A zero phase shift racetrack resonator based on phase change material

Abstract

The application discloses a zero phase shift runway type resonator based on a phase change material, and is characterized by comprising a ridge type waveguide, wherein parallel input and output waveguides are arranged on the ridge type waveguide; a runway waveguide is arranged on the ridge type waveguide and between the input and output waveguides; coupling intervals are arranged between the runway waveguide and the input waveguide and between the runway waveguide and the output waveguide; a phase change slit structure capable of reversibly changing from an amorphous state to a crystalline state under the waveguide evanescent field coupling is arranged in a coupling area of the input waveguide; the phase change slit structure material is selected from Sb2Se3 or Sb2S3 phase change materials; a PIN diode for reversibly changing the phase change material from a crystalline state to an amorphous state under the heating action is arranged on the ridge type waveguide; and the zero phase shift, high transmittance tuning range and low insertion loss are achieved.

Description

Technical Field

[0001] This invention relates to the field of silicon-based photonic integration, and in particular to a zero-phase-shift racetrack resonator based on phase change materials. Background Technology

[0002] As Moore's Law approaches its limits, performance improvements in computing speed and power consumption for electronic systems are hampered by the von Neumann architecture (i.e., the separation of memory and computing units hinders information flow). Photonic memory computing is considered a promising candidate to replace electronic computing due to its wide bandwidth, ultra-high propagation speed, and high energy efficiency. Previously reported photonic computing devices mainly utilize electro-optic effects, thermo-optic effects, and carrier injection to modulate signals. However, these devices are volatile, requiring continuous energy to maintain their current state. High power consumption limits scalability and hinders large-scale integration.

[0003] Chalcogenide phase change materials (PCMs) with Ge, Se, and Te as the main elements have attracted much attention due to their non-volatility and multi-state properties. The phase transition between the amorphous and crystalline states of PCMs results in a significant contrast in optical properties, which can be used to control light propagation. Combining PCMs with integrated waveguides has led to their widespread use in reconfigurable photonic devices such as optical memories, optical memristors, and optical synapses. Microring resonators, due to their wavelength selectivity and high quality factor, are widely used in photonic storage and computing array structures. To avoid mutual interference between microring resonator units and to expand the array scale, it is necessary to establish a device structure with low resonant wavelength shift. For PCM-based microring resonator array structures, the significant change in the refractive index of PCM during the phase transition makes it difficult to avoid resonant wavelength shift (RWS).

[0004] Recently, binary PCMs such as Sb₂Se₃ and Sb₂S₃ have been proposed for reconfigurable electrical and optical devices. The small imaginary part of the refractive index of the crystalline and amorphous states at a wavelength of 1550 nm leads to reduced material absorption. The actual change in refractive index during phase transitions in these two materials is smaller than that of the widely used Ge₂Sb₂Te₅ (GST), which can reduce the device's refractive power loss (RWS). Furthermore, Sb₂Se₃ and Sb₂S₃ can achieve multi-stage phase transitions by employing appropriate optical or electrical pulses. For large-scale array structures, the optical path layout with PCMs is often complex, and the large area of ​​the PCM makes it difficult to induce PCM phase transitions via optical pulses. Electrically pulsed microheaters (such as PIN and ITO) can freely control individual phase transition devices, and the electrical drive technology is relatively mature, making it suitable for large-scale integration of photonic phase transition arrays. Currently, there are no publicly available research reports on zero-phase-shift racetrack-type resonators based on phase transition materials for on-chip integrated photonic storage and computing, either domestically or internationally. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a zero-phase-shift racetrack resonator based on phase change materials with zero phase shift, high transmittance tuning range and low insertion loss.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a zero-phase-shift racetrack resonator based on phase change materials, comprising a ridge waveguide, wherein a parallel input waveguide and an output waveguide are disposed on the ridge waveguide; a racetrack waveguide is disposed on the ridge waveguide and between the input waveguide and the output waveguide; coupling gaps are provided between the racetrack waveguide and the input waveguide, and between the racetrack waveguide and the output waveguide; a phase change slit structure is provided in the coupling region of the input waveguide, which can undergo a reversible phase transition from amorphous to crystalline state under the waveguide evanescent field coupling effect; the phase change slit structure material is selected from Sb₂Se₃ or Sb₂S₃ phase change materials. The phase change material has at least two stable states, namely amorphous and crystalline, and these two states have significantly different refractive indices.

[0007] Furthermore, a PIN diode is disposed on the ridge waveguide for heating the phase change material to cause a reversible phase transition between crystalline and amorphous states. The PIN diode has a p-type-intrinsic-n-type structure.

[0008] Furthermore, the plate portion of the ridge waveguide and the coupling region in the middle of the raceway waveguide are heavily doped with boron ions, and the plate portion of the ridge waveguide and the coupling region outside the input waveguide are heavily doped with phosphorus ions. The upper surfaces of the heavily doped boron ion region and the upper surfaces of the heavily doped phosphorus ion region are both provided with palladium (Pd) metal electrodes with good thermal conductivity.

[0009] Furthermore, the phase change slit structure is vertically embedded into the input waveguide coupling region. The slit structure increases the overlap area between the phase change material and the waveguide mode, enhancing the modulation effect of the phase change on the waveguide mode field.

[0010] Furthermore, the ridge waveguide is a Si waveguide located on a SiO2 substrate.

[0011] Furthermore, both the input waveguide and the output waveguide are strip waveguides, with a height of 150-250 nm and a width of 400-550 nm. The height of the planar portion of the ridge waveguide is 20-100 nm. The microring radius of the racetrack waveguide is 3-20 μm, the microring width is 400-550 nm, and the coupling length is 3-10 μm. The width of the phase change slit structure is 100-300 nm, the thickness is 150-250 nm, and the length is 3-10 μm. The coupling spacing is 200-300 nm. The thickness of the SiO2 substrate is 2-5 μm.

[0012] Compared with existing technologies, the advantages of this invention are as follows: This invention provides a zero-phase-shift racetrack-type resonator based on phase change materials. Utilizing the enhanced light-matter interaction characteristic of phase change slit structures, the phase change material is embedded in the input waveguide coupling region in the form of slits. Compared to conventional silicon-based microring waveguide devices, this achieves non-volatile, near-zero resonant wavelength shift, thus realizing zero phase shift. The zero-phase-shift device structure effectively avoids mutual interference between microring resonators, providing a new solution for large-scale photonic integration. Furthermore, PIN diode microheaters enable the phase change material to be in completely amorphous and completely crystalline states, as well as achieving more multi-level states. Both Sb₂Se₃-based and Sb₂S₃-based devices have transmittance tuning ranges exceeding 80%, and both exhibit low insertion loss and high extinction ratio.

[0013] In summary, this invention proposes a 1×2 racetrack-type resonator based on Sb2Se3-slot and Sb2S3-slot silicon waveguides. By embedding a low-loss PCM into the input waveguide coupling region, not only are their interaction and modulation efficiency improved, but also RWS (Rapid Wavelength Shift) is achieved without offset during phase transitions between multiple PCM states. This device features zero phase shift, a high transmittance tuning range, and low insertion loss, providing an attractive platform for realizing high-efficiency, large-scale neuromorphic network storage computing. Attached Figure Description

[0014] Figure 1 (a) is a schematic diagram of the zero-phase-shift racetrack resonator based on phase change material of the present invention; (b) is a schematic diagram of the cross-section of the region embedded with phase change material; and (c) is a plan view of the top ridge waveguide region.

[0015] Figure 2 (ab) represent the normalized transmittance changes of the racetrack-shaped resonators based on Sb2Se3 and Sb2S3 respectively under different crystallinity ρ of the phase change material, and (cd) represent the normalized electric field distribution of the device in the amorphous and crystalline states of Sb2Se3 respectively.

[0016] Figure 3 (a) shows the temperature response and electrical pulse change of Sb2Se3 during amorphization; (b) shows the temperature response and crystallinity ρ change of Sb2Se3 during crystallization; (cd) shows the two-dimensional cross-sectional temperature distribution of the mixed waveguide region of Sb2Se3 in amorphous and crystalline states, respectively; and (e) shows the relationship between crystallization area and crystallinity ρ. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. I. Specific Implementation Methods

[0019] A zero-phase-shift racetrack-type resonator based on phase change materials, such as Figure 1 (a) Figure 1 (b) and Figure 1 As shown in (c), it includes a ridge waveguide, on which parallel input waveguides and output waveguides are arranged; a raceway waveguide is arranged on the ridge waveguide and between the input waveguide and the output waveguide, and coupling gaps are arranged between the raceway waveguide and the input waveguide and between the raceway waveguide and the output waveguide. The coupling region of the input waveguide is provided with a phase change slit structure that can undergo a reversible phase transition from amorphous to crystalline state under the waveguide evanescent field coupling effect. The phase change slit structure material is selected from Sb2Se3 or Sb2S3 phase change material.

[0020] In this specific embodiment, a PIN diode is disposed on the ridge waveguide for heating the phase change material to undergo a reversible phase transition between crystalline and amorphous states. The PIN diode has a p-type intrinsic-n-type structure. Boron ions are heavily doped within the planar portion of the ridge waveguide and in the coupling region located in the middle of the racetrack waveguide. Phosphorus ions are heavily doped within the planar portion of the ridge waveguide and in the coupling region located outside the input waveguide. Both the upper surfaces of the heavily boron-doped and phosphorus-doped regions are provided with palladium (Pd) metal electrodes with good thermal conductivity. A phase change slit structure is vertically embedded into the coupling region of the input waveguide. The ridge waveguide is a Si waveguide located on a SiO2 substrate.

[0021] In this specific embodiment, both the input and output waveguides are strip waveguides, with the height of the strip waveguide being any value between 150-250 nm and the width being any value between 400-550 nm; the height of the planar portion of the ridge waveguide is any value between 20-100 nm; the microring radius of the runway waveguide is any value between 3-20 μm, the microring width is any value between 400-550 nm, and the coupling length is any value between 3-10 μm; the width of the phase change slit structure is any value between 100-300 nm, the thickness is any value between 150-250 nm, and the length is any value between 3-10 μm; the coupling spacing is any value between 200-300 nm; and the thickness of the SiO2 substrate is any value between 2-5 μm.

[0022] Example 1

[0023] A ridge-shaped Si waveguide was constructed, with a planar section height of 50 nm, and the input and output waveguides having widths of 500 nm and heights of 170 nm. A racetrack-shaped Si waveguide with a radius of 5 μm, a width of 438 nm, and a coupling length of 6 μm was also constructed. A phase change slit structure, capable of undergoing a reversible phase transition from amorphous to crystalline state under evanescent field coupling, was placed on the input waveguide. The phase change slit structure was made of Sb₂Se₃, with a width of 250 nm, a thickness of 170 nm, and a length of 8 μm. The coupling spacing was 270 nm. The silicon substrate was SiO₂ with a thickness of 2 μm. A PIN diode (p-type-intrinsic-n-type junction) was constructed, with heavy boron doping in the middle region of the resonator and heavy phosphorus doping on the sides of the input straight waveguide. An Sb₂Se₃ phase transition was induced using an electrical pulse. A palladium (Pd) metal electrode with good thermal conductivity was constructed. The phase transition slit structure has at least two stable states, namely amorphous and crystalline, and these two states have significantly different absorption coefficients. Under the waveguide evanescent field coupling, a reversible phase transition from amorphous to crystalline occurs, completing a uniform phase flip.

[0024] Table 1. Relevant parameters of each material

[0025] Table 1. Relevant parameters of each material

[0026] Material n <![CDATA[C p (J / K)]]> K(W / mK) <![CDATA[ρ(Kg / m 3 )]]> <![CDATA[aSb2Se3]]> 3.285+0i 507 0.2 5843 <![CDATA[cSb2Se3]]> 4.05+0i 574 0.24 6492 Si 3.48 720 149 2330 <![CDATA[SiO2]]> 1.45 740 1.38 2200 Pd 3.01+8.59i 244 71.8 12023

[0027] Table 1 shows that the different refractive indices of Sb₂Se₃ in its amorphous (aSb₂Se₃) and crystalline (cSb₂Se₃) states are beneficial for constructing non-volatile multi-level memory computing devices. Embedding the phase change material in the input waveguide coupling region in the form of a slit enhances the interaction between light and matter, resulting in lower insertion loss, higher extinction ratio, and lower resonant wavelength shift. The crystallization temperature of Sb₂Se₃ is 473 K, and its amorphization temperature is 884 K. Under the application of a write pulse, the phase change material can be made completely amorphous, such as... Figure 3 As shown in (c). When an erasure electrical pulse is applied, complete crystallization of the phase change material is achieved, as... Figure 3 As shown in (d), by applying erasure electrical pulses of different energies, phase change materials can achieve multi-step crystallization, i.e., multi-level states, such as... Figure 3 As shown in (e).

[0028] Example 2

[0029] Similar to Example 1, the difference lies in the following: a racetrack-ridge Si waveguide with a radius of 5 μm, a width of 452 nm, and a coupling length of 4 μm is constructed; the phase change slit structure on the input waveguide is made of Sb₂S₃, with a width of 200 nm, a thickness of 170 nm, and a length of 6 μm; the coupling spacing is 240 nm. All other parameters are the same as in Example 1. The device structure is as follows... Figure 1 As shown.

[0030] II. Results Analysis

[0031] Figure 1 This diagram illustrates a zero-phase-shift racetrack-type resonator based on phase change materials. A three-dimensional device model was constructed using the Finite-Difference Time-Domain (FDTD) simulation software from LumericalSolutions for simulation optimization. The device operates as follows: When the phase change material is in an amorphous state, the resonator and hybrid waveguide satisfy the phase-matching condition. Light of the resonant wavelength is coupled into the resonator and then output at the pass-through port. When the phase change material is in a crystalline state, the effective refractive index of the hybrid waveguide is much greater than that of the resonator, and light is directly output at the pass-through port.

[0032] Figure 2 (a) To embed Sb₂Se₃ into the input waveguide coupling region, various states of Sb₂Se₃ were achieved by applying an erasure electrical pulse, resulting in the normalized transmittance change curve of the device output port during the transition from amorphous to crystalline state. Based on the proportion of the crystalline region to the entire Sb₂Se₃ region during the phase transition, the degree of crystallinity ρ was used to describe the crystallinity. It can be seen that when ρ is greater than 0.5, the device's resonance peak is essentially suppressed. When ρ is less than 0.4, the resonance wavelength does not change. Furthermore, at the resonance wavelength (1557.95 nm), the insertion loss of the through port is as low as 0.1 dB, while the download port has a high extinction ratio of 35.5 dB.

[0033] Figure 2 (b) When the phase change material is Sb₂S₃, multiple states of Sb₂S₃ are achieved by applying an erasure electrical pulse, and the normalized transmittance curves of the output port of the device at different crystallinity ρ are obtained when Sb₂S₃ transitions from amorphous to crystalline state. It can be seen that when ρ ranges from 0 to 1, the resonant wavelength of the device remains essentially unchanged. At the resonant wavelength, the through port also exhibits a low insertion loss of 0.27 dB. Compared with traditional silicon-based microring devices, the proposed device has lower resonant wavelength shift and insertion loss.

[0034] Figure 2 (c) and Figure 2 (d) shows the normalized electric field distribution of the device in amorphous and crystalline Sb2Se3 at the resonant wavelength (1557.95nm).

[0035] Figure 3 (a) is a graph showing the relationship between the temperature response curve during the Sb2Se3 amorphization process and the applied 12V (~54.7mW)-100ns write pulse. Figure 3(b) shows the transient temperature change and crystallinity ρ change of the Sb2Se3 crystallization process driven by a 5V (~7.7mW)-200ns erasure electrical pulse. Figure 3 (cd) are schematic diagrams showing the cross-sectional temperature distribution of the Sb₂Se₃ region when achieving a completely amorphous state and a completely crystalline state, respectively. It can be seen that Sb₂Se₃ has undergone a complete phase transition. Figure 3 (e) shows that the crystallization region of Sb₂Se₃ gradually increases with increasing ρ during the crystallization process. The areas marked with color represent crystallization regions at temperatures greater than 473 K.

[0036] In summary, the device of this invention embeds phase change material in the input waveguide coupling region in the form of a slit, which not only improves the interaction between light and the phase change material, thus improving the extinction ratio and insertion loss of the device, but also significantly suppresses the resonant wavelength shift, which is beneficial for increasing the number of devices integrated. Furthermore, by using electrical pulses to generate multiple states in the phase change material, it is advantageous for realizing multi-level in-memory computing within the device.

[0037] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A zero-phase-shift racetrack-type resonator based on phase change materials, characterized in that: The device includes a ridge waveguide having a flat section and a ridge, the ridge forming a parallel input waveguide and an output waveguide, and a racetrack waveguide located between the input waveguide and the output waveguide. The racetrack waveguide has coupling gaps with the input waveguide and with the output waveguide. The coupling region of the input waveguide is embedded with a phase change slit structure that can undergo a reversible phase transition between an amorphous and crystalline state by heating. The material of the phase change slit structure is selected from Sb2Se3 or Sb2S3 phase change materials. When the phase change slit structure is in an amorphous state, the racetrack-shaped resonator satisfies the phase matching condition, allowing the optical signal to be coupled from the input waveguide into the racetrack waveguide and output from the output waveguide. When the phase change slit structure is in a crystalline state, the phase matching condition is broken, allowing the optical signal to be directly output from the input waveguide.

2. The zero-phase-shift racetrack-type resonator based on phase change material according to claim 1, characterized in that: The ridge waveguide is provided with a PIN diode for heating the phase change material to cause a reversible phase transition between crystalline and amorphous states. The PIN diode has a p-type-intrinsic-n-type structure.

3. A zero-phase-shift racetrack-type resonator based on phase change materials according to claim 2, characterized in that: The plate portion of the ridge waveguide is heavily doped with boron ions in the coupling region located in the middle of the raceway waveguide, and the plate portion of the ridge waveguide is heavily doped with phosphorus ions in the coupling region located outside the input waveguide. Both the upper surface of the heavily doped boron ion region and the upper surface of the heavily doped phosphorus ion region are provided with palladium metal electrodes with good thermal conductivity.

4. A zero-phase-shift racetrack-type resonator based on phase change materials according to claim 2, characterized in that: The phase change slit structure is embedded in the ridge of the coupling region of the input waveguide along a direction perpendicular to the flat plate portion of the ridge waveguide.

5. A zero-phase-shift racetrack-type resonator based on phase change materials according to claim 1, characterized in that: The ridge waveguide is a Si waveguide located on a SiO2 substrate, and the thickness of the SiO2 substrate is 2-5 μm.

6. A zero-phase-shift racetrack-type resonator based on a phase change material according to any one of claims 2-5, characterized in that: Both the input waveguide and the output waveguide are strip waveguides, with a height of 150-250 nm and a width of 400-550 nm. The height of the planar portion of the ridge waveguide is 20-100 nm. The microring radius of the runway waveguide is 3-20 μm, the microring width is 400-550 nm, and the coupling length is 3-10 μm. The phase change slit structure has a width of 100-300 nm, a thickness of 150-250 nm, and a length of 3-10 μm. The coupling spacing is 200-300 nm.

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