TWI383173B - Film stacked structure - Google Patents

Description

Membrane stack structure

The invention relates to a membrane stack structure, in particular to a membrane stack structure applied to a beam splitting prism.

At present, optical coatings have been widely used in projectors, conventional cameras, digital cameras, mobile phones, lens sets used in astronomical telescopes, filters, etc., to enable these optical components to achieve different optical functions, such as: UV absorption , anti-reflection, color filter, infrared cut-off, etc.

As shown in FIG. 1, the present invention relates to a film stack structure 2 applied to a beam splitting prism 1. The dichroic prism 1 is used in a color separation system of various optical instruments. After the external light enters the dichroic prism 1, it is incident on the surface 3 coated with the film stack structure 2 at an angle of 45 degrees, and the light in the transmission wavelength range is transmitted through the film stack structure 2 from the upper surface 4 of the beam splitting prism 1 at the reflection wavelength. The light in the range is reflected by the film stack structure 2 and is emitted from the side surface 5 of the beam splitting prism 1 to achieve the effect of spectral filtering.

Existing membrane stack structures 2 typically use a periodic structure in which high and low refractive index materials are alternately laminated. The film stack structure 2 can be represented by ( HL ) ⁿ , where H represents a high refractive index film layer and L represents a low refractive index film layer. The ratio of the coefficients of the front of H and L represents the optical thickness ratio of the respective refractive index film layers, the physical meaning of which is the product of the physical thickness of the film layer and the refractive index of the film layer, and the optical thickness 1 is equal to 1/4 of the reference wavelength. The superscript n represents the number of cycles of the ( HL ) ⁿ structure. The high refractive index material has a refractive index greater than 2.1 and the low refractive index material has a refractive index less than 1.5.

As shown in FIG. 2, it is a transmission spectrum diagram of a membrane stack structure 2 ( HL ) ¹⁸ having a reference wavelength of 550 nm and an angle of incidence of 45 degrees. The solid line is the transmission spectrum line of natural light, the broken line is the transmission spectrum line of parallel polarized light (P-Polarized), and the dotted line is the transmission spectrum line of S-Polarized. The vertically polarized light is linearly polarized light having a plane of polarization perpendicular to a plane defined by the normal to the surface of the filter and the incident ray. The parallel polarized light is linearly polarized light whose plane of polarization is parallel to the plane of polarization of the vertically polarized light. Natural light can be seen as a superposition of parallel polarized light (P-Polarized) and vertically polarized light (S-Polarized). Since the vertically polarized light of the same wavelength and the parallel polarized light exhibit different refractive indices for the same material, the parallel polarization spectral characteristics and the vertical polarization spectral characteristics transmitted through the film stack structure 2 ( HL ) ¹⁸ are shifted, that is, The dashed curve and the dotted line in Fig. 2 show a shift in the wavelength direction, and the parallel polarized light transmits the half value wavelength of the spectral line (the wavelength corresponding to the transmittance of 50%) and the half value of the vertical polarized light transmission spectral line. The wavelengths differ by 70 nm or more. At this time, the non-smooth part of the transmission spectrum line of the natural light after mixing at the half-value wavelength affects the effect of the spectral filtering.

Because the parallel light emitted by the light source in the optical system usually has a certain angular error, the variation of the transmission spectral characteristics of the spectral filter film stack with the incident light angle has become one of the criteria for examining the quality of the spectral filter film stack.

Taking the incident angles of 53 degrees and 37 degrees as examples, the variation of the transmission spectrum characteristics of the film structure 2 ( HL ) ¹⁸ with the angle of incident light is investigated. As shown in FIG. 3 and FIG. 4 , the solid line is the transmission spectrum line of natural light, the broken line is the transmission spectrum line of parallel polarized light, and the dotted line is the transmission spectrum line of the vertically polarized light. As can be seen from Fig. 3, when the incident angle is large (incident angle is 53 degrees), the nonlinear non-smooth portion of the natural light transmission spectral line of the stack structure 2 ( HL ) ¹⁸ is more pronounced, and the reflection wavelength range is reflected. The rate is also much lower. From the comparison of Fig. 3 and Fig. 4, it can be found that the transmission spectrum characteristic of the film stack structure 2 changes significantly with the angle. If the wavelength corresponding to the transmittance is 30%, the natural light transmission when the incident angle is 53 degrees is observed. The spectral line differs from the natural light transmission spectral line at an incident angle of 37 degrees by 80 nm.

In summary, the existing membrane stack structure 2 ( HL ) ¹⁸ has a poor difference in refractive index of the high and low refractive index materials, resulting in poor spectral filtering effect, and the transmission spectral characteristics vary significantly with angle and at large angles. Disadvantages such as a decrease in the reflectance of the reflection band at the time of incidence.

In view of this, it is necessary to provide a film stack structure having a better spectral filtering effect.

A membrane stack structure comprising a transparent substrate and a periodic membrane stack superposed thereon. The periodic structure of the periodic film stack is an alternately laminated high refractive index film layer and an intermediate refractive index film layer having a refractive index ranging from 1.71 to 1.79 or 1.81 to 1.86.

Compared to the prior art, the membrane stack structure uses an intermediate refractive index film layer Replacing the low refractive index film layer in the existing film stack structure, the refractive index difference between the two refractive index film layers in the periodic film stack structure is reduced, and the difference between the transmission vertical polarization spectrum and the transmission parallel polarization spectrum is shortened. The purpose of improving the transmission spectrum characteristics of the spectroscopic filter is achieved.

Please refer to FIG. 5 , which is a schematic diagram of a membrane stack structure 10 provided by the present invention. The film stack structure 10 includes a transparent substrate 102 and a periodic film stack 104 stacked thereon. The periodic structure of the periodic film stack 104 is an alternating layer of the high refractive index film layer 106 and the intermediate refractive index layer 108. The periodic structure of the periodic film stack 104 can be expressed as ( HM ) ⁿ , where H represents a high refractive index film layer 106, M represents an intermediate refractive index film layer 104, and the ratio of coefficients in front of H and M represents each The optical thickness ratio of the refractive index film layer, the superscript n indicates the number of cycles of the periodic structure.

The high refractive index film layer 106 and the intermediate refractive index film layer 108 of the periodic film stack 104 ( HM ) ^{n have} the same optical thickness. The number of cycles of the periodic film stack 104 ( HM ) ⁿ is set according to the wavelength range in which transmission and reflection are required. In this embodiment, the periodic film stack 104 ( HM ) ^{n has} a period of 18, a wavelength range of 480 nm to 670 nm, and a wavelength range of 400 nm to 440 nm.

The material of the transparent substrate 102 can be a transparent glass or plastic material, such as a colorless and highly transparent bismuth glass (B270) or a slate glass. The high refractive index film layer 106 has a refractive index greater than 2.1, and the material thereof may be one of titanium dioxide, tantalum pentoxide, and tantalum pentoxide. Refraction of the intermediate refractive index film layer 108 The rate ranges from 1.71 to 1.79 or from 1.81 to 1.86, and the material may be the intermediate refractive index material M2 or M3 produced by Merck & Co., Germany. In addition to the materials mentioned in the present embodiment, other materials which can satisfy the refractive index requirements of the respective film layers can be used, and each film layer is obtained by a physical vapor deposition method.

Please refer to FIG. 6 , which is a transmission spectrum diagram of the periodic film stack 104 ( HM ) ¹⁸ at a reference wavelength of 475 nm and an incident angle of 45 degrees. The solid line is the transmission spectrum line of natural light, the broken line is the transmission spectrum line of parallel polarized light, and the dotted line is the transmission spectrum line of vertically polarized light. Comparing FIG. 6 with FIG. 2, it can be seen that the half-value wavelength difference between the parallel positive polarization spectrum and the vertical polarization spectral line transmitted by the periodic film stack 104 ( HM ) ¹⁸ is only 40 nm. Compared to the prior art stack structure 2 ( HL ) ¹⁸ , the periodic film stack 104 ( HM ) ¹⁸ provided by the present invention greatly reduces the offset effect of the parallel polarization spectral line and the vertical polarization spectral line, so that the periodic film is transmitted through the periodic film. The spectral characteristics of the natural light of the stack 104 ( HM ) ¹⁸ are greatly improved at the half-value wavelength, and the spectral filtering effect of the periodic film stack 104 ( HM ) ¹⁸ is improved.

Please refer to FIG. 7 and FIG. 8 , which are transmission spectrum diagrams of the periodic film stack 104 ( HM ) ¹⁸ provided by the present invention at a reference wavelength of 475 nm and incident angles of 53 degrees and 37 degrees, respectively. The solid line is the transmission spectrum line of natural light, the broken line is the transmission spectrum line of parallel polarized light, and the dotted line is the transmission spectrum line of vertically polarized light. 7 and FIG. 3, the periodic film stack 104 ( HM ) ¹⁸ provided by the present invention is compared with the shift of the parallel polarized light and the vertical polarized light transmission spectrum at a large incident angle (incident angle of 53 degrees). The existing membrane stack 2 ( HL ) ^{18 has} been greatly improved. Secondly, in the reflection wavelength range, the periodic film 104 ( HM ) ¹⁸ provided by the present invention can still maintain a high reflectivity and effectively improve the reflection wavelength range of the existing film stack 2 ( HL ) ¹⁸ at a large incident angle. The problem of increased reflectivity. 7 , FIG. 8 , FIG. 3 and FIG. 4 , the periodic film stack 104 ( HM ) ¹⁸ provided by the present invention has a shift of parallel polarized light and a vertically polarized light transmission spectrum at an incident angle of 37 degrees. The existing film stack 2 ( HL ) ^{18 has} a large improvement, and the transmission spectrum characteristic of the periodic film stack 104 ( HM ) ¹⁸ provided by the present invention varies with the incident angle in the range of the incident angle from 37 to 53. The change is small, and a better transmission spectrum characteristic can be obtained with a larger incident angle range.

Compared with the prior art, the periodic film stack ( HM ) ⁿ provided by the present invention replaces the low refractive index material in the existing film structure ( HL ) ⁿ by using an intermediate refractive index material, so that the refractive index of the different refractive index film layers The difference is reduced to effectively reduce the offset between the parallel polarization spectrum and the vertical polarization spectrum at the half-value wavelength of the transmission spectrum of the spectral filter film at an angle of 45 degrees, which improves the existing film structure ( HL ) ⁿ at a large incidence. The reflectance decreases in the wavelength range of the reflection angle and reduces the transmission spectral shift of the spectrally-filtered film layer when the incident angle changes.

In summary, the present invention has indeed met the requirements of the invention patent, and Patent application. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

1‧‧‧Splitting prism

2‧‧‧membrane structure

4‧‧‧Splitting prism upper surface

3‧‧‧ Surface coated with membrane stack structure

5‧‧‧Split prism side

10‧‧‧membrane structure

102‧‧‧Transparent substrate

104‧‧‧Recurrent membrane stack

106‧‧‧High refractive index film

108‧‧‧Intermediate refractive index film

1 is a schematic view showing the structure of a beam splitting prism.

2 is a transmission spectrum diagram of the film stack structure ( HL ) ¹⁸ when the incident angle is 45 degrees and the reference wavelength is 550 nm.

Fig. 3 is a transmission spectrum diagram of the film stack structure ( HL ) ¹⁸ when the incident angle is 53 degrees and the reference wavelength is 483 nm.

4 is a transmission spectrum diagram of the film stack structure ( HL ) ¹⁸ when the incident angle is 37 degrees and the reference wavelength is 483 nm.

FIG. 5 is a schematic structural view of a periodic film stack ( HM ) ⁿ provided by the present invention.

Fig. 6 is a transmission spectrum diagram of the film stack structure ( HM ) ¹⁸ when the incident angle is 45 degrees and the reference wavelength is 475 nm.

Fig. 7 is a transmission spectrum diagram of the film stack structure ( HM ) ¹⁸ when the incident angle is 53 degrees and the reference wavelength is 475 nm.

Fig. 8 is a transmission spectrum diagram of the film stack structure ( HM ) ¹⁸ when the incident angle is 37 degrees and the reference wavelength is 475 nm.

10‧‧‧membrane structure

102‧‧‧Transparent substrate

104‧‧‧Recurrent membrane stack

106‧‧‧High refractive index film

108‧‧‧Intermediate refractive index film

Claims (10)

A film stack structure comprising a transparent substrate and a periodic film stack stacked thereon, the improvement being that the periodic structure of the periodic film stack is an alternating layer of a high refractive index film layer and an intermediate refractive index The film layer has a refractive index ranging from 1.81 to 1.86. The membrane stack structure of claim 1, wherein the transparent substrate is transparent glass or plastic. The membrane stack structure of claim 2, wherein the material of the transparent substrate is bismuth glass (B270) or blue glazing. The membrane stack structure of claim 1, wherein the high refractive index film layer of the periodic film stack has the same optical thickness as the intermediate refractive index film layer. The membrane stack structure of claim 1, wherein the high refractive index film layer has a refractive index greater than 2.1. The membrane stack structure of claim 1, wherein the number of cycles of the periodic membrane stack is set according to a wavelength range in which transmission and reflection are required. The membrane stack structure of claim 6, wherein the periodic membrane stack has a cycle number of 18. The membrane stack structure according to claim 1, wherein the high refractive index film layer material is one of titanium dioxide, antimony pentoxide or antimony pentoxide. The membrane stack structure according to claim 1, wherein the intermediate refractive index film layer material is one of Merck materials M2 or M3. The membrane stack structure of claim 1, wherein the periodic membrane stack is produced by a physical vapor deposition method.