Asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material

Abstract

The invention discloses an asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material, which comprises a Z-cut lithium niobate film layer and a chalcogenide glass waveguide layer, the chalcogenide glass waveguide layer is arranged on the surface of the Z-cut lithium niobate film layer, the chalcogenide glass waveguide layer comprises a chalcogenide glass film and a Y-type waveguide, and the Y-type waveguide is arranged on the surface of the Z-cut lithium niobate film layer. The Y-shaped waveguide is composed of a first auxiliary waveguide, a second auxiliary waveguide, a coupling area and a main waveguide, the first auxiliary waveguide and the second auxiliary waveguide form a heat insulation coupler, the width of the first auxiliary waveguide is gradually narrowed to W3 from W1, the width of the second auxiliary waveguide is gradually widened to W3 from W2, W1 is larger than W2, and W3 is larger than W2. One ends of the first auxiliary waveguide and the second auxiliary waveguide with the same width of W3 are respectively connected with one end of the coupling area, and the other end of the coupling area is connected with the main waveguide. The multiplexer can realize high-precision phase matching among different modes, effectively suppress mode crosstalk, improve mode separation and transmission efficiency, and has a good application prospect in a high-performance mode division multiplexing integrated optical path.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated photonics and optical communications, and in particular relates to an asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass materials. Background Art

[0002] With the rapid development of emerging technologies such as 5G, the Internet of Things, and artificial intelligence, data traffic in data centers and high-performance computing systems is growing exponentially. Although wavelength division multiplexing (WDM) technology has been widely used in optical communication systems, its reliance on multi-wavelength laser sources and wavelength stability complicates system architecture and significantly increases power consumption and cost. Therefore, exploring new multiplexing methods to further improve communication capacity and energy efficiency has become a key research focus. Mode division multiplexing (MDM) technology has emerged as a response to this challenge. This technology significantly increases the channel capacity of optical communication systems by transmitting multiple orthogonal modes of optical signals in parallel through the same multimode optical waveguide. Although the concept of mode division multiplexing dates back more than 40 years, as the development of optical communication capacity and integrated photonics technology approaches bottlenecks, MDM technology has regained widespread attention and has gradually expanded to on-chip integrated photonic devices.

[0003] On-chip mode division multiplexers typically consist of a coupling structure and multimode waveguides. The key to achieving mode-selective coupling is through asymmetric directional coupling. As a special type of directional coupler, asymmetric directional couplers introduce asymmetry through structural parameters (such as waveguide spacing, width, and refractive index) to regulate the coupling efficiency between different propagation modes, thereby achieving directional selection of optical signals and controlling mode conversion.

[0004] In recent years, chalcogenide glasses have emerged as a promising candidate for asymmetric directional coupling structures due to their high refractive index, high nonlinear coefficient, and excellent infrared transmittance. Meanwhile, optical materials such as silicon, silicon nitride, and lithium niobate have also made significant progress in structural design and process implementation. While silicon offers advantages such as mature processing, its lack of a usable first-order electro-optical effect limits its application in high-speed, tunable multiplexers. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material in response to the shortcomings of the existing technology. The asymmetric Y-type multiplexer can achieve high-precision phase matching between different modes, effectively suppress mode crosstalk, and improve modal separation and transmission efficiency.

[0006] The present invention solves the above-mentioned technical problems by adopting a technical solution: an asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass materials, comprising a Z-cut lithium niobate thin film layer and a chalcogenide glass waveguide layer. The chalcogenide glass waveguide layer is disposed on the surface of the Z-cut lithium niobate thin film layer. The chalcogenide glass waveguide layer comprises a chalcogenide glass thin film and a Y-type waveguide disposed on the surface of the chalcogenide glass thin film. The Y-type waveguide comprises a first auxiliary waveguide, a second auxiliary waveguide, a coupling region, and a main waveguide. The first auxiliary waveguide and the second auxiliary waveguide constitute an adiabatic coupler. The widths of the first auxiliary waveguide at both ends are W1 and W3, respectively, and the width of the first auxiliary waveguide gradually narrows from W1 to W3. The widths of the second auxiliary waveguide at both ends are W2 and W3, respectively, and the width of the second auxiliary waveguide gradually widens from W2 to W3, with W1 greater than W2. The ends of the first and second auxiliary waveguides, both having a width of W3, are connected to one end of the coupling region, and the other ends of the coupling region are connected to the main waveguide.

[0007] The asymmetric Y-type multiplexer of the present invention combines the high electro-optical modulation capability of lithium niobate with the high refractive index and low loss advantages of chalcogenide glass, effectively balancing device performance and manufacturability. To ensure good manufacturing tolerance and robust anti-interference capabilities, the Y-type waveguides of the asymmetric Y-type multiplexer of the present invention utilize single-mode waveguides with varying widths and large gaps: a first auxiliary waveguide and a second auxiliary waveguide. The width of the first auxiliary waveguide gradually narrows from W1 to W3, while the width of the second auxiliary waveguide gradually widens from W2 to W3. The ends of the first and second auxiliary waveguides, both with a width of W3, are connected to one end of the coupling region. This ensures that the first and second auxiliary waveguides meet phase-matching conditions within the coupling region, enabling selective coupling of specific modes. This allows optical signals of different modes to be multiplexed into the main waveguide, achieving phase-matched coupling of the TE0-TE1 mode. Furthermore, W1>W2 prevents degenerate modes and ensures single-mode transmission at the input.

[0008] The asymmetric Y-type multiplexer of this invention achieves high-precision phase matching between different modes, effectively suppressing modal crosstalk and improving modal separation and transmission efficiency. Furthermore, through effective refractive index control strategies, including material selection and cross-sectional dimension design, phase velocity synchronization between different modes is achieved, significantly reducing transmission loss and crosstalk. This results in a highly efficient, low-energy, and integrable mode-division multiplexing device, improving device compactness and transmission efficiency. This device has promising application prospects in high-performance mode-division multiplexing integrated optical circuits.

[0009] Preferably, the first auxiliary waveguide and the second auxiliary waveguide are both ridge stripe waveguides, the cross-sections of the first auxiliary waveguide and the second auxiliary waveguide are both rectangular, the thickness of the first auxiliary waveguide, the second auxiliary waveguide, the coupling region and the main waveguide are the same, and the coupling region and the main waveguide have the same width.

[0010] Preferably, the size of W3 is 795-805 nm, and the size of the width W4 of the main waveguide is 1590-1610 nm.

[0011] As an option, the material of the chalcogenide glass film and the Y-type waveguide are both Ge 28 Sb 12 Se 60 Chalcogenide glass materials.

[0012] Preferably, the thickness of the Z-cut lithium niobate thin film layer is 895-905 nm, the thickness of the chalcogenide glass thin film is 200 nm, and the thickness of the Y-type waveguide is 394-406 nm.

[0013] Compared with the prior art, the present invention has the following advantages: the asymmetric Y-type multiplexer of the present invention realizes the heterogeneous integration of lithium niobate and chalcogenide glass materials for the first time, and realizes TE0 / TE1 mode selective coupling by adopting three-dimensional asymmetric Y-type coupling topology and topological protection mode control, combining the first auxiliary waveguide and the second auxiliary waveguide with the secondary reverse coupling mechanism. The asymmetric Y-type multiplexer of the present invention can achieve high-precision phase matching between different modes, effectively suppress mode crosstalk, and improve modal separation and transmission efficiency. Simulation results show that the insertion loss of the asymmetric Y-type multiplexer of the present invention is as low as 0.7dB at a wavelength of 1550nm, the crosstalk is less than -18dB, and the bandwidth covers more than 100nm, providing a high-performance integrated solution for 5G / 6G high-speed optical communications, and has good application prospects in high-performance mode division multiplexing integrated optical circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the appearance of an asymmetric Y-type multiplexer in an embodiment;

[0015] Figure 2 The electric field distribution in the waveguide under different widths of the first auxiliary waveguide and the second auxiliary waveguide under a determined thickness of the chalcogenide glass film;

[0016] Figure 3 is the graph of effective refractive index as a function of waveguide width;

[0017] Figure 4 is the cross-sectional information at different positions along the multiplexer;

[0018] Figure 5 is the pattern distribution diagram of multiplexers at different positions;

[0019] Figure 6 is the effective refractive index of the two guided modes at different positions along the propagation direction, the relationship between the effective refractive index of the two guided modes and the propagation position at 1550 nm, and the mode distribution at both ends of the adiabatic coupler;

[0020] Figure 7 TE0 mode crosstalk diagram and electric field distribution diagram;

[0021] Figure 8 is the electric field distribution diagram obtained by simulation;

[0022] Figure 9 Bandwidth performance diagram of the mode division multiplexing link. DETAILED DESCRIPTION

[0023] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0024] The asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass materials of the embodiment is as follows: Figure 1 As shown, it includes a Z-cut lithium niobate (LN) thin film layer 12 and a chalcogenide glass waveguide layer. The Z-cut lithium niobate thin film layer 12 is disposed on the surface of a SiO2 substrate 11. The chalcogenide glass waveguide layer is disposed on the surface of the Z-cut lithium niobate thin film layer 12. The chalcogenide glass waveguide layer includes a chalcogenide glass thin film 13 and a Y-type waveguide disposed on the surface of the chalcogenide glass thin film 13. The Y-type waveguide is composed of a first auxiliary waveguide 2, a second auxiliary waveguide 3, a coupling region 4, and a main waveguide 5. The first auxiliary waveguide 2 and the second auxiliary waveguide 3 constitute an adiabatic coupler. The widths of the first auxiliary waveguide 2 at both ends are W1 and W3, respectively, and the width of the first auxiliary waveguide 2 gradually narrows from W1 to W3. The widths of the second auxiliary waveguide 3 at both ends are W2 and W3, respectively, and the width of the second auxiliary waveguide 3 gradually widens from W2 to W3, where W1>W2. The ends of the first auxiliary waveguide 2 and the second auxiliary waveguide 3, both having a width of W3, are connected to one end of the coupling region 4, and the other end of the coupling region 4 is connected to the main waveguide 5.

[0025] In this embodiment, the first auxiliary waveguide 2 and the second auxiliary waveguide 3 are both ridge strip waveguides, the cross-sections of the first auxiliary waveguide 2 and the second auxiliary waveguide 3 are both rectangular, the thickness of the first auxiliary waveguide 2, the second auxiliary waveguide 3, the coupling region 4 and the main waveguide 5 are the same, and the coupling region 4 and the main waveguide 5 have the same width.

[0026] In this embodiment, the materials of the chalcogenide glass film 13 and the Y-type waveguide are both Ge 28 Sb 12 Se 60 Chalcogenide glass material, the thickness of the Z-cut lithium niobate thin film layer 12 is 900nm, the thickness of the chalcogenide glass thin film 13 is 200nm, the thickness h of the Y-type waveguide is 400nm; the size of W1 is 900nm, the size of W2 is 700nm, the size of W3 is 800nm, and the width W4 of the main waveguide 5 is 1600nm.

[0027] Figure 2The electric field distribution in the waveguide under different widths of the first auxiliary waveguide and the second auxiliary waveguide is given when the thickness of the chalcogenide glass film is determined. Figure 2 (a) in the figure is the electric field mode distribution of the TE mode when the waveguide width W is 600nm. It can be seen that when the waveguide width is narrow, a large part of the electric field of the TE0 mode is radiated into the cladding of the chalcogenide glass material, which will lead to higher waveguide losses. Figure 2 (b) in the figure is the electric field mode distribution of the TE0 mode when the waveguide width W is 700nm. Compared with the case where the width W is 600nm, the electric field radiation leakage of the TE0 mode has begun to improve significantly, and most of the energy of light propagation is confined to the waveguide for transmission. Figure 2 (c) and (d) are the electric field distribution of TE0 mode when the waveguide width W is 800nm ​​and 900nm respectively. Figure 2 In the two cases (a) and (b), it can be clearly seen that the electric field radiation leakage of the mode is small and the electric field energy is concentrated. Figure 2 Figures (e), (f), (g), and (h) show the electric field distributions of different waveguide modes when the waveguide width W exceeds 1000 nm. It can be seen that higher-order propagation modes begin to emerge in the waveguide. The selection of the waveguide width requires a certain compromise. To ensure good propagation loss and maximum single-mode transmission, in this example, we ultimately chose W1 = 900 nm and W2 = 700 nm.

[0028] When W1 and W2 are determined, W3 and W4 are determined according to phase matching adjustment. We calculated the effective refractive index of the transverse electric fundamental mode and the transverse electric high-order mode, as shown in the following example: Figure 3 As shown, the effective refractive index of the mode changes with the change of waveguide geometry (mainly the width change). We select a refractive index value of 2.28 to achieve phase matching, and it can be seen that Figure 3 In a dual-mode multiplexer operating at 1550 nm, the TE0 mode of the narrow waveguide (700 nm width) matches the TE1 mode of the wide waveguide (about 1600 nm width), so we ultimately choose W3 = 800 nm and W4 = 1600 nm.

[0029] Figure 4 Figure 1 shows cross-sectional information at different locations along the multiplexer, with the two blue colors representing different materials. The dark blue represents the chalcogenide glass film, the first and second auxiliary waveguides, and the light blue represents the Z-cut lithium niobate thin film layer. Part of the optical field in one waveguide couples into the other. The first and second auxiliary waveguides are closely aligned to form a coupled configuration, supporting two electric field modes, designated S0 and S1. By injecting only the fundamental mode from each auxiliary waveguide, one mode can be selectively excited in the main waveguide.

[0030] The mode distribution of multiplexers at different positions is as follows Figure 5 As shown. After passing through the adiabatic coupler composed of the first auxiliary waveguide and the second auxiliary waveguide, the fundamental mode state propagates to the coupling region and then merges into the main waveguide. One end of the coupling region is a symmetrical structure, and its branches consist of two very short single-mode waveguides with a width of W3. According to the symmetry principle, when the symmetric mode S0 is injected into the coupling region, only the TE0 mode can be excited. Similarly, the antisymmetric mode S1 can only excite the TE1 mode. The working mechanism of the Y-type waveguide can also be described as the evolution of the even mode and odd mode output from the main waveguide blade at the connector of the coupling region. In order to reduce the reflection at the corner between the first auxiliary waveguide and the second auxiliary waveguide, we used a Y-type waveguide with a ridge height h of 400nm. Compared with strip waveguides, ridge waveguides are insensitive to sidewall roughness and therefore have lower transmission loss. In addition, devices based on ridge waveguides can achieve more compact design and more tolerant manufacturing. In order to further explore the mode evolution, we calculated the effective refractive index of the two guided modes at different positions along the propagation direction by finite difference algorithm, as shown in Figure 6 The relationship between the effective refractive index of the two guided modes and the propagation position at 1550nm and the mode distribution at both ends of the adiabatic coupler are also shown in Figure 6 As shown in the inset, the TE0 mode injected into the wide waveguide evolves into the S0 mode due to the close proximity of their effective refractive indices. In contrast, the TE0 mode injected into the narrow branch evolves into the S1 mode.

[0031] After determining the two transition modes, we calculated the crosstalk of the adiabatic coupler at a wavelength of 1550nm, and also considered the effect of three different gap values ​​(G = 100nm, 200nm, and 300nm). Here, we define crosstalk as the power ratio of the TE0 mode output on the bus waveguide to the total input mode when light is injected from the narrow waveguide. Figure 7As shown in the figure, due to the different gaps G, the three gaps exhibit different coupling effects at different coupling lengths. First, the gap with the largest length is 300nm. Due to the large gap, the coupling effect after light is injected is poor, and the overall crosstalk shows a trend of first decreasing and then increasing. It basically stabilizes after 200μm. However, due to the large gap angle, the overall crosstalk effect is not ideal. Secondly, the curve with a gap of 200nm shows a trend of first decreasing, then increasing, and then slowly decreasing. Due to insufficient light coupling in the front part, the data is biased. Therefore, when the coupling length increases, the crosstalk first increases and then decreases. Finally, when the coupling length is 225μm, the crosstalk gradually becomes smaller than that of the curve with a gap of 300nm. Finally, the case with a gap of 100nm is similar to the previous two cases. Due to insufficient coupling, as the coupling length increases, the crosstalk drops rapidly and then rises again. After 100nm, the coupling efficiency increases and the crosstalk decreases. It reaches a minimum value around 200μm, with a crosstalk of about 30dB. The same results can be obtained when light is emitted from a wide waveguide. Therefore, in our design, we chose G = 100nm and L = 200μm, taking into account both crosstalk and device footprint. While a smaller G allows for a more compact design, it significantly increases the manufacturing complexity. Notably, the angle between the branches at one end of our coupling region is approximately 5.72 degrees, greater than the approximately 1 degree of a traditional asymmetric Y-junction, which helps reduce manufacturing complexity. Figure 8 The simulated electric field distribution is shown. When the TE0 mode is launched from a wide input port, the TE0 mode is observed. Furthermore, if the TE0 mode is injected from a narrow input port, the TE1 mode is generated. Thus, a mode-multiplexed signal is achieved in the bus waveguide.

[0032] Next, we calculated the bandwidth performance of the mode division multiplexing link of the proposed asymmetric Y-type multiplexer by the EME method, as shown in Figure 9 The schematic diagram shows a complete mode-division multiplexing link, which includes two proposed designs acting as multiplexers and demultiplexers, with two input ports (I1 & I2) and two output ports (O1 & O2), respectively. The multiplexers and demultiplexers have the same parameters and are connected by a straight bus waveguide with a length of 20 μm. Figure 9The "I1-O1" legend in the figure refers to the transmission from input port I1 to output port O1. In the range of 1500 to 1600 nm, the insertion loss of output port O1 is about 1.36 dB, and the crosstalk (transmission path of I2-O1) is less than -17 dB. The insertion loss of output port O2 is about 0.7 dB, and the crosstalk (transmission path of I1-O2) is less than -18 dB. Therefore, an extinction ratio of more than 16 dB can be obtained within 100 nm, ensuring good performance of mode division multiplexing operation. The difference in insertion loss between the two output ports may be caused by the larger reflection at the corner of the micro Y-connector, since the electric field intensity of the TE0 mode in the center of the waveguide is stronger than that of the TE1 mode. At 1550 nm, the transmission curves as a function of gap G and etching depth are calculated respectively. As shown Figure 9 As shown, when the gap G deviation is from -50 to 50 nanometers, it can be seen that the curve shows a trend of first decreasing and then increasing, and the lowest crosstalk is about 30dB.

Claims

1. An asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material, characterized in that: The invention comprises a Z-cut lithium niobate thin film layer and a chalcogenide glass waveguide layer, wherein the chalcogenide glass waveguide layer is disposed on the surface of the Z-cut lithium niobate thin film layer. The chalcogenide glass waveguide layer comprises a chalcogenide glass thin film and a Y-shaped waveguide disposed on the surface of the chalcogenide glass thin film. The Y-shaped waveguide is composed of a first auxiliary waveguide, a second auxiliary waveguide, a coupling region, and a main waveguide. The first auxiliary waveguide and the second auxiliary waveguide constitute an adiabatic coupler. The widths of the first auxiliary waveguide at both ends are W1 and W3, respectively, and the width of the first auxiliary waveguide gradually narrows from W1 to W3. The widths of the second auxiliary waveguide at both ends are W2 and W3, respectively, and the width of the second auxiliary waveguide gradually widens from W2 to W3, where W1>W2. The ends of the first and second auxiliary waveguides, both having a width of W3, are connected to one end of the coupling region, and the other ends of the coupling region are connected to the main waveguide.

2. The asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material according to claim 1, characterized in that: The first auxiliary waveguide and the second auxiliary waveguide are both ridge stripe waveguides, the cross-sections of the first auxiliary waveguide and the second auxiliary waveguide are both rectangular, the thickness of the first auxiliary waveguide, the second auxiliary waveguide, the coupling region and the main waveguide are the same, and the coupling region and the main waveguide have the same width.

3. The asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material according to claim 2, characterized in that: The size of W3 is 795-805 nm, and the size of the width W4 of the main waveguide is 1590-1610 nm.

4. The asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material according to any one of claims 1 to 3, characterized in that: The materials of the chalcogenide glass film and the Y-type waveguide are Ge 28 Sb 12 Se 60 Chalcogenide glass materials.

5. The asymmetric Y-type multiplexer based on lithium niobate and chalcogenide glass material according to claim 4, characterized in that: The thickness of the Z-cut lithium niobate thin film layer is 895-905 nm, the thickness of the chalcogenide glass thin film is 200 nm, and the thickness of the Y-type waveguide is 394-406 nm.

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