JPS60172012A - Light scanning optical system - Google Patents

Abstract

PURPOSE:To realize easily the shape of a scanning spot which is required for executing good light sanning by constituting the titled system so that a direction orthogonal to a joint surface of a semiconductor laser in a light scanning optical system corresponds in parallel to a main scanning direction. CONSTITUTION:Laser light L' from a semiconductor laser 10 is converted to a parallel luminous flux by a collimator lens 11, and its luminous flux section becomes an elliptical shape L2 having a long axis in the Y direction. Subsequently, the luminous flux transmits through a 1/2 wavelength plate 12, and the electric field vibrating direction rotates from the X direction to the Y direction, in a state that the luminous flux section shape remains held. Next, said luminous flux transmits through a cylindrical lens 4', is made incident on a hologram lattice disk 1, and executes main scanning to a surface to be scanned 9. In this way, when the Y direction orthogonal to a joint surface of the semiconductor laser is made to correspond in advance in parallel to the main scanning direction, a power of the first cylindrical lens itself used for the incident side to the disk 1 is reduced, and also a desired elliptical luminous flux section is obtained on the disk 1.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a light scanning optical system.

(Prior art) A laser beam is deflected by a deflecting means using a rotating polygon mirror, a hologram grating disk, etc., and the deflected laser beam is focused as a scanning spot on the surface to be scanned. An optical scanning method is known in which a surface to be scanned is linearly main-scanned.

FIG. 1 schematically shows only the main parts of an example of such an optical scanning optical system. Hereinafter, the outline of the above-mentioned optical scanning method will be explained using an example of this optical system.

In FIG. 1, numeral 1 is a hologram grating disk, numeral 2 is a motor, numeral 3 is a fixture, numeral 4 is a cylindrical lens, numerals 5 and 6 are plane mirrors, numeral 7 is an fθ lens, numeral 8 is a cylindrical lens, numeral 9 indicate the surfaces to be scanned, respectively.

The hologram grating disk 1 has a disc shape as shown in FIG. 2, and has a plurality of optically equivalent hologram diffraction gratings 1-1 (six in the figure) on one surface of a transparent circular substrate.
．． 1-2. . . , 1-i, . . . are arranged in a circular ring. The hologram diffraction grating 1-i is a linear diffraction grating, and is a surface relief hologram, or
It is configured as a volume type phase hologram or the like.

The hologram grating disk 1 is fixedly mounted on the shaft of the motor 2 by means of a fixture 3, as shown in FIG.
It is designed to be rotated by motor 2.

Although not shown, the laser light from the laser light source is the first
As shown in the figure, the light passes through the cylindrical lens 4, is reflected by the plane mirror 5, is directed toward the hologram grating disk l at a predetermined angle of incidence, and is incident on one of the hologram diffraction gratings on the hologram grating disk 1. FIG. 3 shows this state diagrammatically. In FIG. 3, the symbol L1 indicates a beam cross section of the incident laser beam.

The direction of the grating lines of the diffraction grating in the hologram diffraction grating 1-i is the A-A line, that is, the hologram diffraction grating 1
-1 and the center of rotation of the hologram grating disk l.

When laser light enters the hologram diffraction grating 1-1, diffracted light is generated by the hologram diffraction grating l-i. When the hologram grating disk 1 rotates, the direction of the grating lines of the hologram diffraction grating 1-1 relative to the incident laser beam rotates, so that the direction of the diffracted light follows a conical surface with the apex at the incident position of the laser beam. Then it changes.

Since each hologram diffraction grating 1-i formed on the hologram grating disk 1 is optically equivalent to each other,
As the hologram grating disk 1 rotates, the deflection of the diffracted light is repeated each time the hologram diffraction grating on which the laser light is incident is switched.

Now, the diffracted light generated by the hologram diffraction grating is
As shown in the figure, after being reflected by the plane mirror 6, fθ
Scanning surface 9 via lens 7 and cylindrical lens 8
It focuses into a spot shape. This spot-like convergence point is a scanning spot.

When the hologram grating disk 1 rotates, the scanning spot is linearly displaced on the surface to be scanned 9 and main scans the surface to be scanned 9 . The direction in which the scanning spot moves on the surface to be scanned 9 is called a main scanning direction, and the direction on the surface to be scanned that is perpendicular to the main scanning direction is called a sub-scanning direction. In FIG. 1, the direction perpendicular to the drawing is the main scanning direction, and the vertical direction of the drawing is the sub-scanning direction.

Note that when optical scanning is performed for reading a document, the document to be read is placed on the surface to be scanned, and when optical scanning is performed for writing optical information, a photosensitive medium such as a photoconductive photoreceptor is placed. is placed on the surface to be scanned.

FIG. 4 is an explanatory diagram showing the optical system of FIG. 1 viewed from the sub-scanning direction. When the hologram grating disk 1 rotates, the scanning spot by the diffracted light repeats main scanning from 21 points to 22 points on the scanned surface 9. Po
The point is the center point of the main scanning area, and the scanning spot is 2
When it is at the 0 point, the laser light is as shown in Figure 3.
The light is incident on the center of the hologram diffraction grating 1-i.

Now, as shown in FIG. 1, laser light enters the hologram grating disk 1 via the cylindrical lens 4. Therefore, as shown in FIGS. 3 and 4, the cross-sectional shape (indicated by reference numeral Ll in FIG. 3) of the laser beam incident on the hologram diffraction grating is an ellipse flat in the main scanning direction. Regarding why we do this,
This will be explained below. In optical scanning, linearity of the main scanning line, that is, the trajectory of the main scanning by the scanning spot is generally required.

However, as mentioned above, since the diffracted light by the hologram diffraction grating is deflected so as to draw a conical surface with the apex at the point of incidence on the hologram grating disk 1, the angle of incidence on the plane mirror 6 varies.

Therefore, the problem is how to ensure the linearity of the main scanning line despite variations in the angle of incidence on the plane mirror 6.

This problem is solved by the incident position on the hologram grating disk 1,
In other words, the generation position of the diffracted light by the hologram diffraction grating and the linear main scanning line may be connected in a conjugate relationship in the sub-scanning direction. For this purpose, an anamorphic optical system such as a cylindrical lens, toroidal lens, or cylindrical mirror is required.

In the optical scanning device shown in FIG. A cylindrical lens 8 is used as an optical system. That is, the fθ lens 7 (this is a spherical lens).

) and the cylindrical lens 8 connect the main scanning line and the generation position of the diffracted light in a conjugate relationship in the sub-scanning direction.

Incidentally, the spot cross-sectional shape of the polarized laser beam focused in a spot shape on the surface to be scanned 9 is required to be an ellipse that is slightly elongated in the sub-scanning direction in view of the quality of scanning.

This elliptical shape is 5 e.g.

The width is 100 μm in the main scanning direction (short axis direction) and 120 μm in the sub scanning direction (long axis direction).

The size of the scanning spot depends on the resolution of optical scanning)
Regulated, but required for good scanning, are:
The shape of the scanning spot is preferably an ellipse that is slightly longer in the sub-scanning direction, as described above, and the long axis to short axis is preferably (1±0.1) : (1,2±01). It is said that With such a scanning spot shape, the light intensity distribution within the scanning spot becomes nearly uniform, which is a problem.

In this case, the polarized light beam f-'&, f-theta by the hologram diffraction grating, and the -cylindrical lens 7 are used to focus the elliptical spot on the scanned surface 9. Since the trical lens 8 does not have a longitudinal direction, the f
The lens system consisting of the θ lens 7 and the cylindrical lens 8 has different power in the main scanning direction and in the sub-scanning direction. Regardless of the difference in power between the main scanning direction and the sub-scanning direction, if a desired elliptical spot as described above is to be obtained on the scanned surface 9, the hologram grating disk l As shown in FIG. 3 or FIG. 4, the cross-sectional shape of the laser beam incident on the laser beam needs to be an ellipse flat in the main scanning direction.

That is, as is well known, a laser beam is a Gaussian beam, and when a Gaussian beam is focused by an optical system with a constant power, the larger the beam diameter, the better the focusing performance is. However, if we consider the power of the lens system composed of the fθ lens 7 and the cylindrical lens 8 in the optical system shown in FIG. 1, the power acting in the main scanning direction is the power of the fθ lens 7. However, the power acting in the sub-scanning direction is the power of the fθ lens 7 and the power of the serial/trical lens 8, and the combined power is larger in the sub-scanning direction than in the main scanning direction.

Therefore, as described above, the beam cross section of the laser beam incident on the hologram grating disk 1 must have an elliptical shape that is flat in the main scanning direction.

In the example described now, the laser beam is deflected using a hologram grating disk, but the same applies to the case where the laser beam is deflected using a rotating polygon mirror. That is, even in this case, in order to prevent the main scanning line from wobbling in the sub-scanning direction due to the so-called surface sagging of the reflecting surface of the single-rotation polygon mirror, the deflection position of the rotation polygon mirror and the main scanning line are adjusted in the sub-scanning direction. This is because it is necessary to connect them to a conjugate relationship in the direction.

Note that the fθ lens 7 is only used to make the main scanning at a constant speed, and in some cases, a normal spherical lens may be used.

Now, a semiconductor laser is known as a laser light source. Semiconductor lasers are smaller, cheaper, and consume less power than laser light sources such as gas lasers, and have the characteristics of being able to directly modulate the emission intensity by driving current, making them ideal for optical scanning devices. Suitable as a laser light source.

Therefore, light scanning optical systems that use semiconductor lasers as laser light sources have been proposed.

(Objective) Therefore, an object of the present invention is also to provide a novel optical scanning optical system that uses a semiconductor laser as a laser light source.

(composition) The present invention will be explained below.

The light scanning optical system of the present invention includes a semiconductor laser as a laser light source, a collimating lens, a deflection means, first and second cylindrical lenses, and an optical lens.

The collimating lens converts the laser light emitted from the semiconductor laser into a parallel beam.

The deflection means is a means for deflecting the laser beam, and a rotating polygon mirror, a hologram grating, or the like is used as the deflection means.

The first cylindrical lens is arranged between the collimating lens and the deflection means.

The second cylindrical/trical lens is disposed between the deflection means and the surface to be scanned.

A condensing lens is arranged between the deflection means and the second cylindrical lens.

A semiconductor laser serving as a laser light source has a direction perpendicular to its bonded surface parallel to the main scanning direction.

A specific example will be explained below.

FIG. 5 schematically depicts one embodiment of the invention.

In order to avoid complications, please refer to the following for items that are not likely to be confused with each other.
The same reference numerals as in FIG. 1 are given. This example is
The present invention is applied to the optical system shown in FIG. 1, and equipment having the same reference numerals as in FIG. 1 is arranged in the same manner as in the optical system of FIG.

In FIG. 5, reference numeral 10 indicates a semiconductor laser, reference numeral 11 indicates a collimating lens, reference numeral 12 indicates a 1/2 wavelength plate, and reference numeral 4' indicates a first silicate/trical lens. The fθ lens 7 is a condensing lens, and the cylindrical lens 8 is a second cylindrical lens.
It is a trical lens. Further, the hologram grating tisf 1, the motor 2, the fixture 3, and the plane mirror 5.6 constitute deflection means.

Regarding the semiconductor laser 10, the X direction and Y direction are determined as shown in FIG. The X direction is a direction parallel to the bonding surface of the semiconductor laser 10, and the Y direction is perpendicular to the bonding surface. The laser beam L' can be emitted in a direction perpendicular to both the X and 7 directions.

Now, as is well known, the laser light L' emitted from the semiconductor laser is a divergent light beam, and the divergence angles are different in the X direction and in the X direction (FIG. 6).

As shown in FIG. 5, the X direction in the semiconductor laser 10 is the vertical direction due to the fifth factor, and the X direction, that is, the direction perpendicular to the bonding surface is the direction perpendicular to the drawing of FIG. This Y direction corresponds in parallel to the main scanning direction. The Y direction corresponds parallel to the main scanning direction if we assume that the laser beam emitted from the semiconductor laser 1o is given an X-Y coordinate axis and is placed in one line on the optical path along with the light. , which means that when this laser light reaches the scanned surface, the Y direction on the scanned surface becomes parallel to the main scanning direction.

Now, in FIG. 5, the laser beam LJ emitted from the semiconductor laser 10 is converted into a parallel beam by the collimating lens 11, and the cross section of the beam is X as shown in FIG.
It becomes an elliptical shape L2 whose major axis direction is the direction. Next, the laser beam passes through the half-wave plate 12, and the electric field vibration direction is rotated from the X direction to the Y direction while maintaining the cross-sectional shape of the beam.

Next, it passes through the cylindrical lens 4', enters the hologram grating Tiffl through the plane mirror 5, and is deflected many times by the rotation of the hologram grating Tiffl.
The surface to be scanned 9 is main scanned.

As mentioned above, in an optical scanning device, the cross-sectional shape of the beam beam at the incident part of the laser beam incident on the hologram grating TISF, which serves as the deflection means, must be an ellipse long in the direction parallel to the main scanning direction. (See Figures 3 and 4). However, the laser beam L' emitted from the semiconductor laser already has an elliptical shape long in the Y direction when it is converted into a parallel beam (FIG. 7). Therefore, as in the present invention, if the Y direction perpendicular to the junction surface of the semiconductor laser is made parallel to the main scanning direction, the cross-sectional shape of the beam of the incident laser beam on the hologram grating can be changed. Since the longitudinal direction also corresponds parallel to the Y direction, the power of the first/linear lens itself used on the incident side to the hologram grating disk can be reduced, and the , a desired elliptical beam cross section can be obtained.

Note that the 1/2 wavelength plate 12 is used to increase the efficiency of using light for optical scanning. In other words, the diffraction efficiency of the hologram diffraction grating depends on the polarization direction of the incident laser beam, so the diffraction efficiency is set to 1/2 so that the diffraction efficiency is the highest.
The wavelength plate 12 adjusts the direction of the electric field vibration plane of the laser beam L'.

When a spheroidal chain is used as the deflection means, the 1/2 wavelength plate 12 is not necessary.

Note that if the Y direction does not correspond parallel to the main scanning direction but at an angle to the main scanning direction, the long axis direction of the scanning spot will extend with respect to the sub scanning direction, resulting in good scanning. It is not possible to obtain a scanning spot with the desired shape.

Also, if the Y direction corresponds orthogonally to the main scanning direction,
In order to obtain the traveling spot having the desired shape, the conditions imposed on the optical system become severe.

In this case, the collimator lens 11 needs to have a large diameter, and the first cylindrical lens needs to have a strong power.

Finally, a specific example 7al of using a rotating polygon mirror as a deflecting means will be explained.

FIG. 8 shows an example of the optical system according to the present invention developed in the direction of the optical path from the optical plane to the surface to be scanned 9. As shown in FIG. FIG. 8 il+ shows the state seen from the sub-scanning direction, and FIG. 8 (old version) shows the state seen from the main scanning direction.

Reference numeral 100 indicates a semiconductor laser as a laser light source. Since the semiconductor laser 100 as a laser light source is extremely small, it is shown in FIG.

Shown as points. This semiconductor laser 100,
The direction perpendicular to the bonding surface corresponds to the vertical direction of the drawing in FIG. 8 FI,l, and the direction perpendicular to the drawing in FIG. 8 in+, which of course corresponds to parallel to the main scanning direction.

Furthermore, as mentioned above, in this optical system, a rotating polygon mirror is used as the deflecting means, and the point at which the laser beam is deflected by the rotating polygon mirror is indicated by the symbol q.

The collimating lens designated by numeral 101 has a lens diameter of io.
, 511111, has a focal length of 91 mm and is installed in the lens barrel. The length of this lens barrel in the optical axis direction is 9
．． 8mrn, and the distance from the semi-quadram laser 100 to the incident end of the collimating lens 101 is 37rnm.
It is.

Note that the laser oscillation wavelength of the semiconductor laser 100 is 78
0 mm, and the opening angle of the luminous flux is 28.030 in the direction perpendicular to the bonding surface and 9340 in the direction parallel to the bonding surface with respect to the half value of 1/e2.

The first cylindrical lens 102 has a rectangular shape with a width of 12 m+a in the direction corresponding to the main scanning direction and lQmll in the direction corresponding to the sub-scanning direction, a radius of curvature of 532 mm on the incident side, and a radius of curvature of 532 mm on the exit side. The radius of curvature of is infinite, the distance between lens surfaces on the original axis is 3 oim, and the focal length is to4 oim.

The distance from the exit side end of the collimator lens 101 to the entrance side lens surface of the first cylindrical lens 102 is 36.5111 m, and therefore the distance between the entrance side lens surface and the semiconductor laser 100 is 5o shorter. In addition, the exit side lens surface of the first cylindrical lens 102 and the deflection point q
There are 58 dragons in front of the upper tail of the optical axis.

The fθ lens 103 as a condensing lens has a radius of curvature of the entrance side lens surface of -583,759 mm, a radius of curvature of the exit side lens surface of -166,754 mm+, a distance between lens surfaces on the optical axis of 12 mm, and a focal length of It is 300,111m long.

The optical axis distance from the deflection point q to the incident side lens surface of the fθ lens 103 is &@100 mm.

Next, the second cylindrical lens 104 has a length of 23
0 mm, width 161 mm, the radius of curvature of the entrance side lens surface is 17 mTL, the radius of curvature of the exit side lens surface is infinite, and the distance between the lens surfaces on the optical axis is 5 Tl 1 m.
The focal length is 32.9 mm.

The distance on the optical axis between the exit side lens surface of the fθ lens 103 and the entrance side lens surface of the cylindrical lens 1040 is 266
m+a, the exit side lens surface of the same lens 104 and the scanned surface 9
The distance between them on the optical axis is 315 m+a.

With such a light scanning optical system, it is possible to obtain an elliptical scanning spot f (major axis length: 120 μm, short axis length: 10011 m) on the scanned surface 9, with the major axis aligned with the sub-scanning direction, and Optical scanning with a scanning length of 230 m11+ was successfully achieved.

(Effects) As described above, according to the present invention, a novel optical scanning optical system using a semiconductor laser as a laser light source can be provided.

In this optical scanning optical system, the direction perpendicular to the cemented surface of the semiconductor laser corresponds parallel to the main scanning direction, so it is easy to achieve the shape of the short spot required for good optical scanning. can be 0

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining the optical scanning method,
Figure 5 is a side view showing one embodiment of the present invention, Figures 6 and 7 are diagrams for explaining the characteristics of laser light emitted from a semiconductor laser, and Figure 8 is a side view showing one embodiment of the present invention. FIG. 7 is an optical layout diagram showing another example developed in the optical path direction. 10.100... semiconductor laser, 4', 102.
...first cylindrical lens, 1.. hologram grating disk, 7.. fθ lens as a condensing lens,
8゜104...Second cylindrical lens, 9...
・Scanned surface, Y--direction perpendicular to the bonding surface of the semiconductor laser.

Claims (1)

[Claims] A semiconductor laser, a collimating lens that collimates the laser beam from the semiconductor laser, a deflecting means for deflecting the laser beam, and a device disposed between the collimating lens and the deflecting means. A first cylindrical lens, a condensing lens disposed between the deflection means and the surface to be scanned, and a second cylindrical lens disposed between the condensing lens and the surface to be scanned. , an optical scanning optical system that focuses laser light from a semiconductor laser onto a scanned surface as a scanning spot into a predetermined spot shape r, and linearly main-scans the scanned surface with the scanning spot. An optical scanning optical system, characterized in that a direction perpendicular to a bonded surface of a semiconductor laser corresponds to parallel to a main scanning direction.