Adjustable micro-nano grating structure based on quasi bound state in continuum

Abstract

The invention belongs to the technical field of infrared sensing and infrared light field regulation and control, and particularly relates to an adjustable micro-nano grating structure based on a quasi bound state in a continuum, the adjustable micro-nano grating structure comprises a plurality of basic units in array distribution, and each basic unit comprises a reflecting layer, a phase change layer and a phase change grating layer which are connected in sequence. The phase change layer and the phase change grating layer are made of phase change materials, and the phase change grating layer comprises at least two grating columns which are arranged at intervals and are different in width; according to the present invention, the material has the qBIC excitation capability, has the high Q characteristic, can excite the extremely narrow band emission peak within the wavelength range of 5-6 [mu] m, and has the high mid-infrared refractive index detection sensitivity; by changing the characteristics of the phase change material, the long-wave infrared emissivity of excited Fabry-Perot (FP) resonance is wide in variation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of infrared sensing and infrared light field regulation, and particularly relates to an adjustable micro-nano grating structure based on quasi-bound states in the continuum. BACKGROUND

[0002] The infrared band generally refers to infrared light with a wavelength of 0.78 microns to 300 microns, which is closely related to molecular vibration and heat energy transmission in nature. The regulation technology of the infrared light field, as an important branch of the wavefront light field regulation, has wide application prospects in many fields such as civil, military, aviation, aerospace and the like. In recent years, through the regulation of subwavelength grating structures, it is expected to realize the precise regulation of near-field radiation factors and near-field absorption factors, thereby artificially designing new quasi-bound states in the continuum (qBIC) to form a topologically protected light field resonance and stimulate an infrared narrow-band emitter with a high-quality factor. These studies deepen the understanding of the interaction between light and matter, and also study infrared spectrum sensing and detection technology from a new perspective, which is expected to break through the problems of traditional infrared spectrum equipment such as complexity, bulkiness and single measurement parameter. SUMMARY

[0003] The technical problem to be solved by the application is to provide an adjustable micro-nano grating structure based on quasi-bound states in the continuum, which has the ability to stimulate qBIC, has high Q characteristics, stimulates an extremely narrow-band emission peak in the 5-6 micron wavelength range, has high sensitivity for mid-infrared refractive index detection, and changes the long-wave infrared emissivity by changing the properties of the phase change material and stimulating the Fabry-Perot (FP) resonance.

[0004] The application provides an adjustable micro-nano grating structure based on quasi-bound states in the continuum, which comprises a plurality of array-distributed basic units, the basic unit comprises a reflection layer, a phase change layer and a phase change grating layer connected in sequence, the materials of the phase change layer and the phase change grating layer are phase change materials, and the phase change grating layer comprises at least two spaced-apart grating columns with different widths.

[0005] Preferably, the material of the reflection layer is Au, Ag, Pt, Cr, W or Ni, and the thickness is 100 nm to 1000 nm.

[0006] Preferably, the phase change material is Ge2Sb2Te5, VO2, Ge3Sb2Te6, Ge2Sb2Se4Te1 or In3SbTe2.

[0007] Preferably, the phase change material is Ge2Sb2Te5 or Ge3Sb2Te6.

[0008] Preferably, the thickness of the phase change layer is 40nm~1000nm, more preferably 40~110nm or 130~160nm.

[0009] Preferably, the thickness of the phase change grating layer is 100nm~1000nm.

[0010] Preferably, the periodic unit cell of the phase change grating layer includes two grating pillars with different widths spaced apart, the total periodic width of the two grating pillars is 600nm~20000nm, and the width ratio of the two grating pillars is 0.5~1:1.

[0011] Preferably, the total width of the period is 600~1400nm, and the width ratio of the two grating pillars is 0.6~0.9:1.

[0012] The beneficial effects of this invention are that it combines the high quality factor of qBIC with the tunable characteristics of phase change materials, achieving decoupling of multi-band characteristics and compatibility of multiple functions. Through modulation of the phase change material, this invention achieves both high-quality narrowband emission and dynamically adjustable long-wave infrared (8~14 μm) emissivity, making this device promising for integration with multi-functional technologies such as infrared refractive index sensing, molecular spectroscopy detection, and infrared thermal information encoding.

[0013] This invention achieves narrowband emission at 5.46 μm in an amorphous state of a phase change material, with a full width at half maximum (FWHM) of 28 nm and a q-factor greater than 195. When used for material detection, the high-quality factor resonance peak is extremely sensitive to minute changes in refractive index, exhibiting a sensitivity of 460 nm / RIU. High-resolution observation of the material's spectral information can be achieved through resonance peak modulation. Furthermore, the phase transition of the phase change material can excite the mid-infrared FP resonance, thereby enabling multi-bit thermal information representation in the long-wave infrared range. The average emissivity in the long-wave infrared range can be tuned between 0.02 and 0.57. The results demonstrate that the proposed device can achieve high-precision sensing of infrared refractive index and encoding of at least 10 bits of infrared thermal information.

[0014] This invention features a phase change grating layer on a phase change layer. The phase change grating layer comprises at least two spaced grating pillars of different widths, which are also made of phase change material. The presence of the phase change grating layer and the different widths of the grating pillars enable it to excite a high quality factor qBIC, which generates an extremely narrow band emission peak in the 5-6 μm wavelength range and exhibits high sensitivity for mid-infrared refractive index detection. The high phase change material is used to excite and modulate FP resonance, and the long-wave infrared emissivity varies widely. Attached Figure Description

[0015] Figure 1 This is a two-dimensional structural schematic diagram of an embodiment of the present invention.

[0016] Figure 2 This is a three-dimensional structural diagram of an embodiment of the present invention.

[0017] Figure 3 The graph shows the variation of the quality factor Q value of the structure in the embodiment of the present invention with t2.

[0018] Figure 4 For the structure of the embodiment of the present invention under different values ​​of the conserved quantity D, Δ x The relationship between the distribution of Q-values.

[0019] Figure 5 The emission (absorption) spectrum of the structure in the amorphous state according to an embodiment of the present invention is shown.

[0020] Figure 6 The infrared spectrum under background refractive index variation in an embodiment of the present invention is shown.

[0021] Figure 7 This is a long-wave infrared emissivity encoded spectrum during the phase transition process in an embodiment of the present invention.

[0022] In the figure, 1 is the reflective layer, 2 is the phase change layer, 3 is the phase change grating layer, 31 is grating pillar I, and 32 is grating pillar II. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1 A tunable micro / nano grating structure based on quasi-bound states in a continuum comprises multiple arrayed basic units, such as... Figures 1-2 As shown, the basic unit includes a reflective layer 1 (i.e., ...) connected in sequence. Figures 1-2 The yellow part A), phase change layer 2 (i.e. Figures 1-2 The blue part B) and the phase change grating layer 3 (i.e. Figures 1-2 (Part C in blue) The phase change layer 2 and the phase change grating layer 3 are made of phase change material. The phase change grating layer 3 includes at least two grating pillars with different widths spaced apart. Figures 1-2 The image shows two grating columns with different widths spaced apart, namely grating column I 31 and grating column II 32.

[0025] The tunable micro / nano grating structure described in this invention can be deposited on any smooth substrate surface to achieve infrared functionality. Selectable substrate materials include Si, SiO2, aerogel, PMMA, PET, PI, etc. The reflective layer 1 is made of metal and its thickness meets the requirements for thick optical films (thickness t1 is between 100nm and 1000nm). Selectable materials include Au, Ag, Pt, Cr, W, Ni, etc., with Au being the preferred material.

[0026] Phase change layer 2 is a phase matching layer. The phase change layer 2 and phase change grating layer 3 are made of phase change materials. Optional phase change film materials include Ge2Sb2Te5, VO2, Ge3Sb2Te6, Ge2Sb2Se4Te1, In3SbTe2, etc., with GST material being preferred, i.e., Ge2Sb2Te5 or Ge3Sb2Te6.

[0027] like Figure 1 As shown, the thickness t1 of reflective layer 1 is between 100nm and 1000nm; the thickness t2 of phase change layer 2 is between 40nm and 1000nm; the thickness t3 of phase change grating layer 3 is between 100nm and 1000nm; half the length P of the basic unit is between 300nm and 10000nm; and the length x1 of grating pillar I 31 and the length x2 of grating pillar II 32 are between 100nm and 9000nm.

[0028] Preferably, the thickness of the phase change layer 2 is 40~110nm or 130~160nm, the total width of the period of the two grating pillars is 600nm~20000nm, and the width ratio of the two grating pillars is 0.5~1:1. More preferably, the total width of the period is 600~1400nm, and the width ratio of the two grating pillars is 0.6~0.9:1.

[0029] When the reflective layer 1 is made of gold, the thickness of t1 is preferably 150 nm to achieve a good reflective effect.

[0030] In this embodiment, the basic unit length 2P is determined to be 2000nm (the length of 2P can be other lengths, which are only used as examples here), and the phase change layer 2 and the phase change grating layer 3 are made of GST.

[0031] like Figure 2 As shown, in the y-direction perpendicular to the arrangement direction of multiple grating pillars (i.e., the x-direction), the grating pillars and the basic unit are of equal length, meaning the grating pillars extend to the edge of the basic unit. Thus, after the multiple basic unit arrays are distributed, the grating pillars are continuous in the y-direction.

[0032] like Figure 2 As shown, the two-dimensional grating structure extends infinitely along the Cartesian coordinate axis y-axis, the incident light wave vector k is along the z-direction, and the electric field vibrates along the x-direction. According to the qBIC formation principle, topology protection is achieved by the periodic conservation of the bulk modulus of the micro / nano grating, which can be expressed as: .

[0033] The condition for achieving topology protection is that the sum of x1 and x2 is a constant value, x1 + x2 = D, that is, D is a constant value.

[0034] The resonant wavelength formed by qBIC is determined by the conserved quantity D and the thickness t2 of phase transition layer 2, that is: .

[0035] In order to keep the resonant wavelength in the mid-infrared band and to excite the long-wave infrared absorption peak in the phase transition state, the total thickness of t2 and t3 is preferably t2+t3=500nm.

[0036] When x1 and x2 are 400nm and 600nm respectively, for the same total thickness, parameter space optimization was performed for different t2 and t3. The goal of the optimization was to find the qBIC state evaluation interval with a higher quality factor (Q).

[0037]

[0038] like Figure 3 As shown, with a Q value greater than 100 as a quality factor evaluation, it can be seen that when the t2 thickness is between 50 nm and 150 nm, the resulting structure can excite a qBIC resonance with a high quality factor. To meet the requirements of grating fabrication process and error control, preferably, t2 = 350 nm and t3 = 150 nm.

[0039] The range of the conserved quantity D is set to 600~1800nm. The grating structure is optimized by scanning the parameter spaces x1 and x2 in different conserved quantities D. The goal of the optimization is to find the qBIC state with the optimal quality factor (Q).

[0040]

[0041] Based on the relationship between D and x1 and x2, x1 and x2 can be written as (D+△x) / 2 and (D-△x) / 2 respectively. The above formula can be written as...

[0042] Figure 4 The distribution relationship between Δx and Q values ​​in the parameter optimization interval is presented under different values ​​of the conserved quantity D. In particular, as shown in Table 1, the Q value distribution in the preferred region is given. Taking a conserved quantity of 1400 as an example, in the parameter optimization space distribution, when the Δx:D ratio is between 5% and 25%, a qBIC resonance with high Q (Q>100) topology protection can be excited. After parameter space scanning, when D=1400nm and Δx=70, the optimal parameters x1 and x2 are obtained as 630nm and 770nm, respectively.

[0043] Table 1: Preferred Structural Parameter Dataset

[0044] " / " indicates that the Q factor is less than 100 under this structural parameter.

[0045] In terms of fabrication method, Au and GST multilayer thin film structures were physically deposited using magnetron sputtering. First, a reflective layer 1 (Au) and a phase change layer 2 (GST) were deposited on a substrate. Au and GST thin films were deposited using both DC and RF modes, respectively. The sputtering targets for both films were 99.99% pure Au and GST targets. The vacuum level inside the magnetron sputtering chamber was less than 5 × 10⁻⁶. -4 The beam power of Pa and Au is 30W, and the beam power of GST is 100W. The coating rates of Au optical film and GST optical film are 1 nm / s and 0.5 nm / s, respectively.

[0046] Subsequently, a spin-coating-etching-deposition-lift-stripping process was used to fabricate the GST grating micro / nano structure. A negative photoresist was heated and spin-coated to 800 nm. EBL etching was then used to form the required two-dimensional grating grooves, resulting in staggered two-dimensional grating pattern grooves of 630 nm and 770 nm. Further, the method for preparing the GST film by magnetron sputtering was repeated to deposit a 150 nm thick GST film. The unetched negative photoresist was then lifted using an organic solvent to obtain the final infrared-tunable micro / nano grating structure.

[0047] The optimal parameters for Embodiment 1 of the present invention are: The basic unit 2P has a length of 2000nm, and the reflective layer 1 is made of gold with a thickness t1 of 150nm. The phase change layer 2 and the phase change grating layer 3 are made of GST. The thickness t2 of the phase change layer 2 is 150 nm and the thickness of the phase change grating layer 3 is 350 nm.

[0048] The width x1 of grating pillar I 31 is 630 nm, and the width x2 of grating pillar II 32 is 770 nm.

[0049] Comparative Example 1 Based on Example 1, the phase change grating layer 3 is removed, and everything else is the same as in Example 1.

[0050] Comparative Example 2 Based on Example 1, the widths of grating pillar I 31 and grating pillar II 32 are both 700 nm, and everything else is the same as in Example 1.

[0051] Figure 5 The emission (absorption) spectra of the amorphous state in Example 1 and Comparative Examples 1-2 are given. It can be seen that the resonant wavelength of Example 1 is located at 5.46 μm, its full width at half maximum (FWHM) is 28 nm, and its Q value is 195. Compared with the traditional emitter structure (Q≈10), the Q value of the infrared grating micro / nano structure of the present invention is improved by one order of magnitude.

[0052] also, Figure 5It can also be seen that the two structures in Comparative Examples 1-2 do not have the ability to excite qBIC, the excited FP resonances do not have high Q characteristics, and they cannot excite extremely narrow band emission peaks in the 5~6μm wavelength range.

[0053] Example 2 like Figure 6 As shown, by changing the background refractive index, numerical simulations were performed on materials with varying refractive indices, from air (n=1) to calcium fluoride substrate (n=1.4) to zinc sulfide substrate (n=2.2). The resonant peak position redshifted from 5.46 μm to 6.1 μm as the background refractive index changed from 1 to 2.4. The obtained structure achieved an average mid-infrared refractive index detection sensitivity of up to 460 nm / RIU.

[0054] like Figure 7 As shown, the ability to encode gradient long-wave infrared thermal information is demonstrated. By modulating the doping coefficient of GST material, a 10-bit long-wave infrared emissivity variation can be achieved, with the emissivity variation range between 0.02 and 0.56.

[0055] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0056] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A tunable micro / nano grating structure based on quasi-bound states in a continuum, characterized in that, It includes multiple array-distributed basic units, each of which includes a reflective layer (1), a phase change layer (2), and a phase change grating layer (3) connected in sequence. The phase change layer (2) and the phase change grating layer (3) are made of phase change materials. The phase change grating layer (3) includes at least two grating pillars with different widths that are spaced apart.

2. The tunable micro / nano grating structure as described in claim 1, characterized in that, The material of the reflective layer (1) is Au, Ag, Pt, Cr, W or Ni, and the thickness is 100nm~1000nm.

3. The tunable micro / nano grating structure as described in claim 1, characterized in that, The phase change material is Ge2Sb2Te5, VO2, Ge3Sb2Te6, Ge2Sb2Se4Te1 or In3SbTe2.

4. The tunable micro / nano grating structure as described in claim 3, characterized in that, The phase change material is Ge2Sb2Te5 or Ge3Sb2Te6.

5. The tunable micro / nano grating structure as described in claim 1, characterized in that, The thickness of the phase change layer (2) is 40nm~1000nm.

6. The tunable micro / nano grating structure as described in claim 5, characterized in that, The thickness of the phase change layer (2) is 40~110nm or 130~160nm.

7. The tunable micro / nano grating structure as described in claim 1, characterized in that, The thickness of the phase change grating layer (3) is 100nm~1000nm.

8. The tunable micro / nano grating structure as described in claim 1, characterized in that, The periodic cell of the phase change grating layer (3) includes two grating pillars with different widths spaced apart. The total periodic width of the two grating pillars is 600nm~20000nm, and the width ratio of the two grating pillars is 0.5~1:

1.

9. The tunable micro / nano grating structure as described in claim 8, characterized in that, The total width of the period is 600~1400nm.

10. The tunable micro / nano grating structure as described in claim 8, characterized in that, The width ratio of the two grating pillars is 0.6~0.9:1.

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