Active mode demultiplexing module

Abstract

The invention discloses an active mode demultiplexing module which comprises a mode converter, two optical circulators and a bidirectional semiconductor optical amplifier. The mode converter is used for converting a high-order mode into a fundamental mode to complete primary mode demultiplexing, fundamental mode signals after primary demultiplexing are injected into the bidirectional semiconductor optical amplifier through the two optical circulators from the positive direction and the negative direction respectively, and the signals after being shaped by the bidirectional semiconductor optical amplifier are output by the corresponding optical circulators. A bidirectional symmetrical injection structure is formed, different propagation is beneficial to separation of different signals, and mutual interference, namely mode crosstalk, between forward and reverse signals can be effectively reduced, so that a mode demultiplexing function is better completed, and an output signal has higher signal quality than a primary demultiplexing signal. Besides, by optimizing and adjusting the driving current of the bidirectional semiconductor optical amplifier or an auxiliary optical pumping mode, not only can the gain of the mode channel be dynamically adjusted, but also the power balance of the mode channel and the demultiplexing of a high extinction ratio mode can be realized; the method is especially suitable for receiving few-mode signals in a mode division multiplexing (MDM) optical transmission system and constructing optical switching nodes in a multi-dimensional multiplexing optical network.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to an active mode demultiplexing module having multiple functions such as mode demultiplexing, crosstalk suppression and gain equalization. Background Art

[0002] With the widespread adoption of technologies such as wavelength division multiplexing, polarization multiplexing, and high-order modulation formats, the spectral efficiency of existing single-mode fiber communication systems has been greatly improved. However, the nonlinear effects of optical fibers currently limit the further expansion of single-mode fiber capacity, making it difficult to meet the needs of future high-bandwidth communication networks. To address this, researchers have begun to leverage Mode Division Multiplexing (MDM) technology, which utilizes multiple orthogonal modes transmitted in parallel within few-mode fiber (FMF) to effectively increase fiber channel transmission capacity and spectral efficiency.

[0003] In recent years, multi-mode fiber optic (MDM) technology has become a research hotspot in optical fiber communications, with mode multiplexing and demultiplexing being the most critical processes. In practical few-mode fiber transmission systems and networks, fiber bending and imperfections in modal components such as mode multiplexers and demultiplexers inevitably introduce inter-mode crosstalk. As fiber transmission distances and the number of cascaded MDM optical switching nodes increase, inter-mode crosstalk accumulates, severely impacting system performance. This suggests that inter-mode crosstalk, to a certain extent, restricts the widespread adoption of MDM technology. Currently, crosstalk compensation can be achieved through electrical-domain multiple-input, multiple-output (MIMO) digital signal processing methods. However, this approach increases in complexity exponentially with the number of modal channels and is applicable only to the transceiver side of an MDM system.

[0004] To better meet future communication capacity demands, MDM and wavelength division multiplexing technologies must be used in conjunction, gradually forming a multi-dimensional multiplexed optical network. This requires that the corresponding multi-dimensional optical switching nodes introduce sufficiently low modal crosstalk while also compensating for fiber attenuation and node insertion loss. In reality, mode multiplexers and demultiplexers, core components of MDM fiber transmission systems and multi-dimensional optical switching nodes, still exhibit relatively high modal crosstalk and insertion loss, and uneven optical power across mode channels, hindering the further promotion and application of MDM technology. Furthermore, existing electrical-domain MIMO technologies based on digital signal processing cannot meet the optical-domain transparency requirements of multi-dimensional optical switching nodes. Therefore, there is an urgent need to design and develop a mode demultiplexing module with sufficiently low modal crosstalk while also incorporating optical amplification or gain equalization capabilities to meet the application requirements of MDM fiber transmission systems and multi-dimensional optical switching nodes. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide an active mode demultiplexing module to reduce mode crosstalk and improve the mode extinction ratio during the mode demultiplexing process, while also having optical amplification or gain equalization to meet the application requirements of MDM fiber optic transmission systems and multi-dimensional optical switching nodes.

[0006] To achieve the above-mentioned object of the invention, the active mode demultiplexing module of the present invention includes:

[0007] The mode converter is a passive mode demultiplexer, which is used to convert the two-mode mode-division multiplexed signals in the few-mode fiber into base-mode signals that can be transmitted in the single-mode fiber, completing the primary mode demultiplexing. The two base-mode signals S1 and S2 obtained after the primary mode demultiplexing are output from the two single-mode fiber ends respectively;

[0008] It is characterized by further comprising:

[0009] The two optical circulators CIR1 and CIR2 are both three-port optical devices including an input port, an output port, and a common port. The input ports of the two optical circulators CIR1 and CIR2 are connected to two single-mode optical fiber ends of the mode converter through single-mode optical fibers.

[0010] A bidirectional semiconductor optical amplifier, whose two ports P1 and P2 are connected to the common ports of two optical circulators CIR1 and CIR2 respectively;

[0011] Two fundamental mode signals S1 and S2 are input from the input ports of the two optical circulators CIR1 and CIR2, respectively. The fundamental mode signal S1 is forwardly input to the port P1 of the bidirectional semiconductor optical amplifier through the optical circulator CIR1. After being processed by the bidirectional semiconductor optical amplifier, the signal is output from the port P2 to the common port of the optical circulator CIR2. The signal then passes through the optical circulator CIR2 and is output from the output port of the optical circulator CIR2. The fundamental mode signal S2 is reversely input to the port P2 of the bidirectional semiconductor optical amplifier through the optical circulator CIR2. After being processed by the bidirectional semiconductor optical amplifier, the signal is output from the port P1 to the common port of the optical circulator CIR1. The signal then passes through the optical circulator CIR1 and is output from the output port of the optical circulator CIR1.

[0012] The object of the invention of the present invention is achieved like this:

[0013] The active mode demultiplexing module of the present invention includes a mode converter, two optical circulators, and a bidirectional semiconductor optical amplifier. The mode converter is used to convert high-order modes into fundamental modes, completing primary mode demultiplexing. The fundamental mode signals after primary demultiplexing are injected into the bidirectional semiconductor optical amplifier in both forward and reverse directions through the two optical circulators. The signals shaped by the bidirectional semiconductor optical amplifiers are then output by the corresponding optical circulators, forming a bidirectional symmetrical injection structure. Differential propagation helps separate different signals, effectively reducing mutual interference between forward and reverse signals, namely mode crosstalk, thereby better completing the mode demultiplexing function. The output signal has higher signal quality than the primary demultiplexed signal. In addition, by optimizing and adjusting the driving current or auxiliary optical pumping method of the bidirectional semiconductor optical amplifier, not only can the mode channel gain be dynamically adjusted, but also the power balancing of the mode channel and high extinction ratio mode demultiplexing can be achieved. This makes it particularly suitable for receiving few-mode signals in mode division multiplexing (MDM) optical transmission systems and for constructing optical switching nodes in multi-dimensional multiplexing optical networks.

[0014] Compared with the prior art, the active mode demultiplexing module of the present invention has the following beneficial effects:

[0015] (1) The use of bidirectional semiconductor optical amplifiers can better separate mode signals, avoid inter-channel interference, and facilitate the realization of mode demultiplexing function;

[0016] (2) By utilizing the nonlinear shaping effect of bidirectional semiconductor optical amplifiers, the crosstalk introduced by the mode demultiplexing process can be effectively suppressed, thereby achieving mode demultiplexing with a high extinction ratio;

[0017] (3) The input power required by the bidirectional semiconductor optical amplifier is lower, which is particularly suitable for the activation of the mode demultiplexer, thereby realizing multiple functions such as optical amplification and mode power balancing;

[0018] (4) The active mode demultiplexing module of the present invention can replace the traditional mode demultiplexer and is particularly suitable for extending the transmission distance of the MDM system and building a multi-dimensional optical switching node with low crosstalk. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the principle of the active mode demultiplexing module of the present invention;

[0020] Figure 2 It is a graph showing the output power of a bidirectional semiconductor optical amplifier changing with input power;

[0021] Figure 3 It is the improvement of mode extinction ratio (ER) and the effect of mode channel power equalization;

[0022] Figure 4Schematic diagram of the application of the active mode demultiplexing module of the present invention in the OOK-MDM system;

[0023] Figure 5 This is the impact of the active mode demultiplexing module of the present invention on the bit error rate (BER) of the OOK-MDM system. DETAILED DESCRIPTION

[0024] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0025] Figure 1 It is a schematic diagram of the principle of the active mode demultiplexing module of the present invention.

[0026] In this embodiment, if Figure 1 The active mode demultiplexing module of the present invention comprises a mode converter, namely a passive mode demultiplexer 1, two optical circulators CIR1 and CIR2, and a bidirectional semiconductor optical amplifier 2. 01 With LP 11 (LP 11 The mode signal includes two orthogonal mode signals LP 11e LP 11o ) The demultiplexing process of two spatial mode channels is taken as an example to illustrate the working mechanism of the active mode demultiplexing module of the present invention.

[0027] The mode converter is a passive mode demultiplexer 1 that converts the two-mode mode multiplexing signal in the few-mode fiber (FMF) into LP 01 With LP 11 The mode signal is converted into a fundamental mode signal that can be transmitted in a single-mode fiber (SMF), completing primary mode demultiplexing. The two fundamental mode signals S1 and S2 obtained after primary mode demultiplexing are output from the two ends of the single-mode fiber. In this embodiment, the mode converter has an insertion loss of 2.5dB and a mode extinction ratio greater than 10dB.

[0028] like Figure 1 As shown, the two optical circulators CIR1 and CIR2 are each a three-port optical device consisting of an input port, an output port, and a common port. The input ports of the two optical circulators CIR1 and CIR2 are connected to the two single-mode fiber ends of the mode converter via single-mode fiber. The output ports of the optical circulators CIR1 and CIR2 also serve as the output ports of the entire active mode demultiplexing module.

[0029] The two ports P1 and P2 of the bidirectional semiconductor optical amplifier 2 are connected to the common ports of the two optical circulators CIR1 and CIR2 respectively.

[0030] The two fundamental mode signals S1 and S2 obtained after primary mode demultiplexing are input from the input ports of two optical circulators CIR1 and CIR2 respectively. The fundamental mode signal S1 is L P01 The mode signal is forward input to port P1 of bidirectional semiconductor optical amplifier 2 through optical circulator CIR1, and after being processed by bidirectional semiconductor optical amplifier 2, it is output from port P2 to the common port of optical circulator CIR2, and then passes through optical circulator CIR2 and is output at the output port of optical circulator CIR2. Similarly, the fundamental mode signal S2 is LP 11 The mode signal is reverse-input into port P2 of the bidirectional semiconductor optical amplifier through optical circulator CIR2. After processing by the bidirectional semiconductor optical amplifier, it is output from port P1 to the common port of optical circulator CIR1. It then passes through optical circulator CIR1 and is output at the output port of optical circulator CIR1. This creates a bidirectional symmetrical injection structure, which prevents interference between the two signals and better implements the mode demultiplexing function.

[0031] Structurally, the active mode demultiplexing module of the present invention is equivalent to a mode converter (or traditional passive mode demultiplexer) with the addition of an active device, a bidirectional semiconductor optical amplifier (SOA). This not only suppresses mode signal crosstalk but also achieves balanced amplification of the mode signals. Two mode signals are injected from different ports of the bidirectional semiconductor optical amplifier (SOA) and interact nonlinearly within the same active region. By optimizing and adjusting the drive current or auxiliary optical pumping mode of the bidirectional semiconductor optical amplifier (SOA), high extinction ratio demultiplexing of multi-mode signals can be achieved. Therefore, the active mode demultiplexing module of the present invention has low power input requirements, high extinction ratio mode demultiplexing, and balanced optical amplification. It is particularly suitable for receiving few-mode signals in mode division multiplexing (MDM) optical transmission systems and for constructing optical switching nodes in multi-dimensional multiplexing optical networks.

[0032] In the present invention, the mode converter converts all high-order modes in the few-mode fiber into the fundamental mode and demultiplexes them to multiple output ports. Therefore, the mode converter is also called a passive mode demultiplexer, such as a mode-selective photonic lantern, a mode-selective coupler, or a demultiplexing structure based on an integrated optical waveguide structure.

[0033] In this embodiment, the bidirectional semiconductor optical amplifier (SOA) is a dual-port active device that can process forward and reverse optical signals simultaneously, and has:

[0034] (1) The signals in the two directions can be of the same wavelength or different wavelengths. The two signals act in the same active area of ​​the bidirectional semiconductor optical amplifier (SOA). Different propagation helps to separate different signals, which can effectively reduce the mutual interference between the forward and reverse signals and ensure the ultimate realization of the mode demultiplexing process.

[0035] (2) The bidirectional semiconductor optical amplifier (SOA) operates in a nonlinear effect region, including but not limited to a gain compression effect induced by carrier saturation or a four-wave mixing (FWM) effect under auxiliary optical pumping, and utilizes the nonlinear effect of the bidirectional semiconductor optical amplifier (SOA) to achieve the purpose of signal shaping and improving signal quality, on the one hand, improving the mode extinction ratio in the mode demultiplexing process, and on the other hand, suppressing the amplifier spontaneous emission noise (ASE) noise in the mode channel;

[0036] (3) By adjusting the current injected into the active region of the bidirectional semiconductor optical amplifier (SOA) or the optical pumping method, the bidirectional semiconductor optical amplifier (SOA) can compensate for the imbalance of the mode channel power and achieve balanced optical amplification of the mode channels. For example, it can enhance the main signal and selectively suppress the crosstalk signal, or maintain the same extinction ratio improvement effect under different input power conditions.

[0037] In this embodiment, the structural parameters of the bidirectional semiconductor optical amplifier (SOA) used are shown in Table 1.

[0038] parameter Value Device length 600μm Active area width 3μm Active area thickness 220nm Internal loss coefficient <![CDATA[1000m -1 ]]> Linear recombination rate <![CDATA[0.5ns -1 ]]> Double carrier recombination rate <![CDATA[10 -16 m 3 / s]]> Auger Compounding Rate <![CDATA[1.3×10 -29 m 6 / s]]>

[0039] Table 1

[0040] The two signals act in the same active region of the bidirectional semiconductor optical amplifier (SOA). The bidirectional semiconductor optical amplifier (SOA) operates in the nonlinear effect region, and its gain depends on the carrier density in this region. When the injected signal power is small, the gain increases linearly; as the power increases, the gain gradually tends to saturation, thereby limiting the main signal and suppressing amplitude disturbances. In this embodiment, the bidirectional semiconductor optical amplifier (SOA) injected current is 210mA, the input optical power is -19.5dBm, and the output saturation power is -12.5dBm. The power transfer function is as follows: Figure 2 As shown. Working point selection Figure 2 The gain compression effect is strongest in the flat region (saturation region) of the middle curve. By optimizing and adjusting the driving current of the bidirectional semiconductor optical amplifier (SOA) or the auxiliary optical pumping mode, the extinction ratio performance of the two output signals can be better than that of the primary demultiplexing signal, thereby achieving high extinction ratio mode demultiplexing. P01 With LP 11 When two mode signals pass through the active mode demultiplexing module of the present invention, the extinction ratio (ER) variation curve is as follows: Figure 3 As shown in Figure 3, their modal extinction ratio can be improved by about 7.3dB at most.

[0041] In the present invention, by dynamically adjusting the carrier concentration in the bidirectional SOA, the gain of the two-way signal can be changed, and the power balance of the mode channel can be achieved while suppressing the inter-mode crosstalk. 01 When the mode signal power decreases, the bidirectional SOA can restore its power to the required level through gain compensation while suppressing the LP 11 The crosstalk leakage of the mode signal is reduced, thereby significantly improving the extinction ratio. This mechanism effectively solves the signal degradation problem caused by power imbalance in the passive demultiplexer, providing a key guarantee for the stable transmission of high-density MDM systems.

[0042] Compared with traditional passive demultiplexers, the active demultiplexing module of the present invention can effectively improve the signal transmission performance of MDM systems and networks. Figure 4 This is an application scenario of the present invention in an on-off keying (OOK) signal mode division multiplexing (OOK-MDM) system. Figure 5 (a) and (b) give the LP 01 With LP 11 The improvement of communication performance after the mode multiplexing signal passes through the module of the present invention is represented by the curve of bit error rate (BER) changing with signal-to-sequence ratio. Figure 5 It can be seen that LP 01 and LP 11 The bit error rates of the two modes were reduced from 10-9 to 10-12, and at BER = 10-9, their equivalent signal-to-sequence ratios (SXR) were improved by 5.65dB and 6.17dB, respectively. This shows that the active mode demultiplexing module disclosed in the present invention can suppress amplitude noise, thereby effectively reducing the bit error rate of the OOK-MDM system and greatly improving the reliability of the system's transmission information.

[0043] In this embodiment, two-mode mode division multiplexing signals in a few-mode optical fiber are provided. When more-mode mode division multiplexing signals are provided, any two of the mode division multiplexing signals can be processed according to the method of this embodiment.

[0044] Although the above describes the illustrative specific embodiments of the present invention to facilitate understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concepts of the present invention are protected.

Claims

1. An active mode demultiplexing module, comprising: The mode converter is a passive mode demultiplexer, which is used to convert the two-mode mode-division multiplexed signals in the few-mode fiber into base-mode signals that can be transmitted in the single-mode fiber, completing the primary mode demultiplexing. The two base-mode signals S1 and S2 obtained after the primary mode demultiplexing are output from the two single-mode fiber ends respectively; It is characterized by further comprising: The two optical circulators CIR1 and CIR2 are both three-port optical devices including an input port, an output port, and a common port. The input ports of the two optical circulators CIR1 and CIR2 are connected to two single-mode optical fiber ends of the mode converter through single-mode optical fibers. A bidirectional semiconductor optical amplifier, whose two ports P1 and P2 are connected to the common ports of two optical circulators CIR1 and CIR2 respectively; Two fundamental mode signals S1 and S2 are input from the input ports of the two optical circulators CIR1 and CIR2, respectively. The fundamental mode signal S1 is forwardly input to the port P1 of the bidirectional semiconductor optical amplifier through the optical circulator CIR1. After being processed by the bidirectional semiconductor optical amplifier, the signal is output from the port P2 to the common port of the optical circulator CIR2. The signal then passes through the optical circulator CIR2 and is output from the output port of the optical circulator CIR2. The fundamental mode signal S2 is reversely input to the port P2 of the bidirectional semiconductor optical amplifier through the optical circulator CIR2. After being processed by the bidirectional semiconductor optical amplifier, the signal is output from the port P1 to the common port of the optical circulator CIR1. The signal then passes through the optical circulator CIR1 and is output from the output port of the optical circulator CIR1.

2. The active mode demultiplexing module according to claim 1, characterized in that The bidirectional semiconductor optical amplifier operates in a nonlinear effect region, including but not limited to a gain compression effect induced by carrier saturation or a four-wave mixing effect under auxiliary optical pumping. The nonlinear effect of the bidirectional semiconductor optical amplifier is utilized to achieve the purpose of signal shaping and improving signal quality. On the one hand, the mode extinction ratio in the mode demultiplexing process is improved, and on the other hand, ASE noise in the mode channel is suppressed.

3. The active mode demultiplexing module according to claim 1, characterized in that: By adjusting the current size or optical pumping mode injected into the active region of the bidirectional semiconductor optical amplifier, the bidirectional semiconductor optical amplifier can compensate for the imbalance of mode channel power and realize balanced optical amplification of the mode channels.

Images