Optical time-domain differentiator based on microring resonator and optical non-volatile storage materials

Abstract

The present invention seeks to protect an optical time-domain differentiator based on a microring resonator and optical non-volatile storage materials to address the volatility of current optical time-domain differentiators based on microring resonators. The device comprises a straight waveguide and a ring waveguide, with a Sb2Se3 material layer on the ring waveguide. The differential order is determined by adjusting the self-coupling coefficient of the straight waveguide and the loss coefficient of the ring waveguide. Compared to microring differentiators based on plasma dispersion effects and thermo-optical effects, the combination of silicon and the phase-change material Sb2Se3 offers advantages such as low power consumption, fast response speed, and low manufacturing cost. Most importantly, the phase-change material Sb2Se3 is non-volatile, avoiding static power consumption, and has low light absorption loss, facilitating expansion. The present invention is expected to be applied in the field of photon signal processing, promoting the development of multiple applications such as dark soliton detection, optical sensing, optical pulse shaping, and ultra-high-speed encoding.

Description

Technical Field

[0001] The present invention belongs to the field of photon signal processing, and in particular relates to an optical time domain differentiator structure technology based on a microring resonator and an optical non-volatile storage material. Background Art

[0002] All-optical signal processing technology is a promising solution to overcoming the speed bottleneck of electronic devices. Compared to electrical signal processing, optical signal processing can better meet the high-bandwidth and high-speed computing requirements of today's information transmission, storage, and processing. The optical time-domain differentiator (OTD) is a fundamental component that performs time-domain temporal derivative calculations on the complex envelope of an input optical pulse signal. It has broad applications in optical computing, pulse shaping, ultra-high-speed coding, and other fields.

[0003] Thanks to the continued maturity of silicon photonics, optical time-domain differentiators based on microring resonators have achieved considerable progress. In optical signal processing systems, current photonic components generally rely on optical-to-electrical-to-optical conversion, i.e., optical transmission and electrical processing. Compared to optical-to-electrical-to-optical conversion, optical time-domain differentiators based on microring resonators offer advantages such as simple structure, ease of integration, low power consumption, and high speed. These unique advantages make optical time-domain differentiators promising in both all-optical and hybrid electro-optical networks.

[0004] Typically, optical time-domain differentiators based on microring resonators change the properties of silicon materials through thermo-optical effects or carrier dispersion effects, thereby adjusting the differential order. However, the response time of the thermo-optical effect is relatively slow, usually in the order of milliseconds; the refractive index change of the carrier dispersion effect is in the order of 10 -3 The adjustment range is limited due to the magnitude of the difference. Furthermore, both methods are volatile, especially when the differentiator needs to perform the differential function for a long time, which will generate large static power consumption. To this end, an optical non-volatile storage material Sb2Se3 can be introduced and integrated into a silicon waveguide. The phase change material Sb2Se3 can reversibly switch between an amorphous state and a crystalline state, and each state has different optical properties. After the phase change of Sb2Se3 occurs, the current state can be automatically maintained without external energy maintenance until the next phase change is triggered. Summary of the Invention

[0005] This invention aims to address the volatility of current optical time-domain differentiators based on microring resonators. It proposes an optical time-domain differentiator based on a microring resonator and an optical non-volatile storage material. When the detuning between the center frequency of the optical pulse signal and the resonant frequency of the microring resonator is significantly less than the 3dB bandwidth of the microring resonator, an all-pass microring resonator can be constructed as a time-domain differentiator with a specific gain and constant output. Furthermore, an optical non-volatile storage material, specifically Sb2Se3, is embedded in the microring resonator's ring cavity. Adjusting the crystallinity of the Sb2Se3 material modifies the cavity loss, resulting in different phase jumps at the resonant frequency of the microring resonator, thereby achieving different orders of differentiation. Compared to previously proposed microring differentiator order implementation schemes, such as those based on the plasma dispersion effect and the thermo-optical effect, the Sb2Se3 material is non-volatile, maintaining its state for years without generating static power consumption.

[0006] The technical solution adopted by the present invention is: an optical time domain differentiator based on a microring resonator and an optical non-volatile storage material, which is an all-pass single microring resonator. The all-pass single microring resonator includes a straight waveguide and a ring waveguide, and a Sb2Se3 material layer is provided on the ring waveguide. The differential order is determined by adjusting the size of the straight waveguide self-coupling coefficient and the ring waveguide loss coefficient.

[0007] The Sb2Se3 material layer on the ring waveguide is laser-controlled to a precision of 1μm in crystallinity. The length of the Sb2Se3 layer is determined by design requirements. The crystallinity of the Sb2Se3 material can be controlled by temperature. Once it reaches a certain temperature, rapid quenching allows the Sb2Se3 material to maintain its crystalline length at that temperature. In addition to using a heater, this process can also be controlled using laser pulses. Compared to thermal control, lasers can impart a directional relationship to the grains. Currently, laser control of the crystallinity of the Sb2Se3 material can achieve a precision of 1μm, meaning that a 1μm length of Sb2Se3 material can be manipulated to be either crystalline or amorphous. The longer the Sb2Se3 layer, the more intermediate states it can achieve. For example, a 32μm-long Sb2Se3 layer can achieve 33 states, each with a different absorption loss for light. This means that the attenuation coefficient of the ring cavity varies. Therefore, a longer Sb2Se3 layer can achieve a greater number of differential orders.

[0008] An ideal time-domain differentiator has two key characteristics: 1) its amplitude-frequency response is completely suppressed at the carrier frequency and is bilaterally symmetrical around the optical carrier frequency; 2) its phase response exhibits a strict nπ phase shift at the carrier frequency, where n represents the order of differentiation. However, in practical devices, it is impossible to achieve a transmission spectrum that is completely identical to the transfer function of an ideal differentiator. Therefore, optical differentiators are implemented using components that exhibit linear transmission spectrum characteristics within a certain bandwidth. The transmittance of a microring resonator at its resonant frequency is equal to or very close to zero, and its resonant peak can be approximated as a linear relationship with the amplitude response of an ideal differentiator. Furthermore, the microring resonator also experiences phase jumps at its resonant frequency, with varying degrees of phase jump depending on the microring resonator's operating state. Microring resonators have three operating states: undercoupled, critically coupled, and overcoupled. When the microring resonator is in the undercoupled state, the phase jump at its resonant frequency is less than π, and the microring resonator can achieve fractional-order differentiation between 0 and 1. When the microring resonator is in a critical coupling state, the phase jump at its resonant frequency is equal to π, and the microring resonator can achieve first-order differential. When the microring resonator is in an over-coupling state, the phase jump at its resonant frequency is greater than π, and the microring resonator can achieve fractional-order differentials between 1 and 2.

[0009] The real part of the refractive index of Sb2Se3 in the crystalline and amorphous states is close to that of silicon materials, which is conducive to mode matching. In the communication band, Sb2Se3 has a small light absorption loss, which is also conducive to expansion. These characteristics make Sb2Se3 stand out among many phase change materials. The Sb2Se3 material is integrated into the ring waveguide of the microring resonator. Its refractive index is different at different degrees of crystallinity. The change in the imaginary part of the refractive index will lead to different cavity losses, which will cause different degrees of phase jumps at the resonant frequency, thereby achieving time domain differentiation of different orders without generating static power consumption. Specifically, the phase change material Sb2Se3 has two states, crystalline and amorphous, and the crystallinity of Sb2Se3 can be changed by laser pulses, thereby achieving multiple intermediate states between the crystalline and amorphous states. Sb2Se3 is embedded in the ring waveguide of the microring resonator. The effective refractive index of Sb2Se3 in different states is different, resulting in different cavity losses of the microring differentiator, which in turn causes changes in the phase jump at the resonant frequency. Therefore, Sb2Se3 in different states can achieve different differential orders. Microring differentiators based on plasma dispersion effect or thermo-optical effect are non-volatile and require continuous voltage control while performing the differential function, which generates huge static power consumption. The differentiator proposed in the present invention only needs to change the crystallinity of Sb2Se3 through external laser pulses to achieve different differential orders. In addition, the Sb2Se3 material is non-volatile. Once the phase change occurs, its state can be maintained for several years. No additional energy consumption control is required, and no static power consumption is generated.

[0010] The advantages and beneficial effects of the present invention are as follows:

[0011] This invention proposes an optical time-domain differentiator based on a microring resonator and optical non-volatile storage materials. The microring resonator directly performs time-domain differentiation on the input optical pulse signal, offering the advantages of small size and ease of integration. A non-volatile phase-change material, Sb2Se3, is integrated into the ring waveguide of the microring resonator, achieving different orders of differentiation by varying its crystallinity. Optical time-domain differentiators based on microring resonators commonly utilize plasmon dispersion effects and thermo-optic effects to achieve different orders of differentiation. Compared to these two electrically controlled methods, the phase-change material, Sb2Se3, is directly controlled by optical pulses and offers advantages such as small size, ease of integration, programmability, and scalability. Furthermore, the combination of silicon and the phase-change material, Sb2Se3, offers advantages such as low power consumption, fast response speed, and low manufacturing cost. Most importantly, the non-volatility of the phase-change material, Sb2Se3, significantly reduces energy consumption. The optical time domain differentiator proposed in the present invention is dedicated to overcoming the problem of static power consumption caused by the non-volatility of plasma dispersion effect and thermo-optical effect.

[0012] Integrated non-volatile phase-change materials hold great promise in silicon-based devices. Ge2Sb2Te5 (GST) is the most commonly used phase-change material, but its current achievable states are limited to 5 bits, meaning the number of differential orders achievable when integrated in a microring resonator is limited. Another common phase-change material, VO2, suffers from a low transition temperature, making its metallic state unstable at room temperature. In the past two years, two new phase-change materials have emerged for photonic devices: Sb2S3 and Sb2Se3. The imaginary part of the refractive index of Sb2S3 is very small in the telecom band, resulting in negligible absorption losses in both its crystalline and amorphous states, making it unsuitable for differentiator designs. However, Sb2Se3 exhibits lower absorption losses than GST, allowing it to be arbitrarily extended, even to fully cover the entire ring waveguide. Increasing its length allows for more intermediate states, thereby increasing the ring waveguide attenuation coefficient and, consequently, achieving a greater number of differential orders. The crystallinity accuracy of the Sb2Se3 material on the ring waveguide can reach 1μm, that is, the 1μm length of Sb2Se3 material can be controlled to be crystalline or amorphous. For example, a 32μm length of Sb2Se3 material layer can achieve 33 states. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is the spectrum characteristics of the first-order ideal differentiator and the first-order microring differentiator;

[0014] Figure 2 Schematic diagram of the structure of the optical time domain differentiator proposed in the present invention and the application of Sb2Se3 in optical waveguide;

[0015] Figure 3 Schematic diagram of absorption loss and phase response of Sb2Se3 material with different crystallinity in the structure of the present invention. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be described clearly and in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0017] Figure 1 is the spectrum characteristic of the ideal time domain differentiator and microring differentiator. Assuming that the optical carrier of an input pulse signal is ω0 and the complex envelope of the signal is u(t), the corresponding optical electric field intensity can be expressed as: Perform Fourier transform on the input signal, and the transformed signal expression is: Perform Fourier transform on the output differential signal, and the frequency domain expression converted is: E out (ω)=[j(ω-ω0)] n E in (ω). From this we can see that differentiating the input pulse signal is equivalent to multiplying the input signal by the function [j(ω-ω0)] in the frequency domain. n Therefore, an nth-order time-domain differentiator that calculates the nth-order time derivative of the complex envelope of the optical signal has two important characteristics: 1) The amplitude-frequency response of the differentiator is |ω-ω0| n , which is exponentially related to the detuning of the signal frequency ω relative to the carrier frequency ω0, and is symmetrical around the optical carrier frequency; 2) The phase response has a strict nπ phase shift at the resonant frequency, where n represents the order of differentiation. Therefore, it is only necessary to design a filter device whose transfer function is [j(ω-ω0)] n , which can achieve the function of signal differentiation. The transmission spectrum of the microring resonator at the resonant frequency can be approximated as a linear relationship with the amplitude response of an ideal differentiator within its 3dB bandwidth. The microring resonator also experiences phase jumps at its resonant frequency, with varying degrees of phase jump depending on the microring resonator's operating state.

[0018] When the detuning between the center frequency of the optical pulse signal and the resonant frequency of the microring resonator is much smaller than the 3dB bandwidth of the microring resonator, the transfer function of the microring resonator can be approximated as:

[0019]

[0020] Where ω0 is the optical resonant frequency, is the power attenuation rate caused by intrinsic loss, is the power attenuation rate caused by waveguide coupling, and τ is the photon lifetime. Therefore, an all-pass single microring resonator can be constructed as a resonator with a specific gain jτ(ω-ω0) and a constant output Differentiator. The microring resonator has three working states: undercoupled state Critical coupling state and over-coupling state When the microring resonator is in the critical coupling state, its transfer function is jτ(ω-ω0), which is consistent with the transfer function j(ω-ω0) of the first-order ideal differentiator, indicating that the two are mathematically equivalent, that is, the all-pass single microring resonator in the critical coupling state can achieve the first-order differential function. A resonant frequency was selected and the spectrum response of the critical coupling microring resonator and the first-order ideal differentiator was compared and analyzed. Figure 1 As shown in (a), it can be seen that near the resonant frequency of the microring, the amplitude response of the microring is in good agreement with that of the ideal differentiator, and the phase jump amount at the resonant wavelength is consistent with that of the ideal differentiator, both being π.

[0021] Figure 2 Schematic diagram of the structure of the proposed optical time-domain differentiator and the application of Sb2Se3 in optical waveguides. Figure 2 (a) shows an all-pass microring resonator used as an optical time-domain differentiator. This type of ring resonator consists of a straight waveguide and a ring waveguide, and its specific differential order is determined by the self-coupling coefficient of the straight waveguide and the loss coefficient of the ring cavity. Figure 2 (b) Schematic diagram of the cross-section of the waveguide embedded in Sb2Se3 material. The differential order of the microring resonator is controlled by changing the crystallinity of the Sb2Se3 material.

[0022] The specific process of how the crystallinity of Sb2Se3 affects the differential order:

[0023] Multiple crystallinity levels can be set between the amorphous state and the crystalline state according to the crystallinity formula. The specific formula is as follows:

[0024]

[0025] Among them, p is the crystallinity, ε a and ε c The dielectric constant in the amorphous and crystalline states, ε eff is the dielectric constant of Sb2Se3. Different crystallinity will lead to different dielectric constants, which will result in different real and imaginary parts of the refractive index of Sb2Se3. As the crystallinity increases, the imaginary part of the refractive index of Sb2Se3 increases, resulting in an increase in the loss of the micro-ring cavity, that is, When the self-coupling coefficient of the straight waveguide of the microring resonator remains unchanged, that is, The phase jump at the resonant frequency is reduced, and thus the differential order is reduced. Therefore, time-domain differentials of different orders can be achieved by changing the crystallinity of Sb2Se3.

[0026] Figure 3 Schematic diagram of the absorption loss and phase response of the Sb2Se3 material in the proposed structure at different crystallinity levels. In the present invention, the order control of the microring differentiator is achieved by changing the crystallinity of Sb2Se3, thus avoiding the power loss caused by continuous external power supply. As a non-volatile phase change material, Sb2Se3 can change its crystallinity by applying external light pulses. Once the morphology of Sb2Se3 is fixed, the internally stored value can be saved for years or even decades. The imaginary part of the refractive index of Sb2Se3 is different at different crystallinity levels, indicating that its absorption effect on optical signals is also different. The larger the imaginary part of the refractive index, the greater the absorption loss. From Figure 3 As can be seen in (a), as the degree of crystallization increases, the absorption loss of light increases, that is, the power attenuation rate of the microring resonator cavity will decrease, thereby reducing the phase jump at the resonant frequency, thereby achieving different differential orders, because different phase jumps nπ represent different differential orders n. Figure 3 (b) shows the effect of different crystallinity on phase response. It can be seen that as the crystallinity increases, the microring resonator gradually changes from an over-coupled state to an under-coupled state, and the phase jump also decreases, which means that the differential order decreases. The write, read, and erase operation scheme of Sb2Se3 is as follows:

[0027] Writing: A strong, narrow light pulse is used to induce a phase transition in the Sb2Se3 material. Initially, the Sb2Se3 material is completely crystalline, as its atomically ordered state provides a fast and stable writing environment. If the energy absorbed by the Sb2Se3 material is high enough to reach the transition temperature, the material will melt. Rapid cooling at this point maintains this atomically disordered state, effectively causing the material to partially amorphize. During differential calculations, the input light pulse energy is insufficient to reach the crystallization threshold of Sb2Se3, and therefore does not alter its state.

[0028] Read operation: When performing differential calculations, a low-power light pulse is input. The energy absorbed by the Sb2Se3 material is not enough to reach its crystalline threshold, so it does not change the state of Sb2Se3. At this time, the output result of the microring resonator is the result after differentiation.

[0029] Erase operation: Similarly, a strong light pulse is input to make the temperature of the Sb2Se3 material reach the crystallization temperature but not the melting temperature. At this time, it takes only a few nanoseconds to restore the atomic order, that is, the crystalline state.

[0030] The above examples illustrate the operation of an optical time-domain differentiator based on a microring resonator and nonvolatile phase-change materials. By using external laser pulses to alter the crystallinity of the phase-change material, Sb2Se3, different orders of differentiation are achieved. Because Sb2Se3 is nonvolatile, static power consumption is avoided. Furthermore, Sb2Se3 offers the advantages of small size and ease of integration. This invention is expected to find applications in a variety of fields, including dark soliton detection, optical sensing, optical pulse shaping, and ultra-high-speed coding.

[0031] The above embodiments should be understood as merely illustrating the present invention and not as limiting the scope of protection of the present invention. After reading the contents of the present invention, technicians may make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. An optical time-domain differentiator based on a microring resonator and optical non-volatile storage materials, characterized in that: It is an all-pass single microring resonator, which includes a straight waveguide and a ring waveguide, with an Sb2Se3 material layer on the ring waveguide, and the differential order is determined by adjusting the size of the straight waveguide self-coupling coefficient and the ring waveguide loss coefficient; the refractive index of Sb2Se3 is different at different crystallinity levels, wherein the change of the imaginary part of the refractive index will lead to different cavity losses, thereby causing different degrees of phase jumps at the resonant frequency, thereby realizing time domain differentials of different orders; the microring resonator has three working states: undercoupled state, critical coupling state and overcoupled state. When the microring resonator is in the undercoupled state, the phase jump at its resonant frequency is <π, and the microring resonator can realize fractional-order differentials between 0 and 1. When the microring resonator is in the critical coupling state, the phase jump at its resonant frequency is =π, and the microring resonator can realize first-order differentials. When the microring resonator is in the overcoupled state, the phase jump at its resonant frequency is >π, and the microring resonator can realize fractional-order differentials between 1 and 2.

2. The optical time domain differentiator based on a microring resonator and an optical non-volatile storage material according to claim 1, characterized in that: The crystallinity of the Sb2Se3 material layer on the ring waveguide is controlled by laser to a precision of 1 μm, and the length of the Sb2Se3 material layer is determined according to design requirements.

3. The optical time domain differentiator based on a microring resonator and an optical non-volatile storage material according to claim 1 or 2, characterized in that: By adjusting the crystallinity of the Sb2Se3 material, different orders of time-domain differentials can be achieved. Specifically, the Sb2Se3 material is embedded in the ring waveguide of the microring resonator. When the optical pulse signal is coupled into the microring resonator, Sb2Se3 materials with different crystallinity produce different absorption losses for the optical pulse. Overall, while the self-coupling and coefficient of the straight waveguide of the microring resonator remain unchanged, the Sb2Se3 materials with different crystallinity cause different ring cavity losses, which in turn causes different phase jumps at the resonant frequency, thereby achieving different differential orders.

4. The optical time domain differentiator based on a microring resonator and an optical non-volatile storage material according to claim 3, characterized in that: The specific process of how the crystallinity of Sb2Se3 affects the differential order is as follows: Multiple crystallinity levels are set between the amorphous state and the crystalline state according to the crystallinity formula. The specific formula is as follows: Among them, p is the crystallinity, ε a and ε c is the dielectric constant in the amorphous and crystalline states, ε eff is the dielectric constant of Sb2Se3. With the increase of crystallinity, the imaginary part of the refractive index of Sb2Se3 increases, resulting in an increase in the loss of the micro-ring cavity, that is, When the self-coupling coefficient of the straight waveguide of the microring resonator remains unchanged, that is, The phase jump at the resonant frequency is reduced, and thus the differential order is reduced, thereby achieving time domain differentials of different orders by changing the crystallinity of Sb2Se3.

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