CN112230323B

CN112230323B - Preparation method of optical filter with linearly changed transmittance

Info

Publication number: CN112230323B
Application number: CN202011049837.7A
Authority: CN
Inventors: 苏炎; 李昱; 陈居凯
Original assignee: Suzhou Zhongwei Photoelectric Co ltd
Current assignee: Suzhou Zhongwei Photoelectric Co ltd
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2022-11-11
Anticipated expiration: 2040-09-29
Also published as: CN112230323A

Abstract

The invention provides a preparation method of an optical filter with linearly changed transmittance, which comprises the following steps of; preparing, coating, cutting and detecting; the film coating comprises film system design, film thickness control is carried out on each layer of film according to the film system design, and the film is deposited in a film coating machine; the film system structure of the film system stacked on the base layer in the film system design comprises eight to twenty Fabry-Perot cavities, and the last layer of the Fabry-Perot cavities is used as a connecting layer to cascade the next Fabry-Perot cavity; the last layer of each fabry-perot cavity is a refractive index layer of non-quarter optical thickness. The invention can prepare the optical filter with the linear change of the transmittance, the insertion loss or the linear change of the transmittance of the optical filter along with the wavelength in a specific wavelength range can be used for identifying the wavelength. In addition, the invention selects a proper monitoring method according to the film system structure for a plurality of times of experiments to obtain the accurate optical thickness of the film layer and can realize a high-precision linear change spectral curve.

Description

Preparation method of optical filter with linearly changed transmittance

Technical Field

The invention relates to the technical field of optics, in particular to an optical filter with linearly changing transmittance.

Background

Filters are optical devices used to select a desired wavelength band of radiation. Thin film filters generally transmit longer wavelengths and are often used as infrared filters. The latter is to form alternately metal-medium-metal film or all-medium film with certain thickness and high or low refractive index on certain substrate by vacuum coating process. The choice of the material, thickness and series of the layers is determined by the desired center wavelength and transmission bandwidth λ.

In the prior art, the wavelength of the transmitted light can be obtained according to the performance characteristics of a certain optical filter, but a plurality of wavelengths need to be obtained according to a plurality of optical filters, so the cost is high. Therefore, it is an urgent problem to use fewer filters to obtain more wavelengths. The film system design and the preparation method adopted in the preparation process of the optical filter are critical to the performance of the optical filter. Therefore, it is necessary to provide a new manufacturing method to manufacture a new optical filter, so as to achieve more wavelengths with fewer optical filters.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a preparation method of an optical filter with linearly changed transmittance.

The technical scheme of the invention is summarized as follows:

the invention provides a preparation method of an optical filter with linearly changed transmittance, which comprises the following steps: preparing: carrying out ultrasonic cleaning on the blank base layer or the wafer which is not coated with the film; film coating: the method comprises the steps of designing a film system, controlling the thickness of each film layer according to the design of the film system, and depositing the film by a film coating machine; wherein, in the step of designing the film system, a material with a refractive index in a range of 1550nm from 1.45 to 3.5 is used as a base layer, a film system structure of the film system stacked on the base layer includes eight to twenty fabry-perot cavities, and a last layer of the fabry-perot cavities is used as a connection layer to cascade a next fabry-perot cavity; the last layer of each said fabry-perot cavity is a refractive index layer of non-quarter optical thickness; cutting: cutting the film into the size of the optical filter after the film coating is finished; and (3) detection: and detecting the cut optical filter to obtain a qualified optical filter.

Further, the membrane system design further comprises: the optical thickness of the first layer of each Fabry-Perot cavity is optimized by the optical thickness of the connecting layer, and the optical thickness of the first layer of each Fabry-Perot cavity is 0.975 to 1.025 quarter-wave optical thickness, so that the transmittance at the end of the layer reaches an extreme value

The control of the film thickness of each film layer according to the film system design comprises the following steps: and the first layer of each Fabry-Perot cavity is monitored by adopting an extreme method in coating monitoring, so that the next film layer with the optical thickness of one quarter wavelength of each layer can be monitored by adopting the extreme method.

Further, the controlling the thickness of each thin film layer according to the film system design further comprises: the connection layer is monitored by adopting a crystal control/time control method.

Further, the number of the fabry-perot cavities is 11 to 20.

Further, the membrane system structure of the fabry-perot cavity is as follows: (HL) m aH (LH) m B or (HL) m aH (LH) m BAB; wherein, (HL) m aH (LH) m BAB is the film system structure of the Fabry-Perot cavity of the last layer;

wherein H is a high refractive index layer of quarter-center wavelength optical thickness, and L is a low refractive index layer of quarter-center wavelength optical thickness; m is the number of sets of repeated alternate stacking of sequences of HL and LH, a is a quarter-center-wavelength optical thickness coefficient, a is an integer, B is a low-refractive-index layer of non-quarter optical thickness, A is a high-refractive-index layer of non-quarter optical thickness;

the optical thickness of the first layer of the fabry-perot cavity is optimized by the optical thickness of the last layer of the last fabry-perot cavity.

Further, the non-quarter-optical thickness low refractive index layer B has an optical thickness of 0.371 to 2.605 quarter-wavelength optical thickness.

Further, the material of the high refractive index layer is at least one of Ta2O5, nb2O5 and TiO2, and the refractive index of the high refractive index layer is 1.85-2.5 in the range of 1550 nm.

Further, the material of the low refractive index layer is at least one of SiO2, al2O3 and MgF2, and the refractive index of the low refractive index layer is 1.38-1.6 in the range of 1550 nm.

Further, the detecting the cut optical filter to obtain a qualified optical filter includes: the transmittance of the qualified filter in the 1520-1570nm wave band range is reduced from 90% to 10% with a certain slope; or the insertion loss or transmittance of the wavelength of the prepared optical filter is linearly increased or decreased along with the wavelength under the incident angle of 0-45 degrees.

Further, the step of preparing comprises: the power of the ultrasonic wave is 600W-900W, the cleaning medicament is RS-26, and the frequency value is set to be 28KHZ-40KHZ.

Compared with the prior art, the invention has the beneficial effects that:

the preparation method of the optical filter with the linear change of the transmittance can prepare the optical filter with the linear change of the transmittance, and the insertion loss or the transmittance of the optical filter in a specific wavelength range can be linearly changed along with the wavelength, so that the optical filter can be used for identifying the wavelength. The preparation method is improved on the basis of the film system structure, the film thickness and the monitoring mode, and a proper monitoring method is selected according to multiple experiments of the film system structure, so that the accurate optical thickness of the film layer is obtained, and a high-precision linear change spectrum curve can be realized.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings. The detailed description of the present invention is given in detail by the following examples and the accompanying drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention and do not constitute a limitation of the invention. In the drawings:

FIG. 1 is a schematic diagram of a filter with linearly changing transmittance according to the present invention;

FIG. 2 is a graph of wavelength versus transmittance for a first embodiment of the optical filter of the present invention;

FIG. 3 is a graph showing the actual relationship between the wavelength and the transmittance of the first optical filter of the present invention;

FIG. 4 is a diagram illustrating the difference between the target curve and the actual relationship of the first filter embodiment of the present invention;

FIG. 5 is a graph showing the target wavelength versus transmittance of a second embodiment of the optical filter of the present invention;

FIG. 6 is a graph showing the actual relationship between the wavelength and the transmittance of the second embodiment of the optical filter of the present invention;

FIG. 7 is a diagram showing the difference between the target curve and the actual relationship of a second embodiment of the optical filter of the present invention;

FIG. 8 is a graph of wavelength versus transmittance for a third embodiment of the optical filter of the present invention;

FIG. 9 is a graph showing the actual relationship between the wavelength and the transmittance of the third embodiment of the optical filter of the present invention;

FIG. 10 is a graph showing the difference between the target curve and the actual relationship of the third embodiment of the optical filter of the present invention;

fig. 11 is a flowchart of a method for manufacturing an optical filter with linearly changing transmittance according to the present invention.

Reference numerals: 1. a base layer; 2. a high refractive index layer; 3. a low refractive index layer; 4. a connecting layer; 5. fabry-perot cavity.

Detailed Description

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, which will enable those skilled in the art to practice the present invention with reference to the accompanying specification. In the drawings, the shape and size may be exaggerated for clarity, and the same reference numerals will be used throughout the drawings to designate the same or similar components. In the following description, terms such as center, thickness, height, length, front, back, rear, left, right, top, bottom, upper, lower, and the like are used based on the orientation or positional relationship shown in the drawings. In particular, "height" corresponds to the dimension from top to bottom, "width" corresponds to the dimension from left to right, and "depth" corresponds to the dimension from front to back. These relative terms are for convenience of description and are not generally intended to require a particular orientation. Terms concerning attachments, coupling and the like (e.g., "connected" and "attached") refer to a relationship wherein structures are secured or attached, either directly or indirectly, to one another through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.

The present invention will be further described with reference to the accompanying drawings and the detailed description, and it should be noted that any combination of the embodiments or technical features described below can be used to form a new embodiment without conflict. It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.

Filters are optical devices used to select the desired wavelength band of radiation. The optical filter is formed by stacking a base layer and a plurality of film layers on the base layer, and the thickness of the film layers can be divided into two description modes of physical thickness and optical thickness. Physical thickness refers to thickness on a physical scale, such as 100nm or the like; the optical thickness refers to the path traveled by the light, which relates to the refractive index of the material through which the light travels and the wavelength of the light QW = (n x d)/λ, where n is the refractive index of the material through which the light travels, d is the physical thickness, and λ is the wavelength of the light.

In the prior art, the wavelength of transmitted light can be obtained according to the performance characteristics of a certain optical filter, but a plurality of wavelengths need to be obtained according to a plurality of optical filters, so that the cost is high. Therefore, an object of the present invention is to provide a method for manufacturing an optical filter with linearly changing transmittance, so as to manufacture an optical filter with linearly changing transmittance.

Referring to fig. 11, the present invention provides a method for manufacturing an optical filter with linearly changing transmittance, including:

s1, preparation: and carrying out ultrasonic cleaning on the blank base layer or the wafer which is not coated with the film.

S2, coating: comprises S21 film system design, S22 film thickness control of each film according to the film system design, and S23 film deposition in a film coating machine.

S3, cutting: and cutting the film into the size of the optical filter after the film coating is finished.

S4, detection: and detecting the cut optical filter to obtain a qualified optical filter.

Specifically, in the S1 preparation step, the blank substrate or the wafer which is not coated is subjected to ultrasonic cleaning, the power of ultrasonic waves for cleaning is 600W-900W, the cleaning chemical is RS-26, and the frequency value is set to be 28KHZ-40KHZ.

In the S2 coating step, in the S21 film system designing step, a material with the refractive index in the range of 1550nm being 1.45-3.5 is used as a base layer, a film system structure of the film system stacked on the base layer comprises eight-twenty Fabry-Perot cavities, and the last layer of the Fabry-Perot cavities is used as a connecting layer to cascade the next Fabry-Perot cavity; the last layer of each fabry-perot cavity is a refractive index layer of non-quarter optical thickness.

The optical thickness of the first layer of each fabry-perot cavity is optimized by the optical thickness of the connection layer, which is 0.975 to 1.025 quarter-wave optical thicknesses, in order to reach an extreme value of the transmission at the end of this layer.

In particular, the number of fabry-perot cavities is 11 to 20.

The membrane system structure of the Fabry-Perot cavity is as follows: (HL) m aH (LH) m B or (HL) m aH (LH) m BAB; wherein, (HL) m aH (LH) m BAB is the film system structure of the final layer of Fabry-Perot cavity;

wherein H is a high refractive index layer of quarter-center wavelength optical thickness, and L is a low refractive index layer of quarter-center wavelength optical thickness; m is the number of groups of the HL and LH which are repeatedly and alternately stacked, a is a quarter central wavelength optical thickness coefficient, a is an integer, B is a low-refractive-index layer with a non-quarter optical thickness, and A is a high-refractive-index layer with a non-quarter optical thickness;

the optical thickness of the first layer of a fabry-perot cavity is optimized by the optical thickness of the last layer of the last said fabry-perot cavity.

The non-quarter optical thickness low refractive index layer B has an optical thickness of 0.371-2.605 quarter-wave optical thicknesses.

The material of the high-refractive-index layer is at least one of Ta2O5, nb2O5 and TiO2, and the refractive index of the high-refractive-index layer is in the range of 1550nm and is 1.85-2.5.

The material of the low-refractive-index layer is at least one of SiO2, al2O3 and MgF2, and the refractive index of the low-refractive-index layer ranges from 1.38 to 1.6 in the range of 1550 nm.

S22, controlling the thickness of each thin film according to the design of the film system, comprising the following steps: the first layer of each Fabry-Perot cavity is monitored by extremum in coating monitoring, so that the next film layer with quarter wavelength optical thickness can be monitored by extremum.

The connection layer is monitored by adopting a crystal control/time control method.

Specifically, the crystal control/time control method is carried out by adopting a crystal oscillator controller, and the principle is as follows: in the coating process, a film layer can be deposited on the surface of a crystal oscillator wafer of the crystal controller; the oscillation frequency of the crystal oscillator wafer can change along with the increase of the thickness of the upper surface film layer of the crystal oscillator wafer; the thickness change of the film layer on the crystal oscillator is obtained by obtaining the change of the oscillation frequency of the crystal oscillator plate on the crystal oscillator controller. The control method has the disadvantages that optical thickness supplement cannot be realized, and the peak transmittance of the pass band cannot be improved. And therefore are often used only to control the deposition rate of the coating process.

For a high-precision optical filter, it is often considered to control the film thickness by using a direct light control method. The reason is that in the process of coating, the inherent characteristics of coating, and the differences of production processes and equipment often cause the characteristics of the film to be different from the theoretical characteristics, for example, the refractive index of the film is lower compared with that of the bulk material, and the refractive index of the film is different due to different processes. And the final application of the filter is light, it is contemplated that the optical thickness can be controlled by monitoring the light signal during the deposition process.

In the coating process, because the test error and the error between the process and the theory can cause the actual test value and the theoretical test value to come in and go out, the influence caused by the error needs to be reduced or compensated through an optical monitoring algorithm. Conventional algorithms include a ratio method, an extremum method, and the like. The ratio method is usually used for monitoring of non-regular (non-integer) 1/4 wavelength, but has the disadvantage that in the case of a single monitoring sheet, errors are accumulated, thereby causing the failure of the final product. Are often used in optical products where spectral accuracy requirements are low. The extreme method is used for monitoring the change trend of the light intensity and switching to the next layer after judging that the light intensity signal reaches an extreme point; this algorithm has the function of compensating for the errors of the front film layer.

The invention improves on the consideration of the thickness of the film layer and the monitoring mode, the first layer of each Fabry-Perot cavity is monitored by adopting an extreme method in the film coating monitoring, and the light intensity signal is switched to the next layer after being judged to reach an extreme point, so that the film layer with the optical thickness of one quarter wavelength of each next layer can be monitored by adopting the extreme method, and the error of the previous film layer can be compensated.

The refractive index layer with non-quarter optical thickness is used as a connecting layer to be monitored by adopting a crystal control/time control method, and the thickness change of the film layer on the crystal oscillator plate is obtained by obtaining the change of the oscillation frequency of the crystal oscillator plate and is used for controlling the deposition rate in the film coating process. The crystal control/time control method can be used for plating a complex film layer with any thickness, and the extreme value method is combined for monitoring, so that the error accumulation caused by single monitoring is compensated, and the failure of the product is avoided.

S23, performing film deposition in a film coating machine, specifically adopting hard medium film coating of sputtering or ion beam assisted deposition.

How to precisely control the film layer in the film deposition process is the core of realizing the high-precision optical filter. In this process, there are two important control factors: firstly, how to keep the stable deposition rate of the film layer in the deposition process; secondly, how to ensure the thickness of the film layer to meet the requirement.

In the ion beam assisted deposition process, an electron gun is used for heating the film material to realize the thermal evaporation of the film material, and the crystal oscillator controller is used for acquiring the physical thickness of the film layer in the process so as to control the deposition rate of the film layer. In the deposition process of magnetron sputtering and ion beam sputtering, the target material is bombarded by plasma, the film material is sputtered by utilizing the principle of elastic collision, and the concentration of the plasma is ensured by controlling the power stability of a power supply in the process, so that the stability of the deposition rate is realized.

And in the ion beam assisted deposition process, the method is more beneficial to monitoring the film thickness to meet the requirement by adopting a crystal control/time control method.

S4, detecting the cut optical filter to obtain a qualified optical filter, wherein the method comprises the following steps: the transmittance of the qualified filter in the 1520-1570nm wave band range is reduced from 90% to 10% with a certain slope; or the insertion loss or transmittance of the wavelength of the prepared optical filter is linearly increased or decreased along with the wavelength under the incident angle of 0-45 degrees.

Specifically, there are three embodiments of the filter in the S21 film system design.

The specific embodiment is as follows:

a linear transmittance filter as shown in fig. 1 comprises a substrate 1 and a film system stacked on the substrate 1, wherein the film system structure of the film system comprises eight to twenty fabry-perot cavities 5, and the last layer of the fabry-perot cavities 5 is used as a connecting layer 4 to cascade the next fabry-perot cavity 5.

The last layer of each fabry-perot cavity 5, which serves as the coupling layer 4, is a refractive index layer of non-quarter optical thickness.

The optical thickness of the first layer of each fabry-perot cavity 5 is optimized by the optical thickness of the connecting layer. Preferably, the optical thickness of the first layer of the fabry-perot cavity 5 is between 0.975 and 1.025 quarter-wave optical thicknesses. It will be appreciated that the optical thickness of the first layer of each fabry-perot cavity 5 is approximately a quarter wavelength optical thickness, and the purpose of this design is to better cascade with the connecting layer 4 (i.e. a refractive index layer of non-quarter optical thickness). And the optical thickness of approximate quarter wavelength is used for compensating that the transmittance of the central wavelength reaches an extreme value when the layer is finished, and an extremum method is adopted for monitoring in coating monitoring, so that each next film layer with the optical thickness of the quarter wavelength can be monitored by the extremum method, the optical thickness can be accurately controlled, and the optical filter with the accurate linear transmittance change can be obtained.

Under the incident angle of the optical filter is 0-45 degrees, the insertion loss or transmittance of the wavelength is increased or decreased linearly along with the wavelength.

Specifically, the number of the Fabry-Perot cavities 5 is 11 to 20, and the number of the film layers is 92 to 98.

When the characteristic wavelength of 1515nm is used, the structure of the film system of the Fabry Perot cavity 5 is as follows: (HL) m aH (LH) m B or (HL) m aH (LH) m BAB; wherein, (HL) m aH (LH) m BAB is the film system structure of the final layer of the Fabry-Perot cavity 5;

wherein H is a high refractive index layer of quarter center wavelength optical thickness, L is a low refractive index layer of quarter center wavelength optical thickness; m is the number of sets of repeated alternating stacks of sequences of HL and LH, a is a quarter-center-wavelength optical thickness coefficient, a is an integer, B is a low refractive index layer of non-quarter optical thickness, and A is a high refractive index layer of non-quarter optical thickness.

Preferably, a is 2 or 4.

The optical thickness of the first layer of the fabry perot cavity is optimized from the optical thickness of the last layer of the last fabry perot cavity. The optical thickness of the first layer of the fabry-perot cavity is between 0.975 and 1.025 quarter-wavelength optical thicknesses, i.e. approximately quarter-wavelength optical thicknesses. The transmittance of the film at the end of the layer reaches an extreme value, and an extreme value method is adopted for monitoring in the film coating monitoring, so that the next film layer with the optical thickness of one quarter wavelength can be monitored by the extreme value method. The extreme method is used for monitoring the change trend of the light intensity and switching to the next layer after judging that the light intensity signal reaches an extreme point; the algorithm has the function of compensating the error of the front film layer. The connection layer 4 is used for film coating monitoring by a crystal control/time control method, and the process curves are monitored by various monitoring methods so as to achieve the required filtering effect, errors can not be accumulated, and the accuracy in the thickness of the film layer in the optical filter is improved.

The non-quarter optical thickness low index layer has an optical thickness of 0.371-2.605 quarter-wave optical thicknesses. And the coefficient of the optical thickness of the low refractive index layer of non-quarter optical thickness is a non-integer, i.e. the optical thickness of non-integer quarter-wave in 0.371-2.605.

The transmittance of the filter in the 1520-1570nm band is decreased from 90% to 10% with a certain slope.

The material of the high-refractive-index layer is at least one of Ta2O5, nb2O5 and TiO2, and the refractive index of the high-refractive-index layer is 1.85-2.5 in the range of 1550 nm. Preferably, the material of the high refractive index layer is Ta2O5.

The material of the low-refractive-index layer is at least one of SiO2, al2O3 and MgF2, and the refractive index of the low-refractive-index layer is in the range of 1550nm and is 1.38-1.6. Preferably, the material of the low refractive index layer is SiO2.

The base layer is made of silicon dioxide material or silicon material, and the refractive index of the base layer is 1.45-3.5 in the range of 1550 nm. Preferably, the base layer is at least one of D263T, WMS-15, BK7, FS, si.

The specific embodiment is as follows:

in the first embodiment, as shown in fig. 3, the transmittance in the P-polarization state under 45 degree incidence linearly changes, and under 45 degree incidence, the transmittance in the range of 1520-1570nm decreases from 90% to 10% with a slope of 1.6%/nm according to the target slope curve in table 1, see the target slope graph in fig. 2.

The relationship between the wavelength and the target transmittance of the first embodiment is shown in table 1:

TABLE 1 target transmittance curves

The film system structure comprises 92 layers of film systems formed by stacking two materials. The initial structure with 1550nm as the characteristic wavelength is as follows:

HL2HLHB

HL4HLHB

HLH2LHLHB

HLHL2HLHLHB

HLH2LHLHB

HL4HLHBAB

the film system is formed by 11 Fabry-Perot cavities and is formed by cascading low-refractive-index materials B with optical thickness different from 1/4, wherein A is a high-refractive-index material with optical thickness different from 1/4, and the corresponding film system is obtained by optimizing the thickness of B and the thickness of the first H of the next Fabry-Perot cavity. The order of the layers of the stack and the control of the film thickness of each layer are shown in table 2 below:

TABLE 2 example A film system structure and control method

The material of the high refractive index layer was Ta2O5, and the refractive index in the vicinity of 1550nm was 2.09.

The material of the low refractive index layer is SiO2, and the refractive index in the vicinity of 1550nm is 1.471.

The substrate material is common K9 optical glass and the refractive index is 1.52.

Referring to fig. 4, a difference graph between the target curve and the actual relationship in the first embodiment, it can be seen that the optical filter provided in the first embodiment can accurately realize that the transmittance and the wavelength are in a linear relationship.

The second specific embodiment is as follows:

in the second embodiment of the filter with a linear transmittance change at 0 degree incidence, under the 0 degree incidence condition, the transmittance in the range of 1520-1570nm decreases from 90% to 10% with a slope of 1.6%/nm according to the target slope curve of table 1, see the target slope curve of fig. 5, and fig. 6 is a practical relationship graph of the wavelength and the transmittance of the second embodiment, and it can be seen that the practical wavelength and the transmittance decrease from 90% to 10% in a linear manner.

The film system structure comprises 92 layers of film systems formed by stacking two materials. The initial structure with 1515nm as characteristic wavelength is as follows:

HL2HLHB

HL4HLHB

HLH2LHLHB

HLHL2HLHLHB

HLH2LHLHB

HL4HLHBAB

the film system is formed by 11 Fabry-Perot cavities and is formed by cascading low-refractive-index materials B with optical thickness different from 1/4, wherein A is a high-refractive-index material with optical thickness different from 1/4, and the corresponding film system is obtained by optimizing the thicknesses of A and B and the thickness of the first H of the next Fabry-Perot cavity. The order of the layers stacked and the control of the film thickness of each layer are shown in the following table 3:

TABLE 3 example two-film system structure and control method

The material of the high refractive index layer is Ta2O5, and the refractive index of the high refractive index layer is 2.128 near 1515 nm.

The material of the low refractive index layer was SiO2, and the refractive index in the vicinity of 1515nm was 1.451.

Fig. 7 is a difference diagram between the target curve and the actual relationship in the second embodiment of the present invention, and it can be seen that the linear relationship between the transmittance and the wavelength can be accurately realized by the optical filter provided in the second embodiment.

The third concrete example is as follows:

in the filter embodiment of the present embodiment in which the transmittance of the S-polarized light linearly changes under 45 degree incidence, under 45 degree incidence condition, the transmittance of the S-polarized light in the range of 1520 nm to 1570nm decreases from 90% to 10% with a slope of 1.6%/nm according to the target slope curve of table 1, as shown in the target slope graph of fig. 8, and as shown in the actual relationship diagram of the wavelength and the transmittance of the third embodiment of fig. 9, it can be seen that the actual wavelength and the transmittance decrease from 90% to 10% in a linear manner.

The film system structure comprises 98 layers of film systems formed by stacking two materials. The initial structure with 1675nm as characteristic wavelength is

HL2HLHB

HL4HLHB

HLH2LHLHB

HLHL2HLHLHB

HLH2LHLHB

HL4HLHB

HL2HLHBAB

The film system is formed by 12 Fabry-Perot cavities and is formed by cascading low-refractive-index materials (B) with optical thickness different from 1/4, wherein A is a high-refractive-index material with optical thickness different from 1/4, and the corresponding film system is obtained by optimizing the thicknesses of A and B and the thickness of the first H of the next Fabry-Perot cavity. The control method of the stacking layer sequence and the film thickness of each layer is shown in the following table 4:

TABLE 4 example four-film system structure and control method

The material of the high refractive index layer is Ta2O5, and the refractive index of the high refractive index layer is 2.124 near 1675 nm.

The material of the low refractive index layer is SiO2, and the refractive index of the low refractive index layer is 1.450 at the wavelength of 1675 nm.

Fig. 10 is a difference diagram between the target curve and the actual relationship in the second embodiment of the present invention, and it can be seen that the difference between the target curve and the actual curve of the optical filter provided in the third embodiment is small, and the linear relationship between the transmittance and the wavelength can be accurately realized.

The filter with the linearly changing transmittance provided by the invention has the advantages that the insertion loss or transmittance in a specific wavelength range linearly changes along with the wavelength, and the filter can be used for identifying the wavelength. The invention improves the film system structure, the film thickness and the monitoring mode, and can realize a high-precision linear change spectral curve.

It should be noted that: the sequence of the above embodiments of the present invention is only for description, and does not represent the advantages or disadvantages of the embodiments. And that specific embodiments have been described above. Other embodiments are within the scope of the following claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve desirable results.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments.

The foregoing description has disclosed fully preferred embodiments of the present invention. It should be noted that those skilled in the art can make modifications to the embodiments of the present invention without departing from the scope of the appended claims. Accordingly, the scope of the appended claims is not to be limited to the specific embodiments described above.

Claims

1. A method for manufacturing an optical filter with linearly changing transmittance is characterized by comprising the following steps:

preparing: carrying out ultrasonic cleaning on the blank base layer or the wafer which is not coated with the film;

film coating: the method comprises the steps of designing a film system, controlling the thickness of each film layer according to the design of the film system, and depositing the film by a film coating machine;

wherein, in the step of designing the film system, a material having a refractive index in a range of 1550nm from 1.45 to 3.5 is used as a base layer, a film system structure of the film system stacked on the base layer includes eight to twenty fabry-perot cavities, and a last layer of the fabry-perot cavities cascades a next fabry-perot cavity as a connection layer; the last layer of each said fabry-perot cavity is a refractive index layer of non-quarter optical thickness;

the membrane system structure of the Fabry-Perot cavity is as follows: (HL) m aH (LH) m B or (HL) m aH (LH) m BAB; wherein, (HL) m aH (LH) m BAB is the film system structure of the Fabry-Perot cavity of the last layer;

the optical thickness of the first layer of the fabry-perot cavity is obtained by optimizing the optical thickness of the last layer of the last fabry-perot cavity;

cutting: cutting the film into the size of the optical filter after the film coating is finished;

and (3) detection: and detecting the cut optical filter to obtain a qualified optical filter.

2. The method of claim 1, wherein the film system design further comprises: the optical thickness of the first layer of each fabry-perot cavity is optimized by the optical thickness of the connection layer, and is between 0.975 and 1.025 quarter-wave optical thicknesses, so that the transmission at the end of this layer reaches an extreme value;

the control of the film thickness of each film layer according to the film system design comprises the following steps: and the first layer of each Fabry-Perot cavity is monitored by adopting an extreme method in coating monitoring, so that the next film layer with the optical thickness of one quarter wavelength of each layer is monitored by adopting the extreme method.

3. The method for manufacturing an optical filter having a linear transmittance change according to claim 1, wherein the controlling of the film thickness of each thin film according to the film system design further comprises: the connection layer is monitored by adopting a crystal control/time control method.

4. The method of manufacturing an optical filter having a linearly-varying transmittance according to claim 1, wherein the number of the fabry-perot cavities is 11 to 20.

5. The method of claim 1, wherein the optical thickness of the low refractive index layer B having a non-quarter optical thickness is 0.371 to 2.605 quarter-wavelength optical thicknesses.

6. The method of manufacturing an optical filter having a linear transmittance change according to claim 1, wherein the high refractive index layer is made of at least one of Ta2O5, nb2O5 and TiO2, and has a refractive index in the range of 1550nm of 1.85 to 2.5.

7. The method of manufacturing an optical filter having a linearly changing transmittance according to claim 1, wherein the material of the low refractive index layer is at least one of SiO2, al2O3, and MgF2, and the refractive index of the low refractive index layer is in the range of 1.38 to 1.6 at 1550 nm.

8. The method for manufacturing an optical filter having a linear transmittance change according to claim 1, wherein the step of inspecting the cut optical filter to obtain an acceptable optical filter comprises: the transmittance of the qualified filter in the 1520-1570nm wave band range is reduced from 90% to 10% with a certain slope; or the transmittance of the wavelength of the optical filter prepared by detection is increased or decreased linearly along with the wavelength under the incident angle of 0-45 degrees.

9. The method of manufacturing a filter having a linearly changing transmittance according to claim 1, wherein the step of preparing comprises: the power of the ultrasonic wave is 600W-900W, the cleaning medicament is RS-26, and the frequency value is set to be 28KHZ-40KHZ.