JP2003029031A - Polarizing separation element and polarizing beam splitter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive polarizing separation element having a polarizing separation function in a wide range with a simple film structure and a small number of layers and to provide a polarizing beam splitter by using the above element. SOLUTION: The polarizing separation element 2 has repeated structures (LHL)<m> containing a basic structure LHL consisting of an optically transparent high refractive index layer H having a specified refractive index with respect to incident light OI, and an optically transparent first low refractive index layer L and a second low refractive index layer L disposed to interpose the high refractive index layer H, wherein m is an integer of >=2 and preferably 3 to 7. The beam splitter has the above polarizing separation element 2 and transparent substrates 3 formed in contact with the entrance face 2a and the exiting face 2b of the element 2 to interpose the element 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization separation element which is an optical film for extracting a specific polarized light from natural light and a polarization beam splitter using the same.

[0002]

2. Description of the Related Art Ordinary light is not in a completely polarized state or a completely unpolarized state, and both states are mixed. Various forms of polarizers have been studied in order to obtain a specific polarization state. Examples of these polarizers include a birefringent polarizer that utilizes the birefringence of crystals, a dichroic polarizer that utilizes the dichroism of a polymer, and a reflective polarization that uses the reflected light of S-polarized light. There are children, etc. Then, as this type of optical element, for example, P-polarized light that is the first polarized light of incident light that is incident at a predetermined angle is transmitted, and S-polarized light that is the second polarized light is reflected in a direction different from the transmission direction. A polarization beam splitter is known in which a polarization separation element is sandwiched between glass substrates.

Polarized Beam Splitter
There are many known publications on plitter, PBS). For example, in the "Optical and Thin Film Technology Manual, Supplement, Revised Edition" (1992, published by Optronics, Inc.),
On page 309, a polarizing beam splitter is described.

In this document, for a thin film laminated polarization separation element constituted by alternately laminating a high refractive index material and a low refractive index material, a reference wavelength of 550 nm of incident light is λ _0.
As a low refractive index material layer having a thickness of lambda _0/4 and L,
When a high refractive index material layer having a thickness of lambda _0/4 described as H, giving the design principles indicated by the following equation (1) or (2) or the like.

[0005]

[Formula 1] (HL) ^m (1)

[0006]

(2) (0.5HL0.5H) ^m (2)

Here, m is an arbitrary integer, but usually 4
Is set to a value greater than.

[0008]

By the way, as described in the above document, in the thin film laminated polarization beam splitter, it is necessary to form (apply) several tens of films in order to satisfy desired characteristics. Further, although the basic repeating pattern is simple, in reality, it is necessary to finely adjust the film thickness by finely applying a coefficient. Specific angle (mainly 4
In the beam splitter film corresponding to the oblique incidence of 5 degrees),
Generally, the number of layers of 30 or more with delicate control of film thickness is required, and the total film thickness is 4 μm or more. Such a beam splitter film is disadvantageous in that it is difficult to manufacture and cannot be inexpensively supplied.

The present invention has been made in view of such circumstances, and an object thereof is an inexpensive polarization separation element having a wide band polarization separation function with a simple film structure and a small number of laminated layers, and a polarization using the same. To provide a beam splitter.

[0010]

To achieve the above object, the present invention transmits a first polarized light of incident light incident at a predetermined angle and reflects a second polarized light in a direction different from a transmission direction. A high-refractive-index layer H that is an optically transparent high-refractive-index layer having a predetermined refractive index with respect to the incident light.
And a first low-refractive index layer L and a second low-refractive index layer L which are arranged so as to sandwich the high-refractive index layer H and which have a lower refractive index than the high-refractive index layer and which are optically transparent. Structure film LH
It contains L and has a repeating structure (LHL) ^m of the above basic structure.

In the polarization beam splitting element of the present invention, the thickness of the high refractive index layer and the thicknesses of the first low refractive index layer and the second low refractive index layer are based on the reference wavelength of incident light. Is set.

Further, in the polarization beam splitting element of the present invention, preferably, when the reference wavelength of the incident light is λ ₀ , the thickness of the high refractive index layer, the first low refractive index layer and the second low refractive index layer. The thickness of the low refractive index layer is set to an optical thickness corresponding to a value obtained by dividing the reference wavelength by a predetermined integer.

In the polarization beam splitting element of the present invention, the number of repetitions m of the basic structure is an integer of 3 or more. Preferably, the number of repetitions m of the basic structure is an integer of 3 or more and 7 or less.

Further, in the polarization beam splitting element of the present invention, the center value of the incident angle of the incident light on the optical film surface is set to about 56 degrees.

Further, in the polarization beam splitting element of the present invention, the high refractive index layer has a wavelength dispersion characteristic of an optical constant n in a predetermined range including a reference wavelength of incident light and has a predetermined wavelength shorter than the reference wavelength. In the above, the first and second low refractive index layers have a wavelength dispersion characteristic of an optical constant n in a predetermined range including the reference wavelength of incident light. , And a material having an extinction coefficient of substantially zero in substantially the entire wavelength range.

In the polarization splitting element of the present invention, the basic structure films adjacent to each other are the first low refractive index layer L and the second low refractive index layer L.
Are formed so as to share the low-refractive index layer L.

Further, the present invention is a polarization beam splitter which transmits a first polarized light of incident light incident at a predetermined angle and reflects a second polarized light in a direction different from a transmission direction, wherein the incident light is And an optically transparent high refractive index layer H having a predetermined refractive index, and an optically transparent first layer having a lower refractive index than the high refractive index layers arranged so as to sandwich the high refractive index layer H. First low refractive index layer L and second low refractive index layer L
A polarization separation element having a repeating structure (LHL) ^m of the above basic structure, including a basic structure film LHL, and a transparent substrate arranged in contact with the light incident surface and the light transmission surface of the polarization separation element. Have.

Further, in the polarization beam splitter of the present invention, the thickness of the high refractive index layer of the above-mentioned polarization separation element, and the first
The thicknesses of the low-refractive index layer and the second low-refractive index layer are set based on the reference wavelength of the incident light.

Further, in the polarization beam splitter of the present invention, preferably, when the reference wavelength of the incident light is λ ₀ , the thickness of the high refractive index layer of the polarization separation element and the first
The thicknesses of the low-refractive index layer and the second low-refractive index layer are set to optical thicknesses corresponding to a value obtained by dividing the reference wavelength by a predetermined integer.

Further, in the polarization beam splitter of the present invention, the number of repetitions m of the basic structure of the polarization separation element is
It is an integer of 3 or more. Preferably, the number of repetitions m of the basic structure of the polarization separation element is an integer of 3 or more and 7 or less.

Further, in the polarization beam splitter of the present invention, the center value of the incident angle of the incident light on the optical film surface of the polarization separation element is set to about 56 degrees.

Further, in the polarization beam splitter of the present invention, the high refractive index layer of the polarization beam splitting element has a wavelength dispersion characteristic of an optical constant n in a predetermined range including a reference wavelength of incident light and has the reference wavelength. The first and second low refractive index layers each include a material having a characteristic that an extinction coefficient gradually approaches zero at a shorter predetermined wavelength or longer, and the first and second low refractive index layers have a wavelength of an optical constant n in a predetermined range including a reference wavelength of incident light. It includes a material having a dispersion characteristic and an extinction coefficient of substantially zero over almost the entire wavelength range.

In the polarization beam splitter of the present invention, the refractive index of the high refractive index layer of the polarization splitting element is set higher than that of the transparent substrate, and the first and second low refractive index layers are provided. Has a refractive index lower than that of the transparent substrate.

In the polarization beam splitter of the present invention, the basic structure films adjacent to each other of the polarization separating element are:
It is formed so as to share the first low refractive index layer L and the second low refractive index layer L.

According to the present invention, the polarization separation element is adapted to
Optically transparent high refractive index with a predetermined refractive index for
A high refractive index arranged so as to sandwich the layer H and the high refractive index layer H.
Optically transparent first low refractive index layer having a lower refractive index than layer H
L and the second low refractive index layer L, a basic structure film LHL
Including a repeating structure of this basic structure (LHL)^m (Ta
However, m is an integer of 2 or more, and preferably has 3 to 7).
Configured as Then, for example, the
It is in contact with the reflecting surface and the light transmitting surface, and sandwiches the polarization separation element.
Like this, a transparent substrate made of glass is formed,
For example, a laminated prism type polarization beam splitter
Be done. The high refractive index layer H and the low refractive index layer L are
Reference wavelength λ₀ For example λ ₀ / 4 optical thickness
Composed. For example, as a low refractive index material for the polarization separation element
SiO₂ (N = 1.46) as a high refractive index material
iO₂ Using (n = 2.44) respectively, L is 94.2.
nm · H is 56.4 nm, and per repeat
Has a film thickness of about 250 nm. Common as a transparent substrate
Optical glass (BK7) can be used.
Is the maximum polarization separation for incident light at angles near 56 degrees
Show performance. For these combinations, the basics described above
There is no need to add any correction to the structure, it is extremely simple
High performance can be obtained with the configuration. Also, the number of repetitions of the film m
4 is sufficient for practical use, and the number of layers at this time is only 9 layers.
Therefore, the film thickness is only 1 μm.

According to the present invention, the incident light having the predetermined reference wavelength λ ₀ is incident on the transparent substrate. Then, the incident light including the first polarized light (P polarized light) and the second polarized light (S polarized light) is propagated through the transparent substrate and reaches the light incident surface of the polarization splitting element, and at a predetermined angle with respect to the light incident surface, For example, it is incident on the polarization separation element at an angle of 56 degrees. The light incident on the polarization separation element propagates through, for example, the first basic structure film, the second basic structure film, and the third basic structure film, while the second polarized light, for example, is the second basic structure film. Is reflected at a predetermined angle with respect to the propagation direction (transmission direction) at the low-refractive-index layer L that is the boundary between the first basic structure film and the third basic structure film, propagates through the transparent substrate, and is emitted. On the other hand, the first polarized light goes straight ahead to the third basic structure film,
Alternatively, the light is transmitted through the further basic structure film, emitted from the light transmitting surface, propagated through the transparent substrate, and emitted.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described in detail below with reference to the drawings. In addition,
In the present embodiment, an example of design completion based on the actually measured optical constants of the optical material will be shown. If the optical constants change, the optimum design result may deviate, but it goes without saying that the present invention is not limited to this example and can be arbitrarily changed without departing from the gist of the present invention.

FIG. 1 is a block diagram showing an embodiment of a laminated thin film prism type polarization beam splitter which employs a polarization separation element according to the present invention.

As shown in FIG. 1, the present polarization beam splitter 1 is in contact with the polarization separation element 2 and the light incident surface 2a and the light transmission surface 2b of the polarization separation element 2, and the polarization separation element 2
And a transparent substrate 3 formed so as to sandwich.

The polarization separation element 2 includes an optically transparent high refractive index layer H having a predetermined refractive index with respect to incident light OI, and a high refractive index layer H arranged so as to sandwich the high refractive index layer H. It includes a basic structure film LHL composed of an optically transparent first low refractive index layer L and a second low refractive index layer L having a lower refractive index, and has a repeating structure (LHL) ^m of this basic structure. The number of times m of repeating the basic structure LHL of the polarization separation element 2 is
As described later, it is desirable that it is an integer of 3 or more,
FIG. 1 shows a case where m = 3.

FIG. 2 is a diagram showing a stacking repeating structure of the polarization separation element when the stacking repeating number m is 3.

As shown in FIG. 2, the polarization splitting element 2 is basically composed of a first low refractive index layer L1, a high refractive index layer H, and a second low refractive index layer L2 from the light incident surface 2a side. The structure has a structure in which the structure is simply repeated three times and laminated. That is, from the light incident surface 2a side to the first basic structure film LHL1,
Second basic structure film LHL2 and third basic structure film L
It has a structure in which HL3 is laminated in order, and there is no need to add any correction to the basic structure, and the structure is extremely simple. Since three basic structure films each having three layers are laminated, a simple consideration should be nine layers. However, in practice, as shown in FIG. 2, the first basic structure film L
Second low refractive index layer L2 of HL1 and second basic structure film LH
It can be formed as the same layer so that the first low refractive index film L1 of L2 is shared. Similarly, the second basic structure film LHL
2nd low refractive index layer L2 and 3rd basic structure film LHL3
The first low refractive index film L1 can be formed as the same layer so as to be shared. Therefore, the actual number of layers is 7 instead of 9.

FIG. 3 is a diagram showing a stacking repeating structure of the polarization beam splitting element when the stacking repeating number m is 4.

In this case also, the basic structure film consisting of three layers is
Since two layers are stacked, a simple consideration should be 12 layers. However, in practice, as shown in FIG.
The second low refractive index layer L2 of the basic structural film LHL1 and the first low refractive index film L1 of the second basic structural film LHL2 can be formed as the same layer so as to be shared. Similarly, the second low refractive index layer L2 of the second basic structure film LHL2 and the first low refractive index film L1 of the third basic structure film LHL3 can be formed as the same layer so as to be shared, and Basic structure film LHL
Third low refractive index layer L2 and fourth basic structure film LHL4
The first low refractive index film L1 can be formed as the same layer so as to be shared. Therefore, the actual number of layers is 9 instead of 12.

The number M of stacked layers of the polarization separation element 2 is given by the following equation.

[0036]

[Equation 3] M = 3 × m− (m−1) (3)

That is, the number M of laminated layers of the polarization beam splitting element 2 according to the present invention is two layers less than the number considered when simply laminating the basic structure film LHL consisting of three layers. Therefore, the structure of the polarization separation element 2 according to the present invention can contribute to simplification of the manufacturing process and thinning.

The high refractive index layer H of the polarization separation element 2 has a wavelength dispersion characteristic of an optical constant (refractive index) n in a predetermined range including the reference wavelength λ ₀ of the incident light IO, for example, 550 nm, and the reference wavelength λ. _It is made of a material having a characteristic that the extinction coefficient k gradually approaches zero at a predetermined wavelength shorter than ₀ .

The high refractive index layer H contains TiO ₂ (n = 2.3).
5 to 2.8), ITO (n = 1.95 to 2.1), Zn
O (n = 1.9), CeO ₂ (n = 1.95), SnO
₂ (n = 1.95), Al ₂ O ₃ (n = 1.63), L
a ₂ O ₃ (n = 1.95), ZrO ₂ (n = 2.0
5), Y ₂ O ₃ (n = 1.87) and the like are used.

In this embodiment, an example in which TiO ₂ having the highest refractive index is adopted as the high refractive index layer H is shown.

FIG. 4 shows the optical constant (refractive index) n of TiO ₂ .
It is a figure which shows the chromatic dispersion dependence of. In FIG. 4, the horizontal axis represents wavelength and the vertical axis represents optical constant (refractive index) n. As shown in FIG. 4, TiO ₂ used as the high refractive index layer H has a reference wavelength λ ₀ = 550n of the incident light IO.
A predetermined range including m, specifically, approximately 380 nm to 770
In the range of nm, it has wavelength dispersion characteristics of n = 2.8 to 2.35.

FIG. 5 shows the optical constants (extinction coefficient) of TiO ₂ .
It is a figure which shows the chromatic dispersion dependence of k. In FIG. 5, the horizontal axis represents wavelength and the vertical axis represents optical constant (extinction coefficient) k. As shown in FIG. 5, in TiO ₂ used as the high refractive index layer H, the extinction coefficient k rapidly approaches zero near 380 nm, which is shorter than the reference wavelength λ ₀ = 550 nm of the incident light IO, and the wavelength is 500 nm. It has the property of becoming zero in the vicinity and above.

The first and second low refractive index layers L (L1, L2) of the polarization separation element 2 have wavelength dispersion of an optical constant (refractive index) n in a predetermined range including the reference wavelength of the incident light IO, for example, 550 nm. It is made of a material having characteristics and having an extinction coefficient of substantially zero in substantially the entire wavelength range k.

The low refractive index layer 2 is made of SiO.₂ (N = 1.4
54-1.473) and MgF₂ (N = 1.38), Li
F (n = 1.4), AlF₃ (N = 1.4), Na₃ A
IF ₆ (N = 1.33) or the like is used.

In this embodiment, as the low refractive index layer L, S
An example in which iO ₂ is adopted is shown.

FIG. 6 shows the optical constant (refractive index) n of SiO ₂ .
It is a figure which shows the chromatic dispersion dependence of. In FIG. 6, the horizontal axis represents wavelength and the vertical axis represents optical constant (refractive index) n. As shown in FIG. 6, SiO ₂ used as the low refractive index layer L has a reference wavelength λ ₀ = 550n of incident light IO.
A predetermined range including m, specifically, approximately 380 nm to 770
It has a wavelength dispersion characteristic of n = 1.473 to 1.454 in the range of nm.

[0047] In addition, the extinction coefficient k of SiO ₂ is a zero in the entire wavelength range, there is no absorption by the SiO ₂ film.

The thickness h of the high refractive index layer H of the polarization beam splitting element 2,
The thickness l of the first low refractive index layer L and the second low refractive index layer L is set based on the reference wavelength of incident light, for example, 550 nm. Specifically, when the reference wavelength λ _{0 of} incident light is 550 nm, the thickness h of the high refractive index layer H is
And the thickness l of the first low refractive index layer L and the second low refractive index layer L is the reference wavelength lambda ₀ predetermined divided by the integer, the optical thickness corresponding to e.g. lambda _0/4 Is set

[0049] Thus, the thickness of the high refractive index layer H of the polarization separating element 2, and the thickness of the first low refractive index layer L and the second low refractive index layer L is, lambda _0/4 equivalent Optical thickness.
N = 2 in TiO ₂ (reference wavelength lambda ₀ as the high refractive index material.
44) as a low refractive index material, SiO ₂ (reference wavelength λ ₀
And n = 1.46), h is 56.4n.
m and l are 94.2 nm, and the film thickness per one repetition is about 250 nm. For example, when the number of repetitions m of the film is 4, the number M of stacked layers is only 9 and the film thickness is only 1 μm as described above. Then, in the present embodiment, the center value of the incident angle θ of the incident light IO on the light incident surface 2a of the polarization separation element 2 is set to around 56 degrees.

As the transparent substrate 3, for example, glass (BK7) having an optical constant (refractive index) n of 1.52 is used. An adhesive layer is required when the glass is attached to the opposite side of the film-forming surface, but it is optically meaningless and will not be described in the future.

As described above, in this embodiment, the transparent substrate 3 has, for example, an optical constant (refractive index) n of 1.5.
Since the second glass is used, the refractive index n of the transparent substrate is
3 and the refractive index n (H) of the high refractive index layer H of the polarization separation element 2.
And the refractive index n (L) of the low refractive index layer L are as follows.

[0052]

[Equation 4] n (L) <n3 <n (H)

That is, in this embodiment, the refractive index n (H) of the high refractive index layer H of the polarization separation element 2 is set higher than the refractive index n3 of the transparent substrate 3, and the first and second low refractive indexes are set. The refractive index n (L) of the refractive index layer L is set lower than the refractive index n3 of the transparent substrate 3.

In the polarization beam splitter 1 having the above-described configuration, for example, the reference wavelength λ ₀ is 5
Incident light IO of 50 nm is incident from the left side surface of the transparent substrate 3 in FIG. The incident light including the P-polarized light as the first polarized light and the S-polarized light as the second polarized light is transmitted through the transparent substrate 3
Is transmitted to reach the light incident surface 2a of the polarization separation element 2,
The light is incident on the polarization separation element 2 at a predetermined angle with respect to the light incident surface 2a, preferably 56 degrees. The light incident on the polarization separation element 2 is propagated through the first basic structure film LHL1, the second basic structure film LHL2, and the third basic structure film LHL3, while the S-polarized light is, for example, the second basic structure film. Low refractive index layer L which is a boundary between the film LHL2 and the third basic structure film LHL3
Is reflected at a predetermined angle with respect to the propagation direction (transmission direction), propagates through the transparent substrate 3 and is emitted from the lower side surface in FIG. On the other hand, the P-polarized light goes straight forward, passes through the third basic structure film LHL3, is emitted from the light transmitting surface 2b, is propagated through the transparent substrate 3, and is emitted from the right side surface in FIG.

In this way, the P-polarized light and the S-polarized light are separated by the polarization separation element 2. In this embodiment, the center of the incident angle of the incident light IO on the light incident surface 2a of the polarization separation element 2 is divided. The value is set near 56 degrees. The number m of repetitions of the basic structure film LHL in the polarization separation element 2 and the incident angle of the incident light IO on the polarization separation element 2 will be described below in association with the drawings.

First, the number of repetitions m of the basic structure film LHL in the polarization separation element 2 will be considered.

FIG. 7 shows the wavelength dependence of the P-polarized light transmittance when the number of repetitions m is 3 to 7, and FIG. 8 shows the wavelength dependence of the P-polarized light transmittance when the number of repetitions m is 1 and 2. FIG. Further, in FIG. 9, the number of repetitions m is 3
FIG. 10 is a diagram showing the wavelength dependency of the P-polarized light reflectance in FIGS. 7 to 7, and FIG. 10 is a diagram showing the wavelength dependency of the P-polarized light reflectance in the case where the number of repetitions m is 1 and 2.

In FIGS. 7 and 8, the horizontal axis represents wavelength,
The vertical axis represents the transmittance. 9 and 10, the horizontal axis represents wavelength and the vertical axis represents reflectance. 7 and 9, the solid line indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions is m = 3, and the broken line indicated by is the number of repetitions m =
4 shows the transmittance characteristic and the reflectance characteristic, the broken line indicated by indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions m = 5, and the broken line indicated by indicates the number of repetitions m = 6.
The transmittance characteristic and the reflectance characteristic in the case of are shown, and the alternate long and short dash line represents the transmittance characteristic and the reflectance characteristic when the number of repetitions m = 7. Further, in FIGS. 8 and 10, the solid lines respectively indicate the transmittance characteristics and the reflectance characteristics when the number of repetitions m = 1, and the broken lines indicate the transmittance characteristics and the reflectance when the number of repetitions m = 2. It shows the characteristics.

As can be seen from FIGS. 7 to 10, in the polarization separation element 2 according to this embodiment, the reflection of P-polarized light as the first polarization is very small, and most of the polarization separation element is at wavelengths of 400 nm or more. Permeate through the membrane. From FIGS. 7 and 8, it can be seen that as the number of repetitions m increases, the wavelength at which the polarization separating element film starts to be transmitted shifts to the long wavelength side.

FIG. 11 is a diagram showing the wavelength dependence of the S-polarized light transmittance when the number of repetitions m is 3 to 7.
FIG. 4 is a diagram showing wavelength dependency of S-polarized light transmittance when the number of repetitions m is 1 and 2. 13 is a diagram showing the wavelength dependence of the S-polarized reflectance when the number of repetitions m is 3 to 7, and FIG. 14 shows the wavelength dependency of the S-polarized reflectance when the number of repetitions m is 1 and 2. It is a figure.

In FIGS. 11 and 12, the horizontal axis represents wavelength and the vertical axis represents transmittance. In addition, FIG.
In FIG. 14 and FIG. 14, the horizontal axis represents wavelength and the vertical axis represents reflectance. In FIGS. 11 and 13, the solid line indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions is m = 3, and the broken line indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions is m = 4. In the figure, the broken line indicated by indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions m = 5, and the broken line indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions m = 6. Shows the transmittance characteristic and the reflectance characteristic when the number of repetitions m = 7. In addition, FIG.
In FIG. 14 and FIG. 14, the solid line indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions is m = 1, and the broken line indicates the transmittance characteristic and the reflectance characteristic when the number of repetitions is m = 2. There is.

As can be seen from FIG. 14, the number of repetitions m
When the value is 1, the reflectance of S-polarized light is lower than 70% at maximum, which is not practical. On the other hand, as can be seen from FIGS. 11 to 14, when the number of repetitions m is 2 or more, most of the light is reflected in the wavelength range of 400 nm to 720 nm,
It is clear that it cannot penetrate. When the number of repetitions m is increased, the upper edge of the opaque region becomes steep.

Considering the characteristics shown in FIGS. 7 to 14, the polarization separation element 2 according to this embodiment can separate P-polarized light and S-polarized light with high accuracy in the range of 150 nm to 300 nm which is 400 nm or more. Here, assuming that the transmittance of the P-polarized light is 83% or more and the transmittance of the S-polarized light is 5% or less as the characteristics of the polarization beam splitter, the number of times of stacking repetitions is m.
Is preferably an integer of 3 or more and 7 or less in consideration of the characteristics of FIGS. In this case 400
It is possible to realize a polarization beam splitter capable of supporting an extremely wide wavelength range of nm to 700 nm.

FIG. 15 shows polarization separable wavelength widths when a width of a continuous wavelength range satisfying a condition that the transmittance of P-polarized light is 83% or more and the transmittance of S-polarized light is 5% or less is used as an evaluation function. It is a figure which shows the repetition frequency dependence of. In FIG. 15, the horizontal axis represents the number of repetitions m, and the vertical axis represents the polarization separable wavelength width.

As can be seen from FIG. 15, the number of repetitions m of the basic structure of the polarization beam splitting element 2 should be 2 or more in order to realize a polarization beam splitter capable of supporting a certain wavelength width, which is extremely high from 400 nm to 700 nm. In order to realize a polarization beam splitter that can handle a wide wavelength range, the number of repetitions m is 3 or more (1 in the data of FIG. 15).
(Up to 0), and preferably an integer of 3 or more and 7 or less as described above.

Further, as can be seen from FIG. 15, there is a peak around m = 5, and there is a tendency that the peak decreases thereafter. Therefore, practically, the number of repetitions m of 4 or 5 is sufficient.

FIG. 16 is a diagram showing the wavelength dependence of the transmittance of P-polarized light and S-polarized light when the number of times m of stacking is repeated is 4. In FIG. 16, the horizontal axis represents wavelength and the vertical axis represents transmittance. Further, in FIG. 16, the broken line is P
The transmittance characteristic of polarized light is shown, and the solid line shows the transmittance characteristic of S polarized light.

As shown in FIG. 16, the number of stacking repetitions m
When 4 is set as the characteristic of the polarization beam splitter,
Assuming that the transmittance of P-polarized light is 83% or more and the transmittance of S-polarized light is 5% or less, an extremely wide wavelength range of 400 nm to 700 nm can be supported, and a very practical polarization beam splitter can be realized.

Next, the incident angle of the incident light IO on the polarization separation element 2 will be considered. In the present embodiment, as described above, the center value of the incident angle θ of the incident light IO on the light incident surface 2a of the polarization separation element 2 is set near 56 degrees.

Needless to say, in practice, it is desirable that the polarized light can be separated even if the light beam deviates slightly from the vicinity of the optimum incident angle of 56 degrees.

FIG. 17 is a diagram showing the incident angle dependence of the polarization separable wavelength width. In FIG. 17, the horizontal axis represents the deviation from the central angle, and the vertical axis represents the polarization separable wavelength width. As can be seen from FIG. 17, the polarized light separation can be realized in the wavelength range of 150 nm to 300 nm, which is the light beam incident at an angle deviated from the center value of the incident angle by about ± 5 degrees.

When it deviates ± 3 degrees from the optimum condition, and ±
18 to 21 show the simulation results of the wavelength dependence of the transmittances of P-polarized light and S-polarized light when they are deviated by 5 degrees.

FIG. 18 shows the wavelength dependence of the transmittance of P-polarized light and S-polarized light when the incident angle of the incident light IO on the polarization beam splitting element having the number of repetitions m of 4 deviates by +3 degrees from the optimum condition of 56 degrees. FIG. 19 is a diagram showing the wavelengths of the transmittances of P-polarized light and S-polarized light when the incident angle of the incident light IO to the polarization beam splitting element having the number of repetitions m of 4 deviates from the optimum condition of 56 degrees by −3 degrees. FIG. 20 is a diagram showing the dependency, and FIG. 20 shows the transmittances of P-polarized light and S-polarized light when the incident angle of the incident light IO on the polarization beam splitting element with the number of repetitions m of 4 deviates +5 degrees from the optimum condition of 56 degrees 21 is a diagram showing the wavelength dependence of P polarized light and S polarized light when the incident angle of the incident light IO on the polarization separation element having the number of repetitions m of 4 deviates by −5 degrees from the optimum condition of 56 degrees. It is a figure which shows the wavelength dependence of the transmittance of a.

18 to 21, the horizontal axis represents wavelength,
The vertical axis represents the transmittance. Further, in FIGS. 18 to 21, the broken line shows the transmittance characteristic of P-polarized light, and the solid line shows the transmittance characteristic of S-polarized light.

As can be seen from FIGS. 18 and 19, when the incident angles are 59 ° and 56 ° which are deviated from the optimum condition by ± 3 °, the waveform is slightly disturbed as compared with FIG. 16 showing the characteristic under the optimum condition. However, the condition that the transmittance of P-polarized light is 83% or more and the transmittance of S-polarized light is 5% or less is satisfied over a wide wavelength range.

As can be seen from FIGS. 20 and 21, the incident angles 61 ° and 5 deviated from the optimum condition by ± 5 °.
In the case of 1 degree, compared to FIG. 16 showing the characteristic under the optimum condition,
Furthermore, the waveform is disturbed, but it becomes narrower than when it is deviated by ± 3 degrees, but the transmittance of P-polarized light is still 8 over a wide wavelength range.
The conditions of 3% or more and S-polarized light transmittance of 5% or less are satisfied.

As described above, according to the present invention, the optically transparent high refractive index layer H having a predetermined refractive index with respect to the incident light OI and the high refractive index layer H are disposed so as to sandwich the high refractive index layer H. A basic structure film LHL composed of an optically transparent first low refractive index layer L and a second low refractive index layer L having a lower refractive index than the high refractive index layer H, and a repeating structure (LH
L) ^m (where m is an integer of 2 or more, preferably 3 to 7)
Of the polarization separation element 2 and the light incident surface 2a and the light transmission surface 2b of the polarization separation element 2 are in contact with each other.
Since the transparent substrate 3 is formed so as to sandwich it, there is an advantage that the film structure is extremely simple, and the number of necessary layers is small, and thus inexpensive manufacturing is possible. If this structure is used, the cost of the entire optical element incorporating the polarized beam split can be reduced.

Further, the present polarization beam splitter has an incident angle of 5
It has excellent polarization separation characteristics at 6 degrees. Further, as a low refractive index material of the polarization separation element 2, SiO ₂ (n = 1.4
6) as TiO ₂ (n = 2.44) as a high refractive index material
When each is used, L is 94.2 nm and H is 56.4 nm.
Thus, the film thickness per repeated one is about 250 nm. A common optical glass (BK7) can be used as the transparent substrate, and this element exhibits the maximum polarization separation performance for incident light at an angle near 56 degrees. In the case of these combinations, it is not necessary to make any correction to the basic structure described above, and high performance can be obtained with an extremely simple configuration. Further, the number of repetitions m of the film is practically sufficient to be 4, and the number of laminated layers at this time is only 9 layers and the film thickness is only 1 μm. The laminated thin film prism type polarization beam splitter according to the present invention configured as described above has high productivity and can be provided to the market at low cost by mass production.

[0079]

As described above, according to the present invention,
There is an advantage that an inexpensive polarization separation element having a broadband polarization separation function and a polarization beam splitter using the same can be realized with a simple film structure and a small number of layers.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing an embodiment of a laminated thin film prism type polarization beam splitter that employs a polarization separation element according to the present invention.

FIG. 2 is a diagram showing a stacking repeating structure of a polarization separation element when the stacking repeating number m is 3.

FIG. 3 is a diagram showing a stacking repeating structure of a polarization separation element when the stacking repeating number m is 4.

FIG. 4 is a diagram showing the wavelength dispersion dependence of the optical constant (refractive index) n of TiO ₂ .

FIG. 5 is a diagram showing wavelength dispersion dependence of an optical constant (extinction coefficient) k of TiO ₂ .

FIG. 6 is a diagram showing wavelength dependence of an optical constant (refractive index) n of SiO ₂ .

FIG. 7 is a diagram showing the wavelength dependence of P-polarized light transmittance when the number of times m of lamination is 3 to 7;

FIG. 8 is a diagram showing the wavelength dependence of P-polarized light transmittance when the number of times m of stacking is repeated is 1 and 2.

FIG. 9 is a diagram showing wavelength dependency of P-polarized light reflectance when the number of times m of lamination is 3 to 7;

FIG. 10 is a diagram showing the wavelength dependence of P-polarized light reflectance when the number of times m of lamination is 1, 2;

FIG. 11 is a diagram showing wavelength dependency of S-polarized light transmittance when the number of times m of lamination is repeated 3 to 7.

FIG. 12 is a diagram showing wavelength dependency of S-polarized light transmittance when the number of times m of lamination is repeated 1 and 2.

FIG. 13 is a diagram showing the wavelength dependence of the S-polarized reflectance when the number of times m of lamination is repeated 3 to 7.

FIG. 14 is a diagram showing the wavelength dependence of S-polarized reflectance when the number of times m of lamination is 1 and 2;

FIG. 15 shows the number of repetitions of the wavelength bands that can be separated by polarization when the width of a continuous wavelength range satisfying the conditions that the transmittance of P-polarized light is 83% or more and the transmittance of S-polarized light is 5% or less is used as an evaluation function. It is a figure which shows a dependency.

FIG. 16 is a diagram showing the wavelength dependence of the transmittance of P-polarized light and S-polarized light when the number of times m of stacking is repeated is 4.

FIG. 17 is a diagram showing the incident angle dependence of the polarization separable wavelength width.

FIG. 18 is a diagram showing the wavelength dependence of the transmittance of P-polarized light and S-polarized light when the incident angle of the incident light on the polarization separation element having the number of repetitions m of 4 is deviated by +3 degrees from the optimum condition of 56 degrees. .

FIG. 19 is a diagram showing the wavelength dependence of the transmittance of P-polarized light and S-polarized light when the incident angle of incident light on the polarization separation element with the number of repetitions m of 4 deviates from the optimum condition of 56 degrees by −3 degrees. is there.

FIG. 20 is a diagram showing wavelength dependence of transmittances of P-polarized light and S-polarized light when an incident angle of incident light on a polarization separation element having a repetition number m of 4 deviates by +5 degrees from an optimum condition of 56 degrees. .

FIG. 21 is a diagram showing the wavelength dependence of the transmittance of P-polarized light and S-polarized light when the incident angle of the incident light on the polarization beam splitting element having the number of repetitions m of 4 deviates by −5 degrees from the optimum condition of 56 degrees. is there.

[Explanation of Codes] 1 ... Polarization beam splitter, 2 ... Polarization separation element, 2a ...
Light incident surface, 2b ... Light transmitting surface, 3 ... Transparent substrate, H ... High refractive index layer, L ... Low refractive index layer, L1 ... First low refractive index layer, L2
... second low refractive index layer, LHL1 ... first basic structure film, L
HL2 ... Second basic structure film, LHL3 ... Third basic structure film, LHL4 ... Fourth basic structure film.

Claims (20)

[Claims] 1. A polarization splitting element that transmits a first polarized light of incident light that is incident at a predetermined angle and reflects a second polarized light in a direction different from a transmission direction, wherein An optically transparent high refractive index layer H having a refractive index of, and an optically transparent first low refractive index having a lower refractive index than the high refractive index layers arranged so as to sandwich the high refractive index layer H. A polarization separation element including a basic structure film LHL including an index layer L and a second low refractive index layer L, and having a repeating structure (LHL) ^m of the above basic structure. 2. The thickness of the high refractive index layer and the thicknesses of the first low refractive index layer and the second low refractive index layer are set based on a reference wavelength of incident light. The polarized light separating element described. 3. When the reference wavelength of the incident light is λ ₀ , the thickness of the high refractive index layer and the thicknesses of the first low refractive index layer and the second low refractive index layer are the reference wavelength. The polarization separation element according to claim 1, wherein the polarization separation element has an optical thickness corresponding to a value obtained by dividing by. 4. The polarization separation element according to claim 1, wherein the number of repetitions m of the basic structure is an integer of 3 or more. 5. The polarization beam splitting element according to claim 1, wherein the number of repetitions m of the basic structure is an integer of 3 or more and 7 or less. 6. The polarization beam splitting element according to claim 1, wherein a central value of an incident angle of the incident light on the optical film surface is set in the vicinity of 56 degrees. 7. The polarization beam splitting element according to claim 5, wherein a center value of an incident angle of the incident light on the optical film surface is set in the vicinity of 56 degrees. 8. The high refractive index layer has wavelength dispersion characteristics of an optical constant n in a predetermined range including a reference wavelength of incident light, and has an extinction coefficient of substantially zero at a predetermined wavelength shorter than the reference wavelength. The first and second low refractive index layers each include a material having an asymptotic characteristic, have wavelength dispersion characteristics of an optical constant n in a predetermined range including a reference wavelength of incident light, and extinguish in a substantially entire wavelength range. The polarization separation element according to claim 1, comprising a material having an extinction coefficient of substantially zero. 9. The polarization separation element according to claim 1, wherein the basic structure films adjacent to each other are formed so as to share the first low refractive index layer L and the second low refractive index layer L. 10. A polarization beam splitter, which transmits a first polarized light of incident light incident at a predetermined angle and reflects a second polarized light in a direction different from a transmission direction, wherein An optically transparent high refractive index layer H having a refractive index of, and an optically transparent first low refractive index having a lower refractive index than the high refractive index layers arranged so as to sandwich the high refractive index layer H. A polarization separation element having a basic structure film LHL composed of a refractive index layer L and a second low refractive index layer L and having a repeating structure (LHL) ^m of the above basic structure, and a light incident surface and a light transmission surface of the polarization separation element. And a transparent substrate arranged so as to be in contact with the polarizing beam splitter. 11. The thickness of the high refractive index layer and the thickness of the first low refractive index layer and the second low refractive index layer of the polarization separation element are set based on a reference wavelength of incident light. The polarization beam splitter according to claim 10. 12. When the reference wavelength of the incident light is λ ₀ , the thickness of the high refractive index layer of the polarization separation element, and the first
11. The polarizing beam splitter according to claim 10, wherein thicknesses of the low refractive index layer and the second low refractive index layer are set to optical thicknesses corresponding to a value obtained by dividing the reference wavelength by a predetermined integer. 13. The polarization beam splitter according to claim 10, wherein the number of repetitions m of the basic structure of the polarization separation element is an integer of 3 or more. 14. The polarization beam splitter according to claim 10, wherein the number of repetitions m of the basic structure of the polarization separation element is an integer of 3 or more and 7 or less. 15. The polarization beam splitter according to claim 10, wherein a central value of an incident angle of the incident light on the optical film surface of the polarization separation element is set to around 56 degrees. 16. The polarization beam splitter according to claim 14, wherein a central value of an incident angle of the incident light on the optical film surface of the polarization separation element is set to around 56 degrees. 17. The high refractive index layer of the polarization beam splitting element has wavelength dispersion characteristics of an optical constant n in a predetermined range including a reference wavelength of incident light, and extinguishes at a predetermined wavelength or more shorter than the reference wavelength. The first low refractive index layer and the second low refractive index layer have a wavelength dispersion characteristic of an optical constant n in a predetermined range including a reference wavelength of incident light, The polarization beam splitter according to claim 10, comprising a material having an extinction coefficient of substantially zero over the entire wavelength range. 18. The refractive index of the high refractive index layer of the polarization separation element is set higher than that of the transparent substrate, and the refractive indexes of the first and second low refractive index layers are set to the transparent substrate. 11. The polarization beam splitter according to claim 10, wherein the polarization beam splitter is set to have a refractive index lower than that of. 19. The refractive index of the high refractive index layer of the polarization separation element is set higher than that of the transparent substrate, and the refractive indexes of the first and second low refractive index layers are set to the transparent substrate. 18. The polarizing beam splitter according to claim 17, wherein the polarizing beam splitter is set to have a refractive index lower than that of. 20. The polarized light according to claim 10, wherein the basic structure films adjacent to each other of the polarization separation element are formed so as to share the first low refractive index layer L and the second low refractive index layer L. Beam splitter.