Intermediate infrared narrow-band tunable filter based on phase change material GST

Abstract

The invention discloses a mid-infrared narrow-band tunable filter based on a phase change material GST, and particularly relates to the technical field of micro-nano optical devices, the filter comprises a dielectric substrate layer and a double-rectangular super-structure grating layer which is located on the dielectric substrate layer and is periodically distributed; the double-rectangular super-structure grating layer comprises a first rectangular microstructure and a second rectangular microstructure which are arranged at a certain interval; the first rectangular microstructure is a Ge cuboid block; the second rectangular microstructure is composed of a Ge cuboid block similar to the first rectangular microstructure and a dielectric constant variable phase change material GST block embedded in the bottom of the Ge cuboid block. Tunability of the center wavelength position and the bandwidth of the filter is achieved through changes of the inclination angle of incident light and different phase states of GST, the requirement for dynamic regulation and control of a transmission spectrum is met, the utilization rate of the filter is greatly increased, and the tunable filter has the flexible tuning characteristic in practice.

Description

Technical Field

[0001] The invention relates to the technical field of micro-nano optical devices, and in particular to a mid-infrared narrow-band tunable filter based on a phase change material GST. Background Art

[0002] The mid-infrared band covers the characteristic vibration absorption peaks of many important molecules. People can infer the possible groups of compounds through the characteristics of mid-infrared spectra, and use the molecular resonance fingerprint of mid-infrared absorption spectra to identify the composition of compounds. Therefore, mid-infrared spectroscopy technology has attracted much attention and is widely used in environmental pollution monitoring, biomedicine, optical communications and other fields, becoming a hot research topic at home and abroad. Mid-infrared band-stop filters have the functions of characteristic frequency selection and noise filtering. They can select the frequency of specific molecular absorption bands and are indispensable key optical components. However, most traditional filters are passive devices, that is, once they are manufactured, the central wavelength and bandwidth are fixed and difficult to tune. In addition, optical filters based on plasma resonance or guided mode resonance have a large bandwidth.

[0003] Based on this, in order to solve the above problems and meet the needs of high-resolution dynamic filtering, a narrow-band tunable optical filter in the mid-infrared band is urgently needed. Summary of the invention

[0004] The phase change material germanium antimony telluride (Ge2Sb2Te5, GST) has good thermal stability, reversible phase change and fast transition speed (crystallization time is about 10 -8 s), is an important optical phase change material. GST has three phases: amorphous, metastable face-centered cubic and hexagonal close-packed. Reversible switching between the three phases can be achieved by using appropriate external excitations. The process is accompanied by relatively stable and rapid changes in physical properties, and the optical properties are significantly different. In addition, dynamic metagratings based on bound states in the continuum (Bound States in the Continuum, BICs) have been rapidly developed. BIC is a special state with a specific combination of momentum and frequency, and the coupling with the radiation channel is completely cut off. The ideal BIC mode is non-radiative and has an infinite quality factor (Q). By changing the structural symmetry or dielectric constant symmetry, the BIC can be converted into a quasi-BIC mode with a high quality factor. Therefore, by integrating phase change materials into this optical filtering structure, the adjustability of the filter can be greatly improved, which promotes the high integration of adjustable filtering functions and solves the problem of limited device filtering functions in different application scenarios.

[0005] To this end, the present invention provides a mid-infrared narrow-band tunable filter based on the phase change material GST to solve the problems raised in the background technology.

[0006] In order to achieve the above-mentioned purpose, 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 double rectangular metagrating layer periodically distributed on the dielectric substrate layer; the double rectangular metagrating layer comprises a first rectangular microstructure and a second rectangular microstructure arranged at a certain interval; the first rectangular microstructure is a Ge rectangular block; the second rectangular microstructure is composed of a Ge rectangular block and a phase change material GST block with a variable dielectric constant embedded in its bottom.

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

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

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

[0010] Preferably, the length L1 and L2 of the Ge cuboid blocks in the first rectangular microstructure and the second rectangular microstructure 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 interval 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 angle between the incident direction of the electromagnetic wave and the z-axis is θ (0≤θ≤10), and the electric field polarization direction is parallel to the y-axis.

[0014] Preferably, the dual rectangular metagrating layer breaks the inversion symmetry in the plane 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 resonance peak position is adjusted by the tilt angle of the incident light, 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. The present invention designs a narrow-band tunable optical filter based on the phase change material GST. By utilizing the excellent properties of the phase change material GST, the peak position and bandwidth of the transmission spectrum can be tuned by changing the incident light tilt angle and the different phases of GST, which meets the needs of dynamic regulation 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] Figure 2 Graphs of transmission spectra of different second rectangular microstructure lengths L2 when GST is in a non-crystalline state in this embodiment;

[0020] Figure 3 Graphs showing transmission spectra of different phase change materials GST at different crystal fractions X in this embodiment;

[0021] Figure 4 is the transmission spectrum of the tunable optical filter when the incident light is tilted at 0°, 2°, 4°, 6°, 8°, and 10°;

[0022] Figure 5 The transmission spectra of bandwidth adjustment for the same resonance wavelength at different incident light tilt angles and different GST crystal fractions;

[0023] In the figure: 1, dielectric substrate layer; 2, double rectangular meta-grating layer; 21, first rectangular microstructure; 22, second rectangular microstructure. DETAILED DESCRIPTION

[0024] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work 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, which is composed of a dielectric substrate layer 1 and a double rectangular meta-grating layer 2. The dielectric substrate layer 1 is connected to the double rectangular meta-grating layer 2; the dielectric substrate layer 1 uses calcium fluoride, a high-transmittance material for mid-infrared; the double rectangular meta-grating layer 2 is composed of a first rectangular microstructure 2-1 and a second rectangular microstructure 2-2; the first rectangular microstructure 2-1 is a Ge rectangular block; the second rectangular microstructure 2-2 is composed of a Ge rectangular block and a phase change material GST block with a variable dielectric constant embedded at its bottom, and its initial structural parameters are set to: P = 1.44μm, L1 = 1.28μm, L2 = 1.28μm, W = 0.48μm, H = 0.48μm, G = 0.24μm, a = 0.4μm, h = 0.12μm. The incident light is incident vertically downward from the upper surface of the dual rectangular metagrating layer 2 and is emitted from the lower surface of the dielectric substrate layer 1.

[0026] In addition, the narrowband adjustable meta-grating structure based on the phase change material GST provided in this embodiment works in the quasi-BIC mode, and the double rectangular meta-grating layer 2 can break the inversion symmetry in the plane by changing the length L2 of the second rectangular microstructure 2-2 to form a symmetric protected quasi-continuous domain bound state (SP-BIC) with a high quality factor (Q). At the same time, 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 way for the double rectangular meta-grating layer 2 to dynamically adjust the resonance.

[0027] Figure 2 This is the transmission spectrum of the GST of this embodiment under different second rectangular microstructure lengths L2 when it is in a non-crystalline state. The horizontal axis in the figure represents the wavelength of the incident light, and the vertical axis represents the light emission transmittance (i.e., the transmission coefficient). The 5 different transmission spectrum curves in the figure are the results of simulation when the length L2 is 1.28μm, 1.305μm, 1.33μm, 1.355μm, and 1.38μm, respectively. It can be seen from the figure that when L2=1.28μm, the two rectangular microstructures have the same length. At this time, the structure is in a symmetrical state, and the resonance peak is extremely narrow and almost unobservable. As the length L2 of the second rectangular microstructure 2-2 gradually increases, the transmission valley in the transmission spectrum gradually appears, and the resonance wavelength gradually redshifts, and the resonance bandwidth gradually increases. This phenomenon shows that the resonance bandwidth of the transmission spectrum can be effectively adjusted by changing the length L2 of the second rectangular microstructure 2-2.

[0028] Figure 3 The transmission spectra of the phase change material GST at different crystal fractions X in this embodiment, the horizontal and vertical axes in the figure represent Figure 2The five different transmission spectrum curves in the figure are the simulation results when the GST crystal fraction X is 0.00, 0.25, 0.50, 0.75, and 1.00 respectively, when L2 = 1.28 μm and other parameters remain unchanged. It can be seen from the results in the figure that when X = 0, almost no peak is observed in the transmission spectrum. At this time, the loss of the bound state mode of the symmetry protection continuous domain in the structure is extremely small. As the crystal fraction of the GST layer gradually increases, the same as described above appears. Figure 2 Similarly, in the transmission spectrum, a transmission valley gradually appears and red-shifts, and the resonance bandwidth gradually increases from 0.9 nm to 33.1 nm. This phenomenon indicates that the present embodiment can realize the dynamic tuning function of the bandwidth of the tunable optical filter by controlling the resonance bandwidth through the GST crystal fraction.

[0029] Figure 4 The transmission spectra of the tunable optical filter under different incident light tilt angles of this embodiment, the horizontal axis and the vertical axis in the figure represent Figure 2 Consistent, when L2=1.28μm, X=0.5 and other parameters remain unchanged, the 6 different transmission spectrum curves in the figure are the simulation results when the incident light angles θ are 0°, 2°, 4°, 6°, 8°, and 10° respectively. It can be seen from the figure that with the increase of the incident angle, the peak position of the transmission valley in the transmission spectrum red-shifts from 3.3748μm to 3.4296μm, and the peak position moves 54.8nm within the 10° incident angle range. With the increase of the incident angle, the transmission valley value increases slightly, and the change of the incident angle has no obvious effect on the bandwidth of the resonance. This shows that the frequency selection characteristics of the filter can be realized according to actual needs through the incident angle.

[0030] Figure 5 The transmission spectra of the same resonance wavelength bandwidth adjustment under different incident light tilt angles and different GST crystal fractions in this embodiment, the horizontal and vertical axes in the figure represent Figure 2 Consistent, according to Figure 3 and Figure 4 The results show that the narrowband tunable optical filter can adjust the bandwidth by the GST crystal fraction, and the position of the resonant wavelength can be adjusted by different incident angles. Combining the above two methods, the bandwidth of the same wavelength position is adjusted by the GST crystal fraction X and the incident angle θ. The figure shows that the filter bandwidth is dynamically tuned from 4.1nm to 0.9nm. This shows that the tunable optical filter can realize the dynamic adjustable characteristics of frequency selection and resolution according to actual needs. Therefore, it can be seen that the structure has a good adjustable filtering function.

[0031] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. Mid-infrared narrowband tunable filter based on phase change material GST, characterized by: The invention comprises a dielectric substrate layer (1) and a double rectangular meta-grating layer (2) periodically distributed on the dielectric substrate layer (1); the double rectangular meta-grating layer (2) comprises a first rectangular microstructure (2-1) and a second rectangular microstructure (2-2) arranged at a certain interval; the first rectangular microstructure (2-1) is a Ge rectangular block; the second rectangular microstructure (2-2) is composed of a Ge rectangular block similar to the first rectangular microstructure and a GST phase change material block with a variable dielectric constant embedded at its bottom.

2. The mid-infrared narrow-band tunable filter based on phase change material GST according to claim 1, characterized in that: The substrate layer (1) is directly connected to a periodically distributed double rectangular meta-grating layer (2).

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

4. The mid-infrared narrow-band tunable filter based on phase change material GST according to claim 1, characterized in that: The lengths L1 and L2 of the Ge rectangular blocks in the first rectangular microstructure (2-1) and the second rectangular microstructure (2-2) 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 narrow-band tunable filter based on phase change material GST according to claim 1, characterized in that: The length a of the phase change material GST layer in the second rectangular microstructure (2-2) is 0.35 μm to 0.45 μm, the width is equal to the width W in the second rectangular microstructure (2-2), and the height h is 0.1 μm to 0.13 μm.

6. The mid-infrared narrow-band tunable filter based on phase change material GST according to claim 1, characterized in that: The interval G between the first rectangular microstructure (2-1) and the second rectangular microstructure (2-2) is 0.2 μm to 0.3 μm.

7. The mid-infrared narrow-band tunable filter based on the phase change material GST according to any one of claims 1 to 6, characterized in that: The double rectangular meta-grating layer (2) breaks the inversion symmetry in the plane by changing the length L2 of the second rectangular microstructure (2-2) and the phase state of the phase change material GST, thereby forming and controlling the high quality factor resonance peak; the resonance peak position is adjusted by the tilt angle of the incident light, 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.

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