JP3504680B2 - Optical element and light beam scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element for correcting the converging position of a light beam, and a light beam scanning device for scanning an object to be irradiated with the light beam whose converging position is corrected using this optical element. Regarding

[0002]

2. Description of the Related Art As a device for recording characters, images, etc. on a recording material by a light beam, for example, a laser for scanning a laser beam based on computer output information to directly record information such as characters on a recording material such as microfilm. Computer output Micro filmer (Laser CO
M) is known (Japanese Patent Laid-Open No. 55-67722). In such a laser beam recording apparatus, a laser beam is scanned by scanning means such as a rotary polygon mirror (polygon mirror) or a galvanometer mirror, and then imaged on a recording surface of a recording material by a scanning lens such as an f.theta. Lens. , Characters, images, etc. are recorded on the recording material.

By the way, the field curvature generally remains in the scanning lens, that is, ideal (no wavefront aberration).
Even if the laser beam is incident on the scanning lens, there is a phenomenon that the beam waist position does not match the recording surface of the recording material. Further, because the curvature of the scanning lens is not uniform, the laser beam scanned by the scanning means and passing through the scanning lens does not necessarily have a beam waist position on the recording surface (so-called offset). Further, particularly, the semiconductor laser and the optical system have astigmatism, and when the laser beam emitted from the semiconductor laser is used as the laser beam, the main scanning direction of the laser beam is changed by the astigmatism of the semiconductor laser and the optical system. A deviation (so-called astigmatic difference) occurs between the beam waist position in the (meridional direction) and the beam waist position in the sub-scanning direction (sagittal direction).

For example, as shown in FIG. 8, a semiconductor laser 1
The laser beam emitted from the laser beam 50 and collimated by the collimator 152 is scanned by the polygon mirror 154 in the scanning direction (direction of arrow C in FIG. 8), and the f · θ lens 1
When an image is formed on the recording surface 158 of the recording material by 56, as shown in FIG. 9, the beam waist position W _{M in} the meridional direction (arrow M direction in FIG. 9) and the sagittal direction (arrow S direction in FIG. 9) of the laser beam are obtained. Beam waist position W _S
Astigmatism occurs, and the beam waist position in the meridional direction follows the locus shown by the broken line in FIG. 8 with the scanning of the laser beam, and the beam waist position in the sagittal direction is shown in FIG.
Follow the locus shown by the alternate long and short dash line (the locus of such beam waist position is hereinafter referred to as the image plane).

As is clear from FIG. 8, the image plane 160 in the meridional direction and the image plane 162 in the sagittal direction of the laser beam are curved with respect to the recording surface 158, and the degree of curvature is the same as the image plane 160 and the image plane 162. However, the shape of the laser beam applied to the recording surface 158 is distorted, and the characters, images, etc. recorded on the recording surface are partially blurred. In recent years, there has been an increasing demand for a laser beam recording apparatus capable of recording an image of a larger size, and with the increase in size of a recorded image, deterioration of image quality due to the above phenomenon has become a serious problem.

In order to solve the above problem, it is necessary to correct the beam waist position in the meridional direction and the beam waist position in the sagittal direction of the laser beam. In order to realize this, in Japanese Patent Laid-Open No. 1-230017, an electrode pair is attached to an electro-optical medium such as PLZT into which a light beam is incident, in a shape and arrangement for refracting the light beam along one direction. Optical elements have been proposed.

In this optical element, the electro-optic medium has a rectangular shape, and the refractive index inside the medium is also constant.
If no voltage is applied to the electrode pair, no lens action occurs (focal length is infinite). When a voltage is applied to the electrode pair, an electric field is generated in the electro-optical medium, and the refractive index inside the medium changes, but the shape and arrangement of the electrodes cause the electric field strength along the one direction to be uneven, The refractive index greatly changes in the portion where the electric field strength is high inside the medium. As a result, a distribution of the refractive index that is virtually equal to that of a cylindrical lens having a lens action is formed in the electro-optical medium along the one direction, and a lens power is generated to make the focal length in the one direction. It will be finite.

When a light beam of a parallel light beam is incident on the electro-optical medium by the lens power, for example, the light beam is refracted and emitted along the direction, and a beam waist is generated in the direction. Further, the beam waist position changes according to the magnitude of the voltage applied to the electrode pair.
Therefore, the beam waist position of the light beam in the predetermined direction can be corrected by controlling the voltage applied to the electrode pair. As an example, Japanese Patent Laid-Open No. 3-265817 describes that the above optical element is applied to a light beam scanning device to correct the deviation of the beam waist position of the light beam due to temperature change, the field curvature, and the like. .

[0009]

However, in the above optical element, the shape and arrangement of the electrodes are so arranged that the distribution of the refractive index generated inside the electro-optical medium when a voltage is applied matches the ideal distribution of the refractive index. Is difficult to determine, and aberration will occur. This aberration is caused when the distance (focal length) of the light beam emitted from the optical element to the beam waist position is shortened, that is, when the applied voltage is increased and the lens power of the virtual cylindrical lens is increased. There is a problem that the beam diameter at the beam waist position becomes large.

Thus, when the above optical element is applied to a light beam recording apparatus, if the focal length of the optical element is shortened in order to increase the change in the focal length, the beam waist position, that is, the beam diameter at the irradiation surface is reduced. For example, when an image is recorded on the recording material arranged on the irradiation surface by the light beam, the quality of the image recorded by the light beam deteriorates.

The present invention has been made in consideration of the above facts. It is possible to correct the converging position of a light beam in a predetermined direction, and the beam waist diameter is large even when the distance to the converging position is shortened. The purpose is to obtain an optical element that can prevent such a phenomenon.

Further, according to the present invention, there is provided a light beam scanning device capable of correcting the deviation of the focusing position of the light beam with respect to the irradiation surface and preventing the beam waist diameter of the light beam irradiated on the irradiation surface from increasing. The purpose is to obtain.

[0013]

In order to achieve the above object, the optical element according to the invention of claim 1 has a predetermined planar shape.
Formed by stretching the shape in the direction perpendicular to the plane.
The, Rutotomoni is a pillar shape having a pair of parallel planes, have a lens power in a predetermined direction by an applied electric field
An electro-optic medium having an electro-optic effect formed so that the refractive index is uniformly changed, and the pair of parallel planes so that a uniform electric field is applied between the pair of parallel planes inside the electro-optic medium. And an electrode having a shape corresponding to the predetermined shape provided on each of the.

Further, in the invention according to claim 1, it is preferable that the electro-optic medium is PLZT.

A light beam scanning device according to a third aspect of the present invention comprises a light beam emitting means for emitting a light beam and the optical element according to the first or second aspect, and a direction having the lens power is A first optical element arranged on the optical path of the light beam so as to coincide with a first predetermined direction orthogonal to the optical axis direction of the light beam;
A second optical element, which is configured by the optical element described above and is arranged such that a direction having the lens power is orthogonal to an optical axis direction of a light beam and a second predetermined direction orthogonal to the first predetermined direction. Optical element, the first optical element and the second optical element
A scanning optical system that scans a light beam that has passed through the optical element of FIG .
Obtaining the image plane deviation from the reference plane at each position in advance,
The correction data for correcting the image plane deviation is set to each position.
And a storage means for storing in correspondence with
Based on the corrected data thus obtained, the converging position in the first predetermined direction and the converging position in the second predetermined direction of the light beam with which the irradiation target is irradiated respectively match the irradiation surface of the irradiation target. As described above, the control means for controlling the magnitudes of the voltages applied to the electrodes of the first optical element and the electrodes of the second optical element are included.

A light beam scanning device according to a fourth aspect of the present invention comprises a light beam emitting means for emitting a light beam and the optical element according to the first or second aspect, and the direction having the lens power is , An optical element arranged on the optical path of the light beam so as to coincide with a first predetermined direction orthogonal to the optical axis direction of the light beam, and an optical path length of the incident light beam arranged on the optical path of the light beam. Optical path length changing means that can be changed, a scanning optical system that scans an irradiation target with a light beam that has passed through the optical element and the optical path length changing means, and the scanning
On the reference plane at each position along the scanning direction by the optical system
The image plane deviation corresponding to the image plane is obtained in advance, and the image plane deviation is corrected.
For storing the correction data for
Storage means and the correction data stored in the storage means.
On the basis of the light beam, the light beam applied to the object to be irradiated is converged in the first predetermined direction and the second predetermined direction orthogonal to the optical axis direction of the light beam and orthogonal to the first predetermined direction. Control means for controlling the magnitude of the voltage applied to the electrodes of the optical element and the optical path length changed by the optical path length changing means, respectively, so that the light positions match the irradiation surfaces of the objects to be irradiated. I am configuring.

According to the first aspect of the present invention, an electro-optic medium having an electro-optic effect is formed in a predetermined plane shape on the plane.
A pair of parallels formed by stretching in the vertical direction
Together are a pillar shape having a plane, have a lens power in a predetermined direction, uniformly varying the refractive index by an applied electric field
And an electrode having a shape corresponding to the predetermined shape is provided on each of the pair of parallel planes so that a uniform electric field is applied between the pair of parallel planes inside the electro-optic medium. Are configured. Therefore, when a voltage is applied to the electrodes, an electric field is applied between the parallel planes, and when the magnitude of the applied voltage is changed, the strength of the electric field is changed, thereby changing the refractive index of the electro-optical medium in the predetermined direction. However, the magnitude of the lens power can be changed.

Generally, when a light beam is transmitted through an optical element having a lens power in a predetermined direction, the distance between the converging position of the light beam in the predetermined direction (beam waist position in a laser beam) and the optical element is In the case of shortening and correcting the converging position according to the curvature of field of the light beam or the like, it is necessary to increase the lens power of the optical element in the predetermined direction.

However, according to the present invention, the electro-optic medium has a predetermined lens power in advance depending on the shape of the electro-optic medium when no electric field is applied. Therefore, as described above, when the distance between the light beam condensing position and the optical element is shortened and the condensing position is further corrected, the shape of the electro-optic medium is set to have a large lens power, and the electrode By changing the magnitude of the voltage applied in between, it is possible to change the refractive index and the focal length in a predetermined direction, that is, the lens power, according to the curvature of field at the focus position.

As a result, when the distance between the focusing position of the light beam in a predetermined direction and the optical element is shortened as a whole, a predetermined refractive index is obtained by the electro-optical effect from the state where no lens power is generated as in the conventional case. Compared with the case where a high lens power is obtained by generating a distribution, the voltage applied to the electrodes can be lowered and it is not necessary to generate a predetermined refractive index distribution inside the electro-optic medium. it is possible to eliminate the influence of the yield difference Ru good to the difference between the distribution and the ideal refractive index distribution, also it is possible to prevent the beam waist diameter increases when reducing the distance between the optical element and the condensing position It

In the invention described in claim 1, it is preferable that the electro-optical medium is PLZT. PLZT is a solution of lanthanum oxide in lead zirconate titanate, has an electro-optical effect, and has a large secondary electro-optical coefficient (also called Kerr coefficient). The change in the refractive index and the focal length of the electro-optic medium when the voltage applied to the electrodes is changed is proportional to the quadratic electro-optic coefficient. Therefore,
When PLZT is applied to the electro-optic medium, the change in the refractive index and the focal length with respect to the voltage applied to the electrode becomes large, and the magnitude of the change in the voltage applied to the electrode to change the lens power by a predetermined amount becomes small. can do.

In addition to PLZT, liquid crystal, barium titanate (BaTiO ₃ ), potassium tantalate (KTaO) is used as the electro-optical material for forming the electro-optical medium.
₃ ), lithium niobate (LiNbO ₃ ), BNN (B
It can be applied a ₂ NaNb ₅ O ₁₅₎ or the like.

According to a third aspect of the present invention, in the optical element according to the first or second aspect, the light beam of the light beam emitted from the light beam emitting means is such that the direction having the lens power on the optical path of the light beam. The optical element according to claim 1 or 2 is arranged so as to coincide with a first predetermined direction orthogonal to the optical axis direction of the optical element, and the optical element according to claim 1 or 2 is provided on the optical path of the light beam. The second optical element is arranged so that the direction having the direction of the optical axis coincides with the second predetermined direction orthogonal to the optical axis direction of the light beam and orthogonal to the first predetermined direction.

With the above arrangement, when a voltage is applied to the electrodes of the first optical element and the magnitude of the voltage is changed, the first predetermined light beam irradiated on the irradiation surface of the irradiation target by the scanning optical system. The light collecting position in the direction changes. When a voltage is applied to the second optical element and the magnitude of this voltage is changed, the focus position of the light beam in the second predetermined direction changes. Therefore, at each position along the scanning direction by the scanning optical system
Image plane deviation with respect to the reference plane is obtained in advance to correct the image plane deviation
Corresponding correction data for each position to the storage means
It is stored and based on the correction data stored in the storage means.
Then, the control means causes the electrode of the first optical element and the second electrode of the first optical element so that the converging position of the light beam in the first predetermined direction and the converging position of the second predetermined direction coincide with the irradiation surface of the irradiation target. By controlling the magnitude of the voltage applied to the electrodes of the optical element, it is possible to correct the deviation of the focus position of the light beam with respect to the irradiation surface.

Further, when the distance to the condensing position of the light beam is shortened, as described in the section of the operation of the invention of claim 1, a predetermined refractive index is provided inside the electro-optical medium as compared with the conventional case. Since it is not necessary to generate the distribution and the applied voltage can be lowered, it is possible to prevent the beam waist diameter of the light beam from increasing. As a result, even when a recording material as an irradiation target is irradiated with a light beam to record an image, the beam waist diameter of the light beam causes a problem such as deterioration of image quality. No

According to a fourth aspect of the present invention, in the optical element according to the first or second aspect, the direction in which the lens power is on the optical path of the light beam is the optical axis of the light beam emitted from the light beam emitting means. An optical path length changing unit that can change the optical path length of the incident light beam is arranged on the optical path of the light beam while being arranged so as to coincide with the first predetermined direction orthogonal to the direction. With the above configuration, when a voltage is applied to the electrode of the optical element and the magnitude of this voltage is changed, the converging position of the light beam irradiated on the irradiation surface of the irradiation target by the scanning optical system in the first predetermined direction is changed. Change. Further, when the optical path length of the light beam is changed by the optical path length changing means, both the light collecting position in the first predetermined direction and the light collecting position in the second predetermined direction of the light beam change.

Therefore, along the scanning direction of the scanning optical system.
The image plane deviation from the reference plane at each position
The correction data for correcting the image plane deviation at each position.
It is stored in the storage means according to the
Based on the corrected data, the electrodes of the optical element are controlled by the control means so that the light-collecting position in the first predetermined direction and the light-collecting position in the second predetermined direction of the light beam respectively coincide with the irradiation surface of the irradiation target. By controlling the magnitude of the applied voltage and the optical path length changed by the optical path length changing means, it is possible to correct the deviation of the focusing position of the light beam with respect to the irradiation surface.
More specifically, the above control controls the magnitude of the voltage applied to the electrode of the optical element so that the light collecting position in the first predetermined direction and the light collecting position in the second predetermined direction of the light beam coincide with each other. The optical path length may be controlled and the optical path length changed by the optical path length changing unit may be controlled so that the matched converging position matches the irradiation surface of the irradiation target.

Also, when the distance to the condensing position of the light beam is shortened, it is not necessary to generate a predetermined refractive index distribution inside the electro-optic medium, and the application is performed, as in the invention of claim 3. Since the voltage can also be lowered, it is possible to prevent the beam waist diameter of the light beam with which the irradiation surface is irradiated from increasing.

[0029]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[First Embodiment] First, a first embodiment corresponding to the invention of claim 1 will be described. FIG. 1 shows an optical element 10 according to the first embodiment. Optical element 10
Comprises an electro-optic medium 12. The electro-optical medium 12 is formed of PLZT, and has a shape obtained by cutting a cylinder along a plane parallel to the axis of the cylinder. That is,
The pair of parallel planes has a shape surrounded by an arc and a chord. Therefore, the electro-optic medium 12 has no lens power in the direction of arrow X in FIG.
It has lens power only in the direction. Further, by being formed of PLZT, it has an electro-optical effect.

The focal length f of the electro-optical medium 12 in the Y direction_Y
Is the refractive index n of the electro-optic medium 12. ₀, Of the parallel plane
Assuming that the radius of curvature of the arcuate part is r,
Desired.

F _Y = r ÷ (n ₀ −1) (1) The focal position of the electro-optical medium 12 in the X direction is the point at infinity. As a result, for example, in a state where no voltage is applied between the electrodes 14A and 14B described later, for example, the electro-optical medium 1
When a light beam of a parallel light beam is incident on the light beam 2 in the direction of the arrow Z, the light beam is reflected by the lens power to the arrow Y.
And is refracted in a plane including the arrow Z, and the refraction condenses the light beam in the Y direction at the position of the focal length f _Y on the plane. In the following, the polarization direction of the light beam will be PL
X with a large change in the refractive index of the electro-optic medium 12 made of ZT
Consider a light beam that matches the direction.

Electrodes 14A and 14B are provided on the entire surfaces of the pair of parallel planes of the electro-optical medium 12. Thereby, the electrodes 14A, 1
When a voltage is applied between 4B, between electrodes 14A and 14B,
That is, a uniform electric field is applied between the parallel planes inside the electro-optical medium 12. Here, when the voltage V is applied between the electrodes 14A and 14B, the strength E of the electric field applied between the electrodes 14A and 14B is E = V ÷ d (2), where d is the distance between the electrodes 14A and 14B. ) And the direction of the electric field is in the direction of arrow A in FIG. Due to this electric field, when the secondary electro-optic coefficient (Kerr coefficient) of the electro-optic material forming the electro-optic medium 12 is R ₃₃ , the refractive index in the X direction of the electro-optic medium 12 is from the refractive index n ₀ to the following. It changes like the refractive index n shown in the equation (3).

[0034]

[Equation 1]

From the equation (3), the refractive index of the electro-optical medium 12 is the square of the electric field strength E, that is, the electrodes 14A and 14B.
It changes in proportion to the square of the voltage V applied in between. In addition,
Since the electric field at this time is a uniform electric field, the refractive index of the electro-optic medium 12 in the X direction also changes uniformly. Due to this change in the refractive index, the focal length f _{Y in} the Y direction of the electro-optical medium 12 when the voltage V is applied between the electrodes 14A and 14B is also

[0036]

[Equation 2]

It changes as shown in the equation (4). Therefore,
By changing the voltage applied between the electrodes 14A and 14B, the lens power of the electro-optical medium 12 changes, and the light beam transmitted through the optical element 10 has a predetermined direction (Y in FIG. 1).
Direction) is changed.

As described above, in the optical element 10, the electrode 14
Since a voltage is not applied between A and 14B, the electro-optical medium 12 has a predetermined lens power in the Y direction in FIG. 1A. Therefore, the distance between the condensing position of the light beam in the predetermined direction and the optical element. 14A, 14B when shortening the overall
It is possible to reduce the voltage applied between the electro-optical medium 1 and
It is not necessary to produce a predetermined refractive index distribution inside the 2, it is possible to eliminate the influence of yield differences Ru good the difference <br/> the resulting allowed refractive index distribution and the ideal refractive index distribution , Optical element 10
Even if the distance between the light beam and the condensing position of the light beam is shortened, the beam waist diameter is prevented from increasing.

Next, another example of the optical element according to the present invention will be described. In the optical element 20 shown in FIG. 2A, the electro-optic medium 20A has a cylindrical shape whose parallel plane is circular like a so-called rod lens.
The lens power is in the Y direction. Therefore, when the light beam is incident along the arrow Z direction in FIG. 2, the light beam is refracted in a predetermined plane including the arrow Y and the arrow Z. In addition, electrodes 20B and 20C are provided on the entire surfaces of both bottom surfaces of the electro-optical medium 20 having a cylindrical shape. Therefore, when a voltage is applied between the electrodes 20B and 20C, a uniform electric field is applied between both bottom surfaces, and by changing the magnitude of the voltage, the focusing position of the light beam in the predetermined plane can be changed. You can

Further, in the optical element 22 shown in FIG. 2B, the electro-optical medium 22A has a shape of an elliptic cylinder whose parallel plane is an ellipse. Similarly, it has a lens power in the direction of the arrow Y in FIG. Further, electrodes 22B and 22C are provided on the entire bottom surfaces of the elliptic cylinder. Therefore, the electrode 22
When a voltage is applied between B and 22C, a uniform electric field is applied between both bottom surfaces, and by changing the magnitude of the voltage, the focusing position of the light beam in the predetermined plane can be changed.

Further, in the optical element shown in FIG. 2C, the shape of the parallel plane of the electro-optical medium 24A is the same as the cross section of the Fresnel lens.
A has a columnar shape whose bottom is the parallel plane. For this reason, the electro-optical medium 24 has the same structure as the arrow Y in FIG.
Has lens power in the direction. In addition, electrodes 24B and 24C are provided on the entire bottom surfaces. Therefore, when a voltage is applied between the electrodes 24B and 24C, a uniform electric field is applied between both bottom surfaces, and the magnitude of the voltage is changed, thereby changing the focusing position of the light beam in the predetermined plane. be able to.

As described above, the optical element according to the present invention may be formed so that the electro-optic medium has a pair of parallel flat surfaces and lens power in a predetermined direction as described above.

[Second Embodiment] FIG. 3 shows a laser beam recording apparatus 30 according to the second embodiment. The laser beam recording device 30 includes a laser beam emitting device 32 which emits a laser beam of a substantially parallel light flux, which will be described in detail later. On the emission side of the laser beam emission device 32, a cylindrical lens 31 and a polygon mirror 46 for surface tilt correction are arranged. The rotation of the polygon mirror 46 is controlled by the drive control circuit 47.

A synchronizing semiconductor laser 48 for emitting a synchronizing laser beam is arranged near the polygon mirror 46. A collimator lens 50 is arranged on the laser beam emitting side of the synchronizing semiconductor laser 48. The laser beam emitted from the synchronization semiconductor laser 48 is collimated by the collimator lens 50 and then incident on the polygon mirror 46. The recording laser beam emitted from the laser beam emitting device 32 and the collimator lens 5
The same portion of the polygon mirror 46 is irradiated with the synchronizing laser beam emitted from the polygon mirror 46, and the polygon mirror 4
6 is similarly deflected in the main scanning direction with the rotation of 6, and is arranged on the laser beam emitting side of the polygon mirror 46.
It is incident on the θ lens 52.

On the optical path of the recording laser beam that has passed through the f.theta. Lens 52, a cylindrical lens 33 for surface tilt correction and a drum 54 are provided along the scanning direction of the laser beam.
Are arranged in sequence. A photosensitive material (not shown) is wound around the drum 54, and the recording laser beam is applied to the recording surface of the photosensitive material, and is deflected by the polygon mirror 46 to scan the range shown by the broken line in FIG. Further, by rotating the drum 54, the irradiation position of the laser beam on the photosensitive material also moves in the sub-scanning direction, and an image is recorded on the photosensitive material.

In the following, the polygon mirrors 46, f.
The main scanning direction of the laser beam that passes through the scanning optical system such as the θ lens 52 and is irradiated onto the drum 54 (direction of arrow M in FIG. 1).
The direction corresponding to is called the meridional direction, and the direction corresponding to the sub-scanning direction (direction of arrow S in FIG. 1) is called the sagittal direction. A plane including the optical axis direction of the laser beam and the meridional direction is called a meridional plane, and a plane including the optical axis direction and the sagittal direction is called a sagittal plane.

On the other hand, on the optical path of the synchronizing laser beam,
Reflecting mirror 56 along the scanning direction of the synchronizing laser beam
Is arranged, and a linear encoder 58 is arranged on the laser beam emitting side of the reflection mirror 56. The laser beam is deflected by the polygon mirror 46 so as to scan the range shown by the alternate long and short dash line in FIG. The linear encoder 58 is configured by forming a large number of opaque strip-shaped opaque portions having a constant width on a transparent plate material at a constant pitch.

A photoelectric converter (not shown) is arranged on the laser beam emitting side of the linear encoder 58. When the laser beam scans the linear encoder 58, the laser beam transmitted through the transparent portion is received by the photoelectric converter. ,
A pulse signal is output from the photoelectric converter.

Next, the laser beam emitting device 32 will be described. As shown in FIGS. 4A and 4B, the laser beam emitting device 32 includes a semiconductor laser 34.
The semiconductor laser 34 is modulated by a modulator (not shown) according to an image to be recorded at a timing synchronized with the pulse signal, and emits a laser beam according to the image to be recorded. A gas laser such as a He—Ne laser or an Ar laser may be used instead of the semiconductor laser 34, and a laser beam emitted from the gas laser may be modulated by using a modulator such as an AOM or EOM.

A collimator lens 36 is provided on the emission side of the semiconductor laser 34, and the laser beam emitted from the semiconductor laser 34 is collimated by the collimator lens 36 and emitted. An optical element 38 according to the present invention is arranged on the laser beam emitting side of the collimator lens 36.

The optical element 38 includes an electro-optical medium 38A, which has the same shape as the optical element 10 of the first embodiment, that is, a cylinder is cut along a plane parallel to the axis of the cylinder. It is formed into a shape and is made of PLZT as an electro-optical material, and has an electro-optical effect. Further, electrodes 38B and 38C are formed by vapor deposition on the entire surface of the parallel plane of the electro-optical medium 38A.

As shown in FIGS. 4A and 4B, the optical element 38 is arranged so that the direction having the lens power of the electro-optical medium 38A is along the sagittal plane of the incident laser beam. There is. Therefore, the laser beam incident on the optical element 38 is refracted and emitted only in the sagittal plane of the laser beam. Here, the polarization direction of the laser beam coincides with the direction of arrow M in FIG.

1 is provided on the laser beam emitting side of the optical element 38.
A half wave plate 40 and an optical element 42 are arranged in this order.
The laser beam emitted from the optical element 38 is transmitted through the half-wave plate 40 so that the polarization angle is rotated by 90 ° and the polarization direction is aligned with the arrow S direction in FIG.
It is incident on 2. The optical element 42 has the same configuration as the optical element 38, and includes an electro-optical medium 42A having a shape obtained by cutting a cylinder along a plane parallel to the axis of the cylinder, and the entire parallel plane of the electro-optical medium 42A. The electrodes 42
B and 42C are formed.

The optical element 42 is arranged so that the direction having the lens power of the electro-optical medium 42A is along the meridional plane. Therefore, the laser beam incident on the optical element 42 is refracted and emitted only in the meridional plane of the laser beam. Expander lenses 43 and 44 are arranged on the laser beam emission side of the optical element 42. The laser beam emitted from the optical element 42 is once condensed by the expander lenses 43 and 44 to form a beam waist, and then the beam diameter is expanded into a parallel light beam, which is emitted from the laser beam emitting device 32. It is incident on the polygon mirror 46.

A spatial filter 45 is arranged at a position where a beam waist of the laser beam is generated between the expander lens 43 and the expander lens 44. The spatial filter 45 is formed by forming a pinhole in an opaque plate material and cuts the scattered light component of the laser beam. It is a well-known fact that the scattered light component generated when a light beam passes through PLZT is not negligible, and is described, for example, in P274 to P285 (published on February 25, 1985) of “Optotechnology and high-performance materials”. ing.

On the other hand, as shown in FIG. 3, the drive control circuit 4
7 is connected to the focus position control device 62. The drive control circuit 47 outputs a signal representing the irradiation position of the laser beam along the main scanning direction to the focus position control device 62. The focus position control device 62 is configured as shown in FIG. That is, the signal input from the drive control circuit 47 is controlled by the control unit 68.
Entered in. The control unit 68 includes a CPU, RAM and RO.
It is composed of a microcomputer in which M and the like are connected to each other by a bus such as a data bus and an address bus. A storage device 70 is connected to the control unit 68.

Laser beam recording apparatus 30 of the second embodiment
Then, the beam waist positions in the meridional direction and the sagittal direction of the laser beam when the laser beam is applied to the photosensitive material wound around the drum 54 are sequentially measured while moving the irradiation position along the main scanning direction. As shown in FIG. 6, data representing the image plane 100 in the meridional direction and the image plane 102 in the sagittal direction is obtained in advance.

Then, the deviation ΔZ _S of the image surface 102 in the sagittal direction with respect to the reference surface (recording surface of the photosensitive material) at each position along the main scanning direction is calculated, and the calculated deviation ΔZ _S and the above equation (4) are obtained. Based on the optical element 38, the deviation Δ
The correction data for correcting Z _S is calculated, and the correction data is stored in the storage device 70 as the first table in association with the respective positions.

Further, the deviation ΔZ _M of the image plane 100 in the meridional direction with respect to the reference surface (recording surface of the photosensitive material) at each position along the main scanning direction is calculated, and the calculated deviation ΔZ _M and the above equation (4) Based on this, the optical element 42 calculates the correction data for correcting the deviation ΔZ _M , and the correction data is stored in the storage device 70 as the second table in association with the respective positions.

Digital-analog converters (D / A converters) 72A and 72B are connected to the output side of the control unit 68. The control unit 68 determines the irradiation position of the laser beam along the main scanning direction based on the signal from the drive control device 47, and from the first table stored in the storage device 70, the correction data corresponding to the irradiation position. Capture D / A
The correction data corresponding to the irradiation position is fetched from the second table and output to the D / A converter 72B while being output to the converter 72A.

The amplifier circuit 74A and the electrode 38B of the optical element 38 are sequentially connected to the output terminal of the D / A converter 72A. The electrode 38C is grounded. The correction data output from the control unit 68 is converted by the D / A converter 72A into an analog signal having a voltage level corresponding to the value of the correction data, and is amplified and boosted by the amplifier circuit 74A to be electrode 38.
Supplied to B. Therefore, a voltage corresponding to the magnitude of the correction data output from the control unit 68 is applied between the electrodes 38B and 38C. The amplifier circuit 74B and the electrode 42B are sequentially connected to the output terminal of the D / A converter 72B as well as the electrode 42C is grounded, and a voltage is applied between the electrodes 42B and 42C as described above. To be done.

Next, the operation of the second embodiment will be described. The laser beam emitted from the semiconductor laser 34 sequentially passes through the collimator lens 36, the optical element 38, the half-wave plate 40, the optical element 42, the expander lens 43, the spatial filter 45, and the expander lens 44, and the laser beam is emitted. The beam is emitted from the beam emitting device 32.

The recording laser beam emitted from the laser beam emitting device 32 is deflected along the main scanning direction by the polygon mirror 46 together with the synchronizing laser beam,
The recording surface of the photosensitive material is scanned. Further, the synchronizing laser beam scans the light receiving surface of the linear encoder 58.
By this scanning, the laser beam transmitted through the transparent portion of the linear encoder 58 is received by a photoelectric converter (not shown), and a pulse signal is input from the photoelectric converter to the drive control circuit 47. The drive control circuit 47 outputs a signal indicating the irradiation position of the laser beam along the main scanning direction to the control unit 68 of the focus position control circuit 62.

The control section 68 sequentially fetches corresponding correction data from the first table and the second table according to the movement of the irradiation position of the laser beam along the main scanning direction based on the input signal. , D / A converter 72
Output to A and 72B. As a result, a voltage of a level according to the correction data fetched from the first table is applied between the electrodes 38B and 38C of the optical element 38 via the D / A converter 72A and the amplifier circuit 74A, and the optical element 42
A voltage of a level corresponding to the correction data fetched from the second table is applied between the electrodes 42B and 42C of the No. 2 through the D / A converter 72B and the amplifier circuit 74B.

When a voltage is applied between the electrodes 38 B and 38 C of the optical element 38, the electro-optical medium 38 of the optical element 30 is applied.
A uniform electric field corresponding to the value of the applied voltage is applied to A. PL forming the electro-optical medium 38A of the optical element 38
The sign of the secondary electro-optic coefficient (Kerr coefficient) R ₃₃ of ZT is positive. Therefore, as is apparent from the expression (3), the refractive index of the electro-optical medium 38A in the direction having the lens power is reduced in proportion to the square of the applied voltage by applying the voltage,
The lens power will be reduced.

Since the optical element 38 is arranged so that the direction having the lens power of the electro-optical medium 38A is along the sagittal plane of the laser beam, the laser beam emitted from the laser beam emitting device 32 and applied to the drum 54 is irradiated. The beam waist position of the beam in the sagittal direction moves in a direction away from the f.theta. Lens 52 according to the magnitude of the voltage applied between the electrodes 38B and 38C of the optical element 38. Also, when the applied voltage becomes low,
The beam waist position moves in a direction approaching the f · θ lens 52.

As described above, the focus position control circuit 62 fetches the correction data from the first table based on the signal output from the drive control circuit 47, converts the fetched correction data into an analog signal, and amplifies it. Since the voltage is applied between the electrodes 38B and 38C of the optical element 38, the laser beam emitted to the drum 54 extends from one end to the other end in the main scanning direction, the shift ΔZ _S is substantially “0”, and the sagittal direction. The image surface 102 of is aligned with the recording surface of the photosensitive material wound around the drum 54.

On the other hand, the electrodes 42B and 42C of the optical element 42
Even when a voltage is applied in the meantime, the refractive index of the electro-optical medium 42A in the direction having the lens power decreases in proportion to the square of the applied voltage, and the lens power decreases. Since the optical element 42 is arranged so that the direction having the lens power of the electro-optical medium 42A is along the meridional plane of the laser beam, the meridional of the laser beam emitted from the laser beam emitting device 32 and applied to the drum 54. The beam waist position in the direction is the electrode 4 of the optical element 42.
Depending on the magnitude of the voltage applied between 2B and 42C, f.
It moves in a direction away from the θ lens 52. Further, when the applied voltage becomes low, the beam waist position moves toward the f · θ lens 52.

As described above, the focus position control circuit 62 fetches the correction data from the second table on the basis of the signal output from the drive control circuit 47, converts the fetched correction data into an analog signal, and amplifies it. Since the voltage is applied between the electrodes 42A and 42B of the optical element 42, the laser beam applied to the drum 54 extends from one end to the other end in the main scanning direction, the shift ΔZ _M is substantially “0”, and the laser beam is in the meridional direction. The image surface 100 of 1 is aligned with the recording surface of the photosensitive material wound around the drum 54.

As described above, the beam waist position of the laser beam incident on the f.theta. Lens 52 is moved by the change of the lens power of the optical elements 38 and 42, and this movement extends from one end to the other end in the scanning direction. Thus, the beam waist positions of the laser beam in the meridional direction and the sagittal direction are always aligned with the recording surface of the photosensitive material. Therefore, a high quality image can be obtained without causing inconvenience such as partial blurring of the image recorded on the photosensitive material.

In the second embodiment, the optical elements 38 and 4 are used.
Since the second electro-optical mediums 38A and 42A have a predetermined lens power in the state where no electric field is applied, it is not necessary to generate a predetermined refractive index distribution inside, and for example, the f.theta. Lens 52 and Even when the distance from the drum 54 is shortened, if the electro-optic mediums 38A and 42A are shaped to have a larger lens power, it is not necessary to increase the voltage applied between the electrodes. It is possible to prevent the beam waist diameter of the applied laser beam from increasing. Therefore, an image can be recorded with high quality and high density.

As a prior art of the present invention, Japanese Patent Laid-Open No.
-35211 describes that the cylindrical lens is moved to correct the field curvature, but the present invention does not require moving the optical elements 38 and 42 as described above, and the PLZT or the like is not necessary. Since the electro-optic material has a high rate of change in the refractive index with respect to the change in the strength of the applied electric field,
For example, even when the scanning speed of the laser beam is high, it is easy to follow the correction of the focus position of the light beam.

[Third Embodiment] Next, a third embodiment of the present invention will be described. The same parts as those in the second embodiment are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 7, in the laser beam emitting device 32 according to the third embodiment, a cylindrical lens 80 is arranged on the laser beam emitting side of the optical element 38. The cylindrical lens 80 moves the optical element 3 in a predetermined direction.
8 has the same lens power as the electro-optical medium 38A, and the direction having this lens power is arranged along the meridional plane of the incident laser beam.

On the laser beam emitting side of the cylindrical lens 80, an optical path length changing element 8 as an optical path length changing means.
2 are arranged. The optical path length changing element 82 includes an electro-optical medium 82A. The electro-optical medium 82A is PL
It is formed of ZT in a rectangular shape. Further, electrodes 82B and 82C are provided on the surface of the electro-optical medium 82A so as to sandwich the electro-optical medium 82A and face each other along the meridional direction of the incident laser beam.

The electrode 82B is a second electrode though not shown.
The amplifier circuit 7 is used instead of the electrode 42B of the optical element 42 of the embodiment.
It is connected to the output end of 4B and the electrode 82C is grounded. When a voltage is applied between the electrodes 82B and 82C,
The refractive index of the electro-optic medium 82A changes, and the optical path length in the meridional direction and the optical path length in the sagittal direction of the laser beam incident on the optical path length changing element 82 change similarly.

Further, the expander lens 4 is provided on the laser beam emitting side of the optical path length changing element 82 as in the second embodiment.
3, spatial filter 45, expander lens 4
4 are arranged in order.

On the other hand, in the storage device 70 of the third embodiment, the first
The correction data stored as the table and the second table are different from those in the second embodiment. That is, in the third embodiment, the deviation (astigmatic difference) of the image surface 102 in the sagittal direction from the image surface 100 in the meridional direction at each position along the main scanning direction is calculated, and the calculated deviation and the above equation (4) are obtained. The correction data for correcting the deviation is calculated by the optical element 38 based on the above, and the correction data is stored as the first table in association with the respective positions.

Similarly, the deviation (offset) of the image plane 100 in the meridional direction from the reference surface (recording surface of the photosensitive material) at each position along the main scanning direction is obtained, and the obtained deviation and the above equation (4) are obtained. Based on the optical path length changing element 82
Calculate the correction data to correct the deviation by
The correction data is stored as a second table in association with each of the positions.

Next, the operation of the third embodiment will be described. The laser beam emitted from the semiconductor laser 34 is refracted in the sagittal plane by passing through the optical element 38, and refracted in the meridional plane by passing through the cylindrical lens 80. Here, the focus position control circuit 62 takes in the correction data from the first table on the basis of the signal output from the drive control circuit 47, converts the received correction data into an analog signal, amplifies it, and then the electrode 38B of the optical element 38. , 38C.

As a result, the lens power of the optical element 38 is sequentially changed so that the beam waist position in the sagittal direction of the laser beam applied to the drum 54 coincides with the beam waist position in the meridional direction.
In the laser beam, the image plane 102 in the sagittal direction extends from one end to the other end in the main scanning direction, and the image plane 10 in the meridional direction extends.
Astigmatism is corrected to 0.

Further, the focal position control circuit 62 fetches the correction data from the second table based on the signal output from the drive control circuit 47, converts the fetched correction data into an analog signal, and amplifies it to change the optical path length. The voltage is applied between the electrodes 82B and 82C of the element 82. As a result, the refractive index of the electro-optical medium 82A of the optical path length changing element 82 is changed so that the beam waist positions of the matched laser beam in the meridional direction and the sagittal direction match the recording surface of the photosensitive material. The optical path lengths in the meridional direction and the sagittal direction are sequentially changed.

Therefore, the offset of the laser beam applied to the drum 54 is corrected, and the image plane 100 in the meridional direction and the image plane 102 in the sagittal direction are arranged on the recording surface of the photosensitive material wound around the drum 54 in the main scanning direction. The same effect as in the second embodiment can be obtained by matching from one end to the other end.

Since the optical path length changing element 82 only needs to change the optical path lengths of the laser beam in the meridional direction and the sagittal direction, it is not necessary to form a refractive index distribution in the electro-optical medium 82A as in the conventional case, and it is ideal. It is not affected by the aberration due to the fact that a large refractive index distribution is not formed.

Further, the optical path length changing means is not limited to the optical path length changing element 82, but the applicant of the present invention can apply for a patent application.
As already proposed in 4-188407, it is possible to apply a disk in which optical path length changing portions for changing the optical path length of a light beam that is rotatable and is transmitted are distributed along the rotation direction.
Further, as already proposed in Japanese Patent Application No. 4-188408 by the applicant, by moving a mirror that reflects a laser beam along the optical axis of the laser beam by an actuator such as a piezo element, The optical path length of the laser beam may be changed.

Further, in the above embodiment, the correction data is obtained in advance and stored in the storage device 70, and when the image is recorded, the correction data is fetched from the storage device 70 to obtain the beam waist in the meridional direction and the sagittal direction with respect to the recording surface. Although the position is corrected, the present invention is not limited to this, and the deviation of the beam waist position is measured when recording an image, and the optical element 38 and the optical element 38 are set so that the deviation becomes zero. The optical element 42 or the optical element 38 and the optical path length changing element 82 may be controlled in real time.

Although the image recording has been described above as an example, the present invention can be applied to the case of reading an image, a character or the like by a light beam.

[0088]

As described above, the optical element according to the first aspect of the present invention is an electro-optical medium having an electro-optical effect, which has a pair of parallel planes and is formed to have a lens power in a predetermined direction. , The electrodes are provided on each of a pair of parallel planes so that a uniform electric field is applied between the parallel planes inside the electro-optic medium when a voltage is applied, so the focusing position of the light beam in a predetermined direction can be corrected. In addition, the excellent effect that the beam waist diameter can be prevented from increasing even when the distance to the condensing position is shortened is obtained.

In the light beam scanning device according to the third aspect of the present invention, the first optical element is arranged so that the direction having the lens power coincides with the first predetermined direction orthogonal to the optical axis direction of the light beam. Is placed on the optical path of the light beam,
The second optical element is arranged on the optical path of the light beam so that the direction having the lens power is orthogonal to the optical axis direction of the light beam and coincides with the second predetermined direction which is orthogonal to the first predetermined direction. A light beam converging position in a first predetermined direction and a second
The magnitudes of the voltages applied to the electrodes of the first optical element and the electrodes of the second optical element are controlled so that the light-condensing positions in the predetermined direction of are aligned with the irradiation surface of the object to be irradiated. Therefore, it is possible to correct the deviation of the focusing position of the light beam with respect to the irradiation surface, and it is possible to prevent the beam waist diameter of the light beam with which the irradiation surface is irradiated from increasing, which is an excellent effect.

In the light beam scanning device according to the fourth aspect of the present invention, the optical beam of the light beam is arranged so that the direction having the lens power coincides with the first predetermined direction orthogonal to the optical axis direction of the light beam. The optical path length changing means is arranged on the optical path of the light beam while being arranged on the road, and is orthogonal to the converging position of the light beam in the first predetermined direction and the optical axis direction of the light beam, and orthogonal to the first predetermined direction. The magnitude of the voltage applied to the electrode of the optical element and the optical path length changed by the optical path length changing means are controlled so that the light-collecting positions in the second predetermined direction coincide with the irradiation surface of the irradiation target. Therefore, it is possible to correct the deviation of the converging position of the light beam with respect to the irradiation surface,
An excellent effect is obtained in that the beam waist diameter of the light beam irradiated on the irradiation surface can be prevented from increasing.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of an optical element according to a first example.

FIGS. 2A to 2C are perspective views showing another example of an optical element.

FIG. 3 is a perspective view showing a schematic configuration of a laser beam recording apparatus according to a second embodiment.

FIG. 4A and FIG. 4B are plan views showing a schematic configuration of a laser beam emitting apparatus according to a second embodiment.

FIG. 5 is a block diagram showing a schematic configuration of a focus position control device.

FIG. 6 is a conceptual diagram for explaining an image plane, an astigmatic difference, and an offset in the meridional direction and the sagittal direction.

7A and 7B are plan views showing a schematic configuration of a laser beam emitting apparatus according to a third embodiment.

FIG. 8 is an explanatory diagram illustrating a schematic configuration of a conventional laser beam recording apparatus and curvature of an image plane in a meridional direction and a sagittal direction.

FIG. 9 is a perspective view for explaining an astigmatic difference.

[Explanation of symbols] 10 Optical element 20 Optical element 22 Optical element 24 Optical element 12 Electro-optical medium 14 electrodes 30 Laser beam recorder 32 Laser beam emitting device 38 Optical element 42 Optical element 62 Focus position control circuit 82 Optical path length changing element

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-251718 (JP, A) JP 3-174680 (JP, A) JP 2-254409 (JP, A) JP 2- 53035 (JP, A) Actual development 4-129124 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 26 / 10,27 / 00 G02F 1/29

Claims (4)

(57) [Claims] 1. A plane perpendicular to a predetermined plane shape
Has a pair of parallel planes formed by stretching
One is a pillar shape Rutotomoni, have a lens power in a predetermined direction
However , an electro-optic medium having an electro-optic effect formed so that the refractive index is uniformly changed by an applied electric field, and a uniform plane between the pair of parallel planes inside the electro-optic medium. An optical element having an electrode provided on each of the pair of parallel planes and having a shape corresponding to the predetermined shape so that an electric field is applied. 2. The optical element according to claim 1, wherein the electro-optic medium is PLZT. 3. A light beam emitting means for emitting a light beam, and the optical element according to claim 1 or 2, wherein a direction having the lens power is orthogonal to an optical axis direction of the light beam. The first optical element arranged on the optical path of the light beam so as to match the predetermined direction of the optical beam, and the optical element according to claim 1 or 2, wherein the direction having the lens power is the direction of the light beam. A second optical element that is arranged so as to be orthogonal to the optical axis direction and to coincide with a second predetermined direction that is orthogonal to the first predetermined direction, and transmits the first optical element and the second optical element. a scanning optical system for scanning on the irradiated object light beam, at each position along the scan direction by the scanning optical system
The image plane shift with respect to the reference plane is obtained in advance, and the image plane shift is calculated.
The correction data for correction is described in correspondence with each of the above positions.
Based on the storage means to remember and the correction data stored in the storage means,
The first optical element so that the light-collecting position in the first predetermined direction and the light-collecting position in the second predetermined direction of the light beam with which the irradiation target object is irradiated respectively coincide with the irradiation surface of the irradiation target object. And a control means for controlling the magnitude of the voltage applied to the electrode of the second optical element and the voltage of the electrode of the second optical element, respectively. 4. A light beam emitting means for emitting a light beam, and the optical element according to claim 1 or 2, wherein a direction having the lens power is orthogonal to an optical axis direction of the light beam. An optical element arranged on the optical path of the light beam so as to match a predetermined direction of the optical beam, an optical path length changing means arranged on the optical path of the light beam and capable of changing the optical path length of the incident light beam, and the optical element. And a scanning optical system for scanning the irradiation target with the light beam that has passed through the optical path length changing means, and at each position along the scanning direction by the scanning optical system.
The image plane shift with respect to the reference plane is obtained in advance, and the image plane shift is calculated.
The correction data for correction is described in correspondence with each of the above positions.
Based on the storage means to remember and the correction data stored in the storage means,
The light beam radiated to the object to be irradiated is orthogonal to the converging position in the first predetermined direction and the optical axis direction of the light beam, and
Is changed by the optical path length changing means and the magnitude of the voltage applied to the electrode of the optical element so that the condensing position in the second predetermined direction orthogonal to the predetermined direction coincides with the irradiation surface of the irradiation target. A light beam scanning device including: a control unit that controls each optical path length.