JPH07248417A - Holographic polarization beam splitter - Google Patents

Abstract

PURPOSE:To obtain a polarization beam splitter for which only the hologram recorded with interference fringes is used and other prisms, etc., are not used or the prisms, etc., are used only on either one surface of the hologram and which is simple in constitution, is light in weight, small in size and is easily producible. CONSTITUTION:This polarization beam splitter 20 which separates luminous fluxes 21 mixed with a P polarized light component and S polarized light component at a prescribed ratio between a P polarized light component 22 (23) and S polarized light component 23 (22) is composed of the transmission type hologram having the interference fringes recorded by refractive index modulation in a planar transparent recording material having a thickness. The interference fringes are so set as to allow transmission of the prescribed ratio part of either of the P polarized light component and the S polarized light component among the incident luminous fluxes on the planar transparent f-recording material as zero order light 23 and to separate the P polarized light component from S polarized light component at a prescribed by diffracting other prescribed ratio part as first order light 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a holographic polarization beam splitter, and more particularly to a video disc, a digital audio disc (compact disc),
The present invention relates to a polarization beam splitter used as an analyzer for optical discs, magneto-optical recording discs, mini-disc pickups, and optical isolators.

[0002]

2. Description of the Related Art Pickups for video discs, digital audio discs (compact discs), optical discs, magneto-optical recording discs, and mini discs,
Conventionally, a polarization beam splitter in which two right-angle prisms are bonded together and the bonding surface is coated with a dielectric multilayer film is used. A polarization beam splitter made of calcite is used as the analyzer of the optical isolator. Furthermore, a holographic polarization beam splitter in which a volume hologram is provided on the bonding surface of two right-angle prisms is also known (for example, "SPIE" vol.
1507, pp.426-434 (1991)).

The structure when such a polarization beam splitter is used for a pickup for a magneto-optical disk will be briefly described with reference to FIG. 8 (quoted from Nikkei McGraw-Hill's "Optical Disk Technology Handbook" pp. 77-78). ). In the case of a magneto-optical disk, since the change in the polarization direction is used, λ / that changes the polarization state like a write-once type
4 plates cannot be used. Therefore, the polarization beam splitter 1 has an S-polarized light reflectance of 100% but a P-polarized light transmittance of 40 to 60%. The light beam from the semiconductor laser is P-polarized, but the reflected light from the magneto-optical disk has the S component because the polarization direction is rotated by the Kerr rotation angle. The polarization beam splitter 2 to the photo detector 1 are a focus error detection system by the knife edge method, and the photo detector 2 are a tracking error detection system by the push-pull method. The photodetectors 3 and 4 are a signal detection system, and the polarization beam splitter 3 has a P-polarized light transmittance and an S-polarized light reflectance of 100%, and functions as an analyzer. By rotating the λ / 2 plate,
The polarization direction of the return light is rotated and the polarization beam splitter 3
For maximum signal amplitude. The signals detected by the two photodetectors have a relation of reflection and transmission of the polarization beam splitter, and thus have opposite phases. On the other hand, noise due to fluctuations in light quantity is in phase, so
By taking the difference between the outputs of the two photodetectors,
It is possible to reduce noise.

[0004]

The conventional polarization beam splitter as described above has a structure in which two prisms are attached to each other. Therefore, the size of a pickup using an apparatus using the prism, for example, a reading apparatus for a magneto-optical recording disk is downsized. However, this is an obstacle to weight reduction, and the material cost for the prism and the number of manufacturing steps increase, resulting in high cost. Furthermore, because the beam separation angle has a specific value, the degree of freedom in design is restricted,
From this point as well, it is an obstacle to miniaturization of the device.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to use only a hologram alone in which interference fringes are recorded and not use another prism or the like, or a hologram. (EN) It is possible to provide a holographic polarization beam splitter that uses a prism or the like on only one of the surfaces, has a simple structure, is lightweight, is small in size, and is easy to manufacture.

[0006]

A holographic polarization beam splitter of the present invention which achieves the above object is a P-polarization component at a predetermined ratio of a light beam in which a P-polarization component and an S-polarization component which are two orthogonal polarization components are mixed. And a polarization beam splitter for separating the S-polarized light component into a S-polarized light component, which is composed of a transmission hologram having interference fringes recorded by refractive index modulation in a plate-shaped transparent recording material having a thickness, Among them, the P-polarized component and the S-polarized component are transmitted at a predetermined ratio portion of one of the P-polarized light component and the S-polarized light component as the 0th-order light, and the other predetermined ratio portion is diffracted as the first-order light, thereby converting the P-polarized light component and the S-polarized light component at a predetermined ratio The interference fringes are set so as to be separated.

In this case, the refractive index modulation is Δn, the effective film thickness in which the interference fringes are recorded is d, the angle of the normal line of the interference fringes to the normal line of the hologram is φ, the wavelength of the incident light is λ, and the hologram method is used. When the angle formed by the incident light with respect to the line inside the hologram is θ and the angle of the primary light diffracted by the interference fringes with respect to the normal line of the hologram inside is θ _S , α = Δnd / λ and Four variables of θ, θ _S , and φ satisfy the following three equations, and θ ² + (2AB + B ² −1) θ + A ² = 0 (a) or A ² + 2BθA + {θ ² + (B ² −1 ) Θ} = 0 (a ′) However, as a discriminant, sin θ sin θ _S = −AB− (a ″) φ−θ = (cos ⁻¹ B) / 2 (b) ) 2φ = θ + θ _S ± π (c) where Θ = cos ² θ, A = (α / r _S ) ² , B = r _P /
r _S , r _S = ε _S + i _S , r _P = ε _P + i _P , ε _S is 0
≤ ε _S <1 and ε _S = {sin ^-1 (η _S ^1/2 )} / π, ε _P is 0 ≤ ε _P <1 and ε _P = {sin ^-1 (η _P
^1/2 )} / π real number, i _S is an arbitrary integer i _S ≧ 0, i _P is −i _S − (ε _S + ε _P ) ≦ i _P ≦ i _S + (ε
_S −ε _P ), η _S is the diffraction efficiency of the first-order diffracted light of S-polarized light, η _P is the diffraction efficiency of the first-order diffracted light of P-polarized light, and the average refractive index n of the transparent recording material is used. There was ^{_{θ n = sin -1 (1 /}} n), 0 <θ n <π / 2 becomes theta satisfies at least one of the following condition represented by _{n, -θ n <θ <θ} n ie 1 It is necessary to satisfy −1 / n ² <θ ≦ 1 or −θ _n <θ _S <θ _n and the optical conditions discretely constrained by the above integers i _S and i _P.

The diffraction efficiency of either S-polarized light or P-polarized light can be 0.8 to 1.0, and the diffraction efficiency of the other can be 0.0 to 0.2.

In that case, ε _P = 0.35242-0.6
4758 and ε _S = 0 to 0.14758 or ε _S =
0.85242-1, and the diffraction efficiency of P-polarized light is 0.8.
Is 1.0, even diffraction efficiency of the S polarized light is 0.0 to 0.2, epsilon _S = from .35242 to .64758 and,, epsilon _P = from 0 to 0.14758 or epsilon _P = 0.8524
2 to 1, the diffraction efficiency of S-polarized light may be 0.8 to 1.0, and the diffraction efficiency of P-polarized light may be 0.0 to 0.2.

Further, the diffraction efficiency of either S-polarized light or P-polarized light is 0.8 to 1.0 or 0.0 to 0.2,
The other diffraction efficiency may be 0.2 to 0.8.

In this case, ε _S = 0.35242-0.6
4758 and ε _P = 0.14758 to 0.3524
2 or ε _P = 0.64758 to 0.85242,
Even if the diffraction efficiency of S-polarized light is 0.8 to 1.0 and the diffraction efficiency of P-polarized light is 0.2 to 0.8, ε _S = 0 to 0.1.
4758 or ε _S = 0.85242-1 and ε _P =
0.14758 to 0.35242 or ε _P = 0.647
58 to 0.85242, and the diffraction efficiency of S-polarized light is 0.
0 to 0.2, and the diffraction efficiency of P polarized light is 0.2 to 0.8.
, Ε _P = 0.35242-0.64758,
And ε _S = 0.14758 to 0.35242 or ε _S
= 0.64758 to 0.85242, the diffraction efficiency of P-polarized light is 0.8 to 1.0, and the diffraction efficiency of S-polarized light is 0.2 to 0.8, ε _P = 0 to 0.14
758 or ε _P = 0.85242-1 and ε _S =
0.14758 to 0.35242 or ε _S = 0.647
58 to 0.85242, and the diffraction efficiency of P-polarized light is 0.
0 to 0.2, and the diffraction efficiency of S-polarized light is 0.2 to 0.8.
May be

The holographic polarization beam splitter of the present invention can be used, for example, in a pickup of a reading device for a magneto-optical recording disk.

[0013]

According to the present invention, a transparent hologram having interference fringes recorded by refractive index modulation in a plate-shaped transparent recording material having a thickness is used. It is possible to separate the P-polarized component and the S-polarized component at a predetermined ratio by transmitting a predetermined ratio part of one of the polarization component and the S-polarization component as 0th-order light and diffracting the other predetermined ratio part as the first-order light. Since the above interference fringes are set in, compared to the conventional polarization beam splitter, the structure is only a single hologram and no prism is required, or the hologram and the prism on either one side only. By using the hologram, a polarization beam splitter can be realized by the hologram. Therefore, it is possible to reduce the size, weight and cost of the device using the same. Further, since the polarization beam splitter can be constituted by only one hologram or a hologram in which a prism or the like is installed on only one surface, it can be manufactured extremely easily and inexpensively by duplication or the like. Furthermore, since there are many beam separation angles, there is freedom in design,
Also from this point, the device can be downsized.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle and embodiments of the holographic polarization beam splitter of the present invention will be described below with reference to the drawings. First, the basic principle of the present invention will be described.

Kogelnik's formula (H.Kogelnik "Coupled W
ave Theory for Thick Hologram Gratings "Bell Syst.
From Tech., J.48,2909 (1969)), the diffraction efficiency η under the Bragg condition of a transmission hologram is η = sin ² ν (1) However, for ν, for S-polarized light The value ν _S is ν _S = πΔnd / {λ (cos θ cos θ _S ) ^1/2 } (2) The value ν _P for P-polarized light is ν _P = ν _S cos {2 (φ−θ)} ... (3) (For example, the above-mentioned "SPIE" vol.1507, pp.426-
434 (1991)). Here, the symbols are as shown in FIG.
d is the effective thickness in which the interference fringes of the hologram are recorded, λ is the wavelength of the incident light, Δn is the refractive index modulation of the interference fringes with respect to the average refractive index n of the hologram medium, and φ is the hologram normal of the normal of the interference fringes. Is the angle inside the hologram formed by the incident light on the interference fringes with respect to the normal line of the hologram, and θ _S is the angle with respect to the normal line of the hologram inside the hologram of the first-order light Bragg-diffracted by the interference fringes. Is.

Further, between the directions φ and θ, θ _S of the lattice vector of the interference fringes of the hologram, in general, φ = (θ + θ _S ) / 2 ± π / 2 (composite is one Only) 2φ = θ + θ _S ± π (4) holds.

Here, when the diffraction efficiencies of the P and S polarized lights are arbitrarily given, the optical conditions satisfying these are obtained. That is, when the values of the diffraction efficiency η _{P of P-} polarized light and the diffraction efficiency η _S of S-polarized light are first determined, ν = sin ⁻¹ (± η ^1/2 ) which is a modification of the equation (1) ( 1 ′), ν _P and ν _S are obtained, and from this, (2) to (4)
Consider calculating the other variables Δn, d, λ, θ, θ _S , and φ by the formula. Here, Δn, d, and λ are Δnd /
Since it appears only in the form of λ, it is summarized as one variable α α = Δnd / λ.

Then, since there are three equations (2) to (4) for the four variables of α, θ, θ _S , and φ, by determining one of the four variables to a specific value. , The remaining three are unknowns, and these are calculated as solutions from simultaneous equations.

However, to solve the equations (2) to (4),
Since a mathematical transformation of the formula is required, the procedure for doing this and the formula for directly obtaining the resulting solution are given below.

From equation (2), ν _S = πα / (cos θ cos θ _S ) ^1/2 cos θ cos θ _S = (πα / ν _S ) ² = A (5) (A = (πα / ν _S ) ^2. ). Also, B =
When ν _P / ν _S is set, from the equation (3), B = cos {2 (φ−θ)} (6) φ−θ = (cos- ¹ B) / 2 (7) By substituting the equation (4) into the equation (6), B = cos (θ + θ _S ± π−2θ) = − cos (θ _S −θ) = − cos θ cos θ _S − sin θ sin θ _S = −A− sin θ sin θ _{S sinθ sinθ S = -A-B ···} (8) where (5) from _{^{equation, cos 2 θ S = (a}} / cosθ) 2 = a 2 / Θ ( was Θ = cos ² θ.) · (9) Further, from the expression (8), (A + B) ² = sin ² θsin ² θ _S (10) = (1-cos ² θ) (1-cos ² θ _S ) Expression (9), And substituting cos ² θ = Θ, (A + B) ² = (1-Θ) (1-A ² / Θ) Θ (A + B) ² = (1-Θ) (Θ-A ² ) ΘA ² + 2ΘAB + ΘB ^{2 = ΘA 2 -Θ 2 + ΘA} 2 2ΘAB + ΘB 2 = ΘA 2 -Θ 2 from the variant, quadratic equation for Θ: Θ ² + (2AB ^{B 2 -1) Θ + A 2} = 0 ··· (11) A related quadratic ^{equation: A 2 + 2BΘA + {Θ} 2 + (B 2 -1) Θ} = 0 ··· (11 ') is obtained.

[0021] Here, in general, a medium I having a refractive index n ₁ on the incident side of the hologram, when the medium II of the refractive index n ₂ is filled in close contact with the exit side theta, theta of _S and Θ Find the range. First, θ ₁ is an angle with respect to the normal line of the hologram when the incident light forming an angle θ with respect to the normal line of the hologram inside the hologram enters the hologram medium from the medium I, and θ ₂
Is an angle with respect to the normal line of the hologram when the first-order light Bragg-diffracted by the interference fringes goes out to the medium II (FIG. 1,
(See FIG. 5). First, θ ₁ θ ₂ is the angle of the I quadrant or the IV quadrant, and since it does not need to be a general form, −π / 2 <θ, θ ₁ <π / 2 (12) Can write Further, in the transmission hologram, the same applies to θ _S and θ _{2, and} can be written as −π / 2 <θ _S , θ ₂ <π / 2 (13). Further, at the boundary surface between the mediums I and II and the hologram, according to Snell's law, the incident side: n ₁ sin θ ₁ = n sin θ exit side: n sin θ _S = n ₂ sin θ ₂ holds, and −n ₁ <n sin θ <n ₁ −n ₁ / n <sin θ <n ₁ / n ・ ・ ・ (14) −θ _n1 <θ <θ _n1・ ・ ・ (15) where θ _n1 = sin ⁻¹ (n ₁ / n), 0 < θ _n1 <π / 2 (n> n ₁ ) = π / 2 (n ≦ n ₁ ) and −n ₂ <n sin θ _S <n ₂ −n ₂ / n <sin θ _S <n ₂ / n ... (14 ') −θ _n2 <θ _S <θ _n2・ ・ ・ (1
5 ′) However, θ _n2 = sin ⁻¹ (n ₂ / n) and 0 <θ _n2 <π / 2 (n> n ₂ ) = π / 2 (n ≦ n ₂ ) are obtained. Further, from the square of each side of the equation (14), 0 ≦ sin ² θ <(n ₁ / n) ² 1− (n ₁ / n) ² <1−sin ² θ ≦ 1 1− (n ₁ / n ) ² <cos ² θ ≤ 1 1- (n ₁ / n) ² <Θ ≤ 1 (16) is also obtained. In the case of the conventional type, there are prisms on both the incident side and the exit side, and n ₁ ≠ 1 and n ₂ ≠ 1. In contrast,
In the present invention, contradictory n ₁ = 1 or n ₂ = 1.

By the way, simultaneous equations (11) (or (11 ')) and (4), (7) are used to calculate the solution.
(11) (or (1
1 ')) of the two solutions of the quadratic equation,
There are generally one true solution that satisfies equation (4),
The other may be an inappropriate solution. The cause is
This is because both sides are squared in the transformation from the equation (8) to the equation (10). That is, the solution of the equation (10) is sin θ sin θ _S = ± (A + B) However, from the equations (15) and (15 ′), sin θ sin θ
The sign of _S can be either positive or negative.

## EQU3 ## This is just a necessary condition of the equation (8). Also, in the transformation from the equation (5) to the equation (9), both sides are squared.
From the value range of θ and θ _S, the left side cos θ cos θ _S is a positive value, and the right side (πα / ν _S ) ² (= A) is also a positive value, so (5)
The equation and the equation (9) are equivalent. Therefore, in order to determine the solution of Expression (11) (or (11 ′)), the verification by Expression (8) is required.

In this way, a formula for directly obtaining a solution satisfying the optical condition is obtained from the arbitrary diffraction efficiencies of the P and S polarizations and the specific value of one variable. Organizing this, Θ ² + (2AB + B ² −1) Θ + A ² = 0 (a) or A ² + 2B ΘA + {Θ ² + (B ² −1) Θ} = 0 (a ′) where , As a discriminant, sin θ sin θ _S = -A-B ... (a ") φ-θ = (cos ^-1 B) / 2 ... (b) 2 φ = θ + θ _S ± π (Compound is (C) where Θ = cos ² θ (d) where −θ _n <θ <θ _n, that is, 1-1 / n ² <θ ≦ 1 ( d ′) or −θ _n <θ _S <θ _n ... (d ″) (where θ _n = sin ⁻¹ (1 / n), 0 <θ _n <π / 2) A = (πα / Ν _S ) ²・ ・ ・ (e) B = ν _P / ν _S・ ・ ・ (f) α = Δnd / λ ・ ・ ・ (g) ν _S = sin ^-1 (± η _S ^1/2 ) ・・ ・ (H) ν _P ＝ sin ⁻¹ (± η _P ^1/2 ) ・ ・ ・ (i) holds.

The following table outlines the procedure for obtaining a solution for each variable that first specifies a value. .

As shown in the above table, each variable is directly obtained. However, in case III, when obtaining φ and θ from θ _S , the simultaneous simultaneous equations are solved.

Further, a general solution of ν _S and ν _P to (h) and (i) is solved, and A and B are rewritten accordingly. In the following, since it is common to S-polarized light and P-polarized light except for a part, in that case, the subscripts _S and _P are omitted.

FIG. 6A shows η, ν, ε when η is specific.
A unit circle representing the relationship, in this figure, the relationship between eta and ν, the vertical axis represents the eta ^1/2, position a line parallel to the horizontal axis intersects the unit circle through the ± eta ^1/2 The angle formed with the positive direction of the horizontal axis is ν (radian), and at this time, the expressions (1), (h), and (i) are satisfied. In the figure, 0-2π
4 is represented by using ν = ν _O at 0 to π / 2.

By the way, since the vertical and horizontal symmetry, that is, rotational symmetry, the general solution of ν can be represented by two positions of ν = ν _O or π−ν _O which change in the period π. Note that these two values are equal to sin ⁻¹ (η ^1/2 ) in 0 to π. At this time, using the integer i, ν = ν _O + iπ or π−ν _O + iπ. Here, [ν _O or π−ν _O ] = sin ⁻¹
If (η ^1/2 ) (where 0 to π) = επ, then ν = επ + iπ = (ε + i) π = rπ (assuming r = i + ε) can be expressed in one way. However, since 0 ≦ ν _O ≦ π / 2,
0 ≦ ε ≦ 1, but when ε = 1, it becomes the same as ε = 0 due to the periodicity of ν, so that 0 ≦ ε <1.

Next, the range of integer i (i _S , i _P ) is obtained. From the formula (2), ν _S > 0 (18) Further, according to the formula (3) and −1 ≦ cos {2 (φ−θ)} ≦ 1, −ν _S ≦ ν _P ≦ ν _S ···・ (19) holds. Therefore, from the equations (17) and (18), ν _S = ε _S π + i _S π> 0 i _S > −ε _S > −1 i _S ≧ 0 (20) Further, (17) and (19) From the formula, −ε _S −i _S ≦ ε _P + i _P ≦ ε _S + i _S −i _S − (ε _S + ε _P ) ≦ i _P ≦ i _S + (ε _S −ε _P ) ... (21) and , Ε _S + ε _P <2 and ε _S −ε _P <1, so that i
_P is at most −i _S −1 ≦ i _P ≦ i _S (22). At this time, from equations (e), (f) and (17), A = (α / r _S ) ² ... (e ′) B = r _P / r _S ... (f ′)

Further, when η has a range, it can be similarly expressed by ε having a range, which will be shown below.
First, the range of ν in three typical cases depending on the range of η is represented by the thick line portion of the unit circle showing the relationship between η, ν, and ε when η has a range in FIG. 6B. . Similar to the case where η is a specific value, because of rotational symmetry, ν changes in the period π, and corresponds to the thick line portion in 0 ≦ ν <π (upper semicircle) in FIG. 6B. If ε = ν / π for ν
As a general solution of ν, (17) holds as described above. In this case, the range of ε 0 ≦ ε <1, the range of integers (20),
The equation (21), the equations (e ′) and (f ′) representing A and B, and the like are also established.

Below, the range of ε is shown by a formula for each range of η (common to P-polarized light and S-polarized light).

When η = η _min ˜1, sin ⁻¹ (η _min ^1/2 ) ≦ επ ≦ π− sin
^-1 (η _min ^1/2 ) However, in the following, all sin ^-1 is in the range of 0 to π / 2.

Sin ^-1 (η _min ^1/2 ) / π≤ε≤1-sin
⁻¹ (η _min ^1/2 ) / π For example, when η _min = 0.8, ε = 0.35242-0.64758.

[0035] eta = For ^{_{0~η max 0 ≦ επ ≦ sin -1}} (η max 1/2) or _{^{π- sin -1 (η max 1/2)}} ≦ επ <π 0 ≦ ε ≦ sin -1 ( η _max ^1/2 ) / π or 1-sin ⁻¹ (η _max ^1/2 ) / π ≦ ε <1 For example, when η _max = 0.2, ε = 0 to 0.14758 or ε = 0. 85242-
It becomes 1.

In the case of η = η _{min to} η _max sin ^-1 (η _min ^1/2 ) ≤ επ ≤ sin ^-1 (η _max ^1/2 )
Or π− sin ⁻¹ (η _max ^1/2 ) ≦ επ ≦ π− sin ⁻¹ (η _min
^1/2 ) sin ^-1 (η _min ^1/2 ) / π ≤ ε ≤ sin ^-1 (η _max ^1/2 )
/ Π or 1-sin ^-1 (η _max ^1/2 ) / π ≤ ε ≤ 1-sin ^-1 (η
_min ^1/2 ) / π For example, when η _min = 0.2 and η _max = 0.8, ε = 0.14758 to 0.35242 or ε = 0.64758 to 0.85242. The combination of ε _S and ε _P is determined by the above combination of η _S and η _P for and.

From the above examination results, calculation results for a typical example will be shown in order to examine the characteristics of the present invention.
As a premise of this calculation, η _S = 0, η _P = 1 and φ = π /
In the case of 2, general solutions of θ (= −θ _S ) and d were obtained. However, λ = 0.78 μm and Δn = 0.03. The results are shown in the table below.

[0038] Note) Upper value in each square: θ [°] (= -θ _S ) (value inside hologram) Lower value: d [μm]
.

The following can be said from the above table.

(1) When ν _S is the same, the smaller ν _P is, the more θ
Is small and d is large. At this time, if the average refractive index n = 1.52 and n ₁ = n ₂ = 1 for example, Snell's law does not hold under the condition of () in the table of large θ. Considering the symmetry with respect to the hologram surface, in this case, prisms are required on both the entrance side and the exit side, which is outside the scope of the present invention.

(2) Data at the bottom of each column of the table (* mark)
In the comparison between the two, d increases as ν _S increases, but θ
Becomes smaller. At the same time, the beam separation angle (= | θ−θ _S
| = | 2θ |) also becomes small.

(3) In designing or using a hologram in which it is not necessary to consider the polarization direction, the diffraction efficiency considers only one polarization, and in order to obtain the maximum diffraction efficiency, ν = 1
Select the conditions such that / 2π, 3 / 2π, 5 / 2π ...
If Δn and λ are constant, d also increases in proportion to ν. Therefore, for the reasons of material saving, easiness of manufacturing, etc., conventionally, ν = 1 /
2π is used. For example, in this case, d is 10 μm or less, which is about half of d in the case of ν _S = π in the above table. On the other hand, in order to realize the polarization beam splitter of the present invention, d becomes larger than the conventional one as shown in the above table.
Also, instead of increasing d in this way, ν∝Δnd
Since / λ, Δn may be increased or λ may be decreased.

By the way, when the holographic polarization beam splitter of the present invention as described above is used in an actual pickup for a magneto-optical disk as shown in FIG. 8, how to set the diffraction efficiencies η _S and η _P Consider. "Optical Disc Technology Handbook" published by Nikkei McGraw-Hill, Inc., which is shown in FIG. Describing based on the examples described in 77 to 78, there are two types of light that pass through the polarization beam splitter 1 in FIG. 8, and there are two types of light: incident light from a semiconductor laser (“going”; upward in the figure) and light from a magneto-optical disk. It is reflected light (“return”, downwards in the figure). In the example of this figure, the polarized light includes only P-polarized light emitted from the semiconductor laser, and "returned" includes S-polarized light due to the reflection on the magneto-optical disk and the polarization direction being shifted. Then, it is necessary to transmit a lot of "go" and reflect a lot of "return". Looking at this by polarized light, P-polarized light transmits a lot of "go",
It is necessary to reflect a lot on the "return", and ideally the transmittance is 50%, and it is described in the above document that it is 40 to 60%. Further, S-polarized light needs to reflect a lot on the "return" regardless of the "go", and ideally the reflectance is 100% also in the above literature.

The polarization beam splitter 3 is a signal detection system as described in the above document, and ideally has a P-polarized light transmittance and an S-polarized light reflectance of 100%. In reality, for the reason of easiness of production, cost reduction, etc., the reflectance and transmittance of the polarization beam splitters 1 and 3 are 100% in the above-mentioned literature, and actually 80% or more in the above-mentioned literature. Four
In practice, 0 to 60% must be made to 20 to 80%. When the functions of the polarization beam splitters 1 and 3 are realized by only a single hologram according to the present invention, the transmitted light and the diffracted light play the roles of transmission and reflection as described above, but reverse this role. Alternatively, the roles of P-polarized light and S-polarized light can be reversed. for that reason,
In the present invention, the diffraction efficiency of the hologram having the performance similar to that of the polarization beam splitter 3: [1.1] η _P = 0.0 to 0.2, η _S = 0.8 to 1.
0 [1.2] η _S = 0.0 to 0.2, η _P = 0.8 to 1.
0 Diffraction efficiency of hologram having performance similar to that of the polarization beam splitter 1: [2.1] η _P = 0.2 to 0.8, η _S = 0.8 to 1.
0 [2.2] η _P = 0.2 to 0.8, η _S = 0.0 to 0.
2 [2.3] η _S = 0.2 to 0.8, η _P = 0.8 to 1.
0 [2.4] η _S = 0.2 to 0.8, η _P = 0.0 to 0.
A range of 2 is prepared. These ranges are as shown in FIG.

Next, some examples will be described together with comparative examples. In the production and use of the holographic polarization beam splitter, as a hologram photosensitive material, a photopolymer (DuPont Omnidex 352) having an average refractive index n = 1.52 and a refractive index modulation Δn = 0.03 was also exposed. At the time of use and as a light source, the wavelength λ =
A 0.514 μm, 5 W argon laser (Model SP2020-05S manufactured by Spectra Physics) is used.

[Comparative Example] In the design, regarding the diffraction efficiency of the first-order light of S-polarized light and P-polarized light, η _S is 0.1 or less and η _P
The optical condition for which is 0.9 or more is obtained. First, the film thickness at which the diffraction efficiency η _{S of} the S-polarized first-order light is 0.1 or less is obtained. In use, the media I and II are air (n ₁ = n ₂
= 1), and the incident angle θ _{1 in} air and the diffraction angle θ ₂ of the primary light are θ ₁ = −θ ₂ = 30 ° (in the hologram, θ = −θ _S
= 19.2 °), the above λ and Δn are calculated according to Kogelnik's theory.
Among the multiple solution ranges for, there is, for example, d = 28-35 μm. At this time, the diffraction efficiency η _P of P-polarized light is η _P = 0.64 to 0.17, and the required performance cannot be obtained.

Regarding the diffraction efficiency of the primary light of S-polarized light and P-polarized light, the optical condition that η _S is 0.9 or more and η _P is 0.1 or less is obtained. First, the diffraction efficiency η of S-polarized first-order light
Obtain the film thickness at which _S is 0.9 or more. When using,
The media I and II are air (n ₁ = n ₂ = 1), and the incident angle θ _{1 in} air and the diffraction angle θ ₂ of the primary light are θ ₁ = −θ ₂ = 30 ° (inside the hologram) , Θ = −θ _S
= 19.2 °), the above λ and Δn are calculated according to Kogelnik's theory.
Among the multiple solution ranges for, for example, d = 13-19 μm. At this time, the diffraction efficiency η _P of P-polarized light is η _P = 0.69 to 0.99, and similarly the required performance cannot be obtained.

As described above, it is understood that the hologram having appropriate optical conditions such as the incident angle and the film thickness is not suitable for the polarization beam splitter.

[Embodiment 1] In the design, with respect to the diffraction efficiencies η _S and η _P of the S-polarized and P-polarized primary light, η _S is 0.
1 or less (η _Smax = 0.1), η _P is 0.9 or more (η _Pmin
= 0.9). In use, the mediums I and II are air (n ₁ = n ₂ = 1), and first, the incident angle θ ₁ in air is θ ₁ = 30 ° (θ = 19.2 ° inside the hologram). And

Here, 0 ≦ ε _S ≦ {sin ⁻¹ (0.1) ^1/2 } / π or 1− {sin ⁻¹ (0.1) ^1/2 } / π ≦ ε _S < 10 ≤ ε _S ≤ 0.10242 or 0.89758 ≤ ε
_S <1 and {sin ⁻¹ (0.9) ^1/2 } / π ≦ ε _P ≦ 1- {sin
^{Since −1} (0.9) ^1/2 } / π 0.39758 ≦ ε _P ≦ 0.60242, ε _S = 0.9 and ε _P = 0.4 are selected. Also, i
_S = 0, −0− (0.9 + 0.4) ≦ i _P ≦ 0 + (0.9−0.
4) Since −1.3 ≦ i _P ≦ 0.5 −1 ≦ i _P ≦ 0, i _P = −1 is selected. At this time, r _S = 0.9 and r _P = −0.6. Then, B = −0.667 and Θ = 0.892 are obtained. Equation (b), from (c), 1 single and theta _S for this in the general solution of phi _{is, φ = 85.1 °, θ S} = -29.0 ° ( in air theta ₂
= -47.4 °). Then, the equation (a ′) is determined as A ² −1.189A + 0.300 = 0. The solution is A = 0.826,0.363. Here, -AB is -0.159 and 0.3 in order.
On the other hand, since sin θ sin θ _S = −0.159, A = 0.826 is one of the conditions satisfying the required performance. The film thickness at this time is obtained as d = 14.0 μm. When the diffraction efficiency under this condition is calculated and verified, η _S = 0.10 and η _P = 0.91.

By the way, d obtained from A = 0.363
= When the diffraction efficiency is calculated under the condition of 9.3 .mu.m, eta _S =
Since 0.91 and η _P = 0.90, this condition is not suitable for the polarization beam splitter.

In addition, the hologram photosensitive material 1 described above is actually used.
At 0, the film thickness d = 14.0 μm and the above laser light source were used to photograph a hologram in the arrangement as shown in FIG.
The diffraction efficiency of P polarized light was measured. At the time of photographing, using parallel light, the reference light 11 incident angle in the air θ _rair = θ ₁ = 30.0 ° and the object light 12 incident angle θ _oair =
The photosensitive material 10 was irradiated with θ ₂ = −47.4 °. As shown in FIG. 1, the diffraction efficiency of the S-polarized and P-polarized incident light (reproduction light) at the incident angle of θ ₁ = 30.0 ° with respect to the hologram 20 photographed as described above is determined. Two
1 and the first-order light 22 or zero-order light 23 and the incident light 2
The intensity of No. 1 was measured and determined from the ratio thereof. as a result,
The S-polarized zero-order light 23 is 0.90 (the primary light 22 is about 0.1
0), the primary light 22 of P-polarized light was about 0.90, and performance almost equivalent to the design was obtained.

[Embodiment 2] In the design, with respect to the diffraction efficiencies η _P and η _S of P-polarized light and S-polarized primary light, η _P is 0.
1 or less (η _Pmax = 0.1), η _S is 0.9 or more (η _Smin
= 0.9). First, the film thickness d is set to d = 21 μm.

Here, {sin ^-1 (0.9) ^1/2 } / π≤ε _S ≤1- {sin
^-1 (0.9) ^1/2 } / π 0.39758 ≤ ε _S ≤ 0.60242 and 0 ≤ ε _P ≤ {sin ^-1 (0.1) ^1/2 } / π, or 1- {Sin ⁻¹ (0.1) ^1/2 } / π ≦ ε _P <10 ≦ ε _P ≦ 0.10242 or 0.89758 ≦ ε
_{Since P} <1, choose ε _S = 0.4 and ε _P = 0.9. Also, i
_{If S} = 1, −1− (0.4 + 0.9) ≦ i _P ≦ 1 + (0.4−0.
9) Since -2.3 ≤ i _P ≤ 0.5 -2 ≤ i _P ≤ 0, i _p = -2 is selected. At this time, r _S = 1.4 and r _P = −1.1. Then, A = 0.767 and B = −0.786 are obtained. The equation of (a) is determined as Θ ² −1.587 Θ + 0.588 = 0. The solution is Θ = 0.999,0.588. For example, choose Θ = 0.588 and θ = cos ^-1 (Θ
^As one of the general solutions of ^1/2 ), θ = 39.9 ° is obtained. Here, according to equations (b) and (c), one of the general solutions of φ and a set of θ _S corresponding thereto, φ = 110.8 °, θ _S = 1.7 ° φ = 149.8 ° , Θ _S = 79.7 ° is obtained. Where sin θ sin θ _S is 0.01
9, 0.631, while -AB = 0.019, θ = 39.9 °, φ = 110.8 °, θ _S = 1.7 ° (mediums I and II are air ( n ₁ = n ₂ = 1), and θ ₁ = 77.3 °, θ ₂ = 2.6 °) in the air is one of the conditions for satisfying the required performance. When the diffraction efficiency under this condition is calculated and verified, η _P = 0.10 and η _S = 0.91.

By the way, θ obtained from Θ = 0.999
= 1.7 °, φ = 72.6 °, θ _S = −36.5 °, the diffraction efficiency is calculated, then η _P = 0.05, η _S =
This is 0.84, which is not suitable for a polarizing beam splitter.

In addition, the hologram photosensitive material 1 described above is actually used.
0 and the film thickness d = 21.0 μm and the laser light source described above are used to photograph a hologram in the arrangement as shown in FIG.
The diffraction efficiency of S-polarized light was measured. At the time of photographing, using the values of the above design for parallel light, the incident angle of reference light 11 in air θ _rair = θ ₁ = 77.3 °, the incident angle of object light 12 θ _aair =
The photosensitive material 10 was irradiated with θ ₂ = 2.6 °. As for the diffraction efficiency, as shown in FIG. 1, the hologram 20 photographed as described above is irradiated with P-polarized light and S-polarized incident light 21 at an incident angle of θ ₁ = 77.3 °. The intensities of the primary light 22 or the zero-order light 23 and the incident light 21 were measured, and the intensity was obtained from the ratio thereof. As a result, the P-polarized 0th-order light 23 was 0.90 (the primary light 22 was about 0.10), and the S-polarized 1st-order light 22 was about 0.90. .

[Embodiment 3] In the design, with respect to the diffraction efficiencies η _S and η _P of S-polarized and P-polarized primary light, η _S is 0,
Obtain the film thickness at which η _P becomes 1. In use, the medium I
Is air (n ₁ = 1), and first, the incident angle θ in air
_1, and θ ₁ = 0 ° (also theta = 0 ° within a hologram).

Here, 0 ≦ ε _S ≦ {sin ⁻¹ (0) ^1/2 } / π or 1- {sin ⁻¹ (0) ^1/2 } / π ≦ ε _S <1 and { sin ^-1 (1) ^1/2 } / π ≤ ε _P ≤ 1- {sin ^-1 (1)
^{From 1/2} } / π, ε _S = 0 and ε _P = 0.5. Also, i _S = 1
Then, −1− (0 + 0.5) ≦ i _P ≦ 1 + (0−0.5) −1.5 ≦ i _P ≦ 0.5 −1 ≦ i _P ≦ 0, so i _P = −1 is selected. . At this time, r _S = 1 and r _P = −0.5. Then, B = -0.5 and Θ = 1 are obtained. Equation (b), from (c), 1 single and theta _S for this in the general solution of phi is, φ = 120 °, obtained as θ _S = 60 °. Then, the equation of (a ′) is determined as A ² + 2BA + B ² = (A + B) ² = 0. This solution is A = -B = 0.5 (multi-root). Here, in the discriminant (a "), -AB is sin θ s
Since both inθ _S also become 0, it holds. The film thickness at this time is obtained as d = 12.1 μm. When the diffraction efficiency under this condition is calculated and verified, η _S = 0.00 and η _P = 1.00.

In addition, the hologram photosensitive material 1 described above is actually used.
0 and the film thickness d = 12.1 μm and the above laser light source were used, a glass block (for incident angle adjustment, refractive index 1.52) G ₁ , a glass block (for back reflection prevention, n ₂ ) as shown in FIG. = 1.52) The hologram was photographed in an arrangement using G ₂ and the diffraction efficiency of S-polarized light and P-polarized light was measured. At the time of photographing, the parallel light is converted into the reference light 11 incident angle θ _{r in the} air and the glass blocks G ₁ and G ₂ by using the values of the above design.
= Θ ₁ = 0 °, and the photosensitive material 10 was irradiated with the object light 12 at an incident angle θ _o = θ ₂ = 60 °. As for the diffraction efficiency, as shown in FIG. 3, the hologram 20 photographed as described above is used.
On the other hand, a glass block G ₂ is installed on the exit side, and S-polarized and P-polarized incident light (reproduced light) 21 is irradiated in the air at an incident angle of θ ₁ = 0 ° to emit the primary light 22 or The intensities of the 0th-order light 23 and the incident light 21 were measured and determined from the ratio thereof. As a result, the 0th-order light 23 of S polarization is 0.98.
As described above (the primary light 22 is about 0.02 or less), the P-polarized primary light 22 is 0.98 or more, and performance substantially equivalent to the design was obtained.

[0060]

As is apparent from the above description, according to the holographic polarization beam splitter of the present invention, a transmission hologram having interference fringes recorded by refractive index modulation in a plate-shaped transparent recording material having a thickness is obtained. In the light flux entering the plate-shaped transparent recording material, the P-polarized component and the S-polarized component
The above-mentioned interference so that the P-polarized light component and the S-polarized light component are separated at a predetermined ratio by transmitting one predetermined ratio part of the polarization component as 0th-order light and diffracting the other predetermined ratio part as first-order light. Since the stripes are set, compared with the conventional polarization beam splitter, the structure is only a single hologram and no prism is required, or the prism and the like are used on only one side of the hologram. Then, the polarization beam splitter can be realized by the hologram. Therefore, it is possible to reduce the size, weight and cost of the device using the same. Further, since the polarization beam splitter can be constituted by only one hologram or a hologram in which a prism or the like is installed on only one surface, it can be manufactured extremely easily and inexpensively by duplication or the like. Further, since the beam can have various separation angles, there is a degree of freedom in design, and the size of the device can be reduced in this respect as well.

[Brief description of drawings]

FIG. 1 is a diagram showing how a holographic polarization beam splitter according to an embodiment of the present invention separates polarization components.

2 is a diagram showing an arrangement for capturing an image of the holographic polarization beam splitter of FIG. 1. FIG.

FIG. 3 is a diagram showing how a holographic polarization beam splitter of another embodiment separates polarization components.

4 is a diagram showing an arrangement for photographing the holographic polarization beam splitter of FIG.

FIG. 5 is a diagram showing symbols used in the present invention.

FIG. 6 is a diagram showing a unit circle representing the relationship between η, ν, and ε.

FIG. 7 shows the diffraction efficiency range of the holographic polarization beam splitter according to the present invention.

FIG. 8 is a diagram showing a configuration when a conventional polarization beam splitter is used for a pickup for a magneto-optical disk.

[Explanation of symbols]

10 ... hologram photosensitive material 11 ... reference beam 12 ... object beam 20 ... hologram (holographic polarization beam splitter) 21 ... incident light (reproducing light) 22 ... first-order light 23 ... 0 order light G _1, G ₂ ... glass block

Claims (11)

[Claims] 1. A plate-like transparent recording having a thickness in a polarization beam splitter for separating a light beam, which is a mixture of two orthogonal polarization components, P polarization component and S polarization component, into P polarization component and S polarization component at a predetermined ratio. The material is composed of a transmission hologram having interference fringes recorded by refractive index modulation in the material, and a predetermined ratio portion of one of the P-polarized component and the S-polarized component in the light beam incident on the plate-shaped transparent recording material is 0. The above-mentioned interference fringes are set so that the P-polarized component and the S-polarized component are separated at a predetermined ratio by transmitting as the next light and diffracting the other predetermined ratio portion as the primary light. Graphic polarization beam splitter. 2. The refractive index modulation is Δn, the effective film thickness of the interference fringes recorded is d, the angle of the normal line of the interference fringes to the normal line of the hologram is φ, and the wavelength of incident light is λ. When the angle formed by the incident light with respect to the normal line of the hologram inside the hologram is θ, and the angle of the primary light diffracted by the interference fringes with respect to the normal line of the hologram inside the hologram is θ _S , α = Four variables of Δnd / λ and θ, θ _S , φ satisfy the following three equations, and Θ ² + (2AB + B ² −1) Θ + A ² = 0 (a) or A ² + 2BΘA + {Θ ² + ( B ² −1) Θ} = 0 (a ′) However, as a discriminant, sin θ sin θ _S = −AB− (a ″) φ−θ = (cos ⁻¹ B) / 2 .. (b) 2φ = θ + θ _S ± π (c) where Θ = cos ² θ, A = (α / r _S ) ² , B = r _P /
r _S , r _S = ε _S + i _S , r _P = ε _P + i _P , ε _S is 0
≤ ε _S <1 and ε _S = {sin ^-1 (η _S ^1/2 )} / π, ε _P is 0 ≤ ε _P <1 and ε _P = {sin ^-1 (η _P
^1/2 )} / π real number, i _S is an arbitrary integer i _S ≧ 0, i _P is −i _S − (ε _S + ε _P ) ≦ i _P ≦ i _S + (ε
_S −ε _P ), η _S is the diffraction efficiency of the first-order diffracted light of S-polarized light, η _P is the diffraction efficiency of the first-order diffracted light of P-polarized light, and the average refractive index n of the transparent recording material is Θ _n = sin ⁻¹ (1 / n) used and at least one of the following conditional expressions represented by θ _{n where} 0 <θ _n <π / 2 is satisfied, and −θ _n <θ <θ _n The optical condition which is 1-1 / n ² <θ ≦ 1 or −θ _n <θ _S <θ _n and which is discretely constrained by the integers i _S and i _P is satisfied. Holographic polarization beam splitter. 3. The diffraction efficiency of either S-polarized light or P-polarized light is 0.8-1.0, and the diffraction efficiency of the other is 0.0-1.0.
The holographic polarizing beam splitter according to claim 2, wherein the holographic polarizing beam splitter is 0.2. 4. ε _P = 0.35242-0.6475
8 and ε _S = 0 to 0.14758 or ε _S = 0.8
5242-1, and the diffraction efficiency of P-polarized light is 0.8-1.
The holographic polarizing beam splitter according to claim 3, wherein the holographic polarizing beam splitter has a diffraction efficiency of 0 and an S polarized light diffraction efficiency of 0.0 to 0.2. 5. ε _S = 0.35242-0.6475
8 and ε _P = 0 to 0.14758 or ε _P = 0.8
5242-1, and the diffraction efficiency of S-polarized light is 0.8-1.
The holographic polarization beam splitter according to claim 3, wherein the holographic polarization beam splitter has a diffraction efficiency of 0.0 and a polarization efficiency of P-polarized light of 0.0 to 0.2. 6. The diffraction efficiency of either S-polarized light or P-polarized light is 0.8 to 1.0 or 0.0 to 0.2, and the diffraction efficiency of the other is 0.2 to 0.8. The holographic polarization beam splitter according to claim 2, wherein 7. ε _S = 0.35242-0.6475
8 and ε _P = 0.14758 to 0.35242 or ε _P = 0.64758 to 0.85242, the diffraction efficiency of S-polarized light is 0.8 to 1.0, and the diffraction efficiency of P-polarized light is The holographic polarization beam splitter according to claim 6, wherein the holographic polarization beam splitter has a thickness of 0.2 to 0.8. 8. ε _S = 0 to 0.14758 or ε _S =
0.85242-1 and ε _P = 0.14758
0.35242 or ε _P = 0.64758 to 0.852
42, the S-polarized light diffraction efficiency is 0.0 to 0.2, and the P-polarized light diffraction efficiency is 0.2 to 0.8. . 9. ε _P = 0.35242-0.6475
8 and ε _S = 0.14758 to 0.35242 or ε _S = 0.64758 to 0.85242, the diffraction efficiency of P-polarized light is 0.8 to 1.0, and the diffraction efficiency of S-polarized light is The holographic polarization beam splitter according to claim 6, wherein the holographic polarization beam splitter has a thickness of 0.2 to 0.8. 10. ε _P = 0 to 0.14758 or ε _P =
0.85242-1 and ε _S = 0.14758
0.35242 or ε _S = 0.64758 to 0.852
42, the diffraction efficiency of P-polarized light is 0.0 to 0.2, and the diffraction efficiency of S-polarized light is 0.2 to 0.8. . 11. A pickup according to claim 1, which is used in a reading device for a magneto-optical recording disk.
The holographic polarization beam splitter according to claim 1.