JPS62170902A - Wavelength plate - Google Patents

Abstract

PURPOSE:To easily form a surface releaf grating type wavelength plate by forming a surface releaf grating satisfying 2>lambda/d>=1.472 on a dielectric body when using wavelength is lambda and a grating pitch is (d). CONSTITUTION:The grating 2 is formed on the dielectric body 1, and when rays of light are made incident upon the surface of the grating from the direction of an arrow 3, different diffractive indexes are generated respectively in vertical and horizontal directions to the grating. When a He-Cd laser beam with wavelength lambda=441.6nm is made incident upon the grating having a pitch d=0.3mum satisfying lambda/d>2 for a He-Ne laser beam with wavelength 632.8nm e.g., the grating shows double refracting property and lambda/d=1.472 is obtained. Thereby, the grating satisfying the condition of at least 2>lambda/d>=1.472 indicates the double refracting property. When the ratio of the crest of the grating to its trough is set up to 1 to 1 in such kind of grating, the width l of the groove can be set up to lambda/4<l<=lambda/2.944, so that the width l of the groove can be expanded. Thus, the grating can be easily formed.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention relates to a wavelength control device such as a quarter-wave plate, a half-wave plate, a full-wave plate, etc. that produces a phase difference between two orthogonal linearly polarized lights. It's about the board.

(Prior art) Conventionally, a wave plate is made by polishing a quartz crystal, and the phase difference between ordinary light and extraordinary light is changed to (N + 1/4) wavelength (
N is an integer), (N + 1/2) wavelength for a 172-wave plate,
A full-wavelength plate is manufactured by adjusting the thickness so that it has N wavelengths. In addition to such a method using crystal polishing, a method using a grating has also been proposed because a high-density surface relief grating formed on a dielectric exhibits birefringence. The proposal and experiment of a wave plate using surface relief gratings was carried out by Applied
Physics Letters (Applied Physi
cs Letters, Vol. 42, No. 6 (published March 15, 1983), pp. 492-494, and Applied Optics (Applied Optics).
cs), Vol. 22, No. 20 (published October 15, 1983), pp. 3220-3228. A wavelength plate using a grating takes advantage of the fact that, where the pitch of the grating is d and the wavelength used is λ, the refractive index differs in the direction parallel to and perpendicular to the grooves of the grating in a region where λ is sufficiently large compared to d. are doing.

Conventionally, including the above-mentioned paper, the conditions for a grating to exhibit birefringence are:
It has been experimentally determined that A/d>2, which is also a condition under which no diffracted light is generated.

(Problem to be Solved by the Invention) In a high-density grid with Vd>2, that is, d<)J2, when the ratio of peaks and valleys of the grid is 1:1, the width 1 of the groove is 1<4
Therefore, fine processing is required. Furthermore, the phase difference of a wavelength plate using a grating is given by Δn, which is the refractive index difference of birefringence.
It is given by Δn-t. Here, t is the groove depth of the grating. When a grating is made of a material with a refractive index of 1.5 to 2.0, Δ
Since it is about n-0.2, the required groove depth is t=1.25λ even for a quarter-wave plate. Therefore, the fine groove width results in a grating that is very deep relative to the groove width, making it difficult to manufacture. The cheapest and simplest method for producing a surface relief grating is to fabricate it by stamping it onto a plastic plate, but there is also the problem that the above-mentioned gratings are difficult to fabricate by stamping. An object of the present invention is to provide a surface relief grating type wave plate that solves the above-mentioned problems.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides means for solving the problems described above.
＞Vd≧1.472.

(Function) Vd for He-Ne laser light with a wavelength of 632.8 nm
When a He-Cd laser beam with a wavelength λ = 441.6 nm was incident on a grating with a pitch d = 0.3 pm satisfying >2, it was found that the grating exhibited birefringence. In this case) Jd=1.472. Therefore, a grating that satisfies at least the condition 2>Vd>1.472 exhibits birefringence. In such a lattice, when the ratio of peaks to valleys of the lattice is 1:1, the width l of the groove is A/4<1≦l/2.
．． 944), and the groove width can be made wider than in the case of a lattice with Jd≧2, making manufacturing easier. Furthermore, it becomes easy to manufacture the grid by stamping.

(Example) Next, the present invention will be described in detail with reference to the drawings. The figure is a perspective view for explaining the structure of the wavelength plate of the present invention, and for the sake of clarity, the grating is schematically drawn much larger than it actually is. A grating 2 is formed on a dielectric 1, and when light is incident on the grating surface from the direction of arrow 3, the refractive index is different in the direction perpendicular to the grating and the direction parallel to it, and there is a phase difference due to the groove depth t. The transmitted light is emitted in the direction of arrow 4 and acts as a wave plate. Furthermore, in the wave plate according to the present invention, A
Since /d<2, diffracted light is generated in the air. In actual production, an interferometer was constructed using a light beam of a He-Cd laser with a wavelength of 441.6 nm, and a holographic grating with a pitch of 0.3 pm was formed on a photoresist. A stamper was produced from the surface relief grating after photoresist development using a nickel electroforming method, and this stamper was used to stamp an acrylic plate with a hot press to form a wavelength plate.

(Effects of the Invention) The present invention provides a surface relief grating type wave plate that is easy to manufacture.

[Brief explanation of drawings]

The figure is a perspective view schematically showing an embodiment of the present invention.

Claims (1)

[Claims] For the dielectric material, 2>λ, where the wavelength used is λ and the grating pitch is d.
A wavelength plate characterized by forming a surface relief grating of /d■1.472.