JPH06250008A - Grating prism - Google Patents

Abstract

PURPOSE:To arbitrarily determine an angle formed between two light beams splitted by diffraction by forming a transmissive grating pattern on either of a light entrance surface and a light exit surface which are mutually unparallel and making the incident light beam from the light entrance surface to split into a zero-order light and a first-order light so as to make them go out from the light exit surface. CONSTITUTION:A grating pattern is formed on a light entrance surface, the first-order diffracted light of one of the splitted lights is normally made to go out from a light exit surface as it is and the other zero-order diffracted light is normally made to go out from the light exit surface after internally reflected. When the angles theta at the respective vertexes of a prism and the refractive indice (n) of a medium and the prism are designated as shown in the figuire, the deffracted angles theta0, theta1 of the zero-order and the first-order diffracted lights are determined by n1, n2, the pitch of the grating pattern and a wavelength used. Consequently, since thetaa=theta1, thetab=theta0+(pi-(theta1+theta0))/2 in order to normally transmit the respective diffracted lights, thetac is naturally obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grating prism capable of separating an incident light beam into at least two diffracted light beams having different orders and emitting the diffracted light beams at an arbitrary angle.

[0002]

2. Description of the Related Art A conventional polarization separation element using a grating is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 1-253843 and 3-152428.

Japanese Unexamined Patent Publication No. 1-253843 discloses an optical system for a magneto-optical disk device that separates polarized light by using two holograms, and Japanese Unexamined Patent Publication No. 3-152428 discloses a grating and a light receiving device. A polarization detection device in which an element and an element are integrally configured is disclosed.

[0004]

However, since all the above-mentioned conventional gratings are formed on a plane parallel plate, the emission angle of the separated light flux is determined by the incident angle and the pitch of the grating. There is little freedom.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a grating element capable of arbitrarily setting an angle between two light beams separated by diffraction. .

[0006]

In order to achieve the above object, a grating prism according to the present invention has a transmission type grating pattern having periodicity on either the incident end surface or the exit end surface which are not parallel to each other. Formed,
It is characterized in that the light flux incident from the incident end face is separated into 0th-order light and 1st-order light and emitted from the emission end face.

[0007]

EXAMPLES Examples of the grating prism will be described below. As the grating pattern, a planar pattern in which a transparent portion and a non-transparent portion are continuous and a three-dimensional relief type pattern in which irregularities are continuous are considered,
In the following examples, a relief type pattern having higher energy efficiency is used.

First, one type of grating prism in the embodiment will be described with reference to FIG. In the grating prism shown in FIG. 1, a grating pattern is formed on the incident end surface, one of the separated first-order diffracted lights is directly emitted from the exit end face as it is, and the other zero-order diffracted light is internally reflected from the exit end face. Eject vertically. The incident end surface, the exit end surface, and the reflecting surface are all nonparallel to each other.

The angle of the vertices facing the grating pattern of the prism is θc, and the angles of the remaining vertices are θ, respectively.
Let a and θb be the refractive index of the medium, n1 be the refractive index of the prism, n2 be the incident angle of the light beam on the prism, θ0 be the diffraction angle of the 0th order light, and θ1 be the diffraction angle of the 1st order light. The pitch of the grating pattern is p and the wavelength used is λ.

The light flux incident on the prism is diffracted by the diffraction angle θ0 represented by the following equations (1) and (2) according to the grating pattern:
At θ1, it is separated into 0th-order diffracted light and 1st-order diffracted light. However, the diffraction angle of the first-order diffracted light has a negative sign according to the definition of the angle sign shown in FIG. The definition is
An angle with a positive sign in the counterclockwise direction and a negative sign in the clockwise direction with respect to the normal to the grating surface is used.

[0011]

[Equation 1] sin (θ0) = (n1 · sin θin) / n2 (1) sin (θ1) = − (n1 · sin θin − λ / p) / n2 (2)

Here, in order for the first-order diffracted light to be emitted perpendicularly from the exit end face, it is necessary to set one apex angle θa in contact with the grating surface of the prism to be equal to the diffraction angle θ1 of the first-order diffracted light. Then, in order that the 0th-order light is emitted perpendicularly from the emission end face after being reflected in the prism, the other apex angle θb needs to satisfy the following expression (3).

[0013]

[Equation 2] θb = θ0 + (π− (θ1 + θ0)) / 2 (3)

If two vertex angles are obtained, then θc is inevitably obtained. By setting each apex angle of the prism so as to satisfy the above conditions, both the 0th-order light and the 1st-order light are emitted vertically from the emission end face.

The ratio λ / p between the wavelength λ and the grating pitch p preferably satisfies the following condition.
However, the wavelength λ is based on monochromatic light such as laser light.

[0016]

[Formula 3] λ / p> 1.0 (4)

When the incident angle of the light beam on the grating is set to the Bragg angle and the ratio λ / p between the wavelength λ and the grating pitch p is set to about 1.7, the vibration component parallel to the groove of the grating is parallel. Since the oscillating component is distributed to the 0th-order diffracted light and the 1st-order diffracted light, it is possible to separate polarized light by the grating. Here, the black angle θin is obtained by the following equation (5).

[0018]

[Equation 4] sin (θin) = λ / (2 · n1 · p) (5)

In order that the two light beams that are incident on the grating surface at the Bragg angle and separated are emitted parallel to each other, the apex angle θa contacting the grating surface of the prism,
One of the angles θb may be the black angle and the other may be 90 °.

Next, eight concrete design examples of the grating prism according to the embodiment will be described with reference to FIGS. 2 and 3. In the prisms (a), (b), (c), (d), (e), and (h), the grating is formed on the incident end face, and in the prisms (f) and (g), the grating is formed on the exit end face.

Further, the prism of (a) emits the separated light fluxes from different end faces, and the prisms of (b), (c), (d), and (h) emit one of first-order diffracted light and zero-order diffracted light. One of them is internally reflected, and both are emitted vertically from the same emission end face, (e)
The prism emits the separated light fluxes so that they are parallel to each other but not perpendicular to the exit end face. (b) (c)
According to the configurations of (d) and (e), the separated light beams can be emitted in the same direction with an optical path difference. According to the configurations of (b) and (h), since the incident light flux and the outgoing light flux are vertical,
It has the advantage of being easy to use. Further, according to the configuration of (h), since the incident angle is the Bragg angle, the polarization separation performance is good.

Numerical data of the respective grating prisms shown in FIGS. 2 and 3 are shown in Tables 1 and 2 below. The wavelengths λ used are all 0.78 μm. Note that the incident angle,
The exit angle is the angle with respect to the normal of the surface, 0.00
deg. means vertical.

[0023]

[Table 1] (a) (b) (c) (d) Lattice pitch p 0.4875 0.4490 0.4490 0.4875 (μm) λ / p 1.600 1.737 1.737 1.600 Refractive index n 1.50000 1.51072 1.51072 1.51072 Incident angle θin 30.00 50.00 50.00 53.13 (deg. ) First-order light diffraction angle 47.17 40.00 40.00 31.98 (deg.) Zero-order light diffraction angle 19.47 30.47 30.47 31.97 (deg.) First-order light emission angle 19.46 0.00 0.00 0.00 (deg.) Zero-order light emission angle 77.10 0.00 0.00 0.00 ( deg.) Prism vertical angle θa 60.00 40.00 30.47 31.98 (deg.) Prism vertical angle θb 60.00 85.24 94.76 90.00 (deg.) Prism vertical angle θc 60.00 54.76 54.77 58.02 (deg.)

[0024]

[Table 2] (e) (f) (g) (h) Lattice pitch p 0.4875 0.4875 0.4875 0.4758 (μm) λ / p 1.600 1.600 1.600 1.639 Refractive index n 1.51072 1.78885 1.51072 1.43107 Incident angle θin 53.13 26.57 31.97 55.05 (deg. ) 1st order light diffraction angle 31.98 53.12 53.14 34.94 (deg.) 0th order light diffraction angle 31.97 53.14 53.12 34.94 (deg.) 1st order light exit angle 20.59 53.12 53.14 0.00 (deg.) 0th order light exit angle 20.59 53.14 53.12 0.00 ( deg.) Prism vertical angle θa 53.13 53.12 40.93 34.94 (deg.) Prism vertical angle θb 90.00 63.44 94.07 90.00 (deg.) Prism vertical angle θc 36.87 63.44 45.00 55.06 (deg.)

FIG. 4 shows an example in which a grating prism of the type shown in FIG. 3 (e) is applied to an information recording / reproducing apparatus for a magneto-optical disk. The magneto-optical disk used in the examples is a disk having grooves, that is, guide grooves.

The divergent luminous flux emitted from the semiconductor laser 1 is
The collimator lens 2 collimates the light into a parallel light flux, and the two anamorphic prisms 3 and 4 shape the light into a circular cross section. A rectangular prism 5 is joined to the anamorphic prism 4, and the joining surface is a half mirror 5a. The light flux reflected by the half mirror surface 5a is condensed by the condenser lens 6 on the light receiving element 7 for automatic output adjustment of the semiconductor laser.

The light flux transmitted through the half mirror surface 5a is reflected by the mirror 8 and converged on the signal recording surface of the magneto-optical disk 20 via the objective lens 9. The objective lens 9 and the mirror 8 are provided in a head (not shown) that slides in the radial direction x of the magneto-optical disk 20. The objective lens 9 is provided on an actuator provided in the head, and is driven in the optical axis direction z and the radial direction x of the disk.

On the other hand, the light beam reflected from the disk is reflected by the half mirror surface 5a, the polarization direction is rotated by 45 ° by the λ / 2 plate 10, and is converged by the condensing lens 11 to the grating prism 12. Incident.

The grating prism 12 is shown in FIG.
As shown in (e), the oscillating component parallel to the groove of the grating and the oscillating component perpendicular to the groove of the light beam incident at the Bragg angle are separated as 0th-order diffracted light and 1st-order diffracted light, and both light beams are emitted in parallel to each other. .

The light beam emitted from the grating prism 12 reaches two light receiving regions formed on the light receiving element 13. Since the polarization direction of the laser light reflected by the magneto-optical disk 20 is rotated by the magnetic Kerr effect corresponding to the magnetization direction of the disk at the position where the spot is imaged, it is rotated by 45 ° and the P and S components are rotated. It is possible to read out the magneto-optical recording signal by separating them into two parts, detecting them by separate light receiving areas, and taking the difference.

As described above, in order to make the polarized light beams incident on the light receiving element for signal detection parallel to each other, conventionally, a polarization beam splitter and a reflection for reflecting the component reflected by the polarization beam splitter again are used. It was necessary to provide a prism having a surface. However, according to this embodiment, since the grating prism can serve as both the polarizing beam splitter and the prism, the number of parts can be reduced.

[0032]

As described above, according to the present invention, by forming a grating pattern on one surface of a prism, two or more light beams separated by diffraction can be emitted at a desired angle. Further, if the incident angle is set to be the Bragg angle, it can be used as a polarization separation prism. Therefore, if it is used as an optical element of a magneto-optical disk device, the number of parts can be reduced and the device can be downsized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a principle of a grating prism according to an embodiment.

FIG. 2 is an explanatory diagram showing a specific example of a grating prism according to an example.

FIG. 3 is an explanatory diagram showing a specific example of a grating prism according to an example.

FIG. 4 is an explanatory diagram showing an example in which the grating prism according to the example is used in an optical system of a magneto-optical disk device.

FIG. 5 is an explanatory diagram that defines a diffraction angle of diffracted light by a grating.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Maruyama 2-36 Maeno-cho, Itabashi-ku, Tokyo Inside Asahi Optical Co., Ltd. (72) Masahiro Ohno 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Optical Co., Ltd.

Claims (5)

[Claims] 1. A transmission-type grating pattern having periodicity is formed on either one of an incident end surface and an exit end surface which are not parallel to each other, and a light beam incident from the incident end surface is divided into 0th-order light and 1st-order light. A grating prism, which is separated and emitted from the emission end face. 2. The grating prism according to claim 1, wherein the grating pattern is formed on the incident end face. 3. The grating prism according to claim 2, wherein the apex angle is set so that the two light beams emitted from the emission end surface are parallel to each other. 4. The pitch p of the grating pattern
The grating prism according to claim 1, wherein satisfies the condition of λ / p> 1.0, where λ is the wavelength of the incident light beam. 5. A transmission type grating pattern having periodicity is formed on an incident end surface, and an incident light beam is separated into 0th order light and 1st order light by the grating pattern, and either 0 or 1st order light is separated. One of the light beams is internally reflected by a reflecting surface that is not parallel to the incident end surface, and then both light beams are emitted from the exit end surface that is not parallel to the incident end surface and the reflecting surface in a substantially parallel state. Grating prism.