Mid-infrared narrowband tunable filter based on phase change material gst

Abstract

The application discloses a middle infrared narrow-band tunable filter based on a phase change material GST and particularly relates to the technical field of micro-nano optical devices, and the filter comprises a dielectric substrate layer and a double-rectangular superstructure grating layer arranged periodically on the dielectric substrate layer; the double-rectangular superstructure grating layer comprises first rectangular microstructures and second rectangular microstructures arranged with a certain interval; the first rectangular microstructures are Ge cuboid blocks; and the second rectangular microstructures are composed of Ge cuboid blocks similar to the first rectangular microstructures and phase change material GST blocks with variable dielectric constants embedded at the bottom of the second rectangular microstructures. The tunability of the center wavelength position and the bandwidth of the filter is realized by the change of the incident light inclination angle and the different phase states of the GST, the demand of dynamic regulation of the transmission spectrum is met, and the utilization rate of the filter is greatly improved, so that the filter has the flexible tuning characteristics in practice.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optical device technology, and more specifically to a mid-infrared narrowband tunable filter based on phase change material GST. Background Technology

[0002] The mid-infrared band encompasses the characteristic vibrational absorption peaks of many important molecules. Mid-infrared spectral characteristics can be used to infer the possible functional groups present in compounds, and molecular resonance fingerprints from mid-infrared absorption spectra can be used to identify compound components. Therefore, mid-infrared spectroscopy has attracted considerable attention and is widely used in environmental pollution monitoring, biomedicine, and optical communication, becoming a research hotspot both domestically and internationally. Mid-infrared bandstop filters, with their characteristic frequency selection and noise filtering capabilities, can selectively target the absorption bands of specific molecules, making them indispensable key optical components. However, most traditional filters are passive devices, meaning that once manufactured, their center wavelength and bandwidth are fixed, making tuning difficult. Furthermore, optical filters based on plasmon resonance or guided-mode resonance have relatively large bandwidths.

[0003] Therefore, in order to solve the above problems and meet the requirements of high-resolution dynamic filtering, there is an urgent need for a mid-infrared band narrowband tunable optical filter. Summary of the Invention

[0004] The phase change material germanium-antimony-tellurium (Ge2Sb2Te5, GST) exhibits good thermal stability, reversible phase transition, and a fast transition rate (crystallization time is approximately 10). -8 GST (Gas-Converting Stem Cell) is an important optical phase change material. It possesses three phase states: amorphous, metastable face-centered cubic, and hexagonal close-packed. Reversible switching between these three phase states can be achieved using appropriate external excitation, accompanied by relatively stable and rapid changes in physical properties, with significant differences in optical performance. Furthermore, dynamic metagratings based on Bound States in the Continuum (BICs) have seen rapid development. A BIC is a special state with a specific combination of momentum and frequency, whose coupling with the radiation channel is completely severed. An ideal BIC mode is non-radiative and has an infinitely large quality factor (Q). By changing the structural symmetry or dielectric constant symmetry, a BIC can be transformed into a quasi-BIC mode with a high quality factor. Therefore, integrating phase change materials into such optical filter structures can significantly improve the tunability of the filter, promoting the high integration of tunable filtering functions and solving the problem of limited device filtering capabilities in different application scenarios.

[0005] To address these issues, the present invention provides a mid-infrared narrowband tunable filter based on phase change material GST, thereby resolving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a mid-infrared narrowband tunable filter based on phase change material GST, comprising a dielectric substrate layer and a periodically distributed double rectangular metagrating layer on the dielectric substrate layer; the double rectangular metagrating layer comprises a first rectangular microstructure and a second rectangular microstructure with a certain interval; the first rectangular microstructure is a Ge cuboid block; the second rectangular microstructure is composed of a Ge cuboid block and a GST block with a variable dielectric constant embedded at its bottom.

[0007] Preferably, the substrate layer is directly connected to the periodically distributed double rectangular metagrating layers.

[0008] Preferably, the thickness of the dielectric substrate layer is between 0.8 μm and 1.2 μm, and the material is a low refractive index material with high mid-infrared transmission, including but not limited to calcium fluoride and magnesium fluoride.

[0009] Preferably, the lattice period P of the double rectangular metagrating layer is 1.4 μm to 1.6 μm.

[0010] Preferably, the lengths L1 and L2 of the Ge cuboid blocks in the first and second rectangular microstructures are 1.25 μm to 1.30 μm, the width W is 0.4 μm to 0.5 μm, and the height H is 0.46 μm to 0.52 μm.

[0011] Preferably, the length a of the phase change material GST layer in the second rectangular microstructure is 0.35 μm to 0.45 μm, the width is equal to the width W in the second rectangular microstructure, and the height h is 0.1 μm to 0.13 μm.

[0012] Preferably, the spacing G between the first rectangular microstructure and the second rectangular microstructure is 0.2 μm to 0.3 μm.

[0013] Preferably, the dual rectangular metagrating filter is placed in the xy plane, the electromagnetic wave incident direction makes an angle of θ with the z-axis (0≤θ≤10), and the electric field polarization direction is parallel to the y-axis.

[0014] Preferably, the dual rectangular meta-grating layer breaks the in-plane inversion symmetry by changing the length L2 of the second rectangular microstructure and the phase state of the phase change material GST, thereby forming and controlling the high quality factor resonance peak; the position of the resonance peak is adjusted by the incident light tilt angle, and the filtering bandwidth at the same position is dynamically adjusted by the incident angle and the crystallization fraction of the phase change material GST.

[0015] The present invention has the following advantages:

[0016] 1. This invention designs a narrowband tunable optical filter based on phase change material GST. By utilizing the excellent properties of GST, the peak position and bandwidth of the transmission spectrum can be tunable by changing the incident light tilt angle and different phase states of GST, which meets the needs of dynamic control of the transmission spectrum, greatly improves the utilization rate of the filter, and has flexible tuning characteristics in practice.

[0017] 2. The filter of the present invention has the advantages of simple structure, small size, high integration, excellent performance and strong practicality. Attached Figure Description

[0018] Figure 1 The three-dimensional structure diagram and unit structure diagram of the mid-infrared narrowband tunable optical filter based on phase change material GST provided in this embodiment;

[0019] Figure 2 The transmission spectra of GST in the non-crystalline state in this embodiment are for different lengths L2 of the second rectangular microstructure.

[0020] Figure 3 The following are transmission spectra of different phase change materials GST at crystallization fractions X in this embodiment;

[0021] Figure 4 The transmission spectra of the tunable optical filter are shown when the incident light tilt angle is 0°, 2°, 4°, 6°, 8°, and 10°.

[0022] Figure 5 Transmission spectra showing bandwidth modulation of the same resonance wavelength under different incident light tilt angles and different GST crystal fractions;

[0023] In the figure: 1. Dielectric substrate layer; 2. Double rectangular metagrating layer; 21. First rectangular microstructure; 22. Second rectangular microstructure. Detailed Implementation

[0024] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1As shown, this embodiment provides a mid-infrared narrowband tunable optical filter based on phase change material GST, consisting of a dielectric substrate layer 1 and a double rectangular metagrating layer 2. The dielectric substrate layer 1 is connected to the double rectangular metagrating layer 2; the dielectric substrate layer 1 is made of calcium fluoride, a mid-infrared high-transmittance material; the double rectangular metagrating layer 2 consists of a first rectangular microstructure 21 and a second rectangular microstructure 22; the first rectangular microstructure 21 is a Ge cuboid block; the second rectangular microstructure 22 consists of a Ge cuboid block and a GST block with a variable dielectric constant embedded at its bottom, with initial structural parameters set as follows: P=1.44μm, L1=1.28μm, L2=1.28μm, W=0.48μm, H=0.48μm, G=0.24μm, a=0.4μm, h=0.12μm. Incident light is incident vertically downward from the upper surface of the double rectangular metagrating layer 2 and exits from the lower surface of the dielectric substrate layer 1.

[0026] Furthermore, the narrowband tunable metagrating structure based on the phase change material GST provided in this embodiment operates in quasi-BIC mode. The dual rectangular metagrating layer 2 can break the in-plane inversion symmetry by changing the length L2 of the second rectangular microstructure 22 to form a symmetry-protected quasi-continuous bound state (SP-BIC) with a high quality factor (Q). Simultaneously, since the dielectric constant of amorphous GST is very close to that of Ge, this symmetry breaking can also be achieved by changing the phase state of the GST layer, providing a dynamically adjustable resonance mechanism for the dual rectangular metagrating layer 2.

[0027] Figure 2 The figure shows the transmission spectra of GST in its amorphous state under different lengths L2 of the second rectangular microstructure. The horizontal axis represents the incident light wavelength, and the vertical axis represents the light transmittance (i.e., transmission coefficient). The five different transmission spectrum curves in the figure are simulation results obtained when L2 is 1.28 μm, 1.305 μm, 1.33 μm, 1.355 μm, and 1.38 μm, respectively. As can be seen from the figure, when L2 = 1.28 μm, the two rectangular microstructures have the same length, and the structure is in a symmetrical state, with an extremely narrow resonance peak that is almost unobservable. As the length L2 of the second rectangular microstructure 22 gradually increases, the transmission valley in the transmission spectrum gradually becomes visible, and the resonance wavelength gradually redshifts, while the resonance bandwidth gradually increases. This phenomenon indicates that the resonance bandwidth of the transmission spectrum can be effectively adjusted by changing the length L2 of the second rectangular microstructure 22.

[0028] Figure 3 The figures show the transmission spectra of different phase change materials GST at crystallization fractions X in this embodiment. The horizontal and vertical axes in the figure represent the crystallization fractions X and X, respectively. Figure 2Consistent with L2=1.28μm and other parameters remaining constant, the five different transmission spectrum curves in the figure represent simulation results obtained when the GST crystallization fraction X is 0.00, 0.25, 0.50, 0.75, and 1.00, respectively. As can be seen from the results, when X=0, almost no peak is observed in the transmission spectrum, indicating minimal loss of the symmetry-protected continuous domain bound state mode in the structure. As the GST layer crystallization fraction gradually increases, peaks appear, consistent with the previously mentioned... Figure 2 Similarly, in the transmission spectrum, transmission valleys gradually appear and redshift occurs, with the resonance bandwidth gradually increasing from 0.9 nm to 33.1 nm. This phenomenon indicates that this embodiment can achieve dynamic tuning of the bandwidth of the tunable optical filter by controlling the resonance bandwidth through the GST crystal fraction.

[0029] Figure 4 This figure shows the transmission spectra of the tunable optical filter under different incident light tilt angles in this embodiment. The horizontal and vertical axes in the figure represent the transmission spectra of the filter under different incident light tilt angles. Figure 2 Consistent with L2=1.28μm, X=0.5, and other parameters remaining constant, the six different transmission spectrum curves in the figure represent simulation results obtained when the incident light angle θ is 0°, 2°, 4°, 6°, 8°, and 10°, respectively. As can be seen from the figure, with the increase of the incident angle, the peak position of the transmission valley in the transmission spectrum redshifts from 3.3748μm to 3.4296μm, a shift of 54.8nm within a 10° incident angle variation range. The transmission valley value increases slightly with increasing incident angle, while the change in incident angle has no significant effect on the resonant bandwidth. This indicates that the frequency selectivity of the filter can be achieved according to actual needs by adjusting the incident angle.

[0030] Figure 5 This figure shows the transmission spectra of the same resonance wavelength under different incident light tilt angles and different GST crystal fractions in this embodiment. The horizontal and vertical axes in the figure represent the bandwidth adjustment of the same resonant wavelength. Figure 2 Consistent, according to Figure 3 and Figure 4 The results show that the narrowband tunable optical filter can adjust its bandwidth through the GST crystal fraction and the position of the resonant wavelength through different incident angles. Combining these two methods, the bandwidth of the filter can be dynamically tuned from 4.1 nm to 0.9 nm by adjusting the GST crystal fraction X and the incident angle θ at the same wavelength position. This demonstrates that the tunable optical filter can achieve dynamically adjustable frequency selection and resolution according to actual needs. Therefore, this structure exhibits good tunable filtering capabilities.

[0031] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A mid-infrared narrowband tunable filter based on phase change material GST, characterized in that: It includes a dielectric substrate layer (1) and a double rectangular metagrating layer (2) periodically distributed on the dielectric substrate layer (1); the double rectangular metagrating layer (2) includes a first rectangular microstructure (21) and a second rectangular microstructure (22) arranged at certain intervals; the first rectangular microstructure (21) is a Ge cuboid block; the second rectangular microstructure (22) is composed of the Ge cuboid block of the first rectangular microstructure and a GST block of phase change material with variable dielectric constant embedded at its bottom; The double rectangular meta-grating layer (2) breaks the in-plane inversion symmetry by changing the length L2 of the second rectangular microstructure (22), thereby realizing the static bandwidth tuning of the tunable filter; By taking advantage of the fact that the dielectric constant of amorphous GST is similar to that of Ge, the in-plane inversion symmetry of the phase change material GST can be broken by changing the phase state of GST, thereby realizing the dynamic bandwidth tuning of the tunable filter.

2. The mid-infrared narrowband tunable filter based on phase change material GST according to claim 1, characterized in that: The base layer (1) is directly connected to the periodically distributed double rectangular metagrating layer (2).

3. The mid-infrared narrowband tunable filter based on phase change material GST according to claim 1, characterized in that: The thickness of the dielectric substrate layer (1) is between 0.8 μm and 1.2 μm, and the material is a low refractive index material with high mid-infrared transmission.

4. The mid-infrared narrowband tunable filter based on phase change material GST according to claim 1, characterized in that: The lengths L1 and L2 of the Ge cuboids in the first rectangular microstructure (21) and the second rectangular microstructure (22) are 1.25 μm to 1.30 μm, the width W is 0.4 μm to 0.5 μm, and the height H is 0.46 μm to 0.52 μm.

5. The mid-infrared narrowband tunable filter based on phase change material GST according to claim 1, characterized in that: The length a of the phase change material GST block in the second rectangular microstructure (22) is 0.35 μm to 0.45 μm, the width is equal to the width W in the second rectangular microstructure (22), and the height h is 0.1 μm to 0.13 μm.

6. The mid-infrared narrowband tunable filter based on phase change material GST according to claim 1, characterized in that: The spacing G between the first rectangular microstructure (21) and the second rectangular microstructure (22) is 0.2 μm to 0.3 μm.

7. The mid-infrared narrowband tunable filter based on phase change material GST according to claim 1, characterized in that: By adjusting the tilt angle of the incident light to control the position of the resonant peak, the frequency selection of the tunable filter can be achieved. The tilt angle of the incident light, combined with the crystallization fraction of the phase change material GST, can be used to dynamically adjust the filtering bandwidth at the same position.

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