JPS60254112A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To prevent a shift in scanning position due to the variation in the wavelength of reproduced light by employing double-layer consitution for a hologram disk, making direction of diffraction opposite to each other, and forming at least one disk axially symmetrically about a rotating shaft. CONSTITUTION:Hologram disks H1 and H2 are formed in two layers across a spacer 7. The disk H1 is irradiated with two coherent beams of a divergent spherical wave A and a convergent spherical wave B which have wavelength lambda1 one over another. The, the disk H2 is irradiated with coherent light beams A1 and B1 with wavelength lambda2 shorter than the wavelength lambda1 one over another. When a laser beam (1) with wavelength lambda1 is incident on the disk H1, diffracted light (2) is generated and passes through the disk H2, generating diffracted light (3). This diffracted light (3) is converged on a scanning surface to make a light beam scan. The reproduced light passes through the disks H1 and H2 which have the opposite directions of diffraction and the diffracted light beams (1) and (3) are made parallel to each other. When the reproduced light varies in wavelength, the angle of diffraction of one beam is made large and that of the other is made small, so that the diffracted light beams (1) and (3) are invariably parallel. Thus, the scanning position is held constant.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a light beam scanning device using a hologram disk, and in particular to a method for correcting wavelength fluctuations of a laser beam used as a light source and preventing scanning position deviation on a scanning plane. This invention relates to a light beam scanning device that can be used.

[Prior art and its problems]

When the hologram is moved, it acts as a lens, and the -order diffracted light is deflected to draw a single scanning line. Applying this effect,
By placing a plurality of holograms on a disk and rotating it, various scanning patterns can be obtained.

This scanning principle is used as a barcode reader in POS systems. Compared to conventional devices using rotating polygon mirrors, this hologram scanning device has advantages such as being simpler in construction, lighter in weight, and has a simpler optical system and lower cost. Applications are being attempted.

Laser printers that use holograms have few problems when using light beams with small wavelength fluctuations, such as He-Ne lasers, but when using laser diodes, the wavelength of the laser diode light varies depending on temperature etc. Therefore, sufficient characteristics cannot be obtained. 8th
The figure is a cross-sectional view of a light beam scanning device using a laser diode as a light source. 1 is a hologram disk, 2 is a scanning surface, and 3 is a motor for rotating the hologram disk l. A plurality of holograms are arranged on the hologram disk 1 in the circumferential direction. A laser beam 4 is irradiated to the hologram position, and a motor 3 is used to move the hologram disk 1.
Rotate continuously. Then, due to the interference fringes of the hologram,
The beam becomes a diffracted beam having a diffraction angle θ, converges on the scanning plane 2, and scans as shown by the solid line.

However, in devices that use a laser diode as a light source, changes in temperature cause the laser beam to undergo a so-called mode hopping phenomenon, causing the wavelength to change. Now, when the wavelength changes to the longer wavelength side, the diffraction angle of the hologram increases,
As shown by the broken line, the diffracted light 6 has a diffraction angle of θ°, and the convergence position of the laser beam is shifted.

[Technical problem of the present invention]

A technical object of the present invention is to solve such problems in conventional light beam scanning devices and to prevent the convergence position on the scanning plane from shifting due to wavelength fluctuations of the light source.

[Technical means of invention]

The technical means according to the present invention taken to achieve this object is an apparatus for scanning a light beam by rotating a hologram disk and diffracting a light beam, in which the hologram disk has a 2N configuration and each layer is has a diffraction direction with an opposite tendency, and at least one of the hologram disks is formed axially symmetrically with respect to the rotation axis.

[Operation of technical means] This technical means has a configuration in which two hologram disks are stacked, and the reproduction light passes through the two hologram disks. The diffraction directions of both hologram disks are opposite to each other. Therefore, the reproduced light that is diffracted by the first hologram disk is diffracted in the opposite direction by the second hologram disk and then emitted. Eventually, the light incident on the first hologram disk and the light emitted from the second hologram disk become parallel. When the wavelength of the reproduced light changes to the longer wavelength side, the diffraction angle on the first hologram disk increases, but the opposite diffraction angle on the second hologram disk also increases, so the wavelength on the scanning plane increases. Regardless, it converges to almost the same position, and the deviation in the convergence position is reduced. When the wavelength of the reproduced light changes to the shorter side, the diffraction angle on the first hologram disk becomes smaller, but the diffraction angle in the opposite direction on the second hologram disk also becomes smaller, so it converges at almost the same position, The deviation of the convergence position is reduced.

However, since the diffraction angle changes due to wavelength fluctuations, depending on the spacing between the two hologram disks, the scanning position may shift even if two hologram disks with opposite diffraction directions are used, but the optimal spacing will be explained later. It can be calculated using the following formula.

[Embodiments of the invention]

Next, how the optical beam scanning device according to the present invention is actually implemented will be explained using examples. FIG. 1 is a side view of a first embodiment of a light beam scanning device according to the present invention. H
1 and H2 are hologram disks, and both hologram disks H1 and H2 are fixed together via a spacer 7, and have a two-layer structure.

One hologram disk H1 is created as shown in FIG. 1, and the other hologram disk H2 is created as shown in FIG.

Figure 2 is a cross-sectional view, and by irradiating two coherent lights, a diverging spherical wave A with a wavelength A1 and a converging spherical wave B with a wavelength λ1, in a superimposed manner, one part of the hologram disk can be
Create set H1. The light source of the diverging spherical wave A is the rotation axis a
x, and the convergent spherical wave B converges on the rotation axis ax.

The hologram disk H1 is created so as to be axially symmetrical with respect to the rotation axis ax. As a result, when the reproduction light is irradiated from the same direction as the diverging spherical wave A, the diffracted light converges on the rotation axis as shown by the chain line. The hologram disk H1 may be made by arranging a plurality of hologram pieces prepared in advance in the circumferential direction of the disk, as is usually done, or it may be made directly on one disk using the method shown in FIG. It may be something that has been done.

The other hologram disk H2 is produced by superimposing two coherent diverging spherical waves AI and A2 having a wavelength λ2 shorter than the wavelength λ1, as shown in FIG. 3(A). The long wavelength λ1 can be obtained by a semiconductor laser such as a laser diode, and the short wavelength λ2 can be obtained by H
e N CI % Ar, He=Cd, etc. can be obtained using a gas laser.

This hologram disk H2 may also be one in which hologram pieces created in advance are arranged on the disk in the circumferential direction, or may be created directly on the disk. In addition(
As shown in b), only the hologram disk H2 created in this way is rotated, and the wavelength λ longer than the wavelength λ2 at the time of creation is
It is known that when the light beam 4 of 1 is irradiated from the back side and reproduced, the diffracted light 5 converges and linearly scans the scanning surface 2 as shown in (c). Also in this case, the hologram disk H2 is created axially symmetrically with respect to the central axis ax. Therefore, when the reproduction light 4 is irradiated from above the optical axis of the creation light A1, the transmitted light is transmitted along the rotation axis ax as shown by the chain line.
It will converge upward.

The two hologram disks H1 and H2 created by irradiating a light beam with a wavelength of λ1>λ2 in this way are arranged in a 2N configuration with a predetermined interval a as shown in Fig. 1, and are placed together around the rotation axis ax. The light beam is scanned using a laser diode in the same manner as a conventional light beam scanning device.

Now, when a laser beam of wavelength λ1 is incident on the hologram disk H1, diffracted light (2) is generated. Then, this diffracted light ■ passes through the lower hologram disk H2, and the diffracted light ■
is emitted. Light beam scanning is performed by converging this emitted light (2) onto a scanning surface. In this way, the reproduction light is 2
It passes through two hologram disks H1 and H2. Since the diffraction directions of both hologram disks are opposite, the diffracted light ■ diffracted by the first hologram disk H1 is reflected from the second hologram disk H1.
2 and is diffracted in the opposite direction and emitted.

In the end, the incident light on the first hologram disk H1 ■ and 2
The light emitted from the hologram disk H2 becomes parallel. Then, when the wavelength of the reproduction light changes to the long wavelength side, 1
The diffraction angle on the second hologram disk H1 becomes large, but the opposite diffraction angle on the second hologram disk H2 also becomes large, so the incident light ■ and the emitted light ■ become parallel, and on the scanning plane there is no relation to the wavelength. It converges to almost the same position without any problem, and scanning position deviation is reduced. Even when the wavelength of the reproduction light changes to the shorter side, it converges at approximately the same position and the scanning position shift is reduced in exactly the same way.

However, when the wavelength of the laser diode changes due to mode hopping, the diffraction angle changes as a result, so in order to completely eliminate the shift in the convergence position, it is necessary to select the distance a between the two hologram disks. A method for selecting the interval a will be explained based on FIG. 4. hologram disc h1
, H2 were created using the methods shown in FIGS. 2 and 3, respectively. When a light beam from a laser diode is incident on this hologram disk H1 at a wavelength λ1 and an incident angle θi, the diffraction angle θd is as follows: S stone θd=-smθi+λl-f (rQ) ---
(1) However, 1.7'(ro) is the spatial frequency of the hologram at the reproduction point rQ.

On the other hand, the wavelength λl mode-hops (λl+Δλl
) and the wavelength changes, then the wavelength changes as follows:
Δλl )・f('ro) ・・・・・・・・・・・・
(2): According to equations (1) and (2), approximately, on the other hand,
Due to the deviation of Δθd from the hologram H2, in order to completely eliminate the deviation from the hologram H2 as shown at the 0 point in the figure, a(-(θi'+Δθi')-1 θi')=Δr1...
・・・・・・・・・(4) However, θi′=θd1 Δθi′=ΔθdAlso, t(-(
θd'+Δθd')-10d')=Δr1...
...(5) (4) According to equation (5), approximating Δθ11Δθd as sufficiently small, Δ・−1・θ, −J 0d −°−°°−, (7) Also, according to hologram H2 The equation for diffraction is sinθd'=-
s stone θi'+λ1 f (rl) −・'(8) sin
(θd'''+Δθd')=-sin(θi'+Δθi/
)+(λ1+Δλx)f(rt+Δrs) −−(
9) Approximately from equations 8(8) and (9), Δθd″′μsθd′sa−Δθ□1..θi/−(λl
+Δλ1)・Δrl−f′(rl)+Δλ1−f(rl
)......00 Therefore, substituting equations (6) and (7) into equation 00, -'-f(rt)・Δλl...
......Substituting Δθd in equation (3) into equation (11), .......(6) From equation (12), the following can be found. In other words, it is possible to calculate a that completely cancels out the mode hop Δλ1, that is, satisfies equation (12). Therefore, by selecting this a (the distance between the two hologram disks H1 and H2), the mode hop of the laser beam can be can offset the effects of

Since these two-layer holograms are created and reproduced at equal angles, they also have the effect of being resistant to substrate warping (wedge). FIG. 7 is a side view showing an example in which the board is warped by an angle α, and the position P1 on the board is
The convergence position of the diffracted light differs between when the reproduction light 4 is incident on the hologram disk and when the reproduction light 4 is incident on the printing plate at position P2 after the hologram disk has rotated further by half a rotation. However, according to the present invention, when a 2M hologram disk is used and the diffraction directions of both hologram disks are reversed, the change in the diffraction angle due to the wavelength fluctuation of the reproduction light is canceled out. This eliminates the deviation in the diffraction direction due to warpage.

Figure 5 shows a second embodiment of the hologram disk, in which a hologram H1 is created on one side of the hologram substrate using the method shown in Figure 2, and a hologram H1 is created on the other side using the method shown in Figure 3.
Create 2. At this time, the distance a between the holograms H1 and H2 is selected according to the above calculation formula. Note that hologram pieces prepared in advance may be attached to both sides of the substrate.

Therefore, between the two hologram disks H1 and H2,
It may be hollow or may have glass or the like interposed therebetween.

FIG. 6 is a diagram showing a third embodiment of the hologram disk. In this example, two holograms H1 and H2 are stuck together using an adhesive. The above-mentioned distance a may take a very small value depending on the pitch of the interference fringes of the two hologram disks H1 and H2. In such a hologram, as in this example, it is also possible to adhere the hologram through an adhesive having a thickness of a. The structure in which the two hologram disks Ht and H2 are closely stacked together as in this example reduces light loss.

The waves created by the optical beam scanning device using the hologram of the present invention are not limited to the above-mentioned example, but the so-called IZP
etc. When used as a laser printer, linear scanning is required, so the wavelength λ when creating the two hologram disks H1 and H2 as described above is
1 and λ2 need to be different, but in cases where linear scanning is not necessarily required, such as in a barcode reader, there is no problem even if the wavelength λ1 = λ2, so IZ
It can also be applied to P.

〔Effect of the invention〕

As described above, according to the present invention, the hologram disk can be
By using a layered structure in which each layer has a diffraction direction with an opposite tendency, and by setting the spacing between both hologram disks to a predetermined value, scanning can be achieved even if the diffraction angle changes due to wavelength fluctuations of the reproduction light. It is possible to reliably prevent deviations in the scanning position on the surface, and also eliminate deviations in the convergence position due to warping of the substrate. Furthermore, since the two hologram disks are integrated and rotated together, the configuration is simple, there is no fear of positional deviation of the optical system, and the advantages of the light beam scanning device using the hologram disk are not impaired.

[Brief explanation of drawings]

1 to 6 show embodiments of a light beam scanning device according to the present invention, FIG. 1 is a sectional view showing the first embodiment, and FIG. 2 is a sectional view showing a method for producing one of the hologram disks. Figure 3 is a diagram showing the method for creating the other hologram disk and an example of its use, Figure 4 is a cross-sectional view explaining the formula for selecting the spacing between the two hologram disks, and Figure 5 is a cross-section of the second embodiment. 6 is a sectional view of the third embodiment, and FIG. 7 is a side view showing a state in which the hologram disk substrate is warped.
FIG. 8 is a sectional view of a conventional light beam scanning device. In the figure, 1, Hl, H2 are hologram disks, a
x is the rotation axis (the center of the hologram disk), a is the distance between two holograms, 2 is the scanning plane, 7 is the spacer, ■ is the incident light, ■ is the diffracted light, and ■ is the output light, respectively. Patent applicant: Fujitsu Ltd. Agent: Minoru Aoyagi, patent attorney Figure 5 Figure 6

Claims (1)

[Claims] In a device that scans a light beam by rotating a hologram disk and diffracting a light beam, the hologram disk has a two-layer structure, each layer having an opposite diffraction direction, and the hologram disk A light beam scanning device characterized in that at least one of the two is formed axially symmetrically with respect to a rotation axis.