Mode loss constant type low-threshold tunable phase shifter based on lossy phase change material

Abstract

The invention discloses a mode loss constant type low-threshold tunable phase shifter based on a lossy phase change material, and aims to solve the problem that the phase shifter based on the lossy phase change material is unstable in performance due to large dual-state mode loss difference. The mode loss constant type low-threshold tunable phase shifter based on the lossy phase change material comprises a SiO2 substrate, a silicon waveguide, a VO2 thin film layer and a cladding, the rectangular silicon waveguide is arranged on the SiO2 substrate, the VO2 thin film layer is heterogeneously integrated on the upper surface of the silicon waveguide to form a heterogeneously integrated waveguide, the cladding covers the silicon waveguide, and the VO2 thin film layer is arranged on the upper surface of the silicon waveguide. The size structure of the VO2 thin film layer enables the waveguide mode loss variation before and after the phase change of the VO2 thin film to be zero. According to the phase shifter, the effective refractive index change is realized by regulating the size of the VO2 thin film layer, so that the phase regulation target is achieved, the mode loss is kept constant, the jitter of the amplitude of a system signal in the phase shifter is avoided, and the power consumption of the device is reduced at the same time.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device technology, specifically relating to a tunable phase shifter based on a lossy phase change material. Background Technology

[0002] With the rapid development of technologies such as optical communication, optical computing, and phased array radar, the requirements for the performance and integration of integrated photonic devices are increasing. Among them, optical phase shifters, as a key basic component capable of dynamically controlling the phase of light waves, play a crucial role in systems such as optical phased arrays, Mach-Zehnder interferometers, and tunable filters. Their performance directly affects the size, power consumption, and efficiency of the entire system.

[0003] Currently, the mainstream optical phase shifter technologies mainly include:

[0004] 1. Thermo-optic phase shifter: based on the thermo-optic effect of silicon ( This method involves changing the refractive index of the waveguide by heating. While technically mature and easy to integrate, achieving a π phase shift typically requires waveguides hundreds of micrometers long and incurs watt-level power consumption, resulting in large device size, high power consumption, slow response (milliseconds), and thermal crosstalk.

[0005] 2. Electro-optic phase shifter: Based on the electro-optic effect (electro-optic coefficient) of materials such as lithium niobate. This scheme has a fast response speed (picosecond to nanosecond range), but a small absolute value of refractive index change. It requires millimeter-scale interaction lengths, has poor compatibility with traditional CMOS processes, is difficult to integrate, and is costly.

[0006] 3. Carrier Dispersion Phase Shifter: Based on the plasma dispersion effect of silicon, this type of phase shifter changes the refractive index by injecting or depleting carriers in the silicon waveguide. While offering a fast response, it introduces significant absorption losses, causing the insertion loss of the phase shifter to vary drastically with the phase tuning state, severely impacting system stability and performance. Furthermore, its phase modulation capability (Δn / Δα) is limited, and achieving a π phase shift typically requires a length of several hundred micrometers.

[0007] In recent years, phase change materials (PCMs) have provided a novel path to overcome the aforementioned bottlenecks. For example, germanium-antimony-tellurium (GeAM) and VO2, due to their reversible and rapid refractive index abrupt changes between amorphous and crystalline states (GeAM) or between insulating and metallic phases (VO2), offer revolutionary solutions for next-generation photonic devices. At the 1550 nm wavelength, the real part of the refractive index change for GeAM can reach Δn > 2.0, and for VO2, it can reach Δn > 1.0. This refractive index change is thousands or even tens of thousands of times greater than that of thermo-optic or electro-optic effects. This extremely high modulation efficiency means that only a single submicron-scale PCM unit interacting with an optical waveguide can generate phase changes as high as π or even 2π. This lays the physical foundation for manufacturing ultra-compact, low-power phase shifters, potentially reducing phase shifter sizes from the hundreds of micrometers to the micrometer or even submicrometer scale, thereby significantly increasing the device density of photonic integrated chips.

[0008] However, applying phase change materials (PCMs) to phase shifters faces a fundamental technical challenge that accompanies their high modulation efficiency: for most PCMs with significant refractive index changes (such as germanium, antimony, tellurium, and VO2), the large refractive index change is often accompanied by a large change in optical loss, which differs greatly between the two phase states. When these materials are directly interacted with optical waveguide modes to achieve phase modulation, the phase transition process, while changing the equivalent refractive index, inevitably introduces a large and non-negligible change in mode loss. This results in a huge difference in insertion loss between the phase shifter in different phase states, such as "0" and "π". This unstable loss characteristic causes system signal amplitude jitter, greatly limiting the application of PCM phase shifters in practical systems. In addition, for the volatile PCM VO2, its operation requires a continuous external power supply; therefore, lowering the phase transition threshold of VO2 is also crucial for reducing the overall power consumption of the device.

[0009] Therefore, there is an urgent need in this field for a novel phase shifter structure design scheme. When using lossy phase change materials for device design, it can not only make full use of the ultra-high modulation efficiency of phase change materials to achieve device miniaturization, but also effectively avoid the inherent disadvantage of large differences in waveguide mode loss in the two states caused by intrinsic material loss, thus achieving a pure, stable, and low-power phase modulation function. Summary of the Invention

[0010] This invention aims to address the performance instability of phase shifters based on lossy phase change materials due to large differences in losses between two-state modes, as well as the power consumption problem of devices based on volatile phase change materials due to continuous power supply. This invention proposes a low-power phase shifter with stable losses in two-state (insulating phase and metallic phase) modes based on a low phase change threshold VO2, operating at a wavelength of 1550nm in the C-band.

[0011] This invention relates to a mode loss constant, low-threshold tunable phase shifter based on lossy phase change materials, comprising a SiO2 substrate, a silicon (Si) waveguide, a VO2 thin film layer, and a cladding. A rectangular silicon (Si) waveguide is disposed on the SiO2 substrate. The VO2 thin film layer is heterogeneously integrated onto the upper surface of the silicon waveguide to form a heterogeneous integrated waveguide. The cladding covers the silicon waveguide. The size and structure of the VO2 thin film layer are such that the change in waveguide mode loss before and after the VO2 thin film phase change is zero.

[0012] The loss of waveguide light is mainly related to the loss of the waveguide material and the optical field distribution of the waveguide. That is, when designing a phase shifter using lossy vanadium dioxide material, the waveguide mode loss can be controlled by purposefully adjusting the mode field distribution on the waveguide cross-section. Based on this, this invention optimizes the thickness and size of the W-doped VO2 thin film to achieve the distribution of optical energy on the waveguide cross-section and parametrically characterizes the ability of the optical waveguide to confine optical energy to various material regions, especially the lossy VO2 thin film region (energy binding factor Γ). Therefore, the mode loss of waveguide light is characterized by combining material loss with the waveguide light mode field distribution (the product of the energy binding factor Γ and the VO2 absorption coefficient). Based on this, the size of the VO2 thin film is systematically optimized, and the structural dimensions corresponding to zero change in waveguide mode loss before and after the VO2 thin film phase transition are finally found.

[0013] This invention first dopes VO2 with W to obtain a W-doped VO2 thin film with a low phase transition temperature, reducing its phase transition temperature from the original 68 °C to approximately 58 °C. Then, this low-phase-transition-temperature VO2 thin film is heterogeneously integrated with a single-mode silicon waveguide. By adjusting the size and position of the VO2 thin film and the refractive index of the cladding material, a specific phase shifter structure is found. When the phase shifter adopts this structure, the phase transition of the VO2 thin film between the insulating and metallic phases allows the change in the refractive index of VO2 itself to effectively modulate the equivalent refractive index of the waveguide. However, the change in the extinction coefficient of VO2 itself does not lead to changes in the waveguide mode loss in the two states. That is, while achieving the phase modulation target through a change in the equivalent refractive index, the mode loss remains constant, avoiding jitter in the system signal amplitude in the phase shifter. Simultaneously, the reduced VO2 phase transition temperature further enables the low-power characteristics of the device. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the cross-sectional structure of the mode loss constant low threshold tunable phase shifter based on lossy phase change materials of the present invention.

[0015] Figure 2 The waveguide mode loss difference test diagrams are shown for VO2 thin films with different VO2 thin film sizes before and after the phase transition in the embodiments.

[0016] Figure 3 The diagram shows the waveguide equivalent refractive index difference before and after the phase transition of VO2 films with different VO2 film sizes in the example.

[0017] Figure 4 This is a graph showing the variation of the waveguide mode loss difference with the VO2 film thickness (t1) when the VO2 film width (w1) is 500 nm in the embodiment.

[0018] Figure 5 This is a graph showing the change in the equivalent refractive index difference of the waveguide with the thickness (t1) of the VO2 film when the width (w1) of the VO2 film is 500 nm in the example.

[0019] Figure 6 The following figures illustrate the change in optical transmittance of the W-doped VO2 thin film with temperature in the examples: (a) heating up, (b) cooling down, and (c) the first derivative curve of optical transmittance with temperature.

[0020] Figure 7 This is a schematic diagram of the waveguide cross-sectional dimensions of a mode loss constant low-threshold tunable phase shifter based on a lossy phase change material in the embodiment. Detailed Implementation

[0021] Specific Implementation Method 1: This implementation method is based on a low-threshold tunable phase shifter with constant mode loss using lossy phase change materials. It includes a SiO2 substrate 1, a silicon (Si) waveguide 2, a VO2 thin film layer 3, and a cladding 4. The rectangular silicon (Si) waveguide 2 is disposed on the SiO2 substrate 1. The VO2 thin film layer 3 is heterogeneously integrated on the upper surface of the silicon waveguide 2 to form a heterogeneous integrated waveguide. The cladding 4 covers the silicon waveguide 2. The size and structure of the VO2 thin film layer 3 are such that the change in waveguide mode loss before and after the VO2 thin film phase change is zero.

[0022] In this embodiment, the waveguide energy binding factor Γ quantifies the distribution of the mode field in different dielectric material regions within a specific waveguide configuration and correlates the mode loss with the intrinsic material loss, thereby extracting the material's contribution to the mode loss. The expression for the waveguide energy binding factor is as follows:

[0023]

[0024]

[0025] In the formula Mode loss, : Absorption coefficient of the material Vacuum permittivity Vacuum permeability, Poynting vector, : Material area, n: Material refractive index, E: Electric field strength.

[0026] Specific Implementation Method Two: The difference between this implementation method and Specific Implementation Method One is that the VO2 thin film layer 3 is a W-doped VO2 thin film.

[0027] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that the W (atomic) doping concentration in the W-doped VO2 thin film is 0.5at%-1.5at.

[0028] Specific Implementation Method 4: This implementation method differs from Specific Implementation Method 2 or 3 in that the VO2 thin film layer 3 is heterogeneously integrated onto the upper surface of the silicon waveguide 2, wherein the heterogeneous integration method is magnetron sputtering, thermal evaporation, electron beam evaporation or pulsed laser deposition.

[0029] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the cladding layer 4 is an air cladding layer.

[0030] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the size structure of the VO2 thin film layer 3 includes the width and thickness of the VO2 thin film.

[0031] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that the change in waveguide mode loss before and after the VO2 thin film phase transition is expressed as Γ. 金属相 ×α 金属相 -Γ 绝缘相 ×α 绝缘相 , where Γ 金属相 The energy binding factor Γ, α represents the VO2 thin film in the metallic phase. 金属相 Γ represents the absorption coefficient of the VO2 thin film in the metallic phase. 绝缘相 The energy binding factor Γ, α represents the VO2 thin film in the insulating phase. 绝缘相 This represents the absorption coefficient of the VO2 thin film in the insulating phase.

[0032] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the VO2 thin film drives the phase transition of the VO2 thin film layer 3 through the thermal effect of waveguide light or the Joule heating effect (electric heating).

[0033] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the thickness of the SiO2 substrate 1 is 2-3 μm.

[0034] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that when the width of the rectangular silicon (Si) waveguide 2 is 500 nm and the height is 220 nm, the width of the VO2 layer 3 is 500 nm and the height is 100 nm.

[0035] Example: This example describes a low-threshold tunable phase shifter with constant mode loss based on a lossy phase change material. It includes a SiO2 substrate 1, a silicon (Si) waveguide 2, a VO2 thin film layer 3, and an air cladding 4. The rectangular silicon (Si) waveguide 2 is disposed on the SiO2 substrate 1. The VO2 thin film layer 3 is a W-doped VO2 thin film, deposited on the upper surface of the silicon waveguide 2 by magnetron sputtering to form a heterogeneous integrated waveguide. The air cladding 4 covers the silicon waveguide 2. The following analysis examines the effect of the size and structure of the VO2 thin film layer 3 on the change in waveguide mode loss (Γ) before and after the VO2 thin film phase change. 金属相 ×α 金属相 -Γ 绝缘相 ×α 绝缘相 The impact of ).

[0036] At a wavelength of 1550 nm, when VO2 transitions from a low-temperature insulating phase to a high-temperature metallic phase, the optical refractive index n decreases and the extinction coefficient k increases, meaning the metallic phase corresponds to a higher intrinsic optical loss state. Therefore, in the embodiments, the difference between the refractive indices of the VO2 material and the waveguide is the difference between the state corresponding to insulation and the state corresponding to metal, while the difference between the mode losses of the VO2 material and the waveguide is the difference between the high-loss metallic state and the low-loss insulating state.

[0037] like Figure 1 The cross-sectional structure of the phase shifter is shown, mainly consisting of a SiO2 substrate layer 1, a rectangular Si waveguide 2, a VO2 thin film layer 3, and an air cladding layer 4. The SiO2 layer serves as the substrate, ensuring that light satisfies the law of total internal reflection at the SiO2-Si interface. The rectangular Si waveguide localizes the excited mode light field within itself, enabling forward propagation of the mode. The vanadium dioxide layer and the rectangular Si waveguide form a heterogeneous integrated waveguide, primarily utilizing the phase transition properties of vanadium dioxide. Through interaction with the evanescent wave at the upper boundary of the Si waveguide, efficient control of the waveguide light is achieved.

[0038] like Figure 2 The figure shows a three-dimensional relationship between the difference in waveguide mode loss (metallic phase minus insulating phase) caused by the switching between the two phase transition states of VO2 and the size of VO2, characterized by the combination of the waveguide mode field energy binding factor Γ and the VO2 absorption coefficient. It can be seen that, using the W-doped VO2 thin film and phase shifter structure in this embodiment, even with a large variation in VO2 size, a low difference in mode loss can still be robustly achieved during the switching between the two phase transition states. Furthermore, the change in the waveguide's equivalent refractive index needs to be considered, as this determines the phase shifter's efficiency in controlling the pure phase. Figure 3 As shown, it can be observed that the difference in waveguide equivalent refractive index (insulating phase minus metallic phase) caused by the phase transition of VO2 gradually increases with the increase of VO2 size. Through careful comparison... Figure 2 and Figure 3 It can be observed that as the size of VO2 increases, the mode loss difference caused by the phase transition first increases and then decreases. Especially when the thickness (t1) and width (w1) of VO2 are large, the sign of the mode loss difference reverses, changing from positive to negative, and even achieving lower mode loss characteristics in the case of high-loss materials. This indicates that there exists a critical VO2 size point where the mode loss difference is exactly zero, perfectly achieving stable two-state mode loss. At the same time, the equivalent refractive index difference of the waveguide shows a positive correlation with the increase of the VO2 size, which means that with a larger VO2 thickness (t1) and width (w1), a higher phase modulation efficiency can be achieved.

[0039] In response, the following was extracted Figure 2 and Figure 3 In the figure, when the VO2 width (w1) is 500 nm, the curves showing the variation of the waveguide mode loss difference and equivalent refractive index difference with the VO2 thickness (t1) are as follows: Figure 4 and Figure 5 As shown, when the VO2 layer thickness (t1) is 73.5 nm, the difference in mode loss caused by the VO2 phase transition is exactly zero, and the equivalent refractive index difference is about 0.046, perfectly achieving stable dual-state mode loss. At the same time, high-efficiency phase modulation (about 0.06π / μm) is achieved, realizing a tunable phase shifter structure with constant mode loss based on lossy phase change materials.

[0040] At the same time, from Figure 6 The optical transmittance of the W-doped VO2 thin film as a function of temperature and the first derivative curve of optical transmittance with temperature clearly show that the W-doped VO2 thin film has good phase transition characteristics, and the phase transition temperature is reduced from 68℃ to about 58℃, proving that a VO2 thin film with a low phase transition threshold can be realized. Therefore, its further application in devices can realize a low-power phase shifter structure.

[0041] Furthermore, as shown in Table 1, the optical properties of the W-doped VO2 thin film at 1550 nm reveal significant changes in both refractive index n and extinction coefficient k before and after the phase transition. This demonstrates that the stable dual-mode loss in the phase shifter structure proposed in this invention is achieved through device structure design, perfectly avoiding the impact of increased material loss on mode loss, and even achieving lower mode loss characteristics under high-loss material conditions.

[0042] Table 1 Optical properties of W-doped VO2 thin films at 1550 nm

[0043]

[0044] The cross-sectional structure of the phase shifter in this embodiment is as follows: Figure 7 As shown, the final dimensions and structure of each component of the phase shifter in this embodiment are as follows: the width w2 of the silicon waveguide is 500 nm and the height t2 is 220 nm; the width w1 of the vanadium dioxide thin film layer is 500 nm and the height t1 is 100 nm.

Claims

1. A mode-constant low-threshold tunable phase shifter based on a lossy phase change material, characterized in that The mode loss constant type low threshold tunable phase shifter based on lossy phase change material comprises a SiO2 substrate (1), a silicon waveguide (2), a VO2 thin film layer (3) and a cladding layer (4), the rectangular silicon waveguide (2) is arranged on the SiO2 substrate (1), the VO2 thin film layer (3) is heterogeneously integrated on the upper surface of the silicon waveguide (2) to form a heterogeneously integrated waveguide, the cladding layer (4) covers the upper surface of the silicon waveguide (2), and the size structure of the VO2 thin film layer (3) is such that the waveguide mode loss variation before and after the phase change of the VO2 thin film is zero.

2. A low threshold tunable phase shifter based on lossy phase change material for mode-constant loss according to claim 1, characterized in that The VO2 thin film layer (3) is a W-doped VO2 thin film.

3. A low threshold tunable phase shifter based on lossy phase change material for mode-constant loss according to claim 2, characterized in that The doping concentration of W in the W-doped VO2 thin film is 0.5at%-1.5at%.

4. The low threshold tunable phase shifter based on lossy phase change material for mode-constant loss according to claim 1, characterized in that The VO2 thin film layer (3) is heterogeneously integrated on the upper surface of the silicon waveguide (2), and the heterogeneously integrated mode is magnetic control sputtering, thermal evaporation, electron beam evaporation or pulse laser deposition.

5. The low threshold tunable phase shifter based on lossy phase change material for mode-constant loss according to claim 1, characterized in that The cladding layer (4) is an air cladding layer.

6. The low threshold tunable phase shifter based on lossy phase change material for mode-constant loss according to claim 1, characterized in that The size structure of the VO2 thin film layer (3) comprises the width size and thickness size of the VO2 thin film.

7. The low threshold tunable phase shifter based on lossy phase change material for mode constant loss according to claim 1, characterized in that The change in waveguide mode loss of the VO2 thin film before and after phase transition is represented as 金属相 x a 金属相 - Γ 绝缘相 x a 绝缘相 wherein Γ 金属相 represents the energy binding factor Γ of the VO2 thin film in the metal phase, a 金属相 represents the absorption coefficient of the VO2 thin film in the metal phase, Γ 绝缘相 represents the energy binding factor Γ of the VO2 thin film in the insulating phase, a 绝缘相 represents the absorption coefficient of the VO2 thin film in the insulating phase.

8. A low threshold tunable phase shifter based on lossy phase change material for mode-constant loss according to claim 7, characterized in that The VO2 thin film layer (3) is driven by the thermal effect or Joule heat effect of waveguide light.

9. The low threshold tunable phase shifter based on lossy phase change material for mode constant loss according to claim 1, characterized in that The thickness of the SiO2 substrate (1) is 2-3 μm.

10. The low threshold tunable phase shifter based on lossy phase change material for mode-constant loss according to claim 1, characterized in that When the width of the rectangular silicon waveguide (2) is 500 nm and the height is 220 nm, the width of the VO2 thin film layer (3) is 500 nm and the height is 100 nm.

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