JPS62269104A - Wavelength plate - Google Patents

Abstract

PURPOSE:To facilitate the formation of a wavelength plate by including a substrate dielectric which has a substrate relief grating whose relation between the in-use wavelength and grating pitch is specified on the surface and a dielectric medium which has a surface relief grating formed in phase and at the same pitch with the substrate relief grating and is much larger in refractive index than the substrate dielectric. CONSTITUTION:The wavelength plate is constituted including the substrate dielectric 1 which is provided on the surface with the substrate relief grating 2 whose relation between the in-use wavelength lambda and grating pitch (d) is so specified that lambda/d>=1.472 and the dielectric medium 3 which has the surface relief grating formed on the surface in phase and at the same pitch (d) with the substrate relief grating 2 by being coated or charged on the substrate relief grating 2 and is much larger in refractive index than the substrate 1. Consequently, the groove depth of the grating formed on the dielectric substrate is reducible, so the formation of the grating is facilitated and the wavelength plate is mass-produced at low cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a wave plate such as a 174-wave plate, a 1/2tL long plate, a full-wave plate, etc., which generates phase difference sound between two orthogonal linearly polarized lights. It is related to.

[Conventional technology]

Conventionally, the phase difference between ordinary light and extraordinary light is reduced to (N + 1/4) wavelength (N
is an integer), the thickness is adjusted so that the 1/2 wavelength plate has a wavelength of (N+1/2), and the full wavelength plate has a thickness of N wavelengths. In addition to the sophisticated method of crystal polishing, a method using a grating has also been proposed since a dense surface relief grating formed on a dielectric material exhibits birefringence. Applied Physics Letter on proposal and experiment of wave plate with surface relief grating gold phase.
Letter ) Magazine Vol. 42 No. 6 (published March 15, 1983) No. 492 = 494 pages Nori, C, Fla
and Applied Optics Vol. 22, No. 2.
Issue 0C1111 October 15, 1983) No. 3220~
R and C on page 3228.

Enger and S., in an article written by Ca5e.

In a wavelength plate using a grating, the pitch of the grating is t" d s. If the used wavelength is λ, in a region where λ is sufficiently large compared to d, the refractive index n11 in the direction parallel to the grooves of the grating is perpendicular to the grooves of the grating. It takes advantage of the fact that the refractive index n in the direction is different,
According to the above-mentioned paper by C. Fladers, if the lattice is rectangular, * flll l nl is...
(2) Here, nl is the refractive index of medium 1, n2 is the refractive index of medium 2,
q is the proportion of medium 1 in one period of the lattice, 1≧9≧0
It is. The magnitude of birefringence Δn is given by the following equation.

Δn=In −n I ・・・・・・几・ （j
II L Furthermore, the phase difference ΔΦ experienced by the next light incident on the grating having the magnitude of birefringence Δn is given by the following equation.

jrD ΔΦ[rad]-17-0Δa ・・・・・・・・・
(4) Here is the groove depth of the DH grating. From equation (4),
In order to obtain a large phase difference ΔΦ7, the groove depth Dt may be increased, or the magnitude of birefringence Δn may be increased. This relationship is valid not only when the grid shape is rectangular, but also when the grid shape is sinusoidal,
Even in the case of triangular plates etc., L is applied to the surface relief grating that stands out.
There are two main ways to manufacture wavelength plates:

The first method is to form a surface relief grating on an L photoresist using an interference exposure method, manufacture a mold from the grating using a nickel electroforming method, and transfer it to a thermoplastic resin using a hot press method or an injection bottom molding method. Alternatively, there is a method of transferring to a photocurable resin.

The second method is to form a photoresist grid on a dielectric substrate in the same manner as the first method, and use the photoresist as a mask to ion-etch the dielectric substrate. Law'!
This is a method of obtaining a single surface relief grating by performing etching using a 7'CH reaction injection ion etching method.

[Problem that the invention seeks to solve]

The above-mentioned conventional technique has a problem in that the groove depth of the grating is extremely large compared to the groove width. Tomoe uses the wavelength λ gold H
632.85Im of the e-N e laser.

For this wavelength, thermoplastic resins used in the first manufacturing method described above, such as acrylic resins, photocurable resins such as UVX-S S-89-1 manufactured by ThreeBond; The refractive index of the quartz glass used for this purpose is L5 to 1.6. In the following, thermoplastic resin, photocurable resin, and quartz glass are used as medium 1.
Its refractive index n1f.

1.55 and 0fc% medium 2t-air, its refractive index n! Let t1.00. When the grating shape is rectangular, if the proportion of the medium 1 in one period of the grating is q t o, s, then the magnitude of birefringence Δn tri (]), (
2) and (3), the result is 0.116. Therefore, equation (4)! The groove depth D required for the 1/4 wavelength plate, 1/2 wavelength plate, and full wavelength plate is each 1.36 μm%2.738.5
．． It becomes 46 μm. Further, regarding the grating pitch d, in order to obtain birefringence based on high density, it is necessary that λ/d≧1.475, so the condition d≦0.43AIm must be satisfied. Since q = 0.5, the groove width W of the grating is W≦0.21 μm. Therefore, the groove width is 0.21/Jm or less, and the Sa is 1.36 Am to 5.4
A 6 μm grid must be made.

When manufacturing a grating having an extremely large yt depth with respect to tR+IA using the first manufacturing method, the effective contact surface area between the medium 1 and the electroforming mold increases significantly, so that it is peeled off from the mold surface. The tensile shear force increases. For this reason, during peeling, the hardening medium 1 peels off from the substrate.
There is a problem that it remains on the mold surface, making it difficult to transfer the surface relief grating.

In addition, in the second manufacturing method, the time required for etching
It is difficult to form a photoresist mask because the etching process lasts for several hours and a photoresist mask that can withstand etching is several micrometers thick. Next, even when the lattice formed in the photoresist is transferred to a material with strong etching resistance, such as chromium, and etching is performed using that material as a mask, as the depth of the lattice groove increases, once etched, the dielectric 7 becomes The progress of etching is inhibited by re-attaching the layer to the substrate surface and by reducing the number of active species, ions, and neutral particles reaching the groove bottom, making it difficult to form the desired lattice. . This problem occurs regardless of the shape of the grid.

As stated above, the surface relief grating type wave plate according to the prior art has the disadvantage that it is difficult to manufacture.

An object of the present invention is to solve the problems of the prior art and provide a phase grating type wave plate that is easy to manufacture.

[Friendly means to resolve the problem]

The wavelength plate of the present invention comprises a substrate dielectric material having a substrate relief grating on its surface in which the relationship between the used wavelength λ and the grating pitch d is λ/d≧1.472, and the substrate relief grating is coated or filled. A surface relief grating having the same phase and pitch d as the substrate relief grating is formed on the surface, and includes a dielectric medium having a refractive index sufficiently larger than the refractive index of the substrate dielectric.

[Effect]

The operation of the present invention will be explained in detail with reference to the drawings.

The phase difference Δφ experienced by light incident on the grating is proportional to the groove depth D of the grating and the magnitude of birefringence Δn.

In the present invention, the magnitude of birefringence Δn can be increased without increasing the depth D.
? By increasing the size, the above-mentioned problem is attempted to be solved.

Consider a case where a rectangular grating is formed on a dielectric substrate having a refractive index n1. FIG. 2 shows a rectangular grating 4 provided on the surface of a dielectric substrate 1 having a refractive index of ni gold and a refractive index of n1 and a large refractive index of n*? ! This is a cross-sectional view showing a case in which the lattice is covered with a dielectric medium 3. The lattice in this state is shown along the cross section from the top of the lattice to the first region 5 consisting of the dielectric medium 3 and air, the dielectric substrate 1 and the dielectric It can be considered to be divided into three regions: a second region 6 consisting of the body medium 2 and air F; and a third region 7 consisting of the dielectric substrate 1 and the dielectric medium 3L. The proportion occupied by dielectric medium 1 in one period of the grating t''qt, the proportion occupied by dielectric medium 3 'kqzs, the proportion occupied by air'frq jL
ir. Here q1+q2+qair=1
......(5). The refractive index of air is 1.
If it is 00, then (1), (2).

From equation (3), the magnitude of birefringence Δn1 of the first region 5 is:
・・・・・・・・・(6) It becomes. Expanding equations (1) and (2), the magnitude of birefringence of the second region 6 Δnz jfi slope t = (nt"ql + n7 + qairf' ((1/
nt)2qx+(1/nz)2” +qair)−
A......'(7). The magnitude Δ- of the birefringence of the third region 7 is: = (n1%041+nz"
qtl” −((L/nx)”qt +2 −(1/nz) Q* :l ・・・・・・・・・
(8) becomes. The magnitude of birefringence Δn largely depends on the difference in refractive index between adjacent media, and Δnx>Δn>Δn3.

First area of anger 5, second area 6. The thickness of each layer in the third region 7 is [)1 p Dt e D! Then, the phase difference ΔΦ experienced by the wavelength λ passing through the grating becomes Equation (3). FIG. 3 shows the result of determining the relationship between the phase difference ΔΦ and the thickness of the dielectric medium 3 from equation (9) using the refractive index of the dielectric medium as a parameter. At this time, the friend grating formed on the dielectric substrate 1 has a pitch d = λ/2, a groove depth D = λ, a refractive index n t = 1.55, and the thickness of the dielectric medium 3 is the same at the top and bottom of the grating. The left end of the figure is the case where there is no dielectric medium fi3 and only the next lattice is formed on the dielectric substrate 1-, and the right end is the case where the grooves of the lattice are completely filled with the dielectric medium. It corresponds to

From FIG. 3, it can be seen that by coating the grating surface of the dielectric substrate 1 with the dielectric medium 3 having a refractive index sufficiently higher than that of the substrate 1, the phase difference that the incident light receives can be reduced in the case where there is no coating or when the grating is It can be seen that the bay part is completely filled with the dielectric medium 3 and can be made larger compared to the case where the bay part is completely filled with the dielectric medium 3.

FIG. 4 is a sectional view showing the entire lattice shape when the thickness of the dielectric medium 3 is increased and the second region 6 shown in FIG. 2 disappears. The grooves of the grating are filled with dielectric medium 3.

Since it consists of the first region 5 and the third region 7, the phase difference ΔΦ experienced by the light of wavelength λ incident on the grating is given by −2π ΔΦ−2(Dt, t+D3sΔns)·=−(9). In this case, sD3 is equal to the groove depth D of the surface relief grating formed on the visiting body substrate 1. Dielectric medium 3
Thickness D! compared to when the interface between air and air is flat! The refractive index of substrate 1 (11=l-55, groove depth D=λ
, D, = λ15, refractive index of the dielectric medium n! 2.0,
22. ! 4, ΔΦ is 0.753 and 1, respectively.
．． 227, 1.793[radl9, Even in this unconventional configuration, ΔΦ=0 in the absence of dielectric medium.
．． 728 (rad) Ex is also larger.

Therefore, the groove depth of the grating formed on the IIX body substrate can be reduced, and a phase grating type wave plate that is easy to manufacture can be obtained.

The same is true when the grating is not rectangular but sinusoidal, triangular, etc., and coating the grating surface with a dielectric medium that has a refractive index sufficiently larger than that of the dielectric substrate causes large birefringence. [Embodiments] Examples of the present invention will be described below with reference to five drawings.

FIG. 1 is a sectional view showing a first embodiment of the present invention.

For clarity, the grid has been greatly enlarged. A sinusoidal grating 2 is formed on a dielectric substrate 1, and the surface of the grating 2 is coated with a high refractive index dielectric medium 3 to increase the magnitude of birefringence. In the actual behind the scenes,
The substrate dielectric 1 is a photocurable resin UVX-8889-1 manufactured by Three Bond Co., Ltd., and the high refractive index dielectric medium 3 is polysilastyrene PSS75't manufactured by Nippon Sokako Co., Ltd.
-Used.

The refractive index of the former is 1.52%, and the refractive index of the latter is approximately 2.5. The wavelength used is He-Ne laser 63281111.

be. Transfer of grid pattern to photocurable resin.

First, the wavelength of the He-Cd laser is 441.6tIIOft,
The interferometer is grooved using H-A, and the pitch d that satisfies the holographic J/d 21.472 is 9.3.
A .mu.m grating was formed on a photoresist, and a mold was made using the nickel electroforming method from the sinusoidal surface relief grating after the photoresist phenomenon, and this mold was used. First, liquid polysilastyrene is applied onto the grid formed on the substrate dielectric 1, which is a photocurable resin, and the solvent is dried.
FIG. 5 is a sectional view showing a second embodiment 1+11 of the present invention, in which the wave plate shown in the figure is formed.

The fabrication of the lattice, which is much larger than the real one, is done by forming the lattice on the photocurable resin using the same method as in the first embodiment shown in FIG. In Example 9, the amount of polysilastyrene #4 can also be increased compared to the first example.

〔Effect of the invention〕

According to the present invention, the groove depth of the grating fabricated on the dielectric substrate can be made small, making it easy to fabricate the grating.Therefore, it is possible to obtain a wavelength plate that is easy to fabricate, inexpensive, and has high acidity.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view schematically showing one embodiment of the present invention, Fig. 2 is a cross-sectional view showing an embodiment of the present invention, and Fig. 4 is a cross-sectional view showing an embodiment of the present invention. A schematic cross-sectional view of a dielectric substrate, FIG. 3 is a graph showing the relationship between the thickness of the dielectric medium 3 shown in FIG. 2 and the phase difference experienced by incident light, and FIG. 5 is another embodiment of the present invention. It is a sectional view showing typically. In the figure, 1 is a dielectric substrate, 2 is a lattice part, 3 is a dielectric medium, 4 is a rectangular lattice, 5 is a first region of the lattice, 6 is a second region of the lattice, and 7 is the third region of the lattice. . Kaya l Tuto 2 months

Claims (1)

[Claims] The relationship between the wavelength used λ and the grating pitch d is λ/d≧1.47
A substrate dielectric having two substrate relief gratings provided on its surface; and a substrate dielectric having a surface relief grating coated or filled on the substrate relief grating to form a surface relief grating having the same phase and pitch d as the substrate relief grating. a dielectric medium having a sufficiently larger refractive index than the refractive index of the wavelength plate.