JPS62289804A - Wavelength plate - Google Patents

Abstract

PURPOSE:To easily manufacture a surface relief lattice type wavelength plate by laminating alternately a dielectric of refractive index n1 provided with a surface relief lattice of a specific pitch, and a dielectric of a refractive index n2 for packing said lattice. CONSTITUTION:A rectangular lattice 5 of a pitch (d) of lambda/d>=1.472 at the time of wavelength lambda is formed on the first dielectric medium 4 of a first layer f a refractive index n1. The surface of this lattice 5 is packed with a second dielectric medium 6 of the first layer of a refractive index n2 of n1not equal to n2. Subsequently, by laminating alternately these two dielectric medium layers 4, 6, a wavelength plate is formed. In that case, a phase difference of the wavelength plate is proportional to depth of a lattice group and magnitude of a double refractive index, therefore, by laminating and providing said layers, even if depth of the groove of each layer remains as it is, the phase difference can be enlarged by increasing the whole groove depth. Therefore, depth of the lattice group can be made small, therefore, a surface relief lattice type wavelength plate can easily be manufactured.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] This invention provides an A-wave plate, a two-wave plate, and a full-wave plate that create a phase difference between two orthogonal linearly polarized lights. This relates to wavelength plates such as the following.

[Conventional technology]

Conventionally, wave plates are made by polishing quartz crystals, and the phase difference between ordinary light and extraordinary light is determined by (N+V4) wavelengths (N is an integer) in Z wave plates.
, Z-wave plate is manufactured by adjusting the thickness to (N0%) wavelength, and full-wave plate is manufactured by adjusting the thickness to N wavelength.

In addition to this crystal polishing method, since the high-density surface relief grating formed on the dielectric exhibits birefringence,
A method using a grid has also been proposed. A proposal and experiment on a wave plate using surface relief gratings is published in Applied Physics Letters.
etter) Magazine, Volume 42, No. 6 (March 1, 1983)
Published on the 5th) Pages 492-494 Nori, C, Flan
d-ers and Applied Optics, Vol. 22, No. 2
No. 0 (issued October 15, 1983) No. 3220-32
It is described in an article written by R, C, Enger, and S on page 28, written by Ca5e.

A wavelength plate using a grating has a refractive index nII in a direction parallel to the grating grooves and a refractive index perpendicular to the grating grooves in a region where λ is sufficiently large compared to d, where the grating pitch is d and the wavelength used is λ. According to the above-mentioned paper by C.F. 1anders, when the grating is rectangular, n, , , n, are given by the following equation.

"u = C0% Q-I-nz" (1q))
"" - (1) n, = CH/rz)" q
"(1/nz)" (1-q) ) -172・
...(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≧q≧O
It is. The magnitude of birefringence Δn is given by the following formula % Formula % The phase difference ΔΦ experienced by light incident on a grating having the magnitude of birefringence Δn is given by the following formula.

Here, D is the groove depth of the grating. From equation (4), in order to obtain a large phase difference ΔΦ, it is sufficient to increase the groove depth D or increase the magnitude of birefringence Δn.

This relationship holds true not only when the grid shape is rectangular, but also when the grid shape is sinusoidal, triangular, etc.

Wave plates using surface relief gratings can be manufactured mainly by the following two methods.

The first method is to form a surface relief lattice on photoresist using interference exposure, create a mold from the lattice using Esokel electroforming, and transfer it to thermoplastic resin using hot press or injection molding, or photocure. This method involves transferring the image onto a synthetic resin.

The second method is to form a photoresist lattice on a dielectric substrate in the same manner as the first method, and then use the photoresist as a mask to ion-etch the dielectric substrate, reactive ion etching, or ion beam etching. Alternatively, a surface relief grating can be obtained by etching using a reactive 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. For example, assume that the wavelength λ used is 632.8 nm of a He-Ne laser.

For this wavelength, thermoplastic resins such as acrylic resins, photocurable resins such as UVX-3S-89-1 manufactured by ThreeBond, which are used in the first manufacturing method described above, and those mainly used in the second manufacturing method. The refractive index of quartz glass is approximately 1.5 to 1.6. In the following, a thermoplastic resin, a photocurable resin, and a quartz glass are used as the medium 1, and the refractive index n1 thereof is assumed to be 1.55. Further, the medium 2 is air, and its refractive index n2 is 1.00. When the grating shape is rectangular, the proportion q of the medium 1 in one period of the grating is 0,
5, the magnitude of birefringence Δn is (11, (2).

(3) From 2, it becomes 0.116. Therefore, from equation (4), the groove depths D required for the A wavelength plate, IA wavelength plate, and all wavelength plates are 1.36 μm, 2.73 μm, and 5.46 μm, respectively.
It becomes m. Regarding the grating pitch d, in order to obtain birefringence based on high density, it is necessary that λ/d≧1.472, so the condition that d≦0.43 μm must be satisfied. Since q=0.5, the groove width W of the grating is WS2
゜21 μm. Therefore, the groove width is 0.21 p m
Hereinafter, a grating with a groove depth of 1.36 μm to 5.46 μm must be produced.

When such a lattice is manufactured by the first manufacturing method, the effective contact surface area between the medium 1 and the electroforming mold increases significantly, so that the tensile shearing force when peeling off from the mold surface increases. For this reason, there is a problem that upon separation, the hardened medium 1 peels off from the substrate and remains on the mold surface, making it difficult to transfer the surface relief grating.

Furthermore, in the second manufacturing method, etching takes several hours, and a photoresist mask that can withstand etching has a thickness of several μm, making it difficult to form a photoresist mask. Furthermore, even when a lattice formed in 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, the surface of the dielectric substrate once etched The progress of etching is inhibited due to re-adhesion to the groove bottom and a decrease in the number of active species, ions, and neutral particles that reach the bottom of the groove, making it difficult to form the desired lattice. Such problems occur regardless of the shape of the grid.

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

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and provide a surface relief grating type wave plate that is easy to manufacture.

[Means for solving problems]

The wavelength plate of the present invention includes a first dielectric medium layer having a refractive index n that forms a surface relief grating with a grating pitch d of λ/d≧1.472 at a wavelength λ used, and a first dielectric medium layer that fills the surface relief grating. , or a covering second dielectric medium layer having a refractive index n2, where n2≠n, are alternately laminated.

[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. The present invention improves the above-mentioned conventional technique by increasing the equivalent groove depth D' without increasing the groove depth D of the gratings manufactured by the above-mentioned first manufacturing method and second manufacturing method. This is an attempt to solve the problems of

FIG. 2 is a diagram for explaining the present invention. refractive index n,
A rectangular grating 5 having a pitch d that satisfies the condition λ/d≧1.472, where the used wavelength is λ, is formed in the first dielectric medium 4 of the first layer, and the grating surface is n1.
The second dielectric medium 6 of the first layer having a refractive index n2 of Letting the proportion of the body medium be q, fil, f21. (3
) formula, Δn+= (n+ ” q++nz 2(I
Q+))””((1/n+)”q++(1/nz)
“(1q+))−””・・・・・・・・・(5) If the groove depth of the grating is Dl, the phase difference ΔΦ experienced by the light incident on this first layer grating is , becomes λ from equation (4).

Next, on the second dielectric medium 6 of the first layer, a rectangular grating 8 is formed which has the same direction and pitch of the grating grooves as the grating of the first layer.
A second layer of first dielectric medium 7 is formed.

Here, as shown in FIG. 2, the positions of the concavities and convexities of the first layer lattice and the second layer lattice do not need to match. Furthermore, the grating surface of the first dielectric medium of the second layer is filled with the second dielectric medium 9 of the second layer. The magnitude of birefringence Δn2 of the 2Nth grating portion is 2, which is the same as that of the first layer grating, if q2 is the proportion of the first dielectric medium 7 in one period of the grating. Given, Δnz= (n+ ”
qz+nz ”(1qz)) ””+ ((1/n+
)"qz+(1/nz)"(1-qz))-""...
......(7) The phase difference ΔΦ2 that the incident light receives at the second layer grating is
If the lattice depth of the second layer is D2, then

Thereafter, when m lattice layers (m is an integer) of the first dielectric medium and the second dielectric medium are laminated in the same way, the magnitude of birefringence Δn of the th lattice layer becomes the kth lattice layer. If the proportion of the first dielectric medium in one period of the lattice is qk, then Δrl+ = (n+ ”Qm + nz
"(1-qh))""+ ((1/n+)"q
k + (1/nz)"(1-qm))-""...
(9) If the groove depth of the grating is Dx, then the phase difference ΔΦ which the incident light receives at the crab-th grating is as follows. therefore,
The phase difference ΔΦ experienced by the light that has passed through m grating layers is as follows. By increasing the number of layers m, ΔΦ can be increased without increasing the groove depth Dk of the grating in each layer. In FIG. 2, lO indicates the first dielectric medium of the m-th layer, 11 indicates a rectangular lattice, and 12 indicates the second dielectric medium of the m-th layer.

FIG. 3 is a diagram for explaining the present invention, in which the surface of a lattice formed in a first dielectric medium is covered with a second dielectric medium. In the figure, 4 is the first dielectric medium at the first layer opening;
is a rectangular lattice, 6 is the second dielectric medium of the first layer, 7 is the first dielectric medium of the second layer, 8 is a rectangular lattice, 9 is the second dielectric medium of the second layer It is.

FIG. 4 is an enlarged view of the grid No. JJ in FIG. 3. As the proportion of the first dielectric medium in one period of the grating changes, the grating is vertically divided into three layers 13. b layer 1
Divided into 4,0 layers and 15, the ratio is ql1m+ Q I
If lb+qkc, the magnitude of birefringence of each layer Δnk
, (s=a, b, c) is ΔfikS= (n+ ” qks + nz 2(1
(l, ls) ) ””−((1/n+)” q+ts
+(1/nz)20-qms))-””・・・・・・・・・
...(2), and if the layer thicknesses of each layer are Dk-, Dkb, and D-, the phase difference ΔΦ that the incident light receives in the first layer is λ + DkC・Δn mc)...・・・・・・・・・It becomes alpha hot water. Here, D k = D ka + D * b...
・・・・・・・・・αa. When m layers of such gratings are stacked, the phase difference ΔΦ experienced by light passing through all the grating layers is +Dk(・Δnkc)...a9
becomes. In this case as well, by increasing the number of layers m, a large ΔΦ can be obtained without increasing Dk.

In other words, the surface of the surface relief grating formed on the first dielectric medium having a refractive index n1 is n, and the refractive index n is ≠n2.
filled with or coated with a second dielectric medium having 2;
Thereafter, by sequentially laminating a first dielectric medium having a surface relief grating and a second dielectric medium filling or covering the surface thereof until a necessary phase difference is obtained,
The groove depth of the grating formed in the first dielectric medium can be reduced, and a wave plate that is easy to manufacture can be obtained.

The same goes for cases where the grating is not rectangular but sinusoidal, triangular, etc., and can be manufactured by laminating the first dielectric medium having the grating and the second dielectric medium until the required phase difference is obtained. A simple wave plate can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention, and shows an example of manufacturing a λ/2 plate. In actual production, as the first dielectric medium 1, UVX, a photocurable resin manufactured by Three Bond Co., Ltd.
-3S89-1, and polysilastyrene PSS75 manufactured by Nitta Sokako Co., Ltd. was used as the second dielectric medium 2. The refractive index of the former is 1.52, and the refractive index of the latter is approximately 2.5. The wavelength used is 632.8 nm of He-Ne laser. The grid pattern was transferred to the photocurable resin using a mold.

This mold was manufactured as follows. An interferometer was constructed using a light beam with a wavelength of 441.6 nm from a He-Cd laser, and a holographic grating with a pitch d = 0.3 μm that satisfied λ/d≧1.472 was formed using photoresist on glass. Using the developed photoresist pattern as a mask, the glass was etched by reactive ion beam etching to produce a grid having a rectangular cross section on the glass. The groove depth of the lattice formed in the glass was determined as follows.

Since the refractive index of photocurable resin is 1.52 and the refractive index of polysilastyrene is approximately 2.5, when a rectangular lattice is formed with these dielectric media, when q = 0.5, birefringence The size Δn is Δn=0.232 from equation (7). It is assumed that the qs of the gratings produced in each layer are all 0.5, and the groove depths are all the same. Under these conditions, λ
/2 The groove depth D' required for making the plate is D' = from the 0-layer formula.
It becomes 1.362 μm. If the λ/2 plate is manufactured in five layers as shown in FIG. 1, the groove depth D of the grating formed in each layer is D=D'/5=272.6 nm. From this, a grating with a groove depth of 272.6 nm was formed in the glass. The groove depth of the grating on the glass can be easily controlled by the duration of the reactive ion beam etching. A mold was made from a grid made on glass using the nickel electroforming method.

A single-layer lattice can be produced by forming a lattice 3 on a photocurable resin 1 using this mold, applying liquid polysilastyrene 2 to the surface of the lattice, and drying the solvent. When applying liquid polysilastyrene onto solidified photocurable resin, or when applying liquid polysilastyrene onto solidified polysilastyrene, while one of the solvents reacts with the underlying dielectric medium, However, this problem can be avoided by irradiating the surface of the dielectric medium with argon ion plasma or fluorine plasma after forming each dielectric medium film to improve the resistance of the surface of the dielectric medium to solvents.

A five-layer grating was fabricated using the method described above, and the desired λ/
I got 2 plates.

〔Effect of the invention〕

As described above, according to the present invention, a wave plate using a surface relief grating that is easy to manufacture can be obtained.

In addition, if the surface relief grating is transferred from a mold, mass productivity will be improved. Furthermore, even if the wavelength used is changed, it can be easily handled by changing the number of laminated layers.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the present invention; 2 to 4 are cross-sectional views showing the principle of the present invention. 1...first dielectric medium 2...Second dielectric medium 3... Lattice 4...First layer first dielectric medium 5.8.11...Rectangular grid 6...First layer second dielectric medium 7... Second layer first dielectric medium 9...Second layer second dielectric medium 10...mth layer first dielectric medium 12...mth layer second dielectric medium 13...a layer 14...B layer 15...C layer Representative Patent Attorney/Attorney Yoshiyuki Iwa Figure 1 Horse 4

Claims (1)

[Claims] (1) If the grating pitch d at the used wavelength λ is λ/d≧1.
a first dielectric medium layer having a refractive index n forming a surface relief grating of 472, and a refractive index n_2 filling or covering the surface relief grating with a refractive index n_2≠n_1;
A wavelength plate characterized in that second dielectric medium layers having a dielectric medium layer and a second dielectric medium layer are alternately laminated.