JPH04241312A - Optical scanner - Google Patents

Abstract

PURPOSE:To provide the optical scanner which can correct an constant velocity property and image distortions while reducing the size over the entire part of the device. CONSTITUTION:The optical scanner has a semiconductor laser 30 which emits a light beam 15, a hologram disk 16 which deflects the light beam 15 by diffraction to optically scans the beam on an image plane 14 and an ftheta correcting optical system 10 which is disposed between the hologram disk 16 and the image plane 14 and corrects the constant velocity property, curvature of field and comatic aberration of the light beam 18 on the image plane 14. The ftheta correcting optical system 10 is constituted of a convex lens 11 and concave lens 12 formed to the shapes to correct the constant velocity property and curvature of field and is disposed that its optical axis deviates from the optical axis of the deflected light beam 18 in order to correct the comatic aberrations. The convex lens 11 and the concave lens 12 are arranged in order of the convex lens 11 and the concave lens 12 from the side nearer the hologram disk 16 on the optical path of the deflected light beam 18.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly to an optical scanning device suitable for realizing uniform speed scanning and aberration-free scanning.

0002

[Prior Art] Conventionally, optical scanning devices used in laser beam printers and the like include a rotating polygon mirror as an optical deflector that deflects a light beam from a semiconductor laser, etc. There is one equipped with an fθ correction optical system for scanning the image plane at a constant speed and forming an image without aberration.

FIG. 10 schematically shows the state of optical scanning when such fθ correction is not performed.

In the same figure, considering the case where collimated light deflected by an optical deflector (not shown) is incident on the imaging convex lens 50 having a focal length f at a deflection angle θ, in the case of constant angular velocity deflection, the angular velocity ω and time t, θ=
ω・t, and in a normal optical system, the image height y is y=f・
tan(ωt).

Therefore, the beam velocity v on the image plane 51
is v=f·ω(sec2(ωt)), and the scanning beam 55 does not exhibit uniform velocity. Furthermore, as the deflection angle θ increases, the image plane tends to curve as shown in 59. That is, the scanning beam 55 produces field curvature, which is a type of aberration, on the image plane 51.

For this reason, as an optical system for correcting such uniform velocity and field curvature, correction optical systems 60 and 70 as shown in FIGS. 11 and 12, for example, have been proposed.

In FIG. 11, a correction optical system 60 consists of two large lenses, namely a concave lens 61 and a convex lens 62. Each of these lenses 61 and 62 is thick. The correction optical system 60 has a converging function in addition to a correction function, and a convex lens 62 is disposed on the side closer to the image plane to form a scanning beam on the image plane. Here, in the correction optical system 60, since the deflection angle of the scanning beam is expanded by the concave lens 61, the size of the convex lens 62 necessary to cover the scanning beam whose deflection angle has been expanded is To prevent the lens from becoming too large, the convex lens 62 is replaced by the concave lens 6.
It is located relatively close to 1. Therefore, these lenses 61 and 62 are arranged at narrow intervals as shown in the figure.

In FIG. 12, a correction optical system 70 consists of three large lenses, namely a concave lens 71, a convex lens 72, and a cylindrical lens 73. These lenses 7
1, 72, and 73 are each made thick. Lenses 71 and 72 are the same as lenses 61 and 6 in FIG.
2, and therefore these lenses 7
1, 72, and 73 are arranged at narrow intervals in this order from the side closer to the optical deflector in the optical path of the scanning beam. The cylindrical lens 73 is used to correct the tilt of the rotating polygon mirror.

On the other hand, there is an optical scanning device that uses a hologram instead of the above-mentioned rotating polygon mirror as an optical deflector. When using a hologram, a single hologram can have both deflection and convergence functions, making it possible to configure an optical scanning device without an imaging optical system, which is advantageous from the standpoint of size and weight reduction. It is said that

0010

The conventional correction optical system described above enables aberration-free scanning, but has the problem that the lens is thick and large, resulting in high lens cost. Furthermore, when such a correction optical system is used, there is a problem in that the entire optical scanning device inevitably becomes larger due to the need to hold a large lens.

On the other hand, in the conventional hologram scanner using the above-mentioned hologram, it is difficult to reduce aberrations such as coma and curvature of field when performing optical scanning with a single hologram. Scanning is difficult to implement. Furthermore, there is a problem that the uniform velocity of the scanning beam is poor. In particular, comatic aberration is a problem because it occurs as an aberration unique to holograms. In other words, in optical scanning using the aforementioned rotating polygon mirror, comatic aberration does not occur because the light enters the lens perpendicularly, but in optical scanning using a hologram disk, the light enters the lens at a large angle of view. is incident, so comatic aberration becomes a problem.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an optical scanning device capable of correcting uniform velocity and image distortion while reducing the size of the entire device. .

[0013]

[Means for Solving the Problems] In order to achieve the above-mentioned problems, the optical scanning device of the first invention of the present application includes a light source that emits a light beam, and a device that deflects the light beam and performs optical scanning on an image plane. an fθ correction optical system disposed between the optical deflector and the image plane to correct at least uniformity of the light beam on the image plane and curvature of field; The fθ correction optical system is composed of a convex lens and a concave lens shaped to correct uniform velocity and field curvature. , are arranged in the order of concave lenses.

In order to achieve the above-mentioned object, the optical scanning device of the second invention of the present application includes a light source that emits a light beam, a hologram disk that deflects the light beam by diffraction and scans the light beam on an image plane. , an fθ correction optical system disposed between the hologram disk and the image plane to correct uniformity of the light beam on the image plane, curvature of field, and coma aberration;
The θ correction optical system is composed of a convex lens and a concave lens shaped to correct uniform velocity and curvature of field, and is arranged so that the optical axis is shifted from the optical axis of the deflected light beam to correct coma aberration. The convex lens and the concave lens are arranged on the optical path of the deflected light beam in the order of the convex lens and the concave lens from the side closest to the hologram disk.

[0015]

In the optical scanning device according to the first aspect of the present invention, when the light source emits a light beam, the optical deflector deflects the light beam to scan the image plane. Here, the fθ correction optical system disposed between the optical deflector and the image plane is composed of a convex lens and a concave lens shaped to correct uniform velocity and field curvature, and the convex lens and concave lens are deflected. Convex lenses and concave lenses are arranged in this order on the optical path of the light beam from the side closest to the optical deflector. Therefore, the deflection angle of the scanning beam between the convex lens and the concave lens is reduced by the convex lens, and the size of the concave lens required to cover the scanning beam with such a reduced deflection angle is made relatively small. At the same time, the distance between the convex lens and the concave lens can be increased. scanning bee
When the scanning beam passes through the concave lens, the deflection angle of the scanning beam is expanded to a desired angle, and the scanning beam is focused on the image plane by the converging action of the convex lens in the preceding stage. At this time, the convex lens and the concave lens correct the uniformity of the light beam on the image plane and the curvature of field. As a result of the above, even if these convex lenses and concave lenses are constructed as thin lenses, it is possible to correct the uniform velocity of the light beam on the image plane and the curvature of field without degrading the scanning quality. can.

In the optical scanning device according to the second aspect of the present invention, when the light source emits a light beam, the hologram scanner deflects the light beam by diffraction and scans the light beam on the image plane. Here, the fθ correction optical system disposed between the hologram scanner and the image plane is composed of a convex lens and a concave lens shaped to correct uniform velocity and field curvature, and the optical axis is adjusted to correct coma aberration. The convex lens and the concave lens are arranged offset from the optical axis of the deflected light beam, and the convex lens and the concave lens are arranged on the optical path of the deflected light beam in the order of the convex lens and the concave lens from the side closest to the hologram disk. There is. For this reason, the convex lens reduces the deflection angle of the scanning beam between the convex and concave lenses, thus reducing the size of the concave lens required to cover the scanning beam with such a reduced deflection angle. The distance between the convex lens and the concave lens can be increased while reducing the size. When the scanning beam passes through the concave lens, the deflection angle of the scanning beam is expanded to the desired angle, and the convergence effect of the convex lens in the previous stage further reduces the deflection angle of the scanning beam.
The image is formed on the image plane. At this time, the convex lens and the concave lens correct the uniformity of the light beam on the image plane, curvature of field, and coma aberration. As a result of the above, even if these convex lenses and concave lenses are configured as thin lenses, it is possible to correct the uniform velocity of the light beam on the image plane, as well as correct the field curvature and coma aberration, without degrading the scanning quality. It can be carried out.

From the following examples of the present invention, these effects of the present invention will become clearer, and other effects of the present invention will become clearer.

[0018]

Embodiment FIG. 1 shows a correction optical system according to an embodiment of the present invention.

In the figure, a correction optical system 10 is composed of a meniscus-shaped convex lens 11 and a concave lens 12. Scanning beam 18 deflected by an optical deflector (not shown)
is refracted in two stages by a convex lens 11 and a concave lens 12, and is imaged on an image plane 14. In this embodiment, especially the concave lens 1
The second surface of No. 2 is configured to have an aspherical shape in order to enhance the effect of correcting field curvature and uniform velocity. Therefore, the imaging surface becomes a flat surface, that is, the curvature of field is corrected. Image plane 14
The imaging position y at is proportional to the deflection angle θ (y=f・θ
), and the scanning beam 18 at the image plane 14 scans at a constant speed.

FIG. 2 shows an optical scanning device using the correction optical system 10 of FIG. 1 and a hologram disk as an optical deflector.

In the figure, the optical scanning device is equipped with a hologram disk 16. The hologram disk 16 includes a plurality of holograms 17 arranged along the circumferential direction on a disk substrate. Each hologram 17 is created by the interference of divergent spherical waves from points O and R. The hologram disk 16 is rotated in the direction of the arrow by a motor (not shown).

The optical scanning device includes a semiconductor laser 30 constituting an example of a light source, and an incident light beam that is emitted from the semiconductor laser 30 and is collimated through a collimator lens 31. The beam 15 is configured to be incident on the hologram 17.

Here, the hologram disk surface is assumed to be the XY plane, and the rotation axis 20 of the hologram disk 16 is assumed to be the Z axis.

In the optical scanning device constructed in this way, the light beam 15 incident on the hologram 17 is output as a diffracted light beam 18. At this time, the light beam 1
8 is deflected at a deflection angle β due to the diffraction effect of the hologram 17. As a result, as the hologram disk 16 rotates, the image plane 14 is scanned from A to B. Here, in an optical system including only one hologram disk 16, there is a limit to uniform velocity, curvature of field, and reduction of coma aberration, as described above.

For this reason, in this embodiment, the correction optical system 10 shown in FIG. 1, consisting of a convex lens 11 and a concave lens 12, is arranged between the hologram 17 and the image plane 14. A YZ sectional view at this time is shown in FIG. 3, and an AA sectional view in FIG. 3 is shown in FIG. 4, respectively.

In this case, the uniformity of the scanning beam 18 and the curvature of field are corrected by configuring the second surface of the concave lens 12 as an aspheric surface.

The comatic aberration caused by the hologram 17 is an aberration in which the tail direction is inward (in the direction of the optical axis). In order to cancel this coma aberration, the optical axis of the correction optical system 10 is tilted with respect to the optical axis of the light beam 18 which is the light emitted from the hologram 17 (i.e., the light incident on the correction optical system 10), and the optical axis is corrected. The correction optical system 10 is arranged in such a position that outward coma aberration occurs in the optical system 10 alone. 5 to 7 are explanatory diagrams thereof.

In FIG. 5, the optical axis 21 of the optical beam 18 incident on the lens 11 corresponds to the optical axis 21 of the correction optical system 10.
2, that is, when the axes of the convex lens 11 and the concave lens 12 are rotated clockwise, outward coma aberration occurs on the image plane 14 as shown in FIG.

FIG. 7 shows a case where both eccentricity and rotation are applied to the correction optical system 10. The first vertex A1 of the convex lens 11 is decentered in the Y1 axis direction and moved to the position A1a,
Rotate clockwise around A1a. That is, in FIG. 7, the convex lens 11 is rotated as indicated by 11a, and the concave lens 12 is similarly rotated as indicated by 12a. In this case too,
Outward coma aberration occurs on the image plane, which can cancel out inward coma aberration caused by the hologram. In this manner, by imparting either or both of tilt and eccentricity to the optical axis of the correction lens system 10, it is possible to correct not only uniform velocity and field curvature but also coma aberration at the same time.

As described above, the shapes of the convex lens 11 and the concave lens 12 for correcting uniform velocity and curvature of field, as well as the arrangement of the optical axis 22 for correcting coma aberration, have been optimized.
The scanning performance shown in FIGS. 8 and 9 was obtained using the optical scanning device shown in FIG.

FIGS. 8(a) to 8(d) show lateral aberration curves on the image plane 14. Of these, Figure 8(a) is for the Y direction at the center of the scan, Figure 8(b) is for the X direction at the center of the scan, and Figure 8(c) is for the X direction at the center of the scan.
is about the Y direction at the scanning end, and is shown in Fig. 8(d).
is about the X direction at the scanning end. In addition, for comparison in the figure, the lateral aberration curve when the correction optical system 10 is removed from the configuration of FIG. .

As can be seen from the curve a in these figures, when the correction optical system 10 is removed, inward coma aberration occurs in the Y direction and field curvature occurs in the X direction. On the other hand, as can be seen from curve b, in the case of this example, these comatic aberrations and field curvature are effectively corrected.

FIG. 9 is a graph showing uniform velocity. In the figure, the horizontal axis represents the scanning position, and the vertical axis represents the deviation from the uniform speed scanning reference position. For comparison in the figures, the constant velocity curve when the correction optical system 10 is removed from the configuration of FIG. Indicated by

As can be seen from the figure, in the case of this embodiment, it is possible to keep the deviation within ±0.5 mm over the scanning width of 110 mm (one side scanning area from the scanning center M to the scanning end B in FIG. 2). did it.

Note that when the hologram 17 is provided with a convergence function, the convergence power of the hologram 17 and the correction optical system 10
The correction effect at the image plane 14 can be maximized by optimally dispersing the convergence power. If the hologram 17 does not have a convergence function, its role as an optical deflector is similar to that of the rotating polygon mirror described above. The difference here is that in the case of the hologram 17, the light enters the disk plane obliquely and exits obliquely, whereas in the case of the rotating polygon mirror, the incident beam and the outgoing beam are in the same plane. In the former case, comatic aberration occurs, so as mentioned above, the optical axis 22 of the correction optical system 10 is aligned with the output light beam 1 from the hologram 17.
It is desirable to tilt the optical axis 21 of the lens 8.

In the above embodiment, the incident light beam 15
is collimated light; however, as long as the convergence powers of the hologram 17 and the correction optical system 10 are appropriately set, the incident light beam 15 may be a diverging light or a convergent light.

As described above, according to this embodiment, the distance between the convex lens 11 and the concave lens 12 constituting the correction optical system 10 can be sufficiently widened, and the thickness of the convex lens 11 and the concave lens 12 can be made thin. Therefore, the lens cost can be kept low. Furthermore, in order to hold the convex lens 11 and the concave lens 12 which are constructed thinly in this way, a holding member having a relatively low strength and a simple construction is sufficient, and it is small and compact.
This is advantageous from the viewpoint of weight reduction.

In this embodiment, the hologram disk 16 is particularly used as an optical deflector, and by tilting the optical axis of the correction optical system 10 with respect to the optical axis of the light beam emitted from the hologram 17, the hologram 17 is Since the comatic aberration caused by this is canceled out, it is possible to provide an optical scanning device that satisfies the demands for smaller and thinner optical scanning devices and can correct uniform velocity and image distortion.

[0039]

As explained in detail above, according to the optical scanning device of the first invention, the fθ correction optical system is composed of a convex lens and a concave lens shaped to correct uniform velocity and field curvature. The convex lenses and concave lenses are arranged on the optical path of the deflected light beam in the order of convex lenses and concave lenses from the side closest to the optical deflector, so these convex lenses and concave lenses are spaced apart and can be used as thin lenses. Even with this configuration, the uniformity of the light beam on the image plane and the curvature of field can be corrected without deteriorating the quality of scanning.

Furthermore, according to the optical scanning device of the second invention of the present application, a hologram scanner is used as the optical deflector, and f
The θ correction optical system is composed of a convex lens and a concave lens shaped to correct uniform velocity and field curvature, and the optical axis is shifted from the optical axis of the deflected light beam in order to correct coma aberration. The convex lenses and concave lenses are arranged on the optical path of the deflected light beam in the order of convex lenses and concave lenses from the side closest to the hologram disk.
Even if these convex lenses and concave lenses are spaced apart and configured as thin lenses, the uniform velocity of the light beam on the image plane, field curvature, and coma aberration can be corrected without deteriorating the scanning quality. I can do it.

As a result of the above, according to the present invention, it is possible to realize an optical scanning device that can correct velocity uniformity and image distortion while reducing the size of the entire device.

[Brief explanation of the drawing]

FIG. 1 is a scanning plan view of a correction optical system that is an embodiment of the present invention.

FIG. 2 is a perspective view of a schematic configuration of an optical scanning device using the correction optical system of FIG. 1;

FIG. 3 is a YZ cross-sectional view of the optical scanning device in FIG. 2;

FIG. 4 is a sectional view taken along line AA of the correction optical system in FIG. 3;

FIG. 5 is a cross-sectional view of the correction optical system of FIG. 1 showing an optical arrangement that generates outward coma aberration.

6 is a schematic plan view of an image plane generating outward coma aberration due to the optical arrangement of FIG. 5; FIG.

FIG. 7 is an enlarged cross-sectional view of the correction optical system in FIG. 5 when both eccentricity and rotation are applied.

8 is a characteristic diagram showing lateral aberration on the image plane when optical scanning is performed using the correction optical system of FIG. 1. FIG.

9 is a characteristic diagram showing the uniform velocity of a scanning beam on an image plane when optical scanning is performed using the correction optical system of FIG. 1; FIG.

FIG. 10 is a scanning plan view of a conventional example that does not use a correction optical system.

FIG. 11 is a cross-sectional view of an example of a conventional correction optical system.

FIG. 12 is a sectional view of another example of a conventional correction optical system.

[Explanation of symbols]

10 Correction optical system 11 Convex lens 12 Concave lens 14 Image plane 15 Incident light beam 16 Hologram disk 17 Hologram 18 Scanning beam 21 Optical axis of incident light beam 22 Optical axis of correction optical system 30 Semiconductor laser

Claims (2)

[Claims] 1. A light source that emits a light beam, a light deflector that deflects the light beam to scan the light beam on an image plane, and a light source disposed between the light deflector and the image plane, The fθ correction optical system is provided with an fθ correction optical system that corrects at least uniform velocity and field curvature of the light beam on the image plane, and the fθ correction optical system has a shape that corrects the uniform velocity and field curvature. The light is composed of a convex lens and a concave lens, and the convex lenses and concave lenses are arranged on the optical path of the deflected light beam in the order of the convex lens and the concave lens from the side closest to the optical deflector. scanning device. 2. A light source that emits a light beam, a hologram disk that deflects the light beam by diffraction and scans the light beam on an image plane, and a hologram disk that is disposed between the hologram disk and the image plane, and that is arranged between the hologram disk and the image plane, The fθ correction optical system corrects uniform velocity, field curvature, and comatic aberration of the light beam on the image plane, and the fθ correction optical system corrects the uniform velocity and field curvature. The optical axis is arranged to be offset from the optical axis of the deflected light beam in order to correct the comatic aberration, and the convex lens and the concave lens are arranged to correct the comatic aberration. An optical scanning device characterized in that a convex lens and a concave lens are arranged in this order on the optical path of the beam from the side closest to the hologram disk.