JPH04355423A - Light beam scan device - Google Patents

Abstract

PURPOSE:To obtain the maximum refraction efficiency and set the strength of outgoing light to be uniform by forming a groove to be shallower as a groove pitch of a pattern becomes smaller. CONSTITUTION:In a scan hologram of a surface relief type, a groove 8 is changed to be shallower as a groove pitch (d) of a pattern 7 becomes smaller. The groove pitch (d) of the pattern 7 is set to be smaller than a wavelength of a semiconductor laser 2. A ratio of the groove 8 of the pattern 7 to the groove pitch (d) is fixed to be almost equal to a ratio of the depth of the groove 8 and the groove pitch (d) at the maximum refraction efficiency obtained for the maximum groove pitch (d). For a laser beam 4 outgoing from the semiconductor 2, therefore, the strength of the outgoing beam 5 is set uniform if the groove pitch (d) of the hologram pattern 7 at an incident position is changed by rotation of the scan hologram 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device used in printers, copiers, facsimile machines, etc. to focus and scan a light beam from a semiconductor laser or the like.

0002

2. Description of the Related Art In recent years, light beam scanning devices have been increasingly used in high-speed, high-resolution, low-cost printers, copying machines, facsimile machines, and the like.

As a conventional light beam scanning device, the configuration described in Japanese Patent Laid-Open No. 62-28708 is generally known.

A conventional light beam scanning device will be explained below with reference to the drawings. FIG. 4 is a side view showing a conventional light beam scanning device. In FIG. 4, 41 is a disk-shaped scanning hologram, which rotates around an axis 42. As shown in FIG. 43 is a semiconductor laser, 44 is an aberration correction hologram lens, 45 is an imaging point on a photocondrum (not shown), and 46 and 47 are diverging spherical wave light sources.

The operation of the light beam scanning device constructed as described above will be explained below. A diverging spherical wave 48 emitted from the semiconductor laser 43 enters an aberration correction hologram lens 44 . A diffracted wave 49 diffracted by the aberration correction hologram lens 44 is incident on a disk-shaped scanning hologram 41 rotating about an axis 42 with a beam diameter DH. A diffracted wave 50, which is a convergent spherical wave, from the scanning hologram 41 is directed to an imaging point 4 on the photocondrum.
5, and scanning is performed by rotating the scanning hologram 41. The scanning hologram 41 is produced by interference of divergent spherical waves 51 and 52 from divergent spherical wave light sources 46 and 47.

In the above configuration, the aberration correction hologram lens 44 is set at an appropriate diffraction angle, captures the divergent light emitted from the semiconductor laser 43, and then absorbs the aberrations generated by the scanning hologram 41. It is made to generate a wavefront with aberrations that cancel point and coma aberrations, thereby reducing aberrations at the imaging point 45.

[0007]

However, in the above-mentioned conventional light beam scanning device, although the groove pitch of the pattern of the scanning hologram 41 differs depending on the location, if the scanning hologram 41 is of the surface relief type, Since the depth of the grooves in the pattern is constant, the optimum conditions for obtaining maximum diffraction efficiency are not met. For this reason, there was a problem in that the intensity of the laser light emitted from the scanning hologram 41 varied as the scanning hologram 41 rotated.

The present invention solves the above problems of the prior art, and makes the intensity of the emitted laser beam uniform even if the scanning hologram rotates and the position on the hologram where the laser beam is incident changes. Therefore, an object of the present invention is to provide a light beam scanning device that can improve image quality.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is a surface relief type scanning hologram having a pattern in which the grooves become shallower as the groove pitch becomes smaller.

[0010] The groove pitch of the pattern is set to be smaller than the wavelength of the semiconductor laser, and the ratio of the groove depth and groove pitch of the pattern is such that the groove pitch at the maximum diffraction efficiency obtained at the maximum groove pitch is set. It can be fixed to be approximately equal to the ratio of depth and groove pitch.

[0011]

[Operation] Therefore, according to the present invention, as the groove pitch of the hologram pattern becomes smaller, the grooves become shallower. Therefore, the maximum diffraction efficiency can be obtained, and the intensity of the emitted laser beam can be reduced. It can be made uniform.

0012

Embodiments (Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a side view showing a light beam scanning device according to a first embodiment of the present invention, and FIG. 1(b) shows a groove shape of a scanning hologram pattern used in the light beam scanning device. It is a partially enlarged sectional view.

In FIG. 1(a), reference numeral 1 denotes a scanning hologram, which rotates around an axis (not shown). 2 is a semiconductor laser, and 3 is an image forming point on a photocondrum (not shown). As shown in FIG. 1(b), the scanning hologram 1 has a groove pitch d of the hologram pattern 7 on the substrate 6.
The grooves 8 are formed so that the grooves 8 become deeper at locations where d is large, and the grooves 8 become shallower as the groove pitch d becomes smaller.

The above configuration will be explained in more detail below along with its operation. A laser beam 4 emitted from a semiconductor laser 2 is incident on a scanning hologram 1. The diffracted outgoing beam 5 from the scanning hologram 1 forms an image on an imaging point 3 on the photocondrum, and scanning is performed by rotating the scanning hologram 1.

[0016] Here, the analysis of the diffraction problem in consideration of the shape effect of the pattern grooves and the polarization characteristics of the incident light will be explained. This analysis requires rigorously solving the Maxwell's equations of electromagnetic waves. FIG. 2 shows a dielectric surface relief grating 11 having a periodic structure in the x-axis direction. With the grid shape as the boundary, above the surface of the grid 11 is a free space 12,
The refractive index is n=1, and the refractive index below the surface is n=n0.
The substrate 13 is made of a dielectric medium with no loss. Considering the case where a plane wave of wavelength λ is incident on grating 11 with grating spacing d and grating depth h as incident light 14 at an incident angle θ, calculate the diffraction efficiency of first-order diffracted light 15 for TE polarized light and TM polarized light. is possible. The analysis method is Yokomori:R.
ICOH TECHNICAL REPORT12, (
1984). The diffraction efficiency η is defined by the diffracted wave intensity relative to the incident wave intensity, and in the case of a first-order diffracted wave, the diffraction efficiency η1 is expressed by the following equation from the incident wave intensity P0 and the first-order diffracted wave intensity P1 in FIG.

η1=P1/P0 In FIGS. 3(a), (b), and (c), when the shape of the grooves 8 of the pattern 7 is a sine wave, the groove pitch d is used as a parameter, and the groove pitch d is 1. 3μm, 0.78μm, 0.5μm
FIG. 3 is a diagram showing the relationship between the ratio of groove depth h and groove pitch d and diffraction efficiency in the case of m. The wavelength of the incident light is 788 nm, the solid line indicates the TE wave, and the dotted line indicates the TM wave. Figure 3
As is clear from (a), (b), and (c), even when the groove pitch d becomes small such as 1.3 μm, 0.78 μm, and 0.5 μm, the depth and pitch of the groove 8 that maximizes the diffraction efficiency It can be seen that the ratio h/d is between 1.4 and 2.0 and does not change significantly. Therefore, in order to obtain the maximum diffraction efficiency, it is necessary to make the depth of the grooves 8 shallower as the groove pitch d of the pattern 7 becomes smaller as described above. However, under conditions where the maximum diffraction efficiency corresponding to the groove pitch d is obtained, the intensity of the light beam emitted from the scanning hologram 1 is not uniform, so it is necessary to set the depth of the grooves 8 to be shallower. Table 1 shows the depth of the groove 8 for each groove pitch d when the maximum diffraction efficiency is obtained when the groove pitch d is 1.3 μm.

[0018]

[Table 1]

By setting the pattern 7 as shown in Table 1, the laser beam 4 emitted from the semiconductor laser 2 rotates the scanning hologram 1 and changes the groove pitch d of the hologram pattern 7 at the incident position. However, the intensity of the emitted beam 5 will be made uniform. Furthermore, the groove pitch d
When the wavelength of the semiconductor laser 2 is smaller than the wavelength of the semiconductor laser 2, the maximum diffraction efficiency obtained becomes large.

Although FIGS. 3(a), 3(b), and 3(c) have been described with respect to the case where the groove shape of the pattern is a sine wave, the same applies to a rectangular wave, a triangular wave, or any other shape other than a sine wave.

The pattern is produced by a method such as EB drawing, and deep grooves can be formed by increasing the number of repetitions of drawing.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

In the first embodiment, FIG. 1(b)
The ratio h of the groove depth and groove pitch of the hologram pattern 7 shown in
/d is variable, whereas in this example, the ratio h/d of the groove depth and groove pitch of the hologram pattern 7 is variable, as is clear from FIGS. 3(a), (b), and (c). , is fixed to be approximately equal to the ratio h/d of the groove depth to the groove pitch at the maximum diffraction efficiency obtained at the maximum groove pitch d, so that the diffraction efficiency is approximately equal when the groove pitch d changes. The other configurations are the same as those of the first embodiment.

The groove depth and diffraction efficiency corresponding to each groove pitch d of the hologram pattern 7 in this example are expressed as (
Table 2) shows the results.

[0025]

[Table 2]

In the first and second embodiments described above, the scanning hologram 1 is used as a scanning hologram 1 by transmitting a laser beam.
Although the case where the second-order diffracted light is obtained has been described, it is also possible to construct a reflective type by vapor-depositing metal on the surface of the pattern, and in this case, the same effect as described above can be obtained.

[0027]

[Effects of the Invention] As explained above, according to the present invention, since the grooves are formed so that they become shallower as the groove pitch of the pattern becomes smaller, the maximum diffraction efficiency can be obtained, and the emitted light Strength can be made uniform. Therefore, image quality can be improved.

[Brief explanation of the drawing]

FIG. 1 (a) A side view showing a light beam scanning device according to a first embodiment of the present invention. (b) A cross-sectional view showing the groove shape of a pattern of a scanning hologram used in the light beam scanning device.

[
Figure 2: Explanatory diagram of relief lattice structure

FIG. 3: (a) An explanatory diagram of the groove pitch dependence of diffraction efficiency when the groove pitch is 1.3 μm. (b) An explanatory diagram of the groove pitch dependence of diffraction efficiency when the groove pitch is 0.78 μm. ) Explanatory diagram of the groove pitch dependence of diffraction efficiency when the groove pitch is 0.5 μm

[Fig. 4] Side view showing a conventional optical beam scanning device

[Explanation of symbols]

1 Scanning hologram 2 Semiconductor laser 7 Pattern 8 groove

Claims (3)

[Claims] 1. A light beam scanning device comprising a surface relief type scanning hologram having a pattern in which the grooves become shallower as the groove pitch becomes smaller. 2. The optical beam scanning device according to claim 1, wherein the groove pitch of the pattern is smaller than the wavelength of the semiconductor laser. [Claim 3] The ratio of the groove depth and groove pitch of the pattern is
3. The light beam scanning device according to claim 1, wherein the groove depth is fixed to be substantially equal to the groove pitch ratio at the maximum diffraction efficiency obtained at the maximum groove pitch.