c is the smallest, optical power detected by the photodetector 303d and the photodetector 303e is the same. In this case, the phase control unit 303c may maintain a current output voltage, to enable output optical power of the output port 1 and output optical power of the output port 4 of the MMI 301a to be the same. It should be noted that FIG. 5(b) shows only a part of the control module 1 corresponding to the phase shifter 301c, and a structure corresponding to the phase shifter 301b is similar to the part shown in FIG. 5(b), and details are not described herein again.

[0061] Embodiments of this application provide an optical power adjustment system. A mode demultiplexer may convert N transverse-mode optical signals output by a multi-mode light source into N fundamental-mode optical signals. Then, the N fundamental-mode optical signals are input to an optical power adjustment apparatus. The optical power adjustment apparatus includes a plurality of levels of optical power adjustment modules and a control apparatus. An input/output port of each level of optical power adjustment module may be split into a plurality of groups of input/output ports in pairs. Each group of input/output ports correspond to one phase shifter. The control apparatus may adjust each phase shifter, so that output optical power of each group of output ports of each level of optical power adjustment module is the same. Based on a specific design manner, after each level of optical power adjustment module completes adjustment, some optical signals with the same optical power are added. By analogy, after all optical power adjustment modules complete adjustment, it can be ensured that the optical power of the N optical signals output by the optical power adjustment apparatus is the same. It should be understood that, regardless of a quantity of fundamental-mode optical signals obtained after mode demultiplexing, the foregoing power adjustment manner may be used, so that power of each fundamental-mode optical signal is the same, power adjustment precision is higher, and applicability is wider.

[0062] FIG. 6 is another schematic structural diagram of an optical power adjustment apparatus according to an embodiment of this application. As shown in FIG. 6, different from the optical power adjustment apparatus described in the foregoing embodiments, each optical power adjustment module of the optical power adjustment apparatus uses a same NN MMI. Take N=4 as an example. Both an optical power adjustment module 301 and an optical power adjustment module 302 include only one 44 MMI. In addition, an output port of the optical power adjustment module 301 and an input port of the optical power adjustment module 302 are not connected based on port numbers completely, but are partially cross-connected. The optical power adjustment module 301 is similar to the optical power adjustment module 301 in the embodiment shown in FIG. 3, and details are not described herein again. The following mainly describes a structure of the optical power adjustment module 302.

[0063] Take FIG. 6 as an example. An output port 1 of an MMI 301a is connected to an input port 1 of an MMI 302a, an output port 2 of the MMI 301a is connected to an input port 2 of the MMI 302a, an output port 3 of the MMI 301a is connected to an input port 4 of the MMI 302a, and an output port 4 of the MMI 301a is connected to an input port 3 of the MMI 302a. It should be understood that, for the MMI 302a, the input port 1 and the input port 4 are input ports in a same group, and the input port 2 and the input port 3 are input ports in a same group. Because the output port 3 and the output port 4 of the MMI 301a are cross-connected to the input port 3 and the input port 4 of the MMI 302a, input optical power of the input port 1 and input optical power of the input port 3 of the MMI 302a are the same, and input optical power of the input port 2 and input optical power of the input port 4 are the same. In this case, the input port 1 or the input port 4 of the MMI 302a should be connected to a phase shifter 302b, so that output optical power of an output port 1 or an output port 4 of the MMI 302a is the same after adjustment. The input port 2 or the input port 3 of the MMI 302a should be connected to a phase shifter 302c, so that output optical power of an output port 2 or an output port 3 of the MMI 302a is the same after adjustment. Finally, output optical power of the four output ports of the MMI 302a is the same. A specific power adjustment manner is similar to the manner described in the foregoing embodiment, and details are not described herein again.

[0064] It should be noted that, the connection manner shown in FIG. 6 may be understood as a connection manner in which a port 1 and a port 2 are directly connected, and a port 3 and a port 4 are cross-connected. In addition, based on a same design idea, the port 1 and the port 3 may be directly connected, and the port 2 and the port 4 may be cross-connected; or the port 3 and the port 4 are directly connected, and the port 1 and the port 2 are cross-connected; or the port 2 and the port 4 are directly connected, and the port 1 and the port 3 are cross-connected. It should be understood that, based on the design idea of the embodiment shown in FIG. 6, this implementation may also be extended in this application to a scenario in which a quantity of optical power adjustment modules is greater than 2. Details are not described herein again.

[0065] It should be noted that embodiments of this application further provide an optical power adjustment apparatus. The optical power adjustment apparatus may be the optical power adjustment apparatus in any one of the embodiments shown in FIG. 1 to FIG. 6. For details, refer to related descriptions of the embodiments shown in FIG. 1 to FIG. 6. Details are not described herein again.