A multimode waveguide coupler based on multiphase plane

Abstract

The present invention discloses a multimode waveguide coupler based on a multiphase plane, belonging to the field of optoelectronic communication devices. Combining two-photon polymerization femtosecond laser processing technology, the multiphase plane and microlens structure are utilized to achieve coupling conversion between the modes supported by multimode optical fiber and the modes supported by on-chip multimode waveguides, with low loss and low crosstalk. This invention achieves coupling conversion between the modes supported by multimode optical fiber and the modes supported by on-chip multimode waveguides, overcoming the limitations of mode division multiplexing technology in fiber-chip optical interconnect systems and promoting further improvements in the transmission capacity of optical interconnect systems.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic communication devices, and more particularly, relates to a multimode waveguide coupler based on a multiphase plane. Background Art

[0002] With the ever-increasing demand for internet data, new communication technologies are being rapidly developed and advanced, including various advanced modulation formats, signal multiplexing techniques, and digital signal processing algorithms. Each technological innovation promotes a massive increase in capacity. However, as single-mode optical fiber rapidly approaches its capacity limit, current technologies are reaching their limits in utilizing resources in frequency / wavelength, amplitude / phase, and time dimensions. Therefore, spatial division multiplexing (SDM) technology, as one of the most promising solutions to this new "capacity crisis," is being widely researched. SDM utilizes the lateral spatial dimension to establish multiple data channels for parallel data transmission. SDM can be categorized into two types: one is to utilize multiple orthogonal spatial modes within the same medium for co-linear transmission, known as mode division multiplexing (MDM). The orthogonality of the modes allows for channel separation, thus increasing the number of multiplexed modes and increasing system capacity. The other is to utilize multiple non-overlapping signals for parallel transmission, such as in multi-core optical fiber transmission. Because the spatial locations occupied by each channel do not interfere with each other, increasing the number of spatial channels per unit area can increase system capacity. Research focuses on the design of key components used in various nodes within a mode-division multiplexing system. For example, mode converters and multiplexers are core components for optical communications and interconnects, enabling these crucial functions in mode-division multiplexing systems. Mode conversion involves converting between different modes, while mode multiplexing combines multiple orthogonal modes.

[0003] For today's optical communications and optical interconnect applications, fiber-to-chip interconnection is a key research focus. However, the application of mode division multiplexing technology in fiber-to-chip optical interconnection remains a significant challenge, with mode coupling between multicore fibers and on-chip multimode waveguides being a key issue. On-chip multimode waveguides are square waveguides, and their dimensions differ significantly from those of the fiber. Consequently, the modes excited by silicon-based integrated devices differ significantly from those supported by the fiber, leading to significant mode field matching issues and often significant coupling losses. Common fiber-to-chip optical interconnects include free-space optics, all-fiber devices, and silicon-based integrated devices. Free-space optics are large, often introducing significant insertion loss during coupling with the fiber. Furthermore, as the number of multiplexed modes increases, the system complexity and size also increase significantly, introducing even greater insertion loss. All-fiber devices can achieve single-mode interconnection between fiber and chip systems, but the modes supported by multimode fibers differ significantly from those supported by multimode waveguides, making direct coupling impossible. Furthermore, the required mode conversion is difficult to achieve with all-fiber devices. Silicon-based integrated device solutions typically achieve mode conversion and coupling through on-chip vertical grating arrays. However, this vertical coupling scheme often introduces significant coupling losses and also exhibits certain wavelength and polarization sensitivity. These solutions all have various drawbacks, severely limiting the further development of mode division multiplexing technology in fiber-on-chip optical interconnect systems. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a multimode waveguide coupler based on a polyphase plane, which aims to overcome the limitation that mode division multiplexing technology is difficult to apply to fiber-chip optical interconnection systems. The goal is to achieve the coupling conversion between the modes supported by multimode optical fibers and the modes supported by on-chip multimode waveguides through the end-face coupling scheme of the multimode waveguide coupler based on a polyphase plane, thereby promoting the application of mode division multiplexing technology in fiber-chip optical interconnection systems and further improving the transmission capacity of optical interconnection systems.

[0005] To achieve the above objectives, the present invention provides a multimode waveguide coupler based on a multiphase plane, which can realize the coupling conversion between the modes supported by the multimode optical fiber and the modes supported by the on-chip multimode waveguide.

[0006] The present invention provides a multimode waveguide coupler based on a polyphase surface, comprising a polyphase surface and a microlens. The polyphase surface comprises a multilayer phase plate. The input end face of the polyphase surface is aligned and coupled with a multimode optical fiber to convert the mode of a light beam transmitted in the multimode optical fiber. The output end face is aligned and coupled with the input end of the microlens. The microlens implements a light beam contraction function. The output end of the microlens is aligned and coupled with an on-chip multimode waveguide to couple the contracted light beam to the on-chip multimode waveguide. Multiple modes supported by the multimode optical fiber are coupled and matched with high-order modes in the corresponding on-chip multimode waveguide after conversion by the polyphase surface and contraction by the microlens.

[0007] Furthermore, after the input end face of the multiphase plane is aligned and coupled with the multimode optical fiber, the multiphase plane and the end face of the multimode optical fiber are fixedly assembled to each other. After the input end of the microlens is aligned and coupled with the output end face of the multiphase plane, the microlens is further fixedly assembled to the multiphase plane. After the output end of the microlens is aligned and coupled with the on-chip multimode waveguide, the microlens is finally fixedly assembled to the on-chip multimode waveguide.

[0008] Furthermore, the multi-phase surface and the microlens can be prepared by EBL process, photolithography process or femtosecond laser direct writing technology.

[0009] Furthermore, the multiphase surface comprises N layers of phase plates stacked in an aligned pattern. The phase plate dimensions match the mode field size of the beam excited by the multicore fiber. Each layer of phase plates comprises m×m pixels, with the pixel size and number determined by the manufacturing process. Each pixel achieves phase modulation from 0 to 2π, and there is a certain spacing between the phase plates. The phase structure of each phase plate in the multiphase surface and the spacing between each phase plate are calculated using an optical diffraction neural network algorithm. N is 3, 4, 5, or 6; m is ≥ 50 and is a positive integer.

[0010] Furthermore, the size of the microlens matches the mode field size of the multi-phase plane conversion mode, and the focal length of the microlens is designed so that the mode field size after beam reduction matches the size of the on-chip multimode waveguide.

[0011] Furthermore, the multi-phase surface and microlens can be prepared in a polymer by two-photon polymerization femtosecond laser direct writing technology. Through this technology, pillars can be directly prepared on the edge of each structure for assembly and fixation, including fixedly coupling each phase surface in the multi-phase surface at a certain distance, fixedly assembling the multi-phase surface on the end face of a multimode optical fiber, fixedly assembling the microlens on the multi-phase surface, and then fixedly assembling the microlens and the on-chip multimode waveguide together.

[0012] Furthermore, the coupler couples the 6 LP modes supported by the multimode fiber 01x , LP 01y , and The corresponding conversion coupling is supported by the on-chip multimode waveguide into 6 high-order modes TE0, TM0, TE1, TM1, TE2 and TM2.

[0013] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0014] 1. The multimode waveguide coupler based on multiphase plane proposed in the present invention overcomes the limitation that mode division multiplexing technology is difficult to apply to fiber-chip optical interconnection systems, and realizes the coupling conversion between the modes supported by multimode optical fiber and the modes supported by on-chip multimode waveguide.

[0015] 2. The multimode waveguide coupler based on the multiphase plane proposed in the present invention is prepared in a polymer by two-photon polymerization femtosecond laser direct writing technology. This technology has high processing precision and great flexibility. In addition to processing multiphases and microlenses, it can also simultaneously realize the direct fixed assembly of multiphase planes and microlenses with multimode optical fibers and on-chip multimode waveguides.

[0016] 3. This invention proposes a multimode waveguide coupler based on a polyphase plane. Designed using an optical diffraction neural network algorithm, the polyphase plane enables highly efficient multimode conversion. Microlenses adjust the size of the transmission mode, effectively improving coupling efficiency with the on-chip multimode waveguide. The overall device offers advantages such as a large number of conversion modes, low coupling loss, and low crosstalk.

[0017] 4. The multimode waveguide coupler based on the multiphase plane proposed in the present invention has strong scalability. By adjusting the design of the multiphase plane and the microlens, the coupler can be applied to a larger number, more diverse, and more complex mode coupling conversions, further promoting the application of mode division multiplexing technology in fiber-chip optical interconnection systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of a multimode waveguide coupler based on a multiphase plane provided by the present invention;

[0019] Figure 2 These are the six LP mode light field diagrams supported by the multimode optical fiber and the six high-order mode light field diagrams supported by the on-chip multimode waveguide provided by the present invention;

[0020] Figure 3 This is a schematic diagram of the multi-phase plane provided by the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining 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 may be combined with each other as long as they do not conflict with each other.

[0022] The present invention provides a heterogeneous multimode waveguide coupler, whose main function is to solve the problem that mode division multiplexing technology is difficult to apply to fiber-chip optical interconnection systems, and to realize the direct coupling conversion of multiple guided modes in multimode optical fibers and on-chip multimode waveguides.

[0023] The present invention provides a multimode waveguide coupler based on a polyphase surface, comprising a polyphase surface and a microlens. The polyphase surface comprises a multilayer phase plate. The input end face of the polyphase surface is aligned and coupled with a multimode optical fiber to convert the mode of a light beam transmitted in the multimode optical fiber. The output end face is aligned and coupled with the input end of the microlens. The microlens implements a light beam contraction function. The output end of the microlens is aligned and coupled with an on-chip multimode waveguide to couple the contracted light beam to the on-chip multimode waveguide. Multiple modes supported by the multimode optical fiber are coupled and matched with high-order modes in the corresponding on-chip multimode waveguide after conversion by the polyphase surface and contraction by the microlens.

[0024] Specifically, after the input end face of the multiphase plane is aligned and coupled with the multimode optical fiber, the multiphase plane and the end face of the multimode optical fiber are fixedly assembled to each other. After the input end of the microlens is aligned and coupled with the output end face of the multiphase plane, the microlens is then fixedly assembled to the multiphase plane. After the output end of the microlens is aligned and coupled with the on-chip multimode waveguide, the microlens is finally fixedly assembled to the on-chip multimode waveguide.

[0025] Specifically, the multi-phase surface and the microlens can be prepared by EBL process, photolithography process or femtosecond laser direct writing technology.

[0026] Specifically, the multiphase surface comprises N layers of aligned, stacked phase plates. The phase plate dimensions match the mode field size of the beam excited by the multicore fiber. Each layer of phase plates comprises m×m pixels, with the size and number of pixels determined by the manufacturing process. Each pixel achieves phase modulation from 0 to 2π, and there is a certain spacing between the phase plates. The phase structure and spacing between each phase plate in the multiphase surface are calculated using an optical diffraction neural network algorithm. N is a positive integer, ranging from 3, 4, 5, or 6; m is ≥ 50.

[0027] Specifically, the size of the microlens matches the mode field size of the multi-phase plane conversion mode, and the focal length of the microlens is designed so that the mode field size after beam reduction matches the size of the on-chip multimode waveguide.

[0028] Specifically, the multi-phase surface and microlens can be prepared in a polymer by two-photon polymerization femtosecond laser direct writing technology. Through this technology, pillars can be directly prepared on the edge of each structure for assembly and fixation, including fixing the phase surfaces in the multi-phase surface together at a certain distance, fixing the multi-phase surface on the end face of the multi-mode optical fiber, fixing the microlens on the multi-phase surface, and then fixing the microlens and the on-chip multi-mode waveguide together.

[0029] Specifically, the coupler connects the 6 LP modes supported by the multimode fiber 01x , LP 01y , and The corresponding conversion coupling is supported by the on-chip multimode waveguide into 6 high-order modes TE0, TM0, TE1, TM1, TE2 and TM2.

[0030] The following combination Figure 1-Figure 3 The present invention is described in detail.

[0031] Example

[0032] The present invention provides a multimode waveguide coupler based on a multiphase plane, which is prepared in a polymer by two-photon polymerization femtosecond laser direct writing technology. Figure 1 Figure 1 shows a schematic diagram of a multimode waveguide coupler based on a polyphase plane. 1 represents a multimode fiber, 2 represents a polyphase plane, 3 represents a microlens, and the rightmost side represents an on-chip silicon-based structure, comprising a silicon substrate 6, a buried layer 4 on the substrate, and an on-chip multimode waveguide 5. The buried layer 4 comprises a silica insulating layer and a silica cladding. The on-chip multimode waveguide 5 is a silica waveguide. One side of the polyphase plane structure is aligned and coupled to the multimode fiber, the other side is aligned and coupled to the microlens, and the other side of the microlens is aligned and coupled to the on-chip multimode waveguide.

[0033] The multimode fiber used here supports a total of 6 LP modes including dual polarization 01x , LP 01y , and The on-chip multimode waveguide is a 340nm-high, 1.2μm-wide silicon waveguide with a silicon dioxide cladding. It supports dual-polarization transverse electric and transverse magnetic modes: TE0, 1M0, TE1, TM1, TE2, and TM2. Figure 2 Shown are the light field diagrams of the six LP modes supported by the multimode fiber and the light field diagrams of the six higher-order modes supported by the on-chip multimode waveguide.

[0034] After determining the parameters of the multimode fiber and the on-chip multimode waveguide, the multiphase surface and microlens can be designed. Figure 3As shown, the multi-phase surface includes four layers of phase plates stacked in an aligned manner, with an effective size of 160μm×160μm. Based on the two-photon polymerization process, the pixel size is set to 1.6μm×1.6μm, and each layer of phase plate includes 100×100 pixels. The refractive index of the polymer is approximately 1.5 at a wavelength of 1550nm. The longitudinal processing accuracy of the two-photon polymerization process is approximately 100μm. The height of each pixel ranges from 0 to 3.1μm and is divided into 32 steps, which can achieve phase modulation from 0 to 2π. The spacing between each phase plate is set to 60μm.

[0035] The phase structure of each phase plane in the multiphase surface is determined using an optical diffraction neural network algorithm combined with a beam propagation method. Using the beam propagation method to set up a simulation space, the six modes of light emitted from the multicore fiber are transmitted through the multiphase surface and microlenses to the on-chip multimode waveguide, where they are converted into six higher-order modes supported by the on-chip multimode waveguide. The optical diffraction neural network algorithm is then used to calculate the optimized parameters of the optical system, including the phase structure of each phase plate layer in the multiphase surface, the size and focal length of the microlenses, and the relative positions of the multicore fiber, multiphase surface, microlenses, and on-chip multicore waveguide.

[0036] First, according to the calculation results, the end face of the multi-core optical fiber is covered with polymer, and then the multi-phase surface and microlens are respectively engraved and cured at the designed relative positions in the polymer through two-photon polymerization femtosecond laser direct writing technology. Pillars are prepared at the edges of each structure to fix the above structure on the end face of the multi-core optical fiber. After removing the uncured polymer, a multi-mode waveguide coupler based on the multi-phase surface is obtained on the prepared multi-core optical fiber end face. The multi-core optical fiber combined with the coupler and the on-chip multi-core waveguide are then fixed on a glass substrate together. After coupling and alignment, they are covered with polymer and fixed to the glass substrate through two-photon polymerization femtosecond laser direct writing technology. After removing the excess polymer, a fiber-on-chip optical interconnection system realized by a multi-mode waveguide coupler based on the multi-phase surface is obtained.

[0037] It will be easily understood by those skilled in the art that the above description is merely 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 scope of protection of the present invention.

Claims

1. A multimode waveguide coupler based on a multiphase plane, characterized in that: The device comprises a multiphase surface and a microlens, wherein the multiphase surface comprises a multilayer phase plate, the input end face of the multiphase surface is aligned and coupled with a multimode optical fiber to convert the mode of a light beam transmitted in the multimode optical fiber, the output end face is aligned and coupled with the input end of the microlens, the microlens is used for light beam contraction, the output end of the microlens is aligned and coupled with an on-chip multimode waveguide, and the contracted light beam is coupled to the on-chip multimode waveguide accordingly. Multiple modes supported by the multimode optical fiber are converted into high-order modes in the corresponding on-chip multimode waveguide through post-coupling of the multiphase surface and the microlens; The multi-phase surface includes N layers of phase plates stacked in an aligned manner. The size of the phase plates matches the mode field size of the light beam excited by the multi-core optical fiber. Each layer of phase plates includes m×m pixels. The size and number of pixel points are determined by the processing technology. Each pixel point realizes phase modulation from 0 to 2π, and there is a preset spacing between each phase plate; wherein N=3, 4, 5, 6; m≥50, m is a positive integer; the phase structure of each phase plate of the multi-phase surface and the spacing between each phase plate are calculated and determined by an optical diffraction neural network algorithm.

2. The multimode waveguide coupler based on a multiphase plane according to claim 1, characterized in that: After the input end face of the multiphase surface is aligned and coupled with the multimode optical fiber, the multiphase surface and the end face of the multimode optical fiber are fixedly assembled to each other. After the input end of the microlens is aligned and coupled with the output end face of the multiphase surface, the microlens is then fixedly assembled to the multiphase surface. After the output end of the microlens is aligned and coupled with the on-chip multimode waveguide, the microlens is finally fixedly assembled to the on-chip multimode waveguide.

3. The multimode waveguide coupler based on a multiphase plane according to claim 1, characterized in that: The multi-phase surface and the microlens are prepared by EBL process, photolithography process or femtosecond laser direct writing technology.

4. The multimode waveguide coupler based on a multiphase plane according to claim 1, wherein: The size of the microlens matches the mode field size of the multi-phase plane conversion mode, and the focal length of the microlens is designed so that the mode field size after beam reduction matches the size of the on-chip multimode waveguide.

5. The multimode waveguide coupler based on a multiphase plane according to claim 1, characterized in that: The multi-phase surface and microlens are prepared in a polymer using two-photon polymerization femtosecond laser direct writing technology, and pillars are prepared at the edges of each structure for assembly and fixation, including fixedly coupling each phase surface within the multi-phase surface at a preset spacing, fixedly assembling the multi-phase surface on the end face of a multimode optical fiber, fixedly assembling the microlens on the multi-phase surface, and then fixedly assembling the microlens and the on-chip multimode waveguide together.

6. The multimode waveguide coupler based on a multiphase plane according to claim 1, characterized in that: The coupler converts multimode fiber to support 6 LP modes and The corresponding conversion coupling is supported by the on-chip multimode waveguide into 6 high-order modes TE0, TM0, TE1, TM1, TE2 and TM2.

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