A wavelength division multiplexing / demultiplexing system and its fabrication method

Abstract

This invention provides a wavelength division multiplexing / demultiplexing system based on microring structures and phase change materials modulation, and its fabrication method, belonging to the field of optical coupling devices. The wavelength division multiplexing / demultiplexing system includes a stacked substrate and a buried oxide layer, and n (n is a positive integer ≥ 2) microring units and an upper cladding layer located on the upper surface of the buried oxide layer. The upper cladding layer covers the n microring units and contacts the buried oxide layer. Each microring unit includes a through waveguide and at least one microring waveguide. The n microring units are connected into a whole through the through waveguide. The microring waveguide includes a first ring waveguide and a second ring waveguide located above the first ring waveguide. The second ring waveguide is made of a phase change material, and a fourth spacing exists between it and the first ring waveguide. The microring waveguides are spaced apart along the direction of the through waveguide. A first spacing exists between the through waveguide and the microring waveguide. This wavelength division multiplexing / demultiplexing system has low power consumption, low loss, and non-volatility properties.

Description

Technical Field

[0001] This invention belongs to the field of optical coupling device technology, specifically relating to a wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation, and its preparation method. Background Technology

[0002] Wavelength division multiplexing (WDM) technology can significantly improve the capacity of communication systems by multiplexing or demultiplexing optical signals carrying information at different wavelengths into a single optical fiber for transmission. Current mainstream WDM technologies include microring resonators, arrayed waveguide gratings (AWGs), thin-film filters (TFFs), and fiber Bragg gratings (FBGs). AWGs and TFFs have fixed channel spacing, making dynamic wavelength allocation difficult, and their large size (approaching centimeter scale) hinders high-density integration. FBGs only support reflective filtering, offering low flexibility, and their multiplexing / demultiplexing structures are complex. Microring resonators offer ultra-compact dimensions (on the order of tens of micrometers), but still face challenges such as high tuning power consumption, limited tuning speed, and process sensitivity.

[0003] In traditional WDM microring arrays, the resonant wavelength of the sub-unit microrings is greatly affected by the silicon photonics fabrication process, and the channel wavelength is prone to deviating from the design value. To compensate for process errors, the industry typically uses wavelength thermal tuning, which requires continuous heating to maintain the uniformity of the wavelength channels, leading to accumulated static power consumption. Thermo-optical tuning power consumption can reach tens of milliwatts per channel, making it difficult to support large-scale arrays. In addition, the response time of wavelength thermal tuning is in the millisecond range, which cannot meet the requirements of high-speed dynamic networks (such as microsecond-level switching).

[0004] The prior art CN118732172A discloses a wavelength-selective optical attenuator based on a microring resonator. This attenuator is constructed by connecting second-order microring resonators with Mach-Zehnder interference structures in their outer coupling regions. Each second-order microring resonator can tunably attenuate light waves within a specific wavelength range. By applying wavelength-selective attenuation (i.e., different wavelengths of light signals attenuate differently) to multiple signals using a single 2×2 unit, the light intensity of each wavelength is balanced. Furthermore, when applying wavelength-selective attenuation to the light signal of a certain channel, it is independent of other channels and does not affect them, greatly improving the integration density of the system-on-a-chip (SoC) for long-distance, high-speed, error-free transmission in dense wavelength division multiplexing (DWDM) systems. However, this scheme uses a titanium nitride thermo-optical phase shifter to heat the Mach-Zehnder interference arm of the microring to control the microring coupling coefficient and achieve uniform wavelength channel spacing. Continuous temperature control of multiple regions is also required, resulting in high energy consumption and lacking low-energy-consumption characteristics.

[0005] Existing technology CN116243427A discloses a multi-channel amplitude equalizer based on a microring resonator array. This multi-channel amplitude equalizer includes an upper cladding, a lower cladding, a bus input / output waveguide, and N microring resonator units. The bus input / output waveguide and the N microring resonator units are all disposed between the upper and lower cladding, with the N microring resonator units positioned to the side of the bus input / output waveguide. The N microring resonator units are arranged sequentially at intervals along the transmission direction of the bus input / output waveguide. Multiple wavelength signals are input from the bus waveguide and output from the bus waveguide after simultaneous modulation of the multiple microring resonator units, achieving amplitude equalization of multiple optical signals. This multi-channel amplitude equalizer has a compact structure, high stability, and utilizes the inherent resonant characteristics of the microring resonators to achieve simultaneous amplitude equalization of multiple wavelength signals. It features low energy consumption and additional losses, making it suitable for multi-channel wavelength division multiplexing systems, optical computing and neural networks, and microwave photonics. However, this scheme changes the state of the tuning electrode through thermo-optic or electro-optic effects, and the system is not non-volatile after power failure, so it cannot maintain the channel state.

[0006] Prior art CN110286444A discloses a reconfigurable microring optical switch based on phase change material. This reconfigurable microring optical switch includes two bus waveguides, a microring resonator, and a hybrid waveguide carrying the phase change material. The hybrid waveguide includes a silicon waveguide and the phase change material placed on the silicon waveguide. The hybrid waveguide is positioned outside or inside the microring resonator and arranged in an arc-shaped segment that matches the microring resonator. Lateral evanescent wave coupling occurs between the microring resonator and the input / output waveguides, and the upload / download waveguides, causing optical field resonance within the microring resonator. Lateral evanescent wave coupling occurs between the microring resonator and the hybrid waveguide carrying the phase change material, used to control the optical field resonance within the microring, thereby realizing the switching route of the optical path. This reconfigurable microring optical switch has a simple and compact structure, high stability, overcomes the high loss problem inherent in phase change materials, reduces crosstalk and improves the extinction ratio, achieves self-holding characteristics, and has low energy consumption, making it suitable for reconfigurable and tunable wavelength division multiplexing systems. However, in this scheme, a hybrid waveguide carrying phase change material is placed laterally on the microring. Due to the characteristics of the coupler, light needs to travel a long coupling length to gradually transition from the microring to the hybrid waveguide. This results in a large microring area under horizontal coupling, increases optical loss, and reduces the microring's quality factor. Furthermore, the introduction of a lateral coupling waveguide into the microring waveguide inevitably introduces light field reflection, easily leading to drastic fluctuations in the transmission spectrum. In terms of fabrication, the phase change material deposition region and the coupling region are located in the same position, making them susceptible to the effects of process errors.

[0007] In summary, the wavelength division multiplexing system composed of microring resonators in the prior art has the following limitations: (1) High power consumption: thermo-optical tuning relies on resistor heating, with power consumption as high as tens of milliwatts per channel, and large crosstalk between large-scale microring resonator arrays. (2) Limited tuning speed: The thermal tuning response time is in the millisecond range, which cannot meet the requirements of high-speed dynamic networks with microsecond-level switching. (3) Lack of non-volatility: After tuning, continuous power supply is required to maintain the refractive index, resulting in static energy consumption accumulation. (4) Process sensitivity: The wavelength of the microring resonator is easily affected by manufacturing process errors and temperature drift, requiring complex calibration procedures to compensate. Summary of the Invention

[0008] To address the problems of narrow tuning range, slow tuning speed, high power consumption, lack of non-volatility, and large process errors of microring resonators in wavelength division multiplexing (WDM) systems, this invention provides a WDM / demultiplexing system based on microring structure and phase change material modulation, and its fabrication method.

[0009] Specifically, in order to achieve the above objectives, the present invention adopts the following technical solution:

[0010] A wavelength division multiplexing / demultiplexing system based on microring structures and phase change material modulation includes a substrate, a buried oxide layer on one surface of the substrate, n microring units on the surface of the buried oxide layer facing away from the substrate, and an upper cladding layer; the upper cladding layer covers the n microring units and contacts the buried oxide layer; each microring unit includes a through waveguide and at least one microring waveguide; the n microring units are connected into a whole through the through waveguide; the microring waveguide includes a first ring waveguide and a second ring waveguide located above the first ring waveguide; a fourth spacing exists between the second ring waveguide and the first ring waveguide; the material of the second ring waveguide is a phase change material; the microring waveguides are spaced apart along the direction of extension of the through waveguide; a first spacing exists between the through waveguide and the microring waveguide; n is a positive integer ≥2.

[0011] In a preferred embodiment, the microring unit includes a download waveguide, which is disposed opposite to the through waveguide; a third spacing exists between the download waveguide and the microring waveguide; and the microring waveguide is arranged at intervals between the through waveguide and the download waveguide.

[0012] In a further preferred embodiment, the third spacing is 130~500nm.

[0013] In a further preferred embodiment, the minimum spacing between two adjacent microring waveguides along the direction from the through waveguide to the download waveguide is 130~500nm.

[0014] In a further preferred embodiment, the download waveguide is a straight waveguide or a curved waveguide.

[0015] In a preferred embodiment, the size of the second annular waveguide is 30~300nm along the direction from the substrate to the upper cladding.

[0016] In a preferred embodiment, along the direction in which the through waveguide extends, the ring width of the second ring waveguide is 350~1000nm, and the distance between the center of the first ring waveguide and the center of the second ring waveguide is 100~600nm.

[0017] In a preferred embodiment, the length of the center line of the projected annulus on the upper surface of the first annular waveguide on the buried oxide layer is distributed in an arithmetic sequence along the direction in which the through waveguide extends.

[0018] In a preferred embodiment, the first spacing is 130~500nm.

[0019] In a preferred embodiment, the fourth spacing is 30~300nm.

[0020] In a preferred embodiment, the phase change material is selected from antimony sulfide, antimony selenide, germanium antimony telluride, and germanium antimony selenium telluride.

[0021] In a preferred embodiment, the through waveguide is either a straight waveguide or a curved waveguide.

[0022] This invention also provides a method for preparing the wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation, comprising the following steps:

[0023] S1. Prepare a wafer, wherein the wafer comprises a substrate, a buried oxide layer, and a waveguide layer stacked sequentially.

[0024] S2. Etch the waveguide layer to form a through waveguide and a first ring waveguide;

[0025] S3. A first upper cladding layer is formed on the upper surface of the structure obtained in step S2;

[0026] S4. Etch the first upper cladding above the first annular waveguide to form a groove, and stop etching at a position with a fourth spacing from the first annular waveguide;

[0027] S5. Deposit phase change material on the upper surface of the structure obtained in step S4, and etch to form a second annular waveguide in the groove;

[0028] S6. A second upper cladding layer is formed on the upper surface of the structure obtained in step S5. The second upper cladding layer and the first upper cladding layer are collectively referred to as the upper cladding layer.

[0029] In a preferred embodiment, the waveguide layer is made of silicon, silicon nitride, silicon carbide, lithium niobate, or gallium nitride.

[0030] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0031] This invention cascades microring units integrating phase change materials, enabling multiplexing and demultiplexing of multi-channel wavelength optical signals. Phase change materials exhibit a significant refractive index difference between their crystalline and amorphous states. Optical / electrical modulation of the non-volatile phase change material integrated within the microrings allows for precise adjustment of the crystalline-to-amorphous ratio, achieving quasi-continuous refractive index tuning. This reshaping of wavelength channel spacing enables the wavelength division multiplexing / demultiplexing system to achieve ultra-low energy consumption and low loss.

[0032] Specifically, the present invention has the following beneficial effects:

[0033] (1) Low power consumption: The wavelength division multiplexing / demultiplexing system provided by this invention has a single word tuning power consumption as low as nanojoules (nJ).

[0034] (2) Dynamic reconstruction: Using the wavelength division multiplexing / demultiplexing system provided by the present invention, the phase change material can be rapidly changed between crystalline and amorphous states by applying electrical / optical pulses, thereby rapidly (microsecond level) switching wavelength channels.

[0035] (3) Non-volatile: The wavelength division multiplexing / demultiplexing system provided by the present invention does not require maintenance energy after tuning, which significantly reduces static power consumption.

[0036] (4) Low loss: The material of the second ring waveguide in the wavelength division multiplexing / demultiplexing system provided by the present invention is a phase change material. Due to the ring structure, the phase change material forms a continuous structure in the upper cladding, which can avoid light reflection caused by the discontinuity of the phase change material structure.

[0037] (5) Compensation capability: The structure provided by the present invention, which has a gap between the first ring waveguide and the second ring waveguide in the wavelength division multiplexing / demultiplexing system, can calibrate the fabrication error of the micro-ring waveguide during the fabrication process, so that the wavelength alignment accuracy is <0.02nm. Attached Figure Description

[0038] Figure 1 An exploded view of a three-dimensional structural schematic diagram of a wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation provided by the present invention;

[0039] Figure 2 A schematic diagram showing the distribution of microring units on the surface of a buried oxide layer in another wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation provided by the present invention.

[0040] Figure 3 The present invention provides a wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation along section AA' (refer to...). Figure 2 (a cross-sectional view of)

[0041] Figure 4 A schematic diagram of the microring unit of another wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation provided by the present invention;

[0042] Figure 5 for Figure 4 The diagram shows the distribution of microring units on the surface of the buried oxide layer and the principle of wave decomposition and multiplexing.

[0043] Figure 6 for Figure 4 The diagram shows the distribution of microring units on the surface of the buried oxide layer and the principle of wavelength division multiplexing.

[0044] Figure 7 This is a schematic diagram of the centerline of the first ring waveguide in the wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation in this invention.

[0045] Figure 8 The optical field diagrams of the phase change material in the amorphous state (Figure (a)) and crystalline state (Figure (b)) when the wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation provided by the present invention is used as a wavelength division multiplexing filter;

[0046] Figure 9 The spectrum of a wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation provided by the present invention when used as a wavelength division multiplexing filter;

[0047] Figure 10 The spectrum of the download waveguide output of another wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation provided by the present invention;

[0048] Figure 11 The optical field diagrams of the phase change material in the amorphous state (Figure (a)) and crystalline state (Figure (b)) of another wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation provided by the present invention;

[0049] Figure 12 This is a schematic diagram of the process for preparing a wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation in this invention.

[0050] In the figure: 1. Substrate; 2. Buried oxide layer; 3. Microring unit; 31. Through waveguide; 32. Microring waveguide; 33. Downlink waveguide; 321. First ring waveguide; 3211. Centerline; 322. Second ring waveguide; 4. Upper cladding; gap1. First spacing; gap2. Second spacing; gap3. Third spacing; gap4. Fourth spacing; AA'. Cross section. Detailed Implementation

[0051] The following description, in conjunction with embodiments, clearly and completely describes the technical solutions of this application, so that those skilled in the art can fully understand this application. Obviously, the described embodiments are merely some preferred embodiments of this application, and not all embodiments. Any equivalent modifications or substitutions made by those skilled in the art to the following embodiments without creative effort are within the protection scope of this application.

[0052] The directional terms described in this application, such as "upper," "lower," "inner," "outer," "bottom," and "upper surface," indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings or the orientations or positional relationships commonly used when the product is in use. These terms are used solely for the purpose of describing and understanding the product structure and should not be construed as limitations on this application. In this application, unless otherwise explicitly defined, expressions such as "upper," "above," "above," and "upper surface" for the first feature and the second feature indicate that the first and second features may be in direct contact or indirectly in contact through an intermediate medium; the first feature may be directly above or diagonally above the second feature, or simply indicate that the first feature is at a higher horizontal level than the second feature. Expressions such as "lower," "below," "below," and "lower surface" for the first feature and the second feature indicate that the first and second features may be in direct contact or indirectly in contact through an intermediate medium; the first feature may be directly below or diagonally below the second feature, or simply indicate that the first feature is at a lower horizontal level than the second feature. Ordinal numbers used in this application, such as "first" and "second," are for descriptive purposes only to distinguish similar objects and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Methods not described in detail in the following embodiments are conventional methods well-known to those skilled in the art.

[0053] Example 1

[0054] Reference Figures 1-6 A wavelength division multiplexing / demultiplexing system based on microring structures and phase change materials modulation includes a substrate 1, a buried oxide layer 2, microring units 3, and an upper cladding layer 4. The buried oxide layer 2 is located on the upper surface of the substrate 1. Multiple microring units 3 (refer to...) Figure 2 , Figure 5 , Figure 1Only one microring unit 3 is shown above, located on the upper surface of the buried oxide layer 2. The number n of microring units 3 is a positive integer ≥ 2. The upper cladding 4 covers multiple microring units 3 and contacts the upper surface of the buried oxide layer 2. Each microring unit 3 includes a through waveguide 31 and at least one microring waveguide 32. Multiple microring units 3 are connected into a whole through the through waveguide 31. Each microring waveguide 32 includes a first ring waveguide 321 and a second ring waveguide 322 located on the first ring waveguide 321. The material of the second ring waveguide 322 is a phase change material. The ring structure of the second ring waveguide 322 avoids the light reflection problem caused by the segmented discontinuity of the phase change material. There is a fourth gap 4 between the second ring waveguide 322 and the first ring waveguide 321 (see...). Figure 3 The fourth gap 4 is the distance between the first ring waveguide 321 and the second ring waveguide 322 along the direction from the substrate 1 to the upper cladding 4 (or along the direction from the upper cladding 4 to the substrate 1). The micro-ring waveguides 32 are spaced apart along the direction of the through waveguide 31. The through waveguide 31 is coupled to the micro-ring waveguide 32 closest to the through waveguide 31, and the shortest distance between them is the first gap 1 (see...). Figure 4 ).

[0055] In some more specific embodiments, the microring unit 3 also includes a download waveguide 33 (e.g., Figures 4-6 As shown), the download waveguide 33 is positioned opposite to the through waveguide 31. The download waveguide 33 is coupled to the micro-ring waveguide 32 closest to the download waveguide 33, and the shortest distance between them is the third gap 3 (see...). Figure 4 Micro-ring waveguides 32 are arranged alternately between the through waveguide 31 and the download waveguide 33, and the arrangement direction is the direction in which the through waveguide 31 extends (e.g., ...). Figure 2 , 5 (as shown in Figure 6); or, the arrangement direction is the direction of the extension of the through waveguide 31 and the direction from the through waveguide 31 to the download waveguide 33 (as shown in Figure 6). Figures 4-6 (As shown).

[0056] Along the direction from the through waveguide 31 to the down waveguide 33, multiple micro-ring waveguides 32 form a multi-stage micro-ring resonator (e.g., Figure 5 , 6 As shown), and the centerline of each first ring waveguide (reference) Figure 7 The lengths of the two adjacent microring waveguides 32 are equal. The shortest distance between two adjacent microring waveguides 32 is the second gap 2 (see...). Figure 4 ).

[0057] By adjusting at least one of the first spacing gap1, the second spacing gap2, the third spacing gap3, and the fourth spacing gap4, the channel spacing and extinction ratio of the wavelength division multiplexing / demultiplexing system can be changed, thereby optimizing the performance of the wavelength division multiplexing / demultiplexing system.

[0058] As an example, the first spacing gap1 is 130~500nm, for example, 130nm, 131nm, 132nm, 135nm, 140nm, 145nm, 150nm, 160nm, 170nm, 180nm, 200nm, 201nm, 202nm, 205nm, 208nm, 210nm, 212nm, 215nm, 216nm, 220nm, 225nm...500nm.

[0059] As an example, the second spacing gap2 is 130~500nm, for example, 130nm, 131nm, 132nm, 135nm, 138nm, 140nm, 145nm, 150nm, 160nm, 170nm...500nm.

[0060] As an example, the third spacing gap3 is 130~500nm, for example, 130nm, 132nm, 135nm, 140nm, 145nm, 150nm, 155nm, 160nm...500nm.

[0061] As an example, the fourth spacing gap4 is 30~300nm, for example, 30nm, 31nm, 32nm, 33nm, 35nm, 40nm, 45nm, 50nm, 60nm, 70nm, 80nm, 81nm, 82nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 120nm, 125nm...300nm.

[0062] In some more specific embodiments, by adjusting the dimension (i.e., the thickness of the second ring waveguide 322) along the direction from the substrate 1 to the upper cladding 4 (or from the upper cladding 4 to the substrate 1), vertical coupling between the second ring waveguide 322 and the first ring waveguide 321 can be achieved, thereby changing the coupling coefficient between the second ring waveguide 322 and the first ring waveguide 321 and increasing the tuning range. As an example, the dimension of the second ring waveguide 322 along the direction from the substrate 1 to the upper cladding 4 is 30~300nm, for example, 30nm, 31nm, 32nm, 33nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 100nm...300nm.

[0063] In some other, more specific implementations, such as Figure 2 ( Figure 2 The upper section AA' is perpendicular to the upper surface of the buried oxide layer 2 and parallel to the extension direction of the through waveguide 31, and cuts through the sections of the first annular waveguide 321 and the second annular waveguide 322. Figure 3As shown, by adjusting the ring width W of the second ring waveguide 322 pcm The offset between the center of the first ring waveguide 321 and the center of the second ring waveguide 322 along the extension direction of the straight waveguide 31 allows for adjustment of the optical field confinement factor, controlling the proportion of light entering the second ring waveguide 322. The ring width W... pcm The width of the projection ring of the second annular waveguide 322 on the upper surface of the buried oxide layer 2 along the direction of the straight waveguide 31 is defined as the width of the projection ring of the second annular waveguide 322 on the upper surface of the buried oxide layer 2.

[0064] As an example, the ring width W of the second ring waveguide 322 pcm The range is 350~1000nm, for example, 350nm, 351nm, 352nm, 355nm, 340nm, 350nm, 380nm, 400nm, 500nm, 600nm, 650nm, 651nm, 652nm, 653nm, 655nm, 660nm, 665nm, 670nm, 680nm, 690nm, 700nm, 710nm, 720nm, 725nm...1000nm.

[0065] As an example, along the extension direction of the straight waveguide 31, the distance offset between the center of the first ring waveguide 321 and the center of the second ring waveguide 322 is 100~600nm, for example 100nm, 105nm, 110nm, 120nm, 150nm, 180nm, 200nm, 205nm, 210nm, 230nm, 260nm, 280nm, 300nm, 301nm, 302nm, 303nm, 305nm, 310nm, 315nm, 320nm, 325nm, 330nm, 335nm, 340nm, 345nm, 350nm...600nm.

[0066] In some other, more specific embodiments, in order to form a uniformly spaced wavelength channel, a plurality of first annular waveguides 321 are spaced apart in the direction in which the through waveguide 31 extends, and the center line 3211 of the projected annulus of the first annular waveguides 321 on the upper surface of the buried oxide layer 2 (see...) Figure 7 The lengths of ) are distributed in an arithmetic sequence.

[0067] As an example, straight waveguide 31 is a straight waveguide (such as...) Figure 5 , 6 (as shown) or a curved waveguide (e.g., an Euler-bent waveguide, not shown in the figure).

[0068] As an example, download waveguide 33 as a straight waveguide (e.g.) Figure 1 (as shown) or a curved waveguide (e.g., an Euler-bent waveguide, see...) Figure 5 and Figure 6).

[0069] In some more specific embodiments, the material of the second ring waveguide 322 is any one of antimony sulfide, antimony selenide, germanium-antimony-tellurium, or germanium-antimony-selenium-tellurium. Changing the type of phase change material can achieve wavelength division multiplexing or demultiplexing functions, or wavelength division multiplexing filtering functions. When using phase change materials with small differences in loss between crystalline and amorphous states (such as antimony sulfide and antimony selenide), wavelength division multiplexing or demultiplexing functions can be achieved. When using phase change materials with large differences in loss between crystalline and amorphous states (such as germanium-antimony-tellurium and germanium-antimony-selenium-tellurium), it can be used as a wavelength division multiplexing filter switch.

[0070] As an example, the material of the first ring waveguide 321 is any one of silicon, silicon nitride, and silicon carbide.

[0071] In some more specific embodiments, miniature titanium / gold heating electrodes with a resistance of 30 ohms can be integrated on the upper surface of the cladding. Joule heating is generated by applying electrical pulses (typically 5V, 200ns). The heat energy is conducted from the metal electrodes to the phase change material layer (second ring waveguide), driving the PCM to reversibly switch between an amorphous (low refractive index) and crystalline (high refractive index) state. When the PCM gradually transitions to the crystalline state through pulse modulation, its refractive index change alters the equivalent refractive index distribution of the micro-ring waveguide, resulting in a redshift of approximately 5nm in the resonant wavelength. In the amorphous state, the PCM's refractive index decreases, and the resonant wavelength returns to its initial value. By programming the crystallinity of the phase change material in the micro-ring unit with electrothermal pulses, wavelength shifts in the transmission spectrum of the micro-ring unit can be achieved. For example, the 1553nm and 1556nm channels can be demultiplexed to different output ports, or reverse-multiplexed into a single light source output.

[0072] In any of the above schemes, the number of wavelengths of the input and / or output optical waves of the wavelength division multiplexing / demultiplexing system corresponds to the number n of microring units 3. As an example, such as... Figure 2 As shown, the wavelength division multiplexing / demultiplexing system contains four cascaded microring units 3. This structure does not include a download waveguide. The high-loss characteristics of germanium-antimony-tellurium (GST) crystals selectively "turn off" the filtering function of the wavelength division multiplexing system, enabling flexible spectral adjustment. In the initial state, all GSTs are amorphous, and each microring waveguide 32 independently filters out specific wavelengths, such as... Figure 2The first micro-ring waveguide 32 from left to right filters out light with wavelength λ1, the second micro-ring waveguide 32 filters out light with wavelength λ2, and so on. Specifically, when the material of the second ring waveguide 322 in the wavelength division multiplexing / demultiplexing system is GST, the system is a wavelength division multiplexing filter, and its working principle is as follows: When GST is amorphous, the loss is small, and its influence on the optical field of the micro-ring waveguide is weak. The micro-ring waveguide maintains a high quality factor (Q value > 1000). At this time, if the wavelength of the input optical signal is the same as the resonant wavelength of the micro-ring waveguide, it is filtered out by the micro-ring waveguide, and other wavelengths are output through the direct waveguide. When a laser pulse is applied to the phase change material region to gradually crystallize GST, the high loss characteristics of GST significantly enhance the light absorption of the micro-ring waveguide, causing the Q value of the micro-ring waveguide to drop sharply to Q value < 100, the resonant peak disappears, and the wavelength signal that was originally filtered out directly passes through the direct waveguide, which is equivalent to turning off the filtering function of the micro-ring waveguide. That is, when a portion of the GST in the microring waveguide 32 is selectively crystallized, the corresponding wavelength channel will bypass the filter and transmit directly, thereby reconstructing the output spectrum. More specifically, such as Figure 2 As shown, the width of the through waveguide 31 ( Figure 1 The dimension of the through waveguide 31 along the direction from the substrate 1 to the upper cladding 4 is 500 nm. The centerline 3211 of the first ring waveguide 321 (refer to...) Figure 7 The radius of the first ring waveguide 321 is 10 μm. The first gap 1 is 250 nm. The second ring waveguide 322 has a ring width of 1000 nm and a thickness of 30 nm. The offset between the center of the first ring waveguide 321 and the center of the second ring waveguide 322 is 600 nm. The fourth gap 4 is 80 nm. The fourth gap can prevent the GST from directly contacting the first ring waveguide, thereby reducing optical loss. When a wavelength signal containing λ1, λ2, λ3, and λ4 is input to the through waveguide 31, it makes... Figure 2 GST crystallization of the first and second microring waveguides 32 from left to right (see the optical field under different GST crystal states). Figure 8 Then, light with wavelengths λ1 and λ2 passes directly through the through waveguide 31; while light with wavelengths λ3 and λ4 passes through... Figure 2 The third and fourth uncrystalline microring waveguides 32, from left to right, are filtered out by these two microring waveguides. Therefore, the light ultimately output from the output end of the through waveguide 31 has wavelengths of λ1 and λ2, realizing the selection of programmable wavelengths (the spectrum of the wavelength division multiplexing filter is shown in Figure 32). Figure 9(As shown). The wavelength division multiplexing filter achieves "switching" control of the micro-ring waveguide through GST loss modulation, avoiding crosstalk problems introduced by wavelength offset in traditional tuning, and the high absorption characteristics of the GST crystal ensure that micro-ring resonance is completely suppressed. Multiple cascaded micro-ring units do not require complex coupling designs; they can be connected in series via a through waveguide to construct a multi-channel filter, supporting the combination of output spectra across multiple micro-ring waveguides. This scheme provides a highly flexible and low-power solution for flexible optical networks and dynamic spectrum allocation.

[0073] As an example, Figure 2 The phase change material of the second ring waveguide 322 in the micro-ring waveguide 32 shown is replaced with antimony sulfide with a thickness of 300 nm, and the ring width of the second ring waveguide 322 is 1000 nm. The offset between the center of the first ring waveguide 321 and the center of the second ring waveguide 322 is 600 nm. The fourth spacing gap4 is 200 nm. In this case, the phase change material (PCM) can support optical field transmission independently, instead of the cladding optical field coupling of the traditional PCM. By vertically coupling the thicker PCM layer (second ring waveguide 322) with the first ring waveguide 321, the limitation of tuning freedom of a single ring waveguide can be broken, and the resonant wavelength spacing can be flexibly designed by the size of the two ring waveguides and the coupling distance. The thicker structure of the second ring waveguide 322 enhances the interaction depth between the optical field and the phase change material, extending the wavelength tuning range to over 30 nm.

[0074] As an example, such as Figure 4 , Figure 5 As shown, the wavelength division multiplexing / demultiplexing system comprises an integral system formed by n micro-ring units 3 connected by a through waveguide 31, supporting multiple wavelengths (wavelengths λ1, λ2, ... λ). n The light enters from one end of the through waveguide 31. The resonant wavelength of each microring unit 3 corresponds to a certain wavelength in the input light source. Therefore, when multi-wavelength light passes through each microring unit 3 in sequence, the light corresponding to the resonant wavelength of the microring unit 3 is captured by the microring unit 3 and then output from the download waveguide 33, realizing the function of wave demultiplexing (the spectrum output from the download waveguide 33 is shown in Figure 31). Figure 10 As shown). Conversely, as... Figure 4 , Figure 6 As shown, when multiple single-wavelength lights (wavelengths are λ1, λ2...λ) are emitted, nWhen inputs are received from different microring units 3 via the download waveguide 33, they are coupled through the n microring units 3 and finally converge into the through waveguide 31, from which they are output, thus realizing wavelength division multiplexing. Specifically, the first ring waveguide 321 is made of silicon, with a ring width (the ring width of the first ring waveguide 321 projected onto the upper surface of the buried oxide layer 2) of 450 nm, a radius of 10 μm, and a first spacing gap1 of 200 nm. A phase change material (such as antimony sulfide or antimony selenide) layer is arranged in a specific continuous ring pattern in the upper cladding 4 above the first ring waveguide 321, and partially overlaps with the top of the second ring waveguide 322 in space, so that the second ring waveguide 322 and the first ring waveguide 321 are coupled through an evanescent field. The phase change material layer (second ring waveguide 322) has a thickness of 30 nm and a ring width of 650 nm. The offset between the center of the first ring waveguide 321 and the center of the second ring waveguide 322 is 300 nm to enhance the interaction efficiency between the optical field and the phase change material and to balance the optical loss introduced by the phase change material. It also has a large tolerance for process errors, ensuring that the phase change material layer covers the target area of ​​the upper cladding and does not cover the coupling area between the through waveguide and the first ring waveguide due to process errors. In this scheme, by partially overlapping the second ring waveguide (phase change material waveguide) with the first ring waveguide (silicon waveguide), the low-loss characteristics of the first ring waveguide (silicon waveguide) are retained, and the additional absorption loss introduced by the phase change material waveguide is reduced through evanescent field tuning. Furthermore, the local crystalline state switching of the phase change material only requires sub-microsecond electrical pulses, and the spectral characteristics are retained after tuning, achieving a static zero-power effect (see Optical Field under Different Crystal States of Phase Change Material). Figure 11 Furthermore, by cascading multiple independent micro-ring units, a wavelength division multiplexing system with more than 8 channels can be expanded. An optically controlled phase change scheme (i.e., using laser heating to induce a phase change in the phase change material) can be used instead of an electrically controlled phase change scheme (i.e., heating the phase change material via heating electrodes) to achieve all-optical dynamic reconfiguration. This structure has significant application potential in optical communication, reconfigurable photonic circuits, and intelligent optical sensing.

[0075] Example 2

[0076] Reference Figure 12 (Taking cross section AA' as an example), a method for preparing a wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation includes the following steps:

[0077] S1. Prepare a wafer, which includes a substrate, a buried oxide layer, and a waveguide layer stacked sequentially.

[0078] S2. Etch the waveguide layer to form a through waveguide and a first ring waveguide;

[0079] S3. A first upper cladding layer is formed on the upper surface of the structure obtained in step S2;

[0080] S4. Etch the first upper cladding above the first annular waveguide to form a groove, and stop etching at a position with a fourth spacing from the first annular waveguide;

[0081] S5. Deposit phase change material on the upper surface of the structure obtained in step S4, and etch to form a second annular waveguide in the groove;

[0082] S6. A second upper cladding layer is formed on the upper surface of the structure obtained in step S5. The second upper cladding layer and the first upper cladding layer are collectively referred to as the upper cladding layer.

[0083] As an example, the substrate in step S1 is at least one of a silicon substrate, a silicon carbide substrate, a silicon nitride substrate, a lithium niobate substrate, and a gallium nitride substrate.

[0084] As an example, the material of the buried oxide layer in step S1 is at least one of silicon dioxide, silicon nitride, and aluminum oxide.

[0085] As an example, the waveguide layer in step S1 is made of any one of silicon, silicon nitride, silicon carbide, lithium niobate, and gallium nitride.

[0086] As an example, the specific etching steps in step S2 are as follows: Photoresist is spin-coated onto the waveguide layer surface, soft-baked, and then patterned by exposure to define the straight waveguide and the first annular waveguide. Subsequently, development is performed to remove the photoresist from the exposed areas. The waveguide layer is etched using an etching process, stopping at the upper surface of the buried oxide layer. The photoresist is then removed and cleaned to form the straight waveguide and the first annular waveguide.

[0087] As an example, the material of the first upper cladding layer in step S3 is at least one of silicon dioxide, silicon nitride, and aluminum oxide.

[0088] As an example, the step of forming the first upper cladding in step S3 is as follows: silicon dioxide (or other materials of the first upper cladding) is deposited on the upper surface of the structure obtained in step S2 by plasma-enhanced chemical vapor deposition (PECVD), followed by chemical mechanical polishing to ensure that the silicon dioxide layer is planarized, thus obtaining the first upper cladding.

[0089] As an example, the step of forming the groove in step S4 is as follows: spin-coating photoresist onto the upper surface of the first upper cladding, and exposing and developing to define the pattern of the annular groove. Selective etching of the first upper cladding is performed using wet etching with buffered oxide etchant or dry etching with RIE (reactive ion etching), and the etching stops at a position with a fourth spacing from the first annular waveguide to ensure the etching depth, thus obtaining the annular groove.

[0090] As an example, the step of forming the second ring waveguide in step S5 is as follows: a phase change material film is deposited on the upper surface of the structure obtained in step S4 by magnetron sputtering, and then the phase change material outside the groove is removed, while the phase change material inside the groove is retained to obtain the second ring waveguide.

[0091] As an example, the material of the second upper cladding is at least one of silicon dioxide, silicon nitride, and aluminum oxide.

[0092] As an example, the step of forming the second upper cladding in step S6 is as follows: silicon dioxide (or other materials of the second upper cladding) is grown on the upper surface of the structure obtained in step S5 by PECVD and covered on the upper surface of the second ring waveguide to protect the second ring waveguide.

[0093] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Various modifications and variations can be made to the present invention by any person skilled in the art. Any simple equivalent changes and modifications made based on the scope of protection of this invention and the content of the specification should be included within the scope of protection of the present invention.

Claims

1. A wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation, characterized in that, The system includes a substrate, a buried oxide layer on one surface of the substrate, n microring units on the surface of the buried oxide layer facing away from the substrate, and an upper cladding layer. The upper cladding layer covers the n microring units and contacts the buried oxide layer. Each microring unit includes a through waveguide and at least one microring waveguide. The n microring units are connected into a single unit via the through waveguide. Each microring waveguide includes a first ring waveguide and a second ring waveguide located above the first ring waveguide. A fourth spacing exists between the second ring waveguide and the first ring waveguide. The fourth spacing is along the substrate. The distance between the first annular waveguide and the second annular waveguide in the direction from the bottom to the upper cladding; the material of the second annular waveguide is a phase change material; the micro-ring waveguides are arranged at intervals along the direction of extension of the through waveguide; there is a first spacing between the through waveguide and the micro-ring waveguide; the ring width of the second annular waveguide is 350~1000nm along the direction of extension of the through waveguide, and the distance between the centerline of the first annular waveguide and the centerline of the second annular waveguide on the orthogonal projection of the centerline on the upper surface of the buried oxide layer is 100~600nm; n is a positive integer ≥2.

2. The wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation according to claim 1, characterized in that, The microring unit includes a download waveguide, which is disposed opposite to the through waveguide; there is a third spacing between the download waveguide and the microring waveguide; the microring waveguide is arranged at intervals between the through waveguide and the download waveguide.

3. The wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation according to claim 2, characterized in that, The third spacing is 130~500nm.

4. The wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation according to claim 2, characterized in that, Along the direction from the through waveguide to the download waveguide, the minimum spacing between two adjacent micro-ring waveguides is 130~500nm.

5. The wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation according to claim 1, characterized in that, The size of the second annular waveguide is 30~300nm along the direction from the substrate to the upper cladding.

6. The wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation according to claim 1, characterized in that, The length of the center line of the projected annulus on the upper surface of the first ring waveguide on the buried oxide layer is distributed in an arithmetic sequence in the direction in which the through waveguide extends.

7. The wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation according to claim 1, characterized in that, The first spacing is 130~500nm; or / and the fourth spacing is 30~300nm.

8. The wavelength division multiplexing / demultiplexing system based on microring structure and phase change material modulation according to claim 1, characterized in that, The phase change material is selected from antimony sulfide, antimony selenide, germanium antimony telluride, and germanium antimony selenium telluride; or / and the through waveguide is a straight waveguide or a curved waveguide.

9. A method for preparing a wavelength division multiplexing / demultiplexing system according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Prepare a wafer, wherein the wafer comprises a substrate, a buried oxide layer, and a waveguide layer stacked sequentially. S2. Etch the waveguide layer to form a through waveguide and a first ring waveguide; S3. A first upper cladding layer is formed on the upper surface of the structure obtained in step S2; S4. Etch the first upper cladding above the first annular waveguide to form a groove, and stop etching at a position with a fourth spacing from the first annular waveguide; S5. Deposit phase change material on the upper surface of the structure obtained in step S4, and etch to form a second annular waveguide in the groove; S6. A second upper cladding layer is formed on the upper surface of the structure obtained in step S5. The second upper cladding layer and the first upper cladding layer are collectively referred to as the upper cladding layer.

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