JPH0154685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image scanning device for scanning characters, figures, photographs, etc. using a laser beam, and particularly to a light beam generating device used in a facsimile device.

Methods that detect object shapes and images by scanning a laser beam over an object or paper using a deflector and a condensing lens, and methods that record shapes by scanning a photosensitive material can achieve high speed and high resolution. Because of this characteristic, it is used in optical scanning devices such as POS (point of sales), facsimile machines, and printers. Generally, in the above laser beam scanning device,
The size of one pixel from which information can be obtained at one time and the size of one pixel that can be recorded at one time are determined by the diameter of the light beam focused on the scanning plane. Further, the required resolution differs depending on the optical scanning device, and the diameter of the focused laser beam must be arbitrarily set in accordance with the different resolutions. A commonly used method to meet this requirement is to use an optical system such as an optical beam expander to convert the diameter of the optical beam incident on the optical scanning optical system, thereby changing the focused beam. Generally, the spatial energy distribution of the light beam emitted from a laser light source is a Gaussian distribution, so the light energy distribution in one pixel irradiated by one light beam is always a Gaussian distribution regardless of the light beam diameter. Become. This indicates that information obtained from reflected light is reflected more strongly from the center of one pixel than from the periphery.
Furthermore, the density of the recorded pixel at the center is greater than the density at the periphery.

This effect is noticeable in facsimile machines, where information is missing between light beam scanning lines. A problem arises in that when the diameter of the light beam is increased to prevent this information from being omitted, the resolution is reduced in the scanning line direction. Therefore, a light beam having a rectangular intensity distribution with different aspect ratios is required.

As shown in Fig. 1, a conventional scanning device consists of a laser light source 1, lenses 3 and 4, a scanning mirror 6, an fθ lens 7, a scanning surface 8, and a photodetector 10, and the optical axes of each lens coincide with each other. It is arranged like this. In such a device, a laser beam 2 emitted from a laser light source becomes a light beam 5 having a beam diameter expanded by lenses 3 and 4, and is reflected by a scanning mirror 6 and then reflected by an fθ lens 7. and is focused onto a scanning plane 8 on the xy plane. The focused beam 9 is scanned in the x direction by rotating the scanning mirror 6 in the xz plane, and the scanning plane 8 is sequentially moved in the y direction every time the scanning in the x direction is completed. The reflected light from the scanning surface 8 is received by a photodetector 10, information is read out, and two-dimensional scanning is performed. In this case, since the spatial energy distribution of the laser beam 1 is usually a Gaussian distribution, the energy distribution of the focused beam 9 is also a Gaussian distribution. Generally, the diameter of a laser beam with a Gaussian distribution has an energy of 1/e ² (e is the base of the natural logarithm)
It is expressed as the diameter of a point. The diameter of the light beam 5 is
2ω ₀ , fθ When the focal length of the lens 7 is f, the diameter 2ω of the focused beam 9 is expressed by the following formula, where λ is the wavelength of the laser beam.

2ω=2fλ/πω ₀ (1) Therefore, if the diameter 2ω ₀ of the light beam 5 is decreased, the focused beam diameter 2ω will be increased, and if the diameter 2ω ₀ of the light beam 5 is increased, the focused beam diameter 2ω will be decreased. The diameter of the light beam 5 is usually changed by changing the ratio of the focal lengths of the lenses 3 and 4.

Making the focused beam shape elliptical can be done by inserting a collimating optical system with a cylindrical lens that changes the beam width one-dimensionally in front of lens 3, but since the intensity distribution remains Gaussian, it is possible to It is not possible to compensate for the shortcomings. Another method is to spread the light beam, place a rectangular aperture, and use only the light that passes through the aperture, but this is not practical because the loss of light energy is large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light beam generating device that generates a light beam exhibiting a rectangular intensity distribution.

The light beam generator of the present invention is provided with a light beam converter for converting a light beam emitted from a monochromatic light source into a plurality of light beams on the output side of the monochromatic light source, and further provided with a lens on the output side of the light beam converter. After converting the light beam from a monochromatic light source into multiple light beams using a light beam converter,
These multiple light beams are combined using a lens to generate a light beam that exhibits a rectangular intensity distribution and has an asymmetric shape.

The details of this device will be explained below using the drawings.

FIG. 2 is a diagram for explaining the principle of the light beam generator according to the present invention. A Gaussian beam 1 is sent to a sinusoidal phase plate 12 with a period P which is a light beam converter.
1 (2ω) is incident, and the diffracted light enters the lens 13
The light beam intensity I(ε) at the focal plane of the lens is expressed by the following equation.

I(ε) _〜∞ 〓 ^q=-∞ J ² _q (m)exp{−2π ² ω ² (ε−q/
p)} (2) m=2π(n-1)l/λ (3) ε=X/λf (4) where q is an integer, n is the refractive index of the phase plate, and λ is the wavelength of light.

In Fig. 2, q=0 corresponds to 0th-order diffracted light 14, q=1 corresponds to 1st-order diffracted light 14', and q=-1 corresponds to -1st-order diffracted light 14''. Diffraction corresponding to an order of |q|>2 The intensity of the light is small compared to these diffracted lights. By changing the value of the phase modulation degree m, the intensity of the diffracted light of each order can be changed, and by changing the value of the period P, the degree of overlapping of each diffracted light can be changed. It can be changed.

FIG. 3 shows the shape of a light beam formed by coherently overlapping and combining these diffracted lights. The light beam shape shown in Figure 3 has a phase modulation degree m.
This is the shape of the light beam when it reaches 1.44 rad. At this time, q=0±1st-order diffracted lights with equal light intensity overlap. The light beam shape 20 is when 2ω/P=0.75, and the light beam shape 21 is when 2ω/P=0.875. As can be seen from FIG. 3, a light beam with a fairly rectangular intensity distribution is obtained. The efficiency of obtaining this rectangular beam is calculated from equation (2), and more than 90% of the incident light energy is converted. Even if the phase modulation degree m satisfies m>1.44rad, 2ω/
A similar light beam shape can be obtained by selecting the value of P.
However, this is not desirable because the intensity of higher-order light increases. Further, under the condition of 2ω/p≫1, each diffracted light beam is separated, and a combined rectangular light beam cannot be obtained.

FIG. 4 is a diagram showing an embodiment of a light beam generating device according to the present invention. A laser light source 30 used as a monochromatic light source, a light beam converter 32, and a lens 34 are installed in this order, and a Gaussian light beam 31 emitted from the laser light source 30 is transferred to the light beam converter 3.
2.

The plurality of light beams 33 diffracted by the light beam converter 32 are Fourier transformed by the lens 34, and a composite light beam 35 of the plurality of light beams 33 is obtained at the focal plane. In Fig. 4, a phase plate with a one-dimensional sinusoidal shape carved in the y direction is used, so the combined light beam 35 has a Gaussian distribution in the z direction and a shape shown in Fig. 3 in the y direction. . The width of the light beam 35 is approximately 2 in the y direction when the width in the z direction is 1.
An elliptical beam of size is obtained.

FIG. 5 shows a part of the manufacturing process of a method for manufacturing a light beam converter used in the present invention by a mask exposure method.

A mask 42 on which a sinusoidal density distribution is recorded is placed on a transparent substrate 40 coated with a photoresist 41, and irradiation light 43 is applied from above. Since a sinusoidal light amount is recorded on the photoresist 41, a light beam converter having a desired sinusoidal waveform can be obtained by the development process.

FIG. 6 shows some steps of a method for holographically manufacturing a light beam converter used in the present invention.

Coherent light beams 44 and 45 are applied to a transparent substrate 40 coated with a photoresist 41, and interference fringes are recorded on the photoresist 41. The period and depth of the recorded sine waveform are determined by coherent light44,45
It can be changed depending on the angle formed by the light and the light intensity. After the photoresist 41 is developed, a desired sinusoidal waveform is formed.

FIG. 7 is a diagram showing a part of the process of manufacturing a light beam converter using a curable resin used in the present invention. A curable resin 46 is poured between the transparent substrate 40 and a pressing die 47 having a sinusoidal shape, and a thermal polymerization reaction or a chemical polymerization reaction is started. After the curable resin 46 is cured, the mold 47 is removed to obtain a light beam converter.

FIG. 8 is a diagram showing a part of the process of manufacturing a light beam converter using a heat-deformable resin used in the present invention. A light beam converter is obtained by pressing a mold 47 having a sinusoidal shape into a resin 48 such as acrylic or vinyl chloride, and deforming the resin 48 by applying heat and pressure.

As described above, according to the present invention, it is possible to obtain a light beam generator that can efficiently generate light beams having rectangular intensity distributions with different aspect ratios.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an example of a conventional optical scanning device, FIGS. 2 and 3 are diagrams for explaining the principle of a light beam generator according to the present invention, and FIG. 4 is a diagram for explaining an example of a conventional optical scanning device. A diagram showing an example of a beam generator,
5, 6, 7, and 8 are diagrams showing a part of the manufacturing process of the method for manufacturing a light beam converter used in the present invention. In the figure, 1, 30 are monochromatic light sources, 2, 5,
9, 11, 31, 32, 35 are light beams, 3,
4, 7, 13, 34 are lenses, 6 is a scanning mirror, 8 is a scanning surface, 10 is a light receiver, 12, 32 are light beam converters, 14, 14', 14'', 20, 21 are light beam shapes, 40 is a transparent substrate, 41 is a photoresist, 42 is a mask, 43, 44, 45 are irradiation lights,
46 is a curable resin, 47 is a press mold, and 48 is a heat deformable resin.

Claims (1)

[Claims] 1 A light beam converter that converts a light beam emitted from a monochromatic light source into a plurality of light beams, which has a sinusoidal phase, and has a sinusoidal phase period P and a diameter 2ω of the light beam emitted from the monochromatic light source. 0.75
The relationship is 2ω/P0.875, and the phase modulation degree is 1.44.
A light beam converter of radian is provided on the output side of the monochromatic light source, and a lens is further provided on the output side of the light beam converter to exhibit a rectangular intensity distribution in the x direction and a Gaussian intensity distribution in the y direction. A light beam generator characterized by generating a light beam.