CN115507948A - Optical filter of spectrometer, manufacturing method and spectrum reconstruction method - Google Patents

Abstract

The application provides a spectrometer filter, its production and spectral reconstruction method, the filter comprising: a substrate; a bottom silicon photonic crystal plate and a top silicon photonic crystal plate, located on one side of the substrate; a spacer, located on the bottom silicon photonic crystal plate Between the photonic crystal plate and the top silicon photonic crystal plate; wherein the side of the substrate close to the bottom silicon photonic crystal plate, and the side of the spacer close to the top silicon photonic crystal plate form a pattern, the spacer, the The bottom silicon photonic crystal plate and the top silicon photonic crystal plate form a cavity, so that the application avoids the stress problem caused by repeated thin film deposition caused by the microfabrication method, and at the same time, the optical filter obtained by transfer printing can change the spectrum by changing the driving voltage value The cavity length displacement can be adjusted, so that the optical performance parameters of the filter can be adjusted. When performing spectral reconstruction, a large number of pixels do not need to provide spectral data, and a large amount of spectral information can be obtained only by adjusting the voltage.

Description

Spectrometer filter, production and spectral reconstruction method

technical field

The present application relates to the technical field of spectral analysis, in particular to a spectrometer filter, its production and its spectral reconstruction method.

Background technique

Miniaturized spectrometers in the mid-infrared range can be used in fields such as environmental monitoring, biosensing, and free space communication. The prior art miniaturized spectrometers are mainly computational spectrometers based on wavelength reconstruction methods, which have an ultra-compact footprint. However, , the prior art requires multiple pixel arrays, which inevitably increases the complexity and occupied space of the device, and has many disadvantages.

Contents of the invention

The present application provides a spectrometer filter, its production and its spectral reconstruction method, aiming to solve the problem that the current prior art requires multiple pixel arrays, which inevitably increases the complexity and space of the device.

The embodiment of the first aspect of the present application provides a spectrometer filter, including:

Substrate;

a bottom silicon photonic crystal plate and a top silicon photonic crystal plate on one side of the substrate;

a spacer between the bottom silicon photonic crystal plate and the top silicon photonic crystal plate; wherein the side of the substrate close to the bottom silicon photonic crystal plate and the side of the spacer close to the top silicon photonic crystal plate form a pattern, The spacers, the bottom silicon photonic crystal plate and the top silicon photonic crystal plate form a cavity.

In a preferred embodiment, the bottom silicon photonic crystal plate and the top silicon photonic crystal plate are etched with a plurality of periodic holes.

In a preferred embodiment, electrodes are disposed on the substrate and the spacer.

In a preferred embodiment, it also includes:

An electrical isolation layer is disposed between the spacer and the bottom silicon photonic crystal plate.

The embodiment of the second aspect of the present application provides a method for manufacturing a spectrometer filter, including:

forming substrates and spacers;

patterning a bottom silicon photonic crystal plate and a top silicon photonic crystal plate;

transferring the patterns of the bottom silicon photonic crystal plate and the top silicon photonic crystal plate to transfer printing stamps, respectively;

transferring the pattern on the transfer printing stamp to the spacer and the substrate, respectively;

The bottom silicon photonic crystal plate, the spacers, and the top silicon photonic crystal plate were assembled on the substrate.

In a preferred embodiment, further comprising: depositing a conductive medium on the substrate and the spacer to form electrodes.

In a preferred embodiment, said patterning a bottom silicon photonic crystal plate and a top silicon photonic crystal plate comprises:

Patterning the silicon wafer to form a mask;

applying photoresist to the bottom silicon photonic crystal plate and the top silicon photonic crystal plate;

placing the masks on the bottom silicon photonic crystal plate and the top silicon photonic crystal plate respectively, and exposing for a set duration;

The bottom and top silicon photonic crystal plates are cured to obtain patterned bottom and top silicon photonic crystal plates.

In a preferred embodiment, the silicon wafer is patterned to form a mask, including:

patterning on the silicon wafer to form a rectangular array with a set period and width;

Etching the silicon wafer to form the mask.

The embodiment of the third aspect of the present application provides a spectral reconstruction method, including:

Apply different voltages to the filter shown above, and collect the spectral information of the measured sample;

A standard transmission spectrum is reconstructed from the spectral information.

It can be seen from the above technical solution that the present application provides a spectrometer filter, manufacturing and spectral reconstruction method, by combining transfer printing into the spectral filter, placing the patterned top photonic crystal plate and the bottom photonic crystal plate in the interval Objects and substrates, the patterned silicon film is transferred from the photonic crystal plate to the spacers and substrates by transfer printing, thereby avoiding the stress problem caused by repeated thin film deposition caused by microfabrication methods, and the filter obtained by transfer printing The cavity length displacement of the spectrum can be adjusted by changing the driving voltage value, so that the optical performance parameters of the filter can be adjusted. When performing spectral reconstruction, a large number of pixels do not need to provide spectral data, and a large amount of spectral information can be obtained only by adjusting the voltage. .

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are For some embodiments of the present application, those of ordinary skill in the art can also obtain other drawings based on these drawings without creative effort.

Figure 1a is a schematic diagram of a tunable Fabry Perot filter in an embodiment of the present application, Figure 1b is a schematic diagram of periodic holes, and Figure 1c is a schematic diagram of the principle of spectral information reconstruction in this application.

Fig. 2 is a schematic diagram of the manufacturing process of the tunable FPF in the embodiment of the present application.

(a)-(c) in Fig. 3 are the OM images during the transfer of the top PCS to the silicon spacer, (d)-(e) the OM images during the transfer of the bottom PCS to the CaF substrate, ( _f )–(h) OM images during the transfer of the top PCS with spacers to the substrate.

(a) in Figure 4 is a schematic diagram of the structure of 300nm _SiO2 on a <100> silicon wafer, (b) is a schematic diagram of the process of etching 300nm _SiO2 , (c) is a schematic diagram of wet etching silicon in KOH solution, (d) is a schematic diagram of SU8 exposure, (e) is a schematic diagram of pouring PDMS base material and agent into a mold for curing, (f) is a scanning electron microscope image of a PDMS stamp.

(a) in Figure 5 is a schematic diagram of the structure of 300nm SiO ₂ placed on a <100> silicon wafer, (b) is one of the schematic diagrams of wet etching SiO ₂ in KOH solution, (c) wet etching in KOH solution ₍ d) is a schematic diagram of SU8 exposure, (e) is a schematic diagram of pouring PDMS base material and agent into a mold and curing.

Figure 6a is the simulated transmission spectrum of PCS suspended in air, Figure 6b is the simulated transmission spectrum of PCS suspended in _CaF2 , Figure 6c and Figure 6d show the similar transmission spectrum and electric field distribution of PCS on _CaF2 , Figure 6e is a simulated Fabry Perot filter spectrum with a cavity length of 3.4 μm, and Figure 6f is its electric field distribution at the shaded wavelength of the first-order FP resonance.

Figure 7a is the transmission spectrum of the Fabry Perot filter measured at a driving voltage of 0 to 70V, Figure 7b is its intensity map, and Figure 7c is the peak value of the Fabry Perot filter at different driving voltages Schematic representation of wavelength and fitted shift. Figure 7d is a schematic diagram of the Fabry Perot filter transmission spectra measured at 0 and 68V for carbon dioxide (CO ₂ ) and acetone (C ₃ H ₆ O) as analytes.

Fig. 8 is a schematic diagram of the test setup in the embodiment of the present application.

Figure 9a is the filter matrix measured from 4 to 5 μm, Figure 9b is the correlation coefficient matrix of the filter matrix, Figure 9c is a schematic diagram of the measured tuning spectrum of the Fabry Perot filter with _CO2 as the analyte, Fig. 9d is a schematic diagram of the comparison between the measured (black line) reference spectrum and the reconstructed spectrum (orange dots) of _CO2 absorption.

Fig. 10a is a schematic diagram of the _CO2 transmission spectrum reconstructed with different random noise levels from 2.5% to 0%, Fig. 10b is a schematic diagram of the noise measured in 25 tuning states, and Fig. 10c is a Gaussian dip in the ideal case without measurement noise Schematic diagrams of the reconstruction of 10 and 25 input states, Figure 10d is a schematic diagram of the reconstruction of the step function with 10 and 25 input states in the ideal case without measurement noise.

Fig. 11 is a schematic diagram of the logic flow of the Tikhonov regularization method in the embodiment of the present application.

Fig. 12 is a schematic diagram of simulating the tuning spectrum of a Fabry Perot filter from 2 to 20 μm by changing the parameters of PCS in the embodiment of the present application.

detailed description

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined. It should be noted that the spectrometer filter, production and spectral reconstruction method disclosed in this application can be used in the field of display technology, and can also be used in any field other than the field of display technology. The spectrometer filter, production and spectral reconstruction method disclosed in this application The field of application of the reconstruction method is not limited.

Miniaturized spectrometers in the mid-infrared range in the current exemplary technology can be fabricated by bulk micromachining or surface micromachining. The former creates air cavities through wafer bonding and requires complex wafer etching. The latter, which creates air cavities through the deposition and release of a sacrificial layer, is more popular due to its low cost, however, the thickness of the sacrificial layer is limited to around 3 μm due to the accumulated stress in chemical vapor deposition, which can lead to wafer bending or even cracking , in addition, for computational spectrometers based on wavelength reconstruction methods, which have an ultra-compact footprint, but currently require multiple pixel arrays to collect spectral information, which inevitably increases the complexity of the device while occupying too much space , is not conducive to the development of miniaturization.

Figure 1a shows a spectrometer filter in the embodiment of the present application, as shown in Figure 1a, including: a substrate 1; a bottom silicon photonic crystal plate 2 and a top silicon photonic crystal plate 4, located on one side of the substrate; The spacer 3 is located between the bottom silicon photonic crystal plate and the top silicon photonic crystal plate; wherein the substrate 1 is close to the side of the bottom silicon photonic crystal plate 2, and the spacer 3 is close to one side of the top silicon photonic crystal plate 4 The side forms a pattern, and the spacer, the bottom silicon photonic crystal plate and the top silicon photonic crystal plate form a cavity.

The spectrometer filter provided by this application, by combining the transfer printing into the spectral filter, the patterned top photonic crystal plate and the bottom photonic crystal plate are placed on the spacer and the substrate, and the patterned silicon film is transferred by transfer printing Transfer from the photonic crystal plate to the spacer and the substrate, thereby avoiding the stress problem caused by repeated thin film deposition caused by the microfabrication method, and the optical filter obtained by transfer printing can adjust the cavity length shift of the spectrum by changing the driving voltage value , so that the optical performance parameters of the filter can be adjusted. When performing spectral reconstruction, a large number of pixels do not need to provide spectral data, and a large amount of spectral information can be obtained only by adjusting the voltage.

It can be understood that the spectrometer filter of the present application may be called a tunable Fabry Perot filter (Fabry Perot filter, FPF) because of its tuning function.

In the embodiment of the present application, the material forming the photonic crystals lab (PCS) is silicon, and the semiconductor silicon migrates under electric drive, so that the patterned silicon film on the top photonic crystals lab is transferred to the spacer, and the bottom photonic crystals The patterned silicon film on the plate is transferred to the substrate.

It can be understood that the spacer in the present application is generally a silicon spacer, such as a spacer formed of silicon material. The transfer printing method circumvents the stress limitation by creating the resonant cavity by transferring the reflector onto a spacer, which is the device layer from the SOI wafer. The thickness of this spacer may be much greater than that produced by the sacrificial layer.

Specifically, the schematic diagram of the transfer-printed tunable Fabry Perot interference filter is shown in Figure 1. The filter of the present application consists of a top PCS, a silicon gasket and a bottom PCS. These three components are in silicon technology (SiliconOnInsulator, SOI) wafers are fabricated separately, and then assembled to infrared transparent substrates (such as calcium fluoride, CaF ₂ ).

In a preferred embodiment, calcium fluoride (CaF ₂ ) is used as the substrate of the present application. Of course, other optional infrared transparent substrates may also be used in other embodiments of the present application, and the present application is not limited thereto. In this preferred embodiment, the substrate formed of calcium fluoride has an infrared transparent window reaching a wavelength of 8 μm and a refractive index (refractive index, RI) of 1.4.

In a preferred embodiment, in order to avoid the stress problem of the distributed Bragg reflector (distributedBraggreflectors, DBR) and the sacrificial layer during the film deposition process, the filter of this embodiment is transferred to another Si film on the top and bottom, respectively. On the basis of a thicker Si spacer and a _CaF2 substrate to realize the air cavity between the two PCS reflectors, periodic holes are further etched on the top and bottom Si films, and the incident light is generated through the periodic holes. The phase matching condition is coupled into the PCS.

Furthermore, in a preferred embodiment, the top PCS or the bottom PCS of the present application is a single Si layer with a thickness of 500 nm, which is different from a DBR comprising multiple alternating quarter-wavelength thick layers , the reflectivity of PCS is achieved by guided resonance, rather than Fresnel reflection that occurs at material boundaries with different RIs, so the spectral information can be tuned by adjusting the cavity length of the resonant cavity.

In order to electrostatically drive the FPF, as shown in FIG. 1 c , in a preferred embodiment of the present application, electrodes are provided on the substrate 1 and the spacer 3 . Specifically, taking the aforementioned Si spacer and CaF substrate as an example, gold (Au ₎ can be deposited _on the Si spacer and CaF substrate as top and bottom electrodes, and the top electrode also serves as a bond between Au and the top Si interface.

Further preferably, the present application further includes: an electrical isolation layer disposed between the spacer and the bottom silicon photonic crystal plate.

More specifically, the electrical isolation layer can be a gap, specifically, a gap can be etched on the silicon pad to electrically isolate the top layer and the bottom layer. When a voltage is applied between the top and bottom electrodes, an electrostatic force is generated that pulls down the top Si film of the PCS, and this force is balanced by the restoring force of the V-shaped beams arranged around it, thereby determining the final displacement. The reduced air cavity length enables The resonant peaks of the FPF are blue-shifted and create a set of substrates for spectral reconstruction. Figure 1(b) is a false-color scanning electron microscope (SEM) image of the transferred FPF. The inset shows the magnification of the bilayer photonic crystal, the middle There is an air cavity.

It can be known from the above embodiments that the present application integrates transfer printing into the spectral filter, places the patterned top photonic crystal plate and the bottom photonic crystal plate on the spacer and the substrate, and transfers the patterned silicon film Transfer from the photonic crystal plate to the spacer and the substrate, thereby avoiding the stress problem caused by repeated thin film deposition caused by the microfabrication method, and the optical filter obtained by transfer printing can adjust the cavity length shift of the spectrum by changing the driving voltage value , so that the optical performance parameters of the filter can be adjusted. When performing spectral reconstruction, a large number of pixels do not need to provide spectral data, and a large amount of spectral information can be obtained only by adjusting the voltage.

The embodiment of the second aspect of the present application provides a method for manufacturing a spectrometer filter, including:

S1: Formation of substrates and spacers.

Exemplarily, the substrate may be a CaF ₂ substrate, and the spacer is a silicon spacer formed of simple silicon, which will not be described in detail here.

S2: Patterning a bottom silicon photonic crystal plate and a top silicon photonic crystal plate.

Exemplarily, in this step, an SOI wafer with a device layer with a thickness of 500 nm can be patterned, and the patterning can adopt commonly used processes such as exposure, development, and etching, which are not limited in this application.

S3: Transfer the patterns of the bottom silicon photonic crystal plate and the top silicon photonic crystal plate to transfer printing stamps respectively.

In a preferred embodiment, as shown in FIG. 2, the present application can be implemented as a polydimethylsiloxane (PDMS) transfer stamp with microstructured pyramids.

Specifically, as shown in FIG. 2, the specific treatment process for the substrate 1, the bottom silicon photonic crystal plate 2, the spacer 3, and the top silicon photonic crystal plate 4 is as follows, the electrode region 11 is etched on the substrate 1, and then the electrode region 11 is etched. Deposit electrodes 12 in the area, form a pattern on the bottom silicon photonic crystal plate 2, place the stamp in the spacer, assemble the bottom silicon photonic crystal plate 2 and the top silicon photonic crystal plate 4 in pairs, and press the PDMS stamp 5 into the The silicon film of the pattern of the bottom silicon photonic crystal plate 2 and the top silicon photonic crystal plate 4 is fully contacted, so that the pyramids are "collapsed", thereby maximizing the contact area and surface adhesion.

S4: Transfer the pattern on the transfer printing stamp to the spacer and the substrate respectively.

The imprint is then quickly retracted, and only the tip of the pyramid is in contact with the silicon membrane after retraction, so that the surface adhesion between the stamp and the silicon membrane is minimized, and it is easier to align the silicon membrane to any position at this time.

By aligning the position of the silicon film, the silicon film is kept on the substrate and the silicon spacer, and finally the stamp is slowly retracted to complete the transfer printing.

S5: Assembling the bottom silicon photonic crystal plate, the spacer, and the top silicon photonic crystal plate on the substrate.

After the transfer printing is completed, the top and bottom silicon photonic crystal plates and silicon spacers are assembled on the substrate to form optical filters.

In a specific embodiment, two ink films and two receivers are manufactured separately and then assembled. The two ink films are top PCS and bottom PCS, patterned in a preferred embodiment from a SOI wafer with a 500nm thick device layer. The 2 μm thick buried oxide is then wet etched in dilute hydrofluoric acid (DHF), followed by a drying process in a critical point dryer for suspension. After suspension, the two inks were transferred to their corresponding receiver substrates, which were suspended Si spacers with bottom electrodes and _CaF2 substrates, respectively, and the Si spacers consisted of highly doped SOI for 5.2 μm device layers. The wafer was patterned and its surface was deposited with Au as the bonding interface. After transferring the top PCS to the suspended Si spacer, it was annealed in a furnace at 360 °C for half an hour to diffuse the Au particles into the Si and form an Au-Si alloy.

In this embodiment, as shown in Figure 3, the adhesion between the top PCS and the Si spacer is crucial, since it not only fixes the membrane but also reduces its contact resistance for electrostatic actuation. The above annealing was performed before assembling the whole device on the CaF ₂ substrate, due to the thermal expansion coefficient mismatch between CaF ₂ (18.85x10 ^-6 /°C) and Si (2.6x10 ^-6 /°C). This mismatch can crack the Si spacer and cause the top Si film to warp. After annealing, the top PCS and the underlying Si spacer were retrieved together by another hollow PDMS stamp so as not to damage the top PCS suspended in the middle. They are finally printed onto the _CaF2 substrate through the bottom PCS and the bottom electrode, completing the whole transfer process.

Currently, transfer printing is done under a 50x optical microscope using a manual micropositioner, so alignment accuracy is limited to the micrometer level. Since the two PCSs are placed vertically, far away from each other, and they only show the far-field behavior as two separate reflectors, it does not affect the optical performance of the FFF. The Fano resonance occurs only when the two PCS are placed close together, in which case the lateral displacement between the holes of the two PCS can tune the near-field coupling and the Fano resonance.

In a preferred embodiment, the transfer printing can also be completed electrically, and the alignment accuracy is only required to be ±1.5 μm, which will not be repeated here.

In addition, in a preferred embodiment, step S2 of this application specifically includes:

S21: patterning the silicon wafer to form a mask;

S22: coating photoresist on the bottom silicon photonic crystal plate and the top silicon photonic crystal plate;

S23: placing masks on the bottom silicon photonic crystal plate and the top silicon photonic crystal plate respectively, and exposing for a set duration;

S24: curing the bottom silicon photonic crystal plate and the top silicon photonic crystal plate to obtain patterned bottom silicon photonic crystal plate and top silicon photonic crystal plate.

In a preferred embodiment, the silicon wafer is patterned to form a mask, including:

patterning on the silicon wafer to form a rectangular array with a set period and width;

Etching the silicon wafer to form the mask.

Exemplarily, as shown in Fig. 4, PDMS stamps were fabricated from 300 nm _SiO2 on a <100> silicon wafer, and the _SiO2 was first patterned into a square array with 45 μm period and 15 μm width.

The Si is then wet etched using 30% KOH to create reverse pyramids, where the _SiO2 layer serves as a hard mask. SU83050 was spin-coated at 1000 rpm to about 100 μm on the sample and exposed. Leave the mold in the air for a day before pouring the PDMS substrate and reagents.

In a preferred embodiment, the mixing ratio is 5:1 instead of the conventional 10:1, so as to obtain better elasticity. Finally, the PDMS was cured on a hot plate at 65 °C for 2 h and peeled off.

It can be understood that, as shown in Figure 5, the process flow of the hollow PDMS stamp is similar, but the layout of the SU8 exposure is different, the center is covered by SU8, so this area does not touch the sample, that is, the suspended top PCS.

Next, a simulation verification is carried out on the optical filter manufactured by the above-mentioned method of the present application.

The design of the PCS reflector and V-beam actuator used in the tunable Fabry Perot filter of the present application is shown in Fig. 6 .

Figure 6a is the simulated transmission spectrum of suspended PCS in air (period a = 1.8 μm, radius r = 0.67 μm), the transmittance of suspended PCS reaches zero at 3.37 μm, and gradually increases to 0.57 at 8 μm, this behavior Attributed to guided resonance37,38.

Figure 6b is the resonant electric field distribution of the cross-section of the suspended PCS unit cell, as shown by the blue line in Figure 6(a), two hot spots appear at the edge of the hole along the polarization direction of the incident light, showing strong resonance.

Due to the presence of the low-index substrate, the transmission spectrum of the bottom PCS _on CaF in Fig. 6c is slightly red-shifted compared with that of the suspended PCS. Its resonant electric field distribution at the same section is shown in Figure 6d. Two PCS reflectors are vertically stacked by transfer printing to form a Fabry-Perot (FP) cavity, and its spectrum at a cavity length of 3.4 μm is shown in Figure 6e As shown, first-order and second-order FP resonances are observed.

In the preferred embodiment, since the second-order FP resonance is difficult to detect, such as two perfectly parallel PCS reflectors and a plane wave as the incident light, this non-ideal situation is unavoidable in the experiment, so high Q is difficult to measure . In addition, the tuning range of the high-order FP resonance is also smaller than that of the low-order mode, therefore, for the measurement feasibility and wider tuning range, the first-order FP resonance is chosen, whose electric field distribution is shaded at the FP resonance in Fig. 6(f) The simulations were carried out at the wavelength.

In the embodiment of the present application, in the adjustable FPF, it is very important to maintain the flatness of the membrane and the performance of the FPF during driving, and the initial cavity length is set to 3.4 μm.

In the preferred embodiment, the photonic crystal region within the middle 200×200 μm black dotted line is omitted to save analog memory, and a displacement of 1.03 μm is achieved under a bias of 80V.

In this example, the V-beam actuator is stiffer and results in a higher drive voltage, yet recovers intact, compared to a softer actuator with a longer and narrower beam (e.g. meander shape) at Easily corrupted during retrieval.

In this application, when the characterization of the tunable Fabry Perot filter is fabricated, the FPF is characterized by a Fourier transform infrared (FTIR, AgilentCary620) spectrometer, and the FPF spectrum measured at a driving voltage of 0 to 70V is normalized normalized and plotted in Figure 7a.

In this application the displacement is determined by changing the cavity length so that the simulated resonant peak wavelength matches the measured result, in the specific application, due to the imperfection of the transfer process and the potential film deformation during the annealing, so although the Si spacer The thickness is about 5.2 μm, but the initial gap of the fabricated FPF was determined to be 3.4 μm. Compared with the simulated spectrum, it can be observed that the resonance peak is broadened, which may be caused by the tilt of the FPF membrane, and another reason is that the incident light of the FTIR is a light cone with all incident angles reaching 45 degrees, rather than being collimated beam.

Figure 7b is an intensity plot of the spectra measured in Figure 7a, and Figure 7c summarizes their peak wavelength/shift versus applied voltage. When a voltage of 70 V was applied, the peak position was adjusted from 5.61 to 4.13 μm wavelength. Since there is a fully etched photonic crystal region in the center, the maximum adjustable displacement of 1.1 μm is close to 1/3 of the gap, beyond which a pull-in effect occurs, and the driving voltage is slightly smaller than the simulation result.

In the embodiment of the present application, by optimizing the actuator design and annealing conditions to reduce the contact resistance, the actuation voltage can be further reduced, and at the same time, the FWHM is reduced from 1.09 to 0.41 μm. This trend is consistent with the simulated reflectance spectra of PCS on _CaF2 and suspended PCS in Fig. 6a and (b), where the reflectance increases at shorter wavelengths.

In the embodiment of this application, in order to demonstrate the gas sensing of the FPF, the FPF is fixed on a gas chamber, which is located on the optical path of the FTIR. When the FPF spectrum is tuned at 0 and 68V, the resonance peak shift of 1.48 μm is respectively The main molecular fingerprints of _CO2 and acetone at 4.26 and 5.75 μm are covered, as shown in Fig. 7d, and these two gases can be monitored in human exhaled breath for applications such as healthcare. The entire test setup with gas supply and electrical connections is shown in Figure 8.

It can be known that the above-mentioned optical filter manufacturing method of the present application combines the transfer printing into the spectral filter, places the patterned top photonic crystal plate and the bottom photonic crystal plate on the spacer and the substrate, and transfers the patterned photonic crystal plate by transfer printing. The silicon film is transferred from the photonic crystal plate to the spacer and the substrate, thereby avoiding the stress problem caused by repeated thin film deposition caused by the microfabrication method, and the optical filter obtained by transfer printing can change the cavity length of the spectrum by changing the driving voltage value The displacement is adjusted, so that the optical performance parameters of the filter can be adjusted.

The embodiment of the present application further provides a spectral reconstruction method, including:

S31: apply different voltages to the filter shown above, and collect the spectral information of the measured sample;

S32: Reconstruct a standard transmission spectrum according to the spectral information.

In the preferred embodiment, since _CO contains a single and strong absorption peak in a wide MIR range, at the same time, the RI of the gas is almost 1, so it does not introduce additional reflections, thus making the reconstruction possible. Therefore, this CO ₂ is an ideal target analyte, and the spectral information reconstructed in this application is the transmission spectrum of CO ₂ .

Specifically, a reconstruction matrix may be used, and each data in the reconstruction matrix is the tuning state data of one FPF spectrum, for example, for a 5x5 reconstruction matrix, there are 25 tuning states of the FPF spectrum.

Since when the FPF resonance peak is far away from the characteristic _CO peak, the intensity change caused by _CO absorption is small, and the measured intensity vector is more sensitive to noise, so the embodiment of the present application selects a partial tuning state in which the FPF resonance peak is close to the _CO peak, instead of the full tuned spectrum in Fig. 7(b).

It can be seen that precisely because of the tunable Fabry Perot filter of the present application, different tuning states can be achieved by applying different voltages, thereby obtaining rich spectral information on one filter without requiring a large number of Pixels provide spectral data.

，F_i是F中第i列系数，σ_i是第i列的标准差，E是期望。图中高于0.5的相关系数表示高相关性，在彩色图中为白色。小于0.5的值是较低的相关性，相关系数的平均值为0.5389。在将 N2和CO₂气体的混合物送入气室后，FPF被调谐到与图9a相同的共振状态，并再次通过FTIR测量，这些光谱如图9c所示。Figure 9b is the correlation coefficient of F, the calculation formula is

, F _i is the i-th column coefficient in F, σ _i is the standard deviation of the i-th column, and E is the expectation. Correlation coefficients above 0.5 in the plot indicate high correlation and are white in color plots. Values less than 0.5 are lower correlations, with an average correlation coefficient of 0.5389. After feeding the mixture of N2 and _CO2 gases into the gas cell, the FPF was tuned to the same resonance state as in Fig. 9a and measured again by FTIR, and these spectra are shown in Fig. 9c.

This application summarizes the 4 to 5 μm transport as an intensity vector to simulate integrated systems using wavelength-insensitive detectors such as thermopiles or bolometers, reconstructed using an iterative Tikhonov regularization method with generalized cross-validation. Boundary conditions were applied to constrain the recovered spectra between 0 and 1, which can be used here to reconstruct the _CO2 fingerprint in transport mode.

去评估重建保真度，其中T_r和T_ref是重建和参考光谱，N是波长点的数量。Figure 9d shows the recovered spectrum with the measured reference spectrum, the dip in 170 nm FWHM matches the _CO2 fingerprint at 4.26 μm, two investigations were performed in order to identify the factors limiting the spectral resolution. First, it was studied how measurement noise can distort the reconstruction. In Fig. 10a, the _CO2 spectrum was reconstructed with the filter matrix in Fig. 9a, but different percentages of random noise were added to the intensity vector. As the noise level decreases from 2.5% to 0%, the recovered spectrum gradually converges to the measured CO ₂ spectrum, and the mean square error (MSE) decreases from 0.017 to 1.1×10 ⁻⁴ . MSE is defined as

to evaluate the reconstruction fidelity, where T _r and T _ref are the reconstructed and reference spectra, and N is the number of wavelength points.

Figure 10b reveals the noise level at the 25 measured tuning states by comparing the measured intensity with the ideal intensity, which is the sum of the products of the filter matrix and the reference _CO2 spectrum.

To further determine the overall noise level in this reconstruction, the applicant extracted the average noise as 0.4% by comparing the reconstructed spectrum with the spectrum recovered from different noise levels. This 0.4% noise is mainly attributable to the measurement noise of the FTIR, another potential cause is that the displacement changes very little each time a voltage is applied, resulting in inconsistent formant positions.

Second, the required minimum number of tuning states is studied in the ideal case without any noise, in Fig. 10(c), the Gaussian dip with FWHM of 30 nm is reconstructed without noise but with a different number of input states, These input states come from simulated spectra.

In this application, the MSEs of the reconstructions with 10 and 25 states are 9.8x10 ^-3 and 7x10 ^-5 , and it can be seen that when the input states increase from 10 to 25, the MSE improves by two orders of magnitude. Figure 10d shows the reconstruction results for the extreme case of the step function. Similarly, 25 states can provide a good reconstruction improvement in resolution, and the minimum number of states can also be predicted by sampling theory. Therefore, the current reconstruction resolution is not affected by is limited by the number of tuning stages, but by the measurement noise. To further improve the reconstruction accuracy, higher FPF resonance modes can be employed, with more formants. The simultaneous presence of multiple formants of different orders can also sample a wider spectrum while keeping the tuning range constant, and the reconstruction algorithm can also be optimized for better noise tolerance.

The mechanism of computational reconstruction in this application is shown in Figure 1(c). Firstly, the spectrum of FFF under various voltages is measured as an m×n calibration matrix F, where each row is the FPF spectrum under the corresponding voltage. These spectra are normalized to the background so that the spectra of the light source and the response of the detector cancel out.

.因此所有调谐电压下的整个输出强度可以描述为FT＝I。其中T是n×1要重建的入射光谱的柱向量，I是m×1 在不同电压下测量强度的柱矢量.在理想情况下，可以使用迭代最小二乘法重建未知频谱以最小化

。然而，实验中不可避免的噪声会导致微小的偏差，因此FT±ΔN＝I，这些测量误差导致重建中的不稳定性，因此优选采用更复杂的重建方案，如自适应吉洪诺夫正则化和递归最小二乘法。When the incident radiation T(λ) contains molecular fingerprints of unknown information and irradiates the FPF, its transmission intensity can be described as I=∫F(λ)T(λ)dλ≈∑ _i F(λ _i )T(λ _i ). The latter is discrete format in the measurement, and F(λ)i is the FPF spectrum. When voltages are applied to tune the gap and thus change the resonant peak of the FFF, the emission intensity at each voltage can be described by:

. Thus the overall output intensity at all tuning voltages can be described as FT=I. where T is the n × 1 column vector of the incident spectrum to be reconstructed, and I is the m × 1 column vector of the measured intensities at different voltages. Ideally, the unknown spectrum can be reconstructed using iterative least squares to minimize

. However, unavoidable noise in experiments can lead to small deviations, so FT ± ΔN = I, these measurement errors lead to instability in the reconstruction, so more complex reconstruction schemes such as adaptive Tychonoff regularization are preferred and recursive least squares.

The spectral reconstruction is shown in Figure 1, and the measurement data can be expressed in the following matrix form:

FT=I

where ^Fisam x _n matrix, I = [I ₁ , I ₂ , .

T=[T ₁ , T ₂ ,..., T _n ] ^T

The goal is to find the value of each element in the vector. Since it is overdetermined (m>>n) and may be wrong, Tikhonov regularization (also known as ridge regression) is used here to selectively suppress the noise component. The problem is equivalent to solving the penalized least squares problem γ with a conditioning factor:

最优可以表示为：

Optimum can be expressed as:

I₀是单位矩阵。

I ₀ is the identity matrix.

In order to adaptively select the adjustment factor, the generalized cross-validation (GCV) method is used. In Tikhonov regularization, the optimal regularization factor from cross-validation can be expressed as:

A(γ)＝F(F ^T F+γ ² I ₀ ) ^-1 F ^T

Considering the physics in this application, each element of the vector is constrained between 0 and 1 by imposing boundary conditions. GCV is used for inner iterations, and each outer iteration produces a new approximate solution that meets the boundary conditions.

Further, in this application, the transfer printed FPF has wavelength scalability in the mid-infrared range. Using the scalability of electromagnetic waves and the transfer printing method, the proposed tunable Fabry Perot filter can cover the entire mid-infrared range from 2 to 20 μm by changing the design of the PCS reflector (period, radius, thickness, and Arrangement and other geometric parameters), various FPFs can be formed, as shown in Figure 12. Their key design parameters are summarized in Table 1 below:

Table 1-2 FPF parameters between 20μm

Understandably, it is currently quite challenging to fabricate the required air spacing to match the resonant wavelength, especially as the operating wavelength shifts beyond 8 μm, and spacings beyond 4 μm are difficult to achieve with the deposition of sacrificial layers. The transfer printing technology proposed in this application can solve this limitation. The FPF cavity spacing of this application is determined by the silicon spacer, which is the device layer of the selected SOI wafer. At the same time, the thickness of the device layer of SOI can reach no limit. Further, although most FPFs are electrostatically driven, the pull-in effect limits the tuning range to 1/3 of the air gap.

In addition, it is understood that other MEMS drive schemes, such as piezoelectric actuators, electromagnetic actuators, etc., can also be employed in the tunable FPF to adjust the gap and thus the formant.

It can be seen from the above examples that in order to avoid the stress problem caused by repeated film deposition in the surface micromachining method, the embodiment of the present application uses a single-layer PCS instead of DBR as a reflector, and at the same time forms an air cavity by transfer printing instead of releasing a sacrificial layer, By applying 70 V, the peak wavelength was tuned from 5.61 to 4.13 μm, covering the molecular fingerprints of _CO2 and acetone. It was verified that spectral reconstruction of the _CO2 spectrum from 4 to 5 μm could be achieved, and the FWHM drop of 170 nm was recovered at 4.26 μm.

In addition, it is worth noting that the single-layer PCS is only used as a typical nanophotonic reflector to constitute the FPF. Other single-layer thin-film reflectors and single-layer nanophoton reflectors such as subwavelength gratings (SubwavelengthGrating, SWG), plasmonic resonators (Plasmonicresonators) can also be used as the top and bottom plates of the FPF design, so as to realize the infrared light in the cavity resonance.

Further, the present application also provides a micro-computing mid-infrared spectrometer, which includes a single tunable Fabry Perot filter, which is specifically used for VOC detection, trace gas detection, medical diagnosis, environmental monitoring and industrial process control Wait.

It should be noted that the embodiment of the display device, the embodiment of the test method, and the embodiment of the test circuit provided in the embodiment of the present invention can all refer to each other, and this embodiment of the present application does not limit it. The steps of the embodiment of the test method of the display panel provided in the embodiment of the application can be increased or decreased accordingly according to the situation. Any person familiar with the technical field can easily think of a change method within the technical scope disclosed in the application, which should cover Within the protection scope of the present application, so no more details are given.

The above are only optional embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application shall be included in the protection of the application. within range.

Claims (11)

1. A spectrometer filter, comprising:

a substrate;

the bottom silicon photonic crystal plate and the top silicon photonic crystal plate are positioned on one side of the substrate;

a spacer located between the bottom silicon photonic crystal plate and the top silicon photonic crystal plate; the substrate is arranged on one side close to the bottom silicon photonic crystal plate, a pattern is formed on one side close to the top silicon photonic crystal plate by the spacer, and the spacer, the bottom silicon photonic crystal plate and the top silicon photonic crystal plate form a cavity.

2. The spectrometer filter as in claim 1, wherein the bottom and top silicon photonic crystal plates are etched with a plurality of periodic holes.

3. The spectrometer filter according to claim 1, wherein electrodes are provided on the substrate and the spacer.

4. The spectrometer filter of claim 1, further comprising:

an electrical isolation layer disposed between the spacer and the bottom silicon photonic crystal plate.

5. The spectrometer filter of claim 1, wherein the material forming the substrate comprises calcium fluoride.

6. A method for manufacturing a spectrometer filter is characterized by comprising the following steps:

forming a substrate and a spacer;

patterning a bottom silicon photonic crystal plate and a top silicon photonic crystal plate;

respectively transferring the patterns of the bottom silicon photonic crystal plate and the top silicon photonic crystal plate to a transfer printing stamp;

transferring the pattern on the transfer printing stamp to the spacer and the substrate, respectively;

assembling the bottom silicon photonic crystal plate, the spacer, and the top silicon photonic crystal plate on the substrate.

7. The method of manufacturing according to claim 6, further comprising: and depositing a conductive medium on the substrate and the spacer to form an electrode.

8. The method of claim 7, wherein the patterning a bottom silicon photonic crystal slab and a top silicon photonic crystal slab comprises:

patterning the silicon wafer to form a mask;

applying photoresist to the bottom and top silicon photonic crystal plates;

respectively placing masks on the bottom silicon photonic crystal plate and the top silicon photonic crystal plate, and exposing for a set time length;

and solidifying the bottom silicon photonic crystal plate and the top silicon photonic crystal plate to obtain the patterned bottom silicon photonic crystal plate and the patterned top silicon photonic crystal plate.

9. The method of claim 8, wherein the patterning the silicon wafer to form a mask comprises:

patterning a silicon wafer to form a rectangular array with a set period and width;

and etching the silicon wafer to form the mask.

10. A method for driving a spectrometer filter as claimed in any of claims 1 to 5, wherein electrodes are provided on the spectrometer filter; the driving method includes:

and applying a set voltage generated by the friction nano generator on the electrode, and adjusting the filtering wavelength of the spectral filter through an electrostatic effect.

11. A method of spectral reconstruction, comprising:

applying different voltages to the optical filter according to any one of claims 1 to 5, and collecting spectral information of a sample to be measured;

and reconstructing a standard transmission spectrum according to the spectrum information.

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