Low crosstalk mode division multiplexed optical amplifying device

Abstract

This invention discloses a low-crosstalk mode-division multiplexing optical amplification device, comprising: a mode discrimination module, a beam combiner, a beam splitter, a monitoring module, and a few-mode semiconductor optical amplification module. The mode-division multiplexed signal to be amplified is split into two paths by a mode selection coupler. One path is coupled to a single-mode fiber with different mode coupling efficiencies and converted into an electrical signal, which is then sent to the monitoring module. Based on the signal level, the monitoring module identifies the mode combination information at different times in the input mode-division multiplexed signal and generates control light with corresponding power. The other path is still a mode-division multiplexed signal, which is input to the few-mode semiconductor optical amplification module along with the input signal through the beam combiner. After amplification, the output is sent to the beam splitter to separate the amplified control light and the mode-division multiplexed signal, which are used as the gain control signal and the output signal of the entire device, respectively. In this invention, the sum of the power of the controlled light and the power of the mode multiplexed signal to be amplified is always kept at the same level, so that the carrier concentration is always kept at the same level and the input signal gain at different times can be kept consistent, thereby effectively suppressing the cross-gain modulation effect, while amplifying the optical signals of multiple modes, and can also automatically adjust the mode gain, which can meet the needs of low crosstalk optical amplification modules in long-distance mode division multiplexing systems and mode division multiplexing switching nodes.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber communication technology. More specifically, it relates to a low crosstalk mode division multiplexing optical amplifier that can simultaneously amplify multiple spatial mode signals and can be used to construct mode division multiplexing optical fiber transmission systems and optical switching nodes. Background Technology

[0002] With the rapid development of wavelength division multiplexing (WDM) and polarization multiplexing (PDM) technologies in single-mode fiber, the transmission capacity of fiber optic communication systems has been continuously increasing. However, fiber nonlinearity has gradually become the main factor restricting fiber transmission capacity, making it difficult to meet the exponentially growing capacity demand. Mode division multiplexing (MDM) technology allows multiple orthogonal spatial modes to be transmitted simultaneously in few-mode fiber, breaking through the capacity limitations of single-mode fiber and effectively improving the communication capacity of fiber optic communication systems.

[0003] With the development of MDM technology, corresponding optical devices in optical fiber communication systems have gradually upgraded from single-mode to few-mode, such as mode multiplexers / demultiplexers, few-mode optical couplers, and few-mode optical amplifiers. Among these, the few-mode optical amplifier is a crucial component of MDM optical fiber communication systems, amplifying the power of the mode signals and helping to extend system transmission distance and improve network performance. In long-distance transmission scenarios, the few-mode erbium-doped fiber amplifier (FM-EDFA) offers advantages such as high gain and seamless fiber connections, making it the most researched technology. However, factors such as erbium-doped fiber bending in FM-EDFA introduce significant inter-mode crosstalk, requiring its use in conjunction with multiple-input multiple-output (MIMO) digital signal processing. This significantly increases the system's hardware complexity and power consumption, and also limits the application of FM-EDFA in MIMO-free mode division multiplexing systems.

[0004] In contrast, few-mode semiconductor optical amplifiers (FM-SOA) offer significant advantages in terms of integration, small size, and low power consumption, providing a highly attractive solution for building compact MDM devices / modules. However, in the case of multimode input, FM-SOA suffers from cross-gain modulation (XGM) effects, which introduce additional mode crosstalk and dynamic signal distortion when multimode signals are amplified simultaneously.

[0005] There is an urgent need for a few-mode optical amplifier module in long-distance MDM systems and optical switching nodes that combines low mode crosstalk, high integration, and good amplification performance, and can be applied to various scenarios such as MIMO and MIMO-free. However, devices that meet these requirements are still difficult to obtain, which to some extent restricts the further promotion and application of MDM technology in practical optical communication networks. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a low crosstalk mode division multiplexing optical amplification device that can amplify multiple modes simultaneously while having sufficiently low mode channel crosstalk, thus meeting the requirements of low crosstalk optical amplification modules in long-distance mode division multiplexing systems and mode division multiplexing nodes.

[0007] To achieve the above-mentioned objective, the present invention provides a low crosstalk mode-division multiplexing optical amplification device, characterized in that it comprises:

[0008] The mode discrimination module consists of a mode selection coupler and a photoelectric converter. The mode selection coupler is a 1×2 three-port device, namely a few-mode input port, a few-mode output port, and a single-mode output port. The mode selection coupler consists of two optical fibers: one few-mode fiber and one single-mode fiber. The mode multiplexed signal to be amplified is input to the few-mode input port of the mode selection coupler in the mode discrimination module, and outputs from the few-mode output port through the few-mode fiber. During the transmission process in the few-mode fiber, the optical signals of different modes of the mode multiplexed signal are coupled from the few-mode fiber to the single-mode fiber with different coupling efficiencies of less than 1%, and output from the single-mode output port to the photoelectric converter for photoelectric conversion. The resulting electrical signal is sent to the monitoring module.

[0009] The monitoring module consists of an FPGA signal processor, a control light transmitter, and a control light receiver. The FPGA signal processor identifies the mode combination information at different times in the input modal multiplexed signal based on the signal level output by the photoelectric converter and issues instructions to the control light transmitter to generate control light with corresponding power, so that the power of the control light and the sum of the power of the modal multiplexed signal to be amplified are always kept at the same level.

[0010] The beam combiner controls the control light from the optical transmitter to combine the mode multiplexing signal output from the few-mode output port in the mode discrimination module into a single optical signal, which is then output to the few-mode semiconductor optical amplifier module.

[0011] The few-mode semiconductor optical amplifier module includes a few-mode optical input port, a few-mode optical output port, and an electrical drive interface. The active region volume of the few-mode semiconductor optical amplifier module supports the simultaneous amplification of multiple modes of optical signals. The optical signal from the beam combiner is input to the few-mode optical input port, amplified by the few-mode semiconductor optical amplifier module, and then output to the beam splitter from the few-mode optical output port.

[0012] The beam splitter separates the control light from the amplified optical signal and sends it to the control light receiver in the monitoring module for photoelectric conversion. The FPGA signal processor in the monitoring module outputs a drive current to the few-mode semiconductor optical amplifier module based on this photoelectric conversion signal, and adjusts its gain in real time. The optical signal after the control light is separated by the beam splitter is an amplified mode-multiplexed signal.

[0013] The objective of this invention is achieved as follows:

[0014] The low crosstalk mode-division multiplexing optical amplification device of the present invention includes: a mode discrimination module, a beam combiner, a beam splitter, a monitoring module, and a few-mode semiconductor optical amplification module. The mode-division multiplexed signal to be amplified is split into two paths by a mode selection coupler. One path is coupled to a single-mode optical fiber with different mode coupling efficiencies and is converted into an electrical signal by photoelectric conversion and sent to the monitoring module. In the monitoring module, the FPGA signal processor identifies the mode combination information at different times in the input mode-division multiplexed signal according to the signal level output by the photoelectric converter and issues a command to the control light transmitter to generate control light of corresponding power. The other path is still a mode-division multiplexed signal, which is input to the few-mode semiconductor optical amplification module together with the control light from the monitoring module through the beam combiner. After being amplified by the few-mode semiconductor optical amplification module, it is output from the few-mode optical output port to the beam splitter. The beam splitter separates the amplified control light and the mode-division multiplexed signal, which are used as the gain control signal and the output signal of the entire device, respectively. In this invention, the power of the control light and the sum of the power of the mode-multiplexed signal to be amplified are always kept at the same level. The injection of control light effectively controls the carrier fluctuations caused by the fluctuations in the input signal power in the few-mode semiconductor optical amplification module, so that the carrier concentration is always kept at the same level. Therefore, the input signal gain at different times can remain consistent, thereby effectively suppressing the cross-gain modulation (XGM) effect. At the same time, multiple modes of optical signals are amplified, and the mode gain can be automatically adjusted, which can meet the needs of low crosstalk optical amplification modules in long-distance mode-division multiplexing systems and mode-division multiplexing switching nodes.

[0015] Compared with the prior art, the low crosstalk mode division multiplexing optical amplification device of the present invention has the following beneficial effects:

[0016] (1) It can simultaneously amplify optical signals of multiple modes and maintain low inter-mode crosstalk, making it suitable for long-distance mode division multiplexing systems and mode division multiplexing optical switching nodes;

[0017] (2) The use of optical control effectively suppresses the cross-gain modulation effect in the few-mode semiconductor optical amplifier module, and is compatible with MIMO and MIMO-free mode division multiplexing system applications;

[0018] (3) By changing the power of the drive current of the few-mode semiconductor optical amplifier module, automatic gain control can be easily achieved, flexibly meeting different application requirements. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the principle of a specific embodiment of the low crosstalk mode division multiplexing optical amplification device of the present invention;

[0020] Figure 2These are the input waveforms for two different channel modes;

[0021] Figure 3 These are the output waveforms of the two mode channels without the addition of control light;

[0022] Figure 4 These are the output waveforms of the two mode channels after the control light is added;

[0023] Figure 5 This is a graph showing the input-output characteristics of the device of the present invention under two-mode input conditions. Detailed Implementation

[0024] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0025] Figure 1 This is a schematic diagram illustrating the principle of a specific embodiment of the low crosstalk mode division multiplexing optical amplification device of the present invention.

[0026] In this embodiment, as Figure 1 The low crosstalk mode-division multiplexing optical amplification device of the present invention comprises five parts: a mode discrimination module 1, a monitoring module 2, a beam combiner 3, a few-mode semiconductor optical amplification module 4, and a beam splitter 5, wherein:

[0027] The mode discrimination module 1 consists of a mode selection coupler 101 and a photoelectric converter 102. The mode selection coupler 101 is a 1×2 three-port device, namely, a few-mode input port, a few-mode output port, and a single-mode output port. The mode selection coupler 101 consists of two optical fibers: one few-mode fiber and one single-mode fiber. The mode multiplexed signal to be amplified is input to the few-mode input port of the mode selection coupler in the mode discrimination module, and is output from the few-mode output port through the few-mode fiber. During the transmission process in the few-mode fiber, the optical signals of different modes of the mode multiplexed signal are coupled from the few-mode fiber to the single-mode fiber with different coupling efficiencies of less than 1%, and are output from the single-mode output port to the photoelectric converter 102 for photoelectric conversion. The resulting electrical signal is sent to the monitoring module 2.

[0028] In this embodiment, the two optical fibers of the mode selection coupler are close enough to control the magnitude of the mode phase mismatch factor, so that energy coupling occurs between the corresponding optical fields of the two optical fibers. At the same time, by designing the core radius, refractive index distribution and coupling distance of the two optical fibers, the coupling efficiency of different modes can be changed.

[0029] The monitoring module 2 consists of an FPGA signal processor 201, a control light transmitter 202, and a control light receiver 203. The FPGA signal processor 201 identifies the mode combination information at different times in the input modal-division multiplexed signal based on the signal level output by the photoelectric converter 102 and issues commands to the control light transmitter to generate control light of corresponding power. This ensures that the power of the control light is always kept at the same level as the sum of the power of the modal-division multiplexed signal to be amplified. The injection of control light effectively controls the carrier fluctuations caused by the fluctuations in the input signal power in the few-mode semiconductor optical amplifier module 4, keeping the carrier concentration at a constant level. Therefore, the input signal gain at different times remains consistent, effectively suppressing the cross-gain modulation (XGM) effect.

[0030] The control light of the control light emitter 202 is combined with the mode multiplexing signal output from the few-mode output port of the mode discrimination module 1 through the beam combiner 3 to form a single optical signal, which is then output to the few-mode semiconductor optical amplifier module 4.

[0031] The few-mode semiconductor optical amplifier module 4 includes a few-mode optical input port, a few-mode optical output port, and an electrical drive interface. The active region volume of the few-mode semiconductor optical amplifier module 4 is much larger than that of the active region volume of the single-mode semiconductor optical amplifier, thus supporting the simultaneous amplification of multiple modes of optical signals. The optical signal from the beam combiner is input to the few-mode optical input port, amplified by the few-mode semiconductor optical amplifier module 4, and then output to the beam splitter 5 from the few-mode optical output port.

[0032] The amplified optical signal is separated from the control light by the beam splitter 5 and sent to the control light receiver in the monitoring module 2 for photoelectric conversion. The FPGA signal processor in the monitoring module outputs a drive current to the few-mode semiconductor optical amplifier module according to this photoelectric conversion signal, and adjusts its gain in real time. The optical signal after the control light is separated by the beam splitter is an amplified mode-multiplexed signal.

[0033] Example

[0034] This example uses and The working mechanism of this invention will be explained by taking the amplification process of two-mode 10Gb / s OOK signals as an example. Figure 2 These are the input waveforms of two mode channels.

[0035] In this invention, the mode selection coupler 101 that constitutes the mode identification module 1 can... and A small portion of the light from the two-mode channels is converted to single-mode fiber, while the majority of the light remains in the few-mode fiber. By appropriately designing the fiber structure and core spacing, and controlling the quasi-phase matching state between the two modes in the two fibers, the two modes in the few-mode fiber are coupled to the single-mode output port. In this example... and The coupling efficiencies from the mode optical signal to the single-mode output port (i.e., from the few-mode fiber to the single-mode fiber) are 0.021% and 0.4%, respectively. This ensures that different modes enter the single-mode fiber with different coupling efficiencies, while also ensuring that most of the power continues to propagate in the few-mode fiber. The photoelectric converter 102 in the mode discrimination module 1 converts the optical signal output from the single-mode output port of the mode selection coupler into an electrical signal. The monitoring module 2 then identifies the mode combination information at different times in the input mode-division multiplexed signal based on the signal level and issues a command to the control optical transmitter to generate control light with corresponding power. This ensures that the power of the control light and the sum of the power of the mode-division multiplexed signal to be amplified are always kept at the same level.

[0036] In this example, the structural parameters of the few-mode semiconductor optical amplifier module 4 used are shown in Table 1:

[0037]

[0038] Table 1

[0039] As can be seen from Table 1, in order to enable the active region volume of the few-mode semiconductor optical amplifier module to support the simultaneous amplification of multiple modes of optical signals, the active region volume of the few-mode semiconductor optical amplifier module in this invention is much larger than the active region volume of the single-mode semiconductor optical amplifier.

[0040] Active region volume of a single-mode semiconductor optical amplifier

[0041] Length: Approximately 0.5–2 mm (i.e., 500–2000 μm)

[0042] Width: Approximately 1.0–1.4 μm 56

[0043] Thickness: The active layer itself has a thickness of approximately 0.2 μm.

[0044] Take the median value:

[0045] Length = 1000 μm

[0046] Width = 1.2 μm

[0047] Thickness = 0.2 μm

[0048] The volume of the active region is approximately:

[0049]

[0050] Therefore, the active region volume of a single-mode semiconductor optical amplifier typically ranges from 100 to 600 μm³.

[0051] The active region volume of the few-mode semiconductor optical amplification module in this invention is approximately:

[0052]

[0053] In this example, firstly, the image to be enlarged... and Two-mode 10Gb / s OOK signals are input to mode discrimination module 1 via a few-mode fiber. The output port of its photoelectric converter 102 is connected to monitoring module 2, which generates control light accordingly. The control light and the mode-division multiplexed signal output from mode discrimination module 1 are then combined. and The two-mode 10Gb / s OOK signals are fed into the few-mode semiconductor amplifier module 4 via beam combiner 3, and the subsequent beam splitter 5 separates the amplified control light and the mode-division multiplexed signal. In this example, the relationship between the mode combination input to the few-mode semiconductor optical amplifier module 4 and the corresponding control light power is shown in Table 2.

[0054]

[0055] Table 2

[0056] As shown in Table 2, for different mode combinations in the input modal multiplexed signal at different times, control light with corresponding power is generated, so that the power of the control light and the sum of the power of the mode multiplexed signal to be amplified are always kept at the same level.

[0057] Figure 3 The amplified signal waveforms of the two mode channels without the addition of control light are given, and it can be seen that there is a large crosstalk between the two channels. Figure 4 It is the waveform of the two-mode signal amplified after the control light is added. Figure 4 It can be seen that the addition of control light stabilizes the gain of the two-mode signals and effectively suppresses crosstalk between modes caused by cross-gain modulation.

[0058] Figure 5 These are the input-output characteristic curves of the device of the present invention under two-mode input conditions. Figure 5 It can be seen that as the input power increases, the gain gradually approaches saturation. When the input power of both mode channels is 0dBm, The mode channel output power is 9.94 dBm. The output power of the mode channel is 9.38 dBm. By properly setting the power of the control light and the drive current of the few-mode semiconductor optical amplifier module 4, the gain of each mode can be effectively controlled, achieving adjustable mode gain.

[0059] This example only illustrates the case of two-mode signals. Adjustments can be made based on this example when using inputs with more modes and power combinations.

[0060] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A low crosstalk mode-division multiplexing optical amplification device, characterized in that, include: The mode discrimination module consists of a mode selection coupler and a photoelectric converter. The mode selection coupler is a 1×2 three-port device, namely a few-mode input port, a few-mode output port, and a single-mode output port. The mode selection coupler consists of two optical fibers: one few-mode fiber and one single-mode fiber. The mode multiplexed signal to be amplified is input to the few-mode input port of the mode selection coupler in the mode discrimination module, and outputs from the few-mode output port through the few-mode fiber. During the transmission process in the few-mode fiber, the optical signals of different modes of the mode multiplexed signal are coupled from the few-mode fiber to the single-mode fiber with different coupling efficiencies of less than 1%, and output from the single-mode output port to the photoelectric converter for photoelectric conversion. The resulting electrical signal is sent to the monitoring module. The monitoring module consists of an FPGA signal processor, a control light transmitter, and a control light receiver. The FPGA signal processor identifies the mode combination information at different times in the input modal multiplexed signal based on the signal level output by the photoelectric converter and issues instructions to the control light transmitter to generate control light with corresponding power, so that the power of the control light and the sum of the power of the modal multiplexed signal to be amplified are always kept at the same level. The beam combiner controls the control light from the optical transmitter to combine the mode multiplexing signal output from the few-mode output port in the mode discrimination module into a single optical signal, which is then output to the few-mode semiconductor optical amplifier module. The few-mode semiconductor optical amplifier module includes a few-mode optical input port, a few-mode optical output port, and an electrical drive interface. The active region volume of the few-mode semiconductor optical amplifier module supports the simultaneous amplification of multiple modes of optical signals. The optical signal from the beam combiner is input to the few-mode optical input port, amplified by the few-mode semiconductor optical amplifier module, and then output to the beam splitter from the few-mode optical output port. The beam splitter separates the control light from the amplified optical signal and sends it to the control light receiver in the monitoring module for photoelectric conversion. The FPGA signal processor in the monitoring module outputs a drive current to the few-mode semiconductor optical amplifier module based on this photoelectric conversion signal, and adjusts its gain in real time. The optical signal after the control light is separated by the beam splitter is an amplified mode-multiplexed signal.

2. The low crosstalk mode-division multiplexing optical amplification device according to claim 1, characterized in that, The two optical fibers of the mode selection coupler are close enough to control the magnitude of the mode phase mismatch factor, so that energy coupling occurs between the corresponding optical fields of the two fibers. At the same time, by designing the core radius, refractive index distribution and coupling distance of the two fibers, the coupling efficiency of different modes can be changed.

3. The low crosstalk mode-division multiplexing optical amplification device according to claim 1, characterized in that, The mode multiplexing signal to be amplified is and Two-mode 10Gb / s OOK signals and The coupling efficiencies from the mode optical signal to the single-mode output port, i.e. from the few-mode fiber to the single-mode fiber, are 0.021% and 0.4%, respectively.

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