CN115185030A - A kind of preparation method of Rugate filter - Google Patents

Abstract

The embodiment of the invention discloses a preparation method of a Rugate optical filter, which comprises the following steps: acquiring a target response to be responded, and reconstructing a structure parameter of a Rugate film corresponding to the target response by using a Discrete Layer Peeling (DLP) algorithm; designing the structural parameters of the Rugate film by using a preset sampling function to obtain the structural parameters of a sampling framework; and coating on the surface of a quartz or glass substrate according to the structural parameters of the sampling framework to obtain the Rugate optical filter. The invention applies the sampling technology to the design of the Rugate thin film optical filter, and because the sampling period is usually several times of that of the Rugate single period, the method can equivalently realize the traditional nanometer-level complex fine structure only by the control precision of submicron level, thereby greatly simplifying the manufacturing process, reducing the manufacturing cost and promoting the development of the optical thin film optical filter preparation technology.

Description

A kind of preparation method of Rugate filter

technical field

The embodiments of the present invention relate to the technical field of optical filters, in particular to a method for preparing a Rugate optical filter.

Background technique

The Rugate filter is a periodic graded-index film whose refractive index exhibits a sine or cosine variation, and has potential advantages such as a higher resistance to laser damage threshold and less film stress.

The optical filter prepared by the traditional design method will produce a series of high-order reflection bands on both sides of the cut-off band, which will significantly affect the measurement accuracy. The Rugate filter designed with a non-uniform film structure has a graded refractive index structure that overcomes the transition between high and low refractive index materials at the film interface, which can effectively reduce the high-order reflection band, while suppressing the Second harmonics appearing in large index contrast designs.

However, the refractive indices of materials in nature are not continuously changing in the same wavelength band, which makes the preparation of Rugate filters very difficult. At present, the co-plating technology commonly used to prepare Rugate filters is to obtain a mixed material with a refractive index between high and low refractive index by mixing high and low refractive index materials by evaporation or sputtering. By adjusting the high and low refractive index materials to achieve the purpose of changing the refractive index of the mixed material. However, due to the difficulty of accurately monitoring the deposition rate of high and low refractive index materials, and the inability to accurately detect the film thickness of each layer, the process repeatability of batch preparation of Rugate filters is poor. At present, there are serious limitations in the design and preparation methods of Rugate thin films, including imperfect design methods, complicated experimental preparations, and especially difficulties in preparing fine structures with complex function distributions. These problems greatly restrict the performance improvement and function of Rugate films.

SUMMARY OF THE INVENTION

The embodiment of the present invention provides a preparation method of a Rugate filter,

Obtain the target response to be responded, and use the DLP reconstruction algorithm to reconstruct the structural parameters of the Rugate film corresponding to the target response;

Using a preset sampling function to design the structural parameters of the Rugate film to obtain the structural parameters of the sampling framework;

The Rugate filter is obtained by coating the surface of quartz or glass according to the structural parameters of the sampling structure.

Further, the structural parameters of the Rugate film are obtained by designing the structural parameters of the Rugate film using a preset sampling function, including:

The target response is equivalently achieved through a +1-level Fourier series channel by means of an equivalent response, and a sampling architecture is designed for the structural parameters of the Rugate film corresponding to the reconstructed target response, and the structural parameters of the sampling architecture are obtained.

Further, the expression of the DLP reconstruction algorithm is:

where A ₊₁ (z) is the amplitude apodization of the +1-order Fourier series channel, φ ₊₁ (z) is the phase change of the +1-order Fourier series channel, to nanometer precision, and Λ _{+ 1} (z) is the Rugate period of the +1-order Fourier series channel with nanometer precision, cc is the conjugate complex number, and j is the imaginary unit.

Further, the expression for the sampling architecture design is:

A(z)是+1级傅里叶级数信道的幅度切趾，F_m是傅里叶系数，f(z)是随膜厚z变化的采样函数，P是固定不变的采样周期大小，Λ为固定不变的均匀Rugate周期，Λ₊₁表示+1级傅里叶级数信道的Rugate周期。in,

A(z) is the amplitude apodization of the +1-level Fourier series channel, F _m is the Fourier coefficient, f(z) is the sampling function that varies with the film thickness z, and P is the fixed sampling period size , Λ is a fixed uniform Rugate period, Λ ₊₁ represents the Rugate period of the +1-level Fourier series channel.

Further, the Rugate filter is obtained by coating the surface of the Rugate film according to the structural parameters of the sampling structure, including:

According to the structural parameters of the sampling structure, the physical film formation method is adopted, and the deposition rate of the high and low refractive index target film materials is continuously changed by the double-source rapid alternate deposition, or the deposition rate of the two high and low refractive index target material films is changed simultaneously. Or coating the glass surface to obtain the wrinkled area of the Rugate filter.

Further, it also includes:

The Rugate film of the sampling structure is prepared by sputtering only the low-refractive-index material in the part of the surface of the Rugate film that has a constant refractive index.

Further, the high and low refractive index materials are selected from at least one of SiO ₂ , HfO ₂ or Al ₂ O ₃ .

Further, it also includes:

For the sampling architecture Rugate thin film filter, the sampling period P(z) of the target response of the chirped +1-order Fourier series channel based on the uniform Rugate period Λ is:

Among them, Λ is the Rugate period, and Λ ₊₁ (z) is the Rugate period of the +1-level Fourier series channel.

Further, the target responses are spectral and angular.

Further, the film thickness of the sampling structure is of sub-micron level accuracy.

The beneficial effects of the embodiments of the present invention are: the present invention applies the sampling technology to the design of the Rugate thin film filter. Among the many methods of periodic refractive index modulation (called gratings), sampling techniques offer great design flexibility and are simple to fabricate. This technology utilizes the method of micron-scale sampling structure to equivalently realize nano-scale complex and fine structures, and has not only been widely used in the field of realizing complex functional fiber gratings, but also applied to planar waveguide gratings. The sampling period is usually several times larger than a single Rugate period, so this method only needs sub-micron-level control accuracy to equivalently realize complex and fine structures of traditional nano-level, which greatly simplifies the manufacturing process, reduces manufacturing costs, and promotes The development of optical thin film filter preparation technology.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained from these drawings without creative effort.

1 is a schematic diagram of a sampling architecture Rugate refractive index modulation provided by an embodiment of the present invention;

2 is a combination of a reconstruction algorithm and an equivalent response method provided by an embodiment of the present invention to achieve a specific target response diagram;

3 is a comparison diagram of a Rugate film with a sampling structure provided by an embodiment of the present invention and a method for preparing a traditional Rugate film;

FIG. 4 is a comparison diagram of a sampled equivalent phase-shift Rugate refractive index modulation structure provided by an embodiment of the present invention, a traditional real phase-shifted Rugate refractive index modulation structure, and a corresponding spectrum.

Detailed ways

In order for those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

An embodiment of the present invention provides a method for preparing a Rugate filter, including:

Step 1: Obtain the target response to be responded, and reconstruct the structural parameters of the Rugate film corresponding to the target response by using the DLP reconstruction algorithm;

The embodiment of the present invention analyzes the physical structure of the Rugate film based on the required properties of the Rugate film, and this idea is called reconstruction. The invention adopts the Discrete Layer Peeling (DLP) algorithm to accurately design the Rugate structure required for the target response, and also uses the DLP reconstruction algorithm to analyze and improve the performance of the actually prepared Rugate.

Specifically, the DLP reconstruction algorithm is used to reconstruct the Rugate refractive index modulation corresponding to the target response (spectrum and angular spectrum), that is, the structural parameters. It is assumed that the reconstructed refractive index modulation expression is:

where A ₊₁ (z) is the amplitude apodization of the +1-order Fourier series channel, φ ₊₁ (z) is the phase change of the +1-order Fourier series channel, to nanometer precision, and Λ _{+ 1} (z) is the Rugate period of the +1-order Fourier series channel with nanometer precision, cc is the conjugate complex number, and j is the imaginary unit.

Step 2, using a preset sampling function to design the structural parameters of the Rugate film to obtain the structural parameters of the sampling framework;

It should be noted that the sampling structure Rugate refractive index modulation is shown in Figure 1. The characteristic of this method to realize the periodic structure lies in the introduction of the sampling grating structure. The spectral response of the negative 1-order channel is determined by the sampling function of the micrometer scale, so the target response that can only be achieved by the traditional nanoscale fine structure can be equivalently achieved by the sampling structure of the micrometer scale. Usually, the sampling period is usually several times larger than a single Rugate period, so only the control precision of sub-micron level can be equivalent to realize the complex and fine structure of the traditional nanometer level, which greatly simplifies the manufacturing process and reduces the manufacturing cost.

Specifically, the target response is equivalently achieved through a +1-level Fourier series channel by means of an equivalent response, and a sampling architecture is designed for the structural parameters of the Rugate film corresponding to the reconstructed target response, and the structure of the sampling architecture is obtained. parameters, where the structural parameters of the sampling architecture Rugate are calculated as follows:

A(z)是+1级傅里叶级数信道的幅度切趾，Fm是傅里叶系数，f(z)是随膜厚z变化的采样函数，亚微米量级精度，P是固定不变的采样周期大小，Λ为固定不变的均匀Rugate周期，Λ₊₁表示+1级傅里叶级数信道的Rugate周期。in,

A(z) is the amplitude apodization of the +1-order Fourier series channel, Fm is the Fourier coefficient, f(z) is the sampling function as a function of the film thickness z, with sub-micron accuracy, and P is the fixed variable Variable sampling period size, Λ is a fixed uniform Rugate period, Λ ₊₁ represents the Rugate period of the +1-level Fourier series channel.

Among them, the equivalent response method is to scientifically design the Rugate physical structure that is easy to realize, so that the generated response characteristics are within the range of interest and have the same characteristics and processing capabilities as the target response.

This process shows that, according to the required target response spectrum (spectrum and angular spectrum), the advanced DLP reconstruction algorithm is used to obtain the structural parameters of the target Rugate, but the parameters often contain complex and fine structures on the nanometer scale (such as simple sine, chirp chirp, apodization, etc.), if the target Rugate structure is directly prepared according to the structural parameters of the target Rugate, it is not only extremely demanding for the preparation process, but also difficult to guarantee the performance. However, according to the structural parameters of the sampling architecture Rugate, the target response characteristic can be equivalently achieved on the +1-order Fourier series channel spectrum. The advantage is that since the size of the sampling period is often several times larger than the Rugate period itself, the precise realization of the sampling function can be controlled only with sub-micron level accuracy. In other words, large-scale operations on the sub-micron scale can equivalently realize complex fine structures on the traditional nano-scale. The specific process can be shown in Figure 2.

In one embodiment of the present invention, for the Rugate thin film filter with a sampling structure, in the case of a uniform Rugate period Λ, it has different parameters, such as sine, apodization, chirp, etc., and the target of a +1-level Fourier series channel The response can be obtained by changing the sampling function. For example, the chirped Λ ₊₁ (z) is the Rugate period of the +1-level Fourier series channel, which can be achieved by designing the sampling period P(z) as follows:

Among them, Λ is the Rugate period, and Λ ₊₁ (z) is the Rugate period of the +1-level Fourier series channel.

Since the size of the sampling period is often several times larger than the Rugate period itself, this will help reduce the difficulty of fabrication. The sampling function has a large variation space, and various target responses can be achieved by designing different sampling functions.

Step 3: Coating the surface of the Rugate film according to the structural parameters of the sampling structure to obtain a Rugate filter.

Specifically, according to the structural parameters of the sampling structure, a physical film-forming method, such as magnetron sputtering, is used to continuously change the deposition rates of two high and low refractive index target film materials by using dual-source rapid alternate deposition, or to simultaneously change the two The deposition rate of the high and low refractive index target materials is coated on the surface of the Rugate film to obtain the wrinkled region of the Rugate filter. In addition, the portion of the surface of the Rugate film with a constant refractive index, that is, the sampling region, is prepared by sputtering only the low-refractive-index material to prepare the Rugate film with the sampling structure. Wherein, the high and low refractive index materials are selected from at least one of SiO ₂ , HfO ₂ or Al ₂ O ₃ .

As shown in FIG. 3 , it is a comparison diagram of the Rugate film with the sampling structure and the preparation method of the traditional Rugate film.

The invention proposes to introduce the sampling structure into the Rugate film, which may solve the problems existing in the design and preparation of the traditional Rugate film filter, and further expand the thinking to realize complex and diverse functions. The advantage of this method to achieve a periodic structure lies in the introduction of a sampling architecture, which uses the positive and negative 1-level Fourier series channels of the sampling architecture to achieve the target response equivalently, and the spectral response of the positive and negative 1-level channels is determined by micron-scale sampling. Therefore, the target response that can only be achieved by traditional nano-scale fine structures can be equivalently achieved by micro-scale sampling structures. The Rugate structure required for the target response can be precisely designed by adopting the reconstruction algorithm. In addition, the reconstruction technology can better restore the Rugate structure based on the existing experimental results, which provides direct data for analyzing and finding problems existing in the experimental fabrication process, and provides feedback for further improving the performance of Rugate thin films. The DLP algorithm provides a periodic optical structure reconstruction method with convenient design, effective and intuitive physical meaning, and has the advantages of short calculation time and high reconstruction accuracy. Figure 4 is a schematic diagram of the equivalent phase-shifted Rugate refractive index modulation structure and the corresponding spectrum obtained by changing the sampling period. As shown in the figure, the traditional real phase-shift structure requires nanometer-level control accuracy, while the sampling structure adopted in the present invention only requires sub-micrometer-level control accuracy, and the π phase-shift spectrum achieved by the two is equivalent. of.

Obviously, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation manner. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. And the obvious changes or changes derived from this are still within the protection scope of the present invention.

The above are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (10)

1. A method for manufacturing a Rugate filter includes:

obtaining a target response to be responded, and reconstructing a structure parameter of a Rugate film corresponding to the target response by using a DLP reconstruction algorithm;

designing the structural parameters of the Rugate film by using a preset sampling function to obtain the structural parameters of a sampling framework;

and coating on the surface of a quartz or glass substrate according to the structural parameters of the sampling framework to obtain the Rugate optical filter.

2. The method according to claim 1, wherein the designing the structural parameters of the Rugate film by using the preset sampling function to obtain the structural parameters of the sampling architecture comprises:

and (3) realizing the target response through + 1-level Fourier series channel equivalence by applying an equivalent response mode, and designing a sampling framework aiming at the structural parameters of the Rugate film corresponding to the reconstructed target response to obtain the structural parameters of the sampling framework.

3. The method of manufacturing according to claim 1, wherein the expression of the DLP reconstruction algorithm is:

wherein A₊₁ (z) is the amplitude apodization, φ, of a + 1-stage Fourier series channel ₊₁ (z) is the phase change of +1 order Fourier series channel, with nanometer level accuracy, Λ ₊₁ (z) is a Rugate period of a + 1-stage Fourier series channel, the Rugate period is nanometer-scale precision, c.c represents a complex conjugate, and j represents an imaginary number unit.

4. The method of claim 1 or 2, wherein the sampling architecture design is expressed by:

wherein ,

a (z) is the amplitude apodization of the + 1-stage Fourier series channel, F _m Is the Fourier coefficient, f (z) is the sampling function varying with the film thickness z, P is the fixed and invariable sampling period, Λ is the fixed and invariable uniform Rugate period, Λ ₊₁ Representing the Rugate period of a +1 stage fourier series channel.

5. The method according to claim 1, wherein the step of coating on the surface of quartz or glass according to the structural parameters of the sampling structure to obtain the Rugate filter comprises:

and according to the structural parameters of the sampling framework, a physical film forming method is adopted, the deposition rates of the high-refractive index target material and the low-refractive index target material are continuously changed by using double sources to quickly and alternately deposit, or the deposition rates of the two high-refractive index target material and low-refractive index target material are simultaneously changed to carry out film coating on the surface of quartz or glass, so that the fold area of the Rugate optical filter is obtained.

6. The method of manufacturing according to claim 5, further comprising:

the portion of the Rugate film with the unchanged refractive index is used for preparing the Rugate film with the sampling structure by only sputtering low-refractive index materials.

7. The method according to claim 6, wherein the material with high and low refractive index is SiO ₂ 、HfO ₂ Or Al ₂ O ₃ At least one of (1).

8. The method of claim 1, further comprising:

for a sampling architecture Rugate thin film filter, the sampling period P (z) of the target response of a chirped + 1-level fourier series channel based on a uniform Rugate period Λ is:

wherein Λ is the Rugate period, Λ ₊₁ (z) is the Rugate period of the +1 stage fourier series channel.

9. The method of claim 1, wherein the target response is a spectral and angular spectrum.

10. The method of claim 1, wherein the film thickness of the sampling architecture is of sub-micron precision.

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