A few-mode erbium-doped fiber amplifier system

Abstract

The present invention discloses a few-mode erbium-doped fiber amplifier system, which belongs to the field of space division multiplexing technology. The signal light passes through a tunable attenuator and a first polarization controller, and is coupled to a branch of a photon lantern, such as an LP. 01 , which converts the signal into the mode it supports. After passing through the second polarization controller, the pump light is coupled to the LP of the photonic lantern. 21a Mode branching. The mode-selective photon lantern multiplexes the signal light and the pump light into one optical signal, which is coupled into the few-mode erbium-doped fiber after passing through the third polarization controller. The few-mode erbium-doped fiber is formed by fusion-splicing the erbium-ytterbium co-doped double-clad few-mode erbium-doped fiber and the ring few-mode erbium-doped fiber. In the erbium-ytterbium co-doped double-clad few-mode erbium-doped fiber, the introduction of ytterbium ions can increase the doping concentration of erbium ions, so that higher gain can be achieved at a shorter fiber length, while in the ring few-mode erbium-doped fiber, the fundamental mode LP 01 Compared with the modes, the gains of higher-order modes are higher.

Description

Technical Field

[0001] The present invention belongs to the technical field of space division multiplexing, and more specifically, relates to a few-mode erbium-doped optical fiber amplifier system. Background Art

[0002] With the development of cloud computing, big data analysis and the Internet of Things, people's demand for Internet transmission capacity has exploded. However, the transmission capacity of existing single-mode optical fiber communication systems has approached the Shannon limit, so people urgently need to develop new information transmission dimensions to meet the growing demand for network traffic. On the basis that other multiplexing dimensions of single-mode optical fiber, such as wavelength division multiplexing, time division multiplexing, orthogonal frequency division multiplexing, and code division multiplexing, have been fully utilized, space division multiplexing technology has received widespread attention and developed rapidly in high-speed and large-capacity optical fiber communication systems.

[0003] Space division multiplexing technology includes core division multiplexing and mode division multiplexing. Core division multiplexing refers to using each core of a multi-core optical fiber as an independent transmission channel to transmit signals; while mode division multiplexing technology uses few-mode optical fiber to transmit a small number of spatial modes, loads signals of different channels onto each mode, and uses the orthogonality of the modes to transmit signals. The space division multiplexing transmission system based on few-mode optical fiber can realize the simultaneous transmission of multiple channels, which increases the transmission capacity exponentially. Space division multiplexing technology using few-mode optical fiber as the transmission line must achieve long-distance transmission. Few-mode erbium-doped fiber amplifiers are key components for compensating for the transmission loss of few-mode transmission systems. However, in the process of optical amplification, the overlap of each signal mode optical field, pump optical field, and erbium ion distribution in the optical fiber cross section is inconsistent, resulting in different amplification gains of different modes in few-mode optical fiber. High differential modal gain will lead to transmission limitations. Therefore, it is crucial to minimize differential modal gain in few-mode erbium-doped fiber amplifiers.

[0004] There are two main existing methods for reducing the differential modal gain of few-mode erbium-doped fiber amplifiers: (1) regulating the pump mode ratio. By changing the pump mode and adjusting the power ratio, the difference in the overlapping factor between each signal mode light field, the pump light field and the erbium ion distribution can be reduced to achieve gain balance between modes. However, this method only changes the information of the pump light intensity and has limited gain balance capability. (2) Designing the erbium ion distribution and refractive index profile of the few-mode erbium-doped fiber. By designing the erbium ion distribution and erbium ion concentration of the few-mode erbium-doped fiber, the difference in overlapping factors between modes can be reduced; by designing the refractive index profile, the mode field distribution of various modes of the fiber can be adjusted to increase the overlapping integral factor between the signal light and the pump light, thereby achieving gain balance between modes. This method relies on the design of a complex erbium-doped fiber structure and has a relatively complex manufacturing process. Both of these methods for reducing differential modal gain have limited capabilities and are limited by light intensity information and process technology, and cannot achieve good gain balance between modes. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a few-mode erbium-doped fiber amplifier system, the purpose of which is to use erbium-ytterbium co-doped double-clad few-mode erbium-doped fiber and annular few-mode erbium-doped fiber to fuse into a few-mode amplification fiber, so that the differential mode gain becomes smaller and the gain is balanced. Due to the distribution of erbium ions in the annular few-mode erbium-doped fiber, the gain of the high-order mode is higher than that of the LP01 mode, resulting in a large differential mode gain and possible signal interruption. The introduction of ytterbium ions in the erbium-ytterbium co-doped double-clad few-mode fiber increases the doping concentration of erbium ions, thereby achieving a higher gain at a shorter fiber length. The overlap between the LP01 mode and the doping area is the largest, and the gain obtained is also greater than that of the high-order mode. This solves the technical problem that the prior art cannot achieve gain balance between modes.

[0006] To achieve the above object, according to one aspect of the present invention, a few-mode erbium-doped fiber amplifier system is provided, comprising:

[0007] A signal light source, used to generate signal light including multiple wavelengths;

[0008] A first polarization controller, arranged on an outgoing optical path of the signal light, for ensuring the purity of the signal light;

[0009] A plurality of optical isolators are arranged on the output optical path of the first polarization controller and are used for unidirectionally passing each mode light in the signal light output by the first polarization controller;

[0010] A pump light source, used to generate pump light;

[0011] A second polarization controller, arranged on an outgoing optical path of the pump light, for ensuring the purity of the pump light;

[0012] A mode selection photon lantern is arranged on the output optical path of the plurality of optical isolators and the second polarization controller, and is used to determine one of the plurality of mode lights to be coupled to a branch and converted into a mode supported by the branch, couple the pump light to another branch, and then multiplex the lights corresponding to the two branches into one transmission light;

[0013] A third polarization controller is arranged on the outgoing light path of the transmission light, and is used to ensure the purity of the transmission light;

[0014] A few-mode erbium-doped optical fiber, which is formed by fusion-joining an erbium-ytterbium co-doped double-clad optical fiber and a ring-shaped few-mode erbium-doped optical fiber, is arranged on the output optical path of the third polarization controller and is used to amplify the transmission light and increase its gain, thereby outputting the target light;

[0015] The light detection device is arranged on the output light path of the target light and is used to detect the target light to obtain its light spot information and power information.

[0016] In one embodiment, the few-mode erbium-doped optical fiber is formed by fusion-joining erbium-ytterbium co-doped double-cladding optical fiber and annular few-mode erbium-doped optical fiber.

[0017] In one embodiment, the few-mode erbium-doped optical fiber is formed by fusion-joining a ring-shaped few-mode erbium-doped optical fiber and an erbium-ytterbium co-doped double-cladding optical fiber.

[0018] In one embodiment, the erbium-ytterbium co-doped double-clad optical fiber includes, from inside to outside, a core, an inner cladding, an outer cladding and a coating; the refractive index of the core center is greater than the refractive index of the inner cladding, and the refractive index of the inner cladding is greater than the refractive index of the outer cladding.

[0019] In one embodiment, the annular few-mode erbium-doped optical fiber includes from the inside to the outside: a core and a cladding, and the core includes from the inside to the outside: a first doped region, an undoped region, and a second doped region;

[0020] The refractive index distribution of the annular few-mode erbium-doped optical fiber is a step refractive index distribution.

[0021] In one embodiment,

[0022] The mode selection photon lantern is a six-mode selection photon lantern;

[0023] The mode light in the signal light is: fundamental mode LP 01 Mode light, LP 11a Mode light, LP 11b Mode light, LP 21a Mode light, LP 21b Mode light and LP 02 Mode light.

[0024] In one of the embodiments, the number of the optical isolators is the same as the number of the mode lights, and the multiple optical isolators are also used to reduce the influence of the reflected light in the few-mode erbium-doped optical fiber transmission on the light amplification process.

[0025] In one embodiment, the light detection device comprises:

[0026] A charge coupled camera is arranged on the output optical path of the target light and is used to collect the spot information of the target light;

[0027] A spectrometer is arranged on the output optical path of the target light and is used to obtain power information of the target light.

[0028] In one embodiment, the few-mode erbium-doped fiber amplifier system further comprises:

[0029] A multimode jumper is used to connect the few-mode erbium-doped optical fiber and the spectrometer to measure the power information of the target light.

[0030] In one embodiment, the few-mode erbium-doped fiber amplifier system further comprises:

[0031] The tunable attenuator is arranged on the outgoing light path of the signal light source and is used to adjust the power of the signal light so that each mode light in the signal light reaches a preset power.

[0032] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0033] (1) In the present invention, the signal light is coupled to a branch (LP) of the photon lantern after passing through the tunable attenuator and the first polarization controller. 01 LP 11a or LP 11b ), which converts the signal into the mode it supports. At the same time, the pump light is coupled to the LP of the photon lantern after passing through the second polarization controller. 21a Mode branching. The mode-selective photon lantern multiplexes the signal light and the pump light into one optical signal, and after the optical signal passes through the third polarization controller, it is coupled into the few-mode erbium-doped fiber. The few-mode erbium-doped fiber here is formed by fusion-splicing the erbium-ytterbium co-doped double-clad few-mode erbium-doped fiber and the ring-shaped few-mode erbium-doped fiber. In the erbium-ytterbium co-doped double-clad few-mode erbium-doped fiber, the introduction of ytterbium ions can increase the doping concentration of erbium ions, so that higher gain can be achieved at a shorter fiber length. The few-mode amplifying fiber of the present application supports six modes of photon lantern transmission, but due to the different overlaps between the mode field distribution of each mode light, the mode field distribution of the pump light, and the doping distribution of erbium ions, the differential mode gain of the few-mode fiber is large. Select the LP of the photon lantern with the signal light input mode 01 Branching is described as an example. In the Er-Yb co-doped double-clad few-mode fiber, due to the signal LP 01 mode has the largest overlap with the doped region, so the LP mode is more 01 The mode obtains a higher gain, which makes the gain between modes unbalanced. 01 Compared with the two modes, the gain of the high-order mode is higher, and the two optical fibers complement each other to achieve good gain balance between modes.

[0034] (2) The present invention combines the Er-Yb double-clad few-mode fiber with the annular few-mode Er-doped fiber to achieve high gain while achieving good inter-mode gain balance. After the fused few-mode amplifier fiber amplifies the light, it enters the spectrometer through a multimode jumper with an FC / APC interface, and the spectrometer measures the output power. The amplified light spot is monitored by a charge-coupled device camera. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic structural diagram of a few-mode erbium-doped fiber amplifier system in one embodiment of the present invention;

[0036] Figure 2 is a cross-sectional view and refractive index distribution of an erbium-ytterbium co-doped double-clad optical fiber in one embodiment of the present invention;

[0037] Figure 3 1 is a cross-sectional view and refractive index distribution of an annular few-mode erbium-doped optical fiber in one embodiment of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] The present invention provides a few-mode erbium-doped fiber amplifier system, comprising:

[0040] A signal light source, used to generate signal light including multiple wavelengths;

[0041] A first polarization controller is arranged on the outgoing optical path of the signal light to ensure the purity of the signal light;

[0042] A plurality of optical isolators are arranged on the output optical path of the first polarization controller and are used for unidirectionally passing each mode light in the signal light output by the first polarization controller;

[0043] A pump light source, used to generate pump light;

[0044] A second polarization controller is arranged on an outgoing optical path of the pump light and is used to ensure the purity of the pump light;

[0045] A mode selection photon lantern is arranged on the output optical path of the plurality of optical isolators and the second polarization controller, and is used to determine one of the plurality of mode lights to be coupled to a branch and converted into a mode supported by the branch, couple the pump light to another branch, and then multiplex the light corresponding to the two branches into one transmission light;

[0046] A third polarization controller is arranged on the outgoing light path of the transmitted light to ensure the purity of the transmitted light;

[0047] The few-mode erbium-doped optical fiber is formed by fusion-joining an erbium-ytterbium co-doped double-clad optical fiber and a ring-shaped few-mode erbium-doped optical fiber, and is arranged on the output optical path of the third polarization controller to amplify the transmission light and increase its gain, thereby outputting the target light;

[0048] The light detection device is arranged on the output light path of the target light and is used to detect the target light to obtain its light spot information and power information.

[0049] like Figure 1 As shown, the present invention provides a few-mode erbium-doped fiber amplifier system with improved gain equalization, including: a 31-channel DWDM light source, a tunable attenuator, a polarization controller, an optical isolator, a mode-selective photon lantern, a 1480nm pump light source, a few-mode optical fiber, a multimode jumper, a spectrometer, and a charge-coupled camera. Among them, the 31-channel DWDM light source multiplexes 31 signal lights of different wavelengths into one optical fiber and inputs them to the tunable attenuator; the tunable attenuator adjusts the signal light power output by the 31-channel DWDM light source so that each mode of signal light reaches a preset power. Subsequently, the signal light is input to the first polarization controller; the first polarization controller ensures the purity of the converted signal mode and is input to the first optical isolator; the first optical isolator allows the fundamental mode LP 01 The signal light of the mode passes unidirectionally, reducing the influence of reflected light on the optical amplification process in the transmission of few-mode erbium-doped fiber. Then, the signal light input mode selects the LP of the photon lantern. 01 Branch; second optical isolator, allowing fundamental mode LP 01 The signal light of the mode passes unidirectionally, reducing the influence of reflected light on the optical amplification process in the transmission of few-mode erbium-doped fiber. Then, the signal light input mode selects the LP of the photon lantern. 11a Branch; third optical isolator, allowing fundamental mode LP 01 The signal light of the mode passes unidirectionally, reducing the influence of reflected light on the optical amplification process in the transmission of few-mode erbium-doped fiber. Then, the signal light input mode selects the LP of the photon lantern. 11b Branch.

[0050] The 1480nm pump light source generates single-mode high-power pump light and inputs it into the second polarization controller; the second polarization controller ensures the purity of the converted pump mode. Then, the pump light input mode selects the LP of the photon lantern. 21a Mode; Mode selection Photon Lantern, in base mode LP 01After the mode is coupled to an input branch of the photon lantern, the branch converts the signal into the mode it supports. Then, the signal light and the pump light are multiplexed into one optical signal, which is input into the least-mode fiber through the third polarization controller; the third polarization controller ensures the purity of the multiplexed mode and inputs into the few-mode fiber.

[0051] Then, the few-mode fiber, which is formed by fusion splicing Er-Yb co-doped double-clad fiber and ring few-mode erbium-doped fiber, amplifies the input optical signal and improves the gain of the input optical signal. Then it is input into the spectrometer through a multi-mode jumper with FC / APC port; the FC / APC port multi-mode jumper connects the few-mode fiber and the spectrometer to facilitate the measurement of output power; the charge-coupled camera collects the light spot in the optical path of the few-mode erbium-doped fiber amplifier; the spectrometer detects the input and output optical power.

[0052] The present invention amplifies the signal by fusing the erbium-ytterbium co-doped double-clad few-mode fiber with the ring few-mode erbium-doped fiber as the active fiber in the few-mode erbium-doped fiber amplifier. The introduction of ytterbium ions in the erbium-ytterbium co-doped double-clad few-mode fiber can increase the doping concentration of erbium ions, so that a higher gain can be achieved at a shorter fiber length. 01 The branch is described as an example. Since the signal LP 01 mode has the largest overlap with the doped region, so the LP mode is more 01 The mode obtains a higher gain, which makes the gain between modes unbalanced. 01 Therefore, the present invention can achieve high gain and obtain good inter-mode gain balance by combining erbium-ytterbium double-clad few-mode fiber with annular few-mode erbium-doped fiber.

[0053] In one embodiment, the few-mode erbium-doped optical fiber is formed by fusion-joining an erbium-ytterbium co-doped double-cladding optical fiber and a ring-shaped few-mode erbium-doped optical fiber.

[0054] In one embodiment, the few-mode erbium-doped optical fiber is formed by fusion-joining a ring-shaped few-mode erbium-doped optical fiber and an erbium-ytterbium co-doped double-cladding optical fiber.

[0055] like Figure 2 As shown, in one embodiment, the erbium-ytterbium co-doped double-clad optical fiber includes, from the inside to the outside, a core, an inner cladding, an outer cladding and a coating; the refractive index of the core center is greater than the refractive index of the inner cladding, and the refractive index of the inner cladding is greater than the refractive index of the outer cladding.

[0056] like Figure 3As shown, in one embodiment, the annular few-mode erbium-doped optical fiber includes from the inside to the outside: a core and a cladding, and the core includes from the inside to the outside: a first doped region, an undoped region and a second doped region; the refractive index distribution of the annular few-mode erbium-doped optical fiber is a step refractive index distribution.

[0057] In one embodiment, the mode selection photon lantern is a six-mode selection photon lantern; the mode light in the signal light is: fundamental mode LP 01 Mode light, LP 11a Mode light, LP 11b Mode light, LP 21a Mode light, LP 21b Mode light and LP 02 Mode light.

[0058] In one of the embodiments, the number of optical isolators is the same as the number of mode lights, and the multiple optical isolators are also used to reduce the influence of reflected light on the optical amplification process in the transmission of few-mode erbium-doped optical fiber.

[0059] In one embodiment, the light detection device comprises:

[0060] A charge coupled camera is arranged on the output optical path of the target light and is used to collect the spot information of the target light;

[0061] The spectrometer is arranged on the output optical path of the target light and is used to obtain the power information of the target light.

[0062] In one embodiment, the few-mode erbium-doped fiber amplifier system further includes: a multimode jumper connecting the few-mode erbium-doped fiber and the spectrometer to facilitate measurement of power information of the target light.

[0063] In one of the embodiments, the few-mode erbium-doped fiber amplifier system further includes: a tunable attenuator, which is arranged on the output light path of the signal light source and is used to adjust the power of the signal light so that each mode light in the signal light reaches a preset power.

[0064] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A few-mode erbium-doped fiber amplifier system, characterized in that: include: A signal light source, used to generate signal light including multiple wavelengths; A first polarization controller, arranged on an outgoing optical path of the signal light, for ensuring the purity of the signal light; A plurality of optical isolators are arranged on the output optical path of the first polarization controller and are used for unidirectionally passing each mode light in the signal light output by the first polarization controller; A pump light source, used to generate pump light; A second polarization controller, arranged on an outgoing optical path of the pump light, for ensuring the purity of the pump light; A mode selection photon lantern is arranged on the output optical path of the plurality of optical isolators and the second polarization controller, and is used to determine one of the plurality of mode lights to be coupled to a branch and converted into a mode supported by the branch, couple the pump light to another branch, and then multiplex the lights corresponding to the two branches into one transmission light; A third polarization controller is arranged on the outgoing light path of the transmission light, and is used to ensure the purity of the transmission light; A few-mode erbium-doped optical fiber, which is formed by fusion-joining an erbium-ytterbium co-doped double-clad optical fiber and a ring-shaped few-mode erbium-doped optical fiber, is arranged on the output optical path of the third polarization controller and is used to amplify the transmission light and increase its gain, thereby outputting the target light; The light detection device is arranged on the output light path of the target light and is used to detect the target light to obtain its light spot information and power information.

2. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The few-mode erbium-doped optical fiber is formed by fusion-joining erbium-ytterbium co-doped double-cladding optical fiber and annular few-mode erbium-doped optical fiber in sequence.

3. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The few-mode erbium-doped optical fiber is formed by fusion-joining annular few-mode erbium-doped optical fiber and erbium-ytterbium co-doped double-cladding optical fiber in sequence.

4. The few-mode erbium-doped fiber amplifier system according to claim 1 is characterized in that: The erbium-ytterbium co-doped double-clad optical fiber comprises from the inside to the outside: a core, an inner cladding, an outer cladding and a coating layer; The refractive index of the core is greater than the refractive index of the inner cladding, and the refractive index of the inner cladding is greater than the refractive index of the outer cladding.

5. The few-mode erbium-doped fiber amplifier system according to claim 4, characterized in that: The annular few-mode erbium-doped optical fiber includes, from the inside to the outside: a core and a cladding, and the core includes, from the inside to the outside: a first doped region, an undoped region, and a second doped region; The refractive index distribution of the annular few-mode erbium-doped optical fiber is a step refractive index distribution.

6. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The mode selection photon lantern is a six-mode selection photon lantern; The mode light in the signal light is: fundamental mode LP 01 Mode light, LP 11a Mode light, LP 11b Mode light, LP 21a Mode light, LP 21b Mode light and LP 02 Mode light.

7. The few-mode erbium-doped fiber amplifier system according to claim 6, characterized in that: The number of the optical isolators is the same as the number of the mode lights, and the multiple optical isolators are also used to reduce the influence of reflected light on the light amplification process in the transmission of the few-mode erbium-doped optical fiber.

8. The few-mode erbium-doped fiber amplifier system according to claim 1, characterized in that: The light detection device comprises: A charge coupled camera is arranged on the output optical path of the target light and is used to collect the spot information of the target light; A spectrometer is arranged on the output optical path of the target light and is used to obtain power information of the target light.

9. The few-mode erbium-doped fiber amplifier system according to claim 8, characterized in that: The few-mode erbium-doped fiber amplifier system further comprises: A multimode jumper is used to connect the few-mode erbium-doped optical fiber and the spectrometer to measure the power information of the target light.

10. The few-mode erbium-doped fiber amplifier system according to any one of claims 1 to 9, characterized in that: The few-mode erbium-doped fiber amplifier system further comprises: The tunable attenuator is arranged on the outgoing light path of the signal light source and is used to adjust the power of the signal light so that each mode light in the signal light reaches a preset power.

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