A polarization-insensitive edge-coupled beam splitter

Abstract

This invention relates to the field of beam splitter technology, and in particular to a polarization-insensitive edge-coupled beam splitter, comprising multiple spaced waveguide cores; each waveguide core includes an input region L1, a mode evolution beam splitting region L2, a mode evolution beam splitting region L3, and a decoupled single-mode output region L4; the width of the input region L1 is W. 1 The distance between the input regions L1 of two adjacent waveguide cores is G. 1 The length of the mode evolution beam splitting region L2 is D. 2 The width of the mode evolution beam-splitting region L2 along the light propagation direction is determined by W. 1 Gradually increase to W 2 The length of the mode evolution beam splitting region L3 is D. 3 The width of the mode evolution beam-splitting region L3 along the light propagation direction is determined by W. 2 Gradually increase to W 3 The spacing between the two adjacent decoupled single-mode output regions L4 gradually increases to G along the light propagation direction. 2 The polarization-insensitive edge-coupled beamsplitter outputs power uniformly across the waveguide and offers advantages such as low insertion loss and low polarization.

Description

A polarization-insensitive edge-coupled beam splitter Technical Field

[0001] This invention relates to the field of beam splitter technology, and in particular to a polarization-insensitive edge-coupled beam splitter. Background Technology

[0002] As the size of electronic integrated circuits approaches physical limits and the demand for high-speed interconnects from data centers and AI grows, silicon photonics chips have become an important technological route for realizing high-capacity optical interconnects due to their compatibility with CMOS processes and ease of mass production. The coupling between silicon photonics chips and external light sources or optical fibers is a critical link in device packaging, and its coupling efficiency directly affects link budget and product yield.

[0003] Silicon photonics chip coupling schemes mainly include grating coupling and edge coupling: the former has a compact structure and is easy to test at the wafer level, but its coupling efficiency and bandwidth are limited; the latter usually integrates an edge coupler on the chip end face to achieve mode field matching, which can achieve high bandwidth and low insertion loss performance.

[0004] Currently, silicon photonic chip coupling schemes using edge coupling include, for example, a silicon-based optical waveguide edge coupling structure disclosed in Chinese Patent Publication No. CN118033821A, which includes a beam splitter and at least two silicon waveguides disposed on the output side of the beam splitter; the beam splitter is a silicon dioxide beam splitter based on a cantilever beam structure, and the beam splitter splits the input light before coupling it into each of the silicon waveguides.

[0005] The drawback of the aforementioned silicon-based optical waveguide edge coupling structure is its polarization sensitivity. Since the scheme uses a multimode interferometer for beam splitting, polarization has a significant impact on the beam splitting uniformity and insertion loss of this structure, and it cannot adapt to two polarizations. Summary of the Invention

[0006] Therefore, to address the above problems, this invention proposes a polarization-insensitive edge-coupled beam splitter that uniformly splits the power of the output waveguide and has the advantages of low insertion loss and low polarization.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A polarization-insensitive edge-coupled beam splitter comprising multiple spaced waveguide cores;

[0009] Each waveguide core includes an input region L1, a mode evolution beam splitting region L2, a mode evolution beam splitting region L3, and a decoupled single-mode output region L4, which are continuously connected in the direction of light propagation.

[0010] The width of the input region L1 is W1, 0.1μm≤W1≤0.5μm; the input regions L1 of each waveguide core are arranged in parallel, and the distance between the input regions L1 of adjacent waveguide cores is G1, so that the superposition of the radiation fields of each waveguide core exhibits Gaussian mode field characteristics, 0.1μm≤G1≤1.5μm;

[0011] The length of the mode evolution beam splitting region L2 is D2, 50μm≤D2≤150μm; the width of the mode evolution beam splitting region L2 along the light propagation direction gradually increases from W1 to W2 continuously and gently, 0.1μm≤W2≤0.7μm, and W1<W2.

[0012] The length of the mode evolution beam splitting region L3 is D3, 50μm≤D3≤150μm; the width of the mode evolution beam splitting region L3 along the light propagation direction gradually increases from W2 to W3 continuously and gently, 0.1μm≤W3≤2μm, and W2<W3.

[0013] The spacing between the two adjacent decoupled single-mode output regions L4 along the direction of light propagation gradually increases to G2, so that the waveguides of each waveguide core are completely decoupled, 0.5μm≤G2≤4μm, and G1<G2.

[0014] Furthermore, the length of the input region L1 is D1, where 0.1μm≤D1≤50μm.

[0015] Furthermore, the length of the coupled single-mode output region L4 is D4, 150μm≤D1+D2+D3+D4≤400μm.

[0016] Furthermore, the length of the coupled single-mode output region L4 is D4, where D1+D2+D3+D4=250μm.

[0017] Furthermore, the waveguide core is a single-layer silicon waveguide or a silicon nitride waveguide.

[0018] Furthermore, the width of the coupled single-mode output region L4 is W3.

[0019] Furthermore, the width change rate of the mode evolution beam splitting region L2 is SW1=(W2-W1) / W1, and the width change rate of the mode evolution beam splitting region L3 is SW2=(W3-W2) / W2.

[0020] SW1 < SW2.

[0021] By adopting the aforementioned technical solution, the beneficial effects of the present invention are:

[0022] 1. This polarization-insensitive edge-coupled beamsplitter integrates edge coupling and +3dB beam splitting across multiple waveguide cores. The input region L1, mode evolution beam splitting regions (including L2 and L3), and coupled single-mode output region L4, all positioned along the light propagation direction, are integrated without any other components in between, reducing area footprint and minimizing cascaded component faces. By adjusting the length and width of the mode evolution beam splitting regions for each waveguide core, mode field transformation and power distribution are naturally achieved within a multi-segment continuous adiabatic structure.

[0023] 2. Low insertion loss, fewer refractive index discontinuities, and low reflection. Coupling and beam splitting are achieved without adding extra components, eliminating the transition waveguide from the edge coupler to the beam splitter and the corresponding curved waveguide, reducing mode conversion and refractive index discontinuities, resulting in better total insertion loss and reflection than existing solutions, which is beneficial to improving the overall performance of the edge-coupled beam splitter.

[0024] 3. Polarization insensitive, compatible with TE / TM dual polarization, large operating bandwidth. By rationally designing the waveguide coupling coefficient of multiple segments, the thermal insulation conditions of both TE and TM can be met in the coupling region, thereby achieving uniform beam splitting and similar coupling efficiency for the two polarizations, significantly reducing polarization-related losses and simplifying the system's polarization control requirements.

[0025] 4. Single-layer structure, simple process, and compatibility with mainstream silicon photonics process platforms. This invention achieves functional integration by adjusting the gradual changes in the length, width, and spacing of the mode evolution beam splitting region and the coupled single-mode output region. It does not require additional material layers or special etching windows, which is beneficial for direct implementation on existing mainstream silicon photonics process lines, reducing manufacturing costs and yield risks.

[0026] 5. It is easy to extend to multi-path uniform power splitting, or to achieve different ratios of splitting by adjusting the length and width of the coupling region, such as achieving 0.3:0.7 asymmetric power splitting. Attached Figure Description

[0027] Figure 1 is a schematic diagram of the polarization-insensitive edge-coupled beam splitter structure according to Embodiment 1 of the present invention.

[0028] Figure 2 shows the mode transmission electric field distribution when TE / TM wave input is used.

[0029] Figure 3 shows the refractive index and loss of the edge-coupled beam splitter when TE wave input is applied.

[0030] Figure 4 shows the refractive index and loss of the edge-coupled beam splitter when TM wave input is applied.

[0031] Figure 5 is a schematic diagram of the polarization-insensitive edge-coupled beam splitter structure of Embodiment 2 of the present invention. Detailed Implementation

[0032] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] Referring to Figures 1-4, this embodiment provides a polarization-insensitive edge-coupled beamsplitter, comprising multiple spaced waveguide cores. In this specific embodiment, two waveguide cores are provided, and the two waveguide cores are arranged in a mirror-symmetrical manner. The waveguide cores are single-layer silicon waveguides or silicon nitride waveguides, and the thickness of the waveguide cores is preferably 200 nm. The silicon waveguides or silicon nitride waveguides are existing materials in the art and will not be described in detail here.

[0035] Each waveguide core includes an input region L1, a mode evolution beam splitting region L2, a mode evolution beam splitting region L3, and a decoupled single-mode output region L4, which are continuously connected in the direction of light propagation.

[0036] The length of the input region L1 is D1, 0.1μm≤D1≤50μm, and the width of the input region L1 is W1, 0.1μm≤W1≤0.5μm. The input regions L1 of each waveguide core are arranged in parallel, and the distance between the input regions L1 of adjacent waveguide cores is G1, 0.1μm≤G1≤1.5μm. This ensures that the superposition of the radiation fields of each waveguide core exhibits Gaussian mode field characteristics, matching the Gaussian mode field diameter of the optical fiber or laser. Therefore, the light emitted from the optical fiber or light source can be efficiently coupled into the two waveguide cores, completing the initial conversion from the laser or optical fiber mode field to the polarization-insensitive edge-coupled beamsplitter mode field.

[0037] Preferably, the length of the input region L1 is D1 = 2 μm; the width of the input region L1 is W1 = 0.27 μm; and the spacing between the input regions L1 of adjacent waveguide cores is G1 = 0.9 μm.

[0038] Since the input region L1 width W1 of multiple waveguide cores is submicron, the spacing G1 between the input regions L1 of adjacent waveguide cores is designed to match the optical mode field of the external light source or the single-mode fiber mode field for direct coupling with the external light source (fiber / laser). The width of the entire input region L1 and the spacing between the input regions L1 of adjacent waveguide cores remain constant to maintain the stability of the mode field and reduce the mismatch that may be caused by factors such as chip slicing.

[0039] The length of the mode evolution beam splitting region L2 is D2, 50μm≤D2≤150μm; the width of the mode evolution beam splitting region L2 along the light propagation direction gradually increases from W1 to W2 continuously and gently, 0.1μm≤W2≤0.7μm, and W1<W2.

[0040] Preferably, the length of the mode evolution beam splitting region L2 is D2 = 60 μm; and W2 = 0.33 μm.

[0041] The length of the mode evolution beam splitting region L3 is D3, 50μm≤D3≤150μm; the width of the mode evolution beam splitting region L3 along the light propagation direction gradually increases from W2 to W3 continuously and gently, 0.1μm≤W3≤2μm, and W2<W3.

[0042] Preferably, the length of the mode evolution beam splitting region L3 is D3 = 110 μm; and the length of W3 is 0.7 μm.

[0043] The mode evolution beam splitting regions L2 and L3 constitute the mode evolution beam splitting region. In this structure, the beam splitter does not operate at the conventional single-mode waveguide width; instead, it operates at a very narrow multi-waveguide core size. At this point, the waveguide mode field is dispersed outside the core layer, and the birefringence effect of the waveguide for different polarization states is greatly reduced. The coupling coefficients for different polarizations are almost the same, meaning the coupling strengths for different polarizations are essentially identical. Therefore, with a fixed element length, the performance of different polarization states is very close, and they can all achieve efficient coupling and even beam splitting.

[0044] Along the direction of light propagation, the width of the mode evolution beam-splitting region gradually increases, while the mode evolution beam-splitting regions of adjacent waveguide cores remain constant or slightly varied. The width change rates of mode evolution beam-splitting regions L2 and L3 are different. The width change of mode evolution beam-splitting region L2 is slower to reduce the impact of mode mismatch. The width change of mode evolution beam-splitting region L3 is larger, which can effectively reduce the component size. Experiments show that the coupling coefficient of TE / TM polarization changes slowly in this mode evolution beam-splitting region, all satisfying the adiabatic condition, achieving uniform beam splitting with a large bandwidth.

[0045] The spacing between the two adjacent decoupled single-mode output regions L4 gradually and smoothly increases to G2 along the light propagation direction. The two originally coupled waveguide cores are converted into two independent single-mode waveguide outputs with a width of W3, so that the waveguides of each waveguide core are completely decoupled, 0.5μm≤G2≤4μm, and G1<G2. The width W3 of the entire single-mode output region L4 remains constant, and the waveguide spacing is increased linearly or nonlinearly.

[0046] Preferably, G2 = 3 μm.

[0047] The width of the coupled single-mode output region L4 is W3, and the length of the coupled single-mode output region L4 is D4, where 150μm≤D1+D2+D3+D4≤400μm. Preferably, D4=80μm, and D1+D2+D3+D4=252μm, making the length of this polarization-insensitive edge-coupled beamsplitter comparable to that of existing ordinary edge couplers, eliminating the need for additional on-chip beamsplitters, thereby significantly reducing the layout area and the number of device cascade end faces.

[0048] Since the coupled single-mode output region L4 also adopts a slowly gradient structure, the optical field remains thermally adiabatic when transitioning from the coupled state of the coupled region to the two independent single-mode waveguides (i.e., the coupled single-mode output region L4), avoiding the introduction of additional losses and crosstalk. Finally, the output is obtained in the coupled single-mode output region L4, resulting in two outputs with good coherence and basically equal power, which can be used by subsequent on-chip devices such as modulators, interferometers, and detectors.

[0049] The width variation rate of the mode evolution beam-splitting region L2 is SW1=(W2-W1) / W1, and the width variation rate of the mode evolution beam-splitting region L3 is SW2=(W3-W2) / W2, where SW1<SW2. The width variation of the mode evolution beam-splitting region L2 is relatively slow to reduce the impact of mode mismatch. The width variation of the mode evolution beam-splitting region L3 is relatively large, which can effectively reduce the component size. The polarization coupling coefficient in the coupling region changes slowly, satisfying the adiabatic condition and achieving uniform beam splitting with a large bandwidth.

[0050] The mode evolution beam splitting region L2 and mode evolution beam splitting region L3 constitute a coupling region. The width of the coupling region gradually changes to meet the thermal insulation conditions, so that the electromagnetic field of the input region L1 of the two waveguide cores smoothly evolves from a distribution close to the Gaussian mode field of the optical fiber or laser to the fundamental mode of the two waveguide cores, avoiding strong reflection and radiation loss. As the width of the coupling region gradually increases, the effective refractive index of the coupling region increases, and the optical field begins to be gradually pulled into the core layer of the two waveguide cores. Because the two waveguide cores are symmetrical (i.e., the coupling region lengths and widths of the two waveguide cores are the same) and change slowly (meeting thermal insulation requirements), the optical field always remains symmetrical or anti-symmetrical. Energy is naturally and uniformly distributed at the center of the two waveguide cores, avoiding the energy oscillations between the two waveguide cores that occur in directional couplers. By selecting appropriate coupling region lengths D1 and D2, and a spacing G1, the power distribution within the two waveguide cores corresponding to the waveguide mode field at the end of the decoupled single-mode output region L4 is stabilized at 50:50, achieving nearly 3 dB power splitting. In practical applications, different splitting ratios can be achieved by adjusting the coupling region lengths and widths of each waveguide core, thus realizing asymmetric power splitting (e.g., 0.3:0.7).

[0051] For conventional beam splitters, regardless of whether the design is thermally adiabatic or non-thermally adiabatic, the beam splitting uniformity and insertion loss are strongly affected by the polarization state of the input light. This is because conventional beam splitters are designed with single-mode waveguides. In this case, the waveguide is relatively wide, and most of the waveguide mode field is distributed inside the waveguide. The equivalent refractive index of the waveguide mode field exhibits a strong birefringence effect for different polarization states. This results in significantly different coupling strengths for different polarization states, leading to substantial performance differences for different polarization states with a fixed element length. This application innovatively integrates the beam splitter into an edge coupler. In this structure, the beam splitter does not operate with the conventional single-mode waveguide width; instead, it operates with a very narrow double-waveguide dimension. Here, the waveguide mode field is dispersed outside the core layer, and the birefringence effect of the waveguide for different polarization states is greatly reduced. The coupling coefficients of the two polarizations are almost the same, meaning the coupling strengths for different polarizations are essentially the same. Therefore, with a fixed element length, the performance of different polarization states is very close, and both can achieve efficient coupling and even beam splitting.

[0052] The simulation results of the polarization-insensitive edge-coupled beam splitter are shown in Figure 2. Figure 2 shows the electric field distribution when Gaussian light of different polarizations is input into the polarization-insensitive edge-coupled beam splitter. From the simulation results, it can be clearly observed that both the input TE wave and TM wave are efficiently coupled into the polarization-insensitive edge-coupled beam splitter, and after transmission, they are uniformly split within the polarization-insensitive edge-coupled beam splitter.

[0053] For the input of the TE wave polarization state, the transmission spectrum of the coupled single-mode output region L4 of the two waveguide cores and the loss results of the TE wave are shown in Figure 3. As can be seen from Figure 3, in the waveguide core of the locally polarization-insensitive edge-coupled beam splitter, the TE mode is uniformly split in both waveguide cores throughout the O band, while maintaining low loss.

[0054] For the input of TM wave polarization state, the transmission spectrum of the coupled single-mode output region L4 of the two waveguide cores and the loss results of the TM wave are shown in Figure 4. As can be seen from Figure 4, in the waveguide core of the local polarization-insensitive edge-coupled beam splitter, the TM mode is uniformly split at both ports throughout the O band and maintains low loss.

[0055] The three-segment structure—input region L1, mode evolution beam splitting region (including mode evolution beam splitting regions L2 and L3), and coupled single-mode output region L4—is designed to simultaneously achieve mode field coupling, compression, conversion, and uniform separation of optical power during a single propagation process, while exhibiting very similar loss and beam splitting ratio for TE and TM modes. The waveguide profile curve and waveguide spacing curve can be one or a combination of linear, polynomial, exponential, or Bezier curves.

[0056] Example 2

[0057] As shown in Figure 5, this specific embodiment uses four identical waveguide cores. The four input regions L1 are matched with the Gaussian mode field of the external light source or optical fiber. By selecting appropriate coupling region lengths D1 and D2, and spacing G1, uniform beam splitting output of the four waveguide cores is achieved. Its basic principle is the same as that of Embodiment 1.

[0058] Similarly, the number of waveguide cores can also be set to 8 or other numbers, and the specific principle is the same as in Example 1.

[0059] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A polarization-insensitive edge-coupled beam splitter, characterized in that: The system includes multiple spaced waveguide cores; each waveguide core comprises an input region L1, a mode evolution beam splitting region L2, a mode evolution beam splitting region L3, and a decoupled single-mode output region L4, all continuously connected along the light propagation direction; the width of the input region L1 is W1, 0.1μm≤W1≤0.5μm; the input regions L1 of each waveguide core are arranged in parallel, and the distance between the input regions L1 of adjacent waveguide cores is G1, such that the superposition of the radiation fields of each waveguide core exhibits Gaussian mode field characteristics, 0.1μm≤G1≤1.5μm; the length of the mode evolution beam splitting region L2 is D2, 50μm≤D2≤150μm; the mode evolution... The width of the beam splitting region L2 along the light propagation direction gradually increases from W1 to W2 continuously and smoothly, with 0.1μm≤W2≤0.7μm and W1<W2; the length of the mode evolution beam splitting region L3 is D3, with 50μm≤D3≤150μm; the width of the mode evolution beam splitting region L3 along the light propagation direction gradually increases from W2 to W3 continuously and smoothly, with 0.1μm≤W3≤2μm and W2<W3; the spacing between the two adjacent decoupled single-mode output regions L4 along the light propagation direction gradually increases to G2 continuously and smoothly, so that the waveguides of each waveguide core are completely decoupled, with 0.5μm≤G2≤4μm and G1<G2.

2. The polarization-insensitive edge-coupled beam splitter according to claim 1, characterized in that: The length of the input region L1 is D1, where 0.1μm≤D1≤50μm.

3. A polarization-insensitive edge-coupled beam splitter according to claim 2, characterized in that: The length of the coupled single-mode output region L4 is D4, 150μm≤D1+D2+D3+D4≤400μm.

4. A polarization-insensitive edge-coupled beam splitter according to claim 3, characterized in that: The length of the coupled single-mode output region L4 is D4, where D1+D2+D3+D4=252μm.

5. A polarization-insensitive edge-coupled beam splitter according to claim 1, characterized in that: The waveguide core is a single-layer silicon waveguide or a silicon nitride waveguide.

6. A polarization-insensitive edge-coupled beam splitter according to claim 1, characterized in that: The width of the coupled single-mode output region L4 is W3.

7. A polarization-insensitive edge-coupled beam splitter according to claim 1, characterized in that: The width variation rate of the mode evolution beam splitting region L2 is SW1=(W2-W1) / W1, and the width variation rate of the mode evolution beam splitting region L3 is SW2=(W3-W2) / W2; SW1<SW2.

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