JP3283179B2 - Light intensity control device and light intensity control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light intensity control device and method for dividing a light beam emitted from a light source into a monitor light beam and a main light beam, and controlling the light emission amount of the light source based on the light intensity of the monitor light beam.

[0002]

2. Description of the Related Art This type of light intensity control device has been conventionally used, for example, in the field of optical disk devices. A light beam emitted from a light source such as a semiconductor laser is split by a light splitting element such as a half mirror, one of which is used for light intensity detection as a monitor light beam, and the other is guided to an optical disk located on an image plane as a main light beam to read and write information. Used for The light intensity control device controls the light emission intensity of a light source so as to obtain a predetermined light intensity on an optical disk based on the light intensity of a monitor light beam, so-called APC (Automatic Powe
r Control) operation.

[0003]

However, in a conventional light intensity control apparatus, for example, when a plurality of light sources are used and the polarization states of light beams from the plurality of light sources are different from each other, or at least one light source is used. When the polarization state of the light beam incident on the light splitting element changes due to a change in the environment in the device, the intensity on the image plane may not be maintained at a predetermined value by the APC operation.

In general, the transmittance or reflectance of a light splitting element such as a half mirror and an optical element for guiding a main light beam onto an image plane has polarization dependence. Or the light energy (light amount) of the reflected light changes. In particular, the light intensity of the monitor light beam split by the light splitting element is set to be significantly smaller than the light intensity of the main light beam in order to secure the light use efficiency on the main light beam side. It changes greatly depending on the state.

Therefore, the balance between the light intensity of the main light beam guided on the image plane and the light intensity of the monitor light split by the light splitting element changes depending on the polarization state of the incident light beam. If the light intensity is broken, the light intensity of the main light beam on the image plane cannot be maintained at a predetermined level even if the amount of light emitted from the light source is controlled by operating the APC based on the light intensity of the monitor light beam.

[0006] The above-mentioned problem appears more conspicuously in an optical system using an optical fiber. This has the property that ordinary optical fibers propagate light without preserving the plane of polarization.
(In some cases, the direction of polarization of the incident linearly polarized light and the direction of polarization of the emitted linearly polarized light are orthogonal to each other.) It is because it changes easily by the following. For example, in a multi-beam optical system in which light beams emitted from a plurality of light sources are guided by optical fibers corresponding to each light source to form a point light source, when a light beam emitted from the optical fiber is divided by a half mirror to obtain a monitor light beam, Even if the polarization state of the light incident on the optical fiber from the light source is constant, the polarization state of each light beam emitted from the optical fiber and incident on the half mirror is not constant. Therefore, even if the APC is activated based on the detected light intensity of the monitor light beam, it does not function properly and the light intensity on the image plane cannot be kept constant.

The present invention is directed to a device using a plurality of light sources, in which the polarization states of the light beams from the plurality of light sources are different from each other, or a light beam incident on the light splitting element due to a change in the environment in the device using at least one light source. It is an object of the present invention to provide a light intensity control device and method capable of controlling the amount of the main light beam to be constant based on the intensity of the monitor light beam even when the polarization state of the light beam changes.

[0008]

A light intensity control device according to the present invention is a light splitting element for splitting a light beam emitted from a light source unit having a plurality of light sources whose light emission is independently controlled into a monitor light beam and a main light beam. And light detecting means for detecting the light intensity of the monitor light flux emitted from each light source at different timings, and the light intensity of the monitor light flux and the subsequent stage of the light splitting element regardless of the polarization state of the light incident on the light splitting element. Correction means for correcting the output of the light detection means so that the light intensity of the main light beam guided onto the target surface by the imaging optical system provided in the light detection means, and the light detection means corrected by the correction means Control means for controlling the light emission intensity of the light source based on the output signal of the light source, and the correction means and the control means respond based on the light intensity of the monitor light flux emitted from each light source detected by the light detection means. Do each And controlling the emission intensity of the source.

According to the above arrangement, it is possible to provide a constant correlation between the output of the correcting means on the monitor light beam side and the intensity of the main light beam irrespective of the polarization state of the light beam entering the light splitting element. Accordingly, these effects can be suppressed in a form including not only the polarization dependence of the light splitting element but also the polarization dependence of the optical system for guiding the main light beam. With this, APC
The operation can function normally.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the light intensity control device according to the present invention will be described below. The light intensity control device shown as an embodiment is applied to a multi-beam scanning optical device that simultaneously forms eight scanning lines by one scanning by simultaneously scanning eight laser beams. First,
The schematic configuration of the scanning optical device will be described with reference to FIG. 1 which is a perspective view of the entire scanning optical device, FIG. 2 which shows the arrangement of the optical system, FIG. 3 which is a cross-sectional view, and FIG. In addition,
In the following description, the “main scanning direction” is a direction corresponding to the light beam scanning direction in a plane perpendicular to the optical axis, and the “sub scanning direction”.
Means a direction perpendicular to the main scanning direction in a plane perpendicular to the optical axis.

The scanning optical device is, as shown in FIG.
A scanning optical system is arranged in a flat casing 1 having a substantially rectangular parallelepiped shape. The upper opening of the casing 1 is closed by the upper lid 2 during use.

As shown in FIGS. 1 and 2, the light source unit 100 of the scanning optical system includes eight laser blocks 310a to 310h mounted on a support substrate 300, respectively.
Semiconductor lasers 101 to 108 attached to these laser blocks one by one, eight quartz glass optical fibers 121 to 128, and a coupling lens (shown in FIG. ), And a fiber alignment block 130 that forms eight point light sources arranged in a straight line by holding the ends of the optical fibers on the emitting side in a straight line. The ends of the optical fibers 121 to 128 on the incident side are held by fiber supports 319a to 319h fixed to the laser blocks 310a to 310h.

A divergent light beam emitted from the fiber alignment block 130 of the light source unit 100 is converted into a parallel light beam by a collimating lens 140 held by a cylindrical collimating lens holder 340, and a slit 142
And enters the half mirror 144 which is a light splitting element. The half mirror 144 functions as a light splitting element that splits by transmitting a part of the incident light flux as a monitor light flux and reflecting the remaining light as a main light flux. The transmittance of the half mirror 144 is generally 5 to 10% as an average of the S-polarized light and the P-polarized light.

The monitor light flux transmitted through the half mirror 144 is used as an APC (auto power control) which constitutes a light detecting means and a correcting means of the light intensity control device of the present invention.
The signal enters the signal detection unit 150. APC signal detector 150
Is a condensing lens 151 for converging a transmitted light beam, a polarization beam splitter 153 as a polarization separation element for separating the light beam into two orthogonal polarization components, and a first APC for detecting the light energy of each polarization component. It comprises a light receiving element 155 and an APC second light receiving element 157, and its output signal is used for feedback controlling the output of the semiconductor lasers 101 to 108.

On the other hand, the main luminous flux reflected by the half mirror 144 passes through a dynamic prism 160 rotatably arranged about an axis perpendicular to the optical axis so as to control a spot position in the sub-scanning direction on the image plane. A linear image is formed near the mirror surface of the polygon mirror 180 by the cylindrical lens 170 having a positive power only in the sub-scanning direction. The dynamic prism 160 is used to correct the positional deviation of the spot on the surface to be scanned in the sub-scanning direction due to rotation unevenness of the photosensitive drum, which will be described later. The cylindrical lens 170 is held by a cylindrical cylindrical lens holder 361, and is composed of two lenses 171 and 173 having positive and negative powers in the sub-scanning direction, as shown in FIG.

The polygon mirror 180 has a polygon motor 371 fixed to the casing 1 as shown in FIG.
, And rotates clockwise as indicated by the arrow in FIG. The polygon mirror 180 is shielded from outside air by a cup-shaped polygon cover 373 as shown in FIG. 1 in order to avoid generation of wind noise due to rotation and damage to the mirror surface due to collision with dust in the air. Are located.

An optical path hole 373e is formed on the side surface of the polygon cover 373, and a cover glass 375 is fitted in the optical path hole 373e. The luminous flux transmitted through the cylindrical lens 170 is applied to the cover glass 37.
5, the light enters the cover, is reflected and deflected by the polygon mirror 180, and is emitted again through the cover glass 375 to the outside. The mark M attached to the upper surface of the polygon mirror 180 is provided on the upper surface of the polygon cover 373.
Is provided with a sensor block 376 including a polygon sensor (not shown) for detecting.

On the reflection surface of the polygon mirror 180, for example, an error occurs in the surface shape in the main scanning direction due to processing. In general, the processing error amount of each reflection surface varies. Therefore, the amount of error of each surface is measured and stored in advance, and which reflective surface is used for scanning according to the output of the sensor at the time of use, the unique amount of error for each reflective surface is determined. , The beam position, the beam intensity, and the like can be corrected.

The light beam reflected by the polygon mirror 180 passes through an fθ lens 190 which is an image forming optical system,
As shown in FIG. 3, the light is reflected by the folding mirror 200 and reaches the photosensitive drum 210 to form eight beam spots. These beam spots are scanned simultaneously with the rotation of the polygon mirror 180, and eight scanning lines are formed on the photosensitive drum 210 by one scan.

The photosensitive drum 210 is rotated in the direction of arrow R in synchronization with the scanning of the beam spot, whereby an electrostatic latent image is formed on the photosensitive drum 210. This latent image is transferred to a sheet (not shown) by a known electrophotographic process.

Lens 190 is a polygon mirror 18
From the 0 side to the folding mirror 200 side, in the order of the main scanning direction and the sub scanning direction, negative, positive,
First, second, third, and fourth lenses 191, 193, 195, and 197 having positive and negative powers are arranged and formed, and form a linear image near the mirror surface of the polygon mirror 180 in the sub-scanning direction. It has the power to re-image the light beam on the photosensitive drum 210 in an elliptical shape.

The first lens 191 of the fθ lens 190 is
The polygon mirror 180 is a negative lens having a spherical surface having negative power, and the return mirror 200 is a negative lens having a cylinder surface having negative power only in the sub-scanning direction. It has relatively strong negative power in the direction.

The second lens 193 is a polygon mirror 18
A meniscus toric lens having a convex spherical surface on the 0 side and a positive toric surface on the return mirror 200 side has a relatively weak positive power in the main scanning direction and a relatively strong positive power in the sub-scanning direction. . Third
The lens 195 is a meniscus positive lens having two spherical surfaces. The fourth lens 197 is a negative meniscus lens having a spherical surface on both sides, a surface on the polygon mirror 180 side having a strong negative power, and a surface on the return mirror 200 side having a weak positive power. The four lenses of the fθ lens 190 are a single lens mount 3 as shown in FIGS.
80.

The x-axis in FIG. 1 to FIG.
Are parallel to the optical axis, and the y-axis and the z-axis are axes orthogonal to each other in a plane perpendicular to the x-axis. The y-axis corresponds to the main scanning direction, and the z-axis corresponds to the polygon mirror 180 and the folding mirror 20.
In the optical path between zero and zero, they coincide with the sub-scanning direction.

The luminous flux transmitted through the fθ lens 190 is detected by the synchronizing signal detecting optical system 220 before entering the drawing range for each scan, that is, for each scan by one reflection surface of the polygon mirror. The synchronization signal detecting optical system 220 is disposed in an optical path between the fourth lens 197 of the fθ lens 190 and the return mirror 200, and reflects a light beam before the drawing range, and the first mirror 221. The second mirror 223 and the second mirror 225 sequentially reflect the light beam reflected by the mirror 221 and the light receiving element 230 that receives the light beam guided by these mirrors. The light receiving element 230 is arranged at a position optically equivalent to the photosensitive drum 210. The eight beams
With the scanning, the light enters the light receiving elements 230 one by one in order,
Eight pulses are output from the light receiving element 230 for each scan. When a pulse is detected, one line of image data is transferred to a laser driving unit that drives a semiconductor laser corresponding to the pulse, and writing is started after a certain period of time has elapsed from the detection of the pulse.

The casing 1 has a drawing opening 11 for transmitting the light beam reflected by the return mirror 200 and an inspection opening 12 behind the return mirror 200. A cover glass 201 is attached to the drawing opening 11. Inspection opening 12
Is used for adjusting these optical elements after assembling the optical elements except for the return mirror 200, and is closed by the cover plate 13 as shown in FIG. 3 when used for drawing.

Next, details of each component of the above-described scanning optical system will be described with reference to FIGS. FIG.
FIG. 6 is a cross-sectional view showing a specific configuration of the laser block 310a, and FIG. 6 is a front view of FIG. 5 as seen from the direction of the line VI-VI. Note that the laser blocks 310a to 310h
Since all have the same structure, 310a will be described as a representative. As shown in these figures, the laser block 310a includes a semiconductor laser holding member 311a holding the semiconductor laser 101 and a coupling lens holding member 313a holding the coupling lens 111.
And a fiber fixing member 315a to which the fiber support 319a is fixed. The semiconductor laser holding member 311a and the coupling lens holding member 313a have a columnar shape as shown in FIG.
Almost one of the cylinders so that a pedestal surface consisting of two wall surfaces is formed
The portion corresponding to / 4 is cut out along the axial direction thereof.

The semiconductor laser holding member 311a and the fiber fixing member 315a are fixed by bolts so as to sandwich the coupling lens holding member 313a from both sides along the light traveling direction. 3 by screwing to 300
One member is fixed to the support substrate 300 as an integrated block. Further, the fiber support 319a is fixed to the two wall surfaces of the fiber fixing member 315a by fixing metal fittings 317a.

The divergent light beam emitted from the semiconductor laser 101 is converged by the coupling lens 111 and enters the optical fiber 121. The optical fiber 121 is inserted into a through hole formed along the central axis of the fiber support 319a, and is fixed to the support 319a by an adhesive.

In the example of FIG. 5, the incident end face of the optical fiber 121 is set so as not to be orthogonal to the incident optical axis. Further, the fiber support 319a is also disposed so as to be totally inclined such that, even when the incident end face is tilted, the light rays on the optical axis refracted at the incident end face travel in the fiber in parallel with the central axis of the optical fiber 121.

By tilting the incident end face of the optical fiber 121 so as not to be orthogonal to the optical axis as described above, the reflected light at this incident end face is directed in a direction different from the incident direction as shown in FIG. Never return.
When the reflected light returns to the semiconductor laser, the oscillation of the semiconductor laser becomes unstable, the oscillation mode changes from a single mode to multiple modes, or the oscillation wavelength broadens,
A predetermined spot diameter cannot be obtained on the image plane, and the drawing accuracy is degraded. By preventing return light, such a problem can be avoided.

Here, as shown in FIG. 7, the angle between the optical axis L1 of the coupling lens 111 and the normal L2 of the incident end face 121a of the optical fiber 121 is θ1, the optical axis L1 of the coupling lens 111 and the optical fiber 121 are different. Is the angle between the center axis L3 of the optical fiber 121 and the center axis L of the optical fiber 121.
Assuming that the angle between 3 and the normal L2 of the incident end face 121a is θ3 and the refractive index of the core of the optical fiber 121 is n,
The following relationship is established. That is, once the angle θ1 is determined, the other angles θ2 and θ3 are uniquely determined.

Θ3 = sin ⁻¹ ((sin θ1) / n) θ2 = θ1−θ3

In this example, the optical fiber 121 is integrally polished while being attached to the fiber support 319a, so that the incident end face of the fiber and the incident side end face of the fiber support 319 are flush with each other, and ,
The normals of these surfaces are both processed so as to form an angle θ3 with the center axis of the fiber.

In this example, the exit end face 121b of the optical fiber 121 is cut obliquely so as to be inclined by an angle θ4 with respect to a plane orthogonal to the central axis of the optical fiber. According to this configuration, even if a part of the light beam is reflected at the exit end face of the optical fiber, the return light returns along a different path from the propagation path from the semiconductor laser side, and therefore, no return light to the semiconductor laser is generated.

The exit ends of the optical fibers 121 to 128 are combined by a fiber alignment block 130 as shown in FIG. 8, and the exit ends are positioned so that the central axes of the optical fibers are aligned. . Rectangular fiber alignment block 130
As shown in FIG. 9 which is an exploded perspective view, a main body 130 on which an alignment portion 133 for positioning the emission ends of the optical fibers 121 to 128 is formed;
Holding plate 1 for holding the optical fiber positioned at 0
39. An introduction portion 135 is formed on the light incident side of the alignment portion 133 of the main body 131 with a step in a direction away from the holding plate.

As shown in FIG. 9 and FIG. 10 which is an enlarged front view of the fiber alignment block 130, the alignment portion 133 has eight V-shaped grooves 137, 137 parallel to each other corresponding to the respective optical fibers. ,…
Are formed. At the time of assembly, the optical fiber 12
After setting 1-128 in V-shaped grooves 137,137, ...
The optical fibers 121 to 128 and the fiber alignment block 130 are integrally fixed by pressing strongly with the pressing plate 139 and pouring an adhesive between the main body and the pressing plate.

As shown in FIG. 11, the exit end faces of the optical fibers held by the fiber alignment block 130 are arranged with their central axes aligned on a straight line. The fiber alignment block 130 is held by a holder (not shown), and a straight line connecting the central axes of the fibers is formed so that the beam spot on the photosensitive drum 210 is formed at a predetermined interval in both the main scanning direction and the sub-scanning direction. It is set obliquely so as to form a predetermined angle with respect to the main scanning direction.

FIG. 12 shows an arrangement of beam spots on the photosensitive drum. Figure 1 shows the end of the optical fiber that is the object point
By arranging as in 1, the beam spots are also formed such that their centers are on a straight line. The straight line connecting the centers makes a predetermined angle with respect to the main scanning direction.
Thus, the centers of adjacent beam spots are formed at predetermined intervals in the main scanning direction and the sub-scanning direction.

Next, the operation of the APC signal detecting section 150 constituting the main part of the light intensity control device of the present invention included in the above-described scanning optical device will be described. As described above, in general, an optical fiber has a property of changing the polarization state of incident light, and the influence on the change in the polarization state is slightly different depending on the holding state, routing, and the like of the optical fiber. Therefore, when the light beams from a plurality of semiconductor lasers are guided using optical fibers, respectively, as in the apparatus of the embodiment, even if the polarization directions of the semiconductor lasers are aligned in the same direction on the incident side, the polarization state of the light beams emitted from the optical fibers is changed. Are different from each other. The polarization state also changes due to a change in the attitude of the fiber or a change in the environment.

FIG. 13 shows an optical system for measuring a change in the polarization state of light propagating through an optical fiber. The light beam from the semiconductor laser 101 is converged by the coupling lens 111 and is incident on the optical fiber 121. The light emitted from the optical fiber 121 is transmitted to the collimator lens 40.
2 is converted into parallel light by the sensor 4 via the polarizer 400.
03. Here, by measuring the output of the sensor 403 while rotating the polarizer 400, the polarization state of the emitted light can be known. Here, a system including the semiconductor laser 101 is shown as a representative, but other systems can be similarly examined.

FIG. 14 shows an example of a change in the polarization state.
14 is a graph showing the results of measuring the polarization state of light emitted from each optical fiber when the linearly polarized light having the same polarization direction is incident on four of the eight optical fibers 121 to 126 using the system of FIG. 13. The horizontal axis in the figure is the rotation angle of the polarizer 400
(Unit: deg.), And the vertical axis indicates the light intensity (unit: mW) detected by the power meter 410. A small output fluctuation width means that the emitted light is close to circularly polarized light, and a large fluctuation width means that the emitted light is close to linearly polarized light. FIG.
From this, it has been observed that the plane of polarization rotates during transmission by the optical fiber, that is, the optical rotation of the optical fiber. Some combinations have inverted phases, that is, combinations having orthogonal polarization directions.

Next, how the same optical fiber changes the polarization state due to a change in posture will be described based on actually measured data. Here, between the coupling lens 111 and the optical fiber 121 in FIG. 13, the polarization beam splitter 312a and the λ / 4 plate 31
6a is inserted, circularly polarized light is made incident on the optical fiber 121, and the output of the sensor 403 is measured by rotating the polarizer 400 as in the above example.

FIGS. 15 and 16 are graphs showing changes in sensor output when one optical fiber is focused on and the posture of the optical fiber is intentionally changed. FIG.
FIG. 13 shows an example in which the middle portion of the optical fiber 121 is bent in a “U” shape in order to investigate the influence of the change in the bending state of the optical fiber 121 on the polarization state. As shown in FIG. Example, twice likewise,
The result of measurement is shown for an example in which three loops were performed. FIG. 16 is a graph for measuring the influence of the change due to the twist of the optical fiber 121 on the polarization state.
As shown in FIG. 3, each rotation angle (0 °, 4 °) when the loop portion of the optical fiber 121 looped once is rotated about an axis passing through the straight portion on the incident side and the exit side of the loop portion.
5 °, 90 °, 135 °, and 180 °).

From these results, it can be seen that both the amplitude and the phase of each output waveform change greatly, that is,
It can be seen that the polarization state of the emitted light changes depending on the mounting condition and the posture of the optical fiber. At the time of assembling the actual device, a change in the condition that changes the polarization state can easily occur.

On the other hand, most of the optical elements constituting the scanning optical system have polarization dependence on the reflectance or the transmittance. In particular, the half mirror 144 has a large polarization dependency. When the transmittance of the half mirror is, for example, 7.5% of the total light amount as the monitor light flux, the typical coat characteristics are 10% for P-polarized light and 5% for S-polarized light.
%.

Therefore, for example, the light beam emitted from the first semiconductor laser and emitted from the optical fiber enters the light splitting surface of the half mirror as P-polarized light, and the light beam emitted from the second semiconductor laser and emitted from the optical fiber is S light. When the light is incident as polarized light, even if the first and second semiconductor lasers have the same light amount, the half mirror 14
The ratio of the light amounts of the light beams transmitted through 4 is 2: 1.

When the light emission amount of the semiconductor laser is feedback-controlled based on the light amount of the monitor light beam by the conventional APC method so that the light amount of the light beam transmitted through the half mirror 144 becomes the same, the light emission amount of the first semiconductor laser becomes It is の of the light emission amount of the second semiconductor laser. Here, when the polarization dependence of the optical element from the half mirror to the photosensitive drum 210 is neglected, the maximum amount of the beam spot on the photosensitive drum can be doubled by performing the APC operation. Become. Although the APC originally controls the light amount of the beam spot on the photosensitive drum surface to be equal, the difference in the light amount is enlarged by controlling in the conventional method.

Since the difference in the light quantity of the beam spot appears as a difference in the density of the pattern to be printed, if there is a difference in the light quantity between a plurality of beams, a desired density balance cannot be obtained. There is a problem that the density becomes non-uniform in a portion to be obtained. Note that such a disadvantage can be avoided by eliminating the polarization dependence of the half mirror. However, when a half mirror having a large difference between the reflectance and the transmittance as described in the embodiment is formed, a thin film forming technique is used. In addition, it is actually difficult to make a plane having small polarization dependence. If the difference between the reflectance and the transmittance is reduced, a half mirror with small polarization dependence can be created, but in this case, the efficiency of use as the main light beam used for drawing is reduced, and the output of the light source is reduced. Is relatively small, a sufficient amount of light for drawing cannot be obtained. If a light source having a larger output is used to obtain a sufficient amount of light, the cost of the apparatus is increased.

Therefore, in the apparatus of the embodiment, the light beam transmitted through the half mirror 144 is separated into two orthogonal polarization components, and each of the polarization components is separated by the first APC light receiving element 15.
5. While receiving light by the APC second light receiving element 157, the output signals Ss and Sp of each light receiving element are weighted by the following formula to obtain an APC signal S. Based on the signal S, the APC signal S is obtained. The above problem is solved by feedback control of the output. S = K (Sp + k ・ Ss)

The symbol K in the equation is a constant, for example, 0.5 in this example. The symbol k is a coefficient obtained by the following equation, and is calculated from optical design data once the optical system of the apparatus is determined. Alternatively, a sample of the device may be extracted and obtained experimentally using the optical system of the extracted device, or may be adjusted and set for each device. k = k1 × k2 where k1 = Mp / Ms and k2 = Ps / Pp. M
p and Ms are the light intensities of the transmitted light (monitor light flux) when two linearly polarized lights whose electric field vector oscillation directions are orthogonal to each other are incident on the half mirror 144, respectively.
s and Pp are the light intensity on the image plane of the reflected light (main light flux) at that time. Typically, the measurement can be performed using P-polarized light that oscillates in the plane of incidence of the light splitting surface of the half mirror and S-polarized light that oscillates in a plane perpendicular to the plane of incidence. These ratios are calculated as design values or obtained as measurement data, and by controlling the power of the semiconductor laser based on the correction signal S, the light amount of the beam spot on the photosensitive drum is accurately controlled. can do.

Assuming that the polarization beam splitter 153 has perfect separation characteristics, the half mirror 144
Incident on the first light receiving element 15
5 and the component incident as S-polarized light is detected only by the second light receiving element 157.

Subsequently, the APC calculated by the above equation
The light intensity on the photosensitive drum surface when the output of the semiconductor laser is controlled using the signal S is compared with the light intensity on the photosensitive drum surface when the output is controlled by directly using the intensity of the monitor light flux. I will explain. Here, the half mirror 14
4, the transmittance Hs of S-polarized light is 5% and the transmittance Hp of P-polarized light is 1
0%, and the photosensitive drum 210
Side optical element, that is, the cylindrical lens 17
0, the polarization characteristics of the polygon mirror 180, the fθ lens 190, and the folding mirror 200 are synthesized, and the loss due to these elements is 10% for P-polarized light and 1 for S-polarized light.
%. Accordingly, the ratio Dp of the amount of light reaching the photosensitive drum 210 among the P-polarized light reflected by the half mirror 144 is 90%, and similarly, the ratio Ds of the amount of light of the S-polarized light is 99%. In this case, the values of the coefficients k1 and k2 are as follows. k1 = Mp / Ms = Hp / Hs = 2 k2 = Ps / Pp = {(1-Hs) .Ds} / {(1-Hp) .Dp}
≒ 1.16 k = k1 · k2 = 2.32

Table 1 below shows a conventional example in which the intensity of a monitor light beam detected by a single light receiving element is directly used as an APC control amount, and Table 2 shows two light receiving elements 15 of the embodiment.
5 and 157, an example in which the APC control amount is obtained by substituting the intensities Sp and Ss of the respective polarization components of the monitor light beam detected by the formula S = K (Sp + k · Ss). Here, an example is shown in which APC control is performed so that the intensity of the other P-polarized light and the circularly-polarized light matches the intensity of the S-polarized light based on the intensity of the S-polarized light. As the incident light, P-polarized light and S-polarized light having the largest difference in transmittance and circularly polarized light having an intermediate property between them are illustrated. Further, the numerical values indicating the respective light intensities are shown as percentages when the total amount of light incident on the half mirror is 1.

[0055]

Table 1 Monitor APC Drum intensity Light flux intensity Control amount No APC APC operation P-polarized light 0.100 0.100 0.810 0.405 S-polarized light 0.050 0.050 0.941 0.941 0.941 Circularly polarized light 0.075 0.075 0.874 0.583

[0056]

Table 2 Monitor light flux intensity APC Drum intensity Sp Ss Control amount (S) Without APC APC operation P-polarized light 0.100 0.000 0.050 0.810 0.940 S-polarized light 0.000 0.050 0.058 0.941 0.941 Circularly polarized light 0.050 0.025 0.054 0.874 0.939

In the conventional example shown in Table 1, when P-polarized light and S-polarized light are incident on the half mirror, the APC is operated to allow a maximum of about 2.3 (= 0.941 / 0.40) on the photosensitive drum surface.
5) A two-fold difference in intensity occurs, and the density of the latent image formed on the photoreceptor drum cannot be controlled to a desired value without any change, which is not practical. On the other hand, in the example shown in Table 2, the intensity on the drum surface when the APC was activated was constant irrespective of the change in the polarization state, and there was no problem as in the conventional example. Can be controlled.

FIGS. 17 and 18 are graphs showing the results of actually measuring the variation in the light intensity on the photosensitive drum surface when APC is applied by the conventional method and the method of the present invention, respectively. FIG. 17 shows the light intensity (horizontal axis, unit: mW) on the surface of the photosensitive drum and the output (vertical axis, unit: μA) of the sensor current for monitoring light flux detected by the conventional method shown in Table 1. Shows the relationship. On the other hand, FIG. 18 shows the light intensity (horizontal axis, unit: m) on the surface of the photosensitive drum for the same apparatus as in FIG.
7 shows the relationship between W) and the APC control value S (vertical axis, unit: mV) detected and calculated by the method of the embodiment shown in Table 2. In the example of FIG. 17, the light intensity (b / a) on the image plane changed by ± 33.5% with respect to the same monitor signal due to the variation in the polarization state of the light emitted from each optical fiber. In the example of FIG. 18, this was suppressed to ± 3.5%, and a significant improvement in the uniformity of the light intensity on the photosensitive drum surface was observed.

In the above example, the change in the amount of light on the photosensitive drum 210 is suppressed in consideration of both the polarization characteristics of the half mirror 144 and the polarization characteristics of the optical element on the photosensitive drum 210 side. Although control is performed as described above, it is also possible to perform control by considering only the transmittance of the half mirror 144 having the most significant polarization dependency. In this case, APC
The signal S is obtained by the following equation. The symbols in the formula are the same as those in the above formula. S = K (Sp + k1 · Ss) When 5 to 10% of the total light amount is divided and used as the monitor light as described above, the intensity ratio of the monitor light is, for example, S polarized light (5%) and P depending on the polarization direction. The polarization ratio (10%) is about twice as large, while the intensity ratio of the main light beam after the monitor light is split is
In the above example, the ratio between the S-polarized light (95%) and the P-polarized light (90%) is about 1.06 times, and the ratio of the intensity change depending on the polarized light is small as compared with the monitor light having a low light amount ratio. Therefore, the correction may be performed only for the polarization dependence of the transmittance of the half mirror 144.

Table 3 below shows the same data as Table 2 when the APC is operated in consideration of only the polarization dependence of the half mirror 144. In this example, the ratio of each polarization component has the same value when there is no APC control and when there is no APC control. The values that match in this table are the values of the half mirror 144
This is because it is assumed that the total light amount of the light beam incident on the light source is constant. When the total light amount changes, the intensity after the change is maintained as it is when there is no APC. However, by operating the APC, it is possible to match the following levels.

Table 3 Monitor light flux intensity APC Drum intensity Sp Ss Control amount (S) Without APC APC operation P-polarized light 0.100 0.000 0.050 0.810 0.810 S-polarized light 0.000 0.050 0.050 0.941 0.941 Circularly polarized light 0.050 0.025 0.050 0.874 0.874

Even when the output of the semiconductor laser is controlled in consideration of only the polarization dependence of the half mirror 144 as described above, the intensity difference on the drum surface is about 1.16 times. There is a marked improvement in performance compared to the example.

Next, the configuration and operation of the control system of the scanning optical device will be described with reference to FIG. FIG.
FIG. 3 is a block diagram schematically illustrating a control system of the scanning optical device according to the embodiment. The control system includes a central control device 400 that controls the entire apparatus, a timing signal generation circuit 410 that generates timing signals for setting and drawing for each scan, and a drawing line that inputs drawing data input from the outside. A drawing signal generation circuit 420 that converts the image data into a drawing signal, which is dot data for each pixel, and outputs it; laser driving circuits 451 to 458 that drive the semiconductor lasers 101 to 108 on / off based on the drawing signals; Second light receiving element 15
5, an AP that generates an APC signal based on the outputs of 157
The C signal generation circuit 430 includes a switching circuit 440 that distributes the detected APC signal to each of the laser driving circuits 451 to 458.

The central control circuit 400 includes the polygon motor 3
71 is driven to rotate the polygon mirror 180, and the drum motor 211 is driven so that the photosensitive drum 210 rotates at a constant speed. Also, the central control circuit 400
Is used to determine which surface of the polygon mirror the current or next scan is based on the detection signal of the polygon sensor 374 that detects a mark M attached to a specific position in the circumferential direction of the polygon mirror 180, The rotation unevenness of the photosensitive drum is detected based on the detection signal of the drum sensor 213 that detects the rotation speed of the photosensitive drum 210.

As described above, the influence of the surface tilt of the polygon mirror or the uneven rotation of the photosensitive drum appears as a shift of each spot on the photosensitive drum in the sub-scanning direction. Prism 1
The angle of 60 is changed. The shift amount of the spot on the photosensitive drum due to the surface tilt of each surface of the polygon mirror 180 is measured and input to the central control circuit 400 in advance. The output from the polygon sensor 374 is used for the next scan. When the reflection surface is specified, the dynamic prism 160 that can cancel the shift of the spot due to the reflection surface
The angle of the dynamic prism 160 is set by controlling the prism driving unit 161 based on the angle. The set angle of the dynamic prism 160 is detected by the prism sensor 163, and the prism driving unit 161
Controls the dynamic prism in a closed loop based on the sensor output. Since the spot shift due to the surface inclination has a constant value for each reflection surface, the above-mentioned set angle becomes the reference angle of the dynamic prism 160 on the reflection surface.

On the other hand, since the rotation unevenness of the photosensitive drum is not a known error such as a surface tilt but an error that occurs randomly, the central control circuit 400 determines the drum sensor 213
When the occurrence of rotation unevenness is detected from the output of (1), the prism driving unit 161 is controlled so as to cancel the shift of the spot due to the detected rotation unevenness. Dynamic prism 1
Since the relationship between the adjustment angle of 60 and the variation amount of the declination due to it is non-linear, the adjustment angle for correcting the shift due to surface tilt and the adjustment angle for correcting the shift due to uneven rotation are calculated independently. I can't. For this reason,
The central control circuit 400 calculates the total shift amount by adding the shift amount due to the surface inclination and the shift amount due to the rotation unevenness on the reflection surface, and adjusts the dynamic prism 160 to cancel the total shift amount. The prism driving unit 161 is controlled by obtaining the angle. With the above control,
The surface tilt of the polygon mirror 180, which cannot be completely corrected by the combination of the cylindrical lens and the fθ lens,
In addition, the shift of the spot in the sub-scanning direction due to the uneven rotation of the photosensitive drum 210 can be corrected, and the position of the scanning line in the sub-scanning direction can be accurately controlled.

The timing signal generation circuit 410 generates the first, second, and third timing signals after the previous scanning is completed and the reflection surface of the polygon mirror used for scanning is switched to the next reflection surface. I do.

The first timing signal is a signal for causing each of the semiconductor lasers 101 to 108 to separately emit light sequentially to obtain an APC signal, and is output to each of the laser driving circuits 451 to 458 and the switching circuit 440. You. The APC signal generation circuit 430 detects the output of each semiconductor laser that is sequentially switched and emits light from the first and second light receiving elements 155 and 157 for APC, and outputs an APC signal for each semiconductor laser based on this. .
The switching circuit 440 selects an output destination such that the APC signal output from the APC signal generation circuit 430 is input to the corresponding laser drive circuit according to the first timing signal. For example, for a certain period of time during which the first semiconductor laser 101 emits light, the switch S
W1 is made conductive, and the APC signal output at that time is input to the first laser drive circuit 451. Each of the laser driving circuits 451 to 458 sets a gain based on the input APC signal so that the output of the semiconductor laser becomes a reference level.

The second timing signal is a signal for causing all the semiconductor lasers to emit light simultaneously to obtain a horizontal synchronizing signal, and is output to each of the laser driving circuits 451 to 458. The luminous fluxes from the semiconductor lasers 101 to 108 incident on the synchronization signal detecting light receiving element 230 are separated from each other in the main scanning direction. The light beams from .about.108 arrive at different timings.

The third timing signal is a horizontal synchronizing pulse for each scanning line generated by detecting a signal output from the synchronizing signal detecting light receiving element 230, and this pulse is output to the drawing signal generating circuit 420. Is done. The drawing signal generation circuit 420 supplies a drawing signal to each of the laser driving circuits 451 to 458 to start drawing after a lapse of a predetermined time from the input of each horizontal synchronization pulse.

As shown in FIG. 20, the APC signal generating circuit 430 receives the first linearly polarized light component of the two linearly polarized light components transmitted through the half mirror 144 and separated by the polarizing beam splitter 153, and receives the first polarized light component for APC. A first amplifier 431 that amplifies the output of the light receiving element 155 with an amplification factor α
APC second light receiving element 157 for receiving the S-polarized component
A second amplifier 432 that amplifies the output of the second amplifier 432 with the amplification factor kα, a gain adjustment circuit 433 that adjusts the gain of the second amplifier 432 by adjusting the coefficient k of the amplification factor,
An addition circuit 434 adds the outputs of the amplifiers 431 and 432 and outputs an APC signal. The coefficient k by the gain adjustment circuit 433 may be determined in advance as a design value, or may be set for each unit during assembly adjustment of the apparatus. The APC signal S is, as described above, the light receiving element 155,
When the output voltage of 157 is Sp and Ss, respectively, and is appropriately amplified (K times), the following equation is obtained. S = K (Sp + kSs)

The configuration of the laser driving circuit 451 is as follows.
This is as shown in FIG. Sample hold circuit 451
a captures and holds the APC signal output from the APC signal generation circuit 430 in synchronization with the turning on of the switch SW1 when the timing signal is input from the timing signal generation circuit 410. On the other hand, the reference voltage generation circuit 45
1b generates a reference voltage corresponding to a predetermined reference output of the semiconductor laser.

The differential amplifier 451c calculates the difference between these held signals and the reference voltage, and sets the gain of the laser drive circuit 451d according to the resulting differential signal. The laser drive circuit 451d controls ON / OFF of the semiconductor laser 101 based on the drawing signal input from the drawing signal generation circuit 420, and the drive voltage at this time can be adjusted by the gain set by the differential amplifier. . With the above configuration, the laser driving circuit 45
1c can control the output of the semiconductor laser so that the intensity of the beam spot on the surface of the photosensitive drum becomes the reference level.

The other laser driving circuits 452 to 45
8 also has the same configuration as that of the laser driving circuit 451 described above, and drives the semiconductor lasers 102 to 108 according to the drawing signal while adjusting the output of the corresponding semiconductor laser according to the output of the APC signal generation circuit 430. .

FIG. 22 is a timing chart showing the operation within one scan of the control system configured as described above.
In this timing chart, the ON / OFF state of the semiconductor lasers 101 to 108, the switching circuit 44
The ON / OFF state of each of the switches SW1 to SW8 of 0 and the output timing of the horizontal synchronization signal HS are displayed on the same time axis indicated by the horizontal axis.

One scanning period includes a first period P1 for adjusting the output of each semiconductor laser, a second period P2 for detecting a horizontal synchronizing signal, and a first period P2 for actually drawing a pattern on the photosensitive drum 210. 3 period P3.

In the first period P1, the semiconductor laser 10
1 to 108 are chronologically switched to emit light, and the switching circuit 44 is turned on within the emission time of each semiconductor laser.
The corresponding switch in 0 is turned on, and the APC signal output from the APC signal generation circuit 430 is input to the corresponding laser drive circuit. For example, time t1 in the chart
The semiconductor laser 101 emits light between t2 and t3, and the semiconductor laser 102 emits light between t2 and t3. During these periods, the switches SW1 and SW2 are turned on. The laser drive circuit adjusts the control level of the drive voltage based on this signal so that the amount of light on the photosensitive drum surface becomes the reference level.

In the second period P2, the eight semiconductor lasers 101 to 108 are caused to emit light at the same time from the time t5 to the time t6, and the rising of the horizontal synchronizing signal detecting light-receiving element 230 is detected. A synchronization pulse is generated. In the third period P3, the semiconductor laser is turned on / off based on the drawing signal at a predetermined timing after a predetermined time has elapsed from each horizontal synchronization pulse, and a pattern is formed on the photosensitive drum. Of the eight scanning lines formed at the same time, the first scanning line is formed by controlling the semiconductor laser 101 between times t7 and t11. Similarly, the second scanning line is between times t8 and t12, the third scanning line is between times t9 and t13, and the eighth scanning line is between times t10 and t14. 1
03 and 108 are formed. Since the beam spots formed by the light beams from the respective semiconductor lasers are separated by a predetermined amount in the main scanning direction, the writing by the next beam spot is started when the scanning by the predetermined amount is started after the writing by the preceding beam spot is started. By doing so, the positions of the scanning lines on the photosensitive drum 210 in the main scanning direction can be aligned.

The APC signal generation circuit is not limited to the configuration for electrically setting the gain as shown in FIG.
For example, as in a circuit 430a shown in FIG.
Light adjusting means for adjusting the light amount of at least one of the light beams incident on the light source 5, 157 may be provided. In this example, a filter 158 is inserted between one of the light receiving elements 155 and the polarization beam splitter 153 as a light control means, so that the balance of the received light amount itself is adjusted by optical means. The transmittance of the filter 158 is
Irrespective of the polarization state of the light beam incident on the half mirror 144, the level of the APC signal and the light intensity on the photosensitive drum 210 are determined to have a certain correlation.

As the filter 158, an ND filter, a polarizer or the like can be used. When an ND filter is used, a plurality of filters having different transmittances are prepared at the time of adjustment, and a filter having an appropriate transmittance may be selected and mounted according to the characteristics of each device. Also,
When a polarizer is used, the amount of transmitted light may be adjusted by rotating the polarizer around the optical axis and fixed at a position where an appropriate amount of light can be obtained.

FIG. 24 shows still another APC signal generation circuit 430b. In this example, a single light receiving element 155 is used, and a polarizer 159 is arranged between the half mirror 144 and the light receiving element 155. In this example, the polarizer 159 makes the relationship between the APC signal and the light intensity on the image plane constant with respect to a constant light emission amount of the semiconductor laser regardless of the polarization state of the light beam incident on the half mirror 144. The angle of the transmission axis is set. That is, it is set so as to eliminate the influence based on the polarization dependence of the half mirror 144 and the influence based on the polarization characteristics of the optical system on the main light beam side.

Assuming that the transmission and reflectance of the optical system on the main light beam side do not have polarization dependence for the sake of simplicity, as shown in FIG. The angle θ between the direction of the plane of incidence of the half mirror (axial direction of the P-polarized light) in a plane perpendicular to the plane is defined as Sp when the P-polarized light is incident, and Sp when the S-polarized light is incident. Ss may be set to a value determined by θ = tan ^-1 (Sp / Ss). Since the intensity of each polarized light component transmitted through the polarizing plate 159 is projected onto the transmission axis of each knitted structure, setting the angle of the polarizing plate 159 as described above allows the P-polarized light to reach the light receiving element. The amplitude is cos θ times the intensity when transmitted through the half mirror, and the light amplitude of the S-polarized light is sin θ times. Accordingly, the amplitude intensities of the two polarized lights projected on the transmission axis become equal, and the light amount of the light beam incident on the half mirror 144 can be detected without being affected by the polarization dependence of the half mirror 144.

In the configuration shown in FIG. 24, the correction can be made including the polarization dependency of the optical element between the half mirror 144 and the photosensitive drum 210. In this case, the angle θ of the transmission axis of the polarizer 159 is set so as to satisfy the following condition. θ = tan ⁻¹ √k where k is Mp, the light intensity of the monitor light beam when P-polarized light is incident on the half mirror 144, and Pp is the light intensity of the main light beam on the photosensitive drum 210 at that time. Assuming that the light intensity of the monitor light beam when S-polarized light is incident is Ms and the light intensity of the main light beam on the photosensitive drum 210 at that time is Ps, k = (Mp / Ms) · (Ps / Pp). Can be

[0083]

As described above, according to the present invention, an APC signal is generated in consideration of at least the polarization dependence of a light splitting element for splitting a monitor light beam and a main light beam, thereby providing a light splitting element. The amount of the main light beam can be accurately controlled regardless of the polarization state of the incident light beam. In addition, if the APC signal is generated in consideration of the polarization dependence of the optical element downstream of the light splitting element, the amount of the main light beam can be controlled to be constant with higher accuracy.

Therefore, for example, if a light beam from a plurality of light sources is used in a scanning optical system for a multi-beam, which guides the light beam to a deflector side using an optical fiber, the light beam enters the light splitting element due to a change in the attitude of the optical fiber or a change with time. Even if the polarization state of the light beam changes, the intensity of the spot on the surface to be scanned can be controlled based on the monitor light beam without depending on such a change.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a scanning optical device to which a light intensity control device according to the present invention is applied.

FIG. 2 is a cross-sectional view in the sub-scanning direction of the apparatus of FIG.

FIG. 3 is a plan view of the apparatus of FIG. 1 in the main scanning direction.

FIG. 4 is an explanatory view in the main scanning direction showing only the optical system of the apparatus in FIG. 1;

FIG. 5 is a sectional view showing details of a laser block portion of the apparatus of FIG. 1;

FIG. 6 is a front view of FIG. 5 as viewed from the line VI-VI.

FIG. 7 is an explanatory diagram showing a relationship between an incident direction of a light beam in a laser block and an angle of an incident end face of an optical fiber.

FIG. 8 is a plan view showing a configuration from a fiber support to a fiber alignment block of the apparatus of FIG. 1;

FIG. 9 is an exploded perspective view of a fiber alignment block.

FIG. 10 is an enlarged front view of a fiber alignment block.

FIG. 11 is an explanatory diagram showing an arrangement of fibers.

FIG. 12 is an explanatory diagram showing an arrangement of beam spots on a photosensitive drum.

FIG. 13 is an explanatory diagram showing an optical system for measuring a polarization state of light emitted from an optical fiber.

FIG. 14 is a graph showing the results of measuring the polarization state of light emitted from each optical fiber when linearly polarized light having the same direction of the vibrating surface is incident on six of the eight optical fibers.

FIG. 15 is a graph showing a change in polarization due to bending and a loop of an optical fiber.

FIG. 16 is a graph showing a change in polarization when a loop of an optical fiber is rotated.

FIG. 17 is a graph showing a result of actually measuring a variation in light intensity on a photosensitive drum surface when APC is performed by a conventional method.

FIG. 18 is a graph showing a result of actually measuring a variation in light intensity on a photosensitive drum surface when APC is applied by the method of the present invention.

FIG. 19 is a block diagram illustrating a control system of the scanning optical device according to the embodiment.

20 is a block diagram illustrating details of an APC signal generation circuit in FIG.

FIG. 21 is a block diagram showing details of a laser drive circuit in FIG. 13;

FIG. 22 is a timing chart illustrating the operation of the scanning optical device according to the embodiment.

23 is a block diagram showing another example of the APC signal generation circuit in FIG.

24 is a block diagram showing still another example of the APC signal generation circuit in FIG.

FIG. 25 is a graph showing the operation of the polarizer used in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 100 Light source part 101-108 Semiconductor laser 121-128 Optical fiber 130 Fiber alignment block 140 Collimating lens 144 Half mirror 150 APC signal detection part 153 Polarization beam splitter 155 APC first light receiving element 157 APC second light receiving element 158 Filter 159 Polarizer 180 polygon mirror 190 fθ lens 210 photoconductor drum 430 APC signal generation circuit 433 gain adjustment circuit 451-458 laser drive circuit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Kanazawa 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Optical Industry Co., Ltd. (56) References JP-A-7-65400 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) G02B 26/10 B41J 2/44 G11B 7/125

Claims (31)

(57) [Claims] 1. A light splitting element for splitting a light beam emitted from a light source unit having a plurality of light sources independently controlled in light emission into a monitor light beam and a main light beam, and a light intensity of the monitor light beam emitted from each of the light sources. Light detecting means for detecting at different timings, and regardless of the polarization state of the incident light on the light splitting element, the light intensity of the monitor light flux and the optical system guided to the target surface by an optical system downstream of the light splitting element. Correction means for correcting the output of the light detection means so that the light intensity of the main light beam has a constant correlation; and light emission of the plurality of light sources based on the output signals of the light detection means corrected by the correction means Control means for controlling the intensity, wherein the correction means and the control means are configured to control the light emission intensity of the corresponding light source based on the light intensity of the monitor light flux emitted from each light source detected by the light detection means. Light intensity control apparatus and controls the. 2. The method according to claim 1, wherein the correcting unit is configured to determine a light intensity of a monitor light beam caused by a polarization characteristic of at least one of the light splitting element and the subsequent optical system and a light intensity of the main light beam on a target surface. 2. The light intensity control device according to claim 1, wherein a deviation of the correspondence is corrected. 3. The light intensity control device according to claim 1, wherein the light source unit includes a plurality of optical fibers for transmitting light beams emitted from the respective light sources to the light splitting element side. 4. The polarized light separating element for separating a monitor light flux into first and second linearly polarized light beams whose vibration directions of an electric field vector are orthogonal to each other, wherein the first and second separated light beams are separated from each other.
First and second light receiving elements for receiving the second linearly polarized light, respectively, and outputting a signal in which the light intensity of the light beam separated by the polarization separation element is weighted based on the output of the light receiving element. The light intensity control device according to claim 1, wherein: 5. The light intensity control device according to claim 4, wherein said correction means includes a gain setting means for electrically weighting outputs of said first and second light receiving elements with a predetermined weight. . 6. The correction means sets the light intensity of the monitor light beam when the first linearly polarized light is incident on the light splitting element to Mp, and the light intensity of the main light beam on the target surface at that time. Pp, Ms is the light intensity of the monitor light beam when the second linearly polarized light is incident, Ps is the light intensity of the main light beam on the target surface at that time, and the first light beam separated by the polarization separation element. The output of the first light receiving element for receiving linearly polarized light is represented by S
p, the output of the second light receiving element that receives the second linearly polarized light separated by the polarization splitting element is Ss, and the following expression: S = K (Sp + k · Ss) where K: constant, k = 6. The light intensity control device according to claim 4, wherein an output signal S is obtained by (Mp / Ms). (Ps / Pp). 7. The light according to claim 4, wherein said correction means comprises light control means for adjusting the light amount of at least one of the light beams incident on said first and second light receiving elements. Strength control device. 8. The light intensity control device according to claim 7, wherein said light control means is an ND filter. 9. The light intensity control device according to claim 7, wherein said light control means is a polarizer. 10. The light detecting means comprises a single light receiving element, and the correcting means is a polarizer disposed between the light splitting element and the light receiving element. The light intensity control device according to any one of claims 1 to 3. 11. The light intensity control device according to claim 1, wherein the light source is a semiconductor laser. 12. A light splitting element for splitting a light beam emitted from a plurality of light sources independently controlled in light emission into a monitor light beam and a main light beam, respectively; Light detecting means for detecting at a different timing; correcting means for correcting variations in the output of the light detecting means depending on the polarization state of the light beam incident on the light splitting element; and the light detecting means corrected by the correcting means Control means for controlling the light emission intensity of each light source based on the output signal of the light source. 13. The correction means, irrespective of the polarization state of the light beam incident on the light splitting element, the output of the correction means and the main light guided onto the target surface by an optical system downstream of the light splitting element. The light intensity control device according to claim 12, wherein the light intensity of the light beam is set to have a certain correlation. 14. The correction means is set such that an output of the correction means is constant with respect to a constant light emission amount of the light source regardless of a polarization state of a light beam incident on the light splitting element. The light intensity control device according to claim 12, wherein: 15. The polarized light separating element for separating a monitor light beam into first and second linearly polarized light beams whose electric field vectors vibrate at right angles to each other, and the separated first and second linear light beams. The light intensity control device according to claim 12, further comprising first and second light receiving elements that receive polarized light, respectively. 16. The light intensity control device according to claim 15, wherein said correction means includes gain setting means for electrically weighting outputs of said first and second light receiving elements with a predetermined weight. . 17. The method according to claim 1, wherein the correcting unit sets the intensity of the monitor light flux when the first linearly polarized light is incident on the light splitting element as Mp, and the intensity of the monitor light flux when the second linearly polarized light is incident on the light splitting element. Ms, the output of the first light receiving element that receives the first linearly polarized light separated by the polarization separation element is Sp, and the output of the second light separation element separated by the polarization separation element is Sp.
The output of the second light receiving element that receives the linearly polarized light of
16. The light intensity control device according to claim 15, wherein the output signal S is obtained by the following equation: S = K (Sp + k1.Ss) where K is a constant and k1 = Mp / Ms. 18. The light control device according to claim 15, wherein the correction unit includes a light control unit that adjusts a light amount of at least one of the light beams incident on the first and second light receiving elements.
3. The light intensity control device according to claim 1. 19. The apparatus according to claim 19, wherein said light detecting means comprises a single light receiving element, and said correcting means is a polarizer disposed between said light dividing element and said light receiving element. 15. The light intensity control device according to any one of 12 to 14. 20. Each of the light beams emitted from a plurality of light sources whose light emission is controlled independently is split into a monitor light beam and a main light beam by a light splitting element, and the monitor light beams emitted from each of the light sources are detected by a light detecting means. And a light intensity control method for controlling light emission intensity of each light source based on an output signal of the correction means, wherein a first linearly polarized light is made incident on the light splitting element as a setting step. A first step of measuring the light intensity of the monitor light beam and the intensity of the main light beam guided onto the target surface by an optical system downstream of the light splitting element. The second step of measuring the intensity of the monitor light beam and the intensity of the main light beam on the target surface when linearly polarized light is incident on a second linearly polarized light having an orthogonal vibration direction of an electric field vector, Based on the results measured in the first and second steps,
A third step of adjusting the setting of the correction means so that a correction signal having a constant correlation with the intensity of the main light beam on the target surface is obtained regardless of the polarization state of the light beam incident on the light splitting element. A fourth step of correcting the signal detected by the light detection unit by the correction unit; and a fifth step of controlling the light emission intensity of each of the light sources based on an output signal of the correction unit. And a light intensity control method. 21. Each of the light beams emitted from a plurality of light sources whose light emission is independently controlled is split into a monitor light beam and a main light beam by a light splitting element, and the monitor light beam emitted from each light source is split by a polarization splitting element. The first and second light receiving elements receive the separated light fluxes into two polarization components, and the correction signals obtained by weighting the outputs of the first and second light receiving elements with a predetermined weight are obtained. In the light intensity control method for controlling the light emission intensity of each of the light sources based on the light intensity of the monitor light beam when the first linearly polarized light is incident on the light splitting element, and the light intensity control step after the light splitting element, A first step of measuring the light intensity of the main light beam guided onto the target surface by the optical system, and a second step in which the direction of vibration of the electric field vector is orthogonal to the first linearly polarized light in the light splitting element. Linearly polarized light Isa was, on the basis of a second step of measuring the light intensity on the target surface of the main light beam and the light intensity of the monitor light beam, the first, the results measured at the second step,
The outputs of the first and second light receiving elements are determined so that a correction signal having a constant correlation with the intensity of the main light beam on the target surface is obtained regardless of the polarization state of the light beam incident on the light splitting element. A third step of calculating outputs of the first and second light receiving elements to generate a correction signal, and a step of: A fifth step of controlling the light emission intensity of each light source. 22. A light intensity of a scanning optical system that forms a spot on a scanning target surface by causing light beams emitted from a plurality of semiconductor lasers to be incident on a deflector, and converging a plurality of light beams deflected by the deflector by a scanning lens. In the adjustment device, provided between the semiconductor laser and the deflector, a light splitting element that splits a plurality of light beams emitted from the semiconductor laser into monitor light and a main light beam, respectively, and emitted from each of the light sources. Light detection means for detecting the intensity of the divided monitor light beam, and irrespective of the polarization state of the light beam incident on the light splitting element, the light intensity of the monitor light beam and the light intensity of the main light beam on the surface to be scanned; Correction means for correcting the output of the light detection means so that the light has a constant correlation; and each of the lights based on the output signal of the light detection means corrected by the correction means Light intensity control device of the scanning optical system, characterized in that a control means for controlling the light emission intensity. 23. A plurality of optical fibers, each of which receives a light beam emitted from each of the semiconductor lasers, between the semiconductor laser and the light splitting element, wherein the light splitting element splits light emitted from the optical fiber. 23. The light intensity control device for a scanning optical system according to claim 22, wherein: 24. The light detection means, wherein the monitor light flux is 2
Polarization splitting element for splitting the light into two polarized light components, first and second light receiving elements for receiving the separated light beams, and gain setting means for weighting the outputs of the first and second light receiving elements with a predetermined weight The light intensity control device according to any one of claims 22 and 23, comprising: 25. A luminous flux emitted from a plurality of light sources independently controlled in light emission is divided into a monitor luminous flux and a main luminous flux, and the monitor luminous flux is detected by a light detecting means, and based on the detected signal. In the light intensity control method for controlling the light emission intensity of each light source, the plurality of light sources are sequentially emitted one by one, and a monitor light beam emitted from each light source is separated into two polarization components whose polarization directions are orthogonal to each other. Each of the separated polarized light components is received by the first and second light receiving elements, the outputs of the first and second light receiving elements are added with a predetermined weight, and a light emission state is obtained based on the addition result. A light intensity control method comprising controlling the light emission intensity of a light source. 26. An output of the first and second light receiving elements,
The addition result is weighted so that the light intensity of the monitor light beam and the light intensity of the main light beam on the surface to be scanned have a constant correlation regardless of the polarization state of the light beam incident on the light splitting element. The light intensity control method according to claim 25, wherein: 27. A light intensity control device for a multi-beam optical device, wherein light beams emitted from a plurality of light sources independently controlled in light emission are guided onto a target surface through an optical system including a plurality of optical elements. Controlling the light emission intensity of each light source so as to correct the variation of the intensity of the light beam on the target surface for each of the light sources depending on the polarization characteristics of at least one optical element. Strength control device. 28. A light intensity control means of a scanning optical system for causing a light beam emitted from a light source and deflected by a deflector to converge on a surface to be scanned by a scanning lens, wherein a polarization characteristic of at least one optical element of the scanning optical system is provided. A light intensity control device for controlling the light emission intensity of each light source so as to correct a change in the intensity of the light beam on the scanning target surface, which depends on the light intensity. 29. The light splitter according to claim 29, wherein:
And the case where the first linearly polarized light is incident and the case where the second linearly polarized light whose vibration direction of the electric field vector is orthogonal is incident. The light intensity control device according to claim 10, wherein a relationship between the light intensity and the amount of light transmitted through the element is set to be equal. 30. The light intensity of the monitor light flux when the first linearly polarized light is incident on the light splitting element is Mp,
The light intensity of the main light beam on the target surface at that time is Pp,
The light intensity of the monitor light beam when the linearly polarized light is incident is Ms, and the light intensity of the main light beam on the target surface at that time is Ps, and the polarizer is in a plane perpendicular to the incident direction of the light beam. The angle θ between the oscillation direction of the electric field vector of the first linearly polarized light and the transmission axis of the polarizer is represented by the following equation: θ = tan ⁻¹ √k where k = (Mp / Ms) · (Ps / Pp 30. The light intensity control device according to claim 29, wherein the light intensity control device is arranged to be determined by: 31. Each of light beams emitted from a plurality of light sources whose emission is independently controlled is split into a monitor light beam and a main light beam by a light splitting element, and the monitor light beams emitted from the plurality of light sources are detected by a light detecting means. In a light intensity control method for detecting and correcting by a correction unit and controlling the emission intensity of the plurality of light sources based on an output signal of the correction unit, as a setting step, a first linearly polarized light is incident on the light splitting element. A first step of calculating the light intensity of the monitor light beam and the intensity of the main light beam guided onto the target surface by an optical system downstream of the light splitting element based on a design value, and The second linearly polarized light whose electric field vector vibrates orthogonally to the first linearly polarized light is incident on the splitting element, and the intensity of the monitor light flux and the intensity of the main light flux on the target surface are designed. A second step of calculating based on the value, and a target of the main light beam regardless of the polarization state of the light beam incident on the light splitting element, based on the result obtained by the calculation in the first and second steps. A third step of adjusting the setting of the correction means so that an output signal having a constant correlation with the intensity on the surface can be obtained. And a fifth step of controlling the light emission intensity of the plurality of light sources based on an output signal of the correction unit.