Integratable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation

Abstract

The invention belongs to the technical field of integrated photonic devices, and particularly relates to an integratable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation. Aiming at the bottleneck of insufficient electro-optical tuning capability of a silicon nitride photonic device, a two-dimensional material covering layer (such as molybdenum disulfide, tungsten disulfide and the like) is integrated on the surface of a silicon nitride waveguide, and a multi-layer stacked structure of a metal electrode, a two-dimensional material, an SiO2 upper cladding and the silicon nitride waveguide is formed from top to bottom. Input light is uniformly split to a modulation arm and a reference arm of a directional coupler through a 1 * 2 multimode interference coupler (MMI), wherein the cladding surface of the modulation arm is covered with a two-dimensional material; the two-dimensional material is driven by external bias voltage to change the optical phase of a modulation arm through evanescent field coupling, so that two beams of light generate constructive or destructive interference in an interference coupling area, and dynamic switching of light intensity distribution of an output port and beam splitting ratio regulation and control are realized. Compared with a lithium niobate-silicon nitride heterogeneous integration scheme, the two-dimensional material with the atomic layer thickness is introduced in the design innovation, so that the CMOS process compatibility is improved, a complex heterogeneous bonding process is avoided, and monolithic integration is facilitated. The device has remarkable advantages in a silicon-based optoelectronic integrated system, and is particularly suitable for optical communication, photon calculation and photon neural networks needing high-speed dynamic reconstruction.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated photonic devices, and in particular to an integrable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation. Background Art

[0002] As an important component of integrated photonic circuits, the dynamic routing capability of reconfigurable optical switches directly determines the real-time reconfiguration efficiency of optical communication systems and photonic processors. Among the many integrated optical switch architectures, directional coupler-type optical switches have become the preferred solution for on-chip optical path switching due to their compact structure and low crosstalk. However, when using an ultra-low-loss silicon nitride platform, its intrinsic non-tunable characteristics become a bottleneck: as a centrosymmetric crystal, silicon nitride lacks the asymmetric polarization response required for the linear electro-optic effect, and its wide bandgap characteristics lead to low carrier concentration, making it impossible to achieve effective modulation through the plasma dispersion effect. Traditional solutions all have limitations: slow thermo-optical tuning response and high power consumption; lithium niobate heterogeneous integration faces lattice mismatch stress and mode field mismatch loss, and low evanescent field electro-optic efficiency. These limitations mean that existing silicon nitride directional couplers can only achieve static optical path allocation, which cannot meet the stringent requirements of optical networks for nanosecond dynamic reconfiguration. In recent years, transition metal dichalcogenides (TMDs) have provided a new path to overcome the silicon nitride modulation bottleneck. Two-dimensional materials such as monolayer MoS2 / WS2 exhibit strong electrorefractive effects, and their atomic-scale thickness allows for efficient manipulation of the refractive index of waveguide modes through evanescent field coupling. This offers a new approach to solving the dual-port dynamic tuning challenge of silicon nitride directional couplers.

[0003] To this end, this patent proposes an integrable silicon nitride directional coupler-type electro-optical switch based on two-dimensional material modulation. Its principle is: only a single layer of TMDs is integrated in the upper cladding of the modulation arm, and the input light is evenly distributed to the reference arm and the modulation arm through a 1×2 MMI. Under an external bias, the electro-refractive index change of the TMDs selectively regulates the modulation arm to produce an additional optical path, so that the signals of the two arms produce a reconfigurable phase difference in the interference output region, realizing an optical switch function with a continuously adjustable splitting ratio from 0:100 to 100:0. This solution breaks through the modulation bottleneck of traditional silicon nitride optical switches, achieving nanosecond response and microwatt power consumption. The wet transfer TMDs technology it adopts significantly improves the compatibility of CMOS processes and strongly promotes high-density monolithic integration. This creates a core device with both ultra-low loss and dynamic reconstruction capabilities for the next generation of intelligent optical systems. Summary of the Invention

[0004] This invention proposes an integrated silicon nitride directional coupler electro-optical switch based on two-dimensional material modulation. This invention addresses the lack of electrical tunability in traditional silicon nitride directional couplers. By integrating a two-dimensional material covering layer on the upper cladding surface of the directional coupler's interferometer arm waveguide, it successfully achieves dynamic, electrically controlled switching of the optical path state. This significantly enhances the dynamic reconfiguration capability of photonic integration on the silicon nitride platform and is a core functional module for building the next generation of high-density, programmable optical chips.

[0005] The specific technical solutions of the present invention are as follows:

[0006] Figure 1 This is an integrated silicon nitride directional coupler electro-optical switch based on two-dimensional material modulation. Its core structure includes silicon nitride input and output waveguides (① in the figure), a 1×2 multimode interferometer (② in the figure), a directional coupler modulation arm (③ in the figure), a directional coupler reference arm (④ in the figure), a directional coupler interferometric coupling region (⑤ in the figure), a two-dimensional material cover layer (⑥ in the figure), a metal modulation electrode (⑦ in the figure), a silicon dioxide lower cladding layer (⑧ in the figure), and a silicon dioxide upper cladding layer (⑨ in the figure). To ensure the basic single-mode transmission performance of the device, the single-mode transmission conditions of the silicon nitride waveguide were first simulated and optimized to ensure the mode purity of the input and output optical fields. Figure 2 The simulation of single-mode transmission conditions shown in the figure shows that: under a fixed waveguide thickness, Figure (a) shows the effect of different waveguide widths on the lateral light field distribution, and Figure (b) shows the cutoff width of the waveguide to maintain single-mode operation. In order to achieve device miniaturization, the transmission loss under different bending radii is further simulated ( Figure 3 ), under the optimized bending radius, the curved waveguide structure can simultaneously achieve ultra-low loss transmission of the TE fundamental mode and efficient suppression of the TM fundamental mode, meeting the requirements of high-density integration. In order to meet the requirement of the directional coupler for two input lights with the same phase and equal power, a 1×2 multimode interferometer (MMI) at its input end is designed. By optimizing the key geometric parameters of the MMI: the length of the multimode waveguide region ( Figure 4 (a)), output spot converter spacing ( Figure 4 (b)) and the output spot converter length ( Figure 4 (c)) successfully achieves balanced optical power distribution (~50:50) between the two arms at the MMI output end. Figure 5 The light field distribution diagram shown clearly shows the process of the input light field evolving in the MMI and being evenly split into two output waveguides.

[0007] On this basis, the core area of ​​the directional coupler, the interference coupling zone, was designed. In order to achieve efficient coupling and improve the extinction ratio, key parameters such as the waveguide spacing and coupling length in the coupling zone were accurately optimized through simulation. Figure 6The paper shows the change in transmittance of one of the output ports under different waveguide spacings, with the phase difference between the two transmission arms fixed at 90° (corresponding to a specific voltage operating point). The simulation results show that the change in waveguide spacing can effectively regulate the coupling efficiency and extinction ratio. After the geometric structure of the interference coupling region is determined, the thickness of the silicon dioxide cladding is optimized using COMSOL multi-physics simulation software. Under the premise of ensuring ultra-low transmission loss of the silicon nitride waveguide, the effective mode overlap rate of the two-dimensional material covering layer and the evanescent field of the waveguide is maximized to achieve a balance between low transmission loss and high modulation efficiency. The simulation results are shown in Figure 2. Figure 7 (a) shows the cross section of the optical field of the modulated arm waveguide. Figure 7 (b) As shown. Furthermore, the modulation metal electrode is prepared on the surface of the modulation arm TMDs by electron beam evaporation process. The electro-optical modulation simulation shows that ( Figure 8 ), when an external static bias is applied, the electrorefractive effect of the two-dimensional material can significantly change the effective refractive index of the optical mode in the silicon nitride waveguide in the coverage area, resulting in a controllable additional phase difference in the modulation arm, dynamically destroying the original phase matching conditions in the coupling area, and changing the coupling efficiency between the waveguides, which is ultimately reflected in the controllable change of the optical power ratio of the two output ports, thereby realizing the optical path switching function.

[0008] Based on the above process, compared with existing optical switches based on silicon nitride platforms, the integrated silicon nitride directional coupler electro-optical switch based on two-dimensional material modulation provided by the present invention has the following advantages: (1) Compared with traditional tunable switches that rely on thermo-optical effects, the integrated silicon nitride directional coupler electro-optical switch based on two-dimensional material modulation proposed in this invention, relying on the strong electrorefractive properties of the two-dimensional material, is driven by a low-voltage electrostatic field to achieve ultrafast dynamic control of the refractive index in the nanosecond range, meeting the stringent switching speed requirements of high-speed optical switching matrices and real-time photonic computing interconnections. At the same time, its electro-optical modulation mechanism essentially avoids thermal effects or carrier injection processes, reducing the device's operating power consumption to microwatts, thereby reducing the impact of thermal crosstalk on high-density photonic integration. (2) In response to the challenges faced by lithium niobate heterogeneous integration or silicon-based carrier injection optical switches, such as high process complexity, large insertion loss, and limited modulation efficiency, the present invention proposes an integrated silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation, which fully utilizes the advantages of the atomic-level thickness of two-dimensional materials and their high compatibility with CMOS processes. This design does not require complex heterogeneous bonding or high-energy carrier injection processes, significantly simplifies the manufacturing process, reduces manufacturing costs, and clears the way for high-density photonic integration. More importantly, this solution fully retains the ultra-low transmission loss and wide spectral transparency window inherent in the silicon nitride platform, making it uniquely advantageous in applications such as high-power laser transmission systems, dense wavelength division multiplexing optical networks, and broadband quantum light source processing. (3) The two-dimensional material modulation-based integrated silicon nitride directional coupler type electro-optical switch has the advantages of compact structure and easy large-scale integration. Through accurate design of the geometric parameters of the coupling area and innovative use of the silicon nitride waveguide structure with extremely low aspect ratio, the effective mode overlap rate of the evanescent field and the two-dimensional material covering layer is increased, thereby improving the electro-optical modulation efficiency, and excellent comprehensive performance of high extinction ratio and fast switching response is achieved under low driving voltage, thereby providing a reliable hardware foundation for constructing programmable optical interconnection topology and dynamic photonic neural networks. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a three-dimensional structure schematic diagram of a two-dimensional material modulation-based integrated silicon nitride directional coupler type electro-optical switch. In the figure, ① is a silicon nitride input / output waveguide, ② is a 1x2 multimode interferometer (MMI), ③ is a directional coupler modulation arm, ④ is a directional coupler reference arm, ⑤ is a directional coupler interference coupling area, ⑥ is a two-dimensional material covering layer, ⑦ is a metal modulation electrode, ⑧ is a silicon dioxide lower cladding layer, and ⑨ is a silicon dioxide upper cladding layer. Figure 2 is a simulation result diagram of the single-mode transmission condition of a silicon nitride waveguide. In the figure, (a) is a lateral light field distribution diagram under different waveguide widths, and (b) is a cut-off width diagram for maintaining single-mode operation of the waveguide. Figure 3 is a simulation diagram of the transmission loss of the TE0 mode and the TM0 mode of the waveguide under different bending radii. Figure 4 is a simulation parameter optimization result diagram of a multimode interferometer. In the figure, (a) is a diagram of the influence of the length of the MMI multimode waveguide on the transmittance of the output port, (b) is a diagram of the influence of the spacing of the MMI output mode spot converter on the transmittance of the output port, and (c) is a diagram of the influence of the length of the MMI output mode spot converter on the transmittance of the output port. Figure 5 is a multimode interferometer light field distribution diagram. Figure 6 is a diagram of the influence of the waveguide coupling spacing on the coupling efficiency under a fixed coupling length (the phase difference of the two arms is 90°). Figure 7 is a simulation diagram of a silicon dioxide upper cladding layer. In the figure, (a) is a diagram of the influence of the thickness of the silicon dioxide upper cladding layer on the effective mode overlap rate and the transmission loss, and (b) is a diagram of the coupling distribution of the TMDs and the modulation arm waveguide light field. Figure 8 is a diagram of the change of the optical power ratio of the two output ports under the application of a bias voltage. DETAILED DESCRIPTION

[0010] Specific embodiments are as follows: first, a 5 μm thick silicon dioxide undercladding layer is grown on a silicon substrate by a thermal oxidation process, and an 80 nm silicon nitride film is deposited on its surface as a waveguide core layer by a low-stress chemical vapor deposition (LPCVD) process. Subsequently, deep ultraviolet (DUV) lithography and reactive ion etching (RIE) technology are used to define the key optical waveguide structure, including input and output waveguides with a width of 3 μm to meet the single-mode transmission conditions of the 1550 nm communication waveband; a 1×2 multimode interferometer (MMI) with a size of 85 μm (length) × 12 μm (width) can achieve a 50:50 uniform beam splitting function at the target wavelength through simulation verification; a directional coupler with a coupling length of 300 μm and a waveguide coupling pitch of 1.3 μm to achieve high evanescent field coupling efficiency and high extinction ratio. After the waveguide structure is prepared, a 600 nm thick silicon dioxide overcladding layer is grown on its surface by the TEOS-PECVD process, thereby achieving the best balance between modulation efficiency and transmission loss. Wet transfer technology is used to selectively transfer TMDs onto the directional coupler modulation arm waveguide silicon dioxide cladding layer, and the transfer process ensures that the material interface is free of wrinkles and residual contaminants with the help of an optical microscope. Subsequently, an electron beam evaporation process is used to prepare metal modulation electrodes on the surface of the two-dimensional material and on both sides of the waveguide, ensuring that the electric field is uniformly distributed on the surface of the two-dimensional material. When an external static bias is applied, the electro-optic effect of the two-dimensional material can significantly change the effective refractive index of the optical mode in the covered silicon nitride waveguide, resulting in a controllable additional phase difference in the modulation arm, dynamically destroying the original phase matching condition in the coupling region, changing the coupling efficiency between the waveguides, and ultimately reflecting as a controllable change in the optical power ratio of the two output ports, thereby realizing the optical path switching function.

Claims

1. An integrable silicon nitride directional coupler electro-optical switch based on two-dimensional material modulation, characterized by: The invention comprises a silicon nitride input and output waveguide (1), a 1×2 multimode interferometer (2), a directional coupler modulation arm (3), a directional coupler reference arm (4), a directional coupler interference coupling region (5), a two-dimensional material covering layer (6), a metal modulation electrode (7), a silicon dioxide lower cladding layer (8), and a silicon dioxide upper cladding layer (9).

2. The integrable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation according to claim (1), characterized in that: The cross-sectional dimensions of the input and output waveguides follow the single-mode transmission constraint. The input light is evenly split 50:50 by a geometrically optimized 1×2 multimode interferometer and transmitted to the reference arm and modulation arm of the directional coupler respectively.

3. The integrable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation according to claim (1), characterized in that: The two-dimensional material covering layer is transferred to the upper cladding surface of the directional coupler modulation arm in a large area and without defects through wet transfer technology.

4. The integrable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation according to claim (1), characterized in that: When an external bias is applied, the electrorefractive effect of the two-dimensional material covering layer changes the optical phase of the modulation arm of the directional coupler through evanescent field coupling, causing a phase difference between the signals of the modulation arm and the reference arm in the interference coupling region, causing the light intensity distribution of the two output ports to change, thereby realizing the optical switching function.

5. The integrable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation according to claim (1), characterized in that: The silicon dioxide upper cladding is prepared by TEOS-PECVD process to achieve low-stress optical coverage.

6. The integrable silicon nitride directional coupler type electro-optical switch based on two-dimensional material modulation according to claim (1), characterized in that: The silicon nitride waveguide adopts a cross-sectional structure with an extremely low aspect ratio to enhance the interaction between the evanescent field and the two-dimensional material.

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