Topology protection Hong-Ou-Mandel interferometer based on pi phase regulation and control grating
By introducing a topological protection mechanism of a π-phase modulation grating into the quantum interference device, the problems of sensitivity to manufacturing deviations and low visibility of traditional devices are solved, realizing high-visibility quantum interference at a tiny size. The device performance is significantly better than that of traditional designs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JILIN UNIVERSITY
- Filing Date
- 2026-01-13
- Publication Date
- 2026-04-21
AI Technical Summary
Traditional quantum interference devices are sensitive to manufacturing deviations, have low visibility, and are large in size, making it difficult to achieve high-visibility quantum interference at tiny scales.
A topology-protected Hong-Ou-Mandel interferometer based on a π-phase-tuning grating is employed. By introducing a tunable coupling phase difference Δφ = π in the polarization mode space, a topological phase transition is utilized to support compact topological boundary modes, providing a protected evolution path for two-photon HOM interference.
High-visibility quantum interference was achieved, with interference visibility approaching the theoretical limit v ≈ −0.98, and it was insensitive to propagation distance and manufacturing deviations, resulting in a significant reduction in device size.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of integrated photonics and quantum optics technology, specifically relating to a topologically protected Hong-Ou-Mandel interferometer based on a π-phase modulation grating. Background Technology
[0002] Quantum interference is a core foundation of quantum information processing. Among them, Hong-Ou-Mandel (HOM) interference, as a typical phenomenon of two-photon interference, is widely used in photon indistinguishability measurement, quantum sensing, and entanglement generation. In integrated photonic circuits, traditional schemes for realizing HOM interference are mostly based on directional couplers or waveguide beamsplitters, achieving interference by controlling the photon path. For example, silicon-based grating waveguides can facilitate the conversion between TE and TM modes through periodic modulation, thereby constructing a polarization beamsplitter for HOM experiments. However, such traditional designs have significant limitations: first, interference visibility is highly sensitive to manufacturing tolerances (such as waveguide spacing deviations, propagation length deviations, etc.), leading to beam splitting ratio inaccuracies and decreased visibility; second, to meet thermal insulation requirements, devices typically need to be large in size, which is not conducive to high-density integration.
[0003] In recent years, topological photonics has provided new avenues for improving the robustness of quantum devices. Topologically protected edge modes are immune to structural disorder and have been applied to single-photon transmission and entanglement protection. For example, quantum interference can be tunable through synthetic flux (such as Aharonov-Bohm-type optical lattices), but existing schemes often rely on complex external fields or adiabatic evolution, making it difficult to balance compactness and high performance. Furthermore, the combination of synthetic flux platforms and topological boundary modes has not been fully explored, especially lacking topological protection mechanisms for two-photon interference.
[0004] Therefore, there is an urgent need for a quantum interference scheme that can achieve high visibility at tiny scales and is robust to parameter changes. Summary of the Invention
[0005] This invention aims to address the problems of traditional quantum interference devices, such as sensitivity to manufacturing deviations, low visibility, and large device size, by providing a topology-protected Hong-Ou-Mandel interferometer based on a π-phase modulated grating. The core of this interferometer lies in introducing a tunable coupling phase difference Δφ in the polarization mode space by modulating the relative modulation phase of a pair of long-period grating waveguides. When Δφ = π, a topological phase transition occurs. Under this topologically nontrivial phase, the system supports highly localized compact topological boundary modes, thus providing a protected evolution path for two-photon HOM interference. The innovation of this device stems from its topology protection mechanism, which ensures that the quantum interference visibility not only approaches the theoretical limit v ≈ −0.98 but also remains insensitive to coupling fluctuations caused by propagation distance and manufacturing deviations, thus significantly outperforming traditional directional couplers.
[0006] This invention is achieved through the following technical solution:
[0007] A topology-protected Hong-Ou-Mandel interferometer based on a π-phase modulated grating includes a silicon dioxide substrate 7 and a first waveguide and a second waveguide arranged side-by-side thereon. The first waveguide sequentially includes a first input waveguide 1, a first grating waveguide 3, and a first output waveguide 5. The second waveguide sequentially includes a second input waveguide 2, a second grating waveguide 4, and a second output waveguide 6. Both the first grating waveguide 3 and the second grating waveguide 4 contain N grooves periodically arranged along the optical transmission direction, where the number of grating grooves N is an integer from 1 to 100. The grooves of the first grating waveguide 3 and the second grating waveguide 4 are symmetrically distributed on their respective waveguide cross-sections about the line connecting the centers of the first and second waveguides, thereby introducing a π-coupled phase difference between the waveguide couplings of the two grating waveguides. This can induce topologically nontrivial boundary states in the mode coupling network of the system, thus providing a topology-protected evolution path for the two-photon Hong-Ou-Mandel interferometer.
[0008] Furthermore, the first input waveguide 1, the first output waveguide 5, the second input waveguide 2, and the second output waveguide 6 are all curved S-shaped waveguides;
[0009] The first input waveguide 1 and the second input waveguide 2 extend in different directions, and the first output waveguide 5 and the second output waveguide 6 extend in different directions.
[0010] Furthermore, the period length, size, and longitudinal arrangement of the grooves in the first grating waveguide 3 and the second grating waveguide 4 are the same.
[0011] Furthermore, the spacing d between the first grating waveguide 3 and the second grating waveguide 4, and the geometric scaling factor b of the groove size, are configured to increase the coupling strength between the TE and TM modes within the waveguides. TE mode coupling strength between waveguides and the TM mode coupling strength between waveguides All three are equal; among them, the waveguide coupling strength is... The inter-waveguide coupling strength is inversely proportional to the geometric scaling factor b. and The waveguide spacing d decreases exponentially with increasing waveguide spacing d.
[0012] Furthermore, the groove is rectangular, and its cross-section has the same aspect ratio as the cross-section of the waveguide, and its width and height are 1 / b of the corresponding dimensions of the waveguide, where the geometric scaling factor b is a real number greater than 1.
[0013] Furthermore, the spacing d between the first grating waveguide 3 and the second grating waveguide 4 satisfies: 0.1935λ-0.2452λ;
[0014] The geometric scaling factor b of the groove size satisfies: 0.0308λ-0.0435λ;
[0015] Where λ is the operating wavelength of the interferometer.
[0016] Furthermore, the width of the first input waveguide 1, the first output waveguide 5, the second input waveguide 2, and the second output waveguide 6 is 0.2λ, and the thickness is 0.2λ to 0.35λ, where λ is the operating wavelength of the interferometer, and all support two orthogonal polarization modes, TE mode and TM mode.
[0017] Furthermore, the grating period lengths of the first grating waveguide 3 and the second grating waveguide 4 are... The following phase matching conditions must be met:
[0018]
[0019] in, λ represents the effective refractive index of the TE mode and TM mode in the grating waveguide, respectively, and λ is the operating wavelength of the interferometer.
[0020] The appropriate grating period length was obtained through calculation. It can compensate for the difference in propagation constant between TE mode and TM mode, thereby achieving efficient mode conversion between TE mode and TM mode.
[0021] Furthermore, the method for determining the groove positions and π-coupling phase difference of the first grating waveguide 3 and the second grating waveguide 4 is as follows: based on the TE and TM modes within the waveguides... The sign of the electric field overlap integral is determined by selecting the groove of the first grating waveguide 3 located at the upper left corner (−x, y) of the waveguide cross-section, while selecting the groove of the second grating waveguide 4 located at the upper right corner (x, y) of the waveguide cross-section. This introduces a fixed π-coupling phase difference between the waveguide coupling terms of the two grating waveguides. This ensures that the total phase difference of the HOM interferometer is π; where i is the imaginary unit in physics, which is the core mathematical hub connecting complex number representation and physical phase operation.
[0022] The working principle of the Hong-Ou-Mandel interferometer based on a π-phase modulation grating, according to the present invention, is as follows:
[0023] 1. This interferometer utilizes the inherent TE and TM modes in silicon waveguides as its foundation. Two parallel grating waveguides support a total of four modes: the TE and TM modes of the first grating waveguide, and the TE and TM modes of the second grating waveguide. These four modes and their coupling can be mapped onto an equivalent tetragonal lattice model;
[0024] Inter-waveguide coupling of the same mode (e.g., energy transfer between the TE mode of the first grating waveguide 3 and the TE mode of the second grating waveguide 4): This coupling is achieved by the overlap of the evanescent fields of the waveguides, and the coupling strength depends on the waveguide spacing d, usually denoted as . and .
[0025] Coupling mechanism between different modes within the waveguide (e.g., energy transfer between the TE mode and the TM mode of the first grating waveguide 3): This coupling is achieved by a long-period grating introduced through the waveguide sidewall. The periodic perturbation of the grating breaks the orthogonality between modes, and efficient TE-TM mode conversion can occur when the grating period length satisfies the phase-matching condition. This coupling is denoted as... The coupling phase φ is determined by the lateral position and the initial longitudinal position of the grating period groove.
[0026] 2. Compact Topology Boundary Pattern Principle: When the following conditions are met...
[0027] When Δφ = π, a topologically nontrivial bandgap is opened in its equivalent momentum-space band structure, and the system's energy spectrum exhibits three flat bands. The zero band has a quantized Zak phase γ = π, while the upper and lower bands exhibit non-quantized γ = π / 2. This unique configuration of topological invariants, particularly the non-quantized π / 2 winding, is the direct cause of the emergence of compact topological boundary modes.
[0028] 3. Basic Principle of Topology Protection: The topology protection characteristics of this system originate from its unique square-root topological insulator phase, and the system's robustness is guaranteed by two asymmetric symmetries (Π and χ). These symmetries impose constraints on topological invariants, ensuring that the system's topological properties remain unchanged under symmetry-satisfying perturbations. Specifically, in the interference process, this mechanism achieves topology protection through two paths:
[0029] First, the formation of compact boundary modes originates from complete destructive interference under π-coupled phase differences, which effectively blocks the tunneling path of photons to undesirable output states. The quantum evolution of the two photons is "locked" within the protected edge channel, ensuring the purity and determinism of the evolution path. Second, it provides inherent robustness to disorder. Because the stability of the boundary modes is topologically protected, quantum interference processes using them as a carrier or evolutionary environment exhibit strong immunity to coupling strength perturbations caused by manufacturing errors in key performance indicators (such as HOM interference visibility). This allows interference visibility to remain close to the theoretical limit and does not fluctuate with small changes in device propagation length.
[0030] Compared with the prior art, the advantages of the present invention are as follows:
[0031] (1) High interference visibility: When the coupling phase difference is π, the HOM visibility reaches v ≈ −0.98 (near perfect destructive interference) and remains stable within the propagation distance of 4-32μm (standard deviation σ = 0.01).
[0032] (2) Strong robustness: Compared with traditional beam splitters (visibility in κ), TE-TM When / κ0≈1.4, the visibility decreases to below −0.5. The visibility of this invention decreases slowly under parameter deviations (κ0≈1.4). TE-TM Even at / κ0=1.4, it is still higher than −0.8).
[0033] (3) Compact design: Two grating waveguides can realize topologically protected HOM interference, suppressing the finite size effect and significantly reducing the device size. Attached Figure Description
[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.
[0035] Figure 1 This is a schematic diagram of the structure of a topologically protected Hong-Ou-Mandel interferometer based on π-phase modulated grating polarization beam splitting according to the present invention;
[0036] In the figure: First input waveguide 1, second input waveguide 2, first grating waveguide 3, second grating waveguide 4, first output waveguide 5, second output waveguide 6, silicon dioxide substrate 7;
[0037] Figure 2 A schematic diagram illustrating the mode conversion between TE and TM in a single grating waveguide under phase matching conditions;
[0038] Figure 3 This is a schematic diagram showing the relationship between the coupling strength of the same mode between waveguides and the waveguide spacing d.
[0039] Figure: Coupling strength of the same mode between waveguides and All decrease exponentially with increasing waveguide spacing d;
[0040] Figure 4 This is a schematic diagram showing the relationship between the coupling strength between different modes within the waveguide and the size b of the grating groove.
[0041] Figure: Coupling strength between different modes within the waveguide As the size b of the grating groove decreases in an inverse proportional function;
[0042] Figure 5 A diagram showing the distribution of grating groove positions under π-coupled phase difference;
[0043] Figure 6 A functional simulation diagram of a polarization beam splitter with π phase difference;
[0044] Figure 7 Topological boundary modes and their eigenvalues supported by the Hong-Ou-Mandel interferometer;
[0045] In the figure: when the coupling phase difference Δφ = π, the band collapses into a flat band, and two pairs of topological boundary modes (indicated by red circles) appear within the band gap, with eigenvalues E = ± .
[0046] Figure 8 This is a schematic diagram showing the relationship between the coincidence rate of distinguishable and indistinguishable photons in a Hong-Ou-Mandel interferometer and the propagation distance.
[0047] In the diagram: the coincidence rate of indistinguishable photons The coincidence rate of distinguishable photons remains zero throughout the propagation distance. The oscillation increases with propagation distance, reaching a maximum of 0.5 at z = 32 μm;
[0048] Figure 9 This is a schematic diagram illustrating the relationship between the visibility v of the Hong-Ou-Mandel interferometer and the propagation distance.
[0049] In the figure: the visibility v of the Hong-Ou-Mandel interference remains essentially unchanged with the propagation distance and maintains a high level of interference visibility throughout;
[0050] Figure 10 This is to show the effect of changes in coupling strength caused by deviations in the fabrication structure on the visibility of the topological Hong-Ou-Mandel interference. Detailed Implementation
[0051] To clearly and completely describe the technical solution and its specific working process of the present invention, the specific embodiments of the present invention are as follows, in conjunction with the accompanying drawings:
[0052] A topology-protected Hong-Ou-Mandel interferometer based on a π-phase modulated grating includes a silicon dioxide substrate 7 and a first waveguide and a second waveguide arranged side-by-side thereon. The first waveguide sequentially includes a first input waveguide 1, a first grating waveguide 3, and a first output waveguide 5. The second waveguide sequentially includes a second input waveguide 2, a second grating waveguide 4, and a second output waveguide 6. Both the first grating waveguide 3 and the second grating waveguide 4 contain N grooves periodically arranged along the optical transmission direction, where the number of grating grooves N is an integer from 1 to 100. The grooves of the first grating waveguide 3 and the second grating waveguide 4 are symmetrically distributed on their respective waveguide cross-sections about the line connecting the centers of the first and second waveguides, thereby introducing a π-coupled phase difference between the waveguide couplings of the two grating waveguides. This can induce topologically nontrivial boundary states in the mode coupling network of the system, thus providing a topology-protected evolution path for the two-photon Hong-Ou-Mandel interferometer.
[0053] Example 1
[0054] like Figure 1 As shown, this embodiment provides a topologically protected Hong-Ou-Mandel interferometer based on a π-phase modulated grating. This device is fabricated on a silicon dioxide substrate 7, the refractive index of which is... A first waveguide and a second waveguide were fabricated on a silicon dioxide substrate 7. The refractive index of silicon was... The working wavelength λ is set to 1550nm.
[0055] The first waveguide, along the optical transmission direction, sequentially includes a first input waveguide 1, a first grating waveguide 3, and a first output waveguide 5; the second waveguide similarly includes a second input waveguide 2, a second grating waveguide 4, and a second output waveguide 6; both the input and output waveguides adopt a smooth S-shaped curved design, with identical geometric parameters: the width W can be set to 310 nm; the waveguide height H = 450 nm; and the effective refractive indices of the TE and TM modes in the rectangular waveguide are respectively... =2.5589、 =2.1739.
[0056] The first grating waveguide 3 and the second grating waveguide 4 are the core functional areas of the device, each containing N periodic rectangular grooves arranged along the transmission direction. In this embodiment, N is selected as 8. To support the two basic polarization modes, TE and TM, and to ensure that their effective refractive indices have an appropriate difference to facilitate subsequent grating design, the waveguide cross-sectional dimensions need to be carefully selected. The grooves of the first grating waveguide 3 are located at the upper left corner (−x, y, z) of its cross-section, while the grooves of the second grating waveguide 4 are located at the upper right corner (x, y, z) of its cross-section. The groove size is proportionally reduced to 1 / b of the waveguide size. The groove width W / b = 56.36 nm, the groove height H / b = 81.82 nm, where b = 5.5. The effective refractive indices of the TE and TM modes in the grooved waveguides are respectively... =2.5324、 =2.1286.
[0057] To achieve phase matching between the TE and TM modes in the waveguide grating, based on a duty cycle of 0.5 for both grooved and non-grooved modes along the propagation direction, this example considers the linear superposition of phase matching conditions for both rectangular and grooved waveguide modes. Therefore, the modulation period length of the grating waveguide is... :
[0058]
[0059] Based on the calculated grating period length Perform simulation verification, such as Figure 2 As shown, when the TE mode is input into a single grating waveguide, the propagation distance is... The output is completely converted to TM mode; TM mode is input into a single grating waveguide, and the propagation distance is... The output is completely converted to TE mode; mode conversion between TE mode and TM mode is realized within the waveguide.
[0060] Example 2: Key Parameter Design and Working Principle
[0061] I. Coupling Mechanism and Equivalent Model;
[0062] The Hong-Ou-Mandel interferometer described in this invention exhibits two basic coupling mechanisms: intra-waveguide coupling and inter-waveguide coupling. Intra-waveguide coupling is the coupling between the TE and TM modes induced by grating grooves; its coupling strength is inversely proportional to the groove size *b*, denoted as... ;like Figure 4 As shown, its decay is approximately inversely proportional to the increase of b (the groove becomes shallower). It was found that when b = 5.5, That is, the groove size b = 5.5 and the waveguide spacing d = 340nm are set in the HOM interferometer to achieve the same coupling strength within the waveguide and the coupling strength between waveguides.
[0063] Inter-waveguide coupling is the energy exchange of the same mode (TE-TE or TM-TM) between waveguides, achieved by the overlap of the evanescent fields of the waveguides. The coupling strength decreases exponentially with the waveguide spacing d, and is usually denoted as . and This can be achieved by selecting an appropriate waveguide spacing d. , Figure 3 The relationship between coupling strength and waveguide spacing d is given. It can be seen that as d increases, κ TE-TE and κ TM-TM Exponential decay at different rates can be achieved when d = 340nm. .
[0064] The Hong-Ou-Mandel interferometer has two waveguides that support four waveguide modes. , , , The aforementioned couplings between these nodes can be represented in the mode dimension as an equivalent tetragonal lattice model. To achieve perfect destructive interference, the coupling strength between all nearest-neighbor nodes in this lattice must be strictly equal, i.e., the following must be satisfied: .
[0065] II. Coupling Strength Matching and the Introduction of π Phase Difference
[0066] The key step in achieving topology protection is to introduce a fixed π-phase difference (Δφ = π) between the waveguide couplings of the two grating waveguides. This phase difference originates from the lateral symmetry of the grooves on the two waveguides, and its principle is as follows:
[0067] The coupling strength and sign of the TE and TM modes within a grating waveguide originate from the magnitude and sign of the non-zero overlap integral between the two modes. In an unmodulated rectangular waveguide, the coupling strength and sign of the TE and TM modes... The component mode field overlap exhibits a quadrupole overlap pattern and the overlap integral is 0, therefore no coupling occurs between modes. To achieve mode conversion within the waveguide, refractive index modulation (i.e., grooves) is introduced in a quadrant of the xy plane, which can maximize the breaking of the 0-mode field overlap integral and introduce direct coupling between the TE and TM modes.
[0068] If the grooves of two grating waveguides are positioned exactly the same in cross-section, their initial modulation phases are the same, making it impossible to generate the required coupling phase difference. Based on the sign of the overlap integral of the TE and TM modes within the waveguides, this invention creatively positions the grooves of the two grating waveguides symmetrically about the line connecting the waveguide centers: that is, the groove of the first grating waveguide 3 is located in the upper left corner region (-x, y) of its cross-section, while the groove of the second grating waveguide 4 is located in the upper right corner region (x, y) of its cross-section. Figure 5As shown. This symmetrical layout introduces a fixed π-coupling phase difference between the waveguide coupling terms of the two grating waveguides: This ensures that the total phase difference of the HOM interferometer is π.
[0069] III. Formation and Protection Characteristics of Topological Boundary Patterns
[0070] When both conditions are met—"all coupling strengths are equal" and "waveguide-internal coupling phase difference Δφ = π"—the system enters a topologically nontrivial bandgap, such as... Figure 7 As shown, when the coupling phase difference Δφ = π, the band collapses into a flat band, and two pairs of topological boundary states appear within the band gap, with their eigenvalues (red circles) being E = ± Due to the destructive interference under a π-phase difference, these topological boundary modes are compactly localized at only three locations at the boundary. Furthermore, since the boundary modes on opposite boundaries do not couple with each other, robustness is maintained even in the smallest four-point lattice, effectively mitigating finite-scale effects and reducing the lateral size of the interferometer.
[0071] like Figure 7 The inset on the left illustrates the evolution path of two-photon HOM interference. A TE-mode single photon (represented by a red sphere) is introduced into the first grating waveguide, and a TM-mode single photon (represented by a red sphere) is introduced into the second grating waveguide. The photon pairs can propagate in clockwise and counterclockwise directions within the loop path of the topological boundary, respectively, and interfere with each other due to the coupled phase difference accumulated along the path. The probability of detecting a TM-mode single photon (represented by a blue sphere) in the first grating waveguide and a TE-mode single photon (represented by a blue sphere) in the second grating waveguide is proportional to cos²(Δφ / 2). When Δφ = π, destructive interference reduces the probability to zero, achieving perfect destructive interference.
[0072] Example 3 Performance Verification and Robustness Analysis
[0073] Figure 6 Simulations verified that, under a π phase difference, this structure maintains a transmission length of [missing information]. At this location, 1:1 polarization TE and TM mode beam splitting can be achieved; by inputting the TE mode in the first grating waveguide 3, the propagation distance can be increased. With a 1:1 energy ratio, TM mode is output in the first grating waveguide 3, and TE mode is output in the second grating waveguide 4; TM mode is input into the second grating waveguide 4, and the propagation distance is... With a 1:1 energy ratio, the TM mode is output in the first grating waveguide 3, and the TE mode carrying an additional π phase is output in the second grating waveguide 4; the 1:1 beam splitting of the TE and TM modes and the introduction of the π phase constitute the basis of the topological HOM interference.
[0074] Figure 8and Figure 9 The coincidence rates and corresponding interferometric visibilitys for a range of propagation distances (from 4 μm to 32 μm) are presented. Interferometric visibility is defined as... ,in, and represents the coincidence rate of distinguishable and indistinguishable photons, respectively. A visibility of v = −1 indicates that complete destructive interference can be achieved.
[0075] like Figure 8 As shown, when Δφ = π, the coincidence rate of indistinguishable photons Strong suppression occurs across the entire propagation range (4–32 μm), while the resolvable photon rate exhibits significant variations. This results in near-perfect propagation-invariant HOM interference visibility, such as… Figure 9 As shown, its average value v = -0.98 remains at a high level, and its standard deviation σ = 0.01 is extremely small, strongly establishing the destructive interference phenomenon that is propagated invariantly under topological control.
[0076] Figure 10 This paper demonstrates a robustness comparison of HOM interference visibility between a conventional polarization beamsplitter and the topology-protected polarization beamsplitter proposed in this invention. The system has a length L = π / (4 The traditional polarization beam splitter is used as a reference. Among them, Figure 10 (a) plots the HOM interferometry visibility v of a conventional polarization beam splitter versus the coupling ratio. The functional relationship, as shown by the red curve, is that at the design point... At point 1, the HOM interference visibility v approaches the ideal value of −1. Traditional beam splitters are extremely sensitive to relative deviations, especially when the coupling ratio is... When the deviation from 1, visibility drops sharply. When the value is approximately 1.4, it exceeds the threshold of v = −0.5. In contrast, under topological conditions (Δφ = π), the HOM interference visibility v z Slow change, such as Figure 10 As shown in (b), even with large deviations, (Determined by the actual grating groove size b) or (Determined by the spacing d between the two grating waveguides) reaching 1.4, (As shown by the black curve) It remains above -0.8. (As shown by the blue curve) It remains above -0.9. Compared with the traditional case, it shows strong robustness. This robustness is because the changes in coupling parameters caused by the interferometer fabrication structure deviation do not significantly change the field distribution of the topological boundary mode and have little impact on the visibility of the HOM interferometer.
[0077] In integrated quantum optical devices, traditional two-photon interferometer structures typically rely on adiabatic evolution conditions to ensure high interferometric visibility. This condition requires the device size (especially length) to be much larger than the characteristic coupling length, resulting in typical devices (such as adiabatic tapered waveguide polarization beamsplitters) reaching hundreds of micrometers (200–500 μm) in size, severely limiting integration density. In contrast, the device of this invention achieves two-photon HOM interferometry by inducing compact topological boundary modes through coupling π-phase difference. This mode is topologically protected; its formation is determined by global topological properties, making it robust to local perturbations and thus completely unaffected by adiabatic evolution conditions. This interferometer contains only eight grating periodic grooves, with an overall size of approximately 60 μm × 5 μm. Taking the first waveguide as an example, it sequentially includes a first input waveguide 1 (length 14 μm), a first grating waveguide 3 (length 8 × 3.93 = 31.44 μm), and a first output waveguide 5 (length 14 μm). High-performance quantum interference with visibility of v ≈ −0.98 was achieved at a scale much smaller than that of traditional devices, significantly improving integration and robustness.
[0078] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.
[0079] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.
[0080] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.
Claims
1. A topologically protected Hong-Ou-Mandel interferometer based on a π-phase modulated grating, characterized in that, The system includes a silicon dioxide substrate (7) and a first waveguide and a second waveguide arranged side by side thereon. The first waveguide includes a first input waveguide (1), a first grating waveguide (3), and a first output waveguide (5) in sequence. The second waveguide includes a second input waveguide (2), a second grating waveguide (4), and a second output waveguide (6) in sequence. The first grating waveguide (3) and the second grating waveguide (4) each contain N grooves arranged periodically along the optical transmission direction. The number of grating grooves N is an integer from 1 to 100. The grooves of the first grating waveguide (3) and the grooves of the second grating waveguide (4) are symmetrically distributed on their respective waveguide cross sections about the line connecting the center of the first waveguide and the second waveguide. This introduces a π-coupled phase difference between the waveguide couplings of the two grating waveguides, which can induce topologically nontrivial boundary states in the mode coupling network of the system, thereby providing a topologically protected evolution path for two-photon Hong-Ou-Mandel interference.
2. The Hong-Ou-Mandel interferometer based on a π-phase modulated grating as described in claim 1, characterized in that, The first input waveguide (1), the first output waveguide (5), the second input waveguide (2), and the second output waveguide (6) are all curved S-shaped waveguides; The first input waveguide 1 and the second input waveguide (2) have different extension directions, and the first output waveguide (5) and the second output waveguide (6) have different extension directions.
3. The Hong-Ou-Mandel interferometer based on a π-phase modulated grating as described in claim 1, characterized in that, The period length, size and longitudinal arrangement of the grooves in the first grating waveguide (3) and the second grating waveguide (4) are the same.
4. The Hong-Ou-Mandel interferometer based on a π-phase modulation grating as described in claim 1, characterized in that, The spacing d between the first grating waveguide (3) and the second grating waveguide (4), and the geometric scaling factor b of the groove size, are configured to increase the coupling strength between the TE and TM modes within the waveguide. TE mode coupling strength between waveguides and the TM mode coupling strength between waveguides All three are equal; among them, the waveguide coupling strength is... The inter-waveguide coupling strength is inversely proportional to the geometric scaling factor b. and The waveguide spacing d decreases exponentially with increasing waveguide spacing d.
5. The Hong-Ou-Mandel interferometer based on a π-phase modulated grating as described in claim 1, characterized in that, The groove is rectangular, and its cross-section has the same aspect ratio as the cross-section of the waveguide. The width and height are 1 / b of the corresponding dimensions of the waveguide, where the geometric scaling factor b is a real number greater than 1.
6. The Hong-Ou-Mandel interferometer based on a π-phase modulated grating as described in claim 1, characterized in that, The spacing d between the first grating waveguide (3) and the second grating waveguide (4) satisfies: 0.1935λ-0.2452λ; The geometric scaling factor b of the groove size satisfies: 0.0308λ-0.0435λ; Where λ is the operating wavelength of the interferometer.
7. The Hong-Ou-Mandel interferometer based on a π-phase modulated grating as described in claim 1, characterized in that, The width of the first input waveguide (1), the first output waveguide (5), the second input waveguide (2) and the second output waveguide (6) is 0.2λ and the thickness is 0.2λ to 0.35λ, where λ is the operating wavelength of the interferometer, and all support two orthogonal polarization modes, TE mode and TM mode.
8. The Hong-Ou-Mandel interferometer based on a π-phase modulated grating as described in claim 1, characterized in that, The grating period length of the first grating waveguide (3) and the second grating waveguide (4) The following phase matching conditions must be met:
9. Among them, λ represents the effective refractive index of the TE mode and TM mode in the grating waveguide, respectively, and λ is the operating wavelength of the interferometer.
10. A topologically protected Hong-Ou-Mandel interferometer based on a π-phase modulated grating as described in claim 1, characterized in that, The method for determining the groove positions and π-coupling phase difference of the first grating waveguide (3) and the second grating waveguide (4) is as follows: based on the TE and TM modes within the waveguide... The sign of the electric field overlap integral is determined by selecting the groove of the first grating waveguide (3) located at the upper left corner (−x, y) of the waveguide cross-section, while selecting the groove of the second grating waveguide (4) located at the upper right corner (x, y) of the waveguide cross-section, thereby introducing a fixed π coupling phase difference between the waveguide coupling terms of the two grating waveguides: This ensures that the total phase difference of the HOM interferometer is π; where i is the imaginary unit in physics.