Local guided mode resonance structure and preparation method thereof
By embedding a microstructure array in the dielectric layer and setting a local guided mode resonance structure with a sub-periodic gap cavity, the limitations of existing absorption structures in terms of absorption efficiency, angle dependence, and bandwidth are solved, achieving efficient, wide-angle, and narrow-band optical absorption effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI INSTITUTE OF TECHNICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2025-12-18
- Publication Date
- 2026-05-12
AI Technical Summary
Existing absorption structures have limitations in terms of absorption efficiency, incident angle dependence, and bandwidth, making it difficult to simultaneously meet the requirements of high efficiency, wide angle, and narrow bandwidth.
A local guided mode resonance structure was designed, including a substrate, a reflective layer, a dielectric layer, and a microstructure array. By embedding the microstructure array in the dielectric layer and setting sub-periodic spatial scale gap cavities between adjacent microstructures, a confined unit is formed to achieve local guided mode resonance. The optical field distribution can be controlled by the high refractive index dielectric layer and the microstructure array.
It achieves efficient, single-wavelength absorption over a wide incident angle range, has a narrowband filtering effect that is insensitive to incident angle, has an absorption rate of over 98%, and the resonance peak position remains basically unchanged when the incident angle changes significantly.
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Figure CN122018060A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of optical technology, specifically to a local guided mode resonance structure and its fabrication method. Background Technology
[0002] In modern optics, absorption structures are widely used in various optical devices, such as photodetectors, photovoltaic cells, and photothermal converters. However, existing absorption structures are typically limited in terms of absorption efficiency, incident angle dependence, and bandwidth, making it difficult to simultaneously meet the requirements of high efficiency, wide angle, and narrow bandwidth. Therefore, there is an urgent need for an absorption structure that can simultaneously satisfy these requirements. Summary of the Invention
[0003] In view of this, the embodiments of this application aim to provide a local guided mode resonance structure and its preparation method, which can simultaneously meet the requirements of high efficiency, wide angle and narrow band.
[0004] This application provides the following solution: In a first aspect, a local guided mode resonant structure is provided, comprising: a substrate; a reflective layer disposed on one surface of the substrate; a dielectric layer disposed on one surface of the reflective layer away from the substrate, wherein the refractive index of the dielectric layer is greater than or equal to a preset refractive index threshold; and a microstructure array embedded in the dielectric layer, wherein the microstructure array comprises multiple microstructures and there is a sub-periodic spatial scale gap cavity between two adjacent microstructures.
[0005] In one embodiment, the wavelength of the incident light entering the dielectric layer through the reflective layer matches the resonant frequency of the local guided mode resonant structure.
[0006] In one embodiment, the width of the cavity is smaller than the wavelength of the incident light.
[0007] In one embodiment, the width of the gap cavity is greater than or equal to 900 nanometers and less than or equal to 5.2 micrometers.
[0008] In one embodiment, the period of the microstructure array is greater than or equal to 1000 nanometers and less than or equal to 6 micrometers.
[0009] In one embodiment, the resonant frequency of the local guided mode resonant structure is determined based on at least one of the following: the material of the microstructure, the width of the microstructure, the thickness of the microstructure, the period of the microstructure array, the thickness of the dielectric layer, and the refractive index of the dielectric layer.
[0010] In one embodiment, the width of the microstructure is positively correlated with the resonant frequency; the thickness of the microstructure is negatively correlated with the resonant frequency; the period of the microstructure array is negatively correlated with the resonant frequency; the thickness of the dielectric layer is negatively correlated with the resonant frequency; and the refractive index of the dielectric layer is negatively correlated with the resonant frequency.
[0011] In one embodiment, the microstructure includes at least one of the following: a one-dimensional grating, a two-dimensional grating, and a honeycomb structure.
[0012] In one embodiment, the substrate material includes at least silicon; the reflective layer material includes at least one of the following: gold, aluminum, silver, platinum; the dielectric layer material includes at least one of the following: silicon, germanium, silicon dioxide, silicon nitride; and the microstructure material includes at least one of the following: gold, aluminum, silver, platinum.
[0013] In a second aspect, a method for fabricating a localized mode resonant structure is provided, for fabricating a localized mode resonant structure as described in the first aspect; the method includes: depositing a reflective layer of a first thickness on one surface of a substrate; depositing a dielectric layer of a second thickness on one surface of the reflective layer away from the substrate, and coating a photoresist on the dielectric layer on one surface away from the reflective layer; exposing the photoresist according to a predetermined arrangement of multiple microstructures in a microstructure array to form an array pattern of the microstructure array, wherein the arrangement includes a gap cavity with a sub-periodic spatial scale between adjacent microstructures; etching the dielectric layer according to the array pattern to form multiple grooves of the second thickness; and depositing multiple microstructures in the multiple grooves to obtain a localized mode resonant structure.
[0014] The local guided-mode resonance structure and its fabrication method provided in this application, by embedding a microstructure array in a dielectric layer, with a sub-periodic spatial scale gap cavity between adjacent microstructures in the array, can form confined units, achieving local perturbation of the guided mode and restricting the guided-mode energy to a smaller spatial range, thereby generating a local guided-mode resonance mode. This allows for highly efficient absorption of incident light through an extremely strong local field distribution. Furthermore, the high-refractive-index dielectric layer further strengthens the transverse confinement of the incident light, resulting in a larger transverse wave vector of the local guided-mode resonance mode, thus better confining the light field within the local guided-mode resonance structure. Therefore, this local guided-mode resonance structure can achieve a narrowband filtering effect that is insensitive to the incident angle, i.e., it can achieve highly efficient absorption of a single wavelength over a relatively wide incident angle range. Attached Figure Description
[0015] Figure 1 The diagram shown is a schematic diagram of the local guided mode resonance structure provided in an embodiment of this application.
[0016] Figure 2 The diagram shows the relationship between the resonant center wavelength of the local guided mode resonant structure provided in this embodiment and the incident angle of the incident light in the near-infrared band.
[0017] Figure 3The diagram shows the relationship between the resonant center wavelength of the local guided mode resonant structure provided in this embodiment and the incident angle of the incident light in the long-wave infrared band.
[0018] Figure 4 The diagram shown illustrates the relationship between the width of the microstructure and the resonant frequency provided in the embodiments of this application.
[0019] Figure 5 The diagram shown illustrates the relationship between the thickness and resonant frequency of the microstructure provided in this embodiment.
[0020] Figure 6 The diagram shown illustrates the relationship between the period and the resonant frequency of the microstructure array provided in this embodiment.
[0021] Figure 7 The diagram shown is a schematic representation of the reflectivity of the local guided mode resonance structure provided in this application as a function of the incident light angle.
[0022] Figure 8 The diagram shows the peak position shift at the 1.9-micron resonance peak as a function of the incident light angle, according to an embodiment of this application.
[0023] Figure 9 The diagram shown is a flowchart illustrating the method for preparing a local guided mode resonance structure according to an embodiment of this application. Detailed Implementation
[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0025] In the description of this application, it should be noted that the terms "center," "upper," "lower," "vertical," "horizontal," "inner," "outer," "left," and "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. In addition, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0026] In modern optical technology, absorption structures are widely used in various optical devices, such as photodetectors, photovoltaic cells, and photothermal converters. However, the inventors discovered during their research that existing absorption structures are generally limited in terms of absorption efficiency, incident angle dependence, and bandwidth, making it difficult to simultaneously achieve efficient, wide-angle, and narrow-band absorption.
[0027] In view of this, this application provides a local guided mode resonant structure, comprising: a substrate; a reflective layer disposed on one surface of the substrate; a dielectric layer disposed on one surface of the reflective layer away from the substrate, wherein the refractive index of the dielectric layer is greater than or equal to a preset refractive index threshold; and a microstructure array embedded in the dielectric layer, wherein the microstructure array comprises multiple microstructures and there is a sub-periodic spatial scale gap cavity between two adjacent microstructures.
[0028] Based on the above design, by embedding a microstructure array within a dielectric layer, with sub-periodic spatial-scale gap cavities between adjacent microstructures, confined units can be formed. This allows for local perturbation of the guided mode, limiting the guided mode energy to a smaller spatial range (typically less than one wavelength), thereby generating a localized guided mode resonance mode. This results in highly efficient absorption of incident light through a strong localized field distribution. Furthermore, the high-refractive-index dielectric layer further strengthens the transverse confinement of the incident light, leading to a larger transverse wave vector in the localized guided mode resonance mode, thus better confining the light field within the localized guided mode resonance structure. Therefore, this localized guided mode resonance structure can achieve a narrowband filtering effect insensitive to the incident angle, enabling efficient absorption of a single wavelength over a relatively wide incident angle range.
[0029] In one embodiment of this application, reference is made to Figure 1 . Figure 1 The diagram shown is a schematic representation of a local guided mode resonance structure provided in an embodiment of this application. Figure 1 As shown, the local guided mode resonant structure includes a substrate 11, a reflective layer 12, a dielectric layer 13, and a microstructure array ( Figure 1 The diagram shows the specific structure of the microstructure array.
[0030] The substrate 11 is made of at least silicon. Preferably, the substrate 11 is made of silicon. Since silicon has a high refractive index in the infrared band, using silicon as the substrate material can form a homogeneous or near-homogeneous interface with the reflective layer 12, thereby reducing the problem of light field leakage caused by abrupt changes in the interface refractive index, and thus strengthening the constraint on the transverse transmission waveguide mode.
[0031] The reflective layer 12 is made of at least one of the following materials: gold, aluminum, silver, or platinum. The reflective layer 12 is a material layer deposited on the substrate 11 that absorbs light in the operating wavelength range (1.9 micrometers in the near-infrared and 10 micrometers in the long-wave infrared), and therefore can also be called an absorption layer. Through the reflective layer 12, the transmission of incident light towards the substrate 11 is blocked, thereby causing unabsorbed light to be reflected back to the dielectric layer 13, where it interferes and superimposes with new incident light, further exciting local guided mode resonance and improving absorption efficiency.
[0032] The dielectric layer 13 is made of at least one of the following: silicon, germanium, silicon dioxide, and silicon nitride. The dielectric layer 13 is deposited on a surface of the reflective layer 12 away from the substrate 11. The dielectric layer 13 is preferably made of a high-refractive-index material, such as silicon or germanium. A high-refractive-index dielectric layer 13 supports lateral waveguide modes; therefore, the dielectric layer 13 is preferably made of a material with a high refractive index to more effectively localize light within the dielectric layer 13. If the dielectric layer 13 is made of a material with a low refractive index, the confinement effect of the localized guided mode on light will be weakened, resulting in a larger shift in the resonance peak position with the incident angle, which is detrimental to achieving angle-insensitive characteristics.
[0033] Preferably, since germanium has a sufficiently high refractive index, it can better localize light within the dielectric layer 13. Therefore, germanium can be selected as the material of the dielectric layer 13. By using the dielectric layer 13 with a high refractive index to limit the transverse wave vector of light, the light is better localized in the local guided mode resonant structure, achieving angle-insensitive filtering, that is, achieving efficient absorption of a single wavelength over a wide angle.
[0034] The microstructure array is embedded in the dielectric layer 13. The microstructure array comprises multiple microstructures 14, with sub-periodic spatial scale gap cavities 15 between adjacent microstructures 14. The microstructure array can also be referred to as a blocking layer. Using the microstructure array, waveguide modes can be localized within a finite size, thereby forming localized guided mode resonance. This microstructure array is mainly used to control the wave vector conditions of waveguide modes, thereby exciting guided mode resonance within a localized area of one or a few periods, forming a strong localized optical field.
[0035] Among them, the microstructure 14 is a micro-nano structure embedded in the dielectric layer 13. Its form includes, but is not limited to, one-dimensional grating, two-dimensional grating, honeycomb structure, etc. Its core function is to control the wave vector condition of the waveguide mode through periodic local perturbation, and to excite local guided mode resonance in a local area of a single or a few periods to form a strong local optical field.
[0036] Localized mode resonance is a resonance mechanism applicable to micro- and nano-optical absorption structures. It refers to the physical effect of embedding a microstructure array in a high-refractive-index dielectric layer 13 to break the long-range phase matching constraint of traditional long-period guided mode resonance (GMR), localizing the guided mode energy in a subwavelength scale gap cavity 15 (smaller than the incident light wavelength), forming a strong local optical field, and ultimately enabling near 100% absorption of incident light of a specific wavelength over a wide incident angle range.
[0037] according to Figure 1 It can be seen that this localized guided-mode resonant structure can be regarded as a nanocavity coupling structure. That is, a sub-periodic gap cavity 15 (also called a slit) is introduced into the microstructure array. The size of the gap cavity 15 is much smaller than the period of the microstructure array, which compresses the guided-mode field into a nanoscale region, forming an extremely strong localized field distribution. By adjusting the material or parameters of the microstructure array, or by adjusting the parameters of the dielectric layer 13, the resonant peak position can be controlled. When the wavelength of the incident light matches the resonant frequency of this localized guided-mode resonant structure, high absorption of the incident light can be achieved by utilizing the interference effect between the radiation mode and the guided mode. At the same time, due to the high refractive index of the dielectric layer 13, the light is more strongly confined in the transverse direction, and the transverse wave vector of the localized mode is larger, thus better confining the light field inside the structure.
[0038] Among them, the sub-periodic scale is a size description for the periodic microstructure array. It refers to the fact that the key dimensions (such as width and spacing) of the gap cavity 15 are smaller than the period of the microstructure array, and are usually in the subwavelength order (smaller than the incident light wavelength in the working band). Its core function is to break the translational symmetry of the long-period structure and realize the localization constraint of the guided mode energy.
[0039] The local guided mode resonance structure of this application will be described below through two embodiments.
[0040] Example 1 Taking the near-infrared band as an example, silicon can be selected as the material of the substrate 11. A 200-nanometer-thick silver (Ag) layer is deposited on the substrate 11 as a reflective layer 12, and a 116-nanometer-thick silicon layer is deposited on the reflective layer 12 as a dielectric layer 13. A 1000-nanometer-period, 100-nanometer-width, and 116-nanometer-thick silver microstructure array is then embedded in the dielectric layer 13. Test results show that this local guided-mode resonance structure can achieve an absorption rate of over 98% when exposed to incident light at a wavelength of 1.9 micrometers. As the incident angle increases, the resonance peak position remains almost unchanged; the maximum shift of the resonance peak position at an incident angle of 40° is only 2 nanometers. This indicates that the resonance wavelength of the local guided-mode resonance structure remains essentially unchanged within the 0°-40° incident angle range, thus verifying the insensitivity of the absorption peak to the incident angle of this application.
[0041] refer to Figure 2, Figure 2 The diagram shows the relationship between the resonant center wavelength of the local guided-mode resonant structure provided in this application and the incident angle of the incident light in the near-infrared band. It can be seen that the local guided-mode resonant structure of this application can achieve angle-insensitive ultrawide-angle absorption, and thereby achieve ultrawide-angle narrowband radiation.
[0042] Example 2 Taking the long-wave infrared band as an example, silicon can be selected as the substrate material 11. A 200-nanometer-thick silver layer 12 is deposited on the substrate 11 as a reflective layer 12, and a 2-micrometer-thick silicon layer 13 is deposited on the reflective layer 12 as a dielectric layer 13. A gold (Au) microstructure array with a period of 6 micrometers, a width of 0.8 micrometers, and a thickness of 2 micrometers is then embedded in the dielectric layer 13. Test results show that this local guided-mode resonance structure can achieve an absorption rate of over 99% when incident light has a wavelength of 10 micrometers. With increasing incident angle, the resonance peak position remains almost unchanged; the maximum shift of the resonance peak position at an incident angle of 40° is only 60 nanometers. This indicates that the local guided-mode resonance structure of this application also exhibits excellent incident angle stability in the long-wave infrared band. Even with a 40° tilted incident angle, the 60-nanometer peak position shift is negligible relative to the 10-micrometer center wavelength, further verifying the insensitivity of the absorption peak to the incident angle. (Reference) Figure 3 , Figure 3 The diagram shows the relationship between the resonant center wavelength of the local guided mode resonant structure provided in this embodiment and the incident angle of the incident light in the long-wave infrared band.
[0043] As can be seen from Embodiments 1 and 2, the localized guided mode resonant structure provided in this application can achieve a narrowband filtering effect that is insensitive to the incident angle, that is, it can achieve near-complete absorption of a single wavelength within a wide incident angle range.
[0044] In some embodiments, the wavelength of the incident light entering the dielectric layer 13 through the reflective layer 12 matches the resonant frequency of the local guided mode resonant structure.
[0045] When the wavelength of the incident light matches the resonant frequency, the local guided mode is excited. The incident light is constrained into a transverse guided mode by the high refractive index dielectric layer 13. Then, through the wave vector modulation of the microstructure array, it is precisely coupled into the nano-slit, i.e. the gap cavity 15, to form a strong local field. The high absorption of the incident light can be achieved by utilizing the interference effect of the radiation mode and the guided mode.
[0046] If the wavelength of the incident light does not match the resonant frequency of the local guided mode resonant structure, it will be reflected or transmitted because the resonance condition cannot be met, thus failing to form a strong local field.
[0047] In some embodiments, the width of the gap cavity 15 is smaller than the wavelength of the incident light.
[0048] By setting the width of the gap cavity 15 to be smaller than the wavelength of the incident light, a subwavelength optical field trap can be constructed to achieve localized guided mode excitation. That is, when the width of the gap cavity 15 is smaller than the wavelength of the incident light, the optical field is compressed within a subwavelength scale space, forming a strong localized field, which significantly reduces the dependence of the optical field on the incident angle. Here, the width of the gap cavity 15 refers to the lateral dimension perpendicular to the periodic extension direction of the microstructure array.
[0049] The width of the gap cavity 15 is smaller than the period of the microstructure array. By utilizing the period of the microstructure array, the resonant wavelength can be tuned, thereby ensuring that the microstructure array plays a local perturbation role rather than a long-period diffraction role. This breaks the long-period translational symmetry, forms a local perturbation unit, and improves the absorption rate of incident light. The period of the microstructure array refers to the repetition spacing of the microstructures 14 embedded in the dielectric layer 13 along the periodic extension direction, that is, the distance between corresponding positions of two adjacent identical microstructures 14.
[0050] In some embodiments, the width of the gap cavity 15 is greater than or equal to 900 nanometers and less than or equal to 5.2 micrometers.
[0051] In this application, the gap cavity 15 is a subwavelength gap formed by the microstructure 14 in the microstructure array and the surrounding dielectric layer. This gap can compress the guided mode energy and enhance local resonance. Therefore, the size of the gap cavity 15 needs to be matched with the working wavelength (1.9 micrometers in the near-infrared and 10 micrometers in the long-wave infrared) and the period of the microstructure array (1000 nanometers to 6 micrometers). This allows the high-refractive-index dielectric layer 13 in the gap cavity 15 to enhance the optical field confinement, and the reflection of the microstructure 14 to form a nanocavity coupling effect, ultimately achieving efficient absorption and angle insensitivity.
[0052] In some implementations, the period of the microstructure array is greater than or equal to 1000 nanometers and less than or equal to 6 micrometers.
[0053] By controlling the period of the microstructure array within the range of 1000 nanometers to 6 micrometers, the angle insensitivity can be guaranteed to the greatest extent. If the period is greater than 6 micrometers, the local guided mode resonance structure will approach that of a traditional long-period grating, causing the guided mode field to be distributed throughout the entire periodic structure. The resonance condition depends on long-range phase matching, and the wave vector matching condition is easily destroyed when the incident angle changes, resulting in a significant shift in the resonance peak position. On the other hand, a period of 1000 nanometers to 6 micrometers can ensure that the microstructure array forms subwavelength localized units, and the guided mode energy is compressed within a single or a few periods, greatly reducing the sensitivity of the resonance to angle changes.
[0054] Furthermore, the period of the microstructure array is reasonably matched with the working wavelength (1.9 micrometers in near-infrared and 10 micrometers in long-wave infrared). The period of the microstructure array is smaller than the working wavelength or close to the subwavelength scale, which enables the nanocavity coupling structure formed by the microstructure array, namely the gap cavity 15, to effectively confine the light field, avoid the weakening of the local effect caused by light field leakage, and ensure high absorption efficiency at resonance.
[0055] In some embodiments, the resonant frequency of the local guided mode resonant structure is determined based on at least one of the following: the material of the microstructure 14, the width of the microstructure 14, the thickness of the microstructure 14, the period of the microstructure array, the thickness of the dielectric layer 13, and the refractive index of the dielectric layer 13.
[0056] Microstructure arrays, acting as perturbation sources for localized guided modes, can directly modify the wave vector relationship between incident light and guided modes through their material and geometric parameters (e.g., width, thickness, period), while simultaneously defining the constraint boundaries of the localized field. Specifically: The material of microstructure 14 determines the optical field reflection efficiency and energy loss characteristics, thereby determining the resonant frequency. Microstructure 14 is made of a metallic material; different metals have different plasma resonant frequencies. When the material of microstructure 14 is changed, the effective reflection boundary position of the local field changes, the effective wave vector of the waveguide mode adjusts accordingly, and the resonant frequency shifts. If the material of microstructure 14 is a non-conductive material, a strong reflection boundary cannot be formed, the local field leaks into free space, and the resonance condition fails.
[0057] The width and thickness of the microstructure 14 can define the lateral and longitudinal constraint range of the local field, and affect the resonant frequency by changing the optical path length within the local cavity.
[0058] The period of the microstructure array can define the range of macroscopic wave vector modulation. By influencing the reciprocal lattice vector of the microstructure array to correct the wave vector matching condition, the overall range of resonant frequencies can be determined.
[0059] Dielectric layer 13 is the propagation carrier of local guided modes, and its thickness and refractive index determine the effective characteristics of the waveguide modes. Specifically: The thickness of dielectric layer 13 directly affects the number of guided modes and the resonant order supported within the waveguide. In other words, the thickness of dielectric layer 13 affects the effective refractive index of the waveguide mode (i.e., the wave vector magnitude of the guided mode), which essentially means that the thickness of dielectric layer 13 modulates the resonant frequency through the resonant order.
[0060] The high refractive index of dielectric layer 13 can enhance optical field confinement and wave vector matching, and its value directly affects the effective wave vector of the waveguide mode, thereby determining the resonant frequency. Preferring a high refractive index material as dielectric layer 13 not only enhances optical field confinement and reduces leakage, but also allows for fine-tuning of the resonant frequency within the same period by adjusting the refractive index of dielectric layer 13, thus supplementing the flexibility of periodic control.
[0061] In some embodiments, the width of the microstructure 14 is positively correlated with the resonant frequency; the thickness of the microstructure 14 is negatively correlated with the resonant frequency; the period of the microstructure array is negatively correlated with the resonant frequency; the thickness of the dielectric layer 13 is negatively correlated with the resonant frequency; and the refractive index of the dielectric layer 13 is negatively correlated with the resonant frequency.
[0062] Increasing the width of microstructure 14 will increase the space occupied by the dielectric layer 13, reduce the three-dimensional width of the gap cavity 15, and increase the transverse wave vector of the local field. A smaller wavelength (higher frequency) incident light is required to satisfy the wave vector matching, so the resonance peak position is blue shifted, and thus the width of microstructure 14 is positively correlated with the resonance frequency.
[0063] Figure 4 The diagram shown illustrates the relationship between the width and resonant frequency of the microstructure provided in this embodiment. Figure 4 It can be seen that increasing the width of microstructure 14 will cause a blue shift in the resonance peak position.
[0064] The thickness of microstructure 14 is the same as that of dielectric layer 13. Reducing the thickness of microstructure 14 will shorten the longitudinal constraint length of the local field and reduce the effective refractive index of the waveguide mode. Therefore, reducing the thickness of microstructure 14 will lead to a decrease in resonant wavelength, an increase in resonant frequency, and a blue shift in resonant peak position. Thus, there is a negative correlation between the thickness of microstructure 14 and resonant frequency.
[0065] Figure 5 The diagram shown illustrates the relationship between the thickness and resonant frequency of the microstructure provided in this embodiment. Figure 5 It can be seen that reducing the thickness of microstructure 14 will cause a blue shift in the resonance peak position.
[0066] Although local guided-mode resonance does not depend on long-period collective coupling, it still requires basic phase matching of the incident light wave vector. Increasing the period of the microstructure array will reduce the reciprocal lattice vector of the microstructure array. To satisfy the basic phase matching of the incident light wave vector, the incident light wave vector needs to be reduced, i.e., the resonant wavelength needs to be increased. The resonant frequency decreases, and therefore the resonant peak position is redshifted. Thus, there is a negative correlation between the period of the microstructure array and the resonant frequency.
[0067] Figure 6 The diagram shown illustrates the relationship between the period and resonant frequency of the microstructure array provided in this embodiment. According to... Figure 6 It is known that increasing the period of the microstructure array will cause the resonance peak position to redshift.
[0068] The high-refractive-index dielectric layer 13 supports transversely propagating waveguide modes, with different thicknesses corresponding to different guided mode resonant orders. When the refractive index and guided mode propagation angle of the dielectric layer 13 are fixed, increasing the thickness of the dielectric layer 13 increases the resonant wavelength and decreases the resonant frequency, thus causing a redshift of the resonant peak. Consequently, there is a negative correlation between the thickness of the dielectric layer 13 and the resonant frequency.
[0069] According to the wave vector relationship, the greater the refractive index of the dielectric layer 13, the greater the incident light wave vector. In order to satisfy the basic phase matching of the incident light wave vector, when the refractive index of the dielectric layer 13 increases, the incident light wave vector can be appropriately reduced, that is, the resonant wavelength is increased and the resonant frequency is reduced. Therefore, the resonant peak position is redshifted, so the refractive index of the dielectric layer 13 and the resonant frequency are negatively correlated.
[0070] Therefore, it can be seen that by adjusting the geometric parameters (such as period, thickness, duty cycle, etc.) and material properties of the microstructure 14, and by adjusting the thickness and refractive index of the dielectric layer 13, the local guided-mode resonance structure can achieve local guided-mode resonance within a specific wavelength range, thereby achieving a highly efficient absorption effect. Due to the characteristics of local guided-mode resonance, the resonance wavelength of this local guided-mode resonance structure is not sensitive to the angle of incident light, and it can maintain high absorption efficiency over a wide range of incident angles (the resonance peak position remains basically unchanged from vertical incident to oblique incident).
[0071] In some embodiments, the microstructure 14 includes at least one of the following: a one-dimensional grating, a two-dimensional grating, and a honeycomb structure.
[0072] The essence of localized guided mode resonance is to introduce local perturbations through microstructure 14, confining the waveguide modes within dielectric layer 13 to subwavelength space, thereby achieving wave vector matching and a strong localized optical field. Therefore, microstructure 14 can adopt structures such as one-dimensional gratings, two-dimensional gratings, and honeycomb structures.
[0073] One-dimensional gratings, two-dimensional gratings, and honeycomb structures are all periodically arranged micro-nano units. Their periodicity can derive reciprocal lattice vectors, which can be used to correct the incident light wave vector to excite local guided modes. These structures can all break the translational symmetry of dielectric layer 13, forming perturbations in local space (single or a few periods), confining the guided mode energy within the gap cavity to achieve angle-insensitive characteristics.
[0074] Among them, the structure of a one-dimensional grating can provide a one-dimensional reciprocal lattice vector by periodically arranging metal stripes along a single direction (such as the x-axis), which can be adapted to the wave vector modulation of linearly polarized light.
[0075] The structure of a two-dimensional grating can provide a two-dimensional reciprocal lattice vector by periodically arranging metal dots along the x and y directions, which can be adapted to the wave vector modulation of arbitrary polarized light.
[0076] A honeycomb structure is essentially a special two-dimensional periodic structure with a hexagonal periodic arrangement of metal holes or pillars. It can provide a hexagonal symmetrical reciprocal lattice vector, which is suitable for wave vector manipulation of circularly polarized or unpolarized light.
[0077] The localized guided-mode resonant structure provided in this application, by enhancing the localized field and suppressing non-radiative losses, can simultaneously meet the requirements of high efficiency, wide angle, and narrow bandgap, at least in the following aspects: (1) Formation of local resonance state: The microstructure array breaks the translational symmetry of the periodic structure and generates a local resonance state when it meets the Bragg condition. The electromagnetic field of the local resonance state is highly concentrated in the region of the micro-nano gap cavity 15, and is significantly distributed near the gap cavity 15, and decays rapidly away from the gap cavity 15.
[0078] (2) Localization correction of phase matching: Local guided mode resonance still needs to meet the basic phase matching conditions, but it is more sensitive to the size and shape of the local structure. By adjusting the local geometric parameters such as the material of the microstructure, the width of the microstructure, the thickness of the microstructure, the period of the microstructure array, the thickness of the dielectric layer, and the refractive index of the dielectric layer, the equivalent refractive index at the gap cavity 15 can be changed, thereby finely controlling the resonance wavelength.
[0079] (3) Local enhancement of resonance response: The resonance peak linewidth of the local guided mode resonance is extremely narrow (the quality factor Q value can reach 10). 3 -10 5 The effectiveness stems from the effective decoupling of local modes and radiation losses. The size of the micro / nano local field is much smaller than the wavelength of light, significantly suppressing radiation scattering into free space. Simultaneously, the enhancement of the local field relatively reduces material absorption losses, further improving the resonant Q-value. This means that the local guided-mode resonant structure of this application achieves near-100% absorption while possessing extremely high spectral selectivity and quality factor, enabling the coexistence of high-efficiency absorption and a high Q-value.
[0080] Figure 7 The diagram shown is a schematic representation of the reflectivity of the local guided mode resonance structure provided in this application as a function of the incident light angle. Figure 8 The diagram illustrates the variation of the peak position shift at the 1.9-micron resonance peak with the incident light angle, as provided in this embodiment of the application. Specifically, the resonance peak wavelength is 1900 nm at an incident angle of 0°; 1899.7 nm at 10°; 1899.5 nm at 20°; 1900.1 nm at 30°; and 1901.7 nm at 40°. It can be seen that the maximum shift at 40° is only about 2 nm, demonstrating that this localized guided-mode resonance structure can achieve wide-angle absorption of a single wavelength.
[0081] In one optional implementation, the localized guided-mode resonance structure provided in this application can be applied to, but is not limited to, the following scenarios: Optical sensors: can be used for highly sensitive optical sensing, detecting changes in environmental parameters through minute changes in resonant wavelengths.
[0082] Optical communication: In optical communication systems, it refers to the efficient narrowband filtering and transmission of signals at specific wavelengths.
[0083] Photovoltaic devices: Improving the light absorption efficiency of photovoltaic devices in specific wavelength bands to enhance their photoelectric conversion performance.
[0084] Narrowband radiation source: According to Kirchhoff's law, high absorption corresponds to high radiation. Narrowband radiation sources that are close to those of a Lambert can be prepared for special light source needs.
[0085] In another embodiment of this application, reference is made to Figure 9 . Figure 9 The diagram shown is a schematic flowchart of the fabrication method of the local guided mode resonance structure provided in an embodiment of this application. Figure 9 As shown, this method is used to prepare the local guided mode resonant structure in the aforementioned embodiments. The method includes the following steps: Step 901: Deposit a reflective layer of a first thickness on one surface of the substrate.
[0086] Step 902: Deposit a dielectric layer of a second thickness on the surface of the reflective layer away from the substrate, and coat the dielectric layer on the surface away from the reflective layer with photoresist.
[0087] Photoresist can transfer the array pattern of a pre-designed microstructure onto a dielectric layer; furthermore, it can also protect the dielectric layer. Therefore, in the fabrication of a localized guided-mode resonant structure, photoresist can be coated on a surface of the dielectric layer away from the reflective layer.
[0088] Step 903: Expose the photoresist according to the preset arrangement of multiple microstructures in the microstructure array to form an array pattern of the microstructure array, wherein the arrangement includes a gap cavity with a sub-periodic spatial scale between two adjacent microstructures.
[0089] By exposing the photoresist to a pre-defined arrangement of multiple microstructures within a microstructure array, a photochemical reaction can occur in the photoresist, thereby forming an array pattern of microstructures.
[0090] Step 904: Etch the dielectric layer according to the array pattern to form multiple grooves of a second thickness.
[0091] Etching the dielectric layer according to the array pattern of the microstructure array (for example, by using inductively coupled plasma etching) can create multiple grooves on the dielectric layer with the same thickness as the dielectric layer, so as to facilitate the subsequent formation of microstructures.
[0092] Step 905: Deposit multiple microstructures in multiple grooves to obtain a localized guided mode resonance structure.
[0093] After forming multiple grooves of a second thickness on the dielectric layer, materials such as gold, aluminum, silver, and platinum can be deposited in each groove to form a microstructure. Ultimately, the localized guided-mode resonance structure of this application can be obtained.
[0094] In some embodiments, before etching the dielectric layer according to the array pattern of the microstructure array, a metal hard mask such as chromium, titanium, or gold can be deposited using metal coating instruments such as electron beam evaporation or thermal evaporation. The array pattern of the microstructure array is also formed on this metal hard mask. By covering the dielectric layer with the metal hard mask, the position and shape of each microstructure in the microstructure array can be precisely determined. Then, etching the dielectric layer downwards can effectively improve the accuracy of the multiple grooves formed.
[0095] In some implementations, if a metal hard mask is used, after forming multiple grooves of the second thickness, the metal hard mask can be removed using hydrochloric acid or the like to avoid the metal hard mask affecting the subsequent deposition of multiple microstructures in the multiple grooves.
[0096] In some embodiments, after obtaining the local guided mode resonant structure, the surface of the local guided mode resonant structure can be cleaned with ultraviolet ozone to remove organic contaminants such as photoresist residue and organic impurities from the surface of the local guided mode resonant structure, thereby improving the purity of the surface of the local guided mode resonant structure and thus avoiding the contaminants from affecting the absorption effect of the local guided mode resonant structure on incident light.
[0097] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications or equivalent substitutions made within the spirit and principles of this application should be included within the protection scope of this application.
[0098] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the appended claims.
Claims
1. A local guided mode resonance structure, characterized in that, include: Substrate; A reflective layer disposed on one surface of the substrate; A dielectric layer is disposed on a surface of the reflective layer away from the substrate, and the refractive index of the dielectric layer is greater than or equal to a preset refractive index threshold. A microstructure array embedded in the dielectric layer, the microstructure array comprising multiple microstructures, with a sub-periodic spatial scale gap cavity between adjacent microstructures.
2. The local guided mode resonance structure according to claim 1, characterized in that, The wavelength of the incident light entering the dielectric layer through the reflective layer matches the resonant frequency of the local guided mode resonant structure.
3. The local guided mode resonance structure according to claim 2, characterized in that, The width of the gap cavity is smaller than the wavelength of the incident light.
4. The local guided mode resonance structure according to claim 3, characterized in that, The width of the gap cavity is greater than or equal to 900 nanometers and less than or equal to 5.2 micrometers.
5. The local guided mode resonance structure according to claim 3, characterized in that, The period of the microstructure array is greater than or equal to 1000 nanometers and less than or equal to 6 micrometers.
6. The local guided mode resonance structure according to claim 2, characterized in that, The resonant frequency of the local guided mode resonant structure is determined based on at least one of the following: the material of the microstructure, the width of the microstructure, the thickness of the microstructure, the period of the microstructure array, the thickness of the dielectric layer, and the refractive index of the dielectric layer.
7. The local guided mode resonance structure according to claim 6, characterized in that, The width of the microstructure is positively correlated with the resonant frequency; The thickness of the microstructure is negatively correlated with the resonant frequency; The period of the microstructure array is negatively correlated with the resonant frequency; The thickness of the dielectric layer is negatively correlated with the resonant frequency; The refractive index of the dielectric layer is negatively correlated with the resonant frequency.
8. The local guided mode resonance structure according to any one of claims 1-7, characterized in that, The microstructure includes at least one of the following: a one-dimensional grating, a two-dimensional grating, and a honeycomb structure.
9. The local guided mode resonance structure according to any one of claims 1-7, characterized in that, The substrate is made of at least silicon; The material of the reflective layer includes at least one of the following: gold, aluminum, silver, and platinum; The material of the dielectric layer includes at least one of the following: silicon, germanium, silicon dioxide, and silicon nitride; The material of the microstructure includes at least one of the following: gold, aluminum, silver, and platinum.
10. A method for preparing a local guided mode resonance structure, characterized in that, A method for preparing a local guided-mode resonance structure as described in any one of claims 1 to 9; the preparation method includes: A reflective layer of first thickness is deposited on one surface of the substrate; A dielectric layer of a second thickness is deposited on a surface of the reflective layer away from the substrate, and photoresist is coated on the dielectric layer on a surface away from the reflective layer. The photoresist is exposed according to the preset arrangement of multiple microstructures in the microstructure array to form an array pattern of the microstructure array, wherein the arrangement includes a gap cavity with a sub-periodic spatial scale between two adjacent microstructures. The dielectric layer is etched according to the array pattern to form a plurality of grooves of the second thickness; The multiple microstructures are deposited in the multiple grooves to obtain the local guided mode resonance structure.