JPH0248885B2 - HOROGURAMUHIKARISOSASOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device that uses a linear diffraction grating as a deflection element and has improved light utilization efficiency.

As a laser beam deflector used in laser printers, barcode reading, laser defect inspection, etc.
It is already known that a plurality of equidistant linear gratings are arranged concentrically on a disk that rotates at a constant speed, a laser beam is incident at a fixed radius position, and the diffracted primary light is focused on the scanning surface. It is being

This type of optical deflection device is easier to manufacture than a device that uses a rotating polygon mirror as an optical deflector by manufacturing an equally spaced linear diffraction grating as a hologram, and it is possible to obtain a highly practical device. I can do it. However, in order to improve the practicality of this type of device, it goes without saying that it is desirable to increase the diffraction efficiency of the hologram and to minimize fluctuations in the diffraction efficiency due to disk rotation.

The present invention aims to provide an optical deflection device that can satisfy the above-mentioned desirable conditions in the relationship between the grating direction of the hologram and the polarization plane of the incident light.

A detailed explanation will be given below with reference to the drawings.

FIG. 1 is an optical layout diagram of the optical deflection device in a plane including the scanning direction of the laser beam, the so-called main scanning direction;
FIG. 2 is an optical layout diagram viewed in the so-called sub-scanning direction, which is perpendicular to this. A Gaussian beam from a laser (not shown) is made into a condensed light beam by a cylindrical lens 1 that is linearly focused at point A parallel to the hologram disk 2, and is incident on the linear grating hologram on the hologram disk 2 at an incident angle Θ _i do. The first-order diffracted light from the hologram is diffracted at an exit angle Θ _d , creating a linear beam waist at A' corresponding to the focusing line A. The diverging light from A' is transmitted to the scanning plane P by a lens 3 of fΘ which is a spherical lens and a cylindrical lens 4 which has a convergence effect in the sub-scanning direction.
Create a beam waist. In the main scanning plane, the laser beam changes its diffraction direction due to the rotation of the hologram disk 2, so that the beam waist changes to the scanning plane P.
While the top is scanned from _P1 point to _P2 point, fΘ lens 3 and cylindrical lens 4 are scanned in the sub-scanning plane.
Regarding this, the two hologram disks and the scanning plane P have a geometrically optically conjugate relationship, so that the shake of the disk 2, the error in the mounting angle of the hologram, etc. will not affect the position of the focal point on the scanning plane. It is generally an optical arrangement.

FIG. 3 shows an example of a plan view of the hologram disk 2 used in such an optical scanning device. Each hologram 21, 22... has a linear grating, and in the illustrated example, the grating is arranged perpendicular to the disk radius passing through its center.

It has been found that the diffraction efficiency changes depending on the angle between the hologram grating and the plane of polarization vibration of the beam incident on the hologram. FIG. 4 shows an example of the relationship between the polarization vibration plane and the grating angle (expressed as the polarization plane angle α) and the diffraction efficiency.

For measurements, a hologram of 1860 lines/mm was recorded on a recording material with a photoresist layer with a thickness of 0.8 μm using a He-Cd laser beam using a well-known recording optical system, and for reproduction, a He-Ne laser was used. ing. As the angle of incidence Θi on the hologram, the angle Θio at which the diffraction efficiency is maximized was experimentally found. That is, Θio=sin ^-1 (λu/2) where λ: In-air wavelength of reproduction light u: Spatial frequency of hologram In this example, λ=0.6328×10 ^-3 mm u=1860 lines/
Since it is mm, Θio≒36.1°.

The results of measuring the diffraction efficiency when the laser tube was rotated using a linearly polarized beam and a non-polarized beam as the incident beam to achieve the highest diffraction efficiency. Diffraction efficiency of linearly polarized laser: 62.0% Diffraction efficiency of non-polarized laser: 54.0% Obtained. Here, the diffraction efficiency η is the incident light power P ₀ 1
The power of the next diffracted light is P ₁ and it is calculated as η=P ₁ /P ₀ ×100%.

As a result, it became clear that a linearly polarized laser can obtain higher diffraction efficiency, so next we measured the relationship between the polarization vibration plane and the diffraction efficiency when linearly polarized light was used. Figure 4 shows the results. Here, α = 0° means that the polarization vibration plane of the incident light and the lattice direction of the hologram match, which is so-called S-polarized light, and α = 90° means that the polarization vibration plane and the lattice direction are perpendicular, so-called P-polarized light. becomes. It was found that the diffraction efficiency η approximately satisfies η=Acos ² α+B (AB is a constant).

When applying the above results to the optical deflection device shown in Figs. 1 and 2, the plane of polarization vibration of the illumination beam for reproduction should be set at right angles to the lattice direction of the hologram, that is, the radial direction of the disk 2. . In this way, when scanning the center P ₀ position of the scanning plane,
The lattice direction of the hologram and the polarization vibration plane of the incident beam coincide, exhibiting the highest diffraction efficiency, and at the same time, the decrease in efficiency at the scan start point P ₁ and scan end point P ₂ is also the lowest. The hologram disk shown in Figure 3 is 8
It has several holograms, and each hologram is approximately
Perform a 30° scan. In this case, the variation range of the angle between the hologram grating direction and the polarization vibration plane is the range B in FIG. 4. Results of actual measurements using the illustrated device,
During scanning with a rotation angle of 30° and a scanning length of 210 mm, it was confirmed that it had good scanning characteristics with an average diffraction efficiency of 60.5% and an efficiency variation of ±1.5%.

The above example explained the case where the hologram grating direction is perpendicular to the radial direction of the disk, but when the grating direction coincides with the radial direction of the disk, it is better to make the polarization vibration plane of the incident light coincide with this.
When the grating direction is arranged obliquely to the radial direction as shown in Figure 5, the polarization vibration plane of the incident light is also in the direction of the grating when scanning the scanning center point, as shown by arrow C in the figure. Just make it parallel.

In addition, although the experimental example explained a hologram using photoresist, silver salt, dichromate gelatin, amorphous material, thermoplastic, etc.
The same applies to holograms made of any material, and can also be applied to reflection-type holograms instead of transmission-type holograms.

[Brief explanation of drawings]

Figures 1 and 2 are optical path layout diagrams of an optical scanning device implementing the present invention, and Figure 3 is a diagram of a hologram disk.
FIG. 4 is a plan view of the example, FIG. 4 is a diffraction efficiency curve, and FIG. 5 is a partial plan view of another example of the hologram disk. 1, 4: cylindrical lens, 2: hologram disk, 3: fΘ lens.

Claims (1)

[Claims] 1. In an optical scanning device in which a plurality of holograms are arranged concentrically on a disk rotating at a constant speed and a scanning surface is scanned by the first-order diffracted light of a laser beam incident on the hologram, the incident light is linearly polarized light. , a hologram optical scanning device characterized in that the plane of polarization vibration coincides with the lattice direction of the hologram when scanning the center of the scanning line.