JPS60243604A - Depolarization plate - Google Patents

Abstract

PURPOSE:To permit easy conversion of incident light to a non-polarized state without decreasing the quantity of light to the incident light having all polarization characteristics by disposing plural wedge-shaped transparent plates consisting of a material having double refractions which shifting successively the crystal axes thereof by 45 deg.. CONSTITUTION:The wedge crystal plates 3, 3 have the face 3a perpendicular to one crystal axis except the crystal optical axis. The central wall thickness thereof is d0 and the wedge angle is alpha1, alpha2. The orientation of the crystal optical axis is made coincident with the orientation of the wedge angle. The plates 3, 3 are so positioned that the slopes thereof face each other via the wedge-shaped transparent plate 4 made of ordinary optical glass having the same refractive index as the refractive index of a rock crystal in the state of shifting the crystal optical axis by 45 deg.. Three pieces of such plates are disposed in the joined state and the faces 3a, 3a exposed to the outside are paralleled. The transmitted light which is not polarized with all incident light is obtd. by setting the wedge angles alpha1, alpha2 at which the change rate of the sectional direction changed with respect to the wedge direction of the rock crystal plate are increased with respect to the optical wavelength lambda with the above-mentioned constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a depolarizing plate for making light having any polarization characteristics non-polarized.

[Prior art]

BACKGROUND ART Conventionally, as a depolarizing plate used to depolarize light having polarization characteristics, a depolarizing plate made of a material having birefringence such as quartz and having a shape as shown in FIG. 1 is known. In the figure, d is the thickness of the depolarizing plate, and α is the angle formed between the transmission surfaces.

Next, the principle of such a conventional depolarization plate will be explained using mathematical formulas. In general, if M is a matrix representing the characteristics of a wave plate with an ellipticity of =o, that is, an ordinary wave plate, it is expressed as follows. However, φ is retardation, 2π(
It is expressed as na no)d φ−...f21 λ. Here, n8: refractive index of the material for extraordinary rays no: refractive index of the material for ordinary rays d: wall thickness of the wave plate λ: wavelength of light θ: azimuth angle of the coordinate axis of the incident light with respect to the crystal axis θ': observation system is the azimuth angle of the coordinate axis of , with respect to the crystal axis.

Then, the incident optical axis is in the direction of θ with respect to the crystal axis, and these two
Let the amplitudes of the axes be A1 and A2, the phases A1 and A2, and the coordinate axis X in the direction of θ' of the light after passing through the wave plate.
If the amplitudes in the direction and the X direction are A, M, and A, and the phases at this time are Δx and Δy, then it is expressed as follows. (11 and (3), A, 2 and A
Subtracting y2, -5in2θ' 5in2θcosφ) - A, A2 (
cos2θ' 5in2θ5in(Δ1-Δ2)-si
n2θ' (cos(ΔI-Δz) sinψ-5in(
Δ1−Δ2) CO92θcosφ) )−, −(4−,
)-5ln2θ' 5in2θcosφ) to ten, A2
(cos2θ' 5in2θ5in(Δ1−Δ2)~
5in2θ' (cos(ΔI−Δ2)sinφ−5i
n(△1-Δ2)'CO52θcosφ) ) ,,・
-(4-2).

The above is the result when the wall thickness of the wave plate is uniform.Next, consider a wave plate with uneven wall thickness, and set the wall thickness of the wave plate to f.
(x, y), then from equation (2), 2π(na no
) φ−f (x, y) (5) λ In this case, 6X2, A, and y2 are EX and E.

And if the incident beam is a square with side a, then it is expressed as follows.

Here, as shown in Fig. 1, in the case of a wave plate where the angle formed by both sides of the wave plate, that is, the wedge angle, is α and the center wall thickness is d, f(x, y) −d ytanα...・・・・・・
・・・・・・・・・Since it is expressed as f7+, (4-1
), (4-z), (51, f61 and (7) 2)
When X and Ii are included, ・・・・・・・・・・・・(Ll) ・・・・・・・・・・・・(L2) However, π(nIlno)atanα 5in--cos2θ5in (Δ1-Δ2)・λ (Ll), In equation (L2), if atanα is sufficiently large with respect to λ, it can be assumed that P===, 0 according to (9) 2, so in this case,・・・・・・・・・・・・(1(1,) ・・・・・・・・・・・・(10-z)

(1(L,), In (10-2), if we set the condition for θ' to be E, -Ey, then Only when tilted, the intensity components of the two axes can be made equal for all incident light conditions.

However, as is clear from the equations (10-+) and (1oz), generally EX=E, and unpolarized light cannot be obtained.

Here, as an index for expressing the polarization state in an easy-to-understand manner, the degree of polarization X is defined as follows.

Ex (max) + Ey (min) In formula (12), EX (max) is the maximum value of EX when θ' is changed, and E, (min) is the maximum value of Ey when θ' is also changed. is the minimum value. (LL,), -(10-
2) From equation (12), ・・・・・・・・・(1
3) is obtained. According to this equation (13), the degree of polarization of the transmitted light transmitted through this depolarization plate is determined by the incident conditions θ, A1°A2
．． It can be seen that the values of A1 and A2 vary from 0 to 1.

Therefore, when using the conventional depolarizing plate shown in Figure 1, it is not possible to make the light unpolarized except under certain incident conditions, and depending on the conditions, it may be possible that the linearly polarized light is transmitted as is. . That is, there is a drawback that all incident light cannot be made non-polarized. Furthermore, when this depolarizing plate is used before or after a measuring instrument whose polarization characteristics are to be avoided, there is the complexity of having to accurately adjust the orientation of the depolarizing plate with respect to the measuring instrument.

In addition, conventional methods for making the light non-polarized include using a diffuser plate such as opal glass and using an integrating sphere, but in both cases the light is diffused, resulting in a significant reduction in the amount of light. There is a drawback.

Another known method is to smooth the conventional depolarizing plate shown in Figure 1 by rotating it at high speed with a motor, etc., but this method requires complicated equipment and requires It has the disadvantage that it is limited and can only be used with some measuring instruments.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems of conventional depolarizing plates or depolarizing means, and can be applied to incident light having any wavelength distribution and any polarization condition.
The object of the present invention is to provide a depolarizing plate that can convert incident light into a non-polarized state without reducing the amount of light.

[Summary of the invention]

The present invention converts incident light of any wavelength and polarization state into unpolarized light by arranging a plurality of wedge-shaped transparent plates made of a material with birefringence so that their crystal axes are aligned at an angle of 45 degrees. It is something that converts into a state.

[Principle of the invention]

Next, the present invention will be explained in detail based on the basic configuration of the depolarizing plate according to the present invention.

FIG. 2 shows the basic structure of the depolarizing plate of the present invention, which consists of two transparent plates 1 and 2, each of which is made of a transparent material exhibiting birefringence. And 2
All of the transmission surfaces of the transparent plates are flat, and the crystal axes of each transparent plate are arranged at an angle of 45° from each other.

In the depolarization plate configured in this way, the center thickness of the transparent plate 1 on the incident side is dl, the angle between the two transmission surfaces is α, and the center thickness of the transparent plate 2 on the output side is d2. .2
Letting the angle between the two transmission planes be α2, as mentioned above,
When you add EX, H, +p'...
・・・・・・(14-1)-P' ・・・・・・・・・・・・
...(14-2) However, π(na no)atanα1 π(ne no)atanα plate λ π(ne no)atanα2 2 π(ne no)dz (cos2θ'-5in2θ'5in4θ')co
s 'λ COS □□- λ +5in4θ' cos2θcos -'λ π(na no)a(tanα1-tanα2)λ 2 -sin4θ' sin cos(ΔI-Δ2)λ +cos2θcos -s in (Δ1-Δ2
)λ 2π(ne-no) (at-az)+5in4θ
'cos2θcos 'λ janα2) and a(tanα, -tanα2) are both sufficiently large relative to the wavelength λ, then p'=o, so according to formulas (ILI) and (IC2),...・・・
・・・・・・・・・(16,,l)・・・・・・・・・・・・
・It is expressed as (16-2). The degree of polarization at this time is (,16-,).

According to equation (16-2), it becomes. As is clear from the above equation (17), the degree of polarization in this case is different from the degree of polarization in the conventional depolarizing plate determined by equation (13), and the phase Δ1 of the incident light. Δ2
Since there is no influence of θ-π/4, A1 and A2
By setting , all polarization states can be represented. Therefore, it can be considered as θ-π/4, and the degree of polarization X at this time is independent of the incident conditions, X=O...
...(18).

Therefore, in this case, it becomes an ideal depolarizing plate.

In other words, no matter what the wavelength and polarization state are as the incident conditions, this depolarizing plate allows almost completely unpolarized transmitted light to be obtained without reducing the amount of light.

The relative relationship between the wedge orientations of the two transparent plates in FIG. 2 may be arbitrary, and the relative relationship between the crystal axis orientation of the transparent plates and the wedge orientation may also be arbitrary. Also, for convenience in developing the equation, the incident beam is square (-side is a) as shown above, but even if the incident beam is circular,
Almost identical results are obtained. Similarly, for the convenience of formula development, the ellipticity is set to =Q, but the same effect can be obtained even when k≠0.

[Embodiments of the invention]

Examples of the present invention will be described below. FIG. 4 is a sectional view showing the first embodiment of the depolarizing plate of the present invention.
3, as shown in FIG. 3, has a surface 3(a) perpendicular to one crystal axis other than the crystal optical axis, has a central thickness do and a wedge angle α. It is a quartz plate formed by aligning the orientation of the crystal optical axis and the orientation of the wedge angle. 4 is a wedge-shaped transparent plate made of ordinary optical glass, such as BK7, which has approximately the same refractive index as crystal. And 2
Two crystal plates 3.3 are arranged with their optical axes shifted by 45 degrees, their inclined surfaces facing each other, and a wedge-shaped transparent plate 4 is interposed between them, and these three pieces are arranged in a bonded state. The two surfaces 3+a+, 3ial of the crystal plates 3, 3 exposed to the surface are parallel to each other.

In the depolarizing plate configured in this way, if the cross-sectional direction of the left crystal plate in FIG. 4 with respect to the wedge direction is β, the wedge corner and α2 in this cross section are tan (・(
19-,) tana2 = C03 (β+45°) ta
na0-(1/tan) (cosβ-5inβ)tana
.

......(19-2>) Therefore, tana, + tanα2= ((1+1//'7)
cosβ(1//T) sinβl'tanα0...Koshin(20-+)tana, -tanα2=((1-1
/汀>cosβ+(1//T)sinβ)tana.

・・・・・・・・・(20-2) When β is changed in the above equations (211,) and (20-2), the respective maximum values are (tana, +tanα,)max = ( (1+1/
fT) cos π/80 (1#T) sin'g/8)
tana.

=1.848tanαo...(21-+)(t
anα+−tana, )max = ((1//T)c
osπ/8+ (11//T)sinπ/8) ta
na.

=0.765tanαo ”=...121-z), and similarly, the minimum value is (tanα+ +tanα2)min −-((1+1
//”)cosπ/80(1//T)sinπ/8 1
tantx.

−−1,848 tanαo −・・・・(22−+)(
tanα+−tana2)min=−,((1//
7) cosyr/8+ (1-1//T) sinπ/8
1 tana.

−〇, 765 tar1α0・・・・・・・・・(22-
2).

(21-1), (21-2), (22-1), (22-
2) As is clear from the formula, (tana, tanα
2) is 1.848 tanα.

From 1.848tanα. (tana,
-tana2) is -0,765 tanα. From 0.
765tan (X o. Therefore, if the wedge angle α is set so that these changes are sufficiently large with respect to λ, the above (16-+), (16-z
) holds true, and the depolarizing plate can provide unpolarized transmitted light for all incident light.

The depolarizing plate according to this embodiment has the advantage of being easy to use because the optical path does not bend.

FIG. 5 is a sectional view showing the second embodiment. As shown in the figure, the depolarizing plate of this embodiment has two crystal plates 3 shown in FIG. 3(a) It is formed by joining together. The depolarizing plate of this embodiment has the advantage that it can be made at low cost because it does not include a wedge-shaped transparent plate as in the first embodiment shown in FIG.

FIG. 6 is a sectional view showing the third embodiment. Figure crystal plate,
5 is a holding frame for adhesively fixing the crystal plate 3.3, 6 is an outer frame for accommodating the holding frame 5, and 7 is a presser ring for fixing the holding frame 5 to the outer frame 6. . 2 crystal plates 3
, 3 are held apart and their relative arrangement is exactly the same as in the first embodiment. The depolarizing plate according to this embodiment has the advantage that it can be used for broadband light.

FIG. 7 is a sectional view showing the fourth embodiment. In Fig. 7, 8 is a plane 8 perpendicular to one crystal axis other than the crystal optical axis.
In a wedge quartz plate having a wedge angle α1 having the shape (a), the relationship between the orientation of the crystal optical axis and the orientation of the wedge angle is formed arbitrarily. 9 is a wedge angle α2 different from the wedge crystal plate 8 (
With the rust crystal plate, the surfaces IHal and 9fal of each crystal plate 8 and 9
The sides are facing outward and the inclined surfaces are facing each other and are joined together. As a condition for the depolarizing plate configured in this way, it is necessary that the wedge angle difference (α1-α2) be sufficiently large with respect to λ. This embodiment has the advantage of being easy to use because there are many reference planes that are perpendicular to the incident light.

Nakadai kJki t-
2--Kamiji & E sword 16 In the hill 1, 3 and 4 are the crystal plate and wedge-shaped transparent plate exactly the same as those in the first embodiment shown in FIG. Two sets of depolarizing plates are bonded together. The four wedge crystal plates are arranged with their crystal optical axes sequentially shifted by 45 degrees. This example is based on the 2nd example shown in the first example.
Compared to a single-layer structure, there is an advantage in that the tolerance for orientation during arrangement can be extremely large.

〔Effect of the invention〕

As described above in detail based on the embodiments, the present invention includes:
The depolarizing plate is constructed by arranging a plurality of wedge-shaped transparent plates made of a birefringent material with their crystal axes sequentially shifted by 45 degrees, so that it can detect incident light with any wavelength distribution and polarization conditions. It is also possible to easily convert the light to a non-polarized state without reducing the amount of light.

[Brief explanation of the drawing]

Fig. 1 shows the shape of a conventional depolarizing plate, Fig. 2 shows the basic configuration of the depolarizing plate according to the present invention, and Fig. 3 shows the shape of a wedge quartz plate used in the present invention. Figure shown, 4th
Figures 8 through 8 are sectional views showing embodiments of the present invention. In the figure, 1.2 is a wedge transparent plate with birefringence, 3
(Waste crystal plate, 4 is wedge-shaped transparent plate, 5 is holding frame, 8
．． 9 indicates a wedge crystal plate. Patent Applicant: Olympus Optical Industry Co., Ltd. Representative Patent Attorney Ken Mogami 1 Cause Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Box 8 Figure

Claims (1)

[Claims] Multiple wedge-shaped transparent plates made of a material with birefringence,
A depolarizing plate characterized in that the crystal axes of these crystals are sequentially shifted by 45 degrees.