JP2018185388A - Optical filter and optical device using the same - Google Patents

Abstract

An angle limiting element for input / output light using simple multilayer interference has low sensitivity to an angle and monotonously shifts a short wavelength as the incident angle increases, so that the effect of angle limiting is not high. A simple multilayer film cannot be realized by arranging unit structures in which two one-dimensional multilayer structures having different structure widths are arranged so as to be adjacent to each other with a certain deviation in the depth direction. The angle characteristic of the optical filter is realized. [Selection] Figure 1

Description

  The present invention relates to an optical filter, and more particularly to an optical filter having color selectivity and angle selectivity.

  A color selective filter is used for the purpose of selecting only light in a desired wavelength band of the incident light flux. Among them, a spectral filter using interference of a dielectric multilayer film is known as a general one. A spectral filter using multilayer film interference can be obtained by forming a laminated structure in which the refractive index and the layer thickness are adjusted in accordance with a desired wavelength band. Unlike a spectral filter using absorption, when the light incident angle to the multilayer interference filter changes, the optical path length in the medium changes, and the reflected wavelength changes. By utilizing this incident angle characteristic, it is possible to obtain an angle limiting filter that separates light of the same wavelength with different incident angles.

  Patent Document 1 proposes an angle limiting filter that operates only for a specific LED wavelength by a dielectric multilayer film in order to sharpen an acquired image in a barcode reader. In recent years, image display using fluorescence from phosphors, LEDs, and the like has been proposed, but the problem is that the efficiency of capturing fluorescence is not high. This is because the fluorescence emitted from the light emitting source is Lambert diffused and distributed at a wide angle, so that a capture loss occurs in light collection by a specific Fno optical system.

  Patent Document 2 proposes a wavelength conversion device in which an optical filter for limiting an emission angle is provided on a light source and a reflection structure is provided on the back surface of the light source. By changing the angle in the backside reflection without emitting fluorescent light with a specific angle or more, it is possible to convert light emitted at a high angle that cannot be captured by the optical system to a low angle.

JP 2009-290414 JP JP 2011-118187

  However, an angle limiting filter using a general dielectric multilayer filter is not sensitive to spectral wavelength with respect to an angle near normal incidence. When an angle limitation is set for a desired wavelength band, the transmission wavelength band is limited. There are problems such as a decrease in sensitivity to bandwidth and angle. In Patent Document 1, the transmission bandwidth is about 25 nm, which is a characteristic that functions only in a very narrow band. Wide range of blue band (400-500 nm), green band (500-600 nm), red band (600-700 nm) In principle, it is difficult to realize a multilayer structure. Patent Document 2 does not propose a filter form that can be specifically realized. Therefore, an object of the present invention is to provide an optical filter that functions as an angle limiting filter for a wide wavelength band.

The present invention has been made in view of the above problems, and is an optical filter in which a laminated structure of a dielectric is formed on a light-transmitting substrate.
When incident on the substrate at a low angle, it reflects two wavelength bands and transmits the intermediate wavelength band. When the incident angle increases, the reflected wavelength band changes and transmits when the incident angle is low. By reflecting the light in the intermediate wavelength band, it has a function to limit the incident and output angles for light in a specific wavelength band,
When the direction perpendicular to the lamination plane of the optical filter is the X, Y direction, the depth direction with the direction from the lamination surface toward the substrate as the Z direction, and the direction from the surface layer toward the substrate as the positive direction, Consists of at least two types of optical layers,
A first optical layer having a physical layer thickness dH having the highest refractive index nH;
Of the multilayer film structures with different widths W1 and W2 formed by alternately laminating the second optical layers having the physical layer thickness dL having the lowest refractive index nL, the multilayer film structure having the width W1 is shifted in the Z direction. The unit structure of the shape that is arranged adjacently while being shifted by D has a structure in which the unit structure is formed on the substrate so as to form a lattice in at least a one-dimensional direction, W1, W2, dH, dL, D Satisfies the following relational expression.

0.3 <W2 / W1 <0.6
0.35 <| D | / (dH + dL) <0.65
An optical device according to one aspect of the present invention includes the optical filter.

  According to the present invention, a simple multilayer film is formed by arranging unit structures in which two one-dimensional multilayer structures having different structure widths are arranged so as to be adjacent to each other with a deviation width in a depth direction. An angle limiting filter having an angle characteristic of an optical filter that cannot be realized can be obtained.

(A) Configuration of optical filter (B) Definition of tilt angle φ in unequal width structure Incident angle dependence of spectral reflectance of optical filter (A) Simple multilayer film (B) Alternate multilayer film (A) Incident angle dependence of central reflection wavelength of simple multilayer film (B) Incident angle dependence of central reflection wavelength of staggered multilayer film (C) Diagram showing structure regarded as inclined multilayer film Incident angle dependence of spectral reflectance of optical filters (A) W1 / W2 dependence of spectral reflectance of optical filter (B) W1 / W2 dependence of reflectance ratio R1 / R2 Configuration diagram of optical filter with in-plane two-dimensional periodicity Incident angle dependency of spectral transmittance and reflectance of Example 1G of the present invention (θ ≦ 30 deg.) Incident angle dependence (θ> 30 deg.) Of spectral transmittance and reflectance of Example 1G of the present invention Incident angle dependency of spectral transmittance and reflectance of Example 1B of the present invention (θ ≦ 30 deg.) Incident angle dependence of spectral transmittance and reflectance of Example 1B of the present invention (θ> 30 deg.) Incident angle dependency of spectral transmittance and reflectance of Example 1R of the present invention (θ ≦ 30 deg.) Incident angle dependency of spectral transmittance and reflectance of Example 1R of the present invention (θ> 30 deg.) Incident angle dependence of spectral transmittance and reflectance of Example 2 of the present invention (θ ≦ 30 deg.) Incident angle dependency of spectral transmittance and reflectance of Example 2 of the present invention (θ> 30 deg.) Configuration schematic diagram of wavelength converter of Example 3 of the present invention Configuration schematic diagram of projection image apparatus of Example 4 of the present invention Configuration schematic diagram of image pickup apparatus of Embodiment 5 of the present invention

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1A is a schematic configuration diagram of an optical filter 100 of the present invention. The optical filter 100 is obtained by laminating an optical layer on a substrate 101 having a refractive index ns and a visible light transmitting property. The directions orthogonal to each other in the lamination plane are the X and Y directions, and the depth direction is the Z direction. The sign of the Z direction is positive in the surface layer direction from the substrate. The optical filter 100 is configured by repeatedly stacking optical alternating layers of at least two kinds of materials m times.

  Further, it may be composed of three or more types of optical layers in order to suppress ripples. The material is mainly assumed to be a dielectric. However, in the above repetitive structure, the layer having the highest refractive index nH and the physical layer thickness dH is defined as the first optical layer 102, and the layer having the lowest refractive index nL and the physical layer thickness dL is defined as the second optical layer 103. The optical filter 100 includes a multilayer film structure having a width W1 of two multilayer film structures having widths W1 and W2, in which a first optical layer 102 and a second optical layer 103 are alternately stacked m times. A unit structure 104 having a staggered shape is formed by being shifted to the surface layer side by a shift width D in the direction.

  The embodiment proposed by the present invention does not equalize W1 and W2, and has a unit structure of unequal width. By forming such unit structures of unequal width on the substrate, a band pass characteristic is realized that has a reflection band centered on two wavelengths and transmits an intermediate wavelength band as described later. be able to. The unit structure 104 can be obtained, for example, by repeatedly laminating the first optical layer 102 and the second optical layer 103 on a substrate 101 that has been subjected to concave and convex groove patterning as shown in FIG. It is not always necessary to pattern the groove on the substrate, and a manufacturing method by groove patterning on the first optical layer or the second optical layer may be used.

Fig. 1 (B) shows the inclination angle of the structure defined in the unit structure. When D is smaller than 0.5 (dL + dH), φ = tan ^-1 (| D | / (0.5 (W1 + W2)) ), And when D is greater than 0.5 (dL + dH), it is defined by the formula φ = tan ^-1 (((dL + dH)-| D |) / (0.5 (W1 + W2))) Suppose that

  The optical filter 100 is characterized in that the unit structures 104 are arranged on a substrate 101. At this time, when the unit structure 104 satisfies the following conditional expression, an optical filter that functions as an angle limiting filter for a wide wavelength band is realized.

0.3 <W2 / W1 <0.6… (1)
0.35 <| D | / (dH + dL) <0.65… (2)
Prior to the explanation of the conditional expression, first, a simple explanation will be given on the incident angle dependence of the central reflection wavelength of a simple multilayer film having no in-plane fine shape and a staggered multilayer film structure having a structure width W1 = W2. I do. For comparison in the description, the incidence angle dependency of the transmittance spectrum of the simple multilayer film having the in-plane fine shape having the structural parameters shown in Table 1 and the alternate multilayer film is obtained by calculation.

  The structure of the staggered multilayer film here is a shape that is uniform in the Y direction and arranged so that the unit structures form a one-dimensional lattice in the X direction, and due to the influence of the substrate, the substrate refractive index ns = The calculation was performed as 1. All subsequent spectrum calculations were performed by Finite Difference Time Domain (FDTD) method or Rigorous Coupled Wave Analysis (RCWA) method. The FDTD method is a method of calculating the time evolution of the electric and magnetic fields by dividing the input permittivity distribution into minute mesh spaces and solving the Maxwell equation between adjacent meshes. In the RCWA method, the dielectric constant distribution of each layer of the input staircase lattice is expanded in the Fourier series, the reflection diffraction component and transmission diffraction component obtained from the boundary conditions of each layer given by the Maxwell equation are obtained, and the reflection / This is a calculation method for obtaining transmission diffraction efficiency.

  FIG. 2A shows the incident angle dependence of the spectral reflectance of the simple multilayer film whose structural parameters are shown in Table 1. The horizontal axis represents wavelength and the vertical axis represents reflectance. In order to discuss the dependence of the spectral wavelength shift on the incident angle, as shown in Fig. 2 (A), the definition of the central reflection wavelength λref is the bottom wavelength on the short wavelength side with a reflectance of 50% and the long wavelength with a reflectance of 50%. It is defined as the wavelength of the midpoint of the side skirt wavelength. The results for incident angles θ = 0, 30, 60 deg. Are shown, and the incident light is P-polarized light. In a simple multilayer film, the behavior of a short wavelength shift monotonously with increasing incident angle can be obtained.

  Next, the incidence angle dependency of the uniform width staggered multilayer film when W1 and W2 are equal will be described. FIG. 2B shows the incident angle dependency of the spectral reflectance of the uniform-width staggered multilayer film whose structural parameters are shown in Table 1. The results for incident angles θ = 0, 30, 60 deg. Are shown. The incident plane is an XZ plane perpendicular to the grating, and P-polarized (TM-polarized) incident light. The central reflection wavelength λ ref of the uniform width staggered multilayer film in FIG. 2 (B) monotonically increases as the incident angle increases, and the wavelength in the direction opposite to the incident angle dependence in the simple multilayer film shown in FIG. 2 (A). It has become a shift.

  3A shows the incident angle dependence of the central reflection wavelength λref of the simple multilayer film whose structural parameters are shown in Table 1, and FIG. 3B shows the central reflection of the uniform-width staggered multilayer films whose structural parameters are shown in Table 1. The result of the incident angle dependence of the wavelength λref is plotted. In the figure, the horizontal axis represents the incident angle θ, and the vertical axis represents the center reflection wavelength λref. The incident angle dependence of the central reflection wavelength in the simple multilayer film of FIG. 3A is well explained by the calculation model result derived by Snell's law indicated by the dotted line 301.

  On the other hand, the incident angle dependence of the central reflection wavelength in the uniform-width staggered multilayer film in FIG. 3B is calculated by Snell's law similar to the simple multilayer film because the center reflection wavelength λref shifts longer as the incident angle increases. It cannot be explained by the model. In view of the fact that the structure of this embodiment is an anisotropic structure in which the in-plane X-direction period is substantially the same as the wavelength and sufficiently large with respect to the period in the depth Z direction, FIG. Approximate calculation of the central reflection wavelength was performed with the inclined multilayer film shown. The approximate calculation was performed by using the average traveling angle <θ ′> in the medium for simplicity.

The average advancing angle <θ '> is the effective refractive index neff = {2 / (1 / nH ² + 1 / nL ² ) when vertically polarized light (TM polarized light, in-paper polarized light) parallel to the grating arrangement direction is incident. )} By using ^1/2, we obtain <θ '> = sin ^-1 (sinθ / neff) from Snell's law. In the calculation of neff, a one-dimensional lattice structure in which a medium having a refractive index nH and a medium having a refractive index nL are filled 1: 1 is assumed. When the above <θ ′> was used, the result that the dependence of the central reflection wavelength λref on the incident angle θ in the inclined multilayer film follows λref (θ) = λref ′ cos (<θ ′> − φ) was obtained.

Here, λref ′ is a reflection wavelength determined by the optical distance nd of the constituent film determined by λref ′ = 2 (nHdH + nLdL) cosφ. In the equation of λref ″, cos φ is a term due to a substantial reduction in the optical layer thickness due to the fact that it is regarded as a tilted multilayer film. The calculation model result of the incident angle dependence of the central reflection wavelength λref when regarded as an inclined multilayer film is indicated by a dotted line 302 in FIG. It can be seen that the dotted line 302 of the calculation model result is well reproduced from 0 deg. To an incident angle range of sin ⁻¹ (neff sinφ).

Here, the angle sin ⁻¹ (neff sinφ) is a value corresponding to an incident angle in air in which the average traveling angle <θ ′> in the medium is φ. From the relational expression of λref (θ), the effective layer thickness change increases as the deviation of the average traveling angle <θ '> of light in the medium from the inclination angle φ increases, and the wavelength shift amount increases with respect to the angle change. It is suggested that From the above, the behavior of the long wavelength shift monotonously with increasing the incident angle of the staggered multilayer structure is not explained by the incident angle dependence using Snell's law in the simple multilayer film, but is regarded as an inclined multilayer film. It was shown to be explained by approximate calculation.

  Next, the incident angle dependence of the central reflection wavelength of the unequal width staggered multilayer film having different values of W1 and W2 in the embodiment of the present invention as shown in FIG. I do. FIG. 4 shows the incident angle dependence of the transmittance spectrum of the staggered multilayer film having the unit structure of unequal width having the structural parameters of the unequal width staggered multilayer film shown in Table 1. W1 = 200 nm, W2 = 100 nm, and W2 / W1 = 0.5. The results for incident angles θ = 0, 30, 60 deg. Are shown, and the incident light was P-polarized light (TM-polarized light). In the case of θ = 0 deg., it can be seen that a long wavelength side reflection band 401 having a central wavelength of 475 nm and a short wavelength side reflection band 402 having a central wavelength of 390 nm are formed.

These two center wavelengths are almost the same as the center wavelengths of the simple multilayer film and the uniform-width staggered multilayer film shown in FIGS. 2A and 2B, and this characteristic is common in unequal-width staggered multilayer films. It holds. That is, the center wavelength of the long wavelength side reflection band 401 is approximated by the equation of λ1 = 2 (nHdH + nLdL), and the reflection wavelength of the short wavelength side reflection band 402 is estimated by the equation of λ2 = 2 (nHdH + nLdL) cos ² φ. This reflection wavelength type will be described later. The transmission wavelength at the midpoint between λ1 and λ2 is defined as λ0. The direction of the wavelength shift with respect to the increase in the incident angle of both the long wavelength side reflection band 401 and the short wavelength side reflection band 402 is the direction toward λ0 in the reverse direction, and at θ = 60 deg. Form.

  That is, with respect to the wavelength band centered on λ 0, low angle incident light is transmitted and high angle incident light is reflected, and functions as an angle limiting filter. As shown in FIG. 3A, the reflection wavelength of the simple multilayer film monotonously shifts short as the incident angle increases. Therefore, the simple multilayer film does not function as an angle limiting filter for light at a high incident angle. In addition, the uniform multi-layer film of W1 = W2 shown in FIG. 3B has a constant reflection wavelength at a high incident angle, but has a low wavelength selectivity because there is no reflection band on the long wavelength side, and the incident angle. The sensitivity to is low. From the above, it is explained that the present invention is an embodiment suitable for an angle limiting filter.

  Next, conditions for realizing a band-pass characteristic that forms two reflection bands in a multilayer film with unequal widths at the time of vertical incidence and transmits an intermediate wavelength band will be considered. Fig. 5 (A) shows the parameters of non-uniformly staggered multilayer films in Table 1 except for W1 and W2, and the transmittance spectrum when W2 / W1 is changed while W1 + W2 = 300 nm is constant. Shows W2 / W1 dependence. In the case of W2 / W1 = 0, only the long wavelength side reflection band 501 of the center reflection wavelength λ1 determined by the simple multilayer film interference condition is formed, whereas the center determined by the inclined multilayer film as W2 / W1 is increased. A short wavelength side reflection band 502 having a reflection wavelength λ 2 is formed. When increasing to W2 / W1 = 1, the long wavelength side reflection band 501 of the center reflection wavelength λ1 disappears.

  FIG. 5B shows the W2 / W1 dependence of R1 / R2 on the reflectance ratio of the long wavelength side reflection band 501 and the short wavelength side reflection band 502. It is explained that when the ratio of W2 / W1 is from 0.3 to 0.6, the reflectance of the two reflection bands is almost equal, so that it is easy to realize bandpass performance and to function as an element that limits the incident angle.

  In addition, when the deviation width D has a value of about half cycle 0.5 (dL + dH), it is easy to form two reflection bands, and the calculation result shows that the range of conditional expression (2) is desirable for D value. It has been. From the above, the conditions necessary for forming the staggered structure with the angle limiting performance are the two conditions of the ratio of the structure width by the conditional expression (1) and the deviation width D of about a half cycle by the conditional expression (2). It was shown that there is.

  Subsequently, in order to provide bandpass performance that transmits a band centered on the desired wavelength λ0, it is necessary to control the center reflection wavelengths of the two reflection bands, and the following equation must be satisfied.

0.35 <(nHdH + nLdL) / λ1 <0.65… (3)
0.35 <(nHdH + nLdL) cos ² φ / λ2 <0.65… (4)
Here, φ is an inclination angle determined by the unit structure shown in FIG. 1B, and in the case of | D | <= 0.5 (dL + dH),
φ = tan ^-1 (| D | / (0.5 (W1 + W2)))… (5a)
If | D |> 0.5 (dL + dH),
φ = tan ^-1 (((dL + dH)-| D |) / (0.5 (W1 + W2)))… (5b)
Is defined by Hereinafter, the expressions (5a) and (5b) are collectively referred to as expressions (5).

The term cos ² φ in conditional expression (4) is attributed to the effect of effective film thickness reduction regarded as an inclined multilayer film and the effect of oblique incidence on the inclined multilayer film. When the optical filter has a function of limiting the angle with respect to the entire wide band of about 100 nm, it is necessary to provide a wide transmission band at the time of normal incidence, so it is necessary to increase the value of cosφ. . On the other hand, when the optical filter is provided with an angle limiting function for narrow-band light, the value of cosφ is small and sufficient, and the smaller the value of cosφ, the more parallel light can be transmitted. . If it falls outside the range of conditional expressions (3) and (4), it is not desirable because a reflection band centered on a desired wavelength cannot be formed.

  In addition, the reflection bands determined by the conditional expressions (3) and (4) do not overlap, and it is desirable to satisfy the following conditional expression in order to form a transmission band at the time of vertical incidence.

25 deg. <Φ <45 deg.… (6)
The value on the left-hand side is the lower limit required to form the transmission band when the full width at half maximum of the reflection band with the central reflection wavelength λ1 and the reflection band with the central reflection wavelength λ2 is 50 nm, and the value on the right-hand side is the two reflection bands It is a necessary condition for securing the bandwidth. Outside the range of conditional expression (6), it is not desirable because bandpass characteristics cannot be realized, or performance degradation such as a reduction in reflectance occurs.

  Further, in order to increase the sensitivity to the incident angle, it is desirable that the composition ratio of the low refractive index layer is large. Therefore, it is desirable to satisfy the following conditional expression.

0.5 <(nHdH / nLdL) <1.1… (7)
The maximum value on the right side is determined so as to include dH / dL = nL / nH, which is a general multilayer film design condition for maximizing the reflectance and bandwidth. Also, the minimum value on the left side is set to ensure reflectivity and bandwidth. Outside the range of conditional expression (7), it is necessary to increase the number of layers in order to ensure reflectivity and bandwidth, which is not desirable.

  Up to this point, we have illustrated examples of one-dimensional periodic structures. However, staggered multilayered film structures with two-dimensional periodicity that are arranged so as to form a lattice in the in-plane XY direction are also incident on the XZ plane and YZ plane. This is a desirable structure because it works as an optical filter with suppressed angular dependence. When a multilayer film structure having a two-dimensional periodicity is looked down on from the Z direction, a plan view having an uneven shape as shown in FIG.

  In FIG. 6A, 601 corresponds to a convex region, and 602 corresponds to a concave region. The unit structure of the staggered multilayer film structure having two-dimensional periodicity has a staggered structure in the Y direction due to the shift width D in the unit structure as well as the X direction. The X-direction width is defined as Wx1 and Wx2, and the Y-direction width is defined as Wy1 and Wy2, respectively. The unit structure 605 at this time has a structure width Wx1, Wx2, Wy1, Wy2 in the X direction and the Y direction, respectively, as shown schematically in FIG. A plan view when viewed from the Z direction is a rectangular shape.

The cross-sectional shapes cut out in the YZ plane and the XZ plane are shapes as indicated by reference numerals 603 and 604 in FIGS. 6B and 6C. At this time, as in φ, φX and φY are based on Wx1, Wx2, Wy1, and Wy2, depending on the magnitude relationship between | D | and 0.5 (dL + dH), and the following equations (5a '), (5b'), (5a ''), Defined by (5b'').
φX = tan ^-1 (| D | / (0.5 (Wx1 + Wx2)))… (5a ')
φX = tan ^-1 (((dL + dH)-| D |) / (0.5 (W1 + W2)))… (5b ')
φY = tan ^-1 (| D | / (0.5 (Wy1 + Wy2)))… (5a '')
φY = tan ^-1 (((dL + dH)-| D |) / (0.5 (W1 + W2))) ... (5b '')
Further, in order to realize the incidence angle dependency suppression, it is desirable that φX and φY defined for the X and Y directions satisfy the following equations (6 ′) and (6 ″).
25 deg. <ΦX <45 deg.… (6 ')
25 deg. <ΦY <45 deg.… (6 '')
The above structure can be said to be desirable because the incidence angle dependency in the XZ plane and the YZ plane is suppressed.

  The fine element structure constituting the optical filter of the present invention is produced, for example, by stacking on a finely processed substrate. Examples of the fine processing method include general etching technology and nanoimprint technology. As a laminated film forming method, a general vapor deposition method or a sputtering method can be given. Although the cross-sectional shape is different from the rectangular shape, an auto-cloning technique in which zigzag diffraction gratings are stacked in multiple layers by repeating stacking and etching may be used. The manufacturing method is not limited to the above-described manufacturing method, and a fine uneven shape processing method or a multilayer film forming method suitable for the present invention may be used.

  Also, depending on the layer deposition method, it is assumed that the rectangular shape collapses as it approaches the surface layer due to lateral deposition, etc., but the definition of φ is always the structural width W1 and W2 in the bottom layer, the Z-axis direction in the bottom layer It is assumed that it is defined from the equation (5) using the deviation width D.

[Example 1]
The optical filter according to the first embodiment of the present invention will be described. The optical filter of Example 1G is designed to have an angle limiting capability of transmitting the green band when incident at a low angle and reflecting the green band when incident at a high angle.

  The schematic diagram of the optical filter of the first embodiment 1G is as shown in FIG. A first optical layer 102 made of TiO2 having a refractive index nH = 2.36 and a second optical layer 103 made of SiO2 having a refractive index nL = 1.47 were alternately and repeatedly laminated on a synthetic quartz substrate 101 having a refractive index ns = 1.47. It has a structure. The physical layer thickness dH of the first optical layer 102 is 50 nm, and the physical layer thickness dL of the second optical layer 103 is 130 nm. The optical filter 100 has a multilayer film structure with a width W1 in a multilayer film structure with W1 = 230 nm and W2 = 110 nm in which the first optical layer 102 and the second optical layer 103 are alternately laminated 14 times. The unit structure 104 has a shape that is shifted in the Z direction by D = 90 nm and arranged in the X direction.

  The unit structure 104 has a uniform shape in the Y direction. The optical filter 100 has a structure in which the unit structures 104 are arranged on the substrate 101 so as to form a one-dimensional lattice in the X direction. FIG. 1A shows a shape in which a first optical layer 102 and a second optical layer 103 are stacked on a substrate 101 that has been patterned with a rectangular one-dimensional lattice. There is no need for patterning. The structural parameters of Example 1G are shown in Table 2. Since W2 / W1 of the unit structure 104 is 0.48, the conditional expression (1) is satisfied, and | D | / (dH + dL) satisfies the conditional expression (2) from 0.50. Conditional expression (6) is satisfied from φ = 27.9 deg., And conditional expression (7) is satisfied from nHdH / nLdL = 0.62.

  Next, the transmittance and reflectance spectrum of the green band angle limiting filter of Example 1G at a low incident angle (θ ≦ 30 deg.) Are shown in FIG. Fig. 7 (A) is the transmission spectrum of all order integration, (B) is the transmission spectrum of 0th diffraction order, (C) is the transmission spectrum of 1st diffraction order or higher, and (D) is the total order integration. The reflectance spectrum, (E) shows the reflectance spectrum of the diffraction order 0th order, and (F) shows the reflectance spectrum integrated with the diffraction order 1st order or more. The incident plane is the XZ plane, and the polarization is P polarization (TM polarization).

  At the incident angle θ = 0 deg., The transmission center wavelength λ0 is λ0 = 540 nm, the center reflection wavelength λ1 is λ1 = 620 nm, and the center reflection wavelength λ2 is λ2 = 475 nm. From this result, as shown in Table 2, it was shown that conditional expression (3) and conditional expression (4) were satisfied. As shown in the reflectance spectrum of FIG. 7D, as the incident angle θ increases, the reflectance of the band centering on λ 0 becomes almost 100%. Subsequently, the transmittance and reflectance spectrum of the green band angle limiting filter at a high incident angle (θ> 30 deg.) Are shown in FIG.

  Fig. 8 (A) is the transmission spectrum of all order integration, (B) is the transmission spectrum of 0th diffraction order, (C) is the transmission spectrum of 1st diffraction order or more, and (D) is the total order integration. The reflectance spectrum, (E) shows the reflectance spectrum of the diffraction order 0th order, and (F) shows the reflectance spectrum integrated with the diffraction order 1st order or more. As shown in the reflectance spectrum of FIG. 8 (D), in the range of 45 ≦ θ ≦ 85 deg., The band of 500-550 nm has a reflectance of 90% or more, and the average of 50% or more in the band of 560-600 nm. It was shown to have reflectivity. From the above, even when the incident angle is as high as 85 deg., It has a high reflectance in the wavelength band centered on λ 0, indicating that it functions as an angle limiting filter for the green band.

  A blue band angle limiting filter and a red band angle limiting filter can be designed by substantially multiplying dH, dL, W2 / W1, and D among the structural parameters of Example 1G.

  The transmittance and reflectance spectrum at low incident angles (θ ≦ 30 deg.) Of the blue band angle limiting filter of Example 1B whose structural parameters are shown in Table 2 are shown in FIG. 9, and at high incident angles (θ> 30 deg. FIG. 10 shows the transmittance and reflectance spectrum of). The relationship between the order of transmittance and reflectance in FIGS. 9A to 10F is the same as the relationship from FIGS. 7A to 8F and will not be described. To do. The incident plane is the XZ plane, and the polarization is P polarization (TM polarization). From the results of FIGS. 9 and 10, it is shown in Table 2 that Example 1B satisfies the conditional expressions (1) to (4), and (6) and (7).

  From the above, it was shown that Example 1B behaves as an angle limiting filter that transmits the blue band when incident at a low angle and reflects the blue band when incident at a high angle.

  Subsequently, the transmittance and reflectance spectrum at the low incident angle (θ ≦ 30 deg.) Of the red band angle limiting filter of Example 1R whose structural parameters are shown in Table 2 are shown in FIG. 11, and at the high incident angle (θ> 30). deg.) transmittance and reflectance spectrum are shown in FIG. The relationship between the order of transmittance and reflectance in FIGS. 11 and 12 (A) to (F) is the same as the relationship from (A) to (F) shown in FIGS. To do. The incident plane is the XZ plane, and the polarization is P polarization (TM polarization). From the results of FIGS. 11 and 12, it is shown in Table 2 that Example 1R satisfies the conditional expressions (1) to (4), and (6), (7).

  From the above, it was shown that Example 1R behaves as an angle limiting filter that transmits the red band when incident at a low angle and reflects the red band when incident at a high angle.

  The first embodiment is not limited to the parameters shown in Table 2, but by making dH, dL, W1, W2, D out of the structural parameters almost constant multiples, the optical which acts as an angle limiting filter for other wavelength bands A filter design is also possible.

[Example 2]
An optical filter according to a second embodiment of the present invention will be described. The optical filter of the second embodiment is an angle limiting filter that works for the green band, but is designed so as to widen the angle range through which the green band transmits compared to the first embodiment 1G.

  Since the schematic diagram of the optical filter of Example 2 is as shown in FIG. 1 (A), the details are omitted. A first optical layer 102 made of TiO2 having a refractive index nH = 2.36 and a second optical layer 103 made of SiO2 having a refractive index nL = 1.47 were alternately and repeatedly laminated on a synthetic quartz substrate 101 having a refractive index ns = 1.47. It has a structure. The physical layer thickness dH of the first optical layer 102 is 65 nm, and the physical layer thickness dL of the second optical layer 103 is 105 nm. The optical filter 100 has a multilayer film structure with a width W1 among the multilayer film structures with W1 = 180 nm and W2 = 110 nm, in which the first optical layer 102 and the second optical layer 103 are alternately laminated 18 times. The unit structure 104 has a shape that is shifted in the Z direction by D = 85 nm and arranged in the X direction.

  The unit structure 104 has a uniform shape in the Y direction. The optical filter 100 has a structure in which the unit structures 104 are arranged on the substrate 101 so as to form a one-dimensional lattice in the X direction. FIG. 1A shows a shape in which a first optical layer 102 and a second optical layer 103 are stacked on a substrate 101 that has been patterned with a rectangular one-dimensional lattice. There is no need for patterning. The structural parameters of Example 2 are shown in Table 3. Since W2 / W1 of the unit structure 104 is 0.61, Conditional Expression (1) is satisfied, and | D | / (dH + dL) satisfies Conditional Expression (2) from 0.50. Conditional expression (6) is satisfied from φ = 31.8 deg., And conditional expression (7) is satisfied from nHdH / nLdL = 0.99.

  Next, the transmittance and reflectance spectrum of the green band angle limiting filter of Example 2 at a low incident angle (θ ≦ 30 deg.) Are shown in FIG. FIG. 13 (A) is a transmission spectrum of all order integration, (B) is a transmission spectrum of diffraction order 0, (C) is a transmission spectrum of integration of diffraction orders 1 and higher, and (D) is all order integration. The reflectance spectrum, (E) shows the reflectance spectrum of the diffraction order 0th order, and (F) shows the reflectance spectrum integrated with the diffraction order 1st order or more. The incident plane is the XZ plane, and the polarization is P polarization (TM polarization). At the incident angle θ = 0 deg., The transmission center wavelength λ0 is λ0 = 530 nm, the center reflection wavelength λ1 is λ1 = 615 nm, and the center reflection wavelength λ2 is λ2 = 450 nm.

  From this result, as shown in Table 2, it was shown that conditional expression (3) and conditional expression (4) were satisfied. The steep reflection near the wavelength of 500 nm is a component derived from the film thickness that depends on the number of repetitions m, and thus is not considered in the definition of the center wavelength. In Example 2, about 90% of light having a wavelength of 550 nm is transmitted even at θ = 30 deg., Indicating that the angle range through which the green band is transmitted is wider than that of Example 1G. Yes.

  Next, FIG. 14 shows the transmittance and reflectance spectrum of Example 2 at a high incident angle (θ> 30 deg.). FIG. 14 (A) is a transmission spectrum of all order integration, (B) is a transmission spectrum of diffraction order 0, (C) is a transmission spectrum of integration of diffraction orders 1 and higher, and (D) is all order integration. The reflectance spectrum, (E) shows the reflectance spectrum of the diffraction order 0th order, and (F) shows the reflectance spectrum integrated with the diffraction order 1st order or more. As shown in the reflectance spectrum of FIG. 14D, the band of 500 to 550 nm has a reflectance of 90% or more in the range of 45 ≦ θ ≦ 85 deg.

  A blue band angle limiting filter and a red band angle limiting filter can be designed by substantially multiplying dH, dL, W2 / W1, and D among the structural parameters of the second embodiment.

[Example 3]
Next, an optical apparatus as a wavelength conversion apparatus according to a third embodiment of the present invention will be described. An example of a schematic configuration diagram of the wavelength conversion device 1500 of the present invention is shown in FIG. The wavelength conversion device 1500 includes a reflection structure 1501, a phosphor layer 1502, and the angle limiting filter 1503 of the present invention. The reflection structure 1501 has a characteristic that the incident angle and the absolute value of the reflection angle do not coincide with each other due to diffusion or regressive reflection. In particular, it is desirable that the reflection structure 1501 has an effect of reducing the reflection angle from the incident angle by using condensing type retroreflection. The angle limiting filter 1503 has a feature that limits the angle with respect to a specific wavelength band. The wavelength band that limits the angle in the wavelength converter 1500 is a wavelength band centered on the wavelength of the maximum intensity in the fluorescence spectrum emitted from the phosphor.

  External excitation light 1504 passes through the angle limiting filter 1503 and irradiates the phosphor layer 1502. The phosphor layer 1502 emits fluorescence 1505 a having a longer angular distribution and a longer wavelength than the external excitation light 1504 by absorption of the external excitation light 1504. The fluorescent light 1505a having a wide angular distribution enters the angle limiting filter 1503. Due to the angle limiting property of the angle limiting filter 1503, the fluorescent light 1506a having high parallelism is transmitted and emitted outside the apparatus, and the fluorescent light 1507a having low parallelism is reflected. It returns to the phosphor layer 1502. The reflected fluorescence 1507a having a low parallelism is converted into a fluorescence 1505b having a wide angular distribution by diffusion or regressive reflection by the reflection structure 1501.

  The fluorescence 1505b having a wide angular distribution is repeatedly reflected or transmitted between the reflecting structure 1501 and the angle limiting filter 1503 in the same manner as the fluorescence 1505a having a wide angular distribution. As a result, the fluorescent light 1506a, 1506b, 1506c having high parallelism in the angle limiting filter 1503 is separated from the fluorescent light 1507a, 1507b, 1507c having low parallelism, and the fluorescent light 1505a, 1505b, 1505c having a wide angular distribution in the reflection structure 1501. The angle conversion by the reflection is continued. In FIG. 15, only three fluorescence extractions are shown for simplicity, but in practice, angle-dependent separation and angle conversion are performed infinitely.

  When the angle limiting filter 1503 in the wavelength conversion device 1500 is not present, Lambert-diffused fluorescence with low parallelism is emitted, and fluorescence that cannot be captured by the optical system is generated, resulting in loss. For example, when an attempt is made to capture Lambertian diffused fluorescence with an optical system of Fno = 0.95, a loss of about 35% occurs. By using the optical filter of Example 1G of the present invention as the angle limiting filter 1503, it is possible to obtain a wavelength converter that emits fluorescence with controlled emission parallelism while achieving both bandwidth and sensitivity to the incident angle. .

  Here, the maximum intensity wavelength in the fluorescence spectrum is 550 nm. In addition, the angle limiting filter 1503 is obliquely incident at an angle at which 450 nm light is transmitted as external excitation light of the phosphor. However, in FIG. 15, normal incident external excitation light is depicted for the sake of simplicity.

  As a result, the loss of Fno-derived uptake can be suppressed, and the final fluorescence uptake efficiency can be improved. However, if the reflection structure 1501 in the wavelength conversion device 1500 is made of aluminum, silver, or the like having a substantially constant reflectance in the visible range, a certain reflection loss occurs. When it is considered that a reflection loss occurs in the reflection structure 1501, reducing the reflection in the reflection structure 1501 leads to an improvement in the final extraction efficiency. Therefore, it is desirable that the angle limiting filter 1503 does not have a limiting performance up to an angle of about 30 deg. Which can be captured at Fno = 0.95, and has a performance of reflecting incident light at a high angle of 30 deg or more. From the above, in the comparison between Example 1G and Example 2, it can be said that Example 2 is a more preferable example.

  Subsequently, the capture efficiency was roughly estimated on the assumption that the angle-dependent separation by the angle limiting filter 1503, the angle conversion in the reflection structure 1501, and the light amount loss occurred 10 times. When the permissible transmission angle in the angle limiting filter 1503 is set to -30 deg. To 30 deg. And the reflection loss in the reflecting structure 1501 is set to 15%, the capturing efficiency is improved by about 10% compared to the case where the angle limiting filter is not used. The result was obtained. From the above, by using the second embodiment for the angle limiting filter 1503, a wavelength conversion device with improved extraction efficiency can be obtained.

[Example 4]
Next, an optical apparatus as a projection image apparatus according to the fourth embodiment of the present invention will be described. An example of a schematic configuration diagram of the projection image apparatus 1600 of the present invention is shown in FIG. The projection image device 1600 includes a light source 1601, a polarizer 1603, a lens 1604, a dichroic filter 1605, a polarization separation element 1607, a phase compensation plate 1608, an image display element 1609, an angle limiting filter 1611 of the present invention, a polarizing plate 1612, and a color selective phase. The plate 1613 is configured to generate image light.

  Here, subscripts r, g, and b indicating each wavelength band are omitted. Further, the image light of each band is synthesized and projected by the synthesis prism 1614, the dichroic film 1615, and the projection optical system 1616 in the projection image apparatus 1600. The illumination light beam 1602 emitted from the light source 1601 enters the polarizer 1603, and becomes an illumination light beam 1602p of P-polarized light (in-paper-polarized light).

  Next, the light beam is condensed by the lens 1604 and then incident on the dichroic filter 1605 (green band reflection). The incident light beam to the dichroic filter 1605 (green band reflection) is incident with a half-open angle of the angle θ by condensing. The blue band light beam 1606 bp and the red band light beam 1606 rp are transmitted through the dichroic filter 1605, and the green band light beam 1606 gp is reflected by the dichroic filter 1605 and enters the polarization separation element 1607 g. Of the polarized light incident on the polarization separation surface 1607g1, the polarization separation element 1607g transmits the P-polarized light and reflects the S-polarized light, and transmits the polarization separation element 1607g.

  Further, the green band light beam 1606gp is converted into a distribution having image information by irradiating the phase compensator 1608g and the image display element 1609g, and the green band image light 1610g having become S-polarized light is re-applied to the polarization separation element 1607g. The incident light is reflected by the polarization separation surface 1607g1, is emitted to an optical path different from the incident light, and enters the angle limiting filter 1611. The image light 1610g that has been transmitted after being subjected to the angle restriction by the angle restriction filter 1611 then proceeds toward the synthesis prism 1614.

  The blue band light beam 1606 bp and the red band light beam 1606 rp are transmitted through the polarizing plate 1612 to improve the degree of polarization, and then enter the color selective phase plate 1613. The color-selective phase plate 1613 has a characteristic that the polarization direction of only the blue-band light beam is converted by 90 °, so that the polarization state of the blue-band light beam is rotated by 90 ° while the polarization state of the red-band light beam is maintained. A blue band light beam 1606bs is incident on the polarization separation element 1607br. The polarization separation element 1607br is an element that transmits P-polarized light and reflects S-polarized light out of the polarized light incident on the polarization separation surface 1607r1.

  As an element having such an action, for example, there is an element in which thin films having different refractive indexes are stacked on a polarization separation surface 1607br1. The polarization separation surface 1607br1 of the polarization separation element 1607br reflects the blue band light beam, transmits the red band light beam, separates the color, passes through the phase compensation plates 1608b and 1608r, and irradiates the image display elements 1609b and 1609r corresponding to the respective colors. It is converted into a distribution with image information.

  These image lights again pass through the phase compensation plates 1608b and 1608r, and then reenter the polarization separation element 1607br. Here, the image light 1610b in the blue band is transmitted through the polarization separation element surface 1607br1, and the image light 1610r in the red band is reflected by the polarization separation surface 1607br1. The image lights 1610b and 1610r are combined and further incident on the combining prism 1614. The green band image light 1610g is reflected by the dichroic film 1615 in the combining prism 1614, and the blue band image light 1610b and the red band image light 1610r are transmitted, whereby the blue, green, and red band lights are combined. Are emitted. The color-combined image light is projected and imaged by the projection optical system 1616.

  In the projection image apparatus 1600, when the image display element 1609g is a liquid crystal panel, reflected diffraction light 1610go derived from the pitch is generated. When the angle limiting filter 1611 is not present or the angle limiting performance is not high, the reflected diffracted light 1610go may finally enter the projection optical system and cause image quality degradation. When the optical filter of Example 1G of the present invention is used as the angle limiting filter 1611, the reflected diffracted light 1610go is applied to the projection optical system by the angle limiting performance that achieves both the bandwidth and the sensitivity to the incident angle that are larger than the conventional multilayer film. Incidence can be suppressed and image degradation can be reduced.

[Example 5]
Next, an optical apparatus as an image pickup apparatus according to the fifth embodiment of the present invention will be described. An example of a schematic configuration diagram of the imaging apparatus 1700 of the present invention is shown in FIG. The imaging device 1700 includes photoelectric conversion layers 1701b, 1701g, and 1701r, angle limiting filters 1702b, 1702g, and 1702r of the present invention, absorption color filters 1703b, 1703g, and 1703r, and microlenses 1704b, 1704g, and 1704r. The subscripts b, g, and r indicate elements for the blue band, the green band, and the red band, respectively, and the basic configuration remains unchanged.

  The angle limiting filters 1702b, 1702g, and 1702r have characteristics that limit the angle with respect to the blue band, the green band, and the red band, respectively. Here, a description will be given of the image pickup apparatus in the green band as a representative. The image light 1705g perpendicularly incident on the imaging device 1700 and the stray light 1706g in the green band obliquely incident are collected by the microlens 1704g and then absorbed by the absorption color filter 1703g except for the light in the green band, and the angle limiting filter 1702g. Is incident on.

  On the other hand, the green band stray light 1706g having a large incident angle is reflected by the angle limiting filter 1702g. The light transmitted through the angle limiting filter 1702g is absorbed by the photoelectric conversion layer 1701g and converted into carriers. The description of the imaging device for the blue band and the imaging device for the red band is omitted, but it has the same function.

  By using the optical filters of Embodiments 1B, 1G, and 1R of the present invention for the angle limiting filters 1702b, 1702g, and 1702r, only the image light at a low incident angle is photoelectrically converted while achieving both bandwidth and sensitivity to the incident angle. An imaging device can be obtained. The obliquely incident stray light 1706g is reflected by the angle limiting filter 1702g, becomes reflected stray light 1707g, and is emitted to the outside of the imaging device. Therefore, image quality deterioration due to stray light can be suppressed. This imaging apparatus is effective for suppressing stray light such as flare and ghost incident at a high angle, and also effective for suppressing crosstalk caused by high-angle incident light.

100. Optical filter 101. Substrate 102. First optical layer 103. Second optical layer 104. Unit structure 301. Calculation model result 302. Calculation model result 401. Long wavelength side reflection band 402. Short wavelength side reflection band 501. Long wavelength side reflection band 502. Short wavelength side reflection band 601. Convex region 602. Recessed region 603. Cross-sectional shape cut out in the YZ plane 604. Cross-sectional shape cut out in XZ plane 605. Unit structure 1500. Wavelength converter 1501. Reflective structure 1502. Phosphor layer 1503. Angle limiting filter 1504. External excitation light 1505a, 1505b, 1505c. Fluorescence with wide angular distribution 1506a, 1506b, 1506c. Highly parallel fluorescence 1507a, 1507b, 1507c. Fluorescence with low parallelism 1600. Projection image device 1601. Light source 1602, illumination beam 1602p. Illuminated light beam 1603 of P-polarized light (in-plane polarized light) 1603. Polarizer 1604. Lens 1605. Dichroic filter
1606 gp. Green band luminous flux
1606bp, 1606bs. Blue band luminous flux
1606 rp. Red band luminous flux
1607g, 1607br. Polarization separating elements 1607g1, 1607br1. Polarization separation surfaces 1608b, 1608g, 1608r. Phase compensation plate
1609b, 1609g, 1609r. Image display elements 1610b, 1610g, 1610r. Image light 1610go. Reflected diffracted light 1611. Angle limiting filter 1612. Polarizing plate 1613. Color selective phase plate 1614. Synthetic prism 1615. Dichroic film 1616. Projection optical system
1700. Imaging device 1701b. 1701 g. 1701r. Photoelectric conversion layer 1702b. 1702 g. 1702r. Angle limiting filter 1703b. 1703 g. 1703r. Absorption type color filter 1704b. 1704 g. 1704r. Microlens 1705 g. Normal incident image light 1706 g. Stray light 1707 g. Reflected stray light

Claims (8)

An optical filter having a laminated structure formed of a dielectric on a light-transmitting substrate,
When incident on the substrate at a low angle, it reflects two wavelength bands and transmits the intermediate wavelength band. When the incident angle increases, the reflected wavelength band changes and transmits when the incident angle is low. By reflecting the light in the intermediate wavelength band, it has a function to limit the incident and output angles for light in a specific wavelength band,
When the direction perpendicular to the lamination plane of the optical filter is the X, Y direction, the depth direction with the direction from the lamination surface toward the substrate as the Z direction, and the direction from the surface layer toward the substrate as the positive direction, Consists of at least two types of optical layers,
A first optical layer having a physical layer thickness dH having the highest refractive index nH;
Of the multilayer film structures with different widths W1 and W2 formed by alternately laminating the second optical layers having the physical layer thickness dL having the lowest refractive index nL, the multilayer film structure having the width W1 is shifted in the Z direction. Unit structures having shapes arranged adjacent to each other with a shift of D have a structure in which an array is formed on the substrate so as to form a lattice in at least a one-dimensional direction.
An optical filter characterized in that W1, W2, dH, dL, and D satisfy the following relational expression.
0.3 <W2 / W1 <0.6
0.35 <| D | / (dH + dL) <0.65 In the optical filter, when the incident angle of the light beam is 0 deg, the central reflection wavelengths λ1, λ2 with respect to the polarized light parallel to the direction arranged in a lattice, and dH, dL, nH, nL in any unit structure , ψ is the following relational expression
0.35 <(nHdH + nLdL) / λ1 <0.65
0.35 <(nHdH + nLdL) cos ² φ / λ2 <0.65
2. The optical filter according to claim 1, wherein:
Here, φ is an angle derived from a structural parameter defined by φ = tan ⁻¹ (| D | / (W1 + W2)). The central reflection wavelength is defined as the wavelength of the short wavelength side of the reflection band with a reflectance of 50% and the middle wavelength of the long wavelength side of the bottom wavelength, and λ1 and λ2 have a relationship of λ1> λ2. To do. The φ in the unit structure of the optical filter is any of the following relational expressions
25 deg. <Φ <45 deg.
The optical filter according to claim 2, wherein: DH, dL, nH, dL in the unit structure of the optical filter are all the following relational expressions
0.5 <(nHdH / nLdL) <1.1
The optical filter according to any one of claims 1 to 3, wherein: 5. The unit structure according to claim 1, wherein the unit structures having a deviation width D in the unit structure in the X and Y directions are formed in a periodic array in the X and Y directions so as to form a two-dimensional lattice. The optical filter according to any one of the above. It has a structure in which a phosphor layer and the optical filter are formed on a reflecting structure having a function of diffusing or recurring reflection,
Of the fluorescence emitted from the fluorescent layer by external excitation light,
When fluorescence having the maximum intensity in the emission spectrum is incident on the optical filter,
6. The wavelength conversion device with an optical filter according to claim 1, wherein when the light is incident at a low angle, the light having the wavelength is transmitted, and when the light is incident at a high angle, the light having the wavelength is reflected. As an optical device. By providing the optical filter according to any one of claims 1 to 5, a projection image apparatus having a function of suppressing unnecessary diffracted light and stray light incident on the projection optical system at a high angle. Optical device. An imaging apparatus comprising the optical filter according to any one of claims 1 to 5 that limits an incident angle on the photoelectric conversion layer on the photoelectric conversion layer below the optical filter. Optical device.