Multi-mode fiber optical interconnection coupling connection method and device for mode dispersion suppression

Abstract

The invention discloses a multimode fiber optical interconnection coupling connection method and a multimode fiber optical interconnection coupling connection device for mode dispersion suppression. The connection method is characterized by comprising the following steps of: generating a single-mode optical signal by using a single-mode laser light source and collimating the single-mode optical signal; coupling a single-mode optical signal into a multimode optical fiber, monitoring the optical power of the output end of the multimode optical fiber, and maximizing the optical power to realize initial coupling optimization; the method comprises the following steps: decomposing transmission modes in a multimode fiber through a mode demultiplexer, acquiring light field distribution of each mode by utilizing a CCD (Charge Coupled Device), and marking mode orders in a descending order according to mode effective refractive indexes; through the combination of a high-precision displacement adjusting mechanical structure and the mode demultiplexer, the coupling condition of a single-mode optical signal and the multimode optical fiber can be accurately adjusted, so that the optical power of a high-order mode is minimized, only fundamental mode transmission is reserved, the problem of mode dispersion caused by excitation of the high-order mode of the multimode optical fiber is effectively solved, and the stability of the multimode optical fiber is improved. Therefore, the multimode optical fiber communication bandwidth is obviously improved, the coupling process is simplified, the dependence on complex optical elements is reduced, and the coupling cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a multi-mode optical fiber optical interconnection coupling connection method and device with mode dispersion suppression. Background Art

[0002] With the rapid development of technologies such as artificial intelligence, cloud computing, and the Internet of Things, data center bandwidth demand is doubling every two years, and data transmission rates are evolving toward 800Gbps and above. Currently, the single-channel, single-wavelength PAM4 modulation rate of 800G high-speed optical modules has exceeded 200Gbps, and higher-speed optical modules such as 1.6T and 3.2T, capable of single-channel, single-wavelength transmissions of 400Gbps and above, are also being gradually promoted and iterated to lower-tier markets. This makes it increasingly difficult for existing multimode optical fibers (OM3, OM4, and OM5) to meet the communication speed requirements of optical interconnect applications within data centers over short distances of 1m to 400m, such as those covering SR and DR scenarios. On the other hand, at the optical signal transceiver end, single-mode optical modules based on single-mode laser sources will gradually replace multimode optical modules and become the mainstream choice in this scenario, thanks to their higher transmission rates, longer transmission distances, lower power consumption, and lower cost. Since the operating wavelengths of currently commercially mature single-mode optical fibers are mainly concentrated in the O-band and C-band, the 850nm single-mode optical fiber for SR and DR scenarios has a smaller core, is technically difficult to prepare, and is expensive. Therefore, it is necessary to use single-mode optical modules with multimode optical fibers. This involves the coupling connection between the optical transmitter module (TOSA) inside the single-mode optical module and the multimode optical fiber, as well as between the multimode optical fiber and the multimode optical fiber, and maintaining the fundamental mode transmission in the multimode optical fiber.

[0003] The modal dispersion of multimode fiber is a key factor limiting its bandwidth. Because different modes of light propagate at different speeds in the fiber, the optical signal is broadened and distorted during transmission, thus limiting the data transmission rate. This dispersion phenomenon makes it difficult for multimode fiber to meet high-speed transmission requirements in high-bandwidth scenarios, becoming a technical bottleneck. When a single-mode laser is incident on a multimode fiber, if the laser spot and the center of the multimode fiber core are laterally misaligned, or the laser beam's incident optical axis is offset from the normal direction of the multimode fiber end face, or the laser spot size does not match the size of the fundamental mode within the multimode fiber, the optical signal will generate higher-order modes after entering the multimode fiber. This modal dispersion effect will then cause the bandwidth performance of the multimode fiber to degrade. Therefore, maintaining fundamental mode transmission in multimode fiber is crucial.

[0004] Currently, there are three main methods for coupling single-mode lasers into multimode fibers while maintaining fundamental mode transmission: Optimize fiber design, for example, by using special fiber structures, such as graded-index fiber, where the core refractive index decreases gradually from the center outward, allowing light to propagate in a closer-to-single-mode manner in the fiber core and reducing the excitation of higher-order modes. OM3, OM4, and OM5 fibers fall into this category. The nonlinear effects of optical fibers are used to attenuate and filter out higher-order modes, such as the self-focusing effect. By controlling the optical power and fiber length, the higher-order modes are gradually attenuated due to energy loss during transmission, while the fundamental mode is retained. By controlling the input light conditions and precisely adjusting the single-mode laser spot size, beam quality, and alignment accuracy with the optical fiber to match the fundamental mode distribution of the multimode fiber, or by employing beam shaping techniques such as using a specific lens system or grating to shape the input light to match the fundamental mode distribution of the multimode fiber, the excitation of higher-order modes is reduced. To this end, a method and device for multimode fiber optical interconnection and coupling with modal dispersion suppression is proposed. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems and to provide a multimode optical fiber optical interconnection coupling connection method and device with modal dispersion suppression.

[0006] To achieve the above-mentioned object, the present invention provides the following technical solution: a multimode optical fiber interconnection coupling connection method with modal dispersion suppression, characterized in that the connection method is applied to suppress the modal dispersion of multimode optical fibers, and the specific connection method is as follows: 1) Use a single-mode laser light source to generate and collimate a single-mode optical signal; 2) Couple the single-mode optical signal into the multimode optical fiber, monitor the optical power at the output of the multimode optical fiber and maximize it to achieve preliminary coupling optimization; 3) Decompose the transmission mode in the multimode optical fiber through the mode demultiplexer, use CCD to collect the light field distribution of each mode, and mark the mode order in descending order according to the mode effective refractive index; 4) Couple each mode to the optical fiber array, and use photodetectors to receive and detect the optical power of each output port of the optical fiber array. 5) The coupling position between the single-mode optical signal and the multimode optical fiber is adjusted through a high-precision displacement adjustment mechanical structure to minimize the optical power corresponding to several high-order modes with almost the same effective refractive index; Longitudinal direction: Adjust the spot size of the single-mode laser incident on the multimode fiber to minimize the optical power of at least one set of degenerate high-order modes; Lateral and angular: Adjust the relative misalignment between the center of the incident multimode fiber core and the center of the single-mode laser to minimize the optical power of the residual degenerate high-order mode; 6) Fix the position of the multimode optical fiber to ensure that the power of all higher-order modes except the fundamental mode is minimized to achieve the suppression of modal dispersion.

[0007] Preferably, step 2 is integrated into a transmitter optical module (TOSA) and the curing position is located at the multimode optical fiber input end inside the transmitter optical module (TOSA).

[0008] Preferably, the optical fiber array and the photodetector in step 4 are integrated into a receiving optical module (ROSA).

[0009] Preferably, the optical receiving module (ROSA) and the optical transmitting module (TOSA) are connected via an optical fiber connector; the optical fiber connector satisfies the requirement of lateral dislocation ≤ 1 μm and is of the type of MTP / MPO, LC or SC.

[0010] A connection device prepared by a multimode fiber optical interconnection coupling connection method with suppressed mode dispersion includes a single-mode laser light source for generating a high-purity single-mode optical signal, a multimode optical fiber as a transmission medium coupled to the single-mode optical signal, a mode demultiplexer connected to the multimode optical fiber for decomposing multiple modes in the multimode optical fiber and coupling them into an optical fiber array, a CCD imaging lens aligned with the output surface of the mode demultiplexer for imaging the distribution of each mode light field decomposed by the mode demultiplexer, a photodetector connected to the optical fiber array for detecting the power of the optical signal emitted from each output port of the optical fiber array, and a high-precision displacement adjustment mechanical structure for adjusting the position of the single-mode optical signal and the multimode optical fiber during coupling.

[0011] Preferably, the single-mode laser light source includes a single-mode laser light source and a collimating optical element; and the single-mode laser includes a single-mode VCSEL, PCSEL or LD.

[0012] Preferably, the mode demultiplexer includes a photon lantern, a multi-phase plate cascade transmission device, a reflective multi-plane multiplexing or demultiplexing device composed of a phase plate and a reflective surface, or a reflective multi-plane multiplexing or demultiplexing device composed of a multi-phase plate combination.

[0013] Preferably, the optical fiber array includes a single-mode optical fiber array, a few-mode optical fiber array, a multi-mode optical fiber array or a multi-core optical fiber array with a common cladding.

[0014] Preferably, the high-precision displacement adjustment mechanical structure includes a piezoelectric ceramic driver, a motor-driven fine-tuning platform or a manual fine-tuning device.

[0015] The beneficial effects of the present invention are as follows: through the combination of a high-precision displacement adjustment mechanical structure and a mode demultiplexer, the coupling conditions between single-mode optical signals and multimode optical fibers can be precisely adjusted, minimizing the optical power of high-order modes and retaining only fundamental mode transmission. This effectively solves the problem of modal dispersion caused by high-order mode excitation in multimode optical fibers, thereby significantly improving the communication bandwidth of multimode optical fibers, simplifying the coupling process, reducing dependence on complex optical components, and lowering coupling costs. The coupling device is suitable for multimode optical fibers of various lengths and can be used with mainstream OM3, OM4, and OM5 multimode optical fibers, enhancing the universality of application scenarios. It can be widely used in short-distance optical interconnection scenarios within data centers, such as SR and DR scenarios, meeting the transmission requirements of high-speed optical modules of 800Gbps and above. Through CCD imaging mirrors and photodetectors, the optical power at the output end of the multimode optical fiber is monitored and optimized in real time to ensure that the single-mode optical signal is efficiently coupled into the multimode optical fiber. This overcomes the problems mentioned in the background technology of large energy loss and low efficiency when using the nonlinear effect of optical fiber to attenuate high-order modes. While ensuring the suppression of high-order modes, it can maximize the transmission efficiency of the optical signal and significantly reduce the power consumption and cost of the data center. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the connection relationship and pattern decomposition process of the present invention; Figure 2 This is the connection relationship between the optical transmitter module (TOSA), the optical receiver module (ROSA) and the multimode optical fiber array of the present invention.

[0017] Figure 3 The invention relates to the connection relationship between the optical receiving module (ROSA) and the optical transmitting module (TOSA) of the present invention and the external multimode optical fiber array via the optical fiber connector. DETAILED DESCRIPTION

[0018] Next we combine Figure 1-Figure 3 The multimode optical fiber optical interconnection coupling connection method and device with modal dispersion suppression described in the present invention are further described.

[0019] The present invention takes the mode suppression coupling connection between a 4-channel SR optical module based on an 850nm single-mode VCSEL laser and a multimode optical fiber as an example to describe the specific implementation of the present invention in detail: 1) Using an 850nm single-mode VCSEL as the light source, the integrated collimating lens collimates the divergent light beam emitted by the VCSEL to form a Gaussian-distributed single-mode optical signal. The collimated single-mode optical signal can be more effectively coupled with the multimode optical fiber.

[0020] 2) At connection node 1, the collimated single-mode optical signal is coupled into the multimode optical fiber. By monitoring and adjusting the output optical power, it is ensured that as much single-mode optical signal as possible can enter the multimode optical fiber, laying the foundation for subsequent mode control.

[0021] 3) At connection node 1, the transmission modes in the multimode fiber are decomposed using a photonic lantern-type mode demultiplexer. The light field distribution of each mode is then collected using a CCD. The modes are labeled in descending order of their effective refractive index, namely fundamental mode, high-order mode 1, high-order mode 2, high-order mode 3, high-order mode 4, and high-order mode 5, to facilitate accurate identification of different modes. 4) Each decomposed mode is coupled into a fiber array, which includes but is not limited to single-mode, few-mode, and multi-mode types. The optical signal power from each output port of the fiber array is received and detected by a photodetector, corresponding to the fundamental mode, high-order mode 1, high-order mode 2, high-order mode 3, high-order mode 4, and high-order mode 5, respectively, to achieve accurate measurement of the optical power of each mode.

[0022] 5) The position of the single-mode optical signal and the multimode optical fiber is adjusted at the connection node 1 through a high-precision displacement adjustment mechanical structure. The high-precision displacement adjustment mechanical structure has multi-axis adjustment functions in the horizontal, angular, and vertical directions. Through precise displacement adjustment, effective control of the high-order mode optical power is achieved.

[0023] First, the single-mode laser spot size of the incident multimode fiber is adjusted longitudinally. The optical power at the output port of the fiber array corresponding to each mode is monitored to minimize the optical power corresponding to high-order mode 1 and high-order mode 2. High-order mode 1 and high-order mode 2 should have almost the same effective refractive index and can be regarded as a degenerate mode group. The relative misalignment between the center of the incident multimode fiber core and the center of the single-mode laser is adjusted laterally and angularly to minimize the optical powers corresponding to the remaining high-order modes 3, 4, and 5. High-order modes 3, 4, and 5 have almost identical effective refractive indices and can be considered a degenerate mode group. 6) Fixing the position of the multimode optical fiber to ensure that the power of all higher-order modes except the fundamental mode is minimized, thereby suppressing modal dispersion. Here, the modal isolation between the fundamental mode and the higher-order modes is defined as no less than X dB. The higher the isolation X, the larger the communication bandwidth of the corresponding multimode optical fiber. Typical values ​​of X can be 15, 20, 25, 30, and even larger. The fixing methods described include UV dispensing glue, thermal curing glue, mechanical fixing devices, or optical glue.

[0024] 7) Repeat steps 1-6, and respectively connect the multimode optical fiber and the single-mode laser light source with mode dispersion suppression at connection nodes 2, 3 and 4; wherein the single-mode laser beams connecting nodes 2, 3 and 4 can be composed of collimated single-mode beams emitted by three independent 850nm single-mode VCSEL laser devices or a collimated single-mode beam array emitted by an 850nm single-mode VCSEL array laser, the VCSEL emission units corresponding to each sub-beam of the array can be independently controlled, and the VCSEL array has at least four VCSEL units; the connection is integrated into the optical transmitter module (TOSA), and the multimode optical fiber and the optical fiber detector are connected and integrated into the optical receiver module (ROSA).

[0025] 8) The optical receiver module (ROSA) and the optical transmitter module (TOSA) are connected to the external pluggable multimode fiber array through the optical fiber connector of the optical module port. The optical fiber connector has high alignment and limiting accuracy, with an accuracy of not less than 1um. The selected optical fiber connector can ensure that there is a small lateral misalignment between the multimode fiber array inside the optical module and the external pluggable multimode fiber array. At the same time, the distance between the internal and external optical fiber ports is reasonable to ensure that the fundamental mode size of the internal multimode fiber emitted at the connection nodes 5, 6, 7, 8 and 9, 10, 11 and 12 is incident from the optical transmitter module (TOSA) to the external pluggable multimode fiber or the internal multimode fiber of the optical receiver module (ROSA). When it is incident, the degree of mismatch with the fundamental mode size in the corresponding incident multimode fiber is small, ensuring effective suppression of high-order mode excitation.

[0026] At the same time, a mode demultiplexer is used to monitor the excitation of high-order modes at the output ports of the external multimode fibers on the same side as connection nodes 5, 6, 7, and 8. For connection nodes 9, 10, 11, and 12, this method is slightly different. Before the ROSA module is packaged, the high-order mode excitation at the output ports of the multimode fibers on the opposite sides of connection nodes 9, 10, 11, and 12 must be monitored using this method.

[0027] The above embodiments are intended to illustrate the present invention, not to limit the present invention. Any solution that is a simple transformation of the present invention falls within the protection scope of the present invention.

Claims

1. A multimode fiber optical interconnection coupling connection method with modal dispersion suppression, characterized by: This connection method is used to control the modal dispersion of multimode optical fibers. The specific connection method is as follows: 1) Use a single-mode laser light source to generate and collimate a single-mode optical signal; 2) Couple the single-mode optical signal into the multimode optical fiber, monitor the optical power at the output of the multimode optical fiber and maximize it to achieve preliminary coupling optimization; 3) Decompose the transmission mode in the multimode optical fiber through the mode demultiplexer, use CCD to collect the light field distribution of each mode, and mark the mode order in descending order according to the mode effective refractive index; 4) Couple each mode to the optical fiber array, and use photodetectors to receive and detect the optical power of each output port of the optical fiber array. 5) The coupling position between the single-mode optical signal and the multimode optical fiber is adjusted through a high-precision displacement adjustment mechanical structure to minimize the optical power corresponding to several high-order modes with almost the same effective refractive index; Longitudinal direction: Adjust the spot size of the single-mode laser incident on the multimode fiber to minimize the optical power of at least one set of degenerate high-order modes; Lateral and angular: Adjust the relative misalignment between the center of the incident multimode fiber core and the center of the single-mode laser to minimize the optical power of the residual degenerate high-order mode; 6) Fix the position of the multimode optical fiber to ensure that the power of all higher-order modes except the fundamental mode is minimized to achieve the suppression of modal dispersion.

2. The method for optical interconnection and coupling of multimode optical fibers with modal dispersion suppression according to claim 1, characterized in that: Step 2 is integrated into the optical transmitter assembly (TOSA) and the curing position is located at the multimode optical fiber input end inside the optical transmitter assembly (TOSA).

3. The method for optical interconnection and coupling of multimode optical fibers with modal dispersion suppression according to claim 2, characterized in that: The optical fiber array and photodetector in step 4 are integrated into the optical receiving module (ROSA).

4. The method for optical interconnection and coupling of multimode optical fibers with modal dispersion suppression according to claim 3, characterized in that: The optical receiving module (ROSA) and the optical transmitting module (TOSA) are connected via an optical fiber connector; the optical fiber connector satisfies the requirement of lateral dislocation ≤ 1 μm and is of the type of MTP / MPO, LC or SC.

5. A device prepared by the method for optical interconnection and coupling of multimode optical fibers with modal dispersion suppression according to any one of claims 1 to 4, characterized in that: The invention comprises a single-mode laser light source for generating a high-purity single-mode optical signal, a multi-mode optical fiber as a transmission medium coupled with the single-mode optical signal, a mode demultiplexer connected to the multi-mode optical fiber for decomposing multiple modes in the multi-mode optical fiber and coupling them into an optical fiber array respectively, a CCD imaging lens aligned with the output surface of the mode demultiplexer for imaging the distribution of each mode light field decomposed by the mode demultiplexer, a photoelectric detector connected to the optical fiber array for detecting the power of the optical signal emitted from each output port of the optical fiber array, and a high-precision displacement adjustment mechanical structure for adjusting the position of the single-mode optical signal and the multi-mode optical fiber during coupling.

6. The multimode fiber optical interconnection and coupling device with modal dispersion suppression according to claim 5, characterized in that: The single-mode laser light source includes a single-mode laser light source and a collimating optical element; the single-mode laser includes a single-mode VCSEL, PCSEL or LD.

7. The multimode fiber optical interconnection and coupling device with modal dispersion suppression according to claim 5, characterized in that: The mode demultiplexer includes a photon lantern, a multi-phase plate cascade transmission device, a reflective multi-plane multiplexing or demultiplexing device combining a phase plate and a reflective surface, and a reflective multi-plane multiplexing or demultiplexing device combining multiple phase plates.

8. The multimode fiber optical interconnection and coupling device with modal dispersion suppression according to claim 5, characterized in that: The optical fiber array includes one or more combinations of a single-mode optical fiber array, a few-mode optical fiber array, a multi-mode optical fiber array, or a multi-core optical fiber array with a common cladding.

9. The multimode fiber optical interconnection coupling device with modal dispersion suppression according to claim 5, characterized in that The high-precision displacement adjustment mechanical structure includes a piezoelectric ceramic driver, a motor-driven fine-tuning platform or a manual fine-tuning device.

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